Skin-Friction Measuring System for Large Wind Tunnels

Currently, no instrumentation that can produce distributions of skin friction in a production wind tunnel is available. While the distribution of skin friction is available from computational fluids models, these models must be validated using experimental data. Here we introduce a new sensor for measurement of skin friction and pressure, Surface Stress Sensitive Film, which is compatible with current Pressure-Sensitive Paint experimental hardware. This sensor is based on the distortions of an elastic polymer film which deforms under the action of the applied normal and tangential loads. Skin friction and pressure gradients are determined by monitoring these deformations and applying a finite element model to the elastic film. This technique has been demonstrated by performing quantitative measurements of pressure and skin friction on aerodynamic models in several wind tunnels. Among these test was an experiment that used PSP on one side of the model and S3F on the other side. Data from each sensor was acquired simultaneously, using the same camera and light source for the PSP and S3F thus demonstrating the compatibility of the S3F with existing PSP hardware. The goal of this proposal is to extend this sensor to measurements of skin friction in larger scale facilities.