Optimization and Computational Fluid Dynamics - Department of ...

172 René A. Van den Braembussche
Objective function
1.4
1.2
1
0.8
0.6
0.4
0.2
Fig. 6.18 Convergence history
Objective function with Navier−Stokes results
Objective function with approximate model
0
0 5 10 15
Number of iterations
20 25 30
Table 6.3 Inlet conditions at the 3 operating points
Low ˙m Medium ˙m Large ˙m
α(deg) 68. 60. 54.
P◦ 2 (Pa)
P3/P
218395. 213447. 187666.
◦ 2
T
0.9157 0.9276 0.9430
◦ 2 (K) 365.4 360.3 350.4
procedure. The whole procedure could have been stopped after 15 iterations
but has been continued to verify good convergence.
6.5 Multipoint Optimization of a Low Solidity Diffuser
The radial compressor vaned diffusers provide a higher pressure recovery and
efficiency than vaneless ones but the operating range is limited by stall, at
positive incidence, and diffuser throat choking, at negative incidence. Low
Solidity Diffusers (LSD) are characterized by a small number of short vanes
and do not show a well defined throat section. They intend to stabilize the
flow at low mass flow (avoiding diffuser stall) without limiting the maximum
mass flow by choking. The solidity (chord/pitch) is typically on the order of
1 or less (Fig. 6.19). A multipoint optimization is mandatory for the LSD
design because a wide operating range is the major purpose of these devices.
The optimization of the LSD [12] is done for the 3 operating points listed in
Table 6.3. Inlet conditions are different for each operating point and defined
by the impeller exit flow at the corresponding mass flows.