Seminar: Mach 5 Boundary Layer with Crosshatch Roughness

Abstract

National interest in hypersonic flight provides motivation to develop closure models for high-speed turbulent shear flows with mechanical and/or thermochemical non-equilibrium effects. Crosshatch roughness, which occurs naturally in high-speed ablative materials, produces significant mechanical non-equilibrium. The effects of periodic crosshatch roughness (k+=160) on a Mach 5 turbulent boundary layer (Reθ = 60,000) are examined using particle image velocimetry. The roughness elements generate a series of alternating shock and expansion waves, which span the entire boundary layer, causing significant variations (up to +50%/-30%) in the Reynolds shear stress field. Evidence of the hairpin vortex paradigm of incompressible flows is found in a comparative smooth-wall boundary layer case (Reθ = 50,000), and is used to explain several observations regarding the rough-wall vortex organization. In general, the rough-wall boundary layer near-wall vortices no longer appear to be well-organized into streamwise-aligned packets that straddle relatively low-speed regions like their smooth-wall counterparts; instead, they lean farther away from the wall, become more spatially compact, and their populations become altered. In the lower half of the boundary layer, the net vortex swirling strength and outer-scaled Reynolds stresses increase relative to the smooth-wall case, and decrease in the outer half of the boundary layer; ejection and entrainment processes are strengthened and weakened in these two respective regions, respectively. A spectral analysis suggests homogenization of the most energetic scales to ~0.5δ across the rough-wall boundary layer.

About the Speaker

Dr. Bowersox is the Ford I Professor and Department Head of Aerospace Engineering at Texas A&M University. He has been on the faculty for 13 years. He received his PhD in Aerospace Engineering from Virginia Polytechnic Institute & State University in 1992. His research interests are in turbulent and transitional flows with mechanical and thermochemical non-equilibrium, advanced experiments methods including high-energy laser based optical diagnostics, and innovative flow control. He founded and directs the Texas A&M University National Aerothermochemistry Laboratory. He is a fellow of the ASME, associate fellow of the AIAA, member of the ACS, APS, and OSA. He is also an Associate Editor for the AIAA Journal of Propulsion and Power.

Hostedy by Professor Jim Gregory