Shear stress measurements were required on the suction surface of a turbofan fan blade. The space available for the anemometers was very small and a limited amount of electrical power was available. To compound the difficulties the constant temperature anemometers would have to be contained in the rotating hub of the engine and therefore subjected to very high centrifugal loadings. It was for this application that a miniature hot film anemometer was developed.
The above figure shows the new anemometer system, developed in conjunction with the Electronics Development Section of the Engineering Department. Normal anemometer systems are designed to be used with hot wires and hot films. However, these systems are large, can be very heavy and have a high power consumption. This system uses less than 0.5W of power (not including the power delivered to the hot film sensor), weights only a few grams and is roughly the same size as a 50 pence piece.
Early tests of the system in a high Mach number environment showed that it performed better than expected.
The system has yet to be fully validated in the engine environment.
Howard Hodson and Robert Howell
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