Abstract
The article describes an interpolation–analytical method of reconstruction of the IAPWS-95 equations of state and the modified Benedict–Webb–Rubin equations of state with 32 terms (mBWR32). The method enables us to provide the thermodynamic closure in 3D computational fluid dynamics (CFD) calculations of turbomachinery flows with real working media, such as steam and Organic Rankine Cycle (ORC) fluids. The described approach allows for the sufficient accuracy of 3D flow calculations and does not require a significant increase in computational cost over perfect gas calculations. The method is validated against experimental data from measurements and compared with computational results from the model using the Tammann equation of state. Three turbine blading systems are considered—a multi-stage configuration from a low-pressure cylinder of a large-power steam turbine and two ORC microturbines working with organic media HFE7100 and R227ea. The calculation results obtained using the described method of approximation of the IAPWS-95 and mBWR32 equations exhibit satisfactory agreement with the experimental data, considering pressures, temperatures and enthalpies in key sections, as well as turbine power and efficiency in a wide range of changing thermodynamic parameters. In contrast, the Tammann equation of state provides acceptable results only for relatively small changes of thermodynamic parameters.
Highlights
Computational fluid dynamics (CFD) methods are widely used in various fields of science and technology: power engineering, aviation and astronautics, chemical industry, oil and gas industry, etc
A leading approach in CFD for gas dynamics and turbomachinery applications is based on numerical integration of the Reynolds-averaged Navier–Stokes (RANS) equations
An interpolation–analytical method of representation of thermodynamic functions is used. This method was first applied to take into account the thermodynamic properties of water and steam in 3D calculations based on the IAPWS-95 equation of state in [29]
Summary
Computational fluid dynamics (CFD) methods are widely used in various fields of science and technology: power engineering, aviation and astronautics, chemical industry, oil and gas industry, etc. Direct use of these equations in 3D flow calculations is currently impossible, because in this case, the computing processor time increases by In response to this question, in the present paper, an interpolation–analytical method to represent thermodynamic functions in complex state equations such as IAPWS-95 equations of state and Benedict–Webb–Rubin equations of state is proposed. The use of this method in 3D CFD calculations allows us to ensure sufficient computational accuracy and, on the other hand, does not require a significant increase in computational costs over perfect gas computations. Admissible intervals of change of thermodynamic parameters, for which the use of Tammann equation of state can yield reasonable results, are established
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