Detached-eddy simulation of a supersonic axisymmetric base flow with an unstructured solver

An assessment of unstructured grids for use in Detached-Eddy Simulations (DES) of vortical flowfields over two configurations, a 70 degree delta wing and an F-18C are presented. The role of the grid in detached eddy simulations of vortical flowfields, including complex features such as vortex breakdown, is assessed on a delta wing with comparison to wind tunnel data. Adaptive mesh refinement is applied to the delta wing grid to improve the focus region aft of the vortex breakdown where massively separated flow exists and unsteady pressures are generated that could impact the loads on vertical tails of more complex configurations. The adaptively refined mesh is compared to the baseline mesh to determine the advantage of the adaptive mesh refinement approach for vortex breakdown. The focus region grid resolution is then applied to an F-18C in the region of the vortex generat ed from the leading edge extension (LEX). The resulting unsteady tail loads are compared to flight test data from the NASA F-18 HARV database. This paper represents one of the first times adaptive mesh refinement will be applied to a detached eddy simulati on of a flight vehicle configuration.

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“…al. 29 They determined the constant should C DES be 0.65, consistent with the structured grid implementation of Spalart et. al.…”

Section: Detached-eddy Simulationmentioning

confidence: 99%

DES Grid Resolution Issues for Vortical Flows on a Delta Wing and an F-18C

Morton

Steenman

Cummings

et al. 2003

41st Aerospace Sciences Meeting and Exhibit

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“…al. 30 They determined the DES C constant could be 0.65, consistent with the structured grid implementation of Shur et. al.…”

Section: Spalart-allmaras Turbulence Modelmentioning

confidence: 91%

“…Results from the first three grids were presented in Ref. 30 with a preliminary assessment. The current work adds the next refinement in the grid series (10.7 million cells) and also presents a more complete analysis of the set of grids when coupled with DES in comparison with the experiments.…”

Section: Grid Generationmentioning

confidence: 99%

Analysis of Delta-Wing Vortical Substructures Using Detached-Eddy Simulation

et al. 2006

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An u nderstanding of the vortical structures which comprise the vortical flowfield around slender bodies is essential for the development of highly maneuverable and high angle of attack flight. This is primarily due to the physical limits these phenomena impose on aircraft and missile s at extreme flight conditions. D emands for more maneuverable air vehicles have pushed the limits of current CFD methods in the high Reynolds number regime. Simulation methods must be able to accurately describe the unsteady, vortic al flowfields associated with fighter aircraft at Reynolds numbers more representative of full scale vehicles. It is the goal of this paper to demonstrate the ability of DetachedEddy Simulation, a hybrid RANS-LES method, to accurately model the vortical flowfield over a slender delta wing at Reynolds numbers above 1 million. Detached-Eddy Simulation has successfully predicted the location of the vortex breakdown phenomenon and the goal of the current effort is to analyze and assess the influence of vortical substructures in the separating shear layers which roll up to form the leading-edge vortices. Very detailed experiments performed at O NERA using 3 -D Laser Doppler Velocimetry measurement will be used to compare simulations utilizing DES turbulence models. The computational results provide novel insight into the formation and impact of the vortical substructures in the separating shear layers on the entire vortical flowfield.

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“…This approach was applied to the UIUC experiments by Forsythe & Hoffmann (2000) who reported results agreeing reasonably well with the experimental data for values of the empirical constant smaller than originally suggested. The mean flow quantities in the recirculation region were found to deviate from the experiments and were dependent on the utilized grid, even though they reported very good agreement of the mean base pressure distribution.…”

Section: Turbulence Modellingmentioning

confidence: 93%

Simulation of Supersonic Base Flows: Numerical Investigations Using DNS, LES, and URANS

Fasel¹,

Sandberg²

2006

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Public Reporting Burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comment regarding this burden estimate or any other aspect of this collection of information, including suggesstions for reducing this burden, Simulation of Supersonic Base Flows: Numerical Investigations Using DNS, LES, and URANS Report Title ABSTRACTTransitional and turbulent supersonic axisymmetric wakes were investigated by conducting various numerical experiments. The main objective was to identify hydrodynamic instability mechanisms in the flow at Mach number M = 2.46 for several Reynolds numbers, and relating these to coherent structures that are found from various visualization techniques. The premise for this approach is the assumption that flow instabilities lead to the formation of coherent structures. The effect of these structures on the mean flow is of particular interest, as they strongly affect the base drag. Three high-order accurate compressible codes were developed in cylindrical coordinates for this research: A spatial Navier-Stokes (N-S) code to conduct Direct Numerical Simulations (DNS), a linearized N-S code for linear stability investigations using two-dimensional basic states, and a temporal N-S code for performing local stability analyses. The ability of numerical simulations to deliberately exclude physical effects is exploited. This includes intentionally eliminating certain azimuthal/helical modes by employing DNS for various circumferential domain-sizes. With this approach, the impact of structures associated with certain modes on the global wake-behavior can be scrutinized. It is concluded that azimuthal modes with low wavenumbers are responsible for a flat mean base-pressure distribution and that k=2 and k=4 are the dominant modes in the trailing wake, producing a four-lobe wake pattern. Complementary spatial and temporal calculations are carried out to investigate whether instabilities are of local or global nature. Circumstatial evidence is presented that absolutely unstable global modes within the recirculation region coexist with convectively unstable shear-layer modes. The flow is found to be absolutely unstable with respect to modes k>0 for Re_D > 5,000 and with respect to the axisymmetric mode for Re_D>100,000. Furthermore, it is investigated whether flow control measures designed to weaken the naturally most significant modes can decrease the base drag. Finally, the novel Flow Simulation Methodology (FSM), using state-of-the-art turbulence closures, was shown to reproduce DNS results at a fraction of the computational cost.

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Detached-eddy simulation of a supersonic axisymmetric base flow with an unstructured solver

Cited by 49 publications

References 16 publications

DES Grid Resolution Issues for Vortical Flows on a Delta Wing and an F-18C

DES Grid Resolution Issues for Vortical Flows on a Delta Wing and an F-18C

Analysis of Delta-Wing Vortical Substructures Using Detached-Eddy Simulation

Simulation of Supersonic Base Flows: Numerical Investigations Using DNS, LES, and URANS

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