scholarly journals A quantitative comparison of bird and bat wakes

2009 ◽  
Vol 7 (42) ◽  
pp. 61-66 ◽  
Author(s):  
L. Christoffer Johansson ◽  
Marta Wolf ◽  
Anders Hedenström
Keyword(s):  
Vortex Structure ◽  
Quantitative Comparison ◽  
Flight Speed ◽  
Vortex Wake ◽  
Qualitative Comparison ◽  
Minimum Power ◽  
Induced Drag ◽  
Far Wake ◽  
Total Circulation

Qualitative comparison of bird and bat wakes has demonstrated significant differences in the structure of the far wake. Birds have been found to have a unified vortex wake of the two wings, while bats have a more complex wake with gradients in the circulation along the wingspan, and with each wing generating its own vortex structure. Here, we compare quantitative measures of the circulation in the far wake of three bird and one bat species. We find that bats have a significantly stronger normalized circulation of the start vortex than birds. We also find differences in how the circulation develops during the wingbeat as demonstrated by the ratio of the circulation of the dominant start vortex and the total circulation of the same sense. Birds show a more prominent change with changing flight speed and a relatively weaker start vortex at minimum power speed than bats. We also find that bats have a higher normalized wake loading based on the start vortex, indicating higher relative induced drag and therefore less efficient lift generation than birds. Our results thus indicate fundamental differences in the aerodynamics of bird and bat flight that will further our understanding of the evolution of vertebrate flight.

scholarly journals Desulphurisation of Biogas: A Systematic Qualitative and Economic-Based Quantitative Review of Alternative Strategies

2019 ◽  
Vol 3 (3) ◽  
pp. 76 ◽  
Author(s):  
Oseweuba Valentine Okoro ◽  
Zhifa Sun
Keyword(s):  
Quantitative Comparison ◽  
Negative Consequences ◽  
Qualitative Comparison ◽  
Quantitative Review ◽  
Current State ◽  
Negative Impacts ◽  
State Of Research ◽  
And Performance ◽  
Selection Of

The desulphurisation of biogas for hydrogen sulphide (H2S) removal constitutes a significant challenge in the area of biogas research. This is because the retention of H2S in biogas presents negative consequences on human health and equipment durability. The negative impacts are reflective of the potentially fatal and corrosive consequences reported when biogas containing H2S is inhaled and employed as a boiler biofuel, respectively. Recognising the importance of producing H2S-free biogas, this paper explores the current state of research in the area of desulphurisation of biogas. In the present paper, physical–chemical, biological, in-situ, and post-biogas desulphurisation strategies were extensively reviewed as the basis for providing a qualitative comparison of the strategies. Additionally, a review of the costing data combined with an analysis of the inherent data uncertainties due underlying estimation assumptions have also been undertaken to provide a basis for quantitative comparison of the desulphurisation strategies. It is anticipated that the combination of the qualitative and quantitative comparison approaches employed in assessing the desulphurisation strategies reviewed in the present paper will aid in future decisions involving the selection of the preferred biogas desulphurisation strategy to satisfy specific economic and performance-related targets.

Unsteady Hydrofoils: Theoretical and Computational Analysis

2013 ◽  
Author(s):  
Daniel T. Valentine
Keyword(s):  
Flat Plate ◽  
Computational Analysis ◽  
Vortex Sheet ◽  
Vortex Wake ◽  
Two Dimensional ◽  
Fixed Angle ◽  
Induced Drag ◽  
Wake Model ◽  
Theoretical Results ◽  
Computational Predictions

In this paper the computational problem examined is the impulsive start of a two-dimensional flat-plate hydrofoil at a fixed angle of attack. The method applied is an equally-spaced lumped-vortex panel method. The results from a lumped-vortex wake model and a shed-vortex sheet wake model are reported. Comparisons with the linear theory of Wagner (1925), the theoretical results associated with the single lumped-vortex wake model and the full wake model are presented. In addition, it is shown that the computational predictions are consistent with results reported by Katz and Plotkin (2001); they applied a distribution of vortices to model the wake. In the present paper the importance of resolving the chordwise pressure distribution in unsteady hydrofoil problems is elucidated. New predictions of both the evolution of lift and induced drag are reported for the instantaneously started flat plate. The computational predictions are compared with theorecticalpredictions also discussed in this paper.

scholarly journals Structure of the vortex wake in hovering Anna's hummingbirds ( Calypte anna )

2013 ◽  
Vol 280 (1773) ◽  
pp. 20132391 ◽  
Author(s):  
M. Wolf ◽  
V. M. Ortega-Jimenez ◽  
R. Dudley
Keyword(s):  
Flow Visualization ◽  
Vortex Structure ◽  
Force Production ◽  
Vortex Rings ◽  
Vortex Wake ◽  
Secondary Vortex ◽  
Single Vortex ◽  
Discrete Vortex ◽  
Weight Support ◽  
Calypte Anna

Hummingbirds are specialized hoverers for which the vortex wake has been described as a series of single vortex rings shed primarily during the downstroke. Recent findings in bats and birds, as well as in a recent study on Anna's hummingbirds, suggest that each wing may shed a discrete vortex ring, yielding a bilaterally paired wake. Here, we describe the presence of two discrete rings in the wake of hovering Anna's hummingbirds, and also infer force production through a wingbeat with contributions to weight support. Using flow visualization, we found separate vortices at the tip and root of each wing, with 15% stronger circulation at the wingtip than at the root during the downstroke. The upstroke wake is more complex, with near-continuous shedding of vorticity, and circulation of approximately equal magnitude at tip and root. Force estimates suggest that the downstroke contributes 66% of required weight support, whereas the upstroke generates 35%. We also identified a secondary vortex structure yielding 8–26% of weight support. Lift production in Anna's hummingbirds is more evenly distributed between the stroke phases than previously estimated for Rufous hummingbirds, in accordance with the generally symmetric down- and upstrokes that characterize hovering in these birds.

scholarly journals Functional Ca2+ Channels between Channel Clusters are Necessary for the Propagation of IP3R-Mediated Ca2+ Waves

2019 ◽  
Vol 24 (2) ◽  
pp. 61
Author(s):  
Estefanía Piegari ◽  
Silvina Ponce Dawson
Keyword(s):  
Signal Propagation ◽  
Cell Types ◽  
Quantitative Comparison ◽  
Preliminary Conclusion ◽  
Qualitative Comparison ◽  
Excitable System ◽  
Inositol 1,4,5 Trisphosphate ◽  
Intracellular Ca ◽  
Spatio Temporal ◽  
Ca2 Channels

The specificity and universality of intracellular Ca 2 + signals rely on the variety of spatio-temporal patterns that the Ca 2 + concentration can display. Ca 2 + release into the cytosol through inositol 1,4,5-trisphosphate receptors (IP 3 Rs) is key for this variety. The opening probability of IP 3 Rs depends on the cytosolic Ca 2 + concentration. All of the dynamics are then well described by an excitable system in which the signal propagation depends on the ability of the Ca 2 + released through one IP 3 R to induce the opening of other IP 3 Rs. In most cell types, IP 3 Rs are organized in clusters, i.e., the cytosol is a “patchy” excitable system in which the signals can remain localized (i.e., involving the release through one or more IP 3 Rs in a cluster), or become global depending on the efficiency of the Ca 2 + -mediated coupling between clusters. The spatial range over which the signals propagate determines the responses that the cell eventually produces. This points to the importance of understanding the mechanisms that make the propagation possible. Our previous qualitative comparison between experiments and numerical simulations seemed to indicate that Ca 2 + release not only occurs within the close vicinity of the clearly identifiable release sites (IP 3 R clusters) but that there are also functional IP 3 Rs in between them. In this paper, we present a quantitative comparison between experiments and models that corroborate this preliminary conclusion. This result has implications on how the Ca 2 + -mediated coupling between clusters works and how it can eventually be disrupted by the different Ca 2 + trapping mechanisms.

On the far wake and induced drag of aircraft

2008 ◽  
Vol 603 ◽  
pp. 413-430 ◽  
Author(s):  
PHILIPPE R. SPALART
Keyword(s):  
Mechanical Energy ◽  
Ground Plane ◽  
Momentum Equation ◽  
Vortex Sheets ◽  
Infinite Domains ◽  
Induced Drag ◽  
Counter Example ◽  
Sink Term ◽  
The Subject ◽  
Far Wake

A set of matched asymptotic expansions is proposed for the flow far behind an aircraft, with the primary purpose of identifying lift, thrust and drag, particularly induced drag, in a unified manner in integral statements of the momentum equation. The fluid in the far wake is inviscid and incompressible, and variations of total pressure are allowed, as are vortex sheets. A notable feature is that the Trefftz-plane approximation is not invoked; instead the wake is taken as fully rolled-up, and the analysis proceeds without the assumption of light loading. Attention is paid to the absolute convergence of integrals over infinite domains and handling of discontinuities. The expansion includes a sink term, which appears new, so that the mass flux through a transverse plane is non-zero, as is the flux of mechanical energy. The lift can be formally attributed to the velocity induced by the bound vortex of the wing, which is at odds with some treatments, although consistent with Prandtl's analysis over a ground plane. The drag contains the integral of ρ(v2 + w2 − u2)/2, as in many treatments of the subject, u being the perturbation velocity along the wake. The negative sign for u2 appears paradoxical on two counts, one of which is resolved here. First, its very presence instead of the + sign, which would lead to the perturbation kinetic energy and therefore a compelling explanation of induced drag, is explained by the longitudinal energy flux. This energy, the integral of ρu2, is continuously provided by the unsteady starting-vortex system and was deposited earlier by the aircraft. Second, it appears that negative drag could be predicted by this equation. This is shown to be impossible, because of inequalities between the integrals of (v2 + w2) and of u2, but the proof is valid only if the vorticity is of only one sign on each side. A general proof of positivity has not been derived, because of nonlinearities, but neither has a counter-example.

scholarly journals Downstroke and upstroke conflict during banked turns in butterflies

2021 ◽  
Vol 18 (185) ◽  
Author(s):  
P. Henningsson ◽  
L. C. Johansson
Keyword(s):  
General Feature ◽  
Insect Flight ◽  
Flight Path ◽  
Flight Speed ◽  
Rolling Motion ◽  
Induced Drag ◽  
Turn Radius ◽  
Thrust Production

For all flyers, aeroplanes or animals, making banked turns involve a rolling motion which, due to higher induced drag on the outer than the inner wing, results in a yawing torque opposite to the turn. This adverse yaw torque can be counteracted using a tail, but how animals that lack tail, e.g. all insects, handle this problem is not fully understood. Here, we quantify the performance of turning take-off flights in butterflies and find that they use force vectoring during banked turns without fully compensating for adverse yaw. This lowers their turning performance, increasing turn radius, since thrust becomes misaligned with the flight path. The separation of function between downstroke (lift production) and upstroke (thrust production) in our butterflies, in combination with a more pronounced adverse yaw during the upstroke increases the misalignment of the thrust. This may be a cost the butterflies pay for the efficient thrust-generating upstroke clap, but also other insects fail to rectify adverse yaw during escape manoeuvres, suggesting a general feature in functionally two-winged insect flight. When lacking tail and left with costly approaches to counteract adverse yaw, costs of flying with adverse yaw may be outweighed by the benefits of maintaining thrust and flight speed.

A QUANTITATIVE AND QUALITATIVE COMPARISON OF DISTRIBUTED INFORMATION PROCESSING USING MOBILE AGENTS REALISED IN RMI AND VOYAGER

2001 ◽  
Vol 11 (05) ◽  
pp. 583-605 ◽  
Author(s):  
PATRICK COGAN ◽  
JACEK GOMOLUCH ◽  
MICHAEL SCHROEDER
Keyword(s):  
Information Processing ◽  
Mobile Agent ◽  
Mobile Agents ◽  
Quantitative Comparison ◽  
Qualitative Comparison ◽  
Distributed Information ◽  
Distributed Object Computing ◽  
Distributed Object ◽  
Agent Platforms ◽  
Flexible Load

We review mobile agents in the context of distributed object computing and parallel processing. We compare these three paradigms qualitatively. For a quantitative comparison of RMI and Voyager as mobile agent platforms, we identify distributed information processing with flexible load balancing as a convincing application to evaluate the two platforms.

Induced drag and wake kinetic energy

2008 ◽  
Vol 112 (1127) ◽  
pp. 54
Author(s):  
P Spalart
Keyword(s):  
Kinetic Energy ◽  
Flow Field ◽  
Fluid Mechanics ◽  
Theoretical Result ◽  
Two Dimensions ◽  
Annual Review ◽  
Bernoulli’S Equation ◽  
Induced Drag ◽  
Lift And Drag ◽  
Far Wake

This 2007 Lanchester Lecture covered a theoretical result, thought to be new and in print in the Journal of Fluid Mechanics, and some lines of thought on the interpretation of induced drag and recurring paradoxes which interfere with teaching ‘how wings work’. Some of these were presented in the author's 1998 Annual Review. The difficulties are not confined to drag, but also concern lift; they are no less severe in two dimensions than in three. The flow-field in the far wake of an aircraft is examined with the primary purpose of identifying lift and drag in a simple and unified manner, preferably an intuitive one acceptable by novices (and even by those who mind using Bernoulli's equation!).

scholarly journals Numerical Modelling of the Nearfield Longitudinal Wake Profiles of a High-Speed Prismatic Planing Hull

2020 ◽  
Vol 8 (7) ◽  
pp. 516
Author(s):  
Angus Gray-Stephens ◽  
Tahsin Tezdogan ◽  
Sandy Day
Keyword(s):  
Fluid Dynamics ◽  
Free Surface ◽  
High Speed ◽  
Experimental Testing ◽  
Quantitative Comparison ◽  
Robust Method ◽  
Free Surface Elevation ◽  
Qualitative Comparison ◽  
Computational Fluid Dynamics Cfd ◽  
Insight Into

This study investigates the level of accuracy with which Computational Fluid Dynamics (CFD) is capable of modelling the nearfield longitudinal wake profiles of a high-speed planing hull. It also looks to establish how various set-ups influence the accuracy, with a specific emphasis on turbulence modelling. It analyses a hull over a broad range of conditions to provide detailed insight into the strengths and limitations of CFD, comparing the numerical results to the experimental results previously generated by the authors. A quantitative comparison is made for the centreline (CL) and quarterbeam (QB) longitudinal wake profile plots. Following this, a qualitative comparison is made between photos of the flow pattern from the experimental testing and free surface elevation plots from CFD. The study concluded that CFD is an accurate and robust method of modelling the nearfield longitudinal wake profiles of a high-speed planning hull.

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