The stability and development of tip and root vortices behind a model wind turbine

An inclined turbulent jet discharging a passive scalar into a turbulent crossflow is investigated under conditions of favorable, zero and adverse streamwise pressure gradient. Experiments are conducted in water by means of magnetic resonance velocimetry and magnetic resonance concentration measurements. The velocity ratio and density ratio are equal to one for all cases. The flow configuration is relevant to film cooling technology, the molecular properties of the fluid being immaterial in the fully turbulent regime. Under favorable pressure gradient (FPG), the streamwise acceleration tilts the jet trajectory toward the wall, which would be beneficial for the film cooling performance. However, the counter-rotating vortex pair is strengthened in the accelerating flow by streamwise stretching. Also, the crossflow boundary layer is significantly thickened by increasingly adverse pressure gradient, which affects the mass transfer from the jet. Overall, the more intense counter-rotating vortices and the thinner boundary layer associated with increasingly FPG enhance the scalar dispersion into the main flow, hampering the film cooling performance in terms of surface effectiveness.