Use and calibration of 5-hole pressure probes to measurement of airflow velocity

Multi-hole probes are simple and robust device to measurement of flow velocity magnitude and direction in wide range of angles of attack – up to 75°. They become popular as they may be easily use to measurement of unknown flow velocity, while optical methods, like PIV or LDA, require some knowledge about the flow for proper setting of measurement devices. Multi-hole probes are also more lasting in comparison with CTA hot-wire probes, which may be damaged by a dust. A multi-hole probe measures air pressure with one pressure tap on its tip and a few (usually 2, 4, 6 or more) taps on conical or semispherical surface of the probe tip. Based on measured pressures, some non-dimensional pressure coefficients are calculated, which are related to flow velocity direction (i.e. two angles in Cartesian or spherical coordinate system) and magnitude. Finding relations between these parameters is relatively complex, which for years was limiting application of multi-hole probes. The article summarizes methods of multi-hole probes calibration and use, which may be classified as nulling and non-nulling methods or – with other criteria – as global and local methods. The probe, which was presented in the article, was the 5-hole straight probe manufactured by Vectoflow GmbH and calibrated in the stand designed and manufactured at the Institute of Aviation. The local interpolation algorithm has been used for calibration, with some modifications aimed on mitigate of mounting uncertainty, which is related with the non-alignment of flow velocity direction and probe axis Results of calibration showed that the accuracy of presented methodology is satisfactory. The standard measurement uncertainty was assessed for 0.2° for the pitch angle and yaw angle, which is better than accuracy declared by the probe’s manufacturer (1.0°). The measurement uncertainty of the flow velocity is approximately 0.12 m/s, similarly like in manufacturer’s data.