Date of Award

Winter 2-2010

Document Type

Thesis - Open Access

Degree Name

Master of Aerospace Engineering

Department

Aerospace Engineering

Committee Chair

Vladimir V. Golubev

Committee Member

Eric Perrell

Committee Member

R.R. Mankbadi

Abstract

This thesis details the development and implementation of a module within a high-accuracy numerical viscous analysis code to simulate the nonlinear interaction of SD7003 airfoil with non-uniform, unsteady incoming flow. The study is focused on the low-Re number unsteady flows typical of MAV applications in which a gust encounter can induce a particularly significant aerodynamic and aeroelastic response. Efficient source models are developed to introduce sharp-edge and time-harmonic gust perturbations with specified amplitude, frequency and duration inside the computational domain through the source terms in the governing momentum equations. Parametric analysis of gust-airfoil interactions for different steady airfoil loads is conducted in comparison with equivalent pitch-ramp and time-harmonic pitching simulations. In addition, all obtained solutions are compared with corresponding predictions based on the inviscid, incompressible unsteady aerodynamic theory. The study reveals complex interaction of inviscid and viscous unsteady forces observed for different gust and pitching excitations, and identifies the degree of similarity between the corresponding gust and pitching airfoil responses. The latter part of this work utilizes an implemented iterative procedure in which a set of governing Navier-Stokes equations is solved simultaneously with the nonlinear equations of motion for the structure, so that the fluid and structure are treated as a coupled dynamic system. The numerical procedure employs a high-order low-pass filter operator which selectively damps the poorly resolved high-frequency content to retain numerical accuracy and stability over a wide range of flow regimes. The strongly coupled, nonlinear unsteady aerodynamic and structural responses of an elastically mounted airfoil subject to harmonic, high-amplitude vortical gust are examined in a test study, with emphasis on the wing section transition to limit cycle oscillations (LCO).

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