Sharif Digital Repository

This paper presents the improvements of cavitation modelling for marine propellers particularly developing tip vortex cavitation. The main purpose of the study is to devise a new approach for modelling tip vortex cavitation using Computational Fluid Dynamics (CFD) methods with commercial software, STAR-CCM+. The INSEAN E779A model propeller was used for this study as a benchmark propeller. Utilizing this propeller, firstly, validation studies were conducted in non-cavitating conditions together with grid and time step uncertainty studies. Then, the cavitation was simulated on the propeller using a numerical cavitation model, which is known as the Schnerr–Sauer model, based on the... 

In this study, added resistance and motion responses of KRISO Container Ship (KCS) were evaluated experimentally and numerically in six different trim angles. A series of towing tank experiments were performed for six different trim angles at design speed in calm water and regular head waves. The ship motions and added resistance were measured for several wavelength conditions considering short and long wave ranges with wave steepness of 1/60. Next, computations of the towed model in calm water and waves were performed using Unsteady Reynolds-Averaged Navier-Stokes (URANS) CFD and 3-D potential methods. Effects of trim angles on added resistance were analysed and results concerning the... 

Purpose - The purpose of this paper is to present a fast, economical and practical method for mathematical modeling of aerodynamic characteristics of rectangular wing in ground (WIG) effect. Design/methodology/approach - Reynolds averaged Navier-Stokes (RANS) equations were converted to Bernoulli equation by reasonable assumptions. Also, Helmbold's equation has been developed for calculation of the slope of wing lift coefficient in ground effect by defining equivalent aspect ratio (ARe). Comparison of present work results against the experimental results has shown good agreement. Findings - A practical mathematical modeling with lower computational time and higher accuracy was presented for... 

The hydraulic efficiency of sedimentation basins is reduced by short-circuiting, circulation zones and bottom particleladen jets. Baffles are used to improve the sediment tank performance. In this study, laboratory experiments were used to examine the hydrodynamics of several baffle configurations. An accompanying numerical analysis was performed based on the 2-D Reynolds-averaged Navier-Stokes equations along with the k-ε turbulence closure model. The numerical model was supplemented with the volume-of-fluid technique, and the advection-diffusion equation to simulate the dynamics of particle-laden flow. Model predictions compared well with the experimental data. An empirical function was... 

Multiple square cross section jets into a cross flow at three different velocity ratios, namely 0.5, 1.0 and 1.5, have been computationally simulated, using the Large Eddy Simulation (LES) approach. The finite volume method is applied in the computational methodologies, using an unsteady SIMPLE algorithm and employing a non-uniform staggered grid. All spatial and temporal terms in the Navier-Stokes equations have been discretized using the Power-Law and Crank-Nicolson schemes, respectively. Mean velocity profiles at different X-locations are compared with the existing experimental and Reynolds Averaged Navier-Stokes (RANS) computational results. Although the RANS computations require much... 

This paper has developed an axisymmetric laminar and turbulent two-phase flow solver to simulate pressure-swirl atomizers. Equations include the explicit algebraic Reynolds stress model, the Reynolds-averaged Navier-Stokes, and the level set equation. Applying a high-order compact upwind finite difference scheme with the level set equation being culminated to capture the interface between air-liquid two-phase flow and decreasing the mass conservation error in the level set equation. The results show that some recirculation zones are observed close to the wall in the swirl chamber and to the axis. This model can predict converting the Rankin vortex in the swirl chamber to the forced vortex in... 

Numerical analysis of the nanofluid flow characteristics of perforated conical rings in a heat exchanger tube has been investigated under constant wall temperature condition. The pitch ratio of the perforated conical rings is 4 and the number of holes is varied from 0 (typical conical ring) to 10. The flow regime is fully turbulent with the Reynolds number is varied from 5000 to 14,000 and Cu-water nanofluid 0<ϕ<1.5% is selected as the working fluid. The main novelty of this paper is to perform a 3D simulation of this problem because some previous studies using similar geometry were restricted to experimental analysis. The Reynolds averaged Navier Stokes (RANS) equations are solved with the... 

Determination of high-speed crafts' hydrodynamic coefficients will help to analyze the dynamics of these kinds of vessels and the factors affecting their dynamic stabilities. Also, it can be useful and effective in controlling the vessel instabilities. The main purpose of this study is to determine the coefficients of longitudinal motions of a planing catamaran with and without a hydrofoil using Reynolds-averaged Navier-Stokes method to evaluate the foil effects on them. Determination of hydrodynamic coefficients by experimental approach is costly and requires meticulous laboratory equipment; therefore, utilizing the numerical methods and developing a virtual laboratory seem highly... 

A hydroelastic hybrid model is developed to simulate the fluid-structure interaction in water entry problems using the partitioned approach. The interactions between a flat plate and the water are modeled by a hydroelastic model using explicit and implicit couplings. Both couplings are unstable due to numerical instability associated with the fluid added mass. To overcome the instability, an extended Wagner's model is combined with the hydroelastic model, and a hybrid model is developed. The extended Wagner's model is the extension of the classical Wagner's model that is used to estimate the fluid inertial, damping, and restoring forces of a flexible plate within the potential flow theory.... 

Oxy-moderate or intense low-oxygen dilution (MILD) combustion, which is a novel combination of oxy-fuel technology and MILD regime, is numerically studied in the present work. The effects of external preheating and CO2 dilution level on the combustion field, emission, and CO formation mechanisms are investigated in a recuperative laboratory-scale furnace with a recirculating cross-flow. Reynolds-averaged Navier-Stokes (RANS) equations with eddy dissipation concept (EDC) model are employed to perform a 3-D simulation of the combustion field and the turbulence-chemistry interactions. In addition, a well-stirred reactor (WSR) analysis is conducted to further examine the chemical kinetics of... 

In this paper, the structure of a wall jet deflected by a baffle along with the trajectory of particles has been studied. This baffle is used to produce a stable deflected surface jet, thereby deflecting the high-velocity supercritical stream away from the bed to the surface. An elliptic relaxation turbulence model (ν̄2-f model) has been used to simulate this submerged flow. In recent years, the ν̄2- f turbulence model has become increasingly popular due to its ability to account for near-wall damping without use of damping functions. In addition, it has been proven that the ν̄2- f model is superior to other Reynolds-averaged Navier-Stokes (RANS) methods in many flows where complex flow... 

The accuracy of Reynolds Averaged Navier-Stokes (RANS) turbulence models to predict the behavior of 2-D density currents has been examined. In this work, a steady density current is simulated by the k - ε, k - ε RNG, two-layer k - ε and modified v̄2 - f model, all of which are compared with the experimental data. Density currents, with a uniform velocity and concentration, enter a channel via a sluice gate into a lighter ambient fluid and move forward down-slope. The eddy-viscosity concept cannot accurately simulate this flow because of two stress production structures found within it. Results show that all isotropic models have a weak outcome on this current, but by improving the ability of... 

The accuracy of Reynolds averaged Navier-Stokes (RANS) turbulence models to predict the behavior of two-dimensional (2-D) density current has been examined. In this work, a steady density current is simulated by the κ -ε , κ -ε RNG, two-layer κ -ε and modified v 2̄ - f models. All models are compared with available experimental data. Density current with uniform velocity and concentration enters a channel via a sluice gate into a lighter ambient fluid and moves forward down-slope. The eddy-viscosity concept cannot accurately simulate this flow because of two stress production structures in it. Results show that all isotropic models have a weak outcome for this current, but with improving the... 

Numerical study of pollutant emissions (NO and CO) in a Jet Stirred Reactor (JSR) combustor for methane oxidation under Elevated Pressure Lean Premixed (EPLP) conditions is presented. A Detailed Flow-field Simplified Chemistry (DFSC) method, a low computational cost method, is employed for predicting NO and CO concentrations. Reynolds Averaged Navier Stokes (RANS) equations with species transport equations are solved. Improved-coefficient five-step global mechanisms derived from a new evolutionary-based approach were taken as combustion kinetics. For modeling turbulent flow field, Reynolds Stress Model (RSM), and for turbulence chemistry interactions, finite rate-Eddy dissipation model are... 

In this work, numerical investigation of a gas turbine model combustor (GTMC) was carried out using two different turbulence-chemistry interaction models: the EDC (eddy dissipation concept) and TPDF (transported probability density function). GTMC with good optical access for laser measurements provides a useful database for swirling CH4/Air diffusion flames at atmospheric pressure. Modeling was performed by solving Reynolds-averaged Navier-Stokes (RANS) and Reynolds stress model (RSM) equations for a two-dimensional (2D) axisymmetric computational domain accompanied by swirl and the combustion chamber was investigated for both reacting and nonreacting conditions. A detailed reduced... 

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 study is on combustion modeling of gaseous hydrogen and cryogenic liquid oxygen at the subcritical condition for the well-known Mascotte laboratory combustor. The proposed strategy relies on the hybrid Eulerian-Lagrangian framework in which the continuous phase is evaluated by Reynolds Average Navier-Stokes (RANS) equations and the quick discretization method. The dispersed phase of the combustion field is evaluated by the Discrete Phase Method (DPM). The Eddy Dissipation Concept (EDC) has been performed for combustion-turbulence interaction modeling. Effects of the turbulence model, chemical kinetic mechanism, equation of state, and inlet momentum jet flux are investigated in terms of... 

Moderate or Intense Low-oxygen Dilution (MILD) combustion is a technology with important characteristics such as significant low emission and high-efficiency combustion. The hydrogen enrichment of conventional fuels is also of interest due to its favorable characteristics, such as low carbon-containing pollutants, high reaction intensity, high flammability, and thus fuel usage flexibility. In this study, the effects of adding hydrogen to methane and syngas fuels have been investigated under conditions of MILD combustion through numerical simulation of a well-set-up MILD burner. The Reynolds-Averaged Navier-Stokes (RANS) approach is adopted along the Eddy Dissipation Concept (EDC) combustion... 

Numerical simulation of a dual-swirl gas turbine model combustor is performed under cold and reacting flow conditions using a three-dimensional unsteady Reynolds-averaged Navier-Stokes approach. A multi-species chemical mechanism is used in this study for the analysis of the numerous radicals participating in the ignition process and the flame structure. The other objective of this study is to investigate the flow field under different injector configurations, including both co-rotating and counter-rotating swirler arrangements, different swirl intensities, and vane areas. A comparison of the results with experimental data shows that the predicted velocity and temperature profiles follow the... 

Moderate or intense low-oxygen dilution (MILD) combustion of liquid fuels has attracted attention because of its advantages in industrial burners and gas turbine applications. Here, numerical investigation has been conducted on an experimental MILD turbulent spray burner. The H∥ flame of Delft spray in a hot co-flow burner is selected, and the Reynolds averaged Navier-Stokes/eddy dissipation concept framework with 40 species/180 reversible reactions through a skeletal chemical mechanism is used in addition to unsteady Lagrangian tracking of spray droplets to investigate the flame structure and chemical kinetic of reacting flow field. At first, current numerical results were compared with...