Axial Propeller Blade Sharpening for Viscous Drag Reduction
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Solution Overview
Problem
Existing axially acting propellers experience higher power losses during rotation in viscous media due to unstreamlined trailing edges, leading to increased energy consumption for stirring processes.
Innovation Solution
The propeller blades are sharpened only on the outer half or two-thirds of the outlet side, with optional sharpening on the inlet side, reducing rotational resistance and improving the thrust-to-power ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If propeller blades have constant or almost constant plate thickness, then manufacturing is simpler, but power losses at the trailing edge increase during rotation in viscous media
Solution Approach 1:
The blade thickness is varied locally along the span: the root portion maintains constant thickness for manufacturing simplicity, while the outer portion (at least 20%, preferably 30-50% of blade length) is thinned to create a sharpened trailing edge. This local modification reduces wake turbulence and power losses without complicating the overall manufacturing process.
2Loss of energy
If propeller blades are profiled, then power losses during rotation are reduced, but manufacturing complexity increases significantly
Solution Approach 1:
Instead of profileing the entire blade which complicates manufacturing, only the trailing edge of the outer portion of the blade is thinned. This localized modification provides the hydrodynamic benefits of profiled blades (reduced wake turbulence, lower power losses) while maintaining the manufacturing simplicity of constant-thickness sheet metal construction for the majority of the blade.
3Productivity
If more energy is expended to rotate the propeller through viscous medium at constant high speed, then stirring performance is maintained, but energy consumption increases
Solution Approach 1:
The blade thickness parameter is changed in the outer portion of the blade, creating a tapered or thinned trailing edge. This parameter modification reduces the resistance to rotation in viscous media, allowing the propeller to maintain its stirring performance at lower power consumption, or achieve improved stirring results with the same energy input.
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 design reduces energy consumption while maintaining or improving stirring efficiency, specifically by minimizing power losses through optimized blade sharpening angles and construction.
Implementation Method 1
flows and turbulence occur not only on the inlet side but also on the outlet side (the rear side) of the blades due to the lack of streamlining, which cause rotational resistance and thus loss of performance
Implementation Method 2
flows and turbulence occur not only on the inlet side but also on the outlet side (the rear side) of the blades due to the lack of streamlining
Implementation Method 3
By sharpening, i.e. beveling, a reduction in power losses and thus an improved thrust/power ratio during rotation was achieved
Data Source
Figure 1
Figure 1a
Figure 2
AI summary
The present invention relates to an axially operating stirring element, preferably a propeller (1) manufactured from sheet metal, comprising propeller blades (3) that are arranged radially around an axis (A). In said element there is at least one propeller blade that has a sharpened edge on the discharge side (5).