Papers by Keyword: Large Eddy Simulation (LES)

Abstract: Acoustic modem is one of the most important sensors on the deep sea AUV. A good performance of the acoustic modem has great effect on the safety and operation of deep sea AUV. According to the construction of deep sea AUV, acoustic modem is installed in the cavity behind the GPS antenna, it would cause flow noise around the acoustic modem and thus interference will occur when the communication is established between deep sea AUV and surface. Flow-induced noise around the acoustic modem is studied in this paper. Firstly the unsteady flow around the acoustic modem is studied by large eddy simulation (LES) method. Secondly based on the resolved information of flow field, acoustic noise distribution is studied using equivalent acoustic sources method. Compared with different positions of GPS antenna, flow noise distribution around the acoustic modem and the effect on communication is investigated. Then acoustic modem layout on the AUV is optimized.

Abstract: Fully developed turbulent channel flow with a blade riblet surface has been simulated numerically at Reynolds number by Large Eddy Simulations (LES). The blade riblet is shown to provide a total viscous drag reduction approximately 9% with the riblet spacing and the cross section . For the sake of investigating the interaction of the turbulent flow with riblets, the mean velocity profiles, velocity fluctuations, and instantaneous flow visualization have been analyzed. It has been found that the riblet of certain size reduces drag by damping the dynamics and weakening the cross motions in the near-wall boundary layer, revealing beneficial turbulence controlling.

Abstract: Accurate simulation for airflow structural characteristics in the human mouth-throat model plays an important role in analyzing the filter effect of pharynx and larynx and the diffusion, transition and deposition patterns of aerosol in human upper respiratory tract. Large eddy simulation was used to simulate the airflow movement in human mouth-throat model in the conditions of the cyclic respiratory pattern, and the airflow structural characteristic in mouth-throat model was discussed. The results show that two velocity growth points generated in pharyngeal and laryngeal region; the airflow separates in region near the pharynx and the separation zone appears near the anterior wall of pharynx; A turbulence jet appears in the glottal region and the airflow; the high velocity zone is created in pharynx and larynx, and the phenomenon of airflow separation appeared in the pharynx. In the process of cyclic exhalation, the phenomenon of airflow separation didn’t appear in the pharynx and larynx.

Abstract: large eddy simulation cooperated with a physical fractional-step method is applied to simulate steady flow around a nested type fixed-cone valve; and the equations are solved with the finite volume method. The free fluid surface is simulated by the VOF method. The pressure contours and vorticity magnitude are obtained. The modeling results conform to physical law, and show that the large eddy simulation theory has powerful capacity in simulation of microstructures of turbulent flows, and the function of the nested type fixed-cone valve for energy dissipating is good.

Abstract: This paper is concerned with the numerical study of gas–liquid flow in bubble columns by large eddy simulations (LES). The Euler–Euler approach is used to describe the equations of motion of the two-phase flow. The mean velocities and the fluctuating velocities are obtained. It is found that, when the drag, lift and virtual mass forces are used, the computed results in agreement with experimental transient behavior can be captured.

Abstract: large eddy simulation cooperated with a physical fractional-step method was applied to simulate steady flow around two parallel circular cylinders. The total velocity vectors, pressure contours and vorticity magnitude are obtained. The modeling results conform to physical law, and show that the large eddy simulation theory has powerful capacity in simulation of microstructures of turbulent flows, and can be widely applied to the solution of real engineering problems.

Abstract: This work presents estimates of time histories of pressure coefficients at several taps on the roof of a 1/200 model of a 200 x 100 x 20 ft low-rise building with a 1/24 slope gable roof building. The estimates were obtained by large eddy simulation (LES). The first and second moments as well as peaks for the time histories are compared with those obtained in boundary layer wind-tunnel measurements at the University of Western Ontario. It is noted that the computation times required to obtain records of length comparable to wind tunnel records are at present prohibitively large.

Abstract: Velocity fluctuations in a mixing T-junction were simulated in FLUENT using large-eddy simulation (LES) turbulent flow model with sub-grid scale (SGS) Smagorinsky–Lilly (SL) model. The normalized mean and root mean square velocities are used to describe the time-averaged velocities and the velocities fluctuation intensities. Comparison of the numerical results with experimental data shows that the LES model is valid for predicting the flow of mixing in a T-junction junction. The numerical results reveal the velocity distributions and fluctuations are basically symmetrical and the fluctuation at the upstream of the downstream of the main duct is stronger than that at the downstream of the downstream of the main duct.

Abstract: In the present work the temperature fluctuations in a mixing tee were simulated on FLUENT platform using the large-eddy simulation (LES) turbulent flow model with three kinds of sub-grid scale (SGS) models such as Smagorinsky-Lilly (SL) model, Wall-adapted Local Eddy-viscosity (WALE) model, and Kinetic-energy transport (KET) model. The normalized mean and root mean square temperatures were predicted and analyzed with consideration of buoyancy. The numerical results showed that buoyancy greatly influences the mixing flow and the thermal striping phenomena were quite obvious. These three SGS models have somewhat similar accuracies for prediction of the temperature fluctuation and thermal stripping in a tee of mixing hot and cold fluids.

Abstract: In the present paper, large-eddy simulation (LES) based on commercial computational fluid dynamics (CFD) software FLUENT for prediction of flow and heat transfer in a mixing T-junction was completed. Mean and root mean square (RMS) temperature and velocity were defined to describe the distributions and fluctuations of temperature and velocity. Numerical results indicate that profiles between symmetrical planes are almost same and the root mean square temperature and velocity close to the center of the main duct in the downstream are larger than those near the main duct wall. The prediction of the fluctuations of temperature and velocity is significant to understand the knowledge of the cause of thermal fatigue in a mixing T-junction.