Optimum Design Of Rocket Engine Pre-Cooling System Based On Passive System Functional Reliability Concept

Pre-cooling of a liquid rocket engine system uses the natural circulation pre-cooling. The lack of operation and experimental data result in the understanding limitations about pre-cooling system, so it is necessary to analysis the cooling method, transient flow and heat transfer characteristics of natural circulation pre-cooling and evaluation the system reliability. Since passive systems is more sensitive to the parameters of environmental conditions than passive system, it is necessary to optimize the range of the design parameters using the method base on passive system functional reliability concept combined with the analysis of natural circulation pre-cooling characteristics and a better range of the key parameters can be chosen under the condition of ensuring the reliability of the system. To this end, the paper based on numerical simulation tools and methods, analysis the natural circulation behavior of two-phase natural circulation of the liquid rocket engine system and design parameters were optimized.The composition of the pre-cooling system and the basic physical process was described first, a reasonable simplification of the inside engine structure then be made, the numerical simulation model and numerical methods be established, the border conditions of the pre-cooling system be given. All of this is prepared for the later chapters of the system analysis work and the reliability analysis.Some of the instability phenomenon in natural circulation pre-cooling system was briefly introduced, taking into account the geyser phenomenon is one of the typical flow instability in low-temperature storage and transportation system and it is dangerous to the structure of the system component, so the study of this phenomenon is needed. The geyser phenomenon analysis based on numerical simulation was made to study its flow characteristics, parameters effects was analyzed to give the boundary of geyser phenomenon occurring, than some kind of advice was give to avoid geyser phenomenon.The key design parameters of pre-cooling system were selected based on AHP, the range of these parameters and probability distribution on it was given according to the engineering experience. Functional reliability criteria are defined by the function of the pre-cooling system. Within the engineered possible range, sampling is carried out through Latin Hypercube Sampling (LHS) method with respect of the selected parameters. The sampled data are used as input of computer program for uncertainty propagation calculation. The results of computer program can be help to make sensitivity analysis, all the conditions are verified through the key reliability criteria. Optimum condition was defined then.The design parameter range of the pre-cooling system was optimized based on the better condition proportion of the density distribution function and expert advice. The optimized design parameter range was gained and then sampling is carried out through Latin Hypercube Sampling (LHS) method again in the optimized design parameter range with a small sample obtained which has 10 simulation conditions. Then the comparison was made between the 10 conditions group and the bigger one before.