In collaboration with the University of Bath, HiETA Technologies have designed, manufactured and physically tested a lightweight and internally cooled Radial turbine wheel exploiting the design freedoms of Additive Manufacturing (AM). The objective was to prove that operation in turbine inlet temperatures of 1200°C was possible by an AM internally cooled Radial turbine wheel. By increasing the turbine inlet temperatures to 1200°C, the thermal efficiency of the turbine stage is drastically increased, and thus the overall efficiency of the engine system can be increased. Actively cooling the turbine wheel, increases the component life and by light-weighting the wheel, inertia is reduced and so spool up times are quicker, as well as reducing wear on bearings.
The technology is applicable to Micro Gas Turbine systems where system efficiencies could be drastically increased by running the system hotter, as well as the automotive industry where the lowering inertia is advantageous. To achieve the objective two approaches were combined. HiETA developed the capability to process a high-temperature resilient Nickel Super Alloy material CM247LC. Additionally, AM was exploited to create a novel design combining the required internal structure of the wheel with a targeted internal cooling method. Taking a standard oil cooled turbocharger as a baseline to reference against, the AM cooled wheel was tested back to back with the solid wheel, at the same design point using the same housings and bearings.
Topology optimisation was used to guide the required structural requirements, whilst a full conjugate heat transfer CFD model was created to model the effect of the cooling on the wheel. The CFD model was a full representation of the test setup, with compressor, bearings and turbine side all included. The output from this model was then validated via physical test. Due to limitations on the hot gas stand, it was not possible to test at 1200°C inlet temperatures, and so the wheels were tested at 720C turbine inlet temperature and 70,000rpm. Both the solid and cooled wheels were coated with thermal history paint, which records the highest metal temperature seen by the wheel. Compared to the solid wheel baseline, the cooled wheel showed an LE temperature reduction of 60°C, a TE reduction of 100°C and mid blade reduction of 90-100°C. The Cooled wheel was 22% lighter than the solid baseline. The results from the test correlated very closely to the CFD results, validating the accuracy of the model. CFD was then used to predict the temperature reduction at 1200°C. turbine inlet temperature. At this condition, it is expected that temperature reductions of 200°C at LE, 250°C at TE and 180-200°C at the mid blade would be presented.