Detailed Three-dimensional Numerical Simulations Research Articles

Numerical Analysis of a Scramjet Engine with Intake Sidewalls and Cavity Flameholder

A detailed three-dimensional numerical simulation was conducted to investigate the flow and -air mixing characteristics in a scramjet engine with two intake sidewalls and a cavity flameholder. Turbulence closure was achieved using a model that combines the low-Reynolds-number two-equation model and Sarkar and Wilcox’s compressible turbulent-correction model. The governing equations were solved numerically by means of a finite volume, preconditioned flux-differencing scheme. Cases of with and without intake sidewalls were considered. Intake sidewalls were found to strongly affect the inlet flow structure, which became more complex in the nonuniform flowfield on the cross section perpendicular to the engine axis. The complex and nonuniform flow affected the -air mixing pattern inside the combustion chamber, unlike the pattern of the case of without sidewalls. To verify the accuracy of the simulation, the computed wall pressure was compared with the experimental data. Mixing efficiency and fuel-propagation rate were evaluated for the two cases of with and without sidewalls. The mixing efficiency of the sidewall case is slightly larger than the other case through the combustor, but the fuel spreads toward the combustor center and forms a relatively narrower fuel region with higher equivalence ratio.

3D Heat Transfer Analysis of a Miniature Copper-Water Vapor Chamber with Wicked Pillars Array

A three-dimensional analysis of the heat and mass transfer phenomena inside a vapor chamber is essential for correctly understanding its thermal performance limitations and structural optimization. This paper presents a complete three-dimensional numerical analysis and comparative study of two different miniature vapor chambers designs with identical external geometry and dimensions but different internal structures: one having a wicked pillar array and the other one without the wicked pillars array. The distribution of the wicked pillar array in the vapor core was aligned. Detailed comparative experimental results are also reported, which were performed to verify the calculations from the numerical simulations. It was found that the numerical and experimental results agree quite well, especially at high heat flux values. It is also observed that the vapor chamber with wicked pillars had a better thermal performance than the conventional design, with a 5% decrease in terms of total thermal resistance due to the added extra channels that allow a better flow of the working fluid to the evaporator surface. An insight into how improving the thermal performance of a vapor chamber is provided through the detailed three-dimensional numerical simulations.

A numerical investigation of 3-D flow regimes in a toroidal natural convection loop

Transient laminar natural convection regimes occurring in a thermal convection loop heated from below and cooled from above are investigated numerically for a wide range of Rayleigh numbers spanning the interval from 10 3 to 2.6 × 10 7. In the model system, the lower half of the loop is heated and maintained at a constant high temperature, while the upper half is cooled and maintained at a constant low temperature. A three-dimensional numerical model based on the finite volume method is used to solve the system of governing flow equations. Simulations are performed using water as the working fluid (Pr = 5.83) and detailed numerical results are presented and discussed for conduction, steady convection, and unsteady flow regimes. Although this subject has attracted researchers for decades, there have been no detailed three-dimensional numerical simulations of the dynamics of flow in the thermal convection loop. The objective of the present study is to fill this gap by presenting the temporal evolution of the velocity and temperature fields at key locations within the system. Emphasis is given to the analysis of dynamical behavior of the flow during the unsteady regime. The complexity of flow in the loop, which is characterized by vertical structures and flow recirculation, is visualized for the first time by performing detailed 3-D numerical simulations.

Numerical Study on the Optimum Injection of Urea–Water Solution for SCR DeNOx System of a Heavy-Duty Diesel Engine to Improve DeNOx Performance and Reduce NH3 Slip

Optimization of the urea dosing system to maximize deNOx performance and to minimize NH3 slip during load changes is one of the main challenges for the mobile application of the urea–SCR (selective catalytic reduction) system. A mobile SCR system is restricted to a short distance between the engine exhaust and the catalyst entrance. Therefore, it is likely that urea residence time may not be adequate for complete thermolysis at the catalyst entrance. The key factors affecting the automobile application of SCR technology are the rapid thermolysis, good mixing of ammonia and gas, and reduction of ammonia slip. To this end, in the present study, the effects of the injection angle, urea injector location, and number of injection holes on the uniformity of the ammonia concentration distribution at the entrance of the SCR monolith as well as the maximum ammonia conversion efficiency have been examined in detailed three-dimensional numerical simulations under various engine loads of a heavy-duty diesel engine. A...

Upscaling relative permeabilities in a structured porous medium

Upscaling of multi-phase flow problems for a heterogeneous porous medium requires modification of constitutive functions at the grid-block scale. A particular type of heterogeneity that has important environmental consequences involves thin, continuous streaks of high permeability through lower-permeability background rocks. These streaks, which may correspond to features like abandoned wells in mature sedimentary basins, can become preferential flow paths for an invading fluid. Quantification of flow through these types of heterogeneities in deep, geological formations is necessary for estimates of migration and possible leakage of injected fluids such as hazardous liquid wastes, municipal liquid wastes, and, possibly, carbon dioxide. One of the important constitutive functions for proper estimation of flow through these flow paths is the relative permeability function. In the simple case of a single high-permeability streak in a uniform rock matrix, with both materials having identical (local) relative permeability functions, the upscaled relative permeability must be changed significantly to capture the proper leakage. Standard petroleum reservoir pseudo-functions for relative permeability capture the general features of the upscaled function, but they still produce errors of several hundred percent in the leakage estimation. Detailed three-dimensional numerical simulations and associated upscaled calculations demonstrate the proper form for the upscaled relative permeability, and provide a modified derivation of pseudo-functions to capture the leakage behavior in upscaled models.

Gas dynamic stripping and X-ray emission of cluster elliptical galaxies

Detailed three-dimensional numerical simulations of an elliptical galaxy orbiting in a gas-rich cluster of galaxies indicate that gas dynamic stripping is less efficient than the results from previous, simpler calculations by Takeda et al. and Gaetz et al. implied. This result is consistent with X-ray data for cluster elliptical galaxies. Hydrodynamic torques and direct accretion of orbital angular momentum can result in the formation of a cold gaseous disc, even in a non-rotating galaxy. The gas lost by cluster galaxies via the process of gas dynamic stripping tends to produce a colder, chemically enriched cluster gas core. A comparison of the models with the available X-ray data of cluster galaxies shows that the X-ray luminosity distribution of cluster galaxies may reflect hydrodynamic stripping, but also that a purely hydrodynamic treatment is inadequate for the cooler interstellar medium near the centre of the galaxy.

Three-dimensional temperature measurements in enclosures by using multiview interferometric tomography

Optical tomography using interferometric data is applied in this study to measure three-dimensional flow and heat transfer phenomena in a differentially heated cubic enclosure. The interferometric recording and reconstruction system, associated fringe readout and tomographic reconstruction procedures, and the results from this analysis are described, highlighting the specific challenges facing application of the technique to enclosure flows. The features unique to the investigation of enclosure flows using interferometric tomography include limited view angle, refraction effects and the lack of a visible reference fringe. The experimental results are verified by comparison with independent temperature measurements. The comparisons indicate that this experimental technique can yield three-dimensional perspectives of complex flows having sufficient spatial resolution to verify detailed three-dimensional direct numerical simulations.