Direct Numerical Simulation of Distributed Roughness on a Swept Wing Leading Edge
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abstract
Direct numerical simulation (DNS) is employed in order to describe the subsonic flow past a distributed array of micron-sized discrete roughness elements, which were mounted near the leading edge of a 30 deg swept wing at a chord Reynolds number of 7.4 million. The flow conditions correspond to flight receptivity experiments which were conducted to investigate the effects of roughness on crossflow instabilities. In order to make the computations tractable, the geometry is scaled by the radius of the wing leading edge, which magnifies the region of interest and enhances resolution. The leading-edge region is then approximated by the flow past an infinite parabolic cylinder. The numerical method is based upon a sixth-order-accurate time-implicit scheme to attain high fidelity, and was used in conjunction an eighth-order low-pass Pade-type non-dispersive filter operator to maintain stability. A high-order overset grid approach preserved spatial accuracy on a local mesh system representing the roughness elements, using domain decomposition to perform calculations on a parallel computing platform. The direct simulation for the flow about the roughness elements was used to capture crossflow vortices, and served as input to the nonlinear parabolized stability equations (NPSE), that were then solved in order to determine receptivity of the flow to the geometric perturbations. Three different geometric roughness elemental shapes were investigated in the study. For one shape, the effect of element height was examined. Features of the roughness element flowfields are elucidated, and findings of the stability calculations are compared. Results are presented for receptivity of the crossflow instability to the size and shape of elements, as obtained by the DNS and by two different stability approaches.
name of conference
48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition
