Challenges
TOYOTA Motorsports is a high-performance testing and development facility located in the centre of Europe, in Cologne, Germany. One focus is on chassis and engine design for automotive and motorsports. Specialising this high technology developments for motor sport engines the existing turbocharger components already show a high-performance level. Hence, further improvement by traditional means, i.e. classical trial-and error procedures are hardly compatible with the required turn-around times of a modern design environment. Numerical optimization processes allows to explore many designs in an automatic way, thus, the developer has the opportunity to evaluate many more designs compared to what could be achieved manually.
Aside from an increasing engineering complexity, another challenge is that compressor impellers already work very close to the structure-mechanical limits of the material. Most changes in shape immediately lead to an exceeding of the acceptable stress level. An optimization under exclusive consideration of the aerodynamic behaviour does not guarantee that the resulting optimal design is structurally feasible. Thus, simultaneous optimization including aerodynamic and structural forces is necessary. This is referred to as multi-disciplinary optimization coupling Computational Fluid Dynamic (CFD) with Computational Structural Mechanic (CSM) simulations.
Optimization Targets & Workflow
In the present project, the characteristics of a centrifugal compressor for an exhaust gas turbocharger are optimised by a multidisciplinary coupled CFD-CSM optimization. The considered compressor stage consists of a radial impeller with six main and six splitter blades with a vaneless diffuser (Figure 1). Two aero-thermodynamic objectives and one structure-mechanical as well as two aerodynamic constraints are considered:
1) Increase of isentropic efficiency
2) Same, or higher absolute total pressure ratio
3) Same choke mass flow as original geometry
4) Extension of operating range towards stall margin
5) Maximum von Mises stress are below limit
The objectives listed above require simultaneous optimization at four operating points: design point (target 1, 2, 5), two operating points close to the stall (target 4) and one point at the choke (target 3).