Predictions of mixing enhancement for jets in Cross Flows (original) (raw)
Related papers
Mixing with Jets in Cross-Flow
Industrial & Engineering Chemistry Research, 2009
Mixing of gaseous species using jets in cross-flow is investigated with the help of computational fluid dynamics (CFD) modeling. This situation is encountered in a variety of industrial situations such as combustion, chemical vapor deposition, etc. Such operations are carried out in a specially designed chamber/mixer. For example, hydrocarbons are mixed with oxygen prior to oxidation reactions, in a specially designed oxygen mixer. In the present work, CFD simulations have been carried out for the mixing of two gaseous streams in a mixer. The model has been validated with experimental data reported in the past literature. The effects of different geometric configurations (hole diameter, number of holes) and operating conditions (velocity ratio) on the mixing process have been investigated. The model has helped in the identification of the key parameters in the design of such mixers.
Large Eddy Simulation of Multiple Jets into a Cross Flow
Scientia Iranica
Multiple square cross section jets into a cross ow at three di erent velocity ratios, namely 0.5, 1.0 and 1.5, have been computationally simulated, using the Large Eddy Simulation (LES) approach. The nite 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 P o w e r -L a w and Crank-Nicolson schemes, respectively. Mean velocity pro les at di erent X-locations a r e compared with the existing experimental and Reynolds Averaged Navier-Stokes (RANS) computational results. Although the RANS computations require much fewer computational resources than the LES, the authors' results show reasonably good agreement with existing experimental results, rather than the computational ones. It is shown that, b y increasing the velocity ratio, the jet penetration into the cross ow is increased, accompanied by a high mixing with the cross ow. In addition, the formation of counter rotating vortex pairs after the jet enters the cross ow is explained and its behavior in di erent Y Z -planes is investigated. ratios, say R > 3, and low Reynolds numbers, say Re < 5000, the annular mixing layer of the pipe rolls up and toroidal vortices are formed, similar to those of a jet issuing into`still' air. These well organized vortices, or vortical rings (large structures), carry a vorticity of the same sign as the ones inside the pipe, but opposite www.SID.ir
Impacts of a jet's exit flow pattern on mixing and combustion performance
Progress in Energy and Combustion Science, 2006
The influence of modifying a jet's exit flow pattern on both the near and far-field turbulent mixing processes and on the resulting combustion performance, is explored. This reveals that, in contradiction to some common assumptions, increasing the coherence of large-scale motions can decrease molecular mixing rates, and yet can still be beneficial in some applications.
On High Pressure Real Gas Turbulent Mixing Jets
2017
A database of direct numerical simulation (DNS) of spatially evolving turbulent mixing slot jets of C7H16/O2 and C7H16/Air is developed. The formulation includes the compressible form of the governing equations, a generalized multicomponent diffusion model with Soret and Dufour effects, a cubic real gas equation of state and realistic property models. Simulations are conducted over a wide range of initial pressures (1atm < P0 < 100atm) and jet width based Reynolds numbers of 850 and 1300. High order explicit finite difference schemes in combination with low order boundary closures and Runge-Kutta time integration schemes are used to approximate the spatial and temporal derivatives. Non-reflecting inflow and outflow boundary conditions in combination with absorbing zones are applied for proper convection of flow structures and acoustic waves with minimal reflection of numerical waves. Low level disturbances are imposed on the laminar inflow near the nozzle to initiate instabili...
Direct Numerical Simulation of Jet Mixing Control Using Combined Jets
JSME International Journal Series B, 2006
In order to develop an efficient jet mixing method, direct numerical simulations of combined jets are carried out. The Reynolds number defined with a nozzle diameter is Re = 1 500. Spatial discretization is performed by adopting a hybrid scheme of a sixth order compact scheme in the streamwise direction and Fourier series in the cross section. The distance between two jets is fixed at six times the jet diameter, and the inclination angle of the jets is changed from 45 to 70 deg. The results reveal that the turbulence intensity increases with a decrease in the inclination angle and that the jet width increases via jet excitation. These findings suggest that the diverse requirements of jet mixing control can be satisfied by a flexible combination of jets.
Mixing Analysis and Optimization in Jet Mixer Systems by Means of Large Eddy Simulation
To achieve the analysis, control and optimization of mixing processes by means of Large Eddy Simulation (LES) technique, an advanced subgrid scale (SGS) scalar model package for the description of turbulent mixing in gaseous and liquid flows is developed and validated. This aims to strongly improve the prediction accuracy of the mixing field quantities prior to any mixing modification studies. Both non-reacting and reacting systems are considered. To cover different reaction regimes, the mixing processes with chemical reaction in jet mixer systems under investigation are described in terms of mixture fraction and two reaction progress variables. To assess the accuracy of the SGS model package and focussed on the high Schmidt-number phenomena, the results of LES are compared with experimental data and other previous simulation results for both a non-reacting jet in channel flow configuration and a confined impinging jets reactor (CIJR) featuring a parallel reaction system. The mixing and reaction processes are analyzed. Especially for the CIJR, the influence of operating conditions (active modification) on mixing properties is evaluated and a quality of measure, that is a prerequisite for mixing control and optimization in turbulent reacting flows by means of passive modification, is highlighted.
2015
The present paper discusses experiments and numerical simulations of a gas mixing process. A pulsed jet is injected perpendicular to the cross-flow in a small laboratory wind tunnel. The injection process is recorded with a high-speed camera. Digital image processing is used to analyze the spatial and temporal distribution of the injected gas. The primary goal of this study is to provide validation data for a custom CFD solver based on the OpenFOAM toolkit. Therefore the data processing scripts were implemented in way that they can be run on experimental data as well as simulation results without any changes, thus allowing a direct comparison of both. The overall agreement of CFD and experiment is very good.