Research On The Flow And Combustion In The Chamber Of Solid-Fuel Ramjet

Solid fuel ramjet(SFRJ)is a simple and relative cheaper propulsion system using aerodynamic compression principle,which is suitable for many missiles and projectiles.SFRJ has a higher specific impulse over rocket and is simpler compared to turbojet engine.As ramjet performaces are very complex to predict and some problems exist in engineering applications,therefore,more extensive fundamental studies are necessary at present.In order to solve the critical problems such as the unclear relation between chamber geometry and regression rate,poor flame stability,low regression rate and combustion efficiency,using polyethylene as solid fuel,with connected-pipe facility and developed codes for calculation of turbulent combustion in SFRJ,the flow and combustion in the chamber of solid-fuel ramjet are investigated,and the effect of chamber geometry on SFRJ performance is explored.Firstly,a set of software for turbulent flow and combustion is developed,which can predict two-dimensional,two-dimensional axisymmetric and three-dimensional flow and combustion process.The finite-volume method is used to discretize the governing equations.For Navier-Stokes equations which describe the flow field,the third-order monotone upstream centered scheme for conservation laws(MUSCL)is adopted for convection term,and the convective flux through a cell face is obtained by AUSMPW+ scheme.The central difference scheme is utilized for the viscous term,and jacobian transformation is used to compute the viscous flux.The central difference scheme is also utilized to the energy equation of solid domain,which considers the effects of fuel regression.The heat flux at the solid fuel surface is computed using fluid-solid coupling method.7 species/3 reaction kinetics finite-rate model is adopted.In order to predict the flame stability accurately,the second-order moment turbulence chemistry model is used to describe gas-phase reactions.The Arrhenius law is used to model the regression rate of solid fuel.Some verification examples show that the software developed in present paper is accurate and reliable enough to predict SFRJ performances.Secondly,by simulation,the main parameter influencing the regression rate of solid fuel are analyzed,which is the convection heat-transfer coefficient.The linear relationship between the space-averaged regression rate and chamber geometry is obtained.The effects of chamber geometry on air-fuel ratio and ramjet performances are analyzed.Through connected-pipe tests,the ignition and combustion characteristics of SFRJ with typical structure are investigated.The ignition and combustion process are investigated,and the inner shape of solid fuel and regression rate contour are obtained with 3D-scanning method and the developed data post-processing program.The developed code is verified by comparing the numerical and experimental results.Thirdly,the factor that affects SFRJ sustained combustion is proposed,which is the ratio of chemical reaction characteristic time and residual time of reactants.Based on the analysis,the effect of step height on flame stability is analyzed,and the underlying physical reasons are obtained.Through combustion tests of solid fuel with different backward-facing step heights,the theoretical analysis of SFRJ sustained combustion is verified.Moreover,the effect of ignition process on,the sustained combustion of SFRJ is described,and the weaknesses of the developed software are presented.Fourthly,the design thoughts of three-hole diaphragm are put forward to solve the low regression rate and combustion efficiency problems.The influences of the three-hole diaphragm on the flow field of chamber and regression rate are explored.The simulation results show that the diaphragm has significant effects on the flow field upstream of the diaphragm and the regression rate of solid fuel downstream of the diaphragm increases significantly.Connected-pipe tests are conducted to investigate the effects of diaphragm on the flow and combustion characteristics in the chamber.The developed software is verified by comparing the experimental and calculated regression rates.The effects of diaphragm on pressure loss and combustion efficiency are analyzed.Finally,the design thoughts of solid fuel with star configuration are put forward to solve the low regression rate and combustion efficiency problems.The influences of star solid fuel on the flow field of chamber and regression rate are explored.The calculated results show that the space-averaged regression rate of star solid fuel is higher than that of tubular solid fuel,and the regression rate changes significantly along the circumferential direction.Connected-pipe tests are conducted to investigate the effects of star configuration on the flow and combustion characteristics in the chamber.The developed software is verified by comparing the experimental and calculated regression rates.The combustion process of star solid fuel is analyzed.