ABSTRACT

The force due to wall shear stress is a quantity of primary importance in aerodynamic problems. In engineering applications, its overall value is estimated from the measurement of the gross drag force. Even though there are various direct and indirect methods available for determining the wall shear stress, each technique has got its own limitations and could be applied under certain specified circumstances. Some of the well-known methods are: floating element method, momentum integral method, preston tube technique, force technique, and heat transfer gauge. The floating element method is a direct method for measuring the wall shear stress. Preston tube used with success a hypodermic needle tube to determine the local wall shear stress from the dynamic pressure indicated by the tube. The fence technique is an indirect method for measuring wall shear stress. The heat transfer gauge can be used to measure wall shear over a very small area in laminar or turbulent flows with or without pressure gradient.