Models Based on Dynamical Features of the Wall Layer

1990 ◽  
Vol 43 (5S) ◽  
pp. S232-S239 ◽  
Author(s):  
J. D. A. Walker
Keyword(s):  
Three Dimensional ◽  
Adverse Pressure Gradient ◽  
Wall Layer ◽  
Boundary Layer Turbulence ◽  
Dimensional Boundary ◽  
Layer Velocity ◽  
Wall Flow ◽  
Dynamical Features ◽  
The Mean ◽  
Layer Flow

Recent experimental and theoretical results related to the turbulence production process near a wall are reviewed. It is argued that the principal element of boundary-layer turbulence is the convected hairpin vortex and that bursting of the wall-layer flow is a viscous-inviscid interaction provoked by the adverse pressure gradient due to the vortex. The consequences of this picture for the development of models for the mean near-wall flow are discussed. Recent models for the mean wall-layer velocity profile, in both two- and three-dimensional boundary layers, which are based on the dynamical picture presented here, are reviewed.

scholarly journals A numerical study of strained three-dimensional wall-bounded turbulence

2000 ◽  
Vol 416 ◽  
pp. 75-116 ◽  
Author(s):  
G. N. COLEMAN ◽  
J. KIM ◽  
P. R. SPALART
Keyword(s):  
Pressure Gradient ◽  
Boundary Layers ◽  
Numerical Study ◽  
Three Dimensional ◽  
Adverse Pressure Gradient ◽  
Model Testing ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Dimensional Boundary ◽  
The Mean

Channel flow, initially fully developed and two-dimensional, is subjected to mean strains that emulate the effect of rapid changes of streamwise and spanwise pressure gradients in three-dimensional boundary layers, ducts, or diffusers. As in previous studies of homogeneous turbulence, this is done by deforming the domain of a direct numerical simulation (DNS); here however the domain is periodic in only two directions and contains parallel walls. The velocity difference between the inner and outer layers is controlled by accelerating the channel walls in their own plane, as in earlier studies of three-dimensional channel flows. By simultaneously moving the walls and straining the domain we duplicate both the inner and outer regions of the spatially developing case. The results are used to address basic physics and modelling issues. Flows subject to impulsive mean three-dimensionality with and without the mean deceleration of an adverse pressure gradient (APG) are considered: strains imitating swept-wing and pure skewing (sideways turning) three-dimensional boundary layers are imposed. The APG influences the structure of the turbulence, measured for example by the ratio of shear stress to kinetic energy, much more than does the pure skewing. For both deformations, the evolution of the Reynolds stress is profoundly affected by changes to the velocity–pressure-gradient correlation Πij. This term – which represents the finite time required for the mean strain to modify the shape and orientation of the turbulent motions – is primarily responsible for the difference (lag) in direction between the mean shear and the turbulent shear stresses, a well-known feature of perturbed three-dimensional boundary layers. Files containing the DNS database and model-testing software are available from the authors for distribution, as tools for future closure-model testing.

Instability in a viscous flow driven by streamwise vortices

2001 ◽  
Vol 432 ◽  
pp. 127-166 ◽  
Author(s):  
K. W. BRINCKMAN ◽  
J. D. A. WALKER
Keyword(s):  
Boundary Layer ◽  
Numerical Solutions ◽  
Three Dimensional ◽  
Wall Layer ◽  
External Flow ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Wall Flow ◽  
Turbulent Wall ◽  
Near Wall

Unsteady separation processes at large finite, Reynolds number, Re, are considered, as well as the possible relation to existing descriptions of boundary-layer separation in the limit Re → ∞. The model problem is a fundamental vortex-driven three-dimensional flow, believed to be relevant to bursting near the wall in a turbulent boundary layer. Bursting is known to be associated with streamwise vortex motion, but the vortex/wall interactions that drive the near-wall flow toward breakdown have not yet been fully identified. Here, a simulation of symmetric counter-rotating vortices is used to assess the influence of sustained pumping action on the development of a viscous wall layer. The calculated solutions describe a three-dimensional flow at finite Re that is independent of the streamwise coordinate and consists of a crossflow plane motion, with a developing streamwise flow. The unsteady problem is constructed to mimic a typical cycle in turbulent wall layers and numerical solutions are obtained over a range of Re. Recirculating eddies develop rapidly in the near-wall flow, but these eddies are eventually bisected by alleyways which open up from the external flow region to the wall. At sufficiently high Re, an oscillation was found to develop in the streamwise vorticity field near the alleyways with a concurrent evolution of a local spiky behaviour in the wall shear. Above a critical value of Re, the oscillation grows rapidly in amplitude and eventually penetrates the external flow field, suggesting the onset of an unstable wall-layer breakdown. Local zones of severely retarded streamwise velocity are computed which are reminiscent of the low-speed streaks commonly observed in turbulent boundary layers. A number of other features also bear a resemblance to observed coherent structure in the turbulent wall layer.

Swirling Flow Over an Oscillatory Stretchable Disk

2014 ◽  
Vol 30 (4) ◽  
pp. 339-347 ◽  
Author(s):  
S. Munawar ◽  
A. Ali ◽  
N. Saleem ◽  
A. Naqeeb
Keyword(s):  
Oscillatory Flow ◽  
Swirling Flow ◽  
Three Dimensional ◽  
Finite Domain ◽  
Governing Equations ◽  
Infinite Domain ◽  
Similarity Transformations ◽  
Sinusoidal Oscillations ◽  
Dimensional Boundary ◽  
Layer Flow

AbstractIn this work a numerical investigation has been conducted to study the unsteady oscillatory flow of a viscous fluid induced by a swirling disk. The disk stretches radially with the time-based sinusoidal oscillations. The governing equations for the three-dimensional boundary layer-flow are normalized using a suitable set of similarity transformations. The normalized partial differential equations are then solved numerically using a finite difference scheme by altering the semi-infinite domain to a finite domain. The effects of various imperative parameters on the oscillatory flow are discussed with graphs and tables.

Three-Dimensional Boundary-Layer Flow About an Ablating Slender Cone

1969 ◽  
Vol 91 (4) ◽  
pp. 632-648 ◽  
Author(s):  
T. K. Fannelop ◽  
P. C. Smith
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Flow ◽  
Cone Angle ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Boundary Layer Equations ◽  
Transverse Curvature ◽  
Dimensional Boundary ◽  
Layer Flow

A theoretical analysis is presented for three-dimensional laminar boundary-layer flow about slender conical vehicles including the effect of transverse surface curvature. The boundary-layer equations are solved by standard finite difference techniques. Numerical results are presented for hypersonic flow about a slender blunted cone. The influences of Reynolds number, cone angle, and mass transfer are studied for both symmetric flight and at angle-of-attack. The effects of transverse curvature are substantial at the low Reynolds numbers considered and are enhanced by blowing. The crossflow wall shear is largely unaffected by transverse curvature although the peak velocity is reduced. A simplified “channel flow” analogy is suggested for the crossflow near the wall.

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