August 15, 2017
Turbine design in ANSYS - Part 2: Virtual Lab
In the last blogpost, we coupled an external blade design tool to ANSYS workbench. In this blogpost, we will enter our "virtual lab" and create a Hill-Diagram. This is a chart that links the hydraulic efficiency of a turbine with a non-dimensional mass flow and rotational speed. This chart is often used in characterizing turbines, a sample diagram is included below.
Today, a Hill-Diagram is made by testing a turbine at various operating points, then interpolating to find lines of constant efficiency. This obviously requires a physical turbine and a lot of testing, and is therefore usually not used in a design process. This is what we will try to change.
Now enter the virtual lab. We assume that a turbine is designed, meshed, and loaded into CFX (see Blogpost Part 1 if this is not known). Using the "design of experiments" functionality one can define variable parameters in simulations. In this case, we will not use this to change the geometry, but to change the rotational speed, guide vane angle and mass flow through the turbine. This way one can obtain a Hill-Diagram, just as one would in a laboratory! A workbench project can look like below, where several operating points are simulated, and the hydraulic efficiency is extracted.
The result can be viewed in several ways. The build in "response surface" is shown below to the left, to the right are the same points visualized as a traditional Hill-Diagram, created externally in MATLAB. Once a response surface is created, one can utilize the different search algorithms to find the optimal operating point.
In the final blogpost we will try to couple blogpost 1 and 2; run an optimization algorithm using the Hill-Diagram as performance indicator, and automatically design new turbines with better characteristics!
 C. Trivedi, M. J. Cervantes, B. K. Gandhi, and O. G. Dahlhaug, "Experimental and Numerical Studies for a High Head Francis Turbine at Several Operating Points," J. Fluids Eng., vol. 135, no. 11, pp. 111102–111102, Aug. 2013.