William C. Horne

Bio: William C. Horne is an academic researcher from Ames Research Center. The author has contributed to research in topics: Wind tunnel & Noise. The author has an hindex of 10, co-authored 29 publications receiving 355 citations.

High-Speed Jet Noise Reduction Using Microjets on a Jet Engine

Abstract: by a jet engine. Experiments were conducted at the NASA Ames Research Center using a General Electric YJ97-GE-3 turbofan jet engine that was equipped with a 317.5 mm converging nozzle. The engine was operated at conditions that resulted in jets with fully expanded Mach numbers of 0.9 and 1.3. The microjets were generated using up to 48 evenly spaced micro-nozzles that had exit diameters of 1.2 and 2.4 mm. The operating pressure of the microjets was varied from 7.9 to 42.4 bar. Various microjet configurations were used resulting in a total mass flux of the microjets that ranged from 0.5 to 2.3 % of the primary mass flux for the subsonic jet and from 0.3 to 1.0 % of the primary mass flux for the supersonic jet. Through the various configurations it was found that reductions of up to 2 dB in the OASPL could be obtained for both the subsonic and supersonic jets. The reductions for the subsonic jet were seen at all frequencies while they were seen primarily at the higher frequencies for the supersonic jet. A reduction of about 2 dB in the shock noise of the supersonic jet was also observed.

Advanced Background Subtraction Applied to Aeroacoustic Wind Tunnel Testing

Abstract: An advanced form of background subtraction is presented and applied to aeroacoustic wind tunnel data. A variant of this method has seen use in other fields such as climatology and medical imaging. The technique, based on an eigenvalue decomposition of the background noise cross-spectral matrix, is robust against situations where isolated background auto-spectral levels are measured to be higher than levels of combined source and background signals. It also provides an alternate estimate of the cross-spectrum, which previously might have poor definition for low signal-to-noise ratio measurements. Simulated results indicate similar performance to conventional background subtraction when the subtracted spectra are weaker than the true contaminating background levels. Superior performance is observed when the subtracted spectra are stronger than the true contaminating background levels. Experimental results show limited success in recovering signal behavior for data where conventional background subtraction fails. They also demonstrate the new subtraction technique's ability to maintain a proper coherence relationship in the modified cross-spectral matrix. Beam-forming and de-convolution results indicate the method can successfully separate sources. Results also show a reduced need for the use of diagonal removal in phased array processing, at least for the limited data sets considered.

Almost 40 Years of Airframe Noise Research: What Did We Achieve?

Abstract: With the advent of low noise high bypass ratio turbofan engines airframe noise gained significant importance with respect to the overall aircraft noise impact around airports. Already around 1970 airframe noise, originating from flow around the landing gears and high-lift devices, was recognized as a potential “lower aircraft noise barrier” at approach and landing. Since then, the outcome of extensive acoustic flight tests and aeroacoustic wind tunnel experiments enabled a detailed description and ranking of the major airframe noise sources and the development of noise reduction means. In the last decade advances in numerical and experimental tools led to a better understanding of complex noise source mechanisms. Efficient noise reduction technologies were developed for landing gears while the benefits of high-lift noise reduction means were often compensated by a simultaneous degradation in aerodynamic performance. The focus of this paper is not on the historical sequence of airframe noise research but rather aims to provide a concise survey of the achievements in airframe noise source description and reduction over the last 40 years worldwide. Due to the vast amount of work focused on a variety of airframe noise problems, this review can only provide examples but does not claim to be complete.

A review of acoustic imaging methods using phased microphone arrays

Abstract: Phased microphone arrays have become a well-established tool for performing aeroacoustic measurements in wind tunnels (both open-jet and closed-section), flying aircraft, and engine test beds. This paper provides a review of the most well-known and state-of-the-art acoustic imaging methods and recommendations on when to use them. Several exemplary results showing the performance of most methods in aeroacoustic applications are included. This manuscript provides a general introduction to aeroacoustic measurements for non-experienced microphone-array users as well as a broad overview for general aeroacoustic experts.

Computational Aeroacoustic Analysis of Slat Trailing-Edge Flow

Abstract: An acoustic analysis based on the Ffowcs Williams and Hawkings equation was performed for a high-lift system. As input, the acoustic analysis used un- steady flow data obtained from a highly resolved, time-dependent, Reynolds-averaged Navier-Stokes calculation. The analysis strongly suggests that vor- tex shedding from the trailing edge of the slat results in a high-amplitude, high-frequency acoustic signal, similar to that which was observed in a correspond- ing experimental study of the high-lift system.

Computational Aeroacoustic Analysis of Slat Trailing-Edge Flow

Abstract: An acoustic analysis based on the Ffowcs Williams and Hawkings equation was performed for a high-lift system. As input, the acoustic analysis used unsteady flow data obtained from a highly resolved, time-dependent, Reynolds-averaged Navier-Stokes caclulation. The analysis strongly suggests that vortex shedding from the trailing edge of the slat results in a high-amplitude, high-frequency acoustic signal, similar to that which was observed in a corresponding experimental study of the high-lift system.