Abstract
This paper presents a study regarding the noise reduction of the turbojet engine, in particular the jet noise of a micro turbojet engine. The results of the measurement campaign are presented followed by a performances analysis which is based on the measured data by the test bench. Within the tests, beside the baseline nozzle other two nozzles with chevrons were tested and evaluated. First type of nozzle is foreseen with eight triangular chevrons, the length of the chevrons being L = 10 percentages from the equivalent diameter and an immersion angle of I = 0 deg. For the second nozzle the length and the immersion angle were maintained, only the chevrons number were increased at 16. The micro turbojet engine has been tested at four different regimes of speed. The engine performances were monitored by measuring the fuel flow, the temperature in front of the turbine, the intake air flow, the compression ratio, the propulsion force and the temperature before the compressor. In addition, during the testing, the vibrations were measured on axial and radial direction which indicate a normal functioning of the engine during the chevron nozzles testing. Regarding the noise, it was concluded that at low regimes the noise doesn’t presents any reduction when using the chevron nozzles, while at high regimes an overall noise reduction of 2–3 dB(A) was achieved. Regarding the engine performances, a decrease in the temperature in front of the turbine, compression ratio and the intake air and fuel flow was achieved and also a drop of few percent of the propulsion force.
Highlights
Nowadays, one of the main problems with which aviation is faced is noise pollution [1]and the need to heavily reduce the noise exposure of the areas adjacent to airports.In aviation, the most important noise sources are the take-off and landing phases of flight
ItIt must must be be mentioned micro engine is functioning, besides the jet noise, there are many mentioned that, that,while whilethe the micro engine is functioning, besides the jet noise, there are other generated by: air by: circulation at intake generated by manynoise othersources noise sources generated air circulation at level, intaketurbulences level, turbulences generthe air passage through compressor stage, mechanical noise generated by the speed of the ated by the air passage through compressor stage, mechanical noise generated by the shaft, as Blade
The main conclusion of this paper is related to the overall noise reduction of 2–3 dB for the configurations with chevron nozzles, which is obtained only at high-speed regimes
Summary
One of the main problems with which aviation is faced is noise pollution [1]. There are many studies and research projects treating the jet noise reduction [5,6], but the simplest technique is to manufacture chevrons on the nozzle without having high loss of the propulsion force [7,8,9,10,11]. The chevrons are dynamic gas equipment that, by initiating the vortical flow, smoothens the mixture of the two flows, having different velocities, and decreases the resultant noise of those flow interactions [12]. These solutions were proposed for the first time by the Lighthill in 1952 [13], and since these were studied and developed, and complex geometries resulted.
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