Numerical Study Of Three-dimensional Flow Research Articles

Numerical Study of Three-Dimensional Flow in a Negative Pressure Isolation Room with One Inlet and Two Outlets Ventilation Configurations with Variations in Bed Positions and Variations in Outlets Pressure Differences

Numerical Study of Three-Dimensional Flow in a Negative Pressure Isolation Room with One Inlet and Two Outlets Ventilation Configurations with Variations in Bed Positions and Variations in Outlets Pressure Differences

Numerical study of three-dimensional flow and aerodynamic characteristics of a cylindrical cavity in rarefied hypersonic flows

Cylindrical cavity configuration frequently appears on the surface of an aerospace vehicle while flow physics of rarefied hypersonic flows over it are not clear yet. This work presents a comprehensive numerical study to reveal flow structures inside the cavity and aerodynamic surface quantities, including the pressure on and heat flux to the surfaces of three-dimensional cylindrical cavities using the DSMC method. The results showed that the traditional cavity flow types based on the classical categorization are not suitable for characterizing rarefied hypersonic flows over cylindrical cavities due to more diverse flow patterns induced by the curved cylindrical sidewall, especially for the cylindrical cavity with a shallow depth. Both the pressure on and heat flux to the striped area near the top lip of downstream curved sidewall are always the strongest due to the violent airflow collision there, which is a depth range of about 0.4 y/H away from the top lip, but those for the cavity floor are usually quite weak because the gas over it moves slowly. With the increase of cavity depth, the weaker pressure on and heat flux to the cavity floor appear because the rising curved sidewall makes it more difficult for freestream to permeate into the cavity, whereas the maximum pressure on and peak heat flux to the downstream curved sidewall seem to be unchanged. The severe rarefaction effect at 90 km make the flow pattern and temperature distribution inside the cavity different from those for 50, 60, and 70 km. As the freestream Mach number is increased from 13.4 to 33.5, the streamline patterns and velocity contours around and inside the cavity only change slightly, consequently leading to similar numerical trends of both the pressure on and heat flow to the cavity surfaces.

Numerical study of flow patterns and force characteristics for square and rectangular cylinders with wavy surfaces

This paper presents a numerical study of three-dimensional flow around wavy rectangular cylinders with sinusoidal variations in cross-section area along the spanwise direction over wide Reynolds number regimes. The detailed near wake vortex structures and force characteristics of the wavy rectangular cylinder are captured and the influence of length-to-thickness ratio ( L/ D m =1 to 8) of the wavy rectangular cylinder is discussed and compared with a plain straight rectangular cylinder with the same size and flow conditions. Experimental measurements were also performed for the validation of the present numerical results using the PIV technique. For a square cylinder ( L/ D m =1), significant force reduction occurs for a wavy square cylinder compared with a straight square cylinder. The three-dimensional free shear layers behind the wavy square cylinder are more stable than those of the straight square cylinder. For a rectangular cylinder ( L/ D m ≥2), several vortex shedding patterns can be observed. The free shear layers exhibit a steady flow feature with symmetrical flow patterns behind the wavy cylinder for Re=100. At Re=500, the mean drag coefficient and the fluctuating lift coefficient of the wavy rectangular cylinders are greatly suppressed compared to a plain straight cylinder, while such advantageous features gradually disappear with the increase of the aspect ratio and Reynolds number. At Re=5000, the advantageous characteristics on flow control disappear for wavy cylinders with L/ D m >2 due to breaking down of the periodic repeated additional transverse vortices. Finally, a wavy cylinder L/ D m =8, with an angle of incidence α=15° is studied. Results show that such wavy surface does not possess a significant advantage in flow separation control.

Numerical study of three-dimensional flows around two identical square cylinders in staggered arrangements

With the aim to understand air pollutant dispersion among high-density, high-rise buildings, this paper presents the numerical results of three-dimensional flows around two identical square cylinders (TISCs) in staggered arrangements at a Reynolds number of 250 and zero incident angle when the angle between the incoming velocity vector and the line connecting the centers of the cylinders is 45°. The dependence of the drag and lift, their root mean square values, and the Strouhal number on the horizontal spacing have been evaluated. It was found that the correlation coefficients between the drag and lift of the upstream square cylinder (SC-I) were close to unity, with those for the downstream square cylinder (SC-II) exhibiting a wavy form along the spanwise direction. The wavelength and the magnitude are closely related to the cylinder spacing. Secondary vortex coherent structures as well as the primary vortex structures were reported and discussed.

Experimental and Numerical Study of Three-Dimensional Flows in a Mixed-Flow Pump Stage

Internal flows of a low-specific-speed pump stage, having a mixed-flow impeller and a vaned bowl diffuser combination, have been investigated experimentally and numerically. Air was used as the test fluid, and the internal flows were measured at various locations and under various capacities. Flow calculations were made, for both the isolated impeller case and the complete stage case, using Denton viscous codes LOSS3D and MULTSTAGE14, by which the three-dimensional steady flow through multiple blade rows can be calculated using the interrow mixing process. Experimental results showed the effects of the interaction between the impeller and the reverse flow, originating in the downstream diffuser, even at the design point capacity. While an impeller exit reverse flow occurred at the shroud side in the isolated impeller calculation, it was observed at the hub side in the complete stage case, showing good agreement with the experimental results. Although the flow in the diffuser was highly distorted due to a strong swirl flow, patterns of total pressure distribution could be predicted well by the complete stage calculation.

Numerical analysis of three-dimensional flow past a high-speed electric train with turbulent boundary layer separation

An approach to the numerical study of three-dimensional flow past a high-speed electric train is considered, including the case of turbulent boundary layer separation. The method of viscous-inviscid interaction is used to compute the aerodynamic characteristics. The results of calculating the 3D flow past two configurations of a high-speed electric train, taking into account the close proximity of the ground surface, are presented for a train speedV∞=300 km/h and the per meter Reynolds number Re=5.6·106 m−1. One of these configurations is shown to have the advantage of separationless flow past a front locomotive and less intense diffuser separations on the afterbody of a rear locomotive. A local separation zone on the sides of the front locomotive's nose was detected in one of the cases considered.

Numerical Study of Three-Dimensional Flow within a Cubic Cavity

A finite-difference solution of the unsteady Navier-Stokes equations by the explicit use of the pressure and the velocity is presented. The aims are to test the scheme and to estimate the three-dimensional effect of the side walls. A 20×20×20 grid is used and the Reynolds numbers are 0, 100 and 400. The scheme works well except that it needs a very large amount of computation time. It is shown that the effect of the side walls is restricted to a relatively thin layer and the central part of the cavity is almost two-dimensional.