Abstract
The capabilities of the open-source SU2 software suite for the numerical simulation of viscous flows over unstructured grid are extended to non-ideal compressible-fluid dynamics (NICFD). A built-in thermodynamic library is incorporated to account for the non-ideal thermodynamic characteristics of fluid flows evolving in the close proximity of the liquid-vapour saturation curve and critical point. The numerical methods, namely the Approximate Riemann Solvers (ARS), viscous fluxes and boundary conditions are generalised to non-ideal fluid properties. Quantities of interest for turbomachinery cascades, as loss coefficients and flow angles, can be automatically determined and used for design optimization.A variety of test cases are carried out to assess the performance of the solver. At first, numerical methods are verified against analytical solution of reference NICFD test cases, including steady shock reflection and unsteady shock tube. Then, non-ideal gas effects in planar nozzles and past turbine cascades, typically encountered in Organic Rankine Cycle applications, are investigated and debated. The obtained results demonstrate that SU2 is highly suited for the analysis and the automatic design of internal flow devices operating in the non-ideal compressible-fluid regime.
Highlights
Non-ideal compressible fluid dynamics (NICFD) is the discipline devoted to the study of the thermo-physical characteristics of fluid flows departing from gas ideality, namely flows not obeying to the perfect gas law
They are by far the essential element in Organic Rankine Cycle (ORC) turbogenerators, which are energy conversion systems renowned for the efficient exploitation of renewable energy sources [1, 2, 3, 4]
A series of numerical applications are presented thereafter, in which SU2 is first verified against known analytical solutions and compared to results obtained by a commercial package
Summary
Non-ideal compressible fluid dynamics (NICFD) is the discipline devoted to the study of the thermo-physical characteristics of fluid flows departing from gas ideality, namely flows not obeying to the perfect gas law. 3. Computation of Thermo-physical Properties Unlike standard CFD solvers, the numerical schemes for non-ideal fluid flows require the calculation of primary and secondary, i.e. partial derivatives of primary thermodynamic variables, thermodynamic properties as a function of density ρ and internal energy e, which are in turn a recombination of the conservative variables as follows ρ = U1, e. Equation 6 is explicit for polytropic models, like the ideal gas (PIG), the Van der Waals (PVdW), and the Peng-Robinson (PR) available in the built-in thermodynamic library These models ensure high computational efficiency but are not accurate approaching the critical point. They are useful to initialize simulations where strong non-ideal flow effects are of concern. SU2 can exploit the advantages offered by the direct coupling with a general purpose thermophysical library [13] originally developed at Delft University of Technology
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