Research On Contouring Method And Film Cooling Of Nonaxisymmetric Endwall In A Turbine Vane Cascade

Aeroengine has trended in the direction of higher thrust-to-weight ratio,higher efficiency and lower emission,leading to higher heat load of turbine endwall.In this context,the contouring technology of non-axisymmetric endwall improves aerodynamic efficiency of cascade and reduces the heat transfer of endwall by decreasing the intensity and scale of secondary flow structure close to endwall in cascade.In this paper,numerical analysis and experimental research on secondary flow,heat transfer and film cooling of non-axisymmetric endwall are carried out in a low aspect ratio turbine guide vane cascade.The research contents and related conclusions are as follows:An efficient non-axisymmetric endwall contouring method based on parameterized ridge line was proposed.Multi-objective optimization,to minimize secondary kinetic energy of cascade outlet and heat transfer on endwall was conducted,based on CFD(computational fluid dynamic)simulation of secondary flow and heat transfer CFD which using V2 F turbulence model.The results show that: the effectiveness of contouring of non-axisymmetric endwall,formed by a parametric ridge line,is improved because of the shape of endwall with high on pressure side of but low on suction side was predetermined and the number of control parameters is less than previously reported papers.The secondary loss and heat transfer of the non-axisymmetric endwall are both decreased through altering the location of horseshoe vortex and passage vortex,and reducing the intensity of passage vortex and wall vortex.Furthermore,based on the contoured endwall by the multi-objective optimizing,the effects of inlet conditions on non-axisymmetric endwall were investigated,that include inlet Reynolds number,freestream turbulence intensity and boundary layer thickness.The results show that: the total pressure loss of cascade outlet and endwall heat transfer level were decreased with increasing inlet Reynolds number.However,the secondary kinetic energy and the flow deflection of cascade outlet were almost unchanged.With increasing inlet Reynolds number,the inhibitory effect of aerodynamic loss of nonaxisymmetric endwall didn't change,while the decrease effect of endwall heat transfer reinforced.The profile loss increased with increasing freestream turbulence intensity,and the total pressure loss of cascade and endwall heat transfer increased accordingly.With freestream turbulence intensity increasing,the decreasing effect of aerodynamic loss of non-axisymmetric endwall declined.When the freestream turbulence intensity is off the design point for optimizing,the decreasing effect on endwall heat transfer weakened.Especially,compare to the flat endwall,the Standon number of nonaxisymmetric endwall is higher at low turbulence intensity condition.With increasing inlet boundary layer thickness,the secondary kinetic energy at cascade outlet increase,but the total pressure loss almost unaffected.The Standon number decrease for the flat and non-axisymmetric endwall when the boundary layer thickness is off the design point for optimizing.With increasing boundary layer thickness,the decrease effect of secondary kinetic energy in cascade and endwall heat transfer were declined.A partition method based on line of passage vortex core for endwall film cooling was proposed after analyzing flow structure to endwall and endwall heat load profile characteristic.Conventional and partitioned arrangement of film cooling holes were designed at different zones on endwall.Comparative study on secondary flow and film cooling performance of the two holes arrangements was conducted which adopted numerical simulation and experiment measurement method.The results shows that: The high heat transfer coefficient region on endwall pressure side is consistent with line of passage vortex core,and nothing to do with pressure side separation line of horseshoe vortex.Accordingly,the endwall can be divided into 5 regions by suction side separation line of horseshoe vortex and line of passage vortex core.The 5 regions are upstream-passage wedge zone,leading edge zone,pressure side zone,downstream the pressure side and downstream the suction side.Compared to the conventional arrangement,the energy loss at cascade outlet adopted the partitioned arrangement of film cooling holes,which reduced the mixing of the cold jet flow to the mainstream flow in cascade.In addition,with more film cooling holes on endwall pressure side adopted the partitioned arrangement,the flow distribution through endwall is improved,leading to more uniform film coverage on endwall.The adiabatic film cooling effectiveness has significant improved at middle and low blowing ratio conditions.Based on the research on portioned arrangement of film cooling holes,the effect of spanwise angle(BPA00,BPA30,BPA60)of film cooling holes to endwall secondary flow and film cooling characteristic was been investigated by CFD and experiment method.Afterwards,a film cooling configuration with good comprehensive performance of aerodynamic loss and film cooling effectiveness was drawn.The research shows that: the secondary kinetic energy and energy loss at the cascade outlet are higher,whether small or large spanwise angle.At high blowing ratio condition,a new corner vortex is formed close to the suction side and endwall if the spanwise angle is large,results in sharply increase of energy loss.The endwall BPA30 has better comprehensive performance than other two endwall configurations of spanwise angle,because of higher adiabatic film cooling effectiveness and lower aerodynamic loss.Aerodynamic and film cooling characteristic of flat and non-axisymmetric endwall,both adopted a compound angle film holes based above-mentioned study,were investigated through CFD simulation and experiment measurement.The effects of blowing ratio,Reynolds number and freestream turbulence intensity on cascade aerodynamic and film cooling performance were analyzed specifically,and the effect of endwall contouring on cascade aerodynamic and film cooling performance was discussed too.The results on aerodynamic performance show that: compared with condition of no jets,the secondary flow with film holes jets was reduced.With increasing blowing ratio,the total pressure and secondary kinetic energy at the cascade outlet decreased,the flow deflection become weakened as well.However,the energy loss decreases first and then increases.The aerodynamic loss with non-axisymmetric endwall is smaller than flat endwall,but the decrease ability of aerodynamic loss abates with increasing blowing ratio.The aerodynamic loss decreases with increasing Reynolds number.Higher Reynolds number leads to significantly increasing of energy loss at large blowing ratio.With increasing freestream turbulence intensity,the total pressure loss at cascade outlet increases,the secondary kinetic energy decreases on the contrast.The conditions of blowing ratio and turbulence intensity being equal,the aerodynamic loss is lower compare to flat endwall,but the reduction effect to aerodynamic loss of non-axisymmetric endwall tend to less efficient.The results on film cooling characteristic shows that: with increase of blowing ratio,the adiabatic film cooling effectiveness on flat and non-axisymmetric endwall both increase first and then decrease.When the blowing ratio is high,the streamwise momentum of the cold jet decreases,leading to coverage ability close downstream the film holes weakness.The adiabatic film cooling effectiveness level edges up slightly for flat and non-symmetric endwall with increase of Reynolds number.The film coverage on non-axisymmetric endwall prior to flat endwall at same blowing ration and freestream turbulence intensity condition.The adiabatic effectiveness decreases with increase of turbulence intensity for flat and contoured endwall.The effect of turbulence intensity is small at high blowing ratio.The adiabatic film cooling effectiveness has significant improved at middle and low blowing ratio conditions,no matter how high the turbulence intensity.