Optimization Desigin And Flow Characteristics Research Of Bi-directional Axial-flow Pump

Three-dimensional unsteady flow mechanism and control of trurbomachinery is one of the research hotspot in the discipline. Bi-directional axial-flow pump always used S-shaped blade that designed through traditional binary method, which is the "heart" component of the low head pump station that need pump water bi-directionally to meet the demand for both drainage and irrigation simultaneously. However, when forward and reverse operation conditions is different, energy efficiency will become low. In reverse operation, the flow field include some complex flow phenomenon like adverse pressure gradient changes, boundary layer separation, large scale backflow, and it restricted the overall performance of the pump. Based on theoretical analysis, numerical simulation and experimental methods, this article carried out research work about optimization design of non-symmetry airfoil bi-directional axial-flow pump, internal flow mechanism, active/passive flow control technology and pressure fluctuation characteristic. The main research results are as follows:Firstly, a design method for low arch arc airfoil bidirectional blade was put forward based on the conformal transformation method. The relationship between positive and reverse theoretical head and velocity circulation was established based on Zhukovsky conversion. Through adjusting cascade geometric parameters, the positive and reverse performance was allotted differently. At the same time, the conventional S-shaped model was designed through lifting method for comparative study. The time-averaged flow field and pressure fluctuation characteristic of both S-shaped airfoil and circular arc airfoil bi-directional pump were systematically compared. The pressure fluctuation characteristic on blade and guide vane surface was studied through creating small grid unit on blade and guide vane surface grid, and monitoring the average pressure on it. Then the flow characteristic in saddle zone and tip clearance flow characteristic under both positive and reverse operation was compared. The performance experiments under different setting angles were carried out for two models. The results show that the radial motion of fluid particle near trailing edge was smaller in arc airfoil blade, the pulsation amplitude near blade inlet and outlet was also lower, and the positive efficiency increased by 3.5% while the reverse efficiency increased by 1.3% under 0° setting angle than S-Shaped airfoil model; The pressure pulsation on blade was mainly affected by guide vane number, its dominant frequency was guide vane passing frequency, while the pressure pulsation on guide vane was mainly affected by guide blade number, its dominant frequency was blade rotation frequency; In small flow rate, the stronger low-frequency pulsation appeared which frequency were 1-2 and 4-5 times of rotating frequency in positive operation,0?2 times frequency in reverse operation.Secondly, the model change design research was carried out. The flow model under reverse operation was established for bi-directional axial-flow pump using bend guide vane. Therefore, the straight guide vane was introduced to reduce the high attack angle of suction surface under reverse operation. Based on Q equivalence surface method, the structure and unsteady evolution process of the vortex in straight guide vane area was studied. Then the method was put forward to control the flow separation strength on suction surface through reasonable selection of the airfoil. The influence of relative position between guide vane and elbow on flow field structure and performance was analyzed. The results show that straight guide vane can eliminate the positive pre-swirl in the front of blade, the main flow loss in rear straight guide vane was caused by the boundary layer separation of the suction surface and shedding vortex, and reasonable choice of airfoil can reduce the flow separation strength; elbow can destroy the axial symmetrical distribution of upstream flow field, and change incidence angle of each vanes.At last, the parametric optimization platform for axial-flow pump (fan) was established, which contained blade and flow passage geometrical parameter. The existing axial flow blade optimization method was improved. After that, and a combinatorial optimization method was put forward for blade, which contains design of experiment and velocity gradient optimization algorithm. Based on optimal Latin hypercube method and sequential quadratic programming algorithm, the blade and flow passage was optimized. It's was used to accelerate convergence by increasing the space step. Compared with the conventional experimental design and sequence quadratic programming algorithm, the positive efficiency increased by 3.07% and 0.87%. The radial pressure difference and circumference rotating speed decreased by using diffusion tube. And the positive efficiency increased by 1.52% and 2% respectively after optimizing the blade and flow passage.