Noise Amplification Effects due to Jet-Surface Interaction

A numerical investigation on jet-installation noise is performed using a software based on the Lattice-Boltzmann Method. A flat plate is placed in the irrotational hydrodynamic field of the jet, i.e. outside of the plume, resulting in noise increase due to the scattering of instability waves at the plate trailing edge. The configuration adopted in this work replicates the one used for a benchmark study at NASA Glenn, against which the numerical results are validated. Far-field noise spectra from the isolated and installed jet cases, obtained through the Ffowcs-Williams Hawkings analogy, are compared at different polar angles. The results show a low-frequency noise amplification, occurring mainly in the directions normal to the plate and upstream of the jet axis. It is also shown that strong pressure fluctuations are generated at the trailing-edge of the plate and then propagate to the far-field as acoustic waves. The effects of the plate geometry (length and radial position) and jet flow characteristics (velocity and temperature) on the installation noise are also addressed. Pressure fluctuations on the plate are also computed and correlated to the overall far-field results, showing that, in the installed case, the surface dipoles are the dominant sources at low frequencies