Use of triple hot wires to measure unsteady flows with large direction changes

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Abstract
Geometrical limitations of the probes and inadequate description through the response equations limit existing triple hot wire techniques to measurement in flow fields with small changes in flow direction. A triple hot wire probe together with the related technique is developed to measure in cases where large angular changes occur. Yaw, pitch and velocity parameters are derived as functions of the effective cooling velocities of the hot wires. The dependence of these parameters on flow direction, with respect to the probe, is established through a direct calibration. Uncertainty analysis shows that a wide range of pitch and yaw can be used. Application of the technique in a stalled axial compressor demonstrates the ability to measure mean flow quantities in such cases.