Development of a Near-field Acoustical Holography System for Aircraft Jet Source Noise Measurements

Military jet aircraft are exposing both ground maintenance personnel and the community to high levels of noise. The DoD is funding research to develop advanced modeling tools for community noise exposure and for noise reduction techniques. The lack of understanding of the actual jet noise source limits the progress of these new tools. For these tools to achieve their full potential, innovative measurement and analysis methods are necessary to characterize the noise source region in the jet. Near-field acoustic holography (NAH) offers the best general method to meet this need. The objective of this proposed effort is to develop a portable NAH system to characterize full scale jet noise emissions. Results from our Phase I research have demonstrated that a patch measurement approach is the optimum method, one which balances instrumentation cost and aircraft run-time. With the patch measurement approach, three NAH reconstruction techniques can be used in tandem to provide improved confidence in the resulting reconstructions. Tests with simple sources and jet aircraft will prove and refine the measurement method and procedure as well as the NAH data processing algorithms. This process will lead to a finalized design of the data collection system and data processing algorithms.