The fuel consumption of internal combustion engines is closely linked to the design and efficiency of its turbocharger system, i.e. its compressor and turbine. In the proposed paper a redesign of two geometries is studied numerically using CFD methods: A radial turbine's volute and a 90°-bend laying downstream of the turbine. Both designs are revised with focus on pressure drop or, respectively, turbine efficiency. The baseline design at hand is composed of a nozzled volute, a radial turbine and a 90°-bend, that were designed for an MTU series 4000 gas engine. However, both the inlet guide vanes and the turbine wheel remain untouched throughout this study.

The potential for improvements is studied with a gradient-based methodology. It is iteration based and of local nature as it uses shape gradients to propose the next design iteration. The enabling technology to this approach is an adjoint CFD method, which allows for the calculation of a surface sensitivitiy field by adding roughly the computational effort of one additional simulation.

These sensitivities may directly be used to update the considered shape. Unfortunalety, they tend to be noisy and may lead to bumpy surfaces. This is where the so-called vertex morphing technique comes into play: In addition to the calculated surface sensitivity field a control field is introduced that is used to steer the design update while guaranteeing smooth shape changes and exactly maintaining the number of degrees of freedom. Using the vertex morphing technology, the designer has to choose solely one parameter, the filter radius R, which represtens the characteristic lengthscale of the applied shape update. The limit of R going to zero corresponds to the absence of a vertex morphing, while a large R will lead to rigid body motion like shape changes.

Such a surface sensitivity based approach using vertex morphing offers three major benefits: (1) There is no need for a parametrized CAD-model as one baseline geometry is sufficient for the workflow. (2) The design space is large as every node on the morphable surface represents three degrees of freedom. (3) Vertex morphing guarantees to maintain certain design features of the baseline designs such as for example, in this case, the volute tongue.

A simple steepest descent method is used to drive the optimization processes of the volute and the bend aiming at minimizing the pressure drop within the flow guiding systems.

Eventually, the most important design changes of the optimized volute and 90°-bend are highlighted and turbine maps are generated to compare both baseline and optimized designs on a broad spectrum of boundary conditions.


Gradient-Based Optimization of a Radial Turbine Volute and a Downstream Bend Using Vertex Morphing

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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