1) Explain the details of Free-Vortex Blade Design and Forced-vortex Blade Design for a
compressor blade.
How to apply the Simple Radial Equilibrium (SRE) equation to obtain the velocity triangles at
all radii in a compressor blade.
Sketch the geometry of the blade design by the Free-Vortex and Forced-vortex methods.
(30 marks)
2) 2.1
An axial compressor stage has an inlet hub-tip ratio of 0.7 and an outlet hub-tip ratio of 0.1
with the following conditions at the mean radius.
(i) The flow coefficient is 0.4
(ii) Degree of reaction is 50%
(iii) Absolute flow angle at rotor inlet is 30 degree, i.e. flow after the IGVs
(Iv) The mass flow rate to the compressor is 20 Kg/s
2.2
For free vortex design, determine
(a) the rotor inlet and outlet relative flow angle (β1 and β2) at the mean radius and at the
hub radius,
(b) the degree of reaction at the hub radius.
2.3
Assuming the inlet to outlet area variation is linear and there are 4 stages (rotor and stator
for each stage) within the compressor, construct the velocity diagram at the mean radius for
the entire compressor.
(a)what is the your estimated speed of rotation for the compressor, please provide
justifications.
State all the necessary assumptions
(40 marks)
3) 3.1
Consider an axial turbine stage that is driving the compressor in (2) above with the absolute
velocities entering and leaving the stage in axial direction. The flow exits the stator at an
angle of 65. If the turbine runs with a mass flow rate of 20 kg/s, a flow coefficient Cz /U of
0.6 and mean blade speed of 400 m/s, calculate:
(a) The flow angles relative to the rotor, β2 and β3
(b) The stage loading
(c) The degree of reaction
(d) The power output of the stage
(e) The rotational speed of the turbine
3.2
Construct the velocity diagram at the mean radius of the turbine using the information
above.
State all the necessary assumptions
(20 marks)
4) If the rotational speed of the turbine is found to be different from the compressor, what are
your proposed remedies?
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