Study On Film Cooling Characteristics Of Convergent-divergent Nozzle Expansion Segment

With the rapid development of aviation technology, it is proposed requirement to improveefficiency and thrust to weight ratio of aircraft engine. One method to ameliorate performance ofaviation engine is to raise gas turbine inlet temperature, which resulted in a substantial increase in theheat load of engine exhaust nozzle, infrared radiation of exhaust nozzle thereby enhances, especiallyat the condition of engine afterburner really. One of the most effective mode to reduce infrared ofexhaust nozzle mode is to reduce surface temperature, especially strengthened cooling in theexpansion segment of convergent-divergent nozzle. Contrary to expansion segment ofconvergent-divergent nozzle, numerical simulation is applied to research film cooling features atcondition of supersonic mainstream.Firstly, this paper carried out supersonic fluid characteristics and cooling efficiency of thetwo-dimensional parallel slots about different parameters by software FLUENT, results show: whetherthe mainstream is supersonic or subsonic, cooling efficiency is better when the secondary flow issupersonic, because the secondary stream has relatively large flow momentum, after the incidence ofthe secondary flow, the secondary flow has a relatively short time to blend with mainstream, coolingfilm can be produced at a longer distance, offering good protective effect for the wall, coolingefficiency can be higher45%when the secondary flow is subsonic at the best.Secondly, numerical study is used to research film cooling features of convergent-divergentnozzle expansion section, conclusions as follow: when secondary flow rate is small, film coolingefficiency will be a bit lower as film hole inclination increases; when secondary flow rate is superior,as film hole inclination increases, the decrement of film cooling efficiency is a little great, and thecooling efficiency curves show a trend that it rises again after the first decline in a downward for eachgas downstream, it is because the gas film flow will firstly get off boundary and then attach to it again;increases of film hole angle and secondary flow rates will lead to reduce in film cooling efficiency,because increase of vertical momentum of the film jet will enhance penetration to mainstream,enhance vortex intensity and its scope at downstream, the vortex will turn mainstream into gas film;for the convergent-divergent nozzle whose mainstream temperature is1160K, the use of film coolingcan make wall temperature decrease to808K, and secondary flow rate is only0.2%of themainstream. lastly, numerical study is used to discuss impingement cooling+film cooling features ofconvergent-divergent nozzle, conclusions show: at the role of supersonic nozzle gas film jet, uplift ofboundary layer makes shocks at the upstream and downstream of expansion segment, which hasaspect on the film; the outlet flow rates evidently improved as secondary flow inlet pressure increases;as film and impingement hole spacing reduce, the secondary flow rate decreases; in conditions ofminimum spacing and maximum air pressure, secondary flow rates is5.087kg/s, only9%of themainstream flow, wall temperature of expansion segment in most regions reduces to800K or less,significantly lower than the mainstream temperature of2100K.