Understanding and Calculating Axial Force in Turbomachinery Rotors

Axial force in turbomachinery rotors is a critical factor affecting the design, operation, and longevity of turbines and compressors. It results from pressure differences across the rotor blades and influences bearing loads and rotor stability. Understanding how to calculate this force is essential for engineers working in the field of turbomachinery.

What is Axial Force in Turbomachinery?

Axial force, also known as thrust, is the force exerted along the axis of the rotor. It arises mainly due to pressure differences between the inlet and outlet of the rotor. This force can cause axial displacement of the rotor, which must be managed to prevent mechanical failure or excessive wear.

Factors Influencing Axial Force

The magnitude of axial force depends on several factors, including the pressure ratio, blade geometry, and flow conditions. Higher pressure differences typically lead to increased axial forces. Blade angles and rotor speed also play significant roles in determining the resulting force.

Calculating Axial Force

The basic formula for axial force (F_a) involves the pressure difference and the cross-sectional area of the rotor:

F_a = (P_in – P_out) × A

Where:

• P_in = Inlet pressure
• P_out = Outlet pressure
• A = Cross-sectional area of the rotor

More advanced calculations may incorporate flow velocity, blade angles, and other aerodynamic factors to refine the force estimation.