Turbine Cascade (Viscous case)
Drag =  Effective lift =
Actual lift coefficient,
The drag increases the lift. Thus, thedrag is an useful component for work.
Blade efficiency (or diffusion efficiency)
For a compressor cascade, the blade efficiency is defined as:
Due to viscous effect, static pressure rise is reduced
from velocity triangle:  |
Also we get
 |
| |
|
[Approximation:
 i.e.in the expression for lift, the effect of drag is ignored] |
The value of  for which efficiency is maximum,  |
|
-maximum, if 
