Change search
Link to record
Permanent link

Direct link
BETA
Alternative names
Publications (10 of 148) Show all publications
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
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
Show others...
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
Show others...
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: 2018-05-17Bibliographically 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: 2019-04-04Bibliographically 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: 2016-11-02Bibliographically 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
Show others...
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
Tsuji, Y., Marusic, I. & Johansson, A. V. (2016). Amplitude modulation of pressure in turbulent boundary layer. International Journal of Heat and Fluid Flow
Open this publication in new window or tab >>Amplitude modulation of pressure in turbulent boundary layer
2016 (English)In: International Journal of Heat and Fluid Flow, ISSN 0142-727X, E-ISSN 1879-2278Article in journal (Refereed) Published
Abstract [en]

The interaction between pressure fluctuations associated with large- and small-scale motions is studied. Using a small pressure probe, both static pressure and wall pressure fluctuations were measured inside the zero-pressure gradient boundary layer at relatively high Reynolds numbers. How the large scales in the log-region affect the small scales near the wall is analyzed by means of an amplitude modulation procedure. Analyzing the wall pressure fluctuations, it was found that the large scale interacts with the small scale but there is a time-lag between them. © 2016 Elsevier Inc.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
Amplitude modulation, Boundary layer, Large-scale motion, Pressure fluctuation, Boundary layer flow, Modulation, Reynolds number, Turbulent flow, High Reynolds number, Large scale motion, Pressure probes, Static pressure, Turbulent boundary layers, Wall-pressure fluctuations, Zero-pressure-gradient boundary layers, Boundary layers
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-196152 (URN)10.1016/j.ijheatfluidflow.2016.05.019 (DOI)2-s2.0-84978500094 (Scopus ID)
Note

Correspondence Address: Tsuji, Y.email: c42406a@nucc.cc.nagoya-u.ac.jp. QC 20161116

Available from: 2016-11-16 Created: 2016-11-14 Last updated: 2017-11-29Bibliographically approved
Grigoriev, I., Brethouwer, G., Wallin, S. & Johansson, A. V. (2016). Unified explicit algebraic Reynolds stress model for compressible, heat-releasing and supercritical flowswith large density variation.
Open this publication in new window or tab >>Unified explicit algebraic Reynolds stress model for compressible, heat-releasing and supercritical flowswith large density variation
2016 (English)Report (Other academic)
Abstract [en]

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

Publisher
p. 18
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-183450 (URN)
Note

QC20160314

Available from: 2016-03-11 Created: 2016-03-11 Last updated: 2016-03-14Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-2711-4687

Search in DiVA

Show all publications