A new semi-empirical theory relating aerodynamic wall shear stress to the mean voltage from a surface mounted constant temperature hot film gauge is presented. High spatial resolution thermal images of the sensor area are used to obtain values for the mean sensor temperature and the thermal dimensions of the sensor. These thermal dimensions are shown to be invariant with Reynolds number. This data is used in the derivation of a new theory that effectively decouples the convection and conduction and hence removes the need for a fully conjugate analysis. The correct form of the relationship between sensor voltage and wall shear stress is a necessary prerequisite for gauge calibration and hence the quantification of aerodynamic wall shear stress. A calibration methodology is presented in an accompanying paper.

This content is only available via PDF.