Flow Disruptors for Delaying Boundary Layer Transition

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Solution Overview

Problem

Boundary layer transition from laminar to turbulent flow leads to increased drag on aerodynamic surfaces, and existing technologies fail to effectively delay this transition in supersonic and hypersonic regimes, where different instability mechanisms dominate.

Innovation Solution

The use of flow disruptors, arranged perpendicular to the flow direction, generates modulations within the boundary layer with specific wavelengths to stabilize oblique first-mode instability waves in supersonic flows and planar/axisymmetric Mack-mode waves in hypersonic flows, delaying the laminar-to-turbulent transition by controlling the modulation wavelength.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If boundary layer transition is delayed to reduce drag, then aerodynamic efficiency is improved, but existing technologies fail to effectively delay transition in supersonic and hypersonic regimes where different instability mechanisms dominate

Engineering Contradiction:

Improveaerodynamic dragVSAvoideffectiveness of transition delay

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The patent applies parameter changes by modifying the wavelength of modulations introduced by flow disruptors to specifically target and stabilize different instability mechanisms (oblique first-mode waves in supersonic flow versus planar/axisymmetric Mack-mode waves in hypersonic flow). This parameter adjustment allows the same flow disruptor technology to be effective across different speed regimes by adapting the modulation characteristics to match the dominant instability wavelength at each regime.

Inventive Principle:

Principle #35Parameter changes

2Loss of energy

If flow disruptors are used to generate modulations to stabilize instability waves, then transition delay is achieved, but device complexity increases

Engineering Contradiction:

Improveaerodynamic dragVSAvoidflow disruptor configuration

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The patent employs segmentation by dividing the flow disruptor system into multiple discrete elements arranged in specific patterns across the boundary layer. These segmented disruptors generate modulations at controlled wavelengths that collectively stabilize the boundary layer against transition, distributing the complexity across multiple simple components rather than requiring a single complex device.

Inventive Principle:

Principle #1Segmentation

3Reliability

If modulation wavelength is controlled to be less than one-half of instability wave wavelength, then transition delay effectiveness is improved, but manufacturing precision requirements increase

Engineering Contradiction:

Improvetransition delay effectivenessVSAvoidmodulation wavelength control

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent establishes specific parameter ranges for modulation wavelength (less than one-half of the instability wave wavelength) that optimize transition delay effectiveness. By defining these parameter boundaries, the patent provides clear manufacturing specifications that balance performance requirements with achievable precision levels, ensuring reliable transition delay while maintaining practical manufacturability.

Inventive Principle:

Principle #35Parameter changes

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 significantly delays the boundary layer transition, reducing aerodynamic drag and leading to benefits such as increased range, reduced weight, lower emissions, and noise radiation, while being applicable to both low-sweep and highly-swept configurations.

Implementation Method 1

oblique first-mode instability waves present in the boundary layer and propagating at an oblique angle relative to the flow direction cause a laminar-to-turbulent transition in the boundary layer flow

Methodology Applied

Scientific EffectBoundary layer instability waves:

Implementation Method 2

The flow disruptors generate modulations within the boundary layer flow wherein the wavelength of the modulations is less than one-half of the wavelength of the instability waves

Methodology Applied

Scientific EffectFlow modulation:

Data Source

PatentUS10745112B2Method and system for delaying laminar-to-turbulent transition in high-speed boundary layer flow

Publication Date: 2020.08.18 UNITED STATES OF AMERICA AS REPRESENTED BY THE ADMINISTRATOR NAT AERONAUTICS & SPACE ADMINISTRATION

AI summary

A method and system delay the laminar-to-turbulent transition of a supersonic or hypersonic boundary layer flow moving in a flow direction over a surface. For supersonic boundary layer flow, oblique first-mode instability waves present in the boundary layer and propagating at an oblique angle relative to the flow direction cause a laminar-to-turbulent transition in the boundary layer flow. These instability waves have a wavelength associated therewith in a direction perpendicular to the flow direction. Flow disruptors are used to generate modulations within the boundary layer flow wherein a wavelength of the modulations along the direction perpendicular to the flow direction is less than one-half of the wavelength of the instability waves. For hypersonic boundary layer flow, the flow disruptors generate modulations within the boundary layer flow wherein the wavelength of the modulations is less than streak spacing for optimal transient growth or, equivalently, in the range of one to two times the boundary layer thickness.