Wall Functions (wall + function)

Distribution by Scientific Domains

Selected Abstracts

Three-dimensional flow modelling and sediment transport in the River Klarälven

Bijan Dargahi
Abstract A three-dimensional ,ow model that uses the RNG k - , turbulence model and a non-equilibrium wall function was applied to the River Klarälven in the southwest part of Sweden. The objectives were to study the nature of the ,ow in the river bifurcation and to investigate the short-term sediment transport patterns in the river. The effectiveness of three-dimensional ,ow models depends upon: (1) how well the river geometry and it surface roughness are modelled; and (2) the choice of the closure model. Improvements were obtained by modelling the river in two parts: the entire river reach, and a selected part. Composite Manning coef,cients were used to account for roughness properties. The method requires a calibration process that ensures the water surface pro,les match the ,eld data. The k - , model under-predicted both the extent of ,ow separation zones and the number of secondary ,ow regions having a spiral motion, in comparison with the RNG k - , model. The 3-D model could predict with good accuracy both the general and secondary ,ow ,elds in the river. The results agreed well with the 3-D velocity measurements using an acoustic Doppler current pro,ler. A conceptual model was developed that accounts for the development of secondary ,ows in a river bifurcation having two bends. The main ,ow feature in the river cross-sections was the existence of multiple counter-rotating spiral motions. The number of spiral motions increased as the river bends were approached. The river bends also caused vorticity intensi,cation and increased the vertical velocities. The application of the 3-D ,ow model was extended by solving the sediment continuity equation. The sediment transport patterns were related to the secondary ,ow ,elds in the river. The sediment transport patterns at the river bifurcations are characterized by the growth of a sandbank. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Simulation of coherent structures in turbulent boundary layer using Gao,Yong equations of turbulence

Bo Liu
Abstract The equations of incompressible turbulent flow developed by the Gao,Yong turbulence model have two important features. First, they do not contain any empirical coefficients or wall functions. Second, the series representation of turbulence energy equation reflects multi-scale structures of the nonlinearity of turbulence, and, therefore, is capable of describing both statistical mean flows and the coherent structures. This paper presents some simulation results of a two-dimensional turbulent boundary layer with zero pressure gradient based on Gao,Yong equations of turbulence. With a staggered grid arrangement, an incompressible SIMPLE code was used in the simulations. The simulated coherent structures have verified the adaptability of the newly derived equations to real intermittent turbulent flows. The effect of the orders of the energy equation and computational grid scales on the detection of coherent structures is also investigated. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(5): 287,298, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20019 [source]

Assessment of two-equation turbulence modelling for high Reynolds number hydrofoil flows

N. Mulvany
Abstract This paper presents an evaluation of the capability of turbulence models available in the commercial CFD code FLUENT 6.0 for their application to hydrofoil turbulent boundary layer separation flow at high Reynolds numbers. Four widely applied two-equation RANS turbulence models were assessed through comparison with experimental data at Reynolds numbers of 8.284×106 and 1.657×107. They were the standard k,,model, the realizable k,,model, the standard k,,model and the shear-stress-transport (SST) k,,model. It has found that the realizable k,,turbulence model used with enhanced wall functions and near-wall modelling techniques, consistently provides superior performance in predicting the flow characteristics around the hydrofoil. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Calculation of turbulent fluid flow and heat transfer in ducts by a full Reynolds stress model

Masoud Rokni
Abstract A computational method has been developed to predict the turbulent Reynolds stresses and turbulent heat fluxes in ducts by different turbulence models. The turbulent Reynolds stresses and other turbulent flow quantities are predicted with a full Reynolds stress model (RSM). The turbulent heat fluxes are modelled by a SED concept, the GGDH and the WET methods. Two wall functions are used, one for the velocity field and one for the temperature field. All the models are implemented for an arbitrary three-dimensional channel. Fully developed condition is achieved by imposing cyclic boundary conditions in the main flow direction. The numerical approach is based on the finite volume technique with a non-staggered grid arrangement. The pressure,velocity coupling is handled by using the SIMPLEC-algorithm. The convective terms are treated by the van Leer scheme while the diffusive terms are handled by the central-difference scheme. The hybrid scheme is used for solving the , equation. The secondary flow generation using the RSM model is compared with a non-linear k,, model (non-linear eddy viscosity model). The overall comparison between the models is presented in terms of the friction factor and Nusselt number. Copyright © 2003 John Wiley & Sons, Ltd. [source]