Accelerating Accurate Prediction of Real-Fluid Thermodynamics in Ansys for GPU-based CFD

This work focuses on the development and implementation of the Ansys Fluid Properties (AFP) library module, designed to accelerate accurate real-fluid thermodynamics for GPU-based computational fluid dynamics (CFD). The module provides robust state equation capabilities across Python, Fortran, C, and C++ interfaces, enabling execution on both CPU and GPU architectures. The AFP library consists of two parts – the EoS library and the NIST REFPROP library. The EoS library provides access to cubic equations of state (EoS) such as the Peng-Robinson (PR) and Soave-Redlich-Kwong (SRK), to perform thermodynamic calculations for both pure components and multi-component mixtures. To address the predictive errors often associated with standard cubic EoS models, particularly for hydrocarbons, the library incorporates a volume translation (VT) method. The library also supports both ideal-and real-fluid mixture models, utilizing mixing rules to estimate EoS parameters and fugacity equivalence for saturation (i.e., vapor-liquid equilibrium, VLE) calculations. A comprehensive suite of VLE flash solvers – including isothermal-isobaric (TP), isenthalpic-isobaric (HP), isentropic-isobaric (SP) etc. – is implemented to handle the diverse thermodynamic queries required by CFD solvers. The second part of AFP called the NIST REFPROP library utilizes the FORTRAN-based REFPROP distribution to generate real-gas property (RGP) tables. This approach moves the expensive generation of state points to a pre-processing step. The tabulation is error-controlled and recursively bisects the temperature-pressure space to maintain local accuracy. A novel feature of this tabulation strategy is the handling of element cuts by spinodal or saturation lines, ensuring precise resolution of phase boundaries without over-resolving gradients near the critical point. Finally, the performance metrics determined by defined state point tests on different hardware (CPU and GPU) of the library are discussed.