Experimental investigation of geometry effects and performance of five-hole probe in measuring jets in crossflow

AUTh, Department of Mechanical Engineering, Laboratory of Fluid Mechanics and Turbomachinery, Thessaloniki 54124, Greece

^* Konstantinos Magkoutas: magkoutk@ethz.ch
^† Theofilos Efstathiadis: theofil@auth.gr
^‡ Anestis Kalfas: akalfas@auth.gr

Abstract

Vortical and shear flows are common in turbomachinery. Multi-hole pressure probes are used in turbomachinery flows in order to provide robust and accurate measurements of both pressure and velocity components. In this study, two different miniature five-hole probes are designed and fabricated, both with a cobra shape. The probe tip was 1.45 mm and it was maintained in that size for the length of the cobra shape formation, providing very close proximity to the solid boundaries and reduced flow blockage. The difference among the probes corresponded to the head geometry, as the one probe was formed with a pyramid tip shape, while the other was maintained with a flat shape. The calibration process was carried out in an open-circuit suction wind tunnel for the range of ±32⁰ in yaw and pitch direction. The results showed that the pyramid probe exhibits a high flow angle spatial sensitivity and a reliable measurement range of ±28⁰ in yaw and pitch direction. The flat probe provided unexpected well angle sensitivity and reliable measurements data despite the fact that it is of a very simple form. The pyramid probe showed superior performance. In particular, the pyramid probe offers 12.5% wider operating range. In order to prove the effectiveness of the pyramid probe, measurements were obtained in a jet in cross flow. In order to evaluate the performance of the probe, further, a surface fit model was employed to produce ideal calibration coefficients. These were used to redefine the magnitude of the velocities in the measured flow domain. The accuracy in measurements was assessed, comparing the velocities produced by the two variants of pressure coefficients. The results indicate that the pyramid probe operates reliably in a very large range of constantly changing velocity vector, which occurs in jet in cross flow.