Fluid Mechanics and Thermodynamics of Turbomachinery, 5e

Stage pressure rise
Consider first the ideal compressor stage which has no stagnation pressure losses.
Across the rotor row p0rel is constant and so
Across the stator row p0 is constant and so
(5.23a)
(5.23b)
Adding together the pressure rise for each row and considering a normal stage (c 3 = c1)
gives
(5.24)
For either velocity triangle (Figure 5.2), the cosine rule gives c 2 - U 2 + w 2 = 2Uw
cos(p/2 - b) or
Substituting eqn. (5.25) into the stage pressure rise,
Again, referring to the velocity diagram, wy1 - wy2 = cy2 - cy1 and
Axial-flow Compressors and Fans 155
FIG. 5.6. Effect of design stage loading (yd) on simplified off-design performance
characteristics (adapted from Horlock 1958).
(5.25)
(5.26)
It is noted that, for an isentropic process, Tds = 0 = dh - (1/r)dp and, therefore,
Dh = (1/r)Dp.