Investigation On Simulation Of Hypersonic Ramjet Performance With Subsonic Combustion

The Aircraft using a hypersonic ramjet as its power device has broad application prospects.Generally,the combustion chamber of a hypersonic ramjet adopts supersonic combustion.Could the subsonic combustion technology be used for a hypersonic ramjet at a cruising speed of Mach 5? In view of this problem,a concept of a Mach 5 hypersonic ramjet with subsonic combustion has been proposed for the first time and its performance has been preliminarily calculated.But the combustion chamber under this concept has not been studied in detail at home and abroad,and one of the key technologies of ramjet research is the design of combustion organization scheme of its combustion chamber.The purpose of this thesis is to study the combustion chamber design and combustion characteristics of the Mach 5 hypersonic ramjet with subsonic combustion,so as to obtain the overall performance of the ramjet.(1)This thesis proposes a new combustion organization scheme of direct injection of fuel with a fuel injection ring in the recirculation zone of the head of the dump combustion chamber.Through the simulation technology,the distribution law of combustion flow field parameters is explored,and a scheme meeting the design requirements of ramjet is obtained,so as to verify the feasibility of the design of a hypersonic ramjet with subsonic combustion.(2)The large eddy simulation model and standard k-ε model in CFD numerical simulation method are used to calculate the hot and cold flow field of combustion chamber with Fluent,a business software of CFD.The flame shape,combustion performance and ignition process are analyzed,and the combustion organization scheme is optimized.Based on the obtained combustion chamber performance,the overall performance of the ramjet is calculated.(3)According to the research results,the fuel combustion law of the new combustion organization is as follows.When the direct injector diameter d is within the range of 0.6 mm ~ 1.0 mm,the change of its diameter has less effects on the combustion performance compared with the change of the injection position.When the diameter of the fuel injection ring Φ is less than or equal to 0.7 times of the diameter of the combustion chamber4D(4Φ ≤0.7D),all combustion organization schemes cannot obtain a qualified fuel concentration field and temperature field.As the fuel injection ring diameter Φ gradually increases from 40.5D to 40.9D,the starting position of high temperature flame in the combustion chamber gradually transfers to the head of the combustion chamber and flame fills the whole combustion chamber.Moreover,the combustion efficiency rises first and then falls,but it falls less.After comparative analysis,it is concluded that the optimal combustion organization scheme suitable for the hypersonic ramjet is as follows: the fuel injection ring diameter Φ =40.9D,the injector diameter d =0.8 mm,32 injectors and fuel supply pressure difference ΔP =0.12 MPa ~5.24 MPa.With the optimal combustion organization scheme,the ignition can be successful after 0.02 s.The mean value of the combustion chamber parameters under different operating conditions can ensure that the overall ramjet performance parameters are within a reasonable range and the combustion performance has good robustness.The specific impulses of a ramjet at the booster-to-ramjet transition point,design point,cruising point and diving point are 14826 N·s/kg,15311 N·s/kg,14638 N·s/kg and 12408N·s/kg,respectively.The thrust coefficients are 0.631,0.627,0.394 and 0.266,respectively.(4)Based on the analysis of the calculation results,the research shows that the overall performance of the Mach 5 hypersonic ramjet with subsonic combustion is feasible.Compared with the supersonic combustion technology of Mach 5 hypersonic ramjets such as X-51 A,the subsonic combustion technology designed in this thesis is less difficult.The overall performance of the ramjet can be in well accordance with its design target,which indicates that it is feasible to design a Mach 5 hypersonic ramjet by inheriting the subsonic combustion technology.At the same time,it is also shown that an aircraft with the ramjet can increase the flight Mach number to 5.0.And the working speed and airspace of the ramjet can be expanded,which provides another new feasible choice for the power plant of an aircraft with a hypersonic cruising speed of Mach 5.