Surface Thermal Flow Sensor With Third-Harmonic Detection
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Solution Overview
Problem
Conventional thermal flow sensors are not robust for flight tests due to damage risks from adverse conditions and require complex installation, limiting their use in aviation and providing restricted information with high effort.
Innovation Solution
A method and system using a thermal flow sensor with a heating element that modulates current at specific frequencies to emit thermal waves, measuring voltage amplitudes at the third harmonic to determine fluid flow properties, allowing for rapid data analysis and differentiation between laminar and turbulent flows.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional thermal flow sensors (hot-wire or surface hot-film sensors) are used, then flow velocity measurement is achieved, but the sensors are damaged due to adverse ambient conditions like rain, snow, dust
Solution Approach 1:
The patent replaces conventional mechanical/thermal sensors (hot-wire, hot-film) with a thermal camera-based optical measurement system. The thermal camera captures temperature fields and flow information optically, eliminating direct physical contact with the fluid and protecting the sensor from adverse ambient conditions like rain, snow, and dust while maintaining flow velocity measurement capability.
Solution Approach 2:
The patent introduces a thermal camera as an intermediary device that indirectly measures flow properties through temperature field visualization. Instead of the sensor directly interacting with the fluid, the thermal camera captures thermal information that reflects flow characteristics, serving as a mediator between the measurement system and the fluid environment.
2Loss of information
If thermal camera is used for detection, then flow visualization is achieved, but flight test conditions are restricted to sunshine only
Solution Approach 1:
The patent changes the operational parameters of the thermal camera system by using active thermal excitation (heating elements or laser sources) to generate detectable thermal signals. This allows the system to operate independently of ambient sunlight conditions, as the thermal signal is actively generated rather than passively captured from environmental heat sources, enabling operation in various weather conditions including rain, snow, and dust.
3Loss of information
If hundreds of flow cones are installed for visualization, then flow detachment regions are detected, but installation effort and time consumption increase significantly
Solution Approach 1:
The patent extracts the flow detection function from multiple discrete flow cones and consolidates it into a single thermal camera system. The thermal camera captures temperature field information across the entire surface, eliminating the need for installing hundreds of individual flow cones while maintaining the ability to detect flow detachment regions through thermal visualization.
Solution Approach 2:
The thermal camera serves multiple functions simultaneously: it visualizes flow detachment regions, measures flow velocity, and provides temperature field data all through a single device. This multi-functional capability replaces the need for multiple specialized sensors (flow cones, hot-wires, hot-films) that would otherwise be required to achieve comprehensive flow measurement.
4Measurement precision
If thermal flow sensors are used for flight tests, then flow properties are measured, but system installation and calibration requirements become very complex
Solution Approach 1:
The patent replaces complex mechanical sensor installation (hot-wire, hot-film) with a simpler thermal camera system that can be mounted externally on the aircraft surface. The thermal camera captures temperature fields optically, eliminating the need for complex calibration procedures and intricate sensor installation that characterize conventional thermal flow measurement systems.
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 provides robust, efficient detection of fluid flow characteristics with reduced installation effort, enabling real-time monitoring and improved data processing for flight conditions.
Implementation Method 1
emitting a thermal wave into the fluid flowing along the surface having a penetration depth inversely proportional to the modulation frequency
Implementation Method 2
modulating the current through a heating element of a thermal flow sensor
Implementation Method 3
penetration depth inversely proportional to the modulation frequency
Data Source
AI summary
A method for determining flow properties of a fluid flowing along a surface by: modulating the current through a heating element of a thermal flow sensor located on the surface with at least one modulation frequency, thereby emitting a thermal wave into the fluid flowing along the surface having a penetration depth inversely proportional to the modulation frequency; measuring an amplitude of a voltage across the heating element at the third harmonic of the at least one modulation frequency, the voltage depending on the thermal conductivity and the volumetric heat capacity of the fluid flowing along the surface; determining a flow velocity at the penetration depth from the attenuation value of the determined amplitude of the voltage; and estimating whether the flow at the penetration depth is laminar or turbulent on the basis of the determined flow velocity. Also, a system and an aircraft with such a system.