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Publications (10 of 151) Show all publications
Montecchia, M., Wallin, S., Brethouwer, G. & Johansson, A. V. (2019). Capturing Reynolds number effects in the periodic hill flow by using LES with anisotropy-resolving sub-grid scale model. In: 11th International Symposium on Turbulence and Shear Flow Phenomena (TSFP11): . Paper presented at 11th International Symposium on Turbulence and Shear Flow Phenomena (TSFP11), July 30 to August 2, 2019, Grand Harbour Hotel, Southampton, UK.
Open this publication in new window or tab >>Capturing Reynolds number effects in the periodic hill flow by using LES with anisotropy-resolving sub-grid scale model
2019 (English)In: 11th International Symposium on Turbulence and Shear Flow Phenomena (TSFP11), 2019Conference paper, Published paper (Refereed)
Abstract [en]

Concerning wall resolved large-eddy simulation (LES), a considerable reduction of computational resources is achievable by employing the Explicit Algebraic subgrid scale model (EAM) (\cite{marstorp2009explicit}).LES of periodic hill is carried out using OpenFOAM with the EAM and a low-diffusive implementation that has been previously tested on a turbulent channel flow. The aim of the present study is to evaluate in a broad sense the influence of  the Reynolds number on the flow quantities.

Keywords
SGS modelling, Periodic hill
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-264019 (URN)
Conference
11th International Symposium on Turbulence and Shear Flow Phenomena (TSFP11), July 30 to August 2, 2019, Grand Harbour Hotel, Southampton, UK
Funder
Swedish Research Council, 621-2014- 5700
Note

QC 20191122

Available from: 2019-11-20 Created: 2019-11-20 Last updated: 2019-11-22Bibliographically approved
Zeli, V., Brethouwer, G., Wallin, S. & Johansson, A. V. (2019). Consistent Boundary-Condition Treatment for Computation of the Atmospheric Boundary Layer Using the Explicit Algebraic Reynolds-Stress Model. Boundary-layer Meteorology, 171(1), 53-77
Open this publication in new window or tab >>Consistent Boundary-Condition Treatment for Computation of the Atmospheric Boundary Layer Using the Explicit Algebraic Reynolds-Stress Model
2019 (English)In: Boundary-layer Meteorology, ISSN 0006-8314, E-ISSN 1573-1472, Vol. 171, no 1, p. 53-77Article in journal (Refereed) Published
Abstract [en]

Standard turbulence models for the atmospheric boundary layer (ABL) typically use boundary conditions based on the Monin-Obukhov similarity theory (MOST). This can lead to inconsistency between the boundary condition and the closure model. Here, we propose a new boundary-condition treatment of the stratified ABL, derived for the so-called explicit algebraic Reynolds-stress model. The boundary conditions correspond to the relations for vanishing buoyancy effects that are valid close to the ground. The solution for the stratified surface layer is in agreement with the surface scaling physics and MOST functions. This was validated in a simulation of an idealized diurnal cycle of the ABL based on the second Global Energy and Water cycle Experiment (GEWEX) Atmospheric Boundary Layer Study (GABLS2) case.

Place, publisher, year, edition, pages
SPRINGER, 2019
Keywords
Boundary conditions, Reynolds-stress model, Surface fluxes, Surface layer, Turbulence parametrization
National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:kth:diva-248064 (URN)10.1007/s10546-018-0415-x (DOI)000461378900003 ()2-s2.0-85058438408 (Scopus ID)
Note

QC 20190429

Available from: 2019-04-29 Created: 2019-04-29 Last updated: 2019-04-29Bibliographically approved
Kim, S. J., Sung, H. J., Wallin, S. & Johansson, A. V. (2019). Design of the centrifugal fan of a belt-driven starter generator with reduced flow noise. International Journal of Heat and Fluid Flow, 76, 72-84
Open this publication in new window or tab >>Design of the centrifugal fan of a belt-driven starter generator with reduced flow noise
2019 (English)In: International Journal of Heat and Fluid Flow, ISSN 0142-727X, E-ISSN 1879-2278, Vol. 76, p. 72-84Article in journal (Refereed) Published
Abstract [en]

Large eddy simulations based on the explicit algebraic subgrid-scale stress model were carried out to predict the flow-induced noise generated on the centrifugal fan of a belt-driven starter generator using Lighthill's analogy and the method of Ffowcs Williams and Hawkings. The surrounding air was approximated by an ideal gas at fixed room temperature (T in = 300 K), and the rotating velocity of the fan was considered to be 6000 rpm. The blade array angles were designed using the modulation method, and a large blade curvature was adopted. We identified several centrifugal fan design parameters that could minimize the flow-induced noise while also minimizing fan efficiency losses. Three design parameters: the top serrated edge (θ t ), the step leading edge (0.52 H b ) and the tail edge (d b and r b ), played a critical role in preventing vortex generation and collision, significantly weakening the surface pressure fluctuations on the blade. The maximum sound pressure level at 800 Hz at a specific location was reduced by 5.5 dB (at the top serrated edge) and 6.8 dB (at the step leading edge) relative to the baseline case. The sound power, calculated over a hemisphere surface of 950 mm, was reduced by 77.3% (at the top serrated edge) and 61.0% (at the step leading edge) relative to the baseline whereas the mass flow rates were reduced by 5.2% and 10.6%, respectively. Experiments were performed using the optimally designed fan in a semi-anechoic chamber. The predicted sound pressure level and frequency were in good agreement with the experimentally measured values.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Centrifugal fan, Explicit algebraic subgrid-scale stress model, Fan cooling performance, Flow-induced noise, Large eddy simulation
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-246461 (URN)10.1016/j.ijheatfluidflow.2019.01.016 (DOI)000469905200006 ()2-s2.0-85060885847 (Scopus ID)
Note

QC 20190329

Available from: 2019-03-29 Created: 2019-03-29 Last updated: 2019-06-24Bibliographically approved
Montecchia, M., Brethouwer, G., Wallin, S., Johansson, A. V. & Knacke, T. (2019). Improving LES with OpenFOAM by minimising numerical dissipation and use of explicit algebraic SGS stress model. Journal of turbulence, 20(11-12), 697-722
Open this publication in new window or tab >>Improving LES with OpenFOAM by minimising numerical dissipation and use of explicit algebraic SGS stress model
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2019 (English)In: Journal of turbulence, ISSN 1468-5248, E-ISSN 1468-5248, Vol. 20, no 11-12, p. 697-722Article in journal (Refereed) Published
Abstract [en]

There is a rapidly growing interest in using general-purpose CFD codes based on second-order finite volume methods for Large-Eddy Simulation (LES) in a wide range of applications, and in many cases involving wall-bounded flows. However, such codes are strongly affected by numerical dissipation and the accuracy obtained for typical LES resolutions is often poor. In the present study, we approach the problem of improving the LES capability of such codes by reduction of the numerical dissipation and use of an anisotropy-capturing subgrid-scale (SGS) stress model. The latter is of special importance for wall-resolved LES with resolutions where the SGS anisotropy can be substantial. Here we use the Explicit Algebraic (EA) SGS model [Marstorp L, Brethouwer G, Grundestam O, et al. Explicit algebraic subgrid stress models with application to rotating channel flow. J Fluid Mech. 2009;639:403-432], and comparisons are made for channel flow at friction Reynolds numbers up to 934 with the dynamic Smagorinsky model. The numerical dissipation is reduced by using an OpenFOAM based custom-built flow solver that modifies the Rhie and Chow interpolation and allows to control and minimise its effects without causing numerical instability (in viscous, fully turbulent flows). Different resolutions were used and large improvements of the LES accuracy were demonstrated for skin friction, mean velocity and other flow statistics by use of the new solver in combination with the EA SGS model. By reducing the numerical dissipation and using the EA SGS model the resolution requirements for wall-resolved LES can be significantly reduced.

Place, publisher, year, edition, pages
TAYLOR & FRANCIS LTD, 2019
Keywords
Large-eddy simulation, wall-bounded flows, OpenFOAM, SGS modelling
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-266548 (URN)10.1080/14685248.2019.1706740 (DOI)000504529200001 ()2-s2.0-85077213425 (Scopus ID)
Note

QC 20190115

Available from: 2020-01-15 Created: 2020-01-15 Last updated: 2020-01-15Bibliographically approved
Karlsson, B., Johansson, A. V., Yang, H.-C., Jokura, H., Yamamoto, M., Martinez-Alvarez, R., . . . Yeo, T. T. (2018). A novel method to determine the natural course of unruptured brain arteriovenous malformations without the need for follow-up information. Paper presented at 19th International Meeting of the Leksell-Gamma-Knife-Society (LGKS) on Next-Generation Gamma Knife Research, MAR 04-08, 2018, Dubai, U ARAB EMIRATES. Journal of Neurosurgery, 129, 10-16
Open this publication in new window or tab >>A novel method to determine the natural course of unruptured brain arteriovenous malformations without the need for follow-up information
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2018 (English)In: Journal of Neurosurgery, ISSN 0022-3085, E-ISSN 1933-0693, Vol. 129, p. 10-16Article in journal (Refereed) Published
Abstract [en]

OBJECTIVE There is a strong clinical need to accurately determine the average annual hemorrhage risk in unruptured brain arteriovenous malformations (AVMs). This need motivated the present initiative to use data from a uniquely large patient population and design a novel methodology to achieve a risk determination with unprecedented accuracy. The authors also aimed to determine the impact of sex, pregnancy, AVM volume, and location on the risk for AVM rupture. METHODS The present study does not consider any specific management of the AVMs, but only uses the age distribution for the first hemorrhage, the shape of which becomes universal for a sufficiently large set of patients. For this purpose, the authors collected observations, including age at first hemorrhage and AVM size and location, in 3425 patients. The average annual risk for hemorrhage could then be determined from the simple relation that the number of patients with their first hemorrhage at a specific age equals the risk for hemorrhage times the number of patients at risk at that age. For a subset of the patients, the information regarding occurrence of AVM hemorrhage after treatment of the first hemorrhage was used for further analysis of the influence on risk from AVM location and pregnancy. RESULTS The age distribution for the first AVM hemorrhage was used to determine the average annual risk for hemorrhage in unruptured AVMs at adult ages (25-60 years). It was concluded to be 3.1% +/- 0.2% and unrelated to AVM volume but influenced by its location, with the highest risk for centrally located AVMs. The hemorrhage risk was found to be significantly higher for females in their fertile years. CONCLUSIONS The present methodology allowed the authors to determine the average annual risk for the first AVM hemorrhage at 3.1% +/- 0.2% without the need for individual patient follow-up. This methodology has potential also for other similar types of investigations. The conclusion that centrally located AVMs carry a higher risk was confirmed by follow-up information. Follow-up information was also used to conclude that pregnancy causes a substantially greater AVM hemorrhage risk. The age distribution for AVM hemorrhage is incompatible with AVMs present at birth having the same hemorrhage risk as AVMs in adults. Plausibly, they instead develop in the early years of life, possibly with a lower hemorrhage risk during that time period.

Place, publisher, year, edition, pages
American Association of Neurological Surgeons, 2018
Keywords
AVM, hemorrhage, risk, vascular disorders, stereotactic radiosurgery
National Category
Neurology
Identifiers
urn:nbn:se:kth:diva-240747 (URN)10.3171/2018.7.GKS181278 (DOI)000453374900004 ()30544301 (PubMedID)2-s2.0-85057737975 (Scopus ID)
Conference
19th International Meeting of the Leksell-Gamma-Knife-Society (LGKS) on Next-Generation Gamma Knife Research, MAR 04-08, 2018, Dubai, U ARAB EMIRATES
Note

QC 20190108

Available from: 2019-01-08 Created: 2019-01-08 Last updated: 2019-01-08Bibliographically approved
Tavoularis, S. & Johansson, A. V. (2018). Ninth International Symposium on Turbulence and Shear Flow Phenomena. Journal of turbulence, 19(3), 202-203
Open this publication in new window or tab >>Ninth International Symposium on Turbulence and Shear Flow Phenomena
2018 (English)In: Journal of turbulence, ISSN 1468-5248, E-ISSN 1468-5248, Vol. 19, no 3, p. 202-203Article in journal, Editorial material (Refereed) Published
Place, publisher, year, edition, pages
Taylor & Francis, 2018
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-223290 (URN)10.1080/14685248.2017.1336331 (DOI)000424062000002 ()2-s2.0-85041699539 (Scopus ID)
Note

QC 20180216

Available from: 2018-02-16 Created: 2018-02-16 Last updated: 2018-02-16Bibliographically approved
Schenk, F., Valiranta, M., Muschitiello, F., Tarasov, L., Heikkila, M., Björck, S., . . . Wohlfarth, B. (2018). Warm summers during the Younger Dryas cold reversal. Nature Communications, 9, Article ID 1634.
Open this publication in new window or tab >>Warm summers during the Younger Dryas cold reversal
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2018 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, article id 1634Article in journal (Refereed) Published
Abstract [en]

The Younger Dryas (YD) cold reversal interrupts the warming climate of the deglaciation with global climatic impacts. The sudden cooling is typically linked to an abrupt slowdown of the Atlantic Meridional Overturning Circulation (AMOC) in response to meltwater discharges from ice sheets. However, inconsistencies regarding the YD-response of European summer temperatures have cast doubt whether the concept provides a sufficient explanation. Here we present results from a high-resolution global climate simulation together with a new July temperature compilation based on plant indicator species and show that European summers remain warm during the YD. Our climate simulation provides robust physical evidence that atmospheric blocking of cold westerly winds over Fennoscandia is a key mechanism counteracting the cooling impact of an AMOC-slowdown during summer. Despite the persistence of short warm summers, the YD is dominated by a shift to a continental climate with extreme winter to spring cooling and short growing seasons.

Place, publisher, year, edition, pages
NATURE PUBLISHING GROUP, 2018
National Category
Climate Research
Identifiers
urn:nbn:se:kth:diva-227217 (URN)10.1038/s41467-018-04071-5 (DOI)000430674000023 ()29691388 (PubMedID)2-s2.0-85045988355 (Scopus ID)
Note

QC 20180517

Available from: 2018-05-17 Created: 2018-05-17 Last updated: 2019-08-20Bibliographically approved
Montecchia, M., Brethouwer, G., Johansson, A. V. & Wallin, S. (2017). Taking large-eddy simulation of wall-bounded flows to higher Reynolds numbers by use of anisotropy-resolving subgrid models. Physical Review Fluids, 2, Article ID 034601.
Open this publication in new window or tab >>Taking large-eddy simulation of wall-bounded flows to higher Reynolds numbers by use of anisotropy-resolving subgrid models
2017 (English)In: Physical Review Fluids, E-ISSN 2469-990X, Vol. 2, article id 034601Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
American Physical Society, 2017
National Category
Natural Sciences
Identifiers
urn:nbn:se:kth:diva-220931 (URN)10.1103/PhysRevFluids.2.034601 (DOI)000396070400001 ()2-s2.0-85028541529 (Scopus ID)
Note

QC 20180110

Available from: 2018-01-09 Created: 2018-01-09 Last updated: 2019-11-20Bibliographically approved
Lenaers, P., Schlatter, P., Brethouwer, G. & Johansson, A. V. (2016). A new high-order method for simulating turbulent pipe flow. In: Springer Proceedings in Physics: . Paper presented at 6th International Conference on Progress in Turbulence, iTi 2014, 29 August 2014 through 29 August 2014 (pp. 211-215). Springer
Open this publication in new window or tab >>A new high-order method for simulating turbulent pipe flow
2016 (English)In: Springer Proceedings in Physics, Springer, 2016, p. 211-215Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Springer, 2016
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-194619 (URN)10.1007/978-3-319-29130-7_37 (DOI)2-s2.0-84966937466 (Scopus ID)9783319291291 (ISBN)
Conference
6th International Conference on Progress in Turbulence, iTi 2014, 29 August 2014 through 29 August 2014
Note

Correspondence Address: Schlatter, P.; Linné FLOW Centre, KTH MechanicsSweden; email: pschlatt@mech.kth.se. QC 20161101

Available from: 2016-11-01 Created: 2016-10-31 Last updated: 2019-10-11Bibliographically approved
Grigoriev, I., Wallin, S., Brethouwer, G., Grundestam, O. & Johansson, A. V. (2016). Algebraic Reynolds stress modeling of turbulence subject to rapid homogeneous and non-homogeneous compression or expansion. Physics of fluids, 28(2), 026101
Open this publication in new window or tab >>Algebraic Reynolds stress modeling of turbulence subject to rapid homogeneous and non-homogeneous compression or expansion
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2016 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 28, no 2, p. 026101-Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2016
Keywords
Turbulence, compressible flow, EARSM, DRSM
National Category
Applied Mechanics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-183447 (URN)10.1063/1.4941352 (DOI)000371286500057 ()2-s2.0-84958818780 (Scopus ID)
Funder
Swedish Research Council, 621-2010-3938
Note

QC 20160314. QC 20160704

Available from: 2016-03-11 Created: 2016-03-11 Last updated: 2017-11-30Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-2711-4687

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