published_or_final_version / Mechanical Engineering / Master / Master of Science in Engineering

Thesis (M.S. in Aeronautical Engineering)--Naval Postgraduate School, September 1990. / Thesis Advisor(s): Healey, J. Val. Second Reader: Schmidt, L. V. "September 1990." Description based on title screen as viewed on December 18, 2009. DTIC Descriptor(s): Velocity, Air Flow, Flight Decks, Shear Properties, Measurement, Position(Location), Ships, Models, Layers, Edges, Boundary Layer, Flow Visualization, Tunnels, Curvature, Smoke, Stationary, Bubbles, Patterns, Helium, Flow, Ship Models, Video Signals, Anemometers, Earth Atmosphere, Deflectors, Photographic Equipment. DTIC Identifier(s): Wake, Naval Vessels(Support), Turbulence, Helicopters, Atmospheric Motion, Air Flow, Ship Models, Replenishment at sea, AOR Class Vessels, H-56 Aircraft, Wind Direction, Oilers(Naval Vessels), Rotor Blates(Rotary Wings), Impact, Vertical Replenishment, Blade Strike, Theses, Wind Tunnel Models. Author(s) subject terms: Flow Visualization, Simulated Atmospheric Boundary Layer, Helium Bubble Flow Visualization, Smoke Visualization, AOR Class ship. Includes bibliographical references (p. 84-85). Also available in print.

Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references (p. 219-225). Also available in print.

The velocity profile shape and boundary layer thickness of an equilibrium boundary layer grown over a long fetch of roughness are closely matched with those of a boundary layer artificially thickened using spires (by adjusting the shape and height of the spires). Other turbulent characteristics of these two wind tunnel simula tions of the atmospheric wind are then compared. At the same time, more information on rough wall boundary layers is obtained to allow for a rational choice of the shape and spacing of roughness elements required to produce a particular simulation of the full scale boundary layer. A technique for calculating the shape of boundary layers in exact equilibrium with the roughness beneath, using a data correlation for the wall stress associated with very rough boundaries and a semi-empirical calculation method, is examined experimentally. Wall shear stress, measured directly from a drag plate, i combined with boundary layer integral properties to show that the shear stress formula is reasonably accurate and that the boundary layer grown over a long fetch of roughness is close to equilibrium after passing over a streamwise distance equal to about 350 times the roughness element height. The boundary layer quickly generated using spires proved to be a fair approximation to that grown over a long fetch of roughness, but did not accurately represent the longitudinal turbulence intensity of the full scale atmospheric wind or the naturally grown boundary layer. The boundary layer produced here by spires showed little change in gross characteristics after travelling about eight spire heights downstream of the spires. A distance of six or seven such heights has been advised by other workers in the past. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

Thesis (M. Sc.)--University of Hong Kong, 1982.

The short range dispersion in the atmosphere of buoyant gases, such as hot air or natural gas, may be hazardous and dangerous. The available methods for studying this problem were reviewed. Wind tunnel studies were considered to be the most suitable method for studying near-field dispersion, and methods for accurately modelling the nearfield behaviour of a buoyant plume of gas were examined. The experiments were performed in the Oxford University 4m x 2m low speed wind tunnel at a model scale of 1:200. The mean trajectory and rate of spread of a buoyant plume from a 60 m high (full-scale) stack were measured in the presence of a simulated natural wind. The exact similarity requirements were derived from dimensional analysis and from the equations of motion. In practice, it is not possible to match all the necessary dimensionless groups and exact scaling of the exit gas density ratio and the exit Reynolds number is often relaxed. A series of experiments was performed to examine the effect of these two groups on mean plume behaviour, with the intention of providing guidance for correct simulation of plume dispersion at reduced-scale. The exit density ratio was found to have little effect on the near-field plume behaviour, provided all the other dimensionless groups were matched. Plumes with low Reynolds number were found to rise significantly higher than plumes with higher 'turbulent' Reynolds numbers. This difference in trajectory could not be correlated with the plume exit momentum flux. The effect of the cross-flow on near-field dispersion was examined by performing experiments in four different simulations of the earth's atmospheric boundary-layer. The behaviour of the plume was found to be sensitive to both the velocity profile and the turbulence intensity of the cross-flow. To study dispersion in the wind tunnel, the cross-flow should be an accurate simulation of the velocity profile and turbulence intensity components of the natural wind.

Previously, the concept of the tolerant wind tunnel, developed in the Department of Mechanical Engineering, U. B. C., was tested only for stationary models. In the present study, the concept is investigated for unsteady airfoil motion. The new wind tunnel test section, using the opposite effects of solid and open boundaries, is a new approach to reduce wall blockage effects. Consisting of vertical airfoil slats uniformly spaced on both side walls in the test section, it is designed to produce a nearly free-air test environment for the test model, which leads to negligible or small corrections to the experimental results. The performance of this wind tunnel for unsteady model testing is examined experimentally with a two-dimensional NACA 0015 airfoil in a simple plunging sinusoidal motion. The airfoil is mounted vertically in the center plane of the test section between solid ceiling and floor. An oscillating table is designed to give the airfoil an accurate plunging sinusoidal motion. A full range of open area ratio is tested by varying the number of slats mounted inside the side walls. Pressure distribution along the airfoil surface and displacement of the airfoil are measured as functions of time by a data acquisition system designed for this research. Lift and moment are obtained by integration of the pressure distribution at every time increment. Using a numerical model based on the singularity distribution method, the free air case results for a NACA 0015 airfoil in the same unsteady motion are obtained. Comparison with the linear theory results by Sears¹ are discussed. Comparing with the numerical and the linear theory results, the experimental investigation shows that the new test section produces low-correction data. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Thesis (M.S. in Aeronautical Engineering)--Naval Postgraduate School, September 1990. / Thesis Advisor(s): Howard, Richard M. Second Reader: Healey, J. Val. "September 1990." Description based on title screen as viewed on December 15, 2009. DTIC Identifier(s): Strakes, Yaw, Aerodynamic Forces, Surface To Air Missiles, Angle Of Attack, High Angles, Sides, Side Forces, Wind Tunnel Models, Guided Missile Models, Vortex Shedding, High Angle Of Attack, Turbulence, Forebody Strakes, Ogives, Computer Programs, Theses, Vertical Launch. Author(s) subject terms: Vortex, Vertical Launch, Surface to Air Missile, High Angle of Attack, Turbulence, Strakes, Forebody, Ogive. Includes bibliographical references (p. 154-157). Also available in print.