Fluid Mechanics and Thermodynamics of Turbomachinery, 5e

48 Fluid Mechanics, Thermodynamics of Turbomachinery
Diffuser efficiency, h D
1.0
0.8
0.6
0.4
0.2
p02/p01 = 0.95
0
1.0 1.2 1.4 1.6 1.8 2.0
Substituting these two expressions into eqn. (2.52):
(2.53)
The variation of hD as a function of the static pressure ratio, p2/p1, for specific values
of the total pressure recovery factor, p02/p01, is shown in Figure 2.14.
Some remarks on diffuser performance
It was pointed out by Sovran and Klomp (1967) that the uniformity or steadiness of
the flow at the diffuser exit is as important as the reduction in flow velocity (or the
static pressure rise) produced. This is particularly so in the case of a compressor located
at the diffuser exit since the compressor performance is sensitive to non-uniformities
in velocity in its inlet flow. Figure 2.15, from Sovran and Klomp (1967), shows the
occurrence of flow unsteadiness and/or non-uniform flow at the exit from twodimensional
diffusers (correlated originally by Kline, Abbott and Fox 1959). Four different
flow regimes exist, three of which have steady or reasonably steady flow. The
region of “no appreciable stall” is steady and uniform. The region marked “large transitory
stall” is unsteady and non-uniform, while the “fully developed” and “jet flow”
regions are reasonably steady but very non-uniform.
0.90
p 2 /p 1
FIG. 2.14. Variation of diffuser efficiency with static pressure ratio for constant values
of total pressure recovery factor (g = 1.4).
0.85
0.80