Shape of the Velocity Triangle at the Exit of a Radial Bladed Centrifugal Impeller

The velocity triangle is a graphical representation that helps in understanding the velocity components and their directions in a fluid flow. It is commonly used in turbomachinery analysis to analyze the flow conditions at different stages of the machine.

In the case of a radial bladed centrifugal impeller, the flow enters the impeller radially and is accelerated in the radial direction due to the centrifugal force exerted by the rotating impeller. At the exit of the impeller, the flow is redirected axially by the stationary diffuser vanes.

Effect of Slip
Slip is a phenomenon that occurs in centrifugal compressors and pumps due to the non-ideal behavior of the fluid. It causes a decrease in the actual exit velocity of the fluid compared to the ideal exit velocity predicted by the velocity triangle assuming no slip. Slip is mainly caused by the friction and viscous effects in the impeller.

Velocity Triangle at the Exit
The velocity triangle at the exit of a radial bladed centrifugal impeller can be represented as follows:

1. Inlet Velocity (V1): The flow enters the impeller radially, so the inlet velocity (V1) is purely radial.

2. Blade Velocity (Vb): The impeller blades impart a tangential velocity to the fluid due to the rotation of the impeller. This tangential velocity is known as the blade velocity (Vb).

3. Relative Velocity (Vr2): The relative velocity (Vr2) represents the vector sum of the inlet velocity (V1) and the blade velocity (Vb). It is the velocity of the fluid relative to the moving blades.

4. Absolute Velocity (V2): The absolute velocity (V2) represents the velocity of the fluid with respect to a stationary reference frame. It is the resultant vector of the relative velocity (Vr2) and the circumferential velocity of the impeller.

5. Outlet Velocity (V3): The outlet velocity (V3) is the actual velocity of the fluid at the exit of the impeller. Due to slip, the outlet velocity (V3) is lower than the ideal exit velocity predicted by the velocity triangle assuming no slip.

Shape of the Velocity Triangle
Considering slip, the velocity triangle at the exit of a radial bladed centrifugal impeller will have one angle greater than 90 degrees. This is because the outlet velocity (V3) is lower than the ideal exit velocity, causing a decrease in the magnitude of the resultant vector of the relative velocity (Vr2) and the circumferential velocity of the impeller.

Therefore, option D, "One angle greater than 90," is the correct answer.