Propeller Slipstream Correction for Wind Tunnel Applications

Abstract

In the post processing of acquired wind tunnel force measurements, propeller-driven aircrafts need a preliminary correction of the propeller slipstream. Propeller slipstream effect has two major contributions to the flow field. The first one is the increase in dynamic pressure and the second is the addition of rotation in the flow field. Without a slipstream correction, standard wind tunnel corrections cannot be implemented because powering the propeller violates the underlying assumptions of the standard correction methods according to Eckert. As a result, Eckert has developed a thrust correction formula that only includes the increase of dynamic pressure. This research has been conducted to develop a novel correction to include both the increase in dynamic pressure and the effect of rotation induced by the propeller slipstream. Initially, a non-linear Surface Vorticity Panel Method (SVPM) was chosen in order to have a non-prescribed slipstream strength and shape. However, there were problems with convergence time and slipstream deformation. Therefore, the model was reduced to a linear model first suggested by Schroijen. The propeller was modeled as a mix of BEM and vortex theory. The wing and empennage was modeled by VLM. Fuselage was modeled after Multhopp’s vertical slit representation and a forced potential solution was implemented to simulate the wing root effect. The wind tunnel experiments were conducted in various angle of attacks and thrust ranges. Results show that the panel method can simulate the rotational nature of the slipstream accurately and the wing lift distribution is parallel to the literature. The new proposed correction was adequate at approximating the propeller slipstream lift and can produce closer results than the Eckert correction at some instances.