The proposed project will build on recent work supported by Alstom (now General Electric) at Cambridge and integrate with the ongoing Future Conventional Power Research Consortium project, which also has a wet steam component based in Cambridge. The objectives of the project are as follows:
(a) To develop a non-equilibrium wet steam throughflow calculation method, including modelling of all the loss-generating two-phase phenomena. The basis for this work will be provided by a current Alstom-supported PhD project at Cambridge that is now nearing completion. The current status is that non-equilibrium routines and wake-chopping models have been included within a streamline curvature code, enabling the global effects of condensation within turbines to be predicted, together with droplet size spectra. However, for this method to be of value both at the design stage and as a research tool, a host of additional two-phase phenomena need to be modelled. These include: contributions from heterogeneous condensation; deposition of droplets onto turbine blades by inertial impact and turbulent transport; migration of films under the action of shear and centrifugal forces; coarse water formation at blade trailing edges; computation of losses and their distribution between different phenomena such as thermal relaxation, fog-droplet drag, the braking effect of coarse water impaction etc. Models exist for many of these phenomena (notably due to the pioneering work of Gyarmathy [1]), but some are based on one-dimensional assumptions and require extension and adaption for inclusion into the (two-dimensional) streamline curvature code. Cambridge has considerable experience in this area, including the modelling of similar phenomena in water-injected compressors [2].
(b) Application of the throughflow code to provide a comprehensive study of how machine geometry, operating conditions and model assumptions influence the overall magnitude of losses and their distribution between the different phenomena. For example, changes to the LP turbine inlet temperature are likely to change the location of condensation such that it occurs with a very different expansion rate history. This may have a significant effect on the droplet size distribution, which in turn will affect all the other two-phase processes listed in (a) above. Such a study will require significant interaction with our industrial partners, and the CASE studentship thus provides an ideal framework for this undertaking.
In addition to (a) and (b) it is intended that there should be an additional component to the work, the precise nature of which should depend on the preferences and background of the PhD student.
Possibilities include (i) inclusion of velocity slip modelling within STEAMBLOCK (the 3D unsteady wet steam code recently developed at Cambridge) and application to study inertial relaxation effects in a variety of configurations (e.g., interpretation of Pitot tube measurements); (ii) a comprehensive study of the role of heterogeneous effects; (iii) fundamental phase-change modelling (i.e., nucleation and droplet growth studies).
References

[1] Gyarmathy, G., 1962. "Grundlagen einer Theorie der Nassdampfturbine". PhD Thesis (also
CEGB translation : "Bases for a Theory for Wet Steam Rurbines", T. 781).

[2] White, A.J., and Meacock, A. J., 2011. "Wet Compression Analysis Including Velocity Slip Effects", J. Eng. Gas Turbines Power 133(8), 081701