Browsing by Subject "Aerodynamics"
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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 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 Characterization and simulation of inhomogeneous and non-stationary turbulent wind fields for assessment of wind turbine reliability(2012-05) Mcneill, Jason; Zuo, Delong; Mehta, Kishor C.; Swift, Andrew H. P.; Gilliam, KathleenWind turbines are designed to withstand turbulent inflows that are modeled as stationary Gaussian fields, a general assumption frequently made in wind engineering practice that is partly done out of convenience and partly out of our inadequate understanding of the wind itself. While the reliability of wind turbines continues improve, it also continues to be unsatisfactory and necessitates a re-examination of our assumptions about the wind and how they relate to structural reliability. Using measurements from the 200 m tower at Texas Tech University, the statistical characteristics of wind fields are analyzed and many are shown to deviate from assumed behavior in certain conditions. In particular, wind fields in the stable boundary layer, especially during low-level jet events, are often inhomogeneous in nature, with turbulent winds described by different probability distributions at different heights, while conditions during thunderstorm events are seen to be both inhomogeneous and non-stationary. In order to investigate aerodynamic loads and fatigue on wind turbines due to inhomogeneous inflows, a method for the simulation of non-Gaussian fields is presented based on translations of Gaussian fields. The method allows the simulation of inhomogeneous, non-Gaussian fields that match skewness and kurtosis of local turbulence probability distributions and is combined with conditional simulation to assimilate a subset of measured data points within the field. The effects of the inhomogeneous turbulence as well as direction shear measured during low-level jet events are investigated via the wind turbine simulation software FAST for a 1.5 MW and 5 MW wind turbine and compared the International Technical Commission’s IEC 61400-1 wind turbine design guidelines. Generally the fatigue damage resulting from non-Gaussian inflows are found to be lower than that induced by Gaussian inflows for cases with realistic turbulence intensities seen during LLJ events, however at higher turbulence intensities, small increases (~1%) in fatigue were noted for inhomogeneous inflows and inflows using constant positive skewness and kurtosis. At the same time, however, these inflows are found to be correlated with increased peak loading. Wind fields simulated with direction shear, are shown to substantially increase fatigue (11-60 %) on wind turbine components compared to those simulated without direction shear.Item General ram correlations for automobiles(Texas Tech University, 2000-05) Verner, Debra G.The driving pressure required for the cooling system airflow comes from two sources: the pressure due to the forward motion of the vehicle known as ram pressure, and the radiator fan pressure rise. These internal and external flow fields interact at the cooling air inlets and at the underside of the engine bay. These flow fields are closely related and are considered together in this study. The primary focus of this study is to find general ram pressure correlations for automobiles. The principal test results consist of a set of correlation equations which describe the variation of the ram pressure coefficient with respect to the size and location of the openings, the freestream velocity, and the cooling air flow rate for individual and combinations of openings. These correlations are in a format suitable for use with streamtube cooling system models such as ttu Cool®.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 Non-linear stochastic flutter of aeroelastic structural systems(Texas Tech University, 1985-12) Heo, HunThe main objective of t h i s investigation is to examine the linear and non-linear modal interactions of a two-degree-of-freedom aero-elastic structure subjected to a wide band random excitation. The linear analysis involves linear dynamic coupling and parametric random coupling. In terms of normal coordinates the response mean squares are obtained as functions of the system frequency ratio. The analysis shows that for modest values of mass ratio the first mode is suppressed when the natural frequencies of the two beams are identical. Furthermore, the system mean square responses are governed mainly by the external forced excitation, while the influence of the random parametric component is almost negligible. The non-linear modal analysis involves quadratic non-linearity referred to as autoparametric coupling. This type of coupling gives rise to a new type of instability when the relationship between normal mode frequencies is linear. In the neighborhood of the internal resonance condition w2/w1=0.5 (where w1 and w2 are the normal mode frequencies of the system), a general differential equation of the response moments is derived and found to constitute an infinite hierarchy set. Two different closure schemes, based on a cumulant-neglect concept, are used to truncate the moment differential equations. The first is the Gaussian closure, which leads to fourteen coupled differential equations, while the second, known as the non- Gaussian closure, gives 69 coupled differential equations. These two sets of equations are solved numerically for the response moments. The Gaussian closure solution results in a quasi-stationary response, while the non-Gaussian closure solution gives a strict stationary response. The two solutions exhibit an exchange of energy between the two modes in such a manner that one mode acts as a vibration absorber of the second mode in the neighborhood of internal resonance condition w2/w1=0.5±0(e)f where e is a small parameter. The influence of ranc3cam variation of the system parameters such as damping and stiffness is investigated. It is found that the damping variation has less effect on the random response of the structure than the stiffness variation. Numerical solutions for different initial conditions are obtained to find out if the system possesses more than one limit cycle. It is found that the initial conditions affect only the transition response, while the steady state response does not change by changing the initial conditions.Item Simulation of windborne debris trajectories(2005-08) Lin, Ning; Letchford, Christopher W.; Chen, XinzhongWindborne debris is possibly the major cause of building damage and destruction in strong wind events such as hurricanes and tornadoes. It has been long recognized that fast-flying debris can penetrate building envelopes, inducing internal pressurization and doubling the net loading on roofs, side walls, and leeward walls. Consequently, failed roofing structures, damaged wall cladding panels, and broken glass become debris sources, threatening downwind areas. Knowledge of debris aerodynamics is necessary for proper estimation of debris trajectory and for establishment of rational debris impact criteria. This research aims to investigate the aerodynamics of flying debris through simulating debris trajectories. Extensive wind-tunnel tests on 3D (compact-like), 2D (plate-like), and 1D (rod-like) debris are carried out in the Texas Tech University wind tunnel. The simulation procedure is introduced. Full-scale simulation is explored, employing a C-130 Hercules aircraft to generate strong winds. Three categories of parameters affecting debris trajectories are investigated: wind field, debris properties, and debris initial support. It is determined that although many parameters influence debris trajectory in the vertical direction, the Tachikawa parameter (1983) governs the horizontal trajectory of debris. Aerodynamic functions for debris horizontal trajectory are established based on both experimental data and theoretical equations of debris motion. These functions can be used to predict debris horizontal speed (at a given flight distance) and flight distance (for a given flight time). The application of these functions in debris impact criteria is discussed. The incorporation of these functions into debris risk analysis is recommended for the further research.Item Simulation of windborne debris trajectories(Texas Tech University, 2005-08) Lin, Ning; Letchford, Christopher W.; Chen, XinzhongWindborne debris is possibly the major cause of building damage and destruction in strong wind events such as hurricanes and tornadoes. It has been long recognized that fast-flying debris can penetrate building envelopes, inducing internal pressurization and doubling the net loading on roofs, side walls, and leeward walls. Consequently, failed roofing structures, damaged wall cladding panels, and broken glass become debris sources, threatening downwind areas. Knowledge of debris aerodynamics is necessary for proper estimation of debris trajectory and for establishment of rational debris impact criteria. This research aims to investigate the aerodynamics of flying debris through simulating debris trajectories. Extensive wind-tunnel tests on 3D (compact-like), 2D (plate-like), and 1D (rod-like) debris are carried out in the Texas Tech University wind tunnel. The simulation procedure is introduced. Full-scale simulation is explored, employing a C-130 Hercules aircraft to generate strong winds. Three categories of parameters affecting debris trajectories are investigated: wind field, debris properties, and debris initial support. It is determined that although many parameters influence debris trajectory in the vertical direction, the Tachikawa parameter (1983) governs the horizontal trajectory of debris. Aerodynamic functions for debris horizontal trajectory are established based on both experimental data and theoretical equations of debris motion. These functions can be used to predict debris horizontal speed (at a given flight distance) and flight distance (for a given flight time). The application of these functions in debris impact criteria is discussed. The incorporation of these functions into debris risk analysis is recommended for the further research.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.Item Trajectory generation using a modified simple shooting method(Texas Tech University, 2004-05) Trent, Ashley DeneeceNot available