Experimental investigation of turbulent flow and scalar transport in a inclined jet in crossflow

The present study investigates the turbulent dispersion in a jet-in crossflow relevant to film cooling applications. Magnetic Resonance Imaging is used to obtain the full three-dimensional velocity and concentration fields, whereas Reynolds stresses are obtained along the jet symmetry plane by PIV. The turbulent viscosity is evaluated directly from the mean velocity gradient and the Reynolds shear stresses, and is shown to vary sharply in wall-normal direction, raising the question of the applicability of the eddy viscosity hypothesis. The turbulent diffusivity is inferred from the balance of concentration flux across the streamtube issued from the film cooling hole. It is shown that the coefficients of turbulent transport for momentum and scalar have largely different values. It is therefore argued that Reynolds analogy is not a suitable assumption for this type of flows, and constitutes a weak basis for the widespread turbulent-Prandtl-number approach. Jet entrainment is evaluated along the jet centerline, and the mechanism is found to be different from the perpendicular jets in crossflow, as leeward side and windward side contribute equally to the jet volume flux.