Design and Experimental Assessment of Bladeless Turbines for Axial Inlet Supersonic Flows

Supersonic inlet flow is usually considered to be detrimental to the performance of turbine systems. A new class of bladeless turbines was developed, which allows for power extraction from supersonic axial inflows without swirl with minimal maintenance cost. This is achieved through a wavy hub surface that promotes shocks and expansion fans and hence generates torque. In a first step, a baseline bladeless turbine is designed and the power extraction is analyzed. The bladeless turbine surface is parametrized in matlab and subsequently imported into Hexpress (Numeca) to mesh an unstructured grid. The first layer thickness is kept below one for all the simulations. The unstructured mesh is loaded into cfd++ (Metacomp) to solve the three dimensional steady Reynolds-averaged Navier–Stokes (RANS) equations. Second, the work extraction principle is broken down from a three-dimensional unsteady problem into a two-dimensional steady phenomenon. An experimental campaign is outlined and test details are discussed. Finally, after the experimental characterization, the operational envelope and scaling of the bladeless turbine are described for several reduced mass flows, reduced speeds, and geometrical features of the turbine (amplitude of the wavy surface, helix angle, hub radius, and length of the axial turbine).