(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.