This paper describes, from a theoretical point of view, the behaviour of compression systems during surge and the effect of passive and active control devices on the instability limit of the system.

A lumped parameter model is used to simulate the compression system described in Part I of this work (Arnulfi et al., 1998), based on an industrial multistage centrifugal compressor. A comparison with experimental results shows that the model is accurate enough to describe quantitatively all the features of the phenomenon.

A moveable wall control system is studied in order to suppress surge in the compressor. Passive and active control schemes are analysed; they both address directly the dynamic behaviour of the compression system to displace the surge line to lower flow rates. The influence of system geometry and compressor speed is investigated; the optimum values of the control parameters and the corresponding increase in the extent of the stable operating range are presented in the paper.

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