A New Type Of Tip-jet Self-driving Fan’s Research

For the conventional turbofan engine,the way to increase the bypass ratio also result in incompatibility of spool speed problem among the fan、compressor and low pressure power turbine.Which effective way can eliminates the transmission between fan and compressor to further increase the bypass ratio? Out of this research,a new type of tip-Jet self-driving Fan was identified as a potential attractive option for high bypass ratio turbofan to solve the problem.Through the duct inside the rotate fan blade,the high pressure bleed air from the engine is accelerated and changing directions at the tip ring duct,and finally exhaust through the nozzles which installed in the ring duct,they produce force that applied driving torque to the ring fan,in order to achieve the pressurization function.In this paper,the numerical simulation of tip-jet self-driving fan with a ring is carried out based on the basic theory and structural scheme of tip-jet self-driving fan.Based on the same fan speed,outlet backpressure and jet velocity,the numerical analysis including research the change of bleed air parameters required for the new type of tip-Jet self-driving fan to reach the balance of power under different nozzle outlet cross-sectional area and bleed air temperature conditions,and the jet flow’s influence within the main flow field.Compared to a conventional fan,the new type of tip-jet self-driving fan with a ring can get enough drive torque for rotate.In a single bleed air temperature condition,the difference of nozzle outlet cross-sectional area lead the bleed air pressure and mass flow rate required will have a larger numerical changes.When the nozzle outlet cross-sectional area is constant,the change of bleed air temperature lead to the change of bleed air pressure is not obvious,but it has a greater impact on the bleed air mass flow rate.Because of the relatively high bleed air pressure required for the new type of Tip-Jet self-driving fan under the different cross-sectional area of the nozzle outlet,and the static pressure is relatively low in the main filed,resulting in the exit gas of nozzles will continue to accelerate expansion.The influence of the jet flow on the main flow field of the fan rotor blade downstream under the different nozzle outlet cross-sectional area conditions is studied.It is found that the influence range of jet flow is basically same in any axial section,and the influence range of jet flow is correspondingly increased along with jet gas to the downstream expansion process,and the influence range is mainly concentrated in the region above 85% of the span position,and the blending loss will be correspondingly increased along with the expansion of the influence range.The influence of jet flow on the main flow region of fan blades is also studied.When the cross-sectional area of nozzle outlet is different,it is found that the effect of the jet flow on the mainstream region is all basically same,the influence of jet flow on the surface airflow parameters of fan blades is not significant under the each nozzle outlet cross-sectional area condition,and the influence range is mainly concentrated in the region above 90% of the span position.The effects of jet flow on the parameters of fan outlet are studied.The results show that the influence range of jet flow on the outlet is mainly concentrated in the region above 85% of the span position.According to the analysis of the total pressure parameters,it shows that the total pressure parameters of outlet are different due to the difference of jet mass flow rate and the radial total pressure distribution under different nozzle outlet cross-sectional area conditions.From the overall analysis,under the tip-jet self-driving fan with a ring,the effect of jet flow on the mainstream field of fan blade is very small,but due to the nozzle outlet cross-sectional area and the jet velocity limit,and the fan’s radial size caused the drive torque is too large,leading to the bleed air pressure and bleed air flow are still high.