For an outward-flow reaction turbine used in hydraulic power plants, identify the correct description of the water's path through the runner.

Introduction:
Reaction turbines are categorized by the direction of flow relative to the runner: radial (inward or outward), axial, and mixed. Understanding the flow path is essential to interpret velocity triangles, specific speed, and efficiency ranges.

Given Data / Assumptions:

• Outward-flow reaction turbine (historical designs; modern practice mostly uses inward/mixed).
• Steady incompressible flow; pressure drop occurs partly in the runner.

Concept / Approach:
In an outward-flow machine, water enters near the center (small radius) and moves to larger radii, gaining tangential momentum while experiencing pressure changes through guide and runner passages. This contrasts with inward-flow (e.g., Francis) where entry is near the periphery and exit near the center.

Step-by-Step Solution:
1) Guide vanes admit water toward the runner center.2) Runner blades turn the flow outward to larger radii.3) Energy conversion happens via change of absolute velocity components and pressure (reaction).4) Flow leaves near the outer periphery to the casing/draft path.

Verification / Alternative check:
Velocity triangles for outward-flow runners show increasing radius across the blade passage, consistent with the description.

Why Other Options Are Wrong:
Parallel to axis: that is axial flow (e.g., Kaplan).

Outer to center: describes inward-flow types.

Partly radial and partly axial: a mixed-flow description (e.g., Francis modern).

Tangential in/out only: an impulse idealization, not a reaction radial machine.

Common Pitfalls:
Confusing outward- with inward-flow terminology used in many standard textbooks.

Final Answer:
the water enters at the centre of the wheel and then flows towards the outer periphery of the wheel