How to Reduce Aerodynamic Noise
- 1). Establish the source of the noise to understand what causes it. Use sound intensity maps and pressure spectra to carefully evaluate the noise in order to confirm whether it generates from the control valve.
- 2). Adjust pressure drops into two or more steps. This reduces the individual velocity peaks compared to the velocity peaks resulting from pressure dropped from a single stage. Confirm that noise is reduced using pressure spectra.
- 3). Install diffusers to the control valve to absorb some of the overall pressure drop. The control valve will remain with enough pressure drops across it hence reducing noise. Diffusers can reduce noise up to 10 or 15 decibels (dBA.)
- 4). Make several openings to the valve to divide the fluid flow to pass through more openings in the valves instead of having it pass through a single opening. Confirm that noise is reduced. Smaller openings shift the noise to a higher frequency, which is then calmed as the sound passes through the pipe wall.
- 5). Obtain silencers and install them directly at the downstream of the valve. You may have to contact the aircraft manufacturer to obtain the proper silencers.
- 6). Obtain diffusers and expansion plates and install them to the downstream pipes to increase the downstream pressure. The velocity at the valve outlet is reduced because diffusers and expansion plates increase the pressure to the downstream of the valve. Contact your aircraft manufacturer to obtain the right specification of diffusers or expansion plates suitable for your aircraft. (See Reference 5)
- 7). Increase the thickness of the wall pipes of the downstream piping and install them as far downstream as possible. (See Reference 2) Most of the valve noise spreads out from the downstream piping and the intensity of the noise remains constant for long distances downstream. You can use thermal or acoustic insulation to insulate the pipe. (See Reference 1)
- 8). Increase the soundproof of the aircraft. Add insulating or absorbent material between the outer and the inner panels of the aircraft’s frame. (See Reference 6) Attach foam panels backed with aluminum foil using glue firmly inside the panels. Obtain acoustical sound proof glass and fix them to the aircraft’s windows. You may have to contact your aircraft manufacturer to get the right specification. (See Reference 6)
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