Title

Analysis of high angle of attack maneuvers to enhance understanding of the aerodynamics of perching

Date of Award

2012

Degree Name

M.S. in Aerospace Engineering

Department

Department of Mechanical and Aerospace Engineering

Advisor/Chair

Advisor: Aaron Altman

Abstract

Due to their vastly unsteady aerodynamics, mimicking the flight maneuvers of natural flyers requires a deep understanding of the unsteady flow physics while also demanding the ability to expand the vehicle's flight envelope beyond normal conditions. Experimental and computational investigations are performed to study and improve the flight performance of a perching maneuver. Flowfield images and force history data are acquired to investigate the performance of highly unsteady motions experienced during a perching maneuver. The perching motions studied are divided into two first order approximations, a rapid pitching motion and an impulsively started hold in order to follow the North Atlantic Treaty Organization Research & Technology Organization Applied Vehicle Technology 202 (NATO RTO AVT 202) guidelines. Both types of motions are investigated through experimental testing and using a computational 2D Discrete Vortex Method (DVM). Using the 2D DVM allows the ability to determine whether a low order, two dimensional code can accurately predict an actual 3D flowfield generated by highly unsteady motions. The pitching motions are studied experimentally using 3D plates in the University of Dayton Low Speed Wind Tunnel (UD-LSWT). Results show that despite some 3D instabilities in the experiments, which are not produced by the DVM, overall the DVM matches the experiments well. Results are completed for varying pitch rates and the DVM matches the experiment more closely for the faster, more inertially dominated pitch rates. Upper surface pressure data is also recorded in both the experiment and DVM. The results suggest that differing pressure profiles could have a substantial influence on aerodynamic forces even at high angles of attack. The impulsively started hold motions completed experimentally with 3D plates in the AFRL Horizontal Free Surface Water Tunnel (AFRL HFWT) again produce some three-dimensional instabilities not modeled in the 2D DVM. When comparing the impulsively started results, the DVM did not match the startup of the motion in the force histories due to the use of different startup transients and the constants in the smoothing function. The DVM does well when comparing the flowfield. In an attempt to expand the available performance envelope during these types of motions variable camber is studied for both types of maneuvers using the 2D DVM and in both cases the initial results show that variable camber has the potential to positively influence the boundaries of the flight envelope during a perching maneuver.

Keywords

Angle of attack (Aerodynamics), Unsteady flow (Aerodynamics), Camber (Aerofoils), Aerospace engineering; aerodynamics; perching; variable camber; high reduced frequency pitching motion

Rights Statement

Copyright © 2012, author

Share

COinS