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Large-eddy simulation (LES) has been performed for an axisymmetric piston-cylinder assembly with and without swirl. For both cases, the LES mean and rms velocity profiles show better agreement with experimental data than profiles obtained using a Reynolds-averaged Navier–Stokes (RANS) approach with a standard k − ε turbulence model. The sum of the resolved and modeled contributions to turbulence kinetic energy (TKE) approaches grid independence for the meshes used in this study. The sensitivity of LES to key numerical and physical model parameters has been investigated. Results are especially...
Stability and ride comfort of high-speed rolling stock are, for reasons of external aerodynamics, dependent on the external design in conjunction with properties of the vehicle dynamics and the design of the infrastructure, herein referring to the confining tunnel walls. It is a fact that some Japanese high-speed trains are quite prone to tail vehicle vibrations only inside tunnels, while (to the authors’ knowledge) other nation’s comparable train systems are not. In this context the current work describes our results of external aerodynamics, calculated with large eddy simulations, about two...
Two low Reynolds (Reτ about 180) and Mach numbers turbulent plane channel flows with one wall heated and one wall cooled at temperature ratios of 1.02 and 3.0 were computed using Large Eddy Simulation (LES). CD-adapco code STAR-CD with second-order finite volume scheme and the classical Smagorinsky subgrid-scale model with Van Driest damping at the walls was used to solve 3D transient problem and determine the motion of large eddies. The effects of the fluid property variations on the structure of wall turbulence were investigated and compared with earlier LES studies of similar problem.
The present work is a study of the gas-flow phenomenon known as the “end of the vortex” (EoV), which spontaneously occurs at the lower end, or under, reverse-flow centrifugal separators such as cyclones or swirl tubes. Different CFD models of swirl tubes have been built to study and analyse this phenomenon in detail. The present numerical work is based on — and compared with — previous experimental observations of this phenomenon. The numerical models were built in complete agreement with the geometrical configurations and operating conditions used in these earlier experimental studies. Two...
The present paper deals with thermal fatigue phenomenon, and more particularly with the numerical simulation using Large Eddy Simulation technique of a mixing tee, for which experimental thermal statistics are available. The sensitivity to the sub-grid scale closure is first evaluated by comparing the experimental statistics with the numerical results obtained via both the Smagorinsky and the structure-function models. Because of a difference of temporal resolution between the experiment and the simulation, the direct comparison of the fluctuations is not possible. Therefore, a methodology...
The feasibility of using a commercial CFD code for large eddy simulation (LES) is investigated. A first test on homogeneous turbulence decay allows a fine-tuning of the eddy viscosity with respect to the numerical features of the code. Then, a flow over forward–backward facing step at Reynolds number Reh ¼ 1:7 105 is computed. The results found show good agreement with the new LDA data of Leclercq et al. . The acoustic source term, recorded from the LES and to be fed into a following acoustic propagation simulation,is found to be largest in the separation from the forward step. The source...
Large Eddy Simulations are performed in a T-junction to analyze the feasibility of wall-functions in accurately predicting the thermal fluctuations acting on the pipe walls. The WALE sub-grid-scale model employed in the LES solver is validated by performing OECD/NEA T-Junction benchmark test-case. In order to reduce the computational costs, Reynolds number scaling is performed while preserving the essential flow features. While the wall-function based simulation showed good agreement with the wall-resolved approach for the bulk velocity and temperature field, the corresponding RMS components...
Unfavorable winds are often found in complex terrain and these complicated flow phenomena such as flow separation and vortex shedding can cause difficulties in siting of wind turbines. This paper uses a DES method to depict the unsteady flows observed in the vicinity of a wind turbine location. A costal site is selected for this study. It has been observed that the variations of wind velocities and wind directions may be large across the rotor area. The large differences in wind velocity and wind direction can cause problems to a wind turbine in operation. The CFD simulations may provide...
Gas-liquid slug flow can exert cyclic forces on pipe bends. A knowledge of the time-varying force and its distribution on the bends is highly desirable in designing the piping and piping support systems. A numerical study has been carried out to obtain an understanding of the slug flow induced forces and develop simulation models for engineering applications. The STAR-OLGA coupling has been applied to achieve a co-simulation of 3-D CFD (Computational Fluid Dynamics) and 1-D pipeline models. In the coupling model a horizontally oriented 90° bend with a diameter of 70 mm is modelled using 3-D...

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