Numerical Study On The Altitude Compensating Mechanism Of A Novel Porous-wall Nozzle

For a single-stage-to-orbit(SSTO)propulsion system,the vehicle will keep working from the sea-level to the low-Earth orbit.During the entire flying process,the ambient pressure will vary widely.The nonadaptation of the exhaust flow to the varying ambient pressures will lead to a great thrust loss when using the conventional nozzle.To solve this problem,a perforated nozzle wall is applied innovatively to the divergent section of the Laval nozzle to upgrade the conventional supersonic nozzle.This new altitude compensating nozzle with a perforated divergence is called perforated nozzle.Research on this novel altitude compensating nozzle is conducted as follow:1.The idea of the perforated nozzle was carried out,and relevant parameters of this nozzle was also given.Numerical calculation is conducted to study the internal flow structure and performance of the perforated nozzle working at sea-level.The numerical calculation results show that the performance of the perforated nozzle is close to that of the traditional low-altitude nozzle.The backflow at the tail of the nozzle is eliminated.The Mach disk is also suppressed which will increase the gas velocity at the nozzle outlet and reduce the temperature of the exhaust.2.Numerically investigation of perforated nozzle working at 10 typical altitudes was conducted.According to the numerical results,with the altitude rising up,the flow separation point gradually approaches the position of the starting point of the perforated section,and then the separation shock wave gradually weakens,and the nozzle gradually reaches a full flow state.The average specific impulse over the entire flying process of the perforated nozzle is increased by 5.07% compared with conventional nozzles.The low-altitude performance of the perforated nozzle is close to that of a double bell nozzle,but a perforated nozzle can achieve altitude compensation during a larger altitude range than during a dual bell nozzle.3.The altitude compensation mechanism of the perforated nozzle was explained.The flow separation point is restricted at the starting point of the perforated section duo to the perforation of the perforated section,preventing the separation shock wave moving to the nozzle exit with the altitude increasing,which can increase the pressure on the inner wall and finally enhance the thrust of the nozzle.4.The influence of design parameters on the altitude compensation ability of the perforated nozzle is calculated.The results show that the nozzle expansion ratio,expansion ratio of the basic section,inertial resistance coefficient and initial expansion half-angle have the greatest influence on the thrust performance of the perforated nozzle.The pore angle has a liter influence on the thrust performance of the nozzle.The radius of the transition arc and the exit-half-angle have almost no effect on the thrust performance of the nozzle.