Sonic Boom Overpressure Research Articles

Fully Parabolized Hypersonic Sonic Boom Prediction with Real Gas and Viscous Effects

We present a methodology to predict the aerodynamic near-field and sonic boom signature from slender bodies and waveriders using a fully parabolized approach. We solve the parabolized Navier–Stokes equations, which are integrated via spatial marching in the streamwise direction. We find that unique physics must be accounted for in the hypersonic regime relative to the supersonic, which includes viscous, nonequilibrium, and real gas effects. The near-field aerodynamic pressure is propagated through the atmosphere to the ground via the waveform parameter method. To illustrate the approach, three bodies are analyzed: the Sears–Haack geometry, the HIFiRE-5, and a power-law waverider. Ambient Mach numbers range from 4 through 15. The viscous stress tensor is essential for accurate hypersonic prediction. For example, viscous effects increase near-field and sonic boom overpressure by 15.7 and 8.49%, respectively, for the Sears–Haack geometry. The difference between viscous and inviscid predictions of the near-field is due to the hypersonic boundary layer. The computational cost for predicting the near-field is approximately 6.6% relative to fully nonlinear computational fluid dynamics.

To the issue of evaluating sonic boom overpressure and loudness

At present, in the world there is a growing interest in the development of a new generation of supersonic passenger aircraft. One of the main problems of creating such aircraft is to ensure both an acceptable sonic boom level and high aerodynamic characteristics in the supersonic cruising mode. This requires the development of reliable methods for obtaining the near field under the plane with taking into account the influence of the boundary layer, calculation of overpressure signature on the ground and evaluation of sonic boom loudness. In this work four variants of the equivalent body of revolution of minimum sonic boom with different nose sharpening were investigated for an aircraft weighing 19 tons in supersonic cruising flight at Mach number of 1.7 and altitude of 15.5 km using the software package for solving the Reynolds–averaged Navier–Stokes equations (RANS) ANSYS CFX. A macro for calculating the overpressure signature on the ground for the distribution of disturbances in the near field under the aircraft and a program for evaluating the sonic boom loudness in various metrics were developed. Computational mesh verification of the results was carried out, the obtained overpressure signatures were compared with theoretical data and calculation results from the software package for the integration of complete system of Euler equations by finite–difference method X–CODE. The effect of the sharpening of the nose part on aerodynamic drag and sound boom characteristics was shown. The work was done in the interests of the international project RUMBLE (RegUlation and norM for low sonic Boom LEvels).

Sonic booms in atmospheric turbulence ground measurements in a hot desert climate

The Sonic Booms in Atmospheric Turbulence (SonicBAT) Project flew a series of 20 F-18 flights with 69 supersonic passes at Edwards Air Force Base in July 2016 to quantify the effect of atmospheric turbulence on sonic booms. Most of the passes were at a pressure altitude of 32,000 feet and a Mach number of 1.4, yielding a nominal sonic boom overpressure of 1.6 pounds per square foot. Atmospheric sensors such as GPS sondeballoons, Sonic Detection and Ranging (SODAR) acoustic sounders, and ultrasonic anemometers were used to characterize the turbulence state of the atmosphere for each flight. Spiked signatures in excess of 7 pounds per square foot were measured at some locations, as well as rounded sonic-boom signatures with levels much lower than the nominal. This presentation will quantify the range of overpressure and Perceived Level of the sonic boom as a function of turbulence parameters, and also present the spatial variation of these quantities over the array. Comparison with historical data will also be shown.

Multidisciplinary Optimization of Supersonic Aircraft Including Low-Boom Considerations

This paper presents a multidisciplinary optimization framework developed by the authors and applied to small-size supersonic aircraft. The multidisciplinary analysis suite is based on the combination of low (empirical) and high-fidelity computational fluid dynamics (CFD) and computational structure mechanics (CSM) tools for predicting the overall aircraft performance and the sonic boom overpressure at supersonic flight, which represents the most challenging environmental constraint for supersonic aircraft. The analysis suite is coupled with a multi-objective optimization strategy for quantifying the trade-off between the maximum take-off weight, mission range, and the sonic boom overpressure. The optimization framework is applied to a small-size supersonic business-jet cruising at Mach number M = 1.8 and featuring a double delta wing. The trade-offs between disciplines are well captured and an optimized configuration achieving the target mission range with a lower maximum take-off weight, and a moderate sonic boom signature is obtained through changes in wing dihedral and sweep. A more drastic reduction of the sonic boom signature is also obtained but at the cost of a significant reduction of the aircraft performance.

Sonic Boom Variability Due to Homogeneous Atmospheric Turbulence

This study describes the nondeterministic effect of homogeneous atmospheric turbulence on sonic boom propagation. The Sears-Haack body was calculated in three dimensions by computational fluid dynamics in inviscid flow (Euler) mode to create the near-field pressure wave. The homogeneous atmospheric turbulence field was represented by the finite sum of discrete Fourier modes based on the von Karman and Pao energy spectrum. The sonic boom signature was then calculated by the modified waveform parameter method, considering a random velocity of homogeneous atmospheric turbulence. The results of this study indicated that atmospheric turbulence has a marked influence on sonic boom overpressure during its propagation to the ground. In comparison to the no-turbulence condition, we found that the sonic boom decreased in 59 % of the cases and increased in 41 % of the cases. Thus, homogeneous atmospheric turbulence seems to favor a decrease, rather than an increase, in boom overpressure. In addition, we found that turbulence has a small effect on the propagation path from the flight altitude to the ground. Nonetheless, this small change in the propagation path may result in a variability, of the point at which the sonic boom reaches the ground, of up to 1820 ft in the north-south direction (flight direction) and 115 ft in the east-west direction.

Two Supersonic Business Aircraft Conceptual Designs With and Without Sonic Boom Constraint

A pair of supersonic business jet conceptual designs has been developed to assess the impact of designing for reduced sonic boom. One aircraft was designed without a sonic boom constraint. The other was limited to an initial sonic boom overpressure of 0.4 lb/ft 2 . All other design requirements were the same. Sonic boom mitigation places a requirement on the buildup of lift and volume along the longitudinal axis of the aircraft, with any excess or shortfall adversely impacting the sonic boom. Methods were developed for incorporating this requirement into the conceptual design process. Both the method for incorporating the boom constraint in the design process and the result, a side-by-side comparison of one low-boom and one unconstrained aircraft with substantially identical performance in all other respects, are considered significant. The boom-constrained aircraft was approximately 25% longer with 18% higher takeoff gross weight than the unconstrained aircraft.

An analysis of the response of Sooty Tern eggs to sonic boom overpressures.

It has been proposed that sonic booms caused a mass hatching failure of Sooty Terns in the Dry Tortugas in Florida by cracking the eggshells. This paper investigates this possibility analytically, complementing previous empirical studies. The sonic boom is represented as a plane-wave excitation with an N-wave time signature. Two models for the egg are employed. The first model, intended to provide insight, consists of a spherical shell, with the embryo represented as a rigid, concentric sphere and the albumen as an acoustic fluid filling the intervening volume. The substrate is modeled as a doubling of the incident pressure. The second, numerical model includes the egg-shape geometry and air sac. More importantly, the substrate is modeled as a rigid boundary of infinite extent with acoustic diffraction included. The peak shell stress, embryo acceleration, and reactive force are predicted as a function of the peak sonic boom overpressure and compared with damage criteria from the literature. The predicted peak sonic boom overpressure necessary for egg damage is much higher than documented sonic boom overpressures, even for extraordinary operational conditions. Therefore, as with previous empirical studies, it is concluded that it is unlikely that sonic boom overpressures damage avian eggs.

An analysis of the response of Sooty Tern eggs to sonic boom overpressures

It has been hypothesized that sonic booms caused a mass hatching failure of Sooty Terns on the Dry Tortugas, FL by causing eggs to crack. In this paper the problem is analyzed using two levels of idealization. The first model represents the egg shell as a spherical elastic shell, the embryo as an inertial concentric sphere, and the albumen as an acoustic fluid that completely fills the intervening volume. The substrate is taken to provide a point support for the egg and to double the incident pressure. The second higher fidelity, numerical model accounts for the ‘‘egg shape’’ geometry and allows for an air sac. Here the substrate is modeled as a rigid boundary of infinite extent. In both cases the boom is modeled as an incident, planar N wave. Predictions are compared to each other and with the results of empirical studies previously performed by other investigators. Data from these earlier investigations were obtained with boom-like impulsive noise sources and indicate that the hypothesis that sonic booms crack eggs unlikely. [Work sponsored by Armstrong Lab., WPAFB, U.S. Air Force.]

Comparison of measured and predicted lateral distribution of sonic boom overpressures from the United States Air Force sonic boom database

In 1987 the United States Air Force (USAF) collected the lateral distribution of sonic booms produced by 43 supersonic flights of military aircraft near Edwards Air Force Base (EAFB). These flights were accomplished using eight different aircraft at several Mach number and altitude combinations. The flights were planned for steady and level operation, but unsteadiness and maneuvering in some of the flight profiles caused variability and focusing of the propagated booms along the lateral measurement array. The full sonic boom waveforms collected during this study are included in a digital database, BoomFile, which is accessible to researchers. The database also includes the aircraft tracking and local weather profiles. A comparison of the measured to predicted peak overpressures along the lateral spread of the boom carpet demonstrates the results from this study agree as expected with previous sonic boom studies. The measurements are compared with predictions calculated by Carlson’s simplified sonic boom model and a sonic boom ray tracing model. The analysis demonstrates that, in general, the predictions are in good agreement with the measured data, but the models overestimate the overpressures as the lateral cutoff is approached. Moreover, the comparison reveals that Carlson’s method is a robust tool for predicting sonic booms produced by nonmaneuvering flights.

The dynamic response of a window embedded in a 3-D structure to sonic boom overpressures

Ground level sonic boom overpressures are often in the linear acoustic regime, allowing structural damage assessments to be performed using structural acoustic techniques. In this talk the boom-induced dynamic response and stress of a glass window is computed. The window, modeled as an elastic thin plate, is embedded in an enclosure that may also be elastic. Solutions are obtained numerically using nashua, a general purpose finite element/boundary element computer code. Peak response/stress is calculated as a function of the relative orientation of the incident wave in azimuth and elevation, the former determined by the flight path and the latter by the Mach number. For a given boom spectrum level, the peak response probability density function (PDF) is calculated assuming a uniform probability of flight direction. By invoking structural acoustic reciprocity, this is related to the directivity of the pressure radiated by a force applied to the window at the peak response location. Finally, the effects of enclosure baffling on the surface pressure itself is presented and compared with free field and infinite baffle approximations. [Work sponsored by Armstrong Laboratory, WPAFB, U.S. Air Force.]

Sonic boom of the oblique flying wing

This article presents an analysis of oblique flying wing sonic boom characteristics. This long asymmetric wing provides a reduction in sonic boom loudness as well as aerodynamic and structural improvements over conventional transports. The wing is represented by an oblique line equivalent area distribution, a panel model, and a high-definition surface model. The near-field pressure signature of the first two representations is found using the Whitham F-function method applied to the oblique equivalent area distribution and the panel model. The near-field pressure distribution of the high-definition surface model was found using TranAir, a full-potential analysis code. Good agreement between the methods was found. The near-field signature is extrapolated through the standard atmosphere by the Thomas waveform parameter method. The asymmetry in the geometry leads to an asymmetrical sonic boom under the flight track. The bow shock amplitude is typically between 50-75 N/m2 depending on the size, weight, and altitude of the configuration. The aft shock has only one-half the amplitude of the bow shock due to favorable volume-lift interference. This article also includes a simple method to estimate the maximum sonic boom overpressures of oblique flying wings.

Prediction of sonic boom overpressures near lateral cutoff

Two methods of sonic boom predictions are used to compare predicted overpressures to measured sonic booms to quantify the effects of weather and flight variability on the lateral propagation of the booms. The sonic boom measurements were collected by the US Air Force at Edwards AFB, CA using a variety of supersonic aircraft. The testing included 43 flights from eight different aircraft at several Mach number and altitude combinations. The flights were planned for steady and level operation but some maneuvering of the aircraft caused focusing of the propagated booms at several measurement locations. The comparison of measured to predicted peak overpressures uses both Carlson and Full ray-tracing algorithms. The comparison examines the lateral spread of the boom and the effects on local weather profiles and variability of the flight profile on the propagated boom. This analysis demonstrates that, in general, predictions are in good agreement with the measured values but tend to overestimate the peak overpressures near the lateral cutoff.

A method for predicting community annoyance due to exposure to sonic booms

A method to predict community annoyance due to sonic booms has been formulated in which the exposure is expressed using the equivalent day–night average sound level metric (Ldn). It is based on the paired comparison results of Kryter’s sonic boom flyover tests [K. D. Kryter, TheEffectsofNoiseonMan (Academic, New York, 1970)] and a synthesis of available community response data by Schultz for aircraft, highway, and railway noise sources [T. J. Schultz, ‘‘Synthesis of Social Surveys on Noise Annoyance,’’ J. Acoust. Soc. Am. 64, 377 (1978)]. The method incorporates average indoor–outdoor responses and includes the effects of sonic boom overpressures and frequency rates of exposure. Good agreement is shown between the predicted percentages of highly annoyed persons and the limited results from several community surveys involving aircraft supersonic overflights. [Work conducted in part by Douglas Aircraft Co. and Wyle Labs. under contract to NASA−Langley Research Center.]

Analytical study of sonic boom from supersonic projectiles

Whitham's first-order theory for steady flow at moderate supersonic Mach numbers around slender axisymmetric bodies is reviewed and applied to determine sonic boom overpressure signatures from bodies of various shapes, particularly those of projectiles in steady and rectilinear flight. Based on his theory, certain closed-form solutions are derived, including extended first-order decay laws for signature evolution with increasing distance from the flight path. Also, for the case of arbitrary axisymmetric bodies of simple and smooth shape, whose axial profile can be defined piecewise by segments of polynomial curves, a new analytical solution is presented for Whitham's ‘smooth-body’ F-function integral. An alternate formulation for the F-function that was derived by Lighthill for non-smooth bodies is shown to be better for actual smooth and non-smooth projectile shapes. A computer code was developed to implement the analysis with various F-functions and compute sonic boom signatures for specified body shapes. These numerical studies were conducted to investigate and illustrate important features of these signatures and their evolution with increasing miss distance. The effects of body shape such as surface protuberances and afterbody flow are two examples.

Some Effects of Applying Sonic Boom Minimization to Supersonic Cruise Aircraft Design

This paper presents a discussion of an aircraft shaping method to control sonic boom overpressure levels along with the analysis of wind tunnel data which validated the method. The results indicate that the sonic boom minimization method can guide the design team choices of aircraft planform and component arrangement toward a low-boom-level configuration while permitting sufficient freedom and flexibility to satisfy other design criteria. Further, it is shown that off-design flight conditions do not drastically change the overpressure sonic boom shape and strength.

Hypersonic transport technology

The possibility of developing a hypersonic commercial transport (HST) for the early 21st century is explored in terms of potential performance characteristics and recent advances in propulsion and structures technology. Range-gross weight characteristics indicate that a 200 passenger, Mach 6 aircraft with a range of 9200 km (5000 n.mi.) would have a gross take-off weight not too different from that of current wide-body subsonic transports. The low cruise sonic boom overpressures generated by the HST opens the possibility of supersonic overland flight which, if permitted, would greatly increase the attractiveness of this type of aircraft. Recent advances in hypersonic propulsion systems and long-lived hypersonic aircraft structure are also discussed. The airframe-integrated scramjet and the actively-cooled airframe structure are identified as the most promising candidates for the HST and current approaches are described in some detail.

A one-man portable sonic boom simulator

A portable sonic boom simulator has been developed for field tests on wildlife. Previous portable simulators have been mobile only by truck or trailer; the present device weighs 24·4 pounds including peripherals and is easily carried by one person. It consists of a shock tube charged by a compressed air bottle, coupled to an exponential horn. A low-pass acoustic filter is mounted in the horn; it serves to increase the ultra-short rise time of the shock waves (∼10 μs) to a value more nearly characteristic of sonic booms (∼0·5 ms). The simulated sonic booms mimic the loudness of typical sonic booms and have comparable overpressure and rise times. Calibration of the effective loudness is by subjective comparison with idealized standard sonic booms (N-waves). The calibration is carried out in the recently developed UTIAS loudspeaker driven sonic boom booth. The loud-speakers accurately reproduce the signatures to be compared which have been tape recorded, and they are judged against the N-waves for equal loudness by an observer in the booth. The outcome is expressed as equivalent sonic boom overpressure (Δp) as a function of shock-tube driver pressure and observer position relative to the portable simulator.

Measurements of sonic-boom overpressures from Apollo space vehicles

This paper presents representative results of sonic-boom overpressure data recorded during the launch and reentry of the Apollo 15 and 16 space vehicle systems. Comparisons are made between measured overpressures and those predicted using available theory. The measurements were obtained along the vehicle ground track at 68, 87, 92, 129, and 970 km downrange from the launch site during ascent, and at 9, 13, 55, 185, and 500 km from the splash-down point during reentry. Also included are tracings of the sonic-boom signatures along with a brief description of the launch and recovery test areas in which the measurements were obtained, the sonic-boom instrumentation deployment, flight profiles and operating conditions, and high-altitude weather information for the general measurement areas.

Ballistic Range Investigation of Sonic-Boom Overpressures in Water

An investigation of sonic-boom overpressures in water has been conducted by gun-launching small cone-cylinder models over water. Flights were conducted at Mach numbers of 2.7 and 5.7, in air, corresponding to Mach numbers of 0.6 and 1.3, respectively, in water. Shadowgraph pictures and underwater pressure measurements indicate that for horizontal flights at Mach numbers below Mach 4.4 in air (i.e., subsonic relative to the speed of sound in water) the resulting underwater disturbance is an acoustic wave whose peak pressure attenuates rapidly with water depth. In contrast, at supersonic Mach numbers, relative to water, the incident shock wave at the surface is transmitted into the water as a propagating shock wave and the peak pressure associated with it does not attenuate with water depth.

Sonic boom effects on sleep—A field experiment on military and civilian populations

Sleep interference due to sonic boom exposure was studied in a field experiment involving military and civilian populations. A test area with military recruits lodged in barracks and a surrounding civilian population was overflown on irregular days at 0425 hours. Seven sonic booms with overpressures of 6–64 N/m 2 were generated throughout a three month period. At sonic boom overpressures of around 60 N/m 2, a 10 % increase in awakening frequency was noted in the military population. At the same overpressure 56 % of the civilians reported sleep interference and difficulties in going back to normal sleep. Limited studies on two babies revealed the presence of minor startle reactions at boom overpressures exceeding 70 N/m 2.