Application And Aerodynamic Characteristics Analysis Of Tandem Cascade In Very Low Solidity Tip-turbine

The vertical take-off and landing power system based on the gas-driven ducted fan technology proposed by the research group can realize the vertical take-off and landing of the high-speed fixedwing aircraft.The core component tip-turbine has the characteristics of extremely low solidity and low aspect ratio,and the solidity can be as low as 0.6(conventional solidity is between 1.2~1.6),the aspect ratio can be as low as 0.3(conventional aspect ratio is between 1.5~2.0).At very low solidity,the airflow deflection capability of the tip-turbine blades greatly reduce and a large range of separation vortices appears at the trailing edge of the suction surface of the turbine blade.In view of this feature,based on the existing research,based on the design idea of high-reaction blade,the numerical simulation method is used to carry out the research on the low-thickness and high-reacting tip-turbine flow characteristics and its design technology.The tandem cascade technology is applied to low-solidity and high-reacting tip-turbines,and lays a theoretical foundation for the subsequent development of such vertical take-off and landing power systems.The main work includes:1.Based on the high-reaction tip-turbine blade type,the flow characteristics and loss composition of the low-solidity and high-reacting tip-turbine are studied.The results show: Unlike conventional tipturbines,there is no obvious separation vortex on the back of the high-reaction tip-turbine.The airflow in the flow channel is good,and there is a pneumatic throat that can further accelerate the airflow.At very low solidity,the load distribution on the surface of the high-reacting tip-turbine blade also exhibits a significant pre-loading tendency;under very low solidity conditions,the low-solidity low-strain ratio turbine is compared to the conventional solidity low aspect ratio turbine.The total amount of absolute loss increases sharply,the tip leakage loss decreases,the secondary flow loss increases,and the total amount of high-reaction tip-turbine loss is smaller than that of low-solidity and low-aspect ratio turbine,which is larger than the conventional solidity and lower aspect ratio turbine.Tip leakage losses account for more than half of the total loss,up to 54.15%.2.Research on the design technology of extremely low solidity and high-reaction blade for the vertical take-off and landing power system of air-driving ducted fans.The blade flow field and performance changes are analyzed by factors such as angle of attack variation,blade thickness distribution and leading edge radius.At the same time,the performance evaluation criteria of the extremely low-solidity tip-turbine are supplemented,and the energy utilization rate is used to comprehensively measure the gain of the tip-turbine to the entire ducted fan propulsion power system.The results show that the change of the angle of attack caused by the change of the camber i will not affect the efficiency of the tip-turbine.The suitable negative angle of attack of the rotor inlet can strengthen the pneumatic throat and increase the airflow.The expansion acceleration ability outside the flow path,thereby increasing the turbine drop ratio,improving the energy extraction rate and energy utilization rate,makes the contribution rate of the tip turbine to the propulsion system to a higher level.Although the high-reaction tip-turbine is still lower in efficiency than the conventional solidity turbine,it is close to the conventional solidity turbine in terms of energy extraction rate,and is even higher in energy utilization than the conventional solidity turbine.3.Apply the tandem cascade technology to expand the application effect of the blade strong influence area in the extremely low solidity and high-reaction tip-turbine.Focus on the tandem cascade chord length ratio and camber ratio to the tip-turbine energy extraction and energy utilization.The change of the chord length ratio will affect the addition of the front and rear blades and the mixing of the leakage vortex;the change of the camber ratio will affect the energy extraction effect of the blade and the range of the strong influence zone.When the chord length ratio is 2.04 and the camber ratio is 1.12,the tip turbine performance is the best.The optimal solution has a 13% increase in energy extraction rate compared to the original conventionally low solidity tip turbine,an energy efficiency increase of 21%,and an efficiency increase of 5%.