Acoustics and aeroperformance of nozzles with screwdriver shaped and axisymmetric plugs

Abstract

The recent experimental and numerical tests of corrugated nozzles have shown some acoustic and thrust benefits relative to traditional round nozzles. For example, a Bluebell nozzle which was obtained by 3D nozzle design incorporating a corrugated cross section nozzle shape with a sinusoidal lip line nozzle edge, can provide an acoustic benefit up to 4dB with about a 1% thrust augmentation. In references, this effect was explained as being the result of the corrugated design producing more efficient mixing of the exhausted jet with ambient air. Based on this argument, the authors have proposed the application of this concept for a centerbody (plug) which can form several vortices downstream from the centerbody. Several different corrugated designs are proposed and described in detail in this paper. The main design is a Screwdriver shaped centerbody or plug (SCR) which was tested experimentally and numerically. The acoustic tests were conducted in the anechoic chamber of the Central AeroHydrodynamics Institute (TsAGI, Moscow) under Civilian Research and Development Foundation (CRDF) grant. These experiments have shown an essential acoustic benefit of about 10-13% with the application of the co-annular nozzles by comparison with the reference round nozzle with the same mass flow rate. However, the expected acoustic benefits with the application of the 4-petal Screwdriver shaped centerbody were not obtained by comparison with the reference axisymmetric centerbody (CON) having the same length and the same cross section areas at the same distance from the nozzle throat. Moreover, for some angles (Theta = 60 deg and 90 deg) noise increase was observed (about 1-3%). These tests will be continued with the goal of obtaining better acoustic results. In particular, acoustic characteristics are hoped to be improved by moving t lie centerbody into the nozzle and using penetrable walls for the SCR and/or for the main nozzle. Preliminary results for such approach are very promising. Aeroperformance effects were analyzed numerically. The nozzle thrust, calculations were based on a full Navier--Stokes equations solver (NSE), and both full and marching Euler codes: CFL3D, CRAFT, and Krayko-Godunov . Grid preparation and its optimization were conducted using GRIDGEN and our own codes. The general conclusion of this numerical analysis is some thrust loss with the application of SCR design (about 1 - 1.5%). But, again, some constructive features of SCR design give some promising perspectives for its application in aviation and domestic industries.