Why does a reaction steam turbine need a thrust bearing?

In a reaction steam turbine, a thrust bearing is necessary to manage the axial forces generated during operation. Unlike impulse turbines, where pressure remains constant across the rotor blades, a reaction stage involves a significant pressure drop across both the stationary and rotating passages.1

This pressure drop creates a net force in the tangential direction, which drives the rotation of the wheel, but it also exerts a force in the axial direction. This axial load tends to push the rotor toward the ends of the turbine casing. The thrust bearing is required to absorb this axial load and maintain the rotor's position. In large-scale turbines, engineers may mitigate this effect by admitting steam in the middle of the unit and allowing it to expand in both axial directions, which helps balance the forces.1