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**Harvard**

Bäckar, J. (2016) *Robust Numerical Wall Functions Implemented in OpenFOAM*. Göteborg : Chalmers University of Technology (Technical report - Department of Applied Mechanics, Chalmers University of Technology, Göteborg, Sweden, nr: 1652).

** BibTeX **

@book{

Bäckar2016,

author={Bäckar, Jon-Anders},

title={Robust Numerical Wall Functions Implemented in OpenFOAM},

abstract={This thesis presents two new numerical wall models for computing Reynolds-Averaged-
Navier-Stokes (RANS) equations with low-Reynolds-number turbulence models. The
objective is to considerably reduce the total central processing unit (CPU) cost of the
numerical simulations of wall bounded flows while maintaining the accuracy of any
low-Reynolds-number turbulence model.
When calculating turbulent flow problems, a tremendous speed-up may be achieved
by decoupling the solution of the boundary layer from the bulk region by use of a wall
function. However, most wall functions are quite limited and based on assumptions which
are not valid in complex, non-equilibrium flows. A decade ago, the numerical wall function
was born at the University of Manchester [9], [7], solving boundary-layer-type transport
equations across the boundary layer on a separate sub-grid. This approach removed most
assumptions, but introduced a strong coupling to the turbulence model, and hence, made
it cumbersome to implement and maintain.
The present wall functions solve full momentum and energy equations on a sub-grid,
using face fluxes of advection and dissipation to transfer the solution to and from the
sub-grid. The innovative use of face fluxes, decouples the wall function from the turbulence
models’ production and dissipation terms, and hence, makes it general to all low-Reynolds-
number turbulence models. It has been tested on channel flow, axisymmetric impinging
jet, and backward facing step using Launder-Sharma turbulence model [16]. Compared to
low-Reynolds-number calculations, the results show perfect agreement to one-sixth of the
computational cost.
Further on, an attempt to update the general recommendation on grid design for
low-Reynolds-number turbulence models is also made.},

publisher={Institutionen för tillämpad mekanik, Strömningslära, Chalmers tekniska högskola,},

place={Göteborg},

year={2016},

series={Technical report - Department of Applied Mechanics, Chalmers University of Technology, Göteborg, Sweden, no: 1652},

keywords={Computational Fluid Dynamics, OpenFOAM, impinging jet, numerical wall function, speed-up},

note={65},

}

** RefWorks **

RT Dissertation/Thesis

SR Print

ID 236699

A1 Bäckar, Jon-Anders

T1 Robust Numerical Wall Functions Implemented in OpenFOAM

T2 -- new Recommendations for Near-Wall Resolution using low-Reynolds-number Turbulence Models

YR 2016

AB This thesis presents two new numerical wall models for computing Reynolds-Averaged-
Navier-Stokes (RANS) equations with low-Reynolds-number turbulence models. The
objective is to considerably reduce the total central processing unit (CPU) cost of the
numerical simulations of wall bounded flows while maintaining the accuracy of any
low-Reynolds-number turbulence model.
When calculating turbulent flow problems, a tremendous speed-up may be achieved
by decoupling the solution of the boundary layer from the bulk region by use of a wall
function. However, most wall functions are quite limited and based on assumptions which
are not valid in complex, non-equilibrium flows. A decade ago, the numerical wall function
was born at the University of Manchester [9], [7], solving boundary-layer-type transport
equations across the boundary layer on a separate sub-grid. This approach removed most
assumptions, but introduced a strong coupling to the turbulence model, and hence, made
it cumbersome to implement and maintain.
The present wall functions solve full momentum and energy equations on a sub-grid,
using face fluxes of advection and dissipation to transfer the solution to and from the
sub-grid. The innovative use of face fluxes, decouples the wall function from the turbulence
models’ production and dissipation terms, and hence, makes it general to all low-Reynolds-
number turbulence models. It has been tested on channel flow, axisymmetric impinging
jet, and backward facing step using Launder-Sharma turbulence model [16]. Compared to
low-Reynolds-number calculations, the results show perfect agreement to one-sixth of the
computational cost.
Further on, an attempt to update the general recommendation on grid design for
low-Reynolds-number turbulence models is also made.

PB Institutionen för tillämpad mekanik, Strömningslära, Chalmers tekniska högskola,

T3 Technical report - Department of Applied Mechanics, Chalmers University of Technology, Göteborg, Sweden, no: 1652

LA eng

OL 30