scholarly journals The complex aerodynamic footprint of desert locusts revealed by large-volume tomographic particle image velocimetry

2015 ◽  
Vol 12 (108) ◽  
pp. 20150119 ◽  
Author(s):  
Per Henningsson ◽  
Dirk Michaelis ◽  
Toshiyuki Nakata ◽  
Daniel Schanz ◽  
Reinhard Geisler ◽  
...  
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Aerodynamic Force ◽  
Helmholtz Instability ◽  
Tip Vortices ◽  
Left Behind ◽  
Image Velocimetry ◽  
Secondary Vortices ◽  
Animal Flight ◽  
Wing Tip

Particle image velocimetry has been the preferred experimental technique with which to study the aerodynamics of animal flight for over a decade. In that time, hardware has become more accessible and the software has progressed from the acquisition of planes through the flow field to the reconstruction of small volumetric measurements. Until now, it has not been possible to capture large volumes that incorporate the full wavelength of the aerodynamic track left behind during a complete wingbeat cycle. Here, we use a unique apparatus to acquire the first instantaneous wake volume of a flying animal's entire wingbeat. We confirm the presence of wake deformation behind desert locusts and quantify the effect of that deformation on estimates of aerodynamic force and the efficiency of lift generation. We present previously undescribed vortex wake phenomena, including entrainment around the wing-tip vortices of a set of secondary vortices borne of Kelvin–Helmholtz instability in the shear layer behind the flapping wings.

scholarly journals Tomographic particle image velocimetry of desert locust wakes: instantaneous volumes combine to reveal hidden vortex elements and rapid wake deformation

2012 ◽  
Vol 9 (77) ◽  
pp. 3378-3386 ◽  
Author(s):  
Richard J. Bomphrey ◽  
Per Henningsson ◽  
Dirk Michaelis ◽  
David Hollis
Keyword(s):  
Particle Image Velocimetry ◽  
High Speed ◽  
Particle Image ◽  
Aerodynamic Force ◽  
Three Dimensional ◽  
Flow Fields ◽  
Diagnostic Methods ◽  
Tomographic Particle Image Velocimetry ◽  
Image Velocimetry ◽  
Spatio Temporal

Aerodynamic structures generated by animals in flight are unstable and complex. Recent progress in quantitative flow visualization has advanced our understanding of animal aerodynamics, but measurements have hitherto been limited to flow velocities at a plane through the wake. We applied an emergent, high-speed, volumetric fluid imaging technique (tomographic particle image velocimetry) to examine segments of the wake of desert locusts, capturing fully three-dimensional instantaneous flow fields. We used those flow fields to characterize the aerodynamic footprint in unprecedented detail and revealed previously unseen wake elements that would have gone undetected by two-dimensional or stereo-imaging technology. Vortex iso-surface topographies show the spatio-temporal signature of aerodynamic force generation manifest in the wake of locusts, and expose the extent to which animal wakes can deform, potentially leading to unreliable calculations of lift and thrust when using conventional diagnostic methods. We discuss implications for experimental design and analysis as volumetric flow imaging becomes more widespread.

scholarly journals Experimental measurements of the flow field around a film-cooled blade leading edge using particle image velocimetry

2018 ◽  
Vol 10 (10) ◽  
pp. 168781401880290
Author(s):  
José Omar Dávalos Ramírez ◽  
Juan Carlos García Castrejón ◽  
Francisco Carrillo Pereyra ◽  
Carlos Ponce Corral ◽  
Carlos Felipe Ramírez Espinoza ◽  
...  
Keyword(s):  
Particle Image Velocimetry ◽  
Flow Field ◽  
Particle Image ◽  
Leading Edge ◽  
Cooling Flow ◽  
Image Velocimetry ◽  
Secondary Vortices ◽  
Velocity Turbulence ◽  
Cooled Blade ◽  
Blade Leading Edge

In this article, particle image velocimetry studies were conducted in a low-speed wind tunnel to investigate the effects of blowing ratio and blade span in terms of the characteristics of the flow field around a film-cooled blade leading edge. The measurements were performed at 20%, 40%, 60%, and 80% of blade span and blowing ratios of M = 0.5, M = 0.75, M = 1, M = 1.5, and M = 2. Velocity, turbulence intensity, and structure of vortices during the interaction between cooling flow and mainstream were analyzed in detail. The analysis shows a significant increase in mainstream velocity at low blowing ratios, M < 1. Peaks of turbulence were observed at low- and high-span locations. Aerodynamical losses are expected at higher blowing ratios due to the formation of secondary vortices near the outgoing jet. These vortices were a consequence of velocity gradients at this zone.

Stereo three-dimensional particle image velocimetry measurement and aerodynamic force analysis of non-spinning soccer balls

2020 ◽  
Vol 234 (2) ◽  
pp. 146-153 ◽  
Author(s):  
Masaki Hiratsuka ◽  
Shinichiro Ito ◽  
Keita Miyasaka ◽  
Akihisa Konno
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Aerodynamic Force ◽  
Three Dimensional ◽  
Jet Flow ◽  
Flight Path ◽  
Wake Flow ◽  
Force Measurements ◽  
Flow Measurements ◽  
Image Velocimetry

A knuckle shot, resulting from non-spinning kicking, is an essential technique in soccer. The irregular flight path of the knuckle shot is caused by the aerodynamic force from the three-dimensional twin vortices generated in the wake behind the ball. However, the detailed behavior of the twin vortices and relation between the jet flow and the acting forces on the balls is still not understood. In addition, a more thorough understanding of the effect of ball panels on the formation of twin vortices and jet flow is important to develop balls with high controllability. To study the effect of the ball panel shape on the flight path, stereo three-dimensional particle image velocimetry wake flow measurements and synchronized force measurements were performed on various soccer balls. It was confirmed that the aerodynamic force on the ball is produced by the jet flow generated by the vortices in the wake flow. The directions of the force followed the changes of the jet flow, and the magnitude of the force was strongly associated with the flow rate of the jet. Moreover, the shape of the ball panels, especially the groove volume, determines the critical Reynolds number and the fluttering of the balls.

scholarly journals Turbulence investigation of the NASA common research model wing tip vortex

2017 ◽  
Vol 21 (suppl. 3) ◽  
pp. 851-862
Author(s):  
Djordje Cantrak ◽  
James Heineck ◽  
Laura Kushner ◽  
Novica Jankovic
Keyword(s):  
Particle Image Velocimetry ◽  
High Speed ◽  
Particle Image ◽  
Sampling Rate ◽  
Tip Vortex ◽  
Turbulence Structure ◽  
Research Model ◽  
Image Velocimetry ◽  
Wing Tip Vortex ◽  
Wing Tip

The paper presents high-speed stereo particle image velocimetry investigation of the NASA Common Research Model wing tip vortex. A three-percent scaled semi?span model, without nacelle and pylon, was tested in the 32- by 48-inch Indraft tunnel, at the Fluid Mechanics Laboratory at the NASA Ames Research Center. Turbulence investigation of the wing tip vortex is presented. Measurements of the wing-tip vortex were performed in a vertical cross-stream plane three tip-chords downstream of the wing tip trailing edge with a 2 kHz sampling rate. Experimental data are analyzed in the invariant anisotropy maps for three various angles of attack (0?, 2?, and 4?) and the same speed generated in the tunnel (V? = 50 m/s). This corresponds to a chord Reynolds number 2.68x105, where the chord length of 3? is considered the characteristic length. The region of interest was x = 220 mm and y = 90 mm. The 20 000 particle image velocimetry samples were acquired at each condition. Velocity fields and turbulence statistics are given for all cases, as well as turbulence structure in the light of the invariant theory. Prediction of the wing tip vortices is still a challenge for the computational fluid dynamics codes due to significant pressure and velocity gradients.

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