High-Resolution Source Characterization and Modeling for Efficient Prediction of Propulsion-Airframe Aeroacoustics

ATA Engineering, Inc. (ATA) and partners propose a Phase II SBIR project to further develop methods to efficiently characterize and predict noise performance of aircraft with substantial propulsion airframe aeroacoustics (PAA) effects. The methods utilize near-field surface source models informed by high-spatial-resolution acoustic measurements. Over the last decade, ATA has matured the multireference continuous-scan (CS) acoustic measurement technology that is needed to define and validate such source models. Previous demonstrations of CS measurements include beamforming, near-field acoustical holography, and turbofan tone order tracking. In Phase I, the team applied such measurements to canonical experiments along with a small-scale ducted fan using fixed and scanning sensors in the near, mid, and far field to define stochastic source models. These models supported novel acoustic shielding predictions by directly detecting the wavepacket-like nature of acoustic events that propagate to the far field as well as using this information to define surface-based source models to predict noise shielding/scattering from PAA using the boundary element method (BEM). Additionally, a 60-channel 2D rotating array characterized the sound field generated by a speaker with and without scattering bodies at an unprecedented high-resolution of nearly 10,000 virtual sensors. This provided a clear visualization of the interference patterns of a complex sound field in the presence of a rigid body and demonstrated the ability to couple isolated source characterization measurements to BEM for PAA problems. In Phase II, ATA proposes to extend the methods to more complex geometries in order to (1) define an efficient BEM-based noise prediction process that utilizes PAA sources derived from high-resolution CS measurements and/or state-of-the-art predictive tools, and (2) integrate the process into far-field noise prediction frameworks such as NASAs Aircraft NOise Prediction Program (ANOPP). The innovation has five critical components: (1) surface-based representations of the source within the BEM acoustic propagation and scattering tool, which rely on (2) compact wavepacket and/or distributed point source models, informed by (3) high-resolution multireference CS acoustic measurements (CSAM). Phase II maturation will allow (4) use of flow field solutions to inform model parameters, enabling (5) acoustic design and optimization with multi-fidelity system-level analysis tools such as ANOPP/ANOPP2. The significance of CSAM & BEM innovation includes: (1) effectively infinite spatial resolution, providing the cross-spectrum between any two points along the scan, (2) phase preservation for improved source and propagation modeling, (3) significant reduction of test data acquisition time per operational point, and consequently either (4) reduced test operational cost, or (5) the opportunity to screen more PAA design concepts within a given budget. Integration with ANOPP/ANOPP2 should speed up the design cycle for shielded configurations by enabling trade studies using BEM. The technical approach addresses (1) modeling, (2) array hardware, (3) experiments and data processing, and (4) software. The modeling goal is to develop reduced parameter space models that address fan noise, namely inlet and aft radiation of harmonics, plus fan broadband noise, and the effect of forward flight. The hardware effort will focus on array modifications such as nearfield linear and cylindrical surveys, advanced 2D rotating array surveys, and conceptual design of a direct noise hemisphere measurement array. The experimental effort will focus on generating and processing of experimental databases including university and NASA data. The software effort will integrate BEM, ATA’s Continuous-scan Acoustic Measurements (CSAM) software toolkit, and ANOPP/ANOPP2 system prediction frameworks. Technical Objectives Develop parametric models comprising major subsonic fan noise sources Extend CS measurement methods and array architectures to support noise models Mature computational tools for PAA studies Work Plan Summary Develop fan noise source models Develop CS acoustic arrays Perform experiments and process data Perform scattering computations with BEM Mature continuous-scan acoustic measurement (CSAM) Tools Demonstrate tools in ANOPP framework Deliverables: Quarterly reports Comprehensive final report Source code for new ATA software modules in CSAM toolkit

This technology provides NASA new capabilities to develop next-generation airframes and propulsion systems. The tools will find use at NASA centers like the AAPL and 9′ × 15′ LSWT, the Unitary Plan Wind Tunnels, and the 14′ × 22′ subsonic tunnel and Structural Acoustics Loads and Transmission (SALT) facility. NASA can test PAA in these facilities with devices such as the Compact Jet Engine Simulator, Broadband Engine Noise Simulators, fan engine simulators, and a small turbofan. Non-NASA applications of this high-resolution technology include air mobility vehicle noise, automotive and heavy equipment noise, consumer audio, and factory equipment. Many of these applications rely on source localization using acoustic cameras, implying immediate commercialization opportunities for the superior diagnostics resulting from this effort.

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