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Abstract: A large-eddy simulation (LES) of a round jet penetrating normally into a cross-flow is described. The jet-to-cross-flow velocity ratio is 2.3 at a Reynolds number of 46,700, based on the jet bulk velocity and the jet diameter. The simulations are performed with steady and unsteady boundary conditions. A passive scalar is discretized either with a central or a TVD discretization. The results are compared with each other and the experimental measurements of Crabb, Durão and Whitelaw. The computation reproduced many phenomena present in such a flow, like the shear layer ring vortices and a counter-rotating vortex pair. In general, a reasonable agreement with the measurements was obtained. However, the calculation predicts an intense backflow low near the flat wall. As the measured points do not reach this area it is possible that such a recirculation exists but in any case the LES predicts it too high above the wall and probably too intense. The unsteady boundary condition increases the spreading of the jet slightly. [Copyright &y& Elsevier]

A zero-equation sub-grid scale (SGS) model with a variable eddy-viscosity coefficient C μ is developed for large-eddy simulation. Since C μ is evaluated based on the resolved shear and vorticity parameters accompanied by the hybrid time scale T t (combination of dynamic and Kolmogorov time scales), it is sensitized to non-equilibrium flows, preserving the anisotropic characteristics of turbulence. The current model accounts for the SGS kinetic energy with k s g s = C μ 2 3 ( Δ ¯ S ¯ ) 2 and guarantees the positivity in the energy components. Unlike the original Smagorinsky model, the present SGS model does not need any ad-hoc damping function ( C μ acts as a natural damping function as the wall is approached) or averaging/clipping of the model coefficient for numerical stabilization as required by the dynamic Smagorinsky model (DSM). The model is validated against well-documented flow cases, yielding predictions in good agreement with the direct numerical simulation (DNS) and experimental data. Comparisons indicate some advantages of the new model over the DSM; the current model needs only a single-filtering operation that recovers the numerical stability and computational effort to a greater extent. [ABSTRACT FROM AUTHOR]

An accurate prediction of flow and thermal fields around an human body provides valuable information in designing an efficient ventilation system. This study tries to address this issue by investigating the flow structure around an human body subjected to a displacement ventilation system through the computational fluid dynamics (CFD). For this purpose, both the large eddy simulation (LES) and hybrid LES–RANS methods are employed. The RAST one-equation model (OEM) and the dynamic Smagorinsky model (DSM) are utilized as a sub-grid scale (SGS) modeling for the LES while for the hybrid LES–RANS method, the SST–SAS version is applied. Predicted results are compared with available experimental measurements in the literature. Comparisons show that the OEM has a better performance in reproducing the correct level of velocity and temperature fields around the body as well as in other locations of the room while the SST–SAS model fails to predict these quantities accurately, especially around the occupant's body. Above all, the OEM provides a good compromise between accuracy and robustness in predicting the airflow and temperature fields in an indoor environment. [ABSTRACT FROM AUTHOR]

A detailed understanding of the flow behavior inside a high pressure homogenizer (HPH) valve has a vital importance in designing and optimizing the systems in terms of energy and performance. A large Eddy simulation (LES) method is used in this study to investigate the flow structure in an HPH valve. The current paper utilizes two zero-equation subgrid-scale models: namely the RAST (Rahman–Agarwal–Siikonen–Taghinia) and DSM (dynamic Smagorinsky model). The performance of these two models and their predictions are compared with experimental data available in the literature. Computations dictate that an LES can reproduce the accurate information in terms of main parameters that are necessary in designing and optimizing of the homogenizing process. Comparisons demonstrate that both models are capable of predicting the turbulent-flow structures at the gap exit which are in a good agreement with measurements. However, the RAST model shows a slight superiority over the performance of DSM. [ABSTRACT FROM AUTHOR]

Flow over a circular cylinder is a significant phenomenon encountered in a wide range of engineering and industrial applications. It is a challenging case associated with a complicated flow regime having laminar separation, transition to turbulence, reattachment and vortical motions in the vicinity of cylinder. The current work assesses the performance of RAST (Rahman–Agarwal–Siikonen–Taghinia) model, a zero-equation sub-grid scale (SGS) model in predicting the flow features around a circular cylinder at R e D = 3900 . This SGS model is sensitized to non-equilibrium flows, preserving the anisotropic characteristics of turbulence; this aspect makes it a subtle means to simulate the flow with strong recirculating and separation. Results are compared with available experimental data in the literature as well as with those obtained by the dynamic Smagorinsky model (DSM). The comparisons dictate that the RAST model can accurately produce the mean flow characteristics that are in good agreement with existing experimental data, especially at the near wake of cylinder. Compared with the DSM, the RAST model needs a single-filtering operation that recovers the numerical stability and computational effort to a greater extent. In other words, the RAST model can be considered as a good compromise between accuracy and manageability; particularly, as simple as the original Smagorinsky model and as accurate as the DSM. [ABSTRACT FROM AUTHOR]

In this paper the Potsdam Propeller Test Case is numerically investigated in oblique inflow conditions. We consider three different topics: open water performance curves, cavitation observations, and pressure pulses induced by the propeller to the ceiling of the cavitation tunnel. In the oblique flow case, the inflow is not uniform from the perspective of the propeller, which results in the dependency of the propeller blade loading and cavitation on the blade rate frequency. The numerical simulations were compared to experimental results for each investigated case. Additionally, we analyzed the unsteady features of the cavitation on the blades as well as the pressure peaks in the propeller wake due to collapsing cavities. We found that the global performance and cavitation patterns close to the blades agree well with the tests in the numerical simulations. The agreement with the tests for the pressure pulses on the tunnel ceiling was better in the non-cavitating case. The unsteady cavitation shed behind the propeller and the subsequent collapse events induced a vast increase in recorded maximum pressure values. Root cavitation collapse produced pressure pulses an order of magnitude greater than the collapse of tip vortex cavitation. Also the collapse of cavities on the blades contributed to a significant increase in the pressure fluctuations on the blades. • Marine propeller performance and cavitation is studied in oblique flow. • A compressible numerical viscous flow modelling is employed. • Transient cavitation phenomena are investigated and compared to experiments. • Very high pressure pulses due to collapsing cavity structures in propeller wake are demonstrated. [ABSTRACT FROM AUTHOR]