▪ Abstract In this review we describe the aerodynamic problems that must be addressed in order to design a successful small aerial vehicle. The effects of Reynolds number and aspect ratio (AR) on the design and performance of fixed-wing vehicles are described. The boundary-layer behavior on airfoils is especially important in the design of vehicles in this flight regime. The results of a number of experimental boundary-layer studies, including the influence of laminar separation bubbles, are discussed. Several examples of small unmanned aerial vehicles (UAVs) in this regime are described. Also, a brief survey of analytical models for oscillating and flapping-wing propulsion is presented. These range from the earliest examples where quasi-steady, attached flow is assumed, to those that account for the unsteady shed vortex wake as well as flow separation and aeroelastic behavior of a flapping wing. Experiments that complemented the analysis and led to the design of a successful ornithopter are also described.

Aerodynamics of small vehicles

This paper presents detailed wind tunnel tests data taken on six airfoils having application to small wind turbines. In particular, lift, drag and moment measurements were taken at Reynolds numbers of 100,000, 200,000, 350,000 and 500,000 for both clean and rough conditions. In some cases, data was also taken at a Reynolds number of 150,000. The airfoils included the E387, FX 63-137, S822, S834, SD2030, and SH3055. Prior to carrying out the tests, wind tunnel flow quality measurements were taken to document the low Reynolds number test environment, and also oil flow visualization data and performance data were taken on the E387 for comparison with measurements taken at NASA Langley in the Low Turbulence Pressure Tunnel. The new results compare favorably with the benchmark NASA data. Highlights of the performance characteristics of the six airfoils are then discussed.

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Wind tunnel aerodynamic tests of six airfoils for use on small wind turbines

The development of special-purpose airfoils for horizontal-axis wind turbines (HAWTs) began in 1984 as a joint effort between the National Renewable Energy Laboratory (NREL), formerly the Solar Energy Research Institute (SERI), and Airfoils, Incorporated. Since that time seven airfoil families have been designed for various size rotors using the Eppler Airfoil Design and Analysis Code. A general performance requirement of the new airfoil families is that they exhibit a maximum lift coefficient (c{sub l,max}) which is relatively insensitive to roughness effects. The airfoil families address the needs of stall-regulated, variable-pitch, and variable-rpm wind turbines. For stall-regulated rotors, better peak-power control is achieved through the design of tip airfoils that restrain the maximum lift coefficient. Restrained maximum lift coefficient allows the use of more swept disc area for a given generator size. Also, for stall-regulated rotors, tip airfoils with high thickness are used to accommodate overspeed control devices. For variable-pitch and variable-rpm rotors, tip airfoils having a high maximum lift coefficient lend themselves to lightweight blades with low solidity. Tip airfoils having low thickness result in less drag for blades having full-span pitch control. Annual energy improvements from the NREL airfoil families are projected to be 23% to 35% for stall-regulatedmore » turbines, 8% to 20% for variable-pitch turbines, and 8% to 10% for variable-rpm turbines. The improvement for stall-regulated turbines has been verified in field tests.« less

NREL airfoil families for HAWTs

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The trailing-edge region of a single-element wing fitted with Gurney flaps has been studied. Measurements include surface pressure, force, and velocity by laser Doppler anemometry (LDA). The mean-velocity vectors and streamlines suggest a twin vortex structure downstream of the Gurney flap. Spectral analysis of the LDA data indicates that the wake consists of a von Karman vortex street of alternately shed vortices, and this flow structure is confirmed by smoke visualization of the flow downstreamof the Gurney flap. The vortex shedding increases the trailing-edge suction of the aerofoil, whereas the upstream face of the device decelerates the flow at the trailing edge of the pressure surface. These two changes result in a pressure difference acting across the trailing edge, and it is this that generates the increase in circulation.

Aerodynamics of Gurney Flaps on a Single-Element High-Lift Wing

This book reflects the author's experience in the development of a computer program for the application of potential flow and boundary layer theories to the design and analysis of subsonic airfoils, including the evaluation of total lift, drag and moment coefficients. The design allows readers to compute the airfoil shape by means of a simple mathematical method from the properties of their velocity distribution, which can be specified in such a way that the boundary layer flow fulfills some given requirements. The most significant boundary layer phenomena such as laminar turbulent transition, laminar separation bubbles and boundary layer separation are considered. The first five chapters of this book describe a procedure for the design and analysis of subsonic airfoils. The data section contains 116 new airfoils for a wide range of Reynolds numbers and application requirements, including general aviation aircraft, tailless airplanes, gliders and propellers. The design features are explained and the input data for computer codes are given for all airfoils.

Richard Eppler

Papers

Airfoil design and data