D3,
I would have thought the streamtube shape would reduce the effectiveness of ICE over IGE. The inflow comes from all directions, while the outflow is directed downwards.
After the last discussion, i would agree that there should be a slight reduction in static pressure (ie density) above the rotor, as well as the expected reduction in flow velocity. But the pressure reduction is only due to the rotor forcing a direction change in the inflow. The incompressibility model is just a model intended to make bernoulli calcs simpler.
The blocking is not a friction effect through air viscosity, however. It blocks the inflow from above the rotor, so that the inflow now has a mild upwards component. Basically, the air is being forced to change direction more than if it were free stream. Or another way of putting it is the rotor is creating a flow field similar to descending. Hence the power reduction.
The reason why some machines are more sensitive than others is probably due to the twist and taper of the blades. Some machines will work better in this flow field, while others lose efficiency.
BTW
Leishman on order. Probably won't get a chance to read it properly for a while though. I'll have a skim through when i get it. I'm still interested in your work, but have to fit it in with my own - oh then there's the day job...
