Experimental investigation of turbulent boundary layer separation in adverse pressure gradiant

Abstract

Paper presented at the 7th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Turkey, 19-21 July, 2010.The problem of turbulent boundary-layer separation due to an adverse pressure gradient is an important factor in the design of many devices such as jet engines, rocket nozzles, airfoils and helicopter blades and the design of many fluidic logic systems. As a result, wind tunnel experiments were conducted to investigate the separation developing on a flat-plate in steady and unsteady flow. The nature of upstream flow subjected to the effect of unsteady freestream velocity which changes sinusoidally with time due to the rotation of an elliptical cylinder placed downstream of the flat plate has been studied in the test section. Separation points (or line) were measured in different angles of incidence and at various stations. Pitot-static tube and hot-wire anemometery were used to measure the steady and instantaneous velocities and turbulence. The results indicate that the more the increase in the angle of incidence of the flat plate in steady and unsteady flow, the more is the increase in the thickness of separated region which extends further towards the flat plate trailing edge. Reduced frequency also causes the separation points to move up away from the surface of the flat plate but this movement is restricted to reduced frequencies less than 2 after which the changes are negligible.