Advanced Thermodynamics for Engineers, 2nd Edition

pressure ratios the work done by the HP shaft is high but at high fan pressure ratios the LP shaft work

increases rapidly. The final points on this graph are reached when the exit pressure (p

06

) is less than

atmospheric pressure.

The sfc varies in an inverse manner to the thrust and the minimum sfc coinci des with

maximum thrust. Surp risingly, the minimum sfc is not achieved with the maximum peak tem-

perature and, in this case, a maximum temperature of 1100 K gives the lowest sfc at a fan pressure

ratio, r

f

¼ 1.4. Of course, at these conditions the thrust is significantly less than at other conditions: it

must be remembered that the mass flow through ...