Investigation On The Influence Of Blade Key Parameters On The Internal And External Characteristics Of Multi-blade Axial-flow Pump Impeller

Axial turbine pumps are widely used in high thrust liquid rocket engines because of their high efficiency,light weight and compact structure.As the core component of the axial turbine pump impeller,the key parameters of the vane have a profound influence on the hydraulic performance of the impeller.To address the issue of the influence of blade key parameters on the impeller of multi-blade axial flow pump,this paper adopts a combination of numerical simulation and theoretical analysis,and takes NASAν=0.8（multi-blade axial flow pump impeller with hub ratio of 0.8）as the research object to systematically study the influence of blade key parameters on the internal and external characteristics and energy dissipation characteristics of multi-blade axial flow pump impeller.The specific work and main research results of this paper are as follows:1.The influence of the density of the leaf grid on the internal and external characteristics of the impeller of multi-blade axial flow pump.Based on the SST k-ωturbulence model,numerical simulations were conducted for nine impeller grille densities with different blade chord lengths and inter-blade spacing.The mechanism of the mass flow weighted velocity variation of impeller inlet and outlet under different grille densities is revealed,and the influence of different grille densities on the internal and external characteristics of the impeller is elucidated.The results show that the increase of grille density increases the shaft power,and the efficiency of the impeller with changing chord length has a parabolic shape distribution,reaching a maximum of 93.47%at（l/t）_peri=1.21;the head and efficiency of the impeller with changing grille pitch have similar trends,reaching a maximum of 0.407 at（l/t）_peri=1.42 and the efficiency at（l/t）_peri=0.89 reached a maximum of 93.32%.The pressure coefficient on the working surface and back side of the blade decreases with the increase in the density of the blade grille,while the pressure difference between the two sides of the blade becomes smaller to improve the anti-cavitation performance.At the same grating density,the chord length can be changed to control the impeller speed better than changing the grating distance.The impeller grid density and impeller inlet pressure pulsation amplitude are linearly negatively correlated,while the impeller outlet pressure pulsation amplitude is positively correlated with the grid density,but the influence on the outlet pressure pulsation is small.The proportion of turbulent dissipation in the impeller of multi-blade axial flow pump is the highest,the proportion of wall friction is the second,and the proportion of direct dissipation is the smallest.Optimization of multi-blade axial flow pump impeller can appropriately reduce the number of blades or increase the blade chord length to reduce the relative loss,increase the number of blades can weaken the turbulent dissipation,increase the blade chord length can weaken the turbulent dissipation,the change of friction loss coefficient is not obvious.2.the effect of the relative thickness of the blade on the internal and external characteristics of the impeller of multi-blade axial flow pump.Taking the displacement coefficient as the entry point,numerical simulations are conducted for five different blade relative thickness schemes to reveal the mechanism of impeller inlet and outlet based on the mass flow weighted velocity variation law for changing different blade relative thickness,and to elucidate the influence law of different blade relative thickness on the internal and external characteristics of the impeller.The results show that the highest impeller efficiency is 94.06%at the blade relative thicknessδ_i/δ=0.50,which can be used as a reference for optimal design.The blade displacement coefficient cannot be used as a judgment basis for the change of velocity triangle of impeller inlet of multi-blade axial flow pump based on mass flow weighting.The increase of the relative thickness of the blades will reduce the cavitation resistance of the impeller and have an impact on the impeller inlet pressure pulsation,but will reduce the impeller outlet pressure pulsation.In the small flow condition,the velocity change at the impeller inlet near the hub is opposite to the large flow condition.The relative impeller velocity and axial velocity are positively correlated with the relative blade thickness,while the absolute velocity,the absolute fluid flow angle and the relative fluid flow angle are unstable at the position near the hub under the small flow condition.The friction loss at the impeller wall rises the most and the turbulent dissipation loss accounts for the highest proportion,and the total turbulent dissipation coefficient decreases with the increase of the relative thickness of the blade,that is,increasing the blade thickness can reduce the direct dissipation coefficient of the impeller domain and the friction loss coefficient at the impeller domain wall.3.The influence of blade shape on the internal and external characteristics of the impeller of multi-blade axial flow pump.The external characteristics of the impeller with 791 airfoil blades and the impeller with double-circular-arc blades are quite different,with the maximum efficiency point of the 791 airfoil reaching a maximum of 92.4%at a flow coefficient of 0.408 and the maximum efficiency of the double-circular-arc blade reaching a maximum of 93.67%at a flow coefficient of 0.484.The difference in blade shape has little effect on the mass flow weighted velocity triangle based on the impeller inlet,but the larger curvature of the former creates a deluge on the working surface that affects to the impeller outlet,resulting in a lower velocity in the outlet section.In addition,the 791 airfoil has a higher main frequency amplitude and higher pressure pulsation at the impeller inlet.At the impeller outlet,the pressure coefficients of the impeller of both airfoil types fluctuate more,with a higher peak for the 791 airfoil type and a lower but wider range for the bicircular arc airfoil type.the back pressure coefficient of the791 airfoil type is lower than that of the bicircular arc airfoil type,so it is more likely to produce cavitation.the impeller efficiency of the 791 airfoil type decreases at a higher rate than that of the bicircular arc airfoil type as the radial coefficient increases,while at the close to the wheel edge position,its efficiency is higher than that of the double-arc airfoil.the higher total entropy production value of the 791 airfoil type is mainly due to turbulent dissipation,and the difference between the direct dissipation and wall friction of the two is not significant.