Investigation On Characteristics Of Film Cooling In Channels With Variable Cross-section

Film cooling is widely adopted in the cooling configuration of hot components for modern gas turbine.With the development of aero-turbine engine performance,strong pressure gradient and supersonic flow occurred in the internal flow of engine,all of which can bring about nonignorable impact to film cooling.Numerical simulations of film cooling on the flat wall under the condition of subsonic mainstream in convergent channel,expanded channel and straight channel have been conducted.The flow field and temperature field were comparatively investigated under the condition of different streamwise pressure gradient,different flow blowing radios and different mainstream turbulence intensity.The results showed that boundary layer profile and thickness,mixing intensity of shear layer and the counter-rotating vortex pair distribution are the main factors that lead to the changes of the film cooling effectiveness.Compared with the zero pressure gradient case,adverse pressure gradient weakens the counter-rotating vortex pair and strengths the penetration of the secondary flow by increasing the boundary layer thickness,favorable pressure gradient makes a constraint on the cooling gas by restraining the development of mainstream boundary layer,the accelerated flow enhances the counter-rotating vortex pair and makes it closer to the wall.As a result,adverse pressure gradient increases the film cooling adiabatic effectiveness for the low blowing ratio,while favorable pressure gradient has the opposite effect;favorable pressure gradient increases the film cooling adiabatic effectiveness for the high blowing ratio,while adverse pressure gradient has the opposite effect.The increasement of mainstream turbulence intensity weakens the counter-rotating vortex pair and restrains flow separation by making velocity boundary layer full.As a result,it weakens the influence of pressure gradient on film cooling adiabatic effectiveness.Numerical simulations of film cooling on the flat wall under the condition of supersonic mainstream in different channels have been conducted.The results showed that the influences of pressure gradients on abiabatic film cooling effectiveness are presented in three aspects.One is that mainstream pressure gradient has greater impact on near wall region velocity.Second,the mainstream pressure gradient impacts on the counter-rotating vortex pair and secondary flow vortex.Last,the mainstream has strong compressibility.For the present investigation conditions,whether the velocity of secondary flow is subsonic or supersonic,film cooling adiabatic effectiveness increases along with the favorable pressure gradient,while adverse pressure gradient has the opposite effect.Finally,numerical simulations of Film cooling on the curve wall under the condition of supersonic mainstream in different channels have been conducted.The results showed that film cooling on the curved wall is affected by buoyancy whose direction is perpendicular to the wall,besides the three influence aspects on the flat wall film cooling.The effect of the mainstream pressure gradient on film cooling on curved wall has the same rule as that on flat wall.Compared with the flat walls film cooling under the same streamwise pressure gradient,film cooling adiabatic effectiveness of concave walls is significantly lower on the low blowing ratio;for the high blowing ratio case,film cooling adiabatic effectiveness of convex walls is significantly higher.