Fast and accurate inclusion of steam properties in two- and three-dimensional steam turbine flow calculations

Abstract

Abstract

The Denton time-marching method for turbomachinery flow calculation has been modified for rapid and accurate access to the properties of steam in equilibrium dry and wet states and in the metastable dry region. Transition between metastable dry and equilibrium wet states is accomplished either at the stable equilibrium boundary or by allowing metastable equilibrium expansion followed by a condensation shock whose location depends on the local degree of subcooling of the metastable vapour and the local expansion rate. Steam properties and their derivatives are obtained from a wide-ranging Helmholtz representation of equilibrium (stable and metastable) thermodynamic properties and stored for use in an accurate Taylor series representation. Comparisons have been made of flow development in a low-pressure steam turbine blade row for three expansion assumptions:

equilibrium stable and metastable dry,

stable equilibrium, dry and wet, and

dry expansion prior to a condensation ‘shock’ which is followed by equilibrium wet expansion.

Inclusion of real steam properties extends calculation time for one iteration cycle by about 5 per cent and has little effect on the number of cycles required for convergence in the absence of a condensation shock; however, inclusion of the shock may double the time required for convergence.