From an apparatus previously designed for measuring the Doppler shift using a rotating mirror, an improved, versatile version was developed for speed of light demonstrations in a classroom or a teaching laboratory. By adding a second detector and adequate beam-splitter and mirrors, three different configurations are easily assembled. One configuration is used for time-of-flight measurements between a near and a far detector, allowing one to measure the speed of light provided that the path length between detectors is known. Another variation is the interferometric method obtained by superposing the far and near signals in such a way that a minimum of the combined signal is obtained when the time delay makes the signals arrive out of phase by pi radians. Finally, the standard Doppler configuration allows the measurement of the frequency beat as a function of the rotation frequency. The main advantages of the apparatus are (a) the experimental setup is simple and completely accessible to undergraduate students, (b) the light is visible, students can see the rays, which, with the use of appropriate screens, can be blocked at any point along their paths, (c) the experiment can take place entirely within the teaching laboratory or demonstration room (using the interferometric method, the shortest distance to the far mirror was as small as 0.5 m), and (d) different configurations can be built, including some economical setups within the budget of teaching laboratories.

This work presents, compares and discusses results obtained with two indirect methods for the calculation of aerodynamic forces and pitching moment from 2D Particle Image Velocimetry (PIV) measurements. Both methodologies are based on the formulations of the momentum balance: the integral Navier–Stokes equations and the “flux equation” proposed by Noca et al. (J Fluids Struct 13(5):551–578, 1999), which has been extended to the computation of moments. The indirect methods are applied to spatio-temporal data for different separated flows around a plate with a $$16\mathrm {:}1$$ chord-to-thickness ratio. Experimental data are obtained in a water channel for both a plate undergoing a large amplitude imposed pitching motion and a static plate at high angle of attack. In addition to PIV data, direct measurements of aerodynamic loads are carried out to assess the quality of the indirect calculations. It is found that indirect methods are able to compute the mean and the temporal evolution of the loads for two-dimensional flows with a reasonable accuracy. Nonetheless, both methodologies are noise sensitive, and the parameters impacting the computation should thus be chosen carefully. It is also shown that results can be improved through the use of dynamic mode decomposition (DMD) as a pre-processing step.

This paper presents transient flow phenomena in terms of angles of attack by means of direct force measurement on pitching flat plate wings at a constant pitch acceleration.The wing motion is different from the most commonly used wing motion at constant pitch rates but generates comparable aerodynamics in a relatively short time.The wings were pitched from zero to maximum angles of attack ranging from 3 degrees to 42 degrees at mid-chord in a constant free stream Reynolds number of 8,900.Three wing planform shapes with the same effective aspect ratio four are considered: rectangle, trapezoid, and triangle.Results show that the unsteady forces are developed following the similar trend as the maximum angle of attack is increased, giving a positive normal force and negative axial force extreme.The transient flow, occurring at the maximum angles of attack before steady state, gives oscillatory characteristics on both normal force and axial force coefficients, and further yields oscillatory lift and drag coefficients.The multiple extremes of positive normal force and negative axial force are in phase.These oscillation phenomena are more vigorous for rectangular and trapezoidal wings, especially at the angle of attack higher than 24 degrees, than for triangular wing.Two types of vortex dynamic system are further revealed from Strouhal number analysis.

The pressure and flow rate produced by a 3-chip (2-stage) stacked electrostatic gas micropump has been improved by incorporating structural modifications. Deep vertical trenches are used to create vertical stiffeners to reduce electrode deflection, and consequently increase pump and valve membrane displacement to generate higher compression and pressure. Electrode stiffening has improved pressure and flow rate by 4X and 15X respectively. A 3-chip stacked micropump (2-stage pump) has produced a pressure difference of 4 kPa and flow rate of 1.3 sccm at membrane actuation frequency of 24 kHz and drive amplitude of 190 Vpk·pk. Each micropump chip is 5.5 × 4 × 0.5 mm 3 and pumping/microvalve membrane is 2 × 2 mm 2 . This is the highest pressure per stage (2 kPa) reported by a peristaltic multi-stage MEMS gas micropump with this size.

This paper reports stereo flow evolution and aerodynamics of a pitching wing in water channel from zero to 45-degree pitch angle in still water and reduced pitch rate of 0.39, and earlier stage of transition flow at maximum angle of attack. The wing is a rectangular flat plate with aspect ratio of four at leading-edge pivot. Wall effect on the pitching wing and stationary wing in test environment is examined by means of direct force measurement. The stereo image is captured through two cameras together with PIV system; comparisons among two camera images and stereo images are provided. We ascertain that twodimensional flow features significant aerodynamic forces during the pitching maneuver, and therefore encourages lift generation, which mechanism includes the formation of Starting vortex and Leading-edge vortex together with Pivot vortex. However, the formations of Secondary vortex and Stopping vortex apparently are malignant to the lift generation at high angle of attack. Also revealed in the paper is that the formation of Tip vortex causes a promising drag, and induces detrimental spanwise flow to Leading-edge vortex on span locations other than wingtip, transiting aerodynamic forces decreasingly to steady state. Moreover, the trajectory of vortexes is documented.

This paper presents the results of an experimental investigation of the unsteady flow about pitching flat plates. Hydrodynamic force and two-dimensional particle image velocimetry measurements are reported for three pivot locations (leading edge, midchord, and trailing edge), reduced pitch rates from 0.022 to 0.39, and in still water, which corresponds to infinite reduced pitch rate. The wing has rectangular planform with effective aspect ratio 4, and the wing pitching motion is from 0 to 45 deg angle of attack. The relation between hydrodynamic force and vortical flow development as a function of pivot location and reduced pitch rate is discussed. Reasonable agreement is found between measured hydrodynamic force and quasi-steady potential flow theoretical results. Several vortical flow features are identified and discussed, including 1) the effect of pivot location and pitch acceleration on formation and evolution of vortical structures, 2) the impact of interaction between vortical flow structures on hydrodynamic force development, and 3) three-dimensional flow development and transient vortex development.

This article describes a simple low-order model for the lift produced by rapidly accelerating and pitching flat plate wings. The model is informed by experiments performed as part of NATO’s AVT-202 technical team. The overall agreement of the model with the forces measured as part of this effort is reasonable, however, the main value of the model is to identify a number of contributions to the lift force and classifying these as either circulatory or non-circulatory. Thus the relative effects of viscosity and kinematic accelerations are identified which helps the understanding of unsteady low-Re flows.

This paper is an overview of research results from the NATO-STO AVT 202 panel on “Extensions of Fundamental Flow Physics to Practical MAV Aerodynamics.” The focus is on the unsteady aerodynamics of pitching low aspect ratio wings. We present results from participating teams and discuss relevant flow physics. We consider translating and rotating pitching wings. The pitch motion is from 0 to 45 angle of attack and two pitch rates are considered: A fast pitch rate in which the pitch motion occurs over one convective time and a slow pitch rate in which the pitch motion is over 6 convective times. Unsteady force measurement, flow visualization amd PIV measurements of the velocity and vorticity fields were obtained by AVT 202 team members. Here we focus on unsteady force measurements and flow visualization results of the LEV, TEV and TV vortices.

This chapter provides a systematic review of micromachined gas pumps. After briefly reviewing their applications and general structure, it discusses typical performance metrics for these pumps. Gas pumps are categorized based on their pumping mechanisms and actuation techniques used. A review of four different pumping mechanisms is provided. These include passive, active, diffuser, and valveless pumping. A brief review of all previously reported micromachined pumps based on each of these pumping mechanisms is provided. Following this, a review of different actuation technologies and their use in reported gas micropumps is provided. Finally, the chapter provides a design road map for all previous gas micropumps, summarizing their main features, and ends with concluding remarks about remaining challenges and future directions.

We report the design, fabrication and testing of a new “stacked” multi-stage electrostatic gas micropump. Utilizing a stacked structure provides modularity as well as the ability to change the number of pumping stages post-fabrication to achieve the required pressure for a given application. The stacked design also eliminates the need for bidirectional movement of the pumping membrane. The new design presents a novel method to adjust the volume ratio of a given stage to achieve a uniform pressure increase across individual stages of the multi-stage system. A pressure difference of 1.1kPa and air flow rate of 85 µL/min is obtained by a 3-stage stacked micropump. An individual micropump stage is 5.5×4×0.5 mm 3 and each pumping/microvalve membrane is 2 × 2 mm 2 .

Small autonomous or remotely piloted air vehicles offer new capabilities in agility and maneuverability. A variety of missions have been proposed for these vehicles that require aggressive maneuvers and unique take-off and landing capabilities. From an unsteady aerodynamics point of view these capabilities expand the parameter space toward the high rotation rate and acceleration, and low Reynolds number region of the envelope. In this paper we review recent experimental results, numerical simulations and theoretical analysis of relevant unsteady aerodynamics problems. It is shown that unsteady effects can significantly increase lift generation during maneuvers. Vortex dynamics and other relevant physical processes which contribute to unsteady force generation will be discussed. Simple theoretical models that provide reasonably accurate estimates of unsteady aerodynamic forces are reviewed.

Unsteady, nonlinear aerodynamics at high angles of attack challenges small unmanned aircraft system autopilots that rely heavily on inertial-based instrumentation. This work introduces an expanded aerodynamic sensing system for poststall flight conditions that incorporate high angle of attack and prop-wash aerodynamic forces based on in-flight measurement. A flight vehicle with a 1.8 m wingspan is used in wind-tunnel tests to measure the pitch and yaw moments due to free stream and prop-wash over the tail surfaces at high-thrust, low-airspeed conditions including hover. Test data are used to develop two methods to determine in-flight real-time pitch and yaw moments: a probe designed specifically to measure prop-wash flow and a set of pressure sensors embedded throughout the tail surfaces. Through comparisons with torque-transducer measurements also acquired in the wind-tunnel tests, both methods are shown to provide accurate moment estimates at hover and forward-flight conditions. With information directly provided by in-flight measurement, real-time pitch and yaw control can be enhanced using a simple and reliable framework.

We report the development of fully integrated peristaltic multistage (18-, 4-, and 2-stage) electrostatic gas micropumps with integrated active microvalves. These micropumps uniquely combine a number of approaches to achieve highpressure, high flow rate, multimode, and low-power pumping of compressible gases: (1) multistage (up to 18-stage) configuration to generate high pressure accumulation across the pump, while allowing each stage to operate at low pressure burden; (2) gas resonance-based high-frequency (>10 kHz) operation of both the micropumps and the microvalves to achieve high mass flow rates despite the small volume displacement of microscale membranes; (3) active timing control of microvalves to regulate compressible gas pumping into multiple modes for either high flow rate or high pressure; and (4) electrostatic actuation to minimize power consumption despite multiple (up to 28) membrane operation. The multistage micropumps contain 18, 4, and 2 pumps connected in series sandwiched by 19, 5, and 3 microvalves, respectively. The fabricated 18-, 4-, and 2-stage pumps, respectively, produced high air flow rates of ~4.0, 3.0, and 2.7 sccm and maximum pressure differentials of ~17.5, 7.0, and 2.5 kPa with total power consumptions of only ~57, 15.1 and 9.1 mW, respectively. They have active areas of 15.5 × 12.7 and 18.3 × 7.1, 15.0 × 7.0 mm 2 , and total package volumes of 25.1 × 19.1 × 1, 27.8 × 11.6 × 1, and 23.0 × 12.4 × 1 mm 3 , respectively. They demonstrated two pumping modes using different microvalve timing (high flow rate timing and high pressure timing), resulting in notable changes in flow rates and pressure generation. One 4-stage micropump has been actuated for a total running time of more than 700 min over 32 months.

The unsteady aerodynamics of pitching wings at high reduced pitch rate is investigated experimentally and theoretically.Simple potential flow analysis is used to compute lift, drag and pitching moment, and compared to experimental measurements.The wing motion is a linear pitch ramp between 0 and 45 degrees with smoothing at the start and end of the motion.Recent experimental results are reported for several reduced pitch rates in the range K = 0.06 and 0.39 which corresponds to pitch times of 1 and 6 convective times, respectively, and for several wing planform geometries, pivot locations and Reynolds numbers.It is shown that the lift during the motion is in agreement with linear potential flow theory including rotation rate and finite span effects.The theoretical predictions significantly underestimates drag coefficients in the measurement.At high rotation rates the wing planform shape significantly impacts aerodynamic force for leading edge pivot with a triangular wing producing 25% more transient lift than trapezoidal and rectangular wings.The effect of Reynolds number and smoothing kinematics are investigated experimentally.At high reduced pitch rates a longer smoothing transient produces larger transient lift coefficients.

In this paper, force and particle-image-velocimetry vorticity measurements of biologically inspired hover kinematics are compared to corresponding results of an unsteady aerodynamic vortex model and a Navier-Stokes (NS) solver. The Reynolds number and the reduced frequency are 4.8x103 and 0.38, respectively. Three kinematics derived from the measured hovering kinematics of an Agrius convolvuli are considered: 1)without elevation angle, 2)elevation angle accounted in the pitch angle, and 3)pure sinusoidal pitch-plunge neglecting higher harmonics. The Navier-Stokes computations show good qualitative agreement with experiments with consistent underprediction. The time-averaged thrust coefficients obtained using Navier-Stokes computations are 82 to 87% of the corresponding force measurements. The standard deviation of time history of thrust coefficients, also normalized by the measured time-averaged values, is 13 to 20%. The underprediction is possibly due to blockage effects in the experiments, also reflected in lower values of the vorticity compared to particle-image-velocimetry measurements. The unsteady aerodynamic vortex model captures some of the peaks in a qualitative manner. The relative difference in the time-averaged forces and standard deviation are 8 to 18% and 66 to 93%, respectively. The differences in prediction of time histories are not reflected in the estimation of time-averaged forces due to cancellation effects, wherein the forces are underpredicted in the first half of the stroke and overpredicted in the second half. The discrepancies are attributed to the simplifying assumptions in the unsteady aerodynamic vortex model, which overpredicts the vorticity in the leading-edge vortex and results in significant differences in the wing-wake interaction process.

No AccessTechnical NoteFree-to-Pivot Flat Plates in Hover for Reynolds Numbers 14 to 21,200Kenneth O. Granlund, Michael V. Ol and Luis P. BernalKenneth O. GranlundAerospace Systems Directorate, U.S. Air Force Research Laboratory, Wright–Patterson Air Force Base, Ohio 45433-7542*Aerospace Systems Directorate; . Senior Member AIAA.Search for more papers by this author, Michael V. OlAerospace Systems Directorate, U.S. Air Force Research Laboratory, Wright–Patterson Air Force Base, Ohio 45433-7542†Aerospace Systems Directorate. Associate Fellow AIAA.Search for more papers by this author and Luis P. BernalDepartment of Aerospace Engineering, University of Michigan, Ann Arbor, Michigan 48109-2140‡Department of Aerospace Engineering. Senior Member AIAA.Search for more papers by this authorPublished Online:26 Aug 2014https://doi.org/10.2514/1.J053169SectionsView Full TextPDFPDF Plus ToolsAdd to favoritesDownload citationTrack citations ShareShare onFacebookTwitterLinked InRedditEmail About References [1] Freymuth P., “Thrust Generation by an Airfoil in Hover Modes,” Experiments in Fluids, Vol. 9, Nos. 1–2, 1990, pp. 17–24. doi:https://doi.org/10.1007/BF00575331 EXFLDU 0723-4864 CrossrefGoogle Scholar[2] Sane S. P. and Dickinson M. H., “The Control of Flight Force by a Flapping Wing: Lift and Drag Production,” Journal of Experimental Biology, Vol. 204, Aug. 2001, pp. 2607–2626. JEBIAM 0022-0949 CrossrefGoogle Scholar[3] Dickson W. and Dickinson M., “The Effect of Advance Ratio on the Aerodynamics of Revolving Wings,” Journal of Experimental Biology, Vol. 207, Nov. 2004, pp. 4269–4281. doi:https://doi.org/10.1242/jeb.01266 JEBIAM 0022-0949 CrossrefGoogle Scholar[4] Wan H., Dong H. and Huang G., “Hovering Hinge-Connected Flapping Plate with Passive Deflection,” AIAA Journal, Vol. 50, No. 9, 2012, pp. 2020–2026. doi:https://doi.org/10.2514/1.J051375 AIAJAH 0001-1452 LinkGoogle Scholar[5] Shyy W., Aono H., Kang C.-k. and Liu H., An Introduction to Flapping Wing Aerodynamics, Cambridge Univ. Press, New York, 2013, pp. 95–116. CrossrefGoogle Scholar[6] Granlund K., Ol M. and Bernal L., “Unsteady Pitching Flat Plates,” Journal of Fluid Mechanics, Vol. 733, Oct. 2013, p. R5. doi:https://doi.org/10.1017/jfm.2013.444 JFLSA7 0022-1120 CrossrefGoogle Scholar[7] Granlund K., Ol M. and Bernal L., “Quasi-Steady Response of Free-to-Pivot Flat Plates in Hover,” Journal of Fluids and Structures, Vol. 40, July 2013, pp. 337–355. doi:https://doi.org/10.1016/j.jfluidstructs.2013.02.020 0889-9746 CrossrefGoogle Scholar[8] Gaston Z., Wan H., Dong H. and Ol M., “Analysis of a Hinge-Connected Flapping Plate with an Implemented Torsional Spring Model,” AIAA Paper 2012-0298, 2012. LinkGoogle Scholar[9] Doman D., Oppenheimer M. and Sigthorsson D., “Wingbeat Shape Modulation for Flapping-Wing Micro-Air-Vehicle Control During Hover,” Journal of Guidance, Control, and Dynamics, Vol. 33, No. 3, 2010, pp. 724–739. doi:https://doi.org/10.2514/1.47146 JGCDDT 0162-3192 LinkGoogle Scholar[10] Wood R., “The First Takeoff of a Biologically Inspired At-Scale Robotic Insect,” IEEE Transactions on Robotics, Vol. 24, No. 2, 2007, pp. 341–347. doi:https://doi.org/10.1109/TRO.2008.916997 IRAUEZ 1042-296X CrossrefGoogle Scholar[11] Ol M. V., Bernal L. P., Kang C.-K. and Shyy W., “Shallow and Deep Dynamic Stall for Flapping Low Reynolds Number Airfoils,” Experiments in Fluids, Vol. 46, No. 5, 2009, pp. 883–901. doi:https://doi.org/10.1007/s00348-009-0660-3 EXFLDU 0723-4864 CrossrefGoogle Scholar[12] Chabalko C., Fitzgerald T., Valdez M. and Balachandran B., “Flapping Aerodynamics and Ground Effect,” AIAA Paper 2012-0420, 2012. LinkGoogle Scholar[13] Minier C. S. and Dalton N. N., Physical Properties of Glycerine and it’s Solutions, American Chemical Society Monograph 117, Reinhold, New York, 1953, p. 10. Google Scholar[14] Poelma C., Dickson W. and Dickinson M. H., “Time-Resolved Reconstruction of the Full Velocity Field Around a Dynamically-Scaled Flapping Wing,” Experiments in Fluids, Vol. 41, No. 2, 2006, pp. 213–225. doi:https://doi.org/10.1007/s00348-006-0172-3 EXFLDU 0723-4864 CrossrefGoogle Scholar[15] Dong H., Lian Z. and Harff M., “Optimal Settings of Aerodynamic Performance Parameters in Hovering Flight,” International Journal of Micro Air Vehicles, Vol. 1, No. 3, Sept. 2009, pp. 173–181. doi:https://doi.org/10.1260/175682909789996195 CrossrefGoogle Scholar[16] Bos F. M., van Oudheusden B. and Bijl H., “Wing Performance and 3-D Vortical Structure Formation in Flapping Flight,” Journal of Fluids and Structures, Vol. 42, Oct. 2013, pp. 130–151. doi:https://doi.org/10.1016/j.jfluidstructs.2013.04.002 0889-9746 CrossrefGoogle Scholar Previous article Next article

A new valve-only micropump structure for gas applications is proposed consisting of electrostatically actuated checkerboard microvalves with dual cavities. The valve-only multistage peristaltic design minimizes complexity and footprint of the device, which allows operation at high frequency, better sealing and efficient operation. A previously developed reduced order model is used to design and analyze the performance of the system. In this paper the effect of the cavity height on the performance and stability of this system is explored. The fabricated micropump produced a flow rate of 140 μl/min at 1 kHz operation despite the cavity and membrane resonance being > 20 kHz. Four micropumps having cavity heights of 45, 60, 90 and 120 μm are explored in the modeling efforts using sinusoidal waveforms. It is found that an optimum cavity height exists which maximizes pump performance. Decreasing the cavity height below this value increases acoustic pressure damping, which in turn increases instability of the system.