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NASA NTRS1994

High-Speed Research: Sonic Boom, Volume 1

The second High-Speed Research Program Sonic Boom Workshop was held at NASA Ames Research Center May 12-14, 1993. The workshop was organized into three sessions dealing with atmospheric propagation, acceptability, and configuration design. Volume 1 includes papers on atmospheric propagation and acceptability studies. Significant progress is noted in these areas in the time since the previous workshop a year earlier. In particular, several papers demonstrate an improved capability to model the effect of atmospheric turbulence on sonic booms. This is a key issue in determining the stability and acceptability of shaped sonic booms. In the area of acceptability, the PLdB metric has withstood considerable scrutiny and is validated as a loudness metric for a wide variety of sonic boom shapes. The differential loudness of asymmetric sonic booms is better understood, too.

Edwards, Thomas A.↗

NASA NTRS1992

Atmospheric effects on sonic boom: A program review

The program goals were determined after consideration of the weaknesses in our understanding of atmospheric effects on sonic boom waveforms left in the wake of the cancellation of the U.S. SST in the 70's and the advancements in acoustics and atmospheric science since that time. For example, a considerable body of knowledge on molecular absorption has built up in the acoustics community over the last 15 years and this has not been incorporated into the sonic boom theory. Further, it was felt that the understanding of atmospheric turbulence had also advanced considerably during that time period. Therefore, key elements of the current program are the development of an improved atmospheric absorption model and an improved atmospheric turbulence model. The advances made in computer power over the last 15 years were also considered, and will be utilized to remove restrictions on the analytical model for turbulence effects on sonic boom waveforms. Although the majority of disturbing sonic booms will not occur at focuses or caustics, it was felt that this was an area that required further understanding, thus it will be looked into. Finally, in order to insure that the current effort, which is basically analytical in nature, retains a firm grasp on reality, a data base of sonic boom waveforms and associated weather data is being compiled, and a set of scale model experiments is being planned to guide the overall efforts.

Mcaninch, Gerry L.↗

NASA NTRS1992

Overview of NASA human response to sonic boom program

For some routes the ability to fly at supersonic speeds over land as well as over water would greatly enhance the time benefit to the passenger. It would also increase the productivity and economic viability of the aircraft. There are no reliable guidelines which can be used to determine a sonic boom exposure which would be acceptable for overland supersonic flight. In addition to the peak pressure of the sonic boom, the detailed shape of the signature will also influence the perception, and therefore the community response, to sonic boom exposures. Initially, the program aims to develop the capability to predict human response to individual sonic booms. This will enable a quantitative assessment of the benefit of 'low boom' aircraft configurations and will also serve to guide the design of the aircraft and its operating conditions. This capability will form the foundation of studies to determine the relationship between sonic boom exposure and community response. Only then will it be possible to assess the feasibility of acceptable overland supersonic flight.

Shepherd, Kevin P.↗

NASA NTRS1996

The 1995 NASA High-Speed Research Program Sonic Boom Workshop

The High-Speed Research Program and NASA Langley Research Center sponsored the NASA High-Speed Research Program Sonic Boom Workshop on September 12-13, 1995. The workshop was designed to bring together NASAs scientists and engineers and their counterparts in industry, other Government agencies, and academia working together in the sonic boom element of NASAs High-Speed Research Program. Specific objectives of this workshop were to (1) report the progress and status of research in sonic boom propagation, acceptability, and design; (2) promote and disseminate this technology within the appropriate technical communities; (3) help promote synergy among the scientists working in the Program; and (4) identify technology pacing the development of viable reduced-boom High-Speed Civil Transport concepts. The Workshop included these sessions: Session 1 - Sonic Boom Propagation (Theoretical); Session 2 - Sonic Boom Propagation (Experimental); and Session 3 - Acceptability Studies - Human and Animal.

Baize, Daniel G.↗

NASA NTRS1996

Waveform Freezing of Sonic Booms Revisited

Nonlinear distortion of sonic booms propagating in the atmosphere is strongly affected by stratification and geometrical spreading. For a downward propagating sonic boom in a standard atmosphere, stratification and spreading cause a slowing down of nonlinear distortion. In certain cases a stage is reached where no further distortion takes place. When this happens, the waveform is said to be frozen. In previous work the authors argued that for most HSCT designs and flight conditions being considered, the sonic boom is not frozen when it reaches the ground. The criterion used was the value of the distortion distance x bar is a measure of the nonlinear distortion suffered by the wave (and is closely related to Hayes's E variable). The aircraft must be at an altitude greater than 27 km (80,000 ft) for x bar at the groun be within 95% of its asymptotic value. However, work reported here demonstrates that the ground waveform is much closer to the frozen state than indicated by the previous analysis. In the new analysis, duration of the sonic boom is used as the criterion for judging closeness of approach tz frozen state. In order for the duration of the sonic boom at the ground to be within 95% of its frozen value, the flight altitude of the aircraft needs to be only 15 km (45,000 ft).

Cleveland, Robin O.↗

NASA NTRS1996

USAF Flight Test Investigation of Focused Sonic Booms: Project Have Bears

Supersonic operations from military aircraft generate sonic booms that can affect people, animals and structures. A substantial experimental data base exists on sonic booms for aircraft in steady flight and confidence in the predictive techniques has been established. All the focus sonic boom data that are in existence today were collected during the 60's and 70's as part of the information base to the US Supersonic Transport program and the French Jericho studies for the Concorde. These experiments formed the data base to develop sonic boom propagation and prediction theories for focusing. There is a renewed interest in high-speed transports for civilian application. Moreover, today's fighter aircraft have better performance capabilities, and supersonic flights ars more common during air combat maneuvers. Most of the existing data on focus booms are related to high-speed civil operations such as transitional linear accelerations and mild turns. However, military aircraft operating in training areas perform more drastic maneuvers such as dives and high-g turns. An update and confirmation of USAF prediction capabilities is required to demonstrate the ability to predict and control sonic boom impacts, especially those produced by air combat maneuvers.

Downing, Micah↗

NASA NTRS1999

Mid-Field Sonic Boom Extrapolation Methodology

In the design cycle of low-boom airplanes, sonic boom prediction must be accurate and efficient. The classical linear method, Whitham's F-function theory, has been widely applied to predict sonic boom signatures. However, linear theory fails to capture the nonlinear effects created by large civil transport. Computational fluid dynamics (CFD) has been used successfully to predict sonic boom signals at the near and mid fields. Nevertheless, it is computationally expansive in airplane design runs. In the present study, the method of characteristics is used to predict sonic boom signals in an efficient fashion. The governing equations are the axisymmetric Euler's equations with constant enthalpy. Since the method solves Euler's equations, it captures more nonlinear effects than the classical Whitham's F-function technique. Furthermore, the method of characteristics is an efficient marching scheme for initial value problems. In this study, we will first review the current CFD extrapolation technique and the work previously done in sonic boom extrapolation. Then, we will introduce the governing equations and the method of characteristics. Finally, we will show that the present method yields the same accurate results as previous CFD techniques, but with higher efficiency.

Cheung, Samson↗

NASA NTRS1999

1995 NASA High-Speed Research Program Sonic Boom Workshop: Configuration Design, Analysis, and Testing - Volume 2

The High-Speed Research Program and NASA Langley Research Center sponsored the NASA High-Speed Research Program Sonic Boom Workshop on September 12-13, 1995. The workshop was designed to bring together NASAs scientists and engineers and their counterparts in industry, other Government agencies, and academia working together in the sonic boom element of NASAs High-Speed Research Program. Specific objectives of this workshop were to: (1) report the progress and status of research in sonic boom propagation, acceptability, and design; (2) promote and disseminate this technology within the appropriate technical communities; (3) help promote synergy among the scientists working in the Program; and (4) identify technology pacing, the development C, of viable reduced-boom High-Speed Civil Transport concepts. The Workshop was organized in four sessions: Sessions 1 Sonic Boom Propagation (Theoretical); Session 2 Sonic Boom Propagation (Experimental); Session 3 Acceptability Studies-Human and Animal; and Session 4 - Configuration Design, Analysis, and Testing.

High-speed research↗

NASA NTRS2000

Field Measurements of Sonic Boom Penetration Into the Ocean

Six sonic booms, generated by F-4 aircraft under steady fight at a range of altitudes (610-6100 m) and Mach numbers (1.07-1.26), were measured just above the air/sea interface, and at five depths in the water column. The measurements were made with a vertical hydrophone array suspended from a small spar buoy at the sea surface, and telemetered to a nearby research vessel. The sonic boom pressure amplitude decays exponentially with depth, and the signal fades into the ambient noise field by 30-50 in, depending on the strength of the boom at the sea surface. Low-frequency components of the boom waveform penetrate significantly deeper than high frequencies. Frequencies greater than 20 Hz are difficult to observe at depths greater than about 10 m. Underwater sonic boom pressure measurements exhibit excellent agreement with predictions from analytical theory, despite the assumption of a flat air/sea interface. Significant scattering of the sonic boom signal by the rough ocean surface is not detected. Real ocean conditions appear to exert a negligible effect on the penetration of sonic booms into the ocean unless steady vehicle speeds exceed Mach 3, when the boom incidence angle is sufficient to cause scattering on realistic open ocean surfaces.

Sohn, R. A.↗

NASA NTRS2005

Airborne Shaped Sonic Boom Demonstration Pressure Measurements with Computational Fluid Dynamics Comparisons

The Shaped Sonic Boom Demonstration project showed for the first time that by careful design of aircraft contour the resultant sonic boom can maintain a tailored shape, propagating through a real atmosphere down to ground level. In order to assess the propagation characteristics of the shaped sonic boom and to validate computational fluid dynamics codes, airborne measurements were taken of the pressure signatures in the near field by probing with an instrumented F-15B aircraft, and in the far field by overflying an instrumented L-23 sailplane. This paper describes each aircraft and their instrumentation systems, the airdata calibration, analysis of the near- and far-field airborne data, and shows the good to excellent agreement between computational fluid dynamics solutions and flight data. The flights of the Shaped Sonic Boom Demonstration aircraft occurred in two phases. Instrumentation problems were encountered during the first phase, and corrections and improvements were made to the instrumentation system for the second phase, which are documented in the paper. Piloting technique and observations are also given. These airborne measurements of the Shaped Sonic Boom Demonstration aircraft are a unique and important database that will be used to validate design tools for a new generation of quiet supersonic aircraft.

Haering, Edward A., Jr.↗

NASA NTRS2005

Origins and Overview of the Shaped Sonic Boom Demonstration Program

The goal of the DARPA Shaped Sonic Boom Demonstration (SSBD) Program was to demonstrate for the first time in flight that sonic booms can be substantially reduced by incorporating specialized aircraft shaping techniques. Although mitigation of the sonic boom via specialized shaping techniques was theorized decades ago, until now, this theory had never been tested with a flight vehicle subjected to actual flight conditions in a real atmosphere. The demonstrative success, which occurred on 27 August 2003 with repeat flights in the supersonic corridor at Edwards Air Force Base, is a critical milestone in the development of next generation supersonic aircraft that could one day fly unrestricted over land and help usher in a new era of time-critical air transport. Pressure measurements obtained on the ground and in the air confirmed that the specific modifications made to a Northrop Grumman F-5E aircraft not only changed the shape of the shock wave signature emanating from the aircraft, but also produced a flat-top signature whose shape persisted, as predicted, as the pressure waves propagated through the atmosphere to the ground. This accomplishment represents a major advance towards reducing the startling and potentially damaging noise of a sonic boom. This paper describes the evolution of the SSBD program, including the rationale for test article selection, and provides an overview of the history making accomplishments achieved during the SSBD effort, as well as, the follow-on NASA Shaped Sonic Boom Experiment (SSBE) Program, whose goal was to further evaluate the characteristics and robustness of shaped boom signatures.

Pawlowski, Joseph W.↗

NASA NTRS2008

Realism Assessment of Sonic Boom Simulators

Developments in small supersonic aircraft design are predicted to result in low-intensity sonic booms. Booms generated by current aircraft are similar to those that led to the ban on commercial supersonic fli ght over the US, so are unsuitable for parametric studies of psychoac oustic response to low-intensity booms. Therefore, simulators have be en used to study the impact of predicted low-intensity sonic booms. H owever, simulators have been criticized because, when simulating conv entional-level booms, the sounds were observed to be unrealistic by p eople experienced in listening to sonic booms. Thus, two studies were conducted to measure the perceived realism of three sonic boom simul ators. Experienced listeners rated the realism of conventional sonic boom signatures when played in these simulators. The effects on percei ved realism of factors such as duration of post-boom noise, exclusion of very low frequency components, inclusion of ground reflections, a nd type of simulator were examined. Duration of post-boom noise was f ound to have a strong effect on perceived realism, while type of simu lator had a weak effect. It was determined that post-boom noise had t o be at least 1.5 seconds long for the sound to be rated very realist ic. Loudness level did not affect realism for the range of sounds pla yed in the tests (80-93 dB ASEL).

Sullivan, Brenda M.↗

NASA NTRS2008

Analysis of Plume Effects on Sonic Boom Signature for Isolated Nozzle Configurations

Computational fluid dynamics (CFD) analysis has been performed to study the plume effects on sonic boom signature for isolated nozzle configurations. The objectives of these analyses were to provide comparison to past work using modern CFD analysis tools, to investigate the differences of high aspect ratio nozzles to circular (axisymmetric) nozzles, and to report the effects of underexpanded nozzle operation on boom signature. CFD analysis was used to address the plume effects on sonic boom signature from a baseline exhaust nozzle. Near-field pressure signatures were collected for nozzle pressure ratios (NPRs) between 6 and 10. A computer code was used to extrapolate these signatures to a ground-observed sonic boom N-wave. Trends show that there is a reduction in sonic boom N-wave signature as NPR is increased from 6 to 10. The performance curve for this supersonic nozzle is flat, so there is not a significant loss in thrust coefficient as the NPR is increased. As a result, this benefit could be realized without significant loss of performance. Analyses were also collected for a high aspect ratio nozzle based on the baseline design for comparison. Pressure signatures were collected for nozzle pressure ratios from 8 to 12. Signatures were nearly twice as strong for the two-dimensional case, and trends also show a reduction in sonic boom signature as NPR is increased from 8 to 12. As low boom designs are developed and improved, there will be a need for understanding the interaction between the aircraft boat tail shocks and the exhaust nozzle plume. These CFD analyses will provide a baseline study for future analysis efforts.

Castner, Raymond S.↗

NASA NTRS2008

Analysis of Plume Effects on Sonic Boom Signature for Isolated Nozzle Configurations

Castner, Raymond S.↗

NASA NTRS2011

Sonic Boom Computations for a Mach 1.6 Cruise Low Boom Configuration and Comparisons with Wind Tunnel Data

Accurate analysis of sonic boom pressure signatures using computational fluid dynamics techniques remains quite challenging. Although CFD shows accurate predictions of flow around complex configurations, generating grids that can resolve the sonic boom signature far away from the body is a challenge. The test case chosen for this study corresponds to an experimental wind-tunnel test that was conducted to measure the sonic boom pressure signature of a low boom configuration designed by Gulfstream Aerospace Corporation. Two widely used NASA codes, USM3D and AERO, are examined for their ability to accurately capture sonic boom signature. Numerical simulations are conducted for a free-stream Mach number of 1.6, angle of attack of 0.3 and Reynolds number of 3.85x10(exp 6) based on model reference length. Flow around the low boom configuration in free air and inside the Langley Unitary plan wind tunnel are computed. Results from the numerical simulations are compared with wind tunnel data. The effects of viscous and turbulence modeling along with tunnel walls on the computed sonic boom signature are presented and discussed.

Elmiligui, Alaa A.↗

NASA NTRS2012

A Study in a New Test Facility on Indoor Annoyance Caused by Sonic Booms

A sonic-boom simulator at NASA Langley Research Center has been constructed to research the indoor human response to low-amplitude sonic booms. The research goal is the development of a psychoacoustic model for individual sonic booms to be validated by future community studies. The study in this report assessed the suitability of existing noise metrics for predicting indoor human annoyance. The test signals included a wide range of synthesized and recorded sonic-boom waveforms. Results indicated that no noise metric predicts indoor annoyance to sonic-boom sounds better than Perceived Level, PL. During the study it became apparent that structural vibrations induced by the test signals were contributing to annoyance, so the relationship between sound and vibration at levels of equivalent annoyance has been quantified.

Rathsam, Jonathan↗

NASA NTRS2012

Experimental Sonic Boom Measurements on a Mach 1.6 Cruise Low-Boom Configuration

A wind tunnel test has been conducted by Gulfstream Aerospace Corporation (GAC) to measure the sonic boom pressure signature of a low boom Mach 1.6 cruise business jet in the Langley Unitary Plan Wind Tunnel at Mach numbers 1.60 and 1.80. Through a cooperative agreement between GAC and the National Aeronautics and Space Administration (NASA), GAC provided NASA access to some of the experimental data and NASA is publishing these data for the sonic boom research community. On-track and off-track near field sonic boom pressure signatures were acquired at three separation distances (0.5, 1.2, and 1.7 reference body lengths) and three angles of attack (-0.26deg, 0.26deg, and 0.68deg). The model was blade mounted to minimize the sting effects on the sonic boom signatures. Although no extensive data analysis is provided, selected data are plotted to illustrate salient features of the data. All of the experimental sonic boom pressure data are tabulated. Schlieren images of the configuration are also included.

Wilcox, Floyd J., Jr.↗

NASA NTRS2011

Evaluation of an Indoor Sonic Boom Subjective Test Facility at NASA Langley Research Center

A sonic boom simulator at NASA Langley Research Center has been constructed for research on human response to low-amplitude sonic booms heard indoors. Research in this facility will ultimately lead to development of a psychoacoustic model for single indoor booms. The first subjective test was designed to explore indoor human response to variations in sonic boom rise time and amplitude. Another goal was to identify loudness level variability across listener locations within the facility. Finally, the test also served to evaluate the facility as a laboratory research tool for studying indoor human response to sonic booms. Subjects listened to test sounds and were asked to rate their annoyance relative to a reference boom. Measurements of test signals were conducted for objective analysis and correlation with subjective responses. Results confirm the functionality of the facility and effectiveness of the test methods and indicate that loudness level does not fully describe indoor annoyance to the selected sonic boom signals.

Loubeau, Alexandra↗