CFD Numerical Method Research Articles

Vortex Induced Vibration Numerical Simulation of a Spring-Mounted Cylinder in Current

A 2D CFD numerical method based on loose coupling algorithms was adopted to simulate vortex induce vibration of a spring-mounted cylinder. As the accuracy and reliability were focused, the effect analysis of time-step was applied to three typical reduced velocities, which was represented initial branch, upper branch and lower branch respectively. Under the effective courant number, there exist a time-step which would lead to the highest efficiency and the best match for experiment. Because of the limit of RANS method, the predicted vibration amplitude at the upper branch would be lower than experiment value, while the phase angle is sensitive to time step.

Optimization Design of Self-Excited Oscillation Cavity

Along with the over exploitation of oil and gas resources, complicated reservoirs should be exploited in abominable environments. New drilling methods, drilling tools and drilling crafts for breaking rock are urgently needed. In drilling project, opening radial holes in the wall of self-excited oscillation cavity, more drilling fluid absorbed from annulus and more hydraulic energy could be obtained to break rock efficiently. Therefore, in this paper, self-increasing flux of cavity with different velocity in annulus, ratio of upper and lower nozzle diameters and diameter of aperture were simulated using CFD numerical method. Then flow fields in different aperture conditions and the best aperture parameter were obtained. Some references can be provided to actual drilling for further better jet breaking rock and improving drilling speed, which also have a good economic benefit.

Uniform surface polished method of complex holes in abrasive flow machining

Abrasive flow machining(AFM) is an effective method that can remove the recasting layer produced by wire electrical discharge machining(WEDM). However, the surface roughness will not be easily uniform when a complex hole is polished by this method. CFD numerical method is aided to design good passageways to find the smooth roughness on the complex hole in AFM. Through the present method, it reveals that the shear forces in the polishing process and the flow properties of the medium in AFM play the roles in controlling the roughness on the entire surface. A power law model was firstly set up by utilizing the effect of shear rates on the medium viscosities, and the coefficients of the power law would be found by solving the algebraic equation from the relations between the shear rates and viscosities. Then the velocities, strain rates and shear forces of the medium acting on the surface would be obtained in the constant pressure by CFD software. Finally, the optimal mold core put into the complex hole could be designed after these simulations. The results show that the shear forces and strain rates change sharply on the entire surface if no mold core is inserted into the complex hole, whereas they hardly make any difference when the core shape is similar to the complex hole. Three experimental types of mold core were used. The results demonstrate that the similar shape of the mold core inserted into the hole could find the uniform roughness on the surface.

Effect of a shield on the hydraulic and thermal performance of a plate-fin heat sink

The hydraulic and thermal performance of a plate-fin heat sink undergoing cross flow forced convection with the introduction of a shield was investigated. With a CFD numerical method, the influence of fin width, fin height, number of fins and Reynolds number were assessed without and with a shield. A shield that tends to decrease the bypass flow effect has a great influence on the variation of the thermal fluid field and the performance of the heat sink. The results of attaching a shield show that more coolant fluid is forced to flow into the fin-to-fin channel to enhance the heat transfer, increasing the pressure drop; this trend is significant at low Reynolds numbers. The decrease of thermal resistance due to the shield diminishes with increasing fin height, but increasing the width of the fins has a more radical effect. For a shield at a particular Reynolds number, the fin geometry should be selected carefully to fit the demands of enhanced effectiveness of heat transfer and decreased power consumption.