Micro-roughness Array Drag Modification
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Solution Overview
Problem
Existing methods for reducing skin friction drag on aerodynamic and hydrodynamic surfaces are not effective in high Reynolds number flows, and there is a need for improved surface designs that can either reduce or enhance skin friction drag and heat transfer rates.
Innovation Solution
A micro-array surface design featuring an array of roughness elements with transverse cavities and staggered peaks, which interact with the fluid boundary layer to delay transition and reduce skin friction drag, while also allowing for drag enhancement in applications requiring increased turbulent mixing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If conventional V-shaped riblets are applied to reduce skin friction drag, then the skin friction drag coefficient is reduced by approximately 6%, but the wetted area increases significantly
Solution Approach 1:
The surface is segmented into discrete roughness elements (ribs) with specific spacing and dimensions rather than using continuous riblet structures. This segmentation allows drag reduction while controlling the total wetted area increase.
Solution Approach 2:
The invention changes the geometric parameters of the surface texture from conventional V-shaped riblets to specifically dimensioned ribs with heights and spacing in the range of 10-20 wall units, optimizing the balance between drag reduction and wetted area increase.
2Object-generated harmful factors
If passive methods are used to control turbulent boundary layer flow, then drag reduction is achieved, but the methods are not effective in high Reynolds number flows
Solution Approach 1:
The roughness element dimensions are specifically scaled to wall units (10-20) which maintains effectiveness across different Reynolds numbers by normalizing the geometry to the viscous sublayer thickness, making the solution reliable for high Reynolds number flows.
3Object-generated harmful factors
If smaller V-shaped notches are introduced in the sides of larger V-shaped riblets, then skin friction drag is further reduced, but the manufacturing complexity increases
Solution Approach 1:
The invention extracts the essential drag-reducing function from complex multi-level riblet geometries and implements it through simpler, single-level ribs with optimized dimensions, maintaining effectiveness while reducing geometric complexity.
4Object-generated harmful factors
If the micro-array surface design is applied, then skin friction drag is significantly reduced approaching laminar flat plate levels, but the surface geometry becomes more complex
Solution Approach 1:
The surface uses systematically arranged ribs with specific dimensional parameters (height and spacing in 10-20 wall units) that achieve drag reduction comparable to laminar flow, balancing geometric complexity with performance.
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
The micro-array surface design achieves significant reduction in skin friction drag, potentially approaching that of a laminar flat plate boundary layer, and enhances heat transfer by optimizing turbulent boundary layer flow, with applications in various fluid dynamics and heat transfer scenarios.
Implementation Method 1
the interaction of the roughness elements with a boundary layer of fluid can act to delay transition to reduce the skin friction drag coefficient
Implementation Method 2
enhances heat transfer by optimizing turbulent boundary layer flow
Data Source
AI summary
The present invention is directed to a micro-array surface that provides for either drag reduction or enhancement. In one aspect, an aerodynamic or hydrodynamic wall surface that is configured to modify a fluid boundary layer on the surface comprises at least one array of roughness elements disposed on and extending therefrom the surface. In one example, the interaction of the roughness elements with a turbulent boundary layer of the fluid reduces the skin friction drag coefficient of the surface over an identical smooth surface without the roughness elements.