Note: This page contains sample records for the topic high lift airfoils from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: November 12, 2013.
1

Parametric Investigation of a High-Lift Airfoil at High Reynolds Numbers  

Microsoft Academic Search

A new two-dimensional, three-element, advanced high-lift research airfoil has been tested in the NASA Langley Research CenterÕs Low-Turbulence Pressure Tunnel at a chord Reynolds number up to 1.6 x 10 7. The components of this high-lift airfoil have been designed using a incompressible computational code (INS2D). The design was to provide high maximum-lift values while maintaining attached flow on the

John C. Lin; Chet J. Dominik

1997-01-01

2

Separation control on high lift low-pressure turbine airfoils using pulsed vortex generator jets  

Microsoft Academic Search

Boundary layer separation control has been studied using vortex generator jets (VGJs) on a very high lift, low-pressure turbine airfoil. Experiments were done under low (0.6%) freestream turbulence conditions on a linear cascade in a low speed wind tunnel. Pressure surveys on the airfoil surface and downstream total pressure loss surveys were documented. Instantaneous velocity profile measurements were acquired in

Ralph J. Volino; Mounir B. Ibrahim

3

Effect of wakes from moving upstream rods on boundary layer separation from a high lift airfoil  

NASA Astrophysics Data System (ADS)

Highly loaded airfoils in turbines allow power generation using fewer airfoils. High loading, however, can cause boundary layer separation, resulting in reduced lift and increased aerodynamic loss. Separation is affected by the interaction between rotating blades and stationary vanes. Wakes from upstream vanes periodically impinge on downstream blades, and can reduce separation. The wakes include elevated turbulence, which can induce transition, and a velocity deficit, which results in an impinging flow on the blade surface known as a ``negative jet.'' In the present study, flow through a linear cascade of very high lift airfoils is studied experimentally. Wakes are produced with moving rods which cut through the flow upstream of the airfoils, simulating the effect of upstream vanes. Pressure and velocity fields are documented. Wake spacing and velocity are varied. At low Reynolds numbers without wakes, the boundary layer separates and does not reattach. At high wake passing frequencies separation is largely suppressed. At lower frequencies, ensemble averaged velocity results show intermittent separation and reattachment during the wake passing cycle.

Volino, Ralph J.

2011-11-01

4

High-lift airfoil trailing edge separation control using a single dielectric barrier discharge plasma actuator  

Microsoft Academic Search

Control of flow separation from the deflected flap of a high-lift airfoil up to Reynolds numbers of 240,000 (15 m\\/s) is explored\\u000a using a single dielectric barrier discharge (DBD) plasma actuator near the flap shoulder. Results show that the plasma discharge\\u000a can increase or reduce the size of the time-averaged separated region over the flap depending on the frequency of actuation.

Jesse Little; Munetake Nishihara; Igor Adamovich; Mo Samimy

2010-01-01

5

Turbulence modeling for high-lift multi-element airfoil configurations  

Microsoft Academic Search

This study provides a detailed comparison of two turbulence closures for aerodynamic flows around high-lift airfoils; the first based on turbulent viscosity and the second on the algebraic Reynolds-stress approximation. A detailed analysis of their derivation helps shed light on their inherent limitations in predicting complex flow phenomena such as confluent boundary layers and flow separation found in typical take-off

Philippe Godin

2004-01-01

6

CFD Validation for High-Lift Devices: Two-Element Airfoil  

NASA Astrophysics Data System (ADS)

The objectives of this study are to assess the accuracy of CFD codes, investigate the effect of turbulence models as applied to the flow around high-lift devices, and increase the knowledge for computing this kind of flow. CFD validation is conducted for a two-element airfoil and compared with a wind tunnel test to predict the aerodynamic forces, including the maximum lift and the stall angle. Sensitivity to grid density and influence of the grid extent are investigated. Four RANS codes with the same turbulence model are tested and computational results are compared with each other. Three commonly used turbulence models implemented in a CFD code are applied to investigate the effects of turbulence models for this kind of high-lift flow.

Lei, Zhong; Murayama, Mitsuhiro; Takenaka, Keizo; Yamamoto, Kazuomi

7

Numerical and experimental study of blowing jet on a high lift airfoil  

NASA Astrophysics Data System (ADS)

Active manipulation of separated flows over airfoils at moderate and high angles of attack in order to improve efficiency or performance has been the focus of a number of numerical and experimental investigations for many years. One of the main methods used in active flow control is the usage of blowing devices with constant and pulsed blowing. Through CFD simulation over a 2D high-lift airfoil, this study is trying to highlight the impact of pulsed blowing over its aerodynamic characteristics. The available wind tunnel data from INCAS low speed facility are also beneficial for the validation of the numerical analysis. This study intends to analyze the impact of the blowing jet velocity and slot geometry on the efficiency of an active flow control.

Bobonea, A.; Pricop, M. V.

2013-10-01

8

Optimization design study of low-Reynolds-number high-lift airfoils for the high-efficiency propeller of low-dynamic vehicles in stratosphere  

Microsoft Academic Search

Aerodynamic performance of low-Reynolds-number high-lift airfoil makes a great impact on designing a high-efficiency propeller\\u000a for low-dynamic vehicles in stratosphere. At high altitude, low-Reynolds-number airfoils are supposed to have high lift-drag\\u000a ratio or high endurance factor at cruising attack angle along with good stall characteristics. To design such a high-performance\\u000a low-Reynolds-number high-lift airfoil, the paper established a hierarchical multi-objective optimization

Rong Ma; BoWen Zhong; PeiQing Liu

2010-01-01

9

A study on the mechanism of high-lift generation by an airfoil in unsteady motion at low reynolds number  

NASA Astrophysics Data System (ADS)

The aerodynamic force and flow structure of NACA 0012 airfoil performing an unsteady motion at low Reynolds number ( Re=100) are calculated by solving Navier-Stokes equations. The motion consists of three parts: the first translation, rotation and the second translation in the direction opposite to the first. The rotation and the second translation in this motion are expected to represent the rotation and translation of the wing-section of a hovering insect. The flow structure is used in combination with the theory of vorticity dynamics to explain the generation of unsteady aerodynamic force in the motion. During the rotation, due to the creation of strong vortices in short time, large aerodynamic force is produced and the force is almost normal to the airfoil chord. During the second translation, large lift coefficient can be maintained for certain time period andbar C_L , the lift coefficient averaged over four chord lengths of travel, is larger than 2 (the corresponding steady-state lift coefficient is only 0.9). The large lift coefficient is due to two effects. The first is the delayed shedding of the stall vortex. The second is that the vortices created during the airfoil rotation and in the near wake left by previous translation form a short “vortex street” in front of the airfoil and the “vortex street” induces a “wind”; against this “wind” the airfoil translates, increasing its relative speed. The above results provide insights to the understanding of the mechanism of high-lift generation by a hovering insect.

Mao, Sun; Hamdani, Hossein

2001-05-01

10

Advanced Natural Laminar Flow Airfoil with High Lift to Drag Ratio.  

National Technical Information Service (NTIS)

An experimental verification of a high performance natural laminar flow (NLF) airfoil for low speed and high Reynolds number applications was completed in the Langley Low Turbulence Pressure Tunnel (LTPT). Theoretical development allowed for the achieveme...

J. K. Viken W. Pfenninger R. J. McGhee

1986-01-01

11

Measuring Lift with the Wright Airfoils  

Microsoft Academic Search

In this laboratory or demonstration exercise, we mount a small airfoil with its long axis vertical at one end of a nearly frictionless rotating platform.1 Air from a leaf blower2 produces a sidewise lift force L on the airfoil and a drag force D in the direction of the air flow (Fig. 1). The rotating platform is kept in equilibrium

Richard M. Heavers; Arianne Soleymanloo

2011-01-01

12

Measuring Lift with the Wright Airfoils  

ERIC Educational Resources Information Center

|In this laboratory or demonstration exercise, we mount a small airfoil with its long axis vertical at one end of a nearly frictionless rotating platform. Air from a leaf blower produces a sidewise lift force L on the airfoil and a drag force D in the direction of the air flow (Fig. 1). The rotating platform is kept in equilibrium by adding…

Heavers, Richard M.; Soleymanloo, Arianne

2011-01-01

13

Measuring Lift with the Wright Airfoils  

NASA Astrophysics Data System (ADS)

In this laboratory or demonstration exercise, we mount a small airfoil with its long axis vertical at one end of a nearly frictionless rotating platform.1 Air from a leaf blower2 produces a sidewise lift force L on the airfoil and a drag force D in the direction of the air flow (Fig. 1). The rotating platform is kept in equilibrium by adding weights (the measured values of L) to the lower end of a string passing over a pulley and connected to the other end of the rotating platform (Fig. 2). Our homemade airfoils are similar to those tested by the Wright brothers in 1901. From our lift plots in Fig. 3, we can draw the same conclusions as the Wrights about the influence of an airfoil's curvature and shape on lift.

Heavers, Richard M.; Soleymanloo, Arianne

2011-11-01

14

Unsteady lift of thick airfoils in incompressible turbulent flow  

NASA Astrophysics Data System (ADS)

nuThe unsteady lift forces that act on an airfoil in turbulent flow are an undesirable source of vibration and noise in many industrial applications. Methods to predict these forces have traditionally treated the airfoil as a flat plate. At higher frequencies, where the relevant turbulent length scales are comparable to the airfoil thickness, the at plate approximation becomes invalid and results in overprediction of the unsteady force spectrum. This work provides an improved methodology for the prediction of the unsteady lift forces that accounts for the thickness of the airfoil. An analytical model was developed to calculate the response of the airfoil to high frequency gusts. The approach is based on a time-domain calculation with a sharp-edged gust and accounts for the distortion of the gust by the mean flow around the airfoil leading edge. The unsteady lift is calculated from a weighted integration of the gust vorticity, which makes the model relatively straightforward to implement and verify. For routine design calculations of turbulence-induced forces, a closed-form gust response thickness correction factor was developed for NACA 65 series airfoils. The model was then validated by measuring the unsteady lift spectrum using piezoelectric force gages in a water tunnel with grid-generated turbulence. A series of four airfoils with thickness-to-chord ratios ranging from 8 to 16 percent were tested over a wide range of speeds. In addition, the turbulence spectrum was measured using Laser Doppler Velocimetry. The experimental results confirmed that the analytical model accurately predicts the attenuation of the high frequency gust response due to the airfoil thickness.

Lysak, Peter D.

15

Low-Speed Aerodynamic Characteristics of a Rectangular, Aspect-Ratio-6, Slotted Supercritical Airfoil Wing Having Several High-Lift Flap Systems.  

National Technical Information Service (NTIS)

Tests were conducted in the Langley high-speed 7- by 10-foot tunnel on a rectangular aspect-ratio-6 wing which had a supercritical airfoil section. The wing was fitted with several high-lift flap systems: plain flap, single-slotted flap, and a double-slot...

K. W. Goodson

1971-01-01

16

3 component LDV for near wall measurements on a multi-element high lift airfoil configuration  

Microsoft Academic Search

Flow field investigations in the near wall region of a high lift wing configuration have been performed by means of a 3D laser-Doppler velocimeter with a working distance of 3.5 m. The measurements were conducted on a 1:7.5 AIRBUS A321 model of Daimler-Benz Deutsche Aerospace (DASA) in the closed 6 m×8 m test section of the Deutsch-Niederlandischer Windkanal (DNW), The

U. Seelhorst; K. A. Butefisch; M. Weiland

1995-01-01

17

Multipoint optimization using GAs and Nash\\/Stackelberg games for high lift multi-airfoil design in aerodynamics  

Microsoft Academic Search

This paper presents the discussion and comparison of the different optimization strategies and their associated evolutionary tools for the multi-point design optimization of a multi-element airfoil system during landing and taking off operations of an aircraft. New optimization algorithms based on binary coded genetic algorithms (GAs) coupling with game theory, such as Nash GAs (N-GAs) and Stackelberg GAs (S-GAs), are

Jiang Feng Wang; Jacques Periaux

2001-01-01

18

A study on the mechanism of high-lift generation by an airfoil in unsteady motion at low reynolds number  

Microsoft Academic Search

The aerodynamic force and flow structure of NACA 0012 airfoil performing an unsteady motion at low Reynolds number (Re=100) are calculated by solving Navier-Stokes equations. The motion consists of three parts: the first translation, rotation\\u000a and the second translation in the direction opposite to the first. The rotation and the second translation in this motion\\u000a are expected to represent the

Sun Mao; Hossein Hamdani

2001-01-01

19

Wind tunnel tests of two airfoils for wind turbines operating at high reynolds numbers  

SciTech Connect

The objectives of this study were to verify the predictions of the Eppler Airfoil Design and Analysis Code for Reynolds numbers up to 6 x 106 and to acquire the section characteristics of two airfoils being considered for large, megawatt-size wind turbines. One airfoil, the S825, was designed to achieve a high maximum lift coefficient suitable for variable-speed machines. The other airfoil, the S827, was designed to achieve a low maximum lift coefficient suitable for stall-regulated machines. Both airfoils were tested in the NASA Langley Low-Turbulence Pressure Tunnel (LTPT) for smooth, fixed-transition, and rough surface conditions at Reynolds numbers of 1, 2, 3, 4, and 6 x 106. The results show the maximum lift coefficient of both airfoils is substantially underpredicted for Reynolds numbers over 3 x 106 and emphasized the difficulty of designing low-lift airfoils for high Reynolds numbers.

Sommers, D.; Tangler, J.

2000-06-29

20

Effects of Airfoil Thickness and Maximum Lift Coefficient on Roughness Sensitivity: 1997--1998  

SciTech Connect

A matrix of airfoils has been developed to determine the effects of airfoil thickness and the maximum lift to leading-edge roughness. The matrix consists of three natural-laminar-flow airfoils, the S901, S902, and S903, for wind turbine applications. The airfoils have been designed and analyzed theoretically and verified experimentally in the Pennsylvania State University low-speed, low-turbulence wind tunnel. The effect of roughness on the maximum life increases with increasing airfoil thickness and decreases slightly with increasing maximum lift. Comparisons of the theoretical and experimental results generally show good agreement.

Somers, D. M.

2005-01-01

21

Optimization of an Advanced Design Three-Element Airfoil at High Reynolds Numbers  

NASA Astrophysics Data System (ADS)

New high-lift components have been designed for a three-element advanced high-lift research airfoil using a state-of-the-art computational method. The new components were designed with the aim to provide high maximum-lift values while maintaining attached flow on the single-segment flap at approach conditions. This three-element airfoil has been tested in the NASA Langley Low-Turbulence Pressure Tunnel at chord Reynolds number up to 16 million. The performance of the NASA research airfoil is compared to a reference advanced high-lift research airfoil. Effects of Reynolds number on slat and flap rigging have been studied experimentally. The performance trend of this new high-lift design is comparable to that predicted by the computational method over much of the angle of attack range. Nevertheless, the method did not accurately predict the airfoil performance or the configuration-based trends near maximum lift.

Lin, John C.; Dominik, Chet J.

1995-01-01

22

Investigation of a bio-inspired lift-enhancing effector on a 2D airfoil.  

PubMed

A flap mounted on the upper surface of an airfoil, called a 'lift-enhancing effector', has been shown in wind tunnel tests to have a similar function to a bird's covert feathers, which rise off the wing's surface in response to separated flows. The effector, fabricated from a thin Mylar sheet, is allowed to rotate freely about its leading edge. The tests were performed in the NCSU subsonic wind tunnel at a chord Reynolds number of 4 × 10(5). The maximum lift coefficient with the effector was the same as that for the clean airfoil, but was maintained over an angle-of-attack range from 12° to almost 20°, resulting in a very gentle stall behavior. To better understand the aerodynamics and to estimate the deployment angle of the free-moving effector, fixed-angle effectors fabricated out of stiff wood were also tested. A progressive increase in the stall angle of attack with increasing effector angle was observed, with diminishing returns beyond the effector angle of 60°. Drag tests on both the free-moving and fixed effectors showed a marked improvement in drag at high angles of attack. Oil flow visualization on the airfoil with and without the fixed-angle effectors proved that the effector causes the separation point to move aft on the airfoil, as compared to the clean airfoil. This is thought to be the main mechanism by which an effector improves both lift and drag. A comparison of the fixed-effector results with those from the free-effector tests shows that the free effector's deployment angle is between 30° and 45°. When operating at and beyond the clean airfoil's stall angle, the free effector automatically deploys to progressively higher angles with increasing angles of attack. This slows down the rapid upstream movement of the separation point and avoids the severe reduction in the lift coefficient and an increase in the drag coefficient that are seen on the clean airfoil at the onset of stall. Thus, the effector postpones the stall by 4-8° and makes the stall behavior more gentle. The benefits of using the effector could include care-free operations at high angles of attack during perching and maneuvering flight, especially in gusty conditions. PMID:22498691

Johnston, Joe; Gopalarathnam, Ashok

2012-04-12

23

Design of the Low-Speed NLF (Natural Laminar Flow)(1)-0414F and the High-Speed HSNLF(1)-0213 Airfoils with High-Lift Systems.  

National Technical Information Service (NTIS)

The design and testing of Natural Laminar Flow (NLF) airfoils is examined. The NLF airfoil was designed for low speed, having a low profile drag at high chord Reynolds numbers. The success of the low speed NLF airfoil sparked interest in a high speed NLF ...

J. K. Viken S. A. Watson-Viken W. Pfenninger H. L. Morgan R. L. Campbell

1987-01-01

24

Prediction of high frequency gust response with airfoil thickness effects  

NASA Astrophysics Data System (ADS)

The unsteady lift forces that act on an airfoil in turbulent flow are an undesirable source of vibration and noise in many industrial applications. Methods to predict these forces have traditionally treated the airfoil as a flat plate. At higher frequencies, where the relevant turbulent length scales are comparable to the airfoil thickness, the flat plate approximation becomes invalid and results in overprediction of the unsteady force spectrum. This work provides an improved methodology for the prediction of the unsteady lift forces that accounts for the thickness of the airfoil. An analytical model was developed to calculate the response of the airfoil to high frequency gusts. The approach is based on a time-domain calculation with a sharp-edged gust and accounts for the distortion of the gust by the mean flow around the airfoil leading edge. The unsteady lift is calculated from a weighted integration of the gust vorticity, which makes the model relatively straightforward to implement and verify. For routine design calculations of turbulence-induced forces, a closed-form gust response thickness correction factor was developed for NACA 65 series airfoils.

Lysak, Peter D.; Capone, Dean E.; Jonson, Michael L.

2013-05-01

25

Optimization of an Advanced Design Three-Element Airfoil at High Reynolds Numbers  

Microsoft Academic Search

New high-lift components have been designed for a three-element advanced high-lift research airfoil using a state-of-the-art computational method. The new components were designed with the aim to provide high maximum-lift values while maintaining attached flow on the single-segment flap at approach conditions. This three-element airfoil has been tested in the NASA Langley Low-Turbulence Pressure Tunnel at chord Reynolds number up

John C. Lin; Chet J. Dominik

1995-01-01

26

Blade design trade-offs using low-lift airfoils for stall-regulated HAWTs  

SciTech Connect

A systematic blade design study was conducted to explore the trade-offs in using low-lift airfoils for a 750-kilowatt stall-regulated wind turbine. Tip-region airfoils having a maximum-lift coefficient ranging from 0.7--1.2 were considered in this study, with the main objective of identifying the practical lower limit for the maximum-life coefficient. Blades were optimized for both maximum annual energy production and minimum cost of energy using a method that takes into account aerodynamic and structural considerations. The results indicate that the effect of the maximum-lift coefficient on the cost of energy is small with a slight advantage to the highest maximum lift coefficient airfoils for the tip-region of the blade become more desirable as machine size increases, provided the airfoils yield acceptable stall characteristics. The conclusions are applicable to large wind turbines that use passive or active stall to regulate peak power.

Giguere, P.; Selig, M.S.; Tangler, J.L.

1999-11-01

27

High Resolution PIV Study of Zero-Net-Mass-Flow Lift Enhancement of NACA 0015 Airfoil at High Angles of Attack  

Microsoft Academic Search

\\u000a The effect of changing the pitch to diameter ratio (P\\/D) of a row of round, wall-normal, zero-net-mass-flux (ZNMF) jets located at the leading edge of a NACA 0015 airfoil was investigated.\\u000a A parametric study and particle image velocimetry (PIV) measurements were conducted on a two-dimensional airfoil in a water\\u000a tunnel at a Reynolds number of 6.56 ×104. Different optimal forcing

Trevor Stephens; Julio Soria

28

Lift enhancement and flow structure of airfoil with joint trailing-edge flap and Gurney flap  

NASA Astrophysics Data System (ADS)

The impact of Gurney flaps (GF), of different heights and perforations, on the aerodynamic and wake characteristics of a NACA 0015 airfoil equipped with a trailing-edge flap (TEF) was investigated experimentally at Re = 2.54 × 105. The addition of the Gurney flap to the TEF produced a further increase in the downward turning of the mean flow (increased aft camber), leading to a significant increase in the lift, drag, and pitching moment compared to that produced by independently deployed TEF or GF. The maximum lift increased with flap height, with the maximum lift-enhancement effectiveness exhibited at the smallest flap height. The near wake behind the joint TEF and GF became wider and had a larger velocity deficit and fluctuations compared to independent GF and TEF deployment. The Gurney flap perforation had only a minor impact on the wake and aerodynamics characteristics compared to TEF with a solid GF. The rapid rise in lift generation of the joint TEF and GF application, compared to conventional TEF deployment, could provide an improved off-design high-lift device during landing and takeoff.

Lee, T.; Su, Y. Y.

2011-06-01

29

Wind tunnel tests of two airfoils for wind turbines operating at high reynolds numbers  

Microsoft Academic Search

The objectives of this study were to verify the predictions of the Eppler Airfoil Design and Analysis Code for Reynolds numbers up to 6 x 106 and to acquire the section characteristics of two airfoils being considered for large, megawatt-size wind turbines. One airfoil, the S825, was designed to achieve a high maximum lift coefficient suitable for variable-speed machines. The

D. Sommers; J. Tangler

2000-01-01

30

Investigation of a bio-inspired lift-enhancing effector on a 2D airfoil  

Microsoft Academic Search

A flap mounted on the upper surface of an airfoil, called a ‘lift-enhancing effector’, has been shown in wind tunnel tests to have a similar function to a bird's covert feathers, which rise off the wing's surface in response to separated flows. The effector, fabricated from a thin Mylar sheet, is allowed to rotate freely about its leading edge. The

Joe Johnston; Ashok Gopalarathnam

2012-01-01

31

Lift and drag performances of an axisymmetric airfoil controlled by plasma actuator  

Microsoft Academic Search

A Dielectric Barrier Discharge (DBD) is mounted at the leading edge of a NACA 0015 airfoil model. The effects of steady and unsteady actuations on the lift and drag coefficients are investigated by time-averaged force measurements. Results demonstrate that the stall regime can be delayed of one or two degrees while the drag coefficient is reduced. The aerodynamic performances are

N. Benard; J. Jolibois; E. Moreau

2009-01-01

32

Blade Design Trade-Offs Using Low-Lift Airfoils for Stall-Regulated HAWTs  

SciTech Connect

A systematic blade design study was conducted to explore the trade-offs in using low-lift airfoils for a 750-kilowatt stall-regulated wind turbine. Tip-region airfoils having a maximum lift coefficient ranging from 0.7-1.2 were considered in this study, with the main objective of identifying the practical lower limit for the maximum lift coefficient. Blades were optimized for both maximum annual energy production and minimum cost of energy using a method that takes into account aerodynamic and structural considerations. The results indicate that reducing the maximum lift coefficient below the upper limit considered in this study increases the cost of energy independently of the wind regime. As a consequence, higher maximum lift coefficient airfoils for the tip-region of the blade become more desirable as machine size increases, as long as they provide gentle stall characteristics. The conclusions are applicable to large wind turbines that use passive or active stall to regulate peak power.

Giguere, P.; Selig, M. S. (University of Illinois at Urbana-Champaign); Tangler, J. L. (National Renewable Energy Laboratory)

1999-04-08

33

Closed-Form Equations for the Lift, Drag, and Pitching-Moment Coefficients of Airfoil Sections in Subsonic Flow.  

National Technical Information Service (NTIS)

Closed-form equations for the lift, drag, and pitching moment coefficients of two dimensional airfoil sections in steady subsonic flow were obtained from published theoretical and experimental results. A turbulent boundary layer was assumed to exist on th...

R. L. Smith

1978-01-01

34

High-rate artificial lift  

SciTech Connect

This paper summarizes the major considerations in the selection, design, installation, operation, or repair of high-rate artificial-lift systems. The major types of artificial lift - sucker-rod pumps, gas-lift systems, electrical submersible pumps, hydraulic pumps and jets, and hydraulic turbine-driven pumps - will be discussed. An extensive bibliography of artificial-lift papers is included.

Clegg, J.D.

1988-03-01

35

Large-eddy simulation of an airfoil at maximum lift  

NASA Astrophysics Data System (ADS)

In many complex flows, large-eddy simulation is difficult due to the simultaneous presence of a variety of flow features, often with quite different resolution requirements. A structured-grid approach to this problem would be forced to carry the resolution requirements of the finest region throughout the entire domain making the number of points required impractical. An unstructured-grid method can place points based on local resolution requirements resulting in a large reduction in the number of points required. For this reason, unstructured-grid large-eddy simulation techniques have been developed using the finite element method to solve the compressible Navier-Stokes equations with a dynamic model of the subgrid-scale stresses. Results will be presented for flow over a NACA 4412 airfoil at 12^circ angle of attack at a chord Reynolds number of 1.64× 10^6. In particular, the results will address the effect of the wind tunnel walls and transition strip used in the experiment of Wadcock (1987).

Jansen, Kenneth

1996-11-01

36

Low Speed Airfoil Study.  

National Technical Information Service (NTIS)

Airfoil geometries were developed for low speed high lift applications, such as general aviation aircraft, propellers and helicopter rotors. The primary effort was to determine the extent to which the application of turbulent boundary layer separation cri...

A. I. Ormsbee

1977-01-01

37

High fidelity numerical simulation of airfoil thickness and kinematics effects on flapping airfoil propulsion  

NASA Astrophysics Data System (ADS)

High-fidelity numerical simulations with the spectral difference (SD) method are carried out to investigate the unsteady flow over a series of oscillating NACA 4-digit airfoils. Airfoil thickness and kinematics effects on the flapping airfoil propulsion are highlighted. It is confirmed that the aerodynamic performance of airfoils with different thickness can be very different under the same kinematics. Distinct evolutionary patterns of vortical structures are analyzed to unveil the underlying flow physics behind the diverse flow phenomena associated with different airfoil thickness and kinematics and reveal the synthetic effects of airfoil thickness and kinematics on the propulsive performance. Thickness effects at various reduced frequencies and Strouhal numbers for the same chord length based Reynolds number (=1200) are then discussed in detail. It is found that at relatively small Strouhal number (=0.3), for all types of airfoils with the combined pitching and plunging motion (pitch angle 20°, the pitch axis located at one third of chord length from the leading edge, pitch leading plunge by 75°), low reduced frequency (=1) is conducive for both the thrust production and propulsive efficiency. Moreover, relatively thin airfoils (e.g. NACA0006) can generate larger thrust and maintain higher propulsive efficiency than thick airfoils (e.g. NACA0030). However, with the same kinematics but at relatively large Strouhal number (=0.45), it is found that airfoils with different thickness exhibit diverse trend on thrust production and propulsive efficiency, especially at large reduced frequency (=3.5). Results on effects of airfoil thickness based Reynolds numbers indicate that relative thin airfoils show superior propulsion performance in the tested Reynolds number range. The evolution of leading edge vortices and the interaction between the leading and trailing edge vortices play key roles in flapping airfoil propulsive performance.

Yu, Meilin; Wang, Z. J.; Hu, Hui

2013-10-01

38

Numerical and experimental study of high-lift configurations  

NASA Astrophysics Data System (ADS)

Flow of two high-lift devices is studied on the basis of the solution to two-dimensional Reynolds equations with the Spalart — Allmaras one-equation turbulence model. Computation results are compared with the experiment under the conditions of airfoil flow in the low-speed wind tunnel with open test section. It is shown that such approach is the most correct for this comparison.

Rumyantsev, A. G.; Silantiev, V. A.

2010-06-01

39

TWO-DIMENSIONAL AIRCRAFT HIGH LIFT SYSTEM DESIGN AND OPTIMIZATION  

Microsoft Academic Search

A two-dimensiona l aircraft high-lift system design and optimization method, which can be easily extended to three dimensions, is presented. The need for such a tool is assessed. The method uses a gradient based local optimizer. The aerodynamic performance is predicted using an Interactive Boundary Layer (IBL) approach. Methods to represent general multi-element airfoils by a set of design variables

Eric Besnard; Adeline Schmitz; Erwan Boscher; Nicolas Garcia; Tuncer Cebeci

40

NREL airfoil families for HAWTs  

NASA Astrophysics Data System (ADS)

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-regulated 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.

Tangler, J. L.; Somers, D. M.

1995-01-01

41

Airfoils for wind turbine  

DOEpatents

Airfoils for the blade of a wind turbine wherein each airfoil is characterized by a thickness in a range from 16%-24% and a maximum lift coefficient designed to be largely insensitive to roughness effects. The airfoils include a family of airfoils for a blade 15 to 25 meters in length, a family of airfoils for a blade 1 to 5 meters in length, and a family of airfoils for a blade 5 to 10 meters in length.

Tangler, James L. (Boulder, CO); Somers, Dan M. (State College, PA)

1996-01-01

42

Airfoil shape for flight at subsonic speeds  

DOEpatents

An airfoil having an upper surface shaped to control flow accelerations and pressure distribution over the upper surface and to prevent separation of the boundary layer due to shock wave formulation at high subsonic speeds well above the critical Mach number. A highly cambered trailing edge section improves overall airfoil lifting efficiency.

Whitcomb, Richard T. (Hampton, VA)

1976-01-01

43

An overview of NACA 6-digit airfoil series characteristics with reference to airfoils for large wind turbine blades  

Microsoft Academic Search

This paper investigates the NACA 63 and 64 6-digit series of airfoils tested in the NACA LTPT in view to verify the RFOIL calculated airfoil characteristics for high Reynolds numbers. Some anomalies in the zero-lift angles of 15% and 18% thick airfoils from these series are identified, both in the airfoil clean case and in case of wrap-around roughness. It

W. A. Timmer

2009-01-01

44

Aerodynamic Performance Enhancement of a NACA 66-206 Airfoil Using Supersonic Channel Airfoil Design  

Microsoft Academic Search

Supersonic channel airfoil design techniques have b een shown to significantly reduce drag in high-speed flows over diamond shaped airfoils by Ruffin and colleagues. The effect of applying these techniques to a NACA 66-206 airfoil is presented. The design domain entails channel heights of 8-16.6% thickness-to-cho rd and speeds from Mach 1.5-3.0. Numerical simulations show an increase in the lift-

David M. Giles; David D. Marshall

2008-01-01

45

High-order simulations of low Reynolds number membrane airfoils under prescribed motion  

NASA Astrophysics Data System (ADS)

The aerodynamics and aeroelastic response of a membrane wing under prescribed motion are investigated using a high-order, two-dimensional Navier-Stokes solver coupled to a geometrically nonlinear membrane model. The impact of increasing Reynolds number on the vortex dynamics and unsteady aerodynamic loads is examined for moderate-amplitude plunge and combined pitch-plunge motions at low frequency. Simulation results are compared with classical thin airfoil theory and highlight the differences between rigid and flexible membrane airfoils undergoing small and moderate amplitude motions. The present study demonstrates the ability of lifting membrane surface flexibility to enhance thrust production and propulsive efficiency, which may inform the design of flapping wing membrane fliers.

Jaworski, Justin W.; Gordnier, Raymond E.

2012-05-01

46

A Recontoured, Upper Surface Designed to Increase the Maximum Lift Coefficient of a Modified Naca 65 (0.82) (9.9) Airfoil Section.  

National Technical Information Service (NTIS)

A recontoured upper surface was designed to increase the maximum lift coefficient of a modified NACA 65 (0.82)(9.9) airfoil section which was tested at Mach numbers of 0.3 and 0.4 and Reynolds numbers of 2.3x10(6) and 4.3x10(6). The original 6-series sect...

R. M. Hicks

1984-01-01

47

Wind tunnel test of the S814 thick root airfoil  

SciTech Connect

The objective of this wind-tunnel test was to verify the predictions of the Eppler Airfoil Design and Analysis Code for a very thick airfoil having a high maximum lift coefficient designed to be largely insensitive to leading-edge roughness effects. The 24 percent thick S814 airfoil was designed with these characteristics to accommodate aerodynamic and structural considerations for the root region of a wind-turbine blade. In addition, the airfoil`s maximum lift-to-drag ratio was designed to occur at a high lift coefficient. To accomplish the objective, a two-dimensional wind tunnel test of the S814 thick root airfoil was conducted in January 1994 in the low-turbulence wind tunnel of the Delft University of Technology Low Speed Laboratory, The Netherlands. Data were obtained with transition free and transition fixed for Reynolds numbers of 0.7, 1.0, 1.5, 2.0, and 3.0 {times} 10{sup 6}. For the design Reynolds number of 1.5 {times} 10{sup 6}, the maximum lift coefficient with transition free is 1.32, which satisfies the design specification. However, this value is significantly lower than the predicted maximum lift coefficient of almost 1.6. With transition fixed at the leading edge, the maximum lift coefficient is 1.22. The small difference in maximum lift coefficient between the transition-free and transition-fixed conditions demonstrates the airfoil`s minimal sensitivity to roughness effects. The S814 root airfoil was designed to complement existing NREL low maximum-lift-coefficient tip-region airfoils for rotor blades 10 to 15 meters in length.

Somers, D.M. [Airfoils, Inc., State College, PA (United States); Tangler, J.L. [National Renewable Energy Lab., Golden, CO (United States)

1996-11-01

48

Study on Busemann Biplane Airfoil in Low-Speed Smoke Wind Tunnel  

Microsoft Academic Search

The Busemann biplane airfoil is considered one of the candidates for reducing sonic boom. In aircraft designs utilizing the biplane concept, high-lift devices must be used for takeoff and landing in low-speed conditions. In this work, flow visualizations were performed around a Busemann biplane airfoil equipped with leading and trailing edge flaps in a smoke wind tunnel. The lift coefficient

Masashi Kashitani; Yutaka Yamaguchi; Yoshiharu Kai; Kenichi Hirata; Kazuhiro Kusunose

2010-01-01

49

Lift enhancement and flow structure of airfoil with joint trailing-edge flap and Gurney flap  

Microsoft Academic Search

The impact of Gurney flaps (GF), of different heights and perforations, on the aerodynamic and wake characteristics of a NACA\\u000a 0015 airfoil equipped with a trailing-edge flap (TEF) was investigated experimentally at Re = 2.54 × 105. The addition of the Gurney flap to the TEF produced a further increase in the downward turning of the mean flow (increased\\u000a aft camber), leading to a

T. Lee; Y. Y. Su

2011-01-01

50

Simulation-based aerodynamic design of high-lift devices in ground effect  

NASA Astrophysics Data System (ADS)

A simulation-based aerodynamic design tool is developed for multi-element high-lift airfoils operating in ground effect. A control theory approach is adopted, using the compressible Navier-Stokes equations as the basis for viscous design of airfoil element shapes and relative positioning. Particular considerations of aerodynamic design, high-lift systems, and the ground effect are described, and the suitability of aerodynamic shape optimization of such systems is discussed. The model of fluid flow and its discretization for solution on digital computers is investigated. A cell-centered finite-volume explicit multigrid method is used to solve both the flow and adjoint systems utilizing structured multiblock meshes. The adjoint equations for shape optimization are developed using a continuous adjoint formulation, and implemented with a moving ground boundary condition for the first time. A suite of test cases verified and validated the numerical algorithms and implementation. Realistic case studies were performed, demonstrating significant performance improvements over the baseline configurations. These included two free-air multi-element airfoil drag minimizations, and in addition two inverted two-element airfoil drag minimizations in ground effect.

Melvin, Arron Hector

51

High-fidelity simulations of moving and flexible airfoils at low Reynolds numbers  

NASA Astrophysics Data System (ADS)

The present paper highlights results derived from the application of a high-fidelity simulation technique to the analysis of low-Reynolds-number transitional flows over moving and flexible canonical configurations motivated by small natural and man-made flyers. This effort addresses three separate fluid dynamic phenomena relevant to small fliers, including: laminar separation and transition over a stationary airfoil, transition effects on the dynamic stall vortex generated by a plunging airfoil, and the effect of flexibility on the flow structure above a membrane airfoil. The specific cases were also selected to permit comparison with available experimental measurements. First, the process of transition on a stationary SD7003 airfoil section over a range of Reynolds numbers and angles of attack is considered. Prior to stall, the flow exhibits a separated shear layer which rolls up into spanwise vortices. These vortices subsequently undergo spanwise instabilities, and ultimately breakdown into fine-scale turbulent structures as the boundary layer reattaches to the airfoil surface. In a timeaveraged sense, the flow displays a closed laminar separation bubble which moves upstream and contracts in size with increasing angle of attack for a fixed Reynolds number. For a fixed angle of attack, as the Reynolds number decreases, the laminar separation bubble grows in vertical extent producing a significant increase in drag. For the lowest Reynolds number considered (Re_c = 10^4), transition does not occur over the airfoil at moderate angles of attack prior to stall. Next, the impact of a prescribed high-frequency small-amplitude plunging motion on the transitional flow over the SD7003 airfoil is investigated. The motioninduced high angle of attack results in unsteady separation in the leading edge and in the formation of dynamic-stalllike vortices which convect downstream close to the airfoil. At the lowest value of Reynolds number (Re_c = 10^4), transition effects are observed to be minor and the dynamic stall vortex system remains fairly coherent. For Re_c = 4 × 10^4, the dynamic-stall vortex system is laminar at is inception, however shortly afterwards, it experiences an abrupt breakdown associated with the onset of spanwise instability effects. The computed phased-averaged structures for both values of Reynolds number are found to be in good agreement with the experimental data. Finally, the effect of structural compliance on the unsteady flow past a membrane airfoil is investigated. The membrane deformation results in mean camber and large fluctuations which improve aerodynamic performance. Larger values of lift and a delay in stall are achieved relative to a rigid airfoil configuration. For Re_c = 4.85 × 10^4, it is shown that correct prediction of the transitional process is critical to capturing the proper membrane structural response.

Visbal, Miguel R.; Gordnier, Raymond E.; Galbraith, Marshall C.

52

High-fidelity simulations of moving and flexible airfoils at low Reynolds numbers  

NASA Astrophysics Data System (ADS)

The present paper highlights results derived from the application of a high-fidelity simulation technique to the analysis of low-Reynolds-number transitional flows over moving and flexible canonical configurations motivated by small natural and man-made flyers. This effort addresses three separate fluid dynamic phenomena relevant to small fliers, including: laminar separation and transition over a stationary airfoil, transition effects on the dynamic stall vortex generated by a plunging airfoil, and the effect of flexibility on the flow structure above a membrane airfoil. The specific cases were also selected to permit comparison with available experimental measurements. First, the process of transition on a stationary SD7003 airfoil section over a range of Reynolds numbers and angles of attack is considered. Prior to stall, the flow exhibits a separated shear layer which rolls up into spanwise vortices. These vortices subsequently undergo spanwise instabilities, and ultimately breakdown into fine-scale turbulent structures as the boundary layer reattaches to the airfoil surface. In a time-averaged sense, the flow displays a closed laminar separation bubble which moves upstream and contracts in size with increasing angle of attack for a fixed Reynolds number. For a fixed angle of attack, as the Reynolds number decreases, the laminar separation bubble grows in vertical extent producing a significant increase in drag. For the lowest Reynolds number considered ( Re c = 104), transition does not occur over the airfoil at moderate angles of attack prior to stall. Next, the impact of a prescribed high-frequency small-amplitude plunging motion on the transitional flow over the SD7003 airfoil is investigated. The motion-induced high angle of attack results in unsteady separation in the leading edge and in the formation of dynamic-stall-like vortices which convect downstream close to the airfoil. At the lowest value of Reynolds number ( Re c = 104), transition effects are observed to be minor and the dynamic stall vortex system remains fairly coherent. For Re c = 4 × 104, the dynamic-stall vortex system is laminar at is inception, however shortly afterwards, it experiences an abrupt breakdown associated with the onset of spanwise instability effects. The computed phased-averaged structures for both values of Reynolds number are found to be in good agreement with the experimental data. Finally, the effect of structural compliance on the unsteady flow past a membrane airfoil is investigated. The membrane deformation results in mean camber and large fluctuations which improve aerodynamic performance. Larger values of lift and a delay in stall are achieved relative to a rigid airfoil configuration. For Re c = 4.85 × 104, it is shown that correct prediction of the transitional process is critical to capturing the proper membrane structural response.

Visbal, Miguel R.; Gordnier, Raymond E.; Galbraith, Marshall C.

2009-05-01

53

S825 and S826 Airfoils: 1994--1995  

SciTech Connect

A family of airfoils, the S825 and S826, for 20- to 40-meter, variable-speed and variable-pitch (toward feather), horizontal-axis wind turbines has been designed and analyzed theoretically. The two primary objectives of high maximum lift, insensitive to roughness, and low profile drag have been achieved. The constraints on the pitching moments and the airfoil thicknesses have been satisfied. The airfoils should exhibit docile stalls.

Somers, D. M.

2005-01-01

54

Flatback airfoil wind tunnel experiment.  

SciTech Connect

A computational fluid dynamics study of thick wind turbine section shapes in the test section of the UC Davis wind tunnel at a chord Reynolds number of one million is presented. The goals of this study are to validate standard wind tunnel wall corrections for high solid blockage conditions and to reaffirm the favorable effect of a blunt trailing edge or flatback on the performance characteristics of a representative thick airfoil shape prior to building the wind tunnel models and conducting the experiment. The numerical simulations prove the standard wind tunnel corrections to be largely valid for the proposed test of 40% maximum thickness to chord ratio airfoils at a solid blockage ratio of 10%. Comparison of the computed lift characteristics of a sharp trailing edge baseline airfoil and derived flatback airfoils reaffirms the earlier observed trend of reduced sensitivity to surface contamination with increasing trailing edge thickness.

Mayda, Edward A. (University of California, Davis, CA); van Dam, C.P. (University of California, Davis, CA); Chao, David D. (University of California, Davis, CA); Berg, Dale E.

2008-04-01

55

Trailing edge modifications for flatback airfoils.  

SciTech Connect

The adoption of blunt trailing edge airfoils (also called flatback airfoils) for the inboard region of large wind turbine blades has been proposed. Blunt trailing edge airfoils would not only provide a number of structural benefits, such as increased structural volume and ease of fabrication and handling, but they have also been found to improve the lift characteristics of thick airfoils. Therefore, the incorporation of blunt trailing edge airfoils would allow blade designers to more freely address the structural demands without having to sacrifice aerodynamic performance. These airfoils do have the disadvantage of generating high levels of drag as a result of the low-pressure steady or periodic flow in the near-wake of the blunt trailing edge. Although for rotors, the drag penalty appears secondary to the lift enhancement produced by the blunt trailing edge, high drag levels are of concern in terms of the negative effect on the torque and power generated by the rotor. Hence, devices are sought that mitigate the drag of these airfoils. This report summarizes the literature on bluff body vortex shedding and bluff body drag reduction devices and proposes four devices for further study in the wind tunnel.

Kahn, Daniel L. (University of California, Davis, CA); van Dam, C.P. (University of California, Davis, CA); Berg, Dale E.

2008-03-01

56

Status of the special-purpose airfoil families  

NASA Astrophysics Data System (ADS)

This work is directed at developing thin and thick airfoil families, for rotors with diameters of 10 to 30 m, that enhance energy output at low to medium wind speeds and provide more consistent operating characteristics with lower fatigue loads at high wind speeds. Performance is enhanced through the use of laminar flow, while more consistent rotor operating characteristics at high wind speeds are achieved by tailoring the airfoil such that the maximum lift coefficient C sub 1 max is largely independent of roughness effects. Using the Eppler airfoil design code, two thin and one thick airfoil family were designed; each family has a root, outboard, and tip airfoil. Two-dimensional wind-tunnel tests were conducted to verify the predicted performance characteristics for both a thin and thick outboard airfoil from these families. Atmospheric tests on full-scale wind turbines will complete the verification process.

Tangler, J. L.; Somers, D. M.

1987-12-01

57

Design and experimental results for the S814 airfoil  

SciTech Connect

A 24-percent-thick airfoil, the S814, for the root region of a horizontal-axis wind-turbine blade has been designed and analyzed theoretically and verified experimentally in the low-turbulence wind tunnel of the Delft University of Technology Low Speed Laboratory, The Netherlands. The two primary objectives of high maximum lift, insensitive to roughness, and low profile drag have been achieved. The constraints on the pitching moment and the airfoil thickness have been satisfied. Comparisons of the theoretical and experimental results show good agreement with the exception of maximum lift which is overpredicted. Comparisons with other airfoils illustrate the higher maximum lift and the lower profile drag of the S814 airfoil, thus confirming the achievement of the objectives.

Somers, D.M. [Airfoils, Inc., State College, PA (United States)

1997-01-01

58

Wind-tunnel test of the S814 thick root airfoil  

Microsoft Academic Search

The objective of this wind-tunnel test was to verify the predictions of the Eppler Airfoil Design and Analysis Code for a very thick airfoil having a high maximum lift coefficient (c{sub 1,max} designed to be largely insensitive to leading edge roughness effects. The 24-percent-thick S814 airfoil was designed with these characteristics to accommodate aerodynamic and structural considerations for the root

D. M. Somers; J. L. Tangler

1995-01-01

59

S830, S831, and S832 Airfoils: November 2001-November 2002  

SciTech Connect

A family of quiet, thick, natural-laminar-flow airfoils, the S830, S831, and S832, for 40 - 50-meter-diameter, variable-speed/variable-pitch, horizontal-axis wind turbines has been designed and analyzed theoretically. The two primary objectives of high maximum lift, relatively insensitive to roughness, and low profile drag have been achieved. The airfoils should exhibit docile stalls, which meet the design goal. The constraints on the pitching moment and the airfoils thicknesses have been satisfied.

Somers, D. M.

2005-08-01

60

S833, S834, and S835 Airfoils: November 2001--November 2002  

SciTech Connect

A family of quiet, thick, natural-laminar-flow airfoils, the S833, S834, and S835, for 1 - 3-meter-diameter, variable-speed/variable-pitch, horizontal-axis wind turbines has been designed and analyzed theoretically. The two primary objectives of high maximum lift, relatively insensitive to roughness, and low profile drag have been achieved. The airfoils should exhibit docile stalls, which meet the design goal. The constraints on the pitching moment and the airfoils thicknesses have been satisfied.

Somers, D. M.

2005-08-01

61

Wind-tunnel test of the S814 thick root airfoil.  

National Technical Information Service (NTIS)

The objective of this wind-tunnel test was to verify the predictions of the Eppler Airfoil Design and Analysis Code for a very thick airfoil having a high maximum lift coefficient c(sub 1,max) designed to be largely insensitive to leading edge roughness e...

D. M. Somers J. L. Tangler

1995-01-01

62

S814 and S815 Airfoils. (Report for October 1991-July 1992).  

National Technical Information Service (NTIS)

Two thick laminar-flow airfoils for the root portion of a horizontal-axis wind turbine blade, the S814 and S815, have been designed and analyzed theoretically. For both airfoils, the primary objectives of high maximum lift, insensitive to roughness, and l...

D. M. Somers

2004-01-01

63

Design and Analysis of a Subcritical Airfoil for High Altitude, Long Endurance Missions.  

National Technical Information Service (NTIS)

An airfoil was designed using the 'inverse design' method. The airfoil was tailored to meet the requirements of high altitude, long endurance missions. The cruise Mach number was 0.65 so compressibility effects were included. In the procedure used, a basi...

I. Ahmad

1982-01-01

64

Simulations of airfoil static and dynamic stall  

NASA Astrophysics Data System (ADS)

Simulations of separated flow over stalled airfoils are conducted with an aim to understand post stall flow including separation and transition. A high-order accurate numerical methodology in curvilinear coordinates, along with overlapped zonal meshes is used to solve the compressible flow equations. The simulations resolve the boundary layer and are therefore a DNS in that region, while away from the airfoil, they reduce to LES. For a NACA 0012 airfoil at a high angle of attack (15^o) and low Reynolds number (Re=135,000), boundary layer separation is laminar, while breakdown to turbulence occurs through Kelvin-Helmholtz instabilities in the separated shear layer on the suction side of the airfoil. Boundary layer separation close to the leading edge leads to a significant region of recirculation where most of the turbulent fluctuations are concentrated. Turbulence escapes into the wake when larger vortices detach from the airfoil and convect downstream. The lift coefficient fluctuates in a chaotic manner, typical of stalled airfoils. A simulation of a pitching airfoil is being conducted to throw light on the phenomenon of dynamic stall and the ability of LES to predict large scale unsteady separation. Higher Reynolds number simulations, while not amenable to true LES, will be conducted using wall models.

Nagarajan, Santhanam

2005-11-01

65

Development of the Risø wind turbine airfoils  

NASA Astrophysics Data System (ADS)

This paper presents the wind turbine airfoil development at Risø. The design method is described together with our target characteristics for wind turbine airfoils. The use of the CFD code Ellipsys2D for prediction of final target characteristics is described together with the VELUX wind tunnel testing setup. Three airfoil families were developed; Risø-A1, Risø-P and Risø-B1. The Risø-A1 airfoil family was developed for rotors of 600 kW and larger. Wind tunnel testing and field testing showed that this airfoil family is well suited for stall and active stall control. However, sensitivity to roughness was higher than expected. Field tests of a 600 kW active stall wind turbine showed an estimated reduction in blade fatigue loading of up to 15% at the same annual energy yield and at the same time reduced blade weight and blade solidity. The Risø-P airfoils were developed to replace the Risø-A1 airfoils for use on pitch controlled wind turbines. Improved design objectives should reduce the sensitivity to roughness, but measurements are not yet available. The Risø-B1 airfoil family was developed for variable speed operation with pitch control of large megawatt sized rotors. Wind tunnel testing verified the high maximum lift for these airfoils, and the airfoils were found to be very insensitive to leading edge roughness. Performance with vortex generators and Gurney flaps in combination was found to be attractive for the blade root part. Field testing of a 1.5 MW rotor is in progress. Copyright

Fuglsang, Peter; Bak, Christian

2004-04-01

66

Study on Busemann Biplane Airfoil in Low-Speed Smoke Wind Tunnel  

NASA Astrophysics Data System (ADS)

The Busemann biplane airfoil is considered one of the candidates for reducing sonic boom. In aircraft designs utilizing the biplane concept, high-lift devices must be used for takeoff and landing in low-speed conditions. In this work, flow visualizations were performed around a Busemann biplane airfoil equipped with leading and trailing edge flaps in a smoke wind tunnel. The lift coefficient of the biplane airfoil was estimated by utilizing a method based on measurements of smoke line patterns. The aspect ratio of the baseline Busemann biplane model was 0.75, the thickness ratio of the single element was 5%, and the wave cancellation condition was designed for Mach number 1.7. The length of each of the flap chords was 30% of the baseline. The Reynolds number, which is based on the chord length of the airfoil, is about 2.8×105. The results of the study are summarized as follows. For the baseline Busemann airfoil without flaps, the lift coefficient increases linearly as the angle of attack increases. The slope of the lift coefficient cl is 0.062 (1/deg.), which is in good agreement with reference data. This indicates that measuring smoke line patterns is a valid method for estimating the lift coefficient of biplane airfoils. Based on the visualization of the flow around the biplane model equipped with deflected leading and trailing edge flaps, confirmed that the separation bubble is smaller than in the baseline model due to the effective increase in camber. When the deflection angle of the trailing edge flap is increased, the lift coefficient also increases. The trend of the increasing cl is similar to that of conventional monoplane airfoil models with trailing edge flaps. Therefore, such flaps can be considered effective high-lift devices for Busemann biplane airfoils.

Kashitani, Masashi; Yamaguchi, Yutaka; Kai, Yoshiharu; Hirata, Kenichi; Kusunose, Kazuhiro

67

Use of Riblets to Obtain Drag Reduction on Airfoils at High Reynolds Number Flows,  

National Technical Information Service (NTIS)

An investigation was carried out to study the drag reduction capabilities of riblets (commercially available) when installed on a supercritical airfoil which was aerodynamically tested in the NAE's High Reynolds Number 2 D Test Facility. The flow conditio...

M. Khalid

1988-01-01

68

Gurney flap—Lift enhancement, mechanisms and applications  

Microsoft Academic Search

Since its invention by a race car driver Dan Gurney in 1960s, the Gurney flap has been used to enhance the aerodynamics performance of subsonic and supercritical airfoils, high-lift devices and delta wings. In order to take stock of recent research and development of Gurney flap, we have carried out a review of the characteristics and mechanisms of lift enhancement

J. J. Wang; Y. C. Li; K.-S. Choi

2008-01-01

69

TAKEOFF\\/LANDING ASSESSMENT OF AN HSCT WITH PNEUMATIC LIFT AUGMENTATION  

Microsoft Academic Search

Pneumatic technologies, such as Circulation Control airfoils, have been experimentally demonstrated to generate very high lift coefficients at low angles of attack. These blown airfoils offer great potential for advanced subsonic transports. Yet, the potential of this particular pneumatic technology is not limited to subsonic aircraft. In fact, Circulation Control has been chosen as an enabling technology to be applied

Dimitri N. Mavris; Michelle R. Kirby

70

Experimental and Numerical Investigations of a High Performance Co-Flow Jet Airfoil  

Microsoft Academic Search

The work reflected in this thesis includes a detailed study of co-flow jet (CFJ) technologies as they are applied to a typical thin airfoil, NACA 6415, at take-off and landing speeds. Numerical analysis and experimental testing were conducted on baseline and co-flow jet airfoils of the same plan form. The CFJ mechanism employs high pressure air injected along the span

Danah Kirk

2009-01-01

71

Active Control of the Separation Region on a Two - Airfoil.  

NASA Astrophysics Data System (ADS)

The effectiveness of combat aircraft depends in part on their ability to maintain high lift under extreme conditions. Examples of such conditions include the high angle of attack, rapid pitch motions necessary for combat maneuvers. A well known phenomenon occurring on airfoils undergoing such high angle of attack motions is the formation of a leading edge vortex. This vortex is preceded by significant increases in lift, but is also accompanied by subsequent rapid loss of lift and the ensuing dynamic stall. Prior to dynamic stall vortex formation, the unsteady separating boundary layer resembles the separating boundary layer over a static airfoil. Before developing control methodologies for unsteady flows, it is necessary to obtain a thorough understanding of the controlled flow over a static airfoil. This experimental analysis presents a comprehensive study of the separating boundary layer over a static airfoil under natural and actively controlled conditions. Near-surface hot-film and surface pressure measurements, as well as flow visualization are used to analyze the large-scale nature of the flow and determine forcing effects. Results from the static study are then extended for an initial evaluation of unsteady airfoil control. The fundamental frequency for a two-dimensional NACA-0015 airfoil is found to be an integral multiple of the frequency associated with wake structures. The static separating boundary layer response to active control confirms that it is a boundary layer transitioning to a free shear layer. Qualitative analyses show that significant reduction in overall static separation can be achieved under forcing conditions. Upper airfoil surface suction values are also significantly increased over the natural values. Applying tangential pulsed air control at static fundamental frequencies to a dynamic airfoil results in delay of the dynamic stall vortex formation and a delay of dynamic stall. These discoveries indicate that the developed control methodology may prove successful in increasing unsteady aircraft maneuverability.

Lovato, Julie Anne

72

Effects of turbulence intensity and integral length scale on an asymmetric airfoil at low Reynolds numbers  

NASA Astrophysics Data System (ADS)

In the thesis, the performance of an asymmetric, high-lift S1223 airfoil has been investigated at Reynolds numbers 55,000, 75,000, and 100,000. The airfoil was tested in a quasi-isotropic turbulent flow generated using orificed perforated plates. The independent effects of the turbulence intensity were examined at a constant integral length scale. The stall of the airfoil is delayed by increasing the turbulence intensity. The wake of the airfoil becomes narrower and the strength of the shedding vortices was reduced, which indicates a suppression of the boundary layer of the airfoil. The independent roles of integral length scale were examined at turbulence intensity of 4.1% and 9.5%. At Tu=4.1% with increasing the integral length scale, the stall of the airfoil is delayed, and wider wakes have been observed at the stall region. At Tu=9.5%, the effects of turbulence scale become subtle.

Cao, Ning

73

Root region airfoil for wind turbine  

DOEpatents

A thick airfoil for the root region of the blade of a wind turbine. The airfoil has a thickness in a range from 24%-26% and a Reynolds number in a range from 1,000,000 to 1,800,000. The airfoil has a maximum lift coefficient of 1.4-1.6 that has minimum sensitivity to roughness effects.

Tangler, James L. (Boulder, CO); Somers, Dan M. (State College, PA)

1995-01-01

74

Recent Progress on Development and Understanding of High Lift Systems.  

National Technical Information Service (NTIS)

In aircraft design the constraints between the high speed cruise and the low speed takeoff and landing conditions force the designer to incorporate some form of high lift to device to improve the lift at low speed. Most aircraft, be they civil or military...

D. J. Butter

1984-01-01

75

The inception of stall on thin airfoils at moderately high Reynolds number flows  

NASA Astrophysics Data System (ADS)

The leading-edge stall on smooth thin airfoils at moderately high Reynolds number flows is investigated by an asymptotic approach and numerical simulations. The asymptotic theory is based on Rusak (1994) and demonstrates that a subsonic flow about a thin airfoil can be described in terms of an outer and an inner region that asymptotically match each other. The flow in the outer region is dominated by the classical thin airfoil theory. Scaled (magnified) coordinates and a modified Reynolds number are used to correctly account for the nonlinear behavior in the nose region where both the near stagnation and high suction areas occur. It results in a model problem of a uniform flow past a semi-infinite parabola with a far-field circulation governed by a parameter A that is related to the airfoil's angle of attack, nose radius of curvature, camber and flow Mach number. The model parabola problem consists of a viscous flow that is solved numerically to determine the value of A where the nose flow first separates. The change of this parameter with Reynolds number is computed. It indicates stall onset on the airfoil at various flow conditions. The predictions according to this approach show good agreement with results from both full numerical simulations and much available experimental data. This simplified approach provides for the first time a universal criterion to determine the stall angle of airfoils and the effect of airfoil's thickness ratio, nose radius of curvature, camber and flaps and flow compressibility on the onset of stall. Rusak, Z. 1994 Euro J App Math, 5, 283-311.

Rusak, Zvi; Morris, Wallace J., II

2004-11-01

76

Numerical analysis of the s1020 airfoils in tandem under different flapping configurations  

NASA Astrophysics Data System (ADS)

The objective of this project is to improve the performance of the efficiency, thrust and lift of flapping wings in tandem arrangement. This research investigates the effect of the arrangement of the airfoils in tandem on the performance of the airfoils by varying the phase difference and distance between the airfoils. Three flapping configurations from an earlier phase of a research which gives high efficiency, thrust and lift are used in the tandem simulation. It is found all the different flapping configurations show improvement in the efficiency, thrust or lift when the distance between the two airfoils and the phase angle between the heaving positions of the two airfoils are optimal. The average thrust coefficient of the tandem arrangement managed to attain more than twice that of the single one (4.84 vs. 2.05). On the other hand, the average lift coefficient of the tandem arrangement also increased to 4.59, as compared to the original single airfoil value of 3.04. All these results obtained will aid in the design of a better ornithopter with tandem wing arrangement.

Lim, K. B.; Tay, W. B.

2010-05-01

77

Analytical and computational investigations of airfoils undergoing high-frequency sinusoidal pitch and plunge motions at low Reynolds numbers  

NASA Astrophysics Data System (ADS)

Current interests in Micro Air Vehicle (MAV) technologies call for the development of aerodynamic-design tools that will aid in the design of more efficient platforms that will also have adequate stability and control for flight in gusty environments. Influenced largely by nature MAVs tend to be very small, have low flight speeds, and utilize flapping motions for propulsion. For these reasons the focus is, specifically, on high-frequency motions at low Reynolds numbers. Toward the goal of developing design tools, it is of interest to explore the use of elementary flow solutions for simple motions such as pitch and plunge oscillations to predict aerodynamic performance for more complex motions. In the early part of this research, a validation effort was undertaken. Computations from the current effort were compared with experiments conducted in a parallel, collaborative effort at the Air Force Research Laboratory (AFRL). A set of pure-pitch and pure-plunge sinusoidal oscillations of the SD7003 airfoil were examined. Phase-averaged measurements using particle image velocimetry in a water tunnel were compared with computations using two flow solvers: (i) an incompressible Navier-Stokes Immersed Boundary Method and (ii) an unsteady compressible Reynolds-Averaged Navier-Stokes (RANS) solver. The motions were at a reduced frequency of k = 3.93, and pitch-angle amplitudes were chosen such that a kinematic equivalence in amplitudes of effective angle of attack (from plunge) was obtained. Plunge cases showed good qualitative agreement between computation and experiment, but in the pitch cases, the wake vorticity in the experiment was substantially different from that predicted by both computations. Further, equivalence between the pure-pitch and pure-plunge motions was not attained through matching effective angle of attack. With the failure of pitch/plunge equivalence using equivalent amplitudes of effective angle of attack, the effort shifted to include pitch-rate and wake-effect terms through the use of analytical methods including quasi-steady thin-airfoil theory (QSTAT) and Theodorsen's theory. These theories were used to develop three analytical approaches for determining pitch motions equivalent to plunge motions. A study of variation in plunge height was then examined and followed by a study of the effect of rotation point using the RANS solver. For the range of plunge heights studied, it was observed that kinematic matching between plunge and pitch using QSTAT gave outstanding similarities in flow field, while the matching performed using Theodorsen's theory gave the best equivalence in lift coefficients for all cases. The variation of rotation point revealed that, for the given plunge height, with rotation point in front of the mid-chord location, all three schemes matched flow-field vorticity well, and with rotation point aft of the mid-chord no scheme matched vorticity fields. However, for all rotation points (except for the mid-chord location), CFD prediction of lift coefficients from the Theodorsen matching scheme matched the lift time histories closely to CFD predictions for pure-pitch. Combined pitch and plunge motions were then examined using kinematic parameters obtained from the three schemes. The results showed that QSTAT nearly cancels the vortices emanating from the trailing edge. Theodorsen's matching approach was successful in generating a lift that was close to constant over the entire cycle. Additionally this approach showed the presence of the reverse Karman vortex sheet through the wake. Combined pitch/plunge motions were then analyzed, computationally and experimentally, with a non-zero mean angle of attack. All computational results compared excellently with experiments, capturing vorticity production on the airfoil's surface and through the wake. Lift coefficient through a cycle was shown to tend toward a constant using Theodorsen's parameters, with the constant being dependent on the initial angle of attack. This result points to the possibility of designing an unsteady motion to match a given flig

McGowan, Gregory Z.

78

Towards controlling separated flow past an airfoil  

NASA Astrophysics Data System (ADS)

Separated flow past an airfoil at high angles of attack exhibits mixed features of wall-bounded flows and free-shear flows. The separated flow is known to respond to external forcing at frequencies associated with the shedding frequency. In this study, we explore new control strategies for the separated flow over an airfoil at high angles of attack, the goal being significant lift enhancement. The control law is derived based on the system identification theory and observed shear layer dynamics. Both controlled and uncontrolled separated flows past a NACA0012 airfoil are numerically simulated by the detached-eddy simulation technique over a range of Reynolds numbers and angles of attack. The effects of control actuation, blowing and suction over various portions of the airfoil surface and at different frequencies, on the dynamics of the separated flow are investigated and, in some cases, are shown to be significant. The physical mechanism responsible for lift enhancement is sought by analyzing detailed flow fields obtained from these simulations. Some numerical issues associated with the simulation are also addressed.

Huang, Shao-Ching; Kim, John

2001-11-01

79

An Analytical Evaluation of Airfoil Sections for Helicopter Rotor Applications.  

National Technical Information Service (NTIS)

An analytical technique was used to evaluate airfoils for helicopter rotor application. This technique permits assessment of the influences of airfoil geometric variations on drag divergence Mach number at lift coefficients from near zero to near maximum ...

G. J. Bingham

1975-01-01

80

Computational design and analysis of flatback airfoil wind tunnel experiment.  

SciTech Connect

A computational fluid dynamics study of thick wind turbine section shapes in the test section of the UC Davis wind tunnel at a chord Reynolds number of one million is presented. The goals of this study are to validate standard wind tunnel wall corrections for high solid blockage conditions and to reaffirm the favorable effect of a blunt trailing edge or flatback on the performance characteristics of a representative thick airfoil shape prior to building the wind tunnel models and conducting the experiment. The numerical simulations prove the standard wind tunnel corrections to be largely valid for the proposed test of 40% maximum thickness to chord ratio airfoils at a solid blockage ratio of 10%. Comparison of the computed lift characteristics of a sharp trailing edge baseline airfoil and derived flatback airfoils reaffirms the earlier observed trend of reduced sensitivity to surface contamination with increasing trailing edge thickness.

Mayda, Edward A. (University of California, Davis, CA); van Dam, C.P. (University of California, Davis, CA); Chao, David D. (University of California, Davis, CA); Berg, Dale E.

2008-03-01

81

Exploration in optimal design of an airfoil with a leading edge rotating cylinder  

Microsoft Academic Search

Based on the theory of moving surface boundary layer control (MSBC), a concept of an airfoil having a rotating cylinder at\\u000a the leading edge has been developed and experimentally proven to have good aerodynamic performance even at large angles of\\u000a attack. Thus, this research aims to give guidance on optimizing the design of this kind of airfoil with high lift

Yuan-Yuan Zhang; Dian-Gui Huang; Xiao-Jing Sun; Guo-Qing Wu

2010-01-01

82

CAA boundary conditions for airfoil noise due to high-frequency gusts  

Microsoft Academic Search

This paper proposes inflow and outflow boundary conditions for direct computation of airfoil noise under the influence of impinging gusts with a particular interest in the high frequency response. The proposed boundary conditions are based on an existing zonal sponge technique that has been used mostly to attenuate outgoing disturbances and absorb reflections from computational boundaries. A modified form of

Jae Wook Kim; Alex S. H. Lau; Neil D. Sandham

2010-01-01

83

Computation of Flow around NACA0012 Airfoil at High Angle of Attack.  

National Technical Information Service (NTIS)

Transonic flow around a NACA0012 airfoil at high angle of attack is simulted by solving the two-dimensional Navier-Stokes equations. The block pentadiagonal matrix scheme is employed. Periodic phenomena of shock-wave vortex interaction are observed. For c...

Y. Shida K. Kuwahara

1987-01-01

84

Modeling of Flow about Pitching and Plunging Airfoil Using High-Order Schemes.  

National Technical Information Service (NTIS)

A high-order non-uniform compact finite-difference algorithm with numerical filtering and low storage Runga-Kutta scheme is developed to perform numerical simulations on orthogonal grids generated about plunging and pitching airfoils. The grids, which mov...

A. Povitsky H. Gopalan

2008-01-01

85

Wind-tunnel test of the S814 thick root airfoil  

SciTech Connect

The objective of this wind-tunnel test was to verify the predictions of the Eppler Airfoil Design and Analysis Code for a very thick airfoil having a high maximum lift coefficient (c{sub 1,max} designed to be largely insensitive to leading edge roughness effects. The 24-percent-thick S814 airfoil was designed with these characteristics to accommodate aerodynamic and structural considerations for the root region of a wind-turbine blade. In addition, the airfoil`s maximum lift-to-drag ratio was designed to occur it a high lift coefficient. To accomplish the objective, a two-dimensional wind-tunnel test of the S814 thick root airfog was conducted in January 1994 in the low-turbulence wind tunnel of the Delft University of Technology Low Speed Laboratory. Data were obtained for transition-free and transition-fixed conditions at Reynolds numbers of 0.7, 1.0, 1.5, 2.0, and 3.0 {times} 10{sup 6}. For the design Reynolds numbers of 1.5 {times} l0{sup 6}, the transition-free c{sub 1,max} is 1.3 which satisfies the design specification. However, this value is significantly lower than the predicted c{sub 1,max} of almost l.6. With transition-fixed at the is 1.2. The difference in c{sub 1,max} between the transition-free and transition-fixed conditions demonstrates the airfoil`s minimal sensitivity to roughness effects. The S814 root airfoil was designed to complement existing NREL low c{sub 1,max} tip-region airfoils for rotor blades 10 to 15 meters in length.

Somers, D.M. [Airfoils, Inc., State College, VA (United States); Tangler, J.L. [National Renewable Energy Lab., Golden, CO (United States)

1995-01-01

86

Flow Prediction Around an Oscillating NACA0012 Airfoil at Re = 1,000,000  

NASA Astrophysics Data System (ADS)

The maximum obtainable lift of a rotationally-oscillating airfoil is significantly higher than in the static or quasi-static case. The correct prediction of dynamic stall as the basis of the dynamically increased lift is essential to quantify the time-dependent load on the airfoil structure. This study applies unsteady RANS (URANS) and detached-eddy simulation (DES) with various turbulence models and parameter variations in order to capture the physics around an oscillating NACA0012 airfoil at a relatively high Reynolds number and to identify possible advantages and potential drawbacks of the given methods. The quality of the flow prediction is assessed primarily on the basis of integral force coefficients compared to experimental results, revealing the influence of resolution on maximum lift and the corresponding angle of incidence.

Frederich, O.; Bunge, U.; Mockett, C.; Thiele, F.

87

Multi-objective optimization design of low-Reynolds-number airfoil in Near Space  

Microsoft Academic Search

For the reason of practical use in propeller design for low-dynamic aircrafts in Near Space, it is very important to have high-performance low-Reynolds-number airfoils which should have high lift-drag ratio, high endurance factor and high maximum-lift-coefficient, etc. Multi-objective optimal design can effectively solve the multiple design-points problem, which is an effective means and methods for optimum aerodynamic design. The paper

Rong Ma; Bowen Zhong; Peiqing Liu; Wenhu Wang

2010-01-01

88

Exploration in optimal design of an airfoil with a leading edge rotating cylinder  

NASA Astrophysics Data System (ADS)

Based on the theory of moving surface boundary layer control (MSBC), a concept of an airfoil having a rotating cylinder at the leading edge has been developed and experimentally proven to have good aerodynamic performance even at large angles of attack. Thus, this research aims to give guidance on optimizing the design of this kind of airfoil with high lift coefficients. Using computational fluid dynamics (CFD) technique, the CFD simulation results have been compared with the experimental results available in the literature, and then the SST two-equation model is selected as the appropriate turbulence model. At a given cylinder surface velocity ratio, the cylinder diameter d, the drop height of trailing edge ? and the curvatures of the pressure and suction surfaces of the airfoil are regarded as the optimal design parameters and the airfoil lift coefficient is considered as the optimization objective function. Therefore, using orthogonal optimization method, we herein develop a new design of airfoil favorable for having a rotating leading edge. It has been numerically proven that the resulting airfoil has good capability of achieving a substantially superior performance when compared to the airfoils of the prior art.

Zhang, Yuan-Yuan; Huang, Dian-Gui; Sun, Xiao-Jing; Wu, Guo-Qing

2010-08-01

89

Effects of front-loading and stagger angle on endwall losses of high lift low pressure turbine vanes  

NASA Astrophysics Data System (ADS)

Past efforts to reduce the airfoil count in low pressure turbines have produced high lift profiles with unacceptably high endwall loss. The purpose of the current work is to suggest alternative approaches for reducing endwall losses. The effects of the fluid mechanics and high lift profile geometry are considered. Mixing effects of the mean flow and turbulence fields are decoupled to show that mean flow shear in the endwall wake is negligible compared to turbulent shear, indicating that turbulence dissipation is the primary cause of total pressure loss. The mean endwall flow field does influence total pressure loss by causing excessive wake growth and perhaps outright separation on the suction surface. For equivalent stagger angles, a front-loaded high lift profile will produce less endwall loss than one aft-loaded, primarily by suppressing suction surface flow separation. Increasing the stagger setting, however, increases the endwall loss due to the static pressure field generating a stronger blockage relative to the incoming endwall boundary layer flow and causing a larger mass of fluid to become entrained in the horseshoe vortex. In short, front-loading the pressure distribution suppresses suction surface separation whereas limiting the stagger angle suppresses inlet boundary layer separation. Results of this work suggest that a front-loaded low stagger profile be used at the endwall to reduce the endwall loss.

Lyall, M. Eric

90

High-Lift Systems on Commercial Subsonic Airliners.  

National Technical Information Service (NTIS)

The early breed of slow commercial airliners did not require high-lift systems because their wing loadings were low and their speed ratios between cruise and low speed (takeoff and landing) were about 2:1. However, even in those days the benefit of high-l...

P. K. C. Rudolph

1996-01-01

91

Lift Enhancement Using Pulsed Blowing At Compressible Flow Conditions  

Microsoft Academic Search

Oscillatory wall-jets were introduced through spanwise slots along a NACA 0015 airfoil to establish lift augmentation by the unsteady forcing of the wall layer. Pressure coefficients, lift coefficients, and wake velocity profiles were measured for experiments where the oscillatory blowing momentum coefficient was held constant at various frequencies up to M=0.4. At high angles of attack, it was observed that

Michael Hites; Hassan Nagib; Brian Sytsma; Israel Wygnanski; Avi Seifert; Tomer Bachar

1997-01-01

92

The studies of finite supercavitating airfoil  

Microsoft Academic Search

An aerofoil above which is built the artificial cavity low pressure region is called “cavitating airfoil”. By using generalized Blasius's theorem and conformal transformation, this paper investigates the problem of the flow past the aerofoil of cavitating airfoil with the jetstream above cavitation, and gives the formulae of the lift and thrust.

Lian Guang-chang; Chien Wei-zang

1986-01-01

93

High-fidelity simulations of moving and flexible airfoils at low Reynolds numbers  

Microsoft Academic Search

The present paper highlights results derived from the application of a high-fidelity simulation technique to the analysis\\u000a of low-Reynolds-number transitional flows over moving and flexible canonical configurations motivated by small natural and\\u000a man-made flyers. This effort addresses three separate fluid dynamic phenomena relevant to small fliers, including: laminar\\u000a separation and transition over a stationary airfoil, transition effects on the dynamic

Miguel R. Visbal; Raymond E. Gordnier; Marshall C. Galbraith

2009-01-01

94

Evaluation of Airfoil Dynamic Stall Characteristics for Maneuverability  

Microsoft Academic Search

The loading of an airfoil during dynamic stall is examined in terms of the augmented lift and the associated penalties in pitching moment and drag. It is shown that once stall occurs and a leading-edge vortex is shed from the airfoil there is a unique relationship between the augmented lift, the negative pitching moment, and the increase in drag. This

William G. Bousman

2001-01-01

95

Airfoil structure  

DOEpatents

Past airfoil configurations have been used to improve aerodynamic performance and engine efficiencies. The present airfoil configuration further increases component life and reduces maintenance by reducing internal stress within the airfoil itself. The airfoil includes a chord and a span. Each of the chord and the span has a bow being summed to form a generally ``C`` configuration of the airfoil. The generally ``C`` configuration includes a compound bow in which internal stresses resulting from a thermal temperature gradient are reduced. The structural configuration reduces internal stresses resulting from thermal expansion. 6 figs.

Frey, G.A.; Twardochleb, C.Z.

1998-01-13

96

Airfoil structure  

DOEpatents

Past airfoil configurations have been used to improve aerodynamic performance and engine efficiencies. The present airfoil configuration further increases component life and reduces maintenance by reducing internal stress within the airfoil itself. The airfoil includes a chord and a span. Each of the chord and the span has a bow being summed to form a generally "C" configuration of the airfoil. The generally "C" configuration includes a compound bow in which internal stresses resulting from a thermal temperature gradient are reduced. The structural configuration reduces internal stresses resulting from thermal expansion.

Frey, Gary A. (Poway, CA); Twardochleb, Christopher Z. (Alpine, CA)

1998-01-01

97

Design and Experimental Results for a Natural-Laminar-Flow Airfoil for General Aviation Applications.  

National Technical Information Service (NTIS)

A natural-laminar-flow airfoil for general aviation applications, the NLF(1)-0416, was designed and analyzed theoretically and verified experimentally in the Langley Low-Turbulence Pressure Tunnel. The basic objective of combining the high maximum lift of...

D. M. Somers

1981-01-01

98

Development of Advanced High Lift Leading Edge Technology for Laminar Flow Wings.  

National Technical Information Service (NTIS)

This paper describes the Advanced High Lift Leading Edge (AHLLE) task performed by Northrop Grumman Systems Corporation, Aerospace Systems (NGAS) for the NASA Subsonic Fixed Wing project in an effort to develop enabling high-lift technology for laminar fl...

A. Korntheuer J. C. Lin M. M. Bright S. Komadina

2013-01-01

99

Numerical bifurcation analysis of static stall of airfoil and dynamic stall under unsteady perturbation  

NASA Astrophysics Data System (ADS)

By the finite element method combined with Arbitrary-Lagrangian-Eulerian (ALE) frame and explicit Characteristic Based Split Scheme (CBS), the complex flows around stationary and sinusoidal pitching airfoil are studied numerically. In particular, the static and dynamic stalls are analyzed in detail, and the natures of the static stall of NACA0012 airfoil are given from viewpoint of bifurcations. Following the bifurcation in Map, the static stall is proved to be the result from saddle-node bifurcation which involves both the hysteresis and jumping phenomena, by introducing a Map and its Floquet multiplier, which is constructed in the numerical simulation of flow field and related to the lift of the airfoil. Further, because the saddle-node bifurcation is sensitive to imperfection or perturbation, the airfoil is then subjected to a perturbation which is a kind of sinusoidal pitching oscillation, and the flow structure and aerodynamic performance are studied numerically. The results show that the large-scale flow separation at the static stall on the airfoil surface can be removed or delayed feasibly, and the ensuing lift could be enhanced significantly and also the stalling incidence could be delayed effectively. As a conclusion, it can be drawn that the proper external excitation can be considered as a powerful control strategy for the stall. As an unsteady aerodynamic behavior of high angle of attack, the dynamic stall can be investigated from viewpoint of nonlinear dynamics, and there exists a rich variety of nonlinear phenomena, which are related to the lift enhancement and drag reduction.

Liu, Yan; Li, Kailun; Zhang, Jiazhong; Wang, Hang; Liu, Liguang

2012-08-01

100

High-lift generation and power requirements of insect flight  

NASA Astrophysics Data System (ADS)

Recently, much progress has been made in revealing aerodynamic force mechanisms and predicting power requirements in insect flight. In this article, we review the research works in the past 10 years. We first summarize the kinematics of the flapping wing. Next we explore the unsteady high-lift mechanisms. Then we discuss the power requirements of hovering and forward flight in some insects. Finally, we mention recent studies on dragonfly flight.

Sun, Mao

2005-07-01

101

High-lift chemical heat pump technologies for industrial processes  

SciTech Connect

Traditionally industrial heat pumps (IHPs) have found applications on a process specific basis with reject heat from a process being upgraded and returned to the process. The IHP must be carefully integrated into a process since improper placement may result in an uneconomic application. Industry has emphasized a process integration approach to the design and operation of their plants. Heat pump applications have adopted this approach and the area of applicability was extended by utilizing a process integrated approach where reject heat from one process is upgraded and then used as input for another process. The DOE IHP Program has extended the process integration approach of heat pump application with a plant utility emphasis. In this design philosophy, reject heat from a process is upgraded to plant utility conditions and fed into the plant distribution system. This approach has the advantage that reject heat from any pr@s can be used as input and the output can be used at any location within the plant. Thus the approach can be easily integrated into existing industrial applications and all reject heat streams are potential targets of opportunity. The plant utility approach can not be implemented without having heat pumps with high-lift capabilities (on the order of 65{degree}C). Current heat pumps have only about half the lift capability required. Thus the current emphasis for the DOE IHP Program is the development of high lift chemical heat pumps that can deliver heat more economically to higher heat delivery temperatures. This is achieved with innovative cooling (refrigeration) and heating technologies which are based on advanced cycles and advanced working fluids or a combination of both. This paper details the plan to develop economically competitive, environmentally acceptable heat pump technologies that are capable of providing the delivery temperature and lift required to supply industrial plant utility-grade process heating and/or cooling.

Olszewski, M.; Zaltash, A.

1995-03-01

102

Numerical study of flows past airfoils with wavy surfaces  

NASA Astrophysics Data System (ADS)

The paper presents three-dimensional numerical studies on the aerodynamic characteristics of two different modified NACA0012 airfoils with different wavy surfaces using the large eddy simulations. Two types of wavy airfoils are investigated with wavy airfoil-A having a sinusoidal waviness on upper and lower surfaces with a constant chord length, while wavy airfoil-B having sinusoidal variation in both of the leading and trailing edges as well as on the upper and lower surfaces along the spanwise direction. The force characteristics and the flow structures are captured and compared with a corresponding standard NACA0012 airfoil with a Reynolds number of Re=1.6×105. The flow structures and surface pressure distributions on wavy airfoils were found to be significantly different from those on a conventional NACA0012 airfoil. For angles of attack less than the baseline stall angle of a NACA0012 airfoil, a slight decrease of lift coefficient was observed for both types of wavy airfoils, while the lift coefficient for the wavy airfoil-B increases up to 20% greater than that of a NACA0012 airfoil when the angle of attack is larger than the baseline stall angle of 13°. The flow over the leading edge of wavy airfoil-B remained attached at post stall angles of attack. In general, the wavy airfoil-A just exhibits a suppression the airfoil's fluctuation force, while the wavy airfoil-B demonstrates an advantageous aerodynamic effect on the control of loss of lift in the post stall regime of a conventional NACA0012 airfoil.

Lin, Y. F.; Lam, K.; Zou, L.; Liu, Y.

2013-01-01

103

DES of a turbulent flow over an airfoil at high angles of attack  

NASA Astrophysics Data System (ADS)

Although the computing cost of large-eddy simulation (LES) of turbulent flows is significantly less than that of direct numerical simulation (DNS), it is still too expensive for engineering applications involving thin boundary layers near surface, since the resolution requirements currently are prohibitive for most computers except perhaps for special massively parallel machines. Recently a hybrid approach, known as detached-eddy simulation (DES), has been proposed (Nikitin et al. Phys Fluids 12, 1629-1632, 2000) as an alternative, which utilizes the Reynolds-averaged Navier-Stokes (RANS) approach for thin attached boundary layers and LES elsewhere. DES of turbulent flows over an NACA0012 airfoil at various angles of attack have been performed. Detailed flow structures and global quantities such as lift, drag and pressure coefficients are investigated. Comparison of results from DES and full RANS solutions will be presented. The DES approach, which allows efficient consideration of many different configurations due to its low cost, will be used in exploring various strategies for separation control.

Huang, Shao-Ching; Kim, John

2000-11-01

104

Endplate Effectiveness for a NACA 0015 Airfoil.  

National Technical Information Service (NTIS)

Lift and drag of a NACA 0015 airfoil fitted with five differently shaped endplates are measured at M= .114 and M=.15 while sweeping the angle of attack from -4 to 14 degrees at 2 degree increments. The triangular endplate performs well in enhancing lift, ...

R. I. Chaudhary D. T. Williamson

1992-01-01

105

Leading Edge - Trailing Edge Airfoil Interactions  

Microsoft Academic Search

Computational aerodynamics predictions of airfoil drag and maximum lift continue to be a challenge to aerodynam- icists, even using large computer programs. The reliable calculation of the drag break and maximum lift, including the effects of Reynolds number, are simply not developed to the stage where they can be used routinely in aerody- namic design. This is especially troubling in

W. H. Mason

106

The ultra-low Reynolds number airfoil wake  

NASA Astrophysics Data System (ADS)

Lift force and the near wake of an NACA 0012 airfoil were measured over the angle (?) of attack of 0°-90° and the chord Reynolds number ( Re c ), 5.3 × 103-5.1 × 104, with a view to understand thoroughly the near wake of the airfoil at low- to ultra-low Re c . While the lift force is measured using a load cell, the detailed flow structure is captured using laser-Doppler anemometry, particle image velocimetry, and laser-induced fluorescence flow visualization. It has been found that the stall of an airfoil, characterized by a drop in the lift force, occurs at Re c ? 1.05 × 104 but is absent at Re c = 5.3 × 103. The observation is connected to the presence of the separation bubble at high Re c but absence of the bubble at ultra-low Re c , as evidenced in our wake measurements. The near-wake characteristics are examined and discussed in detail, including the vortex formation length, wake width, spanwise vorticity, wake bubble size, wavelength of K-H vortices, Strouhal numbers, and their dependence on ? and Re c .

Alam, Md. Mahbub; Zhou, Y.; Yang, H. X.; Guo, H.; Mi, J.

2010-01-01

107

An experimental investigation of unsteady surface pressure on an airfoil in turbulence—Part 2: Sources and prediction of mean loading effects  

NASA Astrophysics Data System (ADS)

An experimental investigation into the response of an airfoil in turbulence was undertaken and the results are presented in a two part series of papers. The effects of mean loading on the airfoil response are investigated in Part 1 with the likely origins discussed in this paper (Part 2). Unsteady pressure measurements were made on the surface of a NACA 0015 airfoil immersed in grid turbulence (?/c=13%) for angles of attack ?=0 20°. This paper (Part 2) presents the causes of the low-frequency reduction and high-frequency increase observed in measured lift and pressure spectral levels. Scaling lift spectra on the mean lift reveals the increase in lift spectral level for reduced frequencies greater than 10 is closely related to the airfoils mean pressure field. Based on analysis of the chordwise and spanwise pressure correlation length scale, the reduction in lift spectral level at low reduced frequency appears to result from distortion of the inflow by the mean velocity field. A possible model is developed that accurately predicts mean loading effects on lift spectra. This model uses a circular cylinder fit to the airfoil to compute effects of distortion on the inflow turbulence. The distorted inflow velocity spectrum is then used with Amiet's theory to predict the unsteady loading. This model successfully captures the reduction observed in measured lift spectra at low reduced frequencies. Furthermore, it is shown that the angle of attack effects arising from inflow distortion are significant only when the relative scale of the inflow turbulence to airfoil chord is sufficiently small (?/c=13% for present experiment).

Mish, Patrick F.; Devenport, William J.

2006-09-01

108

Lift Enhancement Using Pulsed Blowing At Compressible Flow Conditions  

NASA Astrophysics Data System (ADS)

Oscillatory wall-jets were introduced through spanwise slots along a NACA 0015 airfoil to establish lift augmentation by the unsteady forcing of the wall layer. Pressure coefficients, lift coefficients, and wake velocity profiles were measured for experiments where the oscillatory blowing momentum coefficient was held constant at various frequencies up to M=0.4. At high angles of attack, it was observed that lift coefficient increased by as much as 80% due to the pulsed blowing and that supercritical flow was detected near the leading edge. Measurements at low angles of attack with the flap set at 20^o (an aft loaded airfoil near cruise conditions) showed that low amplitude pulsed forcing from the flap provided a 27% increasing in lift while steady blowing from the flap reduced lift by as much as 15% even at blowing coefficients as high as 3.5%. Wake profiles showed that not only was the lift enhanced due to the oscillatory blowing, but the drag was reduced, demonstrating the effectiveness of pulsed blowing as a tool to increase lift and reduce drag, especially when compared to the relative ineffectiveness of steady blowing under similar conditions.

Hites, Michael; Nagib, Hassan; Sytsma, Brian; Wygnanski, Israel; Seifert, Avi; Bachar, Tomer

1997-11-01

109

Lift Augmentation on Planar Airfoils in the Transonic Regime - a High Reynolds Number Wind Tunnel Study.  

National Technical Information Service (NTIS)

Tests were carried out at Mach numbers of 0.75, 0.80, and 0.85 and a Reynolds number of 30,000,000/15 inch chord to determine the relative effectiveness of aft camber, jet flaps, or tangential slot blowing, either separately or in combination, to increase...

H. Yoshihara R. Magnus W. Carter R. Murray

1973-01-01

110

Investigation of a Two-Dimensional Hybrid Laminar Flow Control Airfoil at High Subsonic Flow. Part 1: Aerodynamic Characteristic of a Basic Airfoil NLAM78.  

National Technical Information Service (NTIS)

The experimentally determined aerodynamic characteristics of the NLAM 78 airfoil section, a natural-laminar airfoil, over the Mach number range 0.6 to 0.85 and angles of incidence from -1 to 4 as well as the Reynolds numbers 8, 16, and 32 million, respect...

O. Nonaka Y. Ishida M. Sato H. Kanda

1990-01-01

111

Bioinspired Corrugated Airfoil at Low Reynolds Numbers  

Microsoft Academic Search

An experimental study was conducted to investigate the flow behavior around a bioinspired corrugated airfoil compared with a traditional streamlined airfoil and a flat plate at the chord Reynolds number of Re 34; 000 to explore the potential application of such bioinspired corrugated airfoils for micro air vehicle applications. The experiments were conducted in a low-speed wind tunnel. A high-resolution

Hui Hu; Masatoshi Tamai

2008-01-01

112

Wind Tunnel and Numerical Analysis of Thick Blunt Trailing Edge Airfoils  

NASA Astrophysics Data System (ADS)

Two-dimensional aerodynamic characteristics of several thick blunt trailing edge airfoils are presented. These airfoils are not only directly applicable to the root section of wind turbine blades, where they provide the required structural strength at a fraction of the material and weight of an equivalent sharp trailing edge airfoil, but are also applicable to the root sections of UAVs having high aspect ratios, that also encounter heavy root bending forces. The Reynolds averaged Navier-Stokes code, ARC2D, was the primary numerical tool used to analyze each airfoil. The UCD-38-095, referred to as the Pareto B airfoil in this thesis, was also tested in the University of California, Davis Aeronautical Wind Tunnel. The Pareto B has an experimentally determined maximum lift coefficient of 1.64 at 14 degrees incidence, minimum drag coefficient of 0.0385, and maximum lift over drag ratio of 35.9 at a lift coefficient of 1.38, 10 degrees incidence at a Reynolds number of 666,000. Zig-zag tape at 2% and 5% of the chord was placed on the leading edge pressure and suction side of the Pareto B model in order to determine the aerodynamic performance characteristics at turbulent flow conditions. Experimental Pareto B wind tunnel data and previous FB-3500-0875 data is also presented and used to validate the ARC2D results obtained in this study. Additionally MBFLO, a detached eddy simulation Navier-Stokes code, was used to analyze the Pareto B airfoil for comparison and validation purposes.

McLennan, Anthony William

113

Parameter study of simplified dragonfly airfoil geometry at Reynolds number of 6000.  

PubMed

Aerodynamic study of a simplified Dragonfly airfoil in gliding flight at Reynolds numbers below 10,000 is motivated by both pure scientific interest and technological applications. At these Reynolds numbers, the natural insect flight could provide inspiration for technology development of Micro UAV's and more. Insect wings are typically characterized by corrugated airfoils. The present study follows a fundamental flow physics study (Levy and Seifert, 2009), that revealed the importance of flow separation from the first corrugation, the roll-up of the separated shear layer to discrete vortices and their role in promoting flow reattachment to the aft arc, as the leading mechanism enabling high-lift, low drag performance of the Dragonfly gliding flight. This paper describes the effect of systematic airfoil geometry variations on the aerodynamic properties of a simplified Dragonfly airfoil at Reynolds number of 6000. The parameter study includes a detailed analysis of small variations of the nominal geometry, such as corrugation placement or height, rear arc and trailing edge shape. Numerical simulations using the 2D laminar Navier-Stokes equations revealed that the flow accelerating over the first corrugation slope is followed by an unsteady pressure recovery, combined with vortex shedding. The latter allows the reattachment of the flow over the rear arc. Also, the drag values are directly linked to the vortices' magnitude. This parametric study shows that geometric variations which reduce the vortices' amplitude, as reduction of the rear cavity depth or the reduction of the rear arc and trailing edge curvature, will reduce the drag values. Other changes will extend the flow reattachment over the rear arc for a larger mean lift coefficients range; such as the negative deflection of the forward flat plate. These changes consequently reduce the drag values at higher mean lift coefficients. The detailed geometry study enabled the definition of a corrugated airfoil geometry with enhanced aerodynamic properties, such as range and endurance factors, as compared to the nominal airfoil studied in the literature. PMID:20673771

Levy, David-Elie; Seifert, Avraham

2010-07-29

114

Numerical analysis of the s1020 airfoils in tandem under different flapping configurations  

Microsoft Academic Search

The objective of this project is to improve the performance of the efficiency, thrust and lift of flapping wings in tandem arrangement. This research investigates the effect of the arrangement of the airfoils in tandem on the performance of the airfoils by varying the phase difference and distance between the airfoils. Three flapping configurations from an earlier phase of a

K. B. Lim; W. B. Tay

2010-01-01

115

Numerical simulations of iced airfoils and wings  

NASA Astrophysics Data System (ADS)

A numerical study was conducted to understand the effects of simulated ridge and leading-edge ice shapes on the aerodynamic performance of airfoils and wings. In the first part of this study, a range of Reynolds numbers and Mach numbers, as well as ice-shape sizes and ice-shape locations were examined for various airfoils with the Reynolds-Averaged Navier-Stokes approach. Comparisons between simulation results and experimental force data showed favorable comparison up to stall conditions. At and past stall condition, the aerodynamic forces were typically not predicted accurately for large upper-surface ice shapes. A lift-break (pseudo-stall) condition was then defined based on the lift curve slope change. The lift-break angles compared reasonably with experimental stall angles, and indicated that the critical ice-shape location tended to be near the location of minimum pressure and the location of the most adverse pressure gradient. With the aim of improving the predictive ability of the stall behavior for iced airfoils, simulations using the Detached Eddy Simulation (DES) approach were conducted in the second part of this numerical investigation. Three-dimensional DES computations were performed for a series of angles of attack around stall for the iced NACA 23012 and NLF 0414 airfoils. The simulations for both iced airfoils provided the maximum lift coefficients and stall behaviors qualitatively consistent with experiments.

Pan, Jianping

116

Flow Field around NACA0012 Airfoil at Low Reynolds Numbers  

Microsoft Academic Search

Measurements of velocity distributions immediately behind the trailing edge of NACA0012 airfoil at low Reynolds numbers were carried out to disclose the relation between the aerodynamic characteristics described in the previous report and the flow fields around the airfoil. A dead-air region due to laminar separation, which spoils the linear growth of lift, is created near the trailing edge of

Tomohisa Ohtake; Tatsuo Motohashi

2009-01-01

117

Computation of Airfoils at Very Low Reynolds Numbers  

Microsoft Academic Search

We discuss a new numerical scheme involving adaptive boundary condi- tions which allows to compute, at very low Reynolds numbers, drag and lift of airfoils with rough surfaces efficiently with great pre- cision. As an example we present the numeri- cal implementation for an airfoil consisting of a line segment. The solution of the Navier- Stokes equations is singular at

Denis Bichsel; Peter Wittwer; Rue de Prairie

2007-01-01

118

Nasa Low-and Medium-Speed Airfoil Development.  

National Technical Information Service (NTIS)

The status of NASA low and medium speed airfoil research is discussed. Effects of airfoil thickness-chord ratios varying from 9 percent to 21 percent on the section characteristics for a design lift coefficient of 0.40 are presented for the initial low sp...

R. J. Mcghee W. D. Beasley R. T. Whitcomb

1979-01-01

119

Ice-induced unsteady flowfield effects on airfoil performance  

NASA Astrophysics Data System (ADS)

Numerical prediction of iced-airfoil performance prior to and at maximum lift is often inaccurate due to large-scale flow unsteadiness. New computational models are being developed to improve predictions of complex separated flowfields; however, experimental data are required to improve and validate these algorithms. The objective of this investigation was to examine the unsteady flow behavior and the time-dependent performance of an iced airfoil to determine the flowfield characteristics with the most influence on airfoil performance, especially near stall. A NACA 0012 airfoil with two-dimensional and three-dimensional leading-edge simulated glaze ice shapes was tested in a wind tunnel at Reynolds numbers 1.8 x 106 and 1.0 x 106. Time-dependent surface pressure measurements were used to calculate root-mean-square lift and quarter-chord pitching-moment coefficients. Surface and flowfield visualization and wake hot-wire data were acquired. Spectral, correlation and phase-angle analyses were performed. The most significant unsteady flowfield effect on the iced-airfoil performance was a low-frequency flow phenomenon on the order of 10 Hz that resulted in Strouhal numbers of 0.0048--0.0101. The low-frequency oscillation produced large-scale pressure fluctuations nears eparation at high angles of attack and elevated lift and moment fluctuations as low as alpha = 4°. The low-frequency motion of surface pressure coefficients convected downstream at velocities 4%--34% of the freestream value and in one case, upstream at 0.18Uinfinity. The iced-airfoil flowfield exhibited a separation bubble of varying thickness and fluctuating reattachment, characteristics similar to those associated with the low-frequency shear-layer flapping and bubble growth and decay of other separated and reattached flows. Vortex structures observed in the shear layer were presumed to be the cause of large-scale pressure fluctuations upstream of reattachment at small angles of attack. Pressure spectra near reattachment exhibited wide bandwidth frequency peaks that indicated a non-periodic phenomenon and corresponded to the regular mode often associated with vortex movement in and aft of the shear layer. Strouhal numbers ranged from 0.53 to 0.73. Although vortex shedding was rarely observed, the convection of surface pressure fluctuations occurred at approximately half the freestream velocity, similar to shedding velocities reported by others.

Gurbacki, Holly Marie

120

Macro-Fiber Composite actuated simply supported thin airfoils  

NASA Astrophysics Data System (ADS)

A piezoceramic composite actuator known as Macro-Fiber Composite (MFC) is used for actuation in the design of a variable camber airfoil intended for a ducted fan aircraft. The study focuses on response characterization under aerodynamic loads for circular arc airfoils with variable pinned boundary conditions. A parametric study of fluid-structure interaction is employed to find pin locations along the chordwise direction that result in high lift generation. Wind tunnel experiments are conducted on a 1.0% thick, 127 mm chord MFC actuated bimorph airfoil that is simply supported at 5% and 50% of the chord. Aerodynamic and structural performance results are presented for a flow rate of 15 m s - 1 and a Reynolds number of 127 000. Non-linear effects due to aerodynamic and piezoceramic hysteresis are identified and discussed. A lift coefficient change of 1.46 is observed, purely due to voltage actuation. A maximum 2D L/D ratio of 17.8 is recorded through voltage excitation.

Bilgen, Onur; Kochersberger, Kevin B.; Inman, Daniel J.; Ohanian, Osgar J., III

2010-05-01

121

Aerodynamic Issues in the Design of High-Lift Systems for Transport Aircraft.  

National Technical Information Service (NTIS)

The design of the high lift system has a profound effect on the sizing and total performance of transport aircraft, both civil and military. This paper first reviews the fundamentals of high-lift systems design and the phenomena that govern their performa...

B. Dillner F. W. May J. H. McMasters

1984-01-01

122

Modeling of human lower limb and technical analysis of athlete's high leg lift  

Microsoft Academic Search

The appearance of human motion capture system enables the analysis of human motion. In this paper, the athlete's high leg lift exercise is studied. The motion was sampled through NDI motion capture system, and the data was imported into Visual 3D software to establish a lower limb model and to execute the simulation and analysis. The high leg lift exercise

Shuyang Han; Shirong Ge; Hongtao Liu

2010-01-01

123

A High-speed Nature Laminar Flow Airfoil and Its Experimental Study in Wind Tunnel with Nonintrusive Measurement Technique  

Microsoft Academic Search

This article deals with an experimental study on the aerodynamic characteristics of a low-drag high-speed nature laminar flow (NLF) airfoil for business airplanes in the TST27 wind tunnel at Delft University of Technology, the Netherlands. In this experiment, in an attempt to reduce the errors of measurement and improve its accuracy in high-speed flight, some nonintrusive measurement techniques, such as

Zhu Jun; Gao Zhenghong; Zhan Hao; Bai Junqiang

2009-01-01

124

Computational prediction of flow and aerodynamic characteristics for an elliptic airfoil at low Reynolds number  

NASA Astrophysics Data System (ADS)

Lifting surfaces of unmanned aerial vehicles (UAV) are often operated in low Reynolds number (Re) ranges, wherein the transition of boundary layer from laminar-to-turbulent plays a more significant role than in high-Re aerodynamics applications. This poses a challenge for traditional computational fluid dynamics (CFD) simulations, since typical modeling approaches assume either fully laminar or fully turbulent flow. In particular, the boundary layer state must be accurately predicted to successfully determine the separation behavior which significantly influences the aerodynamic characteristics of the airfoil. Reynolds-averaged Navier-Stokes (RANS) based CFD simulations of an elliptic airfoil are performed for time-varying angles of attack, and results are used to elucidate relevant flow physics and aerodynamic data for an elliptic airfoil under realistic operating conditions. Results are also used to evaluate the performance of several different RANS-based turbulence modeling approaches for this class of flowfield.

Chitta, Varun

125

Design and Experimental Results for the S825 Airfoil; Period of Performance: 1998-1999  

SciTech Connect

A 17%-thick, natural-laminar-flow airfoil, the S825, for the 75% blade radial station of 20- to 40-meter, variable-speed and variable-pitch (toward feather), horizontal-axis wind turbines has been designed and analyzed theoretically and verified experimentally in the NASA Langley Low-Turbulence Pressure Tunnel. The two primary objectives of high maximum lift, relatively insensitive to roughness and low-profile drag have been achieved. The airfoil exhibits a rapid, trailing-edge stall, which does not meet the design goal of a docile stall. The constraints on the pitching moment and the airfoil thickness have been satisfied. Comparisons of the theoretical and experimental results generally show good agreement.

Somers, D. M.

2005-01-01

126

Active Control of Shock/Boundary Layer Interaction with Application to Transonic Airfoils  

NASA Astrophysics Data System (ADS)

The objective of this paper is to evaluate, via numerical simulation, the feasibility of weakening the shock wave(s) and reducing the size of the pockets of supersonic flow on wings in transonic flight using active flow control devices such as piston-driven high momentum oscillatory jet actuators (synthetic jets). The computations are performed for transonic flow past a NACA0012 airfoil using a Reynolds-Averaged Navier-Stokes (RANS) solver in conjunction with a two-equation Shear-Stress-Transport (SST) model. It is shown that by a suitable choice of the parameters of the control device such as the jet width, momentum coefficient, frequency, amplitude and locations of the actuators on the airfoil surface, it is possible to weaken the shock(s) and reduce the size of the supersonic regions on the airfoil resulting in reduced drag with minimal change in lift.

Vadillo, Jose; Agarwal, Ramesh

2003-11-01

127

Evaluation of High Lift Devices of the Quiet STOL Experimental Aircraft ASKA.  

National Technical Information Service (NTIS)

The powered high lift device of the ASKA, the NAL Short Take Off and Landing (STOL) experimental aircraft, is an Upper Surface Blowing (USB) device that forces the jet exhaust flow downward, thus producing higher lift due to the Coanda effect. Three piece...

T. Bandou

1991-01-01

128

The effect of high lift to drag ratio on aerobraking  

NASA Astrophysics Data System (ADS)

This work reviews the use of aerodynamic forces to modify the velocity, and therefore, the orbital path of vehicles due to transit through planetary atmospheres, especially when high values of lift can be generated. The concepts of aerobraking and aerocapture are examined, and the limiting factors are discussed. The use of high L/D vehicles, such as hypersonic waveriders, is examined, and the advantages and disadvantages of their use for aerocapture are addressed. This preliminary study of non-optimized aerocapture trajectories suggests that entrance velocities at Mars can be 10 - 12 km/sec for a waverider while sustaining acceptable loads of about 3 - 4 Earth G's over a 3 minute period, diminishing to less than 1 G in about 15 minutes. The entrance velocities are greater than those for a more conventional biconic configuration with similar deceleration loads sustained. The convective heating rate on the waverider, increased due to the higher velocities and sharp leading edges, has an estimated upper bound of 14000 W/sq cm and a corresponding temperature of about 7500 degrees K.

Crouse, Patrick; Lewis, Mark

129

Highly turbulent combustion: A study of lifted and shredded flames  

NASA Astrophysics Data System (ADS)

The impact of turbulence on flame chemistry in highly turbulent flames has been studied in order to test existing theories and produce data that are useful to the computer modeling community. In these flames, the fuel is injected separately from the air, but a significant amount of premixing occurs prior to combustion. By employing Particle Image Velocimetry (PIV), Planar Laser Induced Fluorescence (PLIF) of chemical species, and exhaust gas sampling, the effect of turbulence on flame chemistry has been quantified for a highly lifted, supersonic flame and for a highly swirled, shredded flame. In the supersonic flame, OH PLIF measurements were combined with combustion efficiency measurements and PIV to help to understand the mixing and flame structure. Negative velocities of more than 200 m/s were identified in the recirculating zones. Mechanisms of fuel-air mixing that result in decreased combustion efficiencies were identified. In the shredded flame, an ultra-high turbulence region was generated to examine what occurs when reaction layers encounter high turbulence levels. The flame was probed with simultaneous CH and OH PLIF and then simultaneous PIV and OH PLIF. It was found that the normalized turbulence level, even though it was ten-times greater than any previous imaging study, still produced no measurable impact on flame reaction layer thickness. This flame was also quantified by measurements of Flame Surface Density (Sigma). The thin flamelet assumption of flamelet theory is found to be valid in these highly turbulent flames. Data are presented that can be used to assess computational models as well as to provide insight into the physical processes of turbulent combustion.

Ratner, Albert

130

LES of the trailing-edge flow and noise of a controlled-diffusion airfoil at high angle of attack  

Microsoft Academic Search

Large-eddy simulations (LES) of flow over a low-speed airfoil at high angle of attack (15?) are performed using two different flow solvers, Fluent and CDP, on the same fine structured mesh, whose density was previously shown to provide a reasonably accurate trailing-edge flow for noise predictions at a lower incidence of 8?. These simulations are compared with detailed pressure measurements

J. Christophe; S. Moreau

131

Prediction of high-lift flows with separation  

NASA Astrophysics Data System (ADS)

A calculation method for predicting three-dimensional flows is developed and applied to aircraft high lift systems. The method is based on the interaction of the inviscid flow and boundary layer equations. Transition is calculated as part of the method. The approach has been applied successfully to a variety of two-dimensional problems involving massive flow separation and is extended to three-dimensions. The main difficulty of the subject consists of calculating three-dimensional separated flows. One of the main issues is the modeling of the Reynolds stresses. The original Cebeci-Smith eddy viscosity turbulence model, which was recently modified and validated for two-dimensional separated flows, is extended to three-dimensional flows and evaluated. The second issue deals with an appropriate discretization of the boundary layer equations which are solved using a finite difference approach. In order to gain some insight to the problems encountered for computing separated flows in three dimensions, the discretization of the quasi three-dimensional equations, in which the cross-derivatives are neglected, is analyzed. The need for an inverse formulation and a three-point backward difference is shown. Also, the discretization of the boundary layer equations gives rise to a set of nonlinear equations linearized using Newton's method and solved iteratively. While for laminar flows it is customary to linearize the equations with Newton's method so that the convergence rate is quadratic, it is not customary to linearize the turbulent terms, thus reducing the convergence rate. The effect of partial linearization of the turbulent terms is studied and improvements are made to obtain better convergence rates and solution stability. Of the two applications of the calculation method, the first one deals with low Reynolds number flows. The large separation bubbles present in such flows allow evaluating the main features of the method. The second application of the method deals with single and multi-element wings. Results for the single wing show that stall is well captured. Comparisons of measured and calculated lift and drag coefficients for multi-element wings also show good agreement even if some discrepancies are observed. Finally, in light of the conclusions of the present study, directions for further research are outlined.

Besnard, Eric G.

1998-07-01

132

Advancements in adaptive aerodynamic technologies for airfoils and wings  

NASA Astrophysics Data System (ADS)

Although aircraft operate over a wide range of flight conditions, current fixed-geometry aircraft are optimized for only a few of these conditions. By altering the shape of the aircraft, adaptive aerodynamics can be used to increase the safety and performance of an aircraft by tailoring the aircraft for multiple flight conditions. Of the various shape adaptation concepts currently being studied, the use of multiple trailing-edge flaps along the span of a wing offers a relatively high possibility of being incorporated on aircraft in the near future. Multiple trailing-edge flaps allow for effective spanwise camber adaptation with resulting drag benefits over a large speed range and load alleviation at high-g conditions. The research presented in this dissertation focuses on the development of this concept of using trailing-edge flaps to tailor an aircraft for multiple flight conditions. One of the major tasks involved in implementing trailing-edge flaps is in designing the airfoil to incorporate the flap. The first part of this dissertation presents a design formulation that incorporates aircraft performance considerations in the inverse design of low-speed laminar-flow adaptive airfoils with trailing-edge cruise flaps. The benefit of using adaptive airfoils is that the size of the low-drag region of the drag polar can be effectively increased without increasing the maximum thickness of the airfoil. Two aircraft performance parameters are considered: level-flight maximum speed and maximum range. It is shown that the lift coefficients for the lower and upper corners of the airfoil low-drag range can be appropriately adjusted to tailor the airfoil for these two aircraft performance parameters. The design problem is posed as a part of a multidimensional Newton iteration in an existing conformal-mapping based inverse design code, PROFOIL. This formulation automatically adjusts the lift coefficients for the corners of the low-drag range for a given flap deflection as required for the airfoil-aircraft matching. Examples are presented to illustrate the flapped-airfoil design approach for a general aviation aircraft and the results are validated by comparison with results from post-design aircraft performance computations. Once the airfoil is designed to incorporate a TE flap, it is important to determine the most suitable flap angles along the wing for different flight conditions. The second part of this dissertation presents a method for determining the optimum flap angles to minimize drag based on pressures measured at select locations on the wing. Computational flow simulations using a panel method are used "in the loop" for demonstrating closed-loop control of the flaps. Examples in the paper show that the control algorithm is successful in correctly adapting the wing to achieve the target lift distributions for minimizing induced drag while adjusting the wing angle of attack for operation of the wing in the drag bucket. It is shown that the "sense-and-adapt" approach developed is capable of handling varying and unpredictable inflow conditions. Such a capability could be useful in adapting long-span flexible wings that may experience significant and unknown atmospheric inflow variations along the span. To further develop the "sense-and-adapt" approach, the method was tested experimentally in the third part of the research. The goal of the testing was to see if the same results found computationally can be obtained experimentally. The North Carolina State University subsonic wind tunnel was used for the wind tunnel tests. Results from the testing showed that the "sense-and-adapt" approach has the same performance experimentally as it did computationally. The research presented in this dissertation is a stepping stone towards further development of the concept, which includes modeling the system in the Simulink environment and flight experiments using uninhabited aerial vehicles.

Jepson, Jeffrey Keith

133

Design and experimental results for the S805 airfoil  

SciTech Connect

An airfoil for horizontal-axis wind-turbine applications, the S805, has been designed and analyzed theoretically and verified experimentally in the low-turbulence wind tunnel of the Delft University of Technology Low Speed Laboratory, The Netherlands. The two primary objectives of restrained maximum lift, insensitive to roughness, and low profile drag have been achieved. The airfoil also exhibits a docile stall. Comparisons of the theoretical and experimental results show good agreement. Comparisons with other airfoils illustrate the restrained maximum lift coefficient as well as the lower profile-drag coefficients, thus confirming the achievement of the primary objectives.

Somers, D.M. [Airfoils, Inc., State College, PA (United States)

1997-01-01

134

Design and experimental results for the S809 airfoil  

SciTech Connect

A 21-percent-thick, laminar-flow airfoil, the S809, for horizontal-axis wind-turbine applications, has been designed and analyzed theoretically and verified experimentally in the low-turbulence wind tunnel of the Delft University of Technology Low Speed Laboratory, The Netherlands. The two primary objectives of restrained maximum lift, insensitive to roughness, and low profile drag have been achieved. The airfoil also exhibits a docile stall. Comparisons of the theoretical and experimental results show good agreement. Comparisons with other airfoils illustrate the restrained maximum lift coefficient as well as the lower profile-drag coefficients, thus confirming the achievement of the primary objectives.

Somers, D.M. [Airfoils, Inc., State College, PA (United States)

1997-01-01

135

Performance of Aerofoils with Lift Devices at Low Reynolds Numbers for Use on RPV (Remotely Piloted Vehicles) Wings.  

National Technical Information Service (NTIS)

The effect of low Reynolds numbers upon the characteristics of simple high lift devices for operation on remotely piloted vehicle wings was tested. The wing section profiles and devices tested were: a NACA 23015 airfoil with a 30% chord plain flap, and a ...

S. T. Kohler P. Pithiya

1985-01-01

136

Flow Field around NACA0012 Airfoil at Low Reynolds Numbers  

NASA Astrophysics Data System (ADS)

Measurements of velocity distributions immediately behind the trailing edge of NACA0012 airfoil at low Reynolds numbers were carried out to disclose the relation between the aerodynamic characteristics described in the previous report and the flow fields around the airfoil. A dead-air region due to laminar separation, which spoils the linear growth of lift, is created near the trailing edge of the airfoil at low angles of attack. A laminar separation bubble is observed in the boundary layer on the upper surface at intermediate angles of attack and the existence of the bubble might be responsible for the constant slope of the lift curve. Blunt decrease in lift peculiar to the stall of airfoils at low Reynolds numbers is characterized by the gradual expansion of turbulent separated region.

Ohtake, Tomohisa; Motohashi, Tatsuo

137

Numerical modeling of aerodynamics of airfoils of micro air vehicles in gusty environment  

NASA Astrophysics Data System (ADS)

The superior flight characteristics exhibited by birds and insects can be taken as a prototype of the most perfect form of flying machine ever created. The design of Micro Air Vehicles (MAV) which tries mimic the flight of birds and insects has generated a great deal of interest as the MAVs can be utilized for a number of commercial and military operations which is usually not easily accessible by manned motion. The size and speed of operation of a MAV results in low Reynolds number flight, way below the flying conditions of a conventional aircraft. The insensitivity to wind shear and gust is one of the required factors to be considered in the design of airfoil for MAVs. The stability of flight under wind shear is successfully accomplished in the flight of birds and insects, through the flapping motion of their wings. Numerous studies which attempt to model the flapping motion of the birds and insects have neglected the effect of wind gust on the stability of the motion. Also sudden change in flight conditions makes it important to have the ability to have an instantaneous change of the lift force without disturbing the stability of the MAV. In the current study, two dimensional rigid airfoil, undergoing flapping motion is studied numerically using a compressible Navier-Stokes solver discretized using high-order finite difference schemes. The high-order schemes in space and in time are needed to keep the numerical solution economic in terms of computer resources and to prevent vortices from smearing. The numerical grid required for the computations are generated using an inverse panel method for the streamfunction and potential function. This grid generating algorithm allows the creation of single-block orthogonal H-grids with ease of clustering anywhere in the domain and the easy resolution of boundary layers. The developed numerical algorithm has been validated successfully against benchmark problems in computational aeroacoustics (CAA), and unsteady viscous flows. The numerical results for pure-plunge and pure-pitching motion of SD 7003 airfoil are compared with the particle image velocimetry data of Michael Ol by plotting the contours of streamwise velocity and vorticity and also by observing the wake profile of the streamwise velocity. A very good agreement in the location of the vortices was observed between the numerical and experimental results. Also the numerical tracking of streaklines was compared with the dye injection experiments and excellent agreement in the horizontal and vertical locations of the vortex cores was observed. The importance of using the angle of attack to match the wake structures and lift forces of airfoils in pure-pitch and pure-plunge was investigated and it was found that matching the plunging amplitude with the maximum displacement of the leading edge provides a closer match in the observed wake structures and coefficient of lift. Next, the average coefficient of list of an airfoil in pure-pitch was studied and it was found that the pitching about the leading edge produced the maximum value. Two difference methods of enhancements were considered: (i) axis of rotation, and (ii) moving airfoil, as possible ways to enhance the average coefficient of lift for an airfoil pitching about its leading edge. The first case produced two times increase and the second case produced almost four times increase in the average coefficient of lift respectively. Hence these two kinds of motion can be used for lift enhancement to overcome sudden changes in the flight conditions. Finally the effect of a sinusoidal gust on an airfoil in pure-pitch and pure-plunge motion was examined. The pitching motion showed a much lesser drop in the average coefficient of lift compared to the plunging motion, suggesting its effectiveness to overcome disturbances in the freestream. The plunging motion on the other hand can be employed for cases that require the suppression of the oscillation in the lift coefficient.

Gopalan, Harish

138

Robust control of a morphing airfoil structure  

Microsoft Academic Search

This paper presents several robust control designs for a MIMO morphing airfoil concept. A linear aeroelastic model of the morphing wing is utilized to design an H? controller and a two degree of freedom H? loop shaping controller that track commanded lift and roll moments. These methodologies are developed, along with the robustness conditions for input multiplicative, and real parametric

Christopher E. Whitmer; Atul G. Kelkar

2005-01-01

139

Large-eddy simulation of flow over a multi-element airfoil  

NASA Astrophysics Data System (ADS)

An accurate prediction of turbulent flow over a multiple element high-lift airfoil configuration remains a challenge to computational fluid dynamics. Maximum lift, drag, and pitching moment are difficult to accurately predict especially in the presence of flow separation on one or more of the airfoil elements. In this study, we investigate turbulent flow over a MD30P30N high-lift configuration using large-eddy simulation. The MD30P30N configuration consists of three elements: a slat, a main airfoil, and a flap. Four different attack angles, 16^o, 19^o, 21^o, and 24^o, are considered while deflection angles of the slat and flap are fixed to 30^o. The Reynolds number is 9x10^6 based on the mounted-wing chord-length and freestream velocity. Simulation results obtained on a 54 million-element mesh agree well with experimental data in terms of pressure distribution, velocity profiles, and transition location. A grid sensitivity study is performed to identify the resolution effects on the prediction of flow transition, wakes, and turbulent boundary layers. Accurate prediction of laminar-to-turbulence transition on the slat surface and downstream evolution of the slat wake is found to be crucial for the global accuracy of the simulation.

You, Donghyun

2009-11-01

140

Aerodynamic shape optimization of Airfoils in 2-D incompressible flow  

NASA Astrophysics Data System (ADS)

An optimization framework was developed for maximizing the region of 2-D airfoil immersed in laminar flow with enhanced aerodynamic performance. It uses genetic algorithm over a population of 125, across 1000 generations, to optimize the airfoil. On a stand-alone computer, a run takes about an hour to obtain a converged solution. The airfoil geometry was generated using two Bezier curves; one to represent the thickness and the other the camber of the airfoil. The airfoil profile was generated by adding and subtracting the thickness curve from the camber curve. The coefficient of lift and drag was computed using potential velocity distribution obtained from panel code, and boundary layer transition prediction code was used to predict the location of onset of transition. The objective function of a particular design is evaluated as the weighted-average of aerodynamic characteristics at various angles of attacks. Optimization was carried out for several objective functions and the airfoil designs obtained were analyzed.

Rangasamy, Srinivethan; Upadhyay, Harshal; Somasekaran, Sandeep; Raghunath, Sreekanth

2010-11-01

141

Simplified dragonfly airfoil aerodynamics at Reynolds numbers below 8000  

NASA Astrophysics Data System (ADS)

Effective aerodynamics at Reynolds numbers lower than 10 000 is of great technological interest and a fundamental scientific challenge. The current study covers a Reynolds number range of 2000-8000. At these Reynolds numbers, natural insect flight could provide inspiration for technology development. Insect wings are commonly characterized by corrugated airfoils. In particular, the airfoil of the dragonfly, which is able to glide, can be used for two-dimensional aerodynamic study of fixed rigid wings. In this study, a simplified dragonfly airfoil is numerically analyzed in a steady free-stream flow. The aerodynamic performance (such as mean and fluctuating lift and drag), are first compared to a ``traditional'' low Reynolds number airfoil: the Eppler-E61. The numerical results demonstrate superior performances of the corrugated airfoil. A series of low-speed wind and water tunnel experiments were performed on the corrugated airfoil, to validate the numerical results. The findings indicate quantitative agreement with the mean wake velocity profiles and shedding frequencies while validating the two dimensionality of the flow. A flow physics numerical study was performed in order to understand the underlying mechanism of corrugated airfoils at these Reynolds numbers. Airfoil shapes based on the flow field characteristics of the corrugated airfoil were built and analyzed. Their performances were compared to those of the corrugated airfoil, stressing the advantages of the latter. It was found that the flow which separates from the corrugations and forms spanwise vortices intermittently reattaches to the aft-upper arc region of the airfoil. This mechanism is responsible for the relatively low intensity of the vortices in the airfoil wake, reducing the drag and increasing the flight performances of this kind of corrugated airfoil as compared to traditional low Reynolds number airfoils such as the Eppler E-61.

Levy, David-Elie; Seifert, Avraham

2009-07-01

142

Numerical Simulation of a Powered-Lift Landing, Tracking Flow Features Using Overset Grids, and Simulation of High Lift Devices on a Fighter-Lift-and-Control Wing.  

National Technical Information Service (NTIS)

Attached as appendices to this report are documents describing work performed on the simulation of a landing powered-lift delta wing, the tracking of flow features using overset grids, and the simulation of flaps on the Wright Patterson Lab's fighter-lift...

K. Chawla

1993-01-01

143

Design and validation of a high-lift low-pressure turbine blade  

Microsoft Academic Search

This dissertation is a design and validation study of the high-lift low-pressure turbine (LPT) blade designated L2F. High-lift LPTs offer the promise of reducing the blade count in modern gas turbine engines. Decreasing the blade count can reduce development and maintenance costs and the weight of the engine, but care must be taken in order to maintain turbine section performance

Mark Wayne McQuilling

2007-01-01

144

Investigation of incipient dynamic stall over pitching airfoils at high Reynolds numbers  

NASA Astrophysics Data System (ADS)

Surface shear stress and pressure measurements were obtained on a NACA 0012 airfoil model undergoing a pitch-up motion from 0° to 45° angle of attack at a constant rate. The shear-stress data were obtained using an array of surface-mounted hot-film sensors. Dominant features in these data and in the standard deviations computed from these data were examined and related to events in the development and evolution of the dynamic stall vortex over the suction surface. These features were compared with flow visualization results from prior studies and well-known features of the dynamic stall process seen in the surface-pressure distributions. Trends in the behavior of these features are presented for a range of non-dimensional pitch rates (0.010 < alpha + < 0.150) and chord Reynolds numbers (0.9 x 105 < Rec < 1.74 x 106). In general, at high Reynolds numbers, the events that lead to the formation of the dynamic stall vortex are delayed to higher angles of attack as the pitch rate is increased. This is consistent with prior work performed at low Reynolds numbers. However, significant changes were seen in the behavior of the flow features at high Reynolds numbers. Transition to turbulence in the boundary layer over the airfoil suction surface early in the pitch-up motion significantly modifies the unsteady separation process. The point of transition appears as a sudden increase in wall shear stress accompanied by a distinct peak in the standard deviation of the hot-film sensor output. At low pitch rates, the location and angle of attack of transition in the leading-edge region remain independent of Reynolds number. At high pitch rates, however, there is a significant delay in angle of attack of transition at higher Reynolds numbers. At high pitch rates, dynamic stall vortex formation is delayed to higher angles of attack with increasing Reynolds number. At low pitch rates, however, this delay is noticeably reduced at higher Reynolds numbers. This behavior is due to both the quasi-steady nature of the flow separation in these cases and the effects of compressibility. It is believed that compressibility effects play a significant role at the lower pitch rates and higher Reynolds numbers investigated in this study, since high local Mach numbers were seen in the leading edge region for these cases. Additional experiments are required to separate the effects of Reynolds number and Mach number. Also, since transition noticeably effected all cases investigated in this study, experiments should be performed over a wider range of pitch rates and Reynolds numbers in order to pinpoint the critical Reynolds numbers at each pitch rate where transition first begins to modify the unsteady separation process.

Kiedaisch, John Walter

145

Development of a Fowler Flap System for a High Performance General Aviation Airfoil.  

National Technical Information Service (NTIS)

A two-dimensional wind-tunnel evaluation of two Fowler flap configurations on the new GA(W)-1 airfoil was conducted. One configuration used a computer-designed 29-percent chord Fowler flap. The second configuration was modified to have increased Fowler ac...

W. H. Wentz H. C. Seetharam

1974-01-01

146

Experimental characterization of an airfoil-based actuator using high-temperature shape memory alloys  

NASA Astrophysics Data System (ADS)

This paper reports experimental results of an airfoil-based flap actuator that is actuated using high temperature Nickel-Titanium (NiTi) polycrystal and Copper-Aluminium-Nickel (CuAlNi) single crystal wires with a nominal diameter of 1.5 mm. The stress-free transformation temperatures of the commercially available NiTi wires are Mf = 53°C, Ms = 70°C , As = 95°C , Af = 110°C whereas those for the CuAlNi wires are Mf = 80°C ,Ms = 100.5°C, As = 104.5°C , Af = 117°C. Due to a significantly low electrical resistivity of the CuAlNi, the commonly used joule heating approach for thermal actuation is shelved for a heating coil approach. Uniaxial stress measurements, trailing edge flap deflections and temperature measurements are recorded during a typical heating and cooling cycle using a load cell in line with the SMA wire, a LVDT at the trailing edge tip and a thermocouple on the wire (outside the heating coil). It is seen that actuation by the CuAlNi (with a prestrain = 5.5%) leads to about a 50% higher tip deflection and about a 67% lower cooling time after actuation as compared to the corresponding values for NiTi (with a prestrain = 5.6%). The larger tip deflection is attributed to a higher strain recovery for the CuAlNi as compared to the NiTi during phase transformation whereas the lower actuation time is attributed, in part, to the narrow hysteresis in the stress-free transformation temperatures of the CuAlNi (~ 37°C) as compared to the NiTi (~ 57°C).

Bhattacharyya, Abhijit; Ables, William L.; Kannarpady, Ganesh K.; Qidwai, Muhammad A.

2004-07-01

147

Lifting-based invertible motion adaptive transform (LIMAT) framework for highly scalable video compression  

Microsoft Academic Search

We propose a new framework for highly scalable video compression, using a lifting-based invertible motion adaptive transform (LIMAT). We use motion-compensated lifting steps to implement the temporal wavelet transform, which preserves invertibility, regardless of the motion model. By contrast, the invertibility requirement has restricted previous approaches to either block-based or global motion compensation. We show that the proposed framework effectively

Andrew Secker; David S. Taubman

2003-01-01

148

Unsteady Surface Pressure Measurements on a Pitching Airfoil.  

National Technical Information Service (NTIS)

Surface pressure measurements were taken in an experimental investigation of energetic dynamic stall vortices. The associated unsteady flowfield was generated by a 6-in. NACA 0015 airfoil pitching at high rates to large angles of attack. The airfoil pitch...

J. Walker H. Helin D. Chou

1985-01-01

149

Effects of Gurney Flaps on a NACA0012 Airfoil  

Microsoft Academic Search

Experimental measurements of surface pressure distributions and wake profiles were obtained for a NACA0012 airfoil to determine\\u000a the lift, drag, and pitching-moment coefficients for various configurations. The addition of a Gurney flap increased the maximum\\u000a lift coefficient from 1.37 to 1.74, however there was a drag increment at low-to-moderate lift coefficient. In addition, the\\u000a boundary layer profile measurements were taken

Yachen Li; Jinjun Wang; Panfeng Zhang

2002-01-01

150

Nonlinear Analysis of Airfoil High-Intensity Gust Response Using a High-Order Prefactored Compact Code.  

National Technical Information Service (NTIS)

The nonlinear response of symmetric and loaded airfoils to an impinging vortical gust is investigated in the parametric space of gust dimension, intensity, and frequency. The study, which was designed to investigate the validity limits for a linear analys...

A. Crivellini V. Golubev R. Mankbadi J. R. Scott R. Hixon L. Povinelli

2002-01-01

151

Blowing Circulation Control on a Seaplane Airfoil  

NASA Astrophysics Data System (ADS)

RANS simulations are presented for blowing circulation control on a seaplane airfoil. Realizable k-epsilon turbulent model and pressure-based coupled algorithm with second-order discretization were adopted to simulate the compressible flow. Both clear and simple flap configuration were simulated with blowing momentum coefficient C? = 0, 0.15 and 0.30. The results show that blowing near the airfoil trailing edge could enhance the Coanda effect, delay the flow separation, and increase the lift coefficient dramatically. The blowing circulation control is promising to apply to taking off and landing of an amphibious aircraft or seaplane.

Guo, B. D.; Liu, P. Q.; Qu, Q. L.

2011-09-01

152

Numerical modeling of an S809 airfoil under dynamic stall, erosion and high reduced frequencies  

Microsoft Academic Search

An oscillating freestream over a stationary S809 airfoil is simulated numerically using ANSYS Fluent 12.1. For comparison the laminar-turbulent transition is simulated with the realizable k–? and SST k–? models, and finally the SST k–? model is chosen. Where possible, the resultant aerodynamic coefficients presenting dynamic stall phenomena are compared with aerodynamic coefficients from existing experimental and semi-empirical data for

Kobra Gharali; David A. Johnson

2012-01-01

153

Optimum Gurney flap height determination for “lost-lift” recovery in compressible dynamic stall control  

Microsoft Academic Search

A variable droop leading edge (VDLE) airfoil was successfully used to control compressible dynamic stall and its associated adverse pitching moment variations. But, the price for this success was a 10% loss of lift. A Gurney flap was then attached normally to the airfoil pressure surface at its trailing edge to recover this “lost-lift”. Gurney flaps are seldom used in

M. S. Chandrasekhara

2010-01-01

154

Effect of weak sound on separated flow over an airfoil  

NASA Astrophysics Data System (ADS)

This paper is concerned with the effect of weak acoustic excitation on a separated flow over an airfoil. Two-dimensional numerical simulations are performed for an NACA0012 airfoil at an angle of attack ? = 12° in the flow with the main stream Mach number M = 0.1 and chord Reynolds numbers, Re = 5 × 104 and 1 × 105. The amplitude of the external sound pressure is set at 0.05% of the static pressure at infinity. It is shown that the acoustic waves with appropriate frequencies make time-averaged lift coefficients higher. This effective frequency range depends on the Reynolds number; its mean value agrees with the experimental results of Zaman et al. for different airfoils. In the effective frequency range, the maximum vorticity in the laminar boundary layer of the airfoil becomes larger. On the other hand, the amplitudes of lift coefficient oscillation have the same dependence on the acoustic excitation frequency for both Reynolds numbers.

Ishii, K.; Suzuki, S.; Adachi, S.

2003-10-01

155

Effect of the Gurney flap on a NACA 23012 airfoil  

Microsoft Academic Search

A numerical investigation was performed to determine the effect of the Gurney flap on a NACA 23012 airfoil. A Navier-Stokes\\u000a code, RAMPANT, was used to calculate the flow field about the airfoil. Fully-turbulent results were obtained using the standardk-? two-equation turbulence model. The numerical solutions showed that the Gurney flap increased both lift and drag. These\\u000a results suggested that the

Neung-Soo Yoo

2000-01-01

156

Aerodynamic, aeroacoustic, and aeroelastic investigations of airfoil-vortex interaction using large-eddy simulation  

NASA Astrophysics Data System (ADS)

In helicopters, vortices (generated at the tip of the rotor blades) interact with the next advancing blades during certain flight and manoeuvring conditions, generating undesirable levels of acoustic noise and vibration. These Blade-Vortex Interactions (BVIs), which may cause the most disturbing acoustic noise, normally occur in descent or high-speed forward flight. Acoustic noise characterization (and potential reduction) is one the areas generating intensive research interest to the rotorcraft industry. Since experimental investigations of BVI are extremely costly, some insights into the BVI or AVI (2-D Airfoil-Vortex Interaction) can be gained using Computational Fluid Dynamics (CFD) numerical simulations. Numerical simulation of BVI or AVI has been of interest to CFD for many years. There are still difficulties concerning an accurate numerical prediction of BVI. One of the main issues is the inherent dissipation of CFD turbulence models, which severely affects the preservation of the vortex characteristics. Moreover this is not an issue only for aerodynamic and aeroacoustic analysis but also for aeroelastic investigations as well, especially when the strong (two-way) aeroelastic coupling is of interest. The present investigation concentrates mainly on AVI simulations. The simulations are performed for Mach number, Ma = 0.3, resulting in a Reynolds number, Re = 1.3 x 106, which is based on the chord, c, of the airfoil (NACA0012). Extensive literature search has indicated that the present work represents the first comprehensive investigation of AVI using the LES numerical approach, in the rotorcraft research community. The major factor affecting the aerodynamic coefficients and aeroacoustic field as a result of airfoil-vortex interaction is observed to be the unsteady pressure generated at the location of the interaction. The present numerical results show that the aerodynamic coefficients (lift, moment, and drag) and aeroacoustic field are strongly dependent on the airfoil-vortex vertical miss-distance, airfoil angle of attack, vortex characteristics, and aeroelastic response of airfoil to airfoil-vortex interaction. A decay of airfoil-vortex interactions with the increase of vertical miss-distance and angle of attack was observed. Also, a decay of airfoil-vortex interactions is observed for the case of a flexible structure when compared with the case of a rigid structure. The decay of vortex core size produces a decrease in the aerodynamic coefficients.

Ilie, Marcel

157

Numerical analysis of the s1020 airfoils in tandem under different flapping configurations  

Microsoft Academic Search

The objective of this project is to improve the performance of the efficiency, thrust and lift of flapping wings in tandem\\u000a arrangement. This research investigates the effect of the arrangement of the airfoils in tandem on the performance of the\\u000a airfoils by varying the phase difference and distance between the airfoils. Three flapping configurations from an earlier\\u000a phase of a

K. B. Lim; W. B. Tay

2010-01-01

158

Design of a low Reynolds number airfoil for small horizontal axis wind turbines  

Microsoft Academic Search

A low Reynolds number airfoil was designed for applications in small horizontal axis wind turbines to achieve better startup and low wind speed performances. Experiments were performed on the improved airfoil (AF300) in an open circuit wind tunnel at Reynolds numbers of 38,000, 75,000, 128,000 and 205,000. Pressure distributions were obtained over the surface of the airfoil and the lift

Ronit K. Singh; M. Rafiuddin Ahmed; Mohammad Asid Zullah; Young-Ho Lee

159

High lift function of the pteroid bone and forewing of pterosaurs  

PubMed Central

The pteroid bone is a rod-like element found only in pterosaurs, the flying reptiles of the Mesozoic. It articulated at the wrist, and supported a membranous forewing in front of the inner part of the wing spar. The function of this bone, particularly its orientation, has been much debated. It is widely believed that it pointed towards the body, and that the forewing was relatively narrow. An alternative hypothesis states that it was directed forwards during flight, resulting in a much broader forewing that acted as a leading edge flap. We tested scale models in a wind tunnel to determine the aerodynamic consequences of these conflicting hypotheses, and found that performance is greatly improved if the pteroid is directed forwards: the lift?:?drag ratios are superior and the maximum lift is exceptionally high in comparison with conventional aerofoils. This high lift capability may have enabled even the largest pterosaurs to take off and land without difficulty.

Wilkinson, Matthew T; Unwin, David M; Ellington, Charles P

2005-01-01

160

An experimental study of space vehicle configurations with high lift during reentry  

Microsoft Academic Search

The results of a series of tests on the measurement of forces on a family of shapes leading to those having high maximum lift coefficients are reviewed. Free flight models of cones, a flat delta wing, a caret delta wing, a cone with anhedral wings, and a modified space shuttle orbiter were tested at high angles of attack in the

B. E. Richards; R. Houwink

1976-01-01

161

An investigation on the aerodynamics of a symmetrical airfoil in ground effect  

Microsoft Academic Search

The flow characteristics over a symmetrical airfoil––NACA 0015––are studied experimentally in a low speed wind tunnel. The pressure distribution on the airfoil surface was obtained, lift and drag forces were measured and mean velocity profiles were obtained over the surface. The wake region was also explored in detail and measurements of mean velocity and turbulence intensities were performed at two

M. R. Ahmed; S. D. Sharma

2005-01-01

162

Unsteady fluid-structure interactions of membrane airfoils at low Reynolds numbers  

Microsoft Academic Search

Membrane wings are used both in nature and small aircraft as lifting surfaces. Separated flows are common at low Reynolds numbers and are the main sources of unsteadiness. Yet, the unsteady aspects of the fluid-structure interactions of membrane airfoils are largely unknown. An experimental study of unsteady aerodynamics of two-dimensional membrane airfoils at low Reynolds numbers has been conducted. Measurements

P. Rojratsirikul; Z. Wang; I. Gursul

2010-01-01

163

Gas lifting a major oil field in Argentina with high CO{sub 2} content associated gas  

SciTech Connect

The El Trapial Field in the Neuquen Province of Central Argentina produces more than 55,000 BOPD after 4 years of operation. The associated gas produced at El Trapial contains as much as 75% CO{sub 2}. Immediately after the discovery of the field, a study indicated that gas lift would meet environmental concerns and be an attractive economical alternative for producing the field. The study also concluded that the high CO{sub 2} fraction gas dissolved in the oil could be used satisfactorily for gas lift purposes. A plan was implemented at that time to design and construct the production facilities around gas lift as the primary artificial lift method. This paper addresses special precautions required for design of the production and gas lift facilities to gas lift successfully with high acid content associated gas. Also discussed is Petrolera Argentina San Jorge`s experience with such a system at El Trapial during the first 2 years of operation.

Blann, J.R.; Laville, G.M.

1997-02-01

164

Numerical and Experimental Investigation of Plasma Actuator Control of Modified Flat-back Airfoil  

NASA Astrophysics Data System (ADS)

Flat-back airfoil designs have been proposed for use on the inboard portion of large wind turbine blades because of their good structural characteristics. These structural characteristics are achieved by adding material to the aft portion of the airfoil while maintaining the camber of the origional airfoil shape. The result is a flat vertical trailing edge which increases the drag and noise produced by these airfoils. In order to improve the aerodynamic efficiency of these airfoils, the use of single dielectric barrier discharge (SDBD) plasma actuators was investigated experimentally and numerically. To accomplish this, a rounded trailing edge was added to traditional flat-back airfoil and plasma actuators were used symmetrically to control the flow separation casued by the blunt trailing edge. The actuators were used asymmetrically in order to vector the wake and increase the lift produced by the airfoil similar to adding camber.

Mertz, Benjamin; Corke, Thomas

2010-11-01

165

Improvement of Laminar Lifted Flame Stability Excited by High-Frequency Acoustic Oscillation  

NASA Astrophysics Data System (ADS)

A high-frequency (20kHz) standing wave was applied to the unburned mixture upstream of a methane-air lifted jet flame using a bolt-clamped Langevin transducer (BLT) to improve stability. The flow field near the flame was visualized using acetone planar-laser-induced fluorescence (PLIF). The standing wave decreased the lifted flame height and increased the blow-off limit. The upstream flow field of the center jet then bent. This phenomenon appeared when there was a density difference between the center jet and the surrounding secondary flow. When the density of the center jet was less than that of the co-flow, the center jet was redirected to the pressure anti-node side. Conversely, when the density of the center jet was greater than that of the co-flow, the center jet was redirected to the pressure node side. This redirection tended to stabilize the laminar lifted flame.

Hirota, Mitsutomo; Hashimoto, Kota; Oso, Hiroki; Masuya, Goro

166

Airfoil optimization for morphing aircraft  

NASA Astrophysics Data System (ADS)

Continuous variation of the aircraft wing shape to improve aerodynamic performance over a wide range of flight conditions is one of the objectives of morphing aircraft design efforts. This is being pursued because of the development of new materials and actuation systems that might allow this shape change. The main purpose of this research is to establish appropriate problem formulations and optimization strategies to design an airfoil for morphing aircraft that include the energy required for shape change. A morphing aircraft can deform its wing shape, so the aircraft wing has different optimum shapes as the flight condition changes. The actuation energy needed for moving the airfoil surface is modeled and used as another design objective. Several multi-objective approaches are applied to a low-speed, incompressible flow problem and to a problem involving low-speed and transonic flow. The resulting solutions provide the best tradeoff between low drag, high energy and higher drag, low energy sets of airfoil shapes. From this range of solutions, design decisions can be made about how much energy is needed to achieve a desired aerodynamic performance. Additionally, an approach to model aerodynamic work, which would be more realistic and may allow using pressure on the airfoil to assist a morphing shape change, was formulated and used as part of the energy objective. These results suggest that it may be possible to design a morphing airfoil that exploits the airflow to reduce actuator energy.

Namgoong, Howoong

167

An experimental study of a bio-inspired corrugated airfoil for micro air vehicle applications  

NASA Astrophysics Data System (ADS)

An experimental study was conducted to investigate the aerodynamic characteristics of a bio-inspired corrugated airfoil compared with a smooth-surfaced airfoil and a flat plate at the chord Reynolds number of Re C = 58,000-125,000 to explore the potential applications of such bio-inspired corrugated airfoils for micro air vehicle designs. In addition to measuring the aerodynamic lift and drag forces acting on the tested airfoils, a digital particle image velocimetry system was used to conduct detailed flowfield measurements to quantify the transient behavior of vortex and turbulent flow structures around the airfoils. The measurement result revealed clearly that the corrugated airfoil has better performance over the smooth-surfaced airfoil and the flat plate in providing higher lift and preventing large-scale flow separation and airfoil stall at low Reynolds numbers (Re C < 100,000). While aerodynamic performance of the smooth-surfaced airfoil and the flat plate would vary considerably with the changing of the chord Reynolds numbers, the aerodynamic performance of the corrugated airfoil was found to be almost insensitive to the Reynolds numbers. The detailed flow field measurements were correlated with the aerodynamic force measurement data to elucidate underlying physics to improve our understanding about how and why the corrugation feature found in dragonfly wings holds aerodynamic advantages for low Reynolds number flight applications.

Murphy, Jeffery T.; Hu, Hui

2010-08-01

168

An Experimental Investigation of Three Dimensional Low Speed Minimum Interference Wind Tunnel for High Lift Wings.  

National Technical Information Service (NTIS)

As a means to achieve a minimum interference correction wind tunnel, a partially actively controlled test section was experimentally examined. A jet flapped wing with 0.91 m (36 in) span and R = 4.05 was used as a model to create moderately high lift coef...

S. Shindo R. G. Joppa

1980-01-01

169

Approximate Inviscid Model for Separating-Reattaching Flows on High-Lift Configurations,  

National Technical Information Service (NTIS)

The usual method to calculate the inviscid flow over a high lift system with 'cut outs' is to assume the shape of dividing streamlines from separation to reattachment. The present method relaxes this specification with a modification of the boundary condi...

H. B. Tou G. J. Hancock

1985-01-01

170

Aerodynamic Characteristics of a Propeller-Powered High-Lift Semispan Wing.  

National Technical Information Service (NTIS)

A small-scale semispan high-lift wing-flap system equipped under the wing with a turboprop engine assembly was tested in the LaRC 14- by 22-Foot Subsonic Tunnel. Experimental data were obtained for various propeller rotational speeds, nacelle locations, a...

G. L. Gentry M. A. Takallu Z. T. Applin

1994-01-01

171

Analysis of a jet-controlled high-lift hydrofoil with a flap  

Microsoft Academic Search

A jet-controlled high-lift hydrofoil with a flap is investigated using both experimental and computational methods. Experiments were carried out in a cavitation tunnel to measure forces and moment acting on the hydrofoil, and surface pressure distribution. The measured data show the feasibility of such a device for marine applications. Computational studies have also been carried out in parallel with the

S. H. Rhee; S.-E. Kim; H. Ahn; J. Oh; H. Kim

2003-01-01

172

Flight-Measured Lift and Drag Characteristics of a Large, Flexible, High Supersonic Cruise Airplane.  

National Technical Information Service (NTIS)

Flight measurements of lift, drag, and angle of attack were obtained for the XB-70 airplane, a large, flexible, high supersonic cruise airplane. This airplane had a length of over 57 meters, a takeoff gross mass of over 226,800 kilograms, and a design cru...

H. H. Arnaiz

1977-01-01

173

The aerodynamic design of multi-element high-lift systems for transport airplanes  

Microsoft Academic Search

High-lift systems have a major influence on the sizing, economics, and safety of most transport airplane configurations. The combination of complexity in flow physics, geometry, and system support and actuation has historically led to a lengthy and experiment intensive development process. However, during the recent past engineering design has changed significantly as a result of rapid developments in computational hardware

C. P. van Dam

2002-01-01

174

Ambulatory High Resolution Manometry, Lower Esophageal Sphincter Lift and Transient Lower Esophageal Sphincter Relaxation  

PubMed Central

Introduction Lower esophageal sphincter (LES) lift seen on high resolution manometry (HRM) is a possible surrogate marker of the longitudinal muscle contraction of the esophagus. Recent studies suggest that longitudinal muscle contraction of the esophagus induces LES relaxation. Aim Our goal was to determine, 1) the feasibility of prolonged ambulatory HRM and 2) to detect LES lift with LES relaxation using ambulatory HRM color isobaric contour plots. Methods In vitro validation studies were performed to determine the accuracy of HRM technique in detecting axial movement of the LES. Eight healthy normal volunteers were studied using a custom designed HRM catheter and a 16 channel data recorder, in the ambulatory setting of subject’s home environment. Color HRM plots were analyzed to determine the LES lift during swallow-induced LES relaxation as well as during complete and incomplete transient LES relaxations. Results Satisfactory recordings were obtained for 16 hours in all subjects. LES lift was small (2 mm) in association with swallow-induced LES relaxation. LES lift could not be measured during complete transient LES relaxations (TLESR) because the LES is not identified on the HRM color isobaric contour plot once it is fully relaxed. On the other hand, LES lift, mean 7.6 ± 1.4 mm, range 6–12 mm was seen with incomplete TLESRs (n = 80). Conclusions Our study demonstrates the feasibility of prolonged ambulatory HRM recordings. Similar to a complete TLESR, longitudinal muscle contraction of the distal esophagus occurs during incomplete TLESRs, which can be detected by the HRM. Using prolonged ambulatory HRM, future studies may investigate the temporal correlation between abnormal longitudinal muscle contraction and esophageal symptoms.

Mittal, Ravinder K.; Karstens, Anna; Leslie, Eric; Babaei, Arash; Bhargava, Valmik

2011-01-01

175

Assessment of Lift Augmentation Devices.  

National Technical Information Service (NTIS)

Contents: Aerodynamics of mechanical high-lift devices; Aerodynamics of pneumatic high-lift devices; Aerodynamics of variable sweep; Fundamental aspects of flow separation under high-lift conditions; Some notes on two-dimensional high-lift tests in wind-t...

1971-01-01

176

Wind Tunnel Investigation of Simulated Hoar Frost on a 2 Dimensional Wing Section with and Without High Lift Devices.  

National Technical Information Service (NTIS)

The effect of simulated hoar frost on the lift and drag characteristics of a two-dimensional wing section with and without high lift devices was investigated in a wind tunnel. Three wing configurations were tested. Three different grain size grinding pape...

B. L. Ljungstroem

1972-01-01

177

Surface pressure and aerodynamic loads determination of a transonic airfoil based on particle image velocimetry  

NASA Astrophysics Data System (ADS)

The present investigation assesses a procedure to extract the aerodynamic loads and pressure distribution on an airfoil in the transonic flow regime from particle image velocimetry (PIV) measurements. The wind tunnel model is a two-dimensional NACA-0012 airfoil, and the PIV velocity data are used to evaluate pressure fields, whereas lift and drag coefficients are inferred from the evaluation of momentum contour and wake integrals. The PIV-based results are compared to those derived from conventional loads determination procedures involving surface pressure transducers and a wake rake. The method applied in this investigation is an extension to the compressible flow regime of that considered by van Oudheusden et al (2006 Non-intrusive load characterization of an airfoil using PIV Exp. Fluids 40 988-92) at low speed conditions. The application of a high-speed imaging system allows the acquisition in relatively short time of a sufficient ensemble size to compute converged velocity statistics, further translated in turbulent fluctuations included in the pressure and loads calculation, notwithstanding their verified negligible influence in the computation. Measurements are performed at varying spatial resolution to optimize the loads determination in the wake region and around the airfoil, further allowing us to assess the influence of spatial resolution in the proposed procedure. Specific interest is given to the comparisons between the PIV-based method and the conventional procedures for determining the pressure coefficient on the surface, the drag and lift coefficients at different angles of attack. Results are presented for the experiments at a free-stream Mach number M = 0.6, with the angle of attack ranging from 0° to 8°.

Ragni, D.; Ashok, A.; van Oudheusden, B. W.; Scarano, F.

2009-07-01

178

C++ Classes for Representing Airfoils.  

National Technical Information Service (NTIS)

A library of C++ classes for representing the geometry of airfoils is described. The classes are based on the CurveLib library for representing differentiable curves. Airfoils that have been represented explicitly include Joukowski airfoils, the NACA 4-di...

D. Hally

2010-01-01

179

Experimental Investigation of the High Velocity Coanda Wall Jet Applied to Bluff Trailing Edge Circulation Control Airfoils.  

National Technical Information Service (NTIS)

A two-dimensional experimental investigation, intended to probe the mechanism for reduction in performance of circulation control elliptic airfoils in compressible flow, was conducted subsonically on a 20-percent-thick modified elliptic profile employing ...

R. J. Englar

1975-01-01

180

Hierarchical High Level Information Fusion (H2LIFT).  

National Technical Information Service (NTIS)

The primary objective of this effort was the progression of Level 2/3 fusion of informational content to obtain an advanced multi-intelligent system for hierarchical high-level decision making processes. The goal was to develop an information integration ...

A. Crassidis A. Stotz J. Crassidis M. Sudit R. Nagi

2008-01-01

181

Low Reynolds number airfoil aerodynamic loads determination via line integral of velocity obtained with particle image velocimetry  

NASA Astrophysics Data System (ADS)

The small magnitude lift forces generated by both a NACA 0012 airfoil and a thin flat plate at Re = 29,000 and 54,000 were determined through the line integral of velocity, obtained with particle image velocimetry, via the application of the Kutta-Joukowsky theorem. Surface pressure measurements of the NACA0012 airfoil were also obtained to validate the lift coefficient C l. The bound circulation was found to be insensitive to the size and aspect ratio of the rectangular integration loop for pre-stall angles. The present C l data were also found to agree very well with the surface pressure-determined lift coefficient for pre-stall conditions. A large variation in C l with the loop size and aspect ratio for post-stall conditions was, however, observed. Nevertheless, the present flat-plate C l data were also found to collectively agree with the published force-balance measurements at small angles of attack, despite the large disparity exhibited among the various published data at high angles. Finally, the ensemble-averaged wake velocity profiles were also used to compute the drag coefficient and, subsequently, the lift-to-drag ratio.

Lee, T.; Su, Y. Y.

2012-11-01

182

Comparison Between STOL Aircraft with Mechanical High-Lift Systems and STOL Aircraft with Blown Flap Wings . STOL-Flugzeuge MIT Mechanischen Hochauftriebsystemen im Vergleich Zu STOL-Flugzeugen MIT Blasklappenfluegeln.  

National Technical Information Service (NTIS)

The net lift of modern mechanical high lift devices and externally blown flaps applied to STOL aircraft is compared. The possibilities of achieving higher aerodynamic efficiencies with these high lift devices are discussed. Aerodynamic installation proble...

E. Bielefeldt

1972-01-01

183

Lifting Surface Theory for Thrust Augmenting Ejectors.  

National Technical Information Service (NTIS)

The circulation theory of airfoil lift has been applied to predict the static performance of thrust augmenting ejectors. The ejector shroud is considered to be 'flying' in the velocity field induced by the entrainment of the primary jets, so that the thru...

P. M. Bevilaqua

1982-01-01

184

Low Reynolds Number Flow Dynamics of a Thin Airfoil with an Actuated Leading Edge using Direct Numerical Simulation  

NASA Astrophysics Data System (ADS)

Direct numerical simulations are performed to investigate the effect of a movable leading edge on the unsteady flow at high angles of attack over a flat, thin airfoil at Reynolds number of 14700 based on the chord length. The leading edge of the airfoil is hinged at one-third chord length allowing dynamic variations in the effective angle of attack through specified oscillations (or flapping). A fictitious-domain based finite volume approach [(Apte et al. (JCP 2009)] is used to compute the flow over an airfoil with a flapping leading edge on a fixed background mesh. Cases were run at 20 degrees angle of attack to study the drag and lift characteristics with sinusoidal flapping of the leading edge about the hinge over a range of reduced frequencies (k=?f c/U? = 0.57- 5.7). It is shown that high-frequency low amplitude actuation of the leading edge significantly alters the leading edge boundary-layer and vortex shedding and increases the mean lift- to-drag ratio. The concept of an actuated leading-edge flap has potential for development of control techniques to stabilize and maneuver low-Reynolds number micro-air vehicles in response to unsteady perturbations.

Drost, Kevin; Apte, Sourabh

2010-11-01

185

Flows around two airfoils performing fling and subsequent translation and translation and subsequent clap  

NASA Astrophysics Data System (ADS)

The aerodynamic forces and flow structures of two airfoils performing “fling and subsequent translation” and “translation and subsequent clap” are studied by numerically solving the Navier-Stokes equations in moving overset grids. These motions are relevant to the flight of very small insects. The Reynolds number, based on the airfoil chord length c and the translation velocity U, is 17. It is shown that: (1) For two airfoils performing fling and subsequent translation, a large lift is generated both in the fling phase and in the early part of the translation phase. During the fling phase, a pair of leading edge vortices of large strength is generated; the generation of the vortex pair in a short period results in a large time rate of change of fluid impulse, which explains the large lift in this period. During the early part of the translation, the two leading edge vortices move with the airfoils; the relative movement of the vortices also results in a large time rate of change of fluid impulse, which explains the large lift in this part of motion. (In the later part of the translation, the vorticity in the vortices is diffused and convected into the wake.) The time averaged lift coefficient is approximately 2.4 times as large as that of a single airfoil performing a similar motion. (2) For two airfoils performing translation and subsequent clap, a large lift is generated in the clap phase. During the clap, a pair of trailing edge vortices of large strength are generated; again, the generation of the vortex pair in a short period (which results in a large time rate of change of fluid impulse) is responsible for the large lift in this period. The time averaged lift coefficient is approximately 1.6 times as large as that of a single airfoil performing a similar motion. (3) When the initial distance between the airfoils (in the case of clap, the final distance between the airfoils) varies from 0.1 to 0.2 c, the lift on an airfoil decreases only slightly but the torque decreases greatly. When the distance is about 1 c, the interference effects between the two airfoils become very small.

Mao, Sun; Xin, Yu

2003-04-01

186

Domain optimization of a multi-element airfoil using automatic differentiation  

Microsoft Academic Search

Automatic differentiation is used to study the dependence of drag and lift of a four-element airfoil with respect to the position of some flaps in Euler and turbulent Navier–Stokes flow. Aim is the optimization of a cost functional based on drag and lift with respect to the position of the flaps as design parameters. The position is defined by the

T. Slawig

2000-01-01

187

Explanation of the effects of leading-edge tubercles on the aerodynamics of airfoils and finite wings  

Microsoft Academic Search

A computational study was conducted to explain the aerodynamic effect of leading edge tubercles on maximum lift coefficient, stall angle of attack (AoA), drag, and post stall characteristics for airfoils as well as finite wings. Past experiments demonstrated airfoils with leading edge tubercles do not improve Clmax, drag, or stall AoA but smoothen post stall characteristics to a great degree.

Mehdi Saadat; Hossein Haj-Hariri; Frank Fish

2010-01-01

188

Flexible-Membrane Airfoils at Low Reynolds Numbers  

Microsoft Academic Search

An experimental study was conducted to assess the benefits of using flexible-membrane airfoils\\/wings at low Reynolds numbers for micro air vehicle applications compared with using a conventional rigid airfoil\\/wing. In addition to measuring aerodynamic forces acting on flexible-membrane airfoils\\/wings, a high-resolution particle image velocimetry system was used to conduct flowfield measurements to quantify the transient behavior of vortex and turbulent

Hui Hu; Masatoshi Tamai; Jeffery T. Murphy

2008-01-01

189

Unsteady fluid-structure interactions of membrane airfoils at low Reynolds numbers  

NASA Astrophysics Data System (ADS)

Membrane wings are used both in nature and small aircraft as lifting surfaces. Separated flows are common at low Reynolds numbers and are the main sources of unsteadiness. Yet, the unsteady aspects of the fluid-structure interactions of membrane airfoils are largely unknown. An experimental study of unsteady aerodynamics of two-dimensional membrane airfoils at low Reynolds numbers has been conducted. Measurements of membrane shape with a high-speed camera were complemented with the simultaneous measurements of unsteady velocity field with a high frame-rate particle image velocimetry system and flow visualization. Vibrations of the membrane and mode shapes were investigated as a function of angle of attack and free stream velocity. While the mean membrane shape is not very sensitive to angle of attack, the amplitude and mode of the vibrations of the membrane depend on the relative location and the magnitude of the unsteadiness of the separated shear layer. The results indicate strong coupling of unsteady flow with the membrane oscillations. There is evidence of coupling of membrane oscillations with the vortex shedding in the wake, in particular, for the post-stall incidences. Comparison of rigid (but cambered) and flexible membrane airfoils shows that the flexibility might delay the stall. Hence this is a potential passive flow control method using flexibility in nature and engineering applications.

Rojratsirikul, P.; Wang, Z.; Gursul, I.

190

Unsteady fluid-structure interactions of membrane airfoils at low Reynolds numbers  

NASA Astrophysics Data System (ADS)

Membrane wings are used both in nature and small aircraft as lifting surfaces. Separated flows are common at low Reynolds numbers and are the main sources of unsteadiness. Yet, the unsteady aspects of the fluid-structure interactions of membrane airfoils are largely unknown. An experimental study of unsteady aerodynamics of two-dimensional membrane airfoils at low Reynolds numbers has been conducted. Measurements of membrane shape with a high-speed camera were complemented with the simultaneous measurements of unsteady velocity field with a high frame-rate particle image velocimetry system and flow visualization. Vibrations of the membrane and mode shapes were investigated as a function of angle of attack and free stream velocity. While the mean membrane shape is not very sensitive to angle of attack, the amplitude and mode of the vibrations of the membrane depend on the relative location and the magnitude of the unsteadiness of the separated shear layer. The results indicate strong coupling of unsteady flow with the membrane oscillations. There is evidence of coupling of membrane oscillations with the vortex shedding in the wake, in particular, for the post-stall incidences. Comparison of rigid (but cambered) and flexible membrane airfoils shows that the flexibility might delay the stall. Hence this is a potential passive flow control method using flexibility in nature and engineering applications.

Rojratsirikul, P.; Wang, Z.; Gursul, I.

2009-05-01

191

Optical-velocimetry, wake measurements of lift and induced drag on a wing  

Microsoft Academic Search

Particle Tracking Velocimetry was used, in a low-speed wind-tunnel study, to obtain simultaneous cross-flow velocity measurements in three planar regions downstream of an airfoil having a NACA 0015 profile. In order to measure both the total lift and induced drag, and their distributions on the airfoil, a wake integration technique based on the control volume approach was used. The airfoil

I. Grant; G. McCutcheon; A. H. McColgan; D. Hurst

2006-01-01

192

Jet noise of high aspect-ratio rectangular nozzles with application to pneumatic high-lift devices  

NASA Astrophysics Data System (ADS)

Circulation control wings are a type of pneumatic high-lift device that have been extensively researched as to their aerodynamic benefits. However, there has been little research into the possible airframe noise reduction benefits. The key element of noise is the jet noise associated with the jet sheet emitted from the blowing slot. This jet sheet is essentially a high aspect-ratio rectangular jet. This study directly compared far-field noise emissions from a state-of-the-art circulation control wing high lift configuration, and a conventional wing also configured for high lift. Results indicated that a circulation control wing had a significant acoustic advantage over a conventional wing for identical lift performance. A high aspect-ratio nozzle was fabricated to study the general characteristics of high aspect-ratio jets with aspect ratios from 100 to 3000. The results of this study provided the basic elements in understanding how to reduce the noise from a circulation control wing. High aspect-ratio nozzle results showed that the jet noise of this type of jet was proportional to the 8th power of the jet velocity. It was also found that the jet noise was proportional to the slot height to the 3/2 power and slot width to the 1/2 power. Fluid dynamic experiments were also performed on the high aspect-ratio nozzle. Single hot-wire experiments indicated that the jet exhaust from the high aspect-ratio nozzle was similar to a 2-d turbulent jet. Two-wire space-correlation experiments were performed to attempt to find a relationship between the slot height of the jet and the length-scale of the flow noise generating turbulence structure. The turbulent eddy convection velocity was also calculated, and was found to vary with the local centerline velocity, and also as a function of the frequency of the eddy.

Munro, Scott Edward

193

Influence of Ground and Ceiling Effect on High-Lift Device Using a Circular Cylinder with Tangential Blowing  

NASA Astrophysics Data System (ADS)

The present paper describes the influence of ground and ceiling effect on high-lift device using a circular cylinder with tangential blowing. The experiments and numerical simulations were performed under the condition of Re = 2.7× 104. In the experiments, the test, such as the time-mean surface pressure measurements on the cylinder and flow visualizations were carried out for various momentum coefficients and clearances between the cylinder and the ground (or ceiling). In the numerical simulation, a commercially available computer code, SCRYU/Tetra, was used. Qualitative agreements between the experimental and numerical results were obtained with respect to the flow fields and the lift characteristics. The experimental and numerical results show that ground effect can enhance lift-drag ratio except stalling region, and that ceiling effect can not enhance lift-drag ratio.

Okayasu, Shimpei; Arakawa, Yosuke; Sato, Kotaro; Shakouchi, Toshihiko; Furuya, Okitsugu

194

Analysis of PIV Flow Measurements behind the ALVAST-Model in High-Lift Configuration  

Microsoft Academic Search

\\u000a Flow field measurements with a stereoscopic PIV-system were performed behind the DLR-ALVAST half-model in a high lift configuration\\u000a with and without an ultrahigh bypass ratio engine simulator in the DNW-NWB Low-Speed Wind Tunnel Braunsehweig at Maeh numbers\\u000a of 0.18 and 0.22 (? 62 m\\/s and ? 76 m\\/s). In the plane behind the engine, the vortex position and strength strongly

H. Vollmers; W. Puffert-Meissner; A. Schröder

195

High Reynolds Number Test of a Naca 651-213, a Equals 0.5 Airfoil at Transonic Speeds.  

National Technical Information Service (NTIS)

Wind-Tunnel tests were conducted in the Lockheed-Georgia Company's compressible flow facility to determine the transonic two-dimensional aerodynamic characteristics of a NACA 65 sub 1-213 a = 0.50 airfoil. The results are correlated with data obtained in ...

K. P. Burdges J. A. Blackwell G. A. Pounds

1975-01-01

196

Multiple piece turbine airfoil  

SciTech Connect

A turbine airfoil, such as a rotor blade or a stator vane, for a gas turbine engine, the airfoil formed as a shell and spar construction with a plurality of dog bone struts each mounted within openings formed within the shell and spar to allow for relative motion between the spar and shell in the airfoil chordwise direction while also forming a seal between adjacent cooling channels. The struts provide the seal as well as prevent bulging of the shell from the spar due to the cooling air pressure.

Kimmel, Keith D (Jupiter, FL); Wilson, Jr., Jack W. (Palm Beach Gardens, FL)

2010-11-02

197

Oscillatory Behavior of an Arc Airfoil in Low-Speed Airflow  

NASA Astrophysics Data System (ADS)

A computational investigation is conducted to study the oscillatory behavior of an arc airfoil situated in low-speed airflow. The present work is relevant to situations where the conventional rigid airfoils do not apply, such as the flight of bats. The outcome of this study is also beneficial in the design of micro air vehicles with flexible wings. The computations are performed using a deforming mesh to accommodate the airfoil oscillations. An unsteady, spatially second-order algorithm is employed to capture the time-variations of the lift and drag coefficients. A key feature of the present work is the flow response to airfoil oscillations. Fast Fourier Transform was applied to various parameters of the flow. For certain values of angle of attack for the non-oscillating airfoil, the flow has a dominant frequency and a well-defined vortex shedding. For other values of angle of attack, the flow around the non-oscillating airfoil contains many frequencies and has complex vortical structures. However, the oscillating airfoil in all cases makes the flow field periodic with well-defined patterns of vortex shedding. In this work, the flux of vorticity from the airfoil surface into the airflow is computed and compared with the pressure gradient along the surface of the airfoil. Effects of oscillations on magnitude and behavior of aerodynamic forces are also studied.

Molki, Majid; Sattari, Negin

2011-11-01

198

Low Reynolds Number Flow Dynamics of a Thin, Flat Airfoil with Elastically Mounted Leading Edge Actuator  

NASA Astrophysics Data System (ADS)

Direct numerical simulations are performed to investigate the effect of an elastically mounted leading edge actuator on the unsteady flow at high angles of attack over a flat, thin airfoil at Reynolds number of 14700 based on the chord length. The leading edge actuator is mounted with a torsion spring at one-third the chord length allowing dynamic variations in the effective angle of attack through flow-induced oscillations. The goal is to investigate potential benefits of flow induced flapping motion of the leading edge actuator to the lift and drag characteristics of thin airfoils. The structural model for the rigid actuator is based on a torsional spring-mounted compound pendulum. A fictitious-domain based finite volume approach [(Apte et al. (JCP 2009)] is used to compute this fluid-structure interaction problem on a fixed background mesh. It is shown that a lock-in region leading to limit cycle oscillations of the leading edge actuator can be achieved for certain spring parameters leading to improvements in mean lift-to-drag ratio.

Apte, Sourabh

2011-11-01

199

Application of laser-induced thermal acoustics to a high-lift configuration  

NASA Astrophysics Data System (ADS)

Laser-Induced Thermal Acoustics (LITA) has been used to measure the flow field in the slat region of a two-dimensional, high-lift system in the NASA Langley Basic Aerodynamics Research Tunnel (BART). Unlike other point-wise, non-intrusive measurement techniques, LITA does not require the addition of molecular or particulate seed to the flow. This provides an opportunity to obtain additional insight and detailed flow-field information in complex flows where seeding may be insufficient or detection is problematic. Based on the successful use of LITA to measure the flow over a backward-facing step, the goal of this study was to further evaluate the technique by applying it to a more relevant and challenging flow field such as the slat wake on a high-lift system. Streamwise velocities were measured in the slat wake and over the main element at 11.3 degrees angle of attack and a freestream Mach Number of 0.17. The single-component LITA system is described and velocity profiles obtained using LITA are compared to profiles obtained using two-dimensional, Digital Particle Image Velocimetry (DPIV) and a steady, Reynolds-Averaged Navier-Stokes (RANS) flow solver for the same configuration. The normalized data show good agreement where the number of measurement locations had sufficient density to capture the pertinent flow phenomena.

Jenkins, Luther N.; Hart, Roger C.; Balla, R. J.; Herring, Gregory C.; Khorrami, Mehdi R.; Choudhari, Meelan M.

2003-12-01

200

A hypersonic lift mechanism with decoupled lift and drag surfaces  

NASA Astrophysics Data System (ADS)

In the present study, we propose a novel lift mechanism for which the lifting surface produces only lift. This is achieved by mounting a two-dimensional shock-shock interaction generator below the lifting surface. The shock-shock interaction theory in conjunction with a three dimensional correction and checked with computational fluid dynamics (CFD) is used to analyze the lift and drag forces as function of the geometrical parameters and inflow Mach number. Through this study, though limited to only inviscid flow, we conclude that it is possible to obtain a high lift to drag ratio by suitably arranging the shock interaction generator.

Xu, YiZhe; Xu, ZhiQi; Li, ShaoGuang; Li, Juan; Bai, ChenYuan; Wu, ZiNiu

2013-05-01

201

A new silicon gas-flow sensor based on lift force  

Microsoft Academic Search

This paper presents the first silicon-flow sensor based on lift force. The sensor is a bulk-micromachined airfoil structure that uses the lift force as a sensing principle. The lift force acts normal to the flow in contrast to drag-force sensor types, where the force acts in the flow direction. The sensor utilizes the special distribution of the lift force along

Niklas Svedin; E. Kalvesten; E. Stemme; G. Stemme

1998-01-01

202

Separation control on a NACA 0015 airfoil using a 2D micro ZNMF jet  

Microsoft Academic Search

Purpose – The aims of this study were to investigate the effect of using a wall-normal, 2D micro zero-net-mass-flux (ZNMF) jet located at the leading edge of a NACA 0015 airfoil to actively control flow separation and enhance lift. Design\\/methodology\\/approach – Experiments were conducted over a two-dimensional airfoil in a water tunnel at a Reynolds number of 3.08 × 104

A. Tuck; J. Soria

2008-01-01

203

Comparing optimization under uncertainty and multi-point optimization for airfoil shape design  

Microsoft Academic Search

The 2-D cross-section shape, or the airfoil, of an aircraft wing significantly impacts the lift and drag of the aircraft. While the aircraft may have a dominant design condition (e.g. cruise at a specified altitude and velocity), it will operate at various altitudes and speeds during a mission. To allow good performance across the flight envelope, the traditional airfoil shape

Jason S Bank

2011-01-01

204

Numerical simulation of thrust generating flow past a pitching airfoil  

Microsoft Academic Search

Earlier analytical and experimental studies predict that pitching motions at high frequency can generate thrust on the airfoil. The present work is an effort towards a systematic understanding of the influence of various parameters on thrust generation from a harmonically pitching airfoil. Quantitative instantaneous force computations have been discussed together with qualitative vortex patterns using a 2-D discrete vortex simulation

Sunetra Sarkar; Kartik Venkatraman

2006-01-01

205

Experimental Investigation of a High Lift Device on the Owl Wing.  

National Technical Information Service (NTIS)

A study was made of the aerodynamic function of the comblike fixtures found on the leading edge of owl wings. Microphotographs of an owl's wing showed the comb to resemble a row of spanwise twisted airfoils oriented to form a cascade. Smoke flow visualiza...

G. W. Anderson

1973-01-01

206

Defining a Strategy for Controlling the Dynamic Stall Vortex on an Oscillating Airfoil  

NASA Astrophysics Data System (ADS)

The plasma actuator (a single dielectric barrier discharge) has demonstrated to be effective in controlling the oscillatory lift cycle and dynamic stall vortex on an oscillating airfoil. Using various actuation schemes, steady, unsteady, or the so-called ``smart'' actuation, the maximum lift improvement over the cycle has been shown to be 13%. Plasma actuation has also been able to suppress the dynamic stall vortex. The current control strategy is based on the instantaneous angle of attack of the airfoil. A control strategy derived from in situ instantaneous pressure measurements on the surface of the airfoil is being considered. Phase-averaged pressure distribution traces over one oscillation cycle provide necessary information for determining proper sensor locations and optimal actuation schemes. The performance of the actuators is evaluated on lift enhancement.

Post, Martiqua; Corke, Thomas

2004-11-01

207

Design and Experimental Results for the S827 Airfoil; Period of Performance: 1998--1999  

SciTech Connect

A 21%-thick, natural-laminar-flow airfoil, the S827, for the 75% blade radial station of 40- to 50-meter, stall-regulated, horizontal-axis wind turbines has been designed and analyzed theoretically and verified experimentally in the NASA Langley Low-Turbulence Pressure Tunnel. The primary objective of restrained maximum lift has not been achieved, although the maximum lift is relatively insensitive to roughness, which meets the design goal. The airfoil exhibits a relatively docile stall, which meets the design goal. The primary objective of low profile drag has been achieved. The constraints on the pitching moment and the airfoil thickness have been satisfied. Comparisons of the theoretical and experimental results generally show good agreement with the exception of maximum lift, which is significantly underpredicted.

Somers, D. M.

2005-01-01

208

An experimental study of a bio-inspired corrugated airfoil for micro air vehicle applications  

Microsoft Academic Search

An experimental study was conducted to investigate the aerodynamic characteristics of a bio-inspired corrugated airfoil compared\\u000a with a smooth-surfaced airfoil and a flat plate at the chord Reynolds number of Re\\u000a C\\u000a  = 58,000–125,000 to explore the potential applications of such bio-inspired corrugated airfoils for micro air vehicle designs.\\u000a In addition to measuring the aerodynamic lift and drag forces acting on

Jeffery T. Murphy; Hui Hu

2010-01-01

209

Airfoil treatments for vertical axis wind turbines  

SciTech Connect

Sandia National Laboratories (SNL) has taken three airfoil related approaches to decreasing the cost of energy of vertical axis wind turbine (VAWT) systems; airfoil sections designed specifically for VAWTs, vortex generators (VGs), and ''pumped spoiling.'' SNL's blade element airfoil section design effort has led to three promising natural laminar flow (NLF) sections. One section is presently being run on the SNL 17-m turbine. Increases in peak efficiency and more desirable dynamic stall regulation characteristics have been observed. Vane-type VGs were fitted on one DOE/Alcoa 100 kW VAWT. With approximately 12% of span having VGs, annual energy production increased by 5%. Pumped spoiling utilizes the centrifugal pumping capabilities of hollow blades. With the addition of small perforations in the surface of the blades and valves controlled by windspeed at the ends of each blade, lift spoiling jets may be generated inducing premature stall and permitting lower capacity, lower cost drivetrain components. SNL has demonstrated this concept on its 5-m turbine and has wind tunnel tested perforation geometries on one NLF section.

Klimas, P.C.

1985-01-01

210

The use of high lift-to-drag hypersonic vehicles for aero-assisted orbital maneuvering  

NASA Astrophysics Data System (ADS)

The benefits of using a hypersonic waverider for spacecraft trajectory modification are presented. A waverider is a hypersonic vehicle specifically designed so that the undersurface bow shock is attached to the leading edge, which provides for the highest known lift-to-drag ratios achievable at high Mach number flight. Several viable space missions are suggested which could use such configurations for low-drag aero-assisted maneuvers in planetary atmospheres. It is shown that large changes in the spacecraft velocity vector can be accomplished with acceptably small losses in energy due to drag using a waverider aeroshell. The primary advantage of an aero-assist maneuver is suggested by comparison to a traditional gravity-assist trajectory. Some scaling laws are presented for comparing waveriders designed for different planetary atmospheres, and it is shown that the compositional differences between the terrestrial planets has a minimal impact on waverider design.

Lewis, Mark J.

211

The use of high lift-to-drag hypersonic vehicles for aero-assisted orbital maneuvering  

NASA Astrophysics Data System (ADS)

The benefits of using a hypersonic waverider for spacecraft trajectory modification are presented. A waverider is a hypersonic vehicle specifically designed so that the undersurface bow shock is attached to the leading edge, which provides for the highest known lift-to-drag ratios achievable at high Mach number flight. Several viable space missions are suggested which could use such configurations for low-drag aeroassisted maneuvers in planetary atmospheres. It is shown that large changes in the spacecraft velocity vector can be accomplished with acceptably small losses in energy due to drag using a waverider aeroshell. The primary advantage of an aeroassisted maneuver is suggested by comparison with a traditional gravity assist trajectory. Some scaling laws are presented for comparing waveriders designed for different planetary atmospheres, and it is shown that the compositional differences among the terrestrial planets have a minimal impact on waverider design.

Lewis, Mark J.

1990-02-01

212

Comparison of pressure distributions on model and full-scale NACA 64-621 airfoils with ailerons for wind turbine application  

SciTech Connect

The aerodynamic similarity between a small (4-in. chord) wind tunnel model and a full-scale wind turbine blade (24-ft tip section with a 36-in. chord) was evaluated by comparing selected pressure distributions around the geometrically similar cross sections. The airfoils were NACA 64-621 sections, including trailing-edge ailerons with a width equal to 38 percent of the airfoil chord. The model airfoil was tested in the OSU 6- by 12-In. High Reynolds Number Wind Tunnel; the full-scale blade section was tested in the NASA Langley Research Center 30- by 60-Ft Subsonic Wind Tunnel. The model airfoil contained 61 pressure taps connected by embedded tubes to pressure transducers. A belt containing 29 pressure taps was fixed to the full-scale section at midspan to obtain surface pressure data. Lift coefficients were obtained by integrating pressures, and corrections were made for the three-dimensional effects of blade twist and downwash in the blade tip section. Good correlation was obtained between the results of the two different experimental methods for angles of attack from -4/degree/ to 36/degree/ and aileron deflections from 0/degree/ to 90/degree/. 4 refs., 11 figs., 1 tab.

Gregorek, G.M.; Kuniega, R.J.; Nyland, T.W.

1988-04-01

213

High-Fidelity Simulations of Moving and Flexible Airfoils at Low Reynolds Numbers (Postprint).  

National Technical Information Service (NTIS)

The present paper highlights results derived from the application of a high-fidelity simulation technique to the analysis of low-Reynolds-number transitional flows over moving and flexible canonical configurations motivated by small natural and man-made f...

M. C. Galbraith M. R. Visbal R. E. Gordnier

2010-01-01

214

High-frequency microwave anti-/de-icing system for carbon-reinforced airfoil structures  

NASA Astrophysics Data System (ADS)

An aircraft may be subjected to icing for a variety of meteorological reasons during the flight. Ice formation on the plane and in particular on the aerodynamically carrying structures adversely affects the flight behaviour. Conventional de-icing methods for aluminum wings are characterised by a high energy consumption during the flight and slow ice melting due to thermal diffusion of the heat in the wing material. In addition to advanced turbines, novel materials and composites have to be used in order to reduce the weight and, hence, the fuel consumption. These composite materials have a far worse thermal conductivity than metals and undergo delamination when hot air systems, resistance or ohmic heating mats are used. In the paper, the unique advantages of a novel High Frequency Microwave Anti-/De-icing System for large future aircraft with carbon reinforced leading edge structures are presented.

Feher, Lambert; Thumm, Manfred

2001-08-01

215

Aerodynamics of an Airfoil at Ultra-Low Reynolds Number  

Microsoft Academic Search

A comprehensive experimental study is conducted of the aerodynamic characteristics of an NACA0012 airfoil over a large range\\u000a of angle (?) of attack and low- to ultra-low cord Reynolds numbers, 5.3×103 - 5.1×104, which is of both fundamental and practical importance. While the mean and fluctuating lift and drag coefficients were measured\\u000a using a load cell, the detailed flow structure

Y. Zhou; H. Yang

2009-01-01

216

Noise prediction of a low speed airfoil  

NASA Astrophysics Data System (ADS)

The goal of this work is accurate and efficient prediction of flow generated noise in the presence of solid objects. Flow around a low speed airfoil is considered at chord Reynolds number of Re = 150 000. This flow configuration represents an important aeroacoustics problem with complex physical effects including solid boundaries, boundary layers with pressure gradient, transition and turbulent wake. In the framework of Lighthill's acoustics analogy the procedure of sound prediction is divided into two steps: calculation of sound sources generated by flow and propagation of sound into far field. To calculate flow induced noise sources we performed a high resolution LES as well as a more affordable LES on fewer grid points. Sound propagation and diffraction by the airfoil are accurately are accounted for using numerically computed Green's functions tailored to the airfoil geometry. We will compare the noise spectra using this Green's function with previous calculations using an approximate Green's function.

Khalighi, Yaser; Wang, Meng; Bodony, Daniel; Moin, Parviz

2006-11-01

217

Highly scalable video compression using a lifting-based 3D wavelet transform with deformable mesh motion compensation  

Microsoft Academic Search

This paper continues the development of a new framework for the construction of motion compensated wavelet transforms for highly scalable video compression. The current authors recently proposed a motion adaptive wavelet transform based on motion- compensated lifting steps. This approach overcomes several limitations of existing methods. In particular, frame warping and block displacement methods cannot efficiently exploit complex motion without

Andrew Secker; David Taubman

2002-01-01

218

Samus Counter Lifting Fixture  

SciTech Connect

A lifting fixture has been designed to handle the Samus counters. These counters are being removed from the D-zero area and will be transported off site for further use at another facility. This fixture is designed specifically for this particular application and will be transferred along with the counters. The future use of these counters may entail installation at a facility without access to a crane and therefore a lift fixture suitable for both crane and/or fork lift usage has been created The counters weigh approximately 3000 lbs. and have threaded rods extended through the counter at the top comers for lifting. When these counters were first handled/installed these rods were used in conjunction with appropriate slings and handled by crane. The rods are secured with nuts tightened against the face of the counter. The rod thread is M16 x 2({approx}.625-inch dia.) and extends 2-inch (on average) from the face of the counter. It is this cantilevered rod that the lift fixture engages with 'C' style plates at the four top comers. The strongback portion of the lift fixture is a steel rectangular tube 8-inch (vertical) x 4-inch x .25-inch wall, 130-inch long. 1.5-inch square bars are welded perpendicular to the long axis of the rectangular tube at the appropriate lift points and the 'C' plates are fastened to these bars with 3/4-10 high strength bolts -grade 8. Two short channel sections are positioned-welded-to the bottom of the rectangular tube on 40 feet centers, which are used as locators for fork lift tines. On the top are lifting eyes for sling/crane usage and are rated at 3500 lbs. safe working load each - vertical lift only.

Stredde, H.; /Fermilab

1998-05-27

219

Stabilization of turbulent lifted jet flames assisted by pulsed high voltage discharge  

SciTech Connect

To reduce fuel consumption or the pollutant emissions of combustion (furnaces, aircraft engines, turbo-reactors, etc.), attempts are made to obtain lean mixture combustion regimes. These lead to poor stability of the flame. Thus, it is particularly interesting to find new systems providing more flexibility in aiding flame stabilization than the usual processes (bluff-body, stabilizer, quarl, swirl, etc.). The objective is to enlarge the stability domain of flames while offering flexibility at a low energy cost. Evidence is presented that the stabilization of a turbulent partially premixed flame of more than 10 kW can be enhanced by pulsed high-voltage discharges with power consumption less than 0.1% of the power of the flame. The originality of this work is to demonstrate that very effective stabilization of turbulent flames is obtained when high-voltage pulses with very short rise times are used (a decrease by 300% in terms of liftoff height for a given exit jet velocity can be reached) and to provide measurements of minimum liftoff height obtained with discharge over a large range of the stability domain of the lifted jet flame.

Criner, K.; Cessou, A.; Louiche, J.; Vervisch, P. [CORIA UMR 6614 CNRS-Universite et INSA de Rouen, University of Rouen, 76801 Saint Etienne du Rouvray (France)

2006-01-01

220

Control of Flow Separation Using Adaptive Airfoils.  

National Technical Information Service (NTIS)

A novel way of controlling flow separation is reported. The approach involves using an adaptive airfoil geometry that changes its leading edge shape to adjust to the instantaneous flow at high angles of attack such that the flow over it remains attached. ...

L. W. Carr M. C. Wilder M. S. Chandrasekhara

1997-01-01

221

Enhanced Performance of Airfoils at Moderate Mach Numbers Using Zero-Mass Flux Pulsed Blowing  

Microsoft Academic Search

Oscillatory wall-jets were introduced through spanwise slots along a flapped NACA 0015 airfoil to establish lift augmentation and drag reduction by the unsteady forcing of the separated flow. Pressure coefficient distributions, lift coefficients, and wake velocity profiles, to determine the drag coefficient, were measured over the test-section speed range of 25m\\/s < U? < 140m\\/s in the NDF. The present

Michael Hites; Hassan Nagib

2001-01-01

222

Simulation of flow around a thick airfoil with a vortex trapping cavity  

NASA Astrophysics Data System (ADS)

This paper presents a numerical study of a low Reynolds number flow around a thick airfoil (Eppler's E863 airfoil) with and without an upper-surface vortex-trapping cavity. The numerical model of flow is constructed using an O-grid computational domain around the airfoil and analyzed using four different turbulence models: namely standard k-?, RNG k-?, SST k-? and the one-equation Spallart-Almaras (SA). Enhance wall treatment is employed for the two-equation turbulence models with the non-dimensional first cell height y+ at the wall region kept close to 1. The Reynolds number is kept constant at 354000. Results of lift & drag coefficient as well as velocity profiles are presented for four different angles of attack from 0 to 15 deg. The RNG k-? model is found to better predict the flow field and airfoil lift and drag characteristics as compared to the other turbulence models taken into consideration in this paper. The presence of the vortex-trapping cavity midway on the upper-surface of the airfoil is found to yield higher lift coefficients as well as prevent flow separation but at the cost of increase the drag coefficient.

Saeed, F.; Basha, M.; Al-Garni, A. Z.

2013-10-01

223

An exploratory investigation of airfoil sections in low Reynolds number subsonic compressible flows  

NASA Astrophysics Data System (ADS)

Recent interest in high altitude unmanned aircraft has exposed a lack of experimental data for airfoil sections in low Reynolds number, subsonic compressible flow conditions. Computational methods such as the MSES code developed my Mark Drela of MIT have been used to provide data to aircraft designers, but such codes have not been verified with experimental data. In response to this need, a proof-of-concept wind tunnel facility known as the Low Reynolds Number Transonic Test Facility has been constructed at The Ohio State University Aeronautical and Astronautical Research Laboratory. The flow conditions which may be simulated include Reynolds numbers of 1 × 105 per foot to 1.2 × 106 per foot at Mach numbers of 0.4 to 0.6. Two airfoil sections were tested at these conditions, the NACA 0012 and the PZ(1)-0215, a modern laminar airfoil design. Extensive experimental results are presented for both airfoils, including lift, drag and moment coefficients, as well as surface pressure distributions. Considerable variations in airfoil performance are observed with changes in both Reynolds number and Mach number due to the influence of laminar separation bubbles. Both short and long laminar separation bubbles are observed to increase in length with increasing Mach number, suggesting delayed boundary layer and free shear layer transition at higher Mach numbers. However, measurements of test section freestream turbulence intensity raise questions regarding these conclusions, as both frequency and magnitude of the turbulence are observed to change significantly with Mach number. While incompressible laminar boundary layer stability theory suggests that turbulence frequency content is critical to transition, its effect on the low Reynolds number compressible flow in this study is not clear. Regardless, modifications to the tunnel should be made to reduce freestream turbulence to the levels commonly seen in other low Reynolds number wind tunnel facilities. Comparisons between MSES solutions and the experimental data also suggest further improvements be made to reduce wall interference effects. A comprehensive plan for tunnel renovations is presented, including replacement of the tunnel plenum chamber and choke system, an increase in test section wall porosity, and minor improvements in tunnel instrumentation.

McKee, Michael William

224

Experimental investigation of attachment-line transition in low-speed, high-lift wind-tunnel testing  

Microsoft Academic Search

The state of the attachment-line boundary layer on two typical, low-speed, high-lift wind-tunnel models was investigated experimentally. Transition was observed on both models within the Reynolds number range of the Royal Aerospace Establishment 5 meter, low-speed, pressurized Wind Tunnel, but significant differences were found from the behavior previously observed using infinite swept and high-speed wing configurations. An adverse Reynolds number

B. C. Hardy

1989-01-01

225

Reynolds number, thickness and camber effects on flapping airfoil propulsion  

NASA Astrophysics Data System (ADS)

The effect of varying airfoil thickness and camber on plunging and combined pitching and plunging airfoil propulsion at Reynolds number Re=200, 2000, 20 000 and 2×106 was studied by numerical simulations for fully laminar and fully turbulent flow regimes. The thickness study was performed on 2-D NACA symmetric airfoils with 6-50% thick sections undergoing pure plunging motion at reduced frequency k=2 and amplitudes h=0.25 and 0.5, and for combined pitching and plunging motion at k=2, h=0.5, phase ?=90°, pitch angle ?o=15° and 30° and the pitch axis was located at 1/3 of chord from leading edge. At Re=200 for motions where positive thrust is generated, thin airfoils outperform thick airfoils. At higher Re significant gains could be achieved both in thrust generation and propulsive efficiency by using a thicker airfoil section for plunging and combined motion with low pitch amplitude. The camber study was performed on 2-D NACA airfoils with varying camber locations undergoing pure plunging motion at k=2, h=0.5 and Re=20 000. Little variation in thrust performance was found with camber. The underlying physics behind the alteration in propulsive performance between low and high Reynolds numbers has been explored by comparing viscous Navier-Stokes and inviscid panel method results. The role of leading edge vortices was found to be key to the observed performance variation.

Ashraf, M. A.; Young, J.; Lai, J. C. S.

2011-02-01

226

Inverse design of airfoils using a flexible membrane method  

NASA Astrophysics Data System (ADS)

The Modified Garabedian Mc-Fadden (MGM) method is used to inversely design airfoils. The Finite Difference Method (FDM) for Non-Uniform Grids was developed to discretize the MGM equation for numerical solving. The Finite Difference Method (FDM) for Non-Uniform Grids has the advantage of being used flexibly with an unstructured grids airfoil. The commercial software FLUENT is being used as the flow solver. Several conditions are set in FLUENT such as subsonic inviscid flow, subsonic viscous flow, transonic inviscid flow, and transonic viscous flow to test the inverse design code for each condition. A moving grid program is used to create a mesh for new airfoils prior to importing meshes into FLUENT for the analysis of flows. For validation, an iterative process is used so the Cp distribution of the initial airfoil, the NACA0011, achieves the Cp distribution of the target airfoil, the NACA2315, for the subsonic inviscid case at M=0.2. Three other cases were carried out to validate the code. After the code validations, the inverse design method was used to design a shock free airfoil in the transonic condition and to design a separation free airfoil at a high angle of attack in the subsonic condition.

Thinsurat, Kamon

227

Vertical axis wind turbine airfoil  

SciTech Connect

A vertical axis wind turbine airfoil is described. The wind turbine airfoil can include a leading edge, a trailing edge, an upper curved surface, a lower curved surface, and a centerline running between the upper surface and the lower surface and from the leading edge to the trailing edge. The airfoil can be configured so that the distance between the centerline and the upper surface is the same as the distance between the centerline and the lower surface at all points along the length of the airfoil. A plurality of such airfoils can be included in a vertical axis wind turbine. These airfoils can be vertically disposed and can rotate about a vertical axis.

Krivcov, Vladimir; Krivospitski, Vladimir; Maksimov, Vasili; Halstead, Richard; Grahov, Jurij Vasiljevich

2012-12-18

228

Prediction of Hysteresis Associated with the Static Stall of an Airfoil  

Microsoft Academic Search

rial. It is caused by massive flow separation resulting in sharp drop in lift and increase in the drag acting on the airfoil. In certain cases, hysteresis in the flow has been observed for angles of attack close to the stall angle. However, this phenomenon is not very well un- derstood. Hoffmannl has reported the hysteresis loop in the data

S. Mittal; P. Saxena

2000-01-01

229

The influence of free-stream disturbances on low Reynolds number airfoil experiments  

Microsoft Academic Search

The results of an investigation of the influence of free stream disturbances on the lift and drag performance of the Lissaman 7769 airfoil are presented. The wind tunnel disturbance environment is described using hot-wire anemometer and sound pressure level measurements. The disturbance level is increased by the addition of a `turbulence screen' upstream of the test section and\\/or the addition

T. J. Mueller; L. J. Pohlen; P. E. Conigliaro; B. J. Jansen

1983-01-01

230

The influence of free-stream disturbances on low Reynolds number airfoil experiments  

Microsoft Academic Search

The results of an investigation of the influence of free stream disturbances on the lift and drag performance of the Lissaman 7769 airfoil are presented. The wind tunnel disturbance environment is described using hot-wire anemometer and sound pressure level measurements. The disturbance level is increased by the addition of a ‘turbulence screen’ upstream of the test section and\\/or the addition

T. J. Mueller; L. J. Pohlen; P. E. Conigliaro; B. J. Jansen

1983-01-01

231

Computational study into the flow field developed around a cascade of NACA 0012 airfoils  

Microsoft Academic Search

Numerical simulation of flow past airfoils is important in the aerodynamic design of aircraft wings and turbomachinery components. These lifting devices often attain optimum performance at the condition of onset of separation. Therefore, separation phenomena must be included if the analysis is aimed at practical applications. Consequently, in the present study, numerical simulation of steady flow in a linear cascade

N. Ahmed; B. S. Yilbas; M. O. Budair

1998-01-01

232

Comparison of experimental and numerical work on three dimensional trailing edge modifications on airfoils  

Microsoft Academic Search

Miniflaps at the trailing edge of airfoils (i.e., Gurney flaps) change the Kutta condition and thus produce higher lift. Unfortunately, however, the drag also increases due to the flow separation downstream of such modified trailing edges. The present work describes investigations aimed at the stabilization of the wake flow in order to achieve drag reduction and a decrease of sound

W. Hage; R. Meyer; M. Schatz

233

Synchronization of Animal-Inspired Multiple High-Lift Fins in an Underwater Vehicle Using Olivo–Cerebellar Dynamics  

Microsoft Academic Search

The development of neuroscience-based control methodologies and their integration with the high-lift unsteady hydrodynamics of control surfaces inspired by swimming and flying animals are the subjects of this paper. A biology-inspired rigid autonomous undersea vehicle called the biorobotic autonomous undersea vehicle (BAUV) has been developed at the Naval Undersea Warfare Center (NUWC), Newport, RI. The BAUV is equipped with six

Promode R. Bandyopadhyay; Sahjendra N. Singh; Daniel P. Thivierge; Anuradha M. Annaswamy; Henry A. Leinhos; Albert R. Fredette; David N. Beal

2008-01-01

234

Aerodynamic characteristics of an oscillating airfoil  

NASA Astrophysics Data System (ADS)

Results are reported from wind tunnel tests to study the effects of dynamic aerodynamics on the efficiency of a NACA 0018 airfoil used on a Darreius vertical axis wind turbine (VAWT). The topic is of interest because of uncontrolled pitching which occurs during operation and which produces stall, turbulence and separation effects that reduce efficiency. Present stream-tube theory and axial momentum models are not applicable in the unstable regimes. The wind tunnel tests were conducted with a 45 m/sec flow with an Re of 1.5 million. The situation mimicked typical wind turbine operational conditions. The airfoil was mounted on a hydraulic actuator to allow it to rotate about its quarter-chord location and to control the extent and frequency of oscillations. Data were also gathered on the performance in a steady flow for comparative purposes. Summary data are provided on the static and total pressures over a complete cycle of oscillation, and related to the angles of attack, time of onset of stall, and the lift and drag coefficients. The limitations of the study with regard to the absence of consideration of the flow acceleration experienced by an advancing blade are noted.

Wickens, R. H.

1986-03-01

235

Computational Study of a NACA4415 airfoil using synthetic jet control  

NASA Astrophysics Data System (ADS)

Synthetic jet actuators for flow control applications have been an active topic of experimental research since the 90's. Numerical simulations have become an important complement of that experimental work, providing detailed information of the dynamics of the controlled flow. This study is part of the AVOCET (Adaptive VOrticity Control Enabled flighT) project and is intended to provide computational support for the design and evaluation of closed-loop flow control with synthetic jet actuators for small scale Unmanned Aerial Vehicles (UAVs). The main objective is to analyze active flow control of a NACA4415 airfoil with tangential synthetic jets via computational modeling. A hybrid Reynolds-Averaged Navier-Stokes/Large Eddy Simulation (RANS/LES) turbulent model (called Delayed Detached-Eddy Simulation-DDES) was implemented in CDP, a kinetic energy conserving Computational Fluid Dynamics (CFD) code. CDP is a parallel unstructured grid incompressible flow solver, developed at the Center for Integrated Turbulence Simulations (CITS) at Stanford University. Two models of synthetic jet actuators have been developed and validated. The first is a detailed model in which the flow in and out of the actuator cavity is modeled. A second less costly model (RSSJ) was also developed in which the Reynolds stress produced by the actuator is modeled, based on information from the detailed model. Several static validation test cases at different angle of attack with modified NACA4415 and Dragon Eye airfoils were performed. Numerical results show the effects of the actuators on the vortical structure of the flow, as well as on the aerodynamic properties. The main effect of the actuation on the time averaged vorticity field is a bending of the separation shear layer from the actuator toward the airfoil surface, resulting in changes in the aerodynamic properties. Full actuation of the suction side actuator reduces the pitching moment and increases the lift force, while the pressure side actuator increases the pitching moment and reduces the lift force. These observations are in agreement with experimental results. The effectiveness of the actuator is measured by the change in the aerodynamic properties of the airfoil in particular the lift (Delta Cl) and moment (DeltaCm) coefficients. Computational results for the actuator effectiveness show very good agreement with the experimental values (over the range of --2° to 10°). While the actuation modifies the global pressure distribution, the most pronounced effects are near the trailing edge in which a spike in the pressure coefficient (Cp) is observed. The local reduction of Cp, for both the suction side and pressure side actuators, at xc = 0.96 (the position of the actuators) is about 0.9 with respect to the unactuated case. This local reduction of the pressure is associated with the trapped vorticity and flow acceleration close to the trailing edge. The RSSJ model is designed to capture the synthetic jet time averaged behavior so that the high actuation frequencies are eliminated. This allows the time step to be increased by a factor of 5. This ad hoc model is also tested in dynamic simulations, in which its capacity to capture the detail model average performance was demonstrated. Finally, the RSSJ model was extended to a different airfoil profile (Dragon Eye) with good results.

Lopez Mejia, Omar Dario

236

A DNS study on the stabilization mechanism of a turbulent lifted ethylene jet flame in highly-heated coflow  

SciTech Connect

Direct numerical simulation (DNS) of the near-field of a three-dimensional spatially-developing turbulent ethylene jet flame in highly-heated coflow is performed with a reduced mechanism to determine the stabilization mechanism. The DNS was performed at a jet Reynolds number of 10,000 with over 1.29 billion grid points. The results show that auto-ignition in a fuel-lean mixture at the flame base is the main source of stabilization of the lifted jet flame. The Damkoehler number and chemical explosive mode (CEM) analysis also verify that auto-ignition occurs at the flame base. In addition to auto-ignition, Lagrangian tracking of the flame base reveals the passage of large-scale flow structures and their correlation with the fluctuations of the flame base similar to a previous study (Yoo et al., J. Fluid Mech. 640 (2009) 453-481) with hydrogen/air jet flames. It is also observed that the present lifted flame base exhibits a cyclic 'saw-tooth' shaped movement marked by rapid movement upstream and slower movement downstream. This is a consequence of the lifted flame being stabilized by a balance between consecutive auto-ignition events in hot fuel-lean mixtures and convection induced by the high-speed jet and coflow velocities. This is confirmed by Lagrangian tracking of key variables including the flame-normal velocity, displacement speed, scalar dissipation rate, and mixture fraction at the stabilization point.

Yoo, Chun S [Sandia National Laboratories (SNL)

2011-01-01

237

Turbomachine airfoil vibration control utilizing active and passive piezoelectric elements  

NASA Astrophysics Data System (ADS)

Vibration of turbomachine airfoils due to unsteady aerodynamic loading is a significant cause of gas turbine engine failures and the need for both unscheduled and scheduled maintenance. Minimization of the response to the aerodynamic forcing functions which the components experience can reduce or even alleviate the need for costly repairs and diminish the possibility of failure. This thesis research is directed at investigating a series of preliminary airfoil vibration control experiments which are described. Electrically shunted bonded piezoelectric elements are utilized to actively and passively control airfoil vibrational motion and alleviate the high cycle induced stresses in the airfoil which lead to premature failure. The shunts are optimized to control specific vibrational modes. Data are analyzed and demonstrate the viability of this unique vibration control technique.

Cross, Charles John

238

Experimental and numerical research of lift force produced by Coand? effect  

NASA Astrophysics Data System (ADS)

The paper presents research results of aerodynamics of Coand? airfoil, that is a key element of drones with jet propulsion. The Coand? propulsion allows drones to monitor quickly the large areas in emergencies: forest fires, earthquakes, meteor attacks and so on. The aim of this work consists in establishment of geometric and aerodynamic parameters at which, the lift force produced by Coand? airfoil is maximal.

Constantinescu, S. G.; Niculescu, M. L.

2013-10-01

239

Lift Off!  

NSDL National Science Digital Library

This activity (on page 2 of the PDF) is a full inquiry investigation into the engineering challenges of sending scientific sensors into space. Groups of learners will develop sensors to be deployed on model rockets to measure or indicate selected properties encountered during each rocketâs flight, test launching and modifying as necessary to gather data. Relates to linked video, DragonflyTV: Lift Off!

Twin Cities Public Television, Inc.

2005-01-01

240

Decentralized Vibration Control and Coupled Aeroservoelastic Simulation of Helicopter Rotor Blades with Adaptive Airfoils  

Microsoft Academic Search

\\u000a In helicopters, a high vibration level of the airframe occurs due to higher harmonic aerodynamic loads acting on the rotor\\u000a blades. However, when the airfoil shape is adaptive, the aerodynamic loads can be affected to reduce vibration and moreover,\\u000a the airfoil shape can be adjusted to the periodically changing flow conditions to increase aerodynamic efficiency. Adaptation\\u000a of the airfoil shape

Boris A. Grohmann; Peter Konstanzer; Bernd Kröplin

241

Numerical Simulation of Unsteady Low-Reynolds-Number Separated Flows Over Airfoils  

Microsoft Academic Search

This numerical study is motivated by planned NASA flight tests to measure airfoil low-Reynolds-number aerodynamic data for high-altitude airplanes. Low-Reynolds-number flows, with transitional separation bubbles, over airfoils are simulated using a time-accurate Navier-Stokes solver with turbulence modeling. The test cases considered are low Mach-number flows over airfoils at Reynolds numbers and angles of attack in the range of 100,000-200,000 and

Mahidhar Tatineni; Xiaolin Zhong

1996-01-01

242

THE DESIGN AND TESTING OF A WINGLET AIRFOIL FOR LOW-SPEED AIRCRAFT  

Microsoft Academic Search

The PSU 94-097 airfoil has been designed for use on winglets of high-performance sailplanes. The design problem is difficult because the airfoil must operate over a wide range of Reynolds numbers, and this range includes values that are relatively low. To validate the design tools, as well as the design itself, the airfoil was tested in the Penn State Low-Speed,

Mark D. Maughmer; Timothy S. Swan; Steven M. Willits

2001-01-01

243

Optical-velocimetry, wake measurements of lift and induced drag on a wing  

NASA Astrophysics Data System (ADS)

Particle Tracking Velocimetry was used, in a low-speed wind-tunnel study, to obtain simultaneous cross-flow velocity measurements in three planar regions downstream of an airfoil having a NACA 0015 profile. In order to measure both the total lift and induced drag, and their distributions on the airfoil, a wake integration technique based on the control volume approach was used. The airfoil model was tested in clean wing configuration and with a 3.33% Gurney flap attached to the trailing edge. The Gurney flap was found to increase the complexity of the wake and cause a systematic increase in lift and induced drag values. The changes in total lift and induced drag resulting from the fitting of a Gurney flap compared very favourably to investigations using traditional aerodynamic techniques demonstrating the validity of the method.

Grant, I.; McCutcheon, G.; McColgan, A. H.; Hurst, D.

2006-03-01

244

Lift and drag in intruders moving through hydrostatic granular media at high speeds.  

PubMed

Recently, experiments showed that forces on intruders dragged horizontally through dense, hydrostatic granular packings mainly depend on the local surface orientation and can be seen as the sum of the forces exerted on small surface elements. In order to understand such forces more deeply, we perform a two-dimensional soft-sphere molecular dynamics simulation, on a similar setup, of an intruder dragged through a 50-50 bi-disperse granular packing, with diameters 0.30 and 0.34 cm. We measure, for both circular and half-circle shapes, the forces parallel (drag) and perpendicular (lift) to the drag direction as functions of the drag speed, with V=10.3-309 cm/s, and intruder depths, with D=3.75-37.5 cm. The drag forces on an intruder monotonically increase with V and D, and are larger for the circle. However, the lift force does not depend monotonically on V and D, and this relationship is affected by the shape of the intruder. The vertical force was negative for the half-circle, but for a small range of V and D, we measure positive lift. We find no sign change for the lift on the circle, which is always positive. The explanation for the nonmonotonic dependence is related to the decrease in contacts on the intruder as V increases. This is qualitatively similar to supersonic flow detachment from an obstacle. The detachment picture is supported by simulation measurements of the velocity field around the intruder and force profiles measured on its surface. PMID:23944451

Potiguar, Fabricio Q; Ding, Yang

2013-07-12

245

Symmetric airfoil geometry effects on leading edge noise.  

PubMed

Computational aeroacoustic methods are applied to the modeling of noise due to interactions between gusts and the leading edge of real symmetric airfoils. Single frequency harmonic gusts are interacted with various airfoil geometries at zero angle of attack. The effects of airfoil thickness and leading edge radius on noise are investigated systematically and independently for the first time, at higher frequencies than previously used in computational methods. Increases in both leading edge radius and thickness are found to reduce the predicted noise. This noise reduction effect becomes greater with increasing frequency and Mach number. The dominant noise reduction mechanism for airfoils with real geometry is found to be related to the leading edge stagnation region. It is shown that accurate leading edge noise predictions can be made when assuming an inviscid meanflow, but that it is not valid to assume a uniform meanflow. Analytic flat plate predictions are found to over-predict the noise due to a NACA 0002 airfoil by up to 3?dB at high frequencies. The accuracy of analytic flat plate solutions can be expected to decrease with increasing airfoil thickness, leading edge radius, gust frequency, and Mach number. PMID:24116405

Gill, James; Zhang, X; Joseph, P

2013-10-01

246

Effects of surface roughness and vortex generators on the NACA 4415 airfoil  

SciTech Connect

Wind turbines in the field can be subjected to many and varying wind conditions, including high winds with rotor locked or with yaw excursions. In some cases the rotor blades may be subjected to unusually large angles of attack that possibly result in unexpected loads and deflections. To better understand loadings at unusual angles of attack, a wind tunnel test was performed. An 18-inch constant chord model of the NACA 4415 airfoil section was tested under two dimensional steady state conditions in the Ohio State University Aeronautical and Astronautical Research Laboratory (OSU/AARL) 7 x 10 Subsonic Wind Tunnel (7 x 10). The objective of these tests was to document section lift and moment characteristics under various model and air flow conditions. These included a normal angle of attack range of {minus}20{degree} to +40{degree}, an extended angle of attack range of {minus}60{degree} to +230{degree}, applications of leading edge grit roughness (LEGR), and use of vortex generators (VGs), all at chord Reynolds numbers as high as possible for the particular model configuration. To realistically satisfy these conditions the 7 x 10 offered a tunnel-height-to-model-chord ratio of 6.7, suggesting low interference effects even at the relatively high lift and drag conditions expected during the test. Significantly, it also provided chord Reynolds numbers up to 2.0 million. 167 figs., 13 tabs.

Reuss, R.L.; Hoffman, M.J.; Gregorek, G.M. [Ohio State Univ., Columbus, OH (United States)

1995-12-01

247

Slope seeking for autonomous lift improvement by plasma surface discharge  

NASA Astrophysics Data System (ADS)

The present paper describes an experimental investigation of closed-loop separation control using plasma actuators. The post-stall-separated flow over a NACA 0015 airfoil is controlled using a single dielectric barrier discharge actuator located at the leading edge. Open-loop measurements are first performed to highlight the effects of the voltage amplitude on the control authority for freestream velocities of 10-30 m/s (chord Re = 1.3 × 105 to 4 × 105). The results indicate that partial or full reattachment can be achieved and motivate the choice of the slope seeking approach as the control algorithm. A single-input/single-output algorithm is used to autonomously seek the optimal voltage required to achieve the control objective (full flow reattachment associated with maximum lift). The paper briefly introduces the concept of slope seeking, and a detailed parameterization of the controller is considered. Static (fixed speed) closed-loop experiments are then discussed, which demonstrate the capability of the algorithm. In each case, the flow can be reattached in an autonomous fashion. The last part of the paper demonstrates the robustness of the gradient-based, model-free scheme for dynamic freestream conditions. This paper highlights the capability of slope seeking to autonomously achieve high lift when used to drive the voltage of a plasma actuator. It also describes the advantages and drawbacks of such a closed-loop approach.

Benard, Nicolas; Moreau, Eric; Griffin, John; Cattafesta, Louis N., III

2010-05-01

248

An experimental investigation of unsteady surface pressure on single and multiple airfoils  

NASA Astrophysics Data System (ADS)

This dissertation presents measurements of unsteady surface pressure on airfoils encountering flow disturbances. Analysis of measurements made on an airfoil immersed in turbulence and comparisons with inviscid theory are presented with the goal of determining the effect of angle of attack on an airfoils inviscid response. Unsteady measurements made on the surface of a linear cascade immersed in periodic flow are presented and analyzed to determine the relationship between the blades inviscid response and tip leakage vortex strength. Measurements of fluctuating surface pressure were made on a NACA 0015 airfoil immersed in grid generated turbulence. The airfoil model has a 2? chord and spans the 6? Virginia Tech Stability Wind Tunnel test section. Two grids were used to investigate the effects of turbulence length scale on the surface pressure response. A large grid which produced turbulence with an integral scale 13% of the chord and a smaller grid which produced turbulence with an integral scale 1.3% of the chord. Measurements were performed at angles of attack, a from 0° to 20°. An array of microphones mounted subsurface was used to measure the unsteady surface pressure. The goal of this measurement was to characterize the effects of angle of attack on the inviscid response. Lift spectra calculated from pressure measurements at each angle of attack revealed two distinct interaction regions; for wr=wbUinfinity < 10 a reduction in unsteady lift of up to 7 decibels (dB) occurs while an increase occurs for or > 10 as the angle of attack is increased. The reduction in unsteady lift at low o r with increasing angle of attack is a result that has never before been shown either experimentally or theoretically. The source of the reduction in lift spectral level appears to be closely related to the distortion of inflow turbulence based on analysis of surface pressure spanwise correlation length scales. Furthermore, while the distortion of the inflow appears to be critical in this experiment, this effect does not seem to be significant in larger integral scale (relative to the chord) flows based on the previous experimental work of McKeough (1976) suggesting the airfoils size relative to the inflow integral scale is critical in defining how the airfoil will respond under variation of angle of attack. A prediction scheme is developed that correctly accounts for the effects of distortion when the inflow integral scale is small relative to the airfoil chord.* (Abstract shortened by UMI.) *This dissertation is multimedia (contains text and other applications not available in printed format). The accompanying CD requires the following system requirements: Windows 95 or higher; Adobe Acrobat; Windows MediaPlayer or RealPlayer.

Mish, Patrick Francis

249

Numerical investigations into the asymmetric effects on the aerodynamic response of a pitching airfoil  

NASA Astrophysics Data System (ADS)

The effects of asymmetric sinusoidal motion on pitching airfoil aerodynamics were studied by numerical simulations for 2-D flow around a NACA0012 airfoil at Re=1.35×105. Various unsteady parameters (amplitude of oscillation, d; reduced frequency, k) were applied to investigate the effect of asymmetry parameter S on the instantaneous force coefficients and flow patterns. The results reveal that S has a noticeable effect on the aerodynamic performance, as it affects the instantaneous force coefficient, maximum lift and drag coefficient, hysteresis loops and the flow structures.

Lu, K.; Xie, Y. H.; Zhang, D.; Lan, J. B.

2013-05-01

250

Waste Package Lifting Calculation  

SciTech Connect

The objective of this calculation is to evaluate the structural response of the waste package during the horizontal and vertical lifting operations in order to support the waste package lifting feature design. The scope of this calculation includes the evaluation of the 21 PWR UCF (pressurized water reactor uncanistered fuel) waste package, naval waste package, 5 DHLW/DOE SNF (defense high-level waste/Department of Energy spent nuclear fuel)--short waste package, and 44 BWR (boiling water reactor) UCF waste package. Procedure AP-3.12Q, Revision 0, ICN 0, calculations, is used to develop and document this calculation.

H. Marr

2000-05-11

251

Low Drag Airfoil Design Utilizing Passive Laminar Flow and Coupled Diffusion Control Techniques.  

National Technical Information Service (NTIS)

A two-dimensional high chord Reynolds number passive laminar airfoil was designed for a C sub l = 0.73 at a M at infinity = 0.6 and Re sub c = 4 times 10 to the 7th power providing an extremely high L/D = 240. This laminar airfoil design concept integrate...

R. L. Mask

1980-01-01

252

Nozzle airfoil having movable nozzle ribs  

DOEpatents

A nozzle vane or airfoil structure is provided in which the nozzle ribs are connected to the side walls of the vane or airfoil in such a way that the ribs provide the requisite mechanical support between the concave side and convex side of the airfoil but are not locked in the radial direction of the assembly, longitudinally of the airfoil. The ribs may be bi-cast onto a preformed airfoil side wall structure or fastened to the airfoil by an interlocking slide connection and/or welding. By attaching the nozzle ribs to the nozzle airfoil metal in such a way that allows play longitudinally of the airfoil, the temperature difference induced radial thermal stresses at the nozzle airfoil/rib joint area are reduced while maintaining proper mechanical support of the nozzle side walls.

Yu, Yufeng Phillip (Greenville, SC); Itzel, Gary Michael (Greenville, SC)

2002-01-01

253

Boundary Layer Control on Airfoils.  

ERIC Educational Resources Information Center

|A phenomena, boundary layer control (BLC), produced when visualizing the fluidlike flow of air is described. The use of BLC in modifying aerodynamic characteristics of airfoils, race cars, and boats is discussed. (KR)|

Gerhab, George; Eastlake, Charles

1991-01-01

254

Influence of Lift Offset on Rotorcraft Performance  

Microsoft Academic Search

The influence of lift offset on the performance of several rotorcraft configurations is explored. A lift- offset rotor, or advancing blade concept, is a hingeless rotor that can attain good efficiency at high speed, by operating with more lift on the advancing side than on the retreating side of the rotor disk. The calculated performance capability of modern-technology coaxial rotors

Wayne Johnson

255

Low Speed Aerodynamic Characteristics of Naca 6716 and Naca 4416 Airfoils with 35 Percent-Chord Single-Slotted Flaps.  

National Technical Information Service (NTIS)

An investigation was conducted in a low-turbulence pressure tunnel to determine the two-dimensional lift and pitching-moment characteristics of an NACA 6716 and an NACA 4416 airfoil with 35-percent-chord single-slotted flaps. Both models were tested with ...

G. J. Bingham K. W. Noonan

1974-01-01

256

Experimental Results for the Eppler 387 Airfoil at Low Reynolds Numbers in the Langley Low-Turbulence Pressure Tunnel.  

National Technical Information Service (NTIS)

Experimental results were obtained for an Eppler 387 airfoil in the Langley Low Turbulence Pressure Tunnel. The tests were conducted over a Mach number range from 0.03 to 0.13 and a chord Reynolds number range for 60,000 to 460,000. Lift and pitching mome...

B. F. Millard B. S. Walker R. J. McGhee

1988-01-01

257

Effects of Forward Contour Modification on the Aerodynamic Characteristics of the Naca 641-212 Airfoil Section.  

National Technical Information Service (NTIS)

Two different forward contour modifications designed to increase the maximum lift coefficient of the NACA 64 sub 1-212 airfoil section were evaluated experimentally at low speeds. One modification consisted of a slight droop of the leading edge with an in...

R. M. Hicks J. P. Mendoza A. Bandettini

1975-01-01

258

What's happening in artificial lift  

SciTech Connect

New developments reported this year are primarily in the areas of electrical submersible pumps (ESPs), beam pumps, and gas lift. The available information includes new products, techniques for extending run life, controllers, monitors and various other products. Specific topics in this article include: ESP turn key leases for temporary lifting; Horizontal pumps; Gas diffusion coatings for ESP bushings and sleeves; ESP variable rate current-voltage recording monitor; Power tubing ESP status; Low volume, high efficiency ESP stage; ESP improvements for horizontal and abrasive conditions; ESP computer design program effort; Well analyzer; Beam pump controller with variable frequency drive; Hydraulic pumping units; Mobile swab unit for marginal wells; Device for unseating downhole pumps; Gas lift valve test stand; Plunger lift controllers; Resettable ESP packer; Power generation from wellhead gas; and Artificial lift PC design program.

Lea, J.F. (Amoco Production Research Co., Tulsa, OK (US)); Winkler, H.W.

1991-05-01

259

Transient dynamics of the flow around a NACA 0015 airfoil using fluidic vortex generators  

Microsoft Academic Search

The unsteady activation or deactivation of fluidic vortex generators on a NACA 0015 airfoil is studied to understand the transient dynamics of flow separation control. The Reynolds number is high enough and the boundary layer is tripped, so the boundary layer is fully turbulent prior to separation. Conditional PIV of the airfoil wake is obtained phase-locked to the actuator trigger

W. L. Siauw; J.-P. Bonnet; J. Tensi; L. Cordier; B. R. Noack; L. Cattafesta

2010-01-01

260

Effect of an Extendable Slat on the Stall Behavior of a VR-12 Airfoil.  

National Technical Information Service (NTIS)

Experimental and computational tests were performed on a VR- 1 2 airfoil to determine if the dynamic-stall behavior that normally accompanies high-angle pitch oscillations could be modified by segmenting the forward portion of the airfoil and extending it...

P. P. De Hugues K. W. McAlister C. Tung

1993-01-01

261

Computation aspects and results of low-speed viscous flow about multicomponent airfoils  

Microsoft Academic Search

The viscous flow about multicomponent airfoils was calculated solving incompressible potential flow and boundary layer problems iteratively. The presence of the shear layers is modeled in the potential flow by an outflow boundary condition on the airfoil surface and the wake centerline. Solutions show that high accuracy of the potential flow solution is required to justify the correction for viscous

B. Oskam

1980-01-01

262

A flow physics study of flap-mounted vortex generators on a multi-element airfoil  

NASA Astrophysics Data System (ADS)

Vortex generators are a commonly used aerodynamic "fix" for flow separation problems. They are typically used to remedy flow separation due to design shortcomings or changes in operating conditions that exceed the original design point. Flow separation is often encountered with high lift systems. Flaps and slats can be difficult to design due to complicated flow phenomena and large Reynolds number effects. Previous research has indicated the effectiveness of vortex generators in correcting flow separation over a flap. In fact, significant aerodynamic performance improvements were predicted for high-lift systems that incorporate vortex generators in the original design. Before this may be attempted, a better understanding of vortex generator flow physics must be obtained for the development of appropriate design tools and analysis methods. The research contained herein is focused on a detailed flow physics study of vortex generators mounted to the flap of a three-element high-lift airfoil. Detailed velocity measurements taken using a three-component laser Doppler velocimeter were used to vortex/boundary layer interactions and global flowfield effects. The full Reynolds stress tensor and mean velocity field was measured in addition to surface pressures. Three basic vortex generator arrangements were studied: upflow, downflow, and corotating. Although not optimized, all three types of vortex generators were effective at eliminating boundary layer separation. The vortices demonstrated a tendency to rise from the flap surface regardless of orientation and decayed rapidly, with cross-stream vorticity dropping below measurable levels by 75% flap chord. However, the embedded vortices produced significant perturbations in the turbulence field and mean flow of the flap boundary layer that persisted to the flap trailing edge.

Klausmeyer, Steven Michael

263

Electrokinetic lift  

NASA Astrophysics Data System (ADS)

Electrolyte flow relative to a charged surface induces a bulk electric field (the ``streaming potential'' phenomena). This field, and the flow perturbation it animates, generate both electrical and hydrodynamic ``electro-viscous'' forces whose magnitude has been a matter of ongoing controversy. Recently we have revisited this problem, predicting O(2?) scaling (as opposed to earlier prediction of 4? and 6?), ?1 being the dimensionless Debye width. These electro-viscous forces can explain the anomalous repulsion of polystyrene microspheres from an adjacent wall in the presence of an imposed shear flow, observed by Prieve and co-workers. Owing to the symmetry properties of the linear Stokes equations, such repulsion is inadmissible in the absence of inertial effects. This particle--wall interaction is analyzed using our revised scheme. The undisturbed flow consists of three components: the `driving' shear mechanism and the `induced' particle translation and rotation. We consider a small dimensionless particle--wall gap ?. At leading-order, both the lift and additional drag are contributed by the inner gap region. The lift force is O(2?&-3circ;) while the additional drag is O(2?&-2circ;). The streaming-potential mechanism underlying these forces arises from the `induced' rather than the driving component.

Schnitzer, Ory; Yariv, Ehud; Frankel, Itzchak

2011-11-01

264

Face-Lift  

MedlinePLUS

... lift technique A face-lift (rhytidectomy) is a cosmetic surgical procedure to improve the look of your ... can be done in combination with some other cosmetic procedures, such as a brow lift or eyelid ...

265

The open brow lift.  

PubMed

The open brow lift procedure is discussed in terms of relevant surgical anatomy, preoperative evaluation, and detailed surgical technique for pretrichial coronal forehead lift with hair-bearing temporal lift, direct incisional brow lift, and coronal brow lift. Complications are discussed, and information is presented on patient evaluation and expectations, with a discussion of what patients can expect before and after brow lift surgery. PMID:23186761

Walrath, Joseph D; McCord, Clinton D

2012-08-26

266

Development of the Risø wind turbine airfoils  

Microsoft Academic Search

This paper presents the wind turbine airfoil development at Risø. The design method is described together with our target characteristics for wind turbine airfoils. The use of the CFD code Ellipsys2D for prediction of final target characteristics is described together with the VELUX wind tunnel testing setup. Three airfoil families were developed; Risø-A1, Risø-P and Risø-B1. The Risø-A1 airfoil family

Peter Fuglsang; Christian Bak

2004-01-01

267

Dynamic stall on a supercritical airfoil  

Microsoft Academic Search

For the present investigations of dynamic stall a supercritical airfoil was chosen. This new airfoil designed by DLR will be used in dynamic stall control research activities (project ADASYS) planned for the near future: the leading edge portion of the airfoil will be drooped down dynamically to improve dynamic stall characteristics on the retreating side during blade motion. The optimised

W. Geissler; G. Dietz; H. Mai

2005-01-01

268

Darrieus wind-turbine airfoil configurations  

Microsoft Academic Search

The purpose was to determine what aerodynamic performance improvement, if any, could be achieved by judiciously choosing the airfoil sections for Darrieus wind turbine blades. Ten different airfoils, having thickness to chord ratios of twelve, fifteen and eighteen percent, were investigated. Performance calculations indicated that the NACA 6-series airfoils yield peak power coefficients at least as great as the NACA.

P. G. Migliore; J. R. Fritschen

1982-01-01

269

Ultra Low Reynolds Number Airfoil Testing Facility  

Microsoft Academic Search

This paper documents research being performed under a SBIR Phase II program funded by NASA Dryden Flight Research Center. The paper will discuss the design, set-up, and initial testing of a new ultra low Reynolds number water tunnel airfoil testing facility. The new water tunnel 2-D airfoil facility is designed to test airfoil sections at low Reynolds numbers ranging from

Michael Kerho

270

An experimental and analytical study of a flow vectoring airfoil via macro-fiber-composite actuators  

NASA Astrophysics Data System (ADS)

A type of piezoceramic composite actuator commonly known as Macro-Fiber-Composite (MFC) is used for actuation in a variable camber airfoil design. The study focuses on aerodynamic and kinematical modeling, and static response characterization under aerodynamic loads for three similar concepts. From a broader perspective, the study aims to understand the behavior of solid-state aerodynamic vectoring in high dynamic pressure air flow. Wind tunnel experiments and theoretical analysis is conducted on a 1.15% thick, 54 mm chord, and 108 mm span composite airfoil. The airfoil is fabricated from a fiberglass/epoxy composite material and actuated by six MFC actuators in a unimorph arrangement. Three support concepts are studied: 1) Airfoil hinged at its leading edge and at 50% chord; 2) Airfoil hinged at its leading edge the trailing edge; 3) Clamped-free airfoil. Wind tunnel results and XFOIL studies of the airfoil show comparable effectiveness to conventional actuation systems. Deformation of the airfoils due to pressure distribution is studied by finite element method. All concepts present adequate stiffness for flow speeds up to 30 m/s.

Bilgen, Onur; Kochersberger, Kevin B.; Inman, Daniel J.

2008-04-01

271

Materials for advanced turbine engines (MATE). Project 4: erosion resistant compressor airfoil coating  

SciTech Connect

The ability of coatings to provide at least a 2X improvement in particulate erosion resistance for steel, nickel and titanium compressor airfoils was identified and demonstrated. Coating materials evaluated included plasma sprayed cobalt tungsten carbide, nickel carbide and diffusion applied chromium plus boron. Several processing parameters for plasma spray processing and diffusion coating were evaluated to identify coating systems having the most potential for providing airfoil erosion resistance. Based on laboratory results and analytical evaluations, selected coating systems were applied to gas turbine blades and evaluated for surface finish, burner rig erosion resistance and effect on high cycle fatigue strength. Based on these tests, the following coatings were recommended for engine testing: Gator-Gard plasma spray 88WC-12Co on titanium alloy airfoils, plasma spray 83WC-17Co on steel and nickel alloy airfoils, and Cr+B on nickel alloy airfoils.

Rashid, J.M.; Freling, M.; Friedrich, L.A.

1987-05-01

272

Time resolved PIV analysis of flow over a NACA 0015 airfoil with Gurney flap  

Microsoft Academic Search

A NACA 0015 airfoil with and without a Gurney flap was studied in a wind tunnel with Re c = 2.0 × 105 in order to examine the evolving flow structure of the wake through time-resolved PIV and to correlate this structure with time-averaged measurements of the lift coefficient. The Gurney flap, a tab of small length (1-4% of the

D. R. Troolin; E. K. Longmire; W. T. Lai

2006-01-01

273

Two-dimensional low-Reynolds number wind tunnel results for airfoil NACA 0018  

Microsoft Academic Search

The two-dimensional characteristics of airfoil NACA 0018 have been measured for Reynolds numbers between 0.15x106 and 1.0x106 to establish the lift, drag and moment curves that serve as input to performance calculations of vertical axis wind turbines. At the lower surface laminar separation occurs at low to medium angles of attack, which is of significant influence on the characteristics and

W. A. Timmer

2008-01-01

274

Effect of acoustic excitation on airfoil performance at low Reynolds numbers  

Microsoft Academic Search

External acoustic excitation at particular frequencies and suitable amplitudes can substantially reduce or suppress the separation region of an airfoil so that an increase in lift and\\/or a decrease in drag result. In particular, the effective-frequency range decreases with a decrease of the excitation amplitude. It is speculated that the optimum frequencies found in this investigation match separated shear-layer instability

Serhiy Yarusevych; John Gregory Kawall; Pierre Edward Sullivan

2003-01-01

275

Experimental measurement of the aerodynamic charateristics of two-dimensional airfoils for an unmanned aerial vehicle  

NASA Astrophysics Data System (ADS)

This paper is part of the development of an airfoil for an unmanned aerial vehicle (UAV) with internal propulsion system; the investigation involves the analysis of the aerodynamic performance for the gliding condition of two-dimensional airfoil models which have been tested. This development is based on the modification of a selected airfoil from the NACA four digits family. The modification of this base airfoil was made in order to create a blowing outlet with the shape of a step on the suction surface since the UAV will have an internal propulsion system. This analysis involved obtaining the lift, drag and pitching moment coefficients experimentally for the situation where there is not flow through the blowing outlet, called the no blowing condition by means of wind tunnel tests. The methodology to obtain the forces experimentally was through an aerodynamic wire balance. Obtained results were compared with numerical results by means of computational fluid dynamics (CFD) from references and found in very good agreement. Finally, a selection of the airfoil with the best aerodynamic performance is done and proposed for further analysis including the blowing condition.

Velazquez, Luis; Noži?ka, Ji?í; Vav?ín, Jan

2012-04-01

276

Acoustic forcing to simulate the plunging motion of an airfoil  

NASA Astrophysics Data System (ADS)

An alternative to performing dynamic plunging measurements on an airfoil is presented, which is suitable for high reduced frequencies. Instead of physically displacing the airfoil, the flow is modulated by loudspeakers. The loudspeakers are tuned to the first transversal eigenfrequency of the wind tunnel, which results in a 2D acoustic field. The paper first describes the experimental investigation of the acoustic field without a main flow. Then results of acoustic field measurements are compared to a commercially available boundary-element method. The results of local pressure measurements on the airfoil are compared to predictions of a numerical solution of the Euler equations for in inviscid compressible flow. This solution includes the acoustic field. A strong point of the method is that the excitation amplitude can be varied easily.

Olsman, W. F. J.; Willems, J. F. H.; Hulshoff, S. J.; Hirschberg, A.; Trieling, R. R.

2010-08-01

277

Hook nozzle arrangement for supporting airfoil vanes  

SciTech Connect

A gas turbine engine's nozzle structure includes a nozzle support ring, a plurality of shroud segments, and a plurality of airfoil vanes. The plurality of shroud segments are distributed around the nozzle support ring. Each airfoil vane is connected to a corresponding shroud segment so that the airfoil vanes are also distributed around the nozzle support ring. Each shroud segment has a hook engaging the nozzle support ring so that the shroud segments and corresponding airfoil vanes are supported by the nozzle support ring. The nozzle support ring, the shroud segments, and the airfoil vanes may be ceramic.

Shaffer, James E. (Maitland, FL); Norton, Paul F. (San Diego, CA)

1996-01-01

278

Hook nozzle arrangement for supporting airfoil vanes  

DOEpatents

A gas turbine engine`s nozzle structure includes a nozzle support ring, a plurality of shroud segments, and a plurality of airfoil vanes. The plurality of shroud segments are distributed around the nozzle support ring. Each airfoil vane is connected to a corresponding shroud segment so that the airfoil vanes are also distributed around the nozzle support ring. Each shroud segment has a hook engaging the nozzle support ring so that the shroud segments and corresponding airfoil vanes are supported by the nozzle support ring. The nozzle support ring, the shroud segments, and the airfoil vanes may be ceramic. 8 figs.

Shaffer, J.E.; Norton, P.F.

1996-02-20

279

Time resolved PIV analysis of flow over a NACA 0015 airfoil with Gurney flap  

NASA Astrophysics Data System (ADS)

A NACA 0015 airfoil with and without a Gurney flap was studied in a wind tunnel with Re c = 2.0 × 105 in order to examine the evolving flow structure of the wake through time-resolved PIV and to correlate this structure with time-averaged measurements of the lift coefficient. The Gurney flap, a tab of small length (1-4% of the airfoil chord) that protrudes perpendicular to the chord at the trailing edge, yields a significant and relatively constant lift increment through the linear range of the C L versus ? curve. Two distinct vortex shedding modes were found to exist and interact in the wake downstream of flapped airfoils. The dominant mode resembles a Kàrmàn vortex street shedding behind an asymmetric bluff body. The second mode, which was caused by the intermittent shedding of fluid recirculating in the cavity upstream of the flap, becomes more coherent with increasing angle of attack. For a 4% Gurney flap at ? = 8°, the first and second modes corresponded with Strouhal numbers based on flap height of 0.18 and 0.13. Comparison of flow around ‘filled’ and ‘open’ flap configurations suggested that the second shedding mode was responsible for a significant portion of the overall lift increment.

Troolin, D. R.; Longmire, E. K.; Lai, W. T.

2006-08-01

280

Evaluation of lifting tasks frequently performed during fire brick manufacturing processes using NIOSH lifting equations  

Microsoft Academic Search

A fire brick manufacturing company with a high prevalence of low back injuries was selected for analysis of lifting tasks using the 1991 revised NIOSH lifting equations. We analyzed several manufacturing processes: forming, heating and packing processes involving frequent lifting and lowering in asymmetric postures. A questionnaire survey showed that weight of the load significantly influenced the incidence of back

Min K. Chung; Dohyung Kee

2000-01-01

281

Design of Low Reynolds Number Airfoils with Trips  

Microsoft Academic Search

A design philosophy for low Reynolds number airfoils that judiciously combines the tailoring of the airfoil pressure distribution using a transition ramp with the use of boundary-layer trips is presented. Three airfoils with systematic changes to the shape of the transition ramp have been designed to study the effect of trips on the airfoil performance. The airfoils were wind-tunnel tested

Ashok Gopalarathnam; Benjamin A. Broughton; Bryan D. Mcgranahan; Michael S. Selig

2003-01-01

282

Unsteady airfoil flow control via a dynamically deflected trailing-edge flap  

NASA Astrophysics Data System (ADS)

The control of the flow around a harmonically oscillating NACA 0015 airfoil via a dynamically deflected simply-hinged trailing-edge flap was investigated experimentally at a Reynolds number of 2.46 x 105 by using a combination of techniques, including surface pressure measurements, hot-wire wake velocity surveys and particle image velocimetry flowfield measurements. The tests were conducted under deep-stall conditions, with special attention being focused on identifying the changes in the flow structures that led to the observed modified aerodynamic load characteristics, and on the evaluation of the effects of the prescheduled trapezoidal flap motion profile. In addition, light-stall and attached-flow oscillations were also considered, as were static flap deflections and higher harmonic flap motions. The results indicate that a trailing-edge flap imposed an effective camber in the trailing-edge region, and was highly effective in the control of the aerodynamic loads. This was achieved in large part by the manipulation of the lower flap surface pressure distribution via changes to the windward-side flow stream, and was unaffected by the state of the flow above the airfoil. The leading-edge vortex, the predominant flow structure over the airfoil, was only marginally affected in its strength and initiation. The results also revealed that both the flap angle and deflection rate contributed to the above observations, and that the active motion was crucial in preventing the flow separation observed over the lower flap surface for an equivalent static flap, which would have hindered its performance. Furthermore, control was limited to the duration of the flap motion, and, in general, no effect on the flow or aerodynamic loads was observed while the flap was withdrawn to its initial undeflected position. The detailed parametric study showed the characteristics of the flap motion profile to be highly influential on the degree of control. In the application of an optimum flap motion schedule to dynamic stall, the severe nose-down pitching moment decreased by 40%, the performance ratio improved by 30%, and the aerodynamic damping became positive and increased four-fold; this was, however, accompanied by a 20% reduction in the maximum lift.

Gerontakos, Panayiote

283

Explanation of the effects of leading-edge tubercles on the aerodynamics of airfoils and finite wings  

NASA Astrophysics Data System (ADS)

A computational study was conducted to explain the aerodynamic effect of leading edge tubercles on maximum lift coefficient, stall angle of attack (AoA), drag, and post stall characteristics for airfoils as well as finite wings. Past experiments demonstrated airfoils with leading edge tubercles do not improve Clmax, drag, or stall AoA but smoothen post stall characteristics to a great degree. In contrast to airfoils, finite wings with L.E. tubercles improved all aerodynamic characteristics. We explain the stall mechanism of the tubercled wing by considering each L.E. tubercle as a combination of a swept forward and a swept backward wing.There are 3 mechanisms (streamline curvature, accelerated stall, and upwash) that cause Clmax of airfoils with L.E. tubercles always be lower than that of smooth airfoils. We also identify two additional mechanisms which are responsible for improved post-stall characteristics of airfoils with L.E. tubercles. Finally, we discuss why finite wings with L.E. tubercles have higher Clmax and lower drag than their smooth L.E. counterparts by studying effects of wing tip, sweep, and taper ratio.

Saadat, Mehdi; Haj-Hariri, Hossein; Fish, Frank

2010-11-01

284

Cavitation Induced Lift Fluctuations  

NASA Astrophysics Data System (ADS)

For various reasons, liquid handling devices, such as pumps, turbines, marine propellers and hydrofoils must often operate in the cavitating regime. Considerable research has gone into avoiding cavitation but little effort has been made to understand the complex physics associated with operation in the partially cavitating regime. This is an experimental study of lift oscillations on a NACA 0015 hydrofoil. Fluctuating lift is measured at two different geometric scales in two different water tunnels. The spectral characteristics of the fluctuations are found to vary considerable over a range of 1.0 ?/2×? 8.5. The amplitude of the fluctuations can exceed 100% of the steady state lift and are associated with the periodic shedding of vortical clouds of bubbles into the flow. Two competing mechanisms are found for the induced shedding of cloud cavitation. At high values of ?/2×?, reentrant jet physics dominate, with sheet cavity oscillations at a frequency, based on cavity length, of fl/U equal 0.3. At low values of ?/2×? , bubbly flow shock wave phenomena dominate with a constant Strouhal number based on chord length of fc/U equal 0.2. A significant effect on the wake structure is also noted. Good agreement with numerical simulations based on the LES technique is generally found. Sponsored by the National Science Foundation and the Office of Naval Research.

Arndt, Roger E. A.; Keller, Anreas; Kjeldsen, Morten

1999-11-01

285

Large Eddy Simulations of an Airfoil in Turbulent Inflow  

Microsoft Academic Search

Wind turbines operate in the turbulent boundary layer of the atmosphere and due to the rotational sampling effect the blades experience a high level of turbulence (1). In this project the effect of turbulence is investigated by large eddy simulations of the turbulent flow past a NACA 0015 airfoil at Reynolds number 1.6 million. The effect of increasing the turbulence

Lasse Gilling; Niels N. Sørensen

286

Modeling fluid structure interaction over a flexible fin attached to a NACA0012 airfoil  

NASA Astrophysics Data System (ADS)

Flow separation control is of importance to the performance of air vehicles. Generally, it is desired to postpone separation such that the overall drag is reduced, stall is delayed, lift is enhanced, and pressure recovery is improved. This work explores a new concept of post-stall flow control for airfoils and wings by using a thin flexible fin attached on the upper surface of an airfoil to passively manipulate flow structures in the fully separated flows for drag reduction and lift enhancement. The flow induced oscillations combined with the shape deformations change the overall pressure distribution on the fin, which in turn affect the fin dynamics. This mutual effect of inertial and elastic forces can also be considered through fluid-structure interactions (FSI). In order to study this problem a Navier-Stokes finite difference solver is coupled with a subdivision finite element solver in a segregated manner. The moving interface (i.e. fin) is modeled by a non-boundary conforming method called Immersed Boundary Methods (IBM). In the present dissertation validations for the Computational Fluid Dynamics (CFD), the Computational Structural Dynamics (CSD) and the Immersed boundary method (IBM) are presented. Then the coupled CFD-CSD solver is first used to model flow induced flapping flat plate with a 5° angle of attack at Re = 20,000. Finally, the coupled solver is used to simulate flow over a NACA0012 airfoil with a passive flexible flapping fin attached to the upper surface of the airfoil with a 18° angle of attack at Re = 63,000. The time averaged drag coefficient around the NACA0012 airfoil with the fin is computed at various angles of attack and compared with the baseline drag coefficient. The results show that the computations follow the experimental trend of drag reduction at higher angles of attack.

Pantula, Srinivasa Ravindra

287

Lifting surface performance analysis for horizontal axis wind turbines  

NASA Astrophysics Data System (ADS)

This report describes how numerical lifting-surface theory is applied to the calculation of a horizontal-axis wind turbine's aerodynamic characteristics and performance. The report also describes how such an application is implemented as a computer program. The method evolved from rotary-wing and helicopter applications and features a detailed, prescribed wake. The wake model extends from a hovering-rotor experimental generalization to include the effect of the windmill brake state on the radial and axial displacement rates of the trailing vortex system. Performance calculations are made by coupling the lifting-surface circulation solution to a blade-element analysis that incorporates two-dimensional airfoil characteristics as functions of angle of attack and Reynolds number. Several analytical stall models are also provided to extend the airfoil characteristics beyond the limits of available data. Although this work focuses on the steady-performance problem, the method includes ways to investigate the effects of wind-shear profile, tower shadow, and off-axis shaft alignment. Correlating the method to measured wind-turbine performance, and comparing it to blade-element momentum theory calculations, validate and highlight the extreme sensitivity of predictions to the quality of early post-stall airfoil behavior.

Kocurek, D.

1987-06-01

288

An experimental investigation of unsteady surface pressure on an airfoil in turbulence—Part 1: Effects of mean loading  

NASA Astrophysics Data System (ADS)

An experimental investigation into the response of an airfoil in turbulence is undertaken and the results are presented in a two part series of papers. The effects of mean loading on the airfoil response are investigated in this paper (Part 1) with the likely sources discussed in Part 2. Unsteady surface pressure measurements were made on a NACA 0015 immersed in grid turbulence (?/c=13%) for angles of attack, ?=0 20°, with a dense array of pressure transducers. These measurements reveal a reduction of up to 5 dB in pressure spectral level as the angle of attack is increased for reduced frequencies less than 5. This observed mean-loading effect has never before been measured or shown to occur theoretically. Lift spectra computed from pressure measurements show a similar result. Furthermore, the reduction in lift spectral level appears to have an ?2 dependence. Also, for small angles of attack (?<8°) Amiet's zero-mean-loading theory may be useful for predicting the airfoil response since the reduction in spectral level is less than 1 dB here. Based on comparisons at ?=0°, Amiet's theory predicts with reasonable accuracy (within 4 dB at low frequency) pressure and lift spectral levels. This theory successfully predicts the shape of both pressure and lift spectra and the decrease in pressure spectral level moving away from the airfoil leading edge. Additionally, Reba and Kerschen's theory, which accounts for non-zero-mean loading using Rapid Distortion Theory, predicts large increases in pressure and lift spectral levels not shown to occur in the measurement. The predicted rise in spectral level appears to result from the flat-plate model with leading-edge singularity which does not fully account for the distortion of the inflow.

Mish, Patrick F.; Devenport, William J.

2006-09-01

289

Towards Dynamic Stall Control on a Rotorcraft Airfoil  

NASA Astrophysics Data System (ADS)

The unsteady stall that occurs on the retreating side of a helicopter rotor produces large torsional stresses and large losses in the aerodynamic performance. Previous results have shown that the static stall can be delayed and the hysteresis eliminated by the simple presence of a 'leading-edge wire'. The presence of the wire, of which the airfoil chord to wire diameter measures 400, has been shown to locally reduce the pressure gradient near the upper surface of the leading edge. Experimental tests of the aerodynamic performance of two wings, the Wortmann 69-H-098 and 63-137, in a pitching sinusoidal motion, have displayed the common features of the dynamic stall process. These features include the existence of a 'super-lift' or lift overshoot, a very large lift-stall and a large hysterisis associated with the cycle. Preliminary control results using a small mechanical actuator has shown a reduction in the effect of the dynamic-stall-vortex. The dynamic stall vortex is the major contributing factor to the negative effects associated with dynamic stall. Currently, steady and unsteady pressures are being measured to analyze the transient nature of the dynamic-stall-vortex motion and to verify control techniques.

Alexander, Hani

1997-11-01

290

Cambered Jet-Flapped Airfoil Theory with Tables and Computer Programs for Application.  

National Technical Information Service (NTIS)

A quadrature method is derived for calculating the incompressible-flow aerodynamics of arbitrarily cambered jet-flapped airfoils. The anticipated application of the methodology is to high-speed subsonic flows (combat maneuvering aircraft) via the use of c...

H. W. Woolard B. F. Niehaus

1977-01-01

291

The Investigation of the Airfoil for the Small Wind Turbine Based on the Seagull Airfoil  

Microsoft Academic Search

For the blades of the small wind turbine working under the conditions of Low-Reynolds, the air viscosity has relatively great influence on them. The design of the airfoil influence the performance of the small wind turbine directly. This paper based on the airfoil of the seagull, studied the aerodynamic performance of the airfoil under the Low-Reynolds and the influences of

Limin Qiao; Sidong Wei; Rui Gu; Xiaolin Quan; Yingjun Yang

2011-01-01

292

Low-Speed Aeroelastic Modeling of Very Flexible Slender Wings with Deformable Airfoils  

Microsoft Academic Search

A low-order aeroelastic model is introduced for very flexible high-aspect-ratio wings with adaptive airfoils. A geometrically-nonlinear beam-like model capable of capturing plate-like deformations has been coupled with a 2-D finite-state aerodynamic model with arbitrary airfoil deformations. The proposed approach results in a natural extension to the conventional way of analyzing high-aspect-ratio wings, with very little additional complexity. The control effectiveness

Rafael Palacios

2008-01-01

293

Effect of End Plates on the Surface Pressure Distribution of a Given Cambered Airfoil: Experimental Study  

NASA Astrophysics Data System (ADS)

While conducting 2-D experiments for flow over airfoil in small wind tunnels, models are usually mounted by spanning the tunnel. However, in large wind tunnels, it is a usual practice to test airfoil models with end plates mounted at its both ends. Thus reduces the blockage, eliminates the tip effects, enables two-dimensional configuration for the flow over airfoil, apart of being cost effective and time saving. Main objective of the present investigation is to study the effect of different sized and shaped end plates on the surface pressure distribution for a given airfoil. Experiments were carried out on a single aerofoil GA(W)-2 at National Wind Tunnel Facility in IIT-Kanpur and surface pressures were measured at constant free stream speed of 30 m/s by varying the end-plates shapes at discrete angle of attack (-10° to 30°). Present study employed three different size end plates A, B, and C. Size of the endplate A is extended 20% chord length all along the airfoil cross sectional area. And end plate B is one chord length extended on airfoil except lower surface. In addition end plate B has wedge on the upper side. End plate C is spanning the tunnel height. These selected varied shaped end-plates had a significant affect on the aerodynamic characteristics along with a considerable variations in the flow phenomena involving flow separations, tip and blockage effects. Results indicates that endplate C gives the closest 2-D configuration (Figure a). Lift curve slope increases and stall angle decreases as the end plate size increases from A to C. It appears that for small size end plates (A and B), the stalling angle delayed to higher angles because of the interaction of the outer free stream flow with the flow on the suction side of the airfoil. And this interaction provides the energy to recover pressure and sustains to higher angles at the expense of the lift. And also stalling occurs abruptly. Effect of endplates changes the moment curve slope. Negative slope observed for all the three cases (Figure b).

Reddy, K. S. V.; Sharma, D. M.; Poddar, K.

294

Lift evaluation of a two-dimensional pitching flat plate  

NASA Astrophysics Data System (ADS)

Several previous experimental and theoretical studies have shown that a leading edge vortex (LEV) on an airfoil or wing can provide lift enhancement. In this paper, unsteady two-dimensional (2D) potential flow theory is employed to model the flow field of a pitching flat plate wing. A multi-vortices model is developed to model both the leading edge and trailing edge vortices (TEVs), which offers improved accuracy compared with using only single vortex at each separation location. The lift is obtained by integrating the unsteady Blasius equation. It is found that the motion of vortices contributes significantly to the overall aerodynamic force on the flat plate. A Kutta-like condition is used to determine the vortex intensity and location at the leading edge for large angle of attack cases; however, it is proposed to relax this condition for small angle of attack cases and apply a 2D shear layer model to calculate the circulation of the new added vortex. The results of the simulation are then compared with classical numerical, theoretical, and experimental data for canonical unsteady flat plat problems. Good agreement with these data is observed. Moreover, these results suggested that the leading edge vortex shedding for small angles of attack should be modeled differently than that for large angles of attack. Finally, the results of vortex motion vs. lift indicate that the slow convection of the LEV creates less negative lift while the rapid shedding of the TEV creates more positive lift. The difference between these two contributions of lift results in a total positive lift that lasts for about two chord-length travel of the plate. It is therefore concluded that the lift enhancement during the LEV ``stabilization'' above the wing is a combined effect of both the LEV and TEV motion. This also provides the insights for future active flow control of micro aerial vehicles (MAVs) that the formation and shedding process of LEVs and TEVs can be manipulated to provide lift enhancement.

Xia, X.; Mohseni, K.

2013-09-01

295

Aerodynamics of an Airfoil at Ultra-Low Reynolds Number  

NASA Astrophysics Data System (ADS)

A comprehensive experimental study is conducted of the aerodynamic characteristics of an NACA0012 airfoil over a large range of angle (?) of attack and low- to ultra-low cord Reynolds numbers, 5.3×103 - 5.1×104, which is of both fundamental and practical importance. While the mean and fluctuating lift and drag coefficients were measured using a load cell, the detailed flow structure is documented using particle image velocimetry and laser-induced fluorescence flow visualization. C D increases monotonically from ? = 0° to 90°, whilst C L grows from 0 to its maximum at ? = 45° and then drops. The near wake characteristics examined were found to be consistent with the force measurements, including the vortex formation length, wake width, spanwise vorticity, wake bubble size and wavelength of K-H vortices.

Alam, Md. Mahbub; Zhou, Y.; Yang, H.

296

Experimental investigation of separation and transition processes on a high-lift low-pressure turbine profile under steady and unsteady inflow at low Reynolds number  

Microsoft Academic Search

The effects induced by the presence of incoming wakes on the boundary layer developing over a high-lift low-pressure turbine\\u000a profile have been investigated in a linear cascade at mid-span. The tested Reynolds number is 70000, typical of the cruise\\u000a operating condition. The results of the investigations performed under steady and unsteady inflow conditions are analyzed.\\u000a The unsteady investigations have been

Francesca Satta; Daniele Simoni; Marina Ubaldi; Pietro Zunino; F. Bertini

2010-01-01

297

How plunger lift affects production  

SciTech Connect

Plunger lift is finding an increasing marketplace for application in the US. The system is advantageous in many circumstances because of low inital cost, little maintenance, and because it generally requires no external energy source. Typical applications for plunger lift are removal of liquids from a gas well, high-ratio oil well production, paraffin and hydrate control, and increased efficiency of intermittent gas lift wells. Main advantage of using a plunger to produce a well is economics. An industry-wide average installation will cost $3500 plus some service, which depends on the company furnishing the equipment. Compare this to a pumping unit to do the same job ($28,000) or a small compressor ($32,000). Also, there is no power consumption such as electricity (high initial cost to run to the lease) or gas consumed (at $2.40/mcf). All the energy is furnished by the well, including instrument gas.

Beauregard, E.M.; Ferguson, P.L.

1981-07-01

298

An Investigation of Mist\\/Air Film Cooling with Application to Gas Turbine Airfoils  

Microsoft Academic Search

Film cooling is a cooling technique widely used in high-performance gas turbines\\u000ato protect turbine airfoils from being damaged by hot flue gases. Film injection holes are\\u000aplaced in the body of the airfoil to allow coolant to pass from the internal cavity to the\\u000aexternal surface. The ejection of coolant gas results in a layer or “film” of coolant

lei zhao

2012-01-01

299

Investigation of a low Reynolds number airfoil using molecular tagging velocimetry  

Microsoft Academic Search

Molecular tagging velocimetry (MTV) is used to study flow separation, transition, and reattachment on a SD7003 airfoil at a chord Reynolds number of 20,000. Multi-line tagging is employed to obtain high resolution one-component velocity data near the suction surface of the airfoil. The spatial resolution in the wall-normal direction normalized by the chord length is about 0.0003, nearly ten times

Alan Katz; Ahmed Naguib; Manoochehr Koochesfahani

2009-01-01

300

Calculation of the pressure distribution on a pitching airfoil with application to the Darrieus Rotor. [Computer code DARIUS  

SciTech Connect

An analytical model leading to the pressure distribution on the cross section of a Darrieus Rotor Blade (airfoil) has veen constructed. The model is based on the inviscid flow theory and the contribution of the nonsteady wake vortices was neglected. The analytical model was translated into a computer code in order to study a variety of boundary conditions encountered by the rotating blades of the Darrieus Rotor. Results indicate that, for a pitching airfoil, lift can be adequately approximated by the Kutta-Joukowski forces, despite notable deviations in the pressure distribution on the airfoil. These deviations are most significant at the upwind half of the Darrieus Rotor where higher life is accompanied by increased adverse pressure gradients. The effect of pitching on lift can be approximated by a linear shift in the angle of attack proportional to the blade angular velocity. Tabulation of the fluid velocity about the pitching-only NACA 0015 allowed the principle of superposition to be used to determine the fluid velocity about a translating and pitching airfoil.

Ghodoosian, N.

1984-05-01

301

Flow control over a NACA 0012 airfoil using dielectric-barrier-discharge plasma actuator with a Gurney flap  

NASA Astrophysics Data System (ADS)

Flow control study of a NACA 0012 airfoil with a Gurney flap was carried out in a wind tunnel, where it was demonstrated that a dielectric-barrier-discharge (DBD) plasma actuator attached to the flap could increase the lift further, but with a small drag penalty. Time-resolved PIV measurements of the near-wake region indicated that the plasma forcing shifted the wake downwards, reducing its recirculation length. Analysis of wake vortex dynamics suggested that the plasma actuator initially amplified the lower wake shear layer by adding momentum along the downstream surface of the Gurney flap. This enhanced mutual entrainment between the upper and lower wake vortices, leading to an increase in lift on the airfoil.

Feng, Li-Hao; Jukes, Timothy N.; Choi, Kwing-So; Wang, Jin-Jun

2012-06-01

302

Numerical simulation of a viscous compressible flow around a NACA 0012 airfoil: Low Reynolds number regime  

NASA Astrophysics Data System (ADS)

The two dimensional Navier-Stokes equations for a compressible fluid have been numerically solved to investigate the effect of the viscosity and the compressibility on the instability of the laminar air flow around a NACA0012 airfoil at zero incidence angle of attack. The numerical simulations are carried out at two Re numbers (5,000 and 10,000), and at the Ma number in the range 0.2-0.9. The non-dimensional compressible Navier-Stokes equations have been solved by using a high order Spectral/hp Element Method (SEM) that uses a Discontinuous Galerkin approach. The mesh consists of 2320. The computed values of the pressure coefficient Cp, the lift coefficient CL and the drag coefficient CD, have been compared with numerical simulations and experimental data available in the literature. The Mach number countours allow to identify the presence of shock waves in the transonic flow regime. We may conclude that the discontinuous Galerkin method is capable to predict the transition stages that the laminar flow undergoes as the Ma number increases (at fixed Re number).

Valenzuela, Fernando; Avila, Ruben

2008-11-01

303

Investigation of a low Reynolds number airfoil using molecular tagging velocimetry  

NASA Astrophysics Data System (ADS)

Molecular tagging velocimetry (MTV) is used to study flow separation, transition, and reattachment on a SD7003 airfoil at a chord Reynolds number of 20,000. Multi-line tagging is employed to obtain high resolution one-component velocity data near the suction surface of the airfoil. The spatial resolution in the wall-normal direction normalized by the chord length is about 0.0003, nearly ten times smaller than previously reported PIV measurements on the same airfoil under similar flow conditions. Preliminary data will be presented for the locations of flow separation and reattachment for the airfoil at an angle of attack of 8 degrees, and results will be compared with existing experimental and computational data.

Katz, Alan; Naguib, Ahmed; Koochesfahani, Manoochehr

2009-11-01

304

Soccer Ball Lift Coefficients via Trajectory Analysis  

ERIC Educational Resources Information Center

|We performed experiments in which a soccer ball was launched from a machine while two high-speed cameras recorded portions of the trajectory. Using the trajectory data and published drag coefficients, we extracted lift coefficients for a soccer ball. We determined lift coefficients for a wide range of spin parameters, including several spin…

Goff, John Eric; Carre, Matt J.

2010-01-01

305

Soccer Ball Lift Coefficients via Trajectory Analysis  

ERIC Educational Resources Information Center

We performed experiments in which a soccer ball was launched from a machine while two high-speed cameras recorded portions of the trajectory. Using the trajectory data and published drag coefficients, we extracted lift coefficients for a soccer ball. We determined lift coefficients for a wide range of spin parameters, including several spin…

Goff, John Eric; Carre, Matt J.

2010-01-01

306

Darrieus wind-turbine airfoil configurations  

SciTech Connect

The purpose of this study was to determine what aerodynamic performance improvement, if any, could be achieved by judiciously choosing the airfoil sections for Darrieus wind turbine blades. Analysis was limited to machines using two blades of infinite aspect ratio, having rotor solidites from seven to twenty-one percent, and operating at maximum Reynolds numbers of approximately three million. Ten different airfoils, having thickness to chord ratios of twelve, fifteen and eighteen percent, were investigated. Performance calculations indicated that the NACA 6-series airfoils yield peak power coefficients at least as great as the NACA four-digit airfoils which have historically been chosen for Darrieus turbines. Furthermore, the power coefficient-tip speed ratio curves were broader and flatter for the 6-series airfoils. Sample calculations for an NACA 63/sub 2/-015 airfoil showed an annual energy output increase of 17 to 27% depending upon rotor solidity, compared to an NACA 0015 airfoil. An attempt was made to account for the flow curvature effects associated with Darrieus turbines by transforming the NACA 63/sub 2/-015 airfoil to an appropriate shape.

Migliore, P.G.; Fritschen, J.R.

1982-06-01

307

Effect of Flap Deflection on Section Characteristics of S813 Airfoil; Period of Performance: 1993--1994  

SciTech Connect

The effect of small deflections of a 30% chord, simple flap on the section characteristics of a tip airfoil, the S813, designed for 20- to 30-meter, stall-regulated, horizontal-axis wind turbines has been evaluated theoretically. The decrease in maximum lift coefficient due to leading-edge roughness increases in magnitude with increasing, positive flap deflection and with decreasing Reynolds number.

Somers, D. M.

2005-01-01

308

Preliminary Wind-Tunnel Investigation of the Effects of Engine Nacelles on a Transport Configuration with High Lift Drag Ratios to a Mach Number of 1.00.  

National Technical Information Service (NTIS)

Wind tunnel tests to determine the effect of engine nacelles added to a low wing fuselage vertical tail configuration utilizing the NASA supercritical airfoil and a refined area ruled fuselage are discussed. The engine arrangement consisted of two aft fus...

S. G. Flechner

1971-01-01

309

Tip Vortex Development of an Adaptive Arc Airfoil  

Microsoft Academic Search

The roll-up and development of the wing-tip vortex from an adaptive circular arc airfoil is observed experimentally. A piezoceramic actuator with a steel substrate serves as the adaptive airfoil. The baseline (zero potential) radius of curvature Rc of the airfoil is 16 cm. Rc is varied by changing the voltage applied across the arc airfoil. A maximum input voltage of

Nan Jou Pern; J. D. Jacob

1998-01-01

310

Unsteady Flow Computations around Moving Airfoils by Overset Unstructured Grid Method  

NASA Astrophysics Data System (ADS)

The study presents a computational method for unsteady flows around moving multiple objects using overset unstructured grid method. To capture unsteady flow characteristics, the dual time-stepping method coupled with the LU-SGS implicit scheme is applied to the time integration. Two or more moving boundaries can be treated easily by the overset unstructured grid method. In this study, Chimera-hole cutting is performed automatically along with movement of the objects. For validation, the numerical results for inviscid and viscous flow and the experimental results are compared using the lift coefficient and pressure coefficient distribution of a pitching NACA0012 airfoil. Both results show the tendency of the experimental data, confirming the validity of this method. Furthermore, the flow around several objects is examined and the generality of the overset grid method is verified. Two demonstrations of the unsteady computation flapping airfoil, and a section of a vertical-axis wind turbine with three rotors are also described.

Takahashi, Shun; Monjugawa, Ichie; Nakahashi, Kazuhiro

311

30526 artificial lift  

SciTech Connect

This book focuses on the four major methods of artificial lift: sucker-rod pumping, gas lift, electrical submersible pumping (ESP) and hydraulic pumping. Though more than 80% of artificially lifted wells worldwide are rod-pumped, the large majority of these wells are low-volume, stripper-type producers. For this reason, sucker-rod pumping papers comprise less than 40% of the 26 SPE papers selected.

Not Available

1989-01-01

312

Adaptive Directional Lifting-Based Wavelet Transform for Image Coding  

Microsoft Academic Search

We present a novel 2-D wavelet transform scheme of adaptive directional lifting (ADL) in image coding. Instead of alter- nately applying horizontal and vertical lifting, as in present prac- tice, ADL performs lifting-based prediction in local windows in the direction of high pixel correlation. Hence, it adapts far better to the image orientation features in local windows. The ADL transform

Wenpeng Ding; Feng Wu; Xiaolin Wu; Shipeng Li; Houqiang Li

2007-01-01

313

Computational Simulation of Dynamic Stall on the NLR 7301 Airfoil  

NASA Astrophysics Data System (ADS)

The dynamic stall behavior of the supercritical NLR 7301 airfoil is analyzed with a 2-D thin-layer Navier-Stokes code. The code solves the compressible Reynolds-averaged Navier-Stokes equations with an upwind biased numerical scheme in combination with the Baldwin-Lomax or the Baldwin-Barth turbulence models. The effect of boundary layer transition is incorporated using the transition length model of Gostelow et al. The transition onset location is determined with Michel's formula or it can be specified as an input parameter. The two turbulence models yield significantly different steady-state lift coefficients at incidences greater than 8°. The use of the one-equation Baldwin-Barth model together with the Gostelow transition model is found to give substantially better agreement with the experimental data of McCroskey et al. than the Baldwin-Lomax model. Also, the unsteady computations are strongly affected by the choice of the turbulence model. The Baldwin-Barth model predicts the lift hysteresis loops consistently better than the algebraic turbulence model. However, the one-equation model improves the prediction of the moment hysteresis loops only for one test case.

Weber, S.; Platzer, M. F.

2000-08-01

314

View south; detail of top of lift span and lifting ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

View south; detail of top of lift span and lifting cables. - Naval Base Philadelphia-Philadelphia Naval Shipyard, Lift Bridge, Mouth of Reserve Basin, League Island, Philadelphia, Philadelphia County, PA

315

Gas lift systems make ideal offshore workers  

SciTech Connect

With a low initial installation cost and small footprint, gas lift systems are well suited for offshore installations where compressed gas is usually already available. These systems are used on multiple and slimhole completions and handle sandy conditions well. They are also used to kick off wells that will flow naturally once the heavier completion fluids leave the production string. Gas lift itself is a mature workaday technology. Measurement and control of gas flow is an area of intense development in gas lift technology. One new control method involves production of multiple completions through a single wellbore. Typically, gas lift valves are opened and closed through tubing pressure. But downhole measurement technology does not yet yield information good enough for stable gas lift control of multiple completions. Gas lift is proving to be a useful AL technique in conjunction with electric submersible pumps (ESP). Located above the ESP pump, the gas lift can reduce the head and allow greater flow. This is helpful when small casing restricts the size of the downhole ESP pump. Wells can usually be produced by the gas lift alone in case of ESP failure, or by replacing the ESP where schedules, high repair costs or low prices rule out repair.

NONE

1999-05-01

316

Nonlinear aeroelastic behavior of compliant airfoils  

NASA Astrophysics Data System (ADS)

Since the beginning of aviation and up to the present time, airfoils have always been built as rigid structures. They are designed to fly under their divergence speed in order to avoid static aeroelastic instabilities and the resulting large deformations, which are not compatible with the typically low compliance of such airfoils. In recent years, research on airfoil morphing has generated interest in innovative ideas like the use of compliant systems, i.e. systems built to allow for large deformations without failure, in airfoil construction. Such systems can operate in the neighborhood of divergence and take advantage of large aeroelastic servo-effects. This, in turn, allows compact, advanced actuators to control the airfoil's deformation and loads, and hence complement or even replace conventional flaps. In order to analyze and design such compliant, active aeroelastic structures a nonlinear approach to static aeroelasticity is needed, which takes into account the effect of large deformations on aerodynamics and structure. Such an analytical approach is presented in this paper and applied to a compliant passive airfoil as the preliminary step in the realization of a piezoelectrically driven, active aeroelastic airfoil. Wind tunnel test results are also presented and compared with the analytic prediction. The good agreement and the observed behavior in the wind tunnel give confidence in the potential of this innovative idea.

Thwapiah, G.; Campanile, L. F.

2010-03-01

317

Post stall airfoil data for wind turbines: wind tunnel test results  

SciTech Connect

Wind turbine blades operate over a wide angle of attack range. Unlike aircraft, a wind turbine's angle of attack range extends deep into stall where the three dimensional performance characteristics of airfoils are not generally known. Peak power predictions upon which wind turbine components are sized depend on a good understanding of a blade's post stall characteristics. The purpose of this wind tunnel study is to characterize the performance characteristics of a blade in stall as a function of its aspect ratio, airfoil thickness and Reynolds number. This report documents results of the wind tunnel investigation of constant chord blades having four aspect ratios, with NACA 44XX series airfoil sections, at angles of attack ranging from -10 to 110/sup 0/. Tests were conducted at Reynolds number ranging from one-quarter million to one million. The thickness ratios studied were 0.18, 0.15, 0.12 and 0.09. The aspect ratios were 6, 9, 12 and infinity. Results of force and pitching moment measurements, over the angle of attack range, for all combinations of Reynolds numbers, thickness and aspect ratios, and the effects of boundary layer tripping, have been presented. Both initial and secondary stall are presented. The maximum drag coefficient is found to occur at an angle of attack of 90/sup 0/. The pitching moment is unstable beyond stall. The lift and post-stall drag coefficients decrease with decreasing aspect ratio. The lift coefficient decreases with decreasing thickness ratio, while the drag coefficient increases. The boundary layer tripping is observed to decrease the lift curve slope and stalling angle of attack. The drag coefficient (with tripping) is significantly affected only at low aspect ratio.

Ostowari, C.; Naik, D.

1984-07-01

318

Pressure measurements on a pitching airfoil in a water channel  

Microsoft Academic Search

Measurements of unsteady pressures over a symmetric NACA 0015 airfoil performing pitching maneuvers are reported. The tests were performed in an open-surface water channel specially constructed for this purpose. The design of the apparatus allowed the pressure measurements to be made to a very high degree of spatial and temporal resolution. Reynolds numbers in the range of 5.2 x 10(exp

Rand N. Conger; B. R. Ramaprian

1994-01-01

319

Dynamic stall model for wind turbine airfoils  

Microsoft Academic Search

A model is presented for aerodynamic lift of wind turbine profiles under dynamic stall. The model combines memory delay effects under attached flow with reduced lift due to flow separation under dynamic stall conditions. The model is based on a backbone curve in the form of the static lift as a function of the angle of attack. The static lift

J. W. Larsen; S. R. K. Nielsen; S. Krenk

2007-01-01

320

Interior of lift mechanism area of eastern lift span, looking ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Interior of lift mechanism area of eastern lift span, looking northwest. - Arlington Memorial Bridge, Spanning Potomac River between Lincoln Memorial & Arlington National Cemetery, Washington, District of Columbia, DC

321

Mobile Lifting Jack.  

National Technical Information Service (NTIS)

A mobile jack, particularly for use in installation of support beams in underground mines, is disclosed. The jack comprises a wheel-mounted frame and a hydraulic lifting arm having a jack head which is horizontally rotatable 360 deg. The lifting arm is al...

R. L. Unger T. G. Bobick

1987-01-01

322

Understanding Wing Lift  

ERIC Educational Resources Information Center

The conventional explanation of aerodynamic lift based on Bernoulli's equation is one of the most common mistakes in presentations to school students and is found in children's science books. The fallacies in this explanation together with an alternative explanation for aerofoil lift have already been presented in an excellent article by Babinsky…

Silva, J.; Soares, A. A.

2010-01-01

323

Understanding Wing Lift  

ERIC Educational Resources Information Center

|The conventional explanation of aerodynamic lift based on Bernoulli's equation is one of the most common mistakes in presentations to school students and is found in children's science books. The fallacies in this explanation together with an alternative explanation for aerofoil lift have already been presented in an excellent article by Babinsky…

Silva, J.; Soares, A. A.

2010-01-01

324

Catwalk grate lifting tool  

DOEpatents

A device is described for lifting catwalk grates comprising an elongated bent member with a handle at one end and a pair of notched braces and a hook at the opposite end that act in conjunction with each other to lock onto the grate and give mechanical advantage in lifting the grate. 10 figs.

Gunter, L.W.

1992-08-11

325

Portable Seat Lift.  

National Technical Information Service (NTIS)

A portable seat lift that can help individuals either (1) lower themselves to a sitting position or (2) raise themselves to a standing position is presented. The portable seat lift consists of a seat mounted on a base with two levers, which are powered by...

B. Weddendorf

1992-01-01

326

Experimental and computational study of airfoil load alteration using oscillating fence actuator  

NASA Astrophysics Data System (ADS)

Experimental and computational studies have been conducted for characterizing the effect of a fence actuator on stationary and oscillating airfoils and assessing the authority of the fence actuator for altering the aerodynamic loading of an airfoil to suppress flutter. In particular, an oscillating fence on a NACA-23012 airfoil has been examined using Particle Image Velocimetry (PIV), time-resolved pressure measurements, and numerical simulations of a pitching airfoil. Experiments over stationary and oscillating airfoils show that the fence frequency strongly affects the evolution of the vortical structures generated by the fence and that higher actuation frequencies are more effective in producing higher suction peaks. For an oscillating airfoil, variation of the mean angle of attack strongly affects the baseline pressure distribution as expected. The disturbances, however, remain largely unaffected by the variations in mean angle of attack. It was also observed that the adverse pressure gradient at higher angles of attack caused a reduction in dissipation of the disturbances. Integrated lift and moment are used to quantify the effectiveness of the fence actuator, and the sufficiently large changes produced in these quantities show the potential of this device for altering the aerodynamic loading of a wing and suppressing flutter. Results from the computational study indicate that the fence is capable of producing significant disturbances that diminish airfoil oscillations, more so when the actuator is located close to the trailing edge. Implementation of an appropriate control scheme can be used to enhance the effects of these actuators. Pressure Sensitive Paint experiments conducted for better understanding the production and evolution of the disturbances revealed complex surface pressure behavior. The results indicate that the actuator disturbances develop three-dimensionality soon after the fence penetrates the flow because of the finite fence length effects. Furthermore, the structure was found to evolve faster for slower fence frequencies due to reduction in time scale imposed by the oscillating fence. These results also suggest that the use of a two-dimensional disturbance in the numerical model may have caused over-estimation of the effect of the actuator.

Saini, Manjinder

327

Scalnig of transient lift response to actuation in a 3D separated flow  

NASA Astrophysics Data System (ADS)

The transient lift response of a separated flow to short duration (pulsed) blowing is studied on a low Reynolds number, semicircular-planform, flat-plate wing. Actuators were distributed along the leading edge of the wing. The pulse duration, amplitude (supply pressure), and freestream speed were varied in the experiments. We identify two non-dimensional parameters governing the response, and use the data to find functional forms for the lift coefficient increment. We show that the lift coefficient increment is nearly independent of the pulse duration and increases (solely) with the square root of the supply-pressure coefficient up to a saturation. We also find that the shape of the lift response curve is similar to that produced in other experiments with different airfoils and actuators.

Colonius, Tim; Williams, David; Tadmor, Gilead; Kerstens, Wes; Quach, Vien; Buntain, Seth

2009-11-01

328

Flow past two in-tandem airfoils undergoing sinusoidal oscillations  

NASA Astrophysics Data System (ADS)

The interaction of the wake, generated behind an upstream oscillating NACA 0012 airfoil, with the downstream NACA 0012 airfoil, oscillated at the same conditions but with ? = 0° and 180° different phases (relative to the upstream airfoil), was investigated by particle image velocimetry and surface pressure measurements. The results show that the axial spacing and phase difference determined the strength of the undesirable interference effects and, subsequently, the behavior of the dynamic-load loops of the downstream airfoil. The boundary-layer events on the downstream airfoil were persistently different from those observed on the baseline oscillating airfoil. The downwash induced by the upstream airfoil disrupted leading-edge vortex (LEV) formation on the downstream airfoil. The absence of LEV-induced transient effects also led to a significantly lowered aerodynamic loading and C l -hysteresis compared to the baseline airfoil. The aerodynamic performance of the ? = 180° case, however, outperformed that of the ? = 0° case.

Lee, T.

2011-12-01

329

Submicron-scale surface acoustic wave resonators fabricated by high aspect ratio X-ray lithography and aluminum lift-off  

Microsoft Academic Search

A submicron-scale surface acoustic wave (SAW) resonator fabricated by high-aspect-ratio X-ray lithography (XRL) and metal\\u000a lift-off that operates at microwave frequencies is presented. We demonstrate that XRL is especially well suited for SAW device\\u000a templating, as long submicron-scale interdigitated transducer structures can be batch patterned with excellent structure quality.\\u000a 0.4–2.0 ?m thick PMMA layers were structured by X-ray lithography shadow projection

Sven Achenbach; David Klymyshyn; Timo Mappes; Anton Kachayev; Venkat Subramanian; Garth Wells; Jürgen Mohr

2008-01-01

330

Drag and lift reduction of a 3D bluff-body using active vortex generators  

NASA Astrophysics Data System (ADS)

In this study, a passive flow control experiment on a 3D bluff-body using vortex generators (VGs) is presented. The bluff-body is a modified Ahmed body (Ahmed in J Fluids Eng 105:429-434 1983) with a curved rear part, instead of a slanted one, so that the location of the flow separation is no longer forced by the geometry. The influence of a line of non-conventional trapezoïdal VGs on the aerodynamic forces (drag and lift) induced on the bluff-body is investigated. The high sensitivity to many geometric (angle between the trapezoïdal element and the wall, spanwise spacing between the VGs, longitudinal location on the curved surface) and physical (freestream velocity) parameters is clearly demonstrated. The maximum drag reduction is -12%, while the maximum global lift reduction can reach more than -60%, with a strong dependency on the freestream velocity. For some configurations, the lift on the rear axle of the model can be inverted (-104%). It is also shown that the VGs are still efficient even downstream of the natural separation line. Finally, a dynamic parameter is chosen and a new set-up with motorized vortex generators is proposed. Thanks to this active device. The optimal configurations depending on two parameters are found more easily, and a significant drag and lift reduction (up to -14% drag reduction) can be reached for different freestream velocities. These results are then analyzed through wall pressure and velocity measurements in the near-wake of the bluff-body with and without control. It appears that the largest drag and lift reduction is clearly associated to a strong increase of the size of the recirculation bubble over the rear slant. Investigation of the velocity field in a cross-section downstream the model reveals that, in the same time, the intensity of the longitudinal trailing vortices is strongly reduced, suggesting that the drag reduction is due to the breakdown of the balance between the separation bubble and the longitudinal vortices. It demonstrates that for low aspect ratio 3D bluff-bodies, like road vehicles, the flow control strategy is much different from the one used on airfoils: an early separation of the boundary layer can lead to a significant drag reduction if the circulation of the trailing vortices is reduced.

Aider, Jean-Luc; Beaudoin, Jean-François; Wesfreid, José Eduardo

2010-05-01

331

Development of a 'bi-layer lift-off' method for high flow rate and high frequency Nitinol MEMS valve fabrication  

NASA Astrophysics Data System (ADS)

This paper presents modeling, fabrication and testing results for a high flow rate and high frequency nickel titanium alloy (Nitinol) MEMS valve. ANSYS® is used to evaluate several Nitinol MEMS valve structural designs with the conclusion that a pentagonal flap with five legs produces higher frequencies and higher strengths without the inherent rotation problem present in four-leg designs. The Nitinol penta-leg design was fabricated using a novel bi-layer lift-off method. A polymethylglutarimide (PMGI) polymer layer is initially used as an underlayer while a chromium layer is used as a top layer to produce a non-rotational ortho-planar Nitinol MEMS valve array without the problems inherent in conventional Nitinol wet etching. The array consists of 65 microvalves with a single valve having dimensions of 1 mm circumference, 50 µm leg width and 8.2 µm Nitinol thickness. Each microvalve covers an orifice of 220 µm diameter and 500 µm in length and is capable of producing 150 µm vertical deflection. The Nitinol MEMS valve array was tested for flow rates in a hydraulic system as a function of applied pressure with a maximum water flow rate of 16.44 cc s-1.

Seong, Myunghoon; Mohanchandra, K. P.; Lin, Yohan; Carman, Gregory P.

2008-07-01

332

Computational Investigation of Subsonic Torsional Airfoil Flutter.  

National Technical Information Service (NTIS)

In this thesis single-degree-of-freedom torsional airfoil flutter is investigated using an incompressible potential flow code, a compressible inviscid Euler code and a compressible viscous Navier-Stokes code. It is found that the classical linearized inco...

C. Kakkavas

1998-01-01

333

Aerodynamic Simulation of Ice Accretion on Airfoils.  

National Technical Information Service (NTIS)

This report describes recent improvements in aerodynamic scaling and simulation of ice accretion on airfoils. Ice accretions were classified into four types on the basis of aerodynamic effects: roughness, horn, streamwise, and spanwise ridge. The NASA Ici...

A. P. Broeren E. Montreuil G. T. Busch H. E. Addy M. B. Bragg

2011-01-01

334

Low Reynolds Number Airfoil Survey, Volume 1.  

National Technical Information Service (NTIS)

The differences in flow behavior two dimensional airfoils in the critical chordlength Reynolds number compared with lower and higher Reynolds number are discussed. The large laminar separation bubble is discussed in view of its important influence on crit...

B. H. Carmichael

1981-01-01

335

Second-stage turbine bucket airfoil  

DOEpatents

The second-stage buckets have airfoil profiles substantially in accordance with Cartesian coordinate values of X, Y and Z set forth in inches in Table I wherein Z is a perpendicular distance from a plane normal to a radius of the turbine centerline and containing the X and Y values with the Z value commencing at zero in the X, Y plane at the radially innermost aerodynamic section of the airfoil and X and Y are coordinate values defining the airfoil profile at each distance Z. The X and Y values may be scaled as a function of the same constant or number to provide a scaled-up or scaled-down airfoil section for the bucket. The second-stage wheel has sixty buckets.

Wang, John Zhiqiang (Greenville, SC); By, Robert Romany (Simpsonville, SC); Sims, Calvin L. (Mauldin, SC); Hyde, Susan Marie (Piedmont, SC)

2002-01-01

336

Third-stage turbine bucket airfoil  

DOEpatents

The third-stage buckets have airfoil profiles substantially in accordance with Cartesian coordinate values of X, Y and Z set forth in inches in Table I wherein Z is a perpendicular distance from a plane normal to a radius of the turbine centerline and containing the X and Y values with the Z value commencing at zero in the X, Y plane at the radially innermost aerodynamic section of the airfoil and X and Y are coordinates defining the airfoil profile at each distance Z. The X, Y and Z values may be scaled as a function of the same constant or number to provide a scaled-up or scaled-down airfoil section for the bucket.

Pirolla, Peter Paul (Greenville, SC); Siden, Gunnar Leif (Greenville, SC); Humanchuk, David John (Simpsonville, SC); Brassfield, Steven Robert (Cincinnati, OH); Wilson, Paul Stuart (New Richmond, OH)

2002-01-01

337

The Kutta-Zhukovsky Lift Theorem revisited: Alteration due to the Viscous Wake  

NASA Astrophysics Data System (ADS)

The circulation theory of lift comprised in the classical Kutta-Zhukovsky Lift Theorem forms the foundation of modern aerodynamic wing theory. The theorem has been applied ever since in lifting-line models of aircraft and rotary wings. Reynolds numbers larger than one million support its validity, yet the effect of a viscous wake on a change in the functional relationship between lift and circulation is not taken into account in standard lifting-line analyses. A discrepancy in circulation of more than six percent in comparison to the classical Kutta-Zhukovsky Lift Theorem has been demonstrated by the author (Schmitz & Chattot, Computers & Fluids, 36) for moderately separated flow around a wind turbine airfoil by means of a control volume analysis governed by the Navier-Stokes equations. The present work extends the previous analysis to general three-dimensional flow around a lifting body. An analytical expression is presented that extends the classical Kutta-Zhukovsky Lift Theorem by adding terms to the theorem due to chord- and spanwise vorticity transport. An integrated solution for induced drag is given that has not been documented in previous literature on the subject. The generalized theorem will find future application and quantification in actuator-line methods used to predict wind farm wake interactions with Atmospheric Boundary Layer flow.

Schmitz, Sven

2011-11-01

338

Numerical simulations of iced airfoils and wings  

Microsoft Academic Search

A numerical study was conducted to understand the effects of simulated ridge and leading-edge ice shapes on the aerodynamic performance of airfoils and wings. In the first part of this study, a range of Reynolds numbers and Mach numbers, as well as ice-shape sizes and ice-shape locations were examined for various airfoils with the Reynolds-Averaged Navier-Stokes approach. Comparisons between simulation

Jianping Pan

2004-01-01

339

Steuerung der Vorderkantenablosung an Einem Flugelprofil durch Lokale Anregung (Control of Leading-Edge Separation on an Airfoil by Localized Excitation).  

National Technical Information Service (NTIS)

The experimental investigation on the control of the separated flow over a low Reynolds number airfoil placed at high angles of attack was carried out. To reduce the separated flow and improve the airfoil's performance, some kind of periodic forcing can b...

A. Dovgal

1993-01-01

340

Understanding wing lift  

NASA Astrophysics Data System (ADS)

The conventional explanation of aerodynamic lift based on Bernoulli's equation is one of the most common mistakes in presentations to school students and is found in children's science books. The fallacies in this explanation together with an alternative explanation for aerofoil lift have already been presented in an excellent article by Babinsky (2003 Phys. Educ. 38 497-503). However, in Babinsky's explanation, the air friction forces are ignored and the flow-field curvature introduced by the aerofoil shape is understood intuitively. In this article, a simple analysis of the lift with friction forces incorporated is presented to give a more precise qualitative explanation.

Silva, J.; Soares, A. A.

2010-05-01

341

NOVA: Lift and Drag  

NSDL National Science Digital Library

This interactive tutorial examines the aerodynamic forces of lift and drag. Students explore the two principles that combine to produce lift: the Bernoulli Effect and Newton's Third Law. The tutorial discusses why wing shape alone cannot create lift. Airplanes stay aloft because the wing pushes air down; the corresponding reaction occurs as air pushes the wing up. This paired action/reaction, along with wing shape and airspeed, interact to produce flight. This resource is part of the NOVA digital collection on space and flight.

2011-10-03

342

Technical Report of National Aerospace Laboratory: Experimental Investigations on High Lift Devices for an SST. Part 3 Lift to Drag Ration Improvement by Leading-Edge Flap at Transonic Regions.  

National Technical Information Service (NTIS)

Wind tunnel tests were conducted to investigate lift to drag ratio improvement by the leading-edge flap of the outer wing on an SST model at transonic regions. Force measurements and surface pressure measurements were performed for the SST model with and ...

D. Y. Kwak K. Miyata M. Noguchi K. Yoshida K. Rinoie

2003-01-01

343

Design based on Pro\\/E for a hydraulic scissors lift platform  

Microsoft Academic Search

In this paper, a scissors lift platform is designed which with a wide range, the main platform, lift mechanism and the bottom. When lifting from low to high, the scissors posts, and the hydraulic cylinder layout multiple, mobile way will be changed. The scissors post number and cylinder layout depend on the lifting height needed. This paper is about a

Tian Hongyu; Liu Haiyang

2011-01-01

344

The effect of stance width on trunk kinematics and trunk kinetics during sagitally symmetric lifting  

Microsoft Academic Search

Lifting technique can have a significant impact on spine loading during lifting. The sports biomechanics literature has documented changes in trunk and lower extremity kinematics and muscle coactivation patterns as a function of stance width during high force dead lift and squat exercises. The focus of the current study was to explore whether these lifting stance width effects might translate

Christopher J. Sorensen; Omid Haddad; Samuel Campbell; Gary A. Mirka

2011-01-01

345

Dynamic stall simulation of a pitching airfoil under unsteady freestream velocity  

NASA Astrophysics Data System (ADS)

Effects of horizontal oscillations of the freestream velocity superimposed on a pitch oscillating NACA0012 airfoil were investigated using Computational Fluid Dynamics (CFD). The SST k?? model coupled with a low-Reynolds number correction was applied for Re ?105, when the airfoil was undergoing dynamic stall. The main parameter ?, the phase difference between the freestream oscillation and the airfoil oscillation, was varied from 0 to ?. The ? variation resulted in several times amplitude dynamic loads when ???/2 to several times damping dynamic loads for ?>?/2 where some dynamic stall loads were damped even below static stall load values. It was found that ? variation was divided into two main ranges based on the values of the unsteady freestream velocity at dynamic stall. The load variation also appeared with some differences including the shape of the trailing edge vortex sheet before stall, the circulation of the dynamic stall vortex pairs, the critical angles, vortex growth time and the secondary lift peak location that are discussed in detail.

Gharali, Kobra; Johnson, David A.

2013-10-01

346

Past Projects - Lifting Bodies  

NASA Website

Publications To learn more about the HL-10 check out the following publications: Testing the Lifting Bodies at Edwards Wingless Flight These publications can be purchased by contacting the Dryden Public Affairs office at (661) 276-3449.

347

Hydraulic Lifting Device.  

National Technical Information Service (NTIS)

A piston and cylinder assembly is disclosed which is constructed of polyvinyl chloride that uses local water pressure to perform small lifting tasks. The chamber is either pressurized to extend the piston or depressurized to retract the piston. The presen...

K. Terrell

1990-01-01

348

Aerodynamic Lifting Force.  

ERIC Educational Resources Information Center

|Describes some experiments showing both qualitatively and quantitatively that aerodynamic lift is a reaction force. Demonstrates reaction forces caused by the acceleration of an airstream and the deflection of an airstream. Provides pictures of demonstration apparatus and mathematical expressions. (YP)|

Weltner, Klaus

1990-01-01

349

FREIGHT CONTAINER LIFTING STANDARD  

SciTech Connect

This standard details the correct methods of lifting and handling Series 1 freight containers following ISO-3874 and ISO-1496. The changes within RPP-40736 will allow better reading comprehension, as well as correcting editorial errors.

POWERS DJ; SCOTT MA; MACKEY TC

2010-01-13

350

BIOMECHANICAL SIMULATION OF HUMAN LIFTING  

Microsoft Academic Search

The aim of this paper is to simulate several levels of lifting strategies from parameters depending on the subject's centre of mass movements. Usually, symmetrical lifting strategies were categorized in two major solutions (Chaffin and Andersson, 1991): the squat lift that mainly involves a knee flexion and the back lift that mainly involves hip flexions. In the literature two main

COLOBERT B. MULTON

351

Tool for Automatic Design of Airfoils in Different Operating Conditions.  

National Technical Information Service (NTIS)

An optimization procedure is described which applies to the design of airfoils able to satisfy requirements essentially set for transonic flight. Suitable airfoils are obtained through radical changes of the starting geometry with little time consumption....

L. Ghielmi R. Marazzi A. Baron

1990-01-01

352

Prediction of Unsteady Airfoil Flows at Large Angles of Incidence.  

National Technical Information Service (NTIS)

The effect of the unsteady motion of an airfoil on its stall behavior is of considerable interest to many practical applications including the blades of helicopter rotors and of axial compressors and turbines. Experiments with oscillating airfoils, for ex...

T. Cebeci H. M. Jang H. H. Chen

1992-01-01

353

High Mach Number Leading-edge Flow Separation Control using AC DBD Plasma Actuators  

NASA Astrophysics Data System (ADS)

Wind tunnel experiments were conducted to quantify the effectiveness of alternating current dielectric barrier discharge flow control actuators to suppress leading-edge stall on a NASA energy efficient transport airfoil at compressible freestream speeds. The objective of this research was to increase lift, reduce drag, and improve the stall characteristics of the supercritical airfoil near stall by flow reattachment at relatively high Mach and Reynolds numbers. In addition, the effect of unsteady (or duty cycle) operation on these aerodynamic quantities was also investigated. The experiments were conducted for a range of Mach numbers between 0.1 and 0.4. corresponding to a Reynolds number range of 560,000 through 2,260,000. Lift, drag, quarter chord moment, and suction side pressures were measured near stall for baseline, steady actuation, and a scan of nondimensional duty cycle frequencies. The results show that the plasma actuators were effective at reattaching the leading-edge separated flow as evidenced by the increase in maximum lift coefficient and stall angle (as much as 2.5 degrees). The experiment also showed that lift was increased the most when the plasma actuator was operated unsteady with a nondimensional frequency of unity.

Kelley, Christopher; Bowles, Patrick; Cooney, John; He, Chuan; Corke, Thomas; Osborne, Bradley; Silkey, Joseph; Zehnle, Joseph

2011-11-01

354

Direct simulations of trailing-edge noise generation from two-dimensional airfoils at low Reynolds numbers  

Microsoft Academic Search

The aeroacoustic sound generated from the flow around two NACA four-digit airfoils is investigated numerically, at relatively low Reynolds numbers that do not prompt boundary-layer transition. By using high-order finite-difference schemes to discretize compressible Navier-Stokes equations, the sound scattered on airfoil surface is directly resolved as an unsteady pressure fluctuation. As the wavelength of an emitted noise is shortened compared

Tomoaki Ikeda; Takashi Atobe; Shohei Takagi

2012-01-01

355

SELF-INDUCED PITCHING OSCILLATIONS OF AN AIRFOIL  

Microsoft Academic Search

Self-induced oscillations of a NACA0012 airfoil have been investigated experimentally via particle image velocimetry in conjunction with simultaneous acceleration measurements. The study aims to correlate instantaneous moments acting on and flow structures around the airfoil. The paper constitutes the first phase of the investigation where the flow around the airfoil has been visualized while it undergoes oscillations at various frequencies

E. Tinar; O. Cetiner

356

Recent Progress in the Analysis of Iced Airfoils and Wings.  

National Technical Information Service (NTIS)

Recent work on the analysis of iced airfoils and wings is described. Ice shapes for multielement airfoils and wings are computed using an extension of the LEWICE code that was developed for single airfoils. The aerodynamic properties of the iced wing are ...

T. Cebeci H. H. Chen K. Kaups S. Schimke

1992-01-01

357

On the unsteady motion and stability of a heaving airfoil in ground effect  

NASA Astrophysics Data System (ADS)

This study explores the fluid mechanics and force generation capabilities of an inverted heaving airfoil placed close to a moving ground using a URANS solver with the Spalart-Allmaras turbulence model. By varying the mean ground clearance and motion frequency of the airfoil, it was possible to construct a frequency-height diagram of the various forces acting on the airfoil. The ground was found to enhance the downforce and reduce the drag with respect to freestream. The unsteady motion induces hysteresis in the forces' behaviour. At moderate ground clearance, the hysteresis increases with frequency and the airfoil loses energy to the flow, resulting in a stabilizingmotion. By analogy with a pitching motion, the airfoil stalls in close proximity to the ground. At low frequencies, the motion is unstable and could lead to stall flutter. A stall flutter analysis was undertaken. At higher frequencies, inviscid effects overcome the large separation and the motion becomes stable. Forced trailing edge vortex shedding appears at high frequencies. The shedding mechanism seems to be independent of ground proximity. However, the wake is altered at low heights as a result of an interaction between the vortices and the ground.

Molina, Juan; Zhang, Xin; Angland, David

2011-04-01

358

Reduced-order modeling of transonic flows around an airfoil submitted to small deformations  

NASA Astrophysics Data System (ADS)

A reduced-order model (ROM) is developed for the prediction of unsteady transonic flows past an airfoil submitted to small deformations, at moderate Reynolds number. Considering a suitable state formulation as well as a consistent inner product, the Galerkin projection of the compressible flow Navier-Stokes equations, the high-fidelity (HF) model, onto a low-dimensional basis determined by Proper Orthogonal Decomposition (POD), leads to a polynomial quadratic ODE system relevant to the prediction of main flow features. A fictitious domain deformation technique is yielded by the Hadamard formulation of HF model and validated at HF level. This approach captures airfoil profile deformation by a modification of the boundary conditions whereas the spatial domain remains unchanged. A mixed POD gathering information from snapshot series associated with several airfoil profiles can be defined. The temporal coefficients in POD expansion are shape-dependent while spatial POD modes are not. In the ROM, airfoil deformation is introduced by a steady forcing term. ROM reliability towards airfoil deformation is demonstrated for the prediction of HF-resolved as well as unknown intermediate configurations.

Bourguet, Rémi; Braza, Marianna; Dervieux, Alain

2011-01-01

359

Active Flow Separation Control of a Laminar Airfoil at Low Reynolds Number  

NASA Astrophysics Data System (ADS)

Detailed investigation of the NACA 643-618 is obtained at a Reynolds number of 6.4x104 and angle of attack sweep of -5° < alpha < 25°. The baseline flow is characterized by four distinct regimes depending on angle of attack, each exhibiting unique flow behavior. Active flow control is exploited from a row of discrete holes located at five percent chord on the upper surface of the airfoil. Steady normal blowing is employed at four representative angles; blowing ratio is optimized by maximizing the lift coefficient with minimal power requirement. The range of effectiveness of pulsed actuation with varying frequency, duty cycle and blowing ratio is explored. Pulsed blowing successfully reduces separation over a wide range of reduced frequency (0.1-1), blowing ratio (0.5--2), and duty cycle (0.6--50%). A phase-locked investigation, by way of particle image velocimetry, at ten degrees angle of attack illuminates physical mechanisms responsible for separation control of pulsed actuation at a low frequency and duty cycle. Temporal resolution of large structure formation and wake shedding is obtained, revealing a key mechanism for separation control. The Kelvin-Helmholtz instability is identified as responsible for the formation of smaller structures in the separation region which produce favorable momentum transfer, assisting in further thinning the separation region and then fully attaching the boundary layer. Closed-loop separation control of an oscillating NACA 643-618 airfoil at Re = 6.4x104 is investigated in an effort to autonomously minimize control effort while maximizing aerodynamic performance. High response sensing of unsteady flow with on-surface hot-film sensors placed at zero, twenty, and forty percent chord monitors the airfoil performance and determines the necessity of active flow control. Open-loop characterization identified the use of the forty percent sensor as the actuation trigger. Further, the sensor at twenty percent chord is used to distinguish between pre- and post- leading edge stall; this demarcation enables the utilization of optimal blowing parameters for each circumstance. The range of effectiveness of the employed control algorithm is explored, charting the practicality of the closed-loop control algorithm. To further understand the physical mechanisms inherent in the control process, the transients of the aerodynamic response to flow control are investigated. The on-surface hot-film sensor placed at the leading edge is monitored to understand the time delays and response times associated with the initialization of pulsed normal blowing. The effects of angle of attack and pitch rate on these models are investigated. Black-box models are developed to quantify this response. The sensors at twenty and forty percent chord are also monitored for a further understanding of the transient phenomena.

Packard, Nathan Owen

360

A Moving Airfoil Controlled by Synthetic Jets  

NASA Astrophysics Data System (ADS)

There is a growing interest in synthetic jets in flow controls. Here we consider the use of synthetic jet actuators in active control of an airfoil. An adaptive controller is integrated with a CFD model which includes details of the synthetic jet actuators and detached eddy simulation for turbulent flows at Re=900,000. This integration allows us to investigate a moving airfoil controlled by synthetic jets. Two synthetic jet actuators are mounted on the top and bottom of a NACA 4415 airfoil close to the trailing edge to generate bi-directional aerodynamic moment. Aerodynamic performance is explored using the closed-loop controller to regulate 2-degree-of-freedom motions of the airfoil. The coupled CFD/controller model simulates maneuverings of the airfoil as studied experimentally in wind tunnel tests. Modeling of unsteady aerodynamics with synthetic jets is validated against measurements in the wind tunnel including aerodynamic forces, surface pressure distributions and PIV velocity fields. The coupled model also demonstrates rapid maneuvers on the order of the convecting time scale. The characteristics of the unsteady aerodynamics coupled with the vehicle dynamics and the synthetic jets will be discussed.

Jee, Sol Keun; Lopez, Omar; Moser, Robert; Kutay, Ali; Muse, Jonathan; Calise, Anthony

2009-11-01

361

Boundary Layer Resolved Measurements of Unsteady Leading Edge Separation on a Pitching Airfoil  

NASA Astrophysics Data System (ADS)

When an airfoil pitches rapidly to high angles of attack, the flow can remain attached well beyond the static stall angle. The flow will eventually separate from the leading edge culminating in the formation of the dynamic stall vortex. While this flow has been the subject of numerous studies, the details of the flow within the boundary layer at the onset of separation have not been captured experimentally to date. Using Molecular Tagging Velocimetry (MTV), we have obtained the first boundary layer resolved measurements of flow separation near the leading edge of a pitching airfoil. The data provide a detailed picture of the evolution of the velocity and spanwise vorticity for an airfoil executing a ramp motion trajectory. Results are compared with 2-D Navier-Stokes computations for flow conditions similar to our experiments. The experimental data suggest that the process of boundary layer separation occurs over a shorter time scale, and is more eruptive, than that captured by the computations.

Gendrich, Charles P.; Koochesfahani, Manoochehr

1998-11-01

362

Numerical Simulation of Shock-stall Flutter of an Airfoil using the Navier-Stokes Equations  

NASA Astrophysics Data System (ADS)

In order to confirm qualitatively that the experimentally observed, unusual flutter phenomenon for a high-aspect-ratio (non-tailored) forward swept wing model is indeed shock-stall flutter, the aeroelastic response calculation of a two-dimensional airfoil whose vibration characteristics are similar to those of the typical section of a forward swept wing, has been performed by solving the compressible Navier-Stokes equations. By examination of the flow pattern, pressure distribution and the behavior of the unsteady aerodynamic forces during the diverging oscillation of the airfoil, it is concluded that (i) this is a shock-stall flutter, in which the large-scale shock-induced flow separation plays a dominant role and (ii) there is a mechanism of energy input into the elastic system of the airfoil, leading to nearly a single-degree-of-freedom flutter.

Isogai, K.

1993-08-01

363

Airfoil flow instabilities induced by background flow oscillations  

NASA Astrophysics Data System (ADS)

The effect of background flow oscillations on transonic airfoil (NACA0012) flow was investigated experimentally. The oscillations were generated by means of a rotating plate placed downstream of the airfoil. Owing to oscillating chocking of the flow caused by the plate, the airfoil flow periodically accelerated and decelerated. This led to strong variations in the surface pressure and the airfoil loading. The results are presented for two angles of attack, ?=4° and ?=8.5°, which correspond to the attached and separated steady airfoil flows, respectively.

Selerowicz, W. C.; Szumowski, A. P.

364

4. DETAIL OF VERTICAL LIFT SPAN SHOWING CONCRETE PIERS, LIFT ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

4. DETAIL OF VERTICAL LIFT SPAN SHOWING CONCRETE PIERS, LIFT TOWERS, AND THROUGH TRUSS, LOOKING SOUTHEAST. - Shippingsport Bridge, Spanning Illinois River at State Route 51, La Salle, La Salle County, IL

365

Interior view of lift mechanism area of eastern lift span, ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Interior view of lift mechanism area of eastern lift span, showing trunion gears at left and right, and counterweight above. - Arlington Memorial Bridge, Spanning Potomac River between Lincoln Memorial & Arlington National Cemetery, Washington, District of Columbia, DC

366

Interior view of lift mechanism area of eastern lift span ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Interior view of lift mechanism area of eastern lift span looking south, showing trunion gears at left and right, and counterweight above. - Arlington Memorial Bridge, Spanning Potomac River between Lincoln Memorial & Arlington National Cemetery, Washington, District of Columbia, DC

367

Lift and Drag Prediction in Supersonic Region Based on Momentum Conservation Theory  

NASA Astrophysics Data System (ADS)

Recently, as advanced drag prediction method in transonic region, a drag decomposition method is watched with keen interest. This method is based on and extended from the momentum conservation theory on the closed integral surface around the airplane, which is usually called ‘Control Volume Method’ (CVM). In this paper, aiming the next target which is the drag decomposition in supersonic flows, the validation study of the CVM in the supersonic region was conducted. Two dimensional structured mesh computation of NACA0012 airfoil was used for the investigation. At the lift and drag prediction using the CVM in the supersonic region, the discontinuous variation or oscillation of the lift and drag value was observed when the integral surface was set to some particular positions related to the generated shock waves. By the avoidance of the inappropriate positions, however, the good performance of the lift and drag prediction using CVM was achieved.

Yamazaki, Wataru; Kusunose, Kazuhiro; Matsushima, Kisa; Nakahashi, Kazuhiro

368

On the acoustic radiation of a pitching airfoil  

NASA Astrophysics Data System (ADS)

We examine the acoustic far field of a thin elastic airfoil, immersed in low-Mach non-uniform stream flow, and actuated by small-amplitude sinusoidal pitching motion. The near-field fluid-structure interaction problem is analyzed using potential thin-airfoil theory, combined with a discrete vortex model to describe the evolution of airfoil trailing edge wake. The leading order dipole-sound signature of the system is investigated using Powell-Howe acoustic analogy. Compared with a pitching rigid airfoil, the results demonstrate a two-fold effect of structure elasticity on airfoil acoustic field: at actuation frequencies close to the system least stable eigenfrequency, elasticity amplifies airfoil motion amplitude and associated sound levels; however, at frequencies distant from this eigenfrequency, structure elasticity acts to absorb system kinetic energy and reduce acoustic radiation. In the latter case, and with increasing pitching frequency ?p, a rigid-airfoil setup becomes significantly noisier than an elastic airfoil, owing to an ?p5/2 increase of its direct motion noise component. Unlike rigid airfoil signature, it is shown that wake sound contribution to elastic airfoil radiation is significant for all ?p. Remarkably, this contribution contains, in addition to the fundamental pitching frequency, its odd multiple harmonics, which result from nonlinear interactions between the airfoil and the wake. The results suggest that structure elasticity may serve as a viable means for design of flapping flight noise control methodologies.

Manela, A.

2013-07-01

369

User's manual for ADAM (Advanced Dynamic Airfoil Model)  

SciTech Connect

The computer code for an advanced dynamic airfoil model (ADAM) is described. The code is capable of calculating steady or unsteady flow over two-dimensional airfoils with allowances for boundary layer separation. Specific types of airfoil motions currently installed are steady rectilinear motion, impulsively started rectilinear motion, constant rate pitching, sinusoidal pitch oscillations, sinusoidal lateral plunging, and simulated Darrieus turbine motion. Other types of airfoil motion may be analyzed through simple modifications of a single subroutine. The code has a built-in capability to generate the geometric parameters for a cylinder, the NACA four-digit series of airfoils, and a NASA NLF-0416 laminar airfoil. Other types of airfoils are easily incorporated. The code ADAM is currently in a state of development. It is theoretically consistent and complete. However, further work is needed on the numerical implementation of the method.

Oler, J.W.; Strickland, J.H.; Im, B.J.

1987-06-01

370

Aspects of the influence of an oscillating mini-flap upon the near wake of an airfoil NACA 4412  

NASA Astrophysics Data System (ADS)

A NACA 4412 airfoil was tested, in a boundary layer wind tunnel, with the aim to study the effect of a Gurney mini-flap, as an active and passive flow control device submitted to a turbulent flow field. The main objective was the experimental determination of flow pattern characteristics downstream the airfoil in the near wake. The untwisted wing model used for the experiments had 80cm wingspan and 50cm chord, with airfoil NACA 4412. The mini-flap was located on the lower surface at a distance, from the trailing edge, of 8%c (c airfoil chord). The Reynolds number, based upon the wing chord and the mean free stream velocity was 326,000 and 489,000. The turbulence intensity was 1.8%. The model was located into the wind tunnel between two panels, in order to assure a close approximation to two-dimensional flow over the model. As an active control device a rotating mini-flaps, geared by an electromechanical system (which rotate to a 30°) was constructed. The wake pattern and pressure values near the trailing edge were measured. The results obtained, for this mechanism, show us that the oscillating mini-flap change the wake flow pattern, alleviating the near wake turbulence and enhancing the vortex pair near the trailing edge at the mini-flap level and below that level, magnifying the effect described first by Liebeck [1]. That effect grows with the oscillating frequency. Additionally, the wake alleviation probably affects also the far wake. All of these facts suggest us to continue with the experiments, trying to measure the pressure distribution around the airfoil in all the cases, obtaining the lift and drag characteristics.

Delnero, J. S.; Marañón Di Leo, J.; Colman, J.; García Sainz, M.; Muñoz, F.; Hérouard, N.; Camocardi, M. E.

2011-05-01

371

Mathematical Analysis of Scissor Lifts.  

National Technical Information Service (NTIS)

This document presents mathematical techniques for analyzing reaction forces in scissor lifts. It also presents several design issues including actuator placement, member cross-section, and rigidity. Keywords: Jacks(Lifts), Mathematical analysis, Actuator...

H. M. Spackman

1989-01-01

372

Drag and lift  

NSDL National Science Digital Library

This activity introduces students to the aerodynamic basics of lift and drag. The materials needed are pieces of cardboard 20 x 30 inches and other size cardboard pieces. This would be a suitable activity for small groups. Copyright 2005 International Technology Education Association

Aerospace, Cislunar

1997-01-01

373

ESB Heavy Lift Requirements.  

National Technical Information Service (NTIS)

Operation Iraqi Freedom (OIF) has produced many examples that illustrate the abysmal heavy lift situation within USMC Engineer Support Battalions (ESBs). For example, in one instance during OIF I, Bridge Company C, 8th ESB crossed the Line of Departure in...

C. Darnell

2006-01-01

374

Lifting as You Climb  

ERIC Educational Resources Information Center

This article addresses leadership themes and answers leadership questions presented to "Exchange" by the Panel members who attended the "Exchange" Panel of 300 Reception in Dallas, Texas, last November. There is an old proverb that encourages people to lift as they climb: "While you climb a mountain, you must not forget others along the way." With…

Sullivan, Debra R.

2009-01-01

375

Eyebolts for Lift Suspension.  

National Technical Information Service (NTIS)

BS529 was first published in 1944. It was divided into two parts, Part 1 specified Steel Eyebolts With Collars and Part 2 specified Steel Eyebolts Without Collars for Lift Suspension. Subsequent to its publication, BS529 was amended several times and even...

T. Gorley

1984-01-01

376

Artificial lift concepts and timing  

Microsoft Academic Search

Selecting the best time to install artificial lift is a hard decision, and escalating oil prices are changing previously accepted practices with regard to artificial lift. Operating practices (abandonment water cut, well spacing, capacity of lift system, separator pressure, etc.) all contribute to the decision-making process. Initial equipment cost, and present and predicted future also must be considered. This work

1980-01-01

377

Criteria for the forehead lift  

Microsoft Academic Search

We have developed clinically useful measurements to assist the surgeon in deciding when to do the forehead lift and where to place the incision. Also, we have reviewed our experience over the past decade and discuss the four categories and applications of forehead lifts. We use three indications for forehead lift: ptosis, creases, and previous facelift (PCP). There are four

Peter McKinney; Raymond D. Mossie; Mark L. Zukowski

1991-01-01

378

Computational prediction of airfoil dynamic stall  

Microsoft Academic Search

The term dynamic stall refers to unsteady flow separation occurring on aerodynamic bodies, such as airfoils and wings, which execute an unsteady motion. The prediction of dynamic stall is important for flight vehicle, turbomachinery, and wind turbine applications. Due to the complicated flow physics of the dynamic stall phenomenon the industry has been forced to use empirical methods for its

John A. Ekaterinaris; Max F. Platzer

1998-01-01

379

Drag Characteristics for a Compliant Surface Airfoil.  

National Technical Information Service (NTIS)

As part of a program to investigate the feasibility of reducing aerodynamic skin-friction drag by the use of compliant coatings, a detailed wind-tunnel study was made to determine the drag characteristics of a compliant coating on a airfoil. The compliant...

H. H. Chu

1971-01-01

380

Tailored airfoils for Vertical Axis Wind Turbines*  

SciTech Connect

The evolution of a family of airfoil sections designed to be used as blade elements of a vertical axis wind turbine (VAWT) is described. This evolution consists of extensive computer simulation, wind tunnel testing and field testing. The process reveals that significant reductions in system cost-ofenergy and increases in fatigue lifetime may be expected for VAWT systems using these blade elements.

Klimas, P.C.

1984-08-01

381

Tailored airfoils for vertical axis wind turbines  

SciTech Connect

The evolution of a family of airfoil sections designed to be used as blade elements of a vertical axis wind turbine (VAWT) is described. This evolution consists of extensive computer simulation, wind tunnel testing and field testing. The process reveals that significant reductions in system costs-of-energy and increases in fatigue lifetime may be expected for VAWT systems using these blade elements.

Klimas, P.C.

1984-01-01

382

Tailored airfoils for vertical axis wind turbines  

SciTech Connect

The evolution of a family of airfoil sections designed to be used as blade elements of a vertical axis wind turbine (VAWT) is described. This evolution consists of extensive computer simulation, wind tunnel testing and field testing. The process reveals that significant reductions in system costs-of-energy and increases in fatigue lifetime may be expected for VAWT systems using these blade elements.

Klimas, P.C.

1984-11-01

383

Noise prediction of a low speed airfoil  

Microsoft Academic Search

The goal of this work is accurate and efficient prediction of flow generated noise in the presence of solid objects. Flow around a low speed airfoil is considered at chord Reynolds number of Re = 150 000. This flow configuration represents an important aeroacoustics problem with complex physical effects including solid boundaries, boundary layers with pressure gradient, transition and turbulent

Yaser Khalighi; Meng Wang; Daniel Bodony; Parviz Moin

2006-01-01

384

Leading-Edge Vortices Elevate Lift of Autorotating Plant Seeds  

Microsoft Academic Search

As they descend, the autorotating seeds of maples and some other trees generate unexpectedly high lift, but how they attain this elevated performance is unknown. To elucidate the mechanisms responsible, we measured the three-dimensional flow around dynamically scaled models of maple and hornbeam seeds. Our results indicate that these seeds attain high lift by generating a stable leading-edge vortex (LEV)

D. Lentink; W. B. Dickson; J. L. van Leeuwen; M. H. Dickinson

2009-01-01

385

Drag coefficient accuracy improvement by means of particle image velocimetry for a transonic NACA0012 airfoil  

NASA Astrophysics Data System (ADS)

A method to improve the reliability of the drag coefficient computation by means of particle image velocimetry measurements is made using experimental data acquired on a NACA0012 airfoil tested in the transonic regime, using the combination of a variable pulse separation with a new high-order Poisson spectral pressure reconstruction algorithm.

Ragni, D.; van Oudheusden, B. W.; Scarano, F.

2011-01-01

386

Effects of surface roughness and freestream turbulence on the wake turbulence structure of a symmetric airfoil  

Microsoft Academic Search

The effects of surface roughness on the wake characteristics of a simulated turbine airfoil, operating in a compressible, high-speed environment, are studied at different freestream turbulence levels. The effects of these parameters on wake distributions of mean velocity, turbulence intensity, and turbulence length scale, as well as on power spectral density profiles and vortex shedding frequencies are quantified one chord

Qiang Zhang; Sang Woo Lee; Phillip M. Ligrani

2004-01-01

387

Aerodynamic force and flow structures of two airfoils in flapping motions  

NASA Astrophysics Data System (ADS)

Aerodynamic force and flow structures of two airfoils in a tandem configuration in flapping motions are studied, by solving the Navier-Stokes equations in moving overset grids. Three typical phase differences between the fore- and aftairfoil flapping cycles are considered. It is shown that: (1) in the case of no interaction (single airfoil), the time average of the vertical force coefficient over the downstroke is 2.74, which is about 3 times as large as the maximum steady-state lift coefficient of a dragonfly wing; the time average of the horizontal force coefficient is 1.97, which is also large. The reasons for the large force coefficients are the acceleration at the beginning of a stroke, the delayed stall and the “pitching-up” motion near the end of the stroke. (2) In the cases of two-airfoils, the time-variations of the force and moment coefficients on each airfoil are broadly similar to that of the single airfoil in that the vertical force is mainly produced in downstroke and the horizontal force in upstroke, but very large differences exist due to the interaction. (3) For in-phase stroking, the major differences caused by the interaction are that the vertical force on FA in downstroke is increased and the horizontal force on FA in upstroke decreased. As a result, the magnitude of the resultant force is almost unchanged but it inclines less forward. (4) For counter stroking, the major differences are that the vertical force on AA in downstroke and the horizontal force on FA in upstroke are decreased. As a result, the magnitude of the resultant force is decreased by about 20 percent but its direction is almost unchanged. (5) For 90°-phase-difference stroking, the major differences are that the vertical force on AA in downstroke and the horizontal force on FA in upstroke are decreased greatly and the horizontal force on AA in upstroke increased. As a result, the magnitude of the resultant force is decreased by about 28% and it inclines more forward. (6) Among the three cases of phase angles, inphase flapping produces the largest vertical force (also the largest resultant force); the 90°-phase-difference flapping results in the largest horizontal force, but the smallest resultant force.

Shilong, Lan; Mao, Sun

2001-11-01

388

Development of OTEC lift cycles  

SciTech Connect

An OTEC lift cycle system may be considered an open power cycle that uses an hydraulic turbine for power generation instead of the very low pressure steam turbine used in the Claude open cycle. It offers an alternate approach to the utilization of ocean thermal energy. The lift cycle power plant can have many different system options depending on the lift process employed. Foam and mist lift processes are presently under development sponsored by the US Department of Energy and are currently in the technical feasibility development stage. The concept of lift cycles, recent developments, preliminary cost estimates, and possible further activities are presented.

Chen, F.C.; Michel, J.W.

1980-01-01

389

Numerical investigation of the tone noise mechanism over laminar airfoils  

NASA Astrophysics Data System (ADS)

This paper presents the first numerical investigation via direct numerical simulation of the tone noise phenomenon occurring in the flow past laminar airfoils. This phenomenon corresponds to the radiation of discrete acoustic tones in some specific flow conditions, and has received much attention since the 1970s, and several experimental studies have been carried out to identify and understand the underlying physical mechanisms. However, several points remain to be clarified in order to provide a complete explanation of its origin. The flow around a two-dimensional NACA0012 airfoil is considered in order to have a deeper understanding of the tone noise phenomenon. Consistently with previous experimental studies, it is shown that depending on the Reynolds number and angle of attack, two different types of acoustic spectrum are observed: one which exhibits a broadband contribution with a dominant frequency together with a sequence of regularly spaced discrete frequencies, while the other one is only characterized by a simple broadband contribution. The first configuration is typical of the tone noise phenomenon. The present work shows that in this case, the mean flow on the pressure side of the airfoil exhibits a separation bubble near the trailing edge and the main tone frequency is close to the most amplified frequency of the boundary layer. The mechanism proposed in previous works for the main tone generation is therefore validated by numerical simulation. On the other hand, the analysis of the suction side boundary layer reveals that there is no separation and that the most amplified frequency is different from the main tonal one. However, the suction side boundary layer is highly receptive to the tone frequency. Finally, an original explanation for the existence of the secondary discrete frequencies observed in the radiated pressure spectrum is given. They are associated to a bifurcation of the airfoil wake from a symmetric to a non-symmetric vortex pattern. A possible explanation for the existence of this bifurcation is the interaction between the disturbances which are the most amplified by the suction side boundary layer and those originating in the forcing of the suction side flow by the main tone noise mechanism.

Desquesnes, G.; Terracol, M.; Sagaut, P.

390

Computational analysis of blunt, thin airfoil sections at supersonic and subsonic speeds  

NASA Astrophysics Data System (ADS)

The past decade has brought renewed interest in commercial supersonic aircraft design. Recent wing designs have included regions of low sweep resulting in supersonic leading edges at cruise. Thin biconvex sections are used in those regions to minimize wave drag and skin-friction drag. However, airfoil sections with sharp leading edges exhibit poor aerodynamic behavior at subsonic flight conditions. Blunt leading edges may improve performance by delaying the onset of separation at subsonic and transonic speeds. Their disadvantage is that they increase both wave drag, due to the formation of a detached bow wave, and skin-friction drag, from a loss of laminar flow. The effect of adding bluntness to a 4%-thick biconvex section was investigated using computational analysis tools. The aerodynamic performance of biconvex sections with circular leading edges was computed at supersonic, transonic, and takeoff conditions. At supersonic cruise, the increase in wave drag due to bluntness is a function of Mach number and leading-edge diameter. Some of the drag penalty is offset by the suction created downstream of the circular leading edge. The possibility of further drag reduction was explored with the development of a semi-analytical method to design blunt airfoil shapes which minimize wave drag. The effect on the transition location was evaluated using linear stability analyses of laminar boundary-layer profiles and the eN method. The analysis showed that laminar boundary layers on blunt airfoil sections are considerably less stable to Tollmien-Schlichting waves than that on a sharp biconvex. At transonic speeds, the results suggest a possible improvement in the lift-to-drag ratio over a limited range of angles of attack. At the takeoff condition, slight blunting of the leading edge does improve the lift-to-drag ratio at low angles of attack, but has little effect on maximum lift. It is concluded that the benefit of a blunt leading edge at off-design conditions is not sufficient to warrant the resulting drag penalty at supersonic cruise. Furthermore, if maintaining laminar flow is critical to the design and some bluntness is necessary for manufacturing purposes, then the leading-edge diameter should be minimized to prevent transition and to reduce wave drag.

Goodsell, Aga Myung

391

Face Lift Postoperative Recovery  

Microsoft Academic Search

.   The purpose of this paper is to describe what I have studied and experienced, mainly regarding the control and prediction\\u000a of the postoperative edema; how to achieve an agreeable recovery and give positive support to the patient, who in turn will\\u000a receive pleasant sensations that neutralize the negative consequences of the surgery.\\u000a \\u000a After the skin is lifted, the drainage

A. Aldo Mottura

2002-01-01

392

The subcutaneous forehead lift.  

PubMed

A limited experience (27 patients, all female) is presented utilizing the subcutaneous approach to forehead lifting. This approach has been little utilized and has been condemned in the literature for being dangerous. However, no difficulties in wound healing or alopecia have been encountered, and the procedure has the advantages of more effectively removing the vertical and transverse wrinkles in the glabellar region, raising the brows, and preserving sensation to the scalp posterior to the incision. PMID:2911624

Wolfe, S A; Baird, W L

1989-02-01

393

A Study of Sound Generation by an Airfoil via Direct Numerical Simulation  

NASA Astrophysics Data System (ADS)

Direct numerical simulations of sound generation associated with flow past a NACA0012 airfoil with a blunt trailing edge are performed. The simulations use the high resolution Dispersion-Relation-Preserving (DRP) time marching scheme and a body fitted grid constructed by conformal mapping. It is known experimentally that at Mach number around 0.1 and chord Reynolds number around 200,000 a strong tone is emitted. The primary objective of this study is to investigate the tone generation mechanism. We are also interested to determine the tone frequency and directivity. In the present numerical simulation, vortex shedding at the blunt trailing edge of the airfoil and the emission of a strong tone are observed. The tone frequencies over a range of Reynolds numbers measured in the simulations are in good agreement with experimental measurements. The directivity of the tones resembles closely to that of an oscillating dipole placed with the dipole axis perpendicular to the flow. An examination of the simulation data reveals that vortices are shed at the blunt trailing of the airfoil. However, after a very careful investigation of the wake flow it is believed that the vortex shedding process is not directly responsible for sound generation. The wake flow is highly unstable. A Kelvin-Helmholtz instability wave is excited slightly downstream of the airfoil trailing edge. The processes that generate the instability wave appear to generate the tone as a by-product.

Tam, Christopher; Ju, Hongbin

2004-11-01

394

Optimal aerodynamic design of airfoils in unsteady viscous flows  

Microsoft Academic Search

A continuous adjoint formulation is used to determine optimal airfoil shapes in unsteady viscous flows at Re=1×104. The Reynolds number is based on the free-stream speed and the chord length of the airfoil. A finite element method based on streamline-upwind Petrov\\/Galerkin (SUPG) and pressure-stabilized Petrov\\/Galerkin (PSPG) stabilizations is used to solve both the flow and adjoint equations. The airfoil is

D. N. Srinath; Sanjay Mittal

2010-01-01

395

Customized airfoils and their impact on VAWT cost of energy  

Microsoft Academic Search

Sandia National Laboratories has developed a family of airfoils specifically designed for use in the equatorial portion of a Vertical-Axis Wind Turbine (VAWT) blade. An airfoil of that family has been incorporated into the rotor blades of the DOE\\/Sandia 34-m diameter VAWT Test Bed. The airfoil and rotor design process is reviewed. Comparisons with data recently acquired from flow visualization

Dale E. Berg

1990-01-01

396

Soccer ball lift coefficients via trajectory analysis  

NASA Astrophysics Data System (ADS)

We performed experiments in which a soccer ball was launched from a machine while two high-speed cameras recorded portions of the trajectory. Using the trajectory data and published drag coefficients, we extracted lift coefficients for a soccer ball. We determined lift coefficients for a wide range of spin parameters, including several spin parameters that have not been obtained by today's wind tunnels. Our trajectory analysis technique is not only a valuable tool for professional sports scientists, it is also accessible to students with a background in undergraduate-level classical mechanics.

Goff, John Eric; Carré, Matt J.

2010-07-01

397

Detail of lift wire rope attachment to lift span at ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Detail of lift wire rope attachment to lift span at southeast corner. Note rope-adjustment turnbuckle with strap keepers to prevent its rotation, which could pull the bridge out of alignment. A single rope and light-gauge attachment at each corner were adequate for lifting the span because most of its weight was balanced by the two counterweights. - Potomac Edison Company, Chesapeake & Ohio Canal Bridge, Spanning C & O Canal South of U.S. 11, Williamsport, Washington County, MD

398

Flutter control based on ultrasonic motor for a two-dimensional airfoil section  

NASA Astrophysics Data System (ADS)

This paper presents how to use an ultrasonic motor, which features high torque at low speed, small size and low weight, as an actuator in the flutter control of a two-dimensional airfoil section. The paper begins with the design of a two-dimensional airfoil model with the piecewise-linear torsional stiffness in pitch direction and a control surface driven by an ultrasonic motor. Then, it gives the experimental modeling of the airfoil section and the servo, composed of the control surface and the ultrasonic motor, as well as the identification of system parameters through the use of a simple approach of nonlinear least squares estimation. Afterwards, the paper presents the dynamic equation of the aeroservoelastic equation based on Theodorsen's aerodynamic load, and the numerical simulations for the sub-optimal control of flutter. Finally, the paper outlines the experimental study of the flutter control of the airfoil section in a wind tunnel test, where the critical flutter speed of controlled system could be increased by 13.4%, and the flutter was effectively suppressed when the flow speed exceeded the critical flutter speed of the uncontrolled system.

Yu, Mingli; Hu, Haiyan

2012-01-01

399

Experimental Study of Boundary Layer Transition on an Airfoil Induced by Periodically Passing Wake  

NASA Astrophysics Data System (ADS)

Hot-wire measurements are performed in boundary layers developing on NACA0012 airfoil over which wakes pass periodically. The Reynolds number based on chord length of the airfoil is 200,000 and the wakes are generated by circular cylinders rotating clockwise and counterclockwise around the airfoil. The phase as well as the time averaged streamwise mean velocity, turbulent fluctuations and integral parameters are provided to investigate the phenomena of wake-induced transition. Especially, the phase averaged wall shear stresses are reasonably evaluated using the principle of computational Preston tube method. Due to the passing wake, the turbulent stripe is generated in the laminar boundary layer on the airfoil and the boundary layer become temporalily transitional. The stripes convect downstream with constant propagation rate and merge each other at futher downstream station and finally boundary layer become turbulent. In this transition process, the present experimental data show very similar features to the DNS result of X. Wu et al. (1999) and previous experimental studies. The two phase averaged mean velocitiy dips appear in the outer region of transitional boundary layer for each passing cycle and the calm regions exist in the boundary layer after turbulent stripes pass. Relatively high values of turbulent fluctuations in the outer region indicate the possibility that breakdown occurs in the outer layer not near the wall. * Supported by the grant of Korea Ministry of Education(96ME-B-03)

Kang, Shin-Hyoung; Jeon, Woo-Pyung; Park, Tae-Choon

1999-11-01

400

Turbine engine airfoil and platform assembly  

DOEpatents

A turbine airfoil (22A) is formed by a first process using a first material. A platform (30A) is formed by a second process using a second material that may be different from the first material. The platform (30A) is assembled around a shank (23A) of the airfoil. One or more pins (36A) extend from the platform into holes (28) in the shank (23A). The platform may be formed in two portions (32A, 34A) and placed around the shank, enclosing it. The two platform portions may be bonded to each other. Alternately, the platform (30B) may be cast around the shank (23B) using a metal alloy with better castability than that of the blade and shank, which may be specialized for thermal tolerance. The pins (36A-36D) or holes for them do not extend to an outer surface (31) of the platform, avoiding stress concentrations.

Campbell, Christian X. (Oviedo, FL); James, Allister W. (Chuluota, FL); Morrison, Jay A. (Oviedo, FL)

2012-07-31

401

Thrust vector control control using internal airfoils  

SciTech Connect

This patent describes an exhaust nozzle for an engine which generates thrust expulsion of gaseous products of fuel combustion. It comprises: a generally axisymmetric housing defined along a central thrust axis including a wall structure defining an exhaust duct, and axially adjacent radially inwardly converging portion, throat portion and radially outwardly diverging portion; and at least one airfoil sized to protrude into the exhaust a distance corresponding to about 15 to 35 percent of diameter of the throat portion disposed within the divergent portion at a location axially spaced from the axis portion a distance corresponding to from 20 per cent to 25 per cent of the axial extent of the divergent portion, the airfoil mounted on the wall structure for rotation about an axis substantially perpendicular to the thrust axis.

Herup, E.J.; Franke, M.E.; Friddell, J.H.

1992-10-13

402

A design and analysis approach for drag reduction on aircraft with adaptive lifting surfaces  

NASA Astrophysics Data System (ADS)

Adaptive lifting surfaces, which can be tailored for different flight conditions, have been shown to be beneficial for drag reduction when compared with conventional non-adaptive surfaces. Applying multiple trailing-edge flaps along the wing span allows for the redistribution of lift to suit different flight conditions. The current approach uses the trailing-edge flap distribution to reduce both induced- and profile- components of drag with a trim constraint. Induced drag is reduced by optimally redistributing the lift between the lifting surfaces and along the span of each surface. Profile drag is reduced through the use of natural laminar flow airfoils, which maintain distinct low-drag-ranges (drag buckets) surrounding design lift values. The low-drag-ranges can be extended to include off-design values through small flap deflections, similar to cruise flaps. Trim is constrained for a given static margin by considering longitudinal pitching moment contributions from changes in airfoil section due to individual flap deflections, and from the redistribution of fore-and-aft lift due to combination of flap deflections. The approach uses the concept of basic and additional lift to linearlize the problem, which allows for standard constrained-minimization theory to be employed for determining optimal flap-angle solutions. The resulting expressions for optimal flap-angle solutions are presented as simple matrix equations. This work presents a design and analysis approach which is used to produce flap-angle solutions that independently reduce induced, profile, and total drag. Total drag is defined to be the sum of the induced- and profile-components of drag. The general drag reduction approach is adapted for each specific situation to develop specific drag reduction schemes that are applied to single- and multiple-surface configurations. Successful results show that, for the application of the induced drag reduction schemes on a tailless aircraft, near-elliptical lift distributions are produced which match the classical result for minimum induced drag. Application of the profile drag reduction schemes produce solutions which force the wing to operate in the low-drag-ranges of the natural-laminar-flow airfoil sections, thereby lowering profile drag. The total drag reduction schemes use a curve-fit routine that generates airfoil drag polars given flap angle and Reynolds number. The approximated drag polars allow the prediction of profile drag values to be combined with induced drag values to form a total drag function, which is utilized with a constrained nonlinear optimizer that determines best flap angles for total drag and trim. The different drag reduction schemes each produce independent flap-angle solutions and lift distributions for a given aircraft configuration and operating condition, and provide valuable insight for aerodynamic design and trade studies. The drag reduction approach is intended to be applicable to arbitrary aircraft configurations, and can be adapted to use surface incidence, twist, and flap angles as optimization variables, thereby creating a powerful and flexible aerodynamic design and analysis tool.

Cusher, Aaron Anthony

403

Saturation-free numerical scheme for computing the flow past a lattice of airfoils and the determination of separation points in a viscous fluid  

NASA Astrophysics Data System (ADS)

A numerical method for computing the potential flow past a lattice of airfoils is described. The problem is reduced to a linear integrodifferential equation on the lattice contour, which is then approximated by a linear system of equations with the help of specially derived quadrature formulas. The quadrature formulas exhibit exponential convergence in the number of points on an airfoil and have a simple analytical form. Due to its fast convergence and high accuracy, the method can be used to directly optimize the airfoils as based on any given integral characteristics. The shear stress distribution and the separation points are determined from the velocity distribution at the airfoil boundary calculated by solving the boundary layer equations. The method proposed is free of laborious grid generation procedures and does not involve difficulties associated with numerical viscosity at high Reynolds numbers.

Petrov, A. G.

2011-07-01

404

Effect of differential spoiler settings (DSS) on the wake vortices of a wing at high-lift-configuration (HLC)  

Microsoft Academic Search

An experimental investigation has been carried out to evaluate the capabilities of differential spoiler setting (DSS) in modifying the wingspan loading. The particle image velocimetery (PIV) technique was used in a low speed wind tunnel facility to measure wake velocities at four locations downstream of the half model in the near wake field. The model was investigated at a high

Omer A. Elsayed; Ashraf A. Omar; Waqar Asrar; Kijung Kwon

2011-01-01

405

Image based measurement techniques for aircraft propeller flow diagnostics: Propeller slipstream investigations at high-lift conditions and thrust reverse  

Microsoft Academic Search

The aim of the thesis is to measure the propeller slipstream properties (velocity and vorticity) and to assess the unsteady and instantaneous behavior of the propeller flow field at high disk loadings, zero thrust and thrust reverse using the image based measurement techniques. Along with its implementation of the techniques in industrial facilities particular propeller phenomena are addressed, such as

E. W. M. Roosenboom

2011-01-01

406

How to lift a box that is too large to fit between the knees.  

PubMed

Many studies compared lifting techniques such as stoop and squat lifting. Results thus far show that when lifting a wide load, high back loads result, irrespective of the lifting technique applied. This study compared four lifting techniques in 11 male subjects lifting wide loads. One of these techniques, denoted as the weight lifters' technique (WLT), is characterised by a wide foot placement, moderate knee flexion and a straight but not upright trunk. Net moments were calculated with a 3-D linked segment model and spinal forces with an electromyographic-driven trunk model. When lifting the wide box at handles that allow a high grip position, the WLT resulted in over 20% lower compression forces than the free, squat and stoop lifting technique, mainly due to a smaller horizontal distance between the l5S1 joint and the load. When lifting the wide box at the bottom, none of the lifting techniques was clearly superior to the others. STATEMENT OF RELEVANCE: Lifting low-lying and large objects results in high back loads and may therefore result in a high risk of developing low back pain. This study compares the utility of a WLT, in terms of back load and lumbar flexion, to more familiar techniques in these high-risk lifting tasks. PMID:20865606

Kingma, Idsart; Faber, Gert S; van Dieën, Jaap H

2010-10-01

407

Adaptive wavelet transforms via lifting  

Microsoft Academic Search

This paper develops two new adaptive wavelet transforms based on the lifting scheme. The lifting construction exploits a spatial-domain, prediction-error interpretation of the wavelet transform and provides a powerful framework for designing customized transforms. We use the lifting construction to adaptively tune a wavelet transform to a desired signal by optimizing data-based prediction error criteria. The performances of the new

Roger L. Claypoole; Richard G. Baraniuk; Robert D. Nowak

1998-01-01

408

Aerodynamic Flow Control of a Maneuvering Airfoil  

NASA Astrophysics Data System (ADS)

The unsteady aerodynamic forces and moments on a maneuvering, free-moving airfoil are varied in wind tunnel experiments by controlling vorticity generation/accumulation near the surface using hybrid synthetic jet actuators. The dynamic characteristics of the airfoil that is mounted on a 2-DOF traverse are controlled using position and attitude feedback loops that are actuated by servo motors. Bi-directional changes in the pitching moment are induced using controllable trapped vorticity concentrations on the suction and pressure surfaces near the trailing edge. The dynamic coupling between the actuation and the time-dependent flow field is characterized using simultaneous force and velocity measurements that are taken phase-locked to the commanded actuation waveform. The time scales associated with the actuation process is determined from PIV measurements of vorticity flux downstream of the trailing edge. Circulation time history shows that the entire flow over the airfoil readjusts within about 1.5 TCONV, which is about two orders of magnitude shorter than the characteristic time associated with the controlled maneuver of the wind tunnel model. This illustrates that flow-control actuation can be typically effected on time scales commensurate with the flow's convective time scale, and that the maneuver response is only limited by the inertia of the platform. Supported by AFSOR.

Brzozowski, Daniel P.; Culp, John; Glezer, Ari

2010-11-01

409

But can they lift?  

PubMed

Anybody who screens EMS field candidates will tell you, not just anybody can do EMS. You need a good brain to pass your tests, earn your certs and think your way through calls. You need the manual dexterity and multitasking capabilities of an ED nurse. You need the maturity and psychomotor skills of a professional driver. You need a warm and willing heart. And, no matter how talented you are in all of those areas, you need to be able to lift--often, a lot. PMID:18810957

Dick, Thom; Messersmith, Darrell

2008-06-01

410

Chair Lift Challenge  

NSDL National Science Digital Library

In this activity, learners explore the unique challenges in transportation engineering, such as devising a method for skiers or hikers to get to the top of a mountain. Students work in teams to design a chair lift made out of everyday materials that can carry a tennis ball up a rope line and back down in a controlled manner so that the ball does not fall out of the cup. They sketch their plans, consider material selection, build their system, test it, reflect on the challenge, and present their experiences to their class.

Ieee

2013-07-08

411

Air Lift: Ski Jump  

NSDL National Science Digital Library

The following resource is from Lessonopoly, which has created student activities and lesson plans to support the video series, Science of the Olympic Winter Games, created by NBC Learn and the National Science Foundation. Featuring exclusive footage from NBC Sports and contributions from Olympic athletes and NSF scientists, the series will help teach your students valuable scientific concepts. In this lesson, Students will learn about the ski-jumping competition in the Winter Olympics, to explore concepts about gravity, drag and lift. Students will create their own version of a ski jump complete with jumpers.

2010-01-01

412

Selection of artificial lift method  

SciTech Connect

This paper summarizes the opening remarks of the panel members on a panel discussion of 'Selection of Artificial Lift Method' held at the 56th annual Fall Technical Conference and Exhibition of the Society of Petroleum Engineers of AIME in San Antonio, Texas, October 5-7, 1981. The topics discussed include: (1) reservoir and well considerations involved in artificial lift design; (2) sucker rod pumping; (3) gas lift; (4) submersible pumping; and, (5) hydraulic pumping. Advantages and limitations of each lift method are considered.

Neely, B.; Gipson, F.; Clegg, J.; Capps, B.; Wilson, P.

1981-01-01

413

Optimizing production with artificial lift; Part 2 - How to lower operating costs  

SciTech Connect

This article addresses the costs associated with artificial lift. These include installation costs, power, repair, maintenance, and operating labor costs. The author discusses how these costs can be predicted. The emphasis of this article is on the selection of a proper lift system for cost effectiveness and the development of a program to maintain high lift efficiency throughout the life of the well.

Patton, L.D. (L.D. Patton and Associates, Aurora, CO (US))

1989-10-01

414

Artificial lift with coiled tubing for flow testing the Monterey formation, offshore California  

SciTech Connect

This paper provides a technical comparison of jet-pump and nitrogen lift during the drillstem tests (DST's) of a low-gravity, high-viscosity crude on a semisubmersible drilling vessel. Eight DST testing sequences are presented to demonstrate that jet-pump-lift operations are better suited than nitrogen-lift techniques for obtaining reservoir data during Monterey DST's.

Peavy, M.A.; Fahel, R.A. (Oryx Energy Company (US))

1991-05-01

415

LES of the trailing-edge flow and noise of a NACA6512-63 airfoil at zero angle of attack  

Microsoft Academic Search

Large-eddy simulations (LES) of flow over a low-speed highly cambered airfoil at small negative incidence is performed using two different flow solvers, CFX and Fluent, on a similar multi-block structured mesh. They mimic recent aeroacoustic experiments per- formed in the small anechoic wind tunnel at the University of Siegen. Focus has been put on the experiments where the airfoil was

J. Winkler; S. Moreau

416

Endoscopic brow lifts: have they replaced coronal lifts?  

PubMed

This article describes the use of the endoscopic brow-lifting technique in addressing periorbital aging. This article discusses the advantages and disadvantage of the endoscopic versus traditional techniques of brow lifting and gives our treatment algorithm depending on patient needs. PMID:23731581

Javidnia, Hedyeh; Sykes, Jonathan

2013-05-01

417

Study of a New Airfoil Used in Reversible Axial Fans.  

National Technical Information Service (NTIS)

The characteristics of the reverse ventilation of axial flow are analyzed. An s shaped airfoil with a double circular arc was tested in a wind tunnel. The experimental results showed that the characteristics of this new airfoil in reverse ventilation are ...

C. Li B. Wei C. Gu

1991-01-01

418

Computational Research on Inviscid, Unsteady, Transonic Flow Over Airfoils.  

National Technical Information Service (NTIS)

The inviscid transonic flow over an NACA 64A410 airfoil oscillating in pitch in a Mach 0.72 stream was calculated with a program based on the unsteady Euler equations. The airfoil oscillates about a mid-chord axis with attitude alpha = 1 deg + or - 1 deg ...

R. J. Magnus

1977-01-01

419

Experimental evidence of transient growth of energy before airfoil flutter  

Microsoft Academic Search

This paper presents an experimental evidence of the transient growth of energy for the coupled-mode flutter of an airfoil. The phenomenon occurs even in linearly stable dynamical systems. Its application is rather new in the context of fluid-structure interactions where only theoretical and numerical studies of transient growth exist. The experimental setup allows a NACA 0015 airfoil to oscillate in

P. Hémon; E. de Langre; P. Schmid

420

Sealing apparatus for airfoils of gas turbine engines  

DOEpatents

An improved airfoil tip sealing apparatus is disclosed wherein brush seals are attached to airfoil tips with the distal ends of the brush seal fibers sealingly contacting opposing wall surfaces. Embodiments for variable vanes, stators and both cooled and uncooled turbine blade applications are disclosed.

Jones, Russell B. (San Diego, CA)

1998-01-01

421

A Study of Aerodynamics of Low Reynolds Number Flexible Airfoils  

Microsoft Academic Search

The interaction between aerodynamics and structural flexibility in a low Reynolds number environment is of considerable interest to biological and micro air vehicles. In this study, coupled fluid-structure computations of the Navier-Stokes fluid flow and a flexible airfoil in low Reynolds number environments are conducted to probe the aerodynamic implications. While a flexible airfoil deforms in response to the aerodynamic

Jian Tang; Dragos Viieru; Wei Shyy

422

Method for the Constrained Design of Natural Laminar Flow Airfoils  

Microsoft Academic Search

An automated iterative design method has been developed by which an airfoil with a substantial amount of natural laminar è ow can be designed while maintaining other aerodynamic and geometric constraints. Drag reductions have been realized using the design method over a range of Mach numbers, Reynolds numbers, and airfoil thicknesses. The key features of the method are the compressible

Bradford E. Green; John L. Whitesides; Richard L. Campbell; Raymond E. Mineck

1997-01-01

423

Simplified dragonfly airfoil aerodynamics at Reynolds numbers below 8000  

Microsoft Academic Search

Effective aerodynamics at Reynolds numbers lower than 10 000 is of great technological interest and a fundamental scientific challenge. The current study covers a Reynolds number range of 2000-8000. At these Reynolds numbers, natural insect flight could provide inspiration for technology development. Insect wings are commonly characterized by corrugated airfoils. In particular, the airfoil of the dragonfly, which is able

David-Elie Levy; Avraham Seifert

2009-01-01

424

Adaptive Airfoils for Drag Reduction at Transonic Speeds  

Microsoft Academic Search

Adaptive airfoils and wings can provide superior performance at the expense of increased cost and complexity. In this paper, an aerodynamic optimization algorithm is used to assess an adaptive airfoil concept for drag reduction at transonic speeds. The objective is to quantify both the improvements in drag that can be achieved and the magnitude of the shape changes needed. In

David W. Zingg; Laslo Diosady; Laura Billing

425

Generation of discrete tones from airfoils at low Reynolds numbers  

Microsoft Academic Search

Attention is given to the behavior of flows generated about symmetric airfoils during low speed testing in low turbulence and tunnels; particular emphasis is placed on the discrete tones that are generated under appropriate freestream velocity conditions and appropriate angles of attack. The interactions that occur between the airfoil flows and the geometric acoustical characteristics of the wind tunnel test

M. W. Luttges; M. C. Robinson; H. E. Helin

1986-01-01

426

On the Design of Some Airfoils for Sailplane Application.  

National Technical Information Service (NTIS)

Airfoils were designed such that, by adding material to the surface, an existing wing could be modified and tested in flight. Wind tunnel experiments on inner and outer wing segments are described, giving information on the quality of actual airfoils achi...

L. M. M. Boermans H. J. W. Selen

1981-01-01

427

Influence of trailing edge tab on moment characteristics of NACA 23012 airfoil  

Microsoft Academic Search

A comparison of predicted and measured aerodynamic characteristics of the original NACA 23012 airfoil and an airfoil with a trailing edge tab is presented. XFOIL code is used for prediction. It is shown that the modification of the airfoils only on the upper side at the trailing edge affects practically only moment characteristics. An example of the airfoil modification with

E. Lasauskas; Th. Lutz; M. Dietz

2007-01-01

428

ROBUST AERODYNAMIC AIRFOIL DESIGN OPTIMIZATION AGAINST WIND VARIATIONS FOR MARS EXPLORATORY AIRPLANE  

Microsoft Academic Search

Robust aerodynamic airfoil design optimizations of Mars exploratory airplane against wind variations have been carried out by using DFMOSS coupled with the CFD simula- tion. The present robust optimizations successfully found the airfoil designs with robust aerodynamic performances against wind variations. Obtained airfoil design information about the optimality and the robustness of aerodynamic performances indicated that an airfoil with smaller

Koji Shimoyama; Akira Oyama; Kozo Fujii

429

Lifting as an Industrial Hazard  

Microsoft Academic Search

A great deal of accident prevention education has been directed toward the reduction of back injuries. This has not produced any great change in the incidence of this condition, and the author presents evidence that there can be no specific and mandatory method for lifting all loads. Virtually all types of lifting methods are possible and, in fact, are used

JOHN R. BROWN

1973-01-01

430

Knees Lifted High (Animated Book)  

MedlinePLUS Videos and Cool Tools

... Date: 12/15/2009 Mixing Tamiflu® with Sweet Liquids If your doctor prescribes Tamiflu® capsules for your ... them, they may be mixed with a thick liquid. Release Date: 11/13/2009 Influenza Round Table: ...

431

The synchronized coordinated control of tripartite hydraulic lifting platform  

Microsoft Academic Search

The hardware and software design of a tripartite hydraulic lifting platform control system is discussed in this paper, by which, the position of the platform can be controlled with high precision and its speed can be synchronized perfectly

Zhanming Li; Ruo-Zhu Chen; Juan Li

2000-01-01

432

Development of Nonpowered Lift for Wheelchair Users  

NASA Astrophysics Data System (ADS)

Wheelchair users need lifts to climb up/down steps at entrances with limited space. Lifts driven by motors or hydraulic equipment are large and expensive. They also need switches to start/stop actuators. The aim of our study is to develop a compact nonpowered lift for wheelchair users. We propose a lift driven by the wheels of a wheelchair on it. Coil springs are installed in the lift to decrease driving torque and some mechanisms are attached to the lift so that the small front casters of a wheelchair can cross the lift stage and the large rear wheels can drive the lift. After the lifting speed, driving force, and conditions for driving the rollers were analyzed and a prototype lift was designed and fabricated. The developed lift succeeded in raising a wheelchair with a user, and a continuous motion of a wheelchair from entering to exiting the stage was executed smoothly.

Kobayashi, Yusuke; Seki, Hiroaki; Kamiya, Yoshitsugu; Hikizu, Masatoshi; Maekawa, Mitsuyoshi

433

An improved method for calculating flow past flapping and hovering airfoils  

NASA Astrophysics Data System (ADS)

A method is reported here for calculating unsteady aerodynamics of hovering and flapping airfoil for two-dimensional flow via the following improved methodologies: (a) a correct formulation of the problem using stream function (?) and vorticity (?) as dependent variables; (b) calculating loads and moment by a new method to solve the governing pressure Poisson equation (PPE) in a truncated part of the computational domain on a nonstaggered grid; (c) accurate solution using high accuracy compact difference scheme for the vorticity transport equation (VTE) and (d) accelerating the computations by using a high-order filter after each time step of integration. These have been used to solve Navier-Stokes equation for flow past flapping and hovering NACA 0014 and 0015 airfoils at typical Reynolds numbers relevant to the study of unsteady aerodynamics of micro air vehicle (MAV) and insect/bird flight.

Sengupta, T. K.; Vikas, V.; Johri, A.

2005-12-01

434

Nonadiabatic model wall effects on transonic airfoil performance in a cryogenic wind tunnel  

NASA Astrophysics Data System (ADS)

The need to match the aircraft surface thermal conditions that exist at in-flight conditions when testing models in a cryogenic wind tunnel is addressed. Effects of non-representative heat transfer are reviewed for such basic viscous characteristics as the effect on boundary-layer transition location, the effects on turbulent boundary-layer integral parameters and skin friction, the effect on the transonic turbulent boundary-layer/shock-wave interaction, and the effects on separation onset and the extent of separated flow regions. A complementary experimental and computational investigation was conducted in order to help quantify the impact that nonadiabatic model wall conditions would have on the measured aerodynamic characteristics of transport (and other) airplane configurations tested in a cryogenic wind tunnel, and to help establish the allowable deviation from adiabatic wall conditions that can be tolerated if reliable results are to be obtained. Test results are presented which illustrate the large impact of moderate amounts of heat transfer on the lift and drag characteristics for both free-transition flow in the absence of any shock waves, and for typical cruise conditions with moderate strength shocks on the airfoil. In addition, test results are shown which illustrate a very large effect of heat transfer on buffer onset conditions and conditions near maximum lift.

Lynch, F. T.; Fancher, M. F.; Patel, D. R.; Inger, G. R.

1984-02-01

435

Flow visualization of the effect of pitch amplitude changes on the vortical signatures behind a three-dimensional flapping airfoil  

NASA Astrophysics Data System (ADS)

The structure of the vortical flow behind a symmetrical airfoil of finite aspect ratio undergoing combinations of heave and pitch motions is investigated using qualitative dye flow visualization. The results are contrasted with flow visualizations obtained using electrolytic precipitation. The effect of changing the pitch amplitude is observed from the plan from view and wingtip view of the airfoil. With a Strouhal number of 0.35, Reyholds number based on airfoil chord of 164 and a phase angle of 90o, the maximum pitch amplitude is varied from 0° to 20°. The geometry of the downstream vortical flow is observed to change suggesting that the induced velocity from interacting structures decreases at lower pitch amplitudes. The rate of dynamic stall development may also be affected by variations in pitch amplitude since it appears that the timing of leading edge separation is affected. The flow field of an airfoil flapping periodically about a fixed axis appears to be influenced by the amplitude of pitching oscillations. At the tested Strouhal numbers the vortex formations appear to be primarily dependent on airfoil oscillation rather than heave translation. Furthermore, the results suggest that the wake structures originating from the dynamic stall process are important for the analysis of these complex flows. While the results from the two flow visualization techniques are similar, the dye flow visualization images provide greater qualitative insight. Inherently, precipitative techniques such as the one used here could provide good flow visualizations since the smoke/particles leave the surface of the airfoil, but the setup is found to be very sensitive to potential changes. The ion content in the electrolytic material was also found to play a role. Furthermore, the high ablation rate of the technique presented some practical problems.

Parker, Kamalluddien; von Ellenrieder, K. D.; Soria, J.

2003-04-01

436

Detached and Large Eddy Simulation of Airfoil Flow on Semi-Structured Grids  

Microsoft Academic Search

This study aims at investigating the flow around a NACA 4412 airfoil at high Reynolds numbers and moderate angles of attack\\u000a on semistructured grids, which allow for a blockwise grid refinement in areas of physical interest (e.g. walls). Unlike other\\u000a configurations using Large Eddy Simulation (LES), this flow features only a small pressure-induced separation bubble at the\\u000a trailing edge of

S. Schmidt; F. Thiele

437

Discrete conservation principles in large-eddy simulation with application to separation control over an airfoil  

Microsoft Academic Search

An unstructured-grid large-eddy simulation (LES) technique is used to investigate the turbulent flow separation over an airfoil with and without synthetic-jet control. Numerical accuracy and stability on arbitrary shaped mesh elements at high Reynolds numbers are achieved using a finite-volume discretization of the incompressible Navier-Stokes equations based on higher-order conservation principles-i.e., in addition to mass and momentum conservation, kinetic energy

Donghyun You; Frank Ham; Parviz Moin

2008-01-01

438

An experimental and analytical study of a flow vectoring airfoil via macro-fiber-composite actuators  

Microsoft Academic Search

A type of piezoceramic composite actuator commonly known as Macro-Fiber-Composite (MFC) is used for actuation in a variable camber airfoil design. The study focuses on aerodynamic and kinematical modeling, and static response characterization under aerodynamic loads for three similar concepts. From a broader perspective, the study aims to understand the behavior of solid-state aerodynamic vectoring in high dynamic pressure air

Onur Bilgen; Kevin B. Kochersberger; Daniel J. Inman

2008-01-01

439

Active Control of Shock\\/Boundary Layer Interaction with Application to Transonic Airfoils  

Microsoft Academic Search

The objective of this paper is to evaluate, via numerical simulation, the feasibility of weakening the shock wave(s) and reducing the size of the pockets of supersonic flow on wings in transonic flight using active flow control devices such as piston-driven high momentum oscillatory jet actuators (synthetic jets). The computations are performed for transonic flow past a NACA0012 airfoil using

Jose Vadillo; Ramesh Agarwal

2003-01-01

440

Customized airfoils and their impact on VAWT cost of energy  

NASA Astrophysics Data System (ADS)

Sandia National Laboratories has developed a family of airfoils specifically designed for use in the equatorial portion of a Vertical-Axis Wind Turbine (VAWT) blade. An airfoil of that family has been incorporated into the rotor blades of the DOE/Sandia 34-m diameter VAWT Test Bed. The airfoil and rotor design process is reviewed. Comparisons with data recently acquired from flow visualization tests and from the DOE/Sandia 34-m diameter VAWT Test Bed illustrate the success that was achieved in the design. The economic optimization model used in the design is described and used to evaluate the effect of modifications to the current Test Bed blade.

Berg, Dale E.

1990-08-01

441

Broadband Noise Predictions for an Airfoil in a Turbulent Stream  

NASA Astrophysics Data System (ADS)

Loading noise is predicted from unsteady surface pressure measurements on a NACA 0015 airfoil immersed in grid-generated turbulence. The time-dependent pressure is obtained from an array of synchronized transducers on the airfoil surface. Far field noise is predicted by using the time-dependent surface pressure as input to Formulation 1A of Farassat, a solution of the Ffowcs Williams - Hawkings equation. Acoustic predictions are performed with and without the effects of airfoil surface curvature. Scaling rules are developed to compare the present far field predictions with acoustic measurements that are available in the literature.

Casper, J.; Farassat, F.; Mish, P. F.; Devenport, W. J.

2003-01-01

442

Gas lift valve  

SciTech Connect

A gas lift valve is described which consists of: a body, a main valve seat in the body, a main valve member cooperable with the seat to control flow through the body, a pressure dome including a depending bellows connected to the valve member, the bellows being exposed to pressure within the dome urging the valve member toward the seat and to pressure exterior of the body urging the valve member away from the seat, an internal valve seat between the bellows and the remainder of the dome, an internal valve member separate from and movable relative to and supported on the main valve member and cooperable with the internal valve seat to control flow therethrough, one of the internal valve member and seat constructed of polyimide material, hydraulic fluid in the dome extending to a level above the internal valve seat, and a sleeve of polyimide material having a sliding engagement with the interior of the bellows and supporting the bellows against distortion when subjected to a differential pressure thereacross.

Hamm, E.J.

1986-06-03

443

Unsteady characteristics of the static stall of an airfoil subjected to freestream turbulence level up to 16%  

Microsoft Academic Search

Fluctuation of the separation point on an airfoil under high turbulence level is investigated using pressure measurements and flow visualisations. The characteristics of the unsteady loads induced by Karman vortex shedding are studied. This is related with a local approach based on the study of the oscillation zone. A method based on the pressure standard deviation is proposed to obtain

Christophe Sicot; Sandrine Aubrun; Stephane Loyer; Philippe Devinant

2006-01-01

444

The structure of accelerated flow over an airfoil at an angle of attack  

NASA Astrophysics Data System (ADS)

An investigation of the evolution and structure of flow accelerated from rest over a NACA 0015 airfoil at an angle of attack of 30^o has been performed. Two uniform accelerations of 50 mm/s^2 and 100 mm/s^2 were employed with a final uniform velocity of 100 mm/s. The Reynolds number based on this uniform velocity and the chord length of the airfoil was 8000. The experiments were carried out in a water tunnel where the accelerated flow was generated by a stepper motor driven by a square piston. PIV measurements using high resolution digital single exposed imaging with multigrid cross-correlation digital particle image velocimetry (MCCDPIV) analysis have provided quantitative 2-component 2-dimensional (2C-2D) velocity field and out-of-plane vorticity data of the flow evolution. These measurements have revealed a rich and complex unsteady flow structure.

Soria, Julio; Lim, T. T.; Parker, Kamalluddien; New, T. H.; Das, Debopam

2001-11-01

445

Spectra of lifted Ramanujan graphs  

Microsoft Academic Search

A random $n$-lift of a base graph $G$ is its cover graph $H$ on the vertices $[n]\\\\times V(G)$, where for each edge $u v$ in $G$ there is an independent uniform bijection $\\\\pi$, and $H$ has all edges of the form $(i,u),(\\\\pi(i),v)$. A main motivation for studying lifts is understanding Ramanujan graphs, and namely whether typical covers of such a

Eyal Lubetzky; Benny Sudakov; Van Vu

2009-01-01

446

Physiological, Biomechanical, and Medical Aspects of Lifting and Repetitive Lifting: A Review.  

National Technical Information Service (NTIS)

The literature relating to physiological and medical lifting and repetitive lifting is reviewed. Studies on maximal lifting capacity and maximal acceptable lift (MAL, the amount of weight that can be lifted repetitively over and 8h period) show that as th...

J. Knapik

1983-01-01

447

Shallow and deep dynamic stall for flapping low Reynolds number airfoils  

NASA Astrophysics Data System (ADS)

We consider a combined experimental (based on flow visualization, direct force measurement and phaseaveraged 2D particle image velocimetry in a water tunnel), computational (2D Reynolds-averaged Navier-Stokes) and theoretical (Theodorsen's formula) approach to study the fluid physics of rigid-airfoil pitch-plunge in nominally two-dimensional conditions. Shallow-stall (combined pitch-plunge) and deep-stall (pure-plunge) are compared at a reduced frequency commensurate with flapping-flight in cruise in nature. Objectives include assessment of how well attached-flow theory can predict lift coefficient even in the presence of significant separation, and how well 2D velocimetry and 2D computation can mutually validate one another. The shallow-stall case shows promising agreement between computation and experiment, while in the deepstall case, the computation's prediction of flow separation lags that of the experiment, but eventually evinces qualitatively similar leading edge vortex size. Dye injection was found to give good qualitative match with particle image velocimetry in describing leading edge vortex formation and return to flow reattachment, and also gave evidence of strong spanwise growth of flow separation after leadingedge vortex formation. Reynolds number effects, in the range of 10,000-60,000, were found to influence the size of laminar separation in those phases of motion where instantaneous angle of attack was well below stall, but have limited effect on post-stall flowfield behavior. Discrepancy in lift coefficient time history between experiment, theory and computation was mutually comparable, with no clear failure of Theodorsen's formula. This is surprising and encouraging, especially for the deep-stall case, because the theory's assumptions are clearly violated, while its prediction of lift coefficient remains useful for capturing general trends.

Ol, Michael V.; Bernal, Luis; Kang, Chang-Kwon; Shyy, Wei

448

Shallow and deep dynamic stall for flapping low Reynolds number airfoils  

NASA Astrophysics Data System (ADS)

We consider a combined experimental (based on flow visualization, direct force measurement and phase-averaged 2D particle image velocimetry in a water tunnel), computational (2D Reynolds-averaged Navier-Stokes) and theoretical (Theodorsen’s formula) approach to study the fluid physics of rigid-airfoil pitch-plunge in nominally two-dimensional conditions. Shallow-stall (combined pitch-plunge) and deep-stall (pure-plunge) are compared at a reduced frequency commensurate with flapping-flight in cruise in nature. Objectives include assessment of how well attached-flow theory can predict lift coefficient even in the presence of significant separation, and how well 2D velocimetry and 2D computation can mutually validate one another. The shallow-stall case shows promising agreement between computation and experiment, while in the deep-stall case, the computation’s prediction of flow separation lags that of the experiment, but eventually evinces qualitatively similar leading edge vortex size. Dye injection was found to give good qualitative match with particle image velocimetry in describing leading edge vortex formation and return to flow reattachment, and also gave evidence of strong spanwise growth of flow separation after leading-edge vortex formation. Reynolds number effects, in the range of 10,000-60,000, were found to influence the size of laminar separation in those phases of motion where instantaneous angle of attack was well below stall, but have limited effect on post-stall flowfield behavior. Discrepancy in lift coefficient time history between experiment, theory and computation was mutually comparable, with no clear failure of Theodorsen’s formula. This is surprising and encouraging, especially for the deep-stall case, because the theory’s assumptions are clearly violated, while its prediction of lift coefficient remains useful for capturing general trends.

Ol, Michael V.; Bernal, Luis; Kang, Chang-Kwon; Shyy, Wei

2009-05-01

449

Cosmetic face, neck, and brow lifts with local anesthesia.  

PubMed

The sections on the face, neck, and brow include descriptions of facelift, neck lift, and open brow lift techniques, anesthesia, treatment goals, procedural approaches, complications, management, preoperative and postoperative care, rehabilitation, recovery, and outcomes. The approach to facial rejuvenation the midface and periorbital area is detailed. These operations are often and easily performed entirely with the use of local anesthesia and mild oral sedation. There are very high satisfaction rates. PMID:24093659

Huq, Nasim S; Nakhooda, Tariq I

2013-10-01

450

Progress Towards Computational Method for Circulation Control Airfoils.  

National Technical Information Service (NTIS)

The compressible Reynold-averaged Navier-Stokes equations are solved for circulation control airfoil flows. Numerical solutions are computed with both structured and unstructured grid solvers. Several turbulence models are considered, including the Spalar...

R. C. Swanson C. L. Rumsey S. G. Anders

2005-01-01

451

Predicting aerodynamic characteristic of typical wind turbine airfoils using CFD.  

National Technical Information Service (NTIS)

An investigation was conducted into the capabilities and accuracy of a representative computational fluid dynamics code to predict the flow field and aerodynamic characteristics of typical wind-turbine airfoils. Comparisons of the computed pressure and ae...

W. P. Wolfe S. S. Ochs

1997-01-01

452

Structures and Stability of Lifted Combustion Zones in Preheated Oxidizer  

NASA Astrophysics Data System (ADS)

The structures and stability of lifted combustion zones have been simulated with detailed chemistry and transport properties in an axisymmetric laminar fuel (CH4) jet and outer co-flow of the (O2+N2) oxidizer whose initial temperature is 300K, 700K and 1200K. A set of numerical simulations was executed by increasing the N2 dilution ratio, Z (mole fraction of N2 in the oxidizer). The results showed that at 300K, the lifted combustion zone had a triple flame structure where the rich premixed wing is smaller than the lean one and the trailing diffusion flame immediately inclined to the fuel side from the triple point as well as the leading edge of the triple flame was shifted away from the jet axis as Z increased. As the initial temperature increased, the combustion zones were lifted at larger Z values than the one at 300K. Especially, for 1200K, it was found that the lifted combustion zones, when expressed in terms of the heat release rate, have become so weak that a flameless triple combustion zone was formed due to the high dilution ratio and high preheat temperature. The numerical simulations on the response of the lifted triple combustion zone to the initial fuel velocity were also carried out, and the results showed that the lifted combustion zone using a high preheated temperature was very stable in the near field.

Ruan, Jiongming; Kobayashi, Hideaki; Niioka, Takashi; Abuliti, Abudula; Iida, Fumio

453

An investigation into the effects of unsteady parameters on the aerodynamics of a low Reynolds number pitching airfoil  

NASA Astrophysics Data System (ADS)

The growing applications of low Reynolds number (LRN) operating vehicles impose the need for accurate LRN flow solutions. These applications usually involve complex unsteady phenomena, which depend on the kinematics of the vehicle such as pitching, plunging, and flapping of a wing. The objective of the present study is to address the issues related to LRN aerodynamics of a harmonically pitching NACA0012 airfoil. To this end, the influence of unsteady parameters, namely, amplitude of oscillation, d, reduced frequency, k, and Reynolds number, Re, on the aerodynamic performance of the model is investigated. Computational fluid dynamics (CFD) is utilized to solve Navier-Stokes (N-S) equations discretized based on the Finite Volume Method (FVM). The resulting instantaneous lift coefficients are compared with analytical data from Theodorsen’s method. The simulation results reveal that d, k, and Re are of great importance in the aerodynamic performance of the system, as they affect the maximum lift coefficients, hysteresis loops, strength, and number of the generated vortices within the harmonic motion, and the extent of the so-called figure-of-eight phenomenon region. Thus, achieving the optimum lift coefficients demands a careful selection of these parameters.

Amiralaei, M. R.; Alighanbari, H.; Hashemi, S. M.

2010-08-01

454

Calculation of dynamic stall on an oscillating airfoil  

NASA Astrophysics Data System (ADS)

A mathematical model of an unsteady separated flow around an oscillating airfoil is considered. This model is based on a viscid-inviscid approach. The points of separation and the intensity of vorticity displaced into the external flow are determined using boundary-layer equations in an integral form. Dynamic stall on an oscillating airfoil is studied. The mechanism and nature of antidamping are discovered.

Korotkov, O. Yu.; Shumskii, G. M.

2000-05-01

455

Experimental evidence of transient growth of energy before airfoil flutter  

Microsoft Academic Search

This paper presents experimental evidence of the transient growth of energy for the coupled-mode flutter of an airfoil. The phenomenon occurs even in linearly stable dynamical systems. Its application is new in the context of fluid–structure interactions where only theoretical and numerical studies of transient growth exist. The experimental set-up allows an NACA 0015 airfoil to oscillate in rotational and

P. Hémon; E. de Langre; P. Schmid

2006-01-01

456

Heat transfer measurements from a smooth NACA 0012 airfoil  

Microsoft Academic Search

Local convective heat transfer coefficients were measured from a smooth NACA 0012 airfoil having a chord length of 0.533 m. Flight data were taken for the smooth airfoil at Reynolds numbers based on chord in the range 1.24 to 2.50 million and at various angles of attack up to 4 deg. During these flight tests, the freestream velocity turbulence intensity

Philip E. Poinsatte; G. J. van Fossen; James E. Newton; Kenneth J. de Witt

1991-01-01

457

Dynamic Stall of a NACA 0012 Airfoil in Laminar Flow  

Microsoft Academic Search

The dynamic stall processes of a NACA 0012 airfoil oscillating sinusoidally in pitch and heave in laminar incompressible flow were investigated. The effects of changing the reduced frequency k from 0.6 to 1.2 and the pivot location x_0\\/c from 1\\/4 to 3\\/4 were calculated. The nominal angle of incidence on the airfoil oscillated between 6^circ and 18^circ about a mean

Sasi K. Digavalli

1994-01-01

458

CALCULATION OF MULTIELEMENT AIRFOIL FLOWS, INCLUDING FLAP WELLS  

Microsoft Academic Search

A calculation method for multielement airfoils based on an interactive boundary-layer approach using an improved Cebeci-Smith eddy viscosity formulation is described. Results are first presented for single airfoils at low and moderate Reynolds numbers in order to demonstrate the need to calculate transition for accurate drag polar prediction and the ability of the improved Cebeci-Smith turbulence model to predict flows

Tuncer Cebeci; Eric Besnard

459

Transonic Drag Reduction with Contour Bump on a Supercritical Airfoil  

Microsoft Academic Search

The effect of contour bumps on transonic drag reducing at off-design conditions of a supercritical airfoil have been examined in the paper. Research focuses on two-dimensional flow condition with Mach number of 0.78 and chord Reynolds number of 2.5 million. Different contour bump airfoil configurations are examined using numerical method. Recent tests on these models are conducted in 0.6m×0.6m transonic

Guangyuan Liu; Yang Tao; Qiuting Guo; Yan Sun

2012-01-01

460

The flow over a thin airfoil subjected to elevated levels of freestream turbulence at low Reynolds numbers  

NASA Astrophysics Data System (ADS)

Micro Air Vehicles (MAVs) can be difficult to control in the outdoor environment as they fly at relatively low speeds and are of low mass, yet exposed to high levels of freestream turbulence present within the Atmospheric Boundary Layer. In order to examine transient flow phenomena, two turbulence conditions of nominally the same longitudinal integral length scale (Lxx/c = 1) but with significantly different intensities (Ti = 7.2 % and 12.3 %) were generated within a wind tunnel; time-varying surface pressure measurements, smoke flow visualization, and wake velocity measurements were made on a thin flat plate airfoil. Rapid changes in oncoming flow pitch angle resulted in the shear layer to separate from the leading edge of the airfoil even at lower geometric angles of attack. At higher geometric angles of attack, massive flow separation occurred at the leading edge followed by enhanced roll up of the shear layer. This lead to the formation of large Leading Edge Vortices (LEVs) that advected at a rate much lower than the mean flow speed while imparting high pressure fluctuations over the airfoil. The rate of LEV formation was dependent on the angle of attack until 10° and it was independent of the turbulence properties tested. The fluctuations in surface pressures and consequently aerodynamic loads were considerably limited on the airfoil bottom surface due to the favorable pressure gradient.

Ravi, Sridhar; Watkins, Simon; Watmuff, Jon; Massey, Kevin; Petersen, Phred; Marino, Matthew; Ravi, Anuradha

2012-09-01

461

Visualization of shock tube airfoil flow with a sharp focusing schlieren method  

NASA Astrophysics Data System (ADS)

Visualization of the flow field around the base line model under the flight condition is one of the most valuable and basic steps on the high-speed airplane development. Now we consider a sharp focusing schlieren system that gives a means for observing any cross section of a flow field of perpendicular to the test beam axis of the optical system. This system can be used to examine a complex three-dimensional flow field. As a preliminary study, a sharp focusing schlieren system is designed with referring to the Weinstein's system. And visualization of steady transonic airfoil shock tube flow is performed with this system to investigate the effect of side-wall interference to the shock wave locations on an airfoil surface. The results show that the instrument has a capability for visualizing any cross section in the shock tub airfoil flow. Also, it is pointed out that the main steady shock wave profile focused at the center of the channel is different from the profile focused near the side-wall.

Kashitani, Masashi; Yamaguchi, Yutaka C.

2001-04-01

462

Unsteady flow past an airfoil pitching at a constant rate  

NASA Astrophysics Data System (ADS)

The unsteady flow past a NACA 0012 airfoil in pitching up motion is experimentally investigated in a water towing tank using the Particle Image Displacement Velocimetry (PIDV) technique. The Reynolds number, based on the airfoil chord and the freestream velocity, is 5000. The airfoil pitching motion is from 0 to 30 degrees angle of attack at a dimensionless pitch rate alpha of 0.131. Instantaneous velocity fields at different times were acquired over the entire flow field. Using the whole field data, the out of plane component of vorticity is computed. The following features are observed. Boundary layer separation near the airfoil leading edge leads to the formation of a vortical structure. The evolution of this vortex along the upper surface dominates the aerodynamic performance of the airfoil. Complete stall emerges when the boundary layer near the leading edge detaches from the airfoil, under the influence of the vortex. The vortex further triggers the shedding of a counter rotating vortex near the trailing edge. A parallel computational study using the discrete vortex, random walk approximation was conducted. In general, the computational results agree very well.

Shih, C.; Lourenco, L. M.; Vandommelen, L.; Krothapalli, A.

463

Normalized lift: an energy interpretation of the lift coefficient simplifies comparisons of the lifting ability of rotating and flapping surfaces.  

PubMed

For a century, researchers have used the standard lift coefficient C(L) to evaluate the lift, L, generated by fixed wings over an area S against dynamic pressure, ½?v(2), where v is the effective velocity of the wing. Because the lift coefficient was developed initially for fixed wings in steady flow, its application to other lifting systems requires either simplifying assumptions or complex adjustments as is the case for flapping wings and rotating cylinders.This paper interprets the standard lift coefficient of a fixed wing slightly differently, as the work exerted by the wing on the surrounding flow field (L/?·S), compared against the total kinetic energy required for generating said lift, ½v(2). This reinterpreted coefficient, the normalized lift, is derived from the work-energy theorem and compares the lifting capabilities of dissimilar lift systems on a similar energy footing. The normalized lift is the same as the standard lift coefficient for fixed wings, but differs for wings with more complex motions; it also accounts for such complex motions explicitly and without complex modifications or adjustments. We compare the normalized lift with the previously-reported values of lift coefficient for a rotating cylinder in Magnus effect, a bat during hovering and forward flight, and a hovering dipteran.The maximum standard lift coefficient for a fixed wing without flaps in steady flow is around 1.5, yet for a rotating cylinder it may exceed 9.0, a value that implies that a rotating cylinder generates nearly 6 times the maximum lift of a wing. The maximum normalized lift for a rotating cylinder is 1.5. We suggest that the normalized lift can be used to evaluate propellers, rotors, flapping wings of animals and micro air vehicles, and underwater thrust-generating fins in the same way the lift coefficient is currently used to evaluate fixed wings. PMID:22629326

Burgers, Phillip; Alexander, David E

2012-05-21

464

Normalized Lift: An Energy Interpretation of the Lift Coefficient Simplifies Comparisons of the Lifting Ability of Rotating and Flapping Surfaces  

PubMed Central

For a century, researchers have used the standard lift coefficient CL to evaluate the lift, L, generated by fixed wings over an area S against dynamic pressure, ½?v2, where v is the effective velocity of the wing. Because the lift coefficient was developed initially for fixed wings in steady flow, its application to other lifting systems requires either simplifying assumptions or complex adjustments as is the case for flapping wings and rotating cylinders. This paper interprets the standard lift coefficient of a fixed wing slightly differently, as the work exerted by the wing on the surrounding flow field (L/?·S), compared against the total kinetic energy required for generating said lift, ½v2. This reinterpreted coefficient, the normalized lift, is derived from the work-energy theorem and compares the lifting capabilities of dissimilar lift systems on a similar energy footing. The normalized lift is the same as the standard lift coefficient for fixed wings, but differs for wings with more complex motions; it also accounts for such complex motions explicitly and without complex modifications or adjustments. We compare the normalized lift with the previously-reported values of lift coefficient for a rotating cylinder in Magnus effect, a bat during hovering and