Mechanical Design and Rotor-dynamic Analysis of the ORCHID Turbine

The ORCHID turbine is a 10 kW, high-speed (~100 krpm) radial-inflow organic Rankine cycle (ORC) turbine, under realization in the Propulsion and Power laboratory of Delft University of Technology. The turbine will be installed and tested in the Organic Rankine Cycle Hybrid Integrated Device (ORCHID) facility, the setup for fundamental and applied studies on ORC technology currently in operation in the same lab. Experimental data from future measurement campaigns will be employed to validate numerical tools and develop best practices for designing and operating these unconventional machines. This work documents the recent design efforts to define the functional requirements, the necessary components, and the mechanical assessment of the turbine test bed. In particular, the detailed design of the rotor assembly, carried out in cooperation with the Rotor-dynamic research group of Politecnico di Milano, is described with emphasis on three main aspects. First, the derivation of the damping characteristics of a squeeze-film-damper cartridge for turbochargers, which has been selected as support bearing for the turbine shaft. Secondly, the estimation of the stiffness and damping coefficients of a labyrinth gas seal with swirl breakers, using 3D CFD simulations of the flow path. Finally, linear elastic rotordynamic simulations were performed on a finite beam element model of the resulting turbine shaft. The bearing stiffness, initially estimated using Hertz contact theory, was varied to investigate the sensitivity of the rotor critical speeds to it.