Design And Research On The Flow Characteristics And Cooling Performance Of The Vane Shaped Pre-swirl System

For modern gas turbine engines,with the increase of turbine inlet temperature,the effective cooling method for the high-temperature component has become a crucial issue to ensure the engine reliability and life-time.It is also a core technology that every country develops vigorously.The pre-swirl system which plays an important role in the turbine cooling technology can provide cooling air with an appropriate level of flow rate and pressure for turbine rotor blade.Besides,it will reduce the temperature of cooling air as much as possible and consequently improve the system cooling performance.In the pre-swirl system,the angled pre-swirl nozzles first swirl the cooling air in the direction of the rotor rotation,and this reduces the relative total temperature of the cooling air supplied to the disc for blade cooling.Then,the cooling air passes through the pre-swirl cavity,receiver holes and cover-plate cavity,after which the air enters into the supply holes for blade cooling.Therefore,the pre-swirl cooling air delivery system consists of several components and relates to rotor-stator cavity,rotor-rotor cavity as well as complicated work-heat conversion problems.In order to satisfy the cooling air supply conditions and further improve the cooling efficiency,it is essential to understand the flow mechanisms and explore the temperature drop potential of the pre-swirl system,as well as to obtain the system design method.In this paper,a comprehensive study into the design of vane shaped pre-swirl system was conducted by theoretical analysis,numerical simulations and experimental measurements.At first,the factors that influence the temperature drop of pre-swirl system were deduced theoretically and this can provide guidance and help for system design and structure improvement in the current study.Secondly,for the stationary pre-swirl nozzle,the cascade vane nozzle was designed and the vane shaped hole nozzle was proposed.The flow details and loss mechanisms for four types of nozzle(simple drilled nozzle,aerodynamic nozzle,cascade vane nozzle and vane shaped hole nozzle)were compared through the validated numerical method.In addition,the discharge coefficient were measured in the pre-swirl nozzle test rig.The measurements for the nozzle outlet flow field were designed and the deviation angle and pre-swirl effectiveness of vane shaped nozzles were tested for the first time.The influences of pressure ratio,Reynolds number,rotational speed,scaled up size and structure simplification on the nozzle performance were investigated.Then,according to the radius of pre-swirl nozzle and the work relationship between rotor and cooling air,four types of pre-swirl system were defined:low radius poor-pre-swirl system,high radius poor-pre-swirl system,low radius undue-pre-swirl system and high radius undue-pre-swirl system.The compressor-type vane shaped receiver hole and turbine-type vane shaped receiver hole were designed separately for these four types system.Moreover,the characteristics of system with vane shaped receiver holes were compared to the system with drilled receiver holes and inclined receiver holes in the cover-plate.On this basis,the differences between high and low radius systems were compared to better understand the system behavior.The matching between different components was analyzed and the design method for pre-swirl system was summarized.Finally,the rotational experiments for pre-swirl system with vane shaped nozzle and receiver hole were conducted.The influences of parameters such as nozzle structure,receiver hole structure,pressure ratio,rotational speed on the aerodynamic loss and temperature drop performance were investigated.Most importantly,the matching design method proposed in this current study for the pre-swirl system was also verified.Results indicate that the aerodynamic loss due to the profile of simple drilled nozzle is significant,resulting in nozzle discharge coefficient(CD)and pre-swirl effectiveness(?)both lower than 0.8.The performance of cascade vane nozzle(VN)dramatically improves,but the ratio of passage width to height is too small,which still leads to obvious endwall secondary flow loss and trailing edge loss.The vane shaped hole nozzle(VSH)designed in this paper could adjust the vane height/pitch ratio to an appropriate value,and also has well-performed vane profile and smaller trailing edge.This contributes to lower endwall secondary flow loss and trailing edge loss.The discharge coefficients of these two types vane shaped nozzle are high and similar,both around 0.95,20%higher than that of hole shaped nozzle.However,the deviation angle of VN is relatively large,around 2°?3°and consequently the pre-swirl effectiveness is only 0.85.As for VSH,the pre-swirl effectiveness can be as high as 0.94,about 10.6%higher than that of VN due to the decreased deviation angle,which is smaller than 0.5°.The deviation angle,discharge coefficient and pre-swirl effectiveness all increase with pressure ratio,but the influence of pressure ratio would gradually decrease as the nozzle performance improves.As the Reynolds number rises,CD and?values increase first,and then remain constant.The critical value is about 2×10~5.In addition,rotational speed has little effect on the nozzle discharge behavior and the influence of scaled up size and structure simplification on CD is less than 1.6%.In the engine real operating conditions,CD and?values of vane shaped nozzle almost remain constant with the pressure ratio,Reynolds number and rotational speed.The design of pre-swirl system could not only aim at improving flow characteristics of separate component,instead it is more important to comprehensively consider the matching of air swirl ratio among them.Under the conditions of unchanged pre-swirl nozzle and supply hole,the vane shaped receiver hole designed in this paper could make the matching design among pre-swirl nozzle,receiver hole,cover plate cavity and supply hole available.The vane shaped receiver hole has the characteristics in adjusting swirl ratio distribution in the system reasonably and reducing the overall aerodynamic loss,and consequently improving the system cooling performance.Adopting the compressor-type vane shaped receiver hole,the temperature drop effectiveness(?t)of low radius poor-pre-swirl system reaches 0.55,about 4times the basic model with the drilled receiver hole.?t values of high radius poor-pre-swirl system can be as high as 0.71,about 2.3 times the basic high radius direct system.As for the undue-pre-swirl system,turbine-type vane shaped receiver hole brings about a 44%temperature drop effectiveness rise in low radius system,and the?t value of high radius system is 0.66,about 20%higher than that of basic model.It can be observed in the pre-swirl system rotational experiments that,the CFD results show a good agreement with the experimental data at pressure ratio range 1.1?1.9 and rotational speed range 0?7500rpm.The maximum deviation in nozzle discharge coefficient is around1.6%and that in temperature drop is less than 1.8K.For the same rotor structure,the temperature drop effectiveness of system with the vane shaped hole nozzle is 0.49,8.9%higher than that of system with cascade vane nozzle.For the same nozzle structure,the vane shaped receiver hole applied to the system results in a 22.4%increase in?t,compared to the system with the drilled receiver hole.