Browsing by Subject "Aerofoils"
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Item A numerical method for the calculation of unsteady lifting potential flow problems(Texas Tech University, 1982-08) Im, Bong-jinA potential flow model for two-dimensional airfoils in unsteady motion with boundary layer separation is described. The airfoil and wake surfaces are represented by a finite set of uniform strength doublet panels. The doublet strengths on the airfoil surface are determined by applying a kinematic surface tangency condition to a Green's function representation of the potential field, while simultaneously enforcing the Kutta condition. Wake shedding is governed by a dynamic free surface condition and the characteristics of the flow near any boundary layer separation points. Wake deformation is predicted by applying a geometric free surface condition.Item A numerical model for two-dimensional unsteady flow calculations with a surface panel method(Texas Tech University, 1985-12) Im, Bong-jinA numerical model for two-dimensional airfoils in unsteady motion with boundary layer separation is described. The airfoil and wake surfaces are represented by a finite set of combined source and vortex panels. The source strengths are prescribed to have the same magnitude as the normal relative velocity on the surface due to the freestream and motion of the airfoil. The vertex strengths on the airfoil surface are determined by applying a kinematic surface tangency condition to a Green's function representation of the potential field, while simultaneously enforcing the Kutta condition. Wake shedding is governed by a dynamic free surface condition and the characteristics of the flow near any boundary layer separation points. Wake deformation is predicted by applying a geometric free surface condition. Calculation results are presented for steady motion, impulsively started rectilinear motion, harmonic pitch oscillations, and constant pitching motions. Experimental data and analytical solutions are also presented for comparison.Item An experimental investigation of an airfoil pitching at moderate to high rates to large angles of attack(Texas Tech University, 1985-12) Graham, Gary MAn experimental investigation of the variation in aerodynamic performance of a NACA 0015 airfoil over a range of constant pitching rates was performed in the Texas Tech tow-tank facility. The test results consist of flow visualization data, surface pressure measurements, and load cell data, and encompass a wide range of non-dimensional pitching rates [ K = dc/2Uoo) varying from 0.1 to 1.0 at angles of attack from 0** to 90°. The test Reynolds number was 100,000. These data have yielded several interesting physical correlations associated with large-scale pitch rate motions. Included in these are simple trigonometric correlations for the lift and drag forces and an extension of the Gormont model for the inception of leading edge separation. Very large lift and drag coefficients on the order of 10 have been generated. These large forces, produced by unsteady effects, may perhaps be exploited in the supermaneuverability concept for fighter aircraft.Item An experimental study of an airfoil undergoing cycloidal motion(Texas Tech University, 1978-12) Webster, Barry ThomasExperimental data were obtained for several sets of airfoils moving along cycloidal paths into an otherwise still fluid. This configuration can be used to simulate a two dimensional Darrieus turbine. In this experiment the rotor was towed through a tank filled with water. The use of water instead of air as a working fluid facilitated both the ability to measure aerodynamic blade forces and the utilization of flow visualization techniques. Well-known scaling laws were used to relate the operation in water to that in air. Flow visualization techniques using dye injection and solid particle markers were used to examine details of the flow structure. These details were compared, along with blade loading measurements to predictions of an analytical model developed as a joint part of this effort.Item Measurement of instantaneous pressure distributions and blade forces on an airfoil undergoing cycloidal motion(Texas Tech University, 1982-12) Graham, Gary MInstantaneous pressure distributions and transient blade loads which are typical of those occurring on a Carrieus wind turbine were recorded at three tip-to-windspeed ratios. The turbine was simplified to that of a single air-foil moving along a cycloidal trajectory into otherwise motionless water. The use of water as a working fluid facilitated the ability to make low- frequency measurements while operating at appropriate blade Reynolds numbers- A comparison between the blade force data and the forces predicted by an existing analytical model was made. In addition, the instantaneous pressure distributions were analyzed in an investigation of the dynamic stall phenomenon.Item The cumulative effects of roughness and Reynolds number on NACA 0015 airfoil section characteristics(Texas Tech University, 1984-05) Lewis, Kevin WayneIn this study, wind tunnel tests were made on a NACA 0015 airfoil section to examine the combination of scale and surface roughness effects. Reynolds numbers of 110,000 and 220,000 were used to determine scale effects. Roughness effects were obtained by applying roughness elements with heights of 0.111, 0.282, and 0.564 percent of the airfoil chord length. it was found that each combination of Reynolds number and roughness results in a unique set of lift and drag coefficients for a given angle of attack.