Abstract

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To control and navigate micro air vehicles (MAVs) efficiently, there is a need for small, lightweight, durable, sensitive, fast, and low-power airspeed sensors. When designing sensors to meet these requirements, soft materials are promising alternatives to more traditional materials due to the large deformations they can withstand. In this article, a new concept of a soft material flow sensor is presented based on elastic filament velocimetry, which fulfills all necessary criteria. This technique measures flow velocity by relating it to the strain of a soft ribbon suspended between two static supports and subjected to a flow of interest. The ribbon is manufactured from polydimethylsiloxane and can be made piezoresistive by the addition of silver nanowires. With the described manufacturing method, the sensor can be made using common laboratory tools, outside of a clean room, significantly reducing its complexity. Furthermore, it can be operated using a simple and lightweight circuit, making it a convenient alternative for MAVs. Using a piezoresistive material allows for the flow velocity to be calibrated to the resistance change of the strained ribbon. Although certain challenges remain unsolved, such as polymer creep, the sensor has demonstrated its ability to measure flow velocities down to 4 m/s in air through experiments. A time-dependent analytical model is also provided. The model shows that the current sensor has a bandwidth of 480 Hz. Most importantly, the sensitivity and the bandwidth of the sensor can be varied strictly by modifying the geometry and the material properties of the ribbon.

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Although recent studies of laminar cool flames have provided important advances in understanding the low-temperature chemistry of both hydrocarbons and oxygenates, there has been limited experimental insight into how interactions between turbulence and chemistry occur in cool flames. To address this, a new Co-flow Axisymmetric Reactor-Assisted Turbulent (CARAT) burner has been developed and characterized in this investigation for the purpose of directly studying turbulent cool flames. A methodology for establishing stable turbulent cool diffusion flames under well-defined conditions is proposed. The structure of dimethyl ether flames is examined using both formaldehyde planar laserinduced fluorescence and Rayleigh scattering. It is found that weak turbulence produces wrinkled turbulent cool flames in which fluctuations occur mainly on the fuel side of the flame. However, at increased levels of turbulence, large pockets of unburned reactants appear in the vicinity of the cool flame, and structural fluctuations extend to both sides of the flame. This study offers a well-defined experimental platform for the study of turbulence-chemistry interactions at low temperatures.