Twisted Polygonal Fan Guard Rods for Kármán Noise Reduction
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Solution Overview
Problem
Conventional protective devices for ventilation systems are heavy due to the need for numerous protective elements, which restricts air throughput and generates noise from vortex shedding, particularly at higher flow speeds, due to the formation of Karman vortices.
Innovation Solution
The use of elongate, twisted protective elements with a polygonal cross-section, such as triangular or star profiles, reduces the built-in mass and minimizes vortex detachment, thereby reducing noise and weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional protective elements are used to ensure safety, then protection functionality is maintained, but weight increases due to the high number of protective elements required
Solution Approach 1:
The protective device is segmented into multiple protective elements arranged concentrically around a center point. Each protective element is a separate component that can be individually optimized, allowing the use of lightweight twisted profiles while maintaining collective protective functionality through their arrangement and spacing.
Solution Approach 2:
The protective elements use composite structural design combining twisted geometric forms with polygonal cross-sections. This composite approach creates structures that achieve high strength-to-weight ratios, providing necessary protection while minimizing mass compared to conventional solid protective elements.
2Productivity
If flow velocity is increased to achieve high air throughput, then productivity improves, but noise increases due to Karman vortex shedding
Solution Approach 1:
The protective elements employ asymmetric twisted profiles with polygonal cross-sections rather than symmetric circular sections. This asymmetry disrupts the flow patterns that lead to regular Karman vortex shedding, reducing the periodic forces and associated noise while allowing high flow velocities for improved air throughput.
Solution Approach 2:
The twisted profiles incorporate curved surfaces and varying cross-sectional geometries along their length. These curved asymmetric surfaces modify the boundary layer flow and prevent the formation of stable vortex streets, reducing noise generation at high flow speeds while maintaining productivity.
3Reliability
If the number of protective elements is increased to ensure safety, then protection functionality is maintained, but device complexity increases
Solution Approach 1:
Each protective element is designed as a universal component with identical twisted profile geometry that serves multiple functions: providing physical protection, reducing vortex shedding through its asymmetric shape, and maintaining structural integrity. This universality simplifies the overall device complexity despite having multiple elements, as all elements follow the same design pattern.
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 achieves a significant weight reduction and noise reduction by minimizing Karman vortex shedding, enhancing air throughput while maintaining protective functionality.
Implementation Method 1
a vortex street can form on the downstream side of the protective element around which the flow occurs. According to its discoverer, it is called the Karman vortex street, which consists of two rows of vortices with opposite directions of rotation. Due to this alternating vortex shedding, the flow direction around the cylinder also changes periodically. These forces can cause the body in the flow to vibrate itself. Depending on the vortex shedding frequency, an audible tone can be produced
Data Source
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AI summary
The invention relates to a protective device (1), in particular for a ventilation system, comprising at least one protective element (3) that has an elongated, twisted profile (9) having a polygonal cross-section or is a round tube, wherein the geometric configuration of the protective element considerably reduces the installed mass, such that a weight reduction is achieved owing to saving of material.