Session: 01-08 Propellers and Open Rotors I

Paper Number: 153984

Evaluation of Propeller Self-Aspirated Flow Controls to Suppress Boundary Layer Separation at Low Reynolds Number 

This paper presents experimental results for two propellers with varying self-aspirated, jet-blowing flow controls to suppress boundary layer separation at low Reynolds number operating conditions associated with low-speed, unmanned aircraft.  The motivation is to improve aircraft range and endurance by reducing propeller wake losses and thereby increasing propeller efficiency. The two propellers were first modeled using computer aided design software, starting with a scanned 16-in by 10-in APC propeller. Two novel propeller designs were created, each with integrated flow controls consisting of a singular rectangular jet acting as a self-aspiratied flow control, allowing flow to pass through the blade from the pressure to suction sides of the propeller. One set of jets were fabricated at 20-deg and the other at 40-deg, measured from the propeller suction surface. To evaluate the effect of the jet geometry of each propeller, data was captured for Reynolds numbers ranging from 30,000 to 60,000 based on propeller chord at 75% span, corresponding to 20-, 30-, 40- and 50-ft/s freestream velocities. The thrust coefficient and propeller efficiency at varying advance ratios is compared to baseline unmodified propeller to assess propeller performance. Additionally, a scaled version of the airfoil cross section at the mid-span of a 16-in diameter thin propeller was manufactured with the self-aspirated flow controls. These scaled airfoils were evaluated in a closed-loop, 11.8-in by 11.8-in by 39.8-in water tunnel test section with chord-based Reynolds number ranging from 30,000 to 60,000 at an angle of attack of 15-deg. Each experimental configuration was characterized by jet penetration distance and separation bubble thickness, evaluated using particle image velocimetry. The study revealed that self-aspirated flow controls 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 low Reynolds number conditions.  Observations from this study provide new insight to unmanned aircraft propeller design for low-speed flight to improve propeller efficiency and increase range and endurance.

Presenting Author: Kurt Rouser Oklahoma State University

Presenting Author Biography: Dr. Kurt Rouser is Associate Professor of Mechanical and Aerospace Engineering at Oklahoma State University (OSU). He holds a B.S. in Aeronautical Engineering from the US Air Force Academy (USAFA), an M.S. in Aviation Science from OSU and an M.S. in Aeronautical Engineering and Ph.D. in Mechanical Engineering from the Air Force Institute of Technology (AFIT). During 21 years in the Air Force, he served as Technical Analyst at the National Air Intelligence Center, Maintenance Engineer and Executive Officer at the Oklahoma City Air Logistics Center, and Operations Officer at Arnold Engineering Development Center. He served eight years on USAFA faculty in the Aeronautics Department. He retired from the Air Force in 2016 and transitioned into his current OSU position, teaching and researching aerospace propulsion and power.

Authors:

Dawson Manning Oklahoma State University
Andrew Bellcock Oklahoma State University
Kurt Rouser Oklahoma State University
Ryan Paul Oklahoma State University