The Doubling-Diameter Method for Detecting the Presence of Rig Noise in Jet-Noise Measurements

Often, lossless jet-noise data obtained by various researchers in different facilities do not match after accounting for jet operating conditions, measurement distance, and nozzle dimensions using accepted jet-noise scaling laws. There have been a number of explanations for these differences, but the most contentious of these is attributing rig-noise contamination to be the cause of the differences. This reasoning calls all the measurements that have been acquired in the facility into question. Knowing if jet noise is contaminated by rig noise in a given facility is crucial to obtaining high-quality jet-noise data, and a simple method is needed to determine if rig noise is indeed present in a given set of measurements. One such method is the so-called doubling-diameter method that was first published by the second author. Validation of this method is the focus of the present study. This validation was conducted using cylindrical obstructions upstream of the nozzle exit. Not only it is shown that this method can accurately detect rig-noise contamination, but in a case study, the Georgia Tech Research Institute Anechoic Jet Facility is shown to be free of rig-noise contamination.