Showing papers by "Earl H. Dowell published in 2007"
TL;DR: In this paper, a two-dimensional airfoil including a cubic spring stiffness placed in an incompressible flow was used to investigate the amplitude and frequency of the limit cycle oscillations.
74 citations
TL;DR: In this article, a study of aerodynamic loadings on a NACA 0012 airfoil with a static and an oscillating trailing-edge Gurney flap was made.
Abstract: A study of aerodynamic loadings on a NACA 0012 airfoil with a static and an oscillating trailing-edge Gurney flap was made. The focus is on the experimental measurement of the static and dynamic-pressure distributions on the airfoil surface. The experimental results are also correlated with theoretical results obtained using the Navier-Stokes code INS2D, developed by NASA. A Reynolds number of 348,000, a flow velocity of 20 m/s (65.6 ft/s), and a reduced frequency from 0 to 0.4 based upon half-chord b and freestream velocity U are used. The experimental results show that the effect of the static and oscillating strips located near the trailing edge of the airfoil is to enhance the maximum lift and pitching-moment coefficients for both unstalled and stalled angles of attack. An increase of the oscillating frequency also enhances the aerodynamic loading. Reasonably good agreement between the experiment and theory is obtained. The experimental results confirm the idea that an oscillating small strip located near the trailing edge can be a useful tool for active aerodynamic flow control for a wing.
58 citations
TL;DR: In this paper, the Van der Pol's oscillator was used to investigate a non-linearity in the damping term, and the results from the analysis were compared with those obtained from the classical harmonic balance and the time marching (Runge-Kutta) methods.
Abstract: This study focuses on a novel harmonic balance formulation, the high-dimensional harmonic balance method. To investigate a non-linearity in the damping term, the system chosen for study is the Van der Pol's oscillator. Both unforced and forced oscillators are analyzed. The results from the analysis are compared with those obtained from the classical harmonic balance and the time marching (Runge–Kutta) methods.
53 citations
13 Feb 2007
TL;DR: In this article, a nonlinear harmonic balance compressible Reynolds averaged Navier-Stokes computational fluid dynamic flow solver is used to model the unsteady aerodynamics of the F-16 wing.
Abstract: In the following, we present computational aeroelastic flutter onset and limit cycle oscillation response trends for various stores and weapons configurations of the F-16 fighter. A nonlinear harmonic balance compressible Reynolds averaged Navier-Stokes computational fluid dynamic flow solver is used to model the unsteady aerodynamics of the F-16 wing. However, slender body/wing theory is used as an approximate method in accounting for the unsteady aerodynamic effects of wingtip launchers and missiles.
17 citations
7 citations
01 Jan 2007
TL;DR: This paper demonstrates the utility of the high-dimensional harmonic balance (HDHB) method for locating limit cycles of second-order delay-differential equations (DDEs) and a matrix version of the HDHB method for systems of DDEs is described in detail.
Abstract: In this paper we demonstrate the utility of the High Dimensional Harmonic Balance (HDHB) method to compute periodic orbits of second-order delay-differential equations. In particular, the method has been successfully applied to capture the unstable limit cycles of a model of regenerative machine tool vibrations. Both the conventional harmonic balance and the HDHB methods are employed to investigate the dynamic behavior of the nonlinear delay equation. The results show an excellent agreement with those from time domain solutions. The advantages of HDHB over the classical Harmonic Balance method are highlighted and discussed.© 2007 ASME
6 citations