DES and Hybrid RANS-LES Modelling of Unsteady Pressure Oscillations and Flow Features in a Rectangular Cavity
Using the Detached Eddy Simulation (DES) and an algebraic hybrid RANS-LES model, computations are conducted for the flow over a rectangular cavity at a Mach number of M ∞ =0.85. The emphasis is placed on the prediction of unsteady pressure patterns insid
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FOI, Department of Computational Physics, Sweden 2 EADS-MAS, OPEA3, Germany
Abstract Using the Detached Eddy Simulation (DES) and an algebraic hybrid RANS-LES model, computations are conducted for the flow over a rectangular cavity at a Mach number of M ∞ = 0.85 . The emphasis is placed on the prediction of unsteady pressure patterns inside the cavity in terms of pressure fluctuations and deduced acoustic tonal modes in comparison with available experimental data. Furthermore, some resolved cavity flow features are also compared, for which a set of wall-resolved LES data is taken as reference. It is shown that both modelling approaches have produced similar results that are in good agreement with experimental or LES data. The DES modelling has generated somewhat reduced pressure fluctuations on the cavity floor. The hybrid model pronounces a less diffusive mixing layer over the cavity opening, which makes a slightly better prediction for the mean flow field.
1 Introduction In aeronautic applications, typical cavity flows can be observed over, for example, a landing-gear housing well and weapons-bays, which are often characterized by unsteadiness, boundary-layer detachment and separation, as well as by shear-layer instabilities and vortex motions. Since the pioneering work of Roshko (1955), cavity flows have been extensively studied by means of theoretical and numerical analysis, and by experimental measurements, as highlighted in reviews by, e.g., Rockwell and Naudascher (1978), Colonius (2001) and Grace (2001). Much of previous work has been focused on the self-sustained pressure oscillations arising due to the vorticitypressure feedback loop. According to Stallings and Forrest (1990) and Wilcox (1990), and also being illustrated by Tracy and Plentovich (1993), four types of mean cavity flow may be categorized under supersonic conditions, namely, closed cavity, open cavity, transitional-closed cavity and transitional-open cavity. Due to inherent pressure oscillations, a cavity flow is usually prone to aero-acoustic resonance, which may consequently impose adverse effects on the structure and the avionics housed in the cavity, as well as on the stability of aircraft where the cavity is embedded. For weapons-bay type cavities, an adverse pressure gradient along the cavity may cause a nose-up pitching moment, which is undesirable for store separation. S.-H. Peng and W. Haase (Eds.): Adv. in Hybrid RANS-LES Modelling, NNFM 97, pp. 132–141, 2008. © Springer-Verlag Berlin Heidelberg 2008 springerlink.com
DES and Hybrid RANS-LES Modelling
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It is known that the pressure oscillation generated for closed-cavity type flows may lead to broadband noise, and causing an adverse static pressure gradient over the cavity floor. With open cavities, a nearly uniform pressure distribution is produced along the cavity, but high-intensity acoustic tones may be developed at discrete frequencies. The acoustic tones generated from an open cavity flow have been often understood being a consequence of the interaction between the she
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