Turbulence measurements for a longitudinal vortex interacting with athree-dimensional turbulent boundary layer

Shizawa, Takaaki; Eaton, John K.

doi:10.2514/6.1991-732

Cited by 5 publications

(8 citation statements)

References 5 publications

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“…In this regard, using Navier-Stokes equations, the present initial condition is only a computational artifact. However, generating a single inclined vortex tube itself in a shear flow is realistic as shown in Jukes & Choi [17], Zhang [42], Eibeck & Eaton [10], Shizawa & Eaton [35]. They used a plasma actuator, an air jet and a halfdelta-wing vortex generator for the generation.…”

Section: Generation Of Initial Fields and Computational Casesmentioning

confidence: 99%

Direct numerical simulation of a straight vortex tube in a laminar boundary-layer flow

Matsuura¹

2016

Int. J. CMEM

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Effects of circulation on the evolution of vortex tubes and the associated response of near-wall flows in the shear of laminar boundary-layer flows are investigated using a model proposed by Hon and Walker (Hon, T.L. & Walker, J.D.A, Computers & Fluids, 20(3), pp. 343-358, 1991). Direct numerical simulations with freestream Mach number of 0.5 are conducted. Firstly, the dynamics of single hairpin vortex is investigated. Numerous secondary hairpin vortices, much more than previously reported, which are regularly aligned in the streamwise direction are allowed to be newly generated according to the shear-layer instability of the legs of an initial hairpin vortex. Small-scale turbulence is then produced when the circulation is sufficiently large. Secondly, a straight vortex tube model is investigated. Sinuous deformation of a shear layer, which leads to the generation of discrete hairpin vortices, becomes obvious especially near the upper region of the vortex tube. In order to quantify the initial instability triggering the generation of the secondary hairpin vortices, quasi-linear stability analysis is conducted. While only one unstable mode appears when the circulation is small, two modes, that is, off-wall mode and near-wall mode, appear when the circulation is large. The cases of circulation where the two modes appear correspond to those of circulation where the production of small-scale turbulence is observed in the simulations of the single hairpin vortex.

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Section: Generation Of Initial Fields and Computational Casesmentioning

confidence: 99%

Direct numerical simulation of a straight vortex tube in a laminar boundary-layer flow

Matsuura¹

2016

Int. J. CMEM

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“…v D 0, vortices with opposite sense of rotation will be equally affected by the crossflow and the flow will be essentially 2D. The present interpretative model represents a refinement of the model proposed by Shizawa and Eaton [11] and adopted by Littell and Eaton [7].…”

Section: Summary and Concluding Remarksmentioning

confidence: 58%

“…The mean streamwise (U ) and spanwise (V ) velocity components are in the positive xand y-direction, respectively. (b) Vortex labels as defined by Shizawa and Eaton[11].…”

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confidence: 99%

Turbulence in a skewed three‐dimensional wall‐bounded shear flow: effect of mean vorticity on structure modification

Holstad

Andersson

Pettersen

2011

Numerical Methods in Fluids

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SUMMARY Mean‐flow three‐dimensionalities affect both the turbulence level and the coherent flow structures in wall‐bounded shear flows. A tailor‐made flow configuration was designed to enable a thorough investigation of moderately and severely skewed channel flows. A unidirectional shear‐driven plane Couette flow was skewed by means of an imposed spanwise pressure gradient. Three different cases with 8°, 34°and 52°skewing were simulated numerically and the results compared with data from a purely two‐dimensional plane Couette flow. The resulting three‐dimensional flow field became statistically stationary and homogeneous in the streamwise and spanwise directions while the mean velocity vector V and the mean vorticity vector Ω remained parallel with the walls. Mean flow profiles were presented together with all components of the Reynolds stress tensor. The mean shear rate in the core region gradually increased with increasing skewing whereas the velocity fluctuations were enhanced in the spanwise direction and reduced in the streamwise direction. The Reynolds shear stress is known to be closely related to the coherent flow structures in the near‐wall region. The instantaneous and ensemble‐averaged flow structures were turned by the skewed mean flow. We demonstrated for the medium‐skewed case that the coherent structures should be examined in a coordinate system aligned with V to enable a sound interpretation of 3D effects. The conventional symmetry between Case 1 and Case 2 vortices was broken and Case 1 vortices turned out to be stronger than Case 2. This observation is in conflict with the common understanding on the basis of the spanwise (secondary) mean shear rate. A refined model was proposed to interpret the structure modifications in three‐dimensional wall‐flows. What matters is the orientation of the mean vorticity vector Ω relative to the vortex vorticity vector ωv, that is, the sign of Ω ·ωv. In the present situation, Ω ·ωv > 0 for the Case 1 vortices causing a strengthening relative to the Case 2 vortices. Copyright © 2011 John Wiley & Sons, Ltd.

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“…Investigations of longitudinal vortex production using air jets did identify areas of complex turbulent kinetic energy and stress distributions, 8 ' 15 as indeed did an experimental study of winglet vortex generator by Shizawa and Eaton. 16 However, it has also been shown that the most complex turbulent features exist at an early stage of the vortex production. This stage only lasts for a short distance.…”

Section: A Governing Equationsmentioning

confidence: 99%

Flow and heat transfer in a turbulent boundary layer through skewed and pitched jets

Zhang

Collins

1993

AIAA Journal

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A study was carried out of longitudinal vortices in a low speed turbulent boundary layer due to small jets. The jet was pitched at 45 deg and skewed between 0 and 120 deg. The effects of jet velocity ratio (0 < Ay < 3.0) and skew angle (0 < 0 < 120 deg) were addressed. Mass-averaged Navier-Stokes equations were solved using computational fluid dynamics and heat transfer. Turbulence closure was achieved using k-e model. Three types of vortex production were noted at various jet velocity ratios. When a longitudinal vortex is positioned at the edge or in the outer region of the boundary layer, optimal effects of the flow and heat transfer control were achieved. When the vortex lay deeply in the boundary layer, the effects on heat transfer control could be detrimental. When the jet penetrated the boundary layer, the favorable effects of the vortex on control were reduced due to the larger distance away from the surface. Significant improvements of vortex strength and heat transfer were seen between skew angle 0 < $ < 45 deg, although in 45<0<120 deg the improvements were marginal. Nomenclaturekinetic energy Nu = Nusselt number, h • D/\ Nu -averaged Nusselt number, l/S$ s Nu -djc dz q = heat flux on the wall, W/m 2 5 = surface area T = temperature T f = cross-stream temperature 7} = jet exit temperature T s = wall temperature U, V, W = velocity components V = flow velocity in vector form V e = cross-stream velocity Vj = jet exit velocity x, y, z = Cartesian coordinates a = jet pitch angle 6 = oncoming boundary-layer thickness e = turbulence dissipation rate f = bulk viscosity 0 = jet skew angle X = thermal conductivity of air \j = jet velocity ratio, Vj/V e I* = viscosity p -density a t = turbulent Prandtl number T = shear stress S x = vorticity level on x plane, d/V e [(dW/dy)/-(dV/dz)]

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Turbulence measurements for a longitudinal vortex interacting with athree-dimensional turbulent boundary layer

Cited by 5 publications

References 5 publications

Direct numerical simulation of a straight vortex tube in a laminar boundary-layer flow

Direct numerical simulation of a straight vortex tube in a laminar boundary-layer flow

Turbulence in a skewed three‐dimensional wall‐bounded shear flow: effect of mean vorticity on structure modification

Flow and heat transfer in a turbulent boundary layer through skewed and pitched jets

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