2. Viscosity of flow

Viscosity naturally plays a key role in turbomachinery, as it is the main source of losses. These losses are usually classified into three categories:

• profile losses, linked to the development of viscous layers on the blades and the wakes they create, which are all the more sheared the greater the three-dimensional warping effect mentioned above;

• secondary losses, which appear at the edges of the blades and give rise to significant vortices, as a result of the viscous flow being deflected onto the hub and casing. It should be noted here that the appearance of the main vortices is not a purely viscous phenomenon, but results from the heterogeneous velocity profile at the impeller inlet. Non-viscous calculations clearly demonstrate this behavior qualitatively;

• losses due to...