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Bridges, James

Publications and source records attributed to Bridges, James.

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2019

Rapid Prediction of Installed Jet Noise from RANS

A new method of computing jet noise, called mSrc, was developed on the general principles of acoustic analogies. In the method, the problem of translating turbulent flow energy into acoustic energy at a far-field observer is broken into two parts, a calculation of acoustic source strengths and then their propagation. The acoustic sources are related to turbulent quantities in the jet plume in a robust manner. The propagation, which is more properly computed using a Green's function accounting for nonuniform speed of sound and solid surfaces, is instead modeled using commonly observed features of jet acoustic far field directivity, and by diffraction barrier theory for surfaces. The mSrc method does not require gradients of the predicted flow field, allowing it to make use of robust unstructured RANS CFD methods, including embedded boundary codes. Such codes do not require specification of surface meshes, and auto-refine their grid to resolve flow gradients, putting resolution where it is required without a priori user input. The ability of mSrc to use such radically unstructured flow input results in an efficient method of estimating noise from jet flows from complex nozzles installed on aircraft. Many validation cases are presented to demonstrate the accuracy and range of applicability of the mSrc method for representative jet noise applications.

Bridges, James↗
NASA NTRS2019

Rapid Prediction of Installed Jet Noise From RANS

A new method of computing jet noise, called mSrc, was developed on the general principles of acoustic analogies. In the method, the problem of translating turbulent flow energy into acoustic energy at a far-field observer is broken into two parts, a calculation of acoustic source strengths and then their propagation. The acoustic sources are related to turbulent quantities in the jet plume in a robust manner. The propagation, which is more properly computed using a Green's function accounting for nonuniform speed of sound and solid surfaces, is instead modeled using commonly observed features of jet acoustic far field directivity, and by diffraction barrier theory for surfaces. The mSrc method does not require gradients of the predicted flow field, allowing it to make use of robust unstructured RANS CFD methods, including embedded boundary codes. Such codes do not require specification of surface meshes, and auto-refine their grid to resolve flow gradients, putting resolution where it is required without a priori user input. The ability of mSrc to use such radically unstructured flow input results in an efficient method of estimating noise from jet flows from complex nozzles installed on aircraft. Many validation cases are presented to demonstrate the accuracy and range of applicability of the mSrc method for representative jet noise applications.

Bridges, James↗
NASA NTRS2019

PIV/Phased Array/Far-Field Noise Measurements of a Low-Noise Top-Mounted Propulsion Installation for a Supersonic Airliner

A model-scale exhaust system was tested to validate low-noise concepts and noise prediction methods. The tests involved far-field acoustics, translating phased array, and particle image velocimetry; this report covers the far-field acoustic measurements. Data were acquired for a series of nozzles with different chevron designs, both uninstalled and installed on a representative aircraft planform. The impact of the various chevron treatments on the far-field noise was documented, along with the impact of the pylon and planform. For the baseline nozzle, installation produced a 2 EPNdB (Effective Perceived Noise in deciBels) reduction, as assumed in system studies. Chevrons were used to shift noise sources upstream to maximize the installation benefits and to reduce unshielded sources downstream. These resulted in reductions of 4-5 EPNdB...

Bridges, James↗
NASA NTRS2019

Translating Phased Array Measurements of a Low-Noise Top-Mounted Propulsion Installation for a Supersonic Airliner

A novel translating-phased-array technique was applied during a model-scale validation test of low-noise propulsion concepts for supersonic transport aircraft. The test involved particle image velocimetry, far field and translating phased array acoustic measurements. This paper covers the translating phased array portion. Data were acquired for a series of nozzles with different chevron designs, both uninstalled and installed on a representative aircraft planform. The far field data confirmed the noise reduction potential of top-mounted installation, while the phased array results gave insights into how the reduction occurred and highlighted areas for improvement. This was the inaugural test for the new translating phased array, which measures source maps as seen by observers at different polar angles. Propagation effects through the free jet were documented for the different viewing angles. The source maps obtained were used to understand important aspects of the far field noise measurements.

Beamforming↗
NASA NTRS2019

Noise Measurements of a Low-Noise Top-Mounted Propulsion Installation for a Supersonic Airliner

A model-scale exhaust system was tested to validate low-noise concepts and noise prediction methods. The tests involved far-field acoustics, translating phased array, and particle image velocimetry; this report covers the far-field acoustic measurements. Data were acquired for a series of nozzles with different chevron designs, both uninstalled and installed on a representative aircraft planform. The impact of the various chevron treatments on the far-field noise was documented, along with the impact of the pylon and planform. For the baseline nozzle, installation produced a 2EPNdB reduction, as assumed in system studies. Chevrons were used to shift noise sources upstream to maximize the installation benefits and to reduce unshielded sources downstream. These resulted in reductions of 4-5EPNdB relative to the uninstalled baseline nozzle. Detailed analysis of spectral directivities behind the integrated EPNL metric gave insight into how well these concepts actually work. When correlated with particle image velocimetry measurements and phased array measurements, reported in companion papers, the explanation of acoustic benefits from top-mounted propulsion is clear as is the path toward optimization of the concept.

Supersonics↗
NASA NTRS2019

PIV Measurements of a Low-noise Top-mounted Propulsion Installation for a Supersonic Airliner

A model-scale exhaust system was tested to validate low-noise propulsion concepts and noise prediction methods. The tests involved far-field acoustics, phased array, and particle image velocimetry (PIV). This paper covers the particle image velocimetry portion. Data was acquired at NASA Glenn's Aero-Acoustic Propulsion Lab for a series of nozzles with different chevron designs, both uninstalled and installed on a representative aircraft planform. The impact of the various chevron treatments on the turbulent velocity field was documented, along with the impact of the pylon and planform. When correlated with far-field acoustic measurements and phased array measurements, reported in companion papers, the explanation of acoustic benefits from top-mounted propulsion is clear as is the path toward optimization of the concept.

Propulsion Airframe Integration↗
NASA NTRS2018

Subsonic Jet Noise Simulation with JENRE

JENRE, a large eddy simulation code, is used to simulate an unheated, subsonic jet. Results are compared to experiment, with an emphasis on validating the acoustic power spectral density at the farfield. Problems encountered during the development of the simulations are discussed, with solutions to said problems.

Ingraham, Daniel↗
NASA NTRS2018

NASA's Pursuit of Low-Noise Propulsion for Low-Boom Commercial Supersonic Vehicles

Since 2006, when the Fundamental Aeronautics Program was instituted within NASA's Aeronautics Mission Directorate, there has been a Project looking at the technical barriers to commercial supersonic flight. Among the barriers is the noise produced by aircraft during landing and takeoff. Over the years that followed, research was carried out at NASA aeronautics research centers, often in collaboration with academia and industry, addressing the problem. In 2013, a high-level milestone was established, described as a Technical Challenge, with the objective of demonstrating the feasibility of a low-boom supersonic airliner that could meet current airport noise regulations. The Technical Challenge was formally called a Low Noise Propulsion for Low Boom Aircraft and was completed in late 2016. This paper reports the technical findings from this Technical Challenge, reaching back almost 10 years to review the technologies and tools that were developed along the way. It also discusses the final aircraft configuration and propulsion systems required for a supersonic civilian aircraft to meet noise regulations using the technologies available today. Finally, the paper documents the model-scale tests that validated the acoustic performance of the study aircraft.

aeroacoustic↗
NASA NTRS2018

Aeroacoustic Validation of Installed Low Noise Propulsion for NASA's N+2 Supersonic Airliner

An aeroacoustic test was conducted at NASA Glenn Research Center on an integrated propulsion system designed to meet noise regulations of ICAO Chapter 4 with 10EPNdB cumulative margin. The test had two objectives: to demonstrate that the aircraft design did meet the noise goal, and to validate the acoustic design tools used in the design. Variations in the propulsion system design and its installation were tested and the results compared against predictions. Far-field arrays of microphones measured the acoustic spectral directivity, which was transformed to full scale as noise certification levels. Phased array measurements confirmed that the shielding of the installation model adequately simulated the full aircraft and provided data for validating RANS-based noise prediction tools. Particle image velocimetry confirmed that the flow field around the nozzle on the jet rig mimicked that of the full aircraft and produced flow data to validate the RANS solutions used in the noise predictions. The far-field acoustic measurements confirmed the empirical predictions for the noise. Results provided here detail the steps taken to ensure accuracy of the measurements and give insights into the physics of exhaust noise from installed propulsion systems in future supersonic vehicles.

supersonic↗
NASA NTRS2018

NASA's Pursuit of Low-Noise Propulsion for Low-Boom Commercial Supersonic Vehicles

Since 2006, when the Fundamental Aeronautics Program was instituted within NASA's Aeronautics Mission Directorate, there has been a Project looking at the technical barriers to commercial supersonic flight. Among the barriers is the noise produced by aircraft during landing and takeoff. Over the years that followed, research was carried out at NASA aeronautics research centers, often in collaboration with academia and industry, addressing the problem. In 2013, a high-level milestone was established, described as a Technical Challenge, with the objective of demonstrating the feasibility of a low-boom supersonic airliner that could meet current airport noise regulations. The Technical Challenge was formally called "Low Noise Propulsion for Low Boom Aircraft", and was completed in late 2016. This paper reports the technical findings from this Technical Challenge, reaching back almost 10 years to review the technologies and tools that were developed along the way. It also discusses the final aircraft configuration and propulsion systems required for a supersonic civilian aircraft to meet noise regulations using the technologies available today. Finally, the paper documents the model-scale tests that validated the acoustic performance of the study aircraft.

supersonic↗
NASA NTRS2017

Measurements of Turbulent Convection Speeds in Multistream Jets Using Time-Resolved PIV

Convection speeds of turbulent velocities in jets, including multi-stream jets with and without flight stream, were measured using an innovative application of time-resolved particle image velocimetry. The paper describes the unique instrumentation and data analysis that allows the measurement to be made. Extensive data is shown that relates convection speed, mean velocity, and turbulent velocities for multiple jet cases. These data support the overall observation that the local turbulent convection speed is roughly that of the local mean velocity, biased by the relative intensity of turbulence.

Jet↗
NASA NTRS2017

Tones Encountered with a Coannular Nozzle and a Method for their Suppression

With multi-stream coannular nozzles, sometimes tones are generated that make the nozzle fail noise regulation criteria. A two-stream nozzle was studied experimentally in an attempt to identify the sources of such tones and explore remedies. With the given nozzle configuration, sharp tones occurred in a range of low jet Mach numbers (M (sub j)). The tones could be traced to a coupling of vortex shedding from the struts, that hold the nozzles and the center-body together, and various acoustic resonance modes of the ducts. A leading edge treatment of the struts is shown to suppress the vortex shedding and eliminate the tones.

vortex shedding↗
NASA NTRS2017

Measurements of Turbulence Convection Speeds in Multistream Jets Using Time-Resolved PIV

Convection speeds of turbulent velocities in jets, including multi-stream jets with and without flight stream, were measured using an innovative application of time-resolved particle image velocimetry. The paper describes the unique instrumentation and data analysis that allows the measurement to be made. Extensive data is shown that relates convection speed, mean velocity, and turbulent velocities for multiple jet cases. These data support the overall observation that the local turbulent convection speed is roughly that of the local mean velocity, biased by the relative intensity of turbulence.

Convection Speed↗
NASA NTRS2017

Top-Mounted Propulsion Test Plans (TMP17)

NASA recently completed a study of propulsion cycles and nozzle types applicable to a 70-passenger, M1.6 supersonic airliner, paying especial attention to the noise produced during landing and take-off. The results of the study were validated in a model-scale test at NASA Glenn last summer. The findings of that study and test, along with other studies, have resulted in a new strategy for achieving the Commercial Supersonic Technologys goals for noise and performance. Key to that strategy is moving the propulsion to the top-side of the vehicle and modifying the nozzle and inlet to maximally shield the propulsion noise while maintaining efficient operation. Installed exhaust configurations have been designed to minimize the exhaust noise using new acoustic design tools. A test planned for the fall of 2017 will validate both the new design tools and the low-noise concept using a new translating phased array. During the test, questions regarding modifications of convected waves in the jet near-field that are key to new understandings of aft jet noise will be addressed. Also, to better tie rig results to real-world measurements, a model-scale version of a nozzle that was flight tested by Glenn Research Center in 2001 will be tested.

Jet noise↗
NASA NTRS2017

Flow and Noise From Septa Nozzles

This investigation pertains to distributed propulsion system. Basically, the jet exhaust is divided and channeled through multiple compartments or septa. In one version of the concept each septum is to be driven by an electric fan, the power being supplied by engines suitably mounted on the airframe. In the latter hybrid case the need for heavy power trains is eliminated and system studies indicate a net benefit in efficiency. From aeroacoustics point of view, however, there are concerns. An immediate question is whether the noise from the multiple jets would be equal to or greater than that from an equivalent single jet. When multiple jets are placed side by side sometimes they resonate and produce more noise. In order to address these issues a fundamental model-scale experiment is being carried out at NASA Glenn Research Center (GRC). Preliminary results from this study have been presented recently. One of the key findings is that the noise from the septa nozzle can actually be less than that from the equivalent single nozzle. Continued studies make it clear that the flow from the septa nozzle may be quite sensitive to upstream passage geometry in each septum. This can have a profound impact on the evolution of the flow downstream as well as noise. These issues are currently being researched. The proposed paper is to summarize the results from the mainly experimental study that is to be aided by limited numerical simulation.

nozzle flow↗
NASA NTRS2017

Validating a Monotonically-Integrated Large Eddy Simulation Code for Subsonic Jet Acoustics

The results of subsonic jet validation cases for the Naval Research Lab's Jet Engine Noise REduction (JENRE) code are reported. Two set points from the Tanna matrix, set point 3 (Ma = 0.5, unheated) and set point 7 (Ma = 0.9, unheated) are attempted on three different meshes. After a brief discussion of the JENRE code and the meshes constructed for this work, the turbulent statistics for the axial velocity are presented and compared to experimental data, with favorable results. Preliminary simulations for set point 23 (Ma = 0.5, Tj=T1 = 1.764) on one of the meshes are also described. Finally, the proposed configuration for the farfield noise prediction with JENRE's Ffowcs-Williams Hawking solver are detailed.

subsonic jet↗
NASA NTRS2016

Testing Installed Propulsion For Shielded Exhaust Configurations

Jet-surface interaction (JSI) can be a significant factor in the exhaust noise of installed propulsion. Tests to further understanding and prediction of the acoustic impacts of JSI have been described. While there were many objectives for the NASA JSI1044 test, the overall objective was to prepare for a 2016 test validating the design of a low-noise, low-boom supersonic commercial airliner. In this paper we explore design requirements for a partial aircraft model to be used in subscale acoustic testing, especially focusing on the amount of shielding surface that must be provided to simulate the acoustic environment between propulsion exhaust system and observer. We document the dual-stream jets, both nozzle and flow conditions, which were tested to extend JSI acoustic modeling from simple single-stream jets to realistic dual-stream exhaust nozzles. Examples of observations found as surface geometry and flow conditions were varied were provided. And we have presented initial measurements of the installation impacts of integrating the propulsion on the airframe for a supersonic airliner with realistic airframe geometries and nozzles.

engine airframe integration↗