Model Optimization And Experimental Study Of Ultra-low Specific Speed Axial Turbine

The ultra-low specific speed axial turbine for cooling tower is a new type of cooling tower turbine.Compared with the Francis turbine for cooling tower,it has the advantages of smaller plane size,better ventilation effect and easier welding and processing under the same cooling water volume.In the theoretical analysis,the design of the ultra-low specific speed axial turbine in this paper is aimed at achieving the hydraulic performance of a Francis turbine with similar specific speed.In the initial optimization design of this paper,four factors,namely blade width,guide vane outlet angle,guide vane number and blade number,are selected for four-factor and four-level orthogonal experiment.The orthogonal experiment results indicate that,according to the head assessment index,the influence order of four factors on the turbine is: blade width > guide vane outlet angle > guide vane number > blade number;according to the efficiency assessment index,the influence order of four factors on the turbine is: guide vane number > guide vane outlet angle > blade number > blade width;the optimal parameter combination is: blade width is 35 mm,guide vane outlet angle is 15 °,guide vane number is 8,blade number is 24,and the specific speed of the turbine optimized by the orthogonal test is basically less than 80 m×kW,which meets the specific speed requirements of the cooling tower turbine.Based on the CFD method,this paper studies the hydraulic performance of the ultra-low specific speed axial turbine.It specifically analyzes the law of the hydraulic loss,external characteristics and internal flow field of each flow passage component when the value level of different factors changes.The optimal parameter combination is completely consistent with the conclusion of the orthogonal test optimization design.At this time,the head under the design condition is up to 6.75 m,efficiency is up to 81.15%,power is up to 7.46 kW.According to the conclusion of orthogonal test and CFD analysis,the best parameters are selected to make the prototype,and a cooling tower turbine test-bed is built to test its external characteristics.The errors between the CFD numerical simulation results and the test-bed test results near the optimal operating point are as follows: the head difference is 0.29 m,the efficiency difference is 4.18%,and the power difference is 0.27 kW,it accounts for 5.45%,5.37% and 5.03% of the test results of the test-bed respectively,the error is small and within the allowable range,which verifies the accuracy of the theoretical method and CFD numerical method in the research and analysis of ultra-low specific speed axial turbine.