Investigation of Wedge Probe Wall Proximity Effects: Part 1—Experimental Study

Abstract

Conventional three-hole wedge probes fail to measure the correct static pressure when operating in close proximity to a wall or boundary through which the probe is inserted. The free-stream pressure near the outer wall of a turbomachine may be overindicated by up to 20 percent dynamic head. This paper reports a series of experiments aimed at quantifying this so-called “wall proximity effect.” It is shown from a factorial experiment that probe wedge angle, stem design, and free-stream Mach number all have a significant influence. The yaw angle sensitivity of wedge probes is also found to depend on the proximity of the probe to the wall of introduction. Flow visualization studies on large-scale probe models are described, and a qualitative model of the probe local flow structures is developed. This model is used to explain the near-wall characteristics of the actual size wedge probes. In Part 2 of this paper, the experimental data are used to validate CFD calculations of the flow field around a wedge probe. A simple analytical model of the probe/flow interaction is developed from the CFD solutions.