Scalar power spectra and turbulent scalar length scales of high-Schmidt-number passive scalar fields in turbulent boundary layers

2020 ◽  
Vol 5 (8) ◽  
Author(s):  
Mohammad Mohaghar ◽  
Lakshmi P. Dasi ◽  
Donald R. Webster
Keyword(s):  
Boundary Layers ◽  
Schmidt Number ◽  
Power Spectra ◽  
Scalar Fields ◽  
Passive Scalar ◽  
Turbulent Boundary Layers ◽  
Length Scales ◽  
High Schmidt Number

The geometric properties of high-Schmidt-number passive scalar iso-surfaces in turbulent boundary layers

2007 ◽  
Vol 588 ◽  
pp. 253-277 ◽  
Author(s):  
L. P. DASI ◽  
F. SCHUERG ◽  
D. R. WEBSTER
Keyword(s):  
Scalar Field ◽  
Boundary Layers ◽  
Schmidt Number ◽  
Passive Scalar ◽  
Turbulent Boundary Layers ◽  
Length Scale ◽  
Geometric Properties ◽  
Convective Regime ◽  
High Schmidt Number ◽  
Kolmogorov Scale

The geometric properties are quantified for concentration iso-surfaces of a high-Schmidt-number passive scalar field produced by an iso-kinetic source with an initial finite characteristic length scale released into the inertial layer of fully developed open-channel-flow turbulent boundary layers. The coverage dimension and other measures of two-dimensional transects of the passive scalar iso-surfaces are found to be scale dependent. The coverage dimension is around 1.0 at the order of the Batchelor length scale and based on our data increases in a universal manner to reach a local maximum at a length scale around the Kolmogorov scale. We introduce a new parameter called the coverage length underestimate, which demonstrates universal behaviour in the viscous–convective regime for these data and hence is a potentially useful practical tool for many mixing applications. At larger scales (in the inertial–convective regime), the fractal geometry measures are dependent on the Reynolds number, injection length scale, and concentration threshold of the iso-surfaces. Finally, the lacunarity of the iso-surface structure shows that the instantaneous scalar field is most inhomogenous around the length scale corresponding to the Kolmogorov scale.

High Freestream Turbulence Effects on Turbulent Boundary Layers

1996 ◽  
Vol 118 (2) ◽  
pp. 276-284 ◽  
Author(s):  
K. A. Thole ◽  
D. G. Bogard
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Boundary Layers ◽  
Outer Region ◽  
Power Spectra ◽  
Turbulent Boundary Layers ◽  
Freestream Turbulence ◽  
Length Scales ◽  
Turbulent Eddies ◽  
Viscous Shear

High freestream turbulence levels significantly alter the characteristics of turbulent boundary layers. Numerous studies have been conducted with freestreams having turbulence levels of 7 percent or less, but studies using turbulence levels greater than 10 percent have been essentially limited to the effects on wall shear stress and heat transfer. This paper presents measurements of the boundary layer statistics for the interaction between a turbulent boundary layer and a freestream with turbulence levels ranging from 10 to 20 percent. The boundary layer statistics reported in this paper include mean and rms velocities, velocity correlation coefficients, length scales, and power spectra. Although the freestream turbulent eddies penetrate into the boundary layer at high freestream turbulence levels, as shown through spectra and length scale measurements, the mean velocity profile still exhibits a log-linear region. Direct measurements of total shear stress (turbulent shear stress and viscous shear stress) confirm the validity of the log-law at high freestream turbulence levels. Velocity defects in the outer region of the boundary layer were significantly decreased resulting in negative wake parameters. Fluctuating rms velocities were only affected when the freestream turbulence levels exceeded the levels of the boundary layer generated rms velocities. Length scales and power spectra measurements showed large scale turbulent eddies penetrate to within y+ = 15 of the wall.

scholarly journals On the streamwise evolution of turbulent boundary layers in arbitrary pressure gradients

2002 ◽  
Vol 461 ◽  
pp. 61-91 ◽  
Author(s):  
A. E. PERRY ◽  
IVAN MARUSIC ◽  
M. B. JONES
Keyword(s):  
Boundary Layers ◽  
Scaling Laws ◽  
Power Spectra ◽  
Adverse Pressure Gradient ◽  
Turbulent Boundary Layers ◽  
Stream Velocity ◽  
Mean Flow ◽  
Mean Velocity ◽  
Law Of The Wall ◽  
The Mean

A new approach to the classic closure problem for turbulent boundary layers is presented. This involves, first, using the well-known mean-flow scaling laws such as the log law of the wall and the law of the wake of Coles (1956) together with the mean continuity and the mean momentum differential and integral equations. The important parameters governing the flow in the general non-equilibrium case are identified and are used for establishing a framework for closure. Initially closure is achieved here empirically and the potential for achieving closure in the future using the wall-wake attached eddy model of Perry & Marusic (1995) is outlined. Comparisons are made with experiments covering adverse-pressure-gradient flows in relaxing and developing states and flows approaching equilibrium sink flow. Mean velocity profiles, total shear stress and Reynolds stress profiles can be computed for different streamwise stations, given an initial upstream mean velocity profile and the streamwise variation of free-stream velocity. The attached eddy model of Perry & Marusic (1995) can then be utilized, with some refinement, to compute the remaining unknown quantities such as Reynolds normal stresses and associated spectra and cross-power spectra in the fully turbulent part of the flow.

scholarly journals Spectrum of Passive Scalar at Very High Schmidt Number in Turbulence

2015 ◽  
Vol 9 (0) ◽  
pp. 3401019-3401019 ◽  
Author(s):  
Toshiyuki GOTOH ◽  
Takeshi WATANABE ◽  
Hideaki MIURA
Keyword(s):  
Schmidt Number ◽  
Passive Scalar ◽  
High Schmidt Number ◽  
Very High

Computing Blunt Body Flows on Coarse Grids Using Vorticity Confinement

2002 ◽  
Vol 124 (4) ◽  
pp. 876-885 ◽  
Author(s):  
M. Fan ◽  
Y. Wenren ◽  
W. Dietz ◽  
M. Xiao ◽  
J. Steinhoff
Keyword(s):  
Boundary Layers ◽  
Three Dimensional ◽  
Scalar Fields ◽  
Passive Scalar ◽  
Navier Stokes ◽  
Small Scale ◽  
Eddy Simulation ◽  
Discrete Equations ◽  
Vorticity Confinement ◽  
Helicopter Landing

Over the last few years, a new flow computational methodology, vorticity confinement, has been shown to be very effective in treating concentrated vortical regions. These include thin vortex filaments which can be numerically convected over arbitrary distances on coarse Eulerian grids, while requiring only ∼2 grid cells across their cross section. They also include boundary layers on surfaces “immersed” in nonconforming uniform Cartesian grids, with no requirement for grid refinement or complex logic near the surface. In this paper we use vorticity confinement to treat flow over blunt bodies, including attached and separating boundary layers, and resulting turbulent wakes. In the wake it serves as a new, simple effective large-eddy simulation (LES). The same basic idea is applied to all of these features: At the smallest scales (∼2 cells) the vortical structures are captured and treated, effectively, as solitary waves that are solutions of nonlinear discrete equations on the grid. The method does not attempt to accurately discretize the Euler/Navier-Stokes partial differential equations (pde’s) for these small scales, but, rather, serves as an implicit, nonlinear model of the structures, directly on the grid. The method also allows the boundary layer to be effectively “captured.” In the turbulent wake, where there are many scales, small structures represent an effective small scale energy sink. However, they do not have the unphysical spreading due to numerical diffusion at these scales, which is present in conventional computational methods. The basic modeling idea is similar to that used in shock capturing, where intrinsically discrete equations are satisfied in thin, modeled regions. It is argued that, for realistic high Reynolds number flows, this direct, grid-based modeling approach is much more effective than first formulating model pde’s for the small scale, turbulent vortical regions and then discretizing them. Results are presented for three-dimensional flows over round and square cylinders and a realistic helicopter landing ship. Comparisons with experimental data are given. Finally, a new simpler formulation of vorticity confinement is given together with a related formulation for confinement of passive scalar fields.

Comparison of Subgrid Closure Methods for Passive Scalar Variance at High Schmidt Number

2015 ◽  
Vol 38 (11) ◽  
pp. 2087-2095 ◽  
Author(s):  
Krzysztof Wojtas ◽  
Łukasz Makowski ◽  
Wojciech Orciuch ◽  
Jerzy Bałdyga
Keyword(s):  
Schmidt Number ◽  
Passive Scalar ◽  
High Schmidt Number ◽  
Scalar Variance

scholarly journals A wall-wake model for the turbulence structure of boundary layers. Part 2. Further experimental support

1995 ◽  
Vol 298 ◽  
pp. 389-407 ◽  
Author(s):  
Ivan Marušić ◽  
A. E. Perry
Keyword(s):  
Boundary Layers ◽  
Cone Angle ◽  
Power Spectra ◽  
Turbulent Boundary Layers ◽  
Turbulence Structure ◽  
Reynolds Stresses ◽  
Hot Wire ◽  
Equilibrium Pressure ◽  
Extended Theory ◽  
Wake Model

In Part 1 an extension of the attached eddy hypothesis was developed and applied to equilibrium pressure gradient turbulent boundary layers. In this paper the formulation is applied to data measured by the authors from non-equilibrium layers and agreement with the extended theory is encouraging. Also power spectra of the Reynolds stresses as developed from the extended theory compare favourably with experiment. The experimental data include a check of cone-angle effects by using a flying hot wire.

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