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Publications (10 of 259) Show all publications
Offermans, N., Peplinski, A., Marin, O. & Schlatter, P. (2020). Adaptive mesh refinement for steady flows in Nek5000. Computers & Fluids, 197, Article ID UNSP 104352.
Open this publication in new window or tab >>Adaptive mesh refinement for steady flows in Nek5000
2020 (English)In: Computers & Fluids, ISSN 0045-7930, E-ISSN 1879-0747, Vol. 197, article id UNSP 104352Article in journal (Refereed) Published
Abstract [en]

Adaptive mesh refinement is performed in the framework of the spectral element method augmented by approaches to error estimation and control. The h-refinement technique is used for adapting the mesh, where selected grid elements are split by a quadtree (2D) or octree (3D) structure. Continuity between parent-child elements is enforced by high-order interpolation of the solution across the common faces. Parallel mesh partitioning and grid management respectively, are taken care of by the external libraries ParMETIS and p4est. Two methods are considered for estimating and controlling the error of the solution. The first error estimate is local and based on the spectral properties of the solution on each element. This method gives a local measure of the L-2-norm of the solution over the entire computational domain. The second error estimate uses the dual-weighted residuals method - it is based on and takes into account both the local properties of the solution and the global dependence of the error in the solution via an adjoint problem. The objective of this second approach is to optimize the computation of a given functional of physical interest. The simulations are performed by using the code Nek5000 and three steady-state test cases are studied: a two-dimensional lid-driven cavity at Re = 7, 500, a two-dimensional flow past a cylinder at Re = 40, and a three-dimensional lid-driven cavity at Re = 2,000 with a moving lid tilted by an angle of 30 degrees. The efficiency of both error estimators is compared in terms of refinement patterns and accuracy on the functional of interest. In the case of the adjoint error estimators, the trend on the error of the functional is shown to be correctly represented up to a multiplicative constant.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2020
Keywords
Mesh optimization, Error indicators, Adjoint error estimators, Spectral methods
National Category
Computational Mathematics
Identifiers
urn:nbn:se:kth:diva-267743 (URN)10.1016/j.compfluid.2019.104352 (DOI)000509619300008 ()2-s2.0-85074775338 (Scopus ID)
Note

QC 20200218

Available from: 2020-02-18 Created: 2020-02-18 Last updated: 2020-04-01Bibliographically approved
Canton, J., Rinaldi, E., Örlü, R. & Schlatter, P. (2020). Critical Point for Bifurcation Cascades and Featureless Turbulence. Physical Review Letters, 124(1), Article ID 014501.
Open this publication in new window or tab >>Critical Point for Bifurcation Cascades and Featureless Turbulence
2020 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 124, no 1, article id 014501Article in journal (Refereed) Published
Abstract [en]

In this Letter we show that a bifurcation cascade and fully sustained turbulence can share the phase space of a fluid flow system, resulting in the presence of competing stable attractors. We analyze the toroidal pipe flow, which undergoes subcritical transition to turbulence at low pipe curvatures (pipe-to-torus diameter ratio) and supercritical transition at high curvatures, as was previously documented. We unveil an additional step in the bifurcation cascade and provide evidence that, in a narrow range of intermediate curvatures, its dynamics competes with that of sustained turbulence emerging through subcritical transition mechanisms.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2020
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-266918 (URN)10.1103/PhysRevLett.124.014501 (DOI)000506598700005 ()31976718 (PubMedID)2-s2.0-85078247013 (Scopus ID)
Note

QC 20200322

Available from: 2020-03-22 Created: 2020-03-22 Last updated: 2020-03-22Bibliographically approved
von Deyn, L. H., Forooghi, P., Frohnapfel, B., Schlatter, P., Hanifi, A. & Henningson, D. S. (2020). Direct Numerical Simulations of Bypass Transition over Distributed Roughness. AIAA Journal, 58(2), 702-711
Open this publication in new window or tab >>Direct Numerical Simulations of Bypass Transition over Distributed Roughness
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2020 (English)In: AIAA Journal, ISSN 0001-1452, E-ISSN 1533-385X, Vol. 58, no 2, p. 702-711Article in journal (Refereed) Published
Abstract [en]

Bypass transition in a boundary layer subjected to freestream turbulence and distributed surface roughness is studied numerically. The distributed surface roughness is reproduced with an immersed boundary technique, and the freestream turbulence is artificially generated by a superposition of eigenmodes of the Orr-Sommerfeld and Squire equations. Both an undisturbed laminar inflow and a disturbed inflow with freestream turbulence are studied. In either case a parametric study on the effects of the roughness size and density is carried out. The simulations reveal that the presence of roughness induces streaks in the laminar flow. When the freestream is turbulent, both roughness height and density show an impact on the onset of transition. The superposition of surface roughness and freestream turbulence causes amplified streaks. As a result, the streak instability occurs earlier within the boundary layer. The results show good qualitative and quantitative agreement to both experimental and numerical studies available in the literature.

Place, publisher, year, edition, pages
AMER INST AERONAUTICS ASTRONAUTICS, 2020
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-269475 (URN)10.2514/1.J057765 (DOI)000513533200015 ()
Note

QC 20200310

Available from: 2020-03-10 Created: 2020-03-10 Last updated: 2020-03-10Bibliographically approved
Tanarro, A., Vinuesa, R. & Schlatter, P. (2020). Effect of adverse pressure gradients on turbulent wing boundary layers. Journal of Fluid Mechanics, 883(A8), 1-28
Open this publication in new window or tab >>Effect of adverse pressure gradients on turbulent wing boundary layers
2020 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 883, no A8, p. 1-28Article in journal (Refereed) Published
Abstract [en]

    The characteristics of turbulent boundary layers (TBLs) subjected to adverse pressure gradients are analysed through well-resolved large-eddy simulations. The geometries under study are the NACA0012 and NACA4412 wing sections, at 0 and 5 degrees angle of attack, respectively, both of them at a Reynolds number based on inflow velocity and chord length Rec = 400,000. The turbulence statistics show that adverse pressure gradients (APGs) have a significant effect on the mean velocity, velocity fluctuations and turbulent kinetic energy budget, and this effect is more prominent on the outer region of the boundary layer. Furthermore, the effect of flow history is assessed by means of an integrated Clauser pressure-gradient parameter, β, through the study of cases with matching local values of β and the friction Reynolds number, Reτ, to isolate this effect. Our results show a noticeable effect of the flow history on the outer region, however the differences in the near-wall peak of the tangential velocity fluctuations appear to be mostly produced by the local APG magnitude. The one-dimensional power-spectral density shows energetic small scales in the outer region of APG TBLs, whereas these energetic scales do not appear in zero-pressure-gradient (ZPG) TBLs, suggesting that small scales near the wall are advected towards the outer layer by the APG. Moreover, the linear coherence spectra show that the spectral outer peak of high-Reynolds-number ZPG TBLs is highly correlated with the near-wall region , unlike APG TBLs which do not show such a correlation. This result, together with the different two-dimensional spectra of APG and high-Reynolds-number ZPG TBLs, suggests different energisation mechanisms due to APG and increase in Reynolds number. To the authors' knowledge, this is the first in-depth analysis of the TBL characteristics over wings, including detailed single-point statistics, spectra and coherence.

National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-267017 (URN)10.1017/jfm.2019.838 (DOI)000508121500008 ()
Note

QC 20200203

Available from: 2020-01-31 Created: 2020-01-31 Last updated: 2020-02-17Bibliographically approved
Sanmiguel Vila, C., Vinuesa, R., Discetti, S., Ianiro, A., Schlatter, P. & Örlü, R. (2020). Experimental realisation of near-equilibrium adverse-pressure-gradient turbulent boundary layers. Experimental Thermal and Fluid Science, 112, Article ID 109975.
Open this publication in new window or tab >>Experimental realisation of near-equilibrium adverse-pressure-gradient turbulent boundary layers
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2020 (English)In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 112, article id 109975Article in journal (Refereed) Published
Abstract [en]

A new experimental database of adverse-pressure-gradient (APG) turbulent boundary layers (TBLs) obtained through hot-wire anemometry and oil-film interferometry covering a momentum–loss Reynolds number 450<Reθ<23450 and Clauser pressure-gradient-parameter range up to β≈2.4 is presented. Both increasing and approximately constant β distributions with the same upstream history are characterised. Turbulence statistics are compared among the different pressure-gradient distributions with additional numerical and experimental zero-pressure-gradient (ZPG) TBL data. Cases at approximately constant β, which can be considered as canonical representations of the boundary layer under a certain pressure-gradient magnitude, exhibit skin-friction and shape-factor curves consistent with the ones proposed by Vinuesa et al. (2017). These curves show a similar scaling behaviour as those proposed by Nagib et al. (2007) for ZPG TBLs. The pre-multiplied power-spectral density is employed to study the differences in the large-scale energy content throughout the boundary layer. Two different large-scale phenomena are identified, the first one related to the pressure gradient and the second one (also present in high-Re ZPG TBLs) due to the Reynolds number. Recently proposed scaling laws by Kitsios et al. (2016) and Maciel et al. (2018) are tested over a wider Reynolds-number range and for different β cases. The mean velocity and streamwise velocity fluctuation profiles are found to be dependent on the upstream development. The mean velocity profile is found to be self-similar only in the outer region, in agreement with classical theory. The mean and higher-order statistics of the new APG TBL database are made available under www.flow.kth.se.

Place, publisher, year, edition, pages
Elsevier Inc., 2020
Keywords
Pressure gradient flows, Turbulent boundary layer, Turbulent flows, Boundary layer flow, Boundary layers, Higher order statistics, Pressure gradient, Reynolds number, Spectral density, Turbulence, Turbulent flow, Adverse pressure gradient, Canonical representations, Mean velocity profiles, Oil film interferometries, Pressure-gradient parameters, Stream-wise velocities, Turbulent boundary layers, Zero pressure gradient, Atmospheric thermodynamics
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-267947 (URN)10.1016/j.expthermflusci.2019.109975 (DOI)000512213300017 ()2-s2.0-85075293771 (Scopus ID)
Note

QC 20200401

Available from: 2020-04-01 Created: 2020-04-01 Last updated: 2020-04-01Bibliographically approved
Amor, C., Perez, J. M., Schlatter, P., Vinuesa, R. & Le Clainche, S. (2020). Soft Computing Techniques to Analyze the Turbulent Wake of a Wall-Mounted Square Cylinder. In: Alvarez, FM Lora, AT Munoz, JAS Quintian, H Corchado, E (Ed.), 14th International Conference on Soft Computing Models in Industrial and Environmental Applications, SOCO 2019: . Paper presented at 14th International Conference on Soft Computing Models in Industrial and Environmental Applications (SOCO), MAY 13-15, 2019, Seville, Spain (pp. 577-586). Springer, 950
Open this publication in new window or tab >>Soft Computing Techniques to Analyze the Turbulent Wake of a Wall-Mounted Square Cylinder
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2020 (English)In: 14th International Conference on Soft Computing Models in Industrial and Environmental Applications, SOCO 2019 / [ed] Alvarez, FM Lora, AT Munoz, JAS Quintian, H Corchado, E, Springer, 2020, Vol. 950, p. 577-586Conference paper, Published paper (Refereed)
Abstract [en]

This paper introduces several methods, generally used in fluid dynamics, to provide low-rank approximations. The algorithm describing these methods are mainly based on singular value decomposition (SVD) and dynamic mode decomposition (DMD) techniques, and are suitable to analyze turbulent flows. The application of these methods will be illustrated in the analysis of the turbulent wake of a wall-mounted cylinder, a geometry modeling a skyscraper. A brief discussion about the large and small size structures of the flow will provide the key ideas to represent the general dynamics of the flow using low-rank approximations. If the flow physics is understood, then it is possible to adapt these techniques, or some other strategies, to solve general complex problems with reduced computational cost. The main goal is to introduce these methods as machine learning strategies that could be potentially used in the field of fluid dynamics, and that can be extended to any other research field.

Place, publisher, year, edition, pages
Springer, 2020
Series
Advances in Intelligent Systems and Computing, ISSN 2194-5357 ; 950
Keywords
Soft computing, Fluid dynamics, Turbulence flow, CFD, Data science, POD, DMD
National Category
Computer Systems
Identifiers
urn:nbn:se:kth:diva-263684 (URN)10.1007/978-3-030-20055-8_55 (DOI)000490706700055 ()2-s2.0-85065927402 (Scopus ID)978-3-030-20055-8 (ISBN)978-3-030-20054-1 (ISBN)
Conference
14th International Conference on Soft Computing Models in Industrial and Environmental Applications (SOCO), MAY 13-15, 2019, Seville, Spain
Note

QC 20191108

Available from: 2019-11-08 Created: 2019-11-08 Last updated: 2019-12-19Bibliographically approved
Rezaeiravesh, S., Vinuesa, R. & Schlatter, P. (2019). A statistics toolbox for turbulent pipe flow in Nek5000. Stockholm: KTH Royal Institute of Technology
Open this publication in new window or tab >>A statistics toolbox for turbulent pipe flow in Nek5000
2019 (English)Report (Other academic)
Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2019. p. 8
Series
TRITA-SCI-RAP ; 2019:008
National Category
Fluid Mechanics and Acoustics Computational Mathematics
Research subject
Engineering Mechanics; Applied and Computational Mathematics
Identifiers
urn:nbn:se:kth:diva-265021 (URN)
Note

QC 20191218

Available from: 2019-12-10 Created: 2019-12-10 Last updated: 2020-01-28Bibliographically approved
Negi, P. S., Mishra, M., Schlatter, P. & Skote, M. (2019). Bypass transition delay using oscillations of spanwise wall velocity. Physical Review Fluids, 4(6), Article ID 063904.
Open this publication in new window or tab >>Bypass transition delay using oscillations of spanwise wall velocity
2019 (English)In: Physical Review Fluids, E-ISSN 2469-990X, Vol. 4, no 6, article id 063904Article in journal (Refereed) Published
Abstract [en]

Large eddy simulations are performed to investigate the possibility of bypass transition delay in spatially developing boundary layers. An open loop wall control mechanism is employed which consists of either spatial or temporal oscillations of the spanwise wall velocity. Both spatial and temporal oscillations show a delay in the sharp rise in skin friction coefficient which is characteristic of laminar-turbulent transition. An insight into the mechanism is offered based on a secondary filtering of the continuous Orr-Sommerfeld-Squire (OSQ) modes provided by the Stokes layer, and it is shown that the control mechanism selectively affects the low-frequency penetrating modes of the OSQ spectrum. This perspective clarifies the limitations of the mechanism's capability to create transition delay. Furthermore, we extend the two-mode model of bypass transition proposed by T. Zaki and P. Durbin [j Fluid Mech. 531, 85 (2005)] to cases with wall control and illustrate the selective action of the wall oscillations on the penetrating mode in this simplified case.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2019
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-255189 (URN)10.1103/PhysRevFluids.4.063904 (DOI)000472000300002 ()2-s2.0-85069727063 (Scopus ID)
Note

QC 20190904

Available from: 2019-09-04 Created: 2019-09-04 Last updated: 2019-12-20Bibliographically approved
Friederici, A., Köpp, W., Atzori, M., Vinuesa, R., Schlatter, P. & Weinkauf, T. (2019). Distributed Percolation Analysis for Turbulent Flows. In: 2019 IEEE 9th Symposium on Large Data Analysis and Visualization, LDAV 2019: . Paper presented at 9th IEEE Symposium on Large-Scale Data Analysis and Visualization, LDAV 2019; Vancouver; Canada; 21 October 2019 through (pp. 42-51). Institute of Electrical and Electronics Engineers (IEEE), Article ID 8944383.
Open this publication in new window or tab >>Distributed Percolation Analysis for Turbulent Flows
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2019 (English)In: 2019 IEEE 9th Symposium on Large Data Analysis and Visualization, LDAV 2019, Institute of Electrical and Electronics Engineers (IEEE), 2019, p. 42-51, article id 8944383Conference paper, Published paper (Refereed)
Abstract [en]

Percolation analysis is a valuable tool to study the statistical properties of turbulent flows. It is based on computing the percolation function for a derived scalar field, thereby quantifying the relative volume of the largest connected component in a superlevel set for a decreasing threshold. We propose a novel memory-distributed parallel algorithm to finely sample the percolation function. It is based on a parallel version of the union-find algorithm interleaved with a global synchronization step for each threshold sample. The efficiency of this algorithm stems from the fact that operations in-between threshold samples can be freely reordered, are mostly local and thus require no inter-process communication. Our algorithm is significantly faster than previous algorithms for this purpose, and is neither constrained by memory size nor number of compute nodes compared to the conceptually related algorithm for extracting augmented merge trees. This makes percolation analysis much more accessible in a large range of scenarios. We explore the scaling of our algorithm for different data sizes, number of samples and number of MPI processes. We demonstrate the utility of percolation analysis using large turbulent flow data sets.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2019
Keywords
Computing methodologies, Discrete mathematics, Distributed algorithms, Distributed computing methodologies, Graph theory, Mathematics of computing, Paths and connectivity problems
National Category
Computer and Information Sciences
Identifiers
urn:nbn:se:kth:diva-267897 (URN)10.1109/LDAV48142.2019.8944383 (DOI)2-s2.0-85078123360 (Scopus ID)9781728126050 (ISBN)
Conference
9th IEEE Symposium on Large-Scale Data Analysis and Visualization, LDAV 2019; Vancouver; Canada; 21 October 2019 through
Note

QC 20200302

Available from: 2020-03-02 Created: 2020-03-02 Last updated: 2020-03-02Bibliographically approved
Beneitez Galan, M., Duguet, Y., Schlatter, P. & Henningson, D. S. (2019). Edge tracking in spatially developing boundary layer flows. Journal of Fluid Mechanics, 881, 164-181
Open this publication in new window or tab >>Edge tracking in spatially developing boundary layer flows
2019 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 881, p. 164-181Article in journal (Refereed) Published
Abstract [en]

Recent progress in understanding subcritical transition to turbulence is based on the concept of the edge, the manifold separating the basins of attraction of the laminar and the turbulent state. Originally developed in numerical studies of parallel shear flows with a linearly stable base flow, this concept is adapted here to the case of a spatially developing Blasius boundary layer. Longer time horizons fundamentally change the nature of the problem due to the loss of stability of the base flow due to Tollmien-Schlichting (TS) waves. We demonstrate, using a moving box technique, that efficient long-time tracking of edge trajectories is possible for the parameter range relevant to bypass transition, even if the asymptotic state itself remains out of reach. The flow along the edge trajectory features streak switching observed for the first time in the Blasius boundary layer. At long enough times, TS waves co-exist with the coherent structure characteristic of edge trajectories. In this situation we suggest a reinterpretation of the edge as a manifold dividing the state space between the two main types of boundary layer transition, i.e. bypass transition and classical transition.

Place, publisher, year, edition, pages
Cambridge University Press, 2019
Keywords
boundary layer stability, nonlinear dynamical systems, transition to turbulence, Aerodynamics, Boundary layer flow, Boundary layers, Dynamical systems, Parallel flow, Shear flow, Trajectories, Turbulence, Basins of attraction, Blasius boundary layer, Boundary layer stabilities, Boundary layer transitions, Classical transition, Subcritical transition, Tollmien-Schlichting waves, Atmospheric thermodynamics, boundary layer, fluid dynamics, fluid flow, nonlinearity
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-263766 (URN)10.1017/jfm.2019.763 (DOI)000506237100008 ()2-s2.0-85074285559 (Scopus ID)
Note

QC 20191112

Available from: 2019-11-12 Created: 2019-11-12 Last updated: 2020-01-29Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0001-9627-5903

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