Book Description

The results of the investigation of the noise characteristics of the exhaust jets from coannular nozzles with conventional and inverted velocity profiles are presented. Experiments were carried out on a series of coannular nozzles of equal primary and secondary area. The majority of acoustic tests were carried out holding either the total thrust or the total mass flow constant while varying the rates of secondary velocity to primary velocity. A limited number of tests were also made simulating the takeoff, cutback and approach conditions of the JT8D engine and corresponding inverted conditions. The results of this study show that at high thrust level the coannular flows with inverted velocity profiles are quieter than those with standard velocity profiles at the same thrust and the same mass flow. The acoustic differences are much greater when the velocity ratio is produced by differences in the stagnation temperature rather than by differences in the stagnation pressure. (Author).