DEVELOPMENT OF A GLOBAL INTERFEROMETER SKIN-FRICTION METER

An improved method for measuring skin friction in two-dimensional flow s Is described. The instrument, termed a global interferometer skin-fr iction meter, is used to measure the shape of a thin oil film placed o n a test model subject to aerodynamic shear. The oil film shape is the n related to the applied shear through lubrication theory. Through acq uisition of a single image of the oil film interference pattern, the s kin-friction distribution can be obtained at any point covered by the film. Enhancements to the method are presented that may extend the ins trument's application to fully three-dimensional flows with time-varia nt model temperatures. Results from tests performed on flat plate boun dary layers along with numerical simulations show the instrument can a ccurately measure wall shear over relatively large areas in a single t est. Results show the method provides numerous advantages over other s hear measurement techniques. The instrument's configuration, the theor etical background, and the parameters that influence its accuracy are presented.