Experimental investigation of a separation bubble on a flat plate with semi-circular leading edge for different Reynolds numbers

Abstract

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.The laminar separated layer over a semi-circular leading edge, its transition, turbulent reattachment and downstream development have been investigated in a low-speed wind tunnel. Instantaneous velocity and surface pressure measurements were made along with a planar PIV to visualize flow structures for varying Reynolds number 25000 to 75000 (based on the leading edge diameter). The velocity fluctuations illustrates that the separated shear layer is laminar up to 20% of separation length and then the perturbations are amplified in the second half attributing to breakdown and reattachment. The bubble length is highly susceptible to change in Reynolds number and plays an important role in outer layer activities. It is also evident that the shear layer is inviscidly unstable and the predominant shedding frequency when normalised with respect to the momentum thickness at separation remains almost constant with change in Reynolds number.