Method, model and calculating techniques for the propulsion system’s acoustic radiations in the first 1.5-4.1 seconds of the space rocket flight

1Sokol, GI, 1Kotlov, VYu.
1Oles Honchar National University of Dnipropetrovsk, Dnipro, Ukraine
Space Sci. & Technol. 2019, 25 ;(3):16-24
Publication Language: Russian
Many different acoustic fields appear in the atmosphere during the start of a space rocket. Therefore, it is necessary to identify the features and determine the research directions of acoustic emitting at the start of a space rocket based on existing ideas about the generation and propagation of sound waves. It is important to calculate the amplitude-frequency characteristic of acoustic emitting. Knowledge of the emitting frequency of acoustic waves makes it possible to apply models of long-wave and short-wave emitting, known in classical acoustics. This is an important factor that gives an idea of the acoustic field direction and makes it possible to simplify the calculation of sound pressure magnitude as a function of distance variation from the source of oscillations to the point where the conditioned observer is located.
           The aim of this study was to create a method for modeling a jet flow as a source of acoustic oscillations and to develop a technique for calculating the noise of a propulsion system for a space rocket during the first 1.5—4.1 seconds of flight and also compiling an algorithm and a program for calculating acoustic characteristics.
The calculation technique is based on the modeling of the acoustic field from the propulsion system of the space rocket as a volumetric radiation source. First, it is necessary to determine the frequency range of the oscillation radiation, for which such modeling is applicable. The type of radiator was determined depending on the diameter of the nozzle cut and the acoustic radiator surface’s characteristic size.
The low-frequency acoustic field front sphericity assumes a significant decrease in the magnitude of the sound pressure with distance according to the hyperbolic law which is a significant magnitude.
An acoustic oscillator model and a technique for calculating the noise of a propulsion system (PS) of a space rocket (SR) in the first 1.5—4.1 seconds of flight are proposed. They make it possible to determine the sound pressure in the environment. It is proposed to present the flow of the engine as a three-dimensional acoustic source. An algorithm and a program for calculating acoustic characteristics in the Java programming language were developed.
            According to the results of calculations based on the developed program, the dependence of sound pressure on the frequency at the given temperature levels was obtained. Based on the calculations, a graph was drowned which shows the change in the sound pressure level at adjusted point A with increasing frequency. The sound pressure dependences on frequency are obtained at given temperature levels of the external environment (-32, 20, and 42 °С). The obtained results show that for all acoustic emission frequencies less than 225 Hz the value of the sound pressure level at the point r = 18 m is less than 153 dB. For example, at a frequency of 8000 Hz, the sound pressure level will be 136 dB. Such acoustic radiation is possible on the rocket flight leg from 1.5 to 4.1 seconds. The temperature changes have little effect on the value of the sound pressure level. The developed technique for calculating acoustic radiation at the start of the RCS makes it possible to determine the values of the acoustic pressure amplitudes, the acoustic effects on the rocket body and the nature of the acoustic fields. A method for studying acoustic radiation during the launch of a space rocket based on the determination of the wave parameter kR is presented.
Keywords: acoustic radiation, calculation technique, infrasound, jet engine flow, model, propulsion system, sound pressure, space rocket, volume acoustic source
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