Experimental Characterization of the Surge Onset in a Turbo-compressor for Fuel Cell Application

Abstract

The path to instability of a small centrifugal turbo-compressor included in an air supply system developed by Liebherr-Aerospace was experimentally investigated thanks to high-frequency unsteady static pressure sensors. At the lowest speed line, rotating stall is observed both at impeller inlet and vaned diffuser inlet. It is characterized by one stall cell rotating at 6.4% of the impeller speed. At higher rotational speeds, the compressor experiences deep surge. The surge frequency decreases as the rotational speed increases and as the downstream volume increases. The peak-to-peak pressure amplitude increases as the rotational speed increases but do not depend on the downstream volume. A detailed analysis of the instability onset was performed thanks to Fourier and wavelet transforms showing that the instability inception is disclosed by pressure spikes. Nevertheless the spikes cannot be considered as precursors but as the embryo of the developing instability, which jeopardizes the chances of a control system to damp the perturbation.

Low frequency stall modes of a radial vaned diffuser flow

“…The link between the surge characteristics (typically frequency and amplitude) and the geometry of the test bench no longer needs to be proven. Greitzer [5,6] theoretically and experimentally showed this dependency through the famous parameter B, which was confirmed in numerous studies [7][8][9]. The current questions reside on the onset of the precursory instabilities and their possible evolution into surge.…”

Performance study of centrifugal air compressor for proton exchange membrane fuel cell systems

“…The results show that the compressor provides a sustained air flow rate during the mild stall/surge event. Godard et al 23 tested the surge characterization of a centrifugal compressor for fuel cell, and the compressor surges abruptly with no pre-stall activity at a high rotation speed. An agglomerate model is introduced, and a fuel cell system model including a dynamic compressor is implemented.…”