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The present research work deals with the numerical simulation of double cavity scramjet combustor by using two equation standard k - ε turbulence model and finite-rate/eddy-dissipation reaction models which is again coupled with Reynolds-Averaged Navier-Stokes (RANS) equations to investigate the influence of variation of inlet boundary condition of air as well as H 2 fuel on the combustion flow-field of scramjet engine subsequently. At the same time, the validations of the current computational approach have been completed against a standard experimental data which is available in the literature. An acceptable similarity is observed between present numerical approach with the experimentally attained schlieren photograph and the pressure distribution curve. In the present work, 8 different cases are studied. Among them, first four cases are investigated for the variation of inlet boundary condition of air and the remaining four cases are studied for the variation of inlet boundary condition of H 2 fuel. The obtained results show that the formation of high-pressure region around the cavities for case 3 and case 4 actually helps to push the greater amount of air to the cavity region where it is mixed with adequate amount of H 2 for proper and stable combustion whereas for case 6, it is observed that most of the combustion phenomena closely fitted into a small space of the combustor and mainly occurs near the cavity region. [ABSTRACT FROM AUTHOR]

In the present research work, computational simulation of the double cavity scramjet combustor have been performed by using the two-dimensional compressible Reynolds-Averaged Navier–Stokes (RANS) equations coupled with two equation standard k–ɛ turbulence model as well as the finite-rate/eddy-dissipation reaction model. All the simulations are carried out using ANSYS 14-FLUENT code. Additionally, the computational results of the present double cavity scramjet combustor have been compared with experimental results for validation purpose which is taken from the literature. The computational outcomes are in satisfactory agreement with the experimentally obtained shadowgraph image and pressure variation curve. However, due to numerical calculation, the pressure variation curve obtained computationally is under-predicted in 5 locations. Further, analyses have been carried out to investigate the effect of variation of hydrogen injection pressure as well as the variation of air inlet temperature on the flow-field characteristics of scramjet engine keeping the Mach number constant. The obtained results show that the increase in hydrogen injection pressure is followed by the generation of larger vortex structure near the cavity regions which in turn helps to carry the injectant and also enhance the air/fuel mixing whereas the increase in the inlet temperature of air is characterised by the shifting of incident oblique shock in the downstream of the H 2 injection location. Again for T 0 = 1500 K, the combustion phenomena remains limited to the cavity region and spreads very little towards the downstream of the combustor. [ABSTRACT FROM AUTHOR]

The two equation standard k–ɛ turbulence model and the two-dimensional compressible Reynolds-Averaged Navier–Stokes (RANS) equations have been used to computationally simulate the double cavity scramjet combustor. Here all the simulations are performed by using ANSYS 14-FLUENT code. At the same time, the validation of the present numerical simulation for double cavity has been performed by comparing its result with the available experimental data which is in accordance with the literature. The results are in good agreement with the schlieren image and the pressure distribution curve obtained experimentally. However, the pressure distribution curve obtained numerically is under-predicted in 5 locations by numerical calculation. Further, investigations on the variations of the effects of the length-to-depth ratio of cavity and Mach number on the combustion characteristics has been carried out. The present results show that there is an optimal length-to-depth ratio for the cavity for which the performance of combustor significantly improves and also efficient combustion takes place within the combustor region. Also, the shifting of the location of incident oblique shock took place in the downstream of the H 2 inlet when the Mach number value increases. But after achieving a critical Mach number range of 2–2.5, the further increase in Mach number results in lower combustion efficiency which may deteriorate the performance of combustor. [ABSTRACT FROM AUTHOR]

Abstract: CFD modelling has proven to be a powerful tool for the design of UV reactors. However, the validation of the hydraulics predicted by the CFD model remains a point of attention. Using standard turbulence models such as the k–ɛ model, the CFD model often wrongly predicts local flow features around a UV lamp. Therefore, more advanced modelling approaches such as the LES model were considered. The modelling approaches were explored for a single cross-flow UV lamp. It is shown by means of comparison with experimental data that the LES model predicts the flow around a UV lamp more precisely than the k–ɛ model. The impact of differences in resolved velocity fields on the predicted disinfection was also investigated. Depending on the local geometry (presence and positioning of baffles) the disinfection results were completely different for the different modelling approaches. [ABSTRACT FROM AUTHOR]

Abstract: For fusion reactors, molten salt is one of the candidates for coolant materials. Molten salt is a high-Prandtl-number fluid; thus, it is necessary to enhance the heat transfer coefficient. It is proposed that rods are inserted into a duct to enhance the heat transfer coefficient. The flow field behind the rod in the duct is visualized to compare experimental data with simulation results. The trends and distributions in the numerical simulation are the same as those in the experiment, and furthermore, the magnitudes of the time and space scales in the numerical simulation are of the same order as those in the experiment. Thermohydraulic numerical analysis confirmed that the heat transfer coefficient is improved by inserting the rod when the fluid is a high-Prandtl-number fluid and the flow field is in the turbulent region. However, it is necessary for the rods to be arranged in the streamwise direction. [Copyright &y& Elsevier]

Abstract: This work presents a new CFD model for the hydrodesulfurization process in the petroleum industry. The new model considers the loss of effectiveness of the catalyst by coupling a model that considers the physical structure of the catalyst. The hydrodesulfurization process takes place in a pseudo-three-phase fluidized-bed slurry bubble column reactor with liquid and gas flowing upwards. This reactor presents a transient behavior for the catalytic effectiveness due to the obstruction of the catalyst pores, caused mainly by parallel reactions of hydrodemetalization acting on the catalyst. The emphasis of this work is the introduction of a kinetic model for the reactivity reduction of the catalyst inside slurry bubble column reactors. The hydrodynamic model is simple and adopts an Eulerian–Eulerian approach, where the momentum and mass conservation equations are used to describe the two-phase fluid dynamic fields. The k–ɛ model is used to account for turbulence. The kinetic model considers the reactions controlled by diffusion and occurring on the catalyst pores, which are obstructed along the process by the hydrodemetalization by-products. The model presented in this work allows for an assessment of the influence of the operational conditions of the reactor, such as liquid and gas feed velocities, as well as catalyst properties. The estimation of the yield of the process takes into account the transient activity of the catalyst. [Copyright &y& Elsevier]

Abstract: A single-phase of gas, three-dimensional turbulent flow velocity distribution model –k–ɛ model, which considers the effects of impulse high-voltage electrostatic fields, was founded. The k–ɛ model was dispersed by control-volume method and solved by Semi-Implicit Method for Pressure Linked Equations (SIMPLE) algorithm. The axial-, the tangential-, and the radial-velocity distributions of flow field inside cyclone with impulse electrostatic excitation on the various operating parameters were obtained by computer numerical simulation, and verified partly by experiment. It was concluded that shape of curves of velocity distributions of flow field inside cyclone impulse electrostatic precipitation (CIESP) was similar to that of cyclone with no impulse electrostatic field while the values of the axial-, the tangential-, and the radial-velocity of airflow had distinctly changed in impulse electrostatic field, in particular, the radial-velocity of airflow. Compared to cyclone with no impulse electrostatic field, the radial-velocity of airflow in CIESP was influenced strongly by the electric field at same inlet gas rate. [Copyright &y& Elsevier]

Abstract: The present study deals with the numerical simulation of flow patterns and mixing behaviour in Kenics static mixer over a wide range of Reynolds number. Three different sets of Kenics mixer (aspect ratio=1.5) comprised of 3, 9 and 25 elements each have been characterized. The Reynolds number was varied in the range of 1 to 25,000 (i.e., from laminar to turbulent flow regime). The numerical approach takes into account the aspects of the fluid flow at higher Reynolds number values including circumferential velocity profiles at different cross-sections within the Kenics mixer, which were neglected in previous studies. It was observed that cross-sectional mixing in the turbulent flow regime takes place up to 30% of each element length at element-to-element transition; beyond that velocity profiles were uniform. The experiments were also carried out to measure the circumferential and axial velocity profiles and pressure drop in three different Kenics Mixers using air as fluid. The pressure drop per unit element (ΔP/η) was found to be independent of the number of Kenics mixing elements used in the system. The total pressure drop across Kenics mixer obtained by CFD simulations were compared with the experimental pressure drop values and correlations available in the literature. The numerical results were found in good agreement with the experimental as well as the results reported in the literature. A new pressure drop correlation in the Kenics static mixer has been developed. [Copyright &y& Elsevier]

Abstract: The three-dimensional flow and mixing characteristics of multiple and multi-set three-dimensional confined turbulent round opposing jets in a novel in-line mixer were examined numerically using the standard k–ɛ turbulence model. The model was validated with the available experimental results in a Tee mixer [D.Y. Tang, A.J. Dukat, J.J. Ou, Dynamics of fluid mixing induced at a T-junction, experimental characterization and fluid dynamic computation of temperature distribution in space, Ind. Eng. Chem. Res. 32 (1993) 1727–1733] in which a side stream normally impinges a main stream. Good agreement between the simulated and experimental results is obtained. The effects of multiple opposing jet injection and multi-set opposing jet injections with/without offset on mixing are discussed for this novel opposing jet configuration. [Copyright &y& Elsevier]

Abstract: Computational fluid dynamics (CFD) codes are increasingly being used in the liquefied natural gas (LNG) industry to predict natural gas dispersion distances. This paper addresses several issues regarding the use of CFD for LNG dispersion such as specification of the domain, grid, boundary and initial conditions. A description of the k–ɛ model is presented, along with modifications required for atmospheric flows. Validation issues pertaining to the experimental data from the Burro, Coyote, and Falcon series of LNG dispersion experiments are also discussed. A description of the atmosphere is provided as well as discussion on the inclusion of the Coriolis force to model very large LNG spills. [Copyright &y& Elsevier]

Abstract: The main objective of this work is to improve the conversion inside bubble column reactors by varying the way in which feed is input inside these systems. Bubble column reactors are usually cylindrical in shape, and the reactor feed is at the bottom. The whole idea lies on the fact that the fluid dynamic fields inside the reactor affect its yield. Since the flow pattern in these reactors depend on the radial feed velocities profiles and radial feed holdup profiles at the bottom, several radial feed profiles for these variables were tested in order to analyze how they affect the reactor conversion. The mass flow input for both phases is the same in all situations. This in-house model uses an Eulerian–Eulerian approach to simulate a set of idealized radial profiles feed input situations, that will produce different fluid dynamic fields inside the reactor, and their effect on reactor conversion. The fluid dynamics and concentrations fields, for each phase, is estimated using mass and momentum conservation equations. Turbulence is taken into account using the k–ɛ model. The petroleum thermal hydrocraking is modeled using a pseudo-component model. [Copyright &y& Elsevier]

Abstract: This paper presents a continuous sensitivity equation method (SEM) for incompressible turbulent heat transfer. The k–ɛ model of turbulence with wall functions is used to model turbulence. Heat transfer is handled using an eddy conductivity. The SEM formulation accounts for complex parameter dependence and is suitable for a wide range of problems. It is applied to turbulent flow over a heated backward facing step and to turbulent flow over a heated flat plate. Several uses of the SEM are demonstrated: fast computation of nearby flows, identification of key parameters controlling the flow, and uncertainty analysis. Sensitivities are used to cascade input data uncertainties through the CFD code to yield uncertainty estimates of the skin friction and Stanton number. The SEM also provides detailed information about the contribution of each parameter to the global uncertainty. [Copyright &y& Elsevier]