Date of Award

3-21-2019

Document Type

Thesis

Degree Name

Master of Science in Aeronautical Engineering

Department

Department of Aeronautics and Astronautics

First Advisor

Darrell S. Crowe, PhD

Abstract

A recent research effort, sponsored by the Air Force Office of Scientific Research, numerically investigated the unsteady aerodynamic flow field around an oscillating, straked, delta wing. The study was centered on determining the importance of the unsteady aerodynamic forces acting as a driver for a nonlinear motion known as limit cycle oscillations. The current effort focused on creating a computational model to compare to the results of previous tests and modeling efforts and discover new information regarding the onset of LCO. The computational model was constructed using the Cartesian overset capabilities of the CREATE-AV™ fixed wing fluid dynamics solver Kestrel. The geometry of the model was based on an Euler model that was recently developed to investigate the same experiments. Adaptive mesh refinement was also employed during the numerical simulations to better capture the translation of the shock along the surface of the semispan. The developed numerical model was tested at a variety of flow conditions, including varying free-stream Mach numbers, starting trim angles, oscillation amplitudes and oscillation frequencies. The results showed a number of trends that could influence the onset and sustainment of LCO. First, the aerodynamic phenomena of shock-induced trailing edge separation (SITES) was observed during a number of the simulations. Popular among aeroelasticians as a possible source of LCO, SITES is thought to cause a change in the aerodynamic forces acting on the flexible structure, propagating the LCO motion. Second, the quantitative results of the computational model showed good agreement with published, qualitative observations made during wind tunnel experiments. Third, a separation bubble was observed aft a shock on the top surface of the semispan. This previously unobserved flow feature could have a significant impact on the forces acting on the model during the oscillation.

AFIT Designator

AFIT-ENY-MS-19-M-238

DTIC Accession Number

AD1076362

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