Aerodynamic Design And Research On Adjustable Combined Cycle Nozzle

The theoretical analysis and numerical simulations were both carried out to investigate the design method of asymmetric nozzle,the influence of typical design parameters on nozzle aerodynamic characteristics,the design of combined cycle nozzle and the aerodynamic characteristics in a wide range of velocity in this article.Firstly,the steady flow numerical simulation method and unsteady numerical simulation method of nozzle were verified respectively in order to verify the accuracy of CFD software calculation.The calculation results are in good agreement compared with experimental results.The numerical simulation method adopted in this paper is credible.Secondly,the design idea of the combined dynamic adjustable nozzle was sorted out according to the design task of the combined cycle engine and the geometric constraints.The nozzle design program of the ideal nozzle and the short nozzle design method were obtained,which were both based on method of characteristic.The performance of the original length nozzle based on the two design methods was preliminarily compared and analyzed,which shows that the thrust coefficient and lift of the nozzle under the same design Mach number have the same change law with the flight Mach number.The thrust and lift performance of the ideal nozzle based on the characteristic method is better than that based on the characteristic method.Thirdly,the influences of the typical design parameters on the nozzle performance were explored,which are nozzle geometry design parameters and the air flow conditions on the nozzle inlet.The results show that the two fundamental factors influencing the nozzle aerodynamic performance are the geometry size and the air flow conditions.The length of nozzle should be selected as large as possible to ensure the thrust performance,which ought to meet the size requirements.Reducing Mach number at design points can improve the performance of combined cycle nozzles during subsonic flight and avoid serious overexpansion of nozzles.The higher the total temperature of the nozzle inlet,the greater the thrust coefficient and lift of the nozzle.At each Mach number,the thrust coefficient increases first and then decreases with the increase of the drop pressure ratio.For the determination of the nozzle configuration,there is an appropriate NPR to optimize the thrust performance of the nozzle.Then,A preliminary study on the aerodynamic design of combined cycle nozzle was carried out under strong geometric restricts.The line of the nozzle was designed by method of characteristic.The effects of design Mach number,three-dimensional lateral expansion angle and relative position of two nozzles on the aerodynamic performance were studied.A nozzle aerodynamic design scheme considering both the effective utilization of space and the aerodynamic performance was presented.The numerical simulation results show that the slight increase of thrust coefficient for Ma=0.8 with increase of flying height and the drop of air pressure,but the thrust coefficient decreases by 0.5% for Ma=0.9.However,the lift of the whole nozzle is still in a negative state and the pitching moment increases first and then decreases due to the shut-down of the ramjet.The two channel flow of the parallel combined cycle nozzle interferes seriously in the common working stage,the thrust coefficient of the combined cycle nozzle is about 0.92 at the designed Mach number.The flow field is smooth transition during the transition mode,when the thrust coefficient is not less than 0.918.Finally,the modal conversion device of the combined dynamic adjustable nozzle was designed,and the numerical simulation of the modal conversion process of the nozzle was carried out in 0 ～ 8s by unsteady and dynamic grid technology.The actual axial thrust,lift and pitching moment of the nozzle decrease with time,and the thrust coefficient of the whole nozzle increases with time.