Variable-Profile Riblets for Turbulent Flow Noise Reduction
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Solution Overview
Problem
Turbulent flow-induced noise in fluid dynamic structures, such as airfoils and wind turbine blades, poses significant challenges due to the interaction of energetic eddies with these surfaces, leading to high noise levels that affect stealth capabilities and public acceptance, particularly in military and renewable energy applications.
Innovation Solution
The implementation of microstructures with varying profiles and surface textures on the surface of fluid dynamic structures, such as riblets with different channel spacings, heights, and taper angles, which alter the scales of turbulent eddies to reduce noise spectra.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If microstructures with varying profiles are implemented on the surface, then noise reduction is improved, but device complexity increases
Solution Approach 1:
The patent applies local quality by implementing microstructures with varying profiles (different heights, spacings, and shapes) at different locations along the surface. The microstructures transition from a first profile near the leading edge to a second profile toward the trailing edge, allowing each local region to optimize noise reduction for its specific position in the turbulent boundary layer while maintaining overall system functionality.
Solution Approach 2:
The patent employs parameter changes by systematically varying key microstructure parameters including height, spacing, profile shape, and orientation along the surface. These parameter variations are designed to interact with different scales of turbulent eddies at various positions, creating a gradient structure that broadens the noise reduction effectiveness across different frequencies without requiring a completely new device architecture.
2Object-affected harmful factors
If microstructures alter turbulent eddy scales, then noise spectra reduction is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent utilizes parameter changes by defining specific ranges for microstructure dimensions (height, spacing, profile) and allowing variations within these ranges. The invention specifies that microstructures should have heights between certain fractions of the boundary layer thickness and spacings within particular ratios, providing manufacturing tolerances that balance noise reduction effectiveness with achievable precision levels.
Solution Approach 2:
The patent applies local quality by allowing different microstructure parameters at different locations along the surface. Rather than requiring uniform precision across the entire surface, the invention permits local variations in height, spacing, and profile that are optimized for each region's specific turbulent flow characteristics, reducing overall manufacturing precision requirements while maintaining noise reduction effectiveness.
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 approach effectively reduces noise levels across a wide frequency range, particularly between 0 Hz to 5000 Hz, by optimizing the non-dimensional spacing and height ratios of riblets, leading to improved noise reduction compared to conventional methods, enhancing the stealth capabilities of vehicles and the acceptance of wind turbines.
Implementation Method 1
turbulence or turbulent flow is a fluid regime characterized by chaotic, stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time.
Implementation Method 2
boundary layer noise, i.e, the interaction of turbulence in the boundary layers of the wind turbine blades with the airfoil surface, is one of the primary sources of wind turbine noise.
Data Source
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AI summary
A fluid dynamic structure 10 includes a surface 14 and a microstructure 12 mounted on the surface. The microstructure 12 is defmed by a plurality of peaks and valleys (i.e., riblets) and includes a transition region in which each peak and valley changes from a first profile to a second profile along a chord length of the structure. The peaks and/or valleys may have a variable dimension along the length of the microstructure 12. The peaks and valleys can be non-linear along the chord length and have a smooth transition from the first profile to the second profile. The different profiles of the microstructure 12 are optimized to reduce noise generated by turbulent fluid flow across the structure 10.