Analysis Of The Numerical Model Of High Pre-ssure Internal Gear Pumps Based On CFD And Its Unbalanced Radial Forces

With rapid development of the economy and the demand of various industries, the trend of internal gear pumps is characterized by higher pressure, lower flow pulsation, lower noise, larger displacement and so on. The traditional low-pressure and medium-pressure internal gear pump is no longer suitable for high-pressure situations. Thus, the development and design of a high-pressure internal gear pump is an important direction in the fields of gear pumps. However, the problem of unbalanced radial forces is particularly obvious in high pressure gear pumps, which is one of the main reasons for development restrictions of current domestic production of gear pumps. Therefore, accurately predicting the distribution of the unbalanced radial forces and reasonablely designing the pressure compensation structures become the key to the successful operation of high-pressure internal gear pumps.Based on this, this paper is focused on the problem of the unbalanced radial forces in high pressure internal gear pumps by exploring the CFD numerical calculation method and theoretical research method sutiable for solving the unbalanced radial force of the internal gear pumps under a high pressure condition. Meanwhile, the compensation role of the static pressure slot on the unbalanced radial forces and the effect of its location and size on its compensation role are studied. As a result, the location and size of the static pressure slot are determined to satisfy the demand of the unbalanced radial forces of the high-pressure internal gear pump. In addition, a series of experiments are carried out on the design and operation of the high pressure internal gear pump to verify the reliability of the numerical calculation method and the theoretical method. Main work conducted is as follows:(1) Based on computational fluid dynamics software FLUENT,3D numerical model of an internal gear pump with a high pressure is established by 2.5D moving mesh method. Meanwhile, considering the presence of the engagement point between the two gears, a 3D numerical model using the sticky wall method is adopted to predict the hydraulic performances of the internal gear pumps, including the volumetric efficiency of internal gear pump with a high pressure.(2) Based on the MIXTURE model and Zwart-Gerber-Belamri cavitation model, a numerical model suitable to the cavitation performances of the internal gear pump is established. At the same time, the distribution of pressure and the unbalanced radial force are studied by the numerical model, as well as the compensation role of the hydrostatic support groove and the effect of its size on the radial force compensation.(3) The theoretical equations of the unbalanced radial forces are built according to the specific structure of the internal gear pump and the unbalanced radial forces of the annular gear are obtained. In addition, the equation of the hydrostatic bearing capacity of the static pressure support is derived and the effect of the structure parameters on its bearing capacity and its internal leakage. As a result, the static pressure support of the internal gear pump is determined aimed to satisfy the requirements of the unbalanced radial forces and the volumetric efficiency. And at the same time, the result is verified by the experiments.(4) The experiment rig for testing internal gear pump is built and the effect of the design parameters (clearance size, the hole size on the inner ring and the pump case, et.al) and the operation parameters (medium temperature, working pressure and the rotational speed, et.al) on the hydraulic performances of the internal gear pumps, including the efficiency of the internal gear pump, pressure pulsation and self-absorption properties. Meanwhile, the results of theoretical studies and numerical calculations are verified by the experimental data.Results show that the numerical model of high-pressure internal gear pumps based on CFD and the theriotical method built in this paper are able to predict the pump performance, the circumferential distribution of pressure and the unbalanced radial forces of the internal gear pump. Moreover, the numerical results are verified by experimental data. The mian conclusions includes:the engagement of both gears must be taken into consideration in the CFD numerical caculations when the pump works at a medium or a high pressure; the pressure variation (at the transient region) with the gear rotation along the circumferential direction is:the pressure increases with the gear rotation constantly when the gear addendum and crescent-shaped plate gets into the seals gradually (at the low pressure side of the transition zone) and when the gear addendum and crescent shaped plate disengages from the seals gradually (at the high pressure side of the transition zone), but remains unchanged when the seal position between the gear addendum and crescent shaped plate do not change with the gear rotation; the radial forces of the pump under high pressure conditions do not incerase directly proportional to that under low pressure condisitons, which is mainly decided by the pressure distribution in the high pressure section and the high area of the transition zone; the key that the internal gear pump can work under a high pressure condition is to determine the design parameters of the internal gear pump to achieve the most accurate compensation of the gap and the pressure, especially the position and size of the static pressure supporting groove, and so on.The contents and the conclusions obtained in this paper can provide theoretical guidance for the structure design and the operation of high pressure internal gear pumps.