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 (VG) on film cooling are numerically analyzed. A series of discrete holes on a flat plate with 35 deg 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 freestream velocity and diameter of hole being 15,885. 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.