Fabrication and calibration of a sub-miniature 5-hole probe with embedded pressure sensors for use in extremely confined and complex flow areas in turbomachinery research facilities

Abstract

Multi-hole pressure probes are often employed in experimental facilities to measure the three dimensional flow field due to their ability to simultaneously provide the distributions of the static and total pressures as well as the three components of the velocity vectors. In cases where these probes are employed in turbomachinery research facilities it is essential for them to be accurate, respond to local parameter disturbances quickly and exhibit a high flow angle spatial sensitivity. Thus, the physical dimensions of the probe must be as small as possible. In addition the small size of the probe reduces the flow blockage and the corresponding local disturbances of the flow, especially when it approaches the solid boundaries of the blade channels. The present study refers to the fabrication and calibration of a sub-miniature in dimensions 5-hole probe, for use in complex internal flow areas arising in turbomachinery research. In order to reduce the need for a longer sampling time as the size of the probe gets smaller, the length of the stem that transfers the pressure from the tip of the probe to the sensor has to be minimized. This effect was compensated by embedding the pressure sensors right at the end of the probe׳s stem. This minimizes the air volume and thus the oscillations inside the flexible connecting tubes that usually connect each port of the probe to its corresponding pressure sensor. The fabrication methodology of the probe and data acquisition system is extensively described, as well as the non-nulling method employed for the calibration. Furthermore, application of the probe on a reference configuration geometry often used in turbomachinery research is illustrated in order to validate the effectiveness and novel characteristics of the probe. The result is a construction and calibration technique that allows the relevant laboratories to build on their own such instruments that may cost several thousand dollars (or euros) when bought from the open market.