Following the successful fabrication of a new Gas Turbine (GT) enclosure, the client requested an acoustic Factory Acceptance Test (FAT) prior to dispatch, site installation, and commissioning.
Our objective was to design and execute a completely new acoustic FAT method to demonstrate that the enclosure construction was free from acoustic leaks (flanking paths).
The GT enclosure forms part of a larger acoustic package consisting of: Combustion Air Intake Silencer System. Combustion Air Exhaust Detuner Stack. Package Cooling Air Intake System. Package Cooling Air Exhaust System.
When deployed on site, the enclosure skid is fully sealed against a solid concrete plinth, completing the acoustic boundary conditions.
Challenges: Developing a meaningful acoustic test in the factory environment presented several significant challenges.
Incomplete Acoustic Boundary Conditions: the GT enclosure was fabricated separately from all intake and exhaust systems, with large openings where intake/exhaust modules would normally interface and an open floor since the concrete plinth was not present in the workshop.
Inapplicability of Traditional Transmission Loss Testing: a full Transmission Loss Test requires a fully sealed enclosure, a calibrated internal noise source, and calibrated Class 1 sound level meters, which was not possible here.
Highly Reflective Workshop Environment: hard, reflective surfaces near the enclosure would introduce strong reflections and invalid measurements.
Test Requirements: any alternative method had to be immune to room acoustic reflections, capable of testing with partially sealed/temporary boundary conditions, and able to demonstrate structural acoustic integrity and highlight flanking paths.
Solution: Acoustic Surface Imaging Using Sound Scanner P132.
We developed a new testing methodology using our advanced Sound Scanner P132 acoustic camera, operating from 125 Hz to 10 kHz.
Principle of Operation: the acoustic camera generates visual noise maps similar to thermal imaging, with red/yellow indicating high-intensity noise and blue/green indicating low-intensity noise.
A calibrated noise source is used inside the enclosure with the sound scanner positioned externally, capturing a spatial slice of the sound field at a fixed distance, focused via laser distance measurement on the external surface.
Benefits of the Acoustic Camera Method: immunity to reflections, compatibility with temporary seals, and visual verification of acoustic integrity.
Results: The acoustic camera produced detailed images that accurately pinpointed noise escape.
Several small sealing issues were identified around the personnel doors and promptly rectified before final sign-off and shipment.
Images shown include a pre-rectification image showing a hotspot around the personnel door seal, and a post-rectified image where the leakage path is no longer visible.
Conclusion: The new acoustic FAT method successfully demonstrated that acoustic testing is achievable even when boundary conditions prevent traditional transmission loss measurements, the Sound Scanner P132 camera provides accurate, reflection-free surface acoustic data, structural flanking paths can be identified and resolved prior to dispatch, and the GT enclosure is free of acoustic flanking paths.
This innovative approach now represents a viable testing option for similar enclosures manufactured under workshop conditions.
