Particle image velocimetry was used in a low-speed wind tunnel to investigate and characterize wing tip vortex structures. A rectangular wing of a subsonic wall interference model was used as a vortex generator in two different configurations: 1) plain wing and 2) flapped wing with the trailing-edge flap extended at 20 degrees. Vortex flow quantities and their dependence on angle of attack at Reynolds numbers of 32:8 10 3 and 43:8 10 3 were evaluated. Assessment of measured data reveals that the peak values of tangential velocities, vortex strength, and vorticities are directly proportional to the angle of attack. The vortex core radius value grows slowly as the angle of attack is increased. Both plain and flapped configurations showed similar trends. The peak tangential velocities and circulation almost doubled when the flapped configuration was used instead of the plain wing.
Road vehicles drag is a direct consequence of a large wake area generated behind. This area is created owing to the vehicle shape, which is determined by the class, functional and aesthetic of the vehicle. Aerodynamic characteristics are a ramification and not the reason for the vehicle architecture. To enhance pressure recovery in the wake region, hence reduce drag, three different passive flow control techniques were applied to sport-utility-vehicle (SUV). A three-dimensional SUV was designed in CATIA, and a numerical flow simulation was conducted using Ansys-Fluent to evaluate the aerodynamic effectiveness of the proposed flow control approaches. A closed rectangular flap as an add-on device modifies the wake vortex system topology, enhances vortex merging, and increases base pressure which leads to a drag reduction of 15.87%. The perforated roof surface layer was used to delay flow separation. The measured base pressure values indicate a higher-pressure recovery, which globally reflected in a drag reduction of 19.82%. Finally, air guided through side rams was used as steady blowing. A steady passive air jet introduced at the core of the longitudinal trailing vortices leads to a confined wake area. The net effects appear in a global increase in the base pressure values and the pronounced drag reduction of 22.67%.
A wind turbine blade has the particularity of containing twisted and tapered thick airfoils. The challenge with this configuration is the highly separated flow in the region of high twist. This research presents a numerical investigation of the effectiveness of a Vortex Trapping Cavity (VTC) on the aerodynamics of the National renewable Energy laboratory (NREL) Phase VI wind turbine. First, simulations are conducted on the S809 profile to study the fluid flow compared to the airfoil with the redesigned VTC. Secondly, the blade is simulated with and without VTC to assess its effect on the torque and the flow patterns. The results show that for high angles of incidence at Rec=106, the lift coefficient increases by 10% and the wake region appears smaller for the case with VTC. For wind speeds larger than 10 m/s, the VTC improves the torque by 3.9%. This is due to the separation that takes place in the vicinity of the VTC and leads to trapping early separation eddies inside the cell. These eddies roll up forming a coherent laminar vortex structure, which in turn sheds periodically out of the cell. This phenomenon favourably reshapes excessive flow separation, reenergizes the boundary layer and globally improves blade torque.
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