Prediction of hydraulic inertance using acoustic measurements and CFD modelling

Fluid inertia within passageways of hydraulic components is known to have a significant impact on their dynamic response and fluid-borne noise characteristics. This inertance is often hard to quantify either theoretically or experimentally due to the complex nature of component geometries, and bacause it is related to dynamic, not steady-state behaviour. Previous studies have used the secondary source method to determine the impedance, of which the inertance is an important parameter, of components such as positive displacement pumps and valves. A simple acoustic test for predicting the inertance of a component is proposed. The component must have a direct connection between inlet and outlet, and as such is directly applicable to valves and accumulators. Results were compared to theory for known components, including uniform pipes, and woth predictions made using the commercial computational fluid dynamics (CFD) package ANSYS CFX, using the anology of steady state flow through porous passageways of identical geometry. In general, good agreement between acoustic measurements and CFD predictions was obtained for a number of ball valves, gate valves and an accumulator poppet valve.