8th. World Congress on Computational Mechanics (WCCM8) 5th European Congress on Computational Methods in Applied Sciences and Engineeering (ECCOMAS 2008) June 30 –July 5, 2008 Venice, Italy A Reynolds-Averaged Navier Stokes solver coupled to accurate thermodynamic and transport property models. * S. Rebay 1 , D. Pasquale 1 , J. Harinck 2 and P. Colonna 2 1 Universit` a di Brescia Dip. di Ingegneria Meccanica Via Branze, 38, 25123 Brescia, Italy E-mail rebay@ing.unibs.it 1 Delft University of Technology Energy Technology Section Process and Energy Dept. Leeghwaterstraat 44 2628 CA Delft The Netherlands www.et.3me.tudelft.nl Key Words: CFD, transport property model, thermodynamic model, dense-gas. ABSTRACT zFlow is a CFD computer code linked to the FluidProp library, which allows for the accurate evaluation of thermodynamic and transport properties of a large variety of fluids and fluid mixtures. FluidProp im- plements several thermodynamic models, ranging from comparatively simple cubic equation of states (CEOS) to highly-accurate state-of-the-art multiparameter equations of state (MEOS). The code capa- bilities were recently extended to include the numerical solution of the Reynolds-averaged compressible Navier-Stokes (RANS) equations coupled with a realizable k-ω turbulence model [1]. zFlow is there- fore suitable for the simulation of flows of dense gases in industrial processes and as such it can be considered a fluid dynamic design tool. To improve the accuracy and robustness of the code, a non standard implementation of the k-ω model is adopted. First of all, the logarithm of ω is used as independent variable, instead of ω. This improves the accuracy of the simulations, since the variation of  ω = log(ω) across the boundary layer is much smoother than that of ω. In order to improve the robustness of the code, the admissible values of the predicted eddy viscosity are limited so as to fulfill to the realizability constraints. Fur further details, see e.g. Ref. [1]. The equations are discretized in space with a finite-element/finite-volume method suitable for general unstructured hybrid grids [2,3]. The advective terms are discretized with an upwind TVD scheme, gen- eralized to the case of fluids governed by arbitrary equations of state following the approach introduced by Vinokur and Montagn´ e [5]. Both explicit and implicit Runge-Kutta time stepping methods are avail- able. Significant gains in computational efficiency are obtained by adopting implicit time integration schemes in steady state computations, especially for fluids characterized by complex models for the calculation of the thermodynamic and transport properties. CFD solvers for viscous flows commonly compute the transport properties of the fluid by means of sim- ple models, which are valid only in the dilute-gas region. An example is the Sutherland’s law or Power