European Turbulence Conference 2015

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16:45
15 mins

A COMBINED EXPERIMENTAL AND NUMERICAL INVESTIGATION OF ROUGHNESS INDUCED SUPERSONIC BOUNDARY LAYER TRANSITION
Yunfei Zhao, Wei Liu, Xiaoliang Yang, Shihe Yi, Xiaogang Deng

Session: Instability and Transition 2
Session starts: Tuesday 25 August, 15:00
Presentation starts: 16:45
Room: Room A

Yunfei Zhao (Department of Areospace Science and Engineering, National University of Defense Technology, Changsha, P. R. China, 410073)
Wei Liu (Department of Areospace Science and Engineering, National University of Defense Technology, Changsha, P. R. China, 410073)
Xiaoliang Yang (Department of Areospace Science and Engineering, National University of Defense Technology, Changsha, P. R. China, 410073)
Shihe Yi (Department of Areospace Science and Engineering, National University of Defense Technology, Changsha, P. R. China, 410073)
Xiaogang Deng (Department of Areospace Science and Engineering, National University of Defense Technology, Changsha, P. R. China, 410073)

Abstract:
The laminar-turbulent transition of a supersonic flat-plate boundary layer with isolated roughness element is investigated both numerically and experimentally. Experiments are conducted in a Mach 3 low-noise wind tunnel for three different roughness heights of 1mm, 2mm and 4mm respectively. The flow structures in the transitional boundary layer are measured by a nano-based planar laser scattering (NPLS) flow visualization technique. Calculations are implemented in the same wind tunnel conditions using both second-order scheme and fifth-order weighted compact nonlinear scheme (WCNS-E-5) for comparison. Good agreements are achieved between experimental data and high-order solutions, including the turbulent boundary layer structures and quantitative pressure distribution along the plate centerline. However, the second-order scheme is found to be too dissipative to resolve the unsteadiness and small-scale structures in the transitional flow field. It is observed that the shear layer instability appears to be the leading mechanism for transition to turbulence in the wake of roughness element. With increasing height of roughness, the shear layer breaks up earlier and the transition tends to move forward.