Development of the next generation of spaceflight vehicles has prompted a renewed focus on sound source characterization and near-field propagation modeling. Without advancements in these areas, large uncertainties in vibro-acoustic loading estimates on space vehicles and payloads may result in structural designs that are either insufficient or excessive.
In the near field, even accurate acoustic pressure measurements are insufficient. A set of pressure measurements can reveal the local sound pressure levels at the sensor locations. However, because of the frequencies and source size inherent to a rocket plume, it would require an extremely large array of distributed microphones to adequately map out the critical near-field region and establish how tile sound energy is traveling outside that region. An improved system for determining this near-field energy flow provides source characterization capabilities beyond traditional pressure measurements.
This project has resulted in the development of a new energy-based measurement and analysis system for rocket noise. The robust hardware and novel signal processing algorithms provide NASA with the a unique capability to characterize the near-plume noise environment of full-scale rocket motors. This characterization is necessary to develop physics-based, near-motor noise propagation models that will aid in improving vibro-acoustic loading estimates on space vehicles and payloads.
The hardware and software development consists of four principal innovations:
- An improved energy-based acoustic probe design that extends the operational frequency bandwidth, minimizes scattering, and provides easy access to microphone components for calibration, while being robust enough for harsh near-field rocket environments and inexpensive enough to remain accessible.
- Improved energy-based signal processing and analysis methods using a newly developed phase and amplitude gradient estimation (PAGE) that provides consistently superior results in comparison to previous methods.
- A rugged and reliable field-deployable data acquisition system that will reduce field test setup time and complexity.
- Results from energy-based and other data analyses that detail the near-field intensity flow, assessment of near-field relationships between energy quantities, and other measures of interest, including rms and peak levels, acceleration, etc.