Rotodynamic pumps - Aero-hydrodynamics of profiles and blade impellers

We'll see how similarity coefficients can be used to make the first major choices regarding the free parameters involved in designing the impeller of a propeller pump.

Starting from the specifications (height, throughput, speed), the dimensioning of axial machines requires, as a preliminary step, the definition of the external overall dimensions (R _e external radius of the wheel and rectifier) and the hub ratio T = R _i / R _e .

The operation and performance of propeller pumps are based on the deflection the fluid undergoes as it passes over the impeller, and the pressure increase is thus obtained by a variation in the momentum of the main flow from inlet to outlet. Deflection must be accurately known in order to assess performance correctly.

Wind tunnel tests enabled us to set up numerical functions to solve the two classical calculations:

• direct problem: the grid is fully defined geometrically, and we want to deduce the deflection and losses at a given entry angle;

• Inverse problem: once the inlet and outlet angles have been defined, we need to deduce the best grille to meet these specifications. Depending on the case, the notion of the best grille can be based on different criteria: efficiency, pressure fluctuation and associated vibration level, overall dimensions, NPSH.

The definition of the blades is made possible by solving the local inverse problem of defining, in two-dimensional flow, the flat rotor and stator grids best suited to the proposed velocity triangles. Strictly speaking, this resolution is only possible by imposing the number of vanes and the local diffusion factor, whose influence on the aforementioned optimization criteria is also important.

The general topic of "Rotodynamic pumps" is the subject of several articles:

• [BM 4 300] Presentation. Description ;

• [BM 4 302] How it works ;