Francis Turbine — Relative Pressure at Runner Inlet and Outlet In a reaction (Francis) turbine operating under design conditions, the static pressure at the runner inlet is typically __________ the static pressure at the runner outlet (draft tube entrance). Choose the correct relation.

Introduction:Francis turbines are mixed-flow reaction machines where a portion of the total head is converted to pressure rise/drop within stationary and rotating passages. Understanding how pressure changes across the runner is key to draft tube design and cavitation control.

Given Data / Assumptions:

• Properly designed guide vanes and runner; steady operation.
• Draft tube recovers kinetic energy by diffusion, so outlet pressure is near tailrace pressure.
• Total head drop occurs partly in guide vanes, runner, and draft tube.

Concept / Approach:In a Francis turbine, water enters the runner at a higher static pressure and leaves at a lower static pressure, having done work on the blades. The draft tube then gradually converts some kinetic energy to static pressure before discharge to the tailrace. Therefore, p_inlet > p_outlet across the runner.

Step-by-Step Solution:Across runner: energy is extracted, so pressure plus kinetic head decreases.At outlet: lower static pressure region exists before the draft tube restores part of the velocity head.Hence, static pressure at runner inlet is more than at runner outlet.

Verification / Alternative check:Velocity triangles and Euler’s turbine equation confirm energy transfer from fluid to runner and associated pressure drop.

Why Other Options Are Wrong:

• Less than: contradicts the reaction nature across the runner.

Common Pitfalls:Confusing conditions inside the runner with those at the draft tube exit; the draft tube increases static pressure relative to runner outlet but not above runner inlet.

Final Answer:more than