Research On Adjusting Law And Working Process Of 2-D Variable Inlets For Ramjet

In order to insure the wide working range inlet works efficiently it requires inlet should be easy to start with small internal contraction ratio at low Mach number and has high total pressure recovery coefficient with large internal contraction ratio at high Mach number.This paper analyzed performance of different variable inlets and ramjets which equip variable inlets by program and numerical simulation.Firstly,a calculation program of 0-dimension performance with viscous correction was written and confirmed to be able to calculate performance of variable geometry inlets after compared with the CFD simulation result.Secondly,a variable geometry scheme was presented on a three-shocks two dimension supersonic inlet with the free stream Mach number 2.0~4.5 to keep its second external shock wave touching lip during high Mach number working range.The numerical simulation was applied to investigate the inlet aerodynamic performance.The comparison results between the fixed inlet and the variable one indicate that the variable geometry scheme can improve greatly the performance of the inlet at high Mach number.With the increase of the free stream Maher number,increasing the ramp angle of inlet and the internal contraction ratio could decrease Mach number at inlet throat and improve the critical total pressure recovery coefficient of the inlet.The critical total pressure recovery coefficient of the variable geometry inlet can be twice as high as the fixed one at Mach number 4.5.Then,three schemes of variable geometry inlet whose ramp angle could be adjusted was studied on a three-shocks two dimension supersonic inlet with the free stream Mach number 2.0~4.0.They respectively were adjusting angle of first-ramp,second-ramp and two ramps.Then the flow in the supersonic inlets was analyzed by two-dimensional numerical simulation,the inlet performance comparisons were made between the fixed inlet and the variable inlets at different Mach numbers of free flow.The results indicate that the performance of variable geometry is better than that of the fixed one.The total pressure recovery coefficient and inlet mass are respectively 53.7 % and 22.3 % higher than the fixed one at Ma 4.0.The performance calculation program of ramjet was written after combining the combustor/ nozzle model with inlet model,and we calculated regulating and velocity characteristic by it.Then we designed a ramjet based on the previous inlets and analyzed the performance of ramjets at combustion time.The numerical simulation result was applied to verificate the credibility of program.Finally,as air can't fully expand in fixed geometry nozzle at high Mach number and low excess air coefficient,adjustment was made to increase the expander ratio of nozzle by means of the calculation program.The result of numerical simulation shows thrust performance of ramjet was increased and the ramjets with variable geometry inlet need bigger adjusting range of nozzle.