Diffuser-Type Endplate Propeller Cavitation Control
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Solution Overview
Problem
Current propeller designs, such as the contracted loaded tip (CLT) propeller, experience sheet cavitation phenomena at the endplate under inclined-shaft conditions, leading to increased resistance, vibration, and noise, which are detrimental to low-vibration and low-noise ship designs.
Innovation Solution
A diffuser-type endplate propeller design is introduced, where the endplate is shaped to prevent sheet cavitation by maintaining a negative angle of attack, reducing the likelihood of water flow from the high-pressure side to the low-pressure side, and optimizing the leading and trailing edge distances to minimize cavitation occurrence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a CLT propeller is used to prevent tip vortex and reduce blade load, then the load of blade-tips is suppressed, but sheet cavitation occurs at the endplate under inclined-shaft conditions, increasing resistance and vibration
Solution Approach 1:
The endplate is designed with a diffuser shape where the trailing edge radius is greater than the leading edge radius, inverting the conventional CLT approach. This reverse geometry creates a negative angle of attack that prevents cavitation by directing flow away from the endplate outer surface, while still maintaining tip vortex suppression through the endplate's presence
Solution Approach 2:
The invention changes the geometric parameters of the endplate by defining specific radius relationships (trailing edge radius > leading edge radius) and angle of attack conditions (negative angle). These parameter changes transform the endplate from a cavitation-prone structure to a cavitation-resistant diffuser that maintains aerodynamic efficiency
2Loss of energy
If the endplate is contracted (CLT design) to follow the blade-tip cylindrical surface, then viscous resistance is reduced, but sheet cavitation is generated at the outer-sides of the endplate, reducing propeller efficiency
Solution Approach 1:
Instead of contracting the endplate to follow the blade-tip cylindrical surface, the invention inverts the approach by designing the endplate to diffuse outward (trailing edge radius > leading edge radius). This creates a negative angle of attack that eliminates the adverse pressure gradient causing cavitation, thereby maintaining propeller efficiency while still reducing viscous resistance through streamlined geometry
3Adaptability or versatility
If a CLT propeller is applied to an inclined-shaft hull, then the propeller can be installed on speedboats, but severe sheet cavitation occurs at the endplate when the blade turns to the upper-vertical position, increasing noise and vibration
Solution Approach 1:
The invention changes the operational parameters by maintaining a negative angle of attack throughout the rotation cycle through the diffuser geometry. This parameter change ensures that even when the blade turns to the upper-vertical position in inclined-shaft installations, the flow remains attached to the endplate surface, eliminating severe sheet cavitation and its associated noise and vibration
Solution Approach 2:
The diffuser-type endplate inverts the conventional design by having the trailing edge extend further than the leading edge, creating a geometry that works advantageously under inclined-shaft conditions. This inverted shape maintains favorable pressure gradients throughout the rotation cycle, preventing cavitation-related noise and vibration while preserving inclined-shaft installation capability
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 or significantly reduces sheet cavitation, enhancing propeller efficiency, reducing hull vibration and noise, and maintaining performance across various propeller blade positions.
Implementation Method 1
when a propeller blade rotates, there is a pressure difference existing between a high-pressure side-surface and a low-pressure side-surface of the propeller blade, and the pressure difference forms a thrust to make the ship proceed on the water surface
Implementation Method 2
the diffuser-type endplate propeller effectively eliminates or significantly reduces sheet cavitation
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A diffuser-type endplate propeller (100) driving a hull (20) and including a propeller hub (110) a plurality of blades (120) is provided. The propeller hub (110) has an axis (L) of rotation and is connected to a transmission shaft (22) of the hull (20). The blade (120) has a blade-body (122) and an endplate (124). The blade-body (122) is connected to the propeller hub (110) and extends outward from the propeller hub (110) to the corresponding endplate (124), the endplate (124) bends from the corresponding blade-body (122) to extend towards a stern (24) of the hull (20), and the endplate (124) has a leading edge (124a) and a trailing edge (124b). A cylindrical surface (S1) is imaginarily formed by the leading edges (124a) while the diffuser-type endplate propeller (100) is rotated about the axis (L). Each of the endplates (124) has a first tangent plane (C1) at the leading edge (124a) thereof, the cylindrical surface (S1) has a second tangent plane (C2) at the leading edge (124a). An included angle (α) is measured from the second tangent plane (C2) to the first tangent plane (C1).