Researches And Applications Of Interaction Between Coolant Ejection And Shock Wave In Transonic Turbines

Improving the load of turbine cascade is the most direct mean to enhance the working capacity of turbine,which then increases thrust to weight ratio of the entire engine under the premise of not increasing the stage of turbine.Therefore,looking for a way to control the increase of shock wave loss and the influence of shock wave on film cooling performance,which are caused by the high-load of turbine cascade,has been payed more and more attention to by practitioners.More basis of parameters selection during the cooling design process of high-load transonic turbine can be provided after finding the influence mechanism between coolant ejection and shock wave.Moreover,coolant jet can even be used to arrange the flowfield in order to improve aerodynamic performance of the cascade.In this dissertation,influences of length of cut-back structure and coolant ejection rate at trailing edge on intensity of shock wave have been studied at first by numerical simulation method.Length of cut-back and flow rate of coolant are controlled seperately during the whole simulation process to fully study influence of each parameter on aerodynamic performance of cascade.Results show that cut-back structure at trailing edge can change the structure of shock wave of transonic turbine cascades with high outlet mach number.The influencing mechanism of cut-back on intensity of shock wave at trailing edge is mainly the blocking effect,which is conducted by long cut-back or large coolant ejection rate on main flow come from pressure side near trailing edge.This can make main flow avoid from being over compressed by cut-back structure and anticipation of flow seperation on suction side,which widen the wake flow and increases energy loss.For a fixed length of cut-back or fixed coolant ejection rate,the coolant rate and length of cut-back both have their optimum values.A proper length of cut-back or a suitable coolant rate can improve the aerodynamic performance to some extent under the premise of satisfying the cooling demand and maintaining the feasibility of manufacturing.Next,numerical simulations of cascades with tangential coolant ejecting slots are conducted in this dissertation.Varied coolant ejection rate,location of tangential slot,length of slot and shape of slot wall are selected to investigate how tangential coolant jet flow and shock wave influence each other.Results show that tangential coolant jet flow can effectively cover blade surface downstream of coolant slots.Large amont of coolant with higher blowing ratio results in better cooling performace,which mainly reflect in higher peak value of film cooling efficiency,longer zone with high film cooling efficiency,lower rate of film cooling efficiency decay and lower blade surface temperature downstream of coolant slots.However,blindly increase coolant ejection rate can cause the increasement of thickness of the boundary layer,which then increase blade profile loss.Overall,in this dissertation,longer tangential slot performs well in minimizing the intensity of shock wave and energy loss.Later on,unsteady numerical investigations have been done to study the effect of sweeping outer-extending shock wave at trailing edge of vane on film cooling performance of downstream rotor blade near the leading edge in a high-loaded transonic turbine stage.Blowing ratio has been kept unchanged during the whole research process.Film holes with different directions are located at different positions on blade surface near leading edge to study the influences of sweeping vane trailing edge outer-extending shock wave on film cooling effectiveness near rotor blade leading edge under different conditions.Results show that in the cascade studied in this dissertation,film holes located on sunction side and leading edge are affected in a period time of a cycle.Film holes on pressure side haven't been affecded significantly.The main influence of sweeping shock wave is to cause the periodic seperation of coolant film,which changes the streamwise and spanwise distribution of high film cooling efficiency zone.Among all the film holes researched in this dissertation,the closer the holes to leading edge,the heavier effect the holes suffer from sweeping shock wave.In addition,coolant flow ejected from oblique film holes is harder to separate from the blade surface of rotor,so it suffers less from the sewwping shock wave.At last,the conclusions of the studies above are used in the design of a high-loaded single stage high pressure turbine,the design of a high-powered 2 stage high pressure turbine and the modification design of a vaneless countor rotating turbine,which proved the guidance of those conclusions.During the designing process of those turbines,parameters of film cooling and cut-back have been chosen specifically base on the real aerodynamic parameters.This can contribute to avoiding loss increasement caused by transonic effect and coolant ejection from the very begining of the designing process.