One-Equation Near-Wall Turbulence Modeling With the Aid of Direct Simulation Data

1993 ◽  
Vol 115 (2) ◽  
pp. 196-205 ◽  
Author(s):  
W. Rodi ◽  
N. N. Mansour ◽  
V. Michelassi
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Flow ◽  
Equation Model ◽  
Wall Turbulence ◽  
Mean Flow ◽  
Simulation Data ◽  
Length Scales ◽  
Velocity Scale ◽  
Layer Flow ◽  
Near Wall

The length scales appearing in the relations for the eddy viscosity and dissipation rate in one-equation models were evaluated from direct numerical (DNS) simulation data for developed channel and boundary-layer flow at two Reynolds numbers each. To prepare the ground for the evaluation, the distribution of the most relevant mean-flow and turbulence quantities is presented and discussed, also with respect to Reynolds-number influence and to differences between channel and boundary-layer flow. An alternative model is examined in which (v′2)1/2 is used as velocity scale instead of k1/2. With this velocity scale, the length scales now appearing in the model follow closely a linear relationship near the wall. The resulting length-scale relations together with a DNS based relation between v′2/k and y* = k1/2y/v form a new one-equation model for use in near-wall regions. The new model was tested as near wall component of a two-layer model by application to developed-channel, boundary-layer and backward-facing-step flows.

scholarly journals Explicit Filtering and Reconstruction Turbulence Modeling for Large-Eddy Simulation of Neutral Boundary Layer Flow

2005 ◽  
Vol 62 (7) ◽  
pp. 2058-2077 ◽  
Author(s):  
Fotini Katopodes Chow ◽  
Robert L. Street ◽  
Ming Xue ◽  
Joel H. Ferziger
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Flow ◽  
Eddy Viscosity ◽  
Wall Stress ◽  
Stress Model ◽  
Viscosity Models ◽  
Neutral Boundary Layer ◽  
Large Eddy ◽  
Layer Flow ◽  
Near Wall

Abstract Standard turbulence closures for large-eddy simulations of atmospheric flow based on finite-difference or finite-volume codes use eddy-viscosity models and hence ignore the contribution of the resolved subfilter-scale stresses. These eddy-viscosity closures are unable to produce the expected logarithmic region near the surface in neutral boundary layer flows. Here, explicit filtering and reconstruction are used to improve the representation of the resolvable subfilter-scale (RSFS) stresses, and a dynamic eddy-viscosity model is used for the subgrid-scale (SGS) stresses. Combining reconstruction and eddy-viscosity models yields a sophisticated (and higher order) version of the well-known mixed model of Bardina et al.; the explicit filtering and reconstruction procedures clearly delineate the contribution of the RSFS and SGS motions. A near-wall stress model is implemented to supplement the turbulence models and account for the stress induced by filtering near a solid boundary as well as the effect of the large grid aspect ratio. Results for neutral boundary layer flow over a rough wall using the combined dynamic reconstruction model and the near-wall stress model show excellent agreement with similarity theory logarithmic velocity profiles, a significant improvement over standard eddy-viscosity closures. Stress profiles also exhibit the expected pattern with increased reconstruction level.

PHYSICS OF COHERENT STRUCTURES OF TURBULENT FLOW IN NEAR-WALL REGION OF A VIBRATING PLATE

2010 ◽  
Vol 24 (13) ◽  
pp. 1433-1436
Author(s):  
L. X. ZHANG
Keyword(s):  
Boundary Layer ◽  
Coherent Structures ◽  
Boundary Layer Flow ◽  
Wall Layer ◽  
Basis Functions ◽  
Galerkin Projection ◽  
Wall Region ◽  
Layer Flow ◽  
Near Wall ◽  
Vibrating Plate

The focus of this paper is on physics of coherent structures in boundary layer flow in near-wall region of a vibrating plate. A dynamical model is developed based on Galerkin projection of the governing equation of the wall layer flow onto a subspace spanned by the orthogonal divergence-free Fourier basis functions. The interactive physics of the coherent structures with the wall vibration is studied with the established model truncated at any order. The compared results show that the prevailing coherent structures in the layer flow near a vibrating wall region are captured.

scholarly journals The centrifugal instability of the boundary-layer flow over a slender rotating cone in an enforced axial free stream

2015 ◽  
Vol 788 ◽  
pp. 70-94 ◽  
Author(s):  
Z. Hussain ◽  
S. J. Garrett ◽  
S. O. Stephen ◽  
P. T. Griffiths
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Flow ◽  
Axial Flow ◽  
Instability Mode ◽  
Mean Flow ◽  
Flow Component ◽  
Centrifugal Instability ◽  
Rotating Cone ◽  
Layer Flow ◽  
First Time

In this study, a new centrifugal instability mode, which dominates within the boundary-layer flow over a slender rotating cone in still fluid, is used for the first time to model the problem within an enforced oncoming axial flow. The resulting problem necessitates an updated similarity solution to represent the basic flow more accurately than previous studies in the literature. The new mean flow field is subsequently perturbed, leading to disturbance equations that are solved via numerical and short-wavelength asymptotic approaches, yielding favourable comparisons with existing experiments. Essentially, the boundary-layer flow undergoes competition between the streamwise flow component, due to the oncoming flow, and the rotational flow component, due to effect of the spinning cone surface, which can be described mathematically in terms of a control parameter, namely the ratio of streamwise to axial flow. For a slender cone rotating in a sufficiently strong axial flow, the instability mode breaks down into Görtler-type counter-rotating spiral vortices, governed by an underlying centrifugal mechanism, which is consistent with experimental and theoretical studies for a slender rotating cone in otherwise still fluid.

Turbulent boundary-layer flow over fixed aerodynamically rough two-dimensional sinusoidal waves

1996 ◽  
Vol 312 ◽  
pp. 1-37 ◽  
Author(s):  
W. Gong ◽  
Peter A. Taylor ◽  
Andreas Dörnbrack
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Secondary Flow ◽  
Boundary Layer Flow ◽  
Supporting Evidence ◽  
Mean Flow ◽  
Maximum Slope ◽  
Eddy Simulation ◽  
Turbulent Boundary Layer Flow ◽  
Layer Flow

Results from a wind tunnel study of aerodynamically rough turbulent boundary-layer flow over a sinusoidal surface are presented. The waves had a maximum slope (ak) of 0.5 and two surface roughnesses were used. For the relatively rough surface the flow separated in the wave troughs while for the relatively smooth surface it generally remained attached. Over the relatively smooth-surfaced waves an organized secondary flow developed, consisting of vortex pairs of a scale comparable to the boundary-layer depth and aligned with the mean flow. Large-eddy simulation studies model the flows well and provide supporting evidence for the existence of this secondary flow.

Turbulent Boundary Layer Flow Through a Gap in a Wall Mounted Roughness Element

1981 ◽  
Vol 103 (1) ◽  
pp. 97-103
Author(s):  
W. H. Schofield ◽  
D. S. Barber ◽  
E. Logan
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Boundary Layer Flow ◽  
Roughness Element ◽  
Internal Layer ◽  
Mean Flow ◽  
Equilibrium Conditions ◽  
Flow Through ◽  
Turbulent Boundary Layer Flow ◽  
Layer Flow

The center-line development of a turbulent boundary layer flow through a gap in an isolated wall mounted roughness element has been studied experimentally. The centerline flow downstream of the gap can be divided into a distortion region followed by a readjustment region. The nature of the distortion produced by the gap varies with gap size and thus flows downstream of large gaps were found to differ significantly from those through small gaps. After distortion the layer readjusts itself and approaches equilibrium conditions of an undisturbed zero pressure gradient layer. The readjustment starts near the wall with the turbulence adjustment preceding the mean flow adjustment. For flow through all six gap sizes the growth of the centerline internal layer can be described by a single function if internal layer height and distance from the gap are non-dimensionalized with the local wall length scale. Well downstream of the gap it is shown that all six centerline flows are similar and are approaching equilibrium conditions in a similar manner.

Characterization of Thermals in a Heated Turbulent Boundary Layer

2019 ◽  
Author(s):  
Kadeem Dennis ◽  
Kamran Siddiqui
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Mixed Convection ◽  
Boundary Layer Flow ◽  
Three Dimensional ◽  
Mean Flow ◽  
Buoyant Force ◽  
Viscous Shear ◽  
Turbulent Boundary Layer Flow ◽  
Layer Flow

Abstract The hydrodynamic boundary layer encountered in many practical engineering systems is turbulent in nature and known to play a significant role in governing the induced friction drag and species transport. In turbulent boundary layer flows, heat transfer is often involved which increases flow complexity due to the influence of buoyancy. When the buoyant force is sufficiently large in magnitude, thermals carrying heated fluid are known to detach and rise from the wall. Literature review shows that in mixed convection, thermals have been primarily identified through qualitative flow visualizations and there is a scarcity of their quantitative assessment. Furthermore, the evolution of thermals in the boundary layer with respect to flow inertia and viscous shear is not well-understood. Hence, there is a need for a better understanding of the dynamics of thermals in mixed convection turbulent boundary layer flow. The objective of this study is to experimentally investigate the three-dimensional nature of thermals rising from a turbulent boundary layer flow over a heated smooth horizontal flat plate. Experiments were performed in a closed loop low-disturbance wind tunnel with a test section featuring a 1 m long heated bottom wall. The multi-plane particle image velocimetry (PIV) technique was used to capture images in multiple planes with respect to the turbulent boundary layer mean flow direction for three-dimensional characterization. The measurements were conducted at Richardson numbers (Ri) of 0.3, 1.0, and 2.0. Flow visualization images are used to describe the nature of thermals and the dynamical processes involved during their interaction with bulk boundary layer flow. An image processing algorithm to detect thermals is then detailed and applied to experimental images. The performance of the new algorithm is then assessed in its ability to detect thermals.

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