Investigation of Particle-Laden Flow in a Straight Duct Using Large Eddy Simulation

2007 ◽  
Author(s):  
M. Fairweather ◽  
J. Yao
Keyword(s):  
Large Eddy Simulation ◽  
Fluid Phase ◽  
Particle Dispersion ◽  
Secondary Flows ◽  
Solid Particles ◽  
Duct Flow ◽  
Mean Flow ◽  
Two Phase ◽  
Eddy Simulation ◽  
Large Eddy

A particle-laden turbulent flow in a square duct is predicted using large eddy simulation (LES). The simulation is performed for a Reynolds number of 35,500, and correctly predicts the existence of secondary flows and their effects on the mean flow. The results are also in good qualitative agreement with experimental data obtained at different Reynolds numbers. One-way coupling is assumed between solid particles and the fluid, and a particle equation of motion, including Stokes drag, lift, buoyancy and gravity force terms, solved using a Lagrangian particle tracking technique. Three sizes of particle (1, 50 and 100 μm) are considered, and results demonstrate that size has a significant effect on particle dispersion and deposition in the duct flow. As particle size increases, therefore, they tend to settle on the floor of the duct, with less dispersion in the fluid phase. The study demonstrates the usefulness of LES for nuclear waste processing applications since secondary flows occur in many practically-relevant flows, and since it is desirable that the two-phase waste mixture is kept as homogeneous as possible to prevent, or at least discourage, the settling out of solid particles to form a bed which can promote pipe blockages.

EVALUATION OF PARTICLE STOCHASTIC SEPARATED FLOW MODELS VIA LARGE EDDY SIMULATION

2010 ◽  
Vol 21 (07) ◽  
pp. 867-890 ◽  
Author(s):  
BING WANG ◽  
HUIQIANG ZHANG ◽  
XILIN WANG
Keyword(s):  
Time Series ◽  
Large Eddy Simulation ◽  
Turbulent Flows ◽  
Spatial Dispersion ◽  
Computational Cost ◽  
Separated Flow ◽  
Particle Dispersion ◽  
Two Phase ◽  
Eddy Simulation ◽  
Large Eddy

This paper evaluates three widely used particle stochastic separated flow (SSF) models through large eddy simulation (LES) of gas-particle two-phase turbulent flows over a backward-facing step. The ability of the models to predict mean velocities, fluctuating velocities, and spatial dispersion of particles are carefully examined in comparison with LES reference results. Evaluation shows that the improved time-series SSF model produces good predictions on mean and fluctuating velocities in the particle phase which highly agree with LES results. However, the time-series SSF model has higher computational cost. Further, compared with the two other models, the time-series SSF model predicts better results on the spatial dispersion of particles. It has an overall advantage in terms of accuracy and efficiency in predicting velocity moments and particle dispersion even without the presence of so many particles. The dependence of different SSF models on the number of computational particles in a converged flow field is also discussed. This paper is useful for the selection and application of SSF models in numerical simulations of practical two-phase turbulent flows.

RANS and Large Eddy Simulation of Internal Combustion Engine Flows—A Comparative Study

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
Xiaofeng Yang ◽  
Saurabh Gupta ◽  
Tang-Wei Kuo ◽  
Venkatesh Gopalakrishnan
Keyword(s):  
Large Eddy Simulation ◽  
High Speed ◽  
Combustion Engine ◽  
Flow Analysis ◽  
Partial Geometry ◽  
Computational Domain ◽  
Mean Flow ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Rans Simulations

A comparative cold flow analysis between Reynolds-averaged Navier–Stokes (RANS) and large eddy simulation (LES) cycle-averaged velocity and turbulence predictions is carried out for a single cylinder engine with a transparent combustion chamber (TCC) under motored conditions using high-speed particle image velocimetry (PIV) measurements as the reference data. Simulations are done using a commercial computationally fluid dynamics (CFD) code CONVERGE with the implementation of standard k-ε and RNG k-ε turbulent models for RANS and a one-equation eddy viscosity model for LES. The following aspects are analyzed in this study: The effects of computational domain geometry (with or without intake and exhaust plenums) on mean flow and turbulence predictions for both LES and RANS simulations. And comparison of LES versus RANS simulations in terms of their capability to predict mean flow and turbulence. Both RANS and LES full and partial geometry simulations are able to capture the overall mean flow trends qualitatively; but the intake jet structure, velocity magnitudes, turbulence magnitudes, and its distribution are more accurately predicted by LES full geometry simulations. The guideline therefore for CFD engineers is that RANS partial geometry simulations (computationally least expensive) with a RNG k-ε turbulent model and one cycle or more are good enough for capturing overall qualitative flow trends for the engineering applications. However, if one is interested in getting reasonably accurate estimates of velocity magnitudes, flow structures, turbulence magnitudes, and its distribution, they must resort to LES simulations. Furthermore, to get the most accurate turbulence distributions, one must consider running LES full geometry simulations.

Loss Predictions in the High-Pressure Film-Cooled Turbine Vane of the FACTOR Project by Mean of Wall-Modeled Large Eddy Simulation

2020 ◽  
Author(s):  
Mael Harnieh ◽  
Nicolas Odier ◽  
Jérôme Dombard ◽  
Florent Duchaine ◽  
Laurent Gicquel
Keyword(s):  
Spatial Distribution ◽  
Large Eddy Simulation ◽  
Film Cooling ◽  
Total Pressure ◽  
Mean Flow ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Turbine Vane

Abstract The use of numerical simulations to design and optimize turbine vane cooling requires precise prediction of the fluid mechanics and film cooling effectiveness. This results in the need to numerically identify and assess the various origins of the losses taking place in such systems and if possible in engine representative conditions. Large-Eddy Simulation (LES) has shown recently its ability to predict turbomachinery flows in well mastered academic cases such as compressor or turbine cascades. When it comes to industrial representative configurations, the geometrical complexities, high Reynolds and Mach numbers as well as boundary condition setup lead to an important increase of CPU cost of the simulations. To evaluate the capacity of LES to predict film cooling effectiveness as well as to investigate the loss generation mechanisms in a turbine vane in engine representative conditions, a wall-modeled LES of the FACTOR film-cooled nozzle is performed. After the comparison of integrated values to validate the operating point of the vanes, the mean flow structure is investigated. In the coolant film, a strong turbulent mixing process between coolant and hot flows is observed. As a result, the spatial distribution of time-averaged vane surface temperature is highly heterogeneous. Comparisons with the experiment show that the LES prediction fairly reproduces the spatial distribution of the adiabatic film effectiveness. The loss generation in the configuration is then investigated. To do so, two methodologies, i.e, performing balance of total pressure in the vanes wakes as mainly used in the literature and Second Law Analysis (SLA) are evaluated. Balance of total pressure without the contribution of thermal effects only highlights the losses generated by the wakes and secondary flows. To overcome this limitation, SLA is adopted by investigating loss maps. Thanks to this approach, mixing losses are shown to dominate in the coolant film while aerodynamic losses dominate in the coolant pipe region.

Simulations of rocket launch noise suppression with water injection from impingement pad

2020 ◽  
Vol 19 (3-5) ◽  
pp. 207-239
Author(s):  
Saman Salehian ◽  
Reda R Mankbadi
Keyword(s):  
Large Eddy Simulation ◽  
Fluid Model ◽  
Water Injection ◽  
Broadband Noise ◽  
Computational Domain ◽  
Two Phase ◽  
Effect Of Water ◽  
Eddy Simulation ◽  
Impingement Plate ◽  
Large Eddy

The focus of this work is on understanding the effect of water injection from the launch pad on the noise generated during rocket’s lift-off. To simplify the problem, we consider a supersonic jet impinging on a flat plate with water injection from the impingement plate. The Volume of Fluid model is adopted in this work to simulate the two-phase flow. A Hybrid Large Eddy Simulation – Unsteady Reynolds Averaged Simulation approach is employed to model turbulence, wherein Unsteady Reynolds Averaged Simulation is used near the walls, and Large Eddy Simulation is used elsewhere in the computational domain. The numerical issues associated with simulating the noise of two-phase supersonic flow are addressed. The pressure fluctuations on the impingement plate obtained from numerical simulations agree well with the experimental data. Furthermore, the predicted effect of water injection on the far-field broadband noise is consistent with that of the experiment. The possible mechanisms for noise reduction by water injection are discussed.

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