Development of Low Specific Speed ​​Centrifugal Pump Impeller Based on Flow Control Technology Chen Hongxun U, Liu Weiwei 3, Jian Wen 3, Wei Peiru 3, Zhu Bing 1 (1. Shanghai Institute of Applied Mathematics and Mechanics, Shanghai University, Shanghai 200072, China; Focus on the application of energy engineering.
1.2 Numerical calculation The finite element method based on finite element method in 11.0 software discretes the equations and introduces the shape function into the discrete process of the equation. The diffusion term and the pressure gradient term are represented by the shape function, and the convection term adopts the high resolution format. The solution to the flow field uses a fully implicit multi-grid coupling solution method, while simultaneously solving the momentum equation and the continuity equation. The introduction of algebraic multigrid technology can effectively control the scale of the grid and speed up the solution. In the calculation process, the root mean square residuals of the pressure and momentum in each direction are monitored to converge to 10-6. At the same time, the head error is monitored and converged to 10-3. The pressure distribution and flow lines in the pump are calculated. Show.
It can be seen that there is a large vortex in each flow channel of the water pump. The vortex consumes energy and also blocks the flow channel.
This indicates that the boundary layer of the blade surface is severely separated, which is the main reason for the low efficiency of the low specific speed centrifugal pump.
2 Splitter Blades 2.1 Physical Model The vortex within the impeller is conventionally designed by setting up short splitter blades so as to improve the flow state and make the flow path clear, thereby improving the efficiency of the pump. For two types of splitter vanes, the angles between the center of the splitter vane and the back of the adjacent vane are 45° and 36°, respectively. The flow lines of the splitter vane pump calculated by the numerical calculation of the Journal of Irrigation and Mechanical Engineering 2.2 are shown. It can be seen that the flow state in each flow channel during the operation of the pump for setting the short splitter blades has been improved, there is no longer a large vortex, but the flow line at the front end of the split short blade is still distorted; after changing the position of the short split vane The flow pattern in each flow channel of the water pump has been improved and improved, in particular, the distortion of the flow line at the front end of the short blade has been eliminated.
Partial-flow vane pump inflow line Fig. Efficiency point flow rate 42.36m3/h, the effect of the 36° pump splitter vane under large flow conditions on efficiency improvement is even more pronounced with the 45° pump than the splitter vane; the splitter vane makes the pump efficient When the point is shifted to a large flow, that is, when the pump is operating at a large flow rate, the contribution of the splitter blade to the efficiency can be seen, and the efficiency of the pump at a small flow rate does not increase significantly.
3 Trench Drainage Blades 3.1 Physical Model Prevention of Boundary Layer Separation The method of boundary layer separation is to supply energy to the blocked fluid in the boundary layer. A special device can be set in the pump body, or the energy of the mainstream itself can be used to provide energy. Taking into account the simplification of the process, ease of control and no additional energy loss, the energy of the mainstream itself is used to suppress boundary layer separation. In order to effectively use and guide the flow in the pump itself to inhibit the separation of the boundary layer, the author proposed a design method for the grooved-drainage vanes. A groove is formed between the suction surface and the pressure surface of the blade. Using the pressure difference between the two ends of the groove, the high pressure flow is directed to a proper position in the separation zone to inhibit the separation of the boundary layer and improve the pump efficiency.
Trench Drainage Blades Fig. 2.3 Performance Tests The authors tested the pumps of conventional blades and two splitter blades respectively.
Conventional vane and splitter vane pump efficiency-flow ratio comparison Fig.5Efficiency―lowcomparisons can be seen: the conventional design vane pump is the most efficient working point when the flow rate is 37m3/h, and the maximum efficiency point flow of the pump is 36°. 42.5m3/h, the pump with the 45° diverter vane 3.2 Performance Test The performance curve of the grooved-discharge vane pump was obtained through experiments and compared with the performance curves of the above three vane pumps, as shown.
Sheet-leaflet leaf-leaflet flow meter bow-slotted slot short-sequence convection flow-efficiency comparison diagram of the four-leaf pump type Fig.7Efficiency-flowcomparisons Jet vane (small angle of attack) Split-length vane (30 long splitter vanes (45) Conventional design vane (a) Efficiency - Flow rate (b) Efficiency - Specific speed - Gap jet (large angle of attack) - Gap jet blade (small attack Angle) Grooved Jet Blades One Long Splitter Blade (36") - Short Splitter Blade (45) Conventional Design Blades As can be seen: The highest efficiency point flow rate of the grooved-draft vane pump is 46.42m3/h, and the conventional design vane pump Compared with the splitter vane pump, the grooved drainage vane not only enlarges the operating range of the pump, but also improves the efficiency under all operating conditions, especially the large flow point, the efficiency is improved even more; the efficiency of the grooved-draft vane pump The curve is more flat, that is, the wider efficient area.
4 Gap Drainage Blades 4.1 Physical Model The above-mentioned conventional design of the blade's pump inflow line begins to separate near the blade inlet (see b), which is related to the incoming angle of attack. The author believes that the angle of attack of the incoming flow has a significant effect on the performance of the pump, and it is also the cause of the separation of the boundary layer. Adjusting the angle of attack at the incoming flow can obtain the best conditions for the outflow. The paper is modified at the inlet of the blade to cut a gap of a fixed width. The front end controls the flow angle of attack, and the incoming flow rushes through the gap to the separation zone to suppress flow separation. Based on the initial success of the small angle of attack, the gap form was changed, and the suppression of flow separation was further strengthened. Such as slotted blade schematic diagram.
4.2 Performance test Through the test, the performance curves of small-angle-of-attack and large-angle-of-gap drainage pump have been obtained. Compared with the performance of the above four kinds of blade pumps, as shown.
It can be seen from a that the highest efficiency point flow rate of the small-angle-of-opening slotting vane pump is 51.52m3/h, and the highest efficiency point flow rate of the high-angle gap slotting vane pump is 52. Compared with the vane pump, the gap-draft blade progresses and expands. The pump's operating range; low angle of attack slits in the pump to improve efficiency in multiple operating conditions, even in the small flow rate when the efficiency is significantly improved; high angle of attack slit gap pump pump efficiency in the small angle of attack slit gap blade On the basis of the pump, the progress in the entire operating range is improved.
b Further confirmed the new blade-to-pump efficiency improvement. 5 Conclusion Pumps with drainage vanes Compared to conventionally designed vane pumps, the operating range of drainage vane pumps has not been expanded, but the efficiency of large flow rates has been improved.
Grooved blades increase pump efficiency across the entire flow range and expand the flow range.
Compared with the grooved vane, the slotted-draft blade allows the pump to operate in a larger flow range, and the efficiency can be greatly improved over the entire working range. The slot-drawing blade has the best effect at a large angle of attack.
Flow control technology can be used to improve the efficiency of low specific speed centrifugal pumps. The introduction of drainage blades has also found a new way for the performance improvement of low specific speed pumps. The two technical achievements have already applied for patents and one of them has been authorized.
Acknowledgements: This research work was funded by the Shanghai Municipal Science and Technology Committee and the Shanghai Baoshan District Science and Technology Committee. The funded projects are numbered 06ZR14032, 10100500200, and 07-H-1.
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