Airfoil

About: Airfoil is a research topic. Over the lifetime, 24696 publications have been published within this topic receiving 337709 citations. The topic is also known as: aerofoil & wing section.

The Kutta Condition in Unsteady Flow

Abstract: In several papers published in the first decade of this century, Kutta and Joukowsky independently proposed that the lift on an airfoil at incidence in a steady un separated flow is given by potential-flow theory with the unique value of the circulation that removes the inverse-sQuare-root velocity singularity at the trailing edge. This proposal-tantamount to saying (cf. Batchelor 1967) that in the unsteady start-up phase the action of viscosity is such that, in the ultimate steady motion, viscosity can be explicitly ignored but implicitly incorporated in a single edge condition-is known as the Kutta-Joukowsky hypothesis. Subsequently the name "Kutta condition" (no doubt largely for brevity) has come to be used to connote the removal of a velocity singularity at some distinguished point on a body in unsteady flow. 1 The condition has recently been applied to unsteadiness in a variety of mean configurations. These include trailing-edge flows with the same and with different flows on the two sides of the body upstream of the edge, attached leading-edge flows, and grossly separated flows past bluff bodies. Imposition of a Kutta condition on unsteady perturbations to one of these mean flows has a variety of physical ramifications. It represents the mechanism by which both the lift is changed and the amplitude and directivity of a sound field are modified. It is the analytical step that in many cases describes the conversion-almost total-of acoustic energy in an incident sound wave to energy of vortical motion on a shear layer ; on

Fundamentals of Flight

Abstract: 1 Conversion Factors Between SI Units and English Units 2 Nomenclature 3 A Brief History of Aeronautics 4 The Anatomy of the Airplane 5 The Nature of Aerodynamic Forces: Dimensional Analysis 6 Theory and Experiment Wind Tunnels 7 The Atmosphere 8 Incompressible One-Dimensional Flow 9 One-Dimensional Flow in a Compressible Fluid 10 Two-Dimensional Flow: Lift and Drag 11 The Finite Wing 12 Effects of Viscosity 13 Determination of Total Incompressible Drag 14 Compressibility Drag 15 Airfoils and Wings 16 High-Lift Systems 17 Aerodynamic Performance 18 Stability and Control 19 Propulsion 20 Structures 21 Hypersonic Flow 22 Rocket Trajectories and Orbits Appendix A: Characteristics of the Standard Atmosphere (SI units) Characteristics of the Standard Atmosphere (English Units) Appendix B: Derivation of the Compressible Fluid Bernoulli Equation Appendix C: Summary of State and One-Dimensional Flow Equations Index

On the use of helium-filled soap bubbles for large-scale tomographic PIV in wind tunnel experiments

Abstract: The flow-tracing fidelity of sub-millimetre diameter helium-filled soap bubbles (HFSB) for low-speed aerodynamics is studied. The main interest of using HFSB in relation to micron-size droplets is the large amount of scattered light, enabling larger-scale three-dimensional experiments by tomographic PIV. The assessment of aerodynamic behaviour closely follows the method proposed in the early work of Kerho and Bragg (Exp Fluids 50:929–948, 1994) who evaluated the tracer trajectories around the stagnation region at the leading edge of an airfoil. The conclusions of the latter investigation differ from the present work, which concludes sub-millimetre HFSB do represent a valid alternative for quantitative velocimetry in wind tunnel aerodynamic experiments. The flow stagnating ahead of a circular cylinder of 25 mm diameter is considered at speeds up to 30 m/s. The tracers are injected in the free-stream and high-speed PIV, and PTV are used to obtain the velocity field distribution. A qualitative assessment based on streamlines is followed by acceleration and slip velocity measurements using PIV experiments with fog droplets as a term of reference. The tracing fidelity is controlled by the flow rates of helium, liquid soap and air in HFSB production. A characteristic time response, defined as the ratio of slip velocity and the fluid acceleration, is obtained. The feasibility of performing time-resolved tomographic PIV measurements over large volumes in aerodynamic wind tunnels is also studied. The flow past a 5-cm-diameter cylinder is measured over a volume of 20 × 20 × 12 cm3 at a rate of 2 kHz. The achieved seeding density of <0.01 ppp enables resolving the Karman vortices, whereas turbulent sub-structures cannot be captured.

Concepts for morphing airfoil sections using bi-stable laminated composite structures

Abstract: The present paper investigates the potential of using bi-stable laminated composite structures for morphing an airfoil section. The objective of the paper is to identify geometries and lay-ups of candidate configurations that offer multiple stable shapes for the airfoil section. Carbon-fiber laminated composites with non-symmetric laminate configurations are used for morphing the airfoil section. Thermal curing is used to induce residual stresses into the structure in order to achieve bi-stability. Three concepts that focus on morphing a flap-like structure and the camber and chord of an airfoil section are proposed. Several geometries and laminate configurations are investigated using finite element nonlinear static analysis. The magnitude of loads required to actuate the airfoil section between the stable shapes is evaluated. The impact of manufacturability on producing viable morphing mechanisms within the airfoil section is also discussed.

Measurement of the noise generation at the trailing edge of porous airfoils

Abstract: Owls are commonly known for their quiet flight, enabled by three adaptions of their wings and plumage: leading edge serrations, trailing edge fringes and a soft and elastic downy upper surface of the feathers. In order to gain a better understanding of the aeroacoustic effects of the third property that is equivalent to an increased permeability of the plumage to air, an experimental survey on a set of airfoils made of different porous materials was carried out. Several airfoils with the same shape and size but made of different porous materials characterized by their flow resistivities and one non-porous reference airfoil were subject to the flow in an aeroacoustic open jet wind tunnel. The flow speed has been varied between approximately 25 and 50 m/s. The geometric angle of attack ranged from −16° to 20° in 4°-steps. The results of the aeroacoustic measurements, made with a 56-microphone array positioned out of flow, and of the measurements of lift and drag are given and discussed.