LARGE-EDDY SIMULATION OF FILM COOLING FLOW EJECTED IN A SHALLOW CAVITY

In the present paper the flow field of a film cooling configuration with cylindrical holes embedded in a shallow cavity is investigated using large-eddy simulation (LES). The cooling jet is injected through a single row of inclined holes from a transverse cavity into a turbulent flat plate boundary layer at a temperature ratio of TR = 0.44. The mixing of the cooling fluid and the crossflow within the cavity is a highly unsteady process generating complex vortical structures. The impact of the boundary layer separation at the upstream cavity edge on the jet-crossflow interaction is studied in detail. The driving mechanisms of the momentum and heat exchange between the jet and the crossflow are identified and discussed. The flow field and the adiabatic cooling efficiency is compared to a standard cylindrical film cooling configuration without a cavity. The development of the counter-rotating vortex pair (CVP) downstream of the jet injection is investigated. An analysis of the vortex dynamics shows an impinging behavior of the jet fluid in this area. The Reynolds stress shows a more two-dimensional distribution compared to the anisotropic nature of the jet-in-a-crossflow (JICF) at standard cylindrical holes. Since the heat exchange is closely connected to the transport of momentum in the mixed boundary layer, this observation explains the enhanced lateral spreading of the cooling fluid.