Summary of the 2004 Computational Fluid Dynamics Validation Workshop on Synthetic Jets

Rumsey, Christopher L.; Gatski, Thomas B.; Sellers, William; Vasta, V. N.; Viken, Sally A.

doi:10.2514/1.12957

Cited by 126 publications

(78 citation statements)

References 14 publications

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“…The state of the art in this area is best exemplified by the experimental work of Greenblatt et al (2006) for slot-jet injection into a boundary layer separating from a dune-shaped hump, and a number of computational studies corresponding to this experimental geometry, documented in Rumsey et al (2006), You, Ham & Moin (2008), Krishnan FIGURE 3. Time-averaged representation of the jet shown in figures 1 and 2.…”

Section: Introductionmentioning

confidence: 99%

The interaction of round synthetic jets with a turbulent boundary layer separating from a rounded ramp

Lardeau

Leschziner

2011

J. Fluid Mech.

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A computational large eddy simulation (LES) study is presented of the interaction between a turbulent boundary layer separating from a rounded ramp in a duct and a pair of spanwise-periodic, round synthetic jets, actuated upstream of the nominal separation line. Several scenarios are considered, for different injection angles and velocity ratios. In all cases, the actuation frequency corresponds to the sheddinginstability mode of the separated shear layer. Experimental data, available for both the baseline flow and one actuated configuration, are used to verify the validity of the computational solutions. The analysis includes a separation of coherent and stochastic contributions to the time-averaged statistics of the auto-and cross-correlations of the fluctuations. The control authority is examined by reference to the effects of the actuation on the size of the separated zone, the momentum thickness of the boundary layer, the velocity field, various turbulence quantities and phase-averaged properties. The study demonstrates that the principal aspect of the interaction, at mean-flow level, is an increase in mixing provoked by the formation of strong streamwise vortices away from the wall, the induction of much weaker streamwise vortices close to the wall, and the extra production of stochastic turbulence caused by unsteady straining. The coherent stresses arising from the periodic perturbations are high -typically 5 times the levels of the unperturbed flow -but only within about 5-7 diameters of the jet orifice, and 2 orifice diameters on each side of the jet, and these are dominant primarily in the outer parts of the boundary layer. Stochastic turbulence is also elevated, but more modestly. The global effect of the actuation is a reduction of 10-20 % in the length of the separated region and 20-40 % in the thickness of the reverse-flow layer, depending on the actuation scheme, counter-flow actuation being the most effective. This reduction is mainly associated with a delay in separation. These results highlight the need for synthetic jets to be placed close to the separation zone and for the inter-jet distance to be of order 5 or lower to achieve a high level of separation-control authority.

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Section: Introductionmentioning

confidence: 99%

The interaction of round synthetic jets with a turbulent boundary layer separating from a rounded ramp

Lardeau

Leschziner

2011

J. Fluid Mech.

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“…Although unsteady vortices were clearly present, the attached-flow theory still managed to predict proper trends in lift force. Simulations were preformed with a 2D RANS model, and captured the formation of the LEV, but could not accurately capture the reattachment, which has been previously documented in RANS computations of unsteady flows [18]. In a followup paper, a thin flat plate is compared to the SD7003 airfoil, and it is found the geometry can influence the LEV formation and lift forces by promoting earlier separation [19], and experimental studies have by Rival et al [20] have shown a similar trend in a plunging plate of various leading edge geometries.…”

Section: Introductionmentioning

confidence: 99%

Unsteady high-lift mechanisms from heaving flat plate simulations

Franck

Breuer

2017

International Journal of Heat and Fluid Flow

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Flapping animal flight is often modeled as a combined pitching and heaving motion in order to investigate the unsteady flow structures and resulting forces that could augment the animal's lift and propulsive capabilities. This work isolates the heaving motion of flapping flight in order to numerically investigate the flow physics at a Reynolds number of 40,000, a regime typical for large birds and bats and challenging to simulate due to the added complexity of laminar to turbulent transition in which boundary layer separation and reattachment are traditionally more difficult to predict. Periodic heaving of a thin flat plate at fixed angles of attacks of 1, 5, 9, 13, and 18 degrees are simulated using a large-eddy simulation (LES). The heaving motion significantly increases the average lift compared with the steady flow, and also surpasses the quasi-steady predictions due to the formation of a leading edge vortex (LEV) that persists well into the static stall region. The progression of the high-lift mechanisms throughout the heaving cycle is presented over the range of angles of attack. Lift enhancement compared with the equivalent steady state flow was found to be up to 17% greater, and up to 24% greater than that predicted by a quasi-steady analysis. For the range of kinematics explored it is found that maximum lift enhancement occurs at an angle of attack of 13 degrees, with a maximum lift coefficient of 2.1, a mean lift coefficient of 1.04.

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“…Seifert and Pack investigated many control configurations, including steady-suction and oscillatory zero-net-mass-flux control, over a range of Mach numbers. The wall-mounted hump was also a test case at the CFD Validation of Synthetic Jets and Turbulent Separation Control workshop held at NASA Langley Research Center (LaRC) [3]. The workshop provided a separate set of experimental data of the baseline and controlled flow including additional data from pressure taps, particle image velocimetry (PIV), and oil-film flow visualization along the surface of the hump [4,5].…”

mentioning

confidence: 99%

“…Participants from the workshop simulated the wall-mounted hump flow using a variety of techniques, including Reynolds-averaged Navier-Stokes (RANS) and large-eddy simulation (LES) [3]. These methods displayed varying degrees of success in predicting the surface pressure coefficient of the baseline, steady-suction, and oscillatory-control test cases at a Reynolds number of 9:29 10 5 based on the freestream velocity U 1 and the chord length c. It has been shown that LES generally provides better agreement with the experimental reattachment location and separation-bubble dynamics than RANS-based simulations [6,7].…”

mentioning

confidence: 99%

Compressible Large-Eddy Simulation of Separation Control on a Wall-Mounted Hump

Franck

Colonius

2010

AIAA Journal

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Compressible large-eddy simulations of turbulent flow over a wall-mounted hump with active flow control are performed and compared with previous experiments. The flow is characterized by the unsteady separation before the steep trailing edge, which naturally reattaches downstream of the hump to form an unsteady turbulent separation bubble. The low Mach number large-eddy simulation demonstrated a good prediction of surface pressure coefficient, separation-bubble length, and velocity profiles compared with experiments. The effect of compressibility on the baseline flow is documented and analyzed and is found to increase the separation-bubble size, due to a reduced growth rate. Control is applied just before the natural separation point via steady suction and zero-net-mass-flux oscillatory forcing, and steady suction is shown to be more effective in decreasing the size of the separation bubble and pressure drag for the control parameters investigated. Controlled flow at a compressible subsonic Mach number is applied, and found to be slightly less effective than the same control parameters at low Mach numbers.

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Summary of the 2004 Computational Fluid Dynamics Validation Workshop on Synthetic Jets

Cited by 126 publications

References 14 publications

The interaction of round synthetic jets with a turbulent boundary layer separating from a rounded ramp

The interaction of round synthetic jets with a turbulent boundary layer separating from a rounded ramp

Unsteady high-lift mechanisms from heaving flat plate simulations

Compressible Large-Eddy Simulation of Separation Control on a Wall-Mounted Hump

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