| Summary: | \Yith the current develop111ent in computer technology and Computational
Fluid D)"n<'tlllics techniques, t.he si11utlation within axial flow compressors becomes
1110re and 1110re pract.ical and beneficial to the compressor designs. Due to the
insufficient capabilit)" of today's COll1put.ers for three-dimensional unsteady flow
1110delling of 111Ult i~Llg(' axial flow compressors, sophisticated models of steady
state flow and perfor111ance 1110delling of the C0111prcssors deserve to be thoroughly
investigated.
In l1utltistage C0111pressor sinlulations with steady state methods, frame of reference
is fixed on blades and the c0111putational domains for rotors and stators
haye relati\"e rotation. One of the difficulties in such simulations is how to pass
information across the interfaces between blade rows without losing continuity.
Two 111ajor stead)" state modelling approaches, a mixing plane approach based
on Denton's circu111ferentially non-uniform mixing plane model and a deterministic
stress approach based on Adamczyk's average passage model, are investigated
and compared with each other through the flow predictions of the third stage of
Cranfield Low Speed Research Compressor at peak efficiency operating condition.
In the deterministic stress approach, overlapped solution domains are introduced
to calculate deterministic stresses in order to "close" the time-averaged
governing equation system and the influence of the downstream blade row of the
blade row under investigation has to be imposed through the simulation of bodyforce
and blade blockage effect of the downstream blade row. An effective method
of simulating bodyforce and blade blockage effect has been developed and proven
to be simple in programming.
ConYentionally, boundary conditions are specified in CFD calculations based
on experimental data or other empirical calculations. By taking advantage of the
special flow features in rear stages of multistage axial flow compressors where each
rear stage behaves like a repeating stage of its neighbouring stages in terms of
flow pattern at the inlet and the exit of these stages, a repeating stage model has
been developed aiming at significantly simplifying the boundary conditions when
simulating rear stages of a multistage axial flow compressor with only mass flow
rate and stage exit average static pressure required as global input.
A computer simulation system 1'/ STurbo3D has been developed to investigate
a11d assess different steady state simulation models within multistage compressor
environment. It has been proven that with the mixing plane model M STurbo3D is
able to predict flows in multistage low speed axial flow compressors with acceptable
accuracy. Application of the repeating stage model to the third stage of LS RC
shows that the prediction with this model has equivalent accuracy to the prediction
with the conventional boundary setting, and proves that the repeating stage
model is an effective alternative to the expensive complete compressor simulation.
The deterministic stress model provides more information of rotor-stator interaction
and slightly better performance prediction than the mixing plane model, but
the benefits of the model is not significant when applied to low speed axial flow
compressors.
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