@dlearl476, as to the physics, generally speaking, film cooling over a flat surface always increases with bulk air speed. The engineering issue is usually centered around is the flow laminar or turbulent. Laminar flow occurs under very restrictive conditions and is characterized by lower fluid speeds and hence lower heat transfer rate than if the flow is turbulent. I had some situations with hardware where we purposely introduced tiny obstructions in the flow channel to purposely trip the flow from laminar to turbulent. I can't see how the air flow induced by the engine fan is anything but turbulent, especially at higher engine speeds. So likely we would see ever more heat transferred the higher the velocity through the cooler's fins. Turbulent flow generally requires higher pressure differences in order to achieve a certain bulk flow through a passage and the relationship is non-linear . All of that said the design could reach a point where the turbulence is so great that ever more action by the fan (higher engine speeds and also higher heat generated) might not result in much increase in bulk air flow. At such a point the actual air flow through the cooler fins would not go up in direct proportion to the fan speed and the increase in engine heat output would not be accommodated by the cooler, basically being choked out for flow rate. At high revs, the engine fan might be beating the air to death, but the cooler fins are just not letting enough air through to match the increase in heat load. And a centrifugal fan like we have on these engines does have a performance curve showing output vs rpm at one atmosphere ambient, and I'm betting that CFM falls off at higher rpms, and does not just keep going up the faster it spins. Just a theory.