DESIGN OF GAS TURBINE ENGINES USING CFD

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1 INTRODUCTION
The design of individual gas turbine components using CFD is now commonplace
[1]. Traditional design by analysis methods are increasingly being supplemented with
automated design systems [2] and the use of optimisation systems [3]. At the same time,
fluid machinery can now be modelled and analysed to an unprecedented level using CFD
on powerful multi-processor computers or clusters.
Although CFD can provide essential information to aid the physical understanding of
complicated flow fields, it is generally the requirement to design/modify geometry that
drives the application of CFD. When applied to an individual component, the physical
understanding gained from CFD is often able to guide design improvements to that
component. However, fluid machinery is generally characterised by the interaction of a
number of components, such as multistage turbomachinery; the intake and the fan rotor;
the combustor and the upstream diffuser; and, so on. A truly optimal design can only
be achieved by accounting for all the component interactions. It is here that the design
by analysis approach becomes limited - a designer may know how he/she would like to
change the flow field, but changing the geometry to achieve that is much less intuitive
than in single component design. If the requirement to meet a number of constraints is
added, then design by analysis becomes a very crude tool.
This paper describes an automated design system that has been developed specifically
with multi-component fluid machinery in mind. Section 2 describes the main elements of
the design system. Section 3 describes five novel applications of the system.
2 ELEMENTS OF THE DESIGN SYSTEM
The design systems consists of the following processes:
² Parametric representation
² Geometry construction
² Mesh generation
² CFD solution
² Data extraction and functional evaluation
² Optimisation
The systems that implement these processes are described in the following sections.
An underlying theme of all the systems is that they have a batch execution mode that
allows them to be run automatically by the optimiser.

Leigh Lapworth and Shahrokh Shahpar
2.1 Parametric representation
Although the parametric representation, geometry construction and mesh generation
are logically separate processes, they are intimately linked with the objective of creating a
CFD mesh in the shortest possible time. With this in mind, an integrated design system
has been developed [4] called PADRAM (Parametric Design and Rapid Meshing System)
which provides a very efficient and robust system for parametric geometry and mesh
creation.
The parametrisation follows the strategy successfully adopted in previous work [2] of
using parameters that are already familiar to the designer. In the context of turbomachinery
blades, the parameters include: lean, sweep, stagger, inlet and outlet blade angles,
camber distribution and thickness distribution. The parameters can be independently
specified at a number of radial heights to produce a complete 3D design space. For
multi-passage and/or multi-stage turbomachinery applications, the parameters can be independently
specified for every blade in the calculation domain. Figure 1 illustrates how
a single blade within a ring of blades can be designed independently of the other blades
in the ring. For multipassage simulations, both the pitch and the relative axial position
between adjacent blades are also design parameters.