LOCALISED INSTABILITY IN UNSTEADY SEPARATION BUBBLES
We propose an experimental method to study the instability of thin unsteady separation bubbles, i.e. of unsteady boundary layers with reverse flow. The unsteady boundary layer is created by controlled temporal and spatial variations of the velocity external to the boundary layer. We present results of the evolution of instability in different temporally varying flows in a shallow angle diffuser. Depending on the extent of reverse flow in the boundary we observe that instability can be spatially localised.
- Akhavan, R., Kamm, R. D., and Shapiro, A. H. (1991). An investigation of transition to turbulence in bounded oscillatory stokes flows. Part II. Numerical simulations. J. Fluid. Mech., Vol 225:pp 423-444.Google Scholar
- Gaster, M. (1966). The structure and behaviour of laminar separation bubbles. AGARD CP,Vol 4:pp 813.Google Scholar
- Rist, U. (2002). On instabilities and transition in laminar separation bubbles. Proc. CEAS Aerospace Aerodynamics Research Conference, 10 -12 June 2002, Cambridge, UK.Google Scholar
- Rist, U. (2003). Instability and transition mechanisms in laminar separation bubbles. VKI/RTO-LS “Low Reynolds Number Aerodynamics on Aircraft Including Applications in Emerging UAV Technology”, Rhode-Saint-Genese, Belgium, 24-28 November 2003.Google Scholar
- Schmid, P. J. and Henningson, D. S. (2001). Stability and transition in shear flows. Springer.Google Scholar
- Van Dommelen, L. L. and Shen, S. F. (1980). The spontaneous generation of the singularity in a separating laminar boundary layer. J. Comput. Phys, Vol 38:pp 125-140.Google Scholar