Control of a decelerating boundary layer. Part 3: Optimization of round jets vortex generators

Godard, Gilles; Stanislas, Michel

doi:10.1016/j.ast.2005.11.005

Cited by 75 publications

(69 citation statements)

References 12 publications

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“…It is now well established that active VG's have a similar effect on the flow structure to passive VG's [4,6,[8][9][10][11]14] with the added advantage of no parasitic drag when they are not required. Typically, they could be used, e.g.…”

Section: Introductionmentioning

confidence: 99%

The Flow Structure Produced by Pulsed-jet Vortex Generators in a Turbulent Boundary Layer in an Adverse Pressure Gradient

Kostas¹,

Foucaut²,

Stanislas³

2007

Flow Turbulence Combust

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The effect of pulsed jet vortex generators on the structure of an adverse pressure gradient turbulent boundary layer flow was investigated. Two geometrically optimised vortex generator configurations were used, co-rotating and counterrotating. The duty cycle and pulse frequency were both varied and measurements of the skin friction (using hot films) and flow structure (using stereo PIV) were performed downstream of the actuators. The augmentation of the mean wall shear stress was found to be dependent on the net mass flow injected by the actuators. A quasi steady flow structure was found to develop far downstream of the injection location for the highest pulse frequency tested. The actuator near field flow structure was observed to respond very quickly to variations in the jet exit velocity.

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Section: Introductionmentioning

confidence: 99%

The Flow Structure Produced by Pulsed-jet Vortex Generators in a Turbulent Boundary Layer in an Adverse Pressure Gradient

Kostas¹,

Foucaut²,

Stanislas³

2007

Flow Turbulence Combust

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“…Small holes or slots are machined into the surface from which a jet is blown. To be efficient, such jets must be pitched to the surface and skewed to the main flow direction, so that a longitudinal vortex is generated in the boundary layer by the interaction between the jet and the cross-flow (Godard et al 2006;Godard and Stanislas 2006b). The principle of flow control is the same as for vane-type VGs: momentum transfer between the free-stream and the near-wall region.…”

Section: Introductionmentioning

confidence: 99%

Dielectric-barrier-discharge vortex generators: characterisation and optimisation for flow separation control

Jukes

Choi

2011

Exp Fluids

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We investigated the use of dielectric-barrierdischarge plasma actuators as vortex generators for flow separation control applications. Plasma actuators were placed at a yaw angle to the oncoming flow, so that they produced a spanwise wall jet. Through interaction with the oncoming boundary layer, this created a streamwise longitudinal vortex. In this experimental investigation, the effect of yaw angle, actuator length and plasma-induced velocity ratio was studied. Particular attention was given to the vortex formation mechanism and its development downstream. The DBD plasma actuators were then applied in the form of co-rotating and counter-rotating vortex arrays to control flow separation over a trailing-edge ramp. It was found that the vortex generators were successful in reducing the separation region, even at plasma-to-freestream velocity ratios of less than 10%.

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“…Along with the parameters regarding a single actuator, the control effects are also dependent on the shape of the actuator and the arrangement of the actuator array. [28][29][30] The forcing frequency of the SJ is arguably the most important parameter and is indeed the key parameter to be optimized for better separation control effect. 24,[31][32][33] Experimental and numerical results 31,34,35 reveal that the fundamental mechanism of separation control by a SJ is the formation of coherent roll-up lifting vortices not far from the airfoil surface.…”

Section: Introductionmentioning

confidence: 99%

A direct numerical simulation investigation of the synthetic jet frequency effects on separation control of low-Re flow past an airfoil

Zhang

Samtaney

2015

Physics of Fluids

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CitationA direct numerical simulation investigation of the synthetic jet frequency effects on separation control of low-Re flow past an airfoil 2015, 27 (5) We present results of direct numerical simulations of a synthetic jet (SJ) based separation control of flow past a NACA-0018 (National Advisory Committee for Aeronautics) airfoil, at 10• angle of attack and Reynolds number 10 4 based on the airfoil chord length C and uniform inflow velocity U 0 . The actuator of the SJ is modeled as a spanwise slot on the airfoil leeward surface and is placed just upstream of the leading edge separation position of the uncontrolled flow. The momentum coefficient of the SJ is chosen at a small value 2.13 × 10 −4 normalized by that of the inflow. Three forcing frequencies are chosen for the present investigation: the low frequency (LF) F + = f e C/U 0 = 0.5, the medium frequency (MF) F + = 1.0, and the high frequency (HF) F + = 4.0. We quantify the effects of forcing frequency for each case on the separation control and related vortex dynamics patterns. The simulations are performed using an energy conservative fourth-order parallel code. Numerical results reveal that the geometric variation introduced by the actuator has negligible effects on the mean flow field and the leading edge separation pattern; thus, the separation control effects are attributed to the SJ. The aerodynamic performances of the airfoil, characterized by lift and lift-to-drag ratio, are improved for all controlled cases, with the F + = 1.0 case being the optimal one. The flow in the shear layer close to the actuator is locked to the jet, while in the wake this lock-in is maintained for the MF case but suppressed by the increasing turbulent fluctuations in the LF and HF cases. The vortex evolution downstream of the actuator presents two modes depending on the frequency: the vortex fragmentation and merging mode in the LF case where the vortex formed due to the SJ breaks up into several vortices and the latter merge as convecting downstream; the discrete vortices mode in the HF case where discrete vortices form and convect downstream without any fragmentation and merging. In the MF case, the vortex dynamics is at a transition state between the two modes. The low frequency actuation has the highest momentum rate during the blowing phase and substantially affects the flow upstream of the actuator and triggers early transition to turbulence. In the LF case, the transverse velocity has a 1%U 0 pulsation at the position 18%C upstream of the actuator. C 2015 AIP Publishing LLC.

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Control of a decelerating boundary layer. Part 3: Optimization of round jets vortex generators

Cited by 75 publications

References 12 publications

The Flow Structure Produced by Pulsed-jet Vortex Generators in a Turbulent Boundary Layer in an Adverse Pressure Gradient

The Flow Structure Produced by Pulsed-jet Vortex Generators in a Turbulent Boundary Layer in an Adverse Pressure Gradient

Dielectric-barrier-discharge vortex generators: characterisation and optimisation for flow separation control

A direct numerical simulation investigation of the synthetic jet frequency effects on separation control of low-Re flow past an airfoil

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