Numerical investigation of flow separation control over an airfoil using fluidic oscillator

Abstract

Leading edge flow separation control over a stalled National Advisory Committee for Aeronautics 0015 airfoil using a fluidic oscillator (FO) is investigated by means of numerical simulation possibly for the first time to elucidate the flow control mechanism and evaluate control authority. The flow is assumed to be two-dimensional and fully turbulent and resolved using unsteady Reynolds-averaged Navier–Stokes calculations with the elaborate Reynolds stress turbulence model employed. Our simulation is proved to be able to successfully resolve the basic characteristics of a FO operating in quiescent air, which include both the qualitative prominent flow structures and quantitative jet oscillation frequency. It is seen that the driving force behind the self-induced and self-sustaining oscillation of jet flow inside the oscillator is Coanda effect induced alternating development of a recirculation bubble on either side of the mixing chamber walls. We provide a comprehensive analysis of the flow control procedure over an airfoil at Reynolds number of Re = 4.8 × 105 and an elucidation of the flow control mechanism. It is found that the most prominent flow feature resulting from the interplay between an oscillating jet and external crossflow over an airfoil is the production of spanwise vortices. The strong entrainment effect of the induced spanwise vortices is the dominant mechanism leading to the mitigation of flow separation. Periodic jet oscillation generates a series of downstream moving vortices over an airfoil surface and results in a greatly delayed flow separation. The recovery of a strong suction pressure peak near the leading edge and significant lift enhancement and drag reduction reflects the improvement of an aerodynamic performance of the airfoil under control. Also observed is the phenomenon of local flow frequency lock-in to forcing frequency near the leading edge region. Moreover, the mass supply rate at the inlet of the oscillator is found to have an appreciable effect on the flow control authority. A higher mass flow usually leads to a better flow control performance.

Lift tailoring on unsteady airfoils with leading-edge vortex shedding using an inverse aerodynamic approach

“…The recent advancement in experimental and computational facilities and the improved understanding of the flow physics of unsteady wings have facilitated several approaches to control flow phenomena and modulate the loads on them. A variety of flow-control strategies have been explored for dynamic-stall control including pointwise flow control using electric or fluidic actuators [5][6][7][8][9][10] and leading-edge suction and blowing [11][12][13] to alter the LEV shedding process and thus its effect on the transient loads. Dynamically deforming airfoils have also been suggested as an approach to control dynamic stall.…”

Effect of varying frequency of a synthetic jet on flow separation over an airfoil

“…Among the active control strategies, the synthetic jet (also known as zero-net-mass flux or ZNMF jet) has shown promise as it possesses the features of both the steady blowing or suction devices and the pulsed jet. 4,8,[10][11][12][13] It has proven to be more energy-efficient than the conventional steady blowing or suction devices since it requires one to two orders of magnitude less momentum to produce similar control effects. 9,14 The synthetic jet actuator (SJA) consists of a vibrating diaphragm mounted in a cavity with the exit (i.e., orifice or slot) located on the surface of the airfoil.…”