Engineering and Technology Journal (Apr 2011)
A Numerical Prediction of the Turbulence Parameters in Two-Dimensional Ventilated Rooms
Abstract
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.
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