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Velocity vector files from PIV measurements of the wake behind a flying beetle

Citation

Ribak, Gal; Gurka, Roi (2020), Velocity vector files from PIV measurements of the wake behind a flying beetle, Dryad, Dataset, https://doi.org/10.5061/dryad.pg4f4qrm9

Abstract

These are the velocity vector files from the PIV measurements in the wake of Batocera rufomaculata flying tethered in a wind tunnel. The data correspond to the manuscript: 

The aerodynamics and power requirements of forward flapping flight in the mango stem borer beetle (Batocera rufomaculata), by Urca et al. published by the journal Integrative Organismal Biology. 

The abstract of the coresponding paper is: 

The need for long dispersal flights can drive selection for behavioral, physiological and biomechanical mechanisms to reduce the energy spent flying. However, some energy loss during the transfer of momentum from the wing to the fluid is inevitable, and inherent to the fluid-wing interaction. Here, we analyzed these losses during the forward flight of the mango stem borer (Batocera rufomaculata). This relatively large beetle can disperse substantial distances in search of new host trees, and laboratory experiments have demonstrated continuous tethered flights that can last for up to an hour. We flew the beetles tethered in a wind tunnel and used high-speed videography to estimate the aerodynamic power from their flapping kinematics and particle image velocimetry (PIV) to evaluate drag and kinetic energy from their unsteady wakes. To account for tethering effects, we measured the forces applied by the beetles on the tether arm holding them in place. The drag of the flying beetle over the flapping cycle, estimated from the flow fields in the unsteady wake, showed good agreement with direct measurement of mean horizontal force. Both measurements showed that total drag during flight is ~5-fold higher than the parasite drag on the body. The aerodynamic power estimated from both the motion of the wings, using a quasi-steady blade-element model, and the kinetic energy in the wake, gave mean values of flight-muscle mass-specific power of 87 and 65 W kg muscle-1, respectively. A comparison of the two values suggests that ~25% of the energy is lost within the fluid due to turbulence and heat. The muscle mass-specific power found here is low relative to the maximal power output reported for insect flight muscles. This can be attributed to reduced weight support during tethered flight or to operation at submaximal output that may ensure a supply of metabolic substrates to the flight muscles, thus delaying their fatigue during long-distance flights.  

Methods

vector files in the flow fields measnured using PIV

PIV description:

Plane: streamwise-normal, At mid downstroke, the light sheet intersected the beetle’s left wing at 2/3 the wing length.

Laser: double-head Nd:YAG laser , 532 nm, emitting 200mJ/pulse at 15 Hz (Evergreen, Quantel). The time between the laser pulses was set to 200 msec

The light sheet was formed using a 15 mm cylindrical lens followed by a 500 mm spherical lens.

PIV camera:  8MP (3320x2476 pixle2) CCD double exposure camera operating at 4 Hz with a 12-bit dynamic range capturing a field of view of 220x141 mm2.

Seeding : olive oil droplets with an average dimeter of 1 mm, generated using a Laskin nozzle.

Processing:  vectors were calculated using an interrogation window of 64 × 64 pixle2 with a 50% overlap (Insight 4G, TSI).

Post processing: local vector validation based on a median test from the surrounding 5 × 5 vectors. Holes in the vector maps were filled with the local mean value calculated from surrounding measured vectors. The number of erroneous vectors per map was less than 5%.

Funding

Israel Science Foundation, Award: 849/15