(a) (b)
Figure 7 Static pressure over mid-span: a) IGV (left), b) rotor
blade (right)
In this IGV-rotor configuration with rotor blades designed for free
vortex distribution to ensure a radial equilibrium flow, there is a
swirl velocity at IGV exit giving a spanwise vortex-free pre-rotation
which is balanced by an axial velocity obeying the equation of radial
total pressure variation. From hub to mid-span the axial velocity
concentration tends to reduce the flow incidence, while from the
mid-span to tip the blockage tends to increase incidence. At a reduced
mass flow, the higher angle of attack is responsible for increasing the
aerodynamic loading towards the blade tip, but it is compensated by the
high losses due to the suction side flow. The radial distribution of
axial velocity at rotor exit is related to the axial blockage imposed at
IGV trailing edge which becomes more at low flow rate. Figures 8 present
the subsequent evolutions of total pressure and entropy at a half chord
distance downstream of rotor blade and for three operating conditions of
the fan stage. It is obvious that the most significant variations in
velocity profiles appear in the regions at 15 % span near the hub and
75 % span from the casing, which are relating where high losses are
present.