A NUMERICAL EVALUATION OF A NOVEL METHOD OF USING HEAT TRANSFER MEASUREMENTS TO DETERMINE LOCAL WALL SHEAR STRESS
A new method of using heat transfer measurements as the basis for determining local wall shear stresses has recently been proposed. In this method, the wall under consideration is made from a material with a low thermal conductivity which is covered with a thin metal sheet. A steerable pulsed laser beam is then used to rapidly heat a small portion of the surface of the wall and the temperature-time variation of the heated surface spot following cessation of the irradiation is used as a basis for determining the local wall shear stress. The present study involves an evaluation of this proposed method. In the first part of the study the unsteady conduction in the wall following the essentially instantaneous heating of a small circular portion of the wall has been numerically studied. The results have been used to deduce a variable, that can easily be calculated from the measured temperature-time variation which is relatively strongly dependent on the the convective heat transfer coefficient and, hence, on the wall shear stress. In the second part of the study, in order to relate the value of the measurable variable deduced in the first part of the study to the wall shear stress, a numerical study of the turbulent, thermal three-dimensional boundary layer flow over a heated spot on the wall has been calculated. The relationship between the mean heat transfer coefficient from this spot and the mean wall shear stress has been deduced from the results. These results have then been combined with those of the first part of the study to derive the required relationship between the measured variable and the wall shear stress.