Robust Design Optimisation of a Ford Turbocharger Compressor
Compressor | Turbocharger | Optimisation | Optimisation | Robust Design | Automotive
What is robust design optimisation (RDO), and is it better than standard optimisation? In this customer case, we describe a multi-disciplinary optimisation of a turbocharger compressor from FORD Motor Company, in which we demonstrate it is.
RDO combines standard numerical optimisation with sensitivity analysis to take into account the influence of manufacturing variations and operating uncertainties on product performance early in the design process. This type of CFD optimisation enables engineers to find optimal designs that are less sensitive to these uncertainties, giving more stable performance results.
This Ford turbocharger optimisation case aimed to extend the compressor’s flow capacity and improve surge margins. We used an active self-recirculation casing treatment.
Given their varying geometries, we created two separate meshes for the points near the choke and the stall with Fidelity Automesh. The simulation domain consisted of the impeller, a vaneless diffuser, the self-recirculation casing and the volute for fluid flow simulation (CFD), and the solid blade with a back plate for structural simulations (CS). Fidelity Optimisation was used to run the optimisation on the impeller shape (Figure 1).
The design space consisted of 19 design variables, performed as multi-point optimisations, and three operating points on two different speed lines. The robust optimisation accounted for the following uncertainties:
- Tip gap height ±25%
- Blade thickness ±1%
- ±1% of the total pressure at the inlet or static pressure at the outlet, respectively
- Different boundary conditions for choke and stall
Comparison of Standard Deterministic Versus Robust Design Optimisation
Comparing the performances of Deterministic Design 1 and Robust Design 1, we learned that the mean values of choke mass flow and efficiency varied in a similar range (Figure 2). However, the standard deviations of these objectives were drastically reduced by the robust design only (Figure 3).
The resulting blade designs were also notable different (Figure 3).
Accounting for uncertainties in the optimisation process resulted in designs that are less sensitive to uncertainties. The standard deviation of the choke mass flow was reduced by 33% and the efficiency by nearly 48% in the robust design, leading to significantly more performance stability.