Directional probe sensitivity

Directional calibration of multi-sensor probes (- or tri -axial) provides their individual directional sensitivity coefficients. These are yaw factor and pitch-factor . They are required to decompose effective velocities derived from the calibration data into velocity components in laboratory coordinates. The effective cooling velocity acting on a hot wire can be expressed by means of the normal tangential and binormal components modified by the yaw and pitch factors, and as follows:

Figure 3.34: Calibration data for a -wire hotwire probe (symbols) compared with a fourth order curve tting formula (lines).

During directional calibration, the probe is turned through a number of inclination angles with respect to a known flow vector. In each position, are calculated from the probe velocity transfer function. This provides a set of equations for determining and for each wire in each angular position. The - array probes uses the yaw coefficients, and in order to decompose the calibration velocities and into the U and V components. As the yaw coefficients, and depend only on the geometry, the directional calibration test is needed to be carried out only once in the life of the probe. In the present work, the freshly supplied probe (DANTEC probe 55P63) was used. The default values of and was used during analysis.