Non-explicit large eddy simulations of turbulent channel flows from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si15.svg"><mml:mrow><mml:mi>R</mml:mi><mml:msub><mml:mi>e</mml:mi><mml:mi>τ</mml:mi></mml:msub><mml:mo linebreak="goodbreak">=</mml:mo><mml:mn>180</mml:mn></mml:mrow></mml:math> up to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si80.svg"><mml:mrow><mml:mi>R</mml:mi><mml:msub><mml:mi>e</mml:mi><mml:mi>τ</mml:mi></mml:msub><mml:mo linebreak="goodbreak">=</m

Mahfoze, Omar Ahmed; Laizet, Sylvain

doi:10.1016/j.compfluid.2021.105019

Cited by 10 publications

(3 citation statements)

References 70 publications

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“…The underestimation of the reattachment length of the primary separation bubble in laminar BFS can be attributed to the lower effectiveness of this model in laminar regions compared to transitional and turbulent regimes. This approach has the potential to be improved by recent developments in the iLES approach like spatially-varying artificial viscosity [32] and hyperviscous filtering [33].…”

Section: Discussionmentioning

confidence: 99%

Evaluation of implicit LES modeling of separated flows in a backward-facing step

Malmir,

Vétel

2023

Progress in Canadian Mechanical Engineering. Volume 6

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This paper assesses the implicit Large Eddy Simulation (iLES) technique to model a separated flow over a backwardfacing step (BFS), in comparison with results achieved by Direct Numerical Simulation (DNS). The iLES technique, implemented in the open-source code "Incompact3d", relies on introducing an artificial viscosity in the discretization of the viscous term to control spurious oscillations. To the best of the author's knowledge, this method has not been tested on wall-bounded separated flows where modeling wall regions with classical LES techniques is challenging. An internal flow over a BFS is simulated at Reynolds number Re = 5000 and expansion ratio Er = 2. Two inflow conditions are considered upstream of the expansion: a laminar Poiseuille flow and a turbulent inflow. The underestimation of the reattachment location of the primary geometry-induced separation bubble leads to the spatial shift of the secondary pressure-induced separation bubble formed on the top wall in the laminar BFS. Despite this underestimation in iLES, an excellent agreement has been obtained on the mean flow properties and Reynolds stress budgets with 12 times fewer grid points than DNS.

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Section: Discussionmentioning

confidence: 99%

Evaluation of implicit LES modeling of separated flows in a backward-facing step

Malmir,

Vétel

2023

Progress in Canadian Mechanical Engineering. Volume 6

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“…For brevity, further details are not provided here. However, the reader is referred to Dairay et al (2017), Deskos et al (2019), Frantz et al (2021), Mahfoze and Laizet (2021) for more information about the present ILES strategy.…”

Section: Flow Solvermentioning

confidence: 99%

“…The degree of numerical dissipation is controlled by a single parameter ( 0 ∕ ), which corresponds to the added dissipation at the cutoff wavenumber, and the range of scales over which the numerical dissipation is added is controlled by the parameter c 1 (see Dairay et al (2017) for more details). The present work follows the recommendation of Mahfoze and Laizet (2021), who determined suitable ranges for these parameters for wall-bounded turbulent flows. Therefore, for this work 0 ∕ = 20 and c 1 = 0.1755 (low Reynolds numbers) -0.351 (high Reynolds numbers).…”

Section: Flow Solvermentioning

confidence: 99%

Optimisation and Analysis of Streamwise-Varying Wall-Normal Blowing in a Turbulent Boundary Layer

O’Connor

Diessner

Wilson

et al. 2023

Flow Turbulence Combust

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Skin-friction drag is a major engineering concern, with wide-ranging consequences across many industries. Active flow-control techniques targeted at minimising skin friction have the potential to significantly enhance aerodynamic efficiency, reduce operating costs, and assist in meeting emission targets. However, they are difficult to design and optimise. Furthermore, any performance benefits must be balanced against the input power required to drive the control. Bayesian optimisation is a technique that is ideally suited to problems with a moderate number of input dimensions and where the objective function is expensive to evaluate, such as with high-fidelity computational fluid dynamics simulations. In light of this, this work investigates the potential of low-intensity wall-normal blowing as a skin-friction drag reduction strategy for turbulent boundary layers by combining a high-order flow solver () with a Bayesian optimisation framework. The optimisation campaign focuses on streamwise-varying wall-normal blowing, parameterised by a cubic spline. The inputs to be optimised are the amplitudes of the spline control points, whereas the objective function is the net-energy saving (NES), which accounts for both the skin-friction drag reduction and the input power required to drive the control (with the input power estimated from real-world data). The results of the optimisation campaign are mixed, with significant drag reduction reported but no improvement over the canonical case in terms of NES. Selected cases are chosen for further analysis and the drag reduction mechanisms and flow physics are highlighted. The results demonstrate that low-intensity wall-normal blowing is an effective strategy for skin-friction drag reduction and that Bayesian optimisation is an effective tool for optimising such strategies. Furthermore, the results show that even a minor improvement in the blowing efficiency of the device used in the present work will lead to meaningful NES.

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A Cartesian Immersed Boundary Method Based on 1D Flow Reconstructions for High-Fidelity Simulations of Incompressible Turbulent Flows Around Moving Objects

Giannenas

Bempedelis

Schuch

et al. 2022

Flow Turbulence Combust

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The aim of the present numerical study is to show that the recently developed Alternating Direction Reconstruction Immersed Boundary Method (ADR-IBM) (Giannenas and Laizet in Appl Math Model 99:606–627, 2021) can be used for Fluid–Structure Interaction (FSI) problems and can be combined with an Actuator Line Model (ALM) and a Computer-Aided Design (CAD) interface for high-fidelity simulations of fluid flow problems with rotors and geometrically complex immersed objects. The method relies on 1D cubic spline interpolations to reconstruct an artificial flow field inside the immersed object while imposing the appropriate boundary conditions on the boundaries of the object. The new capabilities of the method are demonstrated with the following flow configurations: a turbulent channel flow with the wall modelled as an immersed boundary, Vortex Induced Vibrations (VIVs) of one-degree-of-freedom (2D) and two-degree-of-freedom (3D) cylinders, a helicopter rotor and a multi-rotor unmanned aerial vehicle in hover and forward motion. These simulations are performed with the high-order fluid flow solver which is based on a 2D domain decomposition in order to exploit modern CPU-based supercomputers. It is shown that the ADR-IBM can be used for the study of FSI problems and for high-fidelity simulations of incompressible turbulent flows around moving complex objects with rotors.

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Non-explicit large eddy simulations of turbulent channel flows from Reτ=180 up to Reτ=

Cited by 10 publications

References 70 publications

Evaluation of implicit LES modeling of separated flows in a backward-facing step

Evaluation of implicit LES modeling of separated flows in a backward-facing step

Optimisation and Analysis of Streamwise-Varying Wall-Normal Blowing in a Turbulent Boundary Layer

A Cartesian Immersed Boundary Method Based on 1D Flow Reconstructions for High-Fidelity Simulations of Incompressible Turbulent Flows Around Moving Objects

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