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Book ChapterDOI

Effect of sinusoidal gust on thrust generated by a plunging airfoil

01 Jan 2017-pp 1401-1409
TL;DR: In this article, the aerodynamic load generation capability of a flapping type MAV subjected to fluctuating wind was investigated in the presence of frontal gusts, and the airfoil response to variation of plunge kinematic parameters was studied in comparison with quasi-steady loads.
Abstract: The present study looks at the aerodynamic load generation capability of a flapping type MAV subjected to fluctuating wind. MAVs are subjected to constantly changing operating conditions. The performance of flapping wing MAVs, under these conditions, have not been explored in great detail. Accordingly, this work investigates the performance of flapping wings in the presence of gusts. Towards this, pure plunging kinematics is chosen and the body is subjected to frontal gusts with sinusoidally modelled temporal variations. Thereafter, the airfoil response to variation of plunge kinematic parameters is studied in comparison with quasi-steady loads. A typical gust cycle is composed of many plunge cycles. The mean thrust produced in each of these plunge cycles vary throughout the gust cycle. This variation depends on the change in non-dimensional plunging velocity in the gust cycle. It is observed that a plunging airfoil is able to suppress variations in thrust due to sharp changes in non-dimensional plunging velocities.
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Journal ArticleDOI
TL;DR: In this article, the authors presented the dynamic analysis of a wing section by considering the engine mass and the resulting thrust effect using a distributed parameter model, and the critical frequencies and flutter speed obtained from the model were validated with available results.
Abstract: Dynamic analysis and instability prediction of immersed bodies under variable loading conditions is an important issue in fluid dynamics. This work presents the dynamic analysis of a wing section by considering the engine mass and the resulting thrust effect using a distributed parameter model. The equations of motion of cantilever wing are obtained using the extended Hamilton’s principle by accommodating the engine mass and the follower force terms. Initially, the stability regions of the clean wing without engine are identified using modal reduction scheme. The critical frequencies and flutter speed obtained from the model are validated with available results. In order to study the influence of other parameters such as position of engine mass, number of store masses and the generated thrust, a series of parametric studies are conducted. To make the study more realistic, the cantilever wing with engine mass is further subjected to a vertical discrete gust loading. It is found that the model is reliable and interactive in further analysis.
References
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Journal ArticleDOI
TL;DR: In this paper, the Navier-Stokes equation is derived for an inviscid fluid, and a finite difference method is proposed to solve the Euler's equations for a fluid flow in 3D space.
Abstract: This brief paper derives Euler’s equations for an inviscid fluid, summarizes the Cauchy momentum equation, derives the Navier-Stokes equation from that, and then talks about finite difference method approaches to solutions. Typical texts for this material are apparently Acheson, Elementary Fluid Dynamics and Landau and Lifschitz, Fluid Mechanics. 1. Basic Definitions We describe a fluid flow in three-dimensional space R as a vector field representing the velocity at all locations in the fluid. Concretely, then, a fluid flow is a function ~v : R× R → R that assigns to each point (t, ~x) in spacetime a velocity ~v(t, ~x) in space. In the special situation where ~v does not depend on t we say that the flow is steady. A trajectory or particle path is a curve ~x : R→ R such that for all t ∈ R, d dt ~x(t) = ~v(t, ~x(t)). Fix a t0 ∈ R; a streamline at time t0 is a curve ~x : R→ R such that for all t ∈ R, d dt ~x(t) = ~v(t0, ~x(t)). In the special case of steady flow the streamlines are constant across times t0 and any trajectory is a streamline. In non-steady flows, particle paths need not be streamlines. Consider the 2-dimensional example ~v = [− sin t cos t]>. At t0 = 0 the velocities all point up and the streamlines are vertical straight lines. At t0 = π/2 the velocities all point left and the streamlines are horizontal straight lines. Any trajectory is of the form ~x = [cos t + C1 sin t + C2] >; this traces out a radius-1 circle centered at [C1 C2] >. Indeed, all radius-1 circles in the plane arise as trajectories. These circles cross each other at many (in fact, all) points. If you find it counterintuitive that distinct trajectories can pass through a single point, remember that they do so at different times. 2. Acceleration Let f : R × R → R be some scalar field (such as temperature). Then ∂f/∂t is the rate of change of f at some fixed point in space. If we precompose f with a 1 Fluid Dynamics Math 211, Fall 2014, Carleton College trajectory ~x, then the chain rule gives us the rate of change of f with respect to time along that curve: D Dt f := d dt f(t, x(t), y(t), z(t)) = ∂f ∂t + ∂f ∂x dx dt + ∂f ∂y dy dt + ∂f ∂z dz dt = ( ∂ ∂t + dx dt ∂ ∂x + dy dt ∂ ∂y + dz dt ∂ ∂z ) f = ( ∂ ∂t + ~v · ∇ ) f. Intuitively, if ~x describes the trajectory of a small sensor for the quantity f (such as a thermometer), then Df/Dt gives the rate of change of the output of the sensor with respect to time. The ∂f/∂t term arises because f varies with time. The ~v ·∇f term arises because f is being measured at varying points in space. If we apply this idea to each component function of ~v, then we obtain an acceleration (or force per unit mass) vector field ~a(t, x) := D~v Dt = ∂~v ∂t + (~v · ∇)~v. That is, for any spacetime point (t, ~x), the vector ~a(t, ~x) is the acceleration of the particle whose trajectory happens to pass through ~x at time t. Let’s check that it agrees with our usual notion of acceleration. Suppose that a curve ~x describes the trajectory of a particle. The acceleration should be d dt d dt~x. By the definition of trajectory, d dt d dt ~x = d dt ~v(t, ~x(t)). The right-hand side is precisely D~v/Dt. Returning to our 2-dimensional example ~v = [− sin t cos t]>, we have ~a = [− cos t − sin t]>. Notice that ~v · ~a = 0. This is the well-known fact that in constant-speed circular motion the centripetal acceleration is perpendicular to the velocity. (In fact, the acceleration of any constant-speed trajectory is perpendicular to its velocity.) 3. Ideal Fluids An ideal fluid is one of constant density ρ, such that for any surface within the fluid the only stresses on the surface are normal. That is, there exists a scalar field p : R × R → R, called the pressure, such that for any surface element ∆S with outward-pointing unit normal vector ~n, the force exerted by the fluid inside ∆S on the fluid outside ∆S is p~n ∆S. The constant density condition implies that the fluid is incompressible, meaning ∇ · ~v = 0, as follows. For any region of space R, the rate of flow of mass out of the region is ∫∫ ∂R ρ~v · ~n dS = ∫∫∫

9,804 citations

01 Feb 2000
TL;DR: In this article, the physical properties of fluids and their properties in terms of flow field and Reynolds number are discussed. But the authors do not consider the effects of viscosity on the flow field.
Abstract: Preface Conventions and notation 1. The physical properties of fluids 2. Kinematics of the flow field 3. Equations governing the motion of a fluid 4. Flow of a uniform incompressible viscous fluid 5. Flow at large Reynolds number: effects of viscosity 6. Irrotational flow theory and its applications 7. Flow of effectively inviscid liquid with vorticity Appendices.

1,161 citations

Journal ArticleDOI
03 May 2013-Science
TL;DR: An 80-milligram, insect-scale, flapping-wing robot modeled loosely on the morphology of flies is built and demonstrated tethered but unconstrained stable hovering and basic controlled flight maneuvers, which validates a sufficient suite of innovations for achieving artificial, insects-like flight.
Abstract: Flies are among the most agile flying creatures on Earth To mimic this aerial prowess in a similarly sized robot requires tiny, high-efficiency mechanical components that pose miniaturization challenges governed by force-scaling laws, suggesting unconventional solutions for propulsion, actuation, and manufacturing To this end, we developed high-power-density piezoelectric flight muscles and a manufacturing methodology capable of rapidly prototyping articulated, flexure-based sub-millimeter mechanisms We built an 80-milligram, insect-scale, flapping-wing robot modeled loosely on the morphology of flies Using a modular approach to flight control that relies on limited information about the robot's dynamics, we demonstrated tethered but unconstrained stable hovering and basic controlled flight maneuvers The result validates a sufficient suite of innovations for achieving artificial, insect-like flight

929 citations

Journal ArticleDOI
TL;DR: Water-tunnel tests of a NACA 0012 airfoil that was oscillated sinusoidally in plunge are described in this article, where dye flow visualization and single-component laser Doppler velocimetry (LDV) measurements for a range of freestream speeds, frequencies, and amplitudes of oscillation are explored.
Abstract: Water-tunnel tests of a NACA 0012 airfoil that was oscillated sinusoidally in plunge are described. The flowered downstream of the airfoil was explored by dye flow visualization and single-component laser Doppler velocimetry (LDV) measurements for a range of freestream speeds, frequencies, and amplitudes of oscillation. The dye visualizations show that the vortex patterns generated by the plunging airfoil change from drag-producing wake flows to thrust-producing jet flows as soon as the ratio of maximum plunge velocity to freestream speed, i.e., the nondimensional plunge velocity, exceeds approximately 0.4. The LDV measurements show that the nondimensional plunge velocity is the appropriate parameter to collapse the maximum streamwise velocity data covering a nondimensional plunge velocity range from 0.18 to 9.3

326 citations

Journal Article
TL;DR: An overview of the application potential and design challenges of micro air vehicles (MAVs), defined as small enough to be practical for a single-person transport and use, is given in this paper.
Abstract: This paper is an overview of the application potential and design challenges of micro air vehicles (MAVs), defined as small enough to be practical for a single-person transport and use. Four types of MAVs are considered: 1) fixed-wing, 2) rotarywing, 3) ornithopters (bird-like flapping) and 4) entomopters (insect-like flapping). In particular, advantages of a propeller-driven delta wing configuration for type 1 are discussed. Some detail is also given for type 4, the least understood of the four, including a new concept of manoeuvre control for such MAVs. The paper concludes with a brief prognostic of the future of each MAV type.

59 citations