Interpretation of gas oscillations in multicylinder fluid machinery manifolds by using lumped parameter descriptions

Abstract Fluid pressure oscillations are complicated in multicylinder positive displacement machinery manifolds because of the cylinder interactions due to (i) the kinematic arrangements between cylinders and (ii) the inter-connected manifold elements. In practice, manifolds possess irregular shapes and geometries. These are difficult to analyze by using a continuous parameters approach; however, the manifold components can be discretized easily and described by acoustic lumped parameters. Additionally, this approach is more suitable for developing design guidelines, which is the primary aim of the present paper. The multicylinder interaction problem is formulated in the frequency domain. Mass flow rates, with proper crank phase relationships, are considered excitation sources. Manifold components are described as acoustic elements. The equations of acoustic motion are solved for the eigenvalues and the natural modes of gas oscillation, and these are used to provide the forced acoustic response. The formulations are then applied to a two-cylinder compressor discharge system. The computed results compare well with measurements.