Fluid Mechanics and Thermodynamics of Turbomachinery, 5e

106 Fluid Mechanics, Thermodynamics of Turbomachinery
(ii) At nozzle exit the Mach number is
and it is necessary to solve the velocity diagram to find c2 and hence to determine T2.
As
Referring to Figure 4.2, across the nozzle h01 = h02 = h2 + 1 – 2 c2 2 , thus
Hence, M2 = 0.97 with g R = (g - 1)Cp.
(iii) The axial velocity, cx = c 2 cos a 2 = 200m/s.
(iv) htt =DW/(h01 + h3ss - 1 – 2 c3 2 ).
After some rearrangement,
Therefore htt = 0.93.
(v) Using eqn. (4.22a), the reaction is
From the velocity diagram, tan b3 = U/cx and tan b2 = tana2 - U/cx
EXAMPLE 4.3. Verify the assumed value of total-to-static efficiency in the above
example using Soderberg’s correlation method. The average blade aspect ratio for the
stage H/b = 5.0, the maximum blade thickness–chord ratio is 0.2 and the average
Reynolds number, defined by eqn. (4.14), is 10 5 .
Solution. The approximation for total-to-static efficiency, eqn. (4.10a), is used and
can be rewritten as
The loss coefficients zR and zN, uncorrected for the effects of blade aspect ratio, are
determined using eqn. (4.12) which requires a knowledge of flow turning angle for
each blade row.
For the nozzles, a1 = 0 and a2 = 70deg, thus N = 70deg.