Design of a Radial-Inflow Turbine for Organic Rankine Cycle

Design Targets

To achieve a very high target efficiency, well above the existing turbine stage efficiency.

Deliverables

Two newly designed turbine rotor and nozzle blade geometries which meet the power or efficiency requirements at the design point, along with trimmed rotor and nozzle blade geometries with variable nozzle blades which meet the power or efficiency requirements for different mass flow and ER conditions.

Impact

CFD results showed that the turbine stage efficiency was improved significantly, with a more than 30% increase compared to the baseline. The efficiency was validated in the test using both scaled and full models.

The client asked ADT to design a turbine stage including the rotor and nozzle within their existing volute to replace a poorly performing current design. The overall stage efficiency needed to be above 83%. The client also required variable nozzle and trimmed rotor to meet different operating conditions.

ADT engineers used TURBOdesign Pre to obtain the initial meridional geometry for the nozzle and the rotor blades. TURBOdesign Pre is a 1D preliminary design code which allows users to quickly get a meridional contour from only a few inputs and exports the meridional geometry to TURBOdesign1, ADT’s unique 3D Inverse Design code where the fully 3D rotor and nozzle blades were then designed.

 

3D streamlines in a turbine stage
3D streamlines in a turbine stage
 

Several design iterations were performed in TURBOdesign1 and examining detailed flow field through CFD calculations at all required operating conditions. The meridional and the blade loading parameters were modified to get a good design with high efficiency. The performance of geometries with different nozzle setting angles, trimmed tip profile, different inlet and outlet conditions were also calculated at the off-design conditions.

In the end, a detailed static structural analysis including the pressure and thermal loading from CFD analysis was performed to make sure the maximum stress of the rotor blade did not exceed the material strength at the maximum power output condition.

 

Von-Mises stress contour of the turbine wheel
Von-Mises stress contour of the turbine wheel
 

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