Shock-free entry

In a vane cascade, shock-free entry is given if the relative flow (see Relative velocity) of the fluid entering the impeller or the absolute flow upstream of the diffuser, hits the vanes (in the same direction as the median line of the vane profile).
See Fig. 1 Vane cascade

Shock-free entry is usually given at the design point, but in certain special cases impellers, such as inducers are designed for non-shock-free entry. Non-shock-free-entry which normally occurs during low flow or overload operation (see Operating behaviour) causes so-called shock loss.