Abstract
Centrifugal compressor applied to turbochargers is required
to operate stably in wide range from choking to surging. In our past
research, it was suggested that impellers which induced tip leakage
vortex breakdown at relatively high flow rate might stabilize
internal flow by generating circumferential uniform blockage
region near blade tip at low flow rate. In this study, authors
investigated whether modifying a given impeller to induce the tip
leakage vortex breakdown could reduce the surging flow rate or
not.
Pressure measurement of the conventional impeller showed that
unstable pressure fluctuation occurred at smaller flow rate side than
the peak pressure point. Furthermore, it was clarified by unsteady
numerical calculation that the rotating stall occurred with
circumferentially non-uniform reverse flow. On the other hand, in
the new impeller increasing its inducer loading, unsteady numerical
calculation showed that the blade tip leakage flow was strengthened
and generated a circumferentially uniform blockage region, which
could stabilize its internal flow.
As a result of performance test of the new impeller, considering
that the surging flow rate at the same shaft speed was reduced by
3% and the pressure ratio at the surging point had been improved
from 2.8 to 2.9, the surging flow rate at the pressure ratio of 2.8
could be reduced by 8%. In this way, it was found that the tip
leakage flow was dominant with the stall phenomenon of the
centrifugal compressor, and it was also confirmed that the tip
leakage vortex control was one of the effective means for the
operation range enhancement.
