Large-scale volumetric flow visualization of the unsteady wake of a flapping-wing micro air vehicle

Gallar, Blanca Martinez; Oudheusden, B.W. van; Sciacchitano, Andrea; Karásek, Matěj

doi:10.1007/s00348-019-2854-7

Cited by 11 publications

(11 citation statements)

References 61 publications

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“…These issues could in principle be resolved with a volumetric visualization approach at a sufficiently large scale, but this is currently not yet achievable with off-the-shelf PIV equipment. Although a few large-scale volumetric studies have been reported [23,24], the general applicability of such approaches is currently limited by the required high laser power for the volume illumination, the low-to-moderate repetition rate of these PIV lasers, and, in consequence of the latter, the necessity for phase-averaging data strategies.…”

Section: Discussionmentioning

confidence: 99%

“…As a result, the flow structures that are observed in the measurement plane depend on both the position of the MAV relative to the light sheet, as well as on the flapping phase of the wings, and can be further complicated when the MAV crosses the plane with a yaw or sideslip angle. Removal of this ambiguity in the flow visualization would best be served by a true volumetric method, see e.g., [23,24], but such is as yet not really feasible for the considered conditions. Nevertheless, the obtained results were found to be informative regarding the generation of streamwise vortical structures during the flapping cycle.…”

Section: Spanwise Planar Flow Visualizationsmentioning

confidence: 99%

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Flow Visualization around a Flapping-Wing Micro Air Vehicle in Free Flight Using Large-Scale PIV

et al. 2018

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Flow visualizations have been performed on a free flying, flapping-wing micro air vehicle (MAV), using a large-scale particle image velocimetry (PIV) approach. The PIV method involves the use of helium-filled soap bubbles (HFSB) as tracer particles. HFSB scatter light with much higher intensity than regular seeding particles, comparable to that reflected off the flexible flapping wings. This enables flow field visualization to be achieved close to the flapping wings, in contrast to previous PIV experiments with regular seeding. Unlike previous tethered wind tunnel measurements, in which the vehicle is fixed relative to the measurement setup, the MAV is now flown through the measurement area. In this way, the experiment captures the flow field of the MAV in free flight, allowing the true nature of the flow representative of actual flight to be appreciated. Measurements were performed for two different orientations of the light sheet with respect to the flight direction. In the first configuration, the light sheet is parallel to the flight direction, and visualizes a streamwise plane that intersects the MAV wings at a specific spanwise position. In the second configuration, the illumination plane is normal to the flight direction, and visualizes the flow as the MAV passes through the light sheet.Aerospace 2018, 5, 99 2 of 15 Quite a variety of visualization PIV studies on animals in free flight have been reported, see e.g., [11][12][13]; however, the direct correspondence to the current MAV configuration is limited. Firstly, most of these studies consider single-wing configurations at relatively fast forward flight, for which the flow dynamics are less complex than for hovering or slow forward flight, especially in the case of counter-flapping wing configurations with large-amplitude and high-frequency stroke behavior, as considered here. Furthermore, flow visualizations reported in literature have predominantly been limited to wake visualizations, while near-wing visualizations suffer in large regions around the wing from reflections or the obstruction of the illumination [13].The MAV used in the current tests is the DelFly II (henceforth called DelFly for simplicity) [3], for which tethered experiments have been previously performed in hovering [14,15] and symmetric forward flight (at zero pitch angle) [9] configurations. These configurations both result in symmetrical flow patterns around the wings, which is not representative of true forward flight, where an appreciable forward velocity is combined with a high pitch angle. This will result in upper and lower wings experiencing distinctly different aerodynamic conditions. Tethered flow visualization experiments have been carried out on a different DelFly version at relatively small pitch angles [16], whereas [17] reports on preliminary results of a setup intend to enable free-flight wake visualization by controlling the MAV at a fixed position in the exit of a large wind tunnel. The current investigation takes a different and novel approach by aiming to visualiz...

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Section: Discussionmentioning

confidence: 99%

Section: Spanwise Planar Flow Visualizationsmentioning

confidence: 99%

Flow Visualization around a Flapping-Wing Micro Air Vehicle in Free Flight Using Large-Scale PIV

et al. 2018

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“…Optical measurements of the unsteady flow field and the structural motion are performed in an integrated manner, using the same PTV data acquisition and processing system. Particle tracking velocimetry via the Lagrangian particle tracking algorithm Shake-The-Box [10] using helium-filled soap bubbles as flow tracers [11] is a technique that is suitable for the measurement of large-scale unsteady flow fields [12][13][14] and can also be used to perform photogrammetric tracking of fiducial markers on moving objects in the flow [15]. After the PTV measurements of the flow and the structural motion are obtained, physical models need to be applied to determine the unsteady interaction of the forces of different nature on the wing.…”

Section: Aeroelasticity Dynamicmentioning

confidence: 99%

Determination of Collar’s Triangle of Forces on a Flexible Wing based on Particle Tracking Velocimetry Measurements

Mertens

Oudheusden

Sodja

et al. 2021

AIAA Scitech 2021 Forum

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“…To simulate this in the windtunnel, the parameters θb, f, and Unormal∞ were set to replicate values measured in previous free forward flight investigations. 9,12 The cases investigated here are shown in Table 1. The Reynolds number, based on freestream velocity and mean wing chord, varies between Re ≈ 2600 and 12,000 for these cases.…”

Section: Wing Deformation In Forward Flightmentioning

confidence: 99%

“…This MAV features two wing pairs in an X-wing configuration, which “clap-and-peel” 5 on each side. Several studies of the force production 9 and flow field around the DelFly have already been carried out 10–12 ; however, the wing deformation was treated comparatively little. 7 So far, the deformation was considered to be purely symmetrical, as only a stationary hover case was studied.…”

Section: Introductionmentioning

confidence: 99%

Effects of asymmetrical inflow in forward flight on the deformation of interacting flapping wings

Heitzig¹,

Oudheusden²,

Olejnik³

et al. 2020

International Journal of Micro Air Vehicles

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This study investigates the wing deformation of the DelFly II in forward flight conditions. A measurement setup was developed that maintains adequate viewing axes of the flapping wings for all pitch angles. Recordings of a high-speed camera pair were processed using a point tracking algorithm, allowing 136 points per wing to be measured simultaneously with an estimated accuracy of 0.25 mm. The measurements of forward flight show little change in the typical clap-and-peel motion, suggesting similar effectiveness in all cases. It was found that an air-buffer remains at all times during this phase. The wing rotation and camber reduction during the upstroke suggests low loading during the upstroke in fast forward flight. In slow cases a torsional wave and recoil is found. A study of the isolated effects showed asymmetric deformations even in symmetric freestream conditions. Furthermore, it shows a dominant role of the flapping frequency on the clap-and-peel, while the freestream velocity reduces wing loading outside this phase.

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Large-scale volumetric flow visualization of the unsteady wake of a flapping-wing micro air vehicle

Cited by 11 publications

References 61 publications

Flow Visualization around a Flapping-Wing Micro Air Vehicle in Free Flight Using Large-Scale PIV

Flow Visualization around a Flapping-Wing Micro Air Vehicle in Free Flight Using Large-Scale PIV

Determination of Collar’s Triangle of Forces on a Flexible Wing based on Particle Tracking Velocimetry Measurements

Effects of asymmetrical inflow in forward flight on the deformation of interacting flapping wings

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