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

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.

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.