SUMMARYA computational study of a high‐fidelity, implicit large‐eddy simulation (ILES) technique with and without the use of the dynamic Smagorinsky subgrid‐scale (SGS) model is conducted to examine the contributions of the SGS model on solutions of transitional flow over the SD7003 airfoil section. ILES without an SGS model has been shown in the past to produce comparable and sometimes favorable results to traditional SGS‐based large‐eddy simulation (LES) when applied to canonical turbulent flows. This paper evaluates the necessity of the SGS model for low‐Reynolds number airfoil applications to affirm the use of ILES without SGS‐modeling for a broader class of problems such as those pertaining to micro air vehicles and low‐pressure turbines. It is determined that the addition of the dynamic Smagorinsky model does not significantly affect the time‐mean flow or statistical quantities measured around the airfoil section for the spatial resolutions and Reynolds numbers examined in this study. Additionally, the robustness and reduced computational cost of ILES without the SGS model demonstrates the attractiveness of ILES as an alternative to traditional LES. Published 2012. This article is a US Government work and is in the public domain in the USA.

A numerical study is conducted to examine the vortex structure and aerodynamic loading on a revolving wing in quiescent flow. A high-fidelity, implicit large eddy simulation technique is employed to simulate a revolving wing configuration consisting of a single, aspect-ratio-one rectangular plate extended out a distance of half a chord from the rotational axis at a fixed angle relative to the axis. Shortly after the onset of the motion, the rotating wing generates a coherent vortex system along the leading-edge. This vortex system remains attached throughout the motion for the range of Reynolds numbers explored, despite the unsteadiness and vortex breakdown observed at higher Reynolds numbers. The average and instantaneous wing loading also increases with Reynolds number. At a fixed Reynolds number, the attachment of the leading-edge vortex is also shown to be insensitive to the geometric angle of the wing. Additionally, the flow structure and forcing generated by a purely translating wing is investigated and compared with that of the revolving wing. Similar features are present at the inception of the motion, however, the two flows evolve very differently for the remainder of the maneuver. Comparisons of the revolving wing simulations with recent experimental particle image velocimetry (PIV) measurements using a new PIV-like data reduction technique applied to the computational solution show very favorable agreement. The success of the data reduction technique demonstrates the need to compare computations and experiments of differing resolutions using similar data-analysis techniques.

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a b s t r a c tThe Chimera overset method is a powerful technique for modeling fluid flow associated with complex engineering problems using structured meshes. The use of structured meshes has enabled engineers to employ a number of high-order schemes, such as the WENO and compact differencing schemes. However, the large stencil associated with these schemes can significantly complicate the inter-grid communication scheme and hole cutting procedures. This paper demonstrates a methodology for using the Discontinuous Galerkin (DG) scheme with Chimera overset meshes. The small stencil of the DG scheme makes it particularly suitable for Chimera meshes as it simplifies the inter-grid communication scheme as well as hole cutting procedures. The DG-Chimera scheme does not require a donor interpolation method with a large stencil because the DG scheme represents the solution as cell local polynomials. The DG-Chimera method also does not require the use of fringe points to maintain the interior stencil across inter-grid boundaries. Thus, inter-grid communication can be established as long as the receiving boundary is enclosed by or abuts the donor mesh. This makes the inter-grid communication procedure applicable to both Chimera and zonal meshes. Details of the DG-Chimera scheme are presented, and the method is demonstrated on a set of two-dimensional inviscid flow problems.Published by Elsevier Ltd.

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A time-accurate double thin-layer Navier-Stokes computation is performed for an unsteady supersonic open cavity with a length-to-depth ratio of 2. The results are used to determine the flow-physics mechanisms responsible for the cavity oscillation cycle. A new cycle is described and compared to previous descriptions. It is found that a shed vortex impinges on the cavity aft lip and forms a pressure pulse that augments or forces, at the vortex shedding frequency, an internal upstream moving wave that has been reflected from the aft corner. This upstream moving wave eventually reflects off the cavity forward wall and forces the shedding of a new vortex. It was found, however, that the reflected wave dissipates before it reaches the aft wall. Instead, a second wave forms beneath the shed vortex and eventually reflects from the aft corner and is forced at the shedding frequency by the shed vortex wave, completing the cycle. IntroductionT HE basic physical structure of cavity flowfields can be described as either closed, open, or transitional. 1 " 4 Closed cavities are typically long and shallow with a length-to-depth ratio (L/D) greater than 13. These are characterized by a shear layer that impinges on the cavity floor, producing two large recirculation regions. Closed cavities are associated with higher drag coefficients 5 " 8 and heat transfer properties 9 " 11 than those of open cavities; as such, they are less desirable. Open cavities are short and deep with an L/D < 10. They contain shear layers that span the cavity and are more typical of those found in aircraft applications. Open-cavity flowfields are remarkably complicated, with internal and external regions that are coupled via self-sustained shear-layer oscillations. Coherent shed vorticity, unsteady weak shock or pressure waves, and interactions between the shed vortices and the vortices that reside in the cavity also are present. Flowfield characteristics appear to depend primarily on the shape of the cavity and the Mach number, with Reynolds number effects considered to be less important. 12 ' 13 Several issues remain to be understood for open-cavity flowfields. Researchers appear to agree that an oscillating shear layer exists, that the primary and secondary vortices residing within the cavity are driven by the shear layer, that a mass breathing effect occurs within the cavity, and that pressure oscillations exist. However, the mechanisms driving this flowfield have not yet been agreed upon.Because of the unsteady nature of supersonic open-cavity flowfields, the measurement of field properties within the cavity is difficult experimentally. As such, surface properties, such as timeaveraged pressure and time-averaged sound-pressure level (SPL), are usually reported in the literature. Unsteady quantities typically are presented in terms of the spectral SPL. Recent experimental work 12 for subsonic to transonic open cavities provides a benchmark for comparing the effects of different Mach numbers, aspect ratios, flowfield dimensionality (i.e., two-and thr...