Liquid film and droplet stability consideration as applied to wet steam flow

The state of art and ongoing research concerning the flow of wet steam in large steam turbines is reviewed, particularly from the viewpoint of the behavior of the liquid film deposited upon the stationary blading. New experimental results concerning the non-steady behavior of the film and the resultant wavelet formation patterns under the action of high-velocity low-pressure steam flow are presented. These results are then correlated as a flow regime “map” showing various flow regions in terms of steam velocity (or relative steam-film velocity since film velocity is relatively very small) vs. film flow rate per unit transverse distance. The distribution of liquid droplets shed from the blade trailing edge in the wake are studied as a function of distance downstream, steam velocity, and liquid film flow rate. In addition the droplet size is correlated in terms of critical droplet Weber number and compared with results of previous investigators. High-speed photographs of droplet distortions in a high-velocity air stream are also included.