Study On The Effects Of Main Geometric Parameters Of Impeller And Volute On Performance Of High-Speed Fuel Pump

With the advancement of aerospace technology,centrifugal pumps have gradually replaced traditional gear pumps as the main and booster pumps in the fuel system of aviation engines due to their advantages of lightweight,strong dirt resistance,and no oil pulsation.Some of the fuel pumps are ultra-low specific speed pumps.However,ultra-low specific speed pumps commonly exhibit problems of low efficiency and unstable operation under small flow rate and high speed conditions.Furthermore,the main geometric parameters of impellers and volutes have significant differences in their impact on pump performance and internal flow field compared to traditional centrifugal pumps.Therefore,this paper focuses on a centrifugal fuel pump equipped with a semi-open compound impeller,and investigates the effects of the outlet angle of the compound impeller,the arrangement of the splitter blades,and the throat area of the volute on the external characteristics,internal flow field,and non-steady pressure pulsation characteristics of the fuel pump under small flow rate and high speed conditions,in order to improve the performance and operational stability of the fuel pump.The main research contents and conclusions of this paper are as follows:（1）Based on the given design parameters(flow rate Q=0.5 m³/h,head H=80 m,speed n=10000 r/min,medium is aviation kerosene,densityρ=786 kg/m³,dynamic viscosityμ=2.5×10^-3Pa·s,specific speed n_s=16),the hydraulic design of the fuel pump impeller and volute was completed by combining the ultra-low specific speed centrifugal pump velocity coefficient method and the enlarged flow rate design method.The influence of small flow rate and high speed operating conditions on the calculated values of various geometric parameters of the fuel pump was analyzed.（2）Four main factors that affect the performance of the composite impeller were selected,which are the blade outlet angle β₂,the number of blades z,the circumferential offsetθ_iof the splitter blades,and the deflection angleα.Using the orthogonal experiment method,16 sets of different parameters and structures of composite impellers were designed and numerically simulated for the entire flow path at the operating condition of Q=0.5 m³/h.After analyzing the range of the orthogonal experiment results,the main and secondary orders of the factors that affect the efficiency were determined,which are the circumferential offset of the splitter blades,the number of blades,the blade outlet angle,and the deflection angle of the splitter blades.Secondly,while ensuring that the head meets the working requirements,the optimal design parameters for the composite impeller of the fuel pump were selected as β₂=35°,z=5+5,θ_i=0.45θ,andα=8°（offset to the suction surface of the longer blade）for achieving the highest efficiency.（3）The optimal design solution and the conventional non-divergent blade design scheme were subjected to steady numerical simulations under 10 different operating conditions to obtain the external characteristic curves and internal flow field distributions of the two schemes.Furthermore,unsteady numerical simulations were performed under the actual operating condition of Q=0.5m³/h and the design operating condition（increased flow rate condition）of Q=1.25m³/h to obtain the pressure pulsation characteristics of the two schemes.Through comparative analysis,it was found that the efficiency and head of the optimal design solution were increased by 5.02%and 12.04%,respectively,under the actual operating condition,and by 8.87%and 18.59%,respectively,under the design operating condition,compared with the conventional scheme.Moreover,the gradient changes of the static pressure along the radial flow passage of the middle section of the optimal solution were more gradual,especially the static pressure distribution at the outlet of the impeller was more uniform.The large-scale vortices in the impeller flow passage were significantly weakened,and the overall turbulence intensity was significantly reduced.In addition,the pressure pulsation amplitudes at the impeller-volute interface and the diffuser throat of the optimal solution were significantly reduced compared with the conventional scheme,with the average pressure pulsation amplitudes at each monitoring point under the two operating conditions decreasing by 52.67%and 57.99%,respectively.（4）Based on the principle of area ratio,four different volutes with area ratios of0.046,0.058,0.069,and 0.081 were selected within the high-efficiency range of the domestic area ratio statistical curve,and matched with the composite impeller obtained from the optimal design.The four schemes were numerically simulated under ten different operating conditions to obtain their external characteristic curves.Non-steady numerical simulation was also performed under the actual operating condition Q=0.5m³/h and design condition Q=1.25m³/h to obtain the pressure pulsation characteristics of the volute and diffuser in the four schemes.After analysis and comparison,it was found that when Y=0.046,the efficiency of the fuel pump was the highest under the actual operating condition,but the head decreased rapidly with the increase of flow rate.The pressure pulsation amplitude on the inner wall of the volute and at the diffuser was the highest among the four schemes,which was not conducive to the stable operation of the fuel pump under multiple operating conditions.When Y=0.058,the overall efficiency was the highest within the range of low flow rates,but the average pressure pulsation amplitude in the volute was second only to that of the Y=0.046 scheme.When Y=0.069,the efficiency and head of the fuel pump were the highest only at the design condition,and the efficiency within the range of low flow rates（0.35m³/h≤Q≤0.95 m³/h）was significantly lower than that of the Y=0.046 and Y=0.058 schemes,but the average pressure pulsation amplitude in the volute was the smallest among the four schemes.When Y=0.081,the H-Q curve of the fuel pump was the flattest,and the maximum efficiency point of theη-Q curve was biased towards the high flow rate direction,which was conducive to the operation of the fuel pump under larger flow rate conditions.However,the efficiency at low flow rates was low,and the pressure pulsation amplitude along the circular direction of the volute appeared a significant sharp change,which was not conducive to the stable operation of the fuel pump.