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  • 51.
    Marstorp, Linus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Grundestam, Olof
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Explicit algebraic subgrid stress models with application to rotating channel flow2009Ingår i: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 639, s. 403-432Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    New explicit subgrid stress models are proposed involving the strain rate and rotation rate tensor, which can account for rotation in a natural way. The new models are based on the same methodology that leads to the explicit algebraic Reynolds stress model formulation for Reynolds-averaged Navier-Stokes simulations. One dynamic model and one non-dynamic model are proposed. The non-dynamic model represents a computationally efficient subgrid scale (SGS) stress model, whereas the dynamic model is the most accurate. The models are validated through large eddy simulations (LESs) of spanwise and streamwise rotating channel flow and are compared with the standard and dynamic Smagorinsky models. The proposed explicit dependence on the system rotation improves the description of the mean velocity profiles and the turbulent kinetic energy at high rotation rates. Comparison with the dynamic Smagorinsky model shows that not using the eddy-viscosity assumption improves the description of both the Reynolds stress anisotropy and the SGS stress anisotropy. LESs of rotating channel flow at Re-tau = 950 have been carried out as well. These reveal some significant Reynolds number influences on the turbulence statistics. LESs of non-rotating turbulent channel flow at Re-tau = 950 show that the new explicit model especially at coarse resolutions significantly better predicts the mean velocity, wall shear and Reynolds stresses than the dynamic Smagorinsky model, which is probably the result of a better prediction of the anisotropy of the subgrid dissipation.

  • 52.
    Marstorp, Linus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Johansson, Arne
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    A code for large-eddy simulation of rotating homogeneous shear flow with passive scalarsManuskript (Övrigt vetenskapligt)
  • 53.
    Marstorp, Linus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Johansson, Arne
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    A new model for the subgrid passive scalar fluxManuskript (Övrigt vetenskapligt)
  • 54.
    Marstorp, Linus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Johansson, Arne
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Near-wall treatment in LES with an explicit algebraic subgrid stress model2007Ingår i: ERCOFTAC Bulletin, nr 72, s. 45-48Artikel i tidskrift (Refereegranskat)
  • 55.
    Marstorp, Linus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Johansson, Arne
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Stochastic SGS modelling in homogeneous shear flow with passive scalars2006Ingår i: Direct and Large-Eddy Simulation VI, DORDRECHT, NETHERLANDS: SPRINGER , 2006, Vol. 10, s. 167-174Konferensbidrag (Refereegranskat)
    Abstract [en]

    A new stochastic Smagorinsky model for the subgrid stress and subgid scalar flux is proposed. The new model is applied in LES of rotating homogeneous shear flow, which is an excellent case for developing and testing subgrid scale models. The proposed model provides for backscatter of energy and scalar variance, and reduces the length scale of the subgrid dissipation compared to the standard Smagorinsky model. At the same time, the flatness factor of the subgrid dissipation obtained from the stochastic model is of the same order of magnitude as for the Smagorinsky model.

  • 56.
    Marstorp, Linus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    A stochastic SGS model with application to turbulent channel flow with a passive scalar2007Ingår i: ADVANCES IN TURBULENCE XI / [ed] Palma, JMLM; Lopes, AS, BERLIN: SPRINGER-VERLAG BERLIN , 2007, Vol. 117, s. 591-593Konferensbidrag (Refereegranskat)
  • 57.
    Marstorp, Linus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    A stochastic subgrid model with application to turbulent flow and scalar mixing2007Ingår i: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 19, nr 3, s. 035107-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A new computationally cheap stochastic Smagorinsky model which allows for backscatter of subgrid scale energy is proposed. The new model is applied in the large eddy simulation of decaying isotropic turbulence, rotating homogeneous shear flow and turbulent channel flow at Re-tau=360. The results of the simulations are compared to direct numerical simulation data. The inclusion of stochastic backscatter has no significant influence on the development of the kinetic energy in homogeneous flows, but it improves the prediction of the fluctuation magnitudes as well as the anisotropy of the fluctuations in turbulent channel flow compared to the standard Smagorinsky model with wall damping of C-S. Moreover, the stochastic model improves the description of the energy transfer by reducing its length scale and increasing its variance. Some improvements were also found in isotropic turbulence where the stochastic contribution improved the shape of the enstrophy spectrum at the smallest resolved scales and reduced the time scale of the smallest resolved scales in better agreement with earlier observations.

  • 58.
    Marstorp, Linus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Explicit Algebraic Subgrid Models for Large Eddy Simulation2010Ingår i: PROGRESS IN TURBULENCE III / [ed] Peinke, J.; Oberlack, M.; Talamelli, A., 2010, Vol. 131, s. 127-129Konferensbidrag (Refereegranskat)
    Abstract [en]

    The objective of this study is to develop models for the subgrid-scale (SGS) stress and the SOS scalar flux by applying the same kind of methodology that leads to the explicit algebraic Reynolds stress model, EARSM [2], and the explicit algebraic scalar flux model, EASFM [3], for RANS. The idea is that these new models can improve the description of the anisotropy compared to eddy viscosity models. Since the new models can include the effect of system rotation in a natural way they have a particular potential for rotating flows.

  • 59.
    Marstorp, Linus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Explicit Algebraic Subgrid Stress Models for Large Eddy Simulation2010Ingår i: Direct and large-eddy simulation vii, 2010, s. 167-172Konferensbidrag (Refereegranskat)
    Abstract [en]

    New explicit subgrid stress models have been developed which are based on the same methodology that leads to the EARSM formulation for RANS. The subgrid models involve the strain rate and rotation rate tensor, and can account for rotation in a natural way. A dynamic and a non-dynamic version are proposed. The non-dynamic version is a computationally cheap SGS model, whereas the dynamic version is more accurate. Large eddy simulations of rotating channel flow have been carried out in order to test the models. Comparison with the standard and dynamic Smagorinsky models shows that the explicit dependence on the system rotation improves the description of the mean velocity profiles and the Reynolds stresses at high rotation rates. Furthermore, large eddy simulations with the new models are less sensitive to the grid resolution.

  • 60.
    Marstorp, Linus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Li, Qiang
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Schlatter, Philipp
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Validation of SGS models in large eddy simulation of turbulent zero pressure gradient boundary layer flow2008Rapport (Övrigt vetenskapligt)
  • 61.
    Montecchia, Matteo
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Brethouwer, Gert
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Wallin, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Taking large-eddy simulation of wall-bounded flows to higher Reynolds numbers by use of anisotropy-resolving subgrid models2017Ingår i: Physical Review Fluids, E-ISSN 2469-990X, Vol. 2, artikel-id 034601Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Properly resolved large-eddy simulations of wall-bounded high Reynolds number flows using standard subgrid-scale (SGS) models requires high spatial and temporal resolution. We have shown that a more elaborate SGS model taking into account the SGS Reynolds stress anisotropies can relax the requirement for the number of grid points by at least an order of magnitude for the same accuracy. This was shown by applying the recently developed explicit algebraic subgrid-scale model (EAM) to fully developed high Reynolds number channel flows with friction Reynolds numbers of 550, 2000, and 5200. The near-wall region is fully resolved, i.e., no explicit wall modeling or wall functions are applied. A dynamic procedure adjusts the model at the wall for both low and high Reynolds numbers. The resolution is reduced, from the typically recommended 50 and 15 wall units in the stream-and spanwise directions respectively, by up to a factor of 5 in each direction. It was shown by comparison with direct numerical simulations that the EAM is much less sensitive to reduced resolution than the dynamic Smagorinsky model. Skin friction coefficients, mean flow profiles, and Reynolds stresses are better predicted by the EAM for a given resolution. Even the notorious overprediction of the streamwise fluctuation intensity typically seen in poorly resolved LES is significantly reduced whenEAMis used on coarse grids. The improved prediction is due to the capability of the EAM to capture the SGS anisotropy, which becomes significant close to the wall.

  • 62.
    Mårtensson, Gustaf
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Direct numerical simulation of rotating turbulent duct flow2006Ingår i: Journal of turbulence, ISSN 1468-5248, E-ISSN 1468-5248Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    A direct simulation of turbulent flow in a rotating square duct using a second-order finite-volume method was performed. The axis of rotation was normal to the direction of the mean flow in theduct. The simulations are performed at Red = 4400 and for Rod = 0 up to 0.77. The strong effect of rotation on both the mean axial and secondary flows is plainly exhibited. A linear increase in the magnitude of the secondary flow was found with increasing rate of rotation. Turbulence quantities are presented to shed some light on the role of the boundary layer structure on the resistance of theflow. The growth of large-scale secondary roll-cells in the axial direction is studied with reference totheir dependence on the rotation number. The case of turbulent flow in a rotating duct that has been tilted 45 degrees around the axis of the mean flow is presented to illustrate the importance of geometric constraints on the characteristics of the flow.

  • 63.
    Mårtensson, Gustaf E.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Direct numerical simulation of rotating turbulent duct flow2005Konferensbidrag (Refereegranskat)
    Abstract [en]

    A direct simulation of turbulent flow in a rotating square duct using a second-order finite-volume method was performed. The axis of rotation was normal to the direction of the mean flow in the duct. The simulations are performed at Re d = 4400 and for Ro d = 0 up to 0.77. The strong effect of rotation on both the mean axial and secondary flows is plainly exhibited. A linear increase in the magnitude of the secondary flow was found with increasing rate of rotation. Turbulence quantities are presented to shed some light on the role of the boundary layer structure on the resistance of the flow. The growth of large-scale secondary roll-cells in the axial direction is studied with reference to their dependence on the rotation number. The case of turbulent flow in a rotating duct that has been tilted 45° around the axis of the mean flow is presented to illustrate the importance of geometric constraints on the characteristics of the flow.

  • 64.
    Pouransari, Zeinab
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Johansson, Arne J.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Direct numerical simulation of an isothermal reacting turbulent wall-jet2011Ingår i: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 23, nr 8, s. 085104-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the present investigation, Direct Numerical Simulation (DNS) is used to study a binary irreversible and isothermal reaction in a plane turbulent wall-jet. The flow is compressible and a single-step global reaction between an oxidizer and a fuel species is solved. The inlet based Reynolds, Schmidt, and Mach numbers of the wall-jet are Re = 2000, Sc = 0.72, and M = 0.5, respectively, and a constant coflow velocity is applied above the jet. At the inlet, fuel and oxidizer enter the domain separately in a non-premixed manner. The turbulent structures of the velocity field show the common streaky patterns near the wall, while a somewhat patchy or spotty pattern is observed for the scalars and the reaction rate fluctuations in the near-wall region. The reaction mainly occurs in the upper shear layer in thin highly convoluted reaction zones, but it also takes place close to the wall. Analysis of turbulence and reaction statistics confirms the observations in the instantaneous snapshots, regarding the intermittent character of the reaction rate near the wall. A detailed study of the probability density functions of the reacting scalars and comparison to that of the passive scalar throughout the domain reveals the significance of the reaction influence as well as the wall effects on the scalar distributions. The higher order moments of both the velocities and the scalar concentrations are analyzed and show a satisfactory agreement with experiments. The simulations show that the reaction can both enhance and reduce the dissipation of fuel scalar, since there are two competing effects; on the one hand, the reaction causes sharper scalar gradients and thus a higher dissipation rate, on the other hand, the reaction consumes the fuel scalar thereby reducing the scalar dissipation.

  • 65.
    Pouransari, Zeinab
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Direct Numerical Simulation of a Turbulent Reacting Wall-Jet2011Ingår i: Direct and large-eddy simulation VIII, 2011, s. 345-350Konferensbidrag (Refereegranskat)
    Abstract [en]

    The turbulent wall-jet includes a number of interesting fluid mechanics phenomena with close resemblance to many mixing and combustion applications. During the last decades, both DNS (Ahlman et al., 2007; Ahlman et al., 2009), and LES (Dejoan & Leschziner, 2005) have been used to study the turbulent wall-jet. Ahlman et al. (2009) performed DNS of nonisothermal turbulent wall jets. Earlier in 2007, Ahlman et al. investigated turbulent statistics and mixing of a passive scalar for an isothermal case by means of DNS. The first three-dimensional DNS of a reacting turbulent flow was performed by Riley et al. (1986) who simulated a single reaction of two scalars, without heat release, for a mixing layer. Recently, Knaus et al. (2009) studied the effect of heat release in non-premixed reacting shear layers (Knaus & Pantano, 2009).

  • 66.
    Pouransari, Zeinab
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH Mech, Linne Flow Ctr, SE-10044 Stockholm, Sweden..
    Brethouwer, Gert
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH Mech, Linne Flow Ctr, SE-10044 Stockholm, Sweden..
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH Mech, Linne Flow Ctr, SE-10044 Stockholm, Sweden..
    Probability Density Functions of Reacting Species Concentrations in Turbulent Wall-Jet2012Ingår i: PROGRESS IN TURBULENCE AND WIND ENERGY IV / [ed] Oberlack, M Peinke, J Talamelli, A Castillo, L Holling, M, SPRINGER-VERLAG BERLIN , 2012, s. 75-78Konferensbidrag (Refereegranskat)
    Abstract [en]

    Direct numerical simulation of a simple reaction between two scalars in a plane turbulent wall jet has been performed. In addition to mean and fluctuation intensities also higher order statistics and the probability density functions of the reacting scalars have been examined. The probability density functions shed light on the behavior of the passive and reacting scalars close to the wall and also to the near-wall characteristics of the reaction.

  • 67.
    Rasam, Amin
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Johansson, Arne
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    A stochastic extension of the explicit algebraic subgrid-scales models2014Ingår i: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 26, nr 5, s. 055113-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The explicit algebraic subgrid-scale (SGS) stress model (EASM) of Marstorp et al. ["Explicit algebraic subgrid stress models with application to rotating channel flow," J. Fluid Mech. 639, 403-432 (2009)] and explicit algebraic SGS scalar flux model (EASFM) of Rasam et al. ["An explicit algebraic model for the subgrid-scale passive scalar flux,"J. Fluid Mech. 721, 541-577 (2013)] are extended with stochastic terms based on the Langevin equation formalism for the subgrid-scales by Marstorp et al. ["A stochastic subgrid model with application to turbulent flow and scalar mixing," Phys. Fluids 19, 035107 (2007)]. The EASM and EASFM are nonlinear mixed and tensor eddy-diffusivity models, which improve large eddy simulation (LES) predictions of the mean flow, Reynolds stresses, and scalar fluxes of wall-bounded flows compared to isotropic eddy-viscosity and eddy-diffusivity SGS models, especially at coarse resolutions. The purpose of the stochastic extension of the explicit algebraic SGS models is to further improve the characteristics of the kinetic energy and scalar variance SGS dissipation, which are key quantities that govern the small-scale mixing and dispersion dynamics. LES of turbulent channel flow with passive scalar transport shows that the stochastic terms enhance SGS dissipation statistics such as length scale, variance, and probability density functions and introduce a significant amount of backscatter of energy from the subgrid to the resolved scales without causing numerical stability problems. The improvements in the SGS dissipation predictions in turn enhances the predicted resolved statistics such as the mean scalar, scalar fluxes, Reynolds stresses, and correlation lengths. Moreover, the nonalignment between the SGS stress and resolved strain-rate tensors predicted by the EASM with stochastic extension is in much closer agreement with direct numerical simulation data.

  • 68.
    Rasam, Amin
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    An explicit algebraic model for the subgrid-scale passive scalar flux2013Ingår i: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 721, s. 541-577Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In Marstorp et al. (J. Fluid Mech., vol. 639, 2009, pp. 403-432), an explicit algebraic subgrid stress model (EASSM) for large-eddy simulation (LES) was proposed, which was shown to considerably improve LES predictions of rotating and non-rotating turbulent channel flow. In this paper, we extend that work and present a new explicit algebraic subgrid scalar flux model (EASSFM) for LES, based on the modelled transport equation of the subgrid-scale (SGS) scalar flux. The new model is derived using the same kind of methodology that leads to the explicit algebraic scalar flux model of Wikstrom et al. (Phys. Fluids, vol. 12, 2000, pp. 688-702). The algebraic form is based on a weak equilibrium assumption and leads to a model that depends on the resolved strain-rate and rotation-rate tensors, the resolved scalar-gradient vector and, importantly, the SGS stress tensor. An accurate prediction of the SGS scalar flux is consequently strongly dependent on an accurate description of the SGS stresses. The new EASSFM is therefore primarily used in connection with the EASSM, since this model can accurately predict SGS stresses. The resulting SGS scalar flux is not necessarily aligned with the resolved scalar gradient, and the inherent dependence on the resolved rotation-rate tensor makes the model suitable for LES of rotating flow applications. The new EASSFM (together with the EASSM) is validated for the case of passive scalar transport in a fully developed turbulent channel flow with and without system rotation. LES results with the new model show good agreement with direct numerical simulation data for both cases. The new model predictions are also compared to those of the dynamic eddy diffusivity model (DEDM) and improvements are observed in the prediction of the resolved and SGS scalar quantities. In the non-rotating case, the model performance is studied at all relevant resolutions, showing that its predictions of the Nusselt number are much less dependent on the grid resolution and are more accurate. In channel flow with wall-normal rotation, where all the SGS stresses and fluxes are non-zero, the new model shows significant improvements over the DEDM predictions of the resolved and SGS quantities.

  • 69.
    Rasam, Amin
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Stochastic explicit algebraic subgrid-scale stress and scalar flux models2011Rapport (Övrigt vetenskapligt)
  • 70.
    Rasam, Amin
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Subgrid-Scale Model and Resolution Influences in Large Eddy Simulations of Channel Flow2011Ingår i: Direct and large-eddy simulation VIII, 2011, s. 113-118Konferensbidrag (Refereegranskat)
  • 71.
    Rasam, Amin
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Li, Qiang
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Schlatter, Philipp
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Subgrid scalemodel and resolution influences in large eddy simulation of channel flow2010Konferensbidrag (Refereegranskat)
  • 72.
    Rasam, Amin
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Schlatter, Philipp
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Li, Qiang
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Effects of modelling, resolution and anisotropy of subgrid-scales on large eddy simulations of channel flow2011Ingår i: Journal of turbulence, ISSN 1468-5248, E-ISSN 1468-5248, Vol. 12, nr 10, s. 1-20Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, the effect of subgrid-scale (SGS) modelling, grid resolution and anisotropy of the subgrid-scales on large eddy simulation (LES) is investigated. LES of turbulent channel flow is performed at Re=934, based on friction velocity and channel half width, for a wide range of resolutions. The dynamic Smagorinsky model (DS), the high-pass filtered dynamic Smagorinsky model (HPF) based on the variational multiscale method and the recent explicit algebraic model (EA), which accounts for the anisotropy of the SGS stresses are considered. The first part of the paper is focused on the resolution effects on LES, where the performances of the three SGS models at different resolutions are compared to direct numerical simulation (DNS) results. The results show that LES using eddy viscosity SGS models is very sensitive to resolution. At coarse resolutions, LES with the DS and the HPF models deviate considerably from DNS, whereas LES with the EA model still gives reasonable results. Further analysis shows that the two former models do not accurately predict the SGS dissipation near the wall, while the latter does, even at coarse resolutions. In the second part, the effect of SGS modelling on LES predictions of near-wall and outer-layer turbulent structures is discussed. It is found that different models predict near-wall turbulent structures of different sizes. Analysis of the spectra shows that although near-wall scales are not resolved at coarse resolutions, large-scale motions can be reasonably captured in LES using all the tested models.

  • 73.
    Rasam, Amin
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Marstorp, Linus
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    An explicit algebraic model for the subgrid-scale passive scalar flux2011Rapport (Övrigt vetenskapligt)
  • 74.
    Rasam, Amin
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Wallin, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Johansson, Arne
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    A comparison between isotropic and anisotropy-resolving closures in large eddy simulation of separated flow2014Rapport (Övrigt vetenskapligt)
    Abstract [en]

    This study compares the conventional isotropic dynamic eddy viscosity model(DEVM) and anisotropy-resolving nonlinear explicit algebraic subgrid-scale(SGS) stress model (EASSM) of Marstorp et al. (J. Fluid Mech., vol. 639,2009, pp. 403–432) in large-eddy simulations (LESs) of flow separation in achannel with streamwise periodic hill-shaped constrictions and spanwise homogeneity(periodic hill flow). The results are validated with well-resolved LESdata of Breuer et al (Computers & Fluids, vol. 38, 2009, pp. 433-457). Threedifferent resolutions ranging from moderate to very coarse are used. LESs arecarried out with the Code Saturne, an unstructured collocated finite volumesolver for incompressible flows with a second-order central difference schemein space and a second-order discretisation in time. It has inherent numericaldissipation due to the low-order of the numerical method. LESs with no SGSmodel (NSM) are also carried out to analyse the influence of the SGS modelsin the presence of discretisation errors. LESs with the NSM show that the inherentnumerical dissipation is sufficient to give a reasonable prediction of themean velocity profiles at the finest resolution. The LES predictions of the meanvelocity and Reynolds stresses with the EASSM are found to be much moreaccurate than the ones with the DEVM at all resolutions. Although the SGSdissipation produced by the EASSM is found to be considerably lower than bythe DEVM, the EASSM predictions show appreciable improvements over theNSM, indicating the importance of the nonlinear part of the model. At thecoarsest resolution, where the SGS anisotropy is large, LES with the EASSMshows a reasonable prediction of the mean separation and reattachment points,whereas LES with the isotropic DEVM predicts a considerably delayed separationand early flow reattachment with a small separation bubble and the LESwith NSM does not display flow separation. At finer resolutions, the DEVMand NSM predict a shorter separation bubble than the EASSM, which has agood agreement with the well-resolved reference LES data. Hence, a correctprediction of the separation and reattachment by LES requires resolving the SGS anisotropy either by a fine grid or by an anisotropy-resolving SGS modelsuch as the EASSM.

  • 75.
    Rasam, Amin
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Wallin, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. Information and Aeronautical Systems, Swedish Defense Research Agency (FOI), Stockholm, Sweden .
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Large eddy simulation of channel flow with and without periodic constrictions using the explicit algebraic subgrid-scale model2014Ingår i: Journal of turbulence, ISSN 1468-5248, E-ISSN 1468-5248, Vol. 15, nr 11, s. 752-775Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We analyse the performance of the explicit algebraic subgrid-scale (SGS) stress model (EASSM) in large eddy simulation (LES) of plane channel flow and the flow in a channel with streamwise periodic hill-shaped constrictions (periodic hill flow) which induce separation. The LESs are performed with the Code_Saturne which is an unstructured collocated finite volume solver with a second-order spatial discretisation suitable for LES of incompressible flow in complex geometries. At first, performance of the EASSM in LES of plane channel flow at two different resolutions using the Code_Saturne and a pseudo-spectral method is analysed. It is observed that the EASSM predictions of the mean velocity and Reynolds stresses are more accurate than the conventional dynamic Smagorinsky model (DSM). The results with the pseudo-spectral method were, in general, more accurate. In the second step, LES with the EASSM of flow separation in the periodic hill flow is compared to LES with the DSM, no SGS model and a highly resolved LES data using the DSM. Results show that the mean velocity profiles, the friction and pressure coefficients, the length and shape of the recirculation bubble, as well as the Reynolds stresses are considerably better predicted by the EASSM than the DSM and the no SGS model simulations. It was also observed that in some parts of the domain, the resolved strain-rate and SGS shear stress have the same sign. The DSM cannot produce a correct SGS stress in this case, in contrast to the EASSM.

  • 76.
    Rasam, Amin
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Wallin, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Brethouwer, Gert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Large-eddy simulation using the explicit algebraic subgrid model in complex geometries2013Ingår i: International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2013, TSFP-8 , 2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    In Rasam et al. (2011) we compared the performance of the explicit algebraic subgrid-scale (SGS) model (EASSM) (Marstorp et al., 2009) with that of the conventional dynamic Smagorinsky model (DSM) in large eddy simulation (LES) of channel flow using a pseudo-spectral Navier-Stokes solver. We showed that, due to the better prediction of the individual SGS stresses in a wide range of grid resolutions and due to the nonlinear SGS stress contribution by the model, the EASSM predictions were less resolution dependent and more accurate than those of the DSM. As the first step in this study towards LES in complex geometries, we extend our previous study and perform LES of turbulent channel flow at Ret = 590 using the EASSM and the code Saturne, which is an unstructured finite volume solver suitable for LES in complex geometries. The results are compared to those of the DSM and show that the EASSM predictions of the wall shear and the Reynolds stresses are more accurate. LES results using the EASSM obtained from the code Saturne are also compared to those obtained using the pseudo-spectral solver obtained in our previous study (Rasam et al., 2013). As the next step, we are performing LES of flow over periodic hill using the EASSM and the code Saturne. The results will be compared with those of the DSM and the reference LES and will be presented at the conference.

  • 77.
    Rasam, Amin
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Wallin, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Brethouwet, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Johansson, Arne
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Large eddy simulation of channel flow with andwithout periodic constrictions using the explicit algebraic subgrid-scale modelIngår i: Journal of turbulence, ISSN 1468-5248, E-ISSN 1468-5248Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    We analyse the performance of the explicit algebraic subgrid-scale stress model(EASSM) of Marstorp et al. (J. Fluid Mech., vol. 639, 2009, pp. 403–432) inlarge eddy simulation (LES) of plane channel and the flow in a channel withstreamwise periodic hill-shaped constrictions (periodic hill flow) which induceseparation. The LESs are performed with Code Saturne which is an unstructuredcollocated finite volume solver with a second-order spatial discretisationsuitable for LES of incompressible flow in complex geometries. At first, performanceof the EASSM in LES of plane channel flow at two different resolutionsusing the Code Saturne and a pseudo-spectral method is analyzed. It is observedthat EASSM predictions of the mean velocity and Reynolds stresses aremore accurate than with the conventional dynamic Smagorinsky model (DSM).The results with the pseudo-spectral method were in general more accurate.In the second step, LES with the EASSM of flow separation in the periodichill flow is compared to LES with the DSM, no subgrid-scale model and thehighly resolved LES data of Breuer et al. (Computers & Fluids, vol. 38, 2009,pp. 433–457) using the DSM. Results show that the mean velocity profiles,the friction and pressure coefficients, the length and shape of the recirculationbubble, as well as the Reynolds stresses are considerably better predicted bythe EASSM than the DSM and the no subgrid-scale model simulations. It wasalso observed that in some parts of the domain the resolved strain-rate andsubgrid-scale shear stress have the same sign. The DSM cannot produce acorrect subgrid-scale stress in this case, in contrast to the EASSM.

  • 78.
    Schlatter, Philip
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Li, Qiang
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Brethouwer, Gert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Henningson, Dan S.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    High-Reynolds number turbulent boundary layers studied by numerical simulation2009Ingår i: Bulletin of the American Physical Society, APS Physics , 2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    Direct and large-eddy simulations (DNS and LES) of spatially developing high-Reynolds number turbulent boundary layers (Reθ up to 4300) under zero pressure gradient are studied. The inflow of the computational domain and the tripping of the boundary layer is located at low Reynolds numbers Reθ 350, a position where natural transition to turbulence can be expected. The simulation thus includes the spatial evolution of the boundary layer for an extended region, providing statistics and budget terms at each streamwise position. The data is obtained with up to O(10^10) grid points using a parallelised, fully spectral method. The DNS and LES results are critically evaluated and validated, in comparison with other relevant data, e.g. the experiments by "Osterlund et al. (1999). Quantities difficult or even impossible to measure, e.g. pressure fluctuations and complete Reynolds stress budgets, shall be discussed. In addition, special emphasis is put on a further quantification of the large-scale structures appearing in the flow, and their relation to other wall-bounded flow as e.g. channel flow. The results clearly show that with today's computer power Reynolds numbers relevant for industrial applications can be within reach for DNS/LES.

  • 79.
    Schlatter, Philipp
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Stabilitet, Transition, Kontroll.
    Li, Qiang
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Stabilitet, Transition, Kontroll.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Henningson, Dan S.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Stabilitet, Transition, Kontroll.
    Simulations of spatially evolving turbulent boundary layers up to Re-theta=43002010Ingår i: International Journal of Heat and Fluid Flow, ISSN 0142-727X, E-ISSN 1879-2278, Vol. 31, nr 3, s. 251-261Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A well-resolved large-eddy simulation (LES) of a spatially developing turbulent boundary layer under zero-pressure-gradient up to comparably high Reynolds numbers (Re-theta = 4300) is performed. The laminar inflow is located at Re-delta = 450 (Re-theta approximate to 1180), a position where natural transition to turbulence can be expected. The simulation is validated and compared extensively to both numerical data sets, i.e. a recent spatial direct numerical simulation (DNS) up to Re-theta = 2500 (Schlatter et al., 2009) and available experimental measurements, e.g. the ones obtained by Osterlund (1999). The goal is to provide the research community with reliable numerical data for high Reynolds-number wall-bounded turbulence, which can in turn be employed for further model development and validation, but also to contribute to the characterisation and understanding of various aspects of wall turbulence. The results obtained via LES show that good agreement with DNS data at lower Reynolds numbers and experimental data can be obtained for both mean and fluctuating quantities. In addition, turbulence spectra characterising large-scale organisation in the flow have been computed and compared to literature results with good agreement. In particular, the near-wall streaks scaling in inner units and the outer layer large-scale structures can clearly be identified in both spanwise and temporal spectra. (C) 2010 Elsevier Inc. All rights reserved.

  • 80.
    Schlatter, Philipp
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Li, Qiang
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Henningson, Dan S.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Structure of a turbulent boundary layer studied by DNS2011Ingår i: Direct and Large-Eddy Simulation VIII, 2011, s. 9-14Konferensbidrag (Refereegranskat)
    Abstract [en]

    Turbulent boundary layers constitute one of the basic building blocks for understanding turbulence, particularly relevant for industrial applications. Although the geometries in technical but also geophysical applications are complicated and usually feature curved surfaces, the flow case of a canonical boundary layer developing on a flat surface has emerged as an important setup for studying wall turbulence, both via experimental and numerical studies. However, only recently spatially developing turbulent boundary layers have become accessible via direct numerical simulations (DNS). The difficulties of such setups are mainly related to the specification of proper inflow conditions, the triggering of turbulence and a careful control of the free-stream pressure gradient. In addition, the numerical cost of such spatial simulations is high due to the long, wide and high domains necessary for the full development of all relevant turbulent scales. We consider a canonical turbulent boundary layer under zero-pressure-gradient via large-scale DNS. The boundary layer is allowed to develop and grow in space. The inflow is a laminar Blasius boundary layer, in which laminar-turbulent transition is triggered by a random volume force shortly downstream of the inflow. This trip force, similar to a disturbance strip in an experiment (Schlatter and Örlü, 2010; Schlatter et al., 2009), is located at a low Reynolds number to allow the flow to develop over a long distance. The simulation covers thus a long, wide and high domain starting at Re θ =180 extending up to the (numerically high) value of Re θ =4300, based on momentum thickness θ and free-stream velocity U ∞. Fully turbulent flow is obtained from Re θ ≈500. The numerical resolution for the fully spectral numerical method (Chevalier et al., 2007) is in the wall-parallel directions Δx +=9 and Δz +=4, resolving the relevant scales of motion. The simulation domain requires a total of 8⋅109 grid points in physical space, and was thus run massively parallel with 4096 processors.

  • 81.
    Schlatter, Philipp
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Li, Qiang
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Henningson, Dan S.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Towards large-eddy simulations of high-Reynolds number turbulent boundary layers2009Ingår i: Proc. 6th Intl Symp. on Turbulence and Shear Flow Phenomena, 2009, s. 271-276Konferensbidrag (Refereegranskat)
  • 82.
    Schlatter, Philipp
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Malm, Johan
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Henningson, Dan S.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Large-scale Simulations of Turbulence: HPC and Numerical Experiments2011Ingår i: 2011 Seventh IEEE International Conference on eScience, 2011, s. 319-324Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we describe some of the methods used at KTH Mechanics in the field of turbulence simulations. High performance computing (HPC) resources, including the dedicated system "Ekman" with 10000 cores at KTH, are employed to perform some of the largest turbulence simulations with up to 10 billion grid points. The results are used to assess the fidelity of such types of simulations by comparing in detail to wind tunnel experiments, excellent agreement is obtained in general. Simulations can thus be considered numerical experiments, and are subject to the same scrutiny as "real" experimental data. Validated simulation data is extremely valuable as it may provide unprecedented insight into the turbulence dynamics. However, given the large size of the computations, the massively parallel simulation codes, post processing tools and storage solutions have to be specifically adapted, making turbulence simulations an interdisplinary area of e-Science.

  • 83.
    Schlatter, Philipp
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Stabilitet, Transition, Kontroll. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Örlü, Ramis
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Li, Qiang
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Fransson, Jens H. M.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Alfredsson, P. Henrik
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strömningsfysik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Henningson, Dan S.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Stabilitet, Transition, Kontroll. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Turbulent boundary layers up to Re-theta=2500 studied through simulation and experiment2009Ingår i: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Physics of Fluids, Vol. 21, nr 5, s. 051702-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Direct numerical simulations (DNSs) and experiments of a spatially developing zero-pressure-gradient turbulent boundary layer are presented up to Reynolds number Re-theta=2500, based on momentum thickness theta and free-stream velocity. For the first time direct comparisons of DNS and experiments of turbulent boundary layers at the same (computationally high and experimentally low) Re-theta are given, showing excellent agreement in skin friction, mean velocity, and turbulent fluctuations. These results allow for a substantial reduction of the uncertainty of boundary-layer data, and cross validate the numerical setup and experimental technique. The additional insight into the flow provided by DNS clearly shows large-scale turbulent structures, which scale in outer units growing with Re-theta, spanning the whole boundary-layer height.

  • 84.
    Schlatter, Philipp
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Örlü, Ramis
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Li, Qiang
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Brethouwer, Gert
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Johansson, Arne
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Alfredsson, P. Henrik
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Henningson, Dan
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Progress in simulations of turbulent boundary layers2011Ingår i: Proc. 7th International Symposium on Turbulence and Shear Flow Phenomena, 2011Konferensbidrag (Refereegranskat)
    Abstract [en]

    Recent efforts in the simulation of turbulent boundary layers using direct and large-eddy simulations are described. The focus is naturally on a series of simulations performed at KTH Stockholm. These results have been used to examine various aspects of the boundary layer; starting from estimates of the extent of the transitional region, the detailed comparison to wind-tunnel experiments, the effect of ambient freestream turbulence on the boundary layer and to quantifications of the spectral composition of the turbulent signal. Furthermore, selected aspects of boundary layers with coupled scalar (e.g. heat) transport are summarised, including profiles of the turbulent Prandtl number.

  • 85.
    Strömgren, Tobias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Benavides, Aldo
    van Wachem, Berend
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Amberg, Gustav
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Numerical computation of turbulent gas-particle flow in a backward-facing step. Model comparison with experimental data.2008Ingår i: Numerical computation of turbulent gas-particle flow in a backward-facing step. Model comparison with experimental data., Milano: ANIMP SERVIZI SRL , 2008, s. 63-70Konferensbidrag (Refereegranskat)
  • 86.
    Strömgren, Tobias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Amberg, Gustav
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    A modelling study of evolving particle-laden turbulent pipe-flow2009Ingår i: Turbulence, Heat And Mass Transfer 6, Begell House, 2009, s. 713-716Konferensbidrag (Refereegranskat)
    Abstract [en]

    An Eulerian turbulent two phase flow model in cylindrical coordinates was developed in order to study evolving turbulent gas particle flows in a downward pipe flow. The model takes the feedback of the particles into account. Simulations shows good agreement with experiments and showed that the pipe length required for particle laden turbulent pipe flow to become fully developed is four times longer than for unladen flows, even for rather low mass loadings. The accumulation of particles in the near wall region showed a nonmonotonic behaviour and was found to be strongest for St=0.5.

  • 87.
    Strömgren, Tobias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Amberg, Gustav
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    A modelling study of evolving particle-laden turbulent pipe-flow2011Ingår i: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987, Vol. 86, nr 3-4, s. 477-495Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An Eulerian turbulent two phase flow model using kinetic theory ofgranular flows for the particle phase was developed in order to studyevolving upward turbulent gas particle flows in a pipe. Themodel takes the feedback of the particles into account and its resultsagree well with experiments. Simulations show that the pipe length required for particle laden turbulent flow to become fully developed is up to five times longer than an unladen flow. To increase theunderstanding of the dependence of the development length on particlediameter a simple model for the expected development length wasderived. It shows that the development length becomes shorter forincreasing particle diameters, which agrees with simulations up to aparticle diameter of 100 μm. Thereafter the development lengthbecomes longer again for increasing particle diameters because largerparticles need a longer time to adjust to the velocity of the carrierphase.

  • 88.
    Strömgren, Tobias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Amberg, Gustav
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    A study of particle feedback in turbulent gas-particle flows2009Ingår i: A study of particle feedback in turbulent gas-particle flows / [ed] K. Hanjalic, Y. Nagano, S. Jakirlic, New York, Wallingford (UK): Begell House Inc. , 2009, s. 713-716Konferensbidrag (Refereegranskat)
    Abstract [en]

    The upward turbulent gas-particle flow in a channel was studied usingan Eulerian-Eulerian two-phase model taking into account the feedbackfrom the particles on the gas-phase. The objective is to study theinfluence of particles with different diameters and volume fractionson the flow and particularly on the accumulation of particles in thenear wall region due to the turbophoretic effect. The results wereobtained with a two-phase flow model that is presented. Theaccumulation of particles in the near-wall region was found to bestrongest for particles with τp+ = 13. The model also shows thatvarying the particle diameters leads to different feedback of theparticles on the turbulent flow.

  • 89.
    Strömgren, Tobias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Amberg, Gustav
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Deriving fluid-particle correlation closures for Eulerian two-fluid models through use of Langevin equations2011Ingår i: European journal of mechanics. B, Fluids, ISSN 0997-7546, E-ISSN 1873-7390, Vol. 30, nr 3, s. 275-280Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The correlation correlation between the fluctuating particle and gas velocity in isotropic turbulence is studied with a set of stochastic differential equations taking into account both particle-particle collisions and the particle feedback on the turbulence. The principal aim of this work is to use the Langevin equations to formulate closures for two-fluid gas-particle flow models. Using Ito calculus we derived solutions for the turbulent kinetic energy of the particle phase and the particle-gas velocity correlations. If particle-particle collisions and particle feedback on the turbulence are neglected the new relations approach the ones derived by Tchen and Hinze but if these effects are included additional terms in the relations appear. In this study we only use a very simple model for the particle-particle collisions. The new relation and the classical relation of Tchen and Hinze for the particle turbulent kinetic energy as well as a relation based on the kinetic theory of granular flows have been implemented in a two-fluid model for turbulent gas-particle flow in a channel in order to make comparison for different particle Stokes numbers. Results show that while the two-fluid model using Hinze's relations only gives good results for small Stokes numbers, the new relation yields significant improvements for a large range of Stokes numbers.

  • 90.
    Strömgren, Tobias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Amberg, Gustav
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Modelling of particle fluctuations in turbulence by stochastic processesManuskript (Övrigt vetenskapligt)
  • 91.
    Strömgren, Tobias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Amberg, Gustav
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Modelling of turbulent gas-particle flows with focus on two-way coupling effects on turbophoresis2012Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 224, s. 36-45Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An Eulerian model was developed for turbulent gas-particle flow that takes into account the influence of particles on the gas-phase turbulence. For the description of the particle-phase stress the kinetic theory of granular flow and the simpler Hinze model were adopted. A K-ω model was used as the gas phase turbulence model. The difference between one- and two-way coupling was investigated for different particle volume fractions and particle diameters. It was found that particles with a much higher density than the fluid substantially affect the gas-phase in turbulent channel flow for particle volume fractions as low as 10 -4. The models with the particle-phase stress described by the kinetic theory of granular flow and the simpler Hinze model produce similar results for particles with small response times but deviate for larger response times. The study shows that two-way coupling and the turbophoretic effect must be taken into account in models even at relatively low particle volume fractions.

  • 92.
    Wei, Liang
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Brethouwer, Gert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Elsinga, G. E.
    Schlatter, Philipp
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Scaling of small-scale motions in wall-bounded turbulent flows2013Ingår i: International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2013, TSFP-8 , 2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    The objective is to investigate flow topology and related Reynolds-number scaling in the eigenframe of the strain-rate tensor for wall-bounded turbulent flows. The databases used in the current study are from direct numerical simulations (DNS) of fully developed channel flow up to friction Reynolds number Ret ≈ 1500, and a spatially developing, zero-pressure-gradient turbulent boundary layer up to Reθ ≈ 4300 (Ret ≈ 1400)., and a spatially developing, zero-pressure-gradient turbulent boundary layer up to Reθ ≈ 4300 (Ret ≈ 1400).. It is found that for all cases considered, the averaged flow patterns in the local strainrate eigenframe appear universal: large scale motions are separated by a shear layer with a pair of vortices. Based on Kolmogorov (η,uη), Taylor (lt) and integral length scales, Reynolds-number scalings of the averaged flow patterns, including the thickness and strength of the shear layer, the distance between the two vortical regions, and the velocity distribution along the most compressing and stretching directions are considered. It is found that the Taylor scaling of the profiles for the thickness of the shear layer seems more suitable than the Kolmogorov scaling, and the integral scaling collapses well away from the shear layer, which confirms that those patterns represent large scales. Generally speaking, the scaling profiles based on the Kolmogorov length and velocity collapse well near the origin, but the Taylor scaling seems best suited in a broader region.

  • 93.
    Wei, Liang
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Elsinga, Gerrit E.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Schlatter, Philipp
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Universality and scaling phenomenology of small-scale turbulence in wall-bounded flows2014Ingår i: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 26, nr 3, s. 035107-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Reynolds number scaling of flow topology in the eigenframe of the strain-rate tensor is investigated for wall-bounded flows, which is motivated by earlier works showing that such topologies appear to be qualitatively universal across turbulent flows. The databases used in the current study are from direct numerical simulations (DNS) of fully developed turbulent channel flow (TCF) up to friction Reynolds number Re-tau approximate to 1500, and a spatially developing, zero-pressure-gradient turbulent boundary layer (TBL) up to Re-theta approximate to 4300 (Re-tau approximate to 1400). It is found that for TCF and TBL at different Reynolds numbers, the averaged flow patterns in the local strain-rate eigenframe appear the same consisting of a pair of co-rotating vortices embedded in a finite-size shear layer. It is found that the core of the shear layer associated with the intense vorticity region scales on the Kolmogorov length scale, while the overall height of the shear layer and the distance between the vortices scale well with the Taylor micro scale. Moreover, the Taylor micro scale collapses the height of the shear layer in the direction of the vorticity stretching. The outer region of the averaged flow patterns approximately scales with the macro scale, which indicates that the flow patterns outside of the shear layer mainly are determined by large scales. The strength of the shear layer in terms of the peak tangential velocity appears to scale with a mixture of the Kolmogorov velocity and root-mean-square of the streamwise velocity scaling. A quantitative universality in the reported shear layers is observed across both wall-bounded flows for locations above the buffer region.

  • 94. Xia, Zhenhua
    et al.
    Brethouwer, Gert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Chen, Shiyi
    High-order moments of streamwise fluctuations in a turbulent channel flow with spanwise rotation2018Ingår i: PHYSICAL REVIEW FLUIDS, ISSN 2469-990X, Vol. 3, nr 2, artikel-id 022601Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is well known that the spanwise rotation in turbulent channel flow alters the mean velocity distribution to a linear law. In the present work, we have studied the higher-order moments of the streamwise fluctuations in a turbulent channel flow with spanwise rotation. Our results show that in a significant part of the channel the 2p-order moments, raised by the power 1/p with p = 1,2, ... ,6, also follow linear behavior according to <(u'(+))(2p)>(1/p) = a(p) (y/h) + b(p). Here, u'(+) is the streamwise velocity fluctuation normalized by the global friction velocity, h is the channel half width, and b(p) and a(p) are the intercept and the slope, respectively, which vary with Reynolds and rotation numbers. The linear regions can be extended by introducing a self-similar scaling, that is, 2p-order moments as a function of 2q-order moments. The slopes in the self-similar scaling a(p)/a(1) do not reveal sub-Gaussian behavior as in nonrotating wall-bounded flows, but rather Gaussian or super-Gaussian behaviors.

12 51 - 94 av 94
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