Installation Effects Characterization of VHBR Engines Part III : CFD Assessment for Jet Mixing

The work described here was performed as part of the European research (FP6) project called VITAL. This paper is the third part of a series of four papers presenting the characterisation of installation effects for a typical high bypass ratio engine using advanced numerical and measurement techniques. The aims are to obtain a better understanding of the link between the jet flow and the noise generated, to validate the methods for computing the flowfield and the noise sources for industrial configurations, and also to assess the benefits of a serrated nozzle when installed under a wing. This paper presents an assessment of the capability of the CFD solvers to predict the aerodynamic flow for different nozzles installed under wing, bearing in mind the final objective of computing the noise sources. Density gradient and compressibility corrections have been introduced into the SST k-ω turbulence model to better capture the physics related to high speed and hot jet flows, and high order discretization scheme and error estimation techniques were evaluated with the objective of increasing the accuracy of the computations. Particle Image Velocimetry (PIV) measurements were performed in the CEPRA19 anechoic facility to better understand the link between the aerodynamic flow and the noise, and to build experimental database for validation purpose. CFD solvers are able to properly capture the effects related to freestream velocity and installation under wing, at least in terms of the noise deltas. The serrated nozzle produces very surprising and unexpected results: it shows a larger potential core length, thinner mixing layers and a turbulent kinetic energy (TKE) peak that occurs further downstream. However, the acoustic signature remains classical with a low-frequency noise reduction and a high-frequency noise increase.

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