# Impact of Using Chevrons Nozzle on the Acoustics and Performances of a Micro Turbojet Engine
###### 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 L = 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.  
chevrons; acoustic; nozzle; performances; experimental; turbojet +
Footnote †: journal: Applied Sciences  
As was mentioned before, these solutions were heavily studied, but there are no studies in which the nozzle with chevrons, to be mounted on a turbojet engine, and the performance influences are assessed [18].  
The research projects performed on Boeing 737-max 747-8, 787 and Bombardier CRJ900 aircrafts, have implemented on the Trent 1000 (Rolls Royce), GE90 and GE CF34--8C5 engines, nozzles with chevrons [19; 20; 21; 22].  
One might observe that, in specialized literature, we find many studies of chevrons' acoustic effects. Most of them present studies of chevrons' effects on nozzles, or on simple pipes working with air, but there is a missing part when we think about the effects of chevrons on the turbojet performances. The present paper proposes a study of the chevrons effects on the acoustic and turbojet performances using a test bench equipped with a micro turbojet engine.  
This paper will focus on noise reduction of the micro turbojet engine JET CAT P80, which is used on drones [23] or for academic purpose [24]. The paper novelty consists in acoustic and performance evaluations of this engine tested with three different nozzles (straight nozzle considered the reference and two nozzles with chevrons one with 8 chevrons and the second one with 16 chevrons, both having the chevrons length of 10 percent from the equivalent diameter and immersion angle of zero degrees) at different functioning regimes of speed. The laboratory tests were focused on acoustic evaluation of each nozzle and the engine parameters (compression ratio, air and fuel flow, temperature after the compressor, and in front of the turbine, and the vibrations on axial and radial directions).