Investigation Of Unsteady Interaction Mechanism And Associated Loss Control Between Turbine Rim Seal Flow And Mainstream

With the increasing demand for power of aircraft,traditional turbine design technology has been unable to meet the further improvement of turbine performance for future gas turbine engine.Thus,precise design that considers various factors affecting the turbine performance has been more popular.Among these factors,the influence of turbine rim seal flow on the characteristics and performance of mainstream has become an important factor.Hence,it is of great academic value and engineering application significance to study the unsteady interaction mechanism and associated loss control method between the rim seal flow and mainstream.In this paper,the flow mechanism,loss mechanism,influencing law of different parameters and structures,and influencing mechanism of the endwall contouring are investigated based on the one and half stage turbine.The main researches are as follows:Firstly,the unsteady flow field distributions in the stator,rotor,inside the cavity,and at the cavity exit were analyzed.The unsteady interaction mechanisms between the rim seal flow and secondary flow in the main passage were studied.The results show that the efficiency of turbine stage decreases by 0.56% for the injection ratio of 0.9%.The ingress is located downstream of the stator trailing edge and the egress is situated downstream of the stator suction side.Moreover,the ingress mainstream is ejected and converged into the egress flow due to the viscous blockage of rim seal flow.The pressure gradient at the axial middle location of the cavity exit could be used to judge the location and intensity of the ingress and egress.In addition,a cross-distributed positive and negative axial vorticity near the stationary wall of the cavity is caused by the upstream vane.The relative rotation of the cavity wall results in the cavity induced vortex.The egress flow weakens the strength of hub secondary flow of the stator by the blockage effect,and continues to extrude hub secondary flow of the stator above and downstream of the cavity exit.Furthermore,the shear induced vortex is formed by the viscous shear between the rim seal flow and mainstream,increasing the radial position and intensity of rotor hub secondary flow.Meanwhile,the momentum exchange between the rim seal flow and mainstream caused by the ingress makes the rim seal flow have a high unsteady fluctuation level.This rim seal flow enters into the main passage and aggravates the unsteady fluctuation level of the rotor.Secondly,the flow characteristic and loss mechanism of various losses were investigated,and a loss decomposition and quantification method for interaction between the rim seal flow and mainstream was proposed.The results show that there exist four kinds of losses: viscous shear loss,blockage effect loss,secondary flow interaction loss,and second stator additional loss.The viscous shear loss is mainly caused by the circumferential velocity difference between the rim seal flow and mainstream.The blockage effect results from the local extrusion and blockage of the rim seal flow with high radial momentum to the mainstream,which results in the reduction in the profile and hub secondary flow loss of the stator and the increase in the profile and tip secondary flow loss of the rotor.Due to the circumferential and radial velocity difference between the rim seal flow and mainstream,and the cross-passage gradient,as well as the blockage effect,the secondary flow interaction loss between the egress flow and rotor secondary flow is developed.In addition,the rim seal flow worsens the inlet condition of the second stator and leads to the second stator additional loss.As four losses have obvious spatial distribution characteristics,a decomposition and quantitative method for the interaction losses is established by combining the distribution of viscous dissipation coefficient difference contours.At the design condition,the proportion of viscous shear loss is67.68%,while the percentages of other three losses are approximately equal.With the increment of rim seal flow rate,four losses all increase.Furthermore,with the increment of swirl ratio,other three losses reduce,except for the secondary flow interaction loss.Thirdly,the effects of different rim seal flow rate,swirl ratio,pressure ratio,rotational speed,axial position of the cavity,inclination angle,and diversion section structure on the flow and loss distributions for unsteady interaction between the rim seal flow and mainstream were performed.The results show the total loss increases with the increment of rim seal flow rate,pressure ratio,axial position ratio,inclination angle,and chamfer angle of diversion section.However,the total loss decreases with the increment of swirl ratio and rotational speed.In terms of the increase or decrease extent,the effect of rim seal flow rate is the most significant,the swirl ratio is the second,and the influence of other parameters is less.Compared with the design condition,1% injection ratio increases the total loss by approximately 104.25% and100% swirl ratio decreases the total loss by about 24.46% on average.Furthermore,the increment of rim seal flow rate,axial position ratio,inclination angle,and chamfer angle increases the unsteady fluctuation level of the rotor,whereas the increment of swirl ratio reduces it.Although the unsteady fluctuation level of the rim seal flow is decreased by the reduction of the ingress with the increment of rim seal flow rate,the unsteady fluctuation level of the rotor is intensified due to an increase in the intensity of the egress flow.Moreover,the unsteady fluctuation level of the rim seal flow and rotor are strengthened due to the enhancement of ingress with the increment of chamfer angle.Finally,the control effects of hub endwall contouring of the stator and rotor as well as convex and concave shape of the diversion section on the losses caused by the rim seal flow were investigated.The results show that the endwall contouring of the stator makes the blade loading aft-loaded,which reduces the blockage effect loss in the stator.In addition,the endwall contouring of the rotor reduces the pressure difference in the middle blade passage,decreasing the secondary flow interaction loss.The combination hub endwall contouring of the stator and rotor further reduces the secondary flow interaction loss and the total loss decreases by 12.11% relative to the baseline.Furthermore,the endwall contouring of stator increases the area of ingress and the radial velocity of the egress flow.The endwall contouring of the rotor controls the flow direction of the rim seal flow in the rotor passage.Thus,the unsteady fluctuation level in the rotor is enhanced by the endwall contouring,and that of the combination hub endwall contouring is reduced.Since convex and concave shape of the diversion section has a weak influence on the improving effect,the chamfer shape of diversion section is selected to combine with the combination hub endwall contouring.For the final combinations,the interaction loss and unsteady fluctuation level of the rotor are further improved and the sensitivity to different rim seal flow rate is reduced.Relative to the baseline,the total loss decreases by 17.64%.