Detection of flow separation and stagnation points using artificial hair sensors

Abstract

Recent interest in fly-by-feel approaches for aircraft control has motivated the development of novel sensors for use in aerial systems. Artificial hair sensors are one type of device that promise to fill a unique niche in the sensory suite for aerial systems. In this work, we investigate the capability of an artificial hair sensor based on structural glass fibers to directly identify flow stagnation and separation points on a cylindrical domain in a steady flow. The glass fibers are functionalized with a radially aligned carbon nanotube forest and elicit a piezoresistive response as the carbon nanotube forest impinges on electrodes in a micropore when the hair is deflected due to viscous drag forces. Particle image velocimetry is used to measure the flow field allowing for the resulting moment and force acting on the hair to be correlated with the electrical response. It is demonstrated that the artificial hair sensor provides estimates for the locations of both the stagnation and separation in steady flow. From this, a simulation of a heading estimation is presented to demonstrate a potential application for hair sensors. These results motivate the construction of large arrays of hair sensors for imaging and resolving flow structures in real time. Keywords:hair sensor, carbon nanotube array, piezoresistive transduction, stagnation point, separation point, heading estimation list) for both air and underwater applications. In particular, the work of Dagamseh et al (2012) is interesting for using AHSs for aerodynamic state estimation. In this work, we offer a preliminary investigation of using AHSs based on structural glass fibers coated with a radially aligned forest of carbon nanotubes (CNTs) to identify the location of stagnation and separation on a quasi-2D domain through piezoresistive transduction. Specifically, we generate a steady flow past a cylinder and measure both the sensor electrical response with a source meter and the flow field stimulating the hair using particle image velocimetry (PIV). The results are correlated to investigate the potential of using AHSs for flow feature identification.Engineered flight systems currently utilize sensors for situational awareness and state/parameter estimation, but the number of sensors is limited and the sensors are comparatively expensive. Emphasis is currently placed on point-wise sensor accuracy rather than redundancy. Hot film/wire anemometers are examples of accurate, point-wise technologies that are already used extensively in industry for aerodynamic control and estimation. In contrast to engineered systems, biology generally employs redundancy in both control and estimation systems (Bekey 2005). For many of the same reasons biology depends upon redundancy, there are several reasons to consider redundant, distributed sensory systems for flight control. First and foremost, redundancy provides robustness to sensor failure, which is a systemic problem in systems with very few, high-grade sensors. Redundancy also provides more information regarding ...

Bat-inspired integrally actuated membrane wings with leading-edge sensing

“…The mapping function between the sensor deformation and the pressure field at the leading edge is, therefore, obtained through calibration that depends on the structure of the hair-like sensor and the flow conditions. These assumptions are supported by the investigations in references (Dickinson 2010, Dickinson et al 2012, Phillips et al 2015.…”

“…In our investigation, a single hair sensor at the leading edge is considered, but the methodology could easily be extended to patches of them, as shown by Dickinson (2010), Dickinson et al (2012) and Phillips et al (2015). In fact, the same model could be used when considering the average signal from a patch of hairsensors.…”

“…For the distributed sensing, we propose flow measurements via hair-like sensors. The concept has been investigated by Dickinson (2010), Dickinson et al (2012) and Phillips et al (2015), who considered both isolated and patch-arranged sensors reproducing the topology of natural fliers.…”

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“…From the previous studies, 25 it has been found that the AHS measurements around the stagnation point might not be as good as the rest of the surface. A specific deign of AHS works well in a range of velocities, in which the sensor is sensitive to the flow.…”

CNT‐Based Artificial Hair Sensors for Predictable Boundary Layer Air Flow Sensing

“…Alternatively, artificial hair sensors (AHS) have also been fabricated by MEMS‐free processes from high stiffness structural glass microfibers and carbon nanotubes (CNTs) . The CNTs in these devices form self‐aligned, radial arrays during synthesis that have been shown to exhibit elastic, foam‐like behavior and large piezoresistance in response to compressive strain against a conductive surface .…”