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1

Unsteady Aerodynamics Experiment Phase V: Test Configuration and Available Data Campaigns  

SciTech Connect

The main objective of the Unsteady Aerodynamics Experiment is to provide information needed to quantify the full-scale, three-dimensional, unsteady aerodynamic behavior of horizontal-axis wind turbines (HAWTs). To accomplish this, an experimental wind turbine configured to meet specific research objectives was assembled and operated at the National Renewable Energy Laboratory (NREL). The turbine was instrumented to characterize rotating-blade aerodynamic performance, machine structural responses, and atmospheric inflow conditions. Comprehensive tests were conducted with the turbine operating in an outdoor field environment under diverse conditions. Resulting data are used to validate aerodynamic and structural dynamics models, which are an important part of wind turbine design and engineering codes. Improvements in these models are needed to better characterize aerodynamic response in both the steady-state post-stall and dynamic-stall regimes. Much of the effort in the first phase of the Unsteady Aerodynamics Experiment focused on developing required data acquisition systems. Complex instrumentation and equipment was needed to meet stringent data requirements while operating under the harsh environmental conditions of a wind turbine rotor. Once the data systems were developed, subsequent phases of experiments were then conducted to collect data for use in answering specific research questions. A description of the experiment configuration used during Phase V of the experiment is contained in this report.

Hand, M. M.; Simms, D. A.; Fingersh, L. J.; Jager, D. W.; Cotrell, J. R.

2001-08-30

2

Conversion of Phase II Unsteady Aerodynamics Experiment Data to Common Format  

SciTech Connect

A vast amount of aerodynamic, structural, and turbine performance data were collected during three phases of the National Renewable Energy Laboratory's Unsteady Aerodynamics Experiment (UAE). To compare data from the three phases, a similar format of engineering unit data is required. The process of converting Phase II data from a previous engineering unit format to raw integer counts is discussed. The integer count files can then be input to the new post-processing software, MUNCH. The resulting Phase II engineering unit files are in a common format with current and future UAE engineering unit files. An additional objective for changing the file format was to convert the Phase II data from English units to SI units of measurement.

Hand, M. M.

1999-07-19

3

An Approximate Analysis of Wing Unsteady Aerodynamics.  

National Technical Information Service (NTIS)

A brief review of the unsteady aerodynamics in lifting surface theory is reported. For utility in design application, simplified but accurate analytical expressions were developed for generalized unsteady aerodynamics of wings of finite aspect ratio and s...

W. R. Wells

1979-01-01

4

Unsteady aerodynamics modeling for flight dynamics application  

NASA Astrophysics Data System (ADS)

In view of engineering application, it is practicable to decompose the aerodynamics into three components: the static aerodynamics, the aerodynamic increment due to steady rotations, and the aerodynamic increment due to unsteady separated and vortical flow. The first and the second components can be presented in conventional forms, while the third is described using a one-order differential equation and a radial-basis-function (RBF) network. For an aircraft configuration, the mathematical models of 6-component aerodynamic coefficients are set up from the wind tunnel test data of pitch, yaw, roll, and coupled yawroll large-amplitude oscillations. The flight dynamics of an aircraft is studied by the bifurcation analysis technique in the case of quasi-steady aerodynamics and unsteady aerodynamics, respectively. The results show that: (1) unsteady aerodynamics has no effect upon the existence of trim points, but affects their stability; (2) unsteady aerodynamics has great effects upon the existence, stability, and amplitudes of periodic solutions; and (3) unsteady aerodynamics changes the stable regions of trim points obviously. Furthermore, the dynamic responses of the aircraft to elevator deflections are inspected. It is shown that the unsteady aerodynamics is beneficial to dynamic stability for the present aircraft. Finally, the effects of unsteady aerodynamics on the post-stall maneuverability are analyzed by numerical simulation.

Wang, Qing; He, Kai-Feng; Qian, Wei-Qi; Zhang, Tian-Jiao; Cheng, Yan-Qing; Wu, Kai-Yuan

2012-02-01

5

Unsteady Aerodynamics Experiment Phase VI: Wind Tunnel Test Configurations and Available Data Campaigns  

SciTech Connect

The primary objective of the insteady aerodynamics experiment was to provide information needed to quantify the full-scale, three-dimensional aerodynamic behavior of horizontal-axis wind turbines. This report is intended to familiarize the user with the entire scope of the wind tunnel test and to support the use of the resulting data.

Hand, M. M.; Simms, D. A.; Fingersh, L. J.; Jager, D. W.; Cotrell, J. R.; Schreck, S.; Larwood, S. M.

2001-12-01

6

Unsteady Aerodynamics of Insect Flight  

NASA Astrophysics Data System (ADS)

The myth `bumble-bees can not fly according to conventional aerodynamics' simply reflects our poor understanding of unsteady viscous fluid dynamics. In particular, we lack a theory of vorticity shedding due to dynamic boundaries at the intermediate Reynolds numbers relevant to insect flight, typically between 10^2 and 10^4, where both viscous and inertial effects are important. In our study, we compute unsteady viscous flows, governed by the Navier-Stokes equation, about a two dimensional flapping wing which mimics the motion of an insect wing. I will present two main results: the existence of a prefered frequency in forward flight and its physical origin, and 2) the vortex dynamics and forces in hovering dragonfly flight.

Wang, Z. Jane

2000-03-01

7

Rotor blade unsteady aerodynamic gust response to inlet guide vane wakes  

Microsoft Academic Search

A series of experiments is performed in an extensively instrumented axial flow research compressor to investigate the fundamental flow physics of wake-generated periodic rotor blade row unsteady aerodynamics at realistic values of the reduced frequency. Unique unsteady data are obtained that describe the fundamental unsteady aerodynamic gust interaction phenomena on the first-stage rotor blades of a research axial flow compressor

S. R. Manwaring; S. Fleetner

1993-01-01

8

NREL Unsteady Aerodynamics Experiment in the NASA-Ames Wind Tunnel: A Comparison of Predictions to Measurements  

SciTech Connect

Currently, wind turbine designers rely on safety factors to compensate for the effects of unknown loads acting on the turbine structure. This results in components that are overdesigned because precise load levels and load paths are unknown. To advance wind turbine technology, the forces acting on the turbine structure must be accurately characterized because these forces translate directly into loads imparted to the wind turbine structure and resulting power production. Once these forces are more accurately characterized, we will better understand load paths and can therefore optimize turbine structures. To address this problem, the National Renewable Energy Laboratory (NREL) conducted the Unsteady Aerodynamics Experiment (UAE), which was a test of an extensively instrumented wind turbine in the giant NASA-Ames 24.4-m (80 feet) by 36.6-m (120 feet) wind tunnel. To maximize the benefits from testing, NREL formed a Science Panel of advisers comprised of wind turbine aerodynamics and modeling experts throughout the world. NREL used the Science Panel's guidance to specify the conditions and configurations under which the turbine was operated in the wind tunnel. The panel also helped define test priorities and objectives that would be effective for wind turbine modeling tool development and validation.

Simms, D.; Schreck, S.; Hand, M.; Fingersh, L.J.

2001-06-22

9

Rotor blade unsteady aerodynamic gust response to inlet guide vane wakes  

SciTech Connect

A series of experiments is performed in an extensively instrumented axial flow research compressor to investigate the fundamental flow physics of wake-generated periodic rotor blade row unsteady aerodynamics at realistic values of the reduced frequency. Unique unsteady data are obtained that describe the fundamental unsteady aerodynamic gust interaction phenomena on the first-stage rotor blades of a research axial flow compressor generated by the wakes from the inlet guide vanes. In these experiments, the effects of steady blade aerodynamic loading and the aerodynamic forcing function, including both the transverse and chordwise gust components, and the amplitude of the gusts, are investigated and quantified.

Manwaring, S.R.; Fleetner, S. (Purdue Univ., West Lafayette, IN (United States). School of Mechanical Engineering)

1993-01-01

10

Unsteady aerodynamics and gust response in compressors and turbines  

SciTech Connect

A comprehensive series of experiments and analyses was performed on compressor and turbine blading to evaluate the ability of current, practical, engineering/analysis models to predict unsteady aerodynamic loading of modern gas turbine blading. This is part of an ongoing effort to improve methods for preventing blading failure. The experiments were conducted in low-speed research facilities capable of simulating the relevant aerodynamic features of turbomachinery. Unsteady loading on compressor and turbine blading was generated by upstream wakes and, additionally for compressors, by a rotating inlet distortion. Fast-response hot-wire anemometry and pressure transducers embedded in the airfoil surfaces were used to determine the aerodynamic gusts and resulting unsteady pressure responses acting on the airfoils. This is the first time that gust response measurements for turbines have been reported in the literature. Several different analyses were used to predict the unsteady component of the blade loading: (1) a classical flat-plate analysis, (2) a two-dimensional linearized flow analysis with a frozen gust model, (3) a two-dimensional linearized flow analysis with a distorted gust model, (4) a two-dimensional linearized Euler analysis, and (5) a two-dimensional nonlinear Euler analysis. Also for the first time, a detailed comparison of these analyses methods is made and the importance of properly accounting for both vortical and potential disturbances is demonstrated. The predictions are compared with experiment and their abilities assessed to help guide designers in using these prediction schemes.

Manwaring, S.R.; Wisler, D.C. (Aerodynamics Research Lab., Cincinnati, OH (United States). GE Aircraft Engines)

1993-10-01

11

The unsteady aerodynamics of a first stage stator vane row  

NASA Astrophysics Data System (ADS)

The fundamental unsteady aerodynamics on a vane row of an axial flow research compressor stage are experimentally investigated, demonstrating the effects of airfoil camber and steady loading. In particular, the rotor wake generated unsteady surface pressure distributions on the first stage vane row are quantified over a range of operating conditions. These cambered airfoil unsteady data are correlated with predictions from a flat plate cascade inviscid flow model. At the design point, the unsteady pressure difference coefficient data exhibit good correlation with the nonseparated predictions, with the aerodynamic phase lag data exhibiting fair trendwise correlation. The quantitative phase lag differences are associated with the camber of the airfoil. An aft suction surface flow separation region is indicated by the steady state surface static pressure data as the aerodynamic loading is increased. This separation affects the increased incidence angle unsteady pressure data.

Capece, V. R.; Fleeter, S.

1986-03-01

12

Unsteady aerodynamic models for agile flight at low Reynolds numbers  

NASA Astrophysics Data System (ADS)

This work develops low-order models for the unsteady aerodynamic forces on a wing in response to agile maneuvers at low Reynolds number. Model performance is assessed on the basis of accuracy across a range of parameters and frequencies as well as of computational efficiency and compatibility with existing control techniques and flight dynamic models. The result is a flexible modeling procedure that yields accurate, low-dimensional, state-space models. The modeling procedures are developed and tested on direct numerical simulations of a two-dimensional flat plate airfoil in motion at low Reynolds number, Re=100, and in a wind tunnel experiment at the Illinois Institute of Technology involving a NACA 0006 airfoil pitching and plunging at Reynolds number Re=65,000. In both instances, low-order models are obtained that accurately capture the unsteady aerodynamic forces at all frequencies. These cases demonstrate the utility of the modeling procedure developed in this thesis for obtaining accurate models for different geometries and Reynolds numbers. Linear reduced-order models are constructed from either the indicial response (step response) or realistic input/output maneuvers using a flexible modeling procedure. The method is based on identifying stability derivatives and modeling the remaining dynamics with the eigensystem realization algorithm. A hierarchy of models is developed, based on linearizing the flow at various operating conditions. These models are shown to be accurate and efficient for plunging, pitching about various points, and combined pitch and plunge maneuvers, at various angle of attack and Reynolds number. Models are compared against the classical unsteady aerodynamic models of Wagner and Theodorsen over a large range of Strouhal number and reduced frequency for a baseline comparison. Additionally, state-space representations are developed for Wagner's and Theodorsen's models, making them compatible with modern control-system analysis. A number of computational tools are developed throughout this work. Highly unsteady maneuvers are visualized using finite-time Lyapunov exponent fields, which highlight separated flows and wake structures. A new fast method of computing these fields is presented. In addition, we generalize the immersed boundary projection method computations to use a moving base flow, which allows for the simulation of complex geometries undergoing large motions with up to an order of magnitude speed-up. The methods developed in this thesis provide a systematic approach to identify unsteady aerodynamic models from analytical, numerical, or experimental data. The resulting models are shown to be reduced-order models of the linearized Navier-Stokes equations that are expressed in state-space form, and they are, therefore, both efficient and accurate. The specific form of the model, which separates added-mass forces, quasi-steady lift, and transient forces, guarantees that the resulting models are accurate over the entire range of frequencies. Finally, the models are low-dimensional linear systems of ordinary differential equations, so that they are compatible with existing flight dynamic models as well as a wealth of modern control techniques.

Brunton, Steven L.

13

Unsteady Free-Wake Viscous Aerodynamic Analysis of Helicopter Rotors.  

National Technical Information Service (NTIS)

The report contains the results for research on unsteady free-wake viscous aerodynamic analysis of helicopter rotors. The effort may be divided into three general areas. The first deals with further developments of the zeroth-order potential-flow analysis...

L. Morino M. Downey S. Sipcic

1989-01-01

14

Prediction of Unsteady Aerodynamic Coefficients at High Angles of Attack.  

National Technical Information Service (NTIS)

The nonlinear indicial response method is used to model the unsteady aerodynamic coefficients in the low speed longitudinal oscillatory wind tunnel test data of the 0.1 scale model of the F-16XL aircraft. Exponential functions are used to approximate the ...

B. N. Pamadi P. C. Murphy V. Klein J. M. Brandon

2001-01-01

15

CFD based unsteady aerodynamic modeling for rotor aeroelastic analysis  

Microsoft Academic Search

A Computational Fluid Dynamics (CFD) analysis is developed for 3-D rotor unsteady aerodynamic load prediction. It is then coupled to a rotor structural analysis for predicting aeroelastic blade response, airloads and vibration. The CFD analysis accounts for the elastic deformations using a dynamically deforming mesh system. All the rotor blades are assumed to be identical, therefore to reduce the computational

Jayanarayanan Sitaraman

2003-01-01

16

Unsteady aerodynamics of fluttering and tumbling plates  

Microsoft Academic Search

We investigate the aerodynamics of freely falling plates in a quasi-two-dimensional flow at Reynolds number of 103, which is typical for a leaf or business card falling in air. We quantify the trajectories experimentally using high-speed digital video at sufficient resolution to determine the instantaneous plate accelerations and thus to deduce the instantaneous fluid forces. We compare the measurements with

U. P ESAVENTO; Z. J ANE W ANG

2005-01-01

17

Unsteady transonic aerodynamics during wing flutter  

NASA Astrophysics Data System (ADS)

Unsteady pressure distributions of a two-dimensional super-critical wing while it was fluttering were measured in the transonic flow regime. The results were compared with those by the Navier-Stokes code which includes wind-tunnel wall effects. Although there were discrepancies between the experimental results and the analytical model for the pressure phase delay distribution, no disagreements were observed for the pitching first harmonics provided that there was no large flow separation. In the tests, the flutter was forced to be suppressed soon after its onset before it reached a limit cycle oscillation (LCO) where the amplitude of the pitching angle was supposed to be over 2 degrees.

Saitoh, Kenichi; Tamayama, Masato; Yoshimoto, Norio; Ueda, Tetsuhiko

2012-09-01

18

Anodized aluminum pressure sensitive paint for unsteady aerodynamic applications  

Microsoft Academic Search

A comprehensive study of anodized aluminum pressure sensitive paint (AA-PSP) is documented. The study consisted of the development of AA-PSP and its application to unsteady aerodynamic fields at atmospheric conditions. Luminophore application mechanism and two-component application on anodized aluminum was studied for the development. Two-component application includes hydrophobic-coated AA-PSP and bi-luminophore system. It was found that the polarity of solvents

Hirotaka Sakaue

2003-01-01

19

The Legacy of Camillo Possio to Unsteady Aerodynamics  

Microsoft Academic Search

First a brief overview is given of Camillo Possio’s short but outstanding and fruitful career. This is followed by an outline\\u000a of the state of the art in flutter and unsteady aerodynamic research, and the challenges and problems like high-speed flight\\u000a that arose in aircraft development at that time. Possio’s first publications on gas dynamic and supersonic problems are reviewed.

R. Voss

2005-01-01

20

Investigation of integral surface formulations for acoustic post-processing of unsteady aerodynamic jet simulations  

Microsoft Academic Search

The acoustic post-processing of unsteady aerodynamic jet simulations using Kirchhoff or Ffowcs Williams and Hawkings (FW–H) surface integral methods is investigated from the theoretical and practical points of view. This analysis is carried out for a supersonic hot jet, starting from the flow fields provided by an unsteady aerodynamic simulation whose characteristics are recalled. Both acoustic integral methods are first

Gilles Rahier; Jean Prieur; François Vuillot; Nicolas Lupoglazoff; Anthoine Biancherin

2004-01-01

21

An unsteady aerodynamic formulation for efficient rotor tonal noise prediction  

NASA Astrophysics Data System (ADS)

An aerodynamic/aeroacoustic solution methodology for predction of tonal noise emitted by helicopter rotors and propellers is presented. It is particularly suited for configurations dominated by localized, high-frequency inflow velocity fields as those generated by blade-vortex interactions. The unsteady pressure distributions are determined by the sectional, frequency-domain Küssner-Schwarz formulation, with downwash including the wake inflow velocity predicted by a three-dimensional, unsteady, panel-method formulation suited for the analysis of rotors operating in complex aerodynamic environments. The radiated noise is predicted through solution of the Ffowcs Williams-Hawkings equation. The proposed approach yields a computationally efficient solution procedure that may be particularly useful in preliminary design/multidisciplinary optimization applications. It is validated through comparisons with solutions that apply the airloads directly evaluated by the time-marching, panel-method formulation. The results are provided in terms of blade loads, noise signatures and sound pressure level contours. An estimation of the computational efficiency of the proposed solution process is also presented.

Gennaretti, M.; Testa, C.; Bernardini, G.

2013-12-01

22

VALIDATION OF METHODOLOGY FOR ESTIMATING AIRCRAFT UNSTEADY AERODYNAMIC PARAMETERS FROM DYNAMIC WIND TUNNEL TESTS  

Microsoft Academic Search

A basic problem in flight dynamics is the mathematical formulation of the aerodynamic model for aircraft. This study is part of an ongoing effort at NASA Langley to develop a more general formulation of the aerodynamic model for aircraft that includes nonlinear unsteady aerodynamics and to develop appropriate test techniques that facilitate identification of these models. A methodology for modeling

Patrick C. Murphy; Vladislav Klein

23

Anodized aluminum pressure sensitive paint for unsteady aerodynamic applications  

NASA Astrophysics Data System (ADS)

A comprehensive study of anodized aluminum pressure sensitive paint (AA-PSP) is documented. The study consisted of the development of AA-PSP and its application to unsteady aerodynamic fields at atmospheric conditions. Luminophore application mechanism and two-component application on anodized aluminum was studied for the development. Two-component application includes hydrophobic-coated AA-PSP and bi-luminophore system. It was found that the polarity of solvents and the surface charge of anodized aluminum determine the optimized luminophore application. As a result, a wide variation of luminophore can be applied on anodized aluminum. To apply both components on anodized aluminum, optimum solvent polarities for each component should match. AA-PSP performances, such as pressure sensitivity, temperature dependency, signal level, and aging were improved by the luminophore application mechanism and two-component application. AA-PSPs demonstrate the capability of measuring surface pressures on unsteady aerodynamic fields. For an application to the Purdue Mach 4 Quiet Flow Ludwieg Tube, surface pressures on the order of a hundred Pascals were measured for approximately 200ms. The measurement uncertainty of the pressure was on the order of 5%. The main uncertainty source comes from fitting the adsorption control model to calibration points. The results compared qualitatively well to CFD calculations. A miniature fluidic oscillator was used to demonstrate the capability of measuring oscillating unsteady aerodynamic fields with 6.4kHz primary frequency. Flow oscillation images as well as pressure maps of various phases were captured by AA-PSP with PtTFPP as a luminophore (AA-PSPPtTFPP ). Main uncertainty source comes from fitting the adsorption control model to calibration points and from the pulse width of illumination. The measurement uncertainty of the pressure was 4.68%. AA-PSPPtTFPP was applied to a high-amplified acoustic fielding in a standing wave tube. The maximum pressure change created was 171dB (1.04psi). Sinusoidal pressure wave images inside a standing wave tube were captured at various phases. From these images, the integrated pressure map was obtained. In this case, measurement uncertainty was 3.64% and was due mainly to the pulse width and from fitting of the adsorption controlled model. Comparison with theoretical model is necessary to validate the integrated map as a streaming pattern.

Sakaue, Hirotaka

2003-06-01

24

CFD based unsteady aerodynamic modeling for rotor aeroelastic analysis  

NASA Astrophysics Data System (ADS)

A Computational Fluid Dynamics (CFD) analysis is developed for 3-D rotor unsteady aerodynamic load prediction. It is then coupled to a rotor structural analysis for predicting aeroelastic blade response, airloads and vibration. The CFD analysis accounts for the elastic deformations using a dynamically deforming mesh system. All the rotor blades are assumed to be identical, therefore to reduce the computational complexity the CFD calculations are performed for a single blade. This accounts for the near wake flow field. But the far wake effects because of the trailed tip vortices from all the blades have to be included separately. This is achieved by the use of the field velocity approach, which is a method for modeling unsteady flows via apparent grid movement. In this method, the induced velocity field caused by the trailed vortex wake is included by modifying the grid time metrics. The CFD method developed is systematically validated for a range of problems starting from simple 2-D model problems to full scale forward flight cases. The CFD analysis shows significant improvements in airloads prediction compared to a table lookup based lifting-line analysis. The CFD analysis is then used to investigate the fundamental mechanisms of rotor vibration. It is found that both the normal forces and pitching moments are dominated by three dimensional aerodynamic effects. The curvature introduced by the blade elasticity appears to play a key role in the generation of the vibratory harmonics in airloads. The pitching moments near the blade tip (85% outboard) are significantly affected by transonic tip relief effects. The fundamental understanding of rotor vibrations gained from this study is then used to develop generic corrections for improving the accuracy of a lifting line analysis. Finally the CFD analysis developed is coupled with an advanced comprehensive rotor aeroelastic analysis. The coupling procedure is formulated in a way such that there is an exchange of information between the structural model and CFD model every rotor revolution. The coupled CFD/structure scheme is found to considerably improve the prediction of rotor vibratory airloads compared to the baseline rotor aeroelastic analysis which uses a lifting line based aerodynamic model.

Sitaraman, Jayanarayanan

25

Development of Unsteady Aerodynamics Prediction Method for Aircraft with External Stores,  

National Technical Information Service (NTIS)

The paper presents a prediction method of unsteady aerodynamics for aircraft with external stores. The method is based on Morino's formulation and uses a boundary element technique. Sample calculations were conducted for a wing-fuselage configuration with...

T. Tanioka M. Kodama S. Tatsumi

1988-01-01

26

Unsteady Low-Reynolds Number Aerodynamics for Micro Air Vehicles (MAVs).  

National Technical Information Service (NTIS)

This report documents recent progress in in-house research in the AFRL Air Vehicles Directorate on unsteady aerodynamics at low Reynolds number. The application is the aerodynamics and flight dynamics of agile Micro Air Vehicles, to include flapping-wings...

M. V. Ol

2007-01-01

27

Unsteady Low Reynolds Number Aerodynamics for Micro Air Vehicles (MAVs).  

National Technical Information Service (NTIS)

This work introduces the Micro Air Vehicle (MAV) problem from the viewpoint of aerodynamics. Water tunnels are assessed as tools for MAV aerodynamics. The design, construction and instrumentation of RB's 'Horizontal Free-surface Water Tunnel' is documente...

M. V. Ol

2010-01-01

28

Predictability of unsteady two-dimensional k-? model on the aerodynamic instabilities of some rectangular prisms  

NASA Astrophysics Data System (ADS)

It is well known that a bluff body cross-section exhibits various kinds of aerodynamic instabilities such as vortex-induced vibration, galloping and torsional flutter. Since these cross-sections are used in long-span bridges and tall buildings, it is important to predict their occurrence in wind resistant structural design. In this paper, the authors make a series of comparisons of unsteady wind forces, unsteady pressure distributions and free vibration responses between previously conducted studies and an unsteady two-dimensional k-? model for rectangular cross-sections with cross-sectional ratios of 2 and 4 in a smooth uniform flow in order to verify computational predictability of aerodynamic instabilities. As a result, the computation successfully predicted the onset velocities and responses of these aerodynamic instabilities for these cross-sectional ratios, which are common to tall buildings and long bridges.

Shimada, Kenji; Ishihara, Takeshi

2012-01-01

29

An Assessment of the Future Roles of the National Transonic Facility and the Langley Transonic Dynamics Tunnel in Aeroelastic and Unsteady Aerodynamic Testing.  

National Technical Information Service (NTIS)

The characteristics and capabilities of the two tunnels, that relate to studies in the fields of aeroelasticity and unsteady aerodynamics are discussed. Scaling considerations for aeroelasticity and unsteady aerodynamics testing in the two facilities are ...

P. W. Hanson

1980-01-01

30

Unsteady Aerodynamic Response of Oscillating Contra-Rotating Annular Cascades Part II: Numerical Study  

NASA Astrophysics Data System (ADS)

The unsteady aerodynamic force and work for contra-rotating annular cascades of oscillating blades are numerically investigated. A comparison among frequency components of unsteady blade loadings on oscillating blades and stationary blades in relative rotational motion is conducted. It is proved that the state of generated acoustic duct mode of the lowest order is a key factor governing the aeroacoustic interaction between the blade rows. The effect of the neighboring blade row on the aerodynamic force and work is never small and will make substantial modifications to the flutter boundaries of an isolated blade row.

Nishino, Ryohei; Namba, Masanobu

31

The influence of neighboring blade rows on the unsteady aerodynamic response of cascades  

SciTech Connect

In this paper, the authors present an analysis of the unsteady aerodynamic response of cascades due to incident gusts (the forced response problem) or blade vibration (the flutter problem) when the cascade is part of a multistage fan, compressor, or turbine. Most current unsteady aerodynamic models assume the cascade to be isolated in an infinitely long duct. This assumption, however, neglects the potentially important influence of neighboring blade rows. They present an elegant and computationally efficient method to model these neighboring blade row effects. In the present method, they model the unsteady aerodynamic response due to so-called spinning modes (pressure and vorticity waves), with each mode corresponding to a different circumferential wave number and frequency. Then, for each mode, they compute the reflection and transmission coefficients for each blade row. These coefficients can be obtained from any of the currently available unsteady linearized aerodynamic models of isolated cascades. A set of linear equations is then constructed that couples together the various spinning modes, and the linear equations are solved via LU decomposition. Numerical results are presented for both the gust response and blade vibration problems. To validate the model, the authors compare their results to other analytical models, and to a multistage vortex lattice model. They show that the effect of neighboring blade rows on the aerodynamic damping of vibrating cascades is significant, but nevertheless can be modeled with a small number of modes.

Hall, K.C.; Silkowski, P.D. [Duke Univ., Durham, NC (United States). Dept. of Mechanical Engineering and Materials Science

1997-01-01

32

Rotor-generated unsteady aerodynamic interactions in a 1½ stage compressor  

NASA Astrophysics Data System (ADS)

Because High Cycle Fatigue (HCF) remains the predominant surprise failure mode in gas turbine engines, HCF avoidance design systems are utilized to identify possible failures early in the engine development process. A key requirement of these analyses is accurate determination of the aerodynamic forcing function and corresponding airfoil unsteady response. The current study expands the limited experimental database of blade row interactions necessary for calibration of predictive HCF analyses, with transonic axial-flow compressors of particular interest due to the presence of rotor leading edge shocks. The majority of HCF failures in aircraft engines occur at off-design operating conditions. Therefore, experiments focused on rotor-IGV interactions at off-design are conducted in the Purdue Transonic Research Compressor. The rotor-generated IGV unsteady aerodynamics are quantified when the IGV reset angle causes the vane trailing edge to be nearly aligned with the rotor leading edge shocks. A significant vane response to the impulsive static pressure perturbation associated with a shock is evident in the point measurements at 90% span, with details of this complex interaction revealed in the corresponding time-variant vane-to-vane flow field data. Industry wide implementation of Controlled Diffusion Airfoils (CDA) in modern compressors motivated an investigation of upstream propagating CDA rotor-generated forcing functions. Whole field velocity measurements in the reconfigured Purdue Transonic Research Compressor along the design speedline reveal steady loading had a considerable effect on the rotor shock structure. A detached rotor leading edge shock exists at low loading, with an attached leading edge and mid-chord suction surface normal shock present at nominal loading. These CDA forcing functions are 3--4 times smaller than those generated by the baseline NACA 65 rotor at their respective operating points. However, the IGV unsteady aerodynamic response to the CDA forcing functions remains significant. The intra-vane transport of NACA 65 and CDA rotor wakes is also observed within the time-variant passage velocity data. In general, the wake width and decay rate increase with rotor speed and compressor steady loading respectively.

Papalia, John J.

33

State-of-the-Art in Unsteady Aerodynamics.  

National Technical Information Service (NTIS)

The accurate prediction of unsteady air loads is essential to avoiding problems and assuring safety in many interdisciplinary regions involving aeroelasticity and the dynamics of active controls. However, the methods to predict such airloads are complex a...

W. P. Rodden

1976-01-01

34

Unsteady supersonic aerodynamics based on BEM, including thickness effects in aeroelastic analysis  

Microsoft Academic Search

A general three-dimensional aeroelastic solver is developed based on coupled finite element and boundary element methods and applied to investigate the flutter boundaries in supersonic flows. The boundary element method is applied to three-dimensional unsteady supersonic potential flow as the aerodynamic model and coupled with the finite element method for structural modelling, in order to construct the system of aeroelastic

N. Soltani; V. Esfahanian; H. Haddadpour; M. Behbahani-Nejad

2004-01-01

35

Investigation of Unsteady Aerodynamic Characteristics of a Seagull Wing in Level Flight  

Microsoft Academic Search

Unsteady aerodynamic characteristics of a seagull wing in level flight are investigated using a boundary element method. A new no-penetration boundary condition is imposed on the surface of the wing by considering its deformation. The geometry and kinematics of the seagull wing are reproduced using the functions and data in the previously published literature. The proposed method is validated by

Cheolheui Han

2009-01-01

36

High performance parallelized implicit Euler solver for the analysis of unsteady aerodynamic flows  

Microsoft Academic Search

Simulation of transient flows is more and more useful for industrial applications in aeronautics. For instance, the unsteady aerodynamic coefficients can be of great importance in order to predict the behavior of flying bodies: this is in particular the case for missiles which are spun around their longitudinal axis. It is also well known that the experimental tools used to

C. Borel; M. Bredif

1992-01-01

37

Transonic unsteady aerodynamics in the vicinity of shock-buffet instability  

NASA Astrophysics Data System (ADS)

A study of transonic unsteady aerodynamic responses in the vicinity of shock-buffet is presented. Navier-Stokes simulations of a NACA 0012 airfoil with a fitted 20% trailing edge flap are performed to compute the aerodynamic responses to prescribed pitch and flap motions, about mean flow conditions at shock-buffet onset, and while exhibiting shock buffet. The unsteady aerodynamic response is found to be fundamentally different from the response predicted by the linear aerodynamic theory. At mean angles of attack close to buffet onset noticeable damped resonance responses are observed at frequencies close to the buffet frequency. The responses grow as the mean angle of attack is increased towards buffet onset. Also, a phase lead is observed for the aerodynamic coefficients, for some range of frequencies. The large aerodynamic responses and phase lead appear in frequencies that are typical of structural elastic frequencies, suggesting that they may be responsible for transonic aeroelastic instabilities. At shock buffet conditions, prescribing sufficiently large pitch or flap harmonic motions results in synchronization of the buffet frequency with the excitation frequencies. At these conditions, the lift and pitching moment responses to prescribed pitch motion also result in resonance and phase lead, as in the pre-buffet case. Large prescribed flap motions eliminate the lift resonance response, and significantly reduce the lift coefficient amplitudes, indicating that the aerodynamic coefficients at these conditions can be controlled by prescribed structural motions.

Iovnovich, M.; Raveh, D. E.

2012-02-01

38

Numerical investigation of unsteady aerodynamic characteristics of a pitching missile  

Microsoft Academic Search

Three-dimensional Reynolds averaged Navier–Stokes numerical simulations were carried out to predict the aerodynamic loads of a pitching winged missile based on the finite volume method. The Baldwin–Lomax eddy viscosity model with the modifications suggested by Degani and Schiff was used here. The computational results of the aerodynamic loads of a slender revolution body are also given, and agreed well with

Lizhi Yang; Minghai Wang; Zhenghong Gao

2011-01-01

39

UNSTEADY AERODYNAMIC PERFORMANCE OF MODEL WINGS AT LOW REYNOLDS NUMBERS  

Microsoft Academic Search

Summary The synthesis of a comprehensive theory of force production in insect flight is hindered in part by the lack of precise knowledge of unsteady forces produced by wings. Data are especially sparse in the intermediate Reynolds number regime (10< Re<1000) appropriate for the flight of small insects. This paper attempts to fill this deficit by quantifying the time-dependence of

MICHAEL H. DICKINSON; KARL G. GÖTZ

1993-01-01

40

Unsteady Aerodynamic Flow Control of a Suspended Axisymmetric Moving Platform  

NASA Astrophysics Data System (ADS)

The aerodynamic forces on an axisymmetric wind tunnel model are altered by fluidic interaction of an azimuthal array of integrated synthetic jet actuators with the cross flow. Four-quadrant actuators are integrated into a Coanda surface on the aft section of the body, and the jets emanate from narrow, azimuthally segmented slots equally distributed around the model's perimeter. The model is suspended in the tunnel using eight wires each comprising miniature in-line force sensors and shape-memory-alloy (SMA) strands that are used to control the instantaneous forces and moments on the model and its orientation. The interaction of the actuation jets with the flow over the moving model is investigated using PIV and time-resolved force measurements to assess the transitory aerodynamic loading effected by coupling between the induced motion of the aerodynamic surface and the fluid dynamics that is driven by the actuation. It is shown that these interactions can lead to effective control of the aerodynamic forces and moments, and thereby of the model's motion.

Lambert, Thomas; Vukasinovic, Bojan; Glezer, Ari

2011-11-01

41

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

42

Wing flutter boundary prediction using unsteady Euler aerodynamic method  

Microsoft Academic Search

Modifications to an existing 3D implicit upwind Euler\\/Navier-Stokes code for the aeroelastic analysis of wings are described. These modifications include the incorporation of a deforming mesh algorithm and the addition of the structural equations of motion for their simultaneous time-integration with the governing flow equations. The paper gives a brief description of these modifications and presents unsteady calculations which check

Elizabeth M. Lee-Rausch; John T. Batina

1993-01-01

43

Aeroelastic coupling of geometrically nonlinear structures and linear unsteady aerodynamics: Two formulations  

NASA Astrophysics Data System (ADS)

Two different time domain formulations of integrating commonly used frequency-domain unsteady aerodynamic models based on a modal approach with full order finite element models for structures with geometric nonlinearities are presented. Both approaches are tailored to flight vehicle configurations where geometric stiffness effects are important but where deformations are moderate, flow is attached, and linear unsteady aerodynamic modeling is adequate, such as low aspect ratio wings or joined-wing and strut-braced wings at small to moderate angles of attack. Results obtained using the two approaches are compared using both planar and non-planar wing configurations. Sub-critical and post-flutter speeds are considered. It is demonstrated that the two methods lead to the same steady solution for the sub-critical case after the transients subside. It is also shown that the two methods predict the amplitude and frequency of limit cycle oscillation (when present) with the same accuracy.

Demasi, L.; Livne, E.

2009-07-01

44

Control of the corner separation in a compressor cascade by steady and unsteady plasma aerodynamic actuation  

Microsoft Academic Search

This paper reports experimental results on using steady and unsteady plasma aerodynamic actuation to control the corner separation,\\u000a which forms over the suction surface and end wall corner of a compressor cascade blade passage. Total pressure recovery coefficient\\u000a distribution was adopted to evaluate the corner separation. Corner separation causes significant total pressure loss even\\u000a when the angle of attack is

Ying-hong LiYun; Yun Wu; Min Zhou; Chang-Bing Su; Xiong-Wei Zhang; Jun-Qiang Zhu

2010-01-01

45

Aerodynamic properties of a wing performing unsteady rotational motions at low Reynolds number  

Microsoft Academic Search

Summary The aerodynamic forces and flow structures of a wing of relatively small aspect ratio in some unsteady rotational motions at low Reynolds number (Re=100) are studied by numerically solving the Navier-Stokes equations. These motions include a wing in constant-speed rotation after a fast start, wing accelerating and decelerating from one rotational speed to another, and wing rapidly pitching-up in

S. L. Lan; M. Sun

2001-01-01

46

Theoretical study on two-dimensional aerodynamic characteristics of unsteady wings.  

PubMed

A simple computing method based on a potential theory is developed for two-dimensional steady and unsteady deflected wings. This method of theoretical analysis is essentially related to thin and angular airfoils. Thus, the method is very simple but is effective to forecast aerodynamic forces for deflected or angular airfoils with a small camber operating in high Reynolds number flow, specifically in unsteady motion. The suction force acting on the leading edge of steady airfoils is theoretically obtained by using the Blasius formula. By Polhamus's leading edge suction analogy, the suction force is considered to be directed upward in partially separated flow for real thin airfoil with sharp leading edge. The theory can also be applied to obtain the aerodynamic characteristics of thin airfoils operating on low Reynolds number flow under some degree of approximation. This is very useful for the unsteady aerodynamic analysis because the Navier-Stokes equation can be solved by neither analytical nor numerical method for the thin and angular airfoils, which are common in the insect wing. PMID:15721036

Azuma, Akira; Okamoto, Masato

2005-01-04

47

Using of large amplitude free oscillations in pitch and roll to investigate unsteady aerodynamic characteristics at separated flow regimes  

Microsoft Academic Search

The experimental technique of large amplitude dynamic setups is given. These setups are using to investigate unsteady aerodynamic characteristics at high angles of attack at low subsonic wind tunnel. The data processing technique and some experimental results are presented. The dynamic properties of separation flow development are investigated on the example of aerodynamic model with high aspect ratio wing large

A. Khrabrov; A. Zhuk

1995-01-01

48

Effects of nonlinear unsteady aerodynamics on performance, stability and control of an F-18 configuration  

NASA Astrophysics Data System (ADS)

Large-amplitude forced oscillation data for an F-18 configuration are analyzed with two modeling methods: Fourier functional analysis to form the indicial integrals, and a generalized dynamic aerodynamic model for stability and control analysis. The indicial integral is first applied to calculate the pitch damping parameter for comparison with the conventional forced oscillation test. It is shown that the reduced frequency affects the damping much more strongly than the test amplitude. Using the indicial integral models in a flight simulation code for an F-18 configuration, it is found that the configuration with unsteady aerodynamics becomes unstable in pitch if the pitch rate is high, in contrast to the quasi-steady configuration which depends mainly on the instantaneous angle of attack. In a pitch-up maneuver in the post-stall regime the configuration with unsteady aerodynamics can stay at a high pitch attitude and angle of attack without losing altitude for a much longer duration than the quasi-steady model. However, the speed will decrease faster because of higher drag. The newly developed generalized dynamic aerodynamic model is of the nonlinear algebraic form with the coefficients being determined from a set of large amplitude oscillatory experimental data by using least-square fitting. The resulting model coefficients are functions of the reduced frequency and amplitude. The new aerodynamic models have been verified with data in harmonic oscillation with a smaller amplitude and in constant pitch-rate motions. The new algebraic models are especially useful in stability and control analysis, and are used in bifurcation analysis and control studies for the same F-18 HARV configuration. The results show significant differences in the equilibrium surfaces and dynamic stability. It is also shown that control gains developed with the conventional quasi-steady aerodynamic data may not be adequate when the effect of unsteady aerodynamics is significant. A numerical longitudinal pilot-induced oscillation (PIO) prediction method is developed. This method is based on modeling the PIO phenomena as limit cycle oscillations and the pilot action as feedback control. Not only the PIO susceptibility but also the PIO severity can be predicted by using the proposed method.

Lin, Guofeng

49

Computationally fast harmonic balance methods for unsteady aerodynamic predictions of helicopter rotors  

NASA Astrophysics Data System (ADS)

A harmonic balance technique for the analysis of unsteady flows about helicopter rotors in forward flight and hover is presented in this paper. The aerodynamics of forward flight are highly nonlinear, with transonic flow on the advancing blade, subsonic flow on the retreating blade, and stalled flow over the inner portion of the rotor. Nevertheless, the unsteady flow is essentially periodic in time making it well suited for frequency domain analysis. The present method uses periodic boundary conditions that allows one to model the flow field on a computational grid around a single helicopter blade, no matter the actual blade count. Using this approach, we compute several solutions, each one corresponding to one of several instants in time over one period. These time levels are coupled to each other through a spectral time derivative operator in the interior of the computational domain and through the far-field and periodic boundary conditions around the boundary of the domain. In this paper, we apply the method to the three-dimensional Euler equations (although the method can also be applied to three-dimensional viscous flows), and examine the steady and unsteady aerodynamics about wings and rotors.

Ekici, Kivanc; Hall, Kenneth C.; Dowell, Earl H.

2008-06-01

50

Evaluation of horizontal-axis wind-turbine-blade loads using unsteady aerodynamics  

SciTech Connect

Most existing analyses of the blade loads on horizontal axis wind turbines are conducted using linear steady-state aerodynamics, but evaluation of loads resulting from wind turbulence or gusts may not be adequate using these techniques. This study develops single-parameter approximations for both the shed wake and trailing wake components of the unsteady aerodynamics and incorporates them into a code that evaluates mean and cyclic blade loading. The effect on loads due to the deterministic effects of wind shear and tower interference and the stochastic effects of wind turbulence are examined. The aeroelastic equations including degrees of freedom for blade flexing and axial tower motion are solved in the time domain using turbulent wind input. Verification of the single-parameter models is by comparison to general analytic solutions and test data available in the literature. The model for shed wake is compared to exact solutions for translating airfoils and to two-dimensional approximations for rotary-wing effects. Two trailing wake models are evaluated using results from wind turbine tests and helicopter analysis. Comparison of loads predictions is made to Howden 330/26 Wind Turbine data showing good agreement for cyclic and mean loads. Results show that the largest contribution from unsteady aerodynamics is an increase in mean loads due to the induced velocity lag caused by the trailing wake.

Hartin, J.R.

1989-01-01

51

Unsteady operation of new type turbofan engine with aerodynamic torque converter reducing front fan speed  

NASA Astrophysics Data System (ADS)

It is desired to increase the rotational speed of the core engine of the turbofan so as to get the best efficiency for the next leap of engine technology. The conventional mechanism in which the front fan is directly connected to the output shaft of a core engine, have a limit of increasing the spool speed, because the fan diameter is very large. The authors have proposed a new driving system in which the front fan is driven through the aerodynamic torque converter. The front fan can work at the best performance at slower speed while the core engine runs more efficiently at higher speed. Continuously, this paper discusses the response of the front fan in the unsteady operation of the core engine, accompanying with the internal flow. The system has the acceptable responsibility in the unsteady operation which is very important for the aircrafts.

Kanemoto, Toshiaki; Seki, Seita; Ideno, Kazunori; Galal, Ahmed Mohamed

2005-09-01

52

Unsteady aerodynamic forces estimation on a square cylinder by TR-PIV  

Microsoft Academic Search

The unsteady aerodynamic forces acting on a square cross-sectional cylinder are investigated by means of time-resolved particle\\u000a image velocimetry (TR-PIV) at Reynolds number 4,900. The objective of the investigation is to prove the feasibility of non-intrusive\\u000a force measurements around two-dimensional bodies. The PIV measurements performed at a rate of 1 kHz enable a time resolved\\u000a (TR) description of the vortex shedding

D. F. Kurtulus; F. Scarano; L. David

2007-01-01

53

Experimental determination of unsteady aerodynamic coefficients and flutter behavior of a rigid wing  

NASA Astrophysics Data System (ADS)

In this paper, unsteady aerodynamic forces acting on a three-dimensional wing and its aeroelastic behavior are determined experimentally using a novel semi-experimental method. Towards this end, a rigid wing specimen was fabricated and tested in a low speed, subsonic wind tunnel with two motion sensors for plunging and pitching. Time history samples of the wing motion were obtained at a single air speed and processed using the “Aerodynamics is Aeroelasticity Minus Structure” (AAEMS) system identification method to generate a reduced-order aerodynamic model in discrete-time, state-space format. Coupling the aerodynamic model with the structural model, obtained from the ground vibration test (GVT), results in a reduced-order aeroelastic model that can be analyzed with a variable dynamic pressure. Despite the absence of pressure measurements the model yields a good prediction of aeroelastic behavior, especially for lightly damped modes and for a wide range of dynamic pressures, including the flutter point. It is shown that when the dynamic pressure is at 29.6% of the critical flutter value the method estimates the flutter speed with less than 2% error. However, as the reference dynamic pressure is lowered (relative to the flutter dynamic pressure) the flutter prediction becomes less accurate due to the lack of pressure data. The experimental procedure outlined in this paper can be useful when predicting flutter based on data obtained at sub-critical dynamic pressures.

Song, Jieun; Kim, Taehyoun; Song, Seung Jin

2012-02-01

54

Unsteady aerodynamics and flow control for flapping wing flyers  

Microsoft Academic Search

The creation of micro air vehicles (MAVs) of the same general sizes and weight as natural fliers has spawned renewed interest in flapping wing flight. With a wingspan of approximately 15cm and a flight speed of a few meters per second, MAVs experience the same low Reynolds number (104–105) flight conditions as their biological counterparts. In this flow regime, rigid

Steven Ho; Hany Nassef; Nick Pornsinsirirak; Yu-Chong Tai; Chih-Ming Ho

2003-01-01

55

Unsteady aerodynamics and flow controlfor flapping wing flyers  

Microsoft Academic Search

The creation of micro air vehicles (MAVs) of the same general sizes and weight as natural fliers has spawned renewed interest in flapping wing flight. With a wingspan of approximately 15 cm and a flight speed of a few meters per second, MAVs experience the same low Reynolds number (104-105) flight conditions as their biological counterparts. In this flow regime,

Steven Ho; Hany Nassef; Nick Pornsinsirirak; Yu-Chong Tai; Chih-Ming Ho

56

Unsteady aerodynamics of missiles. Part 3: Determination of the longitudinal stability of wings at high angles of attack in supersonic flight  

Microsoft Academic Search

A theoretical method for the determination of unsteady aerodynamic coefficients associated with the longitudinal stability of slender wings in supersonic flight is presented. It is based on the indicial functional theory of Tobak. Extension to higher incidences is effected by combining the indicial functions with steady nonlinear coefficients derived from a semiempiricial procedure. The unsteady nonlinear aerodynamic coefficients are determined

C. P. Schneider

1980-01-01

57

Unsteady aerodynamics of rotorcraft at low advance ratios in ground effect  

NASA Astrophysics Data System (ADS)

The aerodynamic characteristics of rotorcraft flying at low speed close to the ground are investigated. This will help better understand and quantify the flow field structures and unsteadiness associated with various in ground effect flight conditions. This study aims to separate out the various phenomena according to their causal factors. Experimental investigations first involved flow visualization, which helped in identifying the various flight regimes and in getting an approximate estimate of the unsteadiness. It was found that there was considerably more unsteadiness in the flowfield while in ground effect. The problem was thereafter divided into its unsteady and quasi-steady aspects. Hotwire measurements were performed and the unsteadiness in the flow structure was quantified. It was found that there were long time scale fluctuations in the upwind side of the rotor disk, with significant changes in the inflow. These fluctuations were quantified and related to the flow parameters, which will help scale the results. On the quasi-steady side, the fuselage loads for two fuselage cross-sectional shapes were investigated both in and out of ground effect. The fuselage cross-section shape had a significant effect on the loads felt by the fuselage in ground effect. It was found that the sideforce on a circular cross-section fuselage was considerably different when flying close to the ground. The power required for the experimental configuration was measured to provide a basis for comparison. Finally, the flowfield around the ground vortex was quantified, and the structure of the ground vortex was investigated using Particle Image Velocimetry. It was found that tip vorticity was ingested by the ground vortex and that the strength of the ground vortex was considerably more than the tip vortex.

Ganesh, Balakrishnan

58

A computational investigation of the three-dimensional unsteady aerodynamics of Drosophila hovering and maneuvering.  

PubMed

Three-dimensional unsteady computations of the flow past a fruit fly Drosophila under hovering and free flight conditions are computed. The kinematics of the wings and the body of the fruit fly are prescribed from experimental observations. The computed unsteady lift and thrust forces are validated with experimental results and are in excellent agreement. The unsteady aerodynamic origin of the time-varying yaw moment is identified. The differences in the kinematics between the right and the left wings show that subtle change in the stroke angle and deviation angle can result in the yaw moment for the turning maneuver. The computed yaw moment reaches a peak value at the beginning of the maneuver and remains positive throughout the remainder of the maneuver. The origin of the yaw moment is investigated by computing the center of pressures on each wing and the individual moment arms. This investigation leads to the conclusion that it is the forward force and a component of the lift force that combine to produce the turning moment while the side force alone produces the restoring torque during the maneuver. The vorticity shed from the wing's leading edge and the tips show a loop like structure that during stroke reversals pinches off into Lambda-like structures that have not been previously observed in the wakes of flapping fliers. PMID:17297147

Ramamurti, Ravi; Sandberg, William C

2007-03-01

59

An investigation into the effects of unsteady parameters on the aerodynamics of a low Reynolds number pitching airfoil  

Microsoft Academic Search

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

M. R. Amiralaei; H. Alighanbari; S. M. Hashemi

2010-01-01

60

Identification of an unsteady aerodynamic model up to high angle of attack regime  

NASA Astrophysics Data System (ADS)

The harmonic oscillatory tests for a fighter aircraft configuration using the Dynamic Plunge-Pitch-Roll (DyPPiR) model mount at Virginia Tech Stability Wind Tunnel are described and analyzed. The corresponding data reduction methods are developed on the basis of multirate digital signal processing techniques. Since the model is sting-mounted to the support system of DyPPiR, the Discrete Fourier Transform (DFT) is first used to identify the frequencies of the elastic modes of sting. Then the sampling rate conversion systems are built up in digital domain to resample the data at a lower rate without introducing distortions to the signals of interest. Finally linear-phase Finite Impulse Response (FIR) filters are designed by Remez exchange algorithm to extract the aerodynamic characteristics responses to the programmed motions from the resampled measurements. These data reduction procedures are also illustrated through examples. The results obtained from the harmonic oscillatory tests are then illustrated and the associated flow mechanisms are discussed. Since no significant hysteresis loops are observed for the lift and the drag coefficients for the current angle of attack range and the tested reduced frequencies, the dynamic lags of separated and vortex flow effects are small in the current oscillatory tests. However, large hysteresis loops are observed for pitch moment coefficient in the current tests. This observation suggests that at current flow conditions, pitch moment has large pitch rate dotalpha dependencies. Then the nondimensional maximum pitch rate \\ qsb{max} is introduced to characterize these harmonic oscillatory motions. It is found that at current flow conditions, all the hysteresis loops of pitch moment coefficient with same \\ qsb{max} are tangential to one another at both top and bottom of the loops, implying approximately same maximum offset of these loops from static values. Several cases are also illustrated. Based on the results obtained and those from references, a state-space model is developed to describe the unsteady aerodynamic characteristics up to the high angle of attack regime. A nondimensional coordinate is introduced as the state variable describing the flow separation or vortex burst. First-order differential equation is used to govern the dynamics of flow separation or vortex bursting through this state variable. To be valid for general configurations, Taylor series expansions in terms of the input variables are used in the determination of aerodynamic characteristics, resembling the current approach of the stability derivatives. However, these derivatives are longer constant. They are dependent on the state variable of flow separation or vortex burst. In this way, the changes in stability derivatives with the angle of attack are included dynamically. The performance of the model is then validated by the wind-tunnel measurements of an NACA 0015 airfoil, a 70sp° delta wing and, finally two F-18 aircraft configurations. The results obtained show that within the framework of the proposed model, it is possible to obtain good agreement with different unsteady wind tunnel data in high angle-of-attack regime.

Fan, Yigang

1997-12-01

61

Unsteady Aerodynamics for Micro Air Vehicles (Aerodynamique instable pour micro-vehicules aeriens).  

National Technical Information Service (NTIS)

Recognizing that the flowfield environments encountered by Micro Air Vehicles (MAVs) are fundamentally unsteady - whether for fixed-wing, rotary- wing or flapping-wing configurations, AVT-149 seeks to address fundamental questions in unsteady low Reynolds...

2010-01-01

62

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

63

Unsteady Aerodynamic Response of Oscillating Contra-Rotating Annular Cascades Part I: Description of Model and Mathematical Formulations  

NASA Astrophysics Data System (ADS)

The purpose of this paper is to study the effect of neighboring blade rows on the unsteady aerodynamic response of oscillating cascade blades on the basis of a genuine three-dimensional model. To this end, mathematical formulations based on the lifting surface theory are developed for a pair of contra-rotating annular cascades of oscillating blades. The mechanism of frequency scattering of blade loadings and mode scattering of acoustic waves resulting from interaction between the blade rows in relative rotational motions is mathematically explained. Simultaneous integral equations for all frequency components of blade loadings are derived from the flow tangency condition on the blade surfaces of both blade rows. The validity of the computation codes is verified.

Namba, Masanobu; Nishino, Ryohei

64

Aerodynamics and performance testing of the VAWT  

NASA Astrophysics Data System (ADS)

The aerodynamics and testing of vertical axis wind turbines are discussed. Experiments designed to both better understand the aerodynamics of a section operating in an unsteady, curvilinear flowfield and achieve some of the desired changes in section properties are discussed. The common goal of all of these experiments is to increase efficiency an system reliability.

Klimas, P. C.

65

Aerodynamics and performance testing of the VAWT  

Microsoft Academic Search

The aerodynamics and testing of vertical axis wind turbines are discussed. Experiments designed to both better understand the aerodynamics of a section operating in an unsteady, curvilinear flowfield and achieve some of the desired changes in section properties are discussed. The common goal of all of these experiments is to increase efficiency an system reliability.

P. C. Klimas

1981-01-01

66

Program User's Manual for an Unsteady Helicopter Rotor-Fuselage Aerodynamic Analysis.  

National Technical Information Service (NTIS)

The Rotor-Fuselage Analysis is a method of calculating the aerodynamic reaction between a helicopter rotor and fuselage. This manual describes the structure and operation of the computer programs that make up the Rotor-Fuselage Analysis, programs which pr...

P. F. Lorber

1988-01-01

67

DEVELOPMENT OF EFFICIENT AND ACCURATE CFD TECHNOLOGIES FOR WIND TURBINE UNSTEADY AERODYNAMICS  

Microsoft Academic Search

This paper focuses on novel unsteady and low- speed algorithmic developments of a structured explicit Euler solver and an unstructured implicit Euler\\/RANS solver for wind turbine CFD. The central topics are a) a discussion on the definition of optimal low-speed preconditioning for explicit solvers featuring state-of-the-art convergence acceleration methods, b) the presentation of a sim- ple optimal mixed preconditioning strategy,

M. Sergio CAMPOBASSO; Aldo BONFIGLIOLI; Mohammad BABA-AHMADI

68

Determination of Compressible Unsteady Aerodynamic Forces on a Finite Number of Weakly Curved Cascade of Arbitrary Depth in Plane Flow Bestimmung Kompressibler, Instationaerer Luftkraefte an Einer Endlichen Zahl Schwach Gekruemmter Kaskadenschaufeln Beliebiger Tiefe in Ebener Stroemung.  

National Technical Information Service (NTIS)

The method described is based on the panel-technique, which allows the calculation of approximate unsteady aerodynamic forces on a finite, harmonically vibrating cascade consisting of slightly curved lifting surfaces (vanes) and boundary surfaces in a two...

W. Schuler

1976-01-01

69

Unsteady aerodynamic forces and power requirements of a bumblebee in forward flight  

Microsoft Academic Search

Aerodynamic forces and power requirements in forward flight in a bumblebee (Bombus terrestris) were studied using the method of computational fluid dynamics. Actual wing kinematic data of free flight were used in the study (the speed ranges from 0 m\\/s to 4.5 m\\/s; advance ratio ranges from 0–0.66). The bumblebee employs the delayed stall mechanism and the fast pitching-up rotation

Jianghao Wu; Mao Sun

2005-01-01

70

Aerodynamics.  

National Technical Information Service (NTIS)

A brief review of aerodynamic investigations currently underway at the Institute for Aerospace Studies is provided. An extensive investigation of airship dynamics and turbulence response has resulted in the development of a numerical analysis of airship d...

J. D. Delaurier G. W. Johnston D. W. Zingg W. D. Mckinney C. Hayball

1989-01-01

71

Application of Two-Dimensional Unsteady Aerodynamic to a Free-Tip Rotor Response Analysis.  

National Technical Information Service (NTIS)

The free-tip rotor utilizes a rotor blade tip which is structurally decoupled from the blade inboard section. The tip is free to pitch about its own pitch axis to respond to the local flow angularity changes. The tip also experiences the heaving motion du...

L. Yates H. Kumagai

1985-01-01

72

A comparison of baseline aerodynamic performance of optimally-twisted versus non-twisted HAWT blades  

SciTech Connect

NREL has completed the initial twisted blade field tests of the ``Unsteady Aerodynamics Experiment.`` This test series continues systematic measurements of unsteady aerodynamic phenomena prevalent in stall-controlled horizontal axis wind turbines (HAWTs). The blade twist distribution optimizes power production at a single angle of attack along the span. Abrupt transitions into and out of stall are created due to rapid changes in inflow. Data from earlier experiments have been analyzed extensively to characterize the steady and unsteady response of untwisted blades. In this report, a characterization and comparison of the baseline aerodynamic performance of the twisted versus non-twisted blade sets will be presented for steady flow conditions.

Simms, D A; Robinson, M C; Hand, M M; Fingersh, L J

1995-01-01

73

Prediction of Unsteady Aerodynamic Loadings Caused by Trailing Edge Control Surface Motions in Subsonic Compressible Flow Analysis and Results.  

National Technical Information Service (NTIS)

A theoretical analysis and a computer program have been developed for the prediction of unsteady lifting surface loadings caused by motions of trailing edge control surfaces having sealed gaps. The final form of the downwash integral equation has been for...

W. S. Rowe B. A. Winther M. C. Redman

1972-01-01

74

Prediction of Unsteady Aerodynamic Loadings Caused by Trailing Edge Control Surface Motions in Subsonic Compressible Flow Computer Program Description.  

National Technical Information Service (NTIS)

A digital computer program has been developed to calculate unsteady loadings caused by motions of lifting surfaces with trailing edge control based on the subsonic kernal function approach. The pressure singularities at hinge line and side edges have been...

M. C. Redman W. S. Rowe B. A. Winther

1972-01-01

75

Aerodynamic, Unsteady, Kinetic and Heat Loss Effects on the Dynamics and Structure of Weakly-Burning Flames.  

National Technical Information Service (NTIS)

The first objective of the program is to introduce the meritorious counterflow methodology in microgravity in order to quantify the steady and unsteady characteristics of weakly-burning premixed and diffusion flames for a wide variety of conditions includ...

F. N. Egolfopoulos

1995-01-01

76

Research of the Rotational Effects on the Aerodynamics Characteristics of Horizontal Axis Wind Turbine  

Microsoft Academic Search

The flow Held of the NREL phase VI horizontal axis wind turbine has been modeled with a full 3-D steady\\/unsteady RANS approach. In the investigations a full Navier Stokes code FLUENT is used instead of engineering models. The calculations are compared with the measurements of the Unsteady aerodynamic experiment at the NASA Ames wind tunnel at wind speeds between 8

Rui Yang; Ren-Nian Li

2009-01-01

77

A Basic Experiment on the Aerodynamics of Sniffing  

NASA Astrophysics Data System (ADS)

Our previous work (APS/DFD97:Ii1 and 98:FA10) used flow visualization to observe canine olfaction. The results raised some basic questions about the aerodynamics of sniffing, e.g. what flow rate is required, as a function of distance from a scent source, to acquire a detectable scent? Commercial sampler technology does not address such questions. A basic experiment was thus designed to investigate the aerodynamic phenomena and performance of sniffing. A stable thermal layer on a horizontal plane was used as a "scent" source per Reynolds Analogy. The detector was a thermocouple inside a sniffer tube. Flow patterns were observed by schlieren. Results show the importance of sniffer proximity to localize a scent source. A transient scent spike occurs at the sniff onset, followed by signal decline due to source depletion. Sniffing shows extreme sensitivity to disruptive air currents. Unstably-stratified scent sources (thermal plumes) are also considered. These results help us understand evolved sniffing behavior, and they suggest sampler design criteria for electronic-nose devices. (Research supported by DARPA.)

Settles, Gary S.; Kester, Douglas A.

1999-11-01

78

Progress in smart rotor research for wind turbines: experimental and computational approaches to active aerodynamic control  

Microsoft Academic Search

Active distributed aerodynamic control for load reduction on wind turbine blades is an innovative concept, inspired by rotorcraft research, often named as smart rotor control. In this stage of research, unsteady aerodynamic models and small scale experimental setups are developed, investigating the potential and implementation of such concepts. This paper describes a successful wind tunnel experiment on a dynamically scaled

A. K. Barlas

2007-01-01

79

Unsteady aerodynamics of dragonfly using a wing-wing model from the perspective of a force decomposition  

NASA Astrophysics Data System (ADS)

The lift and thrust associated with insect flight strongly depend on the complex wake patterns produced by wing-wing and wing-wake interactions. We propose to investigate the aerodynamics of dragonfly using a simplified wing-wing model from the perspective of many-body force decomposition (JFM 600, p95) and the associated force elements. The aerodynamic force, lift or thrust, of the wing-wing system is analyzed in terms of its four constituent components, each of which is directly related to a physical effect. These force components for each individual wing include two potential contributions credited to the wing motion itself, contribution from the vorticity within the flow, and contributions from the surface vorticity on its and other wing's surfaces. The potential contribution due to added-mass effect is often non-negligible. Nevertheless, the major contribution to the forces comes from the vorticity within the flow. The relative importance of these components relies heavily on the motions of the two wings such as the respective angles of attack, the amplitude and speed of translational motions, and the amplitude and speed of wing rotations. In addition to the dynamic stall vortex, several important mechanisms of high lift or thrust are also identified.

Chu, Chin-Chou; Chang, Chien C.; Hsieh, Chen-Ta

2009-11-01

80

Boundary-layer receptivity to unsteady pressure gradients Experiments and overview  

NASA Astrophysics Data System (ADS)

The experimental results on boundary-layer receptivity to unsteady pressure gradients in forced flows are discussed in the framework of a receptivity mechanism for the general case of flows (generating the Tollmien-Schlichting-Schubauer waves) around bodies with finite thickness in which the amplitude of the unsteady pressure gradient varies along the surface. The experiments were conducted in the Illinois Institute of Technology Open-Throat Visualization Facility. Various configurations of a pulsating pressure source and shielding plates located in the free stream supplied the variable-amplitude pressure gradients over the nearby flat-wall boundary layer. Three of the cases studied demonstrated that stationary unsteady pressure fields induce Stokes-like sublayers when the boundary layer is stable, and self-excited vorticity waves when it is unstable. The results of a fourth experiment suggest that unsteady pressure sources in wakes near the boundary layer can force the growth of unstable wall waves at the wake frequencies even though their propagation differs.

Nishioka, M.; Morkovin, M. V.

1986-10-01

81

Aerodynamics and performance testing of the VAWT  

SciTech Connect

Early investigations suggest that reductions in cost of energy (COE) and increases in reliability for VAWT systems may be brought about through relatively inexpensive changes to the current aerodynamic design. This design uses blades of symmetrical cross-section mounted such that the radius from the rotating tower centerline is normal to the blade chord at roughly the 40% chord point. The envisioned changes to this existing design are intended to: (1) lower cut-in windspeed; (2) increase maximum efficiency; (3) limit maximum aerodynamic power; and (4) limit peak aerodynamic torques. This paper describes certain experiments designed to both better understand the aerodynamics of a section operating in an unsteady, curvilinear flowfield and achieve some of the desired changes in section properties. The common goal of all of these experiments is to lower VAWT COE and increase system reliability.

Klimas, P.C.

1981-01-01

82

Aerodynamics and performance testing of the VAWT  

NASA Astrophysics Data System (ADS)

Relatively inexpensive changes to the current aerodynamic design which may bring about reductions in cost of energy (COE) and increases in reliability for VAWT systems are discussed. This design uses blades of symmetrical cross section mounted such that the radius from the rotating tower centerline is normal to the blade chord at roughly the 40% chord point. The envisioned changes to this existing design are intended to: (1) lower cut in windspeed; (2) increase maximum efficiency; (3) limit maximum aerodynamic power; and (4) limit peak aerodynamic torques. Experiments to better understand the aerodynamics of a section operating in an unsteady, curvilinear flowfield and achieve some of the desired changes in section properties are described.

Klimas, P. C.

83

NACA0012 Yokugata Mawari No Kogyokaku Niokeru Hiteijo Kukiryoku No Keisan (Unsteady Aerodynamic Computations around NACA0012 at High Angles of Attack).  

National Technical Information Service (NTIS)

In the present study, periodic flows are simulated around NACA 0012 airfoil at high angle of attack to validate the unsteady Navier-Stokes code. Thin-layer approximated unsteady Navier-Stokes equations are integrated in a time-dependent manner with Baldwi...

K. Miyata J. Nakamichi R. Murao

1992-01-01

84

Effect of Unsteady Variations in Horizontal Flow Velocity on the Unsteady Aerodynamic Forces on a Preloaded Lifting Surface Einfluss Instationaerer Aenderungen der Horizontalen Anstroemgeschwindigkeit Auf die Instationaeren Luftkraefte an Einer Vorbelasteten Auftriebsflaeche.  

National Technical Information Service (NTIS)

Analytical investigations were carried out for the special practical problems of the fixed wing and the rotary wing. Two corresponding mathematical methods were developed in the two-dimensional incompressible case considering the unsteady variation of hor...

D. Herberg W. Schuler

1975-01-01

85

Recent darrieus Vertical-Axis Wind Turbine aerodynamical experiments at Sandia National Laboratories  

NASA Astrophysics Data System (ADS)

The aerodynamics of airfoils operating in the vertical axis wind turbine (VAWT) environment were examined. The experiments are intended to reduce VAWT cost of energy an increase system reliability. The experiments include: (1) chordwise pressure surveys; (2) circumferential blade acceleration surveys; (3) effects of blade camber; (4) pitch and offset; (5) blade blowing; and (6) use of sections designed specifically for VAWT application.

Klimas, P. C.

86

Recent Darrieus vertical axis wind turbine aerodynamical experiments at Sandia National Laboratories  

NASA Astrophysics Data System (ADS)

Experiments contributing to the understanding of the aerodynamics of airfoils operating in the vertical axis wind turbine (VAWT) environment are described. These experiments are ultimately intended to reduce VAWT cost of energy and increase system reliability. They include chordwise pressure surveys, circumferential blade acceleration surveys, effects of blade camber, pitch and offset, blade blowing, and use of sections designed specifically for VAWT application.

Klimas, P. C.

1981-05-01

87

Recent Darrieus vertical-axis wind turbine aerodynamical experiments at Sandia National Laboratories  

SciTech Connect

Experiments contributing to the understanding of the aerodynamics of airfoils operating in the vertical axis wind turbine (VAWT) environment are described. These experiments are ultimately intended to reduce VAWT cost of energy and increase system reliability. They include chordwise pressure surveys, circumferential blade acceleration surveys, effects of blade camber, pitch and offset, blade blowing, and use of sections designed specifically for VAWT application.

Klimas, P.C.

1981-01-01

88

Prediction of Unsteady Aerodynamic Loadings Caused by Leading Edge and Trailing Edge Control Surface Motions in Subsonic Compressible Flow: Analysis and Results.  

National Technical Information Service (NTIS)

A theoretical analysis and computer program was developed for the prediction of unsteady lifting surface loadings caused by motions of leading edge and trailing edge control surfaces having sealed gaps. The final form of the downwash integral equation was...

W. S. Rowe M. C. Redman F. E. Ehlers J. D. Sebastian

1975-01-01

89

Prediction of Unsteady Aerodynamic Loadings Caused by Leading Edge and Trailing Edge Control Surface Motions in Subsonic Compressible Flow: Computer Program Description.  

National Technical Information Service (NTIS)

A digital computer program has been developed to calculate unsteady loadings caused by motions of lifting surfaces with leading edge or trailing edge controls based on the 9subsonic kernel function approach. The pressure singularities at hinge line and si...

M. C. Redman W. S. Rowe

1975-01-01

90

Interaction of unsteady separated flow over multi-bodies moving relatively in the same flow field  

NASA Astrophysics Data System (ADS)

Unsteady separated flow is one of research frontiers in current aerodynamic. Great accomplishments have been acquired; however, most studies are on single body in a stream, such as studies on unsteady separated flows over airfoils. There are typical cases in the nature and engineering applications, in which several interacting bodies with relative motions are within the same flow field. These interacting unsteady separated flow fields not only are closely related to the phenomena of noise and flutter induced by flows, but also have strong influences on aerodynamic performances. With axial flow compressors as background, the present paper carried out studies on ‘interaction of unsteady separated flow over multi-bodies moving relatively in the same flow field’. Experiment investigations carried out in the stationary annular cascade wind tunnel and the single-stage low-speed axial flow compressor experimental facility as well as relevant CFD simulations demonstrate that under properly organized interactions between all unsteady components, the time-space structure of unsteady separated flow field can be remarkably improved and the time-averaged aerodynamic performances be significantly enhanced accordingly. The maximum reduction of the loss coefficient reached 27.4% and 76.5% in the stationary annular cascade wind tunnel and the CFD simulation for single-stage axial flow compressor, respectively.

Zhou, Sheng; Zheng, Xin-Qian; Hou, An-Ping; Lu, Ya-Jun

2005-12-01

91

Studies of mean and unsteady flow in a swirled combustor using experiments, acoustic analysis, and large eddy simulations  

Microsoft Academic Search

The turbulent flow within a complex swirled combustor is studied with compressible large eddy simulation (LES), acoustic analysis, and experiments for both cold and reacting flows. Detailed fields of axial, tangential, and radial velocities (average and RMS) given by LES are compared with experimental values measured by LDV. The unsteady activity is identified using LES and acoustic tools for the

S. Roux; G. Lartigue; T. Poinsot; U. Meier; C. Bérat

2005-01-01

92

Dynamic test rig and test technique for the aircraft models unsteady aerodynamic characteristics measurements in high subsonic and transonic wind tunnels  

Microsoft Academic Search

The new dynamic test rig is designed in TsAGI to investigate the aerodynamic damping derivatives of the aircraft models in wind tunnels at high subsonic and transonic speeds. The action of the rig is based on the free oscillations method with the use of elastic elements. The dynamic test rig is equipped with the five component strain gage balance. Both

S. V. Kabin; K. A. Kolinko; A. N. Khrabrov; P. D. Nushtaev

1995-01-01

93

DOE's Effort to Reduce Truck Aerodynamic Drag-Joint Experiments and Computations Lead to Smart Design  

SciTech Connect

At 70 miles per hour, overcoming aerodynamic drag represents about 65% of the total energy expenditure for a typical heavy truck vehicle. The goal of this US Department of Energy supported consortium is to establish a clear understanding of the drag producing flow phenomena. This is being accomplished through joint experiments and computations, leading to the 'smart' design of drag reducing devices. This paper will describe our objective and approach, provide an overview of our efforts and accomplishments, and discuss our future direction.

McCallen, R; Salari, K; Ortega, J; DeChant, L; Hassan, B; Roy, C; Pointer, W; Browand, F; Hammache, M; Hsu, T; Leonard, A; Rubel, M; Chatalain, P; Englar, R; Ross, J; Satran, D; Heineck, J; Walker, S; Yaste, D; Storms, B

2004-06-17

94

An unsteady airfoil theory applied to pitching motions validated against experiment and computation  

NASA Astrophysics Data System (ADS)

An inviscid theoretical method that is applicable to non-periodic motions and that accounts for large amplitudes and non-planar wakes (large-angle unsteady thin airfoil theory) is developed. A pitch-up, hold, pitch-down motion for a flat plate at Reynolds number 10,000 is studied using this theoretical method and also using computational (immersed boundary method) and experimental (water tunnel) methods. Results from theory are compared against those from computation and experiment which are also compared with each other. The variation of circulatory and apparent-mass loads as a function of pivot location for this motion is examined. The flow phenomena leading up to leading-edge vortex shedding and the limit of validity of the inviscid theory in the face of vortex-dominated flows are investigated. Also, the effect of pitch amplitude on leading-edge vortex shedding is examined, and two distinctly different vortex-dominated flows are studied using dye flow visualizations from experiment and vorticity plots from computation.

Ramesh, Kiran; Gopalarathnam, Ashok; Edwards, Jack R.; Ol, Michael V.; Granlund, Kenneth

2013-11-01

95

Preliminary Results of Unsteady Blade Surface Pressure Measurements for the SR-3 Propeller.  

National Technical Information Service (NTIS)

Unsteady blade surface pressures were measured on an advanced, highly swept propeller known as SR-3. These measurements were obtained because the unsteady aerodynamics of these highly loaded transonic blades is important to noise generation and aeroelasti...

L. J. Heidelberg B. J. Clark

1986-01-01

96

Experimental Studies on the Dynamic Development and Control of Unsteady Separated Flows.  

National Technical Information Service (NTIS)

It appears clear that substantial lift enhancement and stall delay are some of the beneficial consequences of certain unsteady aerodynamic conditions. Energetic vorticity dominated flows elicited through forced unsteady flow separation about a pitch airfo...

H. E. Helin

1986-01-01

97

DEVELOPMENT OF A DISCRETE-TIME AERODYNAMIC MODEL FOR CFD BASED AEROELASTIC ANALYSIS  

Microsoft Academic Search

System identification is used to develop an accurate and computationally efficient discrete-time aerodynamic model of a three-dimensional, unsteady CFD solution. This aerodynamic model is then used in place of the unsteady CFD solution in a coupled aeroelastic analysis resulting in a substantial savings in computational time. The methodology has the advantage of producing an explicit mathematical relationship for the aerodynamic

Timothy J. Cowan; Andrew S. Arena; Kajal K. Gupta

98

Real-Time Unsteady Loads Measurements Using Hot-Film Sensors.  

National Technical Information Service (NTIS)

Several flight-critical aerodynamic problems such as buffet, flutter, stall, and wing rock are strongly affected or caused by abrupt changes in unsteady aerodynamic loads and moments. Advanced sensing and flow diagnostic techniques have made possible simu...

A. S. Mangalam T. R. Moes

2004-01-01

99

Unsteady high-pressure flow experiments with applications to explosive volcanic eruptions  

NASA Astrophysics Data System (ADS)

Motivated by the hypothesis that volcanic blasts can have supersonic regions, we investigate the role of unsteady flow in jets from a high-pressure finite reservoir. We examine the processes for formation of far-field features, such as Mach disk shocks, by using a shock tube facility and numerical experiments to investigate phenomena to previously unobtained pressure ratios of 250:1. The Mach disk shock initially forms at the edges of the vent and moves toward the centerline. The shock is established within a few vent diameters and propagates downstream toward the equilibrium location as the jet develops. The start-up process is characterized by two different timescales: the duration of supersonic flow at the nozzle exit and the formation time of the Mach disk shock. The termination process also is characterized by two different timescales: the travel time required for the Mach disk shock to reach its equilibrium position and the time at which the Mach disk shock begins significantly to collapse away from its equilibrium position. The critical comparisons for the formation of steady state supersonic regions are between the two start-up timescales and the termination timescales. We conclude that for typical vulcanian eruptions and the Mount St. Helens directed blast, the Mach disk shock could have formed near the vent, and that there was time for it to propagate a distance comparable to its equilibrium location. These experiments provide a framework for analysis of short-lived volcanic eruptions and data for benchmarking simulations of jet structures in explosive volcanic blasts.

Orescanin, M. M.; Austin, J. M.; Kieffer, S. W.

2010-06-01

100

Implementing a Remote Laboratory Experience into a Joint Engineering Degree Program: Aerodynamic Levitation of a Beach Ball  

ERIC Educational Resources Information Center

|This paper details a successful and inexpensive implementation of a remote laboratory into a distance control systems course using readily available hardware and software. The physical experiment consists of a beach ball and a dc blower; the control objective is to make the height of the aerodynamically levitated beach ball track a reference…

Jernigan, S. R.; Fahmy, Y.; Buckner, G. D.

2009-01-01

101

Aeroelastic analysis of a non-linear airfoil based on unsteady vortex lattice model  

Microsoft Academic Search

Recent years have witnessed a successful model of unsteady vortex lattice to predict the limit cycle oscillations of an airfoil section. The aerodynamic model is usually in the form of discrete time, and hence, is not convenient for the analysis of non-linear aeroelastic systems. In this paper, the aerodynamic model of unsteady vortex lattice is formulated in continuous time domain

Y. H Zhao; H. Y Hu

2004-01-01

102

Dynamic control of aerodynamic forces on a moving platform using active flow control  

NASA Astrophysics Data System (ADS)

The unsteady interaction between trailing edge aerodynamic flow control and airfoil motion in pitch and plunge is investigated in wind tunnel experiments using a two degree-of-freedom traverse which enables application of time-dependent external torque and forces by servo motors. The global aerodynamic forces and moments are regulated by controlling vorticity generation and accumulation near the trailing edge of the airfoil using hybrid synthetic jet actuators. The dynamic coupling between the actuation and the time-dependent flow field is characterized using simultaneous force and particle image velocimetry (PIV) measurements that are taken phase-locked to the commanded actuation waveform. The effect of the unsteady motion on the model-embedded flow control is assessed in both trajectory tracking and disturbance rejection maneuvers. The time-varying aerodynamic lift and pitching moment are estimated from a PIV wake survey using a reduced order model based on classical unsteady aerodynamic theory. These measurements suggest that the entire flow over the airfoil readjusts within 2--3 convective time scales, 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 that are commensurate with the flow's convective time scale, and that the maneuver response is primarily limited by the inertia of the platform.

Brzozowski, Daniel P.

103

Lifting surface theory to predict aerodynamic forces induced by oscillating blades under interaction of three bladerows  

NASA Astrophysics Data System (ADS)

The paper presents the unsteady lifting surface theory to predict unsteady aerodynamic forces on blades of aerodynamically coupled three annular bladerows. Blades of any one bladerow are assumed to be vibrating. The bladerows are assumed to be individually rotating with arbitrary rotational velocities, and therefore the model can be reduced to a rotor/stator/rotor model or a counter-rotating multi-rotor system model by appropriately specifying rotational velocity parameters. The details of the mathematical formulations and the solution procedures are described. Numerical studies were conducted. The disturbances produced by a simple harmonic blade vibration are composed of multiple frequency components because of aerodynamic interaction between bladerows in mutual rotational motions. Relative magnitudes of the frequency components of the unsteady aerodynamic forces are made clear. Not only the effects of nonoscillating neighboring bladerows on the unsteady aerodynamic response of the oscillating bladerow, but also the unsteady aerodynamic forces on nonoscillating neighboring bladerows induced by the oscillating bladerow are investigated.

Namba, Masanobu; Nakagawa, Hiroyuki; Kubo, Ayumi

2009-10-01

104

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

105

Closed-Loop Aerodynamic Flow Control of a Maneuvering Airfoil  

NASA Astrophysics Data System (ADS)

The unsteady interaction between trailing edge aerodynamic flow control and airfoil motion in pitch and plunge is investigated in wind tunnel experiments using a 2-DOF traverse which enables application of time-dependent external torque and forces by servo motors. The global aerodynamic forces and moments are regulated by controlling vorticity generation and accumulation near the surface using hybrid synthetic jet actuators. 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 effect of the unsteady motion on the model-embedded flow control is assessed in unsteady several maneuvers. Circulation time history that is estimated from a PIV wake survey 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 that are commensurate with the flow's convective time scale, and that the maneuver response is primarily limited by the inertia of the platform.

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

2011-11-01

106

Awesome Aerodynamics!  

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 particular lesson, students will learn about the role of scientific research in the design of competition suits for athletes in the Winter Olympics. Students will also explore and research the concept of aerodynamics, and conduct their own scientific experiment to gain an understanding of this concept.

2010-01-01

107

Investigation of the transient aerodynamic phenomena associated with passing manoeuvres  

NASA Astrophysics Data System (ADS)

Passing manoeuvres and crosswind can have significant effects on the stability of road vehicles. The transient aerodynamics, which interacts with suspension, steering geometry and driver reaction is not well understood. When two vehicles overtake or cross, they mutually influence the flow field around each other, and under certain conditions, can generate severe gust loads that act as additional forces on both vehicles. The transient forces acting on them are a function of the longitudinal and transverse spacings and of the relative velocity between the two vehicles. Wind tunnel experiments have been conducted in one of the automotive wind tunnels of the Institut Aérotechnique of Saint-Cyr l’École to simulate the transient overtaking process between two models of a simple generic automobile shape. The tests were designed to study the effects of various parameters such as the longitudinal and transverse spacing, the relative velocity and the crosswind on the aerodynamic forces and moments generated on the overtaken and overtaking vehicles. Test results characterize the transient aerodynamic side force as well as the yawing moment coefficients in terms of these parameters. Measurements of the drag force coefficient as well as the static pressure distribution around the overtaken vehicle complete the understanding. The main results indicate the aerodynamic coefficients of the overtaken vehicle to be velocity independent within the limit of the test parameters, while unsteady aerodynamic effects appear in the case of an overtaking vehicle. The mutual interference effects between the vehicles vary as a linear function of the transverse spacing and the crosswind does not really generate any new unsteady behaviour.

Noger, C.; Regardin, C.; Széchényi, E.

2005-11-01

108

Experimental study on the effect of unsteadiness on boundary layer development on a linear turbine cascade  

Microsoft Academic Search

The results from an experimental investigation of unsteady boundary layer behavior on a linear turbine cascade are presented\\u000a in this paper. To perform a detailed study on unsteady cascade aerodynamics and heat transfer, a new large-scale, high-subsonic\\u000a research facility for simulating the periodic unsteady flow has been developed. It is capable of sequentially generating up\\u000a to four different unsteady inlet

M. T. Schobeiri; K. Pappu

1997-01-01

109

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

110

Development of the Unsteady Coanda Effect in Human Phonation  

NASA Astrophysics Data System (ADS)

Human speech is initiated as air passing through the glottis triggers self-sustained oscillations of the vocal folds. These oscillations, caused by aerodynamic air pressures, glottal geometry and tissue properties, result in the glottis cyclically forming into a converging, straight, then diverging passage and finally closing. The varying shape of the glottis throughout the cycle causes different coherent structures to form. One such phenomenon evident in quasi-steady flow experiments is the skewing of the glottal jet towards one wall and attachment, i.e. the Coanda effect. It is not understood if the high frequency oscillations inherent in human phonation allow sufficient time for this oscillating jet to attach to the glottal wall, and thereby influence sound production. Unsteady flow through a high aspect ratio slot with an adjacent plate angled at 30 degrees to the streamwise direction was investigated. The driven, unsteady flow oscillation through the slot was chosen to represent known in-vivo velocity wave forms. Particle Image Velocimetry (PIV) was used to measure the phase-averaged development of the Coanda effect. The evolution of the unsteady Coanda effect over a range of frequencies typical of human phonation will be discussed.

Erath, Byron D.; Plesniak, Michael W.

2003-11-01

111

Extracting micro air vehicles aerodynamic forces and coefficients in free flight using visual motion tracking techniques  

NASA Astrophysics Data System (ADS)

This paper describes a methodology to extract aerial vehicles’ aerodynamic characteristics from visually tracked trajectory data. The technique is being developed to study the aerodynamics of centimeter-scale aircraft and develop flight simulation models. Centimeter-scale aircraft remains a largely unstudied domain of aerodynamics, for which traditional techniques like wind tunnels and computational fluid dynamics have not yet been fully adapted and validated. The methodology takes advantage of recent progress in commercial, vision-based, motion-tracking systems. This system dispenses from on-board navigation sensors and enables indoor flight testing under controlled atmospheric conditions. Given the configuration of retro-reflective markers affixed onto the aerial vehicle, the vehicle’s six degrees-of-freedom motion can be determined in real time. Under disturbance-free conditions, the aerodynamic forces and moments can be determined from the vehicle’s inertial acceleration, and furthermore, for a fixed-wing vehicle, the aerodynamic angles can be plotted from the vehicle’s kinematics. By combining this information, we can determine the temporal evolution of the aerodynamic coefficients, as they change throughout a trajectory. An attractive feature of this technique is that trajectories are not limited to equilibrium conditions but can include non-equilibrium, maneuvering flight. Whereas in traditional wind-tunnel experiments, the operating conditions are set by the experimenter, here, the aerodynamic conditions are driven by the vehicle’s own dynamics. As a result, this methodology could be useful for characterizing the unsteady aerodynamics effects and their coupling with the aircraft flight dynamics, providing insight into aerodynamic phenomena taking place at centimeter scale flight.

Mettler, B. F.

2010-09-01

112

DOE's effort to reduce truck aerodynamic drag through joint experiments and computations  

Microsoft Academic Search

Class 8 tractor-trailers are responsible for 11-12% of the total US consumption of petroleum. Overcoming aero drag represents 65% of energy expenditure at highway speeds. Most of the drag results from pressure differences and reducing highway speeds is very effective. The goal is to reduce aerodynamic drag by 25% which would translate to 12% improved fuel economy or 4,200 million

Kambiz Salari; Fred Browand; Kidambi Sreenivas; W. David Pointer; Lafayette Taylor; Ramesh Pankajakshan; David Whitfield; Dennis Plocher; Jason M. Ortega; Tai Merzel; Rose McCallen; Stephen M Walker; James T Heineck; Basil Hassan; Christopher John Roy; B. Storms; James Ross; Robert Englar; Mike Rubel; Anthony Leonard; Charles Radovich; Craig Eastwood; John Paschkewitz; Paul Castellucci; Lawrence Justin. DeChant

2005-01-01

113

The Development and Application of a Simple Method for Determining Unsteady Airloads in Subsonic Compressible Flow.  

National Technical Information Service (NTIS)

A numerical lifting surface method based on velocity potential formulation is applied for predicting aerodynamic loads in steady and unsteady flows for fixed and as well as rotary wings. The theory and the numerical procedures are validated by comparing w...

B. M. Rao V. Elchuri P. R. Schatzle L. J. McQuien

1978-01-01

114

PREFACE: Aerodynamic sound Aerodynamic sound  

Microsoft Academic Search

The modern theory of aerodynamic sound originates from Lighthill's two papers in 1952 and 1954, as is well known. I have heard that Lighthill was motivated in writing the papers by the jet-noise emitted by the newly commercialized jet-engined airplanes at that time. The technology of aerodynamic sound is destined for environmental problems. Therefore the theory should always be applied

Sadao Akishita

2010-01-01

115

Unsteady transonic flow past airfoils in rigid-body motion. [UFLO5  

SciTech Connect

With the aim of developing a fast and accurate computer code for predicting the aerodynamic forces needed for a flutter analysis, some basic concepts in computational transonics are reviewed. The unsteady transonic flow past airfoils in rigid body motion is adequately described by the potential flow equation as long as the boundary layer remains attached. The two dimensional unsteady transonic potential flow equation in quasilinear form with first order radiation boundary conditions is solved by an alternating direction implicit scheme in an airfoil attached sheared parabolic coordinate system. Numerical experiments show that the scheme is very stable and is able to resolve the higher nonlinear transonic effects for filter analysis within the context of an inviscid theory.

Chang, I.C.

1981-03-01

116

Aerodynamic Experiments of Small Scale Combined Cycle Engine in Various Mach Numbers  

NASA Astrophysics Data System (ADS)

A small model aerodynamic tests of the combined cycle engine were carried out to evaluate its performance in subsonic and supersonic conditions. In this regime of the flow speed, the combined cycle engine operates as an ejector-jet or ramjet. The nitrogen gas was exhausted as the substitution for the actual rocket gas. In a subsonic condition, there appeared local pressure rise at the kink point of the ramp, increasing the pressure drag. Both wall pressure and the pitot pressure distribution at the exit of the model suggested that the flow structure is “two-layered” ; one is subsonic induced air flow, and the other is the supersonic rocket exhaust. A slit was carved on the topwall inside the isolator section, expecting a better suction performance in the ejector-jet mode. The modification actually had an effect to enhance the lower limit of the rocket pressure at which the choking of the induced air is achieved.

Tani, Kouichiro; Kouchi, Toshinori; Kato, Kanenori; Sakuranaka, Noboru; Watanabe, Syuuichi

117

Hypersonic Aerodynamics.  

National Technical Information Service (NTIS)

The Gas Dynamics Laboratory of the Department of Aerospace and Mechanical Sciences of Princeton University has performed research in experimental and theoretical hypersonic aerodynamics supported by the Air Force Office of Scientific Research. The two are...

S. M. Bogdonoff

1975-01-01

118

Aerodynamic Drag.  

National Technical Information Service (NTIS)

Current research and future prospects in the field of aerodynamic drag were presented and discussed at this Specialists' Meeting. Main emphasis was placed on subjects of practical value to the aerospace industry in relation to its need for accurate predic...

1973-01-01

119

Evidence that aerodynamic effects, including dynamic stall, dictate HAWT structural loads and power generation in highly transient time frames  

SciTech Connect

Aerodynamic data collected from the National Renewable Energy Laboratory`s Combined Experiment have shown three distinct performance regimes when the turbine is operated under relatively steady flow conditions. Operating at blade angles of attack below static stall, excellent agreement is achieved with two-dimensional wind tunnel data. Around the static stall angle, the cycle average normal force produced is greater than the static test data. Span locations near the hub produce extremely large values of normal force coefficient, well in excess of the two-dimensional data results. These performance regimes have been shown to be a function of the three-dimensional flow structure and cycle averaged dynamic stall effects. Power generation and root bending moments have also been shown to be directly dependent on the inflow wind velocity. Aerodynamic data, including episodes of dynamic stall, have been correlated on a cycle by cycle basis with the structural and power generation characteristics of a horizontal axis wind turbine. Instantaneous unsteady forces and resultant power generation indicate that peak transient levels can significantly exceed cycle averaged values. Strong coupling between transient aerodynamic and resonant response of the turbine was also observed. These results provide some initial insight into the contribution of unsteady aerodynamics on undesirable turbine structural response and fatigue life.

Shipley, D.E.; Miller, M.S.; Robinson, M.C.; Luttges, M.W. [Colorado Univ., Boulder, CO (United States). Dept. of Aerospace Engineering Sciences; Simms, D.A. [National Renewable Energy Lab., Golden, CO (United States)

1994-08-01

120

Evidence that aerodynamic effects, including dynamic stall, dictate HAWT structural loads and power generation in highly transient time frames  

NASA Astrophysics Data System (ADS)

Aerodynamic data collected from the National Renewable Energy Laboratory's Combined Experiment have shown three distinct performance regimes when the turbine is operated under relatively steady flow conditions. Operating at blade angles of attack below static stall, excellent agreement is achieved with two-dimensional wind tunnel data. Around the static stall angle, the cycle average normal force produced is greater than the static test data. Span locations near the hub produce extremely large values of normal force coefficient, well in excess of the two-dimensional data results. These performance regimes have been shown to be a function of the three-dimensional flow structure and cycle averaged dynamic stall effects. Power generation and root bending moments have also been shown to be directly dependent on the inflow wind velocity. Aerodynamic data, including episodes of dynamic stall, have been correlated on a cycle by cycle basis with the structural and power generation characteristics of a horizontal axis wind turbine. Instantaneous unsteady forces and resultant power generation indicate that peak transient levels can significantly exceed cycle averaged values. Strong coupling between transient aerodynamic and resonant response of the turbine was also observed. These results provide some initial insight into the contribution of unsteady aerodynamics on undesirable turbine structural response and fatigue life.

Shipley, D. E.; Miller, M. S.; Robinson, M. C.; Luttges, M. W.; Simms, D. A.

1994-08-01

121

Aerodynamics of sports balls  

NASA Astrophysics Data System (ADS)

Research data on the aerodynamic behavior of baseballs and cricket and golf balls are summarized. Cricket balls and baseballs are roughly the same size and mass but have different stitch patterns. Both are thrown to follow paths that avoid a batter's swing, paths that can curve if aerodynamic forces on the balls' surfaces are asymmetric. Smoke tracer wind tunnel tests and pressure taps have revealed that the unbalanced side forces are induced by tripping the boundary layer on the seam side and producing turbulence. More particularly, the greater pressures are perpendicular to the seam plane and only appear when the balls travel at velocities high enough so that the roughness length matches the seam heigh. The side forces, once tripped, will increase with spin velocity up to a cut-off point. The enhanced lift coefficient is produced by the Magnus effect. The more complex stitching on a baseball permits greater variations in the flight path curve and, in the case of a knuckleball, the unsteady flow effects. For golf balls, the dimples trip the boundary layer and the high spin rate produces a lift coefficient maximum of 0.5, compared to a baseball's maximum of 0.3. Thus, a golf ball travels far enough for gravitational forces to become important.

Mehta, R. D.

122

Wind Turbine Aerodynamics Prediction Using Free-Wake Method in Axial Flow  

NASA Astrophysics Data System (ADS)

Wind turbine aerodynamics remains a particularly challenging and crucial research for wind energy industry. The blade element momentum theory is the most widely used in predicting the performance of wind turbine, since the method is simple and fast numerical algorithm. The flow field generated by rotary wing is considerably important and complicated, however, the BEM method has some limitations to model the unsteady effects. To overcome these limitations, the aerodynamic analysis using a time-marching free-vortex wake method was performed in this paper. Moreover, the inboard region of the blade experience a delay in stall and enhanced values of the normal force coefficient because of rotational boundary layer augmentation and three-dimensional effects. For this reason, Raj-Selig stall delay model was applied in this research. The numerical results were compared with experimental data, and the present results show excellent agreement with experiment.

Jeong, Min-Soo; Yoo, Seung-Jae; Lee, In

123

A theoretical study on the unsteady aerothermodynamics for attached flow models  

NASA Astrophysics Data System (ADS)

The principle of the unsteady aerothermodynamics was theoretically investigated for the attached flow. Firstly, two simplified models with analytic solutions to the N-S equations were selected for the research, namely the compressible unsteady flows on the infinite flat plate with both time-varying wall velocity and time-varying wall temperature boundary conditions. The unsteady temperature field and the unsteady wall heat flux (heat flow) were analytically solved for the second model. Then, the interaction characteristic of the unsteady temperature field and the unsteady velocity field in the simplified models and the effects of the interaction on the transient wall heat transfer were studied by these two analytic solutions. The unsteady heat flux, which is governed by the energy equation, is directly related to the unsteady compression work and viscous dissipation which originates from the velocity field governed by the momentum equation. The main parameters and their roles in how the unsteady velocity field affects the unsteady heat flux were discussed for the simplified models. Lastly, the similarity criteria of the unsteady aerothermodynamics were derived based on the compressible boundary layer equations. Along with the Strouhal number St u , the unsteadiness criterion of the velocity field, St T number, the unsteadiness criterion of the temperature field was proposed for the first time. Different from the traditional method used in unsteady aerodynamics which measures the flow unsteadiness only by the St u number, present results show that the flow unsteadiness in unsteady aerothermodynamics should be comprehensively estimated by comparing the relative magnitudes of the temperature field unsteadiness criterion St T number with the coefficients of other terms in the dimensionless energy equation.

Chen, Hao; Bao, Lin; Tong, Binggang

2010-08-01

124

Coupled Multibody-Aerodynamic Simulation Of High-Speed Trains Manoeuvres  

Microsoft Academic Search

\\u000a In this paper the effects of unsteady aerodynamic loads on the driving dynamics of high speed trains during passing manoeuvres\\u000a in absence of cross wind have been investigated. To this end a co-simulation MBS\\/CFD was implemented. A linear aerodynamic\\u000a model, the panel method, was applied to the computation of the unsteady flow around the driving trailers for the examined\\u000a manoeuvres.

A. Carrarini

125

Nonlinear unsteady flow problems by multidimensional singular integral representation analysis  

Microsoft Academic Search

A two-dimensional nonlinear aerodynamics representation analysis is proposed for the investigation of inviscid flowfields of unsteady airfoils. Such problems are reduced to the solution of a nonlinear multidimensional singular integral equation as the source and vortex strength distributions are dependent on the history of these distributions on the NACA airfoil surface. A turbulent boundary layer model is further investigated, based

E. G. Ladopoulos

2003-01-01

126

Computational aerodynamics of low Reynolds number plunging, pitching and flexible wings for MAV applications  

NASA Astrophysics Data System (ADS)

Micro air vehicles (MAV’s) have the potential to revolutionize our sensing and information gathering capabilities in environmental monitoring and homeland security areas. Due to the MAV’s’ small size, flight regime, and modes of operation, significant scientific advancement will be needed to create this revolutionary capability. Aerodynamics, structural dynamics, and flight dynamics of natural flyers intersects with some of the richest problems in MAV’s, including massively unsteady three-dimensional separation, transition in boundary layers and shear layers, vortical flows and bluff body flows, unsteady flight environment, aeroelasticity, and nonlinear and adaptive control are just a few examples. A challenge is that the scaling of both fluid dynamics and structural dynamics between smaller natural flyer and practical flying hardware/lab experiment (larger dimension) is fundamentally difficult. In this paper, we offer an overview of the challenges and issues, along with sample results illustrating some of the efforts made from a computational modeling angle.

Shyy, W.; Lian, Y.; Tang, J.; Liu, H.; Trizila, P.; Stanford, B.; Bernal, L.; Cesnik, C.; Friedmann, P.; Ifju, P.

2008-08-01

127

Animation aerodynamics  

Microsoft Academic Search

Methods based on aerodynamics are developed to simulate and control the motion of objects in fluid flows. To simplify the physics for animation, the problem is broken down into two parts: a fluid flow regime and an object boundary regime. With this simplification one can approximate the realistic behaviour of objects moving in liquids or air. It also enables a

Jakub Wejchert; David R. Haumann

1991-01-01

128

Effect of flexure on aerodynamic propulsive efficiency of flapping flexible airfoil  

Microsoft Academic Search

The aim of present study is to investigate the effect of chord-wise flexure amplitude on unsteady aerodynamic characteristics for a flapping airfoil with various combinations of Reynolds number and reduced frequency. Unsteady, viscous flows over a single flexible airfoil in plunge motion are computed using conformal hybrid meshes. The dynamic mesh technique is applied to illustrate the deformation modes of

J.-M. Miao; M.-H. Ho

2006-01-01

129

The congenital bicuspid aortic valve can experience high-frequency unsteady shear stresses on its leaflet surface  

PubMed Central

The bicuspid aortic valve (BAV) is a common congenital malformation of the aortic valve (AV) affecting 1% to 2% of the population. The BAV is predisposed to early degenerative calcification of valve leaflets, and BAV patients constitute 50% of AV stenosis patients. Although evidence shows that genetic defects can play a role in calcification of the BAV leaflets, we hypothesize that drastic changes in the mechanical environment of the BAV elicit pathological responses from the valve and might be concurrently responsible for early calcification. An in vitro model of the BAV was constructed by surgically manipulating a native trileaflet porcine AV. The BAV valve model and a trileaflet AV (TAV) model were tested in an in vitro pulsatile flow loop mimicking physiological hemodynamics. Laser Doppler velocimetry was used to make measurements of fluid shear stresses on the leaflet of the valve models using previously established methodologies. Furthermore, particle image velocimetry was used to visualize the flow fields downstream of the valves and in the sinuses. In the BAV model, flow near the leaflets and fluid shear stresses on the leaflets were much more unsteady than for the TAV model, most likely due to the moderate stenosis in the BAV and the skewed forward flow jet that collided with the aorta wall. This additional unsteadiness occurred during mid- to late-systole and was composed of cycle-to-cycle magnitude variability as well as high-frequency fluctuations about the mean shear stress. It has been demonstrated that the BAV geometry can lead to unsteady shear stresses under physiological flow and pressure conditions. Such altered shear stresses could play a role in accelerated calcification in BAVs.

Yap, Choon Hwai; Saikrishnan, Neelakantan; Tamilselvan, Gowthami; Vasilyev, Nikolai

2012-01-01

130

The congenital bicuspid aortic valve can experience high-frequency unsteady shear stresses on its leaflet surface.  

PubMed

The bicuspid aortic valve (BAV) is a common congenital malformation of the aortic valve (AV) affecting 1% to 2% of the population. The BAV is predisposed to early degenerative calcification of valve leaflets, and BAV patients constitute 50% of AV stenosis patients. Although evidence shows that genetic defects can play a role in calcification of the BAV leaflets, we hypothesize that drastic changes in the mechanical environment of the BAV elicit pathological responses from the valve and might be concurrently responsible for early calcification. An in vitro model of the BAV was constructed by surgically manipulating a native trileaflet porcine AV. The BAV valve model and a trileaflet AV (TAV) model were tested in an in vitro pulsatile flow loop mimicking physiological hemodynamics. Laser Doppler velocimetry was used to make measurements of fluid shear stresses on the leaflet of the valve models using previously established methodologies. Furthermore, particle image velocimetry was used to visualize the flow fields downstream of the valves and in the sinuses. In the BAV model, flow near the leaflets and fluid shear stresses on the leaflets were much more unsteady than for the TAV model, most likely due to the moderate stenosis in the BAV and the skewed forward flow jet that collided with the aorta wall. This additional unsteadiness occurred during mid- to late-systole and was composed of cycle-to-cycle magnitude variability as well as high-frequency fluctuations about the mean shear stress. It has been demonstrated that the BAV geometry can lead to unsteady shear stresses under physiological flow and pressure conditions. Such altered shear stresses could play a role in accelerated calcification in BAVs. PMID:22821994

Yap, Choon Hwai; Saikrishnan, Neelakantan; Tamilselvan, Gowthami; Vasilyev, Nikolai; Yoganathan, Ajit P

2012-07-20

131

Aerodynamic characteristics of flapping motion in hover  

Microsoft Academic Search

The aim of the present work is to understand the aerodynamic phenomena and the vortex topology of an unsteady flapping motion\\u000a by means of numerical and experimental methods. Instead of the use of real insect\\/bird wing geometries and kinematics which\\u000a are highly complex and difficult to imitate by an exact modeling, a simplified model is used in order to understand

D. Funda Kurtulus; Laurent David; Alain Farcy; Nafiz Alemdaroglu

2008-01-01

132

Effect of Chord Flexure on Aerodynamic Performance of a Flapping Wing  

Microsoft Academic Search

Inspired by the fact that a high flexible wing in nature generates high aerodynamic performance, we investigated the aerodynamic performance of the flapping wing with different chord flexures. The unsteady, incompressible, and viscous flow over airfoil NACA0012 in a plunge motion was analyzed by using Navier-Stokes equation. Grid deformation, in which finite element and interpolation ideas are mixed, was introduced

Tuyen Quang Le; Jin Hwan Ko; Doyoung Byun; Soo Hyung Park; Hoon Choel Park

2010-01-01

133

BIOMECHANICS OF FLIGHT IN NEOTROPICAL BUTTERFLIES: AERODYNAMICS AND MECHANICAL POWER REQUIREMENTS  

Microsoft Academic Search

Summary A quasi-steady aerodynamic analysis of forward flight was performed on 15 species of neotropical butterflies for which kinematic and morphological data were available. Mean lift coefficients required for flight typically exceeded maximum values obtained on insect wings under conditions of steady flow, thereby implicating unsteady aerodynamic mechanisms even during fast forward flight of some butterflies. The downstroke produced vertical

ROBERT DUDLEY

1991-01-01

134

Computational Aerodynamics of Insects' Flapping Flight  

NASA Astrophysics Data System (ADS)

The kinematics of the Insects' flapping flight is modeled through mathematical and computational observations with commercial software. Recently, study on the insects' flapping flight became one of the challenging research subjects in the field of aeronautics because of its potential applicability to intelligent micro-robots capable of autonomous flight and the next generation aerial-vehicles. In order to uncover its curious unsteady characteristics, many researchers have conducted experimental and computational studies on the unsteady aerodynamics of insects' flapping flight. In the present paper, the unsteady flow physics around insect wings is carried out by utilizing computer software e-AIRS. The e-AIRS (e-Science Aerospace Integrated Research System) analyzes and models the results of computational and experimental aerodynamics, along with integrated research process of these two research activities. Stroke angles and phase angles, the important two factors in producing lift of the airfoils are set as main parameters to determine aerodynamic characteristics of the insects' flapping flight. As a result, the optimal phase angle to minimize the drag and to maximize the lift are found. Various simulations indicate that using proper value of variables produce greater thrust due to an optimal angle of attack at the initial position during down stroke motion.

Yang, Kyung Dong; Kyung, Richard

2011-11-01

135

PREFACE: Aerodynamic sound Aerodynamic sound  

NASA Astrophysics Data System (ADS)

The modern theory of aerodynamic sound originates from Lighthill's two papers in 1952 and 1954, as is well known. I have heard that Lighthill was motivated in writing the papers by the jet-noise emitted by the newly commercialized jet-engined airplanes at that time. The technology of aerodynamic sound is destined for environmental problems. Therefore the theory should always be applied to newly emerged public nuisances. This issue of Fluid Dynamics Research (FDR) reflects problems of environmental sound in present Japanese technology. The Japanese community studying aerodynamic sound has held an annual symposium since 29 years ago when the late Professor S Kotake and Professor S Kaji of Teikyo University organized the symposium. Most of the Japanese authors in this issue are members of the annual symposium. I should note the contribution of the two professors cited above in establishing the Japanese community of aerodynamic sound research. It is my pleasure to present the publication in this issue of ten papers discussed at the annual symposium. I would like to express many thanks to the Editorial Board of FDR for giving us the chance to contribute these papers. We have a review paper by T Suzuki on the study of jet noise, which continues to be important nowadays, and is expected to reform the theoretical model of generating mechanisms. Professor M S Howe and R S McGowan contribute an analytical paper, a valuable study in today's fluid dynamics research. They apply hydrodynamics to solve the compressible flow generated in the vocal cords of the human body. Experimental study continues to be the main methodology in aerodynamic sound, and it is expected to explore new horizons. H Fujita's study on the Aeolian tone provides a new viewpoint on major, longstanding sound problems. The paper by M Nishimura and T Goto on textile fabrics describes new technology for the effective reduction of bluff-body noise. The paper by T Sueki et al also reports new technology for the reduction of bluff-body noise. Xiaoyu Wang and Xiaofeng Sun discuss the interaction of fan stator and acoustic treatments using the transfer element method. S Saito and his colleagues in JAXA report the development of active devices for reducing helicopter noise. The paper by A Tamura and M Tsutahara proposes a brand new methodology for aerodynamic sound by applying the lattice Boltzmann finite difference method. As the method solves the fluctuation of air density directly, it has the advantage of not requiring modeling of the sound generation. M A Langthjem and M Nakano solve the hole-tone feedback cycle in jet flow by a numerical method. Y Ogami and S Akishita propose the application of a line-vortex method to the three-dimensional separated flow from a bluff body. I hope that a second issue on aerodynamic sound will be published in FDR in the not too distant future.

Akishita, Sadao

2010-02-01

136

Missile Aerodynamics: NEAR Conference on Missile Aerodynamics.  

National Technical Information Service (NTIS)

Several aspects of missile aerodynamics were discussed at the conference held in Monterey, California from October 31-November 2, 1988. Missile aerodynamics from an historical perspective, a critical assessment of prediction capabilities, external store s...

M. R. Mendenhall D. Nixon M. F. E. Dillenius

1988-01-01

137

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

138

An Investigation of the Aerodynamic and Ventilation Characteristics of Poultry Transport Vehicles: Part 2, Wind Tunnel Experiments  

Microsoft Academic Search

This is the second part of a three part paper that reports the results of an investigation into the aero-f dynamic and ventilation characteristics of poultryf transport vehicles. In Part 1 the results of full scale aerodynamic measurements were described. In this paper the results of an extensive series of wind tunnel effects are described and discussed, and in Part

C. J. Baker; S. Dalley; X. Yang; P. Kettlewell; R. Hoxey

1996-01-01

139

Shock unsteadiness creation and propagation: experimental analysis  

NASA Astrophysics Data System (ADS)

The possibility of creating unsteady distortions of the tip shock by waves emitted from an aircraft is assessed experimentally. The model chosen is a cylindrical fore body equipped with a spike. This configuration is known for generating an important level of unsteadiness around the spike in supersonic regime. The wind tunnel Mach number is equal to 2. The experiments show that waves emitted from this source propagate along the tip shock and interact with it. It is then assessed that this interaction produces a periodic distortion of the shock that propagates to the external flow. Unsteady pressure sensors, high speed schlieren films, hot wire probing and laser Doppler velocimetry are used as complementary experimental means. The final result is a coherent representation of the complex mechanism of wave propagation that has been evidenced. The principle of creating unsteady shock deformation by onboard equipments could be examined as a possibly promising method of sonic boom control.

Benay, R.; Alaphilippe, M.; Severac, N.

2012-09-01

140

Algorithm for determining the aerodynamic characteristics of a freely flying object from discrete data of ballistic experiment. Part 2  

NASA Astrophysics Data System (ADS)

In part 1 of this paper, an algorithm for numerically solving the inverse problem of motion of a solid through the atmosphere is described that constitutes the basis for identifying the aerodynamic characteristics of an object from trajectory data and the respective identification procedure is presented. In part 2, methods evaluating the significance of desired parameters and adequacy of a mathematical model of motion, approaches to metrological certification of experimental equipment, and results of testing the algorithm are discussed.

Bobashev, S. V.; Mende, N. P.; Popov, P. A.; Sakharov, V. A.; Berdnikov, V. A.; Viktorov, V. A.; Oseeva, S. I.; Sadchikov, G. D.

2009-04-01

141

Aerodynamics of a bio-inspired flexible flapping-wing micro air vehicle.  

PubMed

MAVs (micro air vehicles) with a maximal dimension of 15 cm and nominal flight speeds of around 10 m s?¹, operate in a Reynolds number regime of 10? or lower, in which most natural flyers including insects, bats and birds fly. Furthermore, due to their light weight and low flight speed, the MAVs' flight characteristics are substantially affected by environmental factors such as wind gust. Like natural flyers, the wing structures of MAVs are often flexible and tend to deform during flight. Consequently, the aero/fluid and structural dynamics of these flyers are closely linked to each other, making the entire flight vehicle difficult to analyze. We have recently developed a hummingbird-inspired, flapping flexible wing MAV with a weight of 2.4-3.0 g and a wingspan of 10-12 cm. In this study, we carry out an integrated study of the flexible wing aerodynamics of this flapping MAV by combining an in-house computational fluid dynamic (CFD) method and wind tunnel experiments. A CFD model that has a realistic wing planform and can mimic realistic flexible wing kinematics is established, which provides a quantitative prediction of unsteady aerodynamics of the four-winged MAV in terms of vortex and wake structures and their relationship with aerodynamic force generation. Wind tunnel experiments further confirm the effectiveness of the clap and fling mechanism employed in this bio-inspired MAV as well as the importance of the wing flexibility in designing small flapping-wing MAVs. PMID:22126793

Nakata, T; Liu, H; Tanaka, Y; Nishihashi, N; Wang, X; Sato, A

2011-11-29

142

Steady and Unsteady Flow Phenomena in a Channel Diffuser of a Centrifugal Compressor  

NASA Astrophysics Data System (ADS)

The aim of this paper is to understand the time averaged pressure distributions and unsteady pressure patterns in a channel diffuser of a centrifugal compressor. Pressure distributions from the impeller exit to the channel diffuser exit are measured and discussed for various flow conditions. And unsteady pressure signals from six fast-response sensors in the channel diffuser are analyzed by decomposition method. The strong non-uniformity in the pressure distribution is obtained over the diffuser shroud wall caused by the impeller-diffuser interaction. As the flow rate increases, flow separation near the throat, due to large incidence angle, increases aerodynamic blockage and reduces the aerodynamic flow area downstream. Thus the minimum pressure location occurs downstream of the geometric throat, and it is named as the aerodynamic throat. And at choke condition, normal shock occurs downstream of this aerodynamic throat. The variation in the location of the aerodynamic throat is discussed. The pressure ratio waveforms by blade passing show regular oscillation not only for the normal but also for the surge conditions and the high frequency fluctuations are superposed on the oscillating pressure waveform as the flow rate increases. Periodic unsteadiness by blade passing does not decay in the diffuser channel. It depends on the operating point and is generally larger in the channel than in the vaneless space. Aperiodic unsteadiness rapidly decrease downstream of diffuser channel.

Kang, Jeong-Seek; Kang, Shin-Hyoung

143

Model order reduction of unsteady flow past oscillating airfoil cascades  

NASA Astrophysics Data System (ADS)

This study focuses on developing reduced-order models for unsteady aerodynamic flows past a cascade of two-dimensional airfoils. A reduction method known as System Equivalent Reduction Expansion Process (SEREP) is used. The computational efficiency of the SEREP reduced-order model is compared with a reduced-order model formed using the Proper Orthogonal Decomposition (POD) technique. The present study shows that the SEREP is computationally more efficient than POD.

Sarkar, S.; Venkatraman, K.

2004-02-01

144

Aerodynamic modeling of an aircraft in atmospheric turbulence and correlation to hazard  

NASA Astrophysics Data System (ADS)

Improving aviation safety has become a focal point of present aeronautics research. Quantifying and predicting the hazards of flight into atmospheric turbulence is one area of interest. The present research investigates and extends the use of aerodynamic modeling techniques to better enhance the representation of nonlinear, unsteady effects in a turbulence encounter. The focus of the research is on flight dynamic, versus structural loads, aspects. Flight data from an intentional atmospheric turbulence penetration was used along with fuzzy logic techniques to develop and enhance longitudinal and lateral-directional aerodynamic coefficient models. These models indicated the presence of nonlinear and unsteady aerodynamic effects, including lateral-directional coupling into the longitudinal axis. Effective mass and damping were proposed as one means to correlate loads-induced hazards to the aerodynamic response of the aircraft, which were compared with results from an actual passenger flight. The results suggest that the cause of fast plunging motion may be shock-induced stall in largely static motion, i.e., low reduced frequency, whereas in oscillatory motion with higher reduced frequencies, dynamic stall may inhibit fast plunging motion. Therefore, some form of hazard index may relate to the magnitude of effective damping in plunging motion, or alternatively to the measure of unsteadiness in the aerodynamics of the encounter. A control strategy for countering a rapid plunge may benefit from means to artificially drive unsteady aerodynamic effects.

Stuever, Robert A.

145

The unsteady flow over a bat wing in mid-downstroke.  

NASA Astrophysics Data System (ADS)

Birds, bats and insects have provided inspiration for human-designed small-scale flying machines, and while insects have long been known to rely on unsteady separated flows for their above-average aerodynamic performance at small-scale, the details of air flows over bird and bat wings have been harder to elucidate, mainly because of the extra complexity and precautions required in live experiments. Here we report on the first experiments of the airflow around a bat wing in free (but trained) flight in a low-turbulence wind tunnel. The aerodynamics of fixed wings at these Reynolds numbers are notoriously sensitive to small disturbances of the initially laminar, attached boundary layer, but these flight experiments show that the instantaneous flow fields around the flapping wing bear almost no resemblance to an equivalent fixed-wing experiment. The circulation increment due to the presence of a strong leading-edge vortex is estimated to provide a significant fraction of the total lift. Implications for the design and control of micro-air vehicles are considered.

Muijres, Florian; Johansson, Christoffer; Barfield, Ryan; Wolf, Marta; Spedding, Geoffrey; Hedenstrom, Anders

2008-03-01

146

Experience in laser stereolithography and its application in manufacturing wind-tunnel aerodynamic models of various purposes  

NASA Astrophysics Data System (ADS)

In 2000-2001 the specialists of TsAGI and ILIT of the Russian Academy of Sciences developed the photopolymeric molds and tried up the technology of producing in these molds the wing tips of a complicated shape made of composite materials. During further development a complicated hybrid structure of a balance aerodynamic model was generated including primary metallic elements, contour-forming elements made of composites as well as separate contour- forming elements made directly from photopolymer. Prospects for extending this technology to dynamic and elastic models are considered.

Azarov, Yu. A.; Vermel, V. D.; Kornushenko, A. V.; Novikov, M. M.; Kamaev, S. V.; Markov, Michael A.

2002-04-01

147

Aerodynamics of flapping wings with fluttering trailing edges  

Microsoft Academic Search

Our previous work on the aerodynamics of passive flexible flapping wings showed that there is a strong relationship between the dynamics of trailing edge and the size of the leading edge vortex, therefore aerodynamic forces. Here we investigated the aerodynamic effects of active trailing edges. The experiments were conducted on a model flapping wing in an oil tank. During static

Liang Zhao; Zheng Hu; Jesse Roll; Xinyan Deng

2010-01-01

148

The effect of steady aerodynamic loading on the flutter stability of turbomachinery blading  

SciTech Connect

An aeroelastic analysis is presented that accounts for the effect of steady aerodynamic loading on the aeroelastic stability of a cascade of compressor blades. The aeroelastic model is a two-degree-of-freedom model having bending and torsional displacements. A linearized unsteady potential flow theory is used to determine the unsteady aerodynamic response coefficients for the aeroelastic analysis. The steady aerodynamic loading was caused by the addition of (1) airfoil thickness and camber and (2) steady flow incidence. The importance of steady loading on the airfoil unsteady pressure distribution is demonstrated. Additionally, the effect of the steady loading on the tuned flutter behavior and flutter boundaries indicates that neglecting either airfoil thickness, camber, or incidence could result in nonconservative estimates of flutter behavior.

Smith, T.E. (Sverdrup Technology, Inc., Brook Park, OH (United States)); Kadambi, J.R. (Case Western Reserve Univ., Cleveland, OH (United States))

1993-01-01

149

Reduction of Unsteady Stator-Rotor Interaction Using Trailing Edge Blowing  

NASA Astrophysics Data System (ADS)

An aeroacoustic investigation was performed to assess the effects of adding mass flow at the trailing edges of stators upstream of an aircraft engine simulator. By using trailing edge blowing to minimize the shed wakes of the stators, the flow into the rotor was made more uniform, hence reducing the unsteady stator-rotor interaction. In these experiments, a reduced number of stators (four) was used in a 1/14 scale model inlet which was coupled to a 4.1in (10.4 cm) turbofan engine simulator. Steady state measurements of the aerodynamic flow field and acoustic far field were made in order to evaluate the aeroacoustic performance at three simulator speeds: 30k, 50k, and 70kr.p.m. The lowest test speed (30k r.p.m.) showed a noise reduction as large as 8.9dB in the blade passing tone. At 50k and 70kr.p.m., the reduction in blade passing tone was 5.5 and 2.6dB respectively. In addition, trailing edge blowing reduced the overall sound pressure level in every case. Aerodynamic measurements showed that fan face distortion was significantly reduced due to trailing edge blowing. The addition of trailing edge blowing from the four upstream stators did not change the operating point of the fan, and the mass flow added by the blowing was less than 1% of the fan mass flow rate. The results of these experiments clearly demonstrate that blowing from the trailing edges of the stators is effective in reducing unsteady stator-rotor interaction and the subsequent forward radiated noise.

Leitch, Thomas A.; Saunders, C. A.; Ng, W. F.

2000-08-01

150

A comparison of some aerodynamic resistance methods using measurements over cotton and grass from the 1991 California ozone deposition experiment  

NASA Astrophysics Data System (ADS)

Measurements of dry, deposition velocities ( V d ) of O3 (using the eddy correlation technique) made over a cotton field and senescent grass near Fresno California during July and August 1991 were used to test some dry deposition velocity models. Over the cotton field, the observed maximum daytime V d was about 0.8 cm s-1 and the average nighttime value was about 0.2 cm s-1. Over the grass, daytime values averaged about 0.2 cm s-1 and nighttime values about 0.05 cm s-1. Application of a site-specific model known as ADOM (Acid Deposition and Oxidant Model) over the cotton field generally overestimated the observations except for a few hours in the afternoon when the observations were underestimated The overestimation was attributed to inadequacies in the surface resistance formulation and the underestimation to uncertainties in the aerodynamic formulation. Unlike previous studies which focused on the role of surface resistance, we perform additional tests using a large variety of aerodynamic resistance formulae, in addition to those in ADOM, to determine their influence on the modelled V d of O3 over, cotton. Over grass, ADOM considerably overestimated the observations but showed improvement when other surface resistance formulations were applied.

Padro, J.; Massman, W. J.; Shaw, R. H.; Delany, A.; Oncley, S. P.

1994-12-01

151

Multicomponent Aerodynamic Magnetoelectric Balance.  

National Technical Information Service (NTIS)

The invention pertains to the field of measurement equipment, in particular, to a multicomponent aerodynamic magnetoelectric balance, which can be used for the measurement of small forces and moments in aerodynamic investigations.

N. P. Levitskii

1973-01-01

152

Advanced multistage turbine blade aerodynamics, performance, cooling, and heat transfer  

SciTech Connect

The gas turbine has the potential for power production at the highest possible efficiency. The challenge is to ensure that gas turbines operate at the optimum efficiency so as to use the least fuel and produce minimum emissions. A key component to meeting this challenge is the turbine. Turbine performance, both aerodynamics and heat transfer, is one of the barrier advanced gas turbine development technologies. This is a result of the complex, highly three-dimensional and unsteady flow phenomena in the turbine. Improved turbine aerodynamic performance has been achieved with three-dimensional highly-loaded airfoil designs, accomplished utilizing Euler or Navier-Stokes Computational Fluid Dynamics (CFD) codes. These design codes consider steady flow through isolated blade rows. Thus they do not account for unsteady flow effects. However, unsteady flow effects have a significant impact on performance. Also, CFD codes predict the complete flow field. The experimental verification of these codes has traditionally been accomplished with point data - not corresponding plane field measurements. Thus, although advanced CFD predictions of the highly complex and three-dimensional turbine flow fields are available, corresponding data are not. To improve the design capability for high temperature turbines, a detailed understanding of the highly unsteady and three-dimensional flow through multi-stage turbines is necessary. Thus, unique data are required which quantify the unsteady three-dimensional flow through multi-stage turbine blade rows, including the effect of the film coolant flow. Also, as design CFD codes do not account for unsteady flow effects, the next logical challenge and the current thrust in CFD code development is multiple-stage analyses that account for the interactions between neighboring blade rows. Again, to verify and or direct the development of these advanced codes, complete three-dimensional unsteady flow field data are needed.

Fleeter, S.; Lawless, P.B. [Purdue Univ., West Lafayette, IN (United States). School of Mechanical Engineering

1995-12-31

153

On the near-field aerodynamics of a projectile launched from a ballistic range  

Microsoft Academic Search

A computational fluid dynamics method has been applied to simulate the unsteady aerodynamics of the projectile launched from\\u000a a ballistic range. A moving coordinate scheme for a multi-domain technique was employed to investigate the unsteady flow with\\u000a moving boundary. The coordinate system fixed to each moving domain was applied to the multi-domains, and the effect of virtual\\u000a mass was added

Rajesh Gopalapillai; Heuy-Dong Kim; Toshiaki Setoguchi; Shigeru Matsuo

2007-01-01

154

Advanced Coupled CFD\\/RBD Calculations of Free-Flight Projectile Aerodynamics  

Microsoft Academic Search

This paper describes a new multidisciplinary computational study undertaken to model the flight trajectories and the free flight aerodynamics of both finned and spinning projectile configurations. Actual flight trajectories are computed using an advanced coupled computational fluid dynamics (CFD)\\/rigid body dynamics (RBD) technique. An advanced time-accurate Navier-Stokes computational technique has been used in CFD to compute the unsteady aerodynamics associated

Jubaraj Sahu

2005-01-01

155

Flow control strategies for improved aerodynamic efficiency of micro-rotorcraft  

Microsoft Academic Search

This thesis is aimed at demonstrating substantial improvements in aerodynamic efficiency of micro-rotorcraft. The work investigates the effect of airfoil surface temperature and heat transfer, and unsteady blade pitching motion on the performance of micro-scale rotors. Prior to testing of new strategies to enhance performance, the baseline aerodynamic performance of the micro-rotor system was quantified. This study indicated that the

Jongmin Kim

2004-01-01

156

Aerodynamic Forces Approximations using the Chebyshev Method for Closed-Loop Aero servoelasticity Studies  

Microsoft Academic Search

The approximation of unsteady generalized aerodynamic forces from the frequency domain into the Laplace domain acting on a Fly-By-Wire aircraft presents an important challenge in the aero-servoelasticity area. The aerodynamic forces in the reduced-frequency domain are approximated in the Laplace domain, to be able to study the effects of the control laws on the flexible aircraft structure. In this paper,

Alin Dorian Dinu; Ruxandra Mihaela Botez; Iulian Cotoi

157

Prediction of Aerodynamic Interactions of Helicopter Rotor on its Fuselage  

Microsoft Academic Search

An iterative and full-coupled rotor\\/fuselage aerodynamic interaction analytical method is developed based upon the rotor free wake model and the 3-D fuselage panel model. A close vortex\\/surface interaction model using the Analytical\\/Numerical Matching (ANM) was adopted in the method in order to simulate effectively the unsteady close interaction between the rotor tip-vortex and fuselage surface. By the analytical method, the

Guo-hua XU; Qi-jun ZHAO; Zheng GAO; Jing-gen ZHAO

2002-01-01

158

Optimization of a synthetic jet actuator for aerodynamic stall control  

Microsoft Academic Search

The numerical simulation of aerodynamic stall control using a synthetic jet actuator is presented and the automatic optimization of the control parameters is investigated. Unsteady Reynolds-averaged Navier–Stokes equations are solved on unstructured grids using a near-wall low-Reynolds number turbulence closure to simulate the effects of a synthetic jet, located at 12% of the chord from the leading edge of a

Régis Duvigneau; Michel Visonneau

2006-01-01

159

Suppression of Subsynchronous Vibrations Due to Aerodynamic Response to Surge in a Two-Stage Centrifugal Compressor with Air Foil Bearings  

Microsoft Academic Search

An investigation was conducted on the suppression of subsynchronous vibrations due to aerodynamic response to surge in a two-stage centrifugal compressor with air foil bearings. Unsteady aerodynamic response to surge caused excessive subsynchronous shaft vibration which might result in reduced bearing life. Notably, subsynchronous vibrations associated with rigid mode frequencies were more severe than any other subsynchronous vibrations. The objective

Y. B. Lee; T. H. Kim; C. H. Kim; N. S. Lee

2003-01-01

160

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

161

Beginner's Guide to Aerodynamics  

NSDL National Science Digital Library

NASA's "Beginner's Guide to Aerodynamics" provides some general information on the basics of aerodynamics. The site allows users to explore at their own pace and level of interest. Some of the topics that are available here are: equations of motion, free falling, air resistance, force, gas properties, and atmosphere. Movies, reading materials, and activities are all available to accommodate a variety of different learning styles. This is an excellent resource, with great reference materials for anyone interested in learning more about aerodynamics.

2007-12-07

162

Rolling with the flow: bumblebees flying in unsteady wakes.  

PubMed

Our understanding of how variable wind in natural environments affects flying insects is limited because most studies of insect flight are conducted in either smooth flow or still air conditions. Here, we investigate the effects of structured, unsteady flow (the von Karman vortex street behind a cylinder) on the flight performance of bumblebees (Bombus impatiens). Bumblebees are 'all-weather' foragers and thus frequently experience variable aerial conditions, ranging from fully mixed, turbulent flow to unsteady, structured vortices near objects such as branches and stems. We examined how bumblebee flight performance differs in unsteady versus smooth flow, as well as how the orientation of unsteady flow structures affects their flight performance, by filming bumblebees flying in a wind tunnel under various flow conditions. The three-dimensional flight trajectories and orientations of bumblebees were quantified in each of three flow conditions: (1) smooth flow, (2) the unsteady wake of a vertical cylinder (inducing strong lateral disturbances) and (3) the unsteady wake of a horizontal cylinder (inducing strong vertical disturbances). In both unsteady conditions, bumblebees attenuated the disturbances induced by the wind quite effectively, but still experienced significant translational and rotational fluctuations as compared with flight in smooth flow. Bees appeared to be most sensitive to disturbance along the lateral axis, displaying large lateral accelerations, translations and rolling motions in response to both unsteady flow conditions, regardless of orientation. Bees also displayed the greatest agility around the roll axis, initiating voluntary casting maneuvers and correcting for lateral disturbances mainly through roll in all flow conditions. Both unsteady flow conditions reduced the upstream flight speed of bees, suggesting an increased cost of flight in unsteady flow, with potential implications for foraging patterns and colony energetics in natural, variable wind environments. PMID:24031057

Ravi, Sridhar; Crall, James D; Fisher, Alex; Combes, Stacey A

2013-09-12

163

Integrated modeling of insect flight: From morphology, kinematics to aerodynamics  

NASA Astrophysics Data System (ADS)

An integrated and rigorous model for the simulation of insect flapping flight is addressed. The method is very versatile, easily integrating the modeling of realistic wing body morphology, realistic flapping-wing and body kinematics, and unsteady aerodynamics in insect flight. A morphological model is built based on an effective differential geometric method for reconstructing geometry of and a specific grid generator for the wings and body; and a kinematic model is constructed capable to mimic the realistic wing body kinematics of flapping flight. A fortified FVM-based NS solver for dynamically moving multi-blocked, overset-grid systems is developed and verified to be self-consistent by a variety of benchmark tests; and evaluation of flapping energetics is established on inertial and aerodynamic forces, torques and powers. Validation of this integrated insect dynamic flight simulator is achieved by comparisons of aerodynamic force-production with measurements in terms of the time-varying and mean lift and drag forces. Results for three typical insect hovering flights (hawkmoth, honeybee and fruitfly) over a wide rang of Reynolds numbers from O(102) to O(104) demonstrate its feasibility in accurately modeling and quantitatively evaluating the unsteady aerodynamic mechanisms in insect flapping flight.

Liu, Hao

2009-02-01

164

Flight physiology of migrating Urania fulgens (Uraniidae) moths: kinematics and aerodynamics of natural free flight  

Microsoft Academic Search

Air speeds and wing kinematics were determined for the Neotropical moth Urania fulgens in natural migratory flight over Lake Gatun, Republic of Panama. Morphological parameters are presented for the same insects filmed in free flight. A quasi-steady aerodynamic analysis was used to show that unsteady mechanisms of lift generation are probably not necessary to produce the forces necessary for fast

R. Dudley; P. J. DeVries

1990-01-01

165

Response of Metal Core Piezoelectric Fibers to Unsteady Airflows  

NASA Astrophysics Data System (ADS)

In the previous study, possible applications of metal core piezoelectric fibers with a diameter of 200 to 250 µm as bionic airflow sensors mimicking the flow sensitive receptor hairs of crickets have been proposed. This study aims to investigate the dynamic responses of the metal core piezoelectric fibers to unsteady airflow. The metal core piezoelectric fiber is half coated on the outer surface and is used in the bending mode. Wind tunnel tests were carried out and the output voltage of the fiber under the excitation of the unsteady aerodynamic force during flow acceleration and deceleration was measured when the wind tunnel was suddenly closed or opened by a shutter. The relationship between the maximum voltage and the steady-state velocity and that between the voltage and the acceleration of flow were also obtained.

Qiu, J. H.; Ji, H. L.; Zhu, K. J.; Park, M. J.

166

Numerical simulation of unsteady flows with transient regimes  

NASA Astrophysics Data System (ADS)

Self-oscillatory flows in aerodynamics and astrophysics are studied. The two-dimensional compressible gas equations are solved using the implicit Runge-Kutta scheme of the third order with respect to the inviscid terms and of the second order with respect to the viscous terms. An algebraic Cebeci-Smith turbulence model is used. Weakly unsteady and strongly unsteady flow regimes are observed. The former occur in a supersonic flow past a cylinder with a front projection and in the heliosphere. Such flows became stable when the turbulent diffusion is taken into account. The latter flows occur when a supersonic jet meets an obstacle and when such a jet penetrates a cavity. In these flows, the amplitude of oscillations slightly decreases when the turbulent diffusion is taken into account.

Pinchukov, V. I.

2009-10-01

167

NASA: Beginner's Guide to Aerodynamics - Aerodynamics Index  

NSDL National Science Digital Library

This web page contains an index of all topics available from NASA's Beginner's Guide to Aerodynamics site. Resources include lesson plans, activities, and interactive simulations for grades 3-12 relating to fundamentals of aerodynamics and the forces acting on airborne objects. The scope of content is extensive and includes specific topics such as thrust, lift, drag, relative velocity, air pressure and density, trajectory, and terminal velocity. Resources are also organized by grade level. These resources, available cost-free, were developed by scientists and teacher workshop participants at NASA's Glenn Learning Research Center.

2008-12-16

168

Study of aerodynamic methods for improving truck fuel economy  

Microsoft Academic Search

Results are reported of a 3-year program to investigate aerodynamic means to reduce fuel consumption of tractor-trailer trucks. The study considered the benefit of aerodynamic add-on devices to reduce the aerodynamic drag on existing vehicles, and the influence of design alternatives in reducing the drag of future vehicles. Results are obtained for scaled-models in water table and wind-tunnel experiments, and

F. T. Jr. Buckley; C. H. Marks; W. H. Jr. Walston

1978-01-01

169

A study of aerodynamic methods for improving truck fuel economy  

Microsoft Academic Search

Results of a 3-year program to investigate aerodynamic means to reduce fuel consumption of tractor-trailer trucks are reported. The study considers the benefit of aerodynamic add-on devices to reduce the aerodynamic drag on existing vehicles, and the influence of design alternatives in reducing the drag of future vehicles. Results are obtained for scaled-models in water table and wind-tunnel experiments, and

F. T. Jr. Buckley; C. H. Marks; W. H. Walston Jr

1978-01-01

170

Aerodynamics of Wiffle Balls  

NASA Astrophysics Data System (ADS)

A team of undergraduate students has performed experiments on Wiffle balls in the Harvey Mudd College wind tunnel facility. Wiffle balls are of particular interest because they can attain a curved trajectory with little or no pitcher-imparted spin. The reasons behind this have not previously been quantified formally. A strain gauge device was designed and constructed to measure the lift and drag forces on the Wiffle ball; a second device to measure lift and drag on a spinning ball was also developed. Experiments were conducted over a range of Reynolds numbers corresponding to speeds of roughly 0-40 mph. Lift forces of up to 0.2 N were measured for a Wiffle ball at 40 mph. This is believed to be due to air flowing into the holes on the Wiffle ball in addition to the effect of the holes on external boundary layer separation. A fog-based flow visualization system was developed in order to provide a deeper qualitative understanding of what occurred in the flowfield surrounding the ball. The data and observations obtained in this study support existing assumptions about Wiffle ball aerodynamics and begin to elucidate the mechanisms involved in Wiffle ball flight.

Utvich, Alexis; Jemmott, Colin; Logan, Sheldon; Rossmann, Jenn

2003-11-01

171

Topic in Depth - Aerodynamics  

NSDL National Science Digital Library

Aerodynamics is the study of what makes things go fast, right? More specifically, itâÂÂs the study of the interaction between bodies and the atmosphere. This topic in depth highlights some fun websites on the science of aerodynamics, for beginners to researchers. If youâÂÂve been watching Wimbeldon lately, you might have been wondering about the aerodynamics of tennis. Or maybe you were riding your bike the other day and wondering how you could pick up a little more speed next time. These sites can help explain.

2010-09-17

172

AIAA Applied Aerodynamics Conference, 10th, Palo Alto, CA, June 22-24, 1992, Technical Papers. Pts. 1 AND 2  

SciTech Connect

Consideration is given to vortex physics and aerodynamics; supersonic/hypersonic aerodynamics; STOL/VSTOL/rotors; missile and reentry vehicle aerodynamics; CFD as applied to aircraft; unsteady aerodynamics; supersonic/hypersonic aerodynamics; low-speed/high-lift aerodynamics; airfoil/wing aerodynamics; measurement techniques; CFD-solvers/unstructured grid; airfoil/drag prediction; high angle-of-attack aerodynamics; and CFD grid methods. Particular attention is given to transonic-numerical investigation into high-angle-of-attack leading-edge vortex flow, prediction of rotor unsteady airloads using vortex filament theory, rapid synthesis for evaluating the missile maneuverability parameters, transonic calculations of wing/bodies with deflected control surfaces; the static and dynamic flow field development about a porous suction surface wing; the aircraft spoiler effects under wind shear; multipoint inverse design of an infinite cascade of airfoils, turbulence modeling for impinging jet flows; numerical investigation of tail buffet on the F-18 aircraft; the surface grid generation in a parameter space; and the flip flop nozzle extended to supersonic flows.

Not Available

1992-01-01

173

Unsteady turbulent boundary layers in adverse pressure gradients  

NASA Astrophysics Data System (ADS)

A number of characteristics of an unsteady turbulent boundary layer have been measured on the after part of the upper surface of an 0012 airfoil (X/c = 0.69 and 0.94). The data is taken at chord Reynolds number of 700,000 and over a range of reduced frequencies (based upon the semichord) of 0.5 to 6.4. Mean and unsteady velocity profiles, as well as Reynolds stress profiles, are presented, as is the nonlinear coupling from the unsteady motion into the steady motion. Data is presented and discussed which shows that for this experiment the periodic unsteady turbulent velocity profile tends toward a universal shape.

Covert, E. E.; Lorber, P. F.

1982-06-01

174

Aerodynamics of Parachutes.  

National Technical Information Service (NTIS)

This AGARD report discusses the principal aerodynamic characteristics of parachutes and the factors which affect them. It is anticipated that its main readers will be recent engineering graduates entering research establishments, parachute companies or re...

D. J. Cockrell A. D. Young

1987-01-01

175

Science of Cycling: Aerodynamics  

NSDL National Science Digital Library

This website, from the Exploratorium, reviews the aerodynamics of cycling. Wind resistance is often one of the biggest challenges that professional and amateur cyclists face. This site has a form that lets you "Calculate the Aerodynamic Drag and Propulsive Power of a Bicyclist". Use the form to calculate resistance using different inclines, velocity, weight or wind velocity. At the bottom of the page, you can find useful information and tips on reducing resistance. Check it out before your next bike ride!

2007-12-26

176

Unsteady RANS simulation of oscillating mould flows  

NASA Astrophysics Data System (ADS)

Mould flow oscillations are of major importance for the performance of the continuous casting process. They are suspected to promote entrainment of slag and other unwanted secondary phases into the melt pool. These oscillating turbulent flows are investigated by means of numerical simulations. The numerical model is based on the equation of continuity and the unsteady Reynolds averaged Navier-Stokes equations. The system of flow equations is closed by a Reynolds stress turbulence model in combination with non-equilibrium wall functions.The unsteady simulation resolves low-frequency oscillations of the flow field. These frequencies and numerically resolved mean values are in agreement with results of corresponding model experiments.The proposed model should be advantageous in order to investigate the mechanisms of the oscillations and the process of slag entrainment in more detail.

Schwarze, R.

2006-11-01

177

Unsteady spray-group combustion  

SciTech Connect

An unsteady spray combustion formulation is developed for the study of group combustion in axisymmetric spray combustion systems. The focus of the study ia on the interrelation between vaporization, combustion, and transport processes in a spray combustion system and: how these processes affect the transient development and collapse of group combustion structures. The unsteady formulation is targeted to modeling of unsteadiness at convective time scales. The numerical approach chosen is fully implicit in time. The two-space dimension steady state spray combustion computer code developed by Zhou and Chiu (1983) is extended to perform computations with the unsteady model formulation. Microcomputer software is developed to process the large amounts of data generated in an unsteady spray combustion computation into gray scale encoded picture graphic representations of variable values over the combustion field. These gray scale graphic results are employed in the analysis of processes in unsteady spray group combustion mode transitions. The unsteady spray combustion computer code and supporting microcomputer software is used in a case study to assess group combustion mode transitions and cycles brought on by changing inlet droplet number density in a simple cylindrical combustor. These studies identify the stages and mechanisms of formation and dissolution of global group combustion modes and assess the effects on the process and progress of the transitions when mean droplet size, spray angle, or droplet inlet temperature are changed. A brief look at the transient group combustion modes which develop periodically during the cycling of the spray injection process is also presented.

Lottes, S.A.

1989-01-01

178

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.

179

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

180

Experimental investigation of bedload transport processes under unsteady flow conditions  

NASA Astrophysics Data System (ADS)

Hydraulic engineering is usually based on theoretical analysis and/or numerical modelling simulation. As the dynamic behaviour of sediment movement under unsteady flow is still unclear, and field measurement is comparatively difficult during a large flood, prior investigations through flume experiments are required. A series of flume experiments, conducted using different inflow hydrographs without sediment supply from upstream, was carried out to investigate the sediment transport process under unsteady flow conditions.A series of triangular hydrographs were performed in the experiments. The results indicate that a temporal lag was found between the flow hydrograph peak and the sediment hydrograph peak because large size sand dunes lasted for a short period in the falling limb of the flow hydrograph. The temporal lag was found to be about equal to 6-15% of the flow hydrograph duration. Owing to the temporal lag, the total bedload yield in the rising period was less than that in the falling period. Furthermore, the measured total bedload yield in the unsteady flow experiments was larger than the predicted value, which was estimated by using the results obtained from the equivalent steady flow experiment. The peak bedload transport rate for unsteady flow conditions was also larger than the predicted value. The ratios of the measured to the predicted quantities mentioned above were found to be constant values for different shapes of hydrographs. It is, therefore, expected that the analytical results of sediment transport from equivalent steady flow can be a good reference for sediment transport under unsteady flow conditions.

Lee, Kwan Tun; Liu, Yi-Liang; Cheng, Kai-Hung

2004-09-01

181

An intercomparison of bulk aerodynamic algorithms used over sea ice with data from the Surface Heat Budget for the Arctic Ocean (SHEBA) experiment  

NASA Astrophysics Data System (ADS)

The presence of sea ice fundamentally changes the energy and momentum exchange between the ocean and the atmosphere in the Arctic. Thus an accurate representation of the surface turbulent fluxes in climate models is a necessity. An intercomparison of bulk aerodynamic algorithms that calculate surface turbulent fluxes in four climate and numerical weather prediction models is undertaken using data from the Surface Heat Budget of the Arctic Ocean (SHEBA) field experiment, which occurred on the ice in the Beaufort and Chukchi seas north of Alaska from October 1997 to October 1998. Algorithm deficiencies include the consistently higher wind stresses produced by the Arctic Regional Climate System Model (ARCSYM) algorithm; the lower sensible heat fluxes under stable conditions by the algorithms in ARCSYM, the National Center for Environmental Prediction's Global Forecasting System model, and the European Centre for Medium-Range Weather Forecasts (ECMWF) model; and the lower wind stresses by the National Center for Atmospheric Research's Community Climate System Model (CCSM) algorithm under stable conditions. Unlike the constants used in most of the four model algorithms, the roughness lengths for momentum can be fitted by an exponential function with parameters that account for the seasonality in the roughness length. The roughness lengths for heat, zot, can be considered a constant (e.g., that used in CCSM, 0.5 mm), similar to what was found by Andreas et al. (2004). When these roughness lengths were implemented into the CCSM and ECMWF algorithms, they produced slightly better wind stresses and sensible heat fluxes most of the time.

Brunke, Michael A.; Zhou, Mingyu; Zeng, Xubin; Andreas, Edgar L.

2006-09-01

182

Introduction to unsteady thermofluid mechanics  

NASA Astrophysics Data System (ADS)

Time-dependent flow problems involving heat transfer and thermodynamics are examined in a textbook and reference guide for advanced engineering students and practicing engineers. Chapters are devoted to the foundations of unsteady thermofluid mechanics, unsteady thermodynamics, convective propagation, hydrostatic waves in small- and large-amplitude applications, unsteady thermofluid systems and normalization, one-dimensional bulk and water-hammer flows, one-dimensional large-amplitude pressure waves, and multidimensional incompressible bulk and water-hammer flows. Diagrams, graphs, and sample problems are provided.

Moody, Frederick J.

183

Unsteady low-Re swimming  

NASA Astrophysics Data System (ADS)

In this talk, we focus on unsteady effects relevant to the fluid-based locomotion of micro-organisms. First, we consider transient effects in locomotion arising from the inertia of both the swimmer and the surrounding fluid. We discuss and derive the relevant time scales governing transient effects in low Reynolds number swimming, and illustrate them using the prototypical problem of a 2D swimmer starting from rest. Second, we address geometrical unsteadiness resulting from the finite-size of the swimmer. We solve numerically for the swimming kinematics of active (internally-forced) filaments, as models for eukaryotic flagella, and discuss the resulting unsteadiness of the cell body.

Pak, On Shun; Lauga, Eric

2009-11-01

184

CHARACTERIZATION OF UNSTEADY FLOW STRUCTURES NEAR LEADING-EDGE SLAT: PART I. PIV MEASUREMENTS  

Microsoft Academic Search

A comprehensive computational and experimental study has been performed at the NASA Langley Research Center as part of the Quiet Aircraft Technology (QAT) Program to investigate the unsteady flow near a leading-edge slat of a two-dimensional, high-lift system. This paper focuses on the experimental effort conducted in the NASA Langley Basic Aerodynamics Research Tunnel (BART) where Particle Image Velocimetry (PIV)

Luther N. Jenkins; Mehdi R. Khorrami; Meelan Choudhari

185

Experimental Investigation on Aerodynamic Characteristics of a Paraglider Wing  

Microsoft Academic Search

The fundamental aerodynamic characteristics of a paraglider's canopy are investigated in wind tunnel experiments using an inflatable cell model designed to represent the dynamic behaviors of each cell comprising the canopy. At attack angles greater than a few degrees, the cell model inflates fully. To characterize its aerodynamic characteristics, we focus our attention on the flow around the inflated cell

Mohammad Mashud; Akira Umemura

2006-01-01

186

The effects of wind and posture on the aerodynamic performance during the flight stage of skiing.  

PubMed

Numerical simulation is conducted to evaluate the wind and posture effects on the aerodynamic performance of a skier during the flight stage. Both steady and unsteady models are applied on a 2D geometry. Using the Fluent code, the fundamental equations of fluid flow are solved simultaneously. In particular we focus on the influence of wind speed and direction on aerodynamic forces with several different postures of the skier in steady modeling. For a chosen case, the unsteady models are used to predict the transient characteristics of streamline distributions and aerodynamic forces. It is found that the skier's postures, wind speed, and direction play a significant role. The wind condition affects the pressure force (the form drag) on the skier and makes it a resistance or thrust regarding wind directions. The optimized posture with a minimization of resistance under a facing wind is determined as a moving-forward body of the skier. The unsteady modeling reveals that the wake around the skier and aerodynamic forces are strongly dependent on time. This initial study not only provides a qualitative and theoretical basis for the athletes to understand the effects of wind and postures, and then to optimize their postures according to the wind condition during the flight stage of skiing, but also builds the foundation for the systematic study of skiing process with more advanced CFD models in the future. PMID:22010736

Chen, Zhifeng; Fang, Haisheng

2011-09-01

187

Turbine disk cavity aerodynamics and heat transfer  

NASA Astrophysics Data System (ADS)

Experiments were conducted to define the nature of the aerodynamics and heat transfer for the flow within the disk cavities and blade attachments of a large-scale model, simulating the Space Shuttle Main Engine (SSME) turbopump drive turbines. These experiments of the aerodynamic driving mechanisms explored the following: (1) flow between the main gas path and the disk cavities; (2) coolant flow injected into the disk cavities; (3) coolant density; (4) leakage flows through the seal between blades; and (5) the role that each of these various flows has in determining the adiabatic recovery temperature at all of the critical locations within the cavities. The model and the test apparatus provide close geometrical and aerodynamic simulation of all the two-stage cavity flow regions for the SSME High Pressure Fuel Turbopump and the ability to simulate the sources and sinks for each cavity flow.

Johnson, B. V.; Daniels, W. A.

1992-07-01

188

Unsteady Force and Pressure Measurements.  

National Technical Information Service (NTIS)

Various aspects of the general problem of unsteady pressure and force measurement are described, and a number of examples of solutions to various force- and pressure-measurement problems are outlined. The examples are intended to illustrate the applicatio...

W. W. Willmarth

1971-01-01

189

Numerical modeling of wind turbine aerodynamic noise in the time domain.  

PubMed

Aerodynamic noise from a wind turbine is numerically modeled in the time domain. An analytic trailing edge noise model is used to determine the unsteady pressure on the blade surface. The far-field noise due to the unsteady pressure is calculated using the acoustic analogy theory. By using a strip theory approach, the two-dimensional noise model is applied to rotating wind turbine blades. The numerical results indicate that, although the operating and atmospheric conditions are identical, the acoustical characteristics of wind turbine noise can be quite different with respect to the distance and direction from the wind turbine. PMID:23363200

Lee, Seunghoon; Lee, Seungmin; Lee, Soogab

2013-02-01

190

Applied computational aerodynamics  

SciTech Connect

The present volume discusses the original development of the panel method, the mapping solutions and singularity distributions of linear potential schemes, the capabilities of full-potential, Euler, and Navier-Stokes schemes, the use of the grid-generation methodology in applied aerodynamics, subsonic airfoil design, inverse airfoil design for transonic applications, the divergent trailing-edge airfoil innovation in CFD, Euler and potential computational results for selected aerodynamic configurations, and the application of CFD to wing high-lift systems. Also discussed are high-lift wing modifications for an advanced-capability EA-6B aircraft, Navier-Stokes methods for internal and integrated propulsion system flow predictions, the use of zonal techniques for analysis of rotor-stator interaction, CFD applications to complex configurations, CFD applications in component aerodynamic design of the V-22, Navier-Stokes computations of a complete F-16, CFD at supersonic/hypersonic speeds, and future CFD developments.

Henne, P.A.

1990-01-01

191

Aerodynamic Flow Control using Distributed Active Bleed  

NASA Astrophysics Data System (ADS)

The aerodynamic effects of large-area air bleed that is driven through surface openings by pressure differences across a lifting airfoil and regulated by addressable, arrays of integrated louvers have been investigated in wind tunnel experiments. Time-dependent interactions between the bleed and cross flows alter the apparent aerodynamic shape of the lifting surface and consequently the distributions of aerodynamic forces and moments. The lift and pitching moment can be significantly altered over a wide range of angles of attack from pre- to post-stall by independently-controlled bleed near the leading (LE) and trailing (TE) edges. While TE bleed effects nearly-linear variation of the pitching moment with minimal changes in lift, LE bleed leads to large variations in lift and pitching moment with minimal drag penalty. Phase-locked PIV shows the effects of the bleed on the flow on the suction surface and in the near wake. Supported by AFOSR

Kearney, John M.; Glezer, Ari

2010-11-01

192

The efficiency of aerodynamic force production in Drosophila.  

PubMed

Total efficiency of aerodynamic force production in insect flight depends on both the efficiency with which flight muscles turn metabolic energy into muscle mechanical power and the efficiency with which this power is converted into aerodynamic flight force by the flapping wings. Total efficiency has been estimated in tethered flying fruit flies Drosophila by modulating their power expenditures in a virtual reality flight simulator while simultaneously measuring stroke kinematics, locomotor performance and metabolic costs. During flight, muscle efficiency increases with increasing flight force production, whereas aerodynamic efficiency of lift production decreases with increasing forces. As a consequence of these opposite trends, total flight efficiency in Drosophila remains approximately constant within the kinematic working range of the flight motor. Total efficiency is broadly independent of different profile power estimates and typically amounts to 2-3%. The animal achieves maximum total efficiency near hovering flight conditions, when the beating wings produce flight forces that are equal to the body weight of the insect. It remains uncertain whether this small advantage in total efficiency during hovering flight was shaped by evolutionary factors or results from functional constraints on both the production of mechanical power by the indirect flight muscles and the unsteady aerodynamic mechanisms in flapping flight. PMID:11733168

Lehmann, F O

2001-12-01

193

Dynamic stall and aerodynamic damping  

SciTech Connect

A dynamic stall model is used to analyze and reproduce open air blade section measurements as well as wind tunnel measurements. The dynamic stall model takes variations in both angle of attack and flow velocity into account. The paper gives a brief description of the dynamic stall model and presents results from analyses of dynamic stall measurements for a variety of experiments with different airfoils in wind tunnel and on operating rotors. The wind tunnel experiments comprises pitching as well as plunging motion of the airfoils. The dynamic stall model is applied for derivation of aerodynamic damping characteristics for cyclic motion of the airfoils in flapwise and edgewise direction combined with pitching. The investigation reveals that the airfoil dynamic stall characteristics depend on the airfoil shape, and the type of motion (pitch, plunge). The aerodynamic damping characteristics, and thus the sensitivity to stall induced vibrations, depend highly on the relative motion of the airfoil in flapwise and edgewise direction, and on a possibly coupled pitch variation, which is determined by the structural characteristics of the blade.

Rasmussen, F.; Petersen, J.T.; Madsen, H.A.

1999-08-01

194

Aerodynamics of compliant membrane wings as related to bat and other mammalian flight  

NASA Astrophysics Data System (ADS)

The wings of mammalian flyers and gliders, such as bats or flying squirrels, are characterized by a compliant skin membrane stretched over a thin skeletal support structure. These unique wing structures lead to aeroelastic behavior that is quite distinct from that observed in birds or insects. We present experimental results on the aerodynamic and fluid mechanical behavior of model compliant wings fabricated using both isotropic and anisotropic membrane materials. Unsteady aerodynamic forces are measured simultaneously with time-resolved PIV of the surrounding flow field, illustrating the relationship between the two and the role of vortex shedding on the overall behavior.

Song, Arnold; Breuer, Kenneth

2007-11-01

195

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

196

Freight Wing Trailer Aerodynamics  

Microsoft Academic Search

Freight Wing Incorporated utilized the opportunity presented by this DOE category one Inventions and Innovations grant to successfully research, develop, test, patent, market, and sell innovative fuel and emissions saving aerodynamic attachments for the trucking industry. A great deal of past scientific research has demonstrated that streamlining box shaped semi-trailers can significantly reduce a truck's fuel consumption. However, significant design

Sean Graham; Patrick Bigatel

2004-01-01

197

Aerodynamics of stretched flames  

Microsoft Academic Search

This dissertation presents studies of three distinctive problems associated with the aerodynamics of stretched premixed flames. In Part I, the geometry, stability, and stabilization of premixed flames are studied by treating the entire flame as a structure surface, with emphasis on the importance of appropriately accounting for stretch effects on its propagation velocity. The main objective of Part II is

Chung-Jen Sun

1998-01-01

198

Aerodynamics of Race Cars  

NASA Astrophysics Data System (ADS)

Race car performance depends on elements such as the engine, tires, suspension, road, aerodynamics, and of course the driver. In recent years, however, vehicle aerodynamics gained increased attention, mainly due to the utilization of the negative lift (downforce) principle, yielding several important performance improvements. This review briefly explains the significance of the aerodynamic downforce and how it improves race car performance. After this short introduction various methods to generate downforce such as inverted wings, diffusers, and vortex generators are discussed. Due to the complex geometry of these vehicles, the aerodynamic interaction between the various body components is significant, resulting in vortex flows and lifting surface shapes unlike traditional airplane wings. Typical design tools such as wind tunnel testing, computational fluid dynamics, and track testing, and their relevance to race car development, are discussed as well. In spite of the tremendous progress of these design tools (due to better instrumentation, communication, and computational power), the fluid dynamic phenomenon is still highly nonlinear, and predicting the effect of a particular modification is not always trouble free. Several examples covering a wide range of vehicle shapes (e.g., from stock cars to open-wheel race cars) are presented to demonstrate this nonlinear nature of the flow field.

Katz, Joseph

2006-01-01

199

Aerodynamic performance of a hovering hawkmoth with flexible wings: a computational approach.  

PubMed

Insect wings are deformable structures that change shape passively and dynamically owing to inertial and aerodynamic forces during flight. It is still unclear how the three-dimensional and passive change of wing kinematics owing to inherent wing flexibility contributes to unsteady aerodynamics and energetics in insect flapping flight. Here, we perform a systematic fluid-structure interaction based analysis on the aerodynamic performance of a hovering hawkmoth, Manduca, with an integrated computational model of a hovering insect with rigid and flexible wings. Aerodynamic performance of flapping wings with passive deformation or prescribed deformation is evaluated in terms of aerodynamic force, power and efficiency. Our results reveal that wing flexibility can increase downwash in wake and hence aerodynamic force: first, a dynamic wing bending is observed, which delays the breakdown of leading edge vortex near the wing tip, responsible for augmenting the aerodynamic force-production; second, a combination of the dynamic change of wing bending and twist favourably modifies the wing kinematics in the distal area, which leads to the aerodynamic force enhancement immediately before stroke reversal. Moreover, an increase in hovering efficiency of the flexible wing is achieved as a result of the wing twist. An extensive study of wing stiffness effect on aerodynamic performance is further conducted through a tuning of Young's modulus and thickness, indicating that insect wing structures may be optimized not only in terms of aerodynamic performance but also dependent on many factors, such as the wing strength, the circulation capability of wing veins and the control of wing movements. PMID:21831896

Nakata, Toshiyuki; Liu, Hao

2011-08-10

200

Finite time Lagrangian analysis of an unsteady separation induced by a near wall wake  

NASA Astrophysics Data System (ADS)

Following the Lagrangian theory of unsteady flow separation on slip boundaries proposed by Lekien and Haller [``Unsteady flow separation on slip boundaries,'' Phys. Fluids 20, 097101 (2008)], we use finite time Lagrangian analysis in order to educe large scale, unsteady flow separation downstream a near wall obstacle at a significant Reynolds number. By large scale flow separation, we mean here the ejection of fluid and vorticity outside a neighborhood of the wall at the scale of the obstacle. Indeed, while the separation point at the wall is not spatially resolved by the high speed particle image velocimetry measurements, free-slip boundary conditions are applied before educing unstable manifolds in the near wall region using finite time Lyapunov exponents. For this turbulent flow, conditional statistics are presented in order to discuss the relative contributions of the unsteady aerodynamics and of the turbulence in the separation region. The dynamics of the corresponding separation point has a very clear link with the fluctuating wall pressure induced by this unsteady turbulent flow.

Ruiz, T.; Borée, J.; Tran T., T.; Sicot, C.; Brizzi, L. E.

2010-07-01

201

Investigating Complex Aerodynamic Flows with a Laser Velocimeter.  

National Technical Information Service (NTIS)

The application of the laser velocimeter in the study of two highly complex aerodynamic flows is discussed. In the first experiment, the laser velocimeter was used with frequency tracking electronics to survey the multiple vortex wake structure behind a m...

J. C. Biggers K. L. Orloff T. W. Ekstedt V. R. Corsiglia

1976-01-01

202

Aerodynamic and Related Hydrodynamic Studies Using Water Facilities.  

National Technical Information Service (NTIS)

This report consists of 32 papers which review related problems, experiences and advancements in aeronautical and maritime fluid dynamics through the use of water facilities. There has been an increasing use of water facilities for aerodynamic investigati...

1987-01-01

203

Aerodynamic Design of Heavy Vehicles Reporting Period January 15, 2004 through April 15, 2004  

SciTech Connect

Listed are summaries of the activities and accomplishments during this second-quarter reporting period for each of the consortium participants. The following are some highlights for this reporting period: (1) Experiments and computations guide conceptual designs for reduction of drag due to tractor-trailer gap flow (splitter plate), trailer underbody (wedges), and base drag (base-flap add-ons). (2) Steady and unsteady RANS simulations for the GTS geometry are being finalized for development of clear modeling guidelines with RANS. (3) Full geometry and tunnel simulations on the GCM geometry are underway. (4) CRADA with PACCAR is supporting computational parametric study to determine predictive need to include wind tunnel geometry as limits of computational domain. (5) Road and track test options are being investigated. All is ready for field testing of base-flaps at Crows Landing in California in collaboration with Partners in Advanced Transportation Highways (PATH). In addition, MAKA of Canada is providing the device and Wabash is providing a new trailer. (6) Apparatus to investigate tire splash and spray has been designed and is under construction. Michelin has offered tires with customized threads for this study. (7) Vortex methods have improved techniques for the treatment of vorticity near surfaces and spinning geometries like rotating tires. (8) Wind tunnel experiments on model rail cars demonstrate that empty coal cars exhibit substantial aerodynamic drag compared to full coal cars, indicating that significant fuel savings could be obtained by reducing the drag of empty coal cars. (9) Papers are being prepared for an exclusive conference session on the Heavy Vehicle DOE Aerodynamic Drag Project at the 34th AIAA Fluid Dynamics Conference in Portland, Oregon, June 28-July 1, 2004.

Leonard, A; Chatelain, P; Heineck, J; Browand, F; Mehta, R; Ortega, J; Salari, K; Storms, B; Brown, J; DeChant, L; Rubel, M; Ross, J; Hammache, M; Pointer, D; Roy, C; Hassan, B; Arcas, D; Hsu, T; Payne, J; Walker, S; Castellucci, P; McCallen, R

2004-04-13

204

Aerodynamic Noise: a Critical Survey  

NASA Astrophysics Data System (ADS)

Annoyance due to railway noise is a particularly sensitive aspect of new high-speed projects. Many studies have shown that aerodynamic noise becomes significant above 300 km/h and can become predominant with the reduction of the contribution of rolling noise. At the moment, no further global reduction of high-speed train noise can be achieved if the aerodynamic noise is not reduced. The objective of this paper is to provide a critical survey of the aeroacoustic noise problem for trains, particularly for high-speed trains. The first step in any acoustic study is to identify the different sources. This paper describes the different aeroacoustic phenomena which are representative of high-speed trains and the technical methodologies used to characterize these phenomena. Specific tools have been developed from on-line tests, wind tunnel experiments, theoretical studies or numerical simulations to characterize the different sources. Using examples, the limitations of the methods and the solutions currently available are reveiwed today. Methods of global modelling of a high-speed train emission are also presented. Finally, future development of new tools based on numerical simulation in aeroacoustics are discussed.

Talotte, C.

2000-03-01

205

Improvement of an aerodynamic model for biomimetic flapping-wing robots  

Microsoft Academic Search

Biomimetic flapping-wing robot is a new type of miniature air vehicle mimicking birds or insects to fly, with many unique advantages that traditional fixed-wing and rotary-wing aircrafts do not possess. Unsteady aerodynamics at low Reynolds number is the main theory applied to the flight analysis of such air vehicles with flapping-wings, and it is still a big challenge. Various models

Liang Chen; Yisheng Guan; Xianmin Zhang; Hong Zhang

2010-01-01

206

Numerical and Experimental Study on Unsteady Shedding of Partial Cavitation  

NASA Astrophysics Data System (ADS)

Periodically unsteady shedding of partial cavity and forming of cavitation cloud have a great influence on hydraulic performances and cavitation erosion for ship propellers and hydro machines. In the present study, the unsteady cavitating flow around a hydrofoil has been calculated by using the single fluid approach with a developed cavitation mass transfer expression based on the vaporization and condensation of the fluid. The numerical simulation depicted the unsteady shedding of partial cavity, such as the process of cavity developing, breaking off and collapsing in the downstream under the steady incoming flow condition. It is noted that good agreement between the numerical results and that of experiment conducted at a cavitation tunnel is achieved. The cavitating flow field indicates that the cavity shedding was mainly caused by the re-entrant jet near cavity trailing edge, which was also clearly recorded by high-speed photographing.

Ji, Bin; Luo, Xianwu; Wu, Yulin; Peng, Xiaoxing; Xu, Hongyuan

207

HYSHOT-2 Aerodynamics  

NASA Astrophysics Data System (ADS)

The scramjet flight test Hyshot-2, flew on the 30 July 2002. The programme, led by the University of Queensland, had the primary objective of obtaining supersonic combustion data in flight for comparison with measurements made in shock tunnels. QinetiQ was one of the sponsors, and also provided aerodynamic data and trajectory predictions for the ballistic re-entry of the spinning sounding rocket. The unconventional missile geometry created by the nose-mounted asymmetric-scramjet in conjunction with the high angle of attack during re-entry makes the problem interesting. This paper presents the wind tunnel measurements and aerodynamic calculations used as input for the trajectory prediction. Indirect comparison is made with data obtained in the Hyshot-2 flight using a 6 degree-of-freedom trajectory simulation.

Cain, T.; Owen, R.; Walton, C.

2005-02-01

208

Applied computational aerodynamics  

Microsoft Academic Search

The present volume discusses the original development of the panel method, the mapping solutions and singularity distributions of linear potential schemes, the capabilities of full-potential, Euler, and Navier-Stokes schemes, the use of the grid-generation methodology in applied aerodynamics, subsonic airfoil design, inverse airfoil design for transonic applications, the divergent trailing-edge airfoil innovation in CFD, Euler and potential computational results for

Henne

1990-01-01

209

Three-Dimensional Effects of Unsteadiness on Separated Turbulent Flows.  

National Technical Information Service (NTIS)

A series of experiments is undertaken to take advantage of previous work and state-of-the-art experimental investigate techniques to provide information on a wide class of unsteady flows. Primary objectives of the program are to answer basic questions con...

J. L. Way R. E. Drubka D. J. Koga

1982-01-01

210

Unsteady measurement of dynamic viscosity  

Microsoft Academic Search

The paper describes a rotating coaxial cylinder rheometer based on unsteady flow, and its technique of operation which, unlike that of conventional devices working in steady regime, dispenses with the need of measuring the resulting torque that arises from the viscous forces on the inner cylinder surface. The equation for calculating the dynamic viscosity has a very simple form; it

A. Št?pánek

1982-01-01

211

Aerodynamic sound generated by a wing of complex geometry  

NASA Astrophysics Data System (ADS)

The aerodynamic sound produced by a wing in unsteady flow is computed numerically. A boundary element method is used to calculate both the aerodynamic flow and the sound radiated in an attempt to provide a unified and computationally efficient method. This method is intended to help fill the gap between numerically expensive techniques (e.g., RANS, LES) and analytical methods which are available only for a small subset of the wing geometries of interest. The advances made in the current research are through the incorporation of several previously developed techniques in boundary element and vortex methods and their aggregate application to the present aerodynamic sound problem. The method is capable of modeling general three-dimensional wing geometries with a multiple number of wing elements (e.g., flaps) and with thin shear layer wakes that evolve freely with the unsteady flow. The passage of a vortex filament, which also evolves freely and nonlinearly, can be simulated to study the Blade-Vortex Interaction (BVI) problem. Validations with two-dimensional analytical solutions for parallel BVI show that the lift spectra are computed to within 1 dB up to nondimensional frequencies (scaled by the freestream velocity and the half-chord length) of about 10 using only 40 panels along a streamwise wing section. The parallel BVI problem was used to investigate the effects of wing geometry. These results show that the high frequency response is significantly reduced for high thickness, camber, sweep, and taper, but is increased for high angle of attack and flap deflection angle. The most important parameters affecting the BVI signal is observed to be the minimum separation distance between the vortex filament and the wing. It is shown that the correct separation distance is only achieved when the vortex is modeled as evolving freely and nonlinearly.

Wood, Trevor Howard

2002-09-01

212

Calculation of the Unsteady Airloads on Wind Turbine Blades Under Yawed Flow  

NASA Astrophysics Data System (ADS)

A dynamic stall model is coupled with the blade element momentum theory to calculate the cyclic variation of the aerodynamic characteristics of the wind turbine in yawed flow. In the dynamic stall model, unsteady effects under attached flow conditions are simulated by the superposition of indicial aerodynamic responses. The movement of the unsteady flow separation point is related to the static separation based on the Kirchhoff flow model via a deficiency function, in which the unsteady boundary layer response and the leading edge pressure response are taken into consideration. The induced vortex force and the associated pitching moment are represented empirically in a time-dependent manner during dynamic stall. The required input of the inflow velocity and incidence to the dynamic stall model is calculated using the improved blade element momentum theory. The calculated results are compared well with the NREL UAE Phase VI experimental data. For completeness, possible factors causing the difference between calculated and experimental results are analyzed and discussed in detail in this paper.

Si, Hai-Qing; Wang, Tong-Guang

213

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

214

Flow Structure on Plates in Unsteady Motion  

NASA Astrophysics Data System (ADS)

The unsteady, three-dimensional flow structure is characterized along a flat plate (aspect ratio two) undergoing pitching motion to relatively high angle of attack and plunging motion associated with moderate effective angle of attack. Techniques of particle image velocimetry lead to sectional and volume representations of the phase-averaged velocity, vorticity and streamline topology. Emphasis is on a value of Reynolds number based on chord of 10,000. An inherent feature is pronounced spanwise flow in the vicinity of the leading-edge, either towards or away from the plane of symmetry of the plate, which is associated with formation of large-scale, three-dimensional vortical structures. Such structures can have substantial levels of vorticity oriented in the streamwise/surface-normal direction(s), and they are characterized in relation to the unsteady development of the tip vortices. Their continued evolution along the plate is associated with radical departures from a quasi-two-dimensional flow pattern. This investigation is a sequel to our recent study reported in Experiments in Fluids, Vol. 48, No. 3 (March), pp. 539-544.

Yilmaz, T.; Rockwell, D.

2010-11-01

215

Aerodynamics and interaction noise of streamlined bodies in nonuniform flows  

NASA Astrophysics Data System (ADS)

The unsteady aerodynamics and interaction noise of streamlined bodies are modeled in terms of the Euler equations linearized about a nonuniform flow. The validity of the inviscid approach is supported by recent LES simulations of an airfoil in a gust indicating that for not-too-small impinging excitations, the interaction process is dominated by inertia forces. Results in the present paper are focused on the aerodynamics and interaction noise of a turbofan modeled as an annular cascade. The model accounts for the inflow-fan-duct coupling and the high frequency of the interaction process. Two high-order numerical algorithms are developed with body-fitted coordinate system. One algorithm uses a primitive variable formulation, the other uses an efficient velocity splitting algorithm and is suitable for broadband computations. Analytical and numerical analysis of disturbances in rotational flows is developed and exact inflow/outflow boundary conditions are derived, yielding directly the radiated acoustics. The upstream disturbances evolve in rotational flows and as a result the aerodynamic-aeroacoustic response of the annular cascade depends on the initial conditions location. Computational results show that the three-dimensional geometry of the annular cascade, the mean flow swirl, and the blade geometry have strong influence on the blade sectional lift and the radiated sound. These results also show the inadequacy of using the popular linear cascade model particularly for realistic fan geometry and inflow conditions.

Atassi, H. M.; Logue, M. M.

2011-08-01

216

ROBUST STRUCTURAL DESIGN FOR ACTIVE AEROELASTIC WING WITH AERODYNAMIC UNCERTAINTIES  

Microsoft Academic Search

A multidisciplinary design study for Active Aeroelastic Wing technology considering the uncertainty in maneuver loads estimated by linear aerodynamic theory is presented. The study makes use of a design of experiments\\/response surface methodology and modal-based structural optimization to construct deterministic relationships between wing structural weight and control laws design, based on linear aerodynamics. CFD Navier-Stokes analysis is then used to

P. Scott Zink; Daniella E. Raveh; Dimitri N. Mavris

2000-01-01

217

Freight Wing Trailer Aerodynamics  

SciTech Connect

Freight Wing Incorporated utilized the opportunity presented by this DOE category one Inventions and Innovations grant to successfully research, develop, test, patent, market, and sell innovative fuel and emissions saving aerodynamic attachments for the trucking industry. A great deal of past scientific research has demonstrated that streamlining box shaped semi-trailers can significantly reduce a truck's fuel consumption. However, significant design challenges have prevented past concepts from meeting industry needs. Market research early in this project revealed the demands of truck fleet operators regarding aerodynamic attachments. Products must not only save fuel, but cannot interfere with the operation of the truck, require significant maintenance, add significant weight, and must be extremely durable. Furthermore, SAE/TMC J1321 tests performed by a respected independent laboratory are necessary for large fleets to even consider purchase. Freight Wing used this information to create a system of three practical aerodynamic attachments for the front, rear and undercarriage of standard semi trailers. SAE/TMC J1321 Type II tests preformed by the Transportation Research Center (TRC) demonstrated a 7% improvement to fuel economy with all three products. If Freight Wing is successful in its continued efforts to gain market penetration, the energy and environmental savings would be considerable. Each truck outfitted saves approximately 1,100 gallons of fuel every 100,000 miles, which prevents over 12 tons of CO2 from entering the atmosphere. If all applicable trailers used the technology, the country could save approximately 1.8 billion gallons of diesel fuel, 18 million tons of emissions and 3.6 billion dollars annually.

Graham, Sean (Primary Investigator); Bigatel, Patrick

2004-10-17

218

Unified aeroacoustics analysis for high speed turboprop aerodynamics and noise. Volume 3: Application of theory for blade loading, wakes, noise, and wing shielding  

Microsoft Academic Search

Results of the program for the generation of a computer prediction code for noise of advanced single rotation, turboprops (prop-fans) such as the SR3 model are presented. The code is based on a linearized theory developed at Hamilton Standard in which aerodynamics and acoustics are treated as a unified process. Both steady and unsteady blade loading are treated. Capabilities include

D. B. Hanson; C. J. McColgan; R. M. Ladden; R. J. Klatte

1991-01-01

219

Computational analysis of high resolution unsteady airloads for rotor aeroacoustics  

NASA Astrophysics Data System (ADS)

The study of helicopter aerodynamic loading for acoustics applications requires the application of efficient yet accurate simulations of the velocity field induced by the rotor's vortex wake. This report summarizes work to date on the development of such an analysis, which builds on the Constant Vorticity Contour (CVC) free wake model, previously implemented for the study of vibratory loading in the RotorCRAFT computer code. The present effort has focused on implementation of an airload reconstruction approach that computes high resolution airload solutions of rotor/rotor-wake interactions required for acoustics computations. Supplementary efforts on the development of improved vortex core modeling, unsteady aerodynamic effects, higher spatial resolution of rotor loading, and fast vortex wake implementations have substantially enhanced the capabilities of the resulting software, denoted RotorCRAFT/AA (AeroAcoustics). Results of validation calculations using recently acquired model rotor data show that by employing airload reconstruction it is possible to apply the CVC wake analysis with temporal and spatial resolution suitable for acoustics applications while reducing the computation time required by one to two orders of magnitude relative to that required by direct calculations. Promising correlation with this body of airload and noise data has been obtained for a variety of rotor configurations and operating conditions.

Quackenbush, Todd R.; Lam, C.-M. Gordon; Wachspress, Daniel A.; Bliss, Donald B.

1994-05-01

220

Aerodynamics: The Mathematical Implications  

NSDL National Science Digital Library

This unit from the Yale-New Haven Teachers Institute is "an attempt to develop a unit in mathematics that will provide topics for students interested in the aviation trades." The unit can be used to cover all areas of mathematics from areas in geometry sectors to basic addition of fraction and decimal numbers. These general math concepts will be introduced using aerodynamics and aviation language and it is hoped that students will begin "to understand the applicability of some of the mathematics concepts they have learned." This curriculum unit also includes sample lesson plans and references.

Smikle, Hermine E.

2000-03-11

221

An experimental study of the unsteady vortex structures in the wake of a root-fixed flapping wing  

NASA Astrophysics Data System (ADS)

An experimental study was conducted to characterize the evolution of the unsteady vortex structures in the wake of a root-fixed flapping wing with the wing size, stroke amplitude, and flapping frequency within the range of insect characteristics for the development of novel insect-sized nano-air-vehicles (NAVs). The experiments were conducted in a low-speed wing tunnel with a miniaturized piezoelectric wing (i.e., chord length, C = 12.7 mm) flapping at a frequency of 60 Hz (i.e., f = 60 Hz). The non-dimensional parameters of the flapping wing are chord Reynolds number of Re = 1,200, reduced frequency of k = 3.5, and non-dimensional flapping amplitude at wingtip h = A/C = 1.35. The corresponding Strouhal number (Str) is 0.33 , which is well within the optimal range of 0.2 < Str < 0.4 used by flying insects and birds and swimming fishes for locomotion. A digital particle image velocimetry (PIV) system was used to achieve phased-locked and time-averaged flow field measurements to quantify the transient behavior of the wake vortices in relation to the positions of the flapping wing during the upstroke and down stroke flapping cycles. The characteristics of the wake vortex structures in the chordwise cross planes at different wingspan locations were compared quantitatively to elucidate underlying physics for a better understanding of the unsteady aerodynamics of flapping flight and to explore/optimize design paradigms for the development of novel insect-sized, flapping-wing-based NAVs.

Hu, Hui; Clemons, Lucas; Igarashi, Hirofumi

2011-08-01

222

Oscillating cascade aerodynamics at large mean incidence  

SciTech Connect

The aerodynamics of a cascade of airfoils oscillating in torsion about the midchord is investigated experimentally at a large mean incidence angle and, for reference, at a low mean incidence angle. The airfoil section is representative of a modern, low-aspect-ratio, fan blade tip section. Time-dependent airfoil surface pressure measurements were made for reduced frequencies of up to 1.2 for out-of-phase oscillations at a Mach number of 0.5 and chordal incidence angles of 0 and 10 deg; the Reynolds number was 0.9 {times} 10{sup 6}. For the 10 deg chordal incidence angle, a separation bubble formed at the leading edge of the suction surface. The separated flow field was found to have a dramatic effect on the chordwise distribution of the unsteady pressure. In this region, substantial deviations from the attached flow data were found, with the deviations becoming less apparent in the aft region of the airfoil for all reduced frequencies. In particular, near the leading edge the separated flow had a strong destabilizing influence while the attached flow had a strong stabilizing influence.

Buffum, D.H. [NASA Lewis Research Center, Cleveland, OH (United States); Capece, V.R.; King, A.J. [Univ. of California, Davis, CA (United States). Dept. of Mechanical and Aeronautical Engineering; El-Aini, Y.M. [Pratt and Whitney, West Palm Beach, FL (United States)

1998-01-01

223

Aerodynamic design via control theory  

Microsoft Academic Search

Abstract This paper addresses the question of how to modify in aerodynamic design to improve the performance. Representative examples are given to demonstrate the computational feasibility of using control theory for such a purpose. An introduction and historical survey is included. 1 Introduction and historical survey Computers have had a twofold impact on the science of aerodynamics. On the one

Antony Jameson

1988-01-01

224

Aerodynamics of runback ice accretions  

Microsoft Academic Search

An experimental study of the effects of simulated runback ice accretions has been performed in order to describe their aerodynamic performance penalties and investigate their scaling for use in sub-scale aerodynamic testing. Runback ice accretions corresponding to three flight conditions, warm hold, cold hold and descent, were simulated and tested on the NACA 23012 and NACA 3415. The ice shapes

Edward A. Whalen

2007-01-01

225

On Wings: Aerodynamics of Eagles.  

ERIC Educational Resources Information Center

|The Aerodynamics Wing Curriculum is a high school program that combines basic physics, aerodynamics, pre-engineering, 3D visualization, computer-assisted drafting, computer-assisted manufacturing, production, reengineering, and success in a 15-hour, 3-week classroom module. (JOW)|

Millson, David

2000-01-01

226

Aerodynamics of a Party Balloon  

ERIC Educational Resources Information Center

|It is well-known that a party balloon can be made to fly erratically across a room, but it can also be used for quantitative measurements of other aspects of aerodynamics. Since a balloon is light and has a large surface area, even relatively weak aerodynamic forces can be readily demonstrated or measured in the classroom. Accurate measurements…

Cross, Rod

2007-01-01

227

Three-dimensional flow structure and aerodynamic loading on a revolving wing  

NASA Astrophysics Data System (ADS)

A numerical study is conducted to examine the vortex structure and aerodynamic loading on a revolving wing in quiescent flow. A high-fidelity, implicit large eddy simulation technique is employed to simulate a revolving wing configuration consisting of a single, aspect-ratio-one rectangular plate extended out a distance of half a chord from the rotational axis at a fixed angle relative to the axis. Shortly after the onset of the motion, the rotating wing generates a coherent vortex system along the leading-edge. This vortex system remains attached throughout the motion for the range of Reynolds numbers explored, despite the unsteadiness and vortex breakdown observed at higher Reynolds numbers. The average and instantaneous wing loading also increases with Reynolds number. At a fixed Reynolds number, the attachment of the leading-edge vortex is also shown to be insensitive to the geometric angle of the wing. Additionally, the flow structure and forcing generated by a purely translating wing is investigated and compared with that of the revolving wing. Similar features are present at the inception of the motion, however, the two flows evolve very differently for the remainder of the maneuver. Comparisons of the revolving wing simulations with recent experimental particle image velocimetry (PIV) measurements using a new PIV-like data reduction technique applied to the computational solution show very favorable agreement. The success of the data reduction technique demonstrates the need to compare computations and experiments of differing resolutions using similar data-analysis techniques.

Garmann, Daniel J.; Visbal, Miguel R.; Orkwis, Paul D.

2013-03-01

228

Unsteady low-Re swimming  

Microsoft Academic Search

In this talk, we focus on unsteady effects relevant to the fluid-based locomotion of micro-organisms. First, we consider transient effects in locomotion arising from the inertia of both the swimmer and the surrounding fluid. We discuss and derive the relevant time scales governing transient effects in low Reynolds number swimming, and illustrate them using the prototypical problem of a 2D

On Shun Pak; Eric Lauga

2009-01-01

229

Unsteady 3-D lifting surface theory with the free surface effect  

NASA Astrophysics Data System (ADS)

This theory concerns unsteady fluid/structure interactions with the gravity effect. Usual assumptions of the linear theories are made and the 3-D lifting surface method of the unsteady aerodynamics is used. Starting from the potential of the Havelock source, we are led to an integral equation, the kernel of which is expressed as a Fourier series with respect to the azimuthal angle. The coefficients of the Fourier expansion are simple integrals approximated by an asymptotic method for large indices. The integral equation is solved by the collocation technics. Problems such as flutter of subcavitating foil-systems for control dynamics in flight near the surface wave provide relevant applications of this theory.

Leclerc, J.; Salaun, P.

230

Inviscid-viscous coupled solution for unsteady flows through vibrating blades: Part 2--Computational results  

SciTech Connect

A quasi-three-dimensional inviscid-viscous coupled approached has been developed for unsteady flows around oscillating blades, as described in Part 1. To validate this method, calculations for several steady and unsteady flow cases with strong inviscid-viscous interactions are performed, and the results are compared with the corresponding experiments. Calculated results for unsteady flows around a biconvex cascade and a fan tip section highlight the necessity of including viscous effects in predictions of turbomachinery blade flutter at transonic flow conditions.

He, L.; Denton, J.D. (Cambridge Univ., Cambridge (United Kingdom))

1993-01-01

231

MODELING STRATEGIES FOR UNSTEADY TURBULENT FLOWS IN THE LOWER PLENUM OF THE VHTR  

SciTech Connect

Validation simulations are presented for turbulent flow in a staggered tube bank, geometry similar to that in the lower plenum of a block very high temperature reactor. Steady 2D RANS predictions are compared to unsteady 2D RANS results and experiment. The unsteady calculations account for the fact that nonturbulent fluctuations (due to vortex-shedding) are present in the flow. The unsteady computations are shown to predict the mean variables and the total shear stress quite well. Previous workers have presented results that indicated that 3D simulations were necessary to obtain reasonable results. Best practices are based on requirements for the ASME Journal of Fluids Engineering.

Richard W. Johnson

2006-09-01

232

Aerodynamics of flapping wings with fluttering trailing edges  

NASA Astrophysics Data System (ADS)

Our previous work on the aerodynamics of passive flexible flapping wings showed that there is a strong relationship between the dynamics of trailing edge and the size of the leading edge vortex, therefore aerodynamic forces. Here we investigated the aerodynamic effects of active trailing edges. The experiments were conducted on a model flapping wing in an oil tank. During static tests, the trailing edge bending angle was held constant from the angle of attack of the upper portion of the rigid wing. For dynamic cases, the trailing edge was controlled to flutter with a prescribed frequency and amplitude. Force measurements and PIV results show that trailing edge flexion/camber strongly correlates with the leading edge vortex and the aerodynamic forces. In addition, large instantaneous force variations are observed in the dynamic fluttering cases, suggesting that trailing edge can be used for force modulation in MAVs.

Zhao, Liang; Hu, Zheng; Roll, Jesse; Deng, Xinyan

2010-11-01

233

Investigation into the aerodynamics of swashplateless rotors using CFD-CSD analysis  

NASA Astrophysics Data System (ADS)

This study obtains a better understanding of the aerodynamics of integrated trailing edge flap (TEF) based swashplateless rotors. Both two dimensional (2D) and three dimensional (3D) analysis/simulations are performed to understand the behavior of TEF airfoils and integrated TEF based swashplateless rotors. The 2D aerodynamics of TEF airfoils is explored in detail. A semi-empirical approach is developed for modeling drag for TEF airfoils in steady flows based on baseline airfoil drag data alone. Extensive 2D CFD simulations are performed for a wide range of flow conditions in order to better understand various aspects of the aerodynamics of TEF airfoils. The trends in the airloads (lift, drag, pitching moment, hinge moment) for TEF airfoils are obtained. Nonlinear phenomena such as flow separation, shocks and unsteady vortex shedding are investigated, and the flow conditions and trends associated with them are studied. The effect of airfoil properties such as thickness and overhang are studied. Various approaches are used to model the effect of gaps at the leading edge of the flap. An approximate "gap averaging" technique is developed, which provides good predictions of steady airloads at almost the same computational cost as a simulation where the gap is not modeled. Direct modeling of the gap is done by using a patched mesh in the gap region. To solve problems (such as poor grid quality/control and poor convergence) that are associated with the patched mesh simulations, an alternate approach using overlapping meshes is used. It is seen that for TEF airfoils, the presence of gaps adversely affects the effectiveness of the flap. The change in airloads is not negligible, especially at the relatively higher flap deflections associated with swashplateless TEF rotors. Finally, uncoupled and coupled computational fluid/structural dynamics (CFD-CSD) simulations of conventional (baseline) and swashplateless TEF rotors is performed in hovering flight. The CFD-CSD code is validated against experiment and good agreement is observed. It is observed that the baseline UH-60 rotor performs better than the swashplateless UH-60 rotor. For an untwisted NACA0012 airfoil based rotor, the performance is similar for the baseline and swashplateless configurations. The effect of gaps on the performance of swashplateless TEF rotors is also investigated. It is seen that the presence of chordwise gaps significantly affects the effectiveness of the TEF to control the rotor. Spanwise gaps also affect the performance of swashplateless rotors but their effect is not as significant.

Jose, Arun Isaac

234

Numerical Simulations for Insect `Clap and Fling' with Unsteady Incompressible Solver on Dynamic Hybrid Grids  

NASA Astrophysics Data System (ADS)

For very insect such as tiny wasp Encarsaria Formosa, Weis-Fogh found that the ‘clap-fling’ mechanism of their wings is the main cause for their large lift. In this paper, we simulate the motion numerically and analyze the generation of large lift by the wings with an unsteady incompressible flow solver based on dynamic hybrid mesh. Both one wing flapping and two wings ‘clap and fling’ are considered in the Reynolds number range of 8-128, the difference on flow structures and aerodynamic forces are compared with each other, and then high lift mechanism is analyzed.

Zhang, L. P.; Chang, X. H.; Duan, X. P.; Zhang, H. X.

235

Projectiles and aerodynamic forces  

NASA Astrophysics Data System (ADS)

Most elementary works on physics contain something about the motion of projectiles which, it is commonly assumed, are acted on only by gravity. Yet even on balls used in various games the aerodynamic forces are rarely completely negligible (Daish 1972, especially chs 6 and 12). As for bullets and artillery projectiles, the force of air resistance on them is commonly many times that of gravity (Smith 1962). What purpose, then, is supposed to be served by presenting students with such unphysical notions and asking them to spend time working out conundrums about such matters? Warren (1965) has commented on the lack of realism in many parts of school physics, but does not seem to have said much about this example. The author's purpose is to find simple ways of taking into account the air resistance on projectiles, at least approximately.

Armstrong, H. L.

1984-09-01

236

Two unsteady heat transfer experiments. Part 1: In grid-generated isotropic turbulence. Part 2: In laminar oscillatory flow in straight and conical tubes  

NASA Astrophysics Data System (ADS)

A screen of closely spaced, parallel, thin wires was placed downstream of a grid generating nearly isotropic turbulence. The screen was normal to the flow and was heated in one of two modes: (1) periodically in time, to generate a train of transversely uniform streamwise thermal ramps, each with a uniform streamwise gradient; and (2) steadily, with transverse nonuniformity, to generate a uniform transverse thermal ramp. The simple temperature and temperature gradient fluctuation statistical properties in both cases were comparable to those encountered with a steadily heated grid producing a uniform transverse thermal ramp. In both modes of heating the temperature fluctuations decreased initially behind the screen and then increased monotonically. The skewness of the temperature fluctuation derivative in the direction of the main gradient was found to be nonzero despite the absence of mean shear. Experiments on the flow field and the dispersion of heat in laminar oscillatory flow in straight and conical around tubes obtained the fluid point displacements by hydrogen bubble visualization in water and the velocity field by hot-wire anemometry in air. The heat lost through the heating frame and the insulated walls of the tube is estimated from wall temperatures extrapolated from radial profiles in the flow. The terms in the energy equation roughly balance. A plug oscillatory flow model theoretical model generates temperature fluctuations which resemble those in the core of the experimental flow.

Budwig, R. S.

237

Perturbation dynamics in unsteady pipe flows  

NASA Astrophysics Data System (ADS)

This paper deals with perturbed unsteady laminar flows in a pipe. Three types of flows are considered: a flow accelerated from rest; a flow in a pipe generated by the controlled motion of a piston; and a water hammer flow where the transient is generated by the instantaneous closure of a valve. Methods of linear stability theory are used to analyse the behaviour of small perturbations in the flow. Since the base flow is unsteady, the linearized problem is formulated as an initial-value problem. This allows us to consider arbitrary initial conditions and describe both short-time and long-time evolution of the flow. The role of initial conditions on short-time transients is investigated. It is shown that the phenomenon of transient growth is not associated with a certain type of initial conditions. Perturbation dynamics is also studied for long times. In addition, optimal perturbations, i.e. initial perturbations that maximize the energy growth, are determined for all three types of flow discussed. Despite the fact that these optimal perturbations, most probably, will not occur in practice, they do provide an upper bound for energy growth and can be used as a point of reference. Results of numerical simulation are compared with previous experimental data. The comparison with data for accelerated flows shows that the instability cannot be explained by long-time asymptotics. In particular, the method of normal modes applied with the quasi-steady assumption will fail to predict the flow instability. In contrast, the transient growth mechanism may be used to explain transition since experimental transition time is found to be in the interval where the energy of perturbation experiences substantial growth. Instability of rapidly decelerated flows is found to be associated with asymptotic growth mechanism. Energy growth of perturbations is used in an attempt to explain previous experimental results. Numerical results show satisfactory agreement with the experimental features such as the wavelength of the most unstable mode and the structure of the most unstable disturbance. The validity of the quasi-steady assumption for stability studies of unsteady non-periodic laminar flows is discussed.

Zhao, M.; Ghidaoui, M. S.; Kolyshkin, A. A.

238

Aerodynamic Performances of Corrugated Dragonfly Wings at Low Reynolds Numbers  

NASA Astrophysics Data System (ADS)

The cross-sections of dragonfly wings have well-defined corrugated configurations, which seem to be not very suitable for flight according to traditional airfoil design principles. However, previous studies have led to surprising conclusions of that corrugated dragonfly wings would have better aerodynamic performances compared with traditional technical airfoils in the low Reynolds number regime where dragonflies usually fly. Unlike most of the previous studies of either measuring total aerodynamics forces (lift and drag) or conducting qualitative flow visualization, a series of wind tunnel experiments will be conducted in the present study to investigate the aerodynamic performances of corrugated dragonfly wings at low Reynolds numbers quantitatively. In addition to aerodynamics force measurements, detailed Particle Image Velocimetry (PIV) measurements will be conducted to quantify of the flow field around a two-dimensional corrugated dragonfly wing model to elucidate the fundamental physics associated with the flight features and aerodynamic performances of corrugated dragonfly wings. The aerodynamic performances of the dragonfly wing model will be compared with those of a simple flat plate and a NASA low-speed airfoil at low Reynolds numbers.

Tamai, Masatoshi; He, Guowei; Hu, Hui

2006-11-01

239

Effect of flexure on aerodynamic propulsive efficiency of flapping flexible airfoil  

NASA Astrophysics Data System (ADS)

The aim of present study is to investigate the effect of chord-wise flexure amplitude on unsteady aerodynamic characteristics for a flapping airfoil with various combinations of Reynolds number and reduced frequency. Unsteady, viscous flows over a single flexible airfoil in plunge motion are computed using conformal hybrid meshes. The dynamic mesh technique is applied to illustrate the deformation modes of the flexible flapping airfoil. In order to investigate the influence of the flexure amplitude on the aerodynamic performance of the flapping airfoil, the present study considers eight different flexure amplitudes (a0) ranging from 0 to 0.7 in intervals of 0.1 under conditions of Re=104, reduced frequency k=2, and dimensionless plunge amplitude h0=0.4. The computed unsteady flow fields clearly reveal the formation and evolution of a pair of leading edge vortices along the body of the flexible airfoil as it undergoes plunge motion. Thrust-indicative wake structures are generated when the flexure amplitude of the airfoil is less than 0.5 of the chord length. An enhancement in the propulsive efficiency is observed for a flapping airfoil with flexure amplitude of 0.3 of the chord length. This study also calculates the propulsive efficiency and thrust under various Reynolds numbers and reduced frequency conditions. The results indicate that the propulsive efficiency has a strong correlation with the reduced frequency. It is found that the flow conditions which yield the highest propulsive efficiency correspond to Strouhal number St of 0.255.

Miao, J.-M.; Ho, M.-H.

2006-04-01

240

Certain Problems of Experimental Aerodynamics.  

National Technical Information Service (NTIS)

Experimental results of a study of the aerodynamic characteristics at low subsonic velocities of poorly streamlined bodies having different shapes and of the flow past irregularities on the earth's surface are presented. The stress and the forces acting o...

S. M. Gorlin

1975-01-01

241

Instability and unsteadiness of aircraft wake vortices  

Microsoft Academic Search

This paper presents a review of theoretical and experimental results on stability and other unsteady properties of aircraft wakes. The basic mechanisms responsible for the propagation and the amplification of perturbation along vortices, namely the Kelvin waves and the cooperative instabilities, are first detailed. These two generic unsteady mechanisms are described by considering asymptotic linear stability analysis of model flows

L. Jacquin; D. Fabre; D. Sipp; H. Vollmers; Camille Soul

242

Liquid crystals for unsteady surface shear stress visualization  

Microsoft Academic Search

Oscillating airfoil experiments were conducted to test the frequency response of thermochromic liquid crystal coatings to unsteady surface shear stresses under isothermal-flow conditions. The model was an NACA-0015 airfoil, exposed to an incompressible flow at a freestream Reynolds number (based on chord) of 1.14 x 10⁶. Angle-of-attack forcing functions were sine waves of amplitude +- 10\\/degree\\/ about each of three

Reda

1988-01-01

243

Differential Evolution in Aerodynamic Optimization  

Microsoft Academic Search

Aerodynamic design algorithms require an optimization strategy to search for the best design. The objectof this paper is to compare the performance of some different strategies when used by an aerodynamicshape optimization routine which designs fan blade shapes. A recently developed genetic algorithm,Differential Evolution [1,2], outperforms more traditional techniques.IntroductionAerodynamic shape optimization involvesdesigning the most efficient shapes of bodies thatmove through...

T. Rogalsky; R. W. Derksen; S. Kocabiyik

1999-01-01

244

Break-up in unsteady separation  

NASA Astrophysics Data System (ADS)

The unsteady break-up of otherwise steady or unsteady separating flows, and unsteady boundary layers in general, is addressed theoretically. The aspects involved are intimately bound up with transition to turbulence in practice. The first aspect is the prediction of the critical position for enhanced instability to occur in separating flow. The second, as a consequence, is the break-up of a separated eddy due to nonlinear unsteady effects, on the small or the large scale. The third aspect is the nonlinear receptivity of attached and separating flows to freestream disturbances. Fourth, and again in consequence, the complete break-up of an unsteady interacting boundary layer is described. Two-versus three-dimensional effects, comparisons with some experimental and computational results, and applications in a number of external and internal flows are also discussed.

Smith, F. T.

245

Structural dynamics and aerodynamics measurements of biologically inspired flexible flapping wings.  

PubMed

Flapping wing flight as seen in hummingbirds and insects poses an interesting unsteady aerodynamic problem: coupling of wing kinematics, structural dynamics and aerodynamics. There have been numerous studies on the kinematics and aerodynamics in both experimental and computational cases with both natural and artificial wings. These studies tend to ignore wing flexibility; however, observation in nature affirms that passive wing deformation is predominant and may be crucial to the aerodynamic performance. This paper presents a multidisciplinary experimental endeavor in correlating a flapping micro air vehicle wing's aeroelasticity and thrust production, by quantifying and comparing overall thrust, structural deformation and airflow of six pairs of hummingbird-shaped membrane wings of different properties. The results show that for a specific spatial distribution of flexibility, there is an effective frequency range in thrust production. The wing deformation at the thrust-productive frequencies indicates the importance of flexibility: both bending and twisting motion can interact with aerodynamic loads to enhance wing performance under certain conditions, such as the deformation phase and amplitude. By measuring structural deformations under the same aerodynamic conditions, beneficial effects of passive wing deformation can be observed from the visualized airflow and averaged thrust. The measurements and their presentation enable observation and understanding of the required structural properties for a thrust effective flapping wing. The intended passive responses of the different wings follow a particular pattern in correlation to their aerodynamic performance. Consequently, both the experimental technique and data analysis method can lead to further studies to determine the design principles for micro air vehicle flapping wings. PMID:21339627

Wu, P; Stanford, B K; Sällström, E; Ukeiley, L; Ifju, P G

2011-02-22

246

Calculation of wake-induced unsteady flow in a turbine cascade  

SciTech Connect

Numerical predictions are reported for two-dimensional unsteady flow in a linear turbine cascade, where the unsteadiness is caused by passing wakes generated by the preceding row of blades. In particular, an experiment is simulated in which the passing wakes were generated by cylinders moving on a rotating squirrel cage. Blade-to-blade calculations were carried out by solving the unsteady two dimensional flow equations with an accurate finite-volume procedure, thereby resolving the periodic unsteady motion. The effects of stochastic turbulent fluctuations are simulated with a two-layer turbulence model, in which the standard [kappa]-[epsilon] model is applied in the bulk of the flow and a one-equation model in the near-wall region. This involves also a transition model based on an empirical formula from Abu-Ghannam and Shaw (1980), which was adapted for the unsteady situation by applying it in a Lagrangian way, following fluid parcels in the boundary layer under disturbed and undisturbed free streams on their travel downstream. The calculations are compared with experiments for various wake-passing frequencies. On the whole, the complex unsteady flow behavior is simulated realistically, including the moving forward of transition when the wake-passing frequency increases, but not all details can be reproduced.

Cho, N.H.; Liu, X.; Rodi, W.; Schoenung, B. (Univ. of Karlsruhe (Germany). Inst. for Hydromechanics)

1993-10-01

247

Unsteady Heat Transfer in Erosivity Experiments.  

National Technical Information Service (NTIS)

Although TiO2/wax liners are used in U. S. large caliber guns to reduce erosion, the erosion-reducing mechanisms of these liners is still under investigation. Two sets of investigators found a correlation between specific heat of the metal oxide and its a...

C. W. Nelson J. R. Ward

1972-01-01

248

Computational fluid dynamics analysis of cyclist aerodynamics: performance of different turbulence-modelling and boundary-layer modelling approaches.  

PubMed

This study aims at assessing the accuracy of computational fluid dynamics (CFD) for applications in sports aerodynamics, for example for drag predictions of swimmers, cyclists or skiers, by evaluating the applied numerical modelling techniques by means of detailed validation experiments. In this study, a wind-tunnel experiment on a scale model of a cyclist (scale 1:2) is presented. Apart from three-component forces and moments, also high-resolution surface pressure measurements on the scale model's surface, i.e. at 115 locations, are performed to provide detailed information on the flow field. These data are used to compare the performance of different turbulence-modelling techniques, such as steady Reynolds-averaged Navier-Stokes (RANS), with several k-epsilon and k-omega turbulence models, and unsteady large-eddy simulation (LES), and also boundary-layer modelling techniques, namely wall functions and low-Reynolds number modelling (LRNM). The commercial CFD code Fluent 6.3 is used for the simulations. The RANS shear-stress transport (SST) k-omega model shows the best overall performance, followed by the more computationally expensive LES. Furthermore, LRNM is clearly preferred over wall functions to model the boundary layer. This study showed that there are more accurate alternatives for evaluating flow around bluff bodies with CFD than the standard k-epsilon model combined with wall functions, which is often used in CFD studies in sports. PMID:20488446

Defraeye, Thijs; Blocken, Bert; Koninckx, Erwin; Hespel, Peter; Carmeliet, Jan

2010-05-21

249

Large eddy simulation for aerodynamics: status and perspectives.  

PubMed

The present paper provides an up-to-date survey of the use of large eddy simulation (LES) and sequels for engineering applications related to aerodynamics. Most recent landmark achievements are presented. Two categories of problem may be distinguished whether the location of separation is triggered by the geometry or not. In the first case, LES can be considered as a mature technique and recent hybrid Reynolds-averaged Navier-Stokes (RANS)-LES methods do not allow for a significant increase in terms of geometrical complexity and/or Reynolds number with respect to classical LES. When attached boundary layers have a significant impact on the global flow dynamics, the use of hybrid RANS-LES remains the principal strategy to reduce computational cost compared to LES. Another striking observation is that the level of validation is most of the time restricted to time-averaged global quantities, a detailed analysis of the flow unsteadiness being missing. Therefore, a clear need for detailed validation in the near future is identified. To this end, new issues, such as uncertainty and error quantification and modelling, will be of major importance. First results dealing with uncertainty modelling in unsteady turbulent flow simulation are presented. PMID:19531507

Sagaut, Pierre; Deck, Sébastien

2009-07-28

250

Aerodynamic Drag of Heavy Vehicles (Class 7-8): Simulation and Benchmarking  

Microsoft Academic Search

This paper describes research and development for reducing the aerodynamic drag of heavy vehicles by demonstrating new approaches for the numerical simulation and analysis of aerodynamic flow. Experimental validation of new computational fluid dynamics methods are also an important part of this approach. Experiments on a model of an integrated tractor-trailer are underway at NASA Ames Research Center and the

Rose McCallen; Dan Flowers; Tim Dunn; Jerry Owens; Fred Browand; Mustapha Hammache; Anthony Leonard; Mark Brady; Kambiz Salari; Walter Rutledge; James Ross; Bruce Storms; David Driver J. T. Heineck; James Bell; Steve Walker; Gregory Zilliac

2000-01-01

251

Boundary layer receptivity to unsteady free-stream pressure gradients  

NASA Astrophysics Data System (ADS)

A linear triple-deck theory is applied to an examination of the response of a boundary layer to short-scale variations in an unsteady free-stream disturbance field. Two-dimensional incompressible flows are considered, and a locally-parallel Blasius mean flow is assumed. A simple pulsating pressure source and a traveling pressure field in the free-stream are modeled by introducing appropriate pressure sources in the upper deck of the triple-deck structure. The modification in unsteady thickness is obtained for these cases, the results are related to the Tollmien-Schlichting instability wave, and the generation of unstable Tollmien-Schlichting waves for both experiments modeled is confirmed.

Heinrich, Roland A. E.; Kerschen, Edward J.; Gatski, Thomas B.

252

Numerical simulation of aerodynamics and dynamics of wind turbines  

NASA Astrophysics Data System (ADS)

Processes of aerodynamics and dynamics are described by incompressible Reynolds averaged Navier-Stokes equations and the equation of wind turbine rotation. Three one-equation turbulence models SA, SARC and SALSA are used. Incompressible Navier-Stokes equations were solved in time-accurate manner using the method of pseudocompressibility and Rogers-Kwak scheme. The finite-volume approach in generalized coordinates was used. Verification of the developed CFD algorithms and codes is carried out on the problems on flow around fixed and rotating cylinders. Comparison of turbulence models is given for a flow around the NACA 4412 airfoil. Instantaneous streamlines, vorticity fields and hysteresis of the unsteady aerodynamic characteristics are discussed for an oscillating NACA 0015 airfoil. It is shown that SALSA model demonstrates its advantages on massive flow separation and dynamic stall. Results of numerical simulation for wind turbine rotors with different geometrical characteristics and different number of blades are presented. Physical features of the flow near wind turbine blades, such as boundary layer separation and flow interactions between the blades are discussed.

Redchyts, Dmytro

2007-11-01

253

A method for computing unsteady fully nonlinear interfacial waves  

NASA Astrophysics Data System (ADS)

We derive a time-stepping method for unsteady fully nonlinear two-dimensional motion of a two-layer fluid. Essential parts of the method are: use of Taylor series expansions of the prognostic equations, application of spatial finite difference formulae of high order, and application of Cauchy's theorem to solve the Laplace equation, where the latter is found to be advantageous in avoiding instability. The method is computationally very efficient. The model is applied to investigate unsteady trans-critical two-layer flow over a bottom topography. We are able to simulate a set of laboratory experiments on this problem described by Melville & Helfrich (1987), finding a very good agreement between the fully nonlinear model and the experiments, where they reported bad agreement with weakly nonlinear Korteweg de Vries theories for interfacial waves. The unsteady transcritical regime is identified. In this regime, we find that an upstream undular bore is generated when the speed of the body is less than a certain value, which somewhat exceeds the critical speed. In the remaining regime, a train of solitary waves is generated upstream. In both cases a corresponding constant level of the interface behind the body is developed. We also perform a detailed investigation of upstream generation of solitary waves by a moving body, finding that wave trains with amplitude comparable to the thickness of the thinner layer are generated. The results indicate that weakly nonlinear theories in many cases have quite limited applications in modelling unsteady transcritical two-layer flows, and that a fully nonlinear method in general is required.

Grue, John; André Friis, Helmer; Palm, Enok; Olav Rusås, Per

1997-11-01

254

On the importance of aerodynamic and structural geometrical nonlinearities in aeroelastic behavior of high-aspect-ratio wings  

NASA Astrophysics Data System (ADS)

Theoretical development of a nonlinear aeroelastic analysis for high-aspect-ratio wings is presented. The analysis couples a geometrically exact beam theory with a nonplanar aerodynamic theory. The aim of the present effort is to investigate the effects of geometrical nonlinearities on the aeroelastic behavior of high-aspect-ratio wings. The focus of the present work is on characterizing the physical origins of nonlinearities and assessing their relative importance. Results presented show that the structural geometrical nonlinearities have a significant effect on the structural dynamics and on the dynamic aeroelastic characteristics of a high-aspect-ratio wing. The geometrically exact calculation of the angle of attack and aerodynamically consistent application of the airloads is also important for accurate aeroelastic characterization. On the other hand, the geometrical aerodynamic nonlinearity emerging from the nonplanar wake effects is quite negligible. Nonplanar effects were negligible for both the steady and unsteady airload calculations with the assumption of a fixed wake model.

Patil, M. J.; Hodges, D. H.

2004-08-01

255

Aerodynamic Noise Generated by Jet Wing/Flap Interactions of the External Usb Configuration of STOL Aircraft. Part 2: Full Scale Model Experiment Using FJR710 Turbofan Engine.  

National Technical Information Service (NTIS)

Acoustic characteristics of the external upper surface blowing (USB) concept of a propulsive lift configuration were studied by full scale model static experiments. Test components included an FJR710 turbofan engine with an acoustically treated nacelle an...

M. Maita S. Shindo S. Nakayama M. Matsuki T. Torisaki

1981-01-01

256

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

257

Unsteady Processes in Solid Propellant Combustion.  

National Technical Information Service (NTIS)

The purpose of this work is to develop a theoretical analysis of unsteady processes in solid propellant combustion, particularly combustion stability and extinction by rapid depressurization. It is assumed that the solid decomposes at its surface by a pyr...

A. Crespo M. Kindelan

1977-01-01

258

Unsteady Flow Phenomena in Centrifugal Turbomachinery.  

National Technical Information Service (NTIS)

The research is an experimental investigation of system dynamics, unsteady effects, and detailed flow instabilities in a centrifugal compressor. The surge line, which marks the onset of instability and hence limits the minimum stable operating regime, is ...

D. A. Fink

1986-01-01

259

Unsteady Flows in Rotor-Stator Cascades.  

National Technical Information Service (NTIS)

A time-accurate potential-flow calculation method has been developed for unsteady incompressible flows through two-dimensional multi-blade-row linear cascades. The method represents the boundary surfaces by distributing piecewise linear-vortex and constan...

C. L. Merkle J. Z. Feng T. W. Bein Y. T. Lee

1991-01-01

260

Adaptive flow control of low-Reynolds number aerodynamics using dielectric barrier discharge actuator  

NASA Astrophysics Data System (ADS)

Aerodynamic performance of low-Reynolds number flyers, for a chord-based Reynolds number of 105 or below, is sensitive to wind gusts and flow separation. Active flow control offers insight into fluid physics as well as possible improvements in vehicle performance. While facilitating flow control by introducing feedback control and fluidic devices, major challenges of achieving a target aerodynamic performance under unsteady flow conditions lie on the high-dimensional nonlinear dynamics of the flow system. Therefore, a successful flow control framework requires a viable as well as accessible control scheme and understanding of underlying flow dynamics as key information of the flow system. On the other hand, promising devices have been developed recently to facilitate flow control in this flow regime. The dielectric barrier discharge (DBD) actuator is such an example; it does not have moving parts and provides fast impact on the flow field locally. In this paper, recent feedback flow control studies, especially those focusing on unsteady low-Reynolds number aerodynamics, are reviewed. As an example of an effective flow control framework, it is demonstrated that aerodynamic lift of a high angle-of-attack wing under fluctuating free-stream conditions can be stabilized using the DBD actuator and an adaptive algorithm based on general input-output models. System nonlinearities and control challenges are discussed by assessing control performance and the variation of the system parameters under various flow and actuation conditions. Other fundamental issues from the flow dynamics view point, such as the lift stabilization mechanism and the influence on drag fluctuation are also explored. Both potentiality and limitation of the linear modeling approach are discussed. In addition, guidelines on system identification and the controller and actuator setups are suggested.

Cho, Young-Chang; Shyy, Wei

2011-10-01

261

Non-equilibrium and unsteady fluid degassing during slow decompression  

NASA Astrophysics Data System (ADS)

Decompression experiments were performed on corn syrup-water solutions in order to investigate the effect of viscosity on processes of vesiculation and degassing at low to moderate degrees of volatile supersaturation. Repeat experiments demonstrated similar long term vesiculation behavior at moderate decompression rates despite highly variable initial nucleation styles. Results suggest that magmas may not necessarily achieve chemical equilibrium by vapor exsolution and may require viscosity-dependent critical supersaturations in order to vesiculate. Vesiculation also increased the ambient pressure and decreased supersaturations, resulting in unsteady degassing.

Hammer, Julia E.; Manga, Michael; Cashman, Katharine V.

262

Langley Symposium on Aerodynamics, volume 1  

SciTech Connect

The purpose of this work was to present current work and results of the Langley Aeronautics Directorate covering the areas of computational fluid dynamics, viscous flows, airfoil aerodynamics, propulsion integration, test techniques, and low-speed, high-speed, and transonic aerodynamics. The following sessions are included in this volume: theoretical aerodynamics, test techniques, fluid physics, and viscous drag reduction.

Not Available

1986-12-01

263

Aerodynamic noise generated by jet wing\\/flap interactions of the external USB configuration of STOL aircraft. Part 2: Full scale model experiment using FJR710 turbofan engine  

Microsoft Academic Search

Acoustic characteristics of the external upper surface blowing (USB) concept of a propulsive lift configuration were studied by full scale model static experiments. Test components included an FJR710 turbofan engine with an acoustically treated nacelle and a USB wing\\/flap assembly. These were utilized in conjunction with the ground verification testing of the propulsive systems of the National Aerospace Laboratory Quiet

M. Maita; S. Shindo; S. Nakayama; M. Matsuki; T. Torisaki; M. Morita; A. Yoshida; K. Takeda; S. Sekine; H. Kondo

1981-01-01

264

Aerodynamic aspects on recovery of sounding rocket payload  

Microsoft Academic Search

Aerodynamic experiments for the design of a recovery system for a sounding rocket payload included wind tunnel tests of payload models at high angles of attack over Mach numbers ranging from subsonic to supersonic and airdrop tests of payload models. It was shown that (1) the magnitude of the cross-flow proportionality factor used for predicting the payload normal force coefficient

M. Shirouzu; H. Kubota; Y. Shibato

1980-01-01

265

Low Speed Aerodynamics of the X-38 CRV.  

National Technical Information Service (NTIS)

This project was performed in support of the engineering development of the NASA X-38 Crew Return Vehicle (CRV)system. Wind tunnel experiments were used to visualize various aerodynamic phenomena encountered by the CRV during the final stages of descent a...

N. M. Komerath R. Funk R. G. Ames R. Mahalingam C. Matos

1998-01-01

266

Improvement in Aerodynamic Characteristics of a Paraglider Wing Canopy  

Microsoft Academic Search

To determine the parameters which can improve the overall performance of a paraglider wing canopy, we have been investigating the fundamental aerodynamic characteristics of an inflatable cell model which is designed to represent the dynamic behaviors of each cell comprising the wing canopy. This paper describes the results of a series of wind tunnel experiments. It is shown that significant

Mohammad Mashud; Akira Umemura

2006-01-01

267

An adjoint method for shape optimization in unsteady viscous flows  

NASA Astrophysics Data System (ADS)

A new method for shape optimization for unsteady viscous flows is presented. It is based on the continuous adjoint approach using a time accurate method and is capable of handling both inverse and direct objective functions. The objective function is minimized or maximized subject to the satisfaction of flow equations. The shape of the body is parametrized via a Non-Uniform Rational B-Splines (NURBS) curve and is updated by using the gradients obtained from solving the flow and adjoint equations. A finite element method based on streamline-upwind Petrov/Galerkin (SUPG) and pressure stabilized Petrov/Galerkin (PSPG) stabilization techniques is used to solve both the flow and adjoint equations. The method has been implemented and tested for the design of airfoils, based on enhancing its time-averaged aerodynamic coefficients. Interesting shapes are obtained, especially when the objective is to produce high performance airfoils. The effect of the extent of the window of time integration of flow and adjoint equations on the design process is studied. It is found that when the window of time integration is insufficient, the gradients are most likely to be erroneous.

Srinath, D. N.; Mittal, Sanjay

2010-03-01

268

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.

269

Aerodynamic yawing moment characteristics of bird wings.  

PubMed

The aerodynamic yawing moments due to sideslip are considered for wings of birds. Reference is made to the experience with aircraft wings in order to identify features which are significant for the yawing moment characteristics. Thus, it can be shown that wing sweep, aspect ratio and lift coefficient have a great impact. Focus of the paper is on wing sweep which can considerably increase the yawing moment due to sideslip when compared with unswept wings. There are many birds the wings of which employ sweep. To show the effect of sweep for birds, the aerodynamic characteristics of a gull wing which is considered as a representative example are treated in detail. For this purpose, a sophisticated aerodynamic method is used to compute results of high precision. The yawing moments of the gull wing with respect to the sideslip angle and the lift coefficient are determined. They show a significant level of yaw stability which strongly increases with the lift coefficient. It is particularly high in the lift coefficient region of best gliding flight conditions. In order to make the effect of sweep more perspicuous, a modification of the gull wing employing no sweep is considered for comparison. It turns out that the unswept wing yields yawing moments which are substantially smaller than those of the original gull wing with sweep. Another feature significant for the yawing moment characteristics concerns the fact that sweep is at the outer part of bird wings. By considering the underlying physical mechanism, it is shown that this feature is most important for the efficiency of wing sweep. To sum up, wing sweep provides a primary contribution to the yawing moments. It may be concluded that this is an essential reason why there is sweep in bird wings. PMID:15808868

Sachs, Gottfried

2005-06-21

270

Aerodynamic and functional consequences of wing compliance  

NASA Astrophysics Data System (ADS)

A growing body of evidence indicates that a majority of insects experience some degree of wing deformation during flight. With no musculature distal to the wing base, the instantaneous shape of an insect wing is dictated by the interaction of aerodynamic forces with the inertial and elastic forces that arise from periodic accelerations of the wing. Passive wing deformation is an unavoidable feature of flapping flight for many insects due to the inertial loads that accompany rapid stroke reversals—loads that well exceed the mean aerodynamic force. Although wing compliance has been implicated in a few lift-enhancing mechanisms (e.g., favorable camber), the direct aerodynamic consequences of wing deformation remain generally unresolved. In this paper, we present new experimental data on how wing compliance may affect the overall induced flow in the hawkmoth, Manduca sexta. Real moth wings were subjected to robotic actuation in their dominant plane of rotation at a natural wing beat frequency of 25 Hz. We used digital particle image velocimetry at exceptionally high temporal resolution (2,100 fps) to assess the influence of wing compliance on the mean advective flows, relying on a natural variation in wing stiffness to alter the amount of emergent deformation (freshly extracted wings are flexible and exhibit greater compliance than those that are desiccated). We find that flexible wings yield mean advective flows with substantially greater magnitudes and orientations more beneficial to lift than those of stiff wings. Our results confirm that wing compliance plays a critical role in the production of flight forces.

Mountcastle, Andrew M.; Daniel, Thomas L.

2009-05-01

271

Aerodynamic and functional consequences of wing compliance  

NASA Astrophysics Data System (ADS)

A growing body of evidence indicates that a majority of insects experience some degree of wing deformation during flight. With no musculature distal to the wing base, the instantaneous shape of an insect wing is dictated by the interaction of aerodynamic forces with the inertial and elastic forces that arise from periodic accelerations of the wing. Passive wing deformation is an unavoidable feature of flapping flight for many insects due to the inertial loads that accompany rapid stroke reversals—loads that well exceed the mean aerodynamic force. Although wing compliance has been implicated in a few lift-enhancing mechanisms (e.g., favorable camber), the direct aerodynamic consequences of wing deformation remain generally unresolved. In this paper, we present new experimental data on how wing compliance may affect the overall induced flow in the hawkmoth, Manduca sexta. Real moth wings were subjected to robotic actuation in their dominant plane of rotation at a natural wing beat frequency of 25 Hz. We used digital particle image velocimetry at exceptionally high temporal resolution (2,100 fps) to assess the influence of wing compliance on the mean advective flows, relying on a natural variation in wing stiffness to alter the amount of emergent deformation (freshly extracted wings are flexible and exhibit greater compliance than those that are desiccated). We find that flexible wings yield mean advective flows with substantially greater magnitudes and orientations more beneficial to lift than those of stiff wings. Our results confirm that wing compliance plays a critical role in the production of flight forces.

Mountcastle, Andrew M.; Daniel, Thomas L.

272

Computational Aerodynamics for Aircraft Design  

Microsoft Academic Search

This article outlines some of the principal issues in the development of numerical methods for the prediction of flows over aircraft and their use in the design process. These include the choice of an appropriate mathematical model, the design of shock-capturing algorithms, the treatment of complex geometric configurations, and shape modifications to optimize the aerodynamic performance.

Antony Jameson

1989-01-01

273

POEMS in Newton's Aerodynamic Frustum  

ERIC Educational Resources Information Center

|The golden mean is often naively seen as a sign of optimal beauty but rarely does it arise as the solution of a true optimization problem. In this article we present such a problem, demonstrating a close relationship between the golden mean and a special case of Newton's aerodynamical problem for the frustum of a cone. Then, we exhibit a parallel…

Sampedro, Jaime Cruz; Tetlalmatzi-Montiel, Margarita

2010-01-01

274

Rotary wing aerodynamically generated noise  

Microsoft Academic Search

The history and methodology of aerodynamic noise reduction in rotary wing aircraft are presented. Thickness noise during hover tests and blade vortex interaction noise are determined and predicted through the use of a variety of computer codes. The use of test facilities and scale models for data acquisition are discussed.

F. J. Schmitz; H. A. Morse

1982-01-01

275

Rotor/Body Aerodynamic Interactions.  

National Technical Information Service (NTIS)

A wind tunnel investigation was conducted in which independent, steady state aerodynamic forces and moments were measured on a 2.24 m diam. two bladed helicopter rotor and on several different bodies. The mutual interaction effects for variations in veloc...

M. D. Betzina C. A. Smith P. Shinoda

1983-01-01

276

Dynamic Soaring: Aerodynamics for Albatrosses  

ERIC Educational Resources Information Center

|Albatrosses have evolved to soar and glide efficiently. By maximizing their lift-to-drag ratio "L/D", albatrosses can gain energy from the wind and can travel long distances with little effort. We simplify the difficult aerodynamic equations of motion by assuming that albatrosses maintain a constant "L/D". Analytic solutions to the simplified…

Denny, Mark

2009-01-01

277

NARX modelling of unsteady separation control  

NASA Astrophysics Data System (ADS)

This paper presents the application of Nonlinear Auto-Regressive with eXogenous input (NARX) modelling to model the flow behaviour in response of a periodic forcing. In the first part, the NARX black-box model is presented. The model coefficients are obtained by least-square fitting. The resolution of the associated linear system being ill-conditioned, a Tikhonov regularization is employed. The first application presented is the identification of a NARX model of separation control by a synthetic jet slot over a rounded ramp. It is shown that the pressure at a particular location is representative of the flow state (attached or separated). This quantity will be the output of the model, the input being the forcing signal of the synthetic jet. Then, an identification signal is designed to explore as many flow states as possible with a short signal duration. The next step is dedicated to the selection of the NARX model structure. Input/output correlations, partial output autocorrelations and the Akaike Information Criterion minimization are used. A fit coefficient of 84 % is obtained. Finally, the accuracy of the NARX model, both on the steady and on the unsteady components of the output, is checked by comparison of the results with signals not used in the identification phase. The third part deals with the application of the same methodology to an experiment of separation control by pulsed fluidic vortex generators in a highly curved duct. A fit coefficient of 60 % is obtained in this case.

Dandois, J.; Garnier, E.; Pamart, P.-Y.

2013-02-01

278

Benefits of unsteady swimming near a wall  

NASA Astrophysics Data System (ADS)

The benefits of flying and swimming near the ground have been well-documented for fixed-wing vehicles, and have led to 'wing-in-ground' craft (WIG) with higher efficiencies than their conventional counterparts. Here it is examined whether unsteady propulsion techniques experience these same enhancements. Experimental particle image velocimetry was conducted in the wake of a rigid pitching panel and a flexible triangular fin, both actuated at several distances from a fixed wall. In both cases, an increase in momentum flux behind the trailing edge was observed, suggesting thrust amplification is present. A finite core vortex array model was developed to model the wake behind these propulsors. Mirror image vortex cores were placed across the wall to satisfy the zero flux boundary condition, and the effects of viscosity were estimated by assuming a slowly expanding Gaussian distribution of vorticity around each core. The model offers insight into the origins of the momentum amplification due to the presence of the wall. Supported by ONR MURI Grant N00014-08-1-0642.

Quinn, Daniel; Dewey, Peter; Moored, Keith; Smits, Alexander

2011-11-01

279

Aerodynamics of runback ice accretions  

NASA Astrophysics Data System (ADS)

An experimental study of the effects of simulated runback ice accretions has been performed in order to describe their aerodynamic performance penalties and investigate their scaling for use in sub-scale aerodynamic testing. Runback ice accretions corresponding to three flight conditions, warm hold, cold hold and descent, were simulated and tested on the NACA 23012 and NACA 3415. The ice shapes were simulated on two levels of fidelity. Medium-fidelity simulations captured the chordwise location, cross-section, height distribution and chordwise extent of the ice accretion. Low-fidelity simulations captured their height and chordwise location. Two scaling methods were also employed. Each simulation was scaled based upon the ratio of the aerodynamic model chord to the full-scale icing model, called geometric scaling. The warm hold simulations were also scaled based upon the ratio of the local, clean-model boundary-layer thickness on the aerodynamic model to that of the icing model, called boundary-layer scaling. This method was employed because the geometrically-scaled simulations were found to be on the order of the boundary-layer thickness as the model approached stall. Following aerodynamic performance testing, fluorescent-oil flow visualization and hot-wire anemometry were used to investigate the flowfield resulting from the low-fidelity warm hold simulations. Results for this work have shown that runback ice accretions can cause significant aerodynamic performance penalties. In general, the NACA 23012 experienced greater aerodynamic performance penalties due to the runback simulations than did the NACA 3415. Low-fidelity simulations of the cold hold case agreed quite well with their medium fidelity counterparts. In the descent case, the level of variation in ice accretion height was too small for there to be a distinction between the low- and medium-fidelity cases. Low-fidelity simulations of the warm hold accretion did not agree well with the medium-fidelity simulation. In fact, the geometrically-scaled simulation was observed to increase the maximum lift and stalling angle-of-attack of the NACA 3415. Flowfield investigations using fluorescent-oil flow visualization and hot-wire anemometry showed that the simulations that were similar in height to the clean-model local boundary-layer thickness acted to stabilize the recovering boundary layer, delaying stall past the stalling angle-of-attack of the clean case.

Whalen, Edward A.

280

Unsteady forces on an accelerating plate and application to hovering insect flight  

NASA Astrophysics Data System (ADS)

The aerodynamic forces on a flat plate accelerating from rest at fixed incidence in two-dimensional power-law flow are studied analytically and numerically. An inviscid approximation is made in which separation at the two plate edges is modelled by growing spiral vortex sheets, whose evolution is determined by the Birkhoff Rott equation. A solution based on a similarity expansion is developed, valid when the scale of the separated vortex is much smaller than the plate dimension. The leading order is given by the well-known similarity growth of a vortex sheet from a semi-infinite flat plate, while equations at the second order describe the asymmetric sweeping effect of that component of the free-stream parallel to the plate. Owing to subtle cancellation, the unsteady vortex force exerted on the plate during the starting motion is independent of the sweeping effect and is determined by the similarity solution, to the order calculated. This gives a mechanism for dynamic stall based on a combination of unsteady vortex lift and pure added mass; the incidence angle for maximum vortex lift is arccos sqrt{3/8} {?} 52.2(°) independent of the acceleration profile. Circulation on the flat plate makes no direct contribution. Both lift and drag force predictions from the unsteady inviscid theory are compared with those obtained from numerical solutions of the two-dimensional unsteady Navier Stokes equations for an ellipse of high aspect ratio, and with predictions of Wagner's classical theory. There is good agreement with numerical results at high incidence and moderate Reynolds number. The force per unit span predicted by the vortex theory is evaluated for parameters typical of insect wings and is found to be in reasonable agreement with numerical simulations. Estimates for the shed circulation and the size of the start-up vortices are also obtained. The significance of this flow as a mechanism for insect hovering flight is discussed.

Pullin, D. I.; Wang, Z. Jane

2004-06-01

281

Unsteady thermocapillary migration of bubbles  

NASA Astrophysics Data System (ADS)

Upon the introduction of a gas bubble into a liquid possessing a uniform thermal gradient, an unsteady thermo-capillary flow begins. Ultimately, the bubble attains a constant velocity. This theoretical analysis focuses upon the transient period for a bubble in a microgravity environment and is restricted to situations wherein the flow is sufficiently slow such that inertial terms in the Navier-Stokes equation and convective terms in the energy equation may be safely neglected (i.e., both Reynolds and Marangoni numbers are small). The resulting linear equations were solved analytically in the Laplace domain with the Prandtl number of the liquid as a parameter; inversion was accomplished numerically using a standard IMSL routine. In the asymptotic long-time limit, the theory agrees with the steady-state theory of Young, Goldstein, and Block. The theory predicts that more than 90 percent of the terminal steady velocity is achieved when the smallest dimensionless time, i.e., the one based upon the largest time scale-viscous or thermal-equals unity.

Dill, Loren H.; Balasubramaniam, R.

282

Aerodynamic Aspects of Disk Files  

Microsoft Academic Search

Abstract: Airflows between centrally clamped, rotating, rigid disks are investigated with respect to the type of flow pattern, the parameters that influence nonuniform flow, and the effects of various flow patterns on disk stability. The experimental method uses a waterflow modeling,technique,for the airflow. The observed,flow patterns are highly unsteady. The configuration,and position of the shroud and slider arm are found

Eckart Lennemann

1974-01-01

283

Aerodynamic-structural model of offwind yacht sails  

NASA Astrophysics Data System (ADS)

An aerodynamic-structural model of offwind yacht sails was created that is useful in predicting sail forces. Two sails were examined experimentally and computationally at several wind angles to explore a variety of flow regimes. The accuracy of the numerical solutions was measured by comparing to experimental results. The two sails examined were a Code 0 and a reaching asymmetric spinnaker. During experiment, balance, wake, and sail shape data were recorded for both sails in various configurations. Two computational steps were used to evaluate the computational model. First, an aerodynamic flow model that includes viscosity effects was used to examine the experimental flying shapes that were recorded. Second, the aerodynamic model was combined with a nonlinear, structural, finite element analysis (FEA) model. The aerodynamic and structural models were used iteratively to predict final flying shapes of offwind sails, starting with the design shapes. The Code 0 has relatively low camber and is used at small angles of attack. It was examined experimentally and computationally at a single angle of attack in two trim configurations, a baseline and overtrimmed setting. Experimentally, the Code 0 was stable and maintained large flow attachment regions. The digitized flying shapes from experiment were examined in the aerodynamic model. Force area predictions matched experimental results well. When the aerodynamic-structural tool was employed, the predictive capability was slightly worse. The reaching asymmetric spinnaker has higher camber and operates at higher angles of attack than the Code 0. Experimentally and computationally, it was examined at two angles of attack. Like the Code 0, at each wind angle, baseline and overtrimmed settings were examined. Experimentally, sail oscillations and large flow detachment regions were encountered. The computational analysis began by examining the experimental flying shapes in the aerodynamic model. In the baseline setting, the computational force predictions were fair at both wind angles examined. Force predictions were much improved in the overtrimmed setting when the sail was highly stalled and more stable. The same trends in force prediction were seen when employing the aerodynamic-structural model. Predictions were good to fair in the baseline setting but improved in the overtrimmed configuration.

Mairs, Christopher M.

284

Assessment of CFD Estimation of Aerodynamic Characteristics of Basic Reusable Rocket Configurations  

NASA Astrophysics Data System (ADS)

Flow-fields around the basic SSTO-rocket configurations are numerically simulated by the Reynolds-averaged Navier-Stokes (RANS) computations. Simulations of the Apollo-like configuration is first carried out, where the results are compared with NASA experiments and the prediction ability of the RANS simulation is discussed. The angle of attack of the freestream ranges from 0° to 180° and the freestream Mach number ranges from 0.7 to 2.0. Computed aerodynamic coefficients for the Apollo-like configuration agree well with the experiments under a wide range of flow conditions. The flow simulations around the slender Apollo-type configuration are carried out next and the results are compared with the experiments. Computed aerodynamic coefficients also agree well with the experiments. Flow-fields are dominated by the three-dimensional massively separated flow, which should be captured for accurate aerodynamic prediction. Grid refinement effects on the computed aerodynamic coefficients are investigated comprehensively.

Fujimoto, Keiichiro; Fujii, Kozo

285

Experimental and numerical research on the aerodynamics of unsteady moving aircraft  

Microsoft Academic Search

For the experimental determination of the dynamic wind tunnel data, a new combined motion test capability was developed at the German–Dutch Wind Tunnels DNW for their 3m Low Speed Wind Tunnel NWB in Braunschweig, Germany, using a unique six degree-of-freedom test rig called ‘Model Positioning Mechanism’ (MPM) as an improved successor to the older systems. With that cutting-edge device, several

Andreas Bergmann; Andreas Huebner; Thomas Loeser

2008-01-01

286

Identification of an unsteady aerodynamic model up to high angle of attack regime  

Microsoft Academic Search

The harmonic oscillatory tests for a fighter aircraft configuration using the Dynamic Plunge-Pitch-Roll (DyPPiR) model mount at Virginia Tech Stability Wind Tunnel are described and analyzed. The corresponding data reduction methods are developed on the basis of multirate digital signal processing techniques. Since the model is sting-mounted to the support system of DyPPiR, the Discrete Fourier Transform (DFT) is first

Yigang Fan

1997-01-01

287

A Two-degree-of-Freedom Oscillator for Unsteady Aerodynamics Applications.  

National Technical Information Service (NTIS)

Numerous wind tunnel studies of airfoil dynamic stall have been limited to harmonic model oscillations, but new microcomputers and hybrid servo systems have now been exploited to produce a mechanism which provides a high degree of flexibility in achieving...

M. Francis J. E. Keesee J. P. Retelle

1981-01-01

288

Aerodynamics inside a rapid compression machine  

SciTech Connect

The aerodynamics inside a rapid compression machine after the end of compression is investigated using planar laser-induced fluorescence (PLIF) of acetone. To study the effect of reaction chamber configuration on the resulting aerodynamics and temperature field, experiments are conducted and compared using a creviced piston and a flat piston under varying conditions. Results show that the flat piston design leads to significant mixing of the cold vortex with the hot core region, which causes alternate hot and cold regions inside the combustion chamber. At higher pressures, the effect of the vortex is reduced. The creviced piston head configuration is demonstrated to result in drastic reduction of the effect of the vortex. Experimental conditions are also simulated using the Star-CD computational fluid dynamics package. Computed results closely match with experimental observation. Numerical results indicate that with a flat piston design, gas velocity after compression is very high and the core region shrinks quickly due to rapid entrainment of cold gases. Whereas, for a creviced piston head design, gas velocity after compression is significantly lower and the core region remains unaffected for a long duration. As a consequence, for the flat piston, adiabatic core assumption can significantly overpredict the maximum temperature after the end of compression. For the creviced piston, the adiabatic core assumption is found to be valid even up to 100 ms after compression. This work therefore experimentally and numerically substantiates the importance of piston head design for achieving a homogeneous core region inside a rapid compression machine. (author)

Mittal, Gaurav; Sung, Chih-Jen [Department of Mechanical and Aerospace Engineering, Case Western Reserve University, Cleveland, OH 44106 (United States)

2006-04-15

289

Experimental Aerodynamics of Mesoscale Trailing Edge Actuators  

NASA Astrophysics Data System (ADS)

Experiments were performed on a wing with segmented Gurney flaps. Each of the sixteen active flaps is approximately 1.5can be actuated in only two positions: 90 degrees up or 90 degrees down. Wind tunnel experiments were conducted at chord Reynolds numbers up to 800,000. Measurements include the determination of aerodynamic forces and moments using a 6 DOF balance, surface pressure profiles, and wake surveys. Actuation of the full span of the airfoil from the up position to the down position increases the lift coefficient by approximately 0.6 for low to moderate angles of attack. The flaps have a reduced but still significant effect past stall. The overall changes in wing loads are linear with the number of flaps actuated, suggesting that simple control laws may be used. However, surface pressure measurements indicate that each flap affects the section lift over a substantial span. A study of the transient performance of the flaps is underway.

Solovitz, Stephen; Eaton, John

2001-11-01

290

Aerodynamics of Parachute Opening.  

National Technical Information Service (NTIS)

The velocity field in the near wake of a small-scale, flexible, flat circular parachute canopy was measured by the particle image velocimetry method. The experiments were performed in a water tunnel with the Reynolds number ranging from 3.0-6.0 x10(4). Bo...

H. Johari K. J. Desabrais

2002-01-01

291

Analysis of aerodynamic pendulum oscillations  

NASA Astrophysics Data System (ADS)

Oscillations of an aerodynamic pendulum about the ``along the flow'' equilibrium are studied. The attached oscillator model is used in order to simulate the internal dynamics of the airflow. Stability criteria are found and stability domains in plane of are constructed for different values of parameters. Influence of damping is studied. It is shown that damping depending on airspeed allows describing experimentally registered phenomenon of flutter occurrence in a certain range of airspeeds.

Selyutskiy, Yury D.

2012-11-01

292

Global nonlinear aerodynamic model identification based on NARMAX model  

Microsoft Academic Search

A new method for global nonlinear aerodynamic model identification is presented. Aerodynamic model of aircraft is analyzed, and a simple and effective aerodynamic model is presented. The aerodynamic model of aircraft is then depicted in NARMAX (Nonlinear Auto Regressive Moving Average model with eXogenous inputs) form inside a Linear Regression framework. The items and coefficients of the aerodynamic model are

Hui Xia; Xianyu Meng; Qingwei Chen

2010-01-01

293

The Human Aerodynamic Wake  

NASA Astrophysics Data System (ADS)

The wake that trails behind a walking person in still air is, in effect, that of an irregular 3-D cylinder. At a brisk walking speed of 1.3 m/s (3 mph), the human wake is characterized by a Reynolds number of about 50,000. It is thus turbulent with underlying large-scale vortex motion. We show that buoyancy plays no role at this Reynolds number, even though it is dominant in the plume of a standing person. Computational Navier-Stokes solutions and laser-light-sheet experiments with a human subject reveal a large recirculation zone behind the torso and flow between the legs. The decay of a passive scalar introduced on the human body is found to be exponential with downstream distance. The volume flux in the human wake is roughly constant with downstream distance until the recirculation closes, whence it grows due to turbulent entrainment. Further experiments reveal the development of the wake from the human thermal plume as the Reynolds number (proportional to walking speed) is increased from zero to 50,000. These results pertain to the sensing of chemical traces in the wakes of walking persons for aviation security. Supported by FAA Grant 99-G-040.

Settles, Gary; Moyer, Zachary; Paterson, Eric; Edge, Brian

2003-11-01

294

Optimization of the aerodynamics of small-scale flapping aircraft in hover  

NASA Astrophysics Data System (ADS)

Flapping flight is one of the most widespread mean of transportation. It is a complex unsteady aerodynamic problem that has been studied extensively in the past century. Nevertheless, by its complex nature, flapping flight remains a challenging subject. With the development of micro air vehicles, researchers need new computational methods to design these aircrafts efficiently. In this dissertation, I will present three different methods of optimization for flapping flight with an emphasis on hovering with each their advantages and drawbacks. The first method was developed by Hall et al. It is an extremely fast and powerful three-dimensional approach. However, the assumptions made to develop this theory limit its use to lightly loaded wings. In addition, it only models the motion of the trailing edge and not the actual motion of the wing. In a second part, I will present a two-dimensional unsteady potential method. It uses a freely convected wake which removes the lightly loaded restriction. This method shows the existence of an optimal combination of plunging and pitching motion. The motion is optimal in the sense that for a required force vector, the aerodynamic power is minimal. The last method incorporates the three-dimensional effects. These effects are especially important for low aspect ratio wings. Thus, a three-dimensional unsteady potential vortex method was developed. This method also exhibits the presence of an optimal flapping/pitching motion. In addition, it agrees really well with the two previous methods and with the actual kinematics of birds during hovering flapping flight. To conclude, some preliminary design tools for flapping wings in forward and hovering flight are presented in this thesis.

Lebental, Sidney

295

Dynamic stall behavior from unsteady force measurements  

NASA Astrophysics Data System (ADS)

A direct force measurement technique employing piezoelectric load cells is used to experimentally investigate a two-dimensional airfoil (NACA 0012) undergoing dynamic stall. The load cells are installed at each end of the airfoil and give the force response in two directions in the plane normal to the airfoil axis during oscillations. Experiments are carried out at a Reynolds number based on the airfoil chord equal to 7.7×104, and at four reduced frequencies, k=0.005, 0.01, 0.02, and 0.04. Phase-averaged lift of the airfoil undergoing dynamic stall is presented. It is observed that hysteresis loops of the lift occur both when the airfoil is pitched to exceed its static stall limit and when it is still within its static stall limit, and they grow in size with increasing k at the same pitching mean angle of attack and pitching amplitude. Both the lift and the drag induced by the pitching motion are further analyzed using the methods of higher order correlation analysis and continuous wavelet transforms to undercover their nonlinear and nonstationary features, in addition to classical FFT-based spectral analysis. The results are quantitatively illustrated by an energy partition analysis. It is found that the unsteady lift and drag show opposite trends when the airfoil undergoes transition from the pre-stall regime to the full-stall regime. The degree of nonlinearity of the lift increases, and the lift show a nonstationary feature in the light-stall regime, while the nonlinearity of the drag decreases, and the drag shows nonstationary feature in both the light-stall and the full-stall regimes. Furthermore, the lift and the drag have significant nonlinear interactions as shown by the correlation analysis in the light-stall regime.

Tsang, K. K. Y.; So, R. M. C.; Leung, R. C. K.; Wang, X. Q.

2008-01-01

296

Take-off and Aerodynamic Characteristics of a Taketombo  

NASA Astrophysics Data System (ADS)

The taketombo is a traditional flying toy of Japan transmitted from old times. Since the taketombo is made of a bamboo, it is also called the bamboo dragonfly. The taketombo consists of two parts, the wing and the shaft. The wing generates the lift, and the shaft is for giving rotation to the taketombo. However, the take-off and aerodynamic characteristics are not yet studied. Then, to study the take-off and aerodynamic characteristics of a taketombo, free flight test and wind tunnel test were performed. Free flight test of the taketombo were carried out to obtain base line data to experiment in the wind tunnel test. Flight data of the taketombo at the take-off in free air was reduced by analyzing the flight path from the high speed video which recorded the take-off flights of the taketombo. A wind tunnel test was conducted using two wing section models, normal and super taketombos. Forces were measured to investigate aerodynamic characteristics of the wing section of two taketombos. The aerodynamic characteristics of normal and super taketombos were compared.

Yasuda, Kunio

297

Aerodynamics of Horizontal Axis Wind Turbines  

Microsoft Academic Search

\\u000a This chapter reviews the aerodynamic characteristics of horizontal axis wind turbines (HAWTs). While the aerodynamics of wind\\u000a turbine are relatively complicated in detail, the fundamental operational principle of a HAWT is that the action of the blowing\\u000a wind produces aerodynamic forces on the turbine blades to rotate them, thereby capturing the kinetic energy contained in the\\u000a wind and converting this

J. Gordon Leishman

298

Aerodynamics of a rolling airframe missile  

Microsoft Academic Search

For guidance-related reasons, there is considerable interest in rolling missiles having single-plane steering capability. To aid the aerodynamic design of these airframes, a unique investigation into the aerodynamics of a rolling, steering missile has been carried out. It represents the first known attempt to measure in a wind tunnel the aerodynamic forces and moments that act on a spinning body-canard-tail

L. E. Tisserand

1981-01-01

299

Kinetic Simulations of Unsteady Vortex Structures in the Wake of a Cylinder  

Microsoft Academic Search

The development of an unsteady vortex street in the wake of a cylinder has been studied in computational experiments using recently developed Unified Flow Solver (UFS). A major objective was to investigate a spontaneous breakdown of flow symmetry in the wake and effects of gas compressibility and rarefaction on the laminar vortex shedding. The boundary of the wake instability on

Robert R. Arslanbekov; Vladimir I. Kolobov; Anna A. Frolova

2008-01-01

300

REDUCTION OF UNSTEADY STATOR–ROTOR INTERACTION USING TRAILING EDGE BLOWING  

Microsoft Academic Search

An aeroacoustic investigation was performed to assess the effects of adding mass flow at the trailing edges of stators upstream of an aircraft engine simulator. By using trailing edge blowing to minimize the shed wakes of the stators, the flow into the rotor was made more uniform, hence reducing the unsteady stator–rotor interaction. In these experiments, a reduced number of

THOMAS A. LEITCH; C. A. SAUNDERS; W. F. NG

2000-01-01

301

Reduction of Unsteady Stator-Rotor Interaction Using Trailing Edge Blowing  

Microsoft Academic Search

An aeroacoustic investigation was performed to assess the effects of adding mass flow at the trailing edges of stators upstream of an aircraft engine simulator. By using trailing edge blowing to minimize the shed wakes of the stators, the flow into the rotor was made more uniform, hence reducing the unsteady stator-rotor interaction. In these experiments, a reduced number of

Thomas A. Leitch; C. A. Saunders; W. F. Ng

2000-01-01

302

Management and control of unsteady and turbulent flows  

NASA Astrophysics Data System (ADS)

Conclusions from a wide range of experiments in transitioning, turbulent, separated and unsteady flow fields include the following highlights: The simultaneous generation of controlled phase-coupled plane TS waves and oblique waves was used to investigate the development of three dimensional disturbances and mechanisms of transition in a Blasius boundary layer. From these experiments, the detuning of the fundamental/subharmonic resonance emerges as a primary candidate for the transition process under natural conditions. Three dimensional mappings of the Reynolds stress producing events in turbulent boundary layers over a range of Reynolds numbers and initial conditions have demonstrated that an integral size of these dynamical motions scales better with outer variables as compared with inner variables. While the wall or inner layer is responsible for their initial, the hierarchy of their scales in the log layer expands with Reynolds number according to this outer scaling. Real-time reactive control of a model unsteady separating flow was successfully implemented using a simple scheme for the detention of the separation.

Nagib, Hassan M.; Acharya, Mukund; Corke, Thomas C.; Reisenthel, Patrick H.; Wark, Candace C.

1991-07-01

303

Unsteady distributed wall shear stress measurements in fluid flows  

NASA Astrophysics Data System (ADS)

Wall-bounded flows are amongst the most common flows encountered in fluid mechanics. Wall shear stress on the walls of these flow fields is an important engineering quantity as it is responsible for skin friction drag, which is a significant portion of the drag on bodies ranging from airplanes to flow in biological systems. Measuring, understanding and eventually controlling the wall shear stress has implicit financial significance. In general there is limited literature reporting unsteady, distributed wall shear stress measurements, especially in air, due to the lack of sensors to carry out such measurements. This work is a small step in the direction of filling this gap in the literature. A wall shear stress sensor, referred to as the micro-pillar wall shear stress sensor is presented from concept to actual measurements in a wall jet flow field. The micro-pillar shear stress sensor is based on the principle that a micro-pillar on the wall of a wall-bounded flow deflects an amount proportional to the drag force experienced by it. This drag force in turn is proportional to the wall shear stress. Hence, tracking the tip deflection of an array of micro-pillars provides a means to measure the unsteady, distributed wall shear stress. The sensor from design to manufacture along with static and dynamic characterization is presented. It's ability to measure unsteady, distributed wall shear stress is studied using demonstrative experiments. Finally, wall shear stress measurements are carried out on the wall of a three-dimensional turbulent wall jet. The wall jet is subsequently excited and the effect of excitation on the wall shear stress in the near jet exit flow field is studied.

Gnanamanickam, Ebenezer P.

304

Unsteady influences in droplet dynamics and combustion  

Microsoft Academic Search

This research investigation addresses the problem of the unsteady dynamics associated with the vaporization, ignition and burning of hydrocarbon fuel droplets in laminar and turbulent flowfields. The method of approach is a numerical one with the use of the digital computer, and detailed solutions of the Navier-Stokes equations have been carried out to determine the important physical processes which occur

H. A. Dwyer; B. R. Sanders

1986-01-01

305

Unsteady Influences in Droplet Dynamics and Combustion  

Microsoft Academic Search

This research investigation addresses the problem of the unsteady dynamics associated with the vaporization. ignition and hurning of hydrocarhon fuel droplets in laminar and turhulent flowfields. The method of approach is numerical. and detailed solutians of the Navier-Stokes equations have heen carried out to determine the important physical processes which occur around a burning droplet. For the relatively high pressure

HARRY A. DWYER; B. R. SANDERS

1988-01-01

306

Unsteady Flow past a Circular Cylinder  

Microsoft Academic Search

The symmetrical unsteady vortices behind a circular cylinder started from rest either impulsively of with uniform acceleration were investigated experimentally using a flow visualization technique. The variation of the length of the vortices with time was determined from the photographs obtained at Reynolds numbers ranging from 31 to 1700 and dimensionless accelerations from 195 to 2.44× 105. The length of

Hiroyuki Honji; Sadatoshi Taneda

1969-01-01

307

Chaotic solute advection by unsteady groundwater flow  

Microsoft Academic Search

Solute mixing in fluids is enhanced significantly by chaotic advection, the phenomenon in which fluid pathlines completely fill the spatial domain explored by a laminar flow. Steady groundwater flows are, in general, not well conditioned for this phenomenon because Darcy's law confines them spatially to nonintersecting stream surfaces. Unsteady groundwater flows, however, may, in principle, induce chaotic solute advection if

Garrison Sposito

2006-01-01

308

Unsteady groundwater flow on sloping bedrock  

Microsoft Academic Search

A numerical model based on the equation describing the unsteady groundwater flow on impervious sloping bedrock has been herewith formulated. The case which has been studied concerns the groundwater flow from one canal to another with a sudden rising of the canal level as an upstream boundary condition, while the downstream level remains constant. Initially, at time t = 0,

C. N. Frangakis; C. Tzimopoulos

1979-01-01

309

Steady\\/unsteady gas turbine combustion simulator  

Microsoft Academic Search

A conceptual gas turbine combustion simulator is proposed to study steady and unsteady combustion phenomena at conditions relevant to aviation engines. It is intended to duplicate the flow and combustion characteristics of an aviation engine in a simple laboratory scale device in order to conduct scientific study to provide deeper insight to the complex combustion dynamics problems and other related

Pratikash Prakash Panda

2011-01-01

310

Measurement techniques for unsteady flows in turbomachines  

Microsoft Academic Search

The growing interest for unsteady flows in turbomachines over the last two decades has led to an intensive development of fast response measurement techniques, capable of resolving with high frequency phenomena related to inlet distortion, rotating stall and blade row interference effects with blade passing frequencies ranging from 3 to 30kHz. This development was favoured by major advances in sensor

C. H. Sieverding; T. Arts; R. Dénos; J.-F. Brouckaert

2000-01-01

311

Movable bed roughness in unsteady oscillatory flow  

Microsoft Academic Search

A model to predict the roughness is unsteady oscillatory flows over movable, noncohesive beds is presented. The roughness over movable beds is shown to be a function of the boundary shear stress rather than a fixed geometrical scale as is the case for fully rough turbulent boundary shear flows over immobile beds. The model partitions the roughness into two distinct

William D. Grant; Ole Secher Madsen

1982-01-01

312

Flapping and fixed wing aerodynamics of low Reynolds number flight vehicles  

NASA Astrophysics Data System (ADS)

Lately, micro air vehicles (MAVs), with a maximum dimension of 15 cm and nominal flight speed around 10m/s, have attracted interest from scientific and engineering communities due to their potential to perform desirable flight missions and exhibit unconventional aerodynamics, control, and structural characteristics, compared to larger flight vehicles. Since MAVs operate at a Reynolds number of 105 or lower, the lift-to-drag ratio is noticeably lower than the larger manned flight vehicles. The light weight and low flight speed cause MAVs to be sensitive to wind gusts. The MAV's small overall dimensions result in low aspect ratio wings with strong wing tip vortices that further complicate the aerodynamics of such vehicles. In this work, two vehicle concepts are considered, namely, fixed wings with flexible structure aimed at passive shape control, and flapping wings aimed at enhancing aerodynamic performance using unsteady flow fields. A finite volume, pressure-based Navier-Stokes solver along with moving grid algorithms is employed to simulate the flow field. The coupled fluid-structural dynamics of the flexible wing is treated using a hyperelastic finite element structural model, the above-mentioned fluid solver via the moving grid technique, and the geometric conservation law. Three dimensional aerodynamics around a low aspect ratio wing for both rigid and flexible structures and fluid-structure interactions for flexible structures have been investigated. In the Reynolds numbers range of 7x10 4 to 9x104, the flexible wing exhibits self-initiated vibrations even in steady free-stream, and is found to have a similar performance to the identical rigid wing for modest angles of attack. For flapping wings, efforts are made to improve our understanding of the unsteady fluid physics related to the lift generation mechanism at low Reynolds numbers (75 to 1,700). Alternative moving grid algorithms, capable of handling the large movements of the boundaries (characteristic of flapping wing kinematics) are tested. Two main hovering modes are investigated and compared with experimental and other computational efforts. The analysis shows that, while delayed-stall and rapid pitch-up mechanisms are responsible for most of the lift generation at a Reynolds numbers of O(100) and stroke amplitudes of O(1 chord), other mechanisms, including wake-capturing, are identified to contribute to the overall lift/drag force generation. The effect of the Reynolds number on hovering airfoil aerodynamics is also probed.

Viieru, Dragos

313

Brief Introduction to the Soviet Central Research Institute of Aerodynamics.  

National Technical Information Service (NTIS)

The Central Research Institute of Aerodynamics is a composite research institute of aerodynamics having major activities on solving various practical problems of aerodynamics in addition to general research activities. Its main objectives are: (1) Promote...

Y. Yongziao Z. Ruqing

1985-01-01

314

Effects of Wing Platform on the Aerodynamic Performance of Finite-Span Flapping Wings  

NASA Astrophysics Data System (ADS)

A numerical study is conducted to investigate the effects of wing platform on the aerodynamics performance of finite-span flapping wings. A three-dimensional high-order Navier-Stokes compressible flow solver was developed using the spectral difference method and dynamic grids. An AUSM^+-up Riemann solver was implemented to simulate the unsteady low Mach number flows over finite-span flapping wings with explicit third order Runge-Kutta time integration. The studied finite-span flapping wings, which include a rectangular flapping wing, an elliptic flapping wing and a bio-inspired flapping wing, have the same wing span, aspect ratio of the platform and the characteristics of the flapping motion (i.e., sinusoidal trajectory of the flapping wing tip, Strouhal number and reduced frequency). In the present study, the Strouhul number (Str) of the finite-span flapping wings was selected to be well within the optimal range usually used by flying insects and birds and swimming fishes (i.e., 0.2 < Str < 0.4). The effects of the wing platform on the aerodynamics performance of the finite-span flapping wings were elucidated in the terms of the evolutions and dynamic interaction between the leading edge vortices (LEV) and the wing tip vortices as well as the resultant aerodynamic forces (both lift and thrust) generated by the flapping wings.

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

2010-11-01

315

Aerodynamic performance of a drag reduction device on a full-scale tractor/trailer  

NASA Astrophysics Data System (ADS)

The effectiveness of an aerodynamic boattail on a tractor/trailer road vehicle was measured in the NASA Ames Research Center 80- by 120-Foot Wind Tunnel. Results are examined for the tractor/trailer with and without the drag reduction device. Pressure measurements and flow visualization show that the aerodynamic boattail traps a vortex or eddy in the corner formed between the device and the rear corner of the trailer. This recirculating flow turns the flow inward as it separates from the edges of the base of the trailer. This modified flow behavior increases the pressure acting over the base area of the truck, thereby reducing the net aerodynamic drag of the vehicle. Drag measurements and pressure distributions in the region of the boattail device are presented for selected configurations. The optimum configuration reduces the overall drag of the tractor/trailer combination by about 10 percent at a zero yaw angle. Unsteady pressure measurements do not indicate strong vortex shedding, although the addition of the boattail plates increases high frequency content of the fluctuating pressure.

Lanser, Wendy R.; Ross, James C.; Kaufman, Andrew E.

1991-09-01

316

Development of mathematical models and numerical methods for aerodynamic design on multiprocessor computers  

NASA Astrophysics Data System (ADS)

Complex-geometry design and grid generation are addressed. The gasdynamic equations are solved, and the numerical results are compared with experimental data. For aerodynamic problems, a suite of mathematical and information technology tools is proposed for the support and management of geometric models of actual objects. Based on the mathematical modeling methods developed, numerical experiments can be performed for a wide class of geometric forms and the aerodynamic properties of aircraft can be predicted with allowance for the viscosity effects.

Maksimov, F. A.; Churakov, D. A.; Shevelev, Yu. D.

2011-02-01

317

Inner workings of aerodynamic sweep  

SciTech Connect

The recent trend in using aerodynamic sweep to improve the performance of transonic blading has been one of the more significant technological evolutions for compression components in turbomachinery. This paper reports on the experimental and analytical assessment of the pay-off derived from both aft and forward sweep technology with respect to aerodynamic performance and stability. The single-stage experimental investigation includes two aft-swept rotors with varying degree and type of aerodynamic sweep and one swept forward rotor. On a back-to-back test basis, the results are compared with an unswept rotor with excellent performance and adequate stall margin. Although designed to satisfy identical design speed requirements as the unswept rotor, the experimental results reveal significant variations in efficiency and stall margin with the swept rotors. At design speed, all the swept rotors demonstrated a peak stage efficiency level that was equal to that of the unswept rotor. However, the forward-swept rotor achieved the highest rotor-alone peak efficiency. At the same time, the forward-swept rotor demonstrated a significant improvement in stall margin relative to the already satisfactory level achieved by the unswept rotor. Increasing the level of aft sweep adversely affected the stall margin. A three-dimensional viscous flow analysis was used to assist in the interpretation of the data. The reduced shock/boundary layer interaction, resulting from reduced axial flow diffusion and less accumulation of centrifuged blade surface boundary layer at the tip, was identified as the prime contributor to the enhanced performance with forward sweep. The impact of tip clearance on the performance and stability for one of the aft-swept rotors was also assessed.

Wadia, A.R.; Szucs, P.N.; Crall, D.W. [GE Aircraft Engines, Cincinnati, OH (United States)

1998-10-01

318

Dry deposition onto aerodynamic surfaces and vegetation. Final report  

SciTech Connect

Carnegie-Mellon University measured dry deposition of aerosols and nitric acid gas to aerodynamic surrogate surfaces in three sets of field experiments. The first field study was during the Southern California Air Quality Study (SCAQS) in June and July 1988. The second set was during the extension of SCAQS in August and September. Both these sets of measurements were conducted at the Bernard Biological Station and at Claremont McKenna College in Claremont, CA. The third experiment involved sampling at Emerald Lake in Sequoia National Park. The first field study included measurements of deposition of Waxleaf Privet, Canary Island Pine, and Japanese Privet. All three studies used Teflon plates and nylon filters set into an aerodynamic surface to measure particle and gas deposition.

Wu, Y.L.; Davidson, C.

1989-02-17

319

Aircraft aerodynamic noise during approach  

NASA Astrophysics Data System (ADS)

The effect of approach velocity, nose and flap inclination, and undercarriage position on aircraft noise was studied. The A 300 B and SN 601 aircraft made two approach passes over a chain of noise recorders. The sound fields and noise spectra show that increasing the speed and flap angle or lowering the undercarriage produces a general increase in noise level such that the directivity of the aerodynamic noise source is hardly changed. All noise spectra increase. Pure frequencies (400 to 500 Hz) accompany flap deployment for the SN 601.

Parant, J. L.

320

Aerodynamic damping during body translation in animal flight: modeling and experimental results of flapping counter force (FCF)  

NASA Astrophysics Data System (ADS)

Body movements of flying animals change their effective wing kinematics and influence aerodynamic forces. Our previous studies found that substantial aerodynamic damping was produced by flapping wings during body rotation through a passive mechanism we termed flapping counter-torque (FCT). Here we present the aerodynamic damping produced by flapping wings during body translations, which we termed flapping counter-forces (FCFs). Analytical models were derived and the aerodynamic effect of spanwise flow and wing-wake interaction were also explored. The FCFs are dependent on body velocities, wing beat amplitude and frequency. Aerodynamic force and PIV measurements were compared with the analytical models. The experiments were conducted on a pair of dynamically scaled robotic model wings in an oil tank. Experiments in air using a pair of high frequency flapping wing further validate the models. Complete 6-DOF flight dynamic model was derived.

Cheng, Bo; Hu, Zheng; Deng, Xinyan

2010-11-01

321

Rationalizing the bumps on whale flippers using basic aerodynamic theory  

NASA Astrophysics Data System (ADS)

Recent experiments and numerics demonstrated that bumps on the leading edge of humpback whale flippers can lead to an increase in the lift/drag ratio and an increase in the stall angle, as compared to smooth flippers. Using basic aerodynamic theory (potential flow around a Joukowski profile, combined with lifting-line theory) we attempt to rationalize the experimental and numerical findings. We use this basic theory to find perturbations which could lead to an increase in stall angle.

van Nierop, Ernst; Alben, Silas; Brenner, Michael

2006-11-01

322

Aerodynamics of a Cryogenic Semi-Tanker  

Microsoft Academic Search

The design of a modern cryogenic semi-tanker is based primarily upon functionality with little consideration given to aerodynamic drag. As a result, these tankers have maintained the appearance of a wheeled cylinder for several decades. To reduce the fuel usage of these vehicles, this study investigates their aerodynamics. A detailed understanding of the flow field about the vehicle and its

Jason Ortega; Kambiz Salari

2009-01-01

323

Freight Wing Trailer Aerodynamics Final Technical Report  

Microsoft Academic Search

Freight Wing Incorporated utilized the opportunity presented by a DOE category two Inventions and Innovations grant to commercialize and improve upon aerodynamic technology for semi-tuck trailers, capable of decreasing heavy vehicle fuel consumption, related environmental damage, and U.S. consumption of foreign oil. Major project goals included the demonstration of aerodynamic trailer technology in trucking fleet operations, and the development and

Sean Graham

2007-01-01

324

Recent progress in aerodynamic design optimization  

Microsoft Academic Search

Recent emphasis on reduction of design cycle time and cost in the design of commercial aircraft (P.E. Rubbert, CFD and the changing world of airplane design, AIAA Wright Brothers Lecture, September, 1994) has sparked a renewed interest in design optimization in aerodynamics, structures and aeroelastics. In this paper, recent developments in the use of design optimization in aerodynamics using the

R. G. Melvin; W. P. Huffman; D. P. Young; F. T. Johnson; C. L. Hilmes; M. B. Bieterman

1999-01-01

325

Membrane wing aerodynamics for micro air vehicles  

Microsoft Academic Search

The aerodynamic performance of a wing deteriorates considerably as the Reynolds number decreases from 106 to 104. In particular, flow separation can result in substantial change in effective airfoil shape and cause reduced aerodynamic performance. Lately, there has been growing interest in developing suitable techniques for sustained and robust flight of micro air vehicles (MAVs) with a wingspan of 15cm

Yongsheng Lian; Wei Shyy; Dragos Viieru; Baoning Zhang

2003-01-01

326

Aerodynamic tests of Darrieus wind turbine blades  

Microsoft Academic Search

An indoor facility for the aerodynamic testing of Darrieus turbine blades was developed. Lift, drag, and moment coefficients were measured for two blades whose angle of attack and chord-to-radius ratio were varied. The first blade used an NACA 0015 airfoil section; the second used a 15% elliptical cross section with a modified circular arc trailing edge. Blade aerodynamic coefficients were

P. G. Migliore; R. E. Walters; W. P. Wolfe

1983-01-01

327

Aerodynamic flow visualization in the ONERA facilities  

Microsoft Academic Search

Shadowgraphy, schlieren and interferometry are used in the ONERA facilities for transonic and supersonic aerodynamic flow visualization. Apparatus equipping several wind tunnels are described and results shown. Studies of aerodynamic flows in turbomachinery compressors require special visualization set-ups: an optical system with cylindrical lenses concentric to the hub carrying the blades has been achieved for a supersonic annular blade cascade,

C. Veret; M. Philbert; J. Surget; G. Fertin

1977-01-01

328

Aerodynamics for the Mars Phoenix Entry Capsule.  

National Technical Information Service (NTIS)

Pre-flight aerodynamics data for the Mars Phoenix entry capsule are presented. The aerodynamic coefficients were generated as a function of total angle-of-attack and either Knudsen number, velocity, or Mach number, depending on the flight regime. The data...

K. T. Edquist M. Schoenenberger P. N. Desai

2008-01-01

329

Summary Analysis of the Gemini Entry Aerodynamics.  

National Technical Information Service (NTIS)

The aerodynamic data that were derived in 1967 from the analysis of flight-generated data for the Gemini entry module are presented. These data represent the aerodynamic characteristics exhibited by the vehicle during the entry portion of Gemini 2, 3, 5, ...

A. M. Whitnah D. B. Howes

1972-01-01

330

Cricket Ball Aerodynamics: Myth Versus Science.  

National Technical Information Service (NTIS)

Aerodynamics plays a prominent role in the flight of a cricket ball released by a bowler. The main interest is in the fact that the ball can follow a curved flight path that is not always under the control of the bowler. ne basic aerodynamic principles re...

R. D. Mehta

2000-01-01

331

Aerodynamic Simulation of Runback Ice Accretion.  

National Technical Information Service (NTIS)

This report presents the results of recent investigations into the aerodynamics of simulated runback ice accretion on airfoils. Aerodynamic tests were performed on a full-scale model using a high-fidelity, ice-casting simulation at near-flight Reynolds (R...

A. P. Broeren E. A. Whalen G. T. Busch M. B. Bragg

2009-01-01

332

Unsteady wandering magnetic field lines, turbulence and laboratory flux ropes  

NASA Astrophysics Data System (ADS)

We describe earth bound laboratory experiment investigations of patchy, unsteady, bursty, patchy magnetic field structures that are unifying features of magnetic reconnection and turbulence in helio, space and astro physics. Macroscopic field lines occupy cross sectional areas, fill up three dimensional (3D) volumes as flux tubes. They contain mass with Newtonian dynamics that follow magneto-hydro-dynamic (MHD) equations of motion. Flux rope geometry can be ubiquitous in laminar reconnection sheet geometries that are themselves unstable to formation of secondary "islands" that in 3D are really flux ropes. Flux ropes are ubiquitous structures on the sun and the rest of the heliosphere. Understanding the dynamics of flux ropes and their mutual interactions offers the key to many important astrophysical phenomena, including magnetic reconnection and turbulence. We describe laboratory investigations on RSX, where 3D interaction of flux ropes can be studied in great detail. We use experimental probes inside the the flux ropes to measure the magnetic and electric fields, current density, density, temperatures, pressure, and electrostatic and vector plasma potentials. Macroscopic magnetic field lines, unsteady wandering characteristics, and dynamic objects with structure down to the dissipation scale length can be traced from data sets in a 3D volume. Computational approaches are finally able to tackle simple 3D systems and we sketch some intriguing simulation results that are consistent with 3D extensions of typical 2D cartoons for magnetic reconnection and turbulence.

Intrator, T.; Sears, J.; Weber, T.; Liu, D.; Pulliam, D.; Lazarian, A.

2011-12-01

333

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

334

Micro air vehicle-motivated computational biomechanics in bio-flights: aerodynamics, flight dynamics and maneuvering stability  

NASA Astrophysics Data System (ADS)

Aiming at developing an effective tool to unveil key mechanisms in bio-flight as well as to provide guidelines for bio-inspired micro air vehicles (MAVs) design, we propose a comprehensive computational framework, which integrates aerodynamics, flight dynamics, vehicle stability and maneuverability. This framework consists of (1) a Navier-Stokes unsteady aerodynamic model; (2) a linear finite element model for structural dynamics; (3) a fluid-structure interaction (FSI) model for coupled flexible wing aerodynamics aeroelasticity; (4) a free-flying rigid body dynamic (RBD) model utilizing the Newtonian-Euler equations of 6DoF motion; and (5) flight simulator accounting for realistic wing-body morphology, flapping-wing and body kinematics, and a coupling model accounting for the nonlinear 6DoF flight dynamics and stability of insect flapping flight. Results are presented based on hovering aerodynamics with rigid and flexible wings of hawkmoth and fruitfly. The present approach can support systematic analyses of bio- and bio-inspired flight.

Liu, Hao; Nakata, Toshiyuki; Gao, Na; Maeda, Masateru; Aono, Hikaru; Shyy, Wei

2010-12-01

335

Applications of stroboscopic imaging technique in three-dimensional feature detection of micro flexible aerodynamic shape  

NASA Astrophysics Data System (ADS)

Applications of stroboscopic imaging technique in different areas are illuminated. Several major three-dimensional morphology imaging detection methods for micro flexible adaptive aerodynamic shape, which are based on scaled model in experiment process, are discussed at home and abroad at present. And stroboscopic imaging detection technique and testing device are introduced emphatically, which could be used to obtain deformation information of flexible aerodynamic shape. A flexible aerodynamic shape detection method, based on the combination of stroboscopic imaging technique and optical flow analysis, is proposed to validate experimental model for adaptive aerodynamic shape. This technique could compensate the inadequacy of numerical analysis and provide more aeroelastic characteristics for further analysis. Moreover, this measurement method is of advantages such as non contact, real time and visualization etc.

Yu, Yanan; Wang, Xiangjun; Chen, Hong

2009-07-01

336

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

337

Analysis of rotor wake aerodynamics during maneuvering flight using a free-vortex wake methodology  

NASA Astrophysics Data System (ADS)

The problem of helicopter rotor wake aerodynamics during maneuvering flight conditions was analyzed using a time-accurate, free-vortex wake methodology. The free-vortex method consists of a Lagrangian representation of the rotor flow field using vortex elements, where the evolution of the flow field is simulated by tracking the free motion of these vortex elements and calculating their induced velocity field. Traditionally, free-vortex methods are inviscid, incompressible models, but in the present approach the viscous effects are incorporated using a viscous splitting method where the viscous and inviscid terms are modeled as successive sub-processes. The rotor aerodynamics and rigid blade flapping dynamics are closely coupled with the wake model and solved for in a consistent manner using the same numerical scheme. Validations of the methodology with experimental data were performed to study the wake response to perturbations in collective and cyclic pitch inputs. The numerical simulations captured all the essential wake dynamics observed in flow visualization. The predictions of the transient inflow and airloads response were found to be in excellent agreement with the available experimental measurements. It was observed that the rotor wake was extremely sensitive to perturbations in collective and cyclic blade pitch inputs. The characteristic wake response was found to be the bundling of the wake vorticity into a vortex ring structure. The evolution, convection and subsequent breakdown of this bundled ring of tip-vortices was found to be highly nonlinear, and occurs with a temporal lag. The nonlinear induced velocity field associated with unsteady wake evolution can cause considerable fluctuations in the rotor airloads time-history if the bundled tip-vortex structure comes into close proximity to the rotor blades. Furthermore, the interaction of these tip-vortices with the blades results in steep gradients in the rotor airloads across the rotor disk, thereby contributing to impulsive rotor noise. Several free-flight maneuver simulations were analyzed to gain better insight into the unsteady, nonlinear wake development under high-rate, large-amplitude maneuvers such as roll to starboard or port, roll reversals, and the quickstop maneuver. It is shown that the rotor wake response in almost all maneuvering flight conditions is highly nonlinear and emphasizes the need to accurately predict the transient wake aerodynamics to obtain accurate estimates of the unsteady rotor airloads and the resulting rotor acoustics.

Ananthan, Shreyas

338

Unsteady peristaltic transport in curved channels  

NASA Astrophysics Data System (ADS)

The paper presents a generalized mathematical model describing the unsteady peristaltic flow of a viscous fluid in a two-dimensional curved channel. The flow is investigated in a laboratory frame of reference and the unsteady flow nature is studied by the condition that prescribing volumetric flow rate is equivalent to prescribing normal velocity of the fluid particles at the wall. The momentum and energy equations have been linearized by employing lubrication theory and the analysis is restricted to negligible flow Reynolds number. The expressions for stream function, pressure distribution, shear stress, temperature, and coefficient of heat transfer have been derived. The obtained expressions are utilized to discuss the influences of various emerging parameters on flow phenomenon.

Ramanamurthy, J. V.; Prasad, K. M.; Narla, V. K.

2013-09-01

339

Stability analysis of unsteady ablation fronts  

SciTech Connect

The linear stability analysis of unsteady ablation fronts, is carried out for a semi-infinite uniform medium. For a laser accelerated target, it is shown that a properly selected modulation of the laser intensity can lead to the dynamic stabilization or growth-rate reduction of a large portion of the unstable spectrum. The theory is in qualitative agreement with the numerical results obtained by using the two-dimensional hydrodynamic code ORCHID.

Betti, R.; McCrory, R.L.; Verdon, C.P.

1993-08-01

340

Heat exchanger effectiveness in unsteady state  

NASA Astrophysics Data System (ADS)

A method is proposed to determine the thermal effectiveness of heat exchangers in situ, when one of the fluids is submitted to any kind of flow rate variations. It leads to the definition of the average effectiveness in unsteady state, which forms an extension of the classical effectiveness used in steady state. It requires an unsophisticated equipment of measurement and should lead to an easy and continuous control of the fouling of heat exchangers.

Mai, T. H.; Chitou, N.; Padet, J.

1999-10-01

341

Measurement techniques for unsteady flows in turbomachines  

Microsoft Academic Search

The growing interest for unsteady flows in turbomachines over the last two decades has led to an intensive development of\\u000a fast response measurement techniques, capable of resolving with high frequency phenomena related to inlet distortion, rotating\\u000a stall and blade row interference effects with blade passing frequencies ranging from 3 to 30?kHz. This development was favoured\\u000a by major advances in sensor

C. H. Sieverding; T. Arts; R. Dénos; J.-F. Brouckaert

2000-01-01

342

On cup anemometer rotor aerodynamics.  

PubMed

The influence of anemometer rotor shape parameters, such as the cups' front area or their center rotation radius on the anemometer's performance was analyzed. This analysis was based on calibrations performed on two different anemometers (one based on magnet system output signal, and the other one based on an opto-electronic system output signal), tested with 21 different rotors. The results were compared to the ones resulting from classical analytical models. The results clearly showed a linear dependency of both calibration constants, the slope and the offset, on the cups' center rotation radius, the influence of the front area of the cups also being observed. The analytical model of Kondo et al. was proved to be accurate if it is based on precise data related to the aerodynamic behavior of a rotor's cup. PMID:22778638

Pindado, Santiago; Pérez, Javier; Avila-Sanchez, Sergio

2012-05-10

343

On Cup Anemometer Rotor Aerodynamics  

PubMed Central

The influence of anemometer rotor shape parameters, such as the cups' front area or their center rotation radius on the anemometer's performance was analyzed. This analysis was based on calibrations performed on two different anemometers (one based on magnet system output signal, and the other one based on an opto-electronic system output signal), tested with 21 different rotors. The results were compared to the ones resulting from classical analytical models. The results clearly showed a linear dependency of both calibration constants, the slope and the offset, on the cups' center rotation radius, the influence of the front area of the cups also being observed. The analytical model of Kondo et al. was proved to be accurate if it is based on precise data related to the aerodynamic behavior of a rotor's cup.

Pindado, Santiago; Perez, Javier; Avila-Sanchez, Sergio

2012-01-01

344

A linearized Euler analysis of unsteady transonic flows in turbomachinery  

SciTech Connect

A computational method for efficiently predicting unsteady transonic flows in two- and three-dimensional cascades is presented. The unsteady flow is modeled using a linearized Euler analysis whereby the unsteady flow field is decomposed into a nonlinear mean flow plus a linear harmonically varying unsteady flow. The equations that govern the perturbation flow, the linearized Euler equations, are linear variable coefficient equations. For transonic flows containing shocks, shock capturing is used to model the shock impulse (the unsteady load due to the harmonic motion of the shock). A conservative Lax-Wendroff scheme is used to obtain a set of linearized finite volume equations that describe the harmonic small disturbance behavior of the flow. Conditions under which such a discretization will correctly predict the shock impulse are investigated. Computational results are presented that demonstrate the accuracy and efficiency of the present method as well as the essential role of unsteady shock impulse loads on the flutter stability of fans.

Hall, K.C.; Clark, W.S.; Lorence, C.B. (Duke Univ., Durham, NC (United States). Dept. of Mechanical Engineering and Materials Science)

1994-07-01

345

The Remote Inverse Shape Design of Airfoils in Unsteady Flows  

Microsoft Academic Search

This paper uses a general framework to derive the discrete adjoint equations for the calculation of remote sensitivities in unsteady flows. These sensitivities are then succesfully used in the remote inverse shape design of turbulent unsteady flow around a single-element NACA0012 airfoil as well as the remote inverse design of laminar unsteady flow around the multi-element NLR 7301 configuration, with

Markus P. Rumpfkeil; David W. Zingg

346

Aerodynamics of high aspect-ratio sails  

NASA Astrophysics Data System (ADS)

Experiments studying the aerodynamics of a 25circular-arc sail section (representative of an AC gennaker cross-section) have been undertaken in the 7x10 ft tunnels at NASA-Ames and Georgia Tech. The aims of the study are to gain a deeper physical understanding of the flow past downwind sails at various angles of incidence and Reynolds numbers, and to create a comprehensive database for validation of numerical models and turbulence models used by the yacht research community and competitive sailing industry. The reason for testing a rectangular planform sail with no spanwise variation in twist or cross-section is to first provide a detailed understanding of the flow topology around generic sail sections. Currently, data of sufficient accuracy to be used for CFD validation are not available. 3D experiments with realistic sail planforms and twisted onset flow are planned for the future. Two models have been tested, one with an AR of 15 and constructed from steel and the other with an AR of 10 and constructed from carbon-fiber and foam. The latter model has pressure tappings, whilst the former was coated with PSP. Pressure distributions, surface flow visualization and PIV reveal the details of the changing flow patterns and separation types with varying angle of incidence.

Crook, Andrew; Gerritsen, Margot

2003-11-01

347

The effects of unsteady hydrodynamics on soot formation in a counterflow diffusion flame  

NASA Astrophysics Data System (ADS)

Currently, there is an increased interest in reducing soot emissions from combustors, because environmental regulations are requiring dramatic reductions in particulate emissions. Most practical, large scale combustion processes rely on turbulent diffusion flames. These same combustors, which bum hydrocarbon fuels, are also well known for their high soot emissions. The study of chemical processes, such as soot formation, in a turbulent diffusion flame is complicated by the unsteady multi-dimensional flowfield, complex hydrocarbon chemistry, and the interaction between the flowfield and chemistry. Flamelet theory simplifies the analysis of a turbulent diffusion flames by treating the flame as an ensemble of strained, laminar, one dimensional flamelets which can be described by two variables. Counterflow diffusion flames exhibit many characteristics of flamelets. Currently, researchers assume flamelets respond in a quasi-steady manner to the unsteady strain rates in the real turbulent diffusion flame. However, this assumption has not been verified by experiments. This research involved a series of experiments designed to investigate a flamelet's response to unsteady strain rates by quantitatively measuring soot concentrations in an oscillating propane-air counterflow diffusion flame using the non-intrusive laser induced incandescence (LII) technique. These spatially and temporally resolved measurements were made as a function of initial steady strain rate, forcing frequency, and forcing amplitude of the strain rate fluctuation. Also, laser Doppler velocimetry was used to measure the unsteady strain rate imposed on the flame. The results of this study showed that low frequency oscillations always increased the maximum soot concentration. At high initial strain rates, the soot formation process became insensitive to the strain rate fluctuation. At low initial strain rates, the maximum soot concentration was reduced by up to 90% with high frequency high amplitude fluctuations. These measurements provide important insight into the response of flamelets and the soot formation process to unsteady strain rates.

Riggen-Decroix, Michele Elaine

348

Unsteady Cavitating Flow around a Hydrofoil Simulated Using the Partially-Averaged Navier—Stokes Model  

NASA Astrophysics Data System (ADS)

Numerical simulations of unsteady cavitating flow around a NACA66-mod hydrofoil were performed using the partially-averaged Navier—Stokes method with different values of the resolution control parameters (fk = 1.0-0.2, fin = 1). With decreasing fk, the predicted cavitating flow becomes unsteady as the time-averaged turbulent viscosity at the rear part of the attached cavity is gradually reduced. For fk = 0.9 and 0.8, the cavity becomes unstable and its length dramatically expands and shrinks, but the calculation fails to predict the vapor cloud shedding behavior observed experimentally. With smaller fk less than 0.7, the cloud shedding behavior is simulated numerically and the predicted cavity shedding frequency increases. With fk = 0.2, the whole cavitating flow evolution can be reasonably reproduced including the cavity growth/destabilization observed previously. The reentrant flow along the suction surface of the hydrofoil is the main trigger to cause the vapor cloud shedding. The wall pressure along the hydrofoil surface oscillates greatly due to the dynamic cavity shedding. Comparing the simulations and experiments, it is confirmed that for the PANS method, resolution control parameters of fk = 0.2 and fin = 1 are recommended for numerical simulations of unsteady cavitating flows. Thus, the present study shows that the PANS method is an effective approach for predicting unsteady cavitating flow over hydrofoils.

Ji, Bin; Luo, Xian-Wu; Wu, Yu-Lin; Xu, Hong-Yuan

2012-07-01

349

Unsteady flow about cambered plates  

NASA Astrophysics Data System (ADS)

The evolution of a two dimensional, incompressible, rapidly decelerating, time-dependent viscous flow about a sharp-edged camber is simulated through the use of the discrete vortex model. Vorticity is represented by a distribution of discrete point vortices. Each vortex is convected in the velocity field, calculated locally using the Biot-Savart law. The roll-up of the vortex sheets, the distribution of velocity and pressure on the camber, and the drag force are calculated at suitable time intervals for a prescribed time-dependent flow. Experiments are carried out in a vertical water tunnel partly to measure the drag force and partly to record on a video tape the evolution of the wake. The measured and calculated characteristics of the flow, such as the growth of the wake and the forces acting on the camber are found to be in good agreement. Furthermore, the numerical simulation provided a plausible explanation for the cause of parachute collapse, a phenomenon which gave impetus to the numerical and physical experiments described herein. The numerical model developed during the course of the investigation is applicable to any time-dependent flow about two-dimensional cambered plates (circular arcs).

Munz, Paul D.

1987-06-01

350

Liquid crystals for unsteady surface shear stress visualization  

NASA Astrophysics Data System (ADS)

Oscillating airfoil experiments were conducted to test the frequency response of thermochromic liquid crystal coatings to unsteady surface shear stresses under isothermal-flow conditions. The model was an NACA-0015 airfoil, exposed to an incompressible flow at a freestream Reynolds number (based on chord) of 1.14 x 1000000. Angle-of-attack forcing functions were sine waves of amplitude + or - 10 deg about each of three mean angles of attack: 0 deg 10 deg, and 20 deg. Frequencies of oscillation were 0.2, 0.6 and 1.2 hertz, corresponding to reduced frequencies of 0.0055, 0.0164 and 0.0328. Data acquisition was accomplished by video recording. Observations showed the liquid crystal technique capable of visualizing high surface shear stress zones over the stated dynamic range in a continuous and reversible manner.

Reda, D. C.

1988-04-01

351

Liquid crystals for unsteady surface shear stress visualization  

SciTech Connect

Oscillating airfoil experiments were conducted to test the frequency response of thermochromic liquid crystal coatings to unsteady surface shear stresses under isothermal-flow conditions. The model was an NACA-0015 airfoil, exposed to an incompressible flow at a freestream Reynolds number (based on chord) of 1.14 x 10/sup 6/. Angle-of-attack forcing functions were sine waves of amplitude +- 10/degree/ about each of three mean angles of attack: 0/degree/, 10/degree/, and 20/degree/. Frequencies of oscillation were 0.2, 0.6 and 1.2 hertz, corresponding to reduced frequencies of 0.0055, 0.0164 and 0.0328. Data acquisition was accomplished by video recording. Observations showed the liquid crystal technique capable of visualizing high surface shear stress zones over the stated dynamic range in a continuous and reversible manner. 11 refs.

Reda, D.C.

1988-01-01

352

Unified aeroacoustics analysis for high speed turboprop aerodynamics and noise. Volume 3: Application of theory for blade loading, wakes, noise, and wing shielding  

NASA Astrophysics Data System (ADS)

Results of the program for the generation of a computer prediction code for noise of advanced single rotation, turboprops (prop-fans) such as the SR3 model are presented. The code is based on a linearized theory developed at Hamilton Standard in which aerodynamics and acoustics are treated as a unified process. Both steady and unsteady blade loading are treated. Capabilities include prediction of steady airload distributions and associated aerodynamic performance, unsteady blade pressure response to gust interaction or blade vibration, noise fields associated with thickness and steady and unsteady loading, and wake velocity fields associated with steady loading. The code was developed on the Hamilton Standard IBM computer and has now been installed on the Cray XMP at NASA-Lewis. The work had its genesis in the frequency domain acoustic theory developed at Hamilton Standard in the late 1970s. It was found that the method used for near field noise predictions could be adapted as a lifting surface theory for aerodynamic work via the pressure potential technique that was used for both wings and ducted turbomachinery. In the first realization of the theory for propellers, the blade loading was represented in a quasi-vortex lattice form. This was upgraded to true lifting surface loading. Originally, it was believed that a purely linear approach for both aerodynamics and noise would be adequate. However, two sources of nonlinearity in the steady aerodynamics became apparent and were found to be a significant factor at takeoff conditions. The first is related to the fact that the steady axial induced velocity may be of the same order of magnitude as the flight speed and the second is the formation of leading edge vortices which increases lift and redistribute loading. Discovery and properties of prop-fan leading edge vortices were reported in two papers. The Unified AeroAcoustic Program (UAAP) capabilites are demonstrated and the theory verified by comparison with the predictions with data from tests at NASA-Lewis. Steady aerodyanmic performance, unsteady blade loading, wakes, noise, and wing and boundary layer shielding are examined.

Hanson, D. B.; McColgan, C. J.; Ladden, R. M.; Klatte, R. J.

1991-05-01

353

Unsteady flow about cambered plates  

NASA Astrophysics Data System (ADS)

Impulsively-started uniform flow, decelerating at specified rates, about two-dimensional cambered plates with included angles of 120, 180, and 240 degrees has been investigated both theoretically and experimentally. The experiments were conducted in a vertical water tunnel. The forces acting on the cambered plates have determined as a function of the relative displacement of the fluid. The evolution of the vortices was visualized by means of various dyes and polystyrene beads. A numerical analysis was carried out through the use of the discrete vortex model. Vorticity is represented by a distribution of discrete line vortices. Each vortex is convected in the velocity field according to the Biot Savart law. The rollup of the vortex sheets, the distribution of velocity and pressure on the chambers, and the drag and lift forces are calculated at suitable time intervals for a prescribed time-dependent flow. The results are compared with those obtained experimentally.

Sarpkaya, T.; Mostafa, S. I.; Munz, P. D.

1987-10-01

354

Aerodynamics of Power Plant Installation, Part I.  

National Technical Information Service (NTIS)

Contents: Engine designer's point of view; A discussion of selected aerodynamic problems on integration of propulsion systems with airframe on transport aircraft; The feasibility of supersonic combustion ramjets for low hypersonic speeds; The blunt traili...

1965-01-01

355

Aerodynamic Interference Effects on Tilting Proprotor Aircraft.  

National Technical Information Service (NTIS)

The Green's function method was used to study tilting proprotor aircraft aerodynamics with particular application to the problem of the mutual interference of the wing-fuselage-tail-rotor wake configuration. While the formulation is valid for fully unstea...

P. Soohoo L. Morino R. B. Noll N. D. Ham

1977-01-01

356

Aerodynamic Validation of Emerging Projectile Configurations.  

National Technical Information Service (NTIS)

Ever-increasing demands for accuracy and range in modern warfare have expedited the optimization of projectile design. The crux of projectile design lies in the understanding of its aerodynamic properties early in the design phase. This research first inv...

S. W. Lun

2011-01-01

357

Aerodynamic and Gasdynamic Effects in Cosmogony.  

National Technical Information Service (NTIS)

Senior Scientist Stuart J. Weidenschilling presents his final administrative report for the research program entitled 'Aerodynamic and Gasdynamic Effects in Cosmogony' on which he was the Principal Investigator. The research program produced the following...

S. J. Weidenschilling

2005-01-01

358

Projectile Aerodynamic Jump Due to Lateral Impulsives.  

National Technical Information Service (NTIS)

The linear theory for spinning projectiles is extended to account for the application of a simple lateral square impulse activated during free flight. Analytical results are shown to produce simple contributions to the familiar aerodynamic jump formulatio...

G. R. Cooper

2003-01-01

359

Experimental Facilities and Modelling for Rarefied Aerodynamics.  

National Technical Information Service (NTIS)

The present lecture is devoted to experimental and theoretical modelling for rarefied aerodynamics. General features of experimental studies in rarefied flows are discussed. Experimental facilities designed in Saint Petersburg State University for rarefie...

A. Krylov E. Kustova M. Mekhonoshina V. Lashkov

2011-01-01

360

Review of Aerodynamics for Wind Turbines  

NASA Astrophysics Data System (ADS)

This article reviews the state of the art of wind turbine rotor aerodynamics. It addresses present uncertainties in rotor design and load calculations, recent modelling efforts to reduce these uncertainties, and validation activities regarding the modelling and results thereof.

Snel, Herman

2003-07-01

361

Aerodynamics and Performance Testing of the VAWT.  

National Technical Information Service (NTIS)

Early investigations suggest that reductions in cost of energy (COE) and increases in reliability for VAWT systems may be brought about through relatively inexpensive changes to the current aerodynamic design. This design uses blades of symmetrical cross-...

P. C. Klimas

1981-01-01

362

Steady Incompressible Variable Thickness Shear Layer Aerodynamics.  

National Technical Information Service (NTIS)

A shear flow aerodynamic theory for steady incompressible flows is presented for both the lifting and non lifting problems. The slow variation of the boundary layer thickness is considered. The slowly varying behavior is treated by using multitime scales....

M. R. Chi

1976-01-01

363

Conformable M3 Microsystems for Aerodynamic Control.  

National Technical Information Service (NTIS)

The recently emerging microelectromechanical technology has created a new frontier for the control of aerodynamic, structural and propulsion systems. The micromachining process provides two unique features for transducer technology: large in quantity and ...

H. Chih-Ming T. Yu-Chong

1998-01-01

364

Unstructured Mesh Algorithms for Aerodynamic Calculations.  

National Technical Information Service (NTIS)

The use of unstructured mesh techniques for solving complex aerodynamic flows is discussed. The principle advantages of unstructured mesh strategies, as they relate to complex geometries, adaptive meshing capabilities, and parallel processing are emphasiz...

D. J. Mavriplis

1992-01-01

365

Aerodynamics of Seeing on Large Transport Aircraft.  

National Technical Information Service (NTIS)

Data were obtained in the full scale flight environment of the Kuiper Airborne Observatory (KAO) on the nature of turbulent shear layer over the open cavity. These data were used to verify proposed aerodynamic scaling relationships to describe the behavio...

W. C. Rose

1986-01-01

366

Torso Experienced Aerodynamic Forces Experienced during Ejection.  

National Technical Information Service (NTIS)

The aerodynamic forces which are experienced by an ejecting aircrewmember are momentarily unique in direction and can be of severe magnitude. One difficulty of analyzing extremity injury during emergency escape is the diversity and intensity of the aerody...

A. J. Nestle

1981-01-01

367

Coupled Aerodynamic-Thermal-Structural (CATS) Analysis.  

National Technical Information Service (NTIS)

Coupled Aerodynamic-Thermal-Structural (CATS) Analysis is a focused effort within the Numerical Propulsion System Simulation (NPSS) program to streamline multidisciplinary analysis of aeropropulsion components and assemblies. Multidisciplinary analysis of...

1995-01-01

368

Atmospheric tests of trailing-edge aerodynamic devices  

SciTech Connect

An experiment was conducted at the National Renewable Energy Laboratory`s (NREL`s) National Wind Technology Center (NWTC) using an instrumented horizontal-axis wind turbine that incorporated variable-span, trailing-edge aerodynamic brakes. The goal of the investigation was to directly compare results with (infinite-span) wind tunnel data and to provide information on how to account for device span effects during turbine design or analysis. Comprehensive measurements were used to define effective changes in the aerodynamic and hinge-moment coefficients, as a function of angle of attack and control deflection, for three device spans (7.5%, 15%, and 22.5%) and configurations (Spoiler-Flap, vented sileron, and unvented aileron). Differences in the lift and drag behavior are most pronounced near stall and for device spans of less than 15%. Drag performance is affected only minimally (about a 30% reduction from infinite-span) for 15% or larger span devices. Interestingly, aerodynamic controls with vents or openings appear most affected by span reductions and three-dimensional flow.

Miller, L.S.; Huang, S. [Wichita State Univ., KS (United States); Quandt, G.A.

1998-01-01

369

Wind Tunnel Tests on Aerodynamic Characteristics of Advanced Solid Rocket  

NASA Astrophysics Data System (ADS)

The Advanced Solid Rocket is being developed by JAXA (Japan Aerospace Exploration Agency). Since its configuration has been changed very recently, its aerodynamic characteristics are of great interest of the JAXA Advanced Solid Rocket Team. In this study, we carried out wind tunnel tests on the aerodynamic characteristics of the present configuration for Mach 1.5. Six test cases were conducted with different body configurations, attack angles, and roll angles. A six component balance, oilflow visualization, Schlieren images were used throughout the experiments. It was found that, at zero angle-of-attack, the flow around the body were perturbed and its drag (axial force) characteristics were significantly influenced by protruding body components such as flanges, cable ducts, and attitude control units of SMSJ (Solid Motor Side Jet), while the nozzle had a minor role. With angle-of-attack of five degree, normal force of CN? = 3.50±0.03 was measured along with complex flow features observed in the full-component model; whereas no crossflow separations were induced around the no-protuberance model with CN? = 2.58±0.10. These values were almost constant with respect to the angle-of-attack in both of the cases. Furthermore, presence of roll angle made the flow more complicated, involving interactions of separation vortices. These data provide us with fundamental and important aerodynamic insights of the Advanced Solid Rocket, and they will be utilized as reference data for the corresponding numerical analysis.

Kitamura, Keiichi; Fujimoto, Keiichiro; Nonaka, Satoshi; Irikado, Tomoko; Fukuzoe, Moriyasu; Shima, Eiji

370

Dynamic control of a bistable wing under aerodynamic loading  

NASA Astrophysics Data System (ADS)

The aerodynamic evaluation of a dynamic control technique applied to a bistable unsymmetrical cross-ply composite plate with surface bonded piezoelectric actuators is presented. The plate is clamped on one end to form a low-aspect-ratio wing. A previously proposed dynamic control method, utilizing bending resonance in different stable equilibrium positions, is used to induce snap-through between the two equilibrium states. Compared to quasi-static actuation, driving the bistable plate near resonance using surface bonded piezoelectric materials requires, theoretically, a lower peak excitation voltage to achieve snap-through. First, a set of extensive wind tunnel experiments are conducted on the passive bistable wing to understand the change in the dynamic behavior under various aerodynamic conditions. The passive wing demonstrated sufficient bending stiffness to sustain its shape under aerodynamic loading while preserving the desired bistable behavior. Next, by the use of the resonant control technique, the plate is turned into an effectively monostable structure, or alternatively, both stable equilibrium positions can be reached actively from the other stable equilibrium. Dynamic forward and reverse snap-through is demonstrated in the wind tunnel which shows both the effectiveness of the piezoelectric actuation as well as the load carrying capability of both states of the bistable wing.

Bilgen, Onur; Arrieta, Andres F.; Friswell, Michael I.; Hagedorn, Peter

2013-02-01

371

An Aileron Flutter Experiment and Analysis Using Semi-Span Model for the Small Supersonic Experimental Aircraft  

NASA Astrophysics Data System (ADS)

This paper reports a wind-tunnel experiment and analysis that have been conducted under the National Experimental Airplane for Supersonic Transports (NEXST-1) project of JAXA. In order to perform the flight experiment, the design of the vehicle was examined from the stand point of aeroelasticity. The aileron buzz as well as flutter was of much concern for its aileron system on the main wing. Therefore, both wind-tunnel test and analysis were carried out by using a semi-span model with fuselage. Although the buzz was not observed in the test, damping responses of the aileron rotation mode were obtained. Critical damping was observed in supersonic flow, that meant a buzz could occur in ``region C'' of Lambourne's classification. Linear unsteady aerodynamic analysis is applicable to this type of buzz and the characteristics of the buzz of the model is discussed.

Saitoh, Kenichi; Tamayama, Masato; Kikuchi, Takao; Machida, Shigeru; Nakamichi, Jiro

372

Numerical simulations for transonic aerodynamic flows  

Microsoft Academic Search

Transonic flow is an important aerodynamic phenomenon that occurs in the high subsonic Mach number flight regime. This paper presents the development of a numerical simulation for three-dimensional transonic aerodynamic flows around an isolated wing. The mathematical formulation is based on a transonic small-disturbance equation, which is a nonlinear and mixed elliptic-hyperbolic partial-differential equation. A Newton-like iterative scheme is developed

Yau Shu Wong; Hong Jiang

1991-01-01

373

Recent progress in aerodynamic design optimization  

NASA Astrophysics Data System (ADS)

Recent emphasis on reduction of design cycle time and cost in the design of commercial aircraft (P.E. Rubbert, CFD and the changing world of airplane design, AIAA Wright Brothers Lecture, September, 1994) has sparked a renewed interest in design optimization in aerodynamics, structures and aeroelastics. In this paper, recent developments in the use of design optimization in aerodynamics using the TRANAIR code are considered. Globalization techniques and the extension of the methodology to multipoint design will be discussed. Copyright

Melvin, R. G.; Huffman, W. P.; Young, D. P.; Johnson, F. T.; Hilmes, C. L.; Bieterman, M. B.

1999-05-01

374

Aerodynamics of missiles with slotted fin configurations  

Microsoft Academic Search

Subsonic and transonic aerodynamic data for missiles with solid and slotted wrap around fin configurations are presented. Free-flight aeroballistic tests to obtain this data were conducted at atmospheric pressure over a Mach number range of 0.8 to 1.6. The aerodynamic coefficients and derivatives presented were extracted from the position-attitude-time histories of the experimentally measured trajectories using non-linear numerical integration data

G. L. Abate; G. L. Winchenbach

1991-01-01

375

Darrieus rotor aerodynamics in turbulent wind  

SciTech Connect

The earlier aerodynamic models for studying vertical axis wind turbines (VAWT`s) are based on constant incident wind conditions and are thus capable of predicting only periodic variations in the loads. The purpose of the present study is to develop a model capable of predicting the aerodynamic loads on the Darrieus rotor in a turbulent wind. This model is based on the double-multiple streamtube method (DMS) and incorporates a stochastic wind model. The method used to simulate turbulent velocity fluctuations is based on the power spectral density. The problem consists in generating a region of turbulent flow with a relevant spectrum and spatial correlation. The first aerodynamic code developed is based on a one-dimensional turbulent wind model. However, since this model ignores the structure of the turbulence in the crossflow plane, an extension to three dimensions has been made. The computer code developed, CARDAAS, has been used to predict aerodynamic loads for the Sandia-17m rotor and compared to CARDAAV results and experimental data. Results have shown that the computed aerodynamic loads have been improved by including stochastic wind into the aerodynamic model.

Brahimi, M.T.; Paraschivoiu, I. [Ecole Polytechnique de Montreal, Quebec (Canada). Dept. of Mechanical Engineering

1995-05-01

376

Aerodynamic and Performance Measurements on a SWT-2.3-101 Wind Turbine  

SciTech Connect

This paper provides an overview of a detailed wind turbine field experiment being conducted at NREL under U.S. Department of Energy sponsorship. The purpose of the experiment is to obtain knowledge about the aerodynamics, performance, noise emission and structural characteristics of the Siemens SWT-2.3-101 wind turbine.

Medina, P.; Singh, M.; Johansen, J.; Jove, A.R.; Machefaux, E.; Fingersh, L. J.; Schreck, S.

2011-10-01

377

On current controversy of unsteady separation  

NASA Astrophysics Data System (ADS)

Current controversy about unsteady separation is discussed. Compared to the existing MRS and Goldstein singularity criteria, our proposed analogy criterion is more specific in the detailed steps to identify separation, and those steps are straightforward to follow. The analogous limiting flow pattern in the x, t-plane provides an independent signal of separation in addition to the usual separation symptoms. For the impulsively-started cylinder problem, our prediction of the separation starting time is close to that of Van Dommelen and Shen, but contradicts to Cebeci's in basic terms. Detailed comparisons with Cebeci's calculation are given.

Wang, K. C.

378

The Aerodynamics of Bird Flight  

NASA Astrophysics Data System (ADS)

The manifest success of birds in flight over small and large distances, in confined quarters and also in gusty conditions has inspired admiration, investigation and sometimes imitation from the earthbound human. Birds occupy a range of scales (2 g - 12 kg in mass, and 0.05 - 3 m in wingspan) that overlaps certain micro air vehicle (MAV) designs and there is interest in whether some bird-like properties (flapping wings, deformable feathers, movable tails) might be useful or even necessary for successful MAVs. A bird with 5 cm mean chord flying at 8 m/s has a nominal Reynolds number of 2 - 3 x 10^4. This is an extremely inconvenient range for design, operation and analysis of lifting surfaces, even in steady motion, because their properties are very sensitive to boundary layer separation. The moderate- to high-amplitude flapping motions, together with the complex surface geometry and mechanical properties of the wings themselves lead to yet further challenges. This talk will review some of the theoretical and practical approaches towards understanding and analyzing the aerodynamics of various types of bird flight, including some recent research results that suggest that this effort is far from complete.

Spedding, Geoffrey

2002-11-01

379

Characterization of unsteady on-engine turbocharger turbine performance  

Microsoft Academic Search

The gas exchange process between a heavy duty diesel engine and its turbocharger turbine is characterized through measurements of the unsteady boundary conditions imposed by the engine environment on the turbine. Particle Image Velocimetry is implemented at the inlet of the twin-entry turbine to characterize the unsteady velocity field over a typical engine exhaust valve event. These data indicate that

Daniel Asher Ehrlich

1998-01-01

380

Unsteady Turbulent Simulation and Pressure Fluctuation Analysis for Centrifugal Pumps  

Microsoft Academic Search

The pressure fluctuation in the flow passage of both impeller and casing is addressed on design condition. The initial conditions for the unsteady turbulent simulation are resulted from the steady calculations, and the three dimensional unsteady turbulent simulation concerning the rotor-stator interaction is executed by a Navier-Stoke solver embedded with ? ? k turbulence model and with appropriate moving interface

YUAN Shouqi; NI Yongyan; PAN Zhongyong; YUAN Jianping

381

Unsteady MHD forced flow due to a point sink  

Microsoft Academic Search

Summary An analysis is performed to study the unsteady laminar incompressible boundary-layer flow of an electrically conducting fluid in a cone due to a point sink with an applied magnetic field. The unsteadiness in the flow is considered for two types of motion, viz. the motion arising due to the free stream velocity varying continuously with time and the transient

A. T. Eswara; S. Roy; G. Nath

2000-01-01

382

Aircraft aerodynamic parameter detection using micro hot-film flow sensor array and BP neural network identification.  

PubMed

Air speed, angle of sideslip and angle of attack are fundamental aerodynamic parameters for controlling most aircraft. For small aircraft for which conventional detecting devices are too bulky and heavy to be utilized, a novel and practical methodology by which the aerodynamic parameters are inferred using a micro hot-film flow sensor array mounted on the surface of the wing is proposed. A back-propagation neural network is used to model the coupling relationship between readings of the sensor array and aerodynamic parameters. Two different sensor arrangements are tested in wind tunnel experiments and dependence of the system performance on the sensor arrangement is analyzed. PMID:23112638

Que, Ruiyi; Zhu, Rong

2012-08-07

383

Aircraft Aerodynamic Parameter Detection Using Micro Hot-Film Flow Sensor Array and BP Neural Network Identification  

PubMed Central

Air speed, angle of sideslip and angle of attack are fundamental aerodynamic parameters for controlling most aircraft. For small aircraft for which conventional detecting devices are too bulky and heavy to be utilized, a novel and practical methodology by which the aerodynamic parameters are inferred using a micro hot-film flow sensor array mounted on the surface of the wing is proposed. A back-propagation neural network is used to model the coupling relationship between readings of the sensor array and aerodynamic parameters. Two different sensor arrangements are tested in wind tunnel experiments and dependence of the system performance on the sensor arrangement is analyzed.

Que, Ruiyi; Zhu, Rong

2012-01-01

384

Unsteady-State Flow of Flexible Polymers in Porous Media.  

PubMed

In this paper we report an investigation of the unsteady-state flow of polymer solutions through granular porous media. The experiments were performed using high-molecular-weight nonionic and anionic polyacrylamides dissolved in water containing NaCl and model porous media obtained by packing silicon carbide (SiC) grains having a narrow grain size distribution. Before injection in porous media, the polymer solutions were carefully filtered according to a method that was proved to be efficient in removing any possibly remaining microgels. The SiC grain surface was passively oxidized by a controlled thermal treatment in order to obtain a surface partially covered by a thin silica layer having adsorption properties similar to those of quartzitic sand. By packing SiC grains of different sizes, porous media having identical adsorption properties and well-known pore throats sizes can be obtained with a good reproducibility. Parameters investigated include pore size, velocity gradient, polymer concentration, and adsorption energy. A striking unsteady-state flow behavior (pressure build-up at constant flow rate) is observed when three conditions are fulfilled: (a) the velocity gradient is larger than that known to be able to induce a coil-stretch transition, (b) the polymer adsorbs on the pore surfaces, and (c) the length of stretched macromolecules is larger than the effective pore throat diameter. When one of these conditions is not satisfied the flow remains steady. These observations are interpreted by a mechanism involving the adsorption and bridging across pore restrictions of elongated chains. We propose to refer to this peculiar mode of polymer adsorption as bridging adsorption. Copyright 2001 Academic Press. PMID:11161513

Zitha, Pacelli L. J.; Chauveteau, Guy; Léger, Liliane

2001-02-15

385

The dynamics of unsteady detonation in ozone  

SciTech Connect

An ultra-fine, sub-micron discrete grid is used to capture the unsteady dynamics of a one-dimensional detonation in an inviscid O - O{sub 2} - O{sub 3} mixture. The ultra-fine grid is necessary to capture the length scales revealed by a complementary analysis of the steady detonation wave structure. For the unsteady calculations, shock-fitting coupled with a high order spatio-temporal discretization scheme combine to render numerical corruption negligible. As a result, mathematically verified solutions for a mixture initially of all O{sub 3} at one atmosphere and 298.15 K have been obtained; the solutions are converging at a rate much faster than the sub-first order convergence rate of all shock-capturing schemes. Additionally, the model has been validated against limited experimental data. Transient calculations show that strongly overdriven waves are stable and moderately overdriven waves unstable. New limit cycle behavior is revealed, and the first high resolution bifurcation diagram for etonation with detailed kinetics is found.

Aslam, Tariq D [Los Alamos National Laboratory; Powers, Joseph M [Los Alamos National Laboratory

2008-01-01

386

Unsteady Flow in Stenotic Blood Vessels  

NASA Astrophysics Data System (ADS)

Recent studies show that many heart attacks and strokes occur from sudden rupture of partially occluding atherosclerotic plaque rather than total vessel occlusion. Our goal is to understand how the mechanical forces induced by blood flow on specific plaque deposits makes them vulnerable to rupture. Models of severely stenotic carotid bifurcations are created from MR images and grids generated for the flow domains. The three-dimensional, unsteady, incompressible Navier-Stokes equations in finite-volume form are solved numerically using physiological boundary conditions. During systole a high velocity jet forms at the stenotic throat in one of the branches, and a long recirculation zone is observed downstream of the plaque. During diastole the flow is more stagnant. The flow is highly three-dimensional and unsteady with chaotic streamlines. Whereas flow in healthy arteries is laminar, irregular geometries and sharp changes in vessel diameter of a severely stenotic artery significantly disrupt the flow, with consequences for shear and normal wall stresses at the wall, and important implications for plaque stability. Supported by NIH Grant HL61823

Rayz, Vitaliy L.; Devi Williamson, Shobha; Berger, Stanley A.; Saloner, David

2003-11-01

387

Unsteady influences in droplet dynamics and combustion  

NASA Astrophysics Data System (ADS)

This research investigation addresses the problem of the unsteady dynamics associated with the vaporization, ignition and burning of hydrocarbon fuel droplets in laminar and turbulent flowfields. The method of approach is a numerical one with the use of the digital computer, and detailed solutions of the Navier-Stokes equations have been carried out to determine the important physical processes which occur around a burning droplet. For the relatively high pressure conditions of the present problem the most unsteady feature of the flow was the ignition and flame formation process. The ignition process causes major changes in the drag and heat transfer compared to the influences of eddy turbulence or the natural decay between the droplet and the freestream. However, both eddy turbulence and the natural decay of the difference in velocity between the droplet and the freestream play a very important role in the history of the droplet lifetime. All of the flow processes combine to cause the trajectory or the history of the droplet to be much different than would be expected from a quasi-steady analysis. Therefore, it must be concluded that the use of detailed numerical solution will play a pivotal role in the understanding and prediction of the dynamics of vaporizing droplets in gas streams.

Dwyer, H. A.; Sanders, B. R.

388

Benchmark solution for unsteady state CFD problems  

SciTech Connect

Unsteady convective dominated flows are very common in engineering and science. There is a need to develop an accurate numerical scheme to predict unsteady flow and heat transfer to understand the physics of instability and the flow evolution process. No numerical scheme is free from errors. It is essential to reduce the numerical errors to some extent, so that the prediction results are dependable. This article suggests two platform problems to test the accuracy of a time marching numerical scheme. One problem is buoyancy driven flow in a differentially heated cavity. This problem has importance in melting and solidification processes. The other problem is the forced flow in an oscillatory lid driven cavity. These problems are chosen because they have well-defined geometry, boundary, and initial conditions, yet the flow exhibits complexity and skewness with the grid line. High-order schemes are used to generate benchmark solutions for the mentioned problems. It is believed that the predicted results are numerically correct and oscillation of the fluid is due to physics of the flow.

Mohamad, A.A. [Eastern Mediterranean Univ., Mersin (Turkey). Mechanical Engineering Dept.

1998-11-13

389

Hydrodynamic interaction of two unsteady model microorganisms.  

PubMed

The study of pair-wise interactions between swimming microorganisms is fundamental to the understanding of the rheological and transport properties of semi-dilute suspensions. In this paper, the hydrodynamic interaction of two ciliated microorganisms is investigated numerically using a boundary-element method, and the microorganisms are modeled as spherical squirmers that swim by time-dependent surface deformations. The results show that the inclusion of the unsteady terms in the ciliary propulsion model has a large impact on the trajectories of the interacting cells, and causes a significant change in scattering angles with potential important consequences on the diffusion properties of semi-dilute suspensions. Furthermore, the analysis of the shear stress acting on the surface of the microorganisms revealed that the duration and the intensity of the near-field interaction are significantly modified by the presence of unsteadiness. This observation may account for the hydrodynamic nature of randomness in some biological reactions, and supersedes the distinction between intrinsic randomness and hydrodynamic interactions, adding a further element to the understanding and modeling of interacting microorganisms. PMID:20696173

Giacché, Davide; Ishikawa, Takuji

2010-08-07

390

Accelerated unsteady flow line integral convolution.  

PubMed

Unsteady flow line integral convolution (UFLIC) is a texture synthesis technique for visualizing unsteady flows with high temporal-spatial coherence. Unfortunately, UFLIC requires considerable time to generate each frame due to the huge amount of pathline integration that is computed for particle value scattering. This paper presents Accelerated UFLIC (AUFLIC) for near interactive (1 frame/second) visualization with 160,000 particles per frame. AUFLIC reuses pathlines in the value scattering process to reduce computationally expensive pathline integration. A flow-driven seeding strategy is employed to distribute seeds such that only a few of them need pathline integration while most seeds are placed along the pathlines advected at earlier times by other seeds upstream and, therefore, the known pathlines can be reused for fast value scattering. To maintain a dense scattering coverage to convey high temporal-spatial coherence while keeping the expense of pathline integration low, a dynamic seeding controller is designed to decide whether to advect, copy, or reuse a pathline. At a negligible memory cost, AUFLIC is 9 times faster than UFLIC with comparable image quality. PMID:15747635

Liu, Zhanping; Moorhead, Robert J

391

Clarification of Unsteady Fluid Forces Acting on Limbs in Swimming Using an Underwater Robot Arm  

NASA Astrophysics Data System (ADS)

The objective of this study was to clarify the unsteady characteristics of the fluid force acting on limbs during swimming. For this objective, an underwater robot arm, which has five degrees-of-freedom in order to perform the various complicated limb motions during swimming, was developed. In the previous study, an experiment to measure the unsteady fluid force was conducted for four swimming strokes of the upper and lower limbs. In this paper, the unsteady fluid force model was firstly formulated. Second, the simulation of experimental conditions was conducted. Two fluid force coefficients, which are the parameters in the fluid force model, were identified using optimizing calculation, so that the discrepancies of the forces and moments between the experiment and simulation were minimized. In addition, fluid force models which are dependant only on the limbs’ shapes were determined. Good agreement between the experiment and simulation with the determined fluid force model indicated the validity of the determined model. The identified fluid model will be useful for mechanical analyses of various swimming motions in future studies.

Nakashima, Motomu; Takahashi, Akemi

392

How Bumps on Whale Flippers Delay Stall: An Aerodynamic Model  

NASA Astrophysics Data System (ADS)

Wind tunnel experiments have shown that bumps on the leading edge of model humpback whale flippers cause them to “stall” (i.e., lose lift dramatically) more gradually and at a higher angle of attack. Here we develop an aerodynamic model which explains the observed increase in stall angle. The model predicts that as the amplitude of the bumps is increased, the lift curve flattens out, leading to potentially desirable control properties. We find that stall delay is insensitive to the wavelength of the bumps, in accordance with experimental observations.

van Nierop, Ernst A.; Alben, Silas; Brenner, Michael P.

2008-02-01

393

How bumps on whale flippers delay stall: an aerodynamic model.  

PubMed

Wind tunnel experiments have shown that bumps on the leading edge of model humpback whale flippers cause them to "stall" (i.e., lose lift dramatically) more gradually and at a higher angle of attack. Here we develop an aerodynamic model which explains the observed increase in stall angle. The model predicts that as the amplitude of the bumps is increased, the lift curve flattens out, leading to potentially desirable control properties. We find that stall delay is insensitive to the wavelength of the bumps, in accordance with experimental observations. PMID:18352375

van Nierop, Ernst A; Alben, Silas; Brenner, Michael P

2008-02-07

394

Correlation between vortex structures and unsteady loads for flapping motion in hover  

NASA Astrophysics Data System (ADS)

During the past decade, efforts were made to develop a new generation of unmanned aircrafts, qualified as Micro-Air Vehicles. The particularity of these systems resides in their maximum dimension limited to 15 cm, which, in terms of aerodynamics, corresponds to low Reynolds number flows ( Re ? 102 to 104). At low Reynolds number, the concept of flapping wings seems to be an interesting alternative to the conventional fixed and rotary wings. Despite the fact that this concept may lead to enhanced lift forces and efficiency ratios, it allows hovering coupled with a low-noise generation. Previous studies (Dickinson et al. in Science 284:1954-1960, 1999) revealed that the flow engendered by flapping wings is highly vortical and unsteady, inducing significant temporal variations of the loads experienced by the airfoil. In order to enhance the aerodynamic performance of such flapping wings, it is essential to give further insight into the loads generating mechanisms by correlating the spatial and temporal evolution of the vortical structures together with the time-dependent lift and drag. In this paper, Time Resolved Particle Image Velocimetry is used as a basis to evaluate both unsteady forces and vortical structures generated by an airfoil undergoing complex motion (i.e. asymmetric flapping flight), through the momentum equation approach and a multidimensional wavelet-like vortex parameterization method, respectively. The momentum equation approach relies on the integration of flow variables inside and around a control volume surrounding the airfoil (Noca et al. in J Fluids Struct 11:345-350, 1997; Unal et al. in J Fluids Struct 11:965-971, 1997). Besides the direct link performed between the flow behavior and the force mechanisms, the load characterization is here non-intrusive and specifically convenient for flapping flight studies thanks to its low Reynolds flows’ sensitivity and adaptability to moving bodies. Results are supported by a vortex parameterization which evaluates the circulation of the multiple vortices generated in such complex flows. The temporal evolution of the loads matches the flow behavior and hence reveals the preponderant inertial force component and that due to vortical structures.

Jardin, Thierry; Chatellier, Ludovic; Farcy, Alain; David, Laurent

2009-10-01

395

Sediment Vertical Flux in Unsteady Sheet Flows  

NASA Astrophysics Data System (ADS)

In models for sediment suspension, two different boundary conditions have been employed at the sediment bed. Either the sediment concentration is given or the vertical flux of sediment is specified. The specification of the latter is usually called the pick-up function. Recently, several developments towards a better understanding of the sediment bed boundary condition have been reported. Nielson et al (Coastal Engineering 2002, 45, p61-68) have indicated a better performance using the sediment vertical flux as the bed boundary condition in comparisons with experimental data. Also, Drake and Calantoni (Journal of Geophysical Research 2001, 106, C9, p19859-19868) have suggested that in the nearshore environment with its various unsteady flow conditions, the appropriate sediment boundary conditions of a large-scale morphology model must consider both the magnitude the free stream velocity and the acceleration of the flow. In this research, a small-scale sheet flow model based on the two-phase theory is implemented to further study these issues. Averaged two-phase continuum equations are presented for concentrated flows of sediment that are driven by strong, fully developed, unsteady turbulent shear flows over a mobile bed. The particle inter-granular stress is modeled using collisional granular flow theory and a two-equation closure for the fluid turbulence is adopted. In the context of the two-phase theory, sediment is transported through the sediment vertical velocity. Using the fully developed sediment phase continuity equation, it can be shown that the vertical velocity of the sediment must vanish when the flow reaches a steady state. In other words, in fully developed conditions, it is the unsteadiness of the flow that induces the vertical motion of the sediment and that changes the sediment concentration profile. Therefore, implementing a boundary condition based on sediment vertical flux is consistent with both the two-phase theory and with the observation that the flow acceleration is an important parameter. In this paper, the vertical flux of sediment is studied under various combinations of free stream velocity, acceleration, and sediment material properties using the two-phase sheet flow model. Some interesting features of sediment dynamics within the sheet, such as time history of sediment vertical velocity, collisional and turbulent suspension mechanisms are presented.

Hsu, T.; Jenkins, J. T.; Liu, P. L.

2002-12-01

396

Unsteady heat transfer in stator-rotor interaction by two-equation turbulence model  

SciTech Connect

A transonic turbine stage is computed by means of an unsteady Navier-Stokes solver. A two-equation turbulence model is coupled to a transition model based on integral parameters and an extra transport equation. The transonic stage is modeled in two dimensions with a variable span height for the rotor row. The analysis of the transonic turbine stage with stator trailing edge coolant ejection is carried out to compute the unsteady pressure and heat transfer distribution on the rotor blade under variable operating conditions. The stator coolant ejection allows the total pressure losses to be reduced, although no significant effects on the rotor heat transfer are found both in the computer simulation and the measurements. The results compare favorable with experiments in terms of both pressure distribution and heat transfer around the rotor blade.

Michelassi, V.; Martelli, F, [Univ. of Florence, (Italy). Energetics Dept. Sergio Stecco; Denos, R.; Arts, T.; Sieverding, C.H. [von Karman Inst. for Fluid Dynamics, Rhode Saint Genese (Belgium)

1999-07-01

397

Unsteady modelling of the oscillating S809 aerofoil and NREL phase VI parked blade using the Beddoes-Leishman dynamic stall model  

NASA Astrophysics Data System (ADS)

An implementation of the Beddoes-Leishman dynamic stall model has been developed at CENER, for modelling the unsteady aerodynamics on oscillating blade sections. The parameters of the model were adjusted for the S809 aerofoil, using an optimization based on genetic algorithms, and taking into account the values found in the literature and the physics of the aerodynamic process. Once the parameters were fixed to a unique set, oscillating cases of the 2D S809 aerofoil were computed, and compared with experimental data. Thus, the accuracy of the model was evaluated. On the other hand, oscillating cases of different span stations of the NREL phase VI parked blade were computed and compared with experimental data, to analyze the three-dimensionality of the dynamic stall on the blade sections. For the unsteady computations on the blade, the model was fed with the steady data of the blade section, to directly consider the geometry influence. In general, the results of the computations for the 2D aerofoil and 3D blade sections were very encouraging.

Gonzalez, Alvaro; Munduate, Xabier

2007-07-01

398

On aerodynamic modelling of an insect-like flapping wing in hover for micro air vehicles.  

PubMed

This theoretical paper discusses recent advances in the fluid dynamics of insect and micro air vehicle (MAV) flight and considers theoretical analyses necessary for their future development. The main purpose is to propose a new conceptual framework and, within this framework, two analytic approaches to aerodynamic modelling of an insect-like flapping wing in hover in the context of MAVs. The motion involved is periodic and is composed of two half-cycles (downstroke and upstroke) which, in hover, are mirror images of each other. The downstroke begins with the wing in the uppermost and rearmost position and then sweeps forward while pitching up and plunging down. At the end of the half-cycle, the wing flips, so that the leading edge points backwards and the wing's lower surface becomes its upper side. The upstroke then follows by mirroring the downstroke kinematics and executing them in the opposite direction. Phenomenologically, the interpretation of the flow dynamics involved, and adopted here, is based on recent experimental evidence obtained by biologists from insect flight and related mechanical models. It is assumed that the flow is incompressible, has low Reynolds number and is laminar, and that two factors dominate: (i) forces generated by the bound leading-edge vortex, which models flow separation; and (ii) forces due to the attached part of the flow generated by the periodic pitching, plunging and sweeping. The first of these resembles the analogous phenomenon observed on sharp-edged delta wings and is treated as such. The second contribution is similar to the unsteady aerodynamics of attached flow on helicopter rotor blades and is interpreted accordingly. Theoretically, the fluid dynamic description is based on: (i) the superposition of the unsteady contributions of wing pitching, plunging and sweeping; and (ii) adding corrections due to the bound leading-edge vortex and wake distortion. Viscosity is accounted for indirectly by imposing the Kutta condition on the trailing edge and including the influence of the vortical structure on the leading edge. Mathematically, two analytic approaches are proposed. The first derives all the quantities of interest from the notion of circulation and leads to tractable integral equations. This is an application of the von Kármán-Sears unsteady wing theory and its nonlinear extensions due to McCune and Tavares; the latter can account for the bound leading-edge vortex and wake distortion. The second approach uses the velocity potential as the central concept and leads to relatively simple ordinary differential equations. It is a combination of two techniques: (i) unsteady aerodynamic modelling of attached flow on helicopter rotor blades; and (ii) Polhamus's leading-edge suction analogy. The first of these involves both frequency-domain (Theodorsen style) and time-domain (indicial) methods, including the effects of wing sweeping and returning wake. The second is a nonlinear correction accounting for the bound leading-edge vortex. Connections of the proposed framework with control engineering and aeroelasticity are pointed out. PMID:16210181

Zbikowski, Rafa?

2002-02-15

399

Wind turbine aerodynamics research needs assessment  

NASA Astrophysics Data System (ADS)

A prioritized list is developed for wind turbine aerodynamic research needs and opportunities which could be used by the Department of Energy program management team in detailing the DOE Five-Year Wind Turbine Research Plan. The focus of the Assessment was the basic science of aerodynamics as applied to wind turbines, including all relevant phenomena, such as turbulence, dynamic stall, three-dimensional effects, viscosity, wake geometry, and others which influence aerodynamic understanding and design. The study was restricted to wind turbines that provide electrical energy compatible with the utility grid, and included both horizontal axis wind turbines (HAWT) and vertical axis wind turbines (VAWT). Also, no economic constraints were imposed on the design concepts or recommendations since the focus of the investigation was purely scientific.

Stoddard, F. S.; Porter, B. K.

1986-01-01

400

Aerodynamic tests of Darrieus wind turbine blades  

SciTech Connect

An indoor facility for the aerodynamic testing of Darrieus turbine blades was developed. Lift, drag, and moment coefficients were measured for two blades whose angle of attack and chord-to-radius ratio were varied. The first blade used an NACA 0015 airfoil section; the second used a 15% elliptical cross section with a modified circular arc trailing edge. Blade aerodynamic coefficients were corrected to section coefficients for comparison to published rectilinear flow data. Although the airfoil sections were symmetrical, moment coefficients were not zero and the lift and drag curves were asymmetrical about zero lift coefficient and angle of attack. These features verified the predicted virtual camber and incidence phenomena. Boundary-layer centrifugal effects were manifested by discontinuous lift curves and large differences in the angle of zero lift between th NACA 0015 and elliptical airfoils. It was concluded that rectilinear flow aerodynamic data are not applicable to Darrieus turbine blades, even for small chord-to-radius ratios.

Migliore, P.G.; Walters, R.E.; Wolfe, W.P.

1983-03-01

401

Aerodynamic collection efficiency of fog water collectors  

NASA Astrophysics Data System (ADS)

Fog water collectors (FWC) can provide water to arid zones with persistent advection and orographic fog. A key feature of any FWC is the mesh used to capture fog droplets. Two relevant mesh characteristics are its shade coefficient and the characteristics of the fibers used to weave or knit the mesh. This paper develops a simple superposition model to analyze the effect of these factors on the Aerodynamic Collection Efficiency (ACE) of FWCs. Due to the simplicity of the model it cannot be directly applied to actual FWC meshes, and serve only for guidance on the order of magnitude of the optimum shade coefficient and the corresponding ACE. The model shows that there is a maximum ACE of the order of 20-24.5% for shade coefficients between 0.5 and 0.6, for the particular mesh simulated. Aerodynamic collection efficiency can be increased by making the FWC concave and improving the aerodynamics of the mesh fibers.

Rivera, Juan De Dios

2011-11-01

402

14 CFR 23.371 - Gyroscopic and aerodynamic loads.  

Code of Federal Regulations, 2013 CFR

...Gyroscopic and aerodynamic loads. (a) Each engine mount and its supporting structure must be designed for the gyroscopic, inertial, and aerodynamic loads that result, with the engine(s) and propeller(s), if applicable, at maximum continuous...

2013-01-01

403

Analysis of Prop-Fan/Airframe Aerodynamic Integration.  

National Technical Information Service (NTIS)

An approach to aerodynamic integration of turboprops and airframes, with emphasis placed upon wing mounted installations is addressed. Potential flow analytical techniques were employed to study aerodynamic integration of the prop fan propulsion concept w...

M. L. Boctor C. W. Clay C. F. Watson

1978-01-01

404

Mathematical Modeling of the Aerodynamic Characteristics in Flight Dynamics.  

National Technical Information Service (NTIS)

Basic concepts involved in the mathematical modeling of the aerodynamic response of an aircraft to arbitrary maneuvers are reviewed. The original formulation of an aerodynamic response in terms of nonlinear functionals is shown to be compatible with a der...

G. T. Chapman L. B. Schiff M. Tobak

1984-01-01

405

Static Aerodynamics of the Mars Exploration Rover Entry Capsule.  

National Technical Information Service (NTIS)

The static aerodynamics for the Mars Exploration Rover (MER) aeroshell are presented. This aerodynamic database was an integral part of the end-to-end simulation used in preentry analysis for determining the MER entry design requirements for development o...

M. Schoeneberger F. McNEil Cheatwood P. N. Desai

2005-01-01

406

The dynamics of unsteady detonation with diffusion  

SciTech Connect

Here we consider an unsteady detonation with diffusion included. This introduces an interaction between the reaction length scales and diffusion length scales. Detailed kinetics introduce multiple length scales as shown though the spatial eigenvalue analysis of hydrogen-oxygen system; the smallest length scale is {approx} 10{sup 7} m and the largest {approx} 10{sup -2} m; away from equilibrium, the breadth can be larger. In this paper, we consider a simpler set of model equations, similar to the inviscid reactive compressible fluid equations, but include diffusion (in the form of thermal/energy, momentum, and mass diffusion). We will seek to reveal how the complex dynamics already discovered in one-step systems in the inviscid limit changes with the addition of diffusion.

Aslam, Tariq Dennis [Los Alamos National Laboratory; Romick, Christopher [NOTRE DAME; Powers, Joseph [NOTRE DAME

2010-01-01

407

Numerical simulations for transonic aerodynamic flows  

NASA Astrophysics Data System (ADS)

Transonic flow is an important aerodynamic phenomenon that occurs in the high subsonic Mach number flight regime. This paper presents the development of a numerical simulation for three-dimensional transonic aerodynamic flows around an isolated wing. The mathematical formulation is based on a transonic small-disturbance equation, which is a nonlinear and mixed elliptic-hyperbolic partial-differential equation. A Newton-like iterative scheme is developed for solving the transonic equation, and it is used in conjunction with a preconditioned minimal-residual algorithm. The numerical technique is proven to be efficient and reliable. Computational results for transonic flows around the ONERA M6 wing are presented.

Wong, Yau Shu; Jiang, Hong

1991-04-01

408

Preliminary Studies on Aerodynamic Control with Direct Current Discharge at Hypersonic Speed  

NASA Astrophysics Data System (ADS)

A new idea of an aerodynamic control device for hypersonic vehicles using plasma discharges is presented. The effect of DC plasma discharge on a hypersonic flow is examined with both experiments and CFD analyses. It is revealed that the surface pressure upstream of plasma area significantly increases, which would be preferable in realizing a new aerodynamic control devices. Such pressure rise is also observed in the result of analyses of the Navier-Stokes equations with energy addition that simulates the Joule heating of a plasma discharge. It is revealed that the pressure rise due to the existence of the plasma discharge can be qualitatively explained as an effect of Joule heating.

Watanabe, Yasumasa; Takama, Yoshiki; Imamura, Osamu; Watanuki, Tadaharu; Suzuki, Kojiro

409

Baseball Aerodynamics: What do we know and how do we know it?  

NASA Astrophysics Data System (ADS)

Baseball aerodynamics is governed by three phenomenological quantities: the coefficients of drag, lift, and moment, the latter determining the spin decay time constant. In past years, these quantities were studied mainly in wind tunnel experiments, whereby the forces on the baseball are measured directly. More recently, new tools are being used that focus on measuring accurate baseball trajectories, from which the forces can be inferred. These tools include high-speed motion analysis, video tracking of pitched baseballs (the PITCHf/x system), and Doppler radar tracking. In this contribution, I will discuss what these new tools are teaching us about baseball aerodynamics.

Nathan, Alan

2009-11-01

410

Aerodynamic performance of the feathered dinosaur Microraptor and the evolution of feathered flight.  

PubMed

Understanding the aerodynamic performance of feathered, non-avialan dinosaurs is critical to reconstructing the evolution of bird flight. Here we show that the Early Cretaceous five-winged paravian Microraptor is most stable when gliding at high-lift coefficients (low lift/drag ratios). Wind tunnel experiments and flight simulations show that sustaining a high-lift coefficient at the expense of high drag would have been the most efficient strategy for Microraptor when gliding from, and between, low elevations. Analyses also demonstrate that anatomically plausible changes in wing configuration and leg position would have made little difference to aerodynamic performance. Significant to the evolution of flight, we show that Microraptor did not require a sophisticated, 'modern' wing morphology to undertake effective glides. This is congruent with the fossil record and also with the hypothesis that symmetric 'flight' feathers first evolved in dinosaurs for non-aerodynamic functions, later being adapted to form lifting surfaces. PMID:24048346

Dyke, Gareth; de Kat, Roeland; Palmer, Colin; van der Kindere, Jacques; Naish, Darren; Ganapathisubramani, Bharathram

2013-09-18

411

Identification of Aerodynamic Coefficients of Ground Vehicles Using Neural Network  

Microsoft Academic Search

The purpose of this paper is to demonstrate the application of a combination of neural network and an oscillating model facility as an approach in identification of aerodynamic coefficients of ground vehicle. In literature study, a method for estimating transient aerodynamic data has been introduced and the aerodynamic coefficients are extracted from the measured time response by means of conventional

Nabilah Ramli; Shuhaimi Mansor; Hishamuddin Jamaluddin; Waleed Fekry Faris

2007-01-01

412

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

413

NACRE Powered Tail Concept: Aerodynamic Simulation through Wind Tunnel Testing and CFD  

Microsoft Academic Search

Summary This paper discusses the use of wind tunnel testing and CFD to simulate the aerodynamic characteristics of the powered tail concept as developed within the EU FP6 NACRE (Novel Aircraft Concepts REsearch) project. The instrumentation of the model is described and the value of the different experiment flow visualisation techniques used is noted. Particular emphasis is given to using

M. MAINA; S. LAWSON; P. W. C. WONG; B. MILLARD

414

An experimental and computational study of the aerodynamic and passive ventilation characteristics of small livestock trailers  

Microsoft Academic Search

This paper presents a combined experimental and computational study of the aerodynamics and passive ventilation characteristics of small livestock trailers within which the majority of animals in the United Kingdom are transported to market. Data obtained from a series of wind tunnel experiments using a 1\\/7th scale model of a simplified towing vehicle and trailer are compared with complementary computational

C.A. Gilkeson; H.M. Thompson; M.C.T. Wilson; P.H. Gaskell; R.H. Barnard

2009-01-01

415

Improvement of Aerodynamic Characteristics of Basic Configuration for Winged Vehicles with Lateral Blowing in Subsonic Flow  

Microsoft Academic Search

An experimental study on the improvement of aerodynamic characteristics of basic configuration for winged vehicles with lateral blowing in subsonic flow has been conducted. Wing planform is 75º\\/45º double delta wing whose cross section is modified NACA0010. Lateral blowing is realized by injecting a pair of sonic jets parallel to the trailing edge of the wing. The experiments have been

Kenji Tadakuma; Shigeru Aso; Yasuhiro Tani

2005-01-01

416

Aerodynamic Noise Radiated by the Intercoach Spacing and the Bogie of a High-Speed Train  

NASA Astrophysics Data System (ADS)

Full-scale acoustic experiments on a TGV are performed with on-board measurement techniques. Some spectral characteristics of the intercoach spacing and the bogie region are highlighted and interpreted. Two measurement techniques are described; they both extract the acoustical information of a particular aerodynamic source from the signal given by a flow imbedded probe.

Frémion, N.; Vincent, N.; Jacob, M.; Robert, G.; Louisot, A.; Guerrand, S.

2000-03-01

417

Short Term Microclimatic Change Resulting from Altered Aerodynamics in a Square Fenced Plot  

Microsoft Academic Search

A series of experiments was conducted at Ellerslie, Alberta to investigate the aerodynamically-induced microclamatic changes in a square plot surrounded by a porous fence. A dimensionless formulation describing transport of a passive scalar whose surface emission rate is spatially constant was derived in analogy to diffusion of a gas from a ground -level area source. This formulation involved a scaled

Josefina Calapan Argete

1988-01-01

418

Aerodynamic characteristics of the orbital reentry vehicle experimental probe fins in a supersonic flow  

Microsoft Academic Search

The aerodynamic characteristics of probe fins with a sweep angle of 60 deg, which are equipped on the Orbital Reentry Experiment (OREX) vehicle to measure the surrounding ionized gas temperature and electron number density distributions in the high temperature communication black out regions, have been measured in the supersonic wind tunnel of the National Aerospace Laboratory and compared with those

Mitsunori Watanabe; Hideo Sekine; Atsushi Tate; Junichi Noda

1994-01-01

419

Study of the aerodynamic trap for containerless laser materials processing in microgravity  

Microsoft Academic Search

In the context of containerless laser processing of glasses in microgravity, a systematic study of the aerodynamic trap (ADT) has been done on the ground at both ambient and very high temperatures (?2000 K). This work yielded a better understanding of the ADT and helped in improving its design. Experiments indicate that restoring force and sample stability depend upon the

Paul-François Paradis; François Babin; Jean-Marie Gagné

1996-01-01

420

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

421

Unsteady flows of in homogeneous in compressible fluids  

SciTech Connect

In this paper, we study the unsteady motion of in homogeneous in compressible viscous fluids. We present the results corresponding to Stokes second problem and for the flow between two parallel plates where one is oscillating.

Massoudi, Mehrdad; Vaidya, Ashwin

2011-01-01

422

Studies on High Pressure and Unsteady Flame Phenomena.  

National Technical Information Service (NTIS)

The objective of the present program is to study the structure and response of steady and unsteady laminar premixed and nonpremixed flames in reduced and elevated pressure environments through (a) non-intrusive experimentation, (b) computational simulatio...

C. K. Law

1995-01-01

423

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

424

Analyzing unsteady-state flow in gas pipelines  

SciTech Connect

A new technique for estimating the steady-state and unsteady-state behavior of dry gas pipelines has been developed. It is simple, easy to use, and, compared with other techniques based on finite difference mathematics, gives good accuracy.

Zhou, P.; Erbar, J.H.; Maddox, R.N.

1983-08-01

425

Numerical Integration of Nonequilibrium Internal Flow Using Unsteady Euler Equations.  

National Technical Information Service (NTIS)

A quasi-one dimensional, nonequlibrium, streamtube model and finite difference computer code has been developed to study nonisentropic supercritical, real gas flows. A system of unsteady Euler equations is integrated to a steady state solution utilizing M...

M. J. Trout

1983-01-01

426

A Bibliography of Recent Developments in Unsteady Transonic Flow.  

National Technical Information Service (NTIS)

A bibliography of recent developments in unsteady transonic flow is presented. Papers have been divided into survey, experimental, and theoretical classifications, selected publications have been reviewed, and a more comprehensive set of publications has ...

C. J. Borland

1979-01-01

427

Pressure-sensitive paint in aerodynamic testing  

Microsoft Academic Search

Pressure-sensitive paint (PSP) is a relatively new aerodynamic measurement tool with the unique capability of providing a field measurement of pressure over a test surface. An introductory review of this technology is presented, which is confined to the application of the PSP method to aircraft development wind tunnel testing. This is at present the primary application area and thus the

B. G. McLachlan; J. H. Bell

1995-01-01

428

The bulk aerodynamic formulation over heterogeneous surfaces  

Microsoft Academic Search

This interpretative literature survey examines problems with application of the bulk aerodynamic method to spatially averaged fluxes over heterogeneous surfaces. This task is approached by tying together concepts from a diverse range of recent studies on subgrid parameterization, the roughness sublayer, the roll of large “inactive” boundary-layer eddies, internal boundary-layer growth, the equilibrium sublayer, footprint theory and the blending height.

L. Mahrt

1996-01-01

429

Aerodynamics of high-speed railway train  

Microsoft Academic Search

Railway train aerodynamic problems are closely associated with the flows occurring around train. Much effort to speed up the train system has to date been paid on the improvement of electric motor power rather than understanding the flow around the train. This has led to larger energy losses and performance deterioration of the train system, since the flows around train

Raghu S Raghunathan; H.-D Kim; T Setoguchi

2002-01-01

430

Aerodynamic drag in cycling: methods of assessment.  

PubMed

When cycling on level ground at a speed greater than 14 m/s, aerodynamic drag is the most important resistive force. About 90% of the total mechanical power output is necessary to overcome it. Aerodynamic drag is mainly affected by the effective frontal area which is the product of the projected frontal area and the coefficient of drag. The effective frontal area represents the position of the cyclist on the bicycle and the aerodynamics of the cyclist-bicycle system in this position. In order to optimise performance, estimation of these parameters is necessary. The aim of this study is to describe and comment on the methods used during the last 30 years for the evaluation of the effective frontal area and the projected frontal area in cycling, in both laboratory and actual conditions. Most of the field methods are not expensive and can be realised with few materials, providing valid results in comparison with the reference method in aerodynamics, the wind tunnel. Finally, knowledge of these parameters can be useful in practice or to create theoretical models of cycling performance. PMID:21936289

Debraux, Pierre; Grappe, Frederic; Manolova, Aneliya V; Bertucci, William

2011-09-01

431

Macro aerodynamic devices controlled by micro systems  

Microsoft Academic Search

Micro-ElectroMechanical-Systems (MEMS) have emerged as a major enabling technology across the engineering disciplines. In this study, the possibility of applying MEMS to the aerodynamic field was explored. We have demonstrated that microtransducers can be used to control the motion of a delta wing in a wind tunnel and can even maneuver a scaled aircraft in flight tests. The main advantage

Gwo-Bin Lee; F. K. Jiang; T. Tsao; Y. C. Tai; C. M. Ho

1997-01-01

432

COMPUTER ANALYSIS OF INDUSTRIAL BATCH DRYER AERODYNAMICS  

Microsoft Academic Search

One of the fundamental problems encountered in the batch dryer design field is the determination of appropriate equipment configuration that would ensure uniform distribution of air over the dryer trays. Such industrial batch dryer aerodynamics problems can be successfully investigated using computational fluid dynamics techniques. A mathematical model for predicting the two-dimensional air flow inside a typical industrial batch dryer

C. T. Kiranoudis; N. C. Markatos

1998-01-01

433

Hybrid methods for inverse aerodynamic design  

Microsoft Academic Search

This thesis describes a novel hybrid approach for the multipoint inverse design of airfoils for complex aerodynamic systems. In this approach, an inverse design method for single-element airfoils is coupled with an analysis module for the complex system. The airfoils that comprise the complex system are generated in isolation using the single-element airfoil inverse design method. The analysis module is

Ashok Gopalarathnam

1999-01-01

434

Minimum Energy Guidance for Aerodynamically Controlled Missiles  

Microsoft Academic Search

This paper examines the problem of guiding a missile to a target using minimal energy. First, an optimal controller is de- velopedforamissilethathasarbitrarycontrol overits acceleration vector. Next, an optimal controller is sought for a missile that has a directional control constraint, which is intended to model the ac- tual constraint present in aerodynamically controlled missiles. The optimal guidance law is shown

Robert Wes Morgan; Hal Tharp; Thomas L. Vincent

2011-01-01

435

Aerodynamics of Transport Aircraft Spoiler Solutions  

Microsoft Academic Search

based on wing mean aerodynamic chord. Spoiler or air brake, respectively, deflection angles are varied. Most relevant parameters, regarding steep approach performance, are minimum approach velocity, descent velocity and approach velocity. The corresponding values are theoretically derived. Therewith, the relative performance of the different spoilers is shown. Regarding effectiveness per deflection angle, a vertically deployed air brake with no breather

U. JUNG; C. BREITSAMTER

436

Aerodynamic noise prediction using grey model  

Microsoft Academic Search

In this paper, two methods are described to predict the aerodynamic noise induced by flow around a cylinder using the linear model GM (1, 1) and the nonlinear model Verhult based on grey system theory. The grey prediction initial data is from large eddy simulation and acoustic analogy. The prediction results using the model GM(1, 1) are respectively compared to

Long Shuangli; Nie Hong; Li Lei; Xu Xin

2010-01-01

437

Containerless processing of ceramics by aerodynamic levitation  

Microsoft Academic Search

An inexpensive containerless processing technique based on aerodynamic levitation has been developed for high temperature studies on ceramics. A spherical sample of about 0.5 cm diameter levitates in an upward stream of inert gas in a flared graphite nozzle which also acts as a susceptor and heats the sample by radiation to a maximum temperature of 2200°C. The highest heating

A. S. Gandhi; A. Saravanan; V. Jayaram

1996-01-01

438

Three-dimensional time-marching inviscid and viscous solutions for unsteady flows around vibrating blades  

SciTech Connect

A three-dimensional nonlinear time-marching method of solving the thin-layer Navier-Stokes equations in a simplified form has been developed for blade flutter calculations. The discretization of the equations is made using the cell-vertex finite volume scheme in space and the four-stage Runge-Kutta scheme in time. Calculations are carried out in a single-blade-passage domain and the phase-shifted periodic condition is implemented by using the shape correction method. The three-dimensional unsteady Euler solution is obtained at conditions of zero viscosity, and is validated against a well-established three-dimensional semi-analytical method. For viscous solutions, the time-step limitation on the explicit temporal discretization scheme is effectively relaxed by using a time-consistent two-grid time-marching technique. A transonic rotor blade passage flow (with tip-leakage) is calculated using the present three-dimensional unsteady viscous solution method. Calculated steady flow results agree well with the corresponding experiment and with other calculations. Calculated unsteady loadings due to oscillations of the rotor blades reveal some notable three-dimensional viscous flow features. The feasibility of solving the simplified thin-layer Navier-Stokes solver for oscillating blade flows at practical conditions is demonstrated.

He, L.; Denton, J.D. (Cambridge Univ. (United Kingdom). Whittle Lab.)

1994-07-01

439

Management and control of separation by unsteady and vortical flows  

NASA Astrophysics Data System (ADS)

Management and Control of 2-D and 3-D separated flows by unsteady and/or vortical flows is investigated in a number of configurations aimed at an enhanced basic understanding of governing mechanisms. The investigations are aimed at impacting the design of future generations of aircraft with improved maneuverability for better performance and safety. Also, novel techniques are being developed for the measurement, mapping and documentation of these complex unsteady flowfields.

Nagib, Hassan M.; Acharya, Mukund; Reisenthel, Patrick H.; Way, John L.; Williams, David R.

1988-06-01

440

Numerical treatment of shocks in unsteady potential flow computation  

NASA Astrophysics Data System (ADS)

For moving shocks in unsteady transonic potential flow, an implicit fully-conservative finite-difference algorithm is presented. It is based on time-linearization and mass-flux splitting. For the one-dimensional problem of a traveling shock-wave, this algorithm is compared with the method of Goorjian and Shankar. The algorithm was implemented in the computer program TULIPS for the computation of transonic unsteady flow about airfoils. Numerical results for a pitching ONERA M6 airfoil are presented.

Schippers, H.

1985-04-01

441

An implicit scheme for unsteady compressible Navier-Stokes equations  

NASA Astrophysics Data System (ADS)

In this paper a time accurate scheme for unsteady Navier-Stokes equations is presented. This scheme employs, as unknowns, quantities of order of square of time spacing, thus making a delta square-form of which the right hand side is a numerical approximation of unsteady governing equations. This algorithm makes a scheme especially suitable for accurate simulations. A shock tube flow is calculated as an example. The flow is assumed laminar, and shock wave-boundary layer interaction is simulated.

Matsuno, Kenichi

1988-12-01

442

Geometry of unsteady fluid transport during fluid-structure interactions  

Microsoft Academic Search

We describe the application of tools from dynamical systems to define and quantify the unsteady fluid transport that occurs during fluid-structure interactions and in unsteady recirculating flows. The properties of Lagrangian coherent structures (LCS) are used to enable analysis of flows with arbitrary time-dependence, thereby extending previous analytical results for steady and time-periodic flows. The LCS kinematics are used to

Elisa Franco; David Pekarek; Jifeng Peng; John O. Dabiri

2007-01-01

443

Unsteady-State Performance of Heterogeneous Catalytic Reactions  

Microsoft Academic Search

The opinion that performance of continuous catalytic processes under invariable conditions is highly efficient has gained great popularity, especially among chemical engineers. However, very often the optimal conditions of the process can be achieved with the so-called unsteady-state operation. The steady-state condition thus appears to be a particular case of the variety of unsteady-state conditions which can be obtained, e.g.,

G. K. Boreskov; Y. U. Sh. Matros

1983-01-01

444

Investigation on RANS Computation for an Unsteady Turbulent Flow  

Microsoft Academic Search

With improvements in a computer hardware and CFD software, the problems treated in industry are becoming more complex, both physically and geometrically. Turbulent flow with strong unsteadiness is one such physically complex example. Since Large Eddy Simulation (LES) is still too time-consuming, a great number of unsteady Reynolds-Averaged Navier-Stokes (RANS) computations have been employed in such engineering applications. However, the

Kazuya Kodama; Kazuyuki Toda; Makoto Yamamoto

2007-01-01

445

Investigation of unsteady temperature fields of nonaxisymmetric nozzle inserts  

NASA Astrophysics Data System (ADS)

The problem of calculating unsteady heat-conduction in an eccentric nozzle insert subjected to intense heating is considered with reference to the thrust vector control of supersonic flight vehicles. The third boundary value problem of unsteady heat-conduction is solved analytically for an eccentric ring. Results of calculations are presented for a nozzle insert of small eccentricity, and a comparison is made with finite-difference results.

Makarenkova, L. G.

446

Towards numerical prediction of unsteady sheet cavitation on hydrofoils  

Microsoft Academic Search

The paper presents a study of using a modified k-? model to predict the unsteady cavitating flows around 2D and 3D hydrofoils in the framework of multi-phase mixture flow RANS approach. The cavitation is modeled by Schnerr-Sauer's cavitation model. A 2D NACA0015 foil at cavitation number ?=1.0 (unsteady with cloud shedding) is studied first, followed by the Delft twisted 3D

Da-qing Li; Mikael Grekula; Per Lindell

2010-01-01

447

Approximate Method of Calculating the Interaction of Finite-Span Airfoils in Unsteady Motion Above a Solid Surface (Priblizhennyi Metod Rascheta Vzaimodeistviya Krylev Konechnogo Razmakha pri Neustanovivshiemsya Dvizhenii nad Tverdoi Poverkhnostyu).  

National Technical Information Service (NTIS)

It is important for many practical problems to be able to analyze the aerodynamic characterisQtics of a system of two airfoils moving over a supporting surface on the basis of the known (either through calculations or experiment) aerodynamic characteristi...

V. K. Treshkov

1975-01-01

448

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

449

Freight Wing Trailer Aerodynamics Final Technical Report  

SciTech Connect

Freight Wing Incorporated utilized the opportunity presented by a DOE category two Inventions and Innovations grant to commercialize and improve upon aerodynamic technology for semi-tuck trailers, capable of decreasing heavy vehicle fuel consumption, related environmental damage, and U.S. consumption of foreign oil. Major project goals included the demonstration of aerodynamic trailer technology in trucking fleet operations, and the development and testing of second generation products. A great deal of past scientific research has demonstrated that streamlining box shaped semi-trailers can significantly reduce a truck’s fuel consumption. However, significant design challenges have prevented past concepts from meeting industry needs. Freight Wing utilized a 2003 category one Inventions and Innovations grant to develop practical solutions to trailer aerodynamics. Fairings developed for the front, rear, and bottom of standard semi-trailers together demonstrated a 7% improvement to fuel economy in scientific tests conducted by the Transportation Research Center (TRC). Operational tests with major trucking fleets proved the functionality of the products, which were subsequently brought to market. This category two grant enabled Freight Wing to further develop, test and commercialize its products, resulting in greatly increased understanding and acceptance of aerodynamic trailer technology. Commercialization was stimulated by offering trucking fleets 50% cost sharing on trial implementations of Freight Wing products for testing and evaluation purposes. Over 230 fairings were implemented through the program with 35 trucking fleets including industry leaders such as Wal-Mart, Frito Lay and Whole Foods. The feedback from these testing partnerships was quite positive with product performance exceeding fleet expectations in many cases. Fleet feedback also was also valuable from a product development standpoint and assisted the design of several second generation products intended to further improve efficiency, lower costs, and enhance durability. Resulting products demonstrated a 30% efficiency improvement in full scale wind tunnel tests. The fuel savings of our most promising product, the “Belly Fairing” increased from 4% to 6% in scientific track and operational tests. The project successfully demonstrated the economic feasibility of trailer aerodynamics and positioned the technology to realize significant public benefits. Scientific testing conducted with partners such as the EPA Smartway program and Transport Canada clearly validated the fuel and emission saving potential of the technology. The Smartway program now recommends trailer aerodynamics as a certified fuel saving technology and is offering incentives such as low interest loans. Trailer aerodynamics can save average trucks over 1,100 gallons of fuel an 13 tons of emissions every 100,000 miles, a distance many trucks travel annually. These fuel savings produce a product return on investment period of one to two years in average fleet operations. The economic feasibility of the products was validated by participating fleets, several of which have since completed large implementations or demonstrated an interest in volume orders. The commercialization potential of the technology was also demonstrated, resulting in a national distribution and manufacturing partnership with a major industry supplier, Carrier Transicold. Consequently, Freight Wing is well positioned to continue marketing trailer aerodynamics to the trucking industry. The participation of leading fleets in this project served to break down the market skepticism that represents a primary barrier to widespread industry utilization. The benefits of widespread utilization of the technology could be quite significant for both the transportation industry and the public. Trailer aerodynamics could potentially save the U.S. trucking fleet over a billion gallons of fuel and 20 million tons of emissions annually.

Sean Graham

2007-10-31

450

Aerodynamic Design of Heavy Vehicles Reporting Period January 15, 2004 through April 15, 2004  

Microsoft Academic Search

Listed are summaries of the activities and accomplishments during this second-quarter reporting period for each of the consortium participants. The following are some highlights for this reporting period: (1) Experiments and computations guide conceptual designs for reduction of drag due to tractor-trailer gap flow (splitter plate), trailer underbody (wedges), and base drag (base-flap add-ons). (2) Steady and unsteady RANS simulations

A Leonard; P Chatelain; J Heineck; F Browand; R Mehta; J Ortega; K Salari; B Storms; J Brown; L DeChant; M Rubel; J Ross; M Hammache; D Pointer; C Roy; B Hassan; D Arcas; T Hsu; J Payne; S Walker; P Castellucci; R McCallen

2004-01-01

451

A method for the aerodynamic design of dry powder inhalers.  

PubMed

An inhaler design methodology was developed and then used to design a new dry powder inhaler (DPI) which aimed to fulfill two main performance requirements. The first requirement was that the patient should be able to completely empty the dry powder from the blister in which it is stored by inspiratory effort alone. The second requirement was that the flow resistance of the inhaler should be geared to optimum patient comfort. The emptying of a blister is a two-phase flow problem, whilst the adjustment of the flow resistance is an aerodynamic design problem. The core of the method comprised visualization of fluid and particle flow in upscaled prototypes operated in water. The prototypes and particles were upscaled so that dynamic similarity conditions were approximated as closely as possible. The initial step in the design method was to characterize different blister prototypes by measurements of their flow resistance and particle emptying performance. The blisters were then compared with regard to their aerodynamic performance and their ease of production. Following selection of candidate blisters, the other components such as needle, bypass and mouthpiece were dimensioned on the basis of node-loop operations and validation experiments. The final shape of the inhaler was achieved by experimental iteration. PMID:21718768

Ertunç, O; Köksoy, C; Wachtel, H; Delgado, A

2011-06-28

452

Design, aerodynamics and autonomy of the DelFly.  

PubMed

One of the major challenges in robotics is to develop a fly-like robot that can autonomously fly around in unknown environments. In this paper, we discuss the current state of the DelFly project, in which we follow a top-down approach to ever smaller and more autonomous ornithopters. The presented findings concerning the design, aerodynamics and autonomy of the DelFly illustrate some of the properties of the top-down approach, which allows the identification and resolution of issues that also play a role at smaller scales. A parametric variation of the wing stiffener layout produced a 5% more power-efficient wing. An experimental aerodynamic investigation revealed that this could be associated with an improved stiffness of the wing, while further providing evidence of the vortex development during the flap cycle. The presented experiments resulted in an improvement in the generated lift, allowing the inclusion of a yaw rate gyro, pressure sensor and microcontroller onboard the DelFly. The autonomy of the DelFly is expanded by achieving (1) an improved turning logic to obtain better vision-based obstacle avoidance performance in environments with varying texture and (2) successful onboard height control based on the pressure sensor. PMID:22617112

de Croon, G C H E; Groen, M A; De Wagter, C; Remes, B; Ruijsink, R; van Oudheusden, B W

2012-05-22

453

Aerodynamic Parameters of Urban Building Arrays with Random Geometries  

NASA Astrophysics Data System (ADS)

It is difficult to describe the flow characteristics within and above urban canopies using only geometrical parameters such as plan area index ( ? p ) and frontal area index ( ? f ) because urban surfaces comprise buildings with random layouts, shapes, and heights. Furthermore, two types of `randomness' are associated with the geometry of building arrays: the randomness of element heights (vertical) and that of the rotation angles of each block (horizontal). In this study, wind-tunnel experiments were conducted on seven types of urban building arrays with various roughness packing densities to measure the bulk drag coefficient ( C d ) and mean wind profile; aerodynamic parameters such as roughness length ( z o ) and displacement height ( d) were also estimated. The results are compared with previous results from regular arrays having neither `vertical' nor `horizontal' randomness. In vertical random arrays, the plot of C d and z o versus ? f exhibited a monotonic increase, and z o increased by a factor of almost two for ? f = 48-70%. C d was strongly influenced by the standard deviation of the height of blocks ( ?) when ? p ? 17%, whereas C d was independent of ? when ? p = 7%. In the case of horizontal random arrays, the plot of the estimated C d against ? f showed a peak. The effect of both vertical and horizontal randomness of the layout on aerodynamic parameters can be explained by the structure of the vortices around the blocks; the aspect ratio of the block is an appropriate index for the estimation of such features.

Zaki, Sheikh Ahmad; Hagishima, Aya; Tanimoto, Jun; Ikegaya, Naoki

2011-01-01

454

Elastic response of carbon nanotube forests to aerodynamic stresses.  

PubMed

The ability to determine static and (hydro)dynamic properties of carbon nanotubes (CNTs) is crucial for many applications. While their static properties (e.g., solubility and wettability) are fairly well understood, their mechanical responses (e.g., deflection under shear) to ambient fluid flow are to a large extent unknown. We analyze the elastic response of single-walled CNT forests, attached to the bottom wall of a channel, to the aerodynamic loading exerted by both laminar and turbulent flows. Our analysis yields analytical expressions for velocity distributions, the drag coefficient, and bending profiles of individual CNTs. This enables us to determine flexural rigidity of CNTs in wind-tunnel experiments. The model predictions agree with laboratory experiments for a large range of channel velocities. PMID:21230836

Battiato, Ilenia; Bandaru, Prabhakar R; Tartakovsky, Daniel M

2010-10-01

455

Numerical Simulation of Unsteady Driven Cavity Flow  

NASA Astrophysics Data System (ADS)

A numerical study is performed on the flow of an incompressible fluid driven in a square cavity. The behavior of unsteady flows beyond the first Hopf bifurcation is investigated. The first Hopf bifurcation is localized at \\mathit{Re}cr1=7987± 0.2% with the fundamental frequency fB=0.4519, in good agreement with the previous studies. A secondary Hopf bifurcation occurs at \\mathit{Re}cr2=9575± 3%, which generates a quasi-periodic solution with two incommensurable frequencies fB and fH, up to the annihilation of fB at \\mathit{Re}cr3=10975± 2%. While quasi-periodic flow is observed for \\mathit{Re}cr2?\\mathit{Re}?\\mathit{Re}cr3 on this solution branch, another branch of the periodic solution with fundamental frequency fL (

Osada, Takuya; Iwatsu, Reima

2011-09-01

456

Numerical simulation of unsteady separated flows  

NASA Astrophysics Data System (ADS)

Two unsteady flows dominated by the occurrence of separation are simulated through the use of the discrete vortex model. The first of these is a sinusoidally oscillating flow about a circular cylinder at a Keulegan-Carpenter number of K = 10. The vortex model has been combined with the boundary layer calculations and the positions of the separation and stagnation points, the evolution of the wake, the velocity and pressure distributions, and the instantaneous forces have been calculated and compared, whenever possible, with those obtained experimentally. The model has successfully simulated the occurrence of the transverse half Karman vortex street. The calculated positions of the vortices are in good agreement with those obtained experimentally. The measured and calculated in-line forces and the differential pressure distributions showed reasonably good agreement. The second simulation dealt with a rapidly decelerating flow about a two-dimensional sharp-edged camber. An extensive study of the velocity field in the vicinity of the singular points led to the development of a novel method for the introduction of vorticity at variable time intervals. The measured and calculated characteristics of the flow, such as the evolution of the wake and the forces acting on the camber, were found to be in excellent agreement.

Mostafa, Samir I.

1987-06-01

457

Unsteady turbulent round jets and vortex motion  

NASA Astrophysics Data System (ADS)

A new model to predict the velocity distribution in round jets with time-varying injection profiles has been formulated as an extension of steady jet theory. The approach introduces an effective injection velocity within the jet based on a representative response time. It is assumed that the instantaneous injection velocity affects the velocity within the jet with an exponential response function and that the response time is related to the fluid particle's residence time within the jet, consistent with the theory of translation of jet vortex rings from Helmholtz's vortex motion analysis [P. G. Tait, London Edinburgh Dublin Philos. Mag. J. Sci. 33, 485 (1867)]. The Helmholtz theory is also shown to reduce to the well-known velocity decay rate in the case of steady turbulent gas jets. A Duhamel superposition integral is used to determine the effective injection velocity for time-varying injection rates. The model is tested with different injection profiles and different ambient densities. The results are also compared with numerical results from a computational fluid dynamics code. The comparisons agree very well and the new model is shown to offer an efficient method to predict jet tip penetrations for unsteady jets.

Abani, Neerav; Reitz, Rolf D.

2007-12-01

458

Four-stage computational technology with adaptive numerical methods for computational aerodynamics  

NASA Astrophysics Data System (ADS)

Computational aerodynamics is a key technology in aircraft design which is ahead of physical experiment and complements it. Of course all three components of computational modeling are actively developed: mathematical models of real aerodynamic processes, numerical algorithms, and high-performance computing. The most impressive progress has been made in the field of computing, though with a considerable complication of computer architecture. Numerical algorithms are developed more conservative. More precisely, they are offered and theoretically justified for more simple mathematical problems. Nevertheless, computational mathematics now has amassed a whole palette of numerical algorithms that can provide acceptable accuracy and interface between modern mathematical models in aerodynamics and high-performance computers. A significant step in this direction was the European Project ADIGMA whose positive experience will be used in International Project TRISTAM for further movement in the field of computational technologies for aerodynamics. This paper gives a general overview of objectives and approaches intended to use and a description of the recommended four-stage computer technology.

Shaydurov, V.; Liu, T.; Zheng, Z.

2012-10-01

459

A study of helicopter aerodynamics in ground effect  

NASA Astrophysics Data System (ADS)

The flow around a helicopter is very complex; it becomes much more complex when it comes close to the ground. The presence of the ground changes the aerodynamic characteristics of the rotor and the flow environment becomes much more complex compared with that of flight out-of-ground effect (OGE) and hence the behavior of the rotor wake in the vicinity of the ground is challenging to predict. Under in-ground-effect(IGE) conditions, the wake collides with the ground and causes a significant perturbation to the flow near the blade. Significant interactions between the main rotor wake and the ground have been associated with the formation and passage of the ground vortex in forward flight. The presence of a ground vortex affects the handling qualities of the helicopter. The aim of this research is to capture the physics of the flow features and dynamics of ground effect flows around a rotorcraft, provide an understanding of the rotor wake/vortices near the ground, and generate rigorous models to accurately predict handling qualities, loads and moments acting on the rotor and the power requirements. A free vortex method is used to model the flowfield. The presence of the ground is modeled using the method of images and the lifting-surface theory is used to model each rotor blade. An initial wake geometry is assumed which is allowed to develop in time until the flowfield becomes periodic. The rotor wake is assumed to consist of only the tip vortices and the inboard sheet and the root vortex are neglected. The solution is stepped in time using an Adams-Moulton scheme with a Runge-Kutta starting formula. The wake structure after periodicity is reached is obtained for hover and different forward flight speeds. Also, the nature of the flowfield, as well as the formation of the ground vortex, is understood by obtaining the velocity contours on a longitudinal plane containing the rotor blade after periodicity is obtained. The unsteadiness in the velocities is quantified by obtaining the RMS deviation in velocities on different planes containing the tail rotor around the rotor disk simulating the various kinds of flight. Thrust and power requirements on the rotor disk have been predicted and have been successfully validated by comparison with experimental results obtained from Georgia Institute of Technology. A tail rotor has also been included in the current model to understand its implications on the wake structure and loads. The computational results have been validated against experimental results obtained at Georgia Institute of Technology and Empey and Ormiston.

Pulla, Devi Prasad

460

External aerodynamics of heavy ground vehicles: Computations and wind tunnel testing  

NASA Astrophysics Data System (ADS)

Aerodynamic characteristics of a ground vehicle affect vehicle operation in many ways. Aerodynamic drag, lift and side forces have influence on fuel efficiency, vehicle top speed and acceleration performance. In addition, engine cooling, air conditioning, wind noise, visibility, stability and crosswind sensitivity are some other tasks for vehicle aerodynamics. All of these areas benefit from drag reduction and changing the lift force in favor of the operating conditions. This can be achieved by optimization of external body geometry and flow modification devices. Considering the latter, a thorough understanding of the airflow is a prerequisite. The present study aims to simulate the external flow field around a ground vehicle using a computational method. The model and the method are selected to be three dimensional and time-dependent. The Reynolds-averaged Navier Stokes equations are solved using a finite volume method. The Renormalization Group (RNG) k-epsilon model was elected for closure of the turbulent quantities. Initially, the aerodynamics of a generic bluff body is studied computationally and experimentally to demonstrate a number of relevant issues including the validation of the computational method. Experimental study was conducted at the Langley Full Scale Wind Tunnel using pressure probes and force measurement equipment. Experiments and computations are conducted on several geometric configurations. Results are compared in an attempt to validate the computational model for ground vehicle aerodynamics. Then, the external aerodynamics of a heavy truck is simulated using the validated computational fluid dynamics method, and the external flow is presented using computer visualization. Finally, to help the estimation of the error due to two commonly practiced engineering simplifications, a parametric study on the tires and the moving ground effect are conducted on full-scale tractor-trailer configuration. Force and pressure coefficients and velocity distribution around tractor-trailer assembly are computed for each case and the results compared with each other. Finally, this study demonstrates that it is possible to apply computational fluid dynamics for ground vehicle aerodynamics with substantial detail and fidelity. With the latest developments on computing power, computational fluid dynamics can be applied on real-life transportation problems with reasonable turn-around times, reliability, ease of accessibility and affordability. The next step is deemed to be considering such a computational methodology for analysis within an automated optimization process in improving aerodynamic designs of heavy ground vehicles.

Bayraktar, Ilhan