Design of Directional Probes for High-Frequency Turbine Measurements

Abstract

Aerodynamic probes are prevalent in turbomachinery research and gas turbine monitoring. Regrettably, this measurement technique experiences limitations not only in the transonic range but also in the high frequency range. Calibrated numerical tools offer an alternative procedure in the design of suitable instrumentation for turbine applications. First, two different probe geometries, oval and trapezoidal shapes, were characterized at different incidence angles. In particular, the pressure recovery, angle sensitivity, and induced vortex shedding unsteadiness at several yaw angles were evaluated. The studies were performed over a wide range of Mach numbers from subsonic to the transonic regime. The vortex shedding of the probe was also carefully analyzed. In a second evaluation, we selected the oval probe geometry including the line-cavity effects into the pressure tappings. The resonance frequency of line-cavity system was evaluated and compared with analytical calculations, as well as with the detailed analysis of Bergh and Tijdeman. The comparison of the pressure tapping readings with the actual input signal allowed the identification of the transfer functions, as well as the physical mechanisms that should be corrected during the measurements. Finally, three-dimensional (3D) unsteady evaluations were implemented to compute the blockage effects, as well as the final frequency attenuation experienced by the piezo-resistive sensors. All numerical analyses were performed using unsteady Reynolds-averaged Navier–Stokes (URANS) models.