Method and System for Determining Flow Properties of a Fluid Flowing Along a Surface

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This invention describes a method and system for determining the flow properties of fluids (such as air) flowing along a surface, especially for applications like aircraft wings. The system uses a thermal flow sensor with a heating element applied to the surface. By modulating the current in the heating element at specific frequencies and analyzing the resulting thermal waves and voltages, it can measure flow velocity and determine if the flow is laminar or turbulent, as well as identify the transition point between these flow states. This approach allows for real-time, robust, and detailed flow analysis without the need for bulky and fragile traditional sensors or complex data processing.

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• Real-time monitoring of airflow over aircraft wings or other surfaces to detect stall conditions or optimize flight control.
• Wind tunnel testing and aerodynamic research to precisely map laminar-turbulent transition zones and flow detachment regions.
• Integration into drones, automobiles, or marine vessels to monitor surface flow and improve efficiency or safety.
• Process control in industrial environments where robust, on-surface fluid flow measurement is essential (e.g., pipelines, reactors).
• Embedded flow sensors in HVAC systems or smart building surfaces for energy efficiency optimization.

BenefitsContent extracted from patent full text and abstract with AI.

• Provides direct, real-time detection of laminar/turbulent flow states and flow transitions.
• Robust and mechanically simple sensor design resistant to environmental hazards such as rain, dust, and mechanical shock.
• Low power consumption compared to continuous operation sensors.
• Can be integrated directly onto surfaces (e.g., wings) or embedded during manufacturing, reducing installation effort and cabling.
• Enables multi-depth, high-resolution analysis of flow profiles via modulation frequency variation, improving flow modeling accuracy.
• Reduces data post-processing time due to direct frequency-domain signal processing.
• Allows detection of unsteady (dynamic) flow phenomena, not just steady-state conditions.

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Patent Abstract

The present invention provides a method (M) for determining flow properties of a fluid flowing along a surface (2), the method (M) comprising: modulating (M1) the current through a heating element (5) of a thermal flow sensor (3) located on the surface (2) with at least one modulation frequency (ω), thereby emitting a thermal wave (7) into the fluid flowing along the surface having a penetration depth (L) inversely proportional to the modulation frequency (ω); measuring (M2) an amplitude (U3ω) of a voltage (U) across the heating element (5) at the third harmonic (3ω) of the at least one modulation frequency (ω), the voltage (U) depending on the thermal conductivity and the volumetric heat capacity of the fluid flowing along the surface (2); determining (M3) a flow velocity (VL) at the penetration depth (L) from the attenuation value of the determined amplitude (U3ω) of the voltage (U); and estimating (M4) whether the flow at the penetration depth (L) is laminar or turbulent on the basis of the determined flow velocity (VL). Further the present invention provides a use of such a method, a system and an aircraft.