4. Direct study of operating similarity

4.1 Turbomachinery type and family

Two turbomachines are said to be of the same type when they are geometrically similar, i.e. when we can pass from one to the other by multiplying all linear dimensions by the same factor called the geometric similarity coefficient. All turbomachines of the same type form a family that is therefore characterized by constancy:

• ratios of all linear dimensions to a reference length which we choose to be equal to the rotor outer radius r ;

• homologous angles, in particular angles defining the position of both fixed and moving blades.

Consequently, a pump of a given family is fully determined if only one linear dimension is known. However,...