Compact Helmholtz Resonators for Hydraulic Systems

Noise is an ongoing concern in the fluid power industry. A great deal of research has been invested in reducing flow pulsations in hydraulic systems, from design modifications to adding noise control components. The physical principles of noise reduction are the same as for air, however, the much higher sound speed of hydraulic fluid makes creating compact noise control devices difficult. This paper introduces a Helmholtz resonator design that uses a compliant, voided urethane lining to increase the apparent volume of the device. The addition of the lining permits much smaller physical sizes for the same resonance frequency. Specifically, the design presented here has a total volume of 0.31 L and generates 20 dB of transmission loss at a resonance frequency of 37 Hz when the hydraulic system is pressurized at 2.07 MPa. At this pressure, it has a total volume that is two orders of magnitude smaller than a similar, unlined device of the same resonance frequency. Experimental data is presented that demonstrates the performance of the device. An analytical model was developed and least-squares fit to the experimental data to extract the complex bulk modulus of the liner material at hydrostatic pressures from 2.07–4.83 MPa, which is the range of available test pressures. This work is anticipated to lead to devices and liner materials designed for higher pressures.