Method and system for determining flow properties of a fluid flowing along a surface

Patent metadata

Field	Value
Publication number	US-12411152-B2
Application number	US-202318188688-A
Country	US
Kind code	B2
Filing date	Mar 23, 2023
Priority date	Mar 25, 2022
Publication date	Sep 9, 2025
Grant date	Sep 9, 2025

Abstract

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.

First claim

The invention claimed is:

1. A method for determining flow properties of a fluid flowing along a surface, the method comprising:
modulating a current through a heating element of a thermal flow sensor located on a 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 at least one modulation frequency;
measuring an amplitude of a voltage across the heating element at a third harmonic of the at least one modulation frequency, the voltage depending on a thermal conductivity and a volumetric heat capacity of the fluid flowing along the surface;
determining a flow velocity at the penetration depth from an attenuation value of the measured amplitude of the voltage; and
estimating whether a flow at the penetration depth is laminar or turbulent based on the determined flow velocity.

2. The method according to claim 1 , wherein estimating whether the flow at the penetration depth is laminar or turbulent comprises:
comparing the determined flow velocity with a measurement value of a reference sensor or with a calibration value in quiescent atmosphere.

3. The method according to claim 1 , wherein the current through the heating element of the thermal flow sensor located on the surface is modulated with a plurality of modulation frequencies, and
wherein a plurality of amplitudes of the voltage across the heating element are measured at respective third harmonics of the plurality of modulation frequencies.

4. The method according to claim 3 , wherein a flow velocity profile is determined from flow velocities at different penetration depths based on the attenuation value of the plurality of measured amplitudes.

5. The method according to claim 4 , wherein estimating whether the flow at the penetration depth is laminar or turbulent includes estimating a transition point between laminar and turbulent flow in the flow velocity profile.

6. The method according to claim 5 , wherein estimating the transition point between laminar and turbulent flow in the flow velocity profile includes deriving a threshold of a wall shear stress vector near the surface.

7. The method according to claim 3 , wherein the current through the heating element is modulated with the plurality of modulation frequencies simultaneously.

8. The method according to claim 3 , wherein the at least one modulation frequency of the current through the heating element is sweeped through the plurality of modulation frequencies.

9. The method according to claim 1 , wherein measuring the amplitude of the voltage across the heating element comprises using a lock-in amplifier at the third harmonic of the at least one modulation frequency.

10. The method according to claim 1 , wherein a modulation pattern of the current through the heating element is a sawtooth modulation, a triangular modulation, a square-wave modulation, a stepped modulation, or a sinusoidal modulation.

11. The method according to claim 1 , wherein the surface comprises a surface of an aircraft.

12. A system for determining flow properties of a fluid flowing along a surface, the system comprising:
a thermal flow sensor comprising a substrate and a heating element mounted onto the substrate, the thermal flow sensor located on a surface;
a power supply electronically coupled to the thermal flow sensor and configured to modulate a current through the heating element of the thermal flow sensor 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 at least one modulation frequency; and
a measurement assembly electronically coupled to the thermal flow sensor and configured to measure an amplitude of a voltage across the heating element at a third harmonic of the at least one modulation frequency, the voltage depending on a thermal conductivity and a volumetric heat capacity of the fluid flowing along the surface, to determine a flow velocity at the penetration depth from an attenuation value of the measured amplitude of the voltage, and to estimate whether a flow at the penetration depth is laminar or turbulent based on the determined flow velocity.

13. The system according to claim 12 , wherein the heating element is formed as at least one conductive or semiconductive film partially or wholly coating the substrate of the thermal flow sensor.

14. The system according to claim 12 , wherein the substrate of the thermal flow sensor comprises polyimide with a thickness of 100 μm or less.

15. The system according to claim 12 , wherein the thermal flow sensor further includes a protection layer on top of the heating element.

16. An aircraft comprising:
a thermal flow sensor comprising a substrate and a heating element mounted onto the substrate, the thermal flow sensor located on a surface;
a power supply electronically coupled to the thermal flow sensor and configured to modulate a current through the heating element of the thermal flow sensor 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 at least one modulation frequency; and
a measurement assembly electronically coupled to the thermal flow sensor and configured to measure an amplitude of a voltage across the heating element at a third harmonic of the at least one modulation frequency, the voltage depending on a thermal conductivity and a volumetric heat capacity of the fluid flowing along the surface, to determine a flow velocity at the penetration depth from an attenuation value of the measured amplitude of the voltage, and to estimate whether a flow at the penetration depth is laminar or turbulent based on the determined flow velocity.

17. The aircraft according to claim 16 , wherein the surface comprises a surface of an airfoil.

Assignees

• Airbus Operations Gmbh
• Airbus Sas
• Ostbayerische Technische Hochschule Regensburg
• Ostbayerische Technische Hochschule

Inventors

• Friedberger Alois
• Stefes Bruno
• Berndt Dominik
• Schreiner Rupert

Classifications

• G01P5/12 Primary

  using variation of resistance of a heated conductor · CPC title

• G01M9/065 Primary

  dealing with flow · CPC title