Influence of shear layer dynamics on impingement heat transfer

Measurements of convective heat transfer coefficients on a flat plate with an air jet impinging on it perpendicularly are made to investigate the influence of some governing parameters. Particular attention is focused on the effects of the shear layer dynamics. For certain flow conditions and/or test arrangements, coherent structures and/or recirculation currents are observed affecting the distribution of the heat transfer coefficients. Measurements of wall temperature as well as of adiabatic wall temperature of the stream are made by means of an infrared scanning radiometer, and the heat transfer coefficients are calculated by means of the so-called heated thin foil technique. The data are reduced in dimensionless form as Nusselt numbers and compared with data from the available literature. Both spatial distributions and averaged values of the Nusselt number are discussed. A new explanation for the second peak in the local Nusselt number is proposed.