Flow profile
The flow profile, also referred to as the vane profile, results from the intersection of the flow surface (see Flow line) with the vane (e.g. vane of an impeller or diffuser or a hydraulically ineffective vane supporting a pump bearing).
The flow profile is generated by adding the vane thickness equally on either side along the length of the median line, according to a specified distribution (e.g. NACA profiles). See Fig. 1 Vane cascade
The progression pattern of the profile thickness can be obtained from a table of profiles or it can be calculated according to analytical functions.
This calculation plays an important role, especially with modern NC (Numerical Control) methods.
The vane profile of an impeller is to a large extent dependent on the type of centrifugal pump involved (see Specific speed). Radial impellers and most diffusers almost always have long thin vanes which do not exhibit a distinctive profile. Vane thickness (except for propeller blades) is primarily governed by strength calculation and manufacturing method (e.g. casting, milling, welding, forging, plastic injection) considerations.
In the case of axial propeller blades, flow profiles with a specified thickness distribution and camber dominate. (See also Strouhal number).
Slim profile shapes with the maximum thickness far behind the leading edge (laminar profiles) exhibit favourable characteristics with regard to the NPSHr value and the hydraulic efficiency at the pump's design point.
Thick profiles are less sensitive to approach flow under shock (see Shock loss).
Flow profiles are calculated using singularity methods (imposition of sinks, sources and vortices), for example, and, to an increasing extent, CFD (computational fluid dynamics) methods (see Aerofoil theory).
