Sharif Digital Repository

A new procedure for simulating turbulent flow in three-dimensional arbitrary geometries is presented. Finite volume method using physical covariant velocities on a staggered grid arrangement was used in this investigation. This work is an extension of previous successful work to three-dimensional cases. The ability of the new algorithm was tested using a conventional two-equation turbulence model on a highly separated turbulent flow test case. The low Reynolds number k-ω turbulence model of Wilcox was utilized to evaluate its capability in modeling highly curved flows. Turbulent flow over a three-dimensional hill, which is appropriate in assessment of ability of turbulence models in... 

In this paper, the effects of a baffle plate on flame deflection and its throttling are investigated numerically in a combustor consuming jet propellant JP. We study the plate effects on the resulting soot volume fraction, soot particles diameter, mass fractions of carbon monoxide (CO), carbon dioxide (CO2), and benzene (C6H6). We use a two-equation turbulence model, a PAH-inception two-equation soot model imposing oxidation due to OH agents, a detailed chemical kinetic consisting of 121 species and 2613 elementary reactions, and the flamelet combustion model to perform the current study. We also take into account the turbulence-chemistry interaction using the presumed-shape probability... 

In this work, an efficient bi-implicit strategy is suitably developed within the context of a hybrid finite volume element method to solve axisymmetric turbulent reactive flow in a model gas turbine combustor. Based on the essence of a control-volume-based finite-element method, the formulation benefits from the geometrical flexibility of the finite element methods while the discrete algebraic governing equations are derived through applying the conservation laws to discrete cells distributed in the solution domain. To enhance the efficiency of method, we extend the physical influence upwinding scheme to cylindrical coordinates. This extension helps to improve the advection flux... 

This study investigates GH2/LOX coaxial jet flame at trans- and supercritical conditions using the Reynolds averaged Navier-Stokes approach. Four two-equation-turbulence models, three real equation of states, two chemical mechanisms, and three different chamber pressures are examined. Predictions show good agreement with measurements qualitatively and quantitatively. Based on the results, the predictions of the Soave-Redlich-Kwong equation of state (EOS) are closer to the experiment, while the Aungier-Redlich-Kwong EOS has more deviation than the others. Moreover, the k-ω shear stress transport model has better performance than the other turbulence models. It is also found that the flow... 

This work is conducted with evaluation of different turbulence models capabilities in predicting three dimensional jet-into-crossflow (JICF) interactions. For this purpose, first of all, comprehensive discussions on the near wall flow complexities due to discharge of a jet into a crossflow are presented. In this regards, large scale coherent structures such as: counter rotating vortex pairs (CRVP's), near wall secondary motions, horseshoe vortices, and wall jets like are discussed. Secondly, the abilities of different turbulence models in predicting such flows (JICF) are evaluated. Our evaluation is based on three points of view including: 1) JICF characteristics, 2) computed location, and... 

An ac neutral wire is connected to the midpoint of the dc bus of the three level/phase NPC rectifiers and then a new dual Lagrangian model of the rectifier is presented in this paper. At first, the load current can be obtained in two forms: 1. the load current involving the current of capacitor C1 2. The load current involving the current of capacitor C2 and then the new model is founded based on the superposition law, the load current and The Euler-Lagrange description of the rectifier. The new model is two nonlinear state space equations and as a result we define two positive definite Lyapunov function candidates based on two equations. Finally two Lyapunov-based controllers are designed...