A general procedure for the analysis of gas pulsations in thin compressor or engine manifolds and thin shell type mufflers

Peter Chang-Ching Lai, Purdue University


A general procedure for the analysis of curved or flat, thin two dimensional muffler elements, which can efficiently utilize the limited space of hermetically sealed compressors or small engine compartments, was developed. This procedure can also be applied to analyze thin compressor or engine manifolds as long as the thickness of the cavities is sufficiently small compared to the shortest wavelength of interest. ^ The two dimensional inhomogeneous wave equation, which takes nonuniform thickness into account, is expressed in two dimensional curvilinear coordinates by the application of Hamilton's principle. Four pole parameters are formulated from the pressure response solutions using the modal series expansion method and orthogonality property. ^ This procedure can not only handle a single-input single-output cavity but also multi- input cavities. A practical two-cylinder compressor was analyzed as an application example. Four poles and transfer functions for each input/output set were obtained separately. The pressure response at the exit excited by each input were obtained by multiplying the input volume flow rates from each cylinder with the corresponding transfer functions. The total pressure response was then calculated by superposition of the individual pressure responses. ^ A line impedance method was proposed to analyze the composite gas cavities which consist of two different thin gas cavities sharing a common line-like boundary. Line impedances were formulated from the pressure responses of thin, curved or flat cavities to line volume flow rate inputs which are distributed harmonically along the interface of the two subsystems. The composite system frequency equation was derived and then solved for the natural frequencies and mode shapes of the combined systems. ^




Major Professor: Werner Soedel, Purdue University.

Subject Area

Engineering, Mechanical|Physics, Acoustics

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