Print ISSN: 1681-6900

Online ISSN: 2412-0758

Keywords : w model

A Numerical Prediction of the Turbulence Parameters in Two-Dimensional Ventilated Rooms

Ayad M. Salman

Engineering and Technology Journal, 2011, Volume 29, Issue 6, Pages 1052-1068

Turbulent flow in two-dimensional ventilated room has been numerically
simulated in the present research. A modified form of Wilcox's two-equation LRN
k-w model is proposed for predicting internal turbulent ventilation flows. The
modifications include adding a turbulent cross-diffusion term in the w-equation,
and re-establishing the closure constants and damping functions, with the
application of the wall-function method. The turbulent cross-diffusion for specific
rate, w, is modeled with two parts: a second-order diffusion term and a first-order
cross-diffusion term.
The air was used as the working fluid, and the length of ventilation enclosure (9
m), and height of ventilation enclosure (3 m). The study was made for Reynolds
number values of (Re=7.5´103).
A finite volume method is used with a staggered grid arrangement. The
continuity, momentum and turbulence model equations are solved with hybrid
method by using SIMPLE algorithm. A computer program in FORTRAN (90) was
developed to carry on the numerical solution. The Computational algorithm is
capable of calculating the hydrodynamic and turbulence properties such as the
velocity, and turbulent kinetic energy, specific dissipation rate (w), turbulent
Reynolds stress, and terms of convection, production, diffusion, destruction,
turbulent cross-diffusion and square root mean of fluctuating velocity. The results
showed the peak value of velocity near the wall jet region and negative value of
velocity near the bottom region (floor region) i.e. recirculating zone. The
maximum value of turbulent kinetic energy near wall jet region in the first
horizontal section of ventilation enclosure, and the profile become flattened in the
second section of ventilation enclosure room. The same behavior in the turbulent
Reynolds stress distribution because depending on velocity in his calculations. The
same behavior between production term and destruction term but the values of
production term is positive and the value of destruction term is negative. The
distribution approximately symmetry.
The numerical results were compared with other previous theoretical results.
The agreement was good, confirming the reliability of the proposed mathematical
model and computational algorithm in investigating the performance of turbulence
model in numerical simulation of turbulent ventilation flows.