Global Shear-Stress Distribution Using Water-Proofed Hot-Film Constant Voltage Anemometer (CVA)

Boundary-layer flow characteristics, such as the location of the laminar-to-turbulent transition, flow separation and flow reversal regions, as well as surface shear-stress distribution on marine vehicle models, will be measured using micro-thin, multi-element hot-film sensor arrays coated with electically non-conducting, water-proof polymer material. Tao Systems' Constant Voltage Anemometer (CVA) instrumentation system will be adapted for under-water applications to obtain high sensitivity and high dynamic response at low sensor currents. The low power dissipation in hot-films operated with CVA will significantly reduce or eliminate bubble formation, as well as corrosion causing electrolysis associated with conventional techniques. The high signal-to-noise ratio of CVA, coupled with large bandwidth, even at low sensor currents will eliminate most of the problems encountered by conventional anemometers in under-water applications. Furthermore, since the power dissipated by hot-film sensors in the CVA-mode of operation is linearly proportional to the voltage output (and not to the square of the measured output voltage, as in constant temperature anemometer), an order of magnitude reduction in measurement error will result with the proposed innovation. The feasibility of the proposed approach will be demonstrated during Phase I by conducting tests on an instrumented model in a water tunnel.