scholarly journals Investigation into Reynolds number effects on a biomimetic flapping wing

2018 ◽  
Vol 10 (1) ◽  
pp. 106-122 ◽  
Author(s):  
Daniel K Hope ◽  
Anthony M DeLuca ◽  
Ryan P O’Hara
Keyword(s):  
Reynolds Number ◽  
Natural Frequency ◽  
Air Force ◽  
High Speed ◽  
Force Production ◽  
Vertical Force ◽  
Linkage Mechanism ◽  
Wing Span ◽  
Institute Of Technology ◽  
Wing Stroke

This research investigated the behavior of a Manduca sexta inspired biomimetic wing as a function of Reynolds number by measuring the aerodynamic forces produced by varying the characteristic wing length and testing at air densities from atmospheric to near vacuum. A six degree of freedom balance was used to measure forces and moments, while high speed cameras were used to measure wing stroke angle. An in-house created graphical user interface was used to vary the voltage of the drive signal sent to the piezoelectric actuator which determined the wing stroke angle. The Air Force Institute of Technology baseline 50 mm wing was compared to wings manufactured with 55, 60, 65, and 70 mm spans, while maintaining a constant aspect ratio. Tests were conducted in a vacuum chamber at air densities between 0.5% and 100% of atmospheric pressure. Increasing the wingspan increased the wing’s weight, which reduced the first natural frequency; and did not result in an increase in vertical force over the baseline 50 mm wing. However, if the decrease in natural frequency corresponding to the increased wing span was counteracted by increasing the thickness of the joint material in the linkage mechanism, vertical force production increased over the baseline wing planform. Of the wings built with the more robust flapping mechanism, the 55 mm wing span produced 95% more vertical force at a 26% higher flapping frequency, while the 70 mm wing span produced 165% more vertical force at a 10% lower frequency than the Air Force Institute of Technology baseline wing. Negligible forces and moments were measured at vacuum, where the wing exhibited predominantly inertial motion, revealing flight forces measured in atmosphere are almost wholly limited to interaction with the surrounding air. Lastly, there was a rough correlation between Reynolds number and vertical force, indicating Reynolds number is a useful modelling parameter to predict lift and corresponding aerodynamic coefficients for a specific wing design.

scholarly journals Elytra boost lift, but reduce aerodynamic efficiency in flying beetles

2012 ◽  
Vol 9 (75) ◽  
pp. 2745-2748 ◽  
Author(s):  
L. Christoffer Johansson ◽  
Sophia Engel ◽  
Emily Baird ◽  
Marie Dacke ◽  
Florian T. Muijres ◽  
...  
Keyword(s):  
Force Production ◽  
Aerodynamic Performance ◽  
Vertical Force ◽  
Negative Interaction ◽  
Aerodynamic Efficiency ◽  
Wing Span ◽  
Quantitative Measurements ◽  
Flying Insects ◽  
Weight Support ◽  
Extra Weight

Flying insects typically possess two pairs of wings. In beetles, the front pair has evolved into short, hardened structures, the elytra, which protect the second pair of wings and the abdomen. This allows beetles to exploit habitats that would otherwise cause damage to the wings and body. Many beetles fly with the elytra extended, suggesting that they influence aerodynamic performance, but little is known about their role in flight. Using quantitative measurements of the beetle's wake, we show that the presence of the elytra increases vertical force production by approximately 40 per cent, indicating that they contribute to weight support. The wing-elytra combination creates a complex wake compared with previously studied animal wakes. At mid-downstroke, multiple vortices are visible behind each wing. These include a wingtip and an elytron vortex with the same sense of rotation, a body vortex and an additional vortex of the opposite sense of rotation. This latter vortex reflects a negative interaction between the wing and the elytron, resulting in a single wing span efficiency of approximately 0.77 at mid downstroke. This is lower than that found in birds and bats, suggesting that the extra weight support of the elytra comes at the price of reduced efficiency.

scholarly journals Design and Fabrication of a High-Speed Atomic Force Microscope Scan-Head

Sensors ◽  
2021 ◽  
Vol 21 (2) ◽  
pp. 362
Author(s):  
Luke Oduor Otieno ◽  
Bernard Ouma Alunda ◽  
Jaehyun Kim ◽  
Yong Joong Lee
Keyword(s):  
Atomic Force Microscope ◽  
Natural Frequency ◽  
High Speed ◽  
Contact Mode ◽  
Ongoing Process ◽  
Atomic Force ◽  
Constant Height ◽  
Mode Tracking

A high-speed atomic force microscope (HS-AFM) requires a specialized set of hardware and software and therefore improving video-rate HS-AFMs for general applications is an ongoing process. To improve the imaging rate of an AFM, all components have to be carefully redesigned since the slowest component determines the overall bandwidth of the instrument. In this work, we present a design of a compact HS-AFM scan-head featuring minimal loading on the Z-scanner. Using a custom-programmed controller and a high-speed lateral scanner, we demonstrate its working by obtaining topographic images of Blu-ray disk data tracks in contact- and tapping-modes. Images acquired using a contact-mode cantilever with a natural frequency of 60 kHz in constant deflection mode show good tracking of topography at 400 Hz. In constant height mode, tracking of topography is demonstrated at rates up to 1.9 kHz for the scan size of 1μm×1μm with 100×100 pixels.

scholarly journals Ontogeny of aerial righting and wing flapping in juvenile birds

2014 ◽  
Vol 10 (8) ◽  
pp. 20140497 ◽  
Author(s):  
Dennis Evangelista ◽  
Sharlene Cam ◽  
Tony Huynh ◽  
Igor Krivitskiy ◽  
Robert Dudley
Keyword(s):  
Force Production ◽  
Vertical Force ◽  
Alectoris Chukar ◽  
Avian Flight ◽  
Body Roll ◽  
Chukar Partridge

Mechanisms of aerial righting in juvenile chukar partridge ( Alectoris chukar ) were studied from hatching to 14 days-post-hatching (dph). Asymmetric movements of the wings were used from 1 to 8 dph to effect progressively more successful righting behaviour via body roll. Following 8 dph, wing motions transitioned to bilaterally symmetric flapping that yielded aerial righting via nose-down pitch, along with substantial increases in vertical force production during descent. Ontogenetically, the use of such wing motions to effect aerial righting precedes both symmetric flapping and a previously documented behaviour in chukar (i.e. wing-assisted incline running) hypothesized to be relevant to incipient flight evolution in birds. These findings highlight the importance of asymmetric wing activation and controlled aerial manoeuvres during bird development and are potentially relevant to understanding the origins of avian flight.

Numerical Simulations of Resonant Heat Transfer Augmentation at Low Reynolds Numbers

2001 ◽  
Author(s):  
Miles Greiner ◽  
Paul F. Fischer ◽  
Henry Tufo
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Natural Frequency ◽  
Flow Rate ◽  
Low Reynolds Number ◽  
Reynolds Numbers ◽  
Spectral Element ◽  
Pumping Power ◽  
Number Systems ◽  
Low Reynolds

Abstract The effect of flow rate modulation on low Reynolds number heat transfer enhancement in a transversely grooved passage was numerically simulated using a two-dimensional spectral element technique. Simulations were performed at subcritical Reynolds numbers of Rem = 133 and 267, with 20% and 40% flow rate oscillations. The net pumping power required to modulate the flow was minimized as the forcing frequency approached the predicted natural frequency. However, mixing and heat transfer levels both increased as the natural frequency was approached. Oscillatory forcing in a grooved passage requires two orders of magnitude less pumping power than flat passage systems for the same heat transfer level. Hydrodynamic resonance appears to be an effective method of increasing heat transfer in low Reynolds number systems where pumping power is at a premium, such as micro heat transfer applications.

Optimal Control of a Flexible Mechanism Using a Combined Feedforward-Feedback Strategy: Simulation and Experiment

1999 ◽  
Author(s):  
Hubertus v. Stein ◽  
Heinz Ulbrich
Keyword(s):  
Optimal Control ◽  
Control Strategy ◽  
System Performance ◽  
High Speed ◽  
Time Varying ◽  
Linkage Mechanism ◽  
Additional Degree ◽  
Control Approach ◽  
Feedback Optimal Control ◽  
Four Bar Linkage

Abstract Due to the elasticity of the links in modern high speed mechanisms, increasing operating speeds often lead to undesirable vibrations, which may render a required accuracy unattainable or, even worse, lead to a failure of the whole process. The dynamic effects e.g. may lead to intolerable deviations from the reference path or even to the instability of the system. Instead of suppressing the vibration by a stiffer design, active control methods may greatly improve the system performance and lead the way to a reduction of the mechanism’s weight. We investigate a four-bar-linkage mechanism and show that by introducing an additional degree of freedom for a controlled actuator and providing a suitable control strategy, the dynamically induced inaccuracies can be substantially reduced. The modelling of the four-bar-linkage mechanism as a hybrid multi body system and the modelling of the complete system (including the actuator) is briefly explained. From the combined feedforward-feedback optimal control approach presented in (v. Stein, Ulbrich, 1998) a time-varying output control law is derived that leads to a very good system performance for this linear discrete time-varying system. The experimental results show the effectiveness of the applied control strategy.

A Theoretical Investigation of the Maximum-lift Coefficient

1935 ◽  
Vol 39 (295) ◽  
pp. 619-632
Author(s):  
TH. Von karman ◽  
Clark B. Millikan
Keyword(s):  
Experimental Investigation ◽  
Reynolds Number ◽  
Wind Tunnel ◽  
Theoretical Investigation ◽  
Lift Coefficient ◽  
Wind Tunnels ◽  
California Institute ◽  
California Institute Of Technology ◽  
Junior Author ◽  
Institute Of Technology

The problem of the maximum lift of airfoils has concerned the authors greatly since there were first discovered in the spring of 1932 serious discrepancies in this characteristic between results obtained in the wind tunnel of the Guggenheim Aeronautics Laboratory at the California Institute of Technology (GALCIT) and those reported from certain other wind tunnels. An elaborate experimental investigation by the junior author and A. L. Klein indicated that the value of CLmax for a given airfoil was strongly affected both by Reynolds number and by the degree of turbulence in the tunnel wind stream.

Aerodynamics of a two-dimensional bluff body with the cross-section of a train

2020 ◽  
Vol 23 (12) ◽  
pp. 2679-2693 ◽  
Author(s):  
Huan Li ◽  
Xuhui He ◽  
Hanfeng Wang ◽  
Si Peng ◽  
Shuwei Zhou ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Large Amplitude ◽  
High Speed ◽  
Bluff Body ◽  
Mean Amplitude ◽  
Two Dimensional ◽  
Aerodynamic Forces ◽  
Moderate Reynolds Number ◽  
Amplitude Mode

Experiments on the aerodynamics of a two-dimensional bluff body simplified from a China high-speed train in crosswinds were carried out in a wind tunnel. Effects of wind angle of attack α varying in [−20°, 20°] were investigated at a moderate Reynolds number Re = 9.35 × 104 (based on the height of the model). Four typical behaviors of aerodynamics were identified. These behaviors are attributed to the flow structure around the upper and lower halves of the model changing from full to intermittent reattachment, and to full separation with a variation in α. An alternate transition phenomenon, characterized by an alteration between large- and small-amplitude aerodynamic fluctuations, was detected. The frequency of this alteration is about 1/10 of the predominant vortex shedding. In the intervals of the large-amplitude behavior, aerodynamic forces fluctuate periodically with a strong span-wise coherence, which are caused by the anti-symmetric vortex shedding along the stream-wise direction. On the contrary, the aerodynamic forces fluctuating at small amplitudes correspond to a weak span-wise coherence, which are ascribed to the symmetric vortex shedding from the upper and lower halves of the model. Generally, the mean amplitude of the large-amplitude mode is 3 times larger than that of the small one. Finally, the effects of Reynolds number were examined within Re = [9.35 × 104, 2.49 × 105]. Strong Reynolds number dependence was observed on the model with two rounded upper corners.

scholarly journals Mixing and chemical reactions in a turbulent liquid mixing layer

1986 ◽  
Vol 170 ◽  
pp. 83-112 ◽  
Author(s):  
M. M. Koochesfahani ◽  
P. E. Dimotakis
Keyword(s):  
Reynolds Number ◽  
Gas Phase ◽  
Turbulent Mixing ◽  
High Speed ◽  
High Reynolds Number ◽  
Schmidt Number ◽  
Mixing Layer ◽  
Entrainment Ratio ◽  
High Reynolds ◽  
Mixed Fluid

An experimental investigation of entrainment and mixing in reacting and non-reacting turbulent mixing layers at large Schmidt number is presented. In non-reacting cases, a passive scalar is used to measure the probability density function (p.d.f.) of the composition field. Chemically reacting experiments employ a diffusion-limited acid–base reaction to directly measure the extent of molecular mixing. The measurements make use of laser-induced fluorescence diagnostics and high-speed, real-time digital image-acquisition techniques.Our results show that the vortical structures in the mixing layer initially roll-up with a large excess of fluid from the high-speed stream entrapped in the cores. During the mixing transition, not only does the amount of mixed fluid increase, but its composition also changes. It is found that the range of compositions of the mixed fluid, above the mixing transition and also throughout the transition region, is essentially uniform across the entire transverse extent of the layer. Our measurements indicate that the probability of finding unmixed fluid in the centre of the layer, above the mixing transition, can be as high as 0.45. In addition, the mean concentration of mixed fluid across the layer is found to be approximately constant at a value corresponding to the entrainment ratio. Comparisons with gas-phase data show that the normalized amount of chemical product formed in the liquid layer, at high Reynolds number, is 50% less than the corresponding quantity measured in the gas-phase case. We therefore conclude that Schmidt number plays a role in turbulent mixing of high-Reynolds-number flows.

Observation and Scaling of Tip Vortex Cavitation on Elliptical Hydrofoils

2011 ◽  
Author(s):  
Shigeki Nagaya ◽  
Risa Kimoto ◽  
Kenji Naganuma ◽  
Takayuki Mori
Keyword(s):  
Water Quality ◽  
Reynolds Number ◽  
High Speed ◽  
Tip Vortex ◽  
Video Observation ◽  
Tip Vortex Cavitation ◽  
Air Content ◽  
Sheet Cavitation ◽  
High Speed Video ◽  
Systems Research

Experimental study on tip vortex cavitation (TVC) was carried out for elliptical hydrofoils with various chord lengths. The purpose of the experiment was to clarify the influences of Reynolds number and water quality on tip vortex cavitation. Experiments were made in a large cavitation tunnel of the Naval Systems Research Center, TRDI/Ministry of Defense Japan. The elliptical hydrofoils tested were NACA 0012 cross section with chord lengths of 500mm, 250mm and 50mm. Reynolds number based on hydrofoil chord length was 2×105 < ReC < 7.4×106. Water quality of the tunnel was characterized by air content and nuclei distribution. Air content of the tunnel was varied between 30% and 80%. Nuclei distribution was measured by a cavitation susceptibility meter (CSM) with center-body venturi. Cavitation inception was determined from high speed video observation. A standard formula, (σL/σS) = (ReL/ReS)n, was applied for the scaling. In the present study, exponent of the scaling law n was found to be 0.2 < n < 0.4. High speed video observation showed that the process of the TVC inception strongly depends on water quality. In the experiments, unsteady behaviors of TVC were also investigated. Strong interactions between sheet cavitation and TVC were observed.

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