A comparison of modelling methods for polydispersed wet-steam flow

Spontaneous nucleation of water droplets in moist air or steam may result in droplet spectra which are complex in shape and which span a broad range of sizes. This is particularly true if the ow is transonic or supersonic with shock waves present, or if an already droplet-laden ow re-expands to give secondary or tertiary nucleations. Computation of such ows requires careful modelling of the size distributions if two-phase behaviour is to be accurately predicted. In this paper, three methods are presented for treating size distributions and growth of the liquid phase in condensing steam: a mixed Eulerian–Lagrangian method, a fully Eulerian method, and a method based on moments of the droplet spectra. These are compared by computing condensing ow within a one-dimensional supersonic nozzle under conditions that yield very di erent types of size spectra