Differential-pressure fiber-optic airflow sensor for wind tunnel testing

Abstract

A differential-pressure fiber-optic airflow (DPFA) sensor based on Fabry-Perot (FP) interferometry for wind tunnel testing is proposed and demonstrated. The DPFA sensor can be well coupled with a Pitot tube, similar to the operation of the differential diaphragm capsule in the airspeed indicator on the aircraft. For differential pressure sensing between total pressure and static pressure in the airflow, an FP cavity is formed between the sensing diaphragm and a fiber end-face, and a tubule is inserted into the FP cavity. According to the principle of differential pressure derived from Bernoulli’s equation, the airflow velocity can be determined by monitoring the change of the FP cavity length. The experimental results demonstrate that a DPFA sensor with 0∼11 kPa measurable range, 826.975 nm/kPa sensitivity, and 0.008% (0.89 Pa) resolution can be realized. Combined with a 100 Hz-sweep frequency self-developed white light interferometric (WLI) interrogator and a Pitot tube, the DPFA sensor can be used for measuring the airflow velocity of 2.0∼119.24 m/s with an accuracy of 0.61%. The system is applied to the analysis of the flat-plate boundary layer, a wind tunnel experimental model, where the results are consistent with those of the theoretical analysis and from the standard electronic pressure transducer. With the large measurable range, high sweep frequency, and high precision, the system has potential application value for wind tunnel experimental investigation and in-flight measurement of airspeed.

Recent Progress in MEMS Fiber-Optic Fabry–Perot Pressure Sensors

“…For wind tunnel airflow detection, due to the much lower temperature and pressure, silica, silicon, and even metal film-based sensors can be applicable. In 2020, Liu et al [ 77 ] proposed a differential-pressure fiber-optic airflow (DPFA) sensor, with 826.975 nm/kPa sensitivity and 0.008% (0.89 Pa) resolution under a 0~11 kPa measurable range. The sensor was tested in a wind tunnel and successfully measured the airflow velocity of 2.0~119.24 m/s with an accuracy of 0.61%, as presented in Figure 7 .…”

“…u is the airflow velocity, P 0 is total pressure in the airflow, P s is static pressure in the airflow (reprinted with permission from Ref. [ 77 ] © Optical Society of America).…”

A Miniature Liquid Flowmeter Using All-Fiber Fabry–Perot Cavity for Real-Time Measurement

“…C. Wang et al embedded fiberoptical anemometers based on dual F-P sensors inside a designed cubic holder by 3D printing, with a streamlined upper surface, and proved an airflow velocity measurement range from 20.39 m 3 /h to 209.03 m 3 /h [18]. Y. Liu et al proposed a differential-pressure optical-fiber anemometer based on Fabry-Perot interferometry coupled with a Pitot tube for air flow velocity measurements over a range of 737.28∼43,956.66 m 3 /h in a wind tunnel [19]. Nevertheless, the complexity of real-time liquid flow detection has not been determined, limited by sensor size in the pipeline microchannel.…”

Fiber-optic integrated aerodynamic three-hole vector probe for high-velocity flow field measurement

“…Some recent developments on fiber-optic flow sensors have focused on the measurement of the velocity magnitude in the airflow field. Examples include fiber-optic anemometers based on dual-channel Fabry-Perot (FP) interferometers (Wang et al, 2019), as well as a single-channel differential-pressure FP sensor and a diaphragm-based sensor with built-in fiber Bragg Grating (FBGs), both coupled for use with Pitot tubes (Liu et al, 2020b;Fujiwara et al, 2020). There are also precedents expecting to combine fiber-optic pressure sensors with MHPs for future wind tunnel applications, such as multiple MEMS optical transducers (Zhou and Sheplak, 2020) and differentially dynamic FP pressure sensors (Heckmeier et al, 2019).…”