Optimized aerodynamic design of axial turbines for waste energy recovery

Industrial processes experience waste of energy when throttling valves are used for flow control. In such cases, the overall process efficiency can be improved by means of inline installations of well suited turbines in place of throttling valves, in order to recover useful power from the pressure drops, which otherwise result in a waste of energy. Energy recovery turbines may require an "ad hoc" design when their operating ranges are unsuitable for traditional design methods. For this purpose, a general methodology is proposed, which can be helpful in the aerodynamic design of these non-conventional turbines. The design procedure is iterative and begins with a one dimension (1-D) study for the definition of the main geometric parameters, once appropriate loss coefficients are considered. Then, the blade profiles are designed by means of panel method with "viscous/inviscid interaction". Finally, the actual values of the loss coefficients are evaluated by means of fully 3-D CFD simulations, and used for updating the loss coefficients used in 1-D calculations. The iterative design procedure has been automatized by means of a Matlab script for the 1-D study, a ModeFrontier project for the blade design optimization and a log file for the automated 3D mesh generation. In order to validate the proposed methodology and show its generality, the design of a first stage of a steam turbine whose reference data were available in the literature, is presented.