Originally Posted by
RatherBeFlying
Aerodynamics follows Newtonian principles, even at high Mach numbers.
OK. Let's try this: the Newtonian physics associated with the air acting on a separated fan blade are completely overwhelmed by the Newtonian physics of the moments of inertia acting on the blade. Kinda like a bullet in air-to-air combat. Sure, aerodynamics will affect the bullet's ballistic trajectory. But those affects are overwhelmed by the moments of inertia acting on the bullet.
I think the main issue is that the blade (due to being weakened by the fatigue crack) started to bend and rotate forward and did not break away clean to an explosion, like during the test. How many degrees it rotated forward before failing is something that needs to be analysed and might mean we need to rethink containment requirements.
Two points:
1. A fan blade that "rotates forward" will almost immediately result in a blade tip/case strike. The resulting forces acting on the blade will cause the blade to fail at the fatigue crack.
2. What would cause the fan blade to "rotate forward"? The fan is a compressor section. In other words, in a turbo fan engine the fan blade compresses the air, it does not accelerate the air like a propeller. Further, the huge tension forces resulting from the massive centripetal acceleration of the blade will overwhelm any aero force pushing on the blade. Consider a guitar string. It is under considerable tension. Can you blow on the string to cause it to bend? No. The tension on the fan blade is several orders of magnitude greater than the tension on the guitar string.