Small Duct Propeller with Decreasing Pitch for Cavitation Control
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Solution Overview
Problem
Existing propeller systems with intermediate ducts suffer from weak interference with the propeller, leading to inefficient performance in high propeller loading conditions and cavitation issues, while large ducted propellers face challenges with cavitation erosion and size limitations.
Innovation Solution
A propeller system with a small duct positioned close to the propeller, featuring a decreasing pitch that maximizes at the blade root and minimizes at the blade tip, and a duct diameter between 20% to 50% of the propeller diameter, optimizing load distribution and reducing cavitation through enhanced suction effects and interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a large duct is used to cover the propeller (ducted propeller), then propulsive efficiency is enhanced through large interference between duct and propeller, but cavitation erosion occurs on the inner duct surface and the system becomes too large for practical application
Solution Approach 1:
The patent applies local quality by creating a duct with non-uniform cross-sectional shape that is convex inward, with different curvature radii at different locations. The duct has a larger curvature radius at the upstream side and a smaller curvature radius at the downstream side, optimizing local flow characteristics to enhance propulsive efficiency while preventing cavitation erosion at critical locations.
Solution Approach 2:
The patent employs asymmetry by designing a duct cross-section that is asymmetric with respect to the duct axis. The asymmetric configuration, with different curvature radii on upstream and downstream sides, creates optimized flow distribution that enhances the propulsor performance while avoiding the cavitation problems associated with symmetric large-duct designs.
2Object-affected harmful factors
If an intermediate duct with diameter slightly smaller than propeller is used, then cavitation erosion is reduced, but interference between duct and propeller becomes weak and propulsive efficiency is not significantly enhanced
Solution Approach 1:
The patent overcomes the weakness of intermediate ducts by introducing local quality variations through the convex inward cross-sectional shape with different curvature radii. This localized optimization at different duct positions creates sufficient interference between the duct and propeller to enhance propulsive efficiency, while maintaining a duct diameter smaller than the propeller to avoid cavitation erosion.
Solution Approach 2:
The patent changes geometric parameters of the duct, specifically the curvature radii at different locations and the asymmetric cross-sectional shape. By optimizing these parameters, the duct achieves an optimal balance between creating sufficient interference for enhanced propulsive efficiency and maintaining a size that prevents cavitation erosion.
3Weight of moving object
If duct diameter is reduced to minimize frictional resistance and weight, then frictional resistance and weight are reduced, but interference with propeller becomes too weak to provide significant propulsive benefit
Solution Approach 1:
The patent resolves this contradiction by applying local quality principles - the duct has a smaller overall diameter to reduce weight and frictional resistance, but features localized convex inward cross-sectional shapes with optimized curvature radii that create concentrated interference zones. These localized features provide sufficient propulsive benefit despite the reduced overall duct size.
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
This configuration enhances propulsive efficiency by reducing cavitation, minimizing frictional resistance, noise, and weight, while allowing for a compact and cost-effective design suitable for various ship sizes, including large vessels.
Implementation Method 1
suppress cavitation in an actual sea where a propeller loading is increased
Implementation Method 2
enhance the suction effect at the center portion of the propeller
Data Source
Figure 1
Figure 2(a)~2(b)
Figure 3(a)~3(c)
AI summary
A propeller (10) setting a small duct (20) of the present invention includes a propeller (10) and a duct (20). A diameter Ddin of the duct is set to 20% or more and 50% or less of a diameter Dp of the propeller (10), and a pitch H of the propeller (10) is a decreasing pitch which reduces in a radial direction of the propeller (10), and which becomes a maximum value at a blade root of the propeller (10) and becomes a minimum value at a blade tip of the propeller (10). The small duct (20) is placed in front of and close to the propeller (10). According to this, in an actual sea, cavitation is suppressed, and a load distribution of the propeller (10) in its radial direction which governs efficiency is optimized by utilizing interference with respect to the small duct (20).