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  • 1.
    Ahlman, Daniel
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Brethouwer, Geert
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Johansson, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    A numerical method for simulation of turbulence and mixing in a compressible wall-jet2007Report (Other academic)
  • 2.
    Ahlman, Daniel
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Brethouwer, Geert
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Johansson, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Direct numerical simulation of a plane turbulent wall-jet including scalar mixing2007In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 19, no 6, p. 065102-Article in journal (Refereed)
    Abstract [en]

    Direct numerical simulation is used to study a turbulent plane wall-jet including the mixing of a passive scalar. The Reynolds and Mach numbers at the inlet are Re=2000 and M=0.5, respectively, and a constant coflow of 10% of the inlet jet velocity is used. The passive scalar is added at the inlet enabling an investigation of the wall-jet mixing. The self-similarity of the inner and outer shear layers is studied by applying inner and outer scaling. The characteristics of the wall-jet are compared to what is reported for other canonical shear flows. In the inner part, the wall-jet is found to closely resemble a zero pressure gradient boundary layer, and the outer layer is found to resemble a free plane jet. The downstream growth rate of the scalar is approximately equal to that of the streamwise velocity in terms of the growth rate of the half-widths. The scalar fluxes in the streamwise and wall-normal direction are found to be of comparable magnitude. The scalar mixing situation is further studied by evaluating the scalar dissipation rate and the mechanical to mixing time scale ratio.

  • 3.
    Ahlman, Daniel
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Brethouwer, Geert
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Johansson, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Direct numerical simulation of a reacting turbulent wall-jet2007Report (Other academic)
  • 4.
    Ahlman, Daniel
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Brethouwer, Geert
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Johansson, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Direct numerical simulation of non-isothermal turbulent wall-jets2009In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 21, no 3Article in journal (Refereed)
    Abstract [en]

    Direct numerical simulations of plane turbulent nonisothermal wall jets are performed and compared to the isothermal case. This study concerns a cold jet in a warm coflow with an ambient to jet density ratio of ρa/ρj = 0.4, and a warm jet in a cold coflow with a density ratio of ρa/ρj = 1.7. The coflow and wall temperature are equal and a temperature dependent viscosity according to Sutherland’s law is used. The inlet Reynolds and Mach numbers are equal in all these cases. The influence of the varying temperature on the development and jet growth is studied as well as turbulence and scalar statistics. The varying density affects the turbulence structures of the jets. Smaller turbulence scales are present in the warm jet than in the isothermal and cold jet and consequently the scale separation between the inner and outer shear layer is larger. In addition, a cold jet in a warm coflow at a higher inlet Reynolds number was also simulated. Although the domain length is somewhat limited, the growth rate and the turbulence statistics indicate approximate self-similarity in the fully turbulent region. The use of van Driest scaling leads to a collapse of all mean velocity profiles in the near-wall region. Taking into account the varying density by using semilocal scaling of turbulent stresses and fluctuations does not completely eliminate differences, indicating the influence of mean density variations on normalized turbulence statistics. Temperature and passive scalar dissipation rates and time scales have been computed since these are important for combustion models. Except for very near the wall, the dissipation time scales are rather similar in all cases and fairly constant in the outer region.

  • 5.
    Ahlman, Daniel
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Brethouwer, Gert
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Johansson, Arne V.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Direct numerical simulation of mixing in a plane compressible and turbulent wall jet2005In: 4th International Symposium on Turbulence and Shear Flow Phenomena, 2005, p. 1131-1136Conference paper (Refereed)
    Abstract [en]

    Direct numerical simulation (DNS) is used to simulate the mixing of a passive scalar in a plane compressible and turbulent wall jet. The Mach number of the jet is M = 0.5 at the inlet. The downstream development of the jet is studied and compared to experimental data. Mixing in the inner and outer shear layers of the wall jet is investigated through scalar fluxes, the probability density function of the scalar concentration and the joint probability density function of the wall normal velocity fluctuation and the scalar concentration

  • 6.
    Alvelius, Krister
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Johansson, Arne, V.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    LES computations and comparison with Kolmogorov theory for two-point pressure{velocity correlations and structure functions for globally anisotropic turbulence2000In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 403, p. 23-36Article in journal (Refereed)
    Abstract [en]

    A new extension of the Kolmogorov theory, for the two-point pressure–velocity correlation, is studied by LES of homogeneous turbulence with a large inertial subrange in order to capture the high Reynolds number nonlinear dynamics of the flow. Simulations of both decaying and forced anisotropic homogeneous turbulence were performed. The forcing allows the study of higher Reynolds numbers for the same number of modes compared with simulations of decaying turbulence. The forced simulations give statistically stationary turbulence, with a substantial inertial subrange, well suited to test the Kolmogorov theory for turbulence that is locally isotropic but has significant anisotropy of the total energy distribution. This has been investigated in the recent theoretical studies of Lindborg (1996) and Hill (1997) where the role of the pressure terms was given particular attention. On the surface the two somewhat different approaches taken in these two studies may seem to lead to contradictory conclusions, but are here reconciled and (numerically) shown to yield an interesting extension of the traditional Kolmogorov theory. The results from the simulations indeed show that the two-point pressure–velocity correlation closely adheres to the predicted linear relation in the inertial subrange where also the pressure-related term in the general Kolmogorov equation is shown to vanish. Also, second- and third-order structure functions are shown to exhibit the expected dependences on separation.

  • 7. Aronsson, D.
    et al.
    Johansson, Arne, V.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Löfdahl, Lennart
    Shear-free turbulence near a wall1996In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 338, p. 363-385Article in journal (Refereed)
    Abstract [en]

    The mean shear has a major influence on near-wall turbulence but there are also other important physical processes at work in the turbulence/wall interaction. In order to isolate these, a shear-free boundary layer was studied experimentally. The desired flow conditions were realized by generating decaying grid turbulence with a uniform mean velocity and passing it over a wall moving with the stream speed. It is shown that the initial response of the turbulence field can be well described by the theory of Hunt & Graham (1978). Later, where this theory ceases to give an accurate description, terms of the Reynolds stress transport (RST) equations were measured or estimated by balancing the equations. An important finding is that two different length scales are associated with the near-wall damping of the Reynolds stresses. The wall-normal velocity component is damped over a region extending roughly one macroscale out from the wall. The pressure–strain redistribution that normally would result from the Reynolds stress anisotropy in this region was found to be completely inhibited by the near-wall influence. In a thin region close to the wall the pressure–reflection effects were found to give a pressure–strain that has an effect opposite to the normally expected isotropization. This behaviour is not captured by current models.

  • 8.
    Brethouwer, Geert
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Duguet, Yohann
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Johansson, Arne V.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Recurrent Bursts via Linear Processes in Turbulent Environments2014In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 112, no 14, p. 144502-Article in journal (Refereed)
    Abstract [en]

    Large-scale instabilities occurring in the presence of small-scale turbulent fluctuations are frequently observed in geophysical or astrophysical contexts but are difficult to reproduce in the laboratory. Using extensive numerical simulations, we report here on intense recurrent bursts of turbulence in plane Poiseuille flow rotating about a spanwise axis. A simple model based on the linear instability of the mean flow can predict the structure and time scale of the nearly periodic and self-sustained burst cycles. Poiseuille flow is suggested as a prototype for future studies of low-dimensional dynamics embedded in strongly turbulent environments.

  • 9.
    Brethouwer, Geert
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Johansson, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Effects of rapid spanwise rotation on turbulent channel flow with a passive scalar2011In: Proc. 7th International Symposium on Turbulence and Shear Flow Phenomena, 2011Conference paper (Refereed)
    Abstract [en]

    Direct numerical simulations of fully developed turbulentchannel flow including a passive scalar rotating about thespanwise axis have been performed. The mean bulk Reynoldsnumber, Reb = Ubh/n ≥ 20000, where Ub is the bulk meanvelocity and h the channel half width, is higher than in previoussimulations and the rotation rate covers a wide range.At moderate rotation rates, turbulence on the stable channelside is significantly less damped than in DNS at lower Reb. Athigh rotation rates we observe re-occurring, quasi-periodic instabilitieson the stable channel side. Between these events theturbulence is weak, but during the instability events the wallshear stress and turbulence intensity are much stronger. Theinstabilities are caused by structures resembling Tollmien-Schlichting (TS) waves that at some instant rapidly grow, thenbecome unstable and finally break down into intense turbulence.After some time the TS waves form again and the processrepeats itself in a periodic-like manner.Mean scalar profiles are also strongly affected by rotationand large scalar fluctuations are found on the border of the stableand unstable channel side. The turbulent Prandtl/Schmidtnumber of the scalar is much less than unity if there is rotation.Predicting scalar transport in rotating channel flow willtherefore pose a challenge to turbulence models.

  • 10.
    Brethouwer, Geert
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Johansson, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Turbulence instabilities and passive scalars in rotating channel flow2011In: 13th European Turbulence Conference (ETC13): Instability, Transition, Grid Turbulence And Jets / [ed] K. Bajer, Institute of Physics Publishing (IOPP), 2011, p. 032025-Conference paper (Refereed)
    Abstract [en]

    Fully developed channel flow with a passive scalar rotating about the spanwise axis is studied by direct numerical simulations. The Reynolds number based on the bulk mean velocity Re-b is up to 30000, substantially higher than in previous studies, and the rotation rates cover a broad range. Turbulence on the stable channel side is less strongly damped at moderate rotation rates than in channel flow at lower Re-b. At high rotation rates and sufficiently high Re-b, intermittent strong instabilities occur on the stable side caused by rapidly growing modes resembling two-dimensional Tollmien-Schlichting waves which at some instant become unstable and break down into intense turbulence. The turbulence decays and after some time the waves form again and the process is repeated in a cyclic manner. Rotation also strongly affects the mean passive scalar profiles and turbulent scalar fluxes. Large scalar fluctuations are observed on the border between the stable and unstable channel sides. While in non-rotating channel flow the turbulent Prandtl number of the passive scalar is about one like in other shear flows, it is much smaller in the rotating cases.

  • 11.
    Do-Quang, Minh
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Amberg, Gustav
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Brethouwer, Gert
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Johansson, Arne V.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Simulation of finite-size fibers in turbulent channel flows2014In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 89, no 1, p. 013006-Article in journal (Refereed)
    Abstract [en]

    The dynamical behavior of almost neutrally buoyant finite-size rigid fibers or rods in turbulent channel flow is studied by direct numerical simulations. The time evolution of the fiber orientation and translational and rotational motions in a statistically steady channel flow is obtained for three different fiber lengths. The turbulent flow is modeled by an entropy lattice Boltzmann method, and the interaction between fibers and carrier fluid is modeled through an external boundary force method. Direct contact and lubrication force models for fiber-fiber interactions and fiber-wall interaction are taken into account to allow for a full four-way interaction. The density ratio is chosen to mimic cellulose fibers in water. It is shown that the finite size leads to fiber-turbulence interactions that are significantly different from earlier reported results for point like particles (e.g., elongated ellipsoids smaller than the Kolmogorov scale). An effect that becomes increasingly accentuated with fiber length is an accumulation in high-speed regions near the wall, resulting in a mean fiber velocity that is higher than the mean fluid velocity. The simulation results indicate that the finite-size fibers tend to stay in the high-speed streaks due to collisions with the wall. In the central region of the channel, long fibers tend to align in the spanwise direction. Closer to the wall the long fibers instead tend to toward to a rotation in the shear plane, while very close to the wall they become predominantly aligned in the streamwise direction.

  • 12.
    El Khoury, George K.
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Brethouwer, Geert
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Johansson, Arne V.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Turbulent pipe flow: Statistics, Re-dependence, structures and similarities with channel and boundary layer flows2014In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 506, no 1, p. 012010-Article in journal (Refereed)
    Abstract [en]

    Direct numerical simulation data of fully developed turbulent pipe flow are extensively compared with those of turbulent channel flow and zero-pressure-gradient boundary layer flow for Re-tau up to 1 000. In the near-wall region, a high degree of similarity is observed in the three flow cases in terms of one-point statistics, probability density functions of the wall-shear stress and pressure, spectra, Reynolds stress budgets and advection velocity of the turbulent structures. This supports the notion that the near-wall region is universal for pipe and channel flow. Probability density functions of the wall shear stress, streamwise turbulence intensities, one-dimensional spanwise/azimuthal spectra of the streamwise velocity and Reynolds-stress budgets are very similar near the wall in the three flow cases, suggesting that the three cauonical wall-bounded flows share wally features. In the wake region, the wean streamwise velocity and Reynolds stress budgets show smile expected differences.

  • 13.
    El Khoury, George K.
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Noorani, Azad
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Fischer, Paul F.
    Brethouwer, Geert
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Johansson, Arne V.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Direct Numerical Simulation of Turbulent Pipe Flow at Moderately High Reynolds Numbers2013In: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987, Vol. 91, no 3, p. 475-495Article in journal (Refereed)
    Abstract [en]

    Fully resolved direct numerical simulations (DNSs) have been performed with a high-order spectral element method to study the flow of an incompressible viscous fluid in a smooth circular pipe of radius R and axial length 25R in the turbulent flow regime at four different friction Reynolds numbers Re (tau) = 180, 360, 550 and . The new set of data is put into perspective with other simulation data sets, obtained in pipe, channel and boundary layer geometry. In particular, differences between different pipe DNS are highlighted. It turns out that the pressure is the variable which differs the most between pipes, channels and boundary layers, leading to significantly different mean and pressure fluctuations, potentially linked to a stronger wake region. In the buffer layer, the variation with Reynolds number of the inner peak of axial velocity fluctuation intensity is similar between channel and boundary layer flows, but lower for the pipe, while the inner peak of the pressure fluctuations show negligible differences between pipe and channel flows but is clearly lower than that for the boundary layer, which is the same behaviour as for the fluctuating wall shear stress. Finally, turbulent kinetic energy budgets are almost indistinguishable between the canonical flows close to the wall (up to y (+) a parts per thousand aEuro parts per thousand 100), while substantial differences are observed in production and dissipation in the outer layer. A clear Reynolds number dependency is documented for the three flow configurations.

  • 14. Friedrich, R.
    et al.
    Johansson, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    FOREWORD TO SPECIAL ISSUE Seventh International Symposium on Turbulence and Shear Flow Phenomena2013In: Journal of turbulence, ISSN 1468-5248, E-ISSN 1468-5248, Vol. 14, no 2, p. 1-3Article in journal (Other academic)
  • 15. Friedrich, R.
    et al.
    Johansson, Arne V.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Foreword to special issue: Eighth International Symposium on Turbulence and Shear Flow Phenomena (TSFP-8)2015In: Journal of turbulence, ISSN 1468-5248, E-ISSN 1468-5248, Vol. 16, no 3, p. 203-207Article in journal (Other academic)
  • 16. Friedrich, R.
    et al.
    Johansson, Arne V.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Sixth International Symposium on Turbulence and Shear Flow Phenomena FOREWORD TO SPECIAL ISSUE2011In: Journal of turbulence, ISSN 1468-5248, E-ISSN 1468-5248, Vol. 12, no 14, p. 1-2Article in journal (Other academic)
  • 17.
    Grigoriev, Igor A.
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Wallin, Stefan
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Brethouwer, Gert
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Johansson, Arne V.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    A realizable explicit algebraic Reynolds stress model for compressible turbulent flow with significant mean dilatation2013In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 25, no 10, p. 105112-Article in journal (Refereed)
    Abstract [en]

    The explicit algebraic Reynolds stress model of Wallin and Johansson [J. Fluid Mech. 403, 89 (2000)] is extended to compressible and variable-density turbulent flows. This is achieved by correctly taking into account the influence of the mean dilatation on the rapid pressure-strain correlation. The resulting model is formally identical to the original model in the limit of constant density. For two-dimensional mean flows the model is analyzed and the physical root of the resulting quartic equation is identified. Using a fixed-point analysis of homogeneously sheared and strained compressible flows, we show that the new model is realizable, unlike the previous model. Application of the model together with a K - omega model to quasi one-dimensional plane nozzle flow, transcending from subsonic to supersonic regime, also demonstrates realizability. Negative "dilatational" production of turbulence kinetic energy competes with positive "incompressible" production, eventually making the total production negative during the spatial evolution of the nozzle flow. Finally, an approach to include the baroclinic effect into the dissipation equation is proposed and an algebraic model for density-velocity correlations is outlined to estimate the corrections associated with density fluctuations. All in all, the new model can become a significant tool for CFD (computational fluid dynamics) of compressible flows.

  • 18.
    Grigoriev, Igor A.
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Wallin, Stefan
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. Swedish Defence Research Agency (FOI), Sweden.
    Brethouwer, Geert
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Johansson, Arne V.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Capturing turbulent density flux effects in variable density flow by an explicit algebraic model2015In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 27, no 4, article id 1.4917278Article in journal (Refereed)
    Abstract [en]

    The explicit algebraic Reynolds stress model of Grigoriev et al. ["A realizable explicit algebraic Reynolds stress model for compressible turbulent flow with significant mean dilatation," Phys. Fluids 25, 105112 (2013)] is extended to account for the turbulent density flux in variable density flows. The influence of the mean dilatation and the variation of mean density on the rapid pressure-strain correlation are properly accounted for introducing terms balancing a so-called "baroclinic" production in the Reynolds stress tensor equation. Applying the weak-equilibrium assumption leads to a self-consistent formulation of the model. The model together with a K - ω model is applied to a quasi-one-dimensional plane nozzle flow transcending from subsonic to supersonic regimes. The model remains realizable with constraints put on the model parameters. When density fluxes are taken into account, the model is less likely to become unrealizable. The density variance coupled with a "local mean acceleration" also can influence the model acting to increase anisotropy. The general trends of the behaviour of the anisotropy and production components under the variation of model parameters are assessed. We show how the explicit model can be applied to two- and three-dimensional mean flows without previous knowledge of a tensor basis to obtain the general solution. Approaches are proposed in order to achieve an approximate solution to the consistency equation in cases when analytic solution is missing. In summary, the proposed model has the potential to significantly improve simulations of variable-density flows.

  • 19.
    Grigoriev, Igor
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Brethouwer, Geert
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Wallin, Stefan
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. Swedish Defence Research Agency (FOI), Sweden.
    Johansson, Arne V.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Unified explicit algebraic Reynolds stress model for compressible, heat-releasing and supercritical flowswith large density variation2016Report (Other academic)
    Abstract [en]

    An explicit algebraic model (EARSM) for variable denstiy turbulent flow developed by Grigoriev et al. [Phys. Fluids (2015)] is revisited here. We apply it to a quasi one-dimensional nozzle flow, a wall-jet flow with combustion and large density variation and a supercritical flow of carbon dioxide with heat transfer and buoyancy. It is confirmed that the coupling between strong mean density gradient due to high speed, heat release or thermodynamic variations and the 'local mean acceleration' of the flow produces strong turbulent density and heat fluxes, which strongly affect the turbulence. The possible calibration branches are identified and analyzed. We show that a simple and unified calibration of the model gives good predictions for all cases considered. Therefore, the model is a reliable tool for the computation of compressible flows with large density variation.

  • 20.
    Grigoriev, Igor
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Wallin, Stefan
    Swedish Defence Research Agency (FOI), Stockholm, Sweden.
    Brethouwer, Geert
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Grundestam, Olof
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Johansson, Arne V.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Algebraic Reynolds stress modeling of turbulence subject to rapid homogeneous and non-homogeneous compression or expansion2016In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 28, no 2, p. 026101-Article in journal (Refereed)
    Abstract [en]

    A recently developed explicit algebraic Reynolds stress model (EARSM) by Grigoriev et al. ["A realizable explicit algebraic Reynolds stress model for compressible turbulent flow with significant mean dilatation," Phys. Fluids 25(10), 105112 (2013)] and the related differential Reynolds stress model (DRSM) are used to investigate the influence of homogeneous shear and compression on the evolution of turbulence in the limit of rapid distortion theory (RDT). The DRSM predictions of the turbulence kinetic energy evolution are in reasonable agreement with RDT while the evolution of diagonal components of anisotropy correctly captures the essential features, which is not the case for standard compressible extensions of DRSMs. The EARSM is shown to give a realizable anisotropy tensor and a correct trend of the growth of turbulence kinetic energy K, which saturates at a power law growth versus compression ratio, as well as retaining a normalized strain in the RDT regime. In contrast, an eddy-viscosity model results in a rapid exponential growth of K and excludes both realizability and high magnitude of the strain rate. We illustrate the importance of using a proper algebraic treatment of EARSM in systems with high values of dilatation and vorticity but low shear. A homogeneously compressed and rotating gas cloud with cylindrical symmetry, related to astrophysical flows and swirling supercritical flows, was investigated too. We also outline the extension of DRSM and EARSM to include the effect of non-homogeneous density coupled with "local mean acceleration" which can be important for, e.g., stratified flows or flows with heat release. A fixed-point analysis of direct numerical simulation data of combustion in a wall-jet flow demonstrates that our model gives quantitatively correct predictions of both streamwise and cross-stream components of turbulent density flux as well as their influence on the anisotropies. In summary, we believe that our approach, based on a proper formulation of the rapid pressure-strain correlation and accounting for the coupling with turbulent density flux, can be an important element in CFD tools for compressible flows.

  • 21.
    Grundestam, Olof
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Wallin, Stefan
    Eliasson, P.
    Johansson, Arne V.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Application of Reynolds stress models to high-lift aerodynamics applications2005In: Engineering Turbulence Modelling and Experiments 6 / [ed] Rodi, W; Mulas, M, 2005, p. 607-616Conference paper (Refereed)
    Abstract [en]

    A recently proposed explicit algebraic Reynolds stress model (EARSM) based on a nonlinear pressure strain rate model has been implemented in an industrial CFD code for unstructured grids. The new EARSM was then used to compute the flow around typical three element high-lift devices used on transport aircraft both in 2D and 3D. For 2D mean flow, various angles of attack have been investigated. Two different grids have been used, one coarse grid with 35,000 nodes and fine grid with 340,000 nodes. Furthermore, a 3D take-off configuration including fuselage was computed using a computational grid with about three million grid points. For the 2D case and pre-stall angles of attack, the new EARSM makes fair predictions. For higher angles of attack, the new EARSM and the baseline EARSM show a large sensitivity to the transition point location. The original transition setting leads to a premature stall while an alternative transition setting gives predictions that are in good agreement with experiments. For lower angles of attack, there are indications on minor improvements. One angle of attack close to the maximum lift was computed for the 3D case and compared with previous computations. No significant differences were found with the new EARSM compared with the baseline EARSM. Also the convergence rate and computational effort by using the new EARSM are comparable with the baseline EARSM.

  • 22.
    Grundestam, Olof
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Wallin, Stefan
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Eliasson, Peter
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Johansson, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Application of EARSM turbulence models to high-lift aerodynamics applications2005In: Proc. of Engineering turbulence modelling and measurements 6 (ETMM-6), 2005Conference paper (Refereed)
  • 23.
    Grundestam, Olof
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Wallin, Stefan
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Johansson, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics.
    A priori evaluations and least-squares optimizations of turbulence models for fully developed rotating turbulent channel flow2008In: European journal of mechanics. B, Fluids, ISSN 0997-7546, E-ISSN 1873-7390, Vol. 27, no 2, p. 75-95Article in journal (Refereed)
    Abstract [en]

    The present study involves a priori tests of pressure-strain and dissipation rate tensor models using data from direct numerical simulations (DNS) of fully developed turbulent channel flow with and without spanwise system rotation. Three different pressure-strain rate models are tested ranging from a simple quasi-linear model to a realizable fourth order model. The evaluations demonstrate the difficulties of developing RANS-models that accurately describe the flow for a wide range of rotation numbers. Furthermore, least-squares based tensor representations of the exact pressure-strain and dissipation rate tensors are derived point-wise in space. The relation obtained for the rapid pressure-strain rate is exact for general 2D mean flows. Hence, the corresponding distribution of the optimized coefficients show the ideal behaviour. The corresponding representations for the slow pressure-strain and dissipation rate tensors are incomplete but still optimal in a least-squares sense. On basis of the least-squares analysis it is argued that the part of the representation that is tensorially linear in the Reynolds stress anisotropy is the most important for these parts.

  • 24.
    Grundestam, Olof
    et al.
    KTH, Superseded Departments, Mechanics.
    Wallin, Stefan
    KTH, Superseded Departments, Mechanics.
    Johansson, Arne
    KTH, Superseded Departments, Mechanics.
    An explicit algebraic Reynolds stress model based on a nonlinear pressure strain rate model2004In: International journal of heat fluid flow, ISSN 0142-727X, Vol. 26, no 5, p. 732-745Article in journal (Refereed)
    Abstract [en]

    The use of a pressure strain rate model including terms nonlinear in the mean strain and rotation rate tensors in an explicit algebraic Reynolds stress model (EARSM) is considered. For 2D mean flows the nonlinear contributions can be fully accounted for in the EARSM formulation. This is not the case for 3D mean flows and a suggestion of how to modify the nonlinear terms to make the EARSM formulation in 3D mean flows consistent with its 2D counterpart is given. The corresponding EARSM is derived in conjunction with the use of streamline curvature corrections emanating from the advection of the Reynolds stress anisotropy, The proposed model is tested for rotating homogeneous shear flow. rotating channel flow and rotating pipe flow and the nonlinear contributions are shown to have a significant effect on the predicted flow characteristics. In cases where the 3D effects are strong, the approximations of the production to dissipation ratio made in the EARSM formulation for 3D mean flows must be made carefully and a 3D mean flow correction is considered. For the rotating pipe flow at the highest rotation rate investigated. the standard formulation even prevented convergence, while inclusion of the 3D correction gives reasonable results

  • 25.
    Grundestam, Olof
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Wallin, Stefan
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Johansson, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Observations on the predictions of fully developed rotating pipe flow using differential and explicit algebraic Reynolds stress models2006In: European jounal of mechanics. B, ISSN 0997-7546, Vol. 25, no 1, p. 95-112Article in journal (Refereed)
    Abstract [en]

    The differences between two differential Reynolds stress models (DRSM) and their corresponding explicit algebraic Reynolds stress models (EARSM) are investigated by studying fully developed axially rotating turbulent pipe flow. The mean flow and the turbulence quantities are strongly influenced by the imposed rotation, and is well captured by the differential models as well as their algebraic truncations. All the tested models give mean velocity profiles that are in good qualitative agreement with the experimental data. It is demonstrated that the predicted turbulence kinetic energy levels vary dramatically depending on the diffusion model used, and that this is closely related to the model for the evolution of the length-scale determining quantity. Furthermore, the effect of the weak equilibrium assumption, underlying the EARSMs, and the approximation imposed for 3D mean flows on the turbulence levels are investigated. In general the predictions obtained with the EARSMs rather closely follow those of the corresponding DRSMs

  • 26.
    Grundestam, Olof
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Wallin, Stefan
    KTH, School of Engineering Sciences (SCI), Mechanics. Division of Systems Technology, Swedish Defence Research Agency (FOI), Sweden.
    Johansson, Arne V.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Different explicit algebraic reynolds stress model representations and their predictions of fully developed turbulent rotating pipe flow2005Conference paper (Refereed)
    Abstract [en]

    The least square projection method is used for obtaining optimal EARSMs for different incomplete sets of basis tensors. The possible singular behaviour depending on the choice of the basis tensors has been investigated. It is demonstrated that many of the incomplete representations, expressed in general 3D mean flows, have singularities in some specific flows, such as general 2D mean flows or more specifically, strain and/or rotation free 2D mean flows. The different representations are investigated by computing fully developed rotating pipe flow. It is demonstrated that EARSMs containing basis tensors of odd powers higher than one, of the mean velocity gradients, do indeed predict a parabolic mean azimuthal velocity profile. The predcitions made by the incomplete representations deviate significantly from those by the complete representations, and the actual choice of basis tensors as well as the model parameters have a significant effect on the predictions.

  • 27.
    Grundestam, Olof
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Wallin, Stefan
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Johansson, Arne V.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Direct numerical simulations of rotating channel flowArticle in journal (Other academic)
  • 28.
    Grundestam, Olof
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Wallin, Stefan
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Johansson, Arne V.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Direct numerical simulations of rotating turbulent channel flow2008In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 598, p. 177-199Article in journal (Refereed)
    Abstract [en]

    Fully developed rotating turbulent channel flow has been studied, through direct numerical simulations, for the complete range of rotation numbers for which the flow is turbulent. The present investigation suggests that complete flow laminarization occurs at a rotation number Ro = 2 Omega delta/U-b <= 3.0, where Omega denotes the system rotation, U-b is the mean bulk velocity and 3 is the half-width of the channel. Simulations were performed for ten different rotation numbers in the range 0.98 to 2.49 and complemented with earlier simulations (done in our group) for lower values of Ro. The friction Reynolds number Re-tau = u(tau)delta/v (where u(tau) is the wall-shear velocity and v is the kinematic viscosity) was chosen as 180 for these simulations. A striking feature of rotating channel flow is the division into a turbulent (unstable) and an almost laminarized (stable) side. The relatively distinct interface between these two regions was found to be maintained by a balance where negative turbulence production plays an important role. The maximum difference in wall-shear stress between the two sides was found to occur for a rotation number of about 0.5. The bulk flow was found to monotonically increase with increasing rotation number and reach a value (for Re-tau = 180) at the laminar limit (Ro = 3.0) four times that of the non-rotating case.

  • 29.
    Grundestam, Olof
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Wallin, Stefan
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Johansson, Arne V.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Techniques for deriving explicit algebraic Reynolds stress models based on incomplete sets of basis tensors and predictions of fully developed rotating pipe flow2005In: Physics of fluids, ISSN 1070-6631, Vol. 17, no 11, p. 115103-Article in journal (Refereed)
    Abstract [en]

    Different techniques for deriving explicit algebraic Reynolds stress models (EARSMs) using incomplete sets of basis tensors are discussed. The first is the Galerkin method which has been used by several authors. The second alternative technique, proposed here, is based on the least-squares method. The idea behind the latter method is to minimize the error induced in the implicit relation, i.e., the algebraic Reynolds stress model (ARSM) equation, due to the use of incomplete sets of basis tensors. It is argued that since the system matrix of the ARSM equation is not symmetric and positive definite, the Galerkin method does not give EARSMs that are optimal in the strict classical sense. The possible singular behavior depending on the choice of the basis tensors has also been investigated. It is demonstrated that many of the EARSMs based on incomplete tensor bases, expressed in general three-dimensional mean flows, have singularity problems in some flows, such as general two-dimensional (2D) mean flows or more specifically, strain- and/or rotation-free 2D mean flows. The different EARSMs emanating from the two derivation methods are investigated by computing fully developed rotating pipe flow. The results indicate that the EARSMs derived with the least-squares method capture the behavior of the complete EARSMs significantly better than those derived with the Galerkin method. Furthermore, by using mean flow data from the complete EARSMs to evaluate the square error of the incomplete EARSMs it is demonstrated that the least-squares based EARSMs have square errors significantly smaller than the Galerkin EARSMs, very close to minimum.

  • 30.
    Gullman-Strand, Johan
    et al.
    KTH, Superseded Departments, Mechanics.
    Törnblom, Olle
    KTH, Superseded Departments, Mechanics.
    Lindgren, Björn
    KTH, Superseded Departments, Mechanics.
    Amberg, Gustav
    KTH, Superseded Departments, Mechanics.
    Johansson, Arne V.
    KTH, Superseded Departments, Mechanics.
    Numerical and experimental study of separated flow in a plane asymmetric diffuser2004In: International Journal of Heat and Fluid Flow, ISSN 0142-727X, E-ISSN 1879-2278, Vol. 25, no 3, p. 451-460Article in journal (Refereed)
    Abstract [en]

    Computations of the turbulent flow through plane asymmetric diffusers for opening angles from 8degrees to 10degrees have been carried out with the explicit algebraic Reynolds stress model (EARSM) of Wallin and Johansson [J. Fluid Mech. 403 (2000) 89]. It is based on a two-equation platform in the form of a low-Re K - omega formulation, see e.g. Wilcox [Turbulence Modeling for CFD, DCW Industries Inc., 1993]. The flow has also been studied experimentally for the 8.5degrees opening angle using PIV and LDV. The models under-predict the size and magnitude of the recirculation zone. This is, at least partially, attributed to an over-estimation of the wall normal turbulence component in a region close to the diffuser inlet and to the use of damping functions in the near-wall region. By analyzing the balance between the production and dissipation of the turbulence kinetic energy we find that the predicted dissipation is too large. Hence, we can identify a need for improvement of the modeling the transport equation for the turbulence length-scale related quantity.

  • 31. Hallbäck, M.
    et al.
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Johansson, Arne, V.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Alfredsson, Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics.
    The basics of turbulence modelling1996In: Turbulence and Transition Modelling, Kluwer Academic Publishers, 1996, p. 81-154Chapter in book (Refereed)
  • 32.
    Johansson, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Engineering Turbulence Models and their Development, with Emphasis on Explicit Algebraic Reynolds Stress Models2002In: Theories of Turbulence: CISM Courses and Lectures no. 442 / [ed] M. Oberlack and F. Busse, Springer-Verlag New York, 2002, p. 253-300Chapter in book (Refereed)
  • 33.
    Johansson, Arne, V.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Explicit algebraic Reynolds stress and Reynolds flux modelling: A review of current activities at KTH1999In: ERCOFTAC Series, ISSN 1382-4309, no 40, p. 39-45Article in journal (Refereed)
  • 34.
    Johansson, Arne, V.
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Alvelius, K
    LES computations and comparisons with Kolmogorov theory for two-point pressure-velocity correlations and structure functions for globally anisotropic turbulence2000In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, no 403, p. 23-36Article in journal (Refereed)
  • 35.
    Johansson, Arne, V.
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Burden, A.D
    Transition, Turbulence and Combustion Modelling: An introduction to turbulence modelling1999In: Transition, Turbulence and Combustion Modelling: ERCOFTAC Series, Springer Publishing Company, 1999, vol. 6, p. 159-242Chapter in book (Refereed)
  • 36.
    Johansson, Arne V.
    et al.
    KTH, Superseded Departments, Mechanics.
    Lindgren, Björn
    KTH, Superseded Departments, Mechanics.
    Österlund, Jens M.
    KTH, Superseded Departments, Mechanics.
    Experimental tests of mean velocity distribution laws derived by lie group symmetry methods in turbulent boundary layers2004In: IUTAM SYMPOSIUM ON REYNOLDS NUMBER SCALING IN TURBULENT FLOW / [ed] Smits, AJ, 2004, Vol. 74, p. 257-264Conference paper (Refereed)
    Abstract [en]

    New scaling laws for turbulent boundary layers recently derived (see Oberlack, 2001) using Lie group symmetry methods have been tested against experimental data from the KTH data-base for zero-pressure-gradient turbulent boundary layers. The most significant new law gives an exponential variation of the mean velocity defect in the outer (wake) region. It was shown to fit very well the experimental data over a large part of the boundary layer, from the outer part of the overlap region to about half the boundary layer thickness (delta(99)). A small modification of the innermost part of the log-layer is predicted by the same method, in the form of an additive constant within the log-function, and was confirmed by the experimental data.

  • 37.
    Johansson, Arne, V.
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Wikström, Petra, M.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    DNS and modelling of passive scalar transport in turbulent channel flow with a focus on scalar dissipation rate modelling2000In: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987, ISSN 1573-1987, no 63, p. 223-245Article in journal (Refereed)
  • 38. Karlsson, Bengt
    et al.
    Lindquist, Ch.
    Johansson, Arne, V.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Steiner, L.
    Risk of hemorrhage in cerebral arteriovenous malformations1997In: Minimally Invasive Neurosurgery, ISSN 0946-7211, E-ISSN 1439-2291, Vol. 40, p. 40-46Article in journal (Refereed)
  • 39.
    Lazeroms, Werner
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Brethouwer, Geert
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Wallin, Stefan
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Johansson, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    An explicit algebraic Reynolds-stress and scalar-flux model for stably stratified flows2013In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 723, p. 91-125Article in journal (Refereed)
    Abstract [en]

    This work describes the derivation of an algebraic model for the Reynolds stresses and turbulent heat flux in stably stratified turbulent flows, which are mutually coupled for this type of flow. For general two-dimensional mean flows, we present a correct way of expressing the Reynolds-stress anisotropy and the (normalized) turbulent heat flux as tensorial combinations of the mean strain rate, the mean rotation rate, the mean temperature gradient and gravity. A system of linear equations is derived for the coefficients in these expansions, which can easily be solved with computer algebra software for a specific choice of the model constants. The general model is simplified in the case of parallel mean shear flows where the temperature gradient is aligned with gravity. For this case, fully explicit and coupled expressions for the Reynolds-stress tensor and heat-flux vector are given. A self-consistent derivation of this model would, however, require finding a root of a polynomial equation of sixth-order, for which no simple analytical expression exists. Therefore, the nonlinear part of the algebraic equations is modelled through an approximation that is close to the consistent formulation. By using the framework of a K-omega model (where K is turbulent kinetic energy and omega an inverse time scale) and, where needed, near-wall corrections, the model is applied to homogeneous shear flow and turbulent channel flow, both with stable stratification. For the case of homogeneous shear flow, the model predicts a critical Richardson number of 0.25 above which the turbulent kinetic energy decays to zero. The channel-flow results agree well with DNS data. Furthermore, the model is shown to be robust and approximately self-consistent. It also fulfils the requirements of realizability.

  • 40.
    Lazeroms, Werner
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. Stockholm University, Sweden .
    Brethouwer, Geert
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Wallin, Stefan
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. Swedish Defence Research Agency (FOI), Sweden .
    Johansson, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Efficient treatment of the nonlinear features in algebraic Reynolds-stress and heat-flux models for stratified and convective flows2015In: International Journal of Heat and Fluid Flow, ISSN 0142-727X, E-ISSN 1879-2278, Vol. 53, p. 15-28Article in journal (Refereed)
    Abstract [en]

    This work discusses a new and efficient method for treating the nonlinearity of algebraic turbulence models in the case of stratified and convective flows, for which the equations for the Reynolds stresses and turbulent heat flux are strongly coupled. In such cases, one finds a quasi-linear set of equations, which can be solved through an appropriate linear expansion in basis tensors and vectors, as discussed in earlier work. However, finding a consistent and truly explicit algebraic turbulence model requires solving an additional equation for the production-to-dissipation ratio (P+G)/ε of turbulent kinetic energy. Due to the nonlinear nature of the problem, the equation for (P+G)/ε is a higher-order polynomial equation for which no analytical solution can be found. Here we provide a new method to approximate the solution of this polynomial equation through an analysis of two special limits (shear-dominated and buoyancy-dominated), in which exact solutions are obtainable. The final result is a model that appropriately combines the two limits in more general cases. The method is tested for turbulent channel flow, both with stable and unstable stratification, and the atmospheric boundary layer with periodic and rapid changes between stable and unstable stratification. In all cases, the model is shown to give consistent results, close to the exact solution of (P+G)/ε. This new method greatly increases the range of applicability of explicit algebraic models, which otherwise would rely on the numerical solution of the polynomial equation.

  • 41.
    Lazeroms, Werner
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Brethouwer, Geert
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Wallin, Stefan
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Johansson, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Explicit algebraic models for turbulent flows with buoyancy effects2013Report (Other academic)
    Abstract [en]

    An explicit algebraic model for the Reynolds stresses and turbulent heat fluxis presented for turbulent parallel shear flows in which buoyancy forces arepresent. The derivation is based on a model framework for two-dimensionalmean flows that was already presented in a previous work (Lazeroms et al.2013), and new test cases are investigated here. The model is formulated interms of the Reynolds-stress anisotropy and a normalized heat flux, which areexpanded as a linear combination of appropriate basis tensors. The coefficientsin this expansion can be found from a system of 18 linear equations. Thisformulation is complemented with a nonlinear equation for a quantity relatedto the total production-to-dissipation ratio, the solution of which is modelledwith an appropriate expression. Fully explicit model expressions are found fortwo fundamentally different flow geometries: a horizontal channel for whichthe temperature gradient is aligned with gravity, and a vertical channel wherethe temperature gradient and gravity are perpendicular. In the first case, weconsider both stable and unstable stratification, while in the second case, bothmixed and natural convection flows are investigated. Comparison with DNSdata shows that the model gives predictions that are substantially better thanstandard eddy-viscosity/eddy-diffusivity models.

  • 42.
    Lazeroms, Werner
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Brethouwer, Gert
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Wallin, Stefan
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Johansson, Arne V.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Nonlinear features in explicit algebraic models for turbulent flows with active scalars2015In: 9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015, TSFP-9 , 2015Conference paper (Refereed)
    Abstract [en]

    A detailed discussion of explicit algebraic turbulence models in the case of active scalars is given. In particular, we discuss the appearance of nonlinearities in the models and the need for explicit solutions of the resulting nonlinear equations. Focussing on a recently published model for two-dimensional stratified flows, we present an intuitive way of approximating the solution of a sixth-order polynomial equation for the production-to-dissipation ratio (p + g)/e of turbulent kinetic energy K. This formulation is shown to be consistent for turbulent channel flow with stable and unstable stratification. The result is important for obtaining a robust model with a correct behaviour of the turbulence production in different limits of shear and buoyancy. The results have recently been published in Lazeroms et al. (2015).

  • 43.
    Lazeroms, Werner M. J.
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Svensson, G.
    Bazile, E.
    Brethouwer, Geert
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Wallin, Stefan
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Johansson, Arne V.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Study of Transitions in the Atmospheric Boundary Layer Using Explicit Algebraic Turbulence Models2016In: Boundary-layer Meteorology, ISSN 0006-8314, E-ISSN 1573-1472, Vol. 161, no 1, p. 19-47Article in journal (Refereed)
    Abstract [en]

    We test a recently developed engineering turbulence model, a so-called explicit algebraic Reynolds-stress (EARS) model, in the context of the atmospheric boundary layer. First of all, we consider a stable boundary layer used as the well-known first test case from the Global Energy and Water Cycle Experiment Atmospheric Boundary Layer Study (GABLS1). The model is shown to agree well with data from large-eddy simulations (LES), and this agreement is significantly better than for a standard operational scheme with a prognostic equation for turbulent kinetic energy. Furthermore, we apply the model to a case with a (idealized) diurnal cycle and make a qualitative comparison with a simpler first-order model. Some interesting features of the model are highlighted, pertaining to its stronger foundation on physical principles. In particular, the use of more prognostic equations in the model is shown to give a more realistic dynamical behaviour. This qualitative study is the first step towards a more detailed comparison, for which additional LES data are needed.

  • 44.
    Lazeroms, Werner
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Svensson, Gunilla
    Stockholm University, Department of Meteorology.
    Bazile, Eric
    Météo-France, CNRM-GAME.
    Brethouwer, Geert
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Wallin, Stefan
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Johansson, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Study of transitions in the atmospheric boundary layer using explicit algebraic turbulence models.Manuscript (preprint) (Other academic)
  • 45.
    Lenaers, Peter
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Brethouwer, Geert
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Johansson, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    A new high-order method for the simulation of incompressible wall-bounded turbulent flows2014In: Journal of Computational Physics, ISSN 0021-9991, E-ISSN 1090-2716, Vol. 272, p. 108-126Article in journal (Refereed)
    Abstract [en]

    A new high-order method for the accurate simulation of incompressible wall-bounded flows is presented. In the stream- and spanwise directions the discretisation is performed by standard Fourier series, while in the wall-normal direction the method combines high-order collocated compact finite differences with the influence matrix method to calculate the pressure boundary conditions that render the velocity field exactly divergence-free. The main advantage over Chebyshev collocation is that in wall-normal direction, the grid can be chosen freely and thus excessive clustering near the wall is avoided. This can be done while maintaining the high-order approximation as offered by compact finite differences. The discrete Poisson equation is solved in a novel way that avoids any full matrices and thus improves numerical efficiency. Both explicit and implicit discretisations of the viscous terms are described, with the implicit method being more complex, but also having a wider range of applications. The method is validated by simulating two-dimensional Tollmien-Schlichting waves, forced transition in turbulent channel flow, and fully turbulent channel flow at friction Reynolds number Re-tau = 395, and comparing our data with analytical and existing numerical results. In all cases, the results show excellent agreement showing that the method simulates all physical processes correctly.

  • 46.
    Lenaers, Peter
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Brethouwer, Geert
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    Johansson, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
    A new high-order method for the simulation of incompressible wall-bounded turbulent pipe flowManuscript (preprint) (Other academic)
  • 47.
    Lenaers, Peter
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Mechanics.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Mechanics.
    Brethouwer, Gert
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Mechanics.
    Johansson, Arne
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Mechanics.
    A new high-order method for the accurate simulation of incompressible wall-bounded flows2015In: 9th International Conference on Direct and Large-Eddy Simulation, 2013, Springer Publishing Company, 2015, p. 133-138Conference paper (Refereed)
    Abstract [en]

    A new high-order method for the accurate simulation of incompressible wall-bounded flows is presented. In stream- and spanwise direction the discretisation is performed by standard Fourier series, while in wall-normal direction the method combines high-order collocated compact finite differences with the influence matrix method to calculate the pressure boundary conditions that render the velocity field divergence-free. The main advantage over Chebyshev collocation is that in wall normal direction, the grid can be chosen freely and thus excessive clustering near the wall is avoided. Both explicit and implicit discretisations of the viscous terms are described, with the implicit method being more complex, but also having a wider range of applications. The method is validated by simulating fully turbulent channel flow at friction Reynolds number Reτ=395, and comparing our data with existing numerical results. The results show excellent agreement proving that the method simulates all physical processes correctly.

  • 48.
    Lenaers, Peter
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Brethouwer, Gert
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Johansson, Arne V.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    A new high-order method for simulating turbulent pipe flow2016In: Springer Proceedings in Physics, Springer, 2016, p. 211-215Conference paper (Refereed)
  • 49.
    Lindgren, Björn
    et al.
    KTH, Superseded Departments, Mechanics.
    Johansson, Arne
    KTH, Superseded Departments, Mechanics.
    Tsuji, Yoshiyuki
    Universality of probability density distributions in the overlap region in high Reynolds number turbulent boundary layers2004In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 16, no 7, p. 2587-2591Article in journal (Refereed)
    Abstract [en]

    The probability density functions (PDFs) of the streamwise mean velocity in high Reynolds number turbulent boundary layers have been studied. The hypothesis of self-similar, normalized with the root mean square velocity, PDFs has been tested using the KTH database of high Reynolds number zero pressure-gradient turbulent boundary layer flow. The self-similarity was tested using the Kullback-Leibler divergence measure and it was found that the region of self-similar PDFs extends from about 160 viscous wall units to about 0.3 boundary layer thicknesses (in delta(95)). This region is somewhat larger than the universal overlap region. The PDF shape in the universal overlap region is close to Gaussian allowing for a Gram-Charlier expansion approximation of the measured PDFs. A remarkable collapse was found for 57 normalized PDF distributions for different positions within the universal overlap region and Reynolds numbers based on the momentum-loss thickness between 4300 and 12 600, strongly indicating a high degree of flow universality within the universal overlap region. Within the range studied, the Gram-Charlier expansion coefficients (related to the PDF moments) show no Reynolds number trend further supporting the self-similarity hypothesis.

  • 50.
    Lindgren, Björn
    et al.
    KTH, Superseded Departments, Mechanics.
    Johansson, Arne V.
    KTH, Superseded Departments, Mechanics.
    Evaluation of a new wind tunnel with expanding corners2004In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 36, no 1, p. 197-203Article in journal (Refereed)
    Abstract [en]

    A new low-speed, closed-circuit, closed-test-section wind tunnel, called BLT, has been designed and built at KTH. The turbulence intensity in the test section is <0.04%, the total pressure variation is <+/-0.1% and the temperature variation is <+/-0.07degreesC over the cross-sectional area. The concept of expanding corners with an expansion ratio of 1.32 first investigated by Lindgren et al. in 1998, has been implemented successfully with a two-dimensional total pressure loss coefficient of 0.047 at a chord Reynolds number of 200,000. It is comparable to or even better than the values found in most wind tunnels using nonexpanding corners. The findings in this study prove the usefulness of expanding corners to achieve a compact wind tunnel circuit design without compromising the flow quality.

123 1 - 50 of 148
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