The need for a lower cost and a shorter time of liquid-propellant rocket engine (LPRE) development and production often leads to the decision to use bundles of multiple engines developed individually in launch vehicles' sustainer liquid-propellant rocket propulsion systems (LPRPSs). This opens up prospects for providing a desired thrust by including the necessary number of engines in the bundle. Using sustainer LPRPSs with multiple engines causes additional problems due to the fact that the engines start nonsimultaneously. This may disrupt the operation of engines that start with a delay or produce an overturning moment when rocket detaches from the launcher. The aim of this paper is to study dymanic processes at the start of a multiengine LPRPS with four LPREs with oxidizing generator gas afterburning with account for the possibility of the engines starting nonsimultaneously. The paper presents a mathematical model of the start of the multiengine LPRPS under consideration and the results of calculations by the model. It is shown that, as distinct from all the engines starting simultaneously, their nonsimultaneous start may result in deep prolonged dips in the propellant flow rate accompanied by deep prolonged dips in the pressure at the engine inlets. This may cause cavitation stall in one or more pumps, which may disrupt the operation of the whole of the propulsion system and result in an emergency. The results of mathematical simulation of the four-engine LPRPS start show that the character and degree of the effect of possible engine start delays on transients depend on a variety of factors governed by the LPRPS composition and dynamic performance, start conditions, etc. Because of this, for multiengine LPRPS start reliability to be improved, in each particular case, i.e., for each new or upgraded LPRPS and launch vehicle, start transients should be studied numerically with account for a nonsimultaneous start of the LPRPS engines.
Low-frequency longitudinal (POGO) oscillations of liquid launch vehicles is a phenomenon inherent to almost all liquid rockets. POGO oscillations of launch vehicles can lead to various emergencies: damages of the rocket structure and liquid propellant propulsion system, unacceptable malfunctions of the rocket control system. The use of liquid-propellant rocket engines with an oxidizer-rich staged combustion cycle for the first stage of launch vehicles can introduce a number of features into the POGO stability analysis. First of all, in this case, longitudinal vibrations of launch vehicles can occur due to the low-frequency instability of a liquid propulsion system at frequencies associated with the dynamics of the circuit of the turbopump-gas generator-gas duct. Another feature of these engines is the manifestation of a significant maximum of the module of the engine dynamic pressure gain in the low frequency range (up to 10 Hz), which can lead to POGO instability of the launch vehicle even in the initial part of its flight with significant values of the rocket structure generalized masses for the lower modes of launch vehicle natural vibrations. To predict the POGO stability of the currently designed Cyclone-4M two-staged launch vehicle, the mathematical model of the low-frequency dynamics of the "propulsion system-rocket structure" system has been developed. The model describes the interac
This paper presents the results of the development of silencers, whose design features discrete baffle elements. The advisability of silencers of this type is confirmed by their operational reliability and shot sound suppression efficiency in their actual service as part of light small arms of different types. To design advanced silencers, technical requirements for their design were developed. The paper describes the possibility of using discrete elements (cones, hemispheres, flat baffles, etc.) as the key component of a powder gas spreader. Differently shaped elements are used as additional elements that form a powder gas flow inside a silencer: for example, cylindrical elements, including perforated ones to provide a powder gas flow between the expansion chambers. One way to increase silencer efficiency is an additional expansion chamber that embraces the external part of the barrel and is gas-dynamically connected to a traditional muzzle silencer. In deciding on an optimum design for compact silencers, the following was redetermined: the number of expansion chambers and the dimensions thereof, the powder gas energy converter design, the baffle type, the presence of a gas flow between the chambers near the inner surface of the silencer body, and, if so, the gas flow rate. The silencer design was optimized based on simulating the processes inside the silencer using the authors’ efficiency calculation procedure for silencers with different internal components. Comparison tests of the silencers developed and foreign silencers confirmed a high efficiency of the former. The silencers with discrete baffles for light small arms developed at the Institute of Technical Mechanics of the National Academy of Ukraine and the State Space Agency of Ukraine compare well in performance with their best foreign counterparts. The designs of some of them are covered by Ukrainian patents.
In the tryout of liquid-propellant rocket engines (LPREs), the parameters that govern working processes in the LPRE systems (the pressure, the flow velocity, the gas and liquid temperature, the turbopump speed, etc.) exhibit low-and high-frequency oscillations. High-frequency oscillations in a combustion chamber, which are potentially dangerous to the LPR operational reliability and integrity, are the least understood. The most important tool in the study and development of measures aimed at their elimination in the flight of liquidpropellant launch vehicles is a mathematical simulation of high-frequency processes in a combustion chamber.This paper overviews recent publications and analyzes the state of the art in the numerical study of highfrequency dynamic processes in LPRE combustion chambers with the aim to assess the possibility of using the available numerical methods to simulate the above-mentioned processes in the problem of theoretical prediction of LPRE high-frequency stability and the combustion chamber pressure and flow rate oscillation amplitudes. Consideration is given to the currently adopted mechanisms of high-amplitude oscillations in the LPRE systems involving the dynamic interaction of physical and chemical processes in the mixing and combustion zone in conditions of periodical heat removal under the action of acoustic oscillations and turbulence in the flow and combustion of the propellant components and combustion products.The analysis conducted shows that the methods of mathematical simulation of high-frequency acoustic oscillations in an LPRE can be divided into three basic groups: methods for the calculation of the acoustic oscillation parameters in cylindrical chambers based on analytical mathematical models of a relatively low order with the use of the Bessel functions, methods for the study of thermoacoustic phenomena using approaches of computational fluid dynamics, and hybrid methods, in which combustion dynamics is calculated separately from the combustion product acoustic oscillation parameters. The main results obtained in the framework of the abovementioned groups are overviewed. The advantages and drawbacks of the numerical study of combustion product thermoacoustic oscillations in LPRE chambers are analyzed.
Liquid-propellant rocket propulsion systems of the first stages of launch vehicles of medium, heavy, and super-heavy class usually include POGO-suppressors, which are one of the most widely used methods to eliminate launch vehicle longitudinal structural vibrations (POGO phenomena). However, until now, the theoretical studies and analysis of the effect of the POGO-suppressors’ installation in the feedlines of main liquid rocket engines on transient processes in systems during rocket engine starting have not been carried out due to the complexity of such analysis and the lack, first of all, reliable nonlinear models of cavitation phenomena in rocket engine pumps. A mathematical model for the start-up of a clustered rocket propulsion of the Cyclone-4M launch vehicle has been developed that takes into account the low-frequency dynamics of the POGO-suppressors and the asynchronous start-up timeline sequences of the rocket engines. The first stage of the launch vehicle propulsion system includes four RD-870 rocket engines. A nonlinear mathematical model of low-frequency dynamic processes of the POGO-suppressor with bellows separation of liquid and gaseous media is presented. A significant effect of cavitation in the pumps of engines and the POGO-suppressor installation to the LOX feedline on the propulsion system dynamic gains is shown. Based on the developed mathematical model of the clustered rocket propulsion start-up, the studies of the Cyclone-4M main engines’ start-up transients were carried out. The asynchronous start-up timeline sequences of the rocket engine and the places of installation of the POGO-suppressors in the LOX feedline branches to the RD-870 rocket engine – near the general feedline collector as standard placement or directly at the entrance to the engines – were investigated. The analysis of start-up transients in the oxidizer feed system of the considered propulsion (the time dependences of the flowrate and pressure at the engine inlet) showed the following. Firstly, while the synchronous start-up of the engines, the installation of the POGO-suppressors near the feedline collector makes it possible to eliminate all engine inlet overpressures that exist in the rocket propulsion system in case of the absence of the POGO-suppressors. Secondly, the RD-870 engine asynchronous start-up operation affects negatively the time dependences of the propellant flowrate and pressure at the engine inlet if the POGO-suppressors are located near the feedline collector. So, in the propulsion system’s start-up timeline interval 0.95 s - 1.35 s, for some computational variants of the initial moments of the engine operation start, an abnormally large drop in the LOX flow rate and the overpressures at the engine inlet is observed. The asynchronous start-up of the RD-870 engines with the installation of the POGO-suppressors at the engine inlet does not significantly change the start-up transients compared to the synchronous starting of the engines. Thirdly, thus, it is shown that the installation of the POGO-suppressors both at the engine inlet and at the RD-870 branches near the collector has a significant positive effect on the quality of start-up transient processes for the main engines of the 1st stage of the Cyclone-4M launch vehicle. Placing the POGO-suppressors at the engine inlets is not standard and is considered without reference to the propulsion system layout. Nevertheless, the POGO-suppressors installed at the inlet to the engines are an effective means of preventing overshoots and dips in the parameters of the liquid-propellant rocket engine, including the conditions of asynchronous starting of the liquid rocket engines in the clustered propulsion system. The results obtained can be used in mathematical modeling of the start-up of the first stage propulsion system either for multistage sustainer rockets used in parallel with booster rockets or for the clustered multi-engine rocket propulsion system containing POGO-suppressors.
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