Annotation: At Yuzhnoye State Design Office, the Cyclone-4 launch vehicle 3rd stage engine has been developed and is under testing. For adjustment of the engine and test bench systems, in the first firing tests the radiation-cooled nozzle extension was replaced with a steel water-cooled one. It was planned to start the engine with water-cooled nozzle extension without vacuumizing and without gad dynamic pipe, which conditioned operation with flow separation at the output edge of water-cooled nozzle extension. Therefore, the calculation of flow in the nozzle with water-cooled extension, flow separation place, and thermal load on watercooled nozzle extension during operation in ground conditions is an important task. Selection of turbulent flow model has a noticeable impact on prediction of flow characteristics. The gas dynamic analysis of the nozzle with water-cooled extension showed the importance of using the turbulent flow model k-ω SST for the flows with internal separation of boundary layer and with flow separation at nozzle section. The use the flow model k-ω SST for calculation of nozzle with flow separation or with internal transitional layer allows adequately describing the flow pattern, though, as the comparison with experimental data showed, this model predicts later flow separation from the wall than that obtained in the tests. The calculation allows obtaining a temperature profile of the wall and providing the recommendations for selection of pressure measurement place in the nozzle extension for the purpose of reducing sensors indication error. With consideration for the special nature of the nozzle extension wall temperature field, the cooling mode was selected. The tests of RD861K engine nozzle with water-cooled extension allow speaking about its successful use as a required element for testing engine start and operation in ground conditions without additional test bench equipment.

Annotation: This paper describes the configuration of the rig, designed to fasten the solid-propellant rocket engine (hereunder referred to engine) during their testing, with engine thrust measurements by force transducers. It is determined that rig is the important link in the measurement chain, which directly impacts the thrust measurements, values of which will be used for calculation of the most important engine characteristics (for example, total burn). It was observed that when engine starts the basic mode of operation the thrust-measuring system of the rig is impacted by the dynamic loading caused by the engine thrust, which results in the occurrence of the oscillating processes in the rig, therefore it is important to know the behavior of these oscillating processes to estimate their impact on the thrust measurement during the design of the rigs and their thrustmeasuring systems. It is shown that if there is no procedure in the design practice to define the mode of oscillations in the rig it is rational to do it analyzing experimental thrust – time curves when different engines start the basic mode of operation. Number of experimental thrust (displacement of the engine/rig moving part) – time curves are provided for analysis when four different engines with different ballistic characteristic and capabilities start the basic mode of operation. Oscillating processes in the rig distort the physical behavior of the thrust, which requires additional analysis of the data following the tests, but since the oscillations subside rapidly, they will not significantly affect the calculation of the total burn. It is also observed that frequency of oscillations of the moving part of the rig, registered by the motion sensor, coincides with oscillation frequency, registered by the force transducer, moreover stable behavior of the oscillating processes, registered by the force transducer of the same engines, when they started the basic mode of operation, indicate the stable behavior of those engines and stable performance of the rig.

Annotation: This article dwells on results of firing bench testing of the solid-propellant rocket engine (SPRE), fastened to the thrust-measuring assembly stand. It is shown that when engine enters the steady-state mode of operation, plane (forward and rotation) vibrations of the SPRE can take place in the assembly stand due to the sudden pattern of thrust generation and displacement of the center of mass of the vibrating system from the engine axis. These vibrations distort measured values of engine thrust and pattern of its change versus time. The purpose of this work is to simulate the oscillating processes of the engine atop the assembly stand to single out in the distorted values of the measured thrust the components related to the processes in the engine and components, which are introduced into the thrust measurement by the oscillating processes in the system “assembly stand – engine”. Model of vibrating system is suggested, which consists of two rigidly connected bodies, containing elastic links, enabling forward and rotary motion and limited by the rigidity of the links. Mathematical model of the vibrating system is developed. Internal forces and moments acting in oscillatory system are defined. Method of numerical simulation of plane vibrations within the limits of the developed model is suggested. Plane vibrating motion and elastic force curve (curve based on force sensor readings) were simulated in thrust-measuring system for different cases of thrust curve and values of vibrating system parameters. Resonance condition was simulated and mutual influence of elastic parametrical link between forward and rotary vibrations was established. Impact of thrust-measuring system rigidity on peak values of force sensor readings was found out. Elastic force vibrations in thrust-measuring system with vibrating system parameters were simulated including variant of thrust change versus time, implemented during firing bench tests of one of the SPRE. It is shown that registered simulation results recreate thrust measurement results in pattern and values obtained by the force sensor during the firing bench tests, and owing to this, it was concluded that oscillating process parameters, assumed in the model, meet the actual ones. It is concluded that simulation provides objective interpretation of the thrust curve, reliable and comprehensive analysis of engine run during firing bench tests, more detailed and exact design of the assembly stand.