DOI: 10.5061/dryad.pg4f4qrm9
title: Velocity vector files from PIV measurements of the wake behind a flying beetle

description: 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.  
description: 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
 pixle<sup>2</sup>) CCD double exposure camera operating at 4
 Hz with a 12-bit dynamic range capturing a field of view of 220x141
 mm<sup>2</sup>. 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 pixle<sup>2</sup> 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%.