The directional sensitivities of crossed and triple hot-wire probes

The directional sensitivities of the DISA Type 55P61 crossed-wire probe and DISA Type 55P91 gold-plated triple-wire probe were investigated using a modified calibration set-up with three very accurate orthogonal axes of rotation. The yaw factor k T and pitch factor k N which account for the cooling effects of tangential and binormal velocity components respectively were determined at different yaw angle a and pitch angle theta at velocities of 6 m s -1 , 11 m s -1 and 19 m s -1 . Based on these measured values, the relative errors in the calculated flow velocity were computed with constant values of k T and k N at alpha and theta =60 degrees , 90 degrees and k T =0, k N =1. The effects of k T and k N cannot be neglected, especially at high alpha and theta . For the DISA Type 55P61 crossed-wire probe, the suitable values are k T =0.30 and k N =1.14. For the DISA Type 55P91 triple-wire probe, they are k T =0.20 and k N =1.01.