Flow noise from spoilers in ducts

Area of Science:

• Acoustics
• Fluid Dynamics
• Mechanical Engineering

Background:

• Strip spoilers in ventilation systems can generate significant flow noise.
• Understanding and predicting this noise is crucial for designing quieter HVAC systems.
• Previous research by Nelson and Morfey (1981) established foundational work in this area.

Purpose of the Study:

• To measure flow noise radiated from strip spoilers in a ventilation system's air duct.
• To validate existing models and identify parameters necessary for predicting noise from multiple spoilers.
• To empirically derive the coherence function of noise sources for improved prediction accuracy.

Main Methods:

• Experimental measurements of flow noise were conducted using strip spoilers in an air duct.
• Noise was radiated from an open exhaust termination unit into a reverberation chamber.
• Data analysis involved comparing experimental results with predictions based on drag forces, phase relationships, and coherence functions.

Main Results:

• Measured flow noise data align well with previous findings by Nelson and Morfey.
• The empirical derivation of the coherence function was key to accurate noise prediction.
• Predicted noise levels generally agreed with experimental results within 3 dB across most frequencies.

Conclusions:

• The study confirms the validity of existing models for flow noise prediction from spoilers.
• Accurate prediction of multi-spoiler noise necessitates precise values for drag force ratios, phase relationships, and coherence functions.
• The derived coherence function improves the accuracy of flow noise predictions, particularly at lower to mid-range frequencies.