| Nozzle is a kind of thrust generating device for liquid rocket engine.The performance analysis and heat transfer calculation of nozzle is an important part of nozzle design,and the method to realize them is to simulate the nozzle flow field.In view of the characteristics of the ultra-high Reynolds number in the nozzle flow field of rocket engine,most of the flow areas are actually in the near non-viscous state,only the thin wall layer needs to consider the viscous effect,so the non-viscous flow field combined with the boundary layer correction is the most suitable calculation method for the nozzle flow field analysis in engineering.In this paper,based on the existing flow field solver of inviscid chemical dynamic nozzle,the simulation calculation method of boundary layer of liquid rocket engine is studied,the application program of flow field calculation of nozzle is developed,its engineering application and application scope are studied,and it is pointed out that the thin boundary layer equation is not applicable enough.Improvement measures should be used to calculate the thick boundary layer equation considering the longitudinal curvature term and the normal pressure gradient.Then the theory of thick boundary layer is studied preliminarily,and the following work is completed:1.Based on the two-dimensional/ axisymmetric thin boundary layer equations,the turbulent flow is modeled using the C-S model,the governing equations are transformed and solved numerically by using the Falkner-Skan-Mangler transformation,the boundary layer fortran program which can be used with the inviscid flow field solver is developed,and a complete inviscid flow field combined with the boundary layer to modify the two-dimensional chemical dynamic nozzle flow field solver is preliminarily developed.The calculation time of the total nozzle flow field is about 60 s.2.The influence of different design parameters on the nozzle efficiency of a liquid oxygen methane engine with quasi-parabolic profile is studied by using a complete self-research program.The design parameters include thrust,chamber pressure,mixing ratio,nozzle area ratio,nozzle initial angle and nozzle exit angle.In the calculation of nozzle efficiency,geometric loss,boundary layer loss and chemical dynamic loss are taken into account,and then the optimal parabola surface modeling with maximum vacuum specific impulse is carried out.3.Comparing the differences between self-study program,Bartz formula and CFD in the calculation of heat flux on the wall of SSME(Space Shuttle Main Engine)nozzle,it is found that the boundary layer program and CFD results are almost all accurate,while the Bartz formula is quite different from the two,and then the reasons for the difference are analyzed.4.By using the self-study program,the specific impulse of three hydrogen-oxygen engine nozzles with increasing area ratio is calculated,and the thickness of the boundary layer is increased in turn,which is compared with the CFD results.It is found that the thicker the boundary layer is,the greater the difference between the result of the program and the CFD total N-S solver is,and it is considered that when the ratio of the thickness of the boundary layer to the radius of the exit nozzle is greater than 10 persent,The thin boundary layer procedure is not suitable enough;5.The equations of incompressible thick boundary layer are derived by the method of order of magnitude,and the similar solution is solved by the method of shooting,which lays a foundation for the later development of thick boundary layer program. |
