It can be increased to reduce flare
Constant specific mass flow
The free vortex and constant nozzle angle designs are only two possibilities. Another criterion is to satisfy the RE and obtain a constant mass flow per unit area at all radii: the axial and whirl components are chosen so that
ρ 2 C a2 =const . ∀ r
Even if the axial velocity is constant throughout the annulus before and after the rows of a free vortex turbine, there is a streamline shift. This is due to the presence of a radial velocity component arising from an increase of the density from root to tip, in contrast with the main hypothesis of the RE. In fact, the pressure at the exit of the nozzle increases from root to tip, to balance the centripetal acceleration; on the other hand, if the flow leaves the rotor axially, it is characterized by uniform velocity, pressure, and density.
Even if there is no evidence that this leads to inefficiency, one can assume a design wi..