The flow separation is a common phenomenon in low-speed air vehicles (μUAV, MAV, etc.), which causes loss of lift, increase of drag, and generation of aerodynamic noise. Many flow control techniques have been studied and reported. They are fundamentally categorized as active (blowing/suction, synthetic jet, etc.) and passive (self-adaptive or gurney flap, airfoil with cavity, slotted aerofoil, etc.) flow control techniques. The passive methods do not require any external energy to run constantly, and it involves comparatively lower cost than active methods. Here, the passive approach, a cavity, has been considered on the suction surface of an airfoil to execute flow control. Computations are performed to analyse the effect of cavity on flow dynamics and also on the performance of the airfoil. Here, two different shapes (rectangular and elliptical) of cavity are created at 16% of chord length from the leading edge on the suction surface of airfoil. The opening width size of both cavities is same as 30 mm. All computational studies have been carried out for airfoil S5010 and chord length based Reynolds number of 105, using commercial software ANSYS (v14.5, fluent). The standard airfoil has chord length of 150 mm and is simulated at several angles of attack (0, 4, 10,12,16°). Pressure based SIMPLE scheme is selected for pressure-velocity coupling, and for flow variables, the second-order upwind scheme is used. Spalart-Allmaras turbulence model is employed to solve the transport equation for the kinematic eddy viscosity. For the clean airfoil, the lift coefficient increases with angle of attack from 0° to 12° and after that, it decreases with angle of attack, so the stall phenomenon has been observed after 12°. Maximum lift coefficient is marked at this stall angle and it is 1.2. The drag force of airfoil increases continuously with angle of attack, but the rate of increase slightly higher after 12°. It has been observed that, for angle of 2°, initially the flow is separated from the suction surface at approximately 50% of chord length. As incidence angle increases, the flow separation point starts to move from downstream to upstream on the suction surface of airfoil. At an angle of 14°, the separation point reaches near the leading edge of clean airfoil. The overall effect of cavity on the flow around the airfoil is that, it creates vortices, thereby re-energizes the slower moving boundary layer and delays the flow separation in the downstream direction. Both the cavity configurations have improved the lift to drag ratio compared to clean airfoil for same incidence angles. Details of the simulations, analysis of results, and effectiveness of a cavity shapes will be discussed in the full-length paper.Keywords: Airfoil with cavity, Aerodynamic coefficients, Stall characteristics, Vortices

Cavity for Flow Control and Performance Improvement of Airfoil

Paper Proceedings: https://asmedigitalcollection.asme.org/GTINDIA/GTINDIA2021/volume/85536

ASME 2021 Gas Turbine India Conference (GTINDIA2021)

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