Andrew Eastman

Thrust Force Characterization of Oscillating Cantilevers Operating Near Resonance

Harmonic oscillations from cantileverlike structures have found use in applications ranging from thermal management to atomic force microscopy and propulsion, due to their simplicity in design and ease of implementation. In addition, making use of resonance conditions, a very energy efficient solution is achievable. This paper focuses on the application of providing thrust through cantilever oscillations at or near the first mode of resonance. This method of actuation provides a balance between full biomimicry and ease of fabrication. Previous studies have shown promise in predicting the propulsion performance based on the operating parameters, however, they have only considered a single cantilever geometry. Here, additional cantilever sizes and materials are included, yielding a much larger design space to characterize the thrust trends. The thrust data is experimentally captured and is assembled into two sets of predictive correlations. The first is based on Reynolds and Strouhal numbers, while the second only employs the Keulegan–Carpenter number. Both correlations are proven to predict the experimental data and can be shown to yield nearly identical proportional relationships after accounting for the cantilever frequency response. The findings presented in this research will aid in further understanding and assessing the capabilities of thrust generation for oscillating cantilevers, but also provides a foundation for other applications such as convection heat transfer and fluid transport.

Three Dimensional Flow Around a Biomimetic Unbounded Flapping Cantilever

Macro-sized cantilevers oscillating in a fluid have been employed in applications ranging from thermal management to propulsion and represent a realistic tradeoff between full biomimicry and ease of fabrication. Surprisingly, the flow field generated upstream and downstream of the cantilever remains poorly understood. In order to properly control the resulting flow, further experimental and numerical studies are needed. From a two dimensional perspective, comprehensive analysis has been done, primarily through employing a single, very wide cantilever. However, many applications necessitate the usage of oscillating cantilevers whose oscillating amplitude is comparable to their width. As the region of analysis moves closer to a corner, where two edges of the slender cantilever meet, the flow becomes extremely three dimensional, rendering the two dimensional analysis tools less useful. The following paper seeks to further understand the highly three dimensional nature of the flow in addition to providing further insight into optimized flow control. Two perpendicular flow planes are analyzed in order to gather the x, y and z directional flow velocities using standard Particle Image Velocimetry measurements. It is shown that under certain circumstances, the resulting flow is atypical of what one would expect from a simple extrapolation from previous two dimensional flow analyses.Copyright

Thrust Measurements and Flow Field Analysis of a Piezoelectrically Actuated Oscillating Cantilever

Although not identical to the motion employed by nature’s swimmers and flyers, the simple harmonic oscillations of cantilever-like structures have been shown to provide efficient low-power solutions for applications ranging from thermal management to propulsion. However, in order to quantify their true potential, the resulting flow field and corresponding thrust must be better understood. In this work, a thin, flexible cantilever is actuated via a piezoelectric patch mounted near its base and caused to vibrate in its first resonance mode in air. The flow field is experimentally measured with particle image velocimetry while the thrust produced from the oscillatory motion is quantified using a high-resolution scale. The trends observed in the data are captured using an oscillating Reynolds number, and a clear relationship is defined between the operating parameters and the resulting thrust. Two-dimensional flow fields are extracted from the x–y and y–z planes and are primarily used to motivate future geometry and sidewall configurations that could greatly enhance the thrust capabilities of the cantilever by directing the flow downstream in a more effective manner.

Heat Transfer Analysis of a Novel Piezoelectric Air Pump

With the propagation of ever faster and more powerful electronics, the need for active, low power, cooling is becoming apparent. Piezoelectric materials exhibit reasonable performance with very little power consumption. Therefore a promising potential solution lies in utilizing piezoelectric materials via fans or pumps. However, piezoelectric pumps have mainly been employed in the transport of liquids and aqueous solutions through small microchannels. The structures typically consist of both an outlet nozzle and an inlet nozzle that are geometrically disposed to promote flow in one direction. Device construction is generally simplified compared to mechanically actuated openings, however much of the potential flow is lost due to backflow. The piezoelectric pump studied in this paper consists of a single outlet nozzle with a large inlet. Its unique construction allows it to overcome relatively high pressures as well as promoting better manufacturability. Experimental investigations were undertaken in order to characterize the cooling potential of the device. A thin film heater provided a constant heat flux and an infrared camera was used to determine the resulting temperatures of the heated surface. Full-field data of the convection coefficient were analyzed as a function of vibration amplitude of the piezoelectric diaphragm and distance from the nozzle to the heated target. A maximum heat transfer coefficient was found when the blower was approximately 30 mm from the heated surface and this distance was independent of vibration amplitude. Correlations have been developed which account for both variables considered and can be used to predict the performance of future designs which rely on the same physical characteristics.Copyright

Flow Field Analysis of a Single Piezoelectric Fan

Piezoelectrically actuated fans are relatively simple structures consisting of a piezoelectric material affixed to a thin cantilever beam. It is then subjected to a current that causes the beam to oscillate by the constriction and expansion of the piezoelectric material. A common application is that of electronics cooling where the induced flows can greatly augment natural or forced convection. Previous studies have sought to explore the flow field of piezoelectric fans in relation to its heat transfer application. This research seeks to expand upon that knowledge with a focus on measuring the flow parallel to the fan blade. A fan with length and width of 36.5 mm and 12.7 mm, respectively, is excited with an oscillating voltage input of 62.5 Hz and varying amplitudes. A Particle Image Velocimetry system, able to chart particle movement in the x and y directions, is employed to aid in understanding the flow field created by the fan with an emphasis on studying the vortex shed by a single half period of oscillation. This information has the potential to be a starting point for further exploration into a dual fan application and how their interactions alter vortex shedding in both two and three dimensions.Copyright