Thesis (Ph. D.)--University of Texas at Austin, 2005. / Supervisors: Kenneth S. Ball and David G. Bogard. Vita. Includes bibliographical references.

Thesis--Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution. / Includes bibliographical references (p. 181-186).

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

An experimental parametric sturdy of vane and air-jet vortex generators in a turbulent boundary layer has been carried out. Experiments were carried out in two facilities, one with a free-stream velocity of 20 m/s and a boundary layer thickness (6) of 41.5 mm, and one in a high speed facility at free-stream Mach numbers of between 0.45 and 0.75 and a boundary layer thickness of 20 mm. Cross-stream data were measured at a number of downstream locations using a miniature five-hole pressure probe, such that local cross-stream velocity vectors could be derived. Streamwise vorticity was calculated using the velocity vector data. In the low speed study, vortex generator parameters were as follows: ' Vane vortex generators: thin rectangular vanes with a vane aspect ratio of unity (2h/c = 1), free-stream velocity 20 m/s, incidence (cc = 10', 15', 18', 20'), height-to-boundary- layer- thickness-ratio (h/8 0.554,0.916,1.27,1.639), and strearnwise distance from the vortex generator (x/6 = 3.855,12.048,19.277,26.506). ' Air-jet vortex generators: circular jet nozzles, free-stream velocity = 20 m/s, jet nozzle pitch and skew angles (cc, P= 30', 45', 60'), hole diameter-to-boundary-layer-thickness-ratio (D/5 = 0.098,0.193,0.289), jet-to-free-stream-velocity ratio (VR = 0.7,1.0,1.3,1.6,2.0), and strearnwise distance from the vortex generator (x/8 = 3.855,12.048,19.277,26.506). In the high-speed study, the vortex generator parameters were as follows: Vane vortex generators: thin rectangular vanes with an aspect ratio of unity, incidence ((X 1505 20'), he i ght-to- boundary- I ayer-th i ckne s s-rati o (h/8 = 0.75), strearnwise distance from the vortex generator (x/6 = 8.755 16.25,23.75), and free-stream Mach numbers of 0.45,0.6 and 0.75. Air-jet vortex generators: jet pitch ((x = 30', 45'), jet skew angle (P = 30', 45', 60'), hole diameter-to-boundary-layer-thickness-ratio (D/8 = 0.15,0.3), j et-to- free- strearn-ve loc ity ratio (VR = 1.6), and strearnwise distance from the vortex generator (x/6 = 8.75,16.25,23.75, 31.25), and free-stream Mach numbers of 0.50,0.6 and 0.75. Streamwise vorticity data from the experiment was used to generate prediction techniques that would allow the vorticity profiles, downstream of vane or air-jet vortex generators, to be predicted. Both techniques are based on the approximation of the experimental cross-stream vorticity data to Gaussian distributions of vorticity through the vortex centre. The techniques, which are empirically derived, are simple equations that give the peak vorticity and vortex radius based on the vortex generator parameters. Use of these descriptors allows the assembly of the Gaussian vorticity equation. Both techniques are compared with the experimental data set and were seen to produce peak vorticity results to within 12% and 20% (for the vanes and air-jets respectively), 15% for the radius of the vortex, and 15% and 20% in vortex circulation (for the vanes and air-jets respectively). The two simple prediction techniques allow good prediction of the vortex structure at extremely low computational effort.

Flat plate turbulent boundary layers disturbed by periodic moving wakes have been observed in an experimental rig mounted in a low speed wind tunnel. The wakes are produced periodically by cylinders traversing in front of the leading edge of a flat plate on which the boundary layers are measured. This is to simulate the unsteady flow pattern generated by upstream blades on the downstream blade boundary layer in an axial flow turbomachine. Both the time-averaged and ensemble-averaged data are taken from the free stream and boundary layer at different flow conditions. Free stream steady and unsteady wakes are compared and found to be similar to each other. The wake disturbance in the free stream is a function of time and distance from the cylinder. The periodic disturbance in the inner half of the boundary layer lags behind that in the free stream. This phase lag is due to the lower convection velocity near the solid surface. Similar to a steady wake, the velocity defect of an unsteady wake is higher in boundary layer than in free stream. This results in the maximum velocity defect amplitude in the inner half of the boundary layer. Phase lag and amplitude ratio profiles of the boundary layers are plotted and found to be similar to data obtained from axial flow turbomachines. Phase-averaged velocity and turbulence intensity profiles at different phase angles between two successive wakes are shown in a series of transparencies. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Coherent vortices are generated in flow fields due to flow interaction with sharp solid surfaces. Such vortices generate significant disturbances in the flow and affect its further development. In this dissertation attention is focused on the interaction of vortices with solid or free liquid/air surfaces. We examine vortices with their axis parallel or normal to the surface. Three main cases were examined: the interaction of a vortex pair propagating towards a solid boundary, the interaction of spanwise vortices in a turbulent boundary layer, and finally the interaction of spanwise vortices with a flat-plate wake and a free liquid surface. These problems hold significance in several engineering applications, including investigations into trailing wing tip vortices and their interaction with the ground, vortical effects on the development of turbulent boundary layers and free surface signatures and their detection in ship/submarine wakes. Data are acquired with a laser Doppler velocimetry system (LDV) and with Particle-Image Velocimetry (PIV), using a high-speed digital video camera. The LDV system measures two components of velocity along appropriately chosen planes. Grids of data were acquired for different pitch rates of a disturbing flap that generates vortices. Phase-averaged vorticity and turbulence level contours are estimated and presented. It is found that vortices with diameter the order of the boundary layer quickly diffuse and disappear while their turbulent kinetic energy spreads uniformly across the entire boundary layer. Larger vortices have a considerably longer life span and in turn feed more vorticity into the boundary layer. Trailing edge vortices are generated in a water tunnel by sharp hinged motions of a flap. These vortices are allowed to reconnect with the free surface and mix with a turbulent free shear layer. The flow is conditionally sampled via frame grabbing of free surface shadowgraphs. It is found that the vortex core bends away from the plane of the shear layer. Moreover, contrary to earlier findings, organized velocity fluctuations decrease as the free surface is approached. / Ph. D.

No description available.

Experimental studies were conducted to obtain direct measurements of skin friction, mean velocity profiles, axial and normal turbulence intensity profiles, and Reynolds stress profiles in the boundary layer on a large diameter, axisymmetric body with a smooth, solid surface; a sandpaper-roughened, solid surface; a sintered metal, porous surface; a"smooth", perforated titanium surface, a solid, rough Dynapore surface made of diffusion-bonded screening, and a porous, rough Dynapore surface. The roughness values were in the low range (k⁺ = 5-7) just above what is normally considered"hydraulically smooth. 11 Measurements were taken at several axial locations and two different freestream velocities corresponding to dynamic pressures of 12.7 and 17.8 cm. of H₂O, which gives a Re_𝓁 range of 2.93 x 10⁶ to 3.38 x 10⁶. For the Law of the Wall, Defect Law, and the turbulence quantities, very good agreement was found between the present results and those from well-established studies for a solid, smooth surface. The sandpaper-roughened, solid wall and solid, rough Dynapore wall tests showed a 20%~30% increment in local skin friction and a slight shift in the log region of the Wall Law, as well as an increase in turbulence quantities over the smooth wall results. These results were in accord with the classical results collected by Clauser for rough, solid surfaces in this range. The effect of porosity can be shown by comparing the sintered metal, porous wall results to the sand-roughened, solid wall results. Although there is a difference in roughness patterns for these two cases, the average k⁺ is in the same range of 5 ~ 7. To check the effect of porosity directly without any interference of different surface roughness patterns, one can compare the results between the 11 smooth 11 perforated titanium wall and the solid, smooth wall, or between the porous Dynapore and solid Dynapore walls. The effect of porosity showed a 30%~40% increment in local skin friction and a marked downward shift of the logarithmic portion of the Wall Law, as well as an increase in turbulence quantities over the smooth wall results. The combined effects of small roughness and porosity could be seen by comparing the results between the sintered metal, porous wall and the smooth, solid wall, or between the porous Dynapore wall and the smooth, solid wall. It was observed that the combined effects of small roughness and porosity are roughly additive. The effect of porosity due to the existence of the penetration of turbulence through the porous surfaces was detected experimentally by a hot-wire underneath the porous walls. All these results demonstrate that a rough, porous wall simply does not influence the boundary layer in the same way as a solid, rough wall. Therefore, turbulent boundary layer models with injection or suction must include both surface roughness and porosity effects. / Ph. D.

An examination of selected two- and three-dimensional turbulent boundary layer data sets was made to determine the consistency of these data sets with their appropriate momentum integral equations. Several turbulent boundary layer experiments were reviewed to determined which of these provided adequate data so that they could be examined using this method. The selected data sets were used to numerically integrate and compare the two sides of the appropriate momentum integral equations in an extension of the Coles' momentum integral (PL-PR) method originally derived for two-dimensional flow. The effects of small three-dimensionality in a nominally two-dimensional flow were also studied. Three-dimensionality due to converging or diverging collateral flow and converging or diverging skewed flow about a plane of symmetry was investigated. The momentum integral examination of two-dimensional and quasi two-dimensional data sets was verified to be a useful and convenient means of data set validation. Very small amounts of three dimensionality in a nominally two-dimensional flow could have large effects on and adversely affect the outcome of a momentum integral validation of the data set. Three-dimensionality of the order of magnitude of experimental uncertainty, in the form of collateral or skewed convergence/divergence of the flow at a plane of symmetry, was shown to have large adverse effects on the momentum integral validation. Investigations of arbitrary.three-dimensional flows were generally found to lack sufficient data to perform an accurate validation using this PL-PR technique extended to such flows. / Master of Science

Static pressure and mean velocity data were obtained in a relaxing shear driven three-dimensional incompressible turbulent boundary layer flow produced by a swept rectangular step. The nominally 10 cm (4 in.) thick boundary layer had a freestream velocity of approximately 25 m/sec (80 ft/sec). The two steps investigated were each 3.8 cm (1.5 in.) high by 18.4 cm (7 .25 irt.) long and at angles of 30° and 45° to the transverse wind tunnel direction. Pressure gradients were determined by taking the derivative of least-squares curve fits to the static pressure data. Close to the trailing edge reattachment region, the maximum·gradient was·0.8 kPa/m (5 psf/f) for the 30° step and 0.4 kPa/m (2.5 psf/f) for the 45°step. As expected, a region of nominal pressure gradient (0.03 kPa/m or 0.2 psf/f compared to 1.6 kPa/m or 10 psf/f for a pressure driven flow) was found at greater than 36 cm (14 in.) down.stream of the trailing edge of each step. The wall crossflow angle decayed from 67° at 15 cm (6 in.) behind the trailing edge to 9° at 66 cm (26 in.) for the 30° step. In the same region, the crossflow angle decayed from 45° to 6° for the 45° step. The decay or relaxation was found to be much faster in the near-wall region and in the region close to the trailing edge. A defect in the streamwise velocity profiles indicated that the flow was dominated by the separation and reattachment over the step. For future shear driven investigations, a lower, more streamlined wing-type body is recommended to produce a moderately skewed boundary layer without dominant separation effects. / Master of Science