Skin Friction and Pressure Measurements in Supersonic Inlets

Supersonic propulsion systems include internal ducts, and therefore, the flow often includes shock waves, shear layers, vortices, and separated flows. Passive flow control devices such as micro-vortex generators and micro-ramps have been proposed to improve vehicle performance. The ability to measure surface quantities such as skin friction and unsteady pressure on the inlet model would provide insight into the complex flow characteristics that govern inlet performance. Unfortunately, nonintrusive sensors require optical access that has been difficult to obtain. Optical sensors for measurements of pressure (Fast Pressure-Sensitive Paint) and skin friction (Surface Stress Sensitive Films) offer non-intrusive measurements on surfaces, exactly the capability that is needed. To date, the size of the hardware such as camera and illumination devices have precluded application of these technologies in regions like an internal duct. During the past several years, camera and LED technology has advanced resulting in small packages for both imaging and illumination. Combining this new hardware with state-of-the-art optical technology such as fast responding PSP and S3F will result in a pair of sensors that can be miniaturized and utilized for non-intrusive measurements in traditionally inaccessible regions of the model. These measurements include continuous distributions of skin friction and unsteady pressure.