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

Shizawa, Takaaki; Eaton, John K.

doi:10.2514/3.10881

Cited by 41 publications

(11 citation statements)

References 7 publications

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“…Eaton [29] showed in his review on experimental works of coherent structures in 3DTBLs, that much attention has been focused on the strength and symmetry of the vortices of opposite sign. Shizawa and Eaton [30] used a generator vortex to embed a vortex in the boundary layer approaching a wedge. The vortices decayed faster in the three-dimensional boundary layer than in an equivalent two-dimensional flow.…”

Section: A Rotating Disk Flowsmentioning

confidence: 99%

Turbulence characteristics of the Bödewadt layer in a large enclosed rotor-stator system

Randriamampianina

Poncet

2006

Physics of Fluids

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A three-dimensional direct numerical simulation (3D DNS) is combined with a laboratory study to describe the turbulent flow in an enclosed annular rotor-stator cavity characterized by a large aspect ratio G = (b − a)/h = 18.32 and a small radius ratio a/b = 0.152, where a and b are the inner and outer radii of the rotating disk and h is the interdisk spacing. The rotation rate Ω under consideration is equivalent to the rotational Reynolds number Re = Ωb 2 /ν = 9.5× 10 4 , where ν is the kinematic viscosity of the fluid. This corresponds to a value at which an experiment carried out at the laboratory has shown that the stator boundary layer is turbulent, whereas the rotor boundary layer is still laminar.

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Section: A Rotating Disk Flowsmentioning

confidence: 99%

Turbulence characteristics of the Bödewadt layer in a large enclosed rotor-stator system

Randriamampianina

Poncet

2006

Physics of Fluids

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“…The bulk turning effect on the structures will then be addressed by also aligning the frame of reference with the direction of the mean flow, and comparing the level and distribution of the contour lines of ensemble-averaged velocities and turbulent stresses in the two coordinate systems. The nomenclature of Shizawa and Eaton [40] is adopted to identify vortices of opposite sign; Case 1 vortices have induced near-wall velocity in the direction of the mean crossflow, while Case 2 vortices have induced near-wall velocity in the opposite direction of the mean crossflow. Figure 11 shows isosurfaces of ensemble-averaged 2 -structures 2 ( u i ).…”

Section: Ensemble-averaged Structuresmentioning

confidence: 99%

Turbulence in a three‐dimensional wall‐bounded shear flow

Holstad

Andersson

Pettersen

2009

Numerical Methods in Fluids

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SUMMARYA new turbulent flow with distinct three-dimensional characteristics has been designed in order to study the impact of mean-flow skewing on the turbulent coherent vortices and Reynolds-averaged statistics. The skewing of a unidirectional plane Couette flow was achieved by means of a spanwise pressure gradient. Direct numerical simulations of the statistically steady Couette-Poiseuille flow enabled in-depth explorations of the turbulence field in the skewed flow. The imposition of a modest spanwise gradient turned the mean flow about 8 • away from the original Couette flow direction and this turning angle remained nearly the same over the entire cross section. Nevertheless, a substantial non-alignment between the turbulent shear stress angle and the mean velocity gradient angle was observed. The structure parameter turned out to slightly exceed that in the pure Couette flow, contrary to the observations made in some other three-dimensional shear flows.Coherent flow structures, which are known to be associated with the Reynolds shear stress in near-wall regions, were identified by the 2 -criterion. Instantaneous and ensemble-averaged vortices resembled those found in the unidirectional Couette flow. In the skewed flow, however, the vortex structures were turned to align with the local mean-flow direction. The conventional symmetry between Case 1 and Case 2 vortices was broken due to the mean-flow three-dimensionality. The turning of the coherent vortices and the accompanying symmetry-breaking gave rise to secondary and tertiary turbulent shear stress components. By averaging the already ensemble-averaged shear stresses associated with Case 1 and Case 2 vortices in the homogeneous directions, a direct link between the educed near-wall structures and the Reynolds-averaged turbulent stresses was established. These observations provide evidence in support of the hypothesis that the structural model proposed for two-dimensional turbulent boundary layers remains valid also in flows with moderate mean three-dimensionality.

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“…If Ω · ω v = 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 and adopted by Littell and Eaton .…”

Section: Summary and Concluding Remarksmentioning

confidence: 68%

“…The resulting flow is skewed because of mean three‐dimensionality, such that the mean flow and the near‐wall vortices are aligned at an angle β relative to the x ‐axis. The nomenclature of Shizawa and Eaton is adopted to distinguish between vortices with opposite senses of rotation; Case 1 vortices have induced near‐wall velocity in the direction of the mean crossflow, while Case 2 vortices have induced near‐wall velocity in the opposite direction of the mean crossflow (Figure (b)). Here we suggest that the direction of the mean vorticity vector relative to the direction of the vortex vorticity vector is deciding for structure modification by mean‐flow three‐dimensionality.…”

Section: Introductionmentioning

confidence: 99%

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

Cited by 41 publications

References 7 publications

Turbulence characteristics of the Bödewadt layer in a large enclosed rotor-stator system

Turbulence characteristics of the Bödewadt layer in a large enclosed rotor-stator system

Turbulence in a three‐dimensional wall‐bounded shear flow

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

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