Raised Wing Structure for Crossflow Drag Reduction
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Solution Overview
Problem
Existing technologies fail to effectively reduce frictional drag caused by crossflow instability in sweepback wings, as they either promote turbulence transition or have limited suppression effects due to the shape and arrangement of discrete roughness elements.
Innovation Solution
A raised structure with a sinusoidal shape and bell-shaped envelope is implemented on the wing's surface, featuring unit ridges that increase in height along a convex curve, arranged periodically to selectively excite specific wavenumber disturbances, thereby reducing frictional drag by shifting the turbulence transition location downstream.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If discrete roughness elements are provided to suppress crossflow instability, then frictional drag can be reduced, but the arrangement and shape must be precisely controlled to avoid promoting turbulence transition
Solution Approach 1:
The invention changes the geometric parameters of the roughness elements, specifically using a sine curve cross-section in the spanwise direction and Gaussian distribution in the chord direction. This parameter optimization allows the elements to suppress crossflow instability while avoiding premature turbulence transition, resolving the contradiction between drag reduction and manufacturing precision requirements
Solution Approach 2:
The invention applies different shape characteristics to different directions: sine curve shape in the spanwise direction for instability suppression and Gaussian distribution in the chord direction for controlled turbulence transition. This local quality differentiation enables effective drag reduction without requiring extremely precise control of the entire element geometry
2Stability of the object's composition
If projections extend long in the chord direction to form stable turbulent boundary layer, then boundary layer stability is improved, but frictional drag increases due to promoted turbulence transition
Solution Approach 1:
The invention optimizes the chord direction distribution using Gaussian function, which concentrates the roughness effect near the leading edge where crossflow instability originates. This parameter change allows boundary layer stabilization without extending projections far in the chord direction, thereby avoiding excessive frictional drag
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 frictional drag by suppressing turbulence transition, extending the laminar flow region and minimizing drag, with the maximum height of the ridges optimized to prevent premature turbulence, achieving a significant reduction in crossflow instability-induced drag.
Implementation Method 1
crossflow instability induced by the sweptback wing configuration
Implementation Method 2
turbulence transition induced by the crossflow instability
Data Source
AI summary
A raised structure for reducing frictional drag due to viscosity of a flow toward an object in a direction defining an acute angle with a leading edge of the object. The raised structure includes raised bodies configured to be provided on a surface of the object at the leading edge on a downstream side of a stagnation point of the flow. A height of each raised body changes along a convex curve, and the raised bodies are arranged in an array to define a first uneven shape changing periodically in a first cross section configured to have a constant distance from the stagnation point and be orthogonal to the surface, and a second uneven shape changing in a second cross section configured to be orthogonal to a line composed of the stagnation point and the first cross section, the second uneven shape having concave and convex portions that change periodically.