Reduction of fluid noise in modern aircraft hydraulics by integrated broadband attenuators

New axial piston pumps with fixed displacement volumes, such as the high efficient power package (HEPP) pumps operate at variable rotational speeds and thus variable flow rates in a wide range. Using intelligent pump control systems, small and light packages are possible. In contrast, the fluid pulsations vary due to the rotational speed and have to be controlled avoiding stress or wear in the hydraulic system components (e.g. seals of tubing) and potentially impacting cabin noise. Due to the excitation frequencies, a broadband silencer for high pressure applications is required. This is realised by a multi-Helmholtz-resonator (MHR) concept within one cylindrical volume. The design will be adapted for pump-specific frequency characteristics in aircraft hydraulic conditions and fine adjusted during test verification by means of an adjustable tube-inside a pressure shell. For cost, weight and complexity reason a common broadband attenuator is integrated in the hydraulic circuit connecting the two redundant HEPP motorpumps. The attenuator position is optimised to achieve maximal acoustic performance and minimize pulsation stress on the pump, especially at the main operating point. The proof of concept has been achieved experimentally comparing a HEPP piston pump with and without the MHR.

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629.13: Aviation Engineering

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