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James Bridges

Publications and source records attributed to James Bridges.

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2024

‘Trapped Wave’ Resonance Tones Radiated in the Forward Arc of High-Speed Jets

An experimental study is conducted investigating the characteristics of ‘trapped wave’ resonance tones in the forward arc of jet noise radiation fields. While these spectral peaks disappear in the far acoustic field in the aft and sideline directions, which is why they went unnoticed in decades of jet noise measurements, the present study clearly shows that they radiate in the forward arc (shallow upstream polar locations in the approximate range of θ < 45°). Far-field jet noise spectra in the forward arc, data on which had been lacking in the literature, are not smooth but are characterized by these peaks. This is found for high subsonic to supersonic jets up to the highest jet Mach number covered in the experiment (MJ ≈ 1.9), for round, rectangular as well as convergent-divergent nozzles. With heated jets these spectral peaks are weakened especially around transonic conditions, however, they persist in supersonic conditions. Note that digital files containing all spectral data shown in the following are in a supplemental file to this NASA Technical Memorandum (TM-20240009873-SUPPL). These files can be obtained from the NASA Technical Report Server (NTRS) as a separate download from this report.

jets↗
NASA NTRS2023

Plug20 Test Report: Particle Image Velocimetry (PIV) Measurements

This report provides turbulent flow statistics made using particle image velocimetry (PIV) for several internally mixed exhaust systems with external plugs (Plug20 designs). The tests were conducted at the NASA Glenn Research Center’s Aero-Acoustic Propulsion Laboratory (AAPL) in May and June 2022. The corresponding acoustic data for the configurations and flows presented in this report can be found in an earlier Technical Memorandum, NASA/TM-20210010291, “Plug20 Test Report.” The Plug20 nozzle family was designed to represent commercial supersonic vehicles in the 2025 to 2035 timeframe with a bypass ratio around 4, having an internal mixer, with and without an external plug to improve nacelle boattail drag and shock. The flow conditions measured represent engine cycles for commercial supersonic aircraft at takeoff, having pressure ratios of 2.0 and heated fan and core streams, measured both with and without a flight stream surrounding the plume. A few unheated flow conditions were also tested to tie results to other baseline test results. The PIV measurements in both streamwise and cross-stream planes are described, along with brief analysis to visually catalog the contents and confirm their validity. In this analysis, the streamwise PIV is found to match benchmark datasets within its experimental error. However, the cross-stream turbulent quantities measured by two systems do not match each other or the streamwise measurements in amplitude—caution is required when using the cross-stream data. Data acquired and included in this report are (1) velocity statistics of the plumes in both a streamwise and several cross-stream planes, and (2) the hot nozzle geometry. Tabular forms of the data and computer-aided design (CAD) files of the hot geometry are presented as supplemental files described in Appendix A (TM-20230006779SUPPL1.zip) and Appendix B (TM-20230006779SUPPL2.zip).

Turbulence↗
NASA NTRS2023

Acoustics Technical Working Group and UAM Noise Working Group Proceedings

The NASA Acoustics Technical Working Group Meeting originally started as a program planning meeting in 1992 and has grown through the years. The purpose of these biannual meetings is to foster communication and collaboration among NASA researchers and their university, industry, and government colleagues on activities and work of current and future mutual interest. The NASA-led Urban Air Mobility (UAM) Noise Working Group (UNWG) Meeting began in 2018 as a one-day meeting immediately following the Acoustics Technical Working Group Meeting. The UNWG utilizes four subgroups that conduct regular meetings throughout the year to focus on challenges facing UAM vehicles for community noise and acceptance. The four subgroups coordinate research for development of noise prediction tools/noise reduction technologies, ground and flight test methods, human response and metrics, and regulations and policy (led by the FAA). This work is a compilation of the presentations given at ATWG/UNWG Fall 2022 held in person and via Teams at NASA Glenn Research Center. All NASA content was previously submitted through STRIVES for public presentation. This is merely a compilation. Non-NASA content has permission to distribute. Slide 208 video is included in the Available Downloads as Medial.MOV.

Advanced Air Mobility↗
NASA NTRS2020

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.

Particle Image Velocimetry; Convective Velocity; J↗
NASA NTRSDate not supplied

Experiments to Challenge Jet Noise Prediction

Recent fundamental jet noise tests were conducted with the objective of providing data that challenges jet noise prediction methods. Three cases have been extracted to pose as challenges to the jet noise prediction community. Case 1 targets efforts in LES to appropriately mimic unresolveable turbulent boundary layers in nozzles, and to demonstrate where they are, and are not, important for noise. Case 2 targets acoustic analogy methods, providing cardinal data for the question of azimuthal localization and the broader issue of designing nozzles with favorable azimuthal directivity. Case 3 is an example where nozzle systems exhibit global resonances, which cannot be attacked by steady-state calculations. Given that it is very difficult to foresee such unsteady behavior (speaking from experience), it is crucial that low-cost methods be developed to catch these during the design process. Analysis and documentation of the test data is ongoing.

jet noise↗
NASA NTRSDate not supplied

Basics of Mixer-Ejectors for Quiet Propulsion

A series of numerical and experimental studies were undertaken to take a fresh look at how a mixer-ejector exhaust system might provide noise reduction for the LTO operation of a commercial supersonic vehicle. Historical understandings of aero and acoustic performance were challenged and new details of noise reduction mechanisms were uncovered. New CFD-based noise prediction tools, applied to conceptual designs, predicted noise reductions of 3-5EPNdB for a few percent thrust loss. Recommendations from the study include validation of the acoustic prediction method, and using it to refine variants of practical nozzle systems for low noise exhaust systems that perform well both acoustically and aerodynamically.

jet noise↗
NASA NTRSDate not supplied

Azimuthal Noise Directivity of Non-Axisymmetric Jets

Far-field acoustic measurements of subsonic non-axisymmetric jets were made to carefully show the azimuthal character of the sound field. Nozzles with azimuthal features having periodicity of 2 to 6 show the progression of the azimuthal effects. Compared with predicted velocity profiles, the relationship between jet thickness and sound is demonstrated. The measurements show that even jets with very radical non-axisymmetry, such as an 8:1 rectangular nozzle, produce an axisymmetric sound field at Strouhal numbers less than 1. Significant azimuthal deviations are found for St> 1, mainly at far aft angles. The polar angle where the sound begins to be non-axisymmetric moves aft as the azimuthal order increases. The deviation is more extreme in amplitude with increasing jet speed in subsonic jets. As the azimuthal order reaches m=5 the pattern becomes more complicated, with increases and decreases in the same azimuthal plane, but with relatively small amplitudes. It is hoped that the data can be used in validating high-fidelity jet noise prediction methods.

Jet noise↗
NASA NTRSDate not supplied

Noise of Internally Mixed Exhaust Systems With External Plug For Supersonic Transport Applications

Internally mixed exhaust systems produce more noise than would be expected from an equivalent fully mixed flow. This ‘excess noise’ has never been fully explained and has not been researched recently as it is not as much of a problem for high bypass-ratio exhaust systems. Commercial supersonic vehicles, however, will use more moderate bypass ratio engines. Their exhaust systems will also likely feature external plugs to improve boat tail angle for cruise performance. Thus the problem of excess noise will need to be addressed along with the impacts of having an external plug. Recently, acoustic tests of dual-stream jet flows from both internal and external plug nozzles have been conducted. Measurements of noise from flows with an axisymmetric splitter and lobed forced mixer were made. These measurements show the baseline ‘excess noise’ previously found in forced mixer exhaust systems, and show how this noise source differs depending upon the plug geometry. Background-oriented schlieren measurements acquired simultaneously document the differences in shock structures over the transonic flow regime tested. The far-field acoustic measurements indicate that an external plug can slightly reduce the mixing noise of the jet plume when the flow is completely mixed, e.g. when the core and bypass streams have the same temperature and the flow is a single-stream jet. However, when the flow is not fully mixed, e.g. the usual case of an internally mixed exhaust system, the plug seems to amplify the ‘excess noise’ associated with the mixer. This additional noise source presents a challenge for nozzle designers wanting to use internally mixed exhaust systems with external plug nozzles.

Jet noise↗
NASA NTRSDate not supplied

Landing and Takeoff (LTO) noise aspects of supersonic Flight

Landing and Takeoff (LTO) noise of proposed commercial supersonic vehicles will be compatible with the fleet currently flying today. The aero technology to accomplish this exists, but the lack of noise data for these technologies means there is significant uncertainty about exactly how loud the aircraft will be. This uncertainty is creating a stumbling block in efforts to establish noise regulations for the new supersonic market. The presentation shows NASA’s efforts to quantify this uncertainty and to reduce it using physics-based simulations over the next three years. Note: No voice included or available for this presentation.

James Bridges↗
NASA NTRSDate not supplied

Update on Prediction Uncertainty Reduction (PUR) Tech Challenge

NASA has taken on a Technical Challenge to reduce the uncertainty in prediction of noise from near-term commercial supersonic aircraft. To date, an assessment has been done to baseline this effort, quantifying how much more uncertainty exists when the system-level prediction methods are applied to supersonic aircraft as compared to conventional aircraft. And an assessment has been made for the uncertainty in the physics-based simulations for jets. These will be briefly demonstrated.

supersonic↗
NASA NTRSDate not supplied

Quantifying Uncertainty of Landing and Takeoff Noise for Commercial Supersonic Aircraft

Of the many challenges faced by manufacturers attempting to offer supersonic travel to the public, the uncertainty in predicting the noise of these aircraft in airport operations has an immediate impact. No noise regulation exists in FAA or ICAO for certifying such aircraft, as these organization require solid data, usually from existing aircraft. Manufacturers are taking large risks to design a vehicle not knowing whether it will be allowed to fly. A partial solution to this conundrum is to use physics-based simulations to provide the “data” used to calibrate system-level prediction methods, carefully documenting the uncertainty of the method for application to supersonic aircraft. A close look at the accuracy of empirical prediction methods points to areas where improvements need to be made if noise studies of supersonic aircraft are to be useful. As NASA embarks on a focused research program to improve predictions of noise from the noise-dominant propulsion noise of commercial supersonic aircraft, this paper documents the work done to baseline the uncertainties found in today’s noise prediction methods. A relatively simplistic method was developed, summarizing the error of the empirical methods on a component basis and following their impact on the total aircraft during landing and takeoff operations using Monte Carlo analysis. By this method it is found that current empirical noise prediction methods have an uncertainty of 1.5 EPNdB cumulative for propulsion noise of a representative conventional subsonic passenger aircraft. When applied to likely near-term supersonic commercial aircraft, the uncertainty is 7.6 EPNdB cumulative, a difference that must be reduced if the prediction methods are to guide decision makers.

Airport noise↗
NASA NTRSDate not supplied

Flow and noise from supersonic plug nozzles

Nozzles with external plugs are candidates for propulsion of future supersonic aircraft. A model-scale experimental study is conducted exploring the flow and noise characteristics of various plug nozzles. For a given outer nozzle, the plug geometry is varied from conic with various half-angles (lengths) to plugs designed by the method of characteristics (MoC) as well as truncated and porous plugs. So far, noise characteristics and schlieren flow visualization data have been acquired. Limited numerical simulations have also been done addressing thrust performance. The simulations show that the MoC plugs out-perform the conic cases, especially around high Mach number cruise conditions. The experimental data, however, show that the MoC plugs are noisy relative to the conic cases at low Mach number landing and takeoff (LTO) conditions. The increased noise (with MoC at LTO) is accompanied by unsteady turbulent structures and increased jet spreading, as seen in schlieren pictures. At LTO, the longest conic plug is found to be the least noisy. Furthermore, a porous surface on the long conic plug effectively suppresses broadband shock associated noise (BBSN) at higher Mach numbers. Thus, a dilemma remains. MoC design gives best thrust performance at cruise but it is noisy at LTO. A long conic plug, on the other hand, is quieter at LTO but may have unacceptable thrust at cruise.

jets↗
NASA NTRSDate not supplied

Scale Resolving Jet Simulations to Reduce Airport Noise

- An emerging potential market has generated renewed interest in civil supersonic aircraft - Evidenced by the appearance of several commercial programs despite lack of standards for en route noise or landing and takeoff noise - Overland Flight Restrictions based on unacceptable sonic boom noise are viewed as the main barrier to this vision - National Research and Policy agencies play a central role in developing the data needed for the regulation change that is essential to enabling this new market - The vision of the Supersonics Community is a future where fast air travel is available for a broad spectrum of the traveling public - Future supersonic aircraft will not only be able to fly overland without creating an “unacceptable situation” but compared to Concorde and SST will be efficient, affordable, and environmentally responsible

ARMD↗
NASA NTRSDate not supplied

Diagnosing Noise Features Of Internally Mixed, External Plug Exhaust Systems

In internally mixed exhaust systems, a lobed or forced mixer is employed to mix the core and bypass streams before they exit the common nozzle. For moderate bypass-ratio engines this marginally improves thrust, and provides a significant acoustic benefit. Indeed, it has been thought that a fully mixed jet creates the lowest noise you can get from a two-stream engine. Typically, the forced mixer system produces a bit more noise than a fully mixed equivalent jet, noise that has been called “excess noise”. In recent testing, this excess noise seemed to be amplified when an external plug was employed in the exhaust system to reduce boattail drag. Identifying the mechanism of this excess noise and mitigating it is key to creating commercial supersonic vehicles that are acoustically acceptable around airports. This paper adds to that investigation, analyzing results from recent tests where far-field acoustic data were acquired on two sets of flows with matched fully mixed flow conditions. One set of flows had a heated core stream, making it a dual-stream jet. The other set had both streams heated to the same temperature, making a single-stream jet that matched the fully mixed temperature and velocity of the dual-stream jet. These flows were tested in two lobed-mixer exhaust systems with internal and external plugs. Analysis of flow and noise data from the nozzles with combinations of single- and dual-stream flows, and with and without flight streams, gives insight into how and why the noise of the dual-stream and single-stream jet differ. One additive source, present in nozzles both with and without external plugs, comes from inside the nozzle, likely the internal shear layer coming off the lobed mixer. This noise source is not impacted by a change in flight stream and has a distinctive spectral directivity that is amplified by the presence of the external plug. Finding the exact source mechanism of this new source will be key to making the internally mixed exhaust systems reach their lowest possible sound level.

Noise prediction, supersonic, jet noise↗
NASA NTRSDate not supplied

Flow Fields of Internally Mixed Exhaust Systems With External Plug For Supersonic Transport Applications

Commercial supersonic vehicles of the future will likely use engines with lower bypass ratios, where the design of the internal mixer will have a strong impact on the noise produced by the jet plume. Their exhaust systems may also feature external plugs to improve boattail angle for cruise performance at supersonic speeds. Currently there are no publicly available empirical noise models for such nozzle systems, and insight into their flow fields will help in creating these models. For those attempting to make large eddy simulations and other higher fidelity methods be their main prediction tool, the internally mixed exhaust system is also a good test case when going beyond simple single-stream jets. The turbulent flow statistics of several configurations previously tested for noise and shocks have been measured for flow conditions that can be used in development of empirical models and validating scale-resolving prediction tools. These measurements are presented and briefly analyzed for insights into the noise impacts from the flow impacts observed.

Turbulence, Jets, Particle Image velocimetry↗
NASA NTRSDate not supplied

Flow Fields of Internally Mixed Exhaust Systems With External Plug For Supersonic Transport Applications

Commercial supersonic vehicles of the future will likely use engines with lower bypass ratios, where the design of the internal mixer will have a strong impact on the noise produced by the jet plume. Their exhaust systems may also feature external plugs to improve boattail angle for cruise performance at supersonic speeds. Currently there are no publicly available empirical noise models for such nozzle systems, and insight into their flow fields will help in creating these models. For those attempting to make large eddy simulations and other higher fidelity methods be their main prediction tool, the internally mixed exhaust system is also a good test case when going beyond simple single-stream jets. The turbulent flow statistics of several configurations previously tested for noise and shocks have been measured for flow conditions that can be used in development of empirical models and validating scale-resolving prediction tools. These measurements are presented and briefly analyzed for insights into the noise impacts from the flow impacts observed.

Fluid Mechanics and Thermodynamics↗