ANALYSIS OF THE JET ENGINE NOISE EMISSIONS AT THE INLET AIR TO THE COMPRESSOR AND NOZZLE EXHAUST OUTLET

Abstract

ABSTRACT

The analysis of the noise emitted by jet engines is important, because of its importance to know the characteristics of the noise emitted such as; frequency and sound pressure level and its signal phase, which helps in the design of dampers for the noise level in these type of engines, and among the dampers used is Herschel and Quincke (HQ) technology. In this paper, two acoustic signals were measured instantaneously in two different locations of a small laboratory training jet engine using a microphone system. the first microphone at the inlet of the compressor air, while the other at the exhaust outlet of the engine nozzle. Also, in the same position as the microphone system, the noise level was measured using a decibel noise level meter. The two signals were collected and analysed using advanced data collection technology, with a speed of up to 1.25 Msample/sec, with the Lab View program used to analyze the two signals and calculate the correlation between the two signals and their spectral analysis. The results showed that the noise level at the exit of the exhaust from the nozzle is greater than the noise level at the air inlet of the compressor, and that the noise level at the outlet of the nozzle is directly proportional to the rotational speed of the compressor. While at the entrance of the compressor has a variable behaviour, at low speeds, the noise level was relatively low, when the compressor speed increased, the sound pressure level began to increase to a certain speed until it reached the maximum noise level.
When the compressor speed increases further, the noise level begins to decrease to take the shape of the dome, this is due to the occurrence of acoustic resonance of the noise, and it is often a result of the combustion process that follows the compressor, which is among the problems that occur in the continuous combustion of heat engines, as a result of the reaction between the fluctuation in the heat released and the fluctuating pressure inside the combustion chamber. This phenomenon is called thermo-acoustic instability. Moreover, the results showed that the dominant frequency of the signal emitted from the jetting nozzle of the engine is much greater than the frequency at the air inlet of the compressor, reaching about 20 times, which is normal due to the high velocity of the jet flow at the outlet of the nozzle. In addition, the collected data can be useful in developing modelling schemes that provide sufficient prediction capabilities for the occurrence of combustion instability or for understanding the interactions of sound waves and flames, as well as in developing noise dampening technology for jet engines. https://jer.ly/PDF/Vol-35-2023/JER-05-35-Abstract.php?f=a