Micro-pillar sensor based wall-shear mapping in pulsating flows: In-situ calibration and measurements in an aortic heart-valve tester

Li, Qianhui; Stavropoulos-Vasilakis, Evangelos; Koukouvinis, Phoevos; Gavaises, Manolis; Brücker, Christoph

doi:10.1016/j.jfluidstructs.2021.103346

Cited by 4 publications

(9 citation statements)

References 48 publications

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“…Work was previously carried out by our team to develop and calibrate flexible pillar sensors in boundary layers down to a wall distance of 300 microns, where they acted as wall shear stress sensors ( [19,26]). These sensors followed the principle of a one-sided clamped cantilever beam that was bent by drag forces from the flow around the pillar.…”

Section: Sensing Pillarsmentioning

confidence: 99%

“…As shown in our previous work, the response of such sensors closely followed that of a second-order harmonic oscillator, which was described by a nearly constant gain until 30 percent of the natural frequency f n . In liquids, the response is typically overdamped, and this excludes any ringing ( [26]).…”

Section: Sensing Pillarsmentioning

confidence: 99%

“…The methodology presented herein followed the design of such sensors to be implemented in complex geometries by using the technique of planar inlays made of elastomeric sheets. These pillars were easily laser-cut from the large elastomeric sheets (sheet thickness: 1.5 mm) and then clamped between parts of the model, as shown in [19,26]. The shape of the elastomeric sheet was based on the wing cross-section and also had protuberances in the form of long slender beams with rectangular cross-sections, which represented the biomimetic sensory hairs.…”

Section: Sensing Pillarsmentioning

confidence: 99%

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Fly by Feel: Flow Event Detection via Bioinspired Wind-Hairs

Court,

Bruecker

2024

Fluids

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Bio-inspired flexible pillar-like wind-hairs show promise for the future of flying by feel by detecting critical flow events on an aerofoil during flight. To be able to characterise specific flow disturbances from the response of such sensors, quantitative PIV measurements of such flow-disturbance patterns were compared with sensor outputs under controlled conditions. Experiments were performed in a flow channel with an aerofoil equipped with a 2D array of such sensors when in uniform inflow conditions compared to when a well-defined gust was introduced upstream and was passing by. The gust was generated through the sudden deployment of a row of flaps on the suction side of a symmetric wing that was placed upstream of the aerofoil with the sensors. The resulting flow disturbance generated a starting vortex with two legs, which resembled a horseshoe-type vortex shed into the wake. Under the same tunnel conditions, PIV measurements were taken downstream of the gust generator to characterise the starting vortex, while further measurements were taken with the sensing pillars on the aerofoil in the same location. The disturbance pattern was compared to the pillar response to demonstrate the potential of flow-sensing pillars. It was found that the pillars could detect the arrival time and structural pattern of the flow disturbance, showing the characteristics of the induced flow field of the starting vortex when passing by. Therefore, such sensor arrays can detect the “footprint” of disturbances as temporal and spatial signatures, allowing us to distinguish those from others or noise.

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Section: Sensing Pillarsmentioning

confidence: 99%

Section: Sensing Pillarsmentioning

confidence: 99%

Section: Sensing Pillarsmentioning

confidence: 99%

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Fly by Feel: Flow Event Detection via Bioinspired Wind-Hairs

Court,

Bruecker

2024

Fluids

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“…The design and manufacturing of the pillar sensors follows the concept described in earlier work [9] using flexible micro-pillars to detect and characterise wall shear stress in the aortic artery. The sensors were scaled up to match the scales and application of the current investigation to act as 'digital tufts' over the wing surface.…”

Section: Aerofoil Preparationmentioning

confidence: 99%

“…The effects of angle of attack on the deflection of the first pillar are investigated further later in this section. The instantaneous load distribution g(t,l) acting normal to the longitudinal axis of the pillar is derived in analogy to work from [9]. .…”

Section: Calibrationmentioning

confidence: 99%

Detecting aerofoil separation pre-cursors using on-board optical tracking of flexible pillar sensors

Selim

Brücker

2022

Preprint

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A novel approach for detecting characteristic flow signatures precursory to stall along aerofoils is introduced. It uses arrays of flexible wind-hair like sensors distributed around the aerofoil which are tracked remotely using high-speed imaging and processing. The sensors act as “digital tufts" providing real-time readings of local velocity information with a high temporal resolution. Such sensors are integrated into a NACA0012 aerofoil and tested in a wind-tunnel for varying angles of attack in static tests and dynamically in a ramp-up test. For the static tests, the mean values of the sensor signals provide information on local free-stream velocity and angle of incidence. The fluctuating part of the signals show that at angles approaching separation prominent low frequency oscillations are detected, the magnitudes of which scale with the angle of incidence. These are hypothesised to be linked to breathing modes of the Laminar Separation Bubble causing a shear-layer flapping observed on the sensors. Such low-frequency oscillations were also detected short before separation in the ramp-up studies. As the high-speed cameras are mounted in a simulated “on-board" position, the sensing method could be used for early stall warnings in small-scale UAVs with integrated on-board object tracking cameras.

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Aerofoil Flow Sensing Using On-Board Optical Tracking of Flexible Pillar Sensors

Selim

Brücker

2023

Fluids

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A novel approach for sensing and characterising the flow over an aerofoil is introduced. Arrays of flexible wind-hair-like sensors distributed over an aerofoil, which are tracked remotely using high-speed imaging and processing, acting as “digital tufts”, are used to provide real-time readings of local flow information with high temporal resolution. The use case presented in this paper has the sensors embedded within the suction side of a NACA0012 aerofoil and tested in a wind tunnel for varying angles of attack in static and dynamic tests. The time-averaged signals were able to provide information pertaining to the free-stream velocity and instantaneous angle of attack. The capability of the sensor type to provide temporal flow information is also explored. The sensors were used to detect low-frequency oscillations, which are pre-cursory to stall. These are hypothesised to be linked to breathing modes of the laminar separation bubble, causing a shear-layer flapping observed on the sensors. Such low-frequency oscillations were also detected shortly before separation in the ramp-up studies.

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Micro-pillar sensor based wall-shear mapping in pulsating flows: In-situ calibration and measurements in an aortic heart-valve tester

Cited by 4 publications

References 48 publications

Fly by Feel: Flow Event Detection via Bioinspired Wind-Hairs

Fly by Feel: Flow Event Detection via Bioinspired Wind-Hairs

Detecting aerofoil separation pre-cursors using on-board optical tracking of flexible pillar sensors

Aerofoil Flow Sensing Using On-Board Optical Tracking of Flexible Pillar Sensors

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