On Fast-Response Probes: Part 2—Aerodynamic Probe Design Studies

Abstract

The influence of the probe size and geometry on the quality of fast-response measurements in turbomachines has been experimentally investigated. For investigations in the static domain (time-independent flows) probes were calibrated in two continuously operating wind tunnels in the range 0.2 < M < 1.2. For dynamic calibrations in time-variant flows model experiments in water (0.025 < k < 0.4, reduced frequency) were performed. Aerodynamic characteristics were determined for a great number of probe geometries, such as circular cylinders and wedge-type probes with varied apex angles, locations of the sensing holes, and leading edge shapes. The experiments comprised investigations in tolerance ranges for prismatic total pressure probes, yaw angle sensitivity, yaw angle, and Mach number effects on calibration and influence of dynamic yaw angle fluctuation on probe characteristics. As a result of the experiments errors due to static and dynamic aerodynamic effects could be quantified. The majority of the errors arising during measurements in turbomachines can be directly related to the probe size. An important number of these errors are systematic and can be analytically modeled and hence their influence corrected. In fluctuating flows the most severe measurement errors, which often may exceed the quantity of interest, are due to dynamic stall effects. This phenomenon, which is of transient nature and cannot be corrected, is typical for sharp wedge probes, but is not present with circular cylinders, and the effects are much smaller with very blunt wedges.