Perforated Drag-Reduction Surfaces With Stable Entrapped Fluid Slip
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Solution Overview
Problem
Existing methods for reducing fluid dynamic drag on vehicles, such as ships and aircraft, face challenges with gas film collapse under pressure, gas diffusion, and limitations to specific fluid types, requiring complex microstructures and materials that are not versatile or efficient in maintaining drag reduction.
Innovation Solution
A method involving a perforated surface that traps a gas or liquid next to the surface using independently sized and located pores, allowing for rapid re-initialization and stabilization of the gas film, and can operate with various fluid types, including liquid-liquid and gas-gas interfaces, without the need for hydrophobic materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If superhydrophobic surfaces with microtextured features are used to trap gas film, then fluid dynamic drag is reduced, but the gas film collapses under increased pressure
Solution Approach 1:
The invention changes the physical state of the trapped fluid from gas to liquid, and modifies the surface properties from superhydrophobic to hydrophilic or neutral. The liquid-infused porous structure maintains stability under pressure by using a liquid that remains confined within the porous matrix, preventing the collapse that occurs with gas films under pressure.
Solution Approach 2:
The invention uses porous materials as the substrate surface, which allows for the infusion and confinement of liquid. The porous structure provides a large surface area and capillary forces that hold the liquid in place, creating a stable liquid-infused layer that reduces drag while maintaining reliability under varying pressure conditions.
2Force
If microtextured features are used to create superhydrophobic effect, then gas film is trapped, but the features require close spacing to maintain the gas layer
Solution Approach 1:
The invention uses porous materials with controlled pore sizes and distributions that can be optimized for drag reduction without requiring extremely close spacing of features. The porous structure inherently provides the necessary surface area and fluid confinement properties through its interconnected void spaces.
Solution Approach 2:
By changing from gas trapping to liquid infusion, the invention allows for larger characteristic length scales in the surface structure. The liquid-infused porous surface achieves drag reduction through a different mechanism that does not require the same degree of feature confinement, allowing for more practical feature spacing.
3Reliability
If superhydrophobic surfaces are used, then gas film is stabilized, but the method is slow requiring 150 sec to re-initialize the entire gas film
Solution Approach 1:
The invention changes from gas film to liquid infusion, where the liquid can be rapidly replenished through the porous structure. The liquid-infused surface can be quickly re-initialized by simply allowing liquid to wick into the porous material, which occurs much faster than the 150 seconds required for gas film re-establishment through electrolysis.
Solution Approach 2:
The liquid-infused porous surface can self-replenish the liquid phase through capillary action and gravity-driven flow into the porous structure. This self-service mechanism allows for rapid recovery without requiring external energy input or complex re-initialization systems, significantly reducing the time required to restore the drag-reducing surface condition.
4Reliability
If pneumatic support is used to stabilize air film, then gas interface is stabilized under high hydrodynamic pressure, but only high-density porous hydrophobic materials can be used
Solution Approach 1:
The invention changes from using gas (air) to using liquid as the trapped phase, and from hydrophobic to hydrophilic or neutral surface properties. This allows the use of a wide variety of porous materials including metals, ceramics, polymers, and composites, without being restricted to high-density hydrophobic materials. The liquid infusion mechanism works with diverse material properties.
Solution Approach 2:
The liquid-infused porous surface approach is universally applicable to many different porous materials and fluid combinations. The same basic mechanism can be used with various liquids (water, oils, other fluids) and various porous substrates, providing a versatile drag reduction system that is not limited to specific material types as in the pneumatic support approach.
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 solution effectively reduces fluid shear and flow resistance by introducing an apparent slip effect, enabling rapid drag reduction and maintaining stability under pressure variations, applicable to a wide range of fluid types and flow conditions.
Implementation Method 1
A gas supply channel provides gas to form bubbles in the pores on an outer surface of the perforated material. The bubbles effectively replace the solid material that would be at the surface with gas in contact with the flowing liquid, reducing the flow resistance experienced by the liquid.
Implementation Method 2
The present invention provides a simple method for reducing fluid dynamic drag on vehicles by altering the surface to introduce an apparent fluid slip on the surface that reduces the fluid shear and associated flow resistance developed at the vehicle surface.
Data Source
AI summary
A reduced drag surface involves a perforated or porous surface exposed to a flowing fluid and a slip interface disposed between the surface and the flowing fluid, wherein the slip interface is formed from an entrapped fluid trapped at the surface. A method for modifying a drag coefficient on a reduced drag surface involves the steps of supplying a fluid to a perforated or porous surface exposed to a flowing fluid, wherein the surface traps the fluid at the surface to form an entrapped fluid and forming a slip interface between the surface and the flowing fluid, wherein the slip interface is formed from the entrapped fluid. An apparatus for a reduced drag surface includes the reduced drag surface described above and a source of fluid fluidically coupled to the surface such that the source supplied fluid to the surface to form the entrapped fluid.