REGAL-ORC

Organic Rankine Cycle (ORC) power systems offer a great potential for waste heat recovery and environmental-friendly power generation but relatively little is known regarding the impact of real-gas effects on loss mechanisms in ORC turbine expanders. A further increase of ORC turbine efficiencies can only be achieved if relevant non-ideal compressible fluid dynamical phenomena are better understood and modeled. Computational fluid dynamics (CFD) tools currently used in ORC design, based on Reynolds-averaged Navier-Stokes (RANS) models, are affected by many notorious flaws and uncertainties, and large-eddy-simulation (LES) or direct-numerical-simulation (DNS) methods are a promising tool for improving our fundamental understanding of these flows. The application of LES and DNS methods for real-gas flows in turbomachinery configurations is an open challenge, due to the high Reynolds numbers and the complex thermophysical models required and requires high-quality experimental data for their validation that are not available so far. Wall-resolved and wall-modelled LES methods for organic vapor flows in turbomachinery will be developed in this project based on a combined numerical-experimental approach employing high-accurate numerical solvers, a new organic vapor wind tunnel test facility and a new generation of hot-film surface sensors. The project will explicitly identify and quantify real-gas effects on laminar-to-turbulent transition, flow separation, shock-wave-boundary layer interactions and wake development and, ultimately, their impact on loss mechanisms in the transonic flow regime. Two primary test configurations will be investigated, namely, the flow over a flat plate and though a simplified turbine cascade vane. Flow properties, including turbulence quantities, will be measured by means of hot-wire anemometry, conventional and focusing Schlieren systems, Pitot and five-hole-probes, laser-based anemometry, and by a new generation of miniaturized hot-film surface sensors tailored to the very special needs of organic vapor flows. Thanks to the close collaboration between a theoretical/numerical research group (Paris, France) and an experimental group (Muenster, Germany) and the support by a microsystem technology group (Ilmenau, Germany), the project will enable, for the very first time for organic vapors, several significant advances: 1) characterization of transitional and turbulent flow behavior via simulations and experiments; 2) insight into blade vane loss mechanisms and assessment of the capability of numerical models to capture them; 3) development of innovative high-fidelity CFD tools specifically tailored for ORC turbomachinery; 4) development and release of new thermal surface sensors for measuring flow and turbulence quantities in the very thin wall region for real-gases. The new experimental and CFD data and the outcomes of the present research will constitute benchmark cases for the scientific community and the interested public.