Probe interference on flow measurements in propeller near slipstream

Abstract

Introduction T HE use of pressure probes for flow surveys has long been an accepted practice and has been applied to propeller flowfield measurements.' The question of probe or probe support interference on the flow measurements appears not to have been addressed in published literature, apart from a limited discussion in Ref. 5. In connection with a flow survey in the near slipstream of a propeller, nacelle mounted on a semispan model, using the five-hole probe assembly shown in Fig. 1, it was discovered that the power requirement for a given propeller rpm was sensitive to the angular orientation of the rakes. Furthermore, it was found that with the assembly removed, the power requirement was substantially reduced from that required with the rakes present. These findings suggested that the five-hole probe assembly interfered with the flow it was designed to measure. For instance, the swirl angle, that is directly related to the torque/ power, should consequently be higher with the rakes present than without the rakes for a given rpm. Intuitively, one would think that the presence of the rakes would reduce the swirl angle.