There will be no whirl component of velocity at the entry to the impeller in the centrifugal pump.

Characteristics of a Centrifugal Pump

The figure shows an impeller of a centrifugal pump with velocity triangles drawn at the inlet and outlet. The blades are curved between the inlet and outlet radius. A particle of fluid moves along the broken curve shown in the figure. Hence fluid moves along the blade and is not normal to the blade.

The impeller blades are considered to have a smooth surface finish to avoid losses due to skin friction. Hence fluid is considered to have negligible friction while flowing inside the pump.

As the impeller rotates, the fluid is drawn into the blade passage at the impeller's eye, the center of the impeller. The inlet pipe is axial and a centrifugal pump rarely has any sort of guide vanes at the inlet.

Therefore the fluid approaches the impeller without appreciable whirl and so the inlet angle of the blades is designed to produce a right-angled velocity triangle at the inlet as shown in the figure.