Effect of Vortex Generators on Film Cooling Effectiveness

Film cooling is often adopted, where coolant jets are ejected to form a protective layer on the surface against the hot combustor gases. The bending of jets in crossflow results in Counter Rotating Vortex Pair (CRVP), which is a cause for high jet lift-off and poor film cooling effectiveness in the near field. There are efforts to mitigate this detrimental effect of CRVP and thus to improve the film cooling performance. In the present study, the effects of both downwash and upwash type of vortex generator on film cooling are numerically analysed A series of discrete holes on a flat plate with 3.5 degrees streamwise orientation and connected to a common delivery plenum is used here, where the vortex generators are placed upstream of the holes. The blowing ratio and the density ratio are considered as 0.5 and 1.2 respectively with a Reynolds number based on free-stream velocity and diameter of hole being 15885. The computations are performed by ANSYS Fluent 13.0 using k-epsilon realizable turbulence model. The results show that vortices generated by downwash vortex generator (DWVG) counteracts the effect of CRVP preventing the jet lift-off which results in increased effectiveness in streamwise as well as in spanwise directions. However, upwash vortex generator (UWVG) augments the effect of CRVP, resulting in poor performance of film cooling.