Interpolation-analytical method of taking into account real properties of gases and fluids

Abstract

The article proposed the interpolation-analytical method of taking into account the actual properties of working fluids in calculation of three-dimensional gas-dynamic processes. The method is based on the approximation of the complex thermodynamic functions by simpler dependencies. These dependencies are the equation of state of a perfect gas with variable coefficients of compressibility. The variables of compressibility are calculated with the help of interpolation third-order polynomials on arrays of thermodynamic values obtained with more complex equations of state, such as the modified equation of state of Benedict-Webb-Rubin. This approach provides sufficient accuracy of the thermodynamic values in the whole range of work of modern and advanced steam turbines (maximum error does not exceed ± 0,1%), but it does not require a significant increase in computational cost. It was shown that this method provides more accurate calculation of the flow in a five-stage low-pressure cylinder of the steam turbine with the experimental data compared to calculations that use simple equations of state.