Stodola's analysis showed it could not compete with piston engines unless it could operate at very high gas temperatures. These are temperatures far beyond those at which any then known material can support the centrifugal stresses of the engine. The first hopeful idea came from a German discovery in the 1920s that the process by which a fluid stream heats a solid surface is confined to a thin boundary layer of fluid adjacent to that surface. If this could be done in an engine, it would revolutionize aircraft engines. As a British scientist late in the last Great War, one of the authors was told to figure out whether cold air injection would work here.
Boundary layers come in two types, each similar to an extreme of flow in rivers.
Consider a slow river. Where the water moves slowly, the flow may be smooth and steady. However, in white-water rapids, the river is violently turbulent. The smooth type of boundary layer had become more amenable to mathematical analysis, but the bounndary layer on turbine blades is of the turbulent type. It is full of eddies of all sizes which interact in ways that even today we are just beginning to understand.