Numerical Investigation On The Aerodynamic Performance Of Ram-rotor By Flow-path Configuration

As a new type of rotary power machinery,gas turbines are used as excellent propulsion system of aircrafts and ships.The development of high-performance compressors is one of the means by which gas turbine can be improved.The airflow can be compressed sharply and efficiently through shock systems in the ram-rotor which has the advantages of high pressure ratio,compact structure and light weight.However,there are interaction between shocks and interaction between shock and boundary layer in ram-rotors,which generates complex flow phenomena such as the flow separation induced by the interaction and is responsible for high flow loss and performance degradation.Therefore,it is an important aspect to take measurements for the purpose of reducing flow loss caused by shocks and flow separation.The research about ram-rotor will inevitably be able to effectively improve the gas turbine’s power to weight ratio and reduce the fuel consumption rate,which has broad theoretical significance and application prospects.The ram-rotor is studied in this thesis,and firstly detailed flow field about shocks,flow separation,etc is analyzed.The results show that the interaction between low momentum fluid mass near strake trailing edge,boundary layer on the strake suction side and shocks on S1 stream surfaces lead to serious flow blockage near the strake suction side.After the leakage flow encounters terminating shock/shock train,a large area of low-momentum fluid is formed near the casing wall.The flow loss induced by leakage is one of the major sources of ram-rotor flow losses.Based on the analysis of flow field,the compression and diffusing ramps are built.The results about the starting and ending slope angle of ramps show that the compression ramp mainly affects the strength and the position of the shock system before the throat.Changes in the profile of the diffusing ramp do not affect the flow field before the throat,and the pressure rising and flow separation characteristics are affected by changing the expansion degree of the flow path near the diffusing ramp.Then,the blade design method of conventional turbomachery is used to reconstruct the strake profile of ram-rotor.The effects of strake profile type,leading edge aerodynamic sweep and strake aft part lean on the flow field and performance of ram-rotors are the main focuses of attention.It is found that the ram-rotor scheme with equal thickness distribution at pressure side and quadratic curve distribution at front/rear suction is the best.The more backward the starting point of the maximum thickness is,the better the performance of the rotor is,and when the maximum ending point is shifted backward,the total pressure ratio and the adiabatic efficiency both show a tendency of increasing first and then decreasing.The introduction of the aerodynamic sweep can change the position of the leading edge shock of S1 stream surface,and then affects the flow field and the shock structure near the strake pressure side.For forward swept scheme,it is easier to separate the leading edge shock and the incident shock.The aerodynamic load of tip strake section is minimum,which helps to reduce the flow loss and improve the adiabatic efficiency.The backward swept scheme makes it easier for the leading edge shock and incident shock wave to merge into a stronger shock,which increases the aerodynamic load on the strake front part and improves the total pressure ratio.The leaned strake design can affect the strength and position of the shock system,and the radial transport and accumulation of the low-momentum fluid.For the ram-rotor which maintains the tip profile in line with the baseline,reflected shock and shock trains move upstream and the total pressure ratio reaches 2.902 with an increase of 2.338%.While the leaned ram-rotor which maintains the root section identified can delay the flow separation near the suction surface,and the blockage at the tip corner of strake aft part is relieved.This scheme makes an improvement of 0.462%in terms of adiabatic efficiency which is 0.726,compared to baseline.At last,the type of meridional flow shape is studied,and the influence of contraction and expansion in the meridional throughflow configuration on the total pressure ratio and adiabatic efficiency of the ram-rotor is analyzed.It can be concluded that the ram-rotor scheme with a contracting-and-expanding meridional channel has a reduced incoming Mach number,which decreases the flow loss caused by the shocks and the interaction between the shock and the boundary layer.The range and intensity of high-loss zones are obviously reduced.The total pressure ratio achieves 2.937 with an increase of 2.075%compared to the baseline,and the adiabatic efficiency gets to 0.748 with an increase of 3.160%.When the contraction angle increases,both the total pressure ratio and adiabatic efficiency rise first and then drop.With the increase of the expansion angle,the total pressure ratio gradually increases,and its adiabatic efficiency is presented as a law of increasing first and then decreasing.When the contraction/expansion angle changes at the same time,the geometry contraction in the front meridional channel plays a major role in the flow field of ram-rotor.When the contraction/expansion angle rises,the performance of the ram-rotor will increase first and then decrease.