Bicycle Rim Asymmetric Protrusions Aerodynamic Drag Reduction
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Solution Overview
Problem
Traditional bicycle wheel rims experience aerodynamic issues due to their cross-sectional shapes, leading to increased drag and handling problems when cycling, particularly at non-zero yaw angles, which affect the bicycle's controllability and performance.
Innovation Solution
The design incorporates asymmetric protrusions along the inner circumference of the rim, which are tubercle-shaped and asymmetrically formed to alter airflow patterns, reducing drag and transverse forces by creating stream-wise vortices and optimizing Strouhal Number for improved aerodynamics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traditional cross-sectional shapes of bicycle wheel rims are used, then manufacturing is simple, but aerodynamic drag is large at zero yaw angle
Solution Approach 1:
The patent applies asymmetry by forming protrusions on the inner circumference of the rim that are asymmetric with respect to the radial centerline of the rim. This asymmetric geometry alters the airflow pattern around the wheel, creating stream-wise vortices that reduce pressure drag while maintaining a relatively simple manufacturing process suitable for fiber reinforced plastic composite rims.
2Ease of manufacture
If traditional rim shapes are used, then manufacturing is simple, but flow detachment occurs at certain wind yaw angles causing handling issues
Solution Approach 1:
The asymmetric protrusions are positioned at specific locations on the inner circumference of the rim, creating a non-uniform surface geometry that delays flow detachment at transverse wind yaw angles. This asymmetric configuration generates beneficial vortex structures that maintain attached flow over a wider range of yaw angles, improving bicycle handling stability without complicating the manufacturing process.
Solution Approach 2:
The protrusions formed on the inner circumference of the rim introduce curved surface features that alter the airflow trajectory. These curved geometries promote the formation of stream-wise vortices that help maintain attached flow conditions at higher yaw angles, delaying flow separation and improving handling characteristics.
3Object-affected harmful factors
If asymmetric protrusions are added to the rim, then aerodynamic drag is reduced and stall angle is enhanced, but manufacturing complexity increases
Solution Approach 1:
The patent applies local quality by forming protrusions only on the inner circumference of the rim at specific locations, rather than modifying the entire rim structure. This localized modification creates the necessary asymmetric geometry for aerodynamic benefit while minimizing the overall structural complexity and maintaining compatibility with existing manufacturing processes for fiber reinforced plastic composite rims.
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 results in a 10% reduction in drag forces compared to rims without protrusions and enhances the stall angle, leading to better aerodynamic performance and handling characteristics.
Implementation Method 1
traditional cross-sectional shapes of bicycle wheel rims may cause a large amount of drag on the wheel when moving in a straight forward direction
Implementation Method 2
Airflow across bicycle rims at transverse angles is believed to result in a loss of attached flow around the wheel at certain wind yaw angles
Implementation Method 3
alter airflow patterns, reducing drag and transverse forces by creating stream-wise vortices
Data Source
Figure 1
Figure 2
Figure 3A
AI summary
A rim (210) for a bicycle wheel includes a radially outer tire-engaging portion (214), a first side-wall, and a second sidewall spaced apart from the first sidewall. The first and second sidewalls may extend radially inward of the radially outer tire-engaging portion. The rim includes a radially inner portion having at least one asymmetric protrusion (220).