Bruce T. Vu

Lift-Off Acoustics Predictions for the Ares I Launch Pad

A model has been prepared to predict noise on the mobile launcher and tower for the Ares I launch vehicle. The model is based on classic semi-empirical methods developed during the Apollo program. It has been updated with more recent data and algorithms. It has been implemented in two software modules. The first performs the noise calculations itself, yielding octave band and PSD spectra at specific points on the launcher or on a grid covering a region of interest. These results are written as simple ASCII tables. The second is a display program that graphically presents the results.

On the Scaling Laws for Jet Noise in Subsonic and Supersonic Flow

The scaling laws for the simulation of noise from subsonic and ideally expanded supersonic jets are examined with regard to their applicability to deduce full scale conditions from small-scale model testing. Important parameters of scale model testing for the simulation of jet noise are identified, and the methods of estimating full-scale noise levels from simulated scale model data are addressed. The limitations of cold-jet data in estimating high-temperature supersonic jet noise levels are discussed. It is shown that the jet Mach number (jet exit velocity/sound speed at jet exit) is a more general and convenient parameter for noise scaling purposes than the ratio of jet exit velocity to ambient speed of sound. A similarity spectrum is also proposed, which accounts for jet Mach number, angle to the jet axis, and jet density ratio. The proposed spectrum reduces nearly to the well-known similarity spectra proposed by Tam for the large-scale and the fine-scale turbulence noise in the appropriate limit.

On the Propagation of Plane Acoustic Waves in a Duct With Flexible and Impedance Walls

This Technical Memorandum (TM) discusses the harmonic and random plane acoustic waves propagating from inside a duct to its surroundings. Various duct surfaces are considered, such as rigid, flexible, and impedance. In addition, the effects of a mean flow are studied when the duct alone is considered. Results show a significant reduction in overall sound pressure levels downstream of the impedance wall for both mean flow and no mean flow cases and for a narrow duct. When a wider duct is used, the overall sound pressure level (OSPL) reduction downstream of the impedance wall is much smaller. In the far field, the directivity is such that the overall sound pressure level is reduced by about 5 decibels (dB) on the side of the impedance wall. When a flexible surface is used, the far field directivity becomes asymmetric with an increase in the OSPL on the side of the flexible surface of about 7 dB.

Near-Field Acoustical Characterization of Clustered Rocket Engines

‡This paper presents an approach for the prediction and characterization of the near -fie ld acoustic levels from closely spaced clustered rocket engines. The calculations are based on the method proposed by Eldred , wherein the flowfield fro m the clustered rockets is divided into two zones. Zone 1 contains the isolated nozzles that produce noise independently and extends up to a distance where the individual flows completely mix to form an equivalent single nozzle flow. Zone 2 is occupied by the single mixed stream starting from the station where the jets merge. The acoustic fields from the two zones are computed separately on the basis of the NASA -SP method of Eldred developed for a single equivalent nozzle. A summation of the spectra for th e two zones yields the total effective sound pressure level for the clustered engines. Under certain conditions of nozzle spacing and flow parameters, the combined sound pressure level spectrum for the clustered nozzles displays a double peak . Test case s a re presented here to demonstrate the importance of hydrodynamic interactions re sponsible for the double peak in the sound spectrum in the ca se of clustered rocket nozzles, and the role of ground reflections in t he case of non interfering jets. A graphic al i nterface (Rocket Acoustic Prediction Tool) has been developed to take into account the effects of clustered nozzles and ground reflections.

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 Na...

Overview of acoustic and sonic boom advancements during development of NASA launch vehicles

During the study and development of NASA space vehicles, acoustic environments have been a critical design input. This paper surveys some of the key challenges and focuses on the contributions and collaborations of Kenneth J. Plotkin/Wyle Laboratories with various NASA centers and personnel. In the mid-1960’s and early 1970’s, a method for predicting in-flight fluctuating environments for vehicle systems was developed for the Saturn Development Programs at NASA Marshall Space Flight Center (MSFC). With the Space Shuttle Vehicle development in the 1970’s, sonic boom became a concern and sonic boom focusing was studied. Attention was turned to the Space Shuttle Orbiter entry maneuvers during the approach to the KSC landing site. In 1993, a PC version for sonic boom prediction was developed for the National Launch System study. Near-field pressure data from computational fluid dynamics analyses were used to develop the shape factors used in the X-33 sonic boom analyses. For the X-34 sonic boom analyses, the ...

Testing and Modeling of the Mars Atmospheric Processing Module

Here we report further progress in the development of the MARCO POLO/Mars ISRU Pathfinder Atmospheric Processing Module (APM). The APM is designed to demonstrate in situ resource utilization (ISRU) of the Martian atmosphere, which primarily consists of carbon dioxide (CO2). The APM is part of a larger project with the overall goal of collecting and utilizing CO2 found in the atmosphere and water in the regolith of Mars to produce methane and oxygen to be used as rocket propellant, eliminating the need to import those to Mars for human missions, thus significantly reducing costs. The initial focus of NASA’s new ISRU Project is modeling of key ISRU components, such as the CO2 Freezers and the Sabatier reactor of the APM. We have designed models of those components and verified the models with the APM by gathering additional data for the CO2 Freezer and the Sabatier reactor. Future efforts will be focused on simultaneous operations of the APM and other MARCO POLO/Mars ISRU Pathfinder modules.

Measurements of the ground acoustic environments for small solid rocket motor firings

During the ground launch of a space vehicle, the mobile launcher deck and tower are exposed to severe acoustic environments. These environments, if not properly managed, can weaken ground support equipment and result in structure failure. The ground acoustic environments are different than the vehicle acoustic environments. They are typically more severe because of the close proximity of the rocket plume, which often involves direct impingement. They are more difficult to predict, and their measurement and data reduction remain challenging. This paper discusses these challenges and describes the methods of processing ground acoustic data during a series of static firings of a 5-percent scale solid rocket launch vehicle and mobile launcher, known as the Ares Scale Model Acoustic Test.

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 e...

Launch System Testbed: An Innovative Approach for Design and Development of Future Launch Structures

The launch of space vehicles generates extreme conditions, such as vibrations and acoustics that can affect the launch pad, space vehicles, and their payloads. These acoustic loads are the results of intense acoustic environment generated by the interaction of the rocket‐engine exhaust stream mixing with the ambient atmosphere. The primary source of structural vibrations and internal loads during launch is due to these acoustic loads. Therefore, being able to manage and suppress these undesirable conditions is critical to proper functioning of vehicle components, payloads, and launch support structures. The goal of the Launch System Testbed at NASA‐Kennedy Space Center is to develop new methods to improve the performance of launch systems by reducing noise, vibration, and stress loads generated during launch.