NASA SP-8072 Research Articles

Development of a far-field prediction model for tactical jet noise spectra

Semi-empirical models for predicting far-field jet noise radiation are computationally efficient. One historical example is NASA SP-8072 (1971), which couples source sound power spectra with frequency-dependent directivity indices to obtain far-field radiated spectra for rockets. This paper applies the SP-8072 framework to develop spectra for the T-7A trainer aircraft. Data at 38 and 76 m arcs are used to obtain sound power spectra and frequency-dependent directivity indices for four different engine conditions ranging from 36% thrust through maximum afterburner. Application of a ground reflection correction model is discussed. The model is applied to obtain results at distances between 19 and 229 m and the performance of the model is evaluated using measured data. [Work supported by ONR Grant No. N00014-21-1-2069.]

Recent findings regarding noise from tactical jet engines

This paper reviews the outcomes of several recent investigations into full-scale supersonic jet noise. First, concordance has been shown between a T-7A-installed GE F404 engine’s sound power and classical jet noise theory in both the subsonic and supersonic regimes [M. A. Christian et al., JASA Express Lett. 3, 073601 (2023)]. The results indicate approximate agreement between the “eighth-power” law for subsonic engine conditions and the “third-power” law for supersonic engine conditions, with a radiation efficiency of ∼0.5–0.6% at afterburner. However, a sudden jump in radiation efficiency in the jet’s transonic region is not presently explained. Second, normalized far field-derived sound power spectra for the F404 do not agree well with a curve found in NASA SP-8072 (Eldred, 1971), likely indicating differences between the importance of different Strouhal number regimes in military jet and rocket noise and, possibly, different radiation phenomena. Third, the maximum directivity angle for overall level appears to be primarily driven by the convective Mach number associated with Kelvin–Helmholtz instability waves (M. A. Christian et al., AIAA Paper 2023-3351). Together, these recent findings represent improved understanding of full-scale tactical jet noise phenomena. [Work supported by ONR.]

A look into far-field rocket noise modeling: Approaches and potential sources of error

In recent years, rocket launches have elevated from novelty to being seen as means of transportation, exploration, and delivery. Defense, commercial, and public sectors are looking to increase their cadence in missions and ability to perform them. Like airports before them, spaceports are being developed and regulated. Much research has been done in rockets as a noise source, and how they may affect communities, structures, and wildlife. The most common approach for modeling the far-field rocket noise relies heavily on NASA SP-8072 and work done by Dr. Sally McInerny, a NASA researcher. The approach takes known mechanical properties of the rocket, such as rocket nozzle diameter, exit flow velocity, and number of engines to calculate the sound power of the system, and then propagate the noise to the receiver with an applied directivity factor. The level decay is based on spherical spreading, and additional attenuation factors such as atmospheric conditions and ground impedance. This paper attempts to show an overview of these different components and their effects on model predictions. Their relevance and limitations are also discussed.

Updated frequency-dependent directivity indices for large solid rocket motors

For many years, empirical models for rocket noise radiation relied on the directivity indices published in NASA SP-8072 (K. Eldred, 1971). Because these indices had known issues, NASA led a campaign to update the indices using a Space Shuttle reusable solid rocket motor (RSRM). The RSRM measurements, involving a polar arc at a radius of about 80 nozzle exit diameters, resulted in updated directivity indices (Haynes and Kenny, AIAA 2009–3160). However, because the arc origin was placed at the nozzle exit plane, James et al. [Proc. Mtgs. Acoust., 18, 040008 (2012)] corrected the low-frequency indices using an estimated dominant source position for each frequency and assumed spherical spreading. This paper revisits that correction effort by using near-field vector intensity measurements from a similar, but smaller diameter and lower thrust, GEM-60 motor to determine the frequency-dependent origin to adjust the apparent angles and distances of the measurements. Additionally, an effort is made to account for RSRM plume impingement downstream that likely resulted in lower high-frequency levels than would have been measured if the plume had been entirely free. This analysis results in updated, frequency-dependent directivity indices for a large solid rocket motor. Their applicability to other rockets will be discussed.

Overall sound power levels from four launch vehicles

To better understand the radiated sound from launch vehicles, this paper describes an effort to quantify the overall sound power level (OAPWL) from different launches. The classic NASA SP-8072 report (K. Eldred, 1971) contains data showing OAPWL as a function of mechanical power but little has been published on actual OAPWL since. This paper uses noise data from four different vehicles launched from Vandenberg Space Force Base to examine the relationship between OAPWL and measurement distance from the launch pad. Because OAPWL values calculated from measurements lessen with increased distance, an empirical correction based on nozzle diameter is described. [Work supported in part by NSF.]

Rocket noise models for the US Department of Defense

Accurate rocket noise prediction models are critical to support growing space defense programs. Potential deficiencies in the NASA SP-8072 model developed in the 1970s have been identified, but their impacts on accurate predictions are currently unknown. Cross-validationcomparisons to full-scale rocket measurements are needed to identify and quantify errors and to improve accuracy. This paper will review the DoD programs and policies that motivate rocket noise modeling requirements, summarize the current models in use, discuss some of the potential deficiencies of the models, and propose a roadmap for establishing confidence in models for official DoD use.

Напівемпіричне оцінювання акустичних навантажень на головну частину ракети при нестандартній конфігурації стартових споруд

The paper deals with assessing the acoustic loads on the surface of a launching rocket obtained using the semiempirical technique NASA SP-8072 adapted for a launch pad located above the water area. The features of the launch facilities include the reduced length of the gas duct and the presence of a wedge-shaped gas-dynamic deflector divided into two symmetrical oppositely directed slopes. The calculations are made with the allowance for the limited length of the rocket jet's laminar core during take-off due to interaction with the gas-dynamic deflector. A corrected dependence is used for the overall acoustic energy distribution along the supersonic jet for the first time in domestic practice. The contributions of the sound sources associated with different jet sections and acoustic reflection from the water surface are assessed, depending on the current height of the rocket lift. A significant dependence of the resulting acoustic field around the rocket head on the length of the horizontal section of the gas duct is noted.

Insights into heated, supersonic jet noise gained from writing a review article on launch vehicle noise

At the time of writing this abstract, a review article is being finalized for publication in JASA entitled a “Supersonic jet noise from launch vehicles: 50 years since NASA SP-8072,” it describes the current state-of-the-art in rocket and launch vehicle noise research, including how highly heated, supersonic rocket plumes differ from other jets, the origin and nature of the radiated sound from both free and impinging rocket plumes, and techniques for pad noise mitigation during rocket launches. Existing and candidate methods (both empirical and numerical) for modeling rocket launch noise are reviewed, including the ubiquitous NASA SP-8072 methodology, which has formed the cornerstone of many rocket launch noise prediction models over the past half century. This talk will briefly discuss some of the insights gained as a result of writing this review and show how they led to the inevitable conclusion that an entirely new approach to rocket plume noise modeling—one that incorporates the underlying physics of the noise generation mechanisms—must be pursued.

A tale of two curves and their influence on rocket and supersonic jet noise research.

This letter describes how a landmark 1960s supersonic jet noise experiment influenced subsequent noise models. A discrepancy in other researchers' application of Potter and Jones's axial decomposition of the sound power generated from a laboratory-scale jet can be traced to an erroneous plot in the original report. Whereas most jet noise research indicates the dominant sound power is generated upstream of the supersonic core tip, propagation of this error in the ubiquitous NASA SP-8072 report has caused rocket noise modelers for five decades to disproportionately allocate sound power generation to the subsonic flow.

Improved empirical prediction method for impinging acoustic sources distributed around interactive structures

An improved empirical prediction method has been developed to predict the noise generated by impinging acoustic sources of flight vehicles. A representative empirical prediction method is the second distributed source method (DSM-II) in the report NASA SP-8072. However, since DSM-II is based on specific experimental data, it has limitations of not being able to perfectly reflect some acoustic phenomena such as impingement, reflection, and diffraction effects induced by interactive structures. In this study, we introduce some additional experimental data and a simple theory to the conventional method, and propose an improved empirical method that could reflect the above acoustic phenomena also. First, we describe the improved method that includes the impingement effect and validate the results for the Korean Sounding Rocket-III (KSR-III) in terms of overall sound pressure level (OASPL) and sound spectrum. Next, we expand this method to the case of a high speed vehicle surrounded by a canister that generates additional acoustic phenomena such as reflection and diffraction effects. We inspect the canister effects on the vehicle as the height increases, from the view point of OASPL and spectrum. Finally, the results are discussed.

Integrated simulation model for prediction of acoustic environment of launch vehicle

During a lift-off of a launch vehicle, a large amount of acoustic wave is generated by jet plumes. Acoustic waves lead to pressure fluctuations on the surface of the vehicle in the form of acoustic loads and these are transmitted to the internal payload. In order to evaluate the effects of acoustic loads, we developed the integrated simulation model. The model is mainly divided into two parts, prediction and reduction parts. First, the external acoustic loads are predicted empirically based on the Distributing Source Method-II (DSM-II) of NASA SP-8072. We developed the improved method able to consider the additional effects of surrounding structures. We perform a next prediction process for the internal acoustic environment by using Statistical Energy Analysis (SEA). For the Korean Sounding Rocket-III (KSR-III), we predict the internal acoustic environment and evaluate the stability of the payload in the fairing. After the prediction process, we perform the noise reduction simulation. With an active noise...

A design method of fairing acoustic noise mitigation for Korean space launcher

In this presentation, fairing acoustic protection system (APS) for Korean space launcher is introduced. The design of APS for payload fairing of KSLV-II is summarized. The current APS consists of acoustic blankets for midfrequency range absorption and acoustic resonators for low frequency noise absorption. Detailed design procedures of APS, which include external acoustic loading prediction based on the modified NASA SP-8072 monograph and fairing system vibro-acoustic analysis, are presented. An acoustic test of a cylindrical composite structure with APS is also presented. The effect of spatial correlation of external acoustic excitation on the vibro-acoustic response of fairing structure and its interior volume is discussed. The concept of future APS by using the micro-perforated panel absorber combined with Helmholtz resonators is also introduced. Effects of high pressure environment on the acoustic absorption of micro-perforated panel is discussed.

Comparative Analysis of NASA SP-8072's Core Length with Full-Scale Rocket Data

Comparative Analysis of NASA SP-8072's Core Length with Full-Scale Rocket Data

Scaling metrics for predicting rocket noise

Several years of research at The University of Texas at Austin concerning the sound field produced by large area-ratio rocket nozzles is presented [Baars et al., AIAA J. 50(1), (2012); Baars and Tinney, Exp. Fluids, 54 (1468), (2013); Donald et al., AIAA J. 52(7), (2013)]. The focus of these studies is on developing an in-depth understanding of the various acoustic mechanisms that form during start-up of rocket engines and how they may be rendered less efficient in the generation of sound. The test articles comprise geometrically scaled replicas of large area ratio nozzles and are tested in a fully anechoic chamber under various operating conditions. A framework for scaling laboratory-scale nozzles is presented by combining established methods with new methodologies [Mayes, NASA TN D-21 (1959); Gust, NASA TN-D-1999 (1964); Eldred, NASA SP-8072 (1972); Sutherland AIAA Paper 1993–4383 (1993); Varnier, AIAA J. 39:10 (2001); James et al. Proc. Acoust. Soc. Amer. 18(3aNS), (2012)]. In particular, both hot and cold flow tests are reported which comprise single, three and four nozzle clusters. An effort to correct for geometric scaling is also presented.

Extension of a launch pad noise prediction model to multiple engines and directional receivers

A model, PAD, has been developed for prediction of noise in the vicinity of launch vehicles, with original application to the mobile launcher and tower for the Ares I launch vehicle. It follows the basic principles of a traditional NASA model (NASA SP-8072, 1971), with updated source components, including impingement, water suppression and acoustic shielding by three dimensional launcher configurations. For application to Space Launch System, the model has been extended to multi-engine vehicles, using the plume merging model developed by Kandula, Vu and Lindsay (AIAA Paper 2005-3091) and accommodating multiple flame holes in the deck. The capability has also been added to account for receiver directivity. This can be significant when predicting the load on the surfaces of enclosures on the launch tower. It is also an issue for model scale tests (such as ASMAT) where microphones and their mounts are not small enough to be omnidirectional, and thus do not measure free field levels. (Work supported by the National Aeronautics and Space Administration.)

Further development of a launch pad noise prediction model

A model, PAD, has been developed for prediction of noise in the vicinity of launch vehicles, with specific application to the mobile launcher and tower for the Ares I launch vehicle. It follows the basic principles of a traditional NASA model (NASA SP-8072, 1971), with updated source components, including impingement and water suppression. The recent 5% scale Ares scale model acoustic test (ASMAT) exhibited sources not properly represented in PAD. These sources are noise increase associated with flat plate deflection of a supersonic plume, and generation of noise from impingement of the plume on an edge such as a launch mount or the edge of the exhaust hole in the launcher deck. New sources, based on ASMAT measurements, have been added to PAD to account for these effects. Treatment of the launch deck has also been generalized to permit full three dimensional launcher configurations, rather than a simple two dimensional arrangement with the tower over the flame trench. The prediction domain has also been expanded to include exhaust plume noise levels on the underside of the deck. (Work supported by the National Aeronautics and Space Administration.)

A review of large solid rocket motor free field acoustics

Approximately twice a year, ATK Aerospace Systems has static fired an assembled reusable solid rocket motor (RSRM) in a horizontal configuration at its test facility in Utah. The firings took place on elevated terrain with the nozzle exit plume mostly undeflected and the landscape allowing placement of microphones within direct line of sight to the exhaust plume. NASA and ATK underwent a significant effort over several years to collect acoustic data in the free field and on the motor itself during RSRM static test firings. These data were used to characterize the acoustic field and to update the prediction methodologies in the monograph NASA SP-8072 “Acoustic Loads Generated by the Propulsion System.” This work represents a review of the free field acoustics generated during large solid rocket motor firings and may be the only repeatable free field acoustic experiment on motors like these.