Diffuser Endplate Propeller Cavitation Control
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Solution Overview
Problem
Current endplate propellers, particularly the contracted loaded tip (CLT) type, experience sheet cavitation phenomena at the outer sides of the endplate during rotation, leading to increased resistance, hull vibration, and noise, especially under inclined-shaft conditions.
Innovation Solution
A diffuser-type endplate propeller design is introduced, featuring a propeller hub and blades with endplates that have a leading edge and trailing edge, forming a cylindrical surface during rotation. The endplates have a specific angle of attack, which prevents sheet cavitation by managing the flow between high-pressure and low-pressure surfaces, reducing the likelihood of cavitation regardless of the propeller blade's position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a CLT propeller is used to prevent tip vortex and reduce blade load, then the probability of cavitation on the blade is reduced, but sheet cavitation occurs at the endplate outer-sides increasing resistance and causing hull vibration and noise
Solution Approach 1:
The endplate is designed with different geometric properties at different locations: the inner side near the blade root has a smaller radius while the outer side has a larger radius, creating a diffuser shape. This local variation in geometry optimizes flow characteristics at each location, preventing sheet cavitation at the outer side while maintaining the anti-vortex function near the blade.
Solution Approach 2:
The endplate employs a curved diffuser geometry rather than a straight or contracted shape. The cylindrical surface formed by the endplate outer side has a specific radius of curvature that diffuses the flow, reducing the adverse pressure gradient that causes sheet cavitation. The curved design allows smooth flow transition and prevents flow separation.
2Loss of energy
If the endplate is contracted to follow the blade-tip cylindrical surface, then viscous resistance is reduced, but sheet cavitation occurs at the endplate outer-sides under inclined-shaft conditions
Solution Approach 1:
The endplate is designed with a diffuser shape featuring a cylindrical outer surface with optimized radius of curvature. This curved geometry diffuses the flow at the endplate outer-sides, preventing the adverse pressure gradient that leads to sheet cavitation, while maintaining smooth flow attachment to minimize viscous resistance.
Solution Approach 2:
The endplate geometry parameters are specifically optimized: the outer side radius is larger than the inner side radius, creating a diffuser angle within a specific range. This parameter optimization balances the reduction of viscous resistance with the prevention of sheet cavitation under inclined-shaft operating conditions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The diffuser-type endplate propeller effectively eliminates sheet cavitation, enhancing propeller efficiency, reducing hull vibration, and minimizing noise, even under inclined-shaft conditions.
Implementation Method 1
sheet cavitation phenomenon is always produced at the outer-sides of the endplate
Implementation Method 2
there is a pressure difference existing between a high-pressure side-surface and a low-pressure side-surface of the propeller blade
Data Source
AI summary
A diffuser-type endplate propeller driving a hull and including a propeller hub and a plurality of blades is provided. The propeller hub has an axis of rotation and is connected to a transmission shaft of the hull. A blade has a blade-body and an endplate. The blade-body is connected to the propeller hub and extends outward from the propeller hub to the corresponding endplate, the endplate bends from the corresponding blade-body to extend towards a stern of the hull, and the endplate has a leading edge and a trailing edge. A cylindrical surface is imaginarily formed by the leading edges while the diffuser-type endplate propeller is rotated about the axis. Each of the endplates has a first tangent plane at the leading edge thereof, the cylindrical surface has a second tangent plane at the leading edge. An included angle is measured from the second tangent plane to the first tangent plane.