Analysis of the Correctness Approaches to Determining the Specific Impulse of Thrust Generated by the Working Fluid of a Gas Generator Cycle Rocket Engine Turbine

For liquid rocket engines (LREs) utilizing the gas generator cycle, the resulting engine thrust is composed of two components: the thrust of the engine chamber and the thrust of the turbine exhaust nozzle. Over the years of LRE utilization, methodologies for calculating ideal thermo gas dynamic parameters of the chamber have been developed, large volumes of statistical data regarding specific impulse losses in engine chambers have been obtained, and approaches for predicting specific impulse and, consequently, thrust of the main chambers have been refined. A much more complex situation arises with determining the specific impulse of the thrust generated by the working fluid of an autonomous turbine: significant limitations in information regarding methods for calculating this parameter have been found during literature analysis, and the available statistics exhibit contradictory characteristics. Accurate prediction of the specific impulse of the thrust from turbine exhaust nozzles allows for a more rational selection of design parameters (e.g., combustion chamber pressure) during the development of a new engine and is particularly important in cases where the spent gas generator gas is used to create control efforts. As the rocket and space industry historically developed under conditions of increased secrecy, many approaches and design methods for LREs remain known only to design bureaus and research institutes that were founded and developed during the heyday of rocket and space technology. This complicates the situation for new, young aerospace companies, as they must either conduct physical tests, which require expensive specific test equipment and increase the time and cost of engine development, or use numerical modeling, which, although to some extent allows for the replacement of physical experimentation, requires model verification and confirmation of the assumptions made. Furthermore, considering the military focus of rocket-related topics in the past, it cannot be excluded that intentionally distorted information may be present in open sources. Thus, considering the global trend of increasing the number of startups in the rocket and space industry, the identification of reliable and open sources of information becomes an important task. In this work, data from open sources regarding the specific impulse of the thrust from turbine exhaust nozzles of existing LREs were analyzed, revealing significant inconsistencies in the declared energy parameters. Numerical modeling of generator gas leakage from the nozzle of the exhaust gas duct of the RD-111 engine turbine has been conducted, and the results were compared with the calculations carried out by other methods. As a result of the work, various approaches to evaluating the thrust of exhaust nozzles during the design of an engine utilizing the gas generator cycle were analyzed, and conclusions were drawn regarding the correctness of their application.