Extending the usable range of the calibration map of a four-hole probe for measuring high flow angles

The range of flow angles that can be measured accurately using multi-hole probes is restricted due to limitations, such as singularity, in the calibration techniques used. Several modified techniques have been proposed for five and seven-hole probes to extend their usable range of operation. However fewer techniques are available in the literature for four-hole probe, which has an advantage over its counterparts because of its smaller size. This research fills the gap by reviewing the techniques implemented successfully on either five or seven-hole probes operating in non-nulling mode to extend their calibration maps and then adapting those techniques for four-hole probes. Three techniques, in addition to the traditional technique, are adapted for a four-hole probe by suitable modification. The adapted techniques have been implemented on the calibration data set of actual flow angles and raw pressures from a four-hole probe. The results from the validation of all three techniques are compared with the results from traditional technique to evaluate the resulting extension in the calibration maps. Overall, all methods showed an extension in the region of usable calibration map compared to the traditional technique. However, the results showed an advantage for the new zonal method technique, which offered a significant extension in the calibration map of a four-hole probe. It is the first time that such a consolidated effort has been done to extend the calibration map of a four-hole probe for measuring high flow angles.