Effects of the spanwise heterogeneity of a three-dimensional wavy wall on momentum and scalar transport

2021 ◽  
Vol 33 (5) ◽  
pp. 055116
Author(s):  
Enwei Zhang ◽  
Xiaoliang Wang ◽  
Qingquan Liu
Keyword(s):  
Three Dimensional ◽  
Scalar Transport ◽  
Wavy Wall

Mixing Simulations of a Wankel Pump as a Micromixer

2016 ◽  
Author(s):  
S. Wan ◽  
M. S. W. Lau ◽  
J. Leong ◽  
N. An ◽  
K. L. Goh
Keyword(s):  
Transport Equation ◽  
Flow Structure ◽  
Three Dimensional ◽  
Scalar Transport ◽  
Species Concentration ◽  
Pump Chamber ◽  
Vertical Dispersion ◽  
General Scalar ◽  
Numerical Mixing ◽  
Binary Mixing

The present work was movitated by an earlier study on pumps based on a Wankel geometry (Wankel pumps) which revealed a flow structure, rich in three dimensional vortices (including Taylor like counter-rotating ones), in the pump chamber, suggesting the possibility of a Wankel pump of also functioning as a mixer. To this end, numerical mixing experiments were run using the general scalar transport equation to model the evolution of species concentration. Interestingly, it was observed that species dispersion occurs predominantly sideways (laterally) and that vertical dispersion is almost non-existent. In other words, for binary mixing of two species with a Wankel pump, they must be introduced side by side to ensure effective mixing.

scholarly journals Contrasts between momentum and scalar transport over very rough surfaces

2019 ◽  
Vol 880 ◽  
pp. 32-58 ◽  
Author(s):  
Qi Li ◽  
Elie Bou-Zeid
Keyword(s):  
Large Scale ◽  
Rough Surfaces ◽  
Three Dimensional ◽  
Turbulent Channel Flow ◽  
Passive Scalar ◽  
Scalar Transport ◽  
Roughness Sublayer ◽  
Quadrant Analysis ◽  
Roughness Elements ◽  
Dispersive Fluxes

Large-eddy simulations are conducted to contrast momentum and passive scalar transport over large, three-dimensional roughness elements in a turbulent channel flow. Special attention is given to the dispersive fluxes, which are shown to be a significant fraction of the total flux within the roughness sublayer. Based on pointwise quadrant analysis, the turbulent components of the transport of momentum and scalars are found to be similar in general, albeit with increasing dissimilarity for roughnesses with low frontal blockage. However, strong dissimilarity is noted between the dispersive momentum and scalar fluxes, especially below the top of the roughness elements. In general, turbulence is found to transport momentum more efficiently than scalars, while the reverse applies to the dispersive contributions. The effects of varying surface geometries, measured by the frontal density, are pronounced on turbulent fluxes and even more so on dispersive fluxes. Increasing frontal density induces a general transition in the flow from a wall bounded type to a mixing layer type. This transition results in an increase in the efficiency of turbulent momentum transport, but the reverse occurs for scalars due to reduced contributions from large-scale motions in the roughness sublayer. This study highlights the need for distinct parameterizations of the turbulent and dispersive fluxes, as well as the importance of considering the contrasts between momentum and scalar transport for flows over very rough surfaces.

SUCCA3D—An Alternative Scheme to Reduce False Diffusion in Three-Dimensional Flows

1993 ◽  
Vol 207 (5) ◽  
pp. 307-313 ◽  
Author(s):  
T J Scanlon ◽  
C Carey ◽  
S M Fraser
Keyword(s):  
Three Dimensional ◽  
Higher Order ◽  
Upwind Scheme ◽  
Scalar Transport ◽  
Benchmark Test ◽  
Alternative Scheme ◽  
First Order ◽  
Quick Scheme ◽  
Scalar Variable ◽  
Convection Dominated

An alternative flow-oriented convection algorithm is presented which acts as a replacement for the first-order accurate UPWIND scheme in three-dimensional scalar transport. The scheme, formally titled SUCCA3D (skew upwind corner convection algorithm 3D), attempts to follow local streamlines, thus directly reducing the multi-dimensional false diffusion of the conserved scalar. In a standard benchmark test of pure convection across a three-dimensional cavity the SUCCA3D scheme was found to compare favourably with alternative schemes such as UPWIND and the higher-order QUICK scheme. The results highlight the potential of the SUCCA3D code for the reduction of three-dimensional false diffusion of a scalar variable in convection-dominated flows.

The Effect of Turbulence and Scalar Transport Models on Prediction of Worker Exposure to Aerosols

2003 ◽  
Author(s):  
Jun Li ◽  
Ismail B. Celik ◽  
Ibrahim Yavuz ◽  
Steven E. Guffey ◽  
Aaron J. Bird
Keyword(s):  
Turbulence Model ◽  
Human Body ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Scalar Transport ◽  
Breathing Zone ◽  
Eddy Simulation ◽  
Particle Tracking Method ◽  
Common Location ◽  
Concentration Levels

The present study is concerned with the relative concentrations of contaminants in the breathing-zone (BZ) when toxic airborne contaminants are released within an armlength in front of a worker, a common location that often leads to high exposures. Three-dimensional turbulent flow around a modeled human body in a wind tunnel has been simulated numerically and the results from various models are compared with each other. A model was built using a mesh generator to represent a real human body as closely as possible. Four different turbulence models, namely, standard k-ε turbulence model, RNG k-ε turbulence model, Reynolds Stress turbulence model (RSM) and Large Eddy Simulation (LES), were used to evaluate their effect on the predicted concentration levels used in assessing the exposure of the worker. Results from Eulerian scalar transport method and Lagrangian particle tracking method are also compared. Concentration levels are calculated at various sampling locations in the vicinity of the human face. It is found that the predicted concentration varies significantly from model to model: at the breathing zone the coefficient of variation for predicted concentration is 30%.

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