Browsing by Subject "Wakes (Aerodynamics)"
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Item A computational study of coherent structures in the wakes of two-dimensional bluff bodies(Texas Tech University, 1988-08) Pearce, Jeffrey AlanThe periodic shedding of vortices from bluff bodies was first recognized in the late 1800's. Currently, there is great interest concerning the effect of vortex shedding on structures and on vehicle stability. In the design of bluff structures which will be exposed to a flow, knowledge of the shedding frequency and the amplitude of the aerodynamic forces is critical. The ability to computationally predict parameters associated with periodic vortex shedding is thus a valuable tool. In this study, the periodic shedding of vortices from several bluff body geometries is predicted. The study is conducted with a two-dimensional finite-difference code employed on various grid sizes. The effects of the grid size and time step on the accuracy of the solution are addressed. Strouhal numbers and aerodynamic force coefficients are computed for all of the bodies considered and compared with previous experimental results. Results indicate that the finite-difference code is capable of predicting periodic vortex shedding for all of the geometries tested. Refinement of the finite-difference grid was found to give little improvement in the prediction; however, the choice of time step size was shown to be critical. Predictions of Strouhal numbers were generally accurate, and the calculated aerodynamic forces generally exhibited behavior consistent with previous studies.Item A vortex model of the Darrieus turbine(Texas Tech University, 1978-12) Nguyen, Thong V.An aerodynamic performance prediction model for the Darrieus turbine has been constructed. The primary purpose was to allow reasonable prediction of aerodynamic blade forces and moments to be made. Previous aerodynamic models based on simple momentum principles are inadequate for predicting blade loading. In addition, accurate overall performance predictions for large tip to wind speed ratios cannot be made with the simple momentum models. Detailed prediction of the near wake structure is also within the capability of the present model. Results were obtained from the present vortex model for the one-, two- and three-bladed rotors operating at various tip to wind speed ratios to study the effect of number of blades and tip to wind speed ratios on the rotor performance. Power coefficients predicted by the present vortex model were compared to the vortex model due to Fanucci and the simple momentum or "strip theory". In addition, experimental results were used to compare with predictions obtained from the analytical model in an attempt to validate the analytical model.Item On the charcterization of wakes from three-dimensional single and multiple flat plates on a ground plane(Texas Tech University, 1985-05) Barton, Gregory HaroldA flat plate is a simplified model for a heliostat, which is a large flat tracking mirror used to reflect solar energy onto a central receiving boiler in a solar collector system. This is a study of vortex shedding from 3-dimensional single flat plates on a ground plane and the modifying effect on their wakes when plates are placed upstream. The multiple plate data is characterized by the single plate wake properties based on the plate separation distance referenced to the Strouhal identity length. The new characteristic body length is simply the multiple plate separation distance which produces the same Strouhal number for single and multiple bodies. For separation distances less than the Strouhal identity length, the multiple plate characteristics are very similar to the single plate. For separation distances greater than the Strouhal identity length, a multiple plate wake scale factor is developed which transforms the streamwise wake distance from the front plate into a new streamwise coordinate.Item Transient load measurements on parachute models represented by two-dimensional cambered plates(Texas Tech University, 1990-08) Adamson, Thomas DewayneIf the parachute deceleration of a payload results in a large momentum transfer to the surrounding fluid over a relatively short distance, the resulting wake velocities may be large enough for the wake to overtake and collapse the parachute. This report describes an experimental test program aimed at investigating the aerodynamic interaction between the parachute and its wake. The test program involves examination of the transient loading on rigid two-dimensional circular arcs during their motion through a water-filled tow-tank. The transient loads on circular arcs with included angles of 120, 180, and 240 degrees were obtained by simultaneously measuring instantaneous pressure distributions and drag forces. The loads are reduced to a drag history which shows the variation of the drag coefficient with time for each circular arc.Item Vortex shedding from square plates near a ground plane: an experimental study(Texas Tech University, 1979-12) Matty, Rosemary RicohermosoVortex shedding frequencies were obtained experimentally for square plates near a ground plane in the Texas Tech wind tunnel. These frequencies, in the form of Strouhal numbers, were obtained as a function of Reynolds number, distance above a ground plane, and elevation and azimuth angle. Experiments involving various combinations of these parameters were conducted. From these experiments an equation describing the relationship between these parameters was obtained.