E. Brocher, A. Makhsud

The free surface hydraulic analogy was used to study the screech noise for two nozzle inlet geometries. Nozzle 1 had walls converging at a half angle of 5°, generating a converging flow at the exit. Nozzle 2 was designed for parallel flow at the exit. According to the analogy, for a onedimensional flow, when the ratio of the total head of the jet (htod is equal to 3/2 times the water depth on the water table (ha), the Froude number should be equal to unity at the exit. This is actually the case with Nozzle 2, whereas the Froude number is only equal to 0.83 with Nozzle 1. However, downstream of this nozzle, the streamtubes form converging-diverging channels so that a Froude number even higher than unity is reached and shock-cell structures appear. Consequently, screech noise, which results from shear layer/shock cell interaction, already occurs at the critical height ratio with Nozzle 1. Over the range 1.5 < htot/ha < 1.9, corresponding to pressure ratios going from 2.25 to 3.61 for the "hydraulic" gas, screech noise is much lower (up to 15 dB) for parallel flow (Nozzle 2) than for converging flow (Nozzle 1). This finding should be very useful for reducing screech noise of jet engines.

First Joint CEAS/AIAA Aeroacoustics Conference, München, 1995

Conference Paper

englisch

21,0 x 29,7 cm, 6 Seiten

DGLR-Bericht, 1995, 1995-01, First Joint CEAS/AIAA Aeroacoustics Conference - Proceedings; S.513-518; 1995; Deutsche Gesellschaft für Luft- und Raumfahrt - Lilienthal-Oberth e.V., Bonn

NA

aeroacoustics

Bibliothek

1995