LARGE EDDY SIMULATION OF ACOUSTIC CHARACTERISTICS OF A SUBSONIC JET OUTFLOWING FROM CONICAL NOZZLE

The calculation of noise generated by a jet of viscous compressible gas flowing out from a conical nozzle is considered. The calculations used the implicit version of the LES (Implicit LES, ILES), in which the role of the subgrid turbulence model performs numerical dissipation used finite-difference scheme. The distributions of the gas-dynamic and acoustic characteristics of the jet upon changing the conditions of its outflow are discussed. The analysis of the modal composition of the received noise is carried out and the correspondence between the features of the received directionality of the noise is determined by its various components and sources. The numerical simulation results are compared with the available experimental and calculated data.

Multiparameter optimization of operating control by the trust vector based on the jet injection into the supersonic part of a nozzle

Рассматриваются процессы, сопровождающие вдув сверхзвуковой струи газа в расширяющуюся часть сопла, применительно к созданию управляющих усилий в ракетных двигателях. Разрабатывается подход к многопараметрической оптимизации геометрической формы сопла и параметров вдува струи в сверхзвуковой поток, основанный на применении численной модели турбулентного течения вязкого сжимаемого газа. В качестве параметров оптимизации используются степень нерасчетности вдуваемой струи, угол наклона сопла вдува к оси основного сопла, удаление сопла вдува от критического сечения основного сопла и форма выходного сечения сопла вдува. Проводится сравнение результатов расчетов, полученных для различных конфигураций системы подвода вдуваемого газа. Делаются выводы о влиянии входных параметров задачи на коэффициент изменения тяги сопла. The processes accompanying the supersonic jet injection into the divergent part of a nozzle are considered for the creation of control forces in rocket engines. An approach to the multiparameter optimization of the nozzle's geometric shape and the parameters of jet injection into the supersonic flow based on the application of a numerical model of the turbulent flow of a viscous compressible gas is proposed. The optimization parameters include the pressure ratio in the injection flow and nozzle flow, the angle of inclination of the nozzle to the axis of the main nozzle, the distance from the injection nozzle to the critical section of the main nozzle, and the shape of the injection nozzle outlet section. The numerical results obtained for various configurations of the trust control system are compared. A number of conclusions concerning the effect of input parameters on the trust coefficient are made.

A leakage model of metallic static seals based on micromorphology characteristics of turning flange surface

Purpose – The purpose of this paper is to develop a leakage model of metallic static seals, which can be used to accurately predict the leakage rate and study the corresponding seal characteristics. The metallic static seal is effectively applied to severe rugged environments where conventional seals cannot meet the needs. More research efforts for deepening the understanding of its seal characteristics are important for its effective and safe applications, of which the study about its leak is one key component. Design/methodology/approach – In the microscopic observations of the turning surface that is general in the processing of flange surfaces, it is found that the spiral morphology is dominant, which had been also obtained by other researches. There are two potential leakage paths for the flange surface of spiral morphology, one is the radial direction perpendicular to the spiral ridges and the other is the circumferential direction along the spiral groove. Based on the microgeometry characteristics of spiral morphology, the micromorphology of turning flange surface is simplified for the calculation of leakage rate, and the simplified methods of the radial and circumferential leakage paths are presented separately. The topography of flange surface studied in this paper is actually measured, and the Abbott bearing surface curve is adopted to represent the micro-profiles parameters. The radial and circumferential leakage models are further developed based on the assumption of laminar flow of the viscous compressible gas. Findings – The experiments used to verify the leakage models were carried out, and the experimental values are well agreed with the calculated values. As the contact pressure increases, the change rules of both radial and circumferential leakage rates are obtained and the obvious transition from radial leak to circumferential leak can be found. Using the proposed leakage models, the effects of the key micro-profiles parameters on the leakage rates are studied, and some specific conclusions are given simultaneously, which are favorable for the theoretical study and practical application of the metallic static seal. Practical implications – By the interpretations of the micromorphology characteristics of turning flange surface, the leakage mechanism of the metallic static seal is further made clear. The proposed leakage model reveals the relationships between the key micro-profiles parameters and some sealing performances about the leakage and can predict the leakage rates of the metallic static seal used in various working conditions. Originality/value – For the metallic static seal, the simplification of the radial leakage path and the radial leakage model are put forward for the first time, so the total leakage model can be systematically reported based on the micromorphology characteristics of turning flange surface. The effects of the key micro-profiles parameters on the seal behaviors including of the leak rate, critical contact pressure and transition from radial leak to circumferential leak etc are also clarified firstly.