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Old 1st October 2009 | 00:23
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HarryMann
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Yes, they're divergent. The normal assumption is that all the dynamic head is converted to pressure at the compressor face (fan face in a turbofan) and then that first stage compresses further.
This means that the engine experiences a Momentum Drag equivalent to the nacelle intake area x density x free-stream velocity (a/c speed)
This is subtracted from the gross thrust, which is why the nett thrust of a big fan drops off with speed much faster than a turbojet.
A high speed at the first-stage face (or fan face) would seriously compromise the fan blade design, due to shocks or excessive Mach drag, as well as noise.
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