Simple Models of Zero-Net Mass-Flux Jets for Flow Control Simulations

Raju, Reni; Aram, Ehsan; Mittal, Rajat; Cattafesta, Louis N.

doi:10.1260/175682509789877092

Cited by 40 publications

(11 citation statements)

References 34 publications

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“…Hence, computational analysis of flow control at moderate Reynolds number requires substantial resources to perform a sizable number of parameter study with high fidelity. In addition to resolving the baseline conditions at Reynolds numbers similar to experiments, replicating an actuator introduces added complexity [34]. Earlier numerical studies have examined the effectiveness of blowing/suction [8,35] and vortex generators [36].…”

Section: Introductionmentioning

confidence: 99%

Effects of Wall-Normal and Angular Momentum Injections in Airfoil Separation Control

Munday

Taira

2018

AIAA Journal

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The objective of this computational study is to quantify the influence of wall-normal and angular momentum injections in suppressing laminar flow separation over a canonical airfoil. Open-loop control of fully separated, incompressible flow over a NACA 0012 airfoil at α = 9 • and Re = 23, 000 is examined with large-eddy simulations. This study independently introduces wall-normal momentum and angular momentum into the separated flow using swirling jets through model boundary conditions. The response of the flow field and the surface vorticity fluxes to various combinations of actuation inputs are examined in detail. It is observed that the addition of angular momentum input to wall-normal momentum injection enhances the suppression of flow separation. Lift enhancement and suppression of separation with the wall-normal and angular momentum inputs are characterized by modifying the standard definition of the coefficient of momentum. The effect of angular momentum is incorporated into the modified coefficient of momentum by introducing a characteristic swirling jet velocity based on the non-dimensional swirl number. With this single modified coefficient of momentum, we are able to categorize each controlled flow into separated, transitional, and attached flows. Nomenclature A = Planform area Aj = Actuator jet area c = Chord length CD = Coefficient of drag CL = Coefficient of lift Cµ = Coefficient of momentum C * µ = Modified coefficient of momentum Fx = Drag force Fy = Lift force Gn = Wall-normal momentum flux G θ = Tangential momentum flux lz = Spanwise extent M∞ = Freestream Mach number n = Wall-normal unit vector Nact = Number of actuators p = Pressure p = Time-average pressure p∞ = Freestream pressure Q = Q criteria r = Radial direction ra = Radius of actuator Re = Reynolds number RMS = Root mean square S = Swirl number t = Time u = (ux, uy, uz) = Velocity (streamwise, vertical, spanwise) u = (u x , u y , u z ) = Velocity fluctuation (streamwise, vertical, spanwise) u = (ux, uy, uz) = Time-average velocity (streamwise, vertical, spanwise) Uc = Convective velocity uj = Characteristic jet velocity u * j = Modified characteristic jet velocity un = Wall-normal actuator velocity u θ = Azimuthal/rotational actuator velocity uτ = Friction velocity U∞ = Freestream velocity x = (x, y, z) = Spatial coordinates (streamwise, vertical, spanwise) x + = (x + , y + , z + ) = Spatial coordinates in wall units Greek symbols α = Angle of attack, deg Γn = Wall-normal circulation of actuator jet ν = Kinematic viscosity ρ∞ = Freestream density Σ = Diffusive vorticity flux (σx, σy, σz) = Time-average wall-normal diffusive vorticity flux (streamwise, vertical, spanwise) τxy = Spanwise Reynolds stress ω = (ωx, ωy, ωz) = Vorticity (streamwise, vertical, spanwise)

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Section: Introductionmentioning

confidence: 99%

Effects of Wall-Normal and Angular Momentum Injections in Airfoil Separation Control

Munday

Taira

2018

AIAA Journal

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“…More recent experimental studies, exploring mainly basic aspects of the formation of the jets and/or statistical properties of synthetic jets relative to continuous jets, are those of Zhong et al (2007), Smith & Swift (2003) and Cater & Soria (2002), with a corresponding LES realisation of the last reported by Wu & Leschziner (2009). Simulation studies by Rizzetta, Visbal & Stanek (1999), Raju et al (2009), Aram, Mittal & Cattafesta (2010 and Mittal & Rampunggoon (2002), for two-dimensional or high-aspect-ratio slots jets at low Reynolds numbers, are also noteworthy, in so far as they identify the importance of including the cavity in the computational realisation -in particular, the effect of the cavity flow on the near-field vortical structure during the ejection phase and the non-uniform conditions across the orifice. While these investigations bring to light some fundamentally interesting consequences of the manner in which the ejected vortex rings form, propagate and interact to form a jet, they are only weakly pertinent to the subject of this paper, simply because the fluid mechanics of such jets differ greatly from those in a cross-flow.…”

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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“…Note that such approach accounts for the effect of synthetic-jet interaction with grazing flow that modifies the jet structure at the orifice exit, which thus precludes specifying fluctuating jet velocity directly at the orifice's exit (i.e., on the airfoil surface). (Raju et al, 2009)…”

Section: Boundary Conditionsmentioning

confidence: 99%

A Numerical Study of Synthetic-Jet Actuation Effect on Airfoil Trailing Edge Noise

Sansone¹

2016

22nd AIAA/CEAS Aeroacoustics Conference

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Simple Models of Zero-Net Mass-Flux Jets for Flow Control Simulations

Cited by 40 publications

References 34 publications

Effects of Wall-Normal and Angular Momentum Injections in Airfoil Separation Control

Effects of Wall-Normal and Angular Momentum Injections in Airfoil Separation Control

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

A Numerical Study of Synthetic-Jet Actuation Effect on Airfoil Trailing Edge Noise

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