Three Dimensional Unsteady Flow and Active Morphing Effect in Flapping Wings

Bumble b ee cannot fly, if we ignore the significant differences b etween flappin

Aerodynamic Characteristics of the Ventilated Design for Flapping Wing Micro Air Vehicle

Inspired by superior flight performance of natural flight masters like birds and insects and based on the ventilating flaps that can be opened and closed by the changing air pressure around the wing, a new flapping wing type has been proposed. It is known that the net lift force generated by a solid wing in a flapping cycle is nearly zero. However, for the case of the ventilated wing, results for the net lift force are positive which is due to the effect created by the “ventilation” in reducing negative lift force during the upstroke. The presence of moving flaps can serve as the variable in which, through careful control of the areas, a correlation with the decrease in negative lift can be generated. The corresponding aerodynamic characteristics have been investigated numerically by using different flapping frequencies and forward flight speeds

Plant-pollinator aerodynamics

Interactions between plants and pollinators have adapted over long evolutionary timescales and fill a vital ecological role. For flying pollinators, the same coherent aerodynamic mechanisms are employed across the broad Reynolds number range of 100-10,000. This thesis aims to understand some of the physics involved in plant-pollinator aerodynamics. First, studying the impact of an artificial flower wake on maneuverability revealed emergent simplicity in hawkmoth flower tracking dynamics with increased tracking error at the vortex shedding frequencies of the 3D-printed flower. These results establish that unsteady flow affects complex behaviors as well as steady flight performance. Next, the interplay between steady airflow and wing flexibility was explored in two flow regimes: (1) matching airflow conditions for Manduca sexta flight and (2) matching flow conditions known to produce decoherent leading-edge vortices (LEVs) on rigid wings. Although LEVs still burst on flexible hawkmoth wings, the LEV is decoherent over more of the wingspan as flexibility decreases. Enhanced LEV stability in the hawkmoth flight regime revealed that trade-offs between Coriolis forces (from wing rotation) and inertial forces (from both wing translation and the incoming airflow) influence LEV structure and lift force. Last, the wakes of hawkmoth-pollinated flowers were found to be turbulent but some irregular periodic structures were present downstream of small flowers (diameter less than 40 mm). Like many bluff body flow interactions, flower wakes are dominated by a re-circulation zone downstream and hawkmoths hover-feed within the re-circulation bubble. In addition to characterizing the local flow environment for a hovering hawkmoth, this work showed how flow in the flower wake impacts aerodynamic force (with a blade-element model). Despite the broad diversity in floral environments for pollinators, flapping flight (and the LEV in particular) remains a highly effective strategy. Future work can investigate how insects achieve consistent performance across variable environments from behavioral, neurological, and aerodynamic perspectives.Ph.D

Aeronautical Engineering: A special bibliography with indexes, supplement 64, December 1975

This bibliography lists 288 reports, articles, and other documents introduced into the NASA scientific and technical information system in November 1975

Somatosensory Signaling for Flight Control in the Echolocating Bat Eptesicus fuscus

Bats are the only mammals to have evolved powered flight. Their specialized hand-wings with elongated digits and a thin membrane spanning the digits not only enable flight, but give them unrivaled aerial maneuverability. Bat wing membrane is endowed with an array of microscopic hairs that are hypothesized to monitor airflow and provide sensory feedback to guide rapid motor adjustments for flight control. The goal of this thesis is to contribute to a broader understanding of the response properties of wing-associated tactile receptive fields, and the representation of aerodynamic feedback in the bat's nervous system. Using the big brown bat, Eptesicus fuscus, a series of neurophysiological experiments were performed where the primary somatosensory cortical (S1) responses to tactile and airflow stimulation of the wings were analyzed. Results demonstrate that the body surface is organized topographically across the surface of S1, with an overrepresentation of wings, head and foot. The wings have an inverted orientation compared to hand representation of terrestrial mammals, with tactile thresholds that are remarkably close to human fingertips. Airflow stimulation of the wings was achieved by brief puffs of air generated using a portable fluid dispensing system. By changing the intensity, duration and direction, airflow sensitive receptive fields were characterized based on responses of S1 neurons. Results reveal that neuronal responses are rapidly adapting, encompassing relatively large and overlapping receptive fields with well-defined centers. S1 responses are directionally selective, with a majority preferring reversed airflow. The onset latency of evoked activity decreases as a function of airflow intensity, with no effect on response magnitude. Furthermore, when dorsal and ventral wings surfaces are stimulated simultaneously, S1 responses are either inhibited or facilitated compared to either wing surface stimulation alone. This finding suggests that outputs from the two wing surfaces are integrated in a manner that reflects the interplay of aerodynamic forces experienced by the wings. To evaluate the central coding mechanisms of airflow sensing by bat wings, I applied an information theoretic framework to spike train data. Results indicate that the strength and direction of airflow can be encoded by the precise timing of spikes, where first post-stimulus spikes transmit bulk of the information, evidence for a latency code

The Near Wake of a European Starling

The wake of a freely flying European starling (Sturnus vulgaris) was measured using high speed, time-resolved, particle image velocimetry, simultaneously with high speed cameras which imaged the bird. These measurements have been used to generate vector maps in the near wake that can be associated with the bird’s location and wing configuration. A kinematic analysis has been performed on select sequences of measurements to characterize the motion of the bird, as well as provide a point of comparison between the bird of the present study and other birds or flapping wings. Time series of measurements have been expressed as composite wake plots which relate to segments of the wing beat cycle for various spanwise locations in the wake. The wake composites invoke Taylor’s Frozen Flow Hypothesis. The applicability of Taylor’s Frozen Flow Hypothesis to the starling wake is discussed and evaluated. Measurements of the wake indicate that downwash is not produced during the upstroke, suggesting that the upstroke does not generate lift. Additional characteristics of the wake are discussed which imply the presence of (secondary) streamwise vortical structures, in addition to the wing tip vortices. The lack of downwash during the upstroke and the suggestion of secondary streamwise vortical structures constitute a deviation from a wake model which has been developed and supported by other bird species. Furthermore, these flow features indicate similarities between the wakes of birds and bats. In light of recent studies reported in the literature, the presence of secondary streamwise vortical structures may not only be a feature shared by birds and bats, but a general feature of flapping wings. Measurements also show spanwise vortical structures a short distance downstream of the bird. Based on existence of these spanwise vortical structures at such a close proximity to the bird, it is speculated that the wings of a starling may undergo dynamic stall during flight. This is also implied by the results of the kinematic analysis of the bird’s wing motion and comparison to other flapping wing studies. Dynamic stall, thought to be limited to hovering and slow flight, would enable high efficiency and high force coefficient generation

Aeronautical Engineering: A special bibliography with indexes, supplement 54

This bibliography lists 316 reports, articles, and other documents introduced into the NASA scientific and technical information system in January 1975

Numerical And Experimental Investigation Of 2D Membrane Airfoil Performance

The characteristic feature of a mammalian flight is the use of thin compliant wings as the lifting surface. This unique feature of flexible membrane wings found in flying mammals such as bats and flying squirrel was studied in order to explore its possibility as flexible membrane wings in aerodynamics performance study. The unsteady aspects of the fluid-structure interaction of membrane wings are very complicated and therefore did not receive much attention compared to the rigid wing. Motivated by this, a membrane airfoil consisting of latex sheet mounted on a NACA 643-218 airfoil frame was developed to study effect of membrane flexibility on laminar separation bubble (LSB), effects of membrane thickness, Reynolds number (Re), and membrane rigidity on the aerodynamic performance (lift and drag), meant for low Re applications. Unsteady, two dimensional (2D) simulations were also carried out on rigid and membrane airfoils with the air flow modeled as Laminar and the turbulent cases being modeled using Spalart-Allmaras viscous model. FLUENT 6.3 was employed to study the fluid flow behavior, whereas ABAQUS 6.8-1 was utilized as structural solver, both of which were coupled in real time using the MpCCI 3.1 software. It has been established that, the LSB is greatly influenced by the membrane flexibility, and the membrane airfoil has superior flow separation characteristics over rigid one

DESIGN AND EVALUATION OF INFLATABLE WINGS FOR UAVs

Performance of inflatable wings was investigated through laboratory, wind tunnel and flight-testing. Three airfoils were investigated, an inflatable-rigidazable wing, an inflatable polyurethane wing and a fabric wing restraint with a polyurethane bladder. The inflatable wings developed and used within this research had a unique outer airfoil profile. The airfoil surface consisted of a series of chord-wise \bumps.andamp;quot; The effect of the bumps or \surface perturbationsandamp;quot; on the performance of the wings was of concern and was investigated through smoke-wire flow visualization. Aerodynamic measurements and predictions were made to determine the performance of the wings at varying chord based Reynolds Numbers and angles of attack. The inflatable baffes were found to introduce turbulence into the free-stream boundary layer, which delayed separation and improved performance. Another area of concern was aeroelasticity. The wings contain no solid structural members and thus rely exclusively on inflation pressure for stiffness. Inflation pressure was varied below the design pressure in order to examine the effect on wingtip twist and bending. This lead to investigations into wing deformation due to aerodynamic loading and an investigation of wing flutter. Photogrammetry and laser displacement sensors were used to determine the wing deflections. The inflatable wings exhibited wash-in deformation behavior. Alternately, as the wings do not contain structural members, the relationship between stiffness and inflation pressure was exploited to actively manipulate wing through wing warping. Several warping techniques were developed and employed within this re-search. The goal was to actively influence the shape of the inflatable wings to affect the flight dynamics of the vehicle employing them. Researchers have developed inflatable beam theory and models to analyze torsion and bending of inflatable beams and other inflatable structures. This research was used to model the inflatable wings to predict the performance of the inflatable wings during flight. Design elements of inflatable wings incorporated on the UAVs used within this research are also discussed. Finally, damage resistance of the inflatable wings is shown from results of flight tests

Mathematical Modeling and Simulation of Biologically Inspired Hair Receptor Arrays in Laminar Unsteady Flow Separation

Bats possess arrays of distributed ow-sensitive hair-like mechanoreceptors on their dorsal and ventral wing surfaces. It is generally hypothesized that the hair sensor array provides air ow feedback during ight. Speci cally, the sensing of leading and trailing edge vortices that are shed during apping ight has been proposed. In this work, we consider the mechanics of exible hair-like structures for the time accurate measurement and visualization of hydrodynamic images associated with unsteady near surface ow phenomena. A nonlinear viscoelastic model of a hair-like structure coupled to an unsteady nonuniform ow environment is proposed. Writing the hair model in nondimensional form, we perform an order of magnitude analysis of the physical forces involved in the uid-structure hair response. Through the proper choice of hair material, we show how the time accurate measurement of near surface ow velocity may be obtained from hair tip displacement and resultant moment. Furthermore, we show how a surface mounted hair array may provide a time accurate hydrodynamic image of a laminar unsteady ow separation over a cylinder.This is the publisher’s final pdf. The published article is copyrighted by Elsevier and can be found at: http://www.elsevier.com/Keywords: low Reynolds number, bats, micro air vehicles, nite element