Radial turbine featuring a Multi-channel Casing (MC) is a
new design under investigation for enhancing the turbine
controllability. The idea behind this new design is to replace the
traditional spiral casing with a MC, which allows controlling the
mass flow by means of opening and closing control valves in
each channel. The arrangement of the closed and opened
channel is called the admission configuration, while the ratio
between the counts of the open channels to the total number of
channels is called the admission percentage.
Among several aspects, when applying different admission
configurations, the aerodynamic damping during resonant
excitation is considered during the design of the turbine. The
present study aims at investigating the effect of different MC
admission configurations on the aerodynamic damping as an
extension to an aerodynamic forcing study, which already
assessed the different forcing patterns associated with these
different admission configurations.
Due to the asymmetry of the flow in circumferential direction
resulting from the different partial admission configurations, the
computational model is solved as full 3D time-marching,
unsteady flow using ANSYS CFX in a one-way fluid-structure
analysis. Two different modeling approaches have been
considered in this study to investigate their capability of
predicting the damping ratio for different MC admission
configurations: a) the conventional isolated rotor approach and
b) a full model consisting of the rotor and its casing. The results
show that the casing affects the aerodynamic damping behavior,
which can only be captured by the full model. Furthermore, the
damping ratios for all different admission configurations have
been calculated using the full stage model.