AN APPROXIMATE SOLUTION FOR THE DYNAMIC-RESPONSE OF WALL TRANSFER PROBES

An approximate solution for the transient Leveque problem has been dev eloped based on the approximate integral method and the method of weig hted residuals. This solution can be used to explore the dynamic respo nse of thermal or mass boundary layers in large amplitude, but non-rev ersing, unsteady flows. The accuracy of this approximate solution has been proven over a wide range of dimensionless frequencies (omega = OM EGA(L2/S02D)1/3). The approximate solution forms the basis of a simple method for calculating the instantaneous shear rate from the measurem ent of instantaneous heat or mass flux at the surface of a wall transf er probe when the quasi-steady state assumption is not valid.