Originally Posted by
mrfox
From the text referenced above - locked rotor is not necessarly less drag than windmilling - it depends on the bypass ratio. In straight jets and low bypass fans the losses from the increased flow through the core more than offsets the spillage. The crossover point was mentioned to be around 5:1 bypass - right around where the last gen turbofans live.
For now, I'm going stick with the thermodynamics model, and to that point I would say that the minimum drag stable point of a low vs high bypass would show up in the speed of rotation.