Dynamics of Scalar Injection in Freestream Turbulence

We report an experiment about the process of temperature injection from a heated patch, situated in a flat plate boundary layer, submitted to freestream turbulence. We measure simultaneously the incoming turbulent velocity, the heat flux released in the flow by the controlled constant-temperature heated patch and the outgoing temperature. The heat flux signal and the outgoing temperature shows a f -7/3 temporal spectral scaling, in agreement with the prediction for scalar flux in homogeneous turbulence. Cross-correlations shows that the outgoing scalar field is anti-correlated with the incoming turbulence and the heat flux, showing the importance of slow events in scalar injection.