Laser interferometric measurement of shear stress in low-density flows

A direct and non-intrusive method of measurement of skin friction in low-density flows is developed applying the Laser Interferometric Skin Friction (LISF) technique. The LISF Meter developed by this technique is used to measure the skin friction on a flat plate, due to the impingement of low-density jets at various operating conditions and when the plate is kept at different inclinations to the jet axis. A black reflecting acrylic plate is used as the test surface. A CW 10mW He-Ne laser and a low vapour pressure silicone oil are used in the LISF Meter experiments. This method is found to be operationally successful and effective for skin friction measurement in low-density conditions. The measured skin friction is found to be in agreement with the results of an earlier study in the overlapping range of experiments. © 2005 American Institute of Physics.