Measurement Drift in 3-Hole Yaw Pressure Probes From 5 Micron Sand Fouling at 1050° C

3-hole pressure probes are capable of accurately measuring flow angles in the yaw plane. These probes can be utilized inside a jet engine hot section for diagnostics and flow characterization. Sand and other particulate pose a significant risk to hot section components and measurement devices in gas turbine engines. The objective of this experiment was to develop a better understanding of the sensitivity of experimental 3-hole pressure probe designs to engine realistic sand fouling. In this study, Wedge, Cylindrical, and Trapezoidal probes were exposed to realistic hot section turbine environments of 1050 C at 65-70 m/s. 0-5 micron Arizona Road Dust(ARD) is heated under these conditions and used to foul the yaw probes. The sand deposited on the probe was observed to peel off the probe in thin sheets during ambient cool down.

Sand fouling was assessed using a stereoscope and digital camera. Probe calibrations were performed in an ambient temperature, open air, calibration jet to mimic engine cold start conditions at Mach numbers of 0.3 and 0.5. Yaw coefficients were calculated for each probe using probe pressure and jet dynamic pressure readings. These coefficients were used to develop calibration curves for each probe initially, and again for every fouling test. Each probe performed differently, but the trends showed that the sand fouling had little impact on the probe error at Mach 0.3, and a slightly increased effect on the probe error at Mach 0.5. The experiment showed that when flow direction was determined using a true dynamic pressure reading from the jet, the probes were able to accurately measure flow direction even after being significantly sanded, some probes holes being over 50% blocked by sand accumulation.

Accelerated erosion testing showed that the trapezoidal yaw probe was by far the most sensitive to sand accumulation, followed by the cylindrical probes, and the least sensitive was the wedge probe. A yaw angle range of interest was chosen to ±10 deg of yaw. The least errors from the Yaw Coefficient, as defined in this report, were found to be in the Trapezoidal and Perpendicular probe configurations. The least error found in the wedge probe.