Self-Aspirated Vortex Generator Jet Application for Propeller Boundary Layer Separation Suppression

Abstract

This paper presents a novel propeller flow control design to suppress boundary layer separation for improved propeller performance at low Reynolds number conditions or highly loaded operation. The design includes a series of self-aspirated vortex generator jets across a propeller suction surface, to entrain freestream momentum into the boundary layer flow. The jets are supplied by airflow obtained through inlets arranged on the propeller pressure surface and channeled through the propeller blade. The objective of this jet blowing flow control technique is propeller wake drag reduction and enhanced lift, which leads to greater propeller efficiency. A scaled version of the airfoil cross section at the mid-span of a 10-inch diameter thin electric propeller was manufactured with various vortex generator jet configurations. These 3:1 scale airfoils were evaluated in a closed loop, 30x30x100 centimeter (11.8x11.8x39.8-inch) water tunnel with chord-based Reynolds number ranging from 15,000 to 90,000 and angles of attack ranging from 0° to 30°. Each experimental configuration was characterized by jet penetration distance and separation bubble thickness. The momentum coefficient of each jet configuration was estimated, to allow for comparison with other flow control methods. The study revealed that self-aspirated vortex generator jet arrays located at or just upstream of the separation chord location on a propeller airfoil are effective at creating vortices which suppress boundary layer separation under certain flow conditions.