Figure 12 Total-total isentropic efficiency vs. axial
inter-distance
UNSTEADY FLOW ANALYSIS
The transient relative motion on each side of GGI connection was
simulated and the interface position updated at each time step. The
high-resolution advection scheme and second order backward Euler
transient scheme were used. For every time step ten internal coefficient
loops were selected and the pressure was monitored at the same spatial
locations. In this section the expected dominant modes and frequencies
and the sequence of interactions were determined analytically, followed
by a characterization of the pressure fluctuations computed and recorded
at several monitor points. The development of instabilities negatively
affects the overall operating performance of axial fan stage which could
be alleviated by understanding the unsteady flow interactions. Also it
is useful to know the modal frequencies to ensure that any applied
periodic loading frequency does not induce resonance leading to large
oscillations. This section addresses the unsteadiness arising from both
periodic (correlated with speed of rotation) and non-periodic
fluctuations induced by RSI.