Reprint of: Towards Noise Prediction for Rudimentary Landing Gear

Abstract

A four-wheel landing gear truck was designed for research purposes, with the level of complexity which is felt to be manageable in current numerical simulations, and a weak Reynolds-number sensitivity. An experiment is underway, aimed at measuring wallpressure fluctuations, leading to a meaningful test of unsteady simulations with emphasis on noise generation at a June 2010 workshop. We present two Detached-Eddy Simulations (DES) using up to 18 million points in the high-order NTS code. The first is incompressible and placed in the wind tunnel, as requested for the workshop. The second is at Mach 0.115, with only one wall analogous to a wing (but infinite and inviscid), and is used to exercise far-field noise prediction by coupling the DES and a Ffowcs-Williams/Hawkings calculation (FWH). The results include force, wall-pressure, and noise intensities and spectra. The wall pressure signals in the two simulations are very similar. In the absence of detailed experimental data, the attention is focused on internal quality checks, in particular by varying the permeable FWH surface and outflow-patch treatment. An unexpected finding at this Mach number, well below airliner approach values, is the strong role of the quadrupoles revealed by a difference of up to 7dB between results from the solid and permeable FWH surfaces. The DES system and the FWH utility have proven accurate for jet noise, but landing-gear specific checks will continue. A semi-quantitative estimate of the two terms actually supports the idea that dipoles would not dominate quadrupoles until the Mach number is lowered even further. If confirmed, this finding will complicate airframe-noise calculations, hinder the attribution of noise to a given area or component of the aircraft, and conflict with the classical scaling for acoustic power. Progress appears real, but deep comparisons with experiment or other simulations have yet to occur.