Parallel computations of high-lift airfoil flows using two-equation turbulence models

Lee

6th AIAA Flow Control Conference

et al. 2012

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Flow characteristics of synthetic jets have been computationally investigated for different exit configurations under a cross flow condition. The exit configuration of a synthetic jet substantially affects the process of vortex generation and evolution, which eventually determines the mechanism of jet momentum transport. Two types of exit configurations were considered: one is a conventional rectangular exit, and the other is a series of circular holes. The interactions of synthetic jets with a free stream were performed by analyzing the vortical structure characteristics. The effectiveness of flow control was evaluated by examining the behavior of the wall shear stress. It was observed that the circular exit provides better performance than the rectangular exit in terms of sustainable vortical structure and flow control capability. In order to obtain an optimal shape of a multiple serial circular exits, comparative studies were then conducted according to hole gap and hole diameter. Detailed computations revealed that the hole gap yields a much more significant effect on flow characteristics than the hole diameter, which turned out to be relatively minor. Based on the initial strength and persistency of jet vortices, the circular exit with a suitable hole gap formed critical jet vortices that benefically affected separation control. This indicates that the flow control performance of circular exit array could be remarkably improved by applying a suitable dimensionless hole parameter. NomenclatureA jet = suction or blowing amplitude, instantaneous peak velocity at orifice h = slot width f = frequency of periodic excitation U = velocity d = boundary-layer thickness x = streamwise distance y = spanwise distance from centerline z = normal distance from wall G = gap of multiple serial circular exit D = diameter of circular exit Subscripts 0 = reference value ∞ = freestram value

Section: A Governing Equationsmentioning

confidence: 99%

“…The governing equations were then solved in a time-accurate manner by employing the method of pseudocompressibility, where τis the pseudo-time and ß is the pseudo compressibility parameter 20,21 .…”

Section: A Governing Equationsmentioning

confidence: 99%

Numerical Study on Flow Characteristics of Synthetic Jets with Rectangular and Circular Exits

Lee

6th AIAA Flow Control Conference

et al. 2012

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“…4. For the blowfly's forward flight, seven cases of body AOA are investigated at 0, 15,25,30,35,45, and 60 deg., all with the same wing trajectory.…”

Section: Geometric Modeling and Boundary Conditionmentioning

confidence: 99%

Three-dimensional Unsteady Aerodynamic Characteristics of Wing-body-vortex Interactions in Insects' Flapping Flight

Lee

31st AIAA Applied Aerodynamics Conference

2013

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This paper investigates the unsteady aerodynamic features of wing-body-vortex interactions and the effects of geometric factors such as wing shape and body angle in insects' flapping motions under forward flight condition. A realistic wing trajectory, called the 'figure-of-eight' motion, is extracted from a blowfly (Phormia regina)'s tethered flight experiment under the freestream velocity of 2.75m/s. Since the flow field around the blowfly exhibits the characteristics of low-Reynolds number flow, three-dimensional unsteady incompressible Navier-Stokes equations are employed as the governing equations. In order to simulate the realistic insect flapping flight including geometric and kinematical complexity with a sufficient level of grid quality, the overset grid technique is used. From the authors' previous researches on two-and three-dimensional rigid wing simulation, it has been observed that the pattern of vortical flows and the interaction of vortices play an significant role in generating unsteady aerodynamic forces and determining the propulsive efficiency of flapping motion. Detailed numerical simulations of five types of wings are carried out under various body angles to examine unsteady flow characteristics resulting from the wing-body-vortex interactions, and the results are compared with those of the wing only case. Nomenclature c m = mean chord length U ∞ = freestream velocity U max = maximum wing velocity at aerodynamic mean chord ν = freestream kinematic viscosity Re = Reynolds number (=U max c m /ν)= flapping frequency in Hertz k = reduced frequency in terms of c m (= fc m /U max ) t = non-dimensional time T = non-dimensional flapping period χ = body angle α(t) = pitch angle motion ф(t) = position angle motion θ(t) = elevation angle motion

“…Bardina et aL (1997) reported that this turbulence model can provide excellent prediction of flows with separation. All computations were performed with a finite volume based in-house code, which has been extensively tested by Kim et aL (2000). In all calculations presented here, the boundary layer was assumed to be fully turbulent with the Reynolds number of2.19x 10 6 •…”

Section: Governing Equationsmentioning

confidence: 99%

Separation control mechanism of airfoil using synthetic jet

2007

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Numerical simulation of separation control using a synthetic jet was performed on NACA23012 airfoil. The computed results showed that stall characteristics and control surface performance could be improved substantially by resizing the separation vortices. It was observed that actual flow control mechanism was fundamentally different depending on the range of synthetic jet frequency. For low frequency range, small vortices due to synthetic jet penetrated to the large leading edge separation vortex flow, and as a result, the size of the leading edge separation vortex remarkably decreased. For high frequency range, however, the small vortex did not grow enough to penetrate into the large separation vortex, but the syntheticjet changed airfoil circulation directly. The synthetic jet conditions for effective lift increase are as follows: the non-dimensional frequency of the synthetic jet is I; the location of the synthetic jet slot is the same as the separation point; and the jet velocity is large enough to perturb the separated flow. By exploiting these conditions, it was observed that the combination of the synthetic jet with a simple high lift device could be as good as a conventional fowler flap system.