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Daniel Guggenheim School of Aerospace Engineering

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Now showing 1 - 10 of 11
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Development of a Sonic Sensor for Aircraft Applications

2021-12-14 , Carroll, Jonathan D.

The field of aeroacoustics has been an area of constant research over the past six decades. Acoustic waves have some special characteristics that allow for heating, cooling, and even active flow control over airfoil shapes using synthetic jets and other methods. They can also be used to measure properties of the flow over an aircraft, including the free-stream pressure ratio, density ratio, and total temperature. The current measurement techniques to obtain these parameters applied to aircraft require a specific probe. It is desired to apply knowledge of acoustics to develop an aircraft sensor that can measure multiple flow properties with minimal impact to the flow field. Adding a sensor that can read total temperature, static temperature, airspeed, and angle of attack will have the added benefit of reducing the number of sensors sticking into the flow and may result in a reduction in failure mode analysis due to the minimization of the number of sensors on the aircraft. This work explores the applicability of sonic anemometry to aircraft for high subsonic and sonic speeds. A computational simulation is developed as a validation of the concept and low speed experiments are shown to validate the theory. This effort identifies the underlying issues associated with applying sonic anemometry to high-speed flows and provides methods to overcome them. This work investigates the use of phased array technology to increase the accuracy and applicability at the higher speeds and smaller footprints (lighter and fewer systems). Phased arrays use the constructive and destructive interference to boost and direct the desired signal, in this case, acoustic waves. These acoustic waves have been shown to provide haptic feedback and levitate small particles utilizing a relatively inexpensive ultrasonic phased array system. It is shown that the ultrasonic phased array overcomes the hydrodynamic noise to produce a strong signal for use in the calculation of the flow parameters up to the maximum speed tested. It is also shown that the signal is strong enough to produce consistent time delay estimations, via cross-correlation, with a 0.05 second sample time to integrate into modern air data systems.

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Validity of the point source assumption of a rotor for farfield acoustic measurements with and without shielding

2010-11-15 , Turkdogru, Nurkan

Measuring the farfield noise levels of full-scale rotor systems is not trivial and can be costly. Researchers prefer to perform small-scale experiments in the laboratory so that they can extrapolate the model scaled results to the larger scale. Typically Inverse Square Law (ISL) is used to extrapolate the sound pressure levels (SPL), obtained from model-scale experiments at relatively small distances to predict noise at much larger distances for larger scale systems. The assumption underlying this extrapolation is that the source itself can be treated as a point sound source. At what distance from a rotor system it can be treated as a point source has never been established. Likewise, many theoretical models of shielding by hard surfaces assume the source to be a point monopole source. If one is interested in shielding the noise of a rotor system by interposing a hard surface between the rotor and the observer, can the rotor system really be considered to be a monopole? If rotating noise sources are under consideration what is the effect of configuration and design parameters? Exploring the validity of point source assumption alluded to above for a rotor for farfield acoustic measurements with and without shielding form the backbone of the present work.

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Acoustic excitation of wing wake flows

2000-12 , Elkoby, Ronen

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Flow/acoustic coupling in heated and unheated free and ducted jets

1997-05 , Massey, Kevin C.

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Source location of subsonic and supersonic jets of various geometeries via acoustic beamforming

2018-11-30 , Breen, Nicholas Paul

Over the years, the need to understand and reduce aircraft noise emissions has led numerous researchers to apply various source location techniques to jet noise. Prior to 1985, several methods for determining jet-noise source locations were explored: acoustic mirrors, microphone arrays, two-microphone methods, causality correlation and coherence techniques, nearfield contour surveys, and automated source breakdown. More recently there have been developments in the microphone array, notably acoustic beamforming, and two-microphone method techniques. Many of the older techniques require significant amount of time to acquire data at each jet condition; this requirement is often caused by the necessity to move microphones in order to obtain source locations at all frequencies. The acoustic beamformer does not need to be moved during the acquisition of data, resulting in very rapid tests compared to other source-location methods. Upon examination of prior studies containing jet noise source location measurements, it is clear that there are a few areas in the field that need additional work: (1) no study has compared the results of the acoustic beamforming method with another method using the same nozzles and facilities, (2) no study has been performed that analyzes the effects of differing nozzle geometry, and hence the nozzle exit boundary layer, on the jet noise source location, (3) no study has performed a detailed analysis of the noise source distributions of supersonic jets, and (4) no study has examined the noise source distribution of twin jets and the effect of separation distance on the said distribution. The goal of this thesis is to systematically address these areas with the use of source location measurements, schlieren flow visualization, farfield spectra, and jet velocity measurements. The source location measurements are primarily acquired using an acoustic beamformer. Jet velocity measurements include both nozzle exit boundary layer profiles and downstream velocity profiles and are obtained with the use of boundary layer probes and particle imaging velocimetry.

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Separating Contributions of Small-Scale Turbulence, Large-Scale Turbulence, and Core Noise from Far-Field Exhaust Noise Measurements

2007-08-24 , Nance, Donald Kirby

The two-noise source model for predicting jet noise claims that the radiated jet noise is composed of two distinct sources one associated with the small-scale turbulence and another associated with the large-scale turbulence. The former source is claimed to radiate noise predominantly at larger angles with respect to the downstream jet axis, whereas the large-scale turbulence radiates predominantly at the shallower angles. A key objective of this effort is to experimentally validate this model using correlation and coherence measurements. Upon the successful validation of the two-noise source model for jets exhausting from multiple nozzle geometries driven at Mach numbers ranging from subsonic to supersonic, a three-microphone signal enhancement technique is employed to separate the contribution of the small-scale turbulence from that of the large-scale turbulence in the far-field. This is the first-ever quantitative separation of the contributions of the turbulence scales in far-field jet noise measurements. Furthermore, by suitable selection of far-field microphone positions, the separation of the contribution of any internal or core noise from that of the jet-mixing noise is achieved. Using coherence-based techniques to separate the contributions of the small-scale turbulence, large-scale turbulence, and any internal or core noise from far-field exhaust noise measurements forms the backbone of this effort. In the application of coherence-based multiple-microphone signal processing techniques to separate the contributions of the small-scale turbulence, large-scale turbulence, and any internal or core noise in the far-field, research efforts focus on three techniques (1) the coherent output power spectrum using two microphones, (2) an ordinary coherence method using the three-microphone technique, and (3) the partial-coherence method using five microphones. The assumption of jet noise incoherence between correlating microphone is included in each of these methods. In light of the noise radiation mechanisms described within the framework of the two-noise source model and their spatial characteristics as experimentally determined in the far-field, the assumption of jet noise incoherence is evaluated through a series of experiments designed to study jet noise coherence across a variety of nozzle geometries and jet Mach numbers ranging from subsonic to supersonic. Guidelines for the suitable selection of far-field microphone locations are established.

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Liner impedance modification by varying perforate orifice geometry

1998-12 , Gaeta, Richard Joseph, Jr.

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Potential factors responsible for discrepancies in jet noise measurements of different studies

2016-08-26 , Karon, Aharon Z.

Jet noise measurements have been acquired at many anechoic jet-facilities around the world. These measurements have been used to form the basis for prediction schemes and to understand the generation and radiation of jet noise. Often, when jet noise measurements from different jet-facilities that are thought to be acquired at or corrected to similar conditions are compared, differences are observed in the spectra. These comparisons are typically performed on the basis of the same nozzle-exit diameter, jet velocity, microphone distance from the jet flow, and ambient conditions. This phenomenon has spurred much discussion in the aeroacoustics community, with some even claiming that some of the measurements are contaminated with rig-noise. This study investigates following four factors that can be responsible for the differences in jet noise measurements: (1) rig noise contamination, (2) the jet’s Reynolds number, (3) the nozzle-exit boundary layer of the jet, and (4) reflections and shielding from surfaces inside the anechoic jet-facility. First, the Doubling-Diameter Method, a scheme used to detect rig-noise contamination in jet-noise measurements, is verified and used on jet noise measurements acquired in the Georgia Tech Research Institute (GTRI) Anechoic Jet-Facility to verify the cleanliness of the jet noise measurements. Second, the effect of Reynolds number of the jet is investigated qualitatively and quantitatively for its effect on jet noise measurements. Third, the effect of the nozzle-exit boundary layer on jet noise measurements is categorized qualitatively and quantitatively. In addition, a potential correction is developed that can be used to account for the differences in jet noise measurements from jets with different nozzle-exit boundary layer states. Finally, surfaces inside the anechoic chamber itself, such as, the plenum chamber, and a secondary nozzle are investigated as potential reflectors and shields that can cause waviness and modifications in the jet noise spectra, respectively.

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Jet noise of high aspect-ratio rectangular nozzles with application to pneumatic high-lift devices

2001-12 , Munro, Scott Edward

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Effects of cavity dimensions, boundary layer, and temperature on cavity noise generation and control

1997-12 , Mendoza, Jeffrey Michael

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