The tool makes use of
an S2 ‘throughflow' calculation to provide the aerodynamic feedback, which
makes the process orders of magnitude faster than a 3D CFD-based optimization
process. This is a major productivity enhancement and
ensures that any new design both builds on a successful empirical database and
is truly optimum in the selection of design parameters. The goal is not to
replace CFD in the final refinement of the design, merely to ensure that the
time invested in CFD is wisely spent.
The optimising tool takes the results from PCA's 1D preliminary design tool Vista CCD and uses these to define a parameterised blade geometry, which incorporates features that are required for low mechanical stresses and simple manufacturing. This geometry is then adjusted to minimise a global objective function using Vista TF, PCA's 2D throughflow (S2) analysis tool. The adjustment is based on selection with a breeder genetic algorithm (BGA). The initial population includes "elite" designs from a database of earlier well-proven experience, and the final design is then honed with a hill-climbing method.
With the help of a
suitable global objective function incorporating mechanical and aerodynamic
criteria and taking into account PCA's extensive experience with the design of
impellers for a wide range of applications, the new tool provides a fast
screening of various design possibilities to produce an optimised geometrical
input for more advanced computational fluid dynamic (CFD) and mechanical finite
element (FE) analyses.
The process has
been validated at PCA on impellers from a wide range of applications including
small gas turbines, automotive turbocharger compressors and process compressors
over a range of specific flow or specific speed. It is equally valid for both
open and shrouded wheels
More details can be
found in a forthcoming IGTI paper (GT2008-50561) to be presented in Berlin in
June 2008 or by contacting PCA Engineers Limited.