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2.25.15 Iyer

HIGH-SPEED BOUNDARY-LAYER TRANSITION INDUCED BY A DISCRETE ROUGHNESS ELEMENT

Prahladh S. Iyer, Postdoctoral Researcher, Dept. of Aerospace Engineering and Mechanics, University of Minnesota
February 25, 2015, 10:00 am, NIA, Rm 137

Abstract:
Direct numerical simulation (DNS) is used to study laminar to turbulent transition induced by a discrete hemispherical roughness element in a high-speed laminar boundary layer using an unstructured finite volume methodology. The simulations are performed under conditions matching the experiments of Danehy et al. (AIAA Paper 2009–394, 2009) for free-stream Mach numbers of 3.37, 5.26 and 8.23. Qualitative comparison to experiment shows good agreement. It is observed that the Mach 8.23 flow remains laminar downstream of the roughness, while the lower Mach numbers undergo transition. A phenomenological mechanism is proposed for the observed behavior. For Mach 3.37 and 5.26, mean statistics downstream of the roughness is compared with available turbulent boundary layer data which show good agreement. The effect of boundary layer thickness on Mach 3.37 flow past a hemispherical bump is also studied keeping all other parameters constant. While the essential mechanism of transition is similar for the conditions studied, differences are observed in the number of trains of hairpin vortices downstream of the roughness element.

Biography:
Prahladh S. Iyer is a postdoctoral researcher at the University of Minnesota, Twin Cities. He obtained his PhD from the Dept. of Aerospace Engg. & Mechanics, University of Minnesota in 2015 and B.Tech in Chemical Engineering from the National Institute of Technology, Surathkal, India in 2008.

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