What specific blade characteristic adjustment maximizes axial flow turbine efficiency under consistently decreasing tidal flow velocity?

To maximize axial flow turbine efficiency under consistently decreasing tidal flow velocity, the blade pitch angle must be continuously adjusted to maintain an optimal angle of attack. The blade pitch angle refers to the angle at which the turbine blade meets the incoming water flow. The angle of attack is the angle between the blade's chord line (an imaginary line from the leading edge to the trailing edge of the blade) and the relative water flow direction. As the tidal flow decreases, the blade pitch angle should be decreased proportionally. This maintains the optimal angle of attack, ensuring the blades continue to extract the maximum possible energy from the slower moving water. Maintaining the optimal angle of attack is essential because it directly impacts the lift-to-drag ratio of the blade. Lift is the force that causes the turbine to rotate, while drag is the force that resists rotation. A properly adjusted pitch angle ensures that the lift force is maximized relative to the drag force, resulting in higher turbine efficiency. Failing to adjust the blade pitch will cause the angle of attack to become suboptimal, leading to flow separation and reduced lift, which significantly decreases the turbine's power output and overall efficiency. For example, if the tidal current slows significantly, and the blade pitch remains fixed, the angle of attack will become too large, causing the water flow to stall on the blade surface. This stall reduces lift and increases drag, dramatically decreasing energy extraction. Therefore, continuous pitch adjustment is vital for maintaining optimal performance during fluctuating tidal conditions.