Modelling of fluid flow in multiple axial groove water lubricated bearings using computational fluid dynamics

摘要

Extensive research has been conducted in the area of journal bearings over many years for various operating conditions and geometry, effects of different types of lubricants (oil and water), different numbers (zero, one and three) and positions of grooves and the flow of lubricant between the shaft and bearing. One area of research has been developing methods to minimize the experimental time and cost of predicting the performance of journal bearings operating over a wide variety of conditions. This has led to numerical methods being developed and utilised for this purpose. Numerical methods are an important foundation for the development of Computational Fluid Dynamics (CFD). CFD method has proved to be a very useful tool in this research field.This project uses a CFD (specifically FLUENT) approach to simulate the fluid flow in a water lubricated journal bearing with equal spaced axial grooves. Water is fed into the bearing from one end. The lubricant is subjected to a velocity induced flow, as the shaft rotates and a pressure induced flow, as the water is pumped from one end of the bearing to the other. CFD software is used to simulate the fluid flow phenomenon that occurs during the process. Different parameters such as eccentricity ratio, number of grooves and groove orientation to the load line were examined. Lubricant pressure and velocity profiles were obtained and compared with available theoretical and experimental results.Two dimensional studies showed that the predicted maximum pressure and load carrying capacity from CFD were similar to the results from theoretical calculations. A small percentage difference (1.78% - 3.76%) between experimental and theoretical results was found. The pressure distribution in the lubricant shows that grooves decrease the pressure and load carrying capacity of the bearing. Swirl or turbulence does occur in the groove is affected by the viscosity of the lubricant. Three dimensional studies show that the pressure drops linearly from one end of the bearing to the other for no groove, concentric and three grooves cases. As the eccentricity increases, for one groove cases, the shape of the pressure profile changes to parabolic shape at positive region while the other pressure profiles drop linearly. The magnitude of the velocity it the bearing gap increased from 0.8 m/s to about 2.9 m/s when the shaft speed increased from zero to 5.5 m/s for a concentric and no groove case, similar changes were noted for all other cases.An interesting observation occurs when implementing the pressure profiles along the bearing. At cases such as zero and one groove condition and e = 0.4 and 0.6, lubricant flow back is observed at both inlet and outlet i.e. at certain area of the inlet, lubricant flowed out of the bearing against the supply pressure, a similar situation occurred at the exit of the bearing.