Streamwise pseudo-vortical structures and associated vorticity in the near-wall region of a wall-bounded turbulent shear flow

Kasagi, Nobuhide; Hirata, Masaru; Nishino, Kouichi

doi:10.1007/bf00266296

Cited by 30 publications

(7 citation statements)

References 33 publications

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“…One of the first contributions to the issue of the presence of vortices in the boundary layer is due to Theodorsen [6] who introduced the hairpin vortex model. Robinson [7] confirmed the existence of arch vortices and quasi-streamwise vortices (outward-tilted, the latter observed since 1983 and 1986 by Smith and Shwartz [8] and Kasagi et al [9], respectively) on the basis of DNS results. The composition of a quasi-streamwise vortex with an arch vortex may result in a hairpin vortex, but this conclusion may strongly depend on the particular technique used for vortex detection.…”

Section: More Recent Contextsupporting

confidence: 67%

Temporal Evolution of Vortical Structures in the Wall Region of Turbulent Channel Flow

Alfonsi

Primavera

2008

Flow Turbulence Combust

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Hairpin-like vortical structures that form in the wall region of turbulent channel flow are investigated. The analysis is performed by following a procedure in which the Navier-Stokes equations are first integrated by means of a computational code based on a mixed spectral-finite difference technique in the case of the flow in a plane channel. A DNS turbulent-flow database, representing the turbulent statistically steady state of the velocity field through 10 viscous time units, is computed and the vortex-detection method of the imaginary part of the complex eigenvalue pair of the velocity-gradient tensor is applied to the velocity field. As a result, hairpin-like vortical structures are educed. Flow visualizations are provided of the processes of evolution that characterize hairpin vortices in the wall region of turbulent channel flow. The relationship is investigated between vortex dynamics and 2nd-and 4th-quadrant events, showing that ejections and sweeps play a fundamental role in the way the morphological evolution of a hairpin vortex develops with time.

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Section: More Recent Contextsupporting

confidence: 67%

Temporal Evolution of Vortical Structures in the Wall Region of Turbulent Channel Flow

Alfonsi

Primavera

2008

Flow Turbulence Combust

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“…These structures populate in the near-wall region, present quasi-regular distribution along the spanwise direction, and are always accompanied by trains of quasi-streamwise vortices with shorter length located in higher layer [ 3 , 4 ]. The origin of these streaks was attributed to the lift-up of low-momentum fluids from the wall under the induction of streamwise vortices [ 3 , 5 , 6 , 7 , 8 , 9 ], which transfers the energy from mean shear to turbulent fluctuations [ 10 , 11 , 12 ] and can be mathematically explained by a transient growth of three-dimensional (3D) disturbances due to the non-orthogonal eigenmodes in the linearized Navier-Stokes operator [ 13 , 14 , 15 , 16 ].…”

Section: Introductionmentioning

confidence: 99%

Wall-Normal Variation of Spanwise Streak Spacing in Turbulent Boundary Layer With Low-to-Moderate Reynolds Number

Wang

Pan

Wang

2018

Entropy

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Low-speed streaks in wall-bounded turbulence are the dominant structures in the near-wall turbulent self-sustaining cycle. Existing studies have well characterized their spanwise spacing in the buffer layer and below. Recent studies suggested the existence of these small-scale structures in the higher layer where large-scale structures usually receive more attention. The present study is thus devoted to extending the understanding of the streak spacing to the log layer. An analysis is taken on two-dimensional (2D) wall-parallel velocity fields in a smooth-wall turbulent boundary layer with Ret = 4402400, obtained via either 2D Particle Image Velocimetry (PIV) measurement taken here or public Direct Numerical Simulation (DNS). Morphological-based streak identification analysis yields a Re-independent log-normal distribution of the streak spacing till the upper bound of the log layer, based on which an empirical model is proposed to account for its wall-normal growth. The small-scale part of the spanwise spectra of the streamwise fluctuating velocity below y? = 100 is reasonably restored by a synthetic simulation that distributes elementary streak units based on the proposed empirical streak spacing model, which highlights the physical significance of streaks in shaping the small-scale part of the velocity spectra beyond the buffer layer.

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“…This layered structure of streamwise vorticity was experimentally discovered by Kasagi et al [21], and then numerically confirmed by Kim et al [22]. Although the vortex at the center is attenuated, the vorticity of the opposite sign becomes more intense in the cyclonic case than in the other cases, which can be verified by the values of the contour of the vorticity.…”

Section: Effects Of System Rotation On Tiltingmentioning

confidence: 79%

The Tilting Mechanism of a Longitudinal Vortical Structure in a Homogeneous Shear Flow with and Without Spanwise Rotation

Iida

Tsukamoto

Nagano

2007

Flow Turbulence Combust

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A longitudinal vortical structure is typically observed in near-wall turbulence. This vortical structure is elongated in the streamwise direction, though it is also tilted in the spanwise direction. The sense of this spanwise tilting is determined by the sign of the streamwise vorticity associated with the vortex, and longitudinal vortical structures with a different streamwise vorticity become asymmetric (mirror symmetric). The tilting must be due to the combined effects of the non-linear terms and mean spanwise vorticity associated with the mean shear. However, the detailed mechanism of the tilting is not well known. To study the tilting in detail, we performed direct numerical simulations of a homogeneous shear flow where the longitudinal vortical structures similar to those in the near-wall region are observed. In particular, the effects of spanwise system rotation as well as the Reynolds number on the vortical structure are studied. As a result, we found that spanwise system rotation has more marked effects on the vortical structure than the Reynolds number. When the system rotation is imposed in the same direction as the mean spanwise vorticity, the tilting is enhanced, while the system rotation of the opposite direction attenuates it. We also found that when the longitudinal vortical structure is tilted in the spanwise direction, it is sandwiched between the streamwise vorticity of the opposite sign. The cyclonic rotation enhances the streamwise vorticity of the opposite sign, though the longitudinal vortical structure at the center is attenuated. In the anticyclonic case, the streamwise vorticity of the opposite sign almost disappears and the longitudinal vortical structure is isolated from the surrounding flow.

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Streamwise pseudo-vortical structures and associated vorticity in the near-wall region of a wall-bounded turbulent shear flow

Cited by 30 publications

References 33 publications

Temporal Evolution of Vortical Structures in the Wall Region of Turbulent Channel Flow

Temporal Evolution of Vortical Structures in the Wall Region of Turbulent Channel Flow

Wall-Normal Variation of Spanwise Streak Spacing in Turbulent Boundary Layer With Low-to-Moderate Reynolds Number

The Tilting Mechanism of a Longitudinal Vortical Structure in a Homogeneous Shear Flow with and Without Spanwise Rotation

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