Investigation of Numerical Dissipation in Classical and Implicit Large Eddy Simulations

Rafei, Moutassem El; Könözsy, László; Rana, Zeeshan A.

doi:10.3390/aerospace4040059

Cited by 16 publications

(8 citation statements)

References 35 publications

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“…A Gaussian integration, in which the surface normal gradient was specified by a limiter for the nonorthogonal correction, was used for the diffusion term (specified as "laplacianSchemes {Gauss linear limited 0.333;}"). Although assessing the numerical schemes for the accuracy of the simulation is attractive, the numerical dissipation from the second-order central difference scheme for the convective term [25] is also a valuable topic, but it is to be explored in further studies.…”

Section: Methodsmentioning

confidence: 99%

Wind Pressure Distributions on Buildings Using the Coherent Structure Smagorinsky Model for LES

et al. 2018

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A subgrid-scale model based on coherent structures, called the Coherent Structure Smagorinsky Model (CSM), has been applied to a large eddy simulation to assess its performance in the prediction of wind pressure distributions on buildings. The study cases were carried out for the assessment of an isolated rectangular high-rise building and a building with a setback (both in a uniform flow) and an actual high-rise building in an urban city with turbulent boundary layer flow. For the isolated rectangular high-rise building in uniform flow, the CSM showed good agreement with both the traditional Smagorinsky Model (SM) and the experiments (values within 20%). For the building with a setback as well as the actual high-rise building in an urban city, both of which have a distinctive wind pressure distribution with large negative pressure caused by the complicated flow due to the strong influence of neighboring buildings, the CSM effectively gives more accurate results with less variation than the SM in comparison with the experimental results (within 20%). The CSM also yielded consistent peak pressure coefficients for all wind directions, within 20% of experimental values in a relatively high-pressure region of the case study of the actual high-rise building in an urban city.

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Section: Methodsmentioning

confidence: 99%

Wind Pressure Distributions on Buildings Using the Coherent Structure Smagorinsky Model for LES

et al. 2018

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“…In the code, a 2 nd -order scheme has been implemented to solve the flow in the circumferential direction; however, the decision of which EAR to use is not straight-forward. As far as Euler equations is concerned, the literature on the topic of quantitative measurement of numerical diffusion is very scarce, some limited literature exists for Navier Stokes equation [26,27]. Furthermore, while methods are available to calculate analytically the truncation error of a scheme due to interpolation [28], there is no study on the effect of the presence of a Riemann solver on the truncation error.…”

Section: Solver Improvementmentioning

confidence: 99%

On the prediction of the reverse flow and rotating stall characteristics of high-speed axial compressors using a three-dimensional through-flow code

Righi

Pachidis

Könözsy

2020

Aerospace Science and Technology

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This paper presents the development of a low-order three-dimensional through-flow code created at Cranfield University in the UK, named ACROSS (Axial Compressor Rotating Stall and Surge simulator), and its application to create the reverse flow and rotating stall characteristics of a modern high-speed compressor. The compressor modelled is a six-stage axial-flow machine, representative of a modern aero-engine highpressure compressor. The tool has been previously validated using experimental data from two low-speed compressor rigs. This article describes how the tool's robustness and computational speed have been improved by introducing higher-order schemes to model the circumferential fluxes and the rigid movement of the flow in the rotating blade rows. Further improvements include variable axial discretization, an algorithm to introduce random flow perturbations in the flow field and an improved plenum model. The compressor is first modelled in reverse flow conditions to create its reverse-flow characteristics and these are then compared against results from high-fidelity 3D CFD simulations. Results obtained suggest that despite the presence of three-dimensional flow features, 2D axi-symmetric simulations are adequate to generate the full range of reverse flow characteristics of the compressor. The rotating stall characteristics at 77% and 100% corrected rotational speed are created by modelling several steady rotating stall cases in 3D. Using the code ACROSS, the complete map of the compressor modelled, comprising of forward flow, reverse flow and rotating stall characteristics, was created in only 5 days using 3 desktop workstations. For comparison, state-of-the-art high-fidelity 3D CFD requires several days to simulate a single rotating stall case on a high performance computing facility.

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“…Measuring the numerical dissipation is inherently difficult and we restrict the discussion here on the symptoms such as reduced accuracy and increased oscillatory behaviour. It should be noted, however, that first promising results were published by El Rafei et al [59] who computed the numerical dissipation directly through the modified equation analysis for the complete set of Navier-Stokes equations. Despite the reduced accuracy, the number of iterations were reduced for some cases up to 14% compared to a non Rusanov Riemann solver treatment.…”

Section: Flow Inside a Lid-driven Cavity At Sub-critical Reynolds Nummentioning

confidence: 99%

A generalised and low-dissipative multi-directional characteristics-based scheme with inclusion of the local Riemann problem investigating incompressible flows without free-surfaces

Teschner

Könözsy

Jenkins

2019

Computer Physics Communications

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In the present study, we develop a generalised Godunov-type multi-directional characteristics-based (MCB) scheme which is applicable to any hyperbolic system for modelling incompressible flows. We further extend the MCB scheme to include the solution of the local Riemann problem which leads to a hybrid mathematical treatment of the system of equations. We employ the proposed scheme to hyperbolic-type incompressible flow solvers and apply it to the Artificial Compressibility (AC) and Fractional-Step, Artificial Compressibility with Pressure Projection (FSAC-PP) method. In this work, we show that the MCB scheme may improve the accuracy and convergence properties over the classical single-directional characteristics-based (SCB) and non-characteristic treatments. The inclusion of a Riemann solver in conjunction with the MCB scheme is capable of reducing the number of iterations up to a factor of 4.7 times compared to a solution when a Riemann solver is not included. Furthermore, we found that both the AC and FSAC-PP method showed similar levels of accuracy while the FSAC-PP method converges up to 5.8 times faster than the AC method for steady state flows. Independent of the characteristics-and Riemann solver-based treatment of all primitive variables, we found that the FSAC-PP method is 7-200 times faster than the AC method per pseudo-time step for unsteady flows. We investigate low-and high-Reynolds number problems for well-established validation

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Investigation of Numerical Dissipation in Classical and Implicit Large Eddy Simulations

Cited by 16 publications

References 35 publications

Wind Pressure Distributions on Buildings Using the Coherent Structure Smagorinsky Model for LES

Wind Pressure Distributions on Buildings Using the Coherent Structure Smagorinsky Model for LES

On the prediction of the reverse flow and rotating stall characteristics of high-speed axial compressors using a three-dimensional through-flow code

A generalised and low-dissipative multi-directional characteristics-based scheme with inclusion of the local Riemann problem investigating incompressible flows without free-surfaces

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