Stall Inception in a Vaneless Diffuser of a Centrifugal Compressor

Abstract

This paper presents an experimental and analytical investigation of a rotating stall inception in a vaneless diffuser of a centrifugal compressor. Eight fast-response pressure transducers are equally spaced around the circumference at the inlet and exit of a parallel vaneless diffuser. Instantaneous pressure data is measured near the stall inception point and characteristics of a rotating stall, a stall-initiating mechanism, a stall precursor and its warning schemes are discussed. It is found that one-cell, two-cell and three-cell structures of small amplitude wave grow and decay repeatedly before they are fully developed to a rotating stall, which is named as “pre-cell.” When it appears, the phase of spatial Fourier coefficient increases linearly and the traveling wave energy increases. The pre-cell travels at, or slightly lower than, the speed of the fully developed rotating stall. Its growing-decaying life span is about several decades of the impeller revolution. Pre-cells of one-cell, two-cell, and three-cell structures are found to interact frequently with their growing and decaying mechanism through transferring energy from one structure to another. Two stall warning schemes are used for the stall in the vaneless diffuser. The first scheme is to detect the linear increase region in the phase of the spatial Fourier coefficient from where the according warning time is about 0.3∼1.4 sec. (300∼700 impeller revs.) The second scheme is to detect the increase of traveling wave energy from where the according warning time is about 0.2∼2.3 sec. (200∼1200 impeller revs.) These warning schemes are useful because their warning time is long enough to be applied in active control of a compressor stall.

Experimental Investigation of Surge and Stall in a High-Speed Centrifugal Compressor

“…Kämmer and Rautenberg [19] found that low-frequency rotating stall tended to happen in the diffuser at high speeds, in contrast with high-frequency rotating stall upstream and downstream of the impeller at lower speeds. Kang and Kang [20] discovered one-cell, two-cell, and threecell aerodynamic structures traveling around the diffuser. Building on Moore's simplified models [15][16][17][18], Spakovszky and Roduner [21,22] added three subcomponent modules -impeller, vaneless space, and diffuser modules -to predict the system resonances.…”

Numerical simulation of rotating stall in a centrifugal compressor with vaned diffuser

“…While the successful control of rotating stall to improve compressor stability is based on the detection of early precursors to stall, Lawless [1] experimentally studied the rotating stall acoustic signatures in a low speed centrifugal compressor with vaneless and vaned diffusers. Recently Kang et al [2][3][4] examined the stall inception in a high speed centrifugal compressor through a series of experiments. Both of them wanted to find stall precursors and develop reliable stall warning method.…”