Showing 4 results for Turbulent Flow
J.bazargan and H. Bayat,
Volume 21, Issue 1 (7-2002)
Abstract
As a result of the limitations in the application of Darcy Law (V=ki) to linear-laminar flow regimes through porous media and due to the fact that in coarse alluviums, the Reynolds number may exceed its critical value, the so-called Laplas equation cannot be used for precise analyses of coarse granular foundations. A more general relationship is, therefore, required for such cases. However, a common relationship between piezometric gradient "i" and the approach velocity "v" within porous media shown as i=mVn leads to major difficulties in undertaking complicated tests to determine the values of m and n. It is shown that by combining the above-mentioned relationship with the continuity equation, a differential equation may be obtained to give piezometric head and a potential function Φ, which in turn, leads to the uplift force distributions and the seepage quantities through porous media. To overcome difficulties associated with m and n estimations in the model and as a result of fulfilling an extensive research programme, a fresh and reliable procedure has been developed and explained to assess m and n by means of a simple stepped pump-out test. The practical applicability of the method for a given confined aquifer is also examined. Findings indicates that the proposed procedure a) makes the use of the differential equation for turbulent flow in porous media possible, and b) provides means to determine the nonlinear equation parameters (m&n) at an acceptable precision. The computed values of the parameters are also submitted.
Keywords: Turbulent flow, Rock fill, Alluvium foundation, Reynolds number, Aquifer
A. Saboonchi and S. Kheradmand,
Volume 22, Issue 2 (1-2004)
Abstract
This paper presents a numerical solution for a changing combustor geometry. The effects of the geometric change on the main parameters of the chamber are considered. For this purpose the original geometry and the new one are simulated numerically by a 3-D CFD code and the results are compared. Finally, comments are presented regarding this change. A model is used for turbulence modeling and an eddy dissipation model for reaction. Effect of thermal radiation is considered through solving an extra transport equation. The DO model is used to obtain radiation intensity.
M. Talebi, E. Shirani, and M. Ashrafizadeh,
Volume 25, Issue 2 (1-2007)
Abstract
In this study, turbulent flow around a tube bundle in non-orthogonal grid is simulated using the Large Eddy Simulation (LES) technique and parallelization of fully coupled Navier – Stokes (NS) equations. To model the small eddies, the Smagorinsky and a mixed model was used. This model represents the effect of dissipation and the grid-scale and subgrid-scale interactions. The fully coupled NS equations with the multiblock method was parallelized. Parallelization of the computer code was accomplished by splitting the calculation domain into several subdomains and using different processors in such a way that the computational work was equally distributed among processors. The discretized governing equations are second order in time and in space and the pressure is calculated by Momentum Interpolation Method (MIM) to prevent the checkerboard problem. The results are obtained for the turbulent flow over five parallel tube rows. The computational efficiency, flow patterns, and flow properties are also determined. The results showed high parallelization efficiency and high speed up for the computer code. The flow characteristics were determined and compared with experimental results which showed good agreement. Also, the results showed that the mixed model is better than the Smagorinsky model for evaluation of flow characteristics and lift and drag forces on tubes.
A. Nouri, and M. Nili-Ahmadabadi,
Volume 26, Issue 1 (7-2007)
Abstract
In this article, turbulent flow heat transfer in the air gap between rotor and stator of a generator under nonhomogeneous heat flux is studied experimentally. The rotor consists of four symmetrical triangular grooves. The stator surface is smooth and does not include any grooves. The relative heat flux between the rotor and the stator is 1 to 3. Temperature and heat flux are measured locally at three axial and two angular positions of inner and outer surface. The pressure drop of air flow through the air gap is also measured. In this work, the axial Reynolds number and rotational velocity of the rotor ranges are 4000
