Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session E26: Experiments: Sensing and Field Measurements |
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Chair: Jianzhong Zhu, Univeristy of Virginia Room: 306 |
Sunday, November 22, 2015 4:50PM - 5:03PM |
E26.00001: Expandable and retractable self-rolled structures based on metal/polymer thin film for flow sensing Jianzhong Zhu, Carl White, Mehdi Saadat, Hilary Bart-Smith Most aquatic animals such as fish rely heavily on their ability of detect and respond to ambient flows in order to explore and inhabit various habitats or survive predator-prey encounters. Fish utilize neuromasts in their skin surface and lateral lines in their bodies to align themselves while swimming upstream for migration, avoid obstacles, reduce locomotion cost, and detect flow variations caused by potential predators. In this study, a thin film MEMS sensor analogous to a fish neuromast has been designed for flow sensing. Residual stress arises in many thin film materials during processing. Metal and polymer thin film materials with a significant difference in elastic modular were chosen to form a multiple-layer structure. Upon releasing, the structure rolls into a tube due to mechanical property mismatch. The self-rolled tube can expand or retract, depending on the existence of external force such as flow. An embedded strain sensor detects the deformation of the tube and hence senses the ambient flow. Numerical simulations were conducted to optimize the structural design. Experiments were performed in a flow tank to quantify the performance of the sensor. [Preview Abstract] |
Sunday, November 22, 2015 5:03PM - 5:16PM |
E26.00002: High-resolution compact shear stress sensor for direct measurement of skin friction in fluid flow Muchen Xu, Chang-Jin ``CJ'' Kim The high-resolution measurement of skin friction in complex flows has long been of great interest but also a challenge in fluid mechanics. Compared with indirect measurement methods (e.g., laser Doppler velocimetry), direct measurement methods (e.g., floating element) do not involve any analogy and assumption but tend to suffer from instrumentation challenges, such as low sensing resolution or misalignments. Recently, silicon micromachined floating plates showed good resolution and perfect alignment but were too small for general purposes and too fragile to attach other surface samples repeatedly. In this work, we report a skin friction sensor consisting of a monolithic floating plate and a high-resolution optical encoder to measure its displacement. The key for the high resolution is in the suspension beams, which are very narrow (e.g., 0.25 mm) to sense small frictions along the flow direction but thick (e.g., 5 mm) to be robust along all other directions. This compact, low profile, and complete sensor is easy to use and allows repeated attachment and detachment of surface samples. The sheer-stress sensor has been tested in water tunnel and towing tank at different flow conditions, showing high sensing resolution for skin friction measurement. [Preview Abstract] |
Sunday, November 22, 2015 5:16PM - 5:29PM |
E26.00003: Bio-Inspired Pressure Sensitive Foam Arrays for use in Hydrodynamic Sensing Applications Jeff Dusek, Michael Triantafyllou, Jeffrey Lang Shallow, turbid, and highly dynamic coastal waters provide a challenging environment for safe and reliable operation of marine vehicles faced with a distinct environmentally driven perceptual deficit. In nature, fish have solved this perplexing sensory problem and exhibit an intimate knowledge of the near-body flow field. This enhanced perception is mediated by the ability to discern and interpret hydrodynamic flow structures through the velocity and pressure sensing capabilities of the fish's lateral line. Taking cues from biological sensory principles, highly conformal pressure sensor arrays have been developed utilizing a novel piezoresistive carbon black-PDMS foam active material. By leveraging the low Young's modulus and watertight structure of closed-cell PDMS (silicone) foam, the sensor arrays are well suited for hydrodynamic sensing applications and prolonged exposure to fluid environments. Prototype arrays were characterized experimentally using hydrodynamic stimuli inspired by biological flows, and were found to exhibit a high degree of sensitivity while improving on the flexibility, robustness, and cost of existing pressure sensors. [Preview Abstract] |
Sunday, November 22, 2015 5:29PM - 5:42PM |
E26.00004: Daylight Operable PIV for Use in the Field Larry Brock, Jian Sheng Particle Image Velocimetry (PIV) is widely used in laboratory scale studies, however, has considerable difficulties for application in the field. The issue mainly arise due to the presence of background sunlight and undesirable environmental conditions. To overcome the strong ambient light during the double exposure PIV operation, one must reduce substantially the total ambient illuminations to the tracer particle scattering. To achieve the above mentioned objective, we increase the scattering by using a pulsed laser with short pulse width (\textless 7ns) at the same time shortening the image exposure. The laser light is introduced via fiber optic cable where the laser is located in a remote location and delivered to the encapsulated pod to form a thin collimated 50 x 1mm sheet, latter being the thickness. The sheet is then reflected between a series of mirrors to create a light-in-flight. The light sheet is overlapped slightly between the reflections and illuminates the entire field of view in the time of camera exposure (e.g. 1us). The DOPIV system is capable of measuring 2D velocity in a .5 m X .5 m field of view with 0.2 mm spatial resolution and 7.6 mm vector spacing. The bench-top and fields experiments are performed to demonstrate the feasibility of the systems in understanding near surface transport phenomenon such as wake in a wind farm, atmospheric/oceanic boundary layer, etc. [Preview Abstract] |
Sunday, November 22, 2015 5:42PM - 5:55PM |
E26.00005: Adapting unmanned aerial vehicles for turbulence measurement Brandon Witte, Jacob Helvey, Jon Mullen, Michael Thamann, Sean Bailey We describe the approach of using highly instrumented and autonomous unmanned aerial vehicles (UAVs) to spatially interrogate the atmospheric boundary layer's turbulent flow structure. This approach introduces new capabilities not available in contemporary micro-meteorological measurement techniques such as instrumented towers, balloons, and manned aircraft. A key advantage in utilizing UAVs as an atmospheric turbulence research tool is that it reduces the reliance on assumptions regarding temporal evolution of the turbulence inherent within Taylor's frozen flow hypothesis by facilitating the ability to spatially sample the flow field over a wide range of spatial scales. In addition, UAVs offer the ability to measure in a wide range of boundary conditions and distance from the earth's surface, the ability to gather many boundary layer thicknesses of data during brief periods of statistical quasi-stationarity, and the ability to acquire data where and when it is needed. We describe recent progress made in manufacturing purpose-built airframes and adapting pre-fabricated airframes for these measurements by integrating sensors into those airframes and developing data analysis techniques to isolate the atmospheric turbulence from the measured velocity signal. [Preview Abstract] |
Sunday, November 22, 2015 5:55PM - 6:08PM |
E26.00006: Characterization of floating element balance for field panel testing J. Travis Hunsucker, Harrison Gardner, Geoffrey Swain Multiple experiments were performed to investigate and characterize the uncertainty and bias of a through-hull flush mounted floating element balance designed to measure the hydrodynamic drag forces of biofouling and marine coatings on 25 x 30 cm test panels. The instrument is located in a wet well on the aft portion of a 27' Chris Craft Commander. Testing occurs over a series of speeds ranging from a Froude number of 0.50-2.20 on calm days (force 3 or less) in waters along the central east coast of Florida. Recent modifications have been made to the instrumentation in an effort to improve the overall accuracy of the system. This study compares frictional drag measurements of the floating element balance to those obtained using the Clauser chart and Preston tube methods for a smooth surface. Boundary layer velocity profiles are examined to understand the nature of the flow over the testing section. Roughness function values for 60 and 220 grit sandpaper were calculated from data obtained using the floating element balance. These values were compared with previous work to examine the overall bias of the methodology. Repeat measurements for a smooth panel were analyzed to characterize the overall uncertainty in the system. [Preview Abstract] |
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