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Last update: November 12, 2013.

1

Aerodynamic Aspects of Wind Energy Conversion

NASA Astrophysics Data System (ADS)

This article reviews the most important aerodynamic research topics in the field of wind energy. Wind turbine aerodynamics concerns the modeling and prediction of aerodynamic forces, such as performance predictions of wind farms, and the design of specific parts of wind turbines, such as rotor-blade geometry. The basics of the blade-element momentum theory are presented along with guidelines for the construction of airfoil data. Various theories for aerodynamically optimum rotors are discussed, and recent results on classical models are presented. State-of-the-art advanced numerical simulation tools for wind turbine rotors and wakes are reviewed, including rotor predictions as well as models for simulating wind turbine wakes and flows in wind farms.

Sørensen, Jens Nørkær

2011-01-01

2

Performance characteristics of aerodynamically optimum turbines for wind energy generators

NASA Technical Reports Server (NTRS)

This paper presents a brief discussion of the aerodynamic methodology for wind energy generator turbines, an approach to the design of aerodynamically optimum wind turbines covering a broad range of design parameters, some insight on the effect on performance of nonoptimum blade shapes which may represent lower fabrication costs, the annual wind turbine energy for a family of optimum wind turbines, and areas of needed research. On the basis of the investigation, it is concluded that optimum wind turbines show high performance over a wide range of design velocity ratios; that structural requirements impose constraints on blade geometry; that variable pitch wind turbines provide excellent power regulation and that annual energy output is insensitive to design rpm and solidity of optimum wind turbines.

Rohrbach, C.; Worobel, R.

1975-01-01

3

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

4

Aerodynamics/ACEE: Aircraft energy efficiency

NASA Technical Reports Server (NTRS)

An overview is presented of a 10 year program managed by NASA which seeks to make possible the most efficient use of energy for aircraft propulsion and lift as well as provide a technology that can be used by U.S. manufacturers of air transports and engines. Supercritical wings, winglets, vortex drag reduction, high lift, active control, laminar flow control, and aerodynamics by computer are among the topics discussed. Wind tunnel models in flight verification of advanced technology, and the design, construction and testing of various aircraft structures are also described.

1981-01-01

5

Aerodynamic Drag and Drag Reduction: Energy and Energy Savings (Invited).

National Technical Information Service (NTIS)

An assessment of the role of fluid dynamic resistance and/or aerodynamic drag and the relationship to energy use in the United States is presented. Existing data indicates that up to 25% of the total energy consumed in the United States is used to overcom...

R. M. Wood

2003-01-01

6

Resonance versus aerodynamics for energy savings in agile natural flyers

NASA Astrophysics Data System (ADS)

Insects are the most diverse natural flyers in nature, being able to hover and perform agile manoeuvres. Dragon- flies in particular are aggressive flyers, attaining accelerations of up to 4g. Flight in all insects requires demanding aerodynamic and inertial loads be overcome. It has been proposed that resonance is a primary mechanism for reducing energy costs associated with flapping flight, by storing energy in an elastic thorax and releasing it on the following half-stroke. Certainly in insect flight motors dominated by inertial loads, such a mechanism would be extremely beneficial. However in highly manoeuvrable, aerodynamically dominated flyers, such as the dragonfly, the use of elastic storage members requires further investigation. We show that employing resonant mechanisms in a real world configuration produces minimal energy savings that are further reduced by 50 to 133% across the operational flapping frequency band of the dragonfly. Using a simple harmonic oscillator analysis to represent the dynamics of a dragonfly, we further demonstrate a reduction in manoeuvring limits of ˜1.5 times for a system employing elastic mechanisms. This is in contrast to the potential power reductions of ?2/2 from regulating aerodynamics via active wing articulation. Aerodynamic means of energy storage provides flexibility between an energy efficient hover state and a manoeuvrable state capable of large accelerations. We conclude that active wing articulation is preferable to resonance for aerodynamically dominated natural flyers.

Kok, Jia M.; Chahl, Javaan

2014-03-01

7

High speed propeller acoustics and aerodynamics - A boundary element approach

NASA Technical Reports Server (NTRS)

The Boundary Element Method (BEM) is applied in this paper to the problems of acoustics and aerodynamics of high speed propellers. The underlying theory is described based on the linearized Ffowcs Williams-Hawkings equation. The surface pressure on the blade is assumed unknown in the aerodynamic problem. It is obtained by solving a singular integral equation. The acoustic problem is then solved by moving the field point inside the fluid medium and evaluating some surface and line integrals. Thus the BEM provides a powerful technique in calculation of high speed propeller aerodynamics and acoustics.

Farassat, F.; Myers, M. K.; Dunn, M. H.

1989-01-01

8

National Technical Information Service (NTIS)

A simple matrix polynomial approach is introduced for approximating unsteady aerodynamics in the s-plane and ultimately, after combining matrix polynomial coefficients with matrices defining the structure, a matrix polynomial of the flutter equations of m...

A. S. Pototzky

2008-01-01

9

NASA Technical Reports Server (NTRS)

The aerodynamic energy method is used to synthesize control laws for NASA's drone for aerodynamic and structural testing-aerodynamic research wing 1 (DAST-ARW1) mathematical model. The performance of these control laws in terms of closed-loop flutter dynamic pressure, control surface activity, and robustness is compared with other control laws that relate to the same model. A control law synthesis technique that makes use of the return difference singular values is developed. It is based on the aerodynamic energy approach and is shown to yield results that are superior to those results given in the literature and are based on optimal control theory. Nyquist plots are presented, together with a short discussion regarding the relative merits of the minimum singular value as a measure of robustness as compared with the more traditional measure involving phase and gain margins.

Nissim, Eli

1990-01-01

10

Aerodynamics/ACEE: Aircraft Energy Efficiency.

National Technical Information Service (NTIS)

An overview is presented of a 10 year program managed by NASA which seeks to make possible the most efficient use of energy for aircraft propulsion and lift as well as provide a technology that can be used by U.S. manufacturers of air transports and engin...

1981-01-01

11

Optimal cycling time trial position models: Aerodynamics versus power output and metabolic energy.

The aerodynamic drag of a cyclist in time trial (TT) position is strongly influenced by the torso angle. While decreasing the torso angle reduces the drag, it limits the physiological functioning of the cyclist. Therefore the aims of this study were to predict the optimal TT cycling position as function of the cycling speed and to determine at which speed the aerodynamic power losses start to dominate. Two models were developed to determine the optimal torso angle: a 'Metabolic Energy Model' and a 'Power Output Model'. The Metabolic Energy Model minimised the required cycling energy expenditure, while the Power Output Model maximised the cyclists? power output. The input parameters were experimentally collected from 19 TT cyclists at different torso angle positions (0-24°). The results showed that for both models, the optimal torso angle depends strongly on the cycling speed, with decreasing torso angles at increasing speeds. The aerodynamic losses outweigh the power losses at cycling speeds above 46km/h. However, a fully horizontal torso is not optimal. For speeds below 30km/h, it is beneficial to ride in a more upright TT position. The two model outputs were not completely similar, due to the different model approaches. The Metabolic Energy Model could be applied for endurance events, while the Power Output Model is more suitable in sprinting or in variable conditions (wind, undulating course, etc.). It is suggested that despite some limitations, the models give valuable information about improving the cycling performance by optimising the TT cycling position. PMID:24726654

Fintelman, D M; Sterling, M; Hemida, H; Li, F-X

2014-06-01

12

Energy harvesting under combined aerodynamic and base excitations

NASA Astrophysics Data System (ADS)

This paper investigates the transduction of a piezoaeroelastic energy harvester under the combination of vibratory base excitations and aerodynamic loadings. The harvester which consists of a rigid airfoil supported by nonlinear flexural and torsional springs is placed in an incompressible air flow and subjected to a harmonic base excitation in the plunge direction. Under this combined loading, the airfoil undergoes complex motions which strain a piezoelectric element producing a voltage across an electric load. To capture the qualitative behavior of the harvester, a five-dimensional lumped-parameter model which adopts nonlinear quasi-steady aerodynamics is used. A center manifold reduction is implemented to reduce the full model into one nonlinear first-order ordinary differential equation. The normal form of the reduced system is then derived to study slow modulation of the response amplitude and phase near the flutter instability. Below the flutter speed, the response of the harvester is observed to be always periodic with the air flow serving to amplify the influence of the base excitation on the response by reducing the effective stiffness of the system, and hence, increasing the RMS output power. Beyond the flutter speed, two distinct regions are observed. The first occurs when the base excitation is small and/or when the excitation frequency is not close to the frequency of the self-sustained oscillations induced by the flutter instability. In this case, the response of the harvester is two-period quasiperiodic with amplitude modulation due to the presence of two incommensurate frequencies in the response. This amplitude modulation reduces the RMS output power. In the second region, the amplitude of excitation is large enough to eliminate the quasiperiodic response by causing the two frequencies to lock into each other. In this region, the response becomes periodic and the output power increases exhibiting little dependence on the base excitation.

Bibo, Amin; Daqaq, Mohammed F.

2013-09-01

13

A new approach to optimization for aerodynamic applications

NASA Technical Reports Server (NTRS)

A new approach to solving optimization problems that involve nonlinear partial differential equations is presented. The approach eliminates the need for an inner-outer iterative procedure, solving the partial differential equation only once, thereby reducing the cost of computation to an extent which would allow its use as a practical tool in optimization problems. The approach is tested on a single design parameter problem through the use of a specially developed scheme. The results indicate comparable convergence properties for the present iterative process and the standard iterative scheme. The presented ideas are also applicable to multidesign parameter problems.

Rizk, M. H.

1983-01-01

14

Aerodynamics of trans-atmopsheric vehicles : a non-dimensional approach

NASA Technical Reports Server (NTRS)

The non-dimensional approach to aerodynamics of trans-atmospheric flight is discussed, which explicitly takes into account the vertical span of the atmosphere as well as atmospheric mass load (atmospheric pressure) at the current flight level. As an example, a simple analytic model of the dynamics of trans-atmospheric flight is considered for both powered boost and non-powered glide of a trans-atmospheric vehicle, and the applicability to more general, numerical models of atmospheric flight is discussed.

Ustinov, Eugene A.

2005-01-01

15

NASA Technical Reports Server (NTRS)

A simple matrix polynomial approach is introduced for approximating unsteady aerodynamics in the s-plane and ultimately, after combining matrix polynomial coefficients with matrices defining the structure, a matrix polynomial of the flutter equations of motion (EOM) is formed. A technique of recasting the matrix-polynomial form of the flutter EOM into a first order form is also presented that can be used to determine the eigenvalues near the origin and everywhere on the complex plane. An aeroservoelastic (ASE) EOM have been generalized to include the gust terms on the right-hand side. The reasons for developing the new matrix polynomial approach are also presented, which are the following: first, the "workhorse" methods such as the NASTRAN flutter analysis lack the capability to consistently find roots near the origin, along the real axis or accurately find roots farther away from the imaginary axis of the complex plane; and, second, the existing s-plane methods, such as the Roger s s-plane approximation method as implemented in ISAC, do not always give suitable fits of some tabular data of the unsteady aerodynamics. A method available in MATLAB is introduced that will accurately fit generalized aerodynamic force (GAF) coefficients in a tabular data form into the coefficients of a matrix polynomial form. The root-locus results from the NASTRAN pknl flutter analysis, the ISAC-Roger's s-plane method and the present matrix polynomial method are presented and compared for accuracy and for the number and locations of roots.

Pototzky, Anthony S.

2008-01-01

16

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

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.

Nakata, Toshiyuki; Liu, Hao

2012-01-01

17

NASA Astrophysics Data System (ADS)

Dispersion of bulk powders is important for a number of technological applications such as particle characterisation, and drug delivery through lungs using dry powder inhalers (DPIs). Over the last decade, the analysis of dynamics of particle-fluid systems using the distinct element method (DEM), coupled with continuum models for the fluid phase, has received much attention. In this paper these computational techniques are used to investigate the aerodynamic dispersion of loose aggregates of cohesive powders in a uniform flow field. As intuitively expected, with an increase in particle surface energy, hence bond strength, it is progressively more difficult to disperse loose aggregates. However, once the relative particle-fluid velocity goes beyond a threshold, dispersion occurs readily and approaches a completely dispersed state asymptotically. A mechanistic analysis, based on a balance between the external forces, including the fluid drag acting on a spherical aggregate and the bonding force given by the well-established JKR model, leads to a dimensionless group which includes the Weber number. It is shown that the effect of surface energy on loose aggregate behaviour can be described by the above dimensionless group.

Calvert, G.; Hassanpour, A.; Ghadiri, M.

2009-06-01

18

NASA Technical Reports Server (NTRS)

Previous wind tunnel tests of fighter configurations have shown that thrust reverser jets can induce large, unsteady aerodynamic forces and moments during operation in ground proximity. This is a concern for STOL configurations using partial reversing to spoil the thrust while keeping the engine output near military (MIL) power during landing approach. A novel test technique to simulate approach and landing was developed under a cooperative Northrop/NASA/USAF program. The NASA LaRC Vortex Research Facility was used for the experiments in which a 7-percent F-18 model was moved horizontally at speeds of up to 100 feet per second over a ramp simulating an aircraft to ground rate of closure similar to a no-flare STOL approach and landing. This paper presents an analysis of data showing the effect of reverser jet orientation and jet dynamic pressure ratio on the transient forces for different angles of attack, and flap and horizontal tail deflection. It was found, for reverser jets acting parallel to the plane of symmetry, that the jets interacted strongly with the ground, starting approximately half a span above the ground board. Unsteady rolling moment transients, large enough to cause the probable upset of an aircraft, and strong normal force and pitching moment transients were measured. For jets directed 40 degrees outboard, the transients were similar to the jet-off case, implying only minor interaction.

Humphreys, A. P.; Paulson, J. W., Jr.; Kemmerly, G. T.

1988-01-01

19

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

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

2012-02-22

20

Optimal shape design of aerodynamic configurations: A Newton-Krylov approach

Optimal shape design of aerodynamic configurations is a challenging problem due to the nonlinear effects of complex flow features such as shock waves, boundary layers, and separation. A Newton-Krylov algorithm is presented for aerodynamic design using gradient-based numerical optimization. The flow is governed by the two-dimensional compressible Navier-Stokes equations in conjunction with a one-equation turbulence model, which are discretized on

Marian Nemec

2003-01-01

21

Uncertainty in Computational Aerodynamics

NASA Technical Reports Server (NTRS)

An approach is presented to treat computational aerodynamics as a process, subject to the fundamental quality assurance principles of process control and process improvement. We consider several aspects affecting uncertainty for the computational aerodynamic process and present a set of stages to determine the level of management required to meet risk assumptions desired by the customer of the predictions.

Luckring, J. M.; Hemsch, M. J.; Morrison, J. H.

2003-01-01

22

NASA Technical Reports Server (NTRS)

This paper describes an integrated aerodynamic, dynamic, and structural (IADS) optimization procedure for helicopter rotor blades. The procedure combines performance, dynamics, and structural analyses with a general purpose optimizer using multilevel decomposition techniques. At the upper level, the structure is defined in terms of local quantities (stiffnesses, mass, and average strains). At the lower level, the structure is defined in terms of local quantities (detailed dimensions of the blade structure and stresses). The IADS procedure provides an optimization technique that is compatible with industrial design practices in which the aerodynamic and dynamic design is performed at a global level and the structural design is carried out at a detailed level with considerable dialogue and compromise among the aerodynamic, dynamic, and structural groups. The IADS procedure is demonstrated for several cases.

Walsh, Joanne L.; Young, Katherine C.; Pritchard, Jocelyn I.; Adelman, Howard M.; Mantay, Wayne R.

1994-01-01

23

NASA Technical Reports Server (NTRS)

A computer program written to calculate the proximity aerodynamic force and moment coefficients of the Orbiter/Shuttle Carrier Aircraft (SCA) vehicles based on flight instrumentation is described. The ground reduced aerodynamic coefficients and instrumentation errors (GRACIE) program was developed as a tool to aid in flight test verification of the Orbiter/SCA separation aerodynamic data base. The program calculates the force and moment coefficients of each vehicle in proximity to the other, using the load measurement system data, flight instrumentation data and the vehicle mass properties. The uncertainty in each coefficient is determined, based on the quoted instrumentation accuracies. A subroutine manipulates the Orbiter/747 Carrier Separation Aerodynamic Data Book to calculate a comparable set of predicted coefficients for comparison to the calculated flight test data.

Homan, D. J.

1977-01-01

24

Intelligent aerodynamic\\/propulsion flight control for flight safety: a nonlinear adaptive approach

This paper presents an intelligent fault tolerant flight control system that blends aerodynamic and propulsion actuation for safe flight operation in the presence of actuator failures. Fault tolerance is obtained by a nonlinear adaptive control strategy based on on-line learning neural networks and actuator reallocation scheme. The adaptive control block incorporates a recently developed technique for adaptation in the presence

Moshe Idan; Matthew Johnson; Anthony J. Calise; John Kaneshige

2001-01-01

25

Traditionally, aeropropulsion structural performance and aerodynamic performance have been designed separately and later mated together via flight testing. In today`s atmosphere of declining resources, it is imperative that more productive ways of designing and verifying aeropropulsion performance and structural interaction be made available to the aerospace industry. One method of obtaining a more productive design and evaluation capability is through the use of numerical simulations. Currently, Lawrence Livermore National Laboratory has developed a generalized fluid/structural interaction code known as ALE3D. This code is capable of characterizing fluid and structural interaction for components such as the combustor, fan/stators, inlet and/or nozzles. This code solves the 3D Euler equations and has been applied to several aeropropulsion applications such as a supersonic inlet and a combustor rupture simulation. To characterize aerodynamic-structural interaction for rotating components such as the compressor, appropriate turbomachinery simulations would need to be implemented within the ALE3D structure. The Arnold Engineering Development Center is currently developing a three-dimensional compression system code known as TEACC (Turbine Engine Analysis Compressor Code). TEACC also solves the 3D Euler equations and is intended to simulate dynamic behavior such as inlet distortion, surge or rotating stall. The technology being developed within the TEACC effort provides the necessary turbomachinery simulation for implementation into ALE3D. This paper describes a methodology to combine three-dimensional aerodynamic turbomachinery technology into the existing aerodynamic-structural interaction simulation, ALE3D to obtain the desired aerodynamic and structural integrated simulation for an aeropropulsion system.

Naziar, J. [Boeing Commerical Airplane Group, Seattle, WA (United States). Propulsion Research; Couch, R. [Lawrence Livermore National Lab., CA (United States); Davis, M. [Sverdrup Technology, Inc., Arnold Air Force Base, TN (United States). Arnold Engineering Development Center

1996-01-01

26

Laboratory evaluation of fan/filter units' aerodynamic and energy performance

The paper discusses the benefits of having a consistent testing method to characterize aerodynamic and energy performance of FFUs. It presents evaluation methods of laboratory-measured performance of ten relatively new, 1220 mm x 610 mm (or 4 ft x 2 ft) fan-filter units (FFUs), and includes results of a set of relevant metrics such as energy performance indices (EPI) based upon the sample FFUs tested. This paper concludes that there are variations in FFUs' performance, and that using a consistent testing and evaluation method can generate compatible and comparable FFU performance information. The paper also suggests that benefits and opportunities exist for our method of testing FFU energy performance to be integrated in future recommended practices.

Xu, Tengfang; Jeng, Ming-Shan

2004-07-27

27

NASA Astrophysics Data System (ADS)

The aerodynamic forces on a stay cable under a rain-wind induced vibration (RWIV) are difficult to measure directly in a wind tunnel test. This paper presents a hybrid approach that combines an experiment with computational fluid dynamics (CFD) for the investigation on aerodynamic forces of a stay cable under a RWIV. The stay cable and flow field were considered as two substructures of the system. The oscillation of the stay cable was first measured by using a wind tunnel test of a RWIV under an artificial rainfall condition. The oscillation of the cable was treated as a previously known moving boundary condition and applied to the flow field. Only the flow field with the known moving cable boundary was then numerically simulated by using a CFD method (such as Fluent 6.3). The transient aerodynamic forces of the stay cable with a predetermined cable oscillation were obtained from numerical calculations. The characteristics of the aerodynamic forces in the time domain and frequency domain were then analysed for various cases. To verify the feasibility and accuracy of the proposed hybrid approach, the transient aerodynamic forces were applied to a single-degree-of-freedom model (SDOF) of the stay cable to calculate the RWIV of the cable. A comparison was performed between the oscillation responses of the stay cable obtained from the calculated (SDOF model) and experimental results, and the results indicate that the hybrid approach accurately simulates the transient aerodynamic forces of the stay cable. The equivalent damping ratios induced by the aerodynamic forces were obtained for various wind speeds. Furthermore, a nonlinear model of the aerodynamic force is proposed based on the calculation results, and the coefficients in the model were identified by a nonlinear least-squares technique.

Li, Hui; Chen, Wen-Li; Xu, Feng; Li, Feng-Chen; Ou, Jin-Ping

2010-10-01

28

NASA Technical Reports Server (NTRS)

Bifurcation theory is used to analyze the nonlinear dynamic stability characteristics of an aircraft subject to single-degree-of-freedom. The requisite moment of the aerodynamic forces in the equations of motion is shown to be representable in a form equivalent to the response to finite amplitude oscillations. It is shown how this information can be deduced from the case of infinitesimal-amplitude oscillations. The bifurcation theory analysis reveals that when the bifurcation parameter is increased beyond a critical value at which the aerodynamic damping vanishes, new solutions representing finite amplitude periodic motions bifurcate from the previously stable steady motion. The sign of a simple criterion, cast in terms of aerodynamic properties, determines whether the bifurcating solutions are stable or unstable. For the pitching motion of flat-plate airfoils flying at supersonic/hypersonic speed and for oscillation of flaps at transonic speed, the bifurcation is subcritical, implying either the exchanges of stability between steady and periodic motion are accompanied by hysteresis phenomena, or that potentially large aperiodic departures from steady motion may develop.

Hui, W. H.

1985-01-01

29

Comparison of Computational Approaches for Rapid Aerodynamic Assessment of Small UAVs

NASA Technical Reports Server (NTRS)

Computational Fluid Dynamic (CFD) methods were used to determine the basic aerodynamic, performance, and stability and control characteristics of the unmanned air vehicle (UAV), Kahu. Accurate and timely prediction of the aerodynamic characteristics of small UAVs is an essential part of military system acquisition and air-worthiness evaluations. The forces and moments of the UAV were predicted using a variety of analytical methods for a range of configurations and conditions. The methods included Navier Stokes (N-S) flow solvers (USM3D, Kestrel and Cobalt) that take days to set up and hours to converge on a single solution; potential flow methods (PMARC, LSAERO, and XFLR5) that take hours to set up and minutes to compute; empirical methods (Datcom) that involve table lookups and produce a solution quickly; and handbook calculations. A preliminary aerodynamic database can be developed very efficiently by using a combination of computational tools. The database can be generated with low-order and empirical methods in linear regions, then replacing or adjusting the data as predictions from higher order methods are obtained. A comparison of results from all the data sources as well as experimental data obtained from a wind-tunnel test will be shown and the methods will be evaluated on their utility during each portion of the flight envelope.

Shafer, Theresa C.; Lynch, C. Eric; Viken, Sally A.; Favaregh, Noah; Zeune, Cale; Williams, Nathan; Dansie, Jonathan

2014-01-01

30

NASA Technical Reports Server (NTRS)

The NASA Ames Research Center (ARC) Arc Jet Facilities' Aerodynamic Heating Facility (AHF) has been instrumented for the Enthalpy By Energy Balance (EB2) method. Diagnostic EB2 data is routinely taken for all AHF runs. This paper provides an overview of the EB2 method implemented in the AHF. The chief advantage of the AHF implementation over earlier versions is the non-intrusiveness of the instruments used. For example, to measure the change in cooling water temperature, thin film 1000 ohm Resistance Temperature Detectors (RTDs) are used with an Anderson Current Loop (ACL) as the signal conditioner. The ACL with 1000 ohm RTDs allows for very sensitive measurement of the increase in temperature (Delta T) of the cooling water to the arc heater, which is a critical element of the EB2 method. Cooling water flow rates are measured with non-intrusive ultrasonic flow meters.

Hightower, T. Mark; MacDonald, Christine L.; Martinez, Edward R.; Balboni, John A.; Anderson, Karl F.; Arnold, Jim O. (Technical Monitor)

2002-01-01

31

NASA Technical Reports Server (NTRS)

Aerodynamic developments for vertical axis and horizontal axis wind turbines are given that relate to the performance and aerodynamic loading of these machines. Included are: (1) a fixed wake aerodynamic model of the Darrieus vertical axis wind turbine; (2) experimental results that suggest the existence of a laminar flow Darrieus vertical axis turbine; (3) a simple aerodynamic model for the turbulent windmill/vortex ring state of horizontal axis rotors; and (4) a yawing moment of a rigid hub horizontal axis wind turbine that is related to blade coning.

Wilson, R. E.

1981-01-01

32

A Newton-Krylov Approach to Aerodynamic Shape Optimization in Three Dimensions

NASA Astrophysics Data System (ADS)

A Newton-Krylov algorithm is presented for aerodynamic shape optimization in three dimensions using the Euler equations. An inexact-Newton method is used in the flow solver, a discrete-adjoint method to compute the gradient, and the quasi-Newton optimizer to find the optimum. A Krylov subspace method with approximate-Schur preconditioning is used to solve both the flow equation and the adjoint equation. Basis spline surfaces are used to parameterize the geometry, and a fast algebraic algorithm is used for grid movement. Accurate discrete- adjoint gradients can be obtained in approximately one-fourth the time required for a converged flow solution. Single- and multi-point lift-constrained drag minimization optimization cases are presented for wing design at transonic speeds. In all cases, the optimizer is able to efficiently decrease the objective function and gradient for problems with hundreds of design variables.

Leung, Timothy Man-Ming

33

Coupled flow, thermal and structural analysis of aerodynamically heated panels

NASA Technical Reports Server (NTRS)

A finite element approach to coupling flow, thermal and structural analyses of aerodynamically heated panels is presented. The Navier-Stokes equations for laminar compressible flow are solved together with the energy equation and quasi-static structural equations of the panel. Interactions between the flow, panel heat transfer and deformations are studied for thin stainless steel panels aerodynamically heated by Mach 6.6 flow.

Thornton, Earl A.; Dechaumphai, Pramote

1986-01-01

34

Uncertainty-Based Approach for Dynamic Aerodynamic Data Acquisition and Analysis

NASA Technical Reports Server (NTRS)

Development of improved modeling methods to provide increased fidelity of flight predictions for aircraft motions during flight in flow regimes with large nonlinearities requires improvements in test techniques for measuring and characterizing wind tunnel data. This paper presents a method for providing a measure of data integrity for static and forced oscillation test techniques. Data integrity is particularly important when attempting to accurately model and predict flight of today s high performance aircraft which are operating in expanded flight envelopes, often maneuvering at high angular rates at high angles-of-attack, even above maximum lift. Current aerodynamic models are inadequate in predicting flight characteristics in the expanded envelope, such as rapid aircraft departures and other unusual motions. Present wind tunnel test methods do not factor changes of flow physics into data acquisition schemes, so in many cases data are obtained over more iterations than required, or insufficient data may be obtained to determine a valid estimate with statistical significance. Additionally, forced oscillation test techniques, one of the primary tools used to develop dynamic models, do not currently provide estimates of the uncertainty of the results during an oscillation cycle. A method to optimize the required number of forced oscillation cycles based on decay of uncertainty gradients and balance tolerances is also presented.

Heim, Eugene H. D.; Bandon, Jay M.

2004-01-01

35

Free Wake Analysis of Wind Turbine Aerodynamics. Wind Energy Conversion. ASRL-TR-184-14.

National Technical Information Service (NTIS)

The underlying theory is presented for determining blade and rotor/tower vibration and dynamic stability characteristics as well as the basic dynamic (as opposed to aerodynamic) operating loads. Starting with a simple concept of equivalent hinged rotors, ...

J. C. Gohard

1978-01-01

36

Wing shape allometry and aerodynamics in calopterygid damselflies: a comparative approach

Background Wing size and shape have important aerodynamic implications on flight performance. We explored how wing size was related to wing shape in territorial males of 37 taxa of the damselfly family Calopterygidae. Wing coloration was also included in the analyses because it is sexually and naturally selected and has been shown to be related to wing shape. We studied wing shape using both the non-dimensional radius of the second moment of wing area (RSM) and geometric morphometrics. Lower values of the RSM result in less energetically demanding flight and wider ranges of flight speed. We also re-analyzed previously published data on other damselflies and dragonflies. Results The RSM showed a hump-shaped relationship with wing size. However, after correcting for phylogeny using independent contrast, this pattern changed to a negative linear relationship. The basal genus of the study family, Hetaerina, was mainly driving that change. The obtained patterns were specific for the study family and differed from other damselflies and dragonflies. The relationship between the RSM and wing shape measured by geometric morphometrics was linear, but relatively small changes along the RSM axis can result in large changes in wing shape. Our results also showed that wing coloration may have some effect on RSM. Conclusions We found that RSM showed a complex relationship with size in calopterygid damselflies, probably as a result of other selection pressures besides wing size per se. Wing coloration and specific behavior (e.g. courtship) are potential candidates for explaining the complexity. Univariate measures of wing shape such as RSM are more intuitive but lack the high resolution of other multivariate techniques such as geometric morphometrics. We suggest that the relationship between wing shape and size are taxa-specific and differ among closely-related insect groups.

2013-01-01

37

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

38

Aerodynamics of Trans-Atmospheric Vehicles: A Non-Dimensional Approach

NASA Technical Reports Server (NTRS)

A novel non-dimensional approach to flight dynamics of a trans-atmospheric vehicle is proposed. This approach explicitly takes into account the vertical span of the atmosphere (atmospheric scale height) as well as atmospheric mass load (atmospheric pressure) at the given flight level. As an example of application of this approach, a simple analytic model of the flight dynamics is considered for the powered boost and non-powered glide of a trans-atmospheric vehicle.

Ustinov, Eugene A.

2006-01-01

39

Aerodynamic optimization of railway motor coaches

The rapid development of very high speed trains and the increasing operational speeds of conventional passenger and freight rolling stock are the cause of a growing interest in railways aerodynamics. Environmental issues, comfort demands and reduction of energy consumption are the key points to which aerodynamic improvements can largely contribute. Railways aerodynamics has to be performed on the complete system

E. Lorriaux; N. Bourabaa; F. Monnoyer

40

NASA Technical Reports Server (NTRS)

The static aeroelastic effects on the longitudinal stability and elevon/aileron effectiveness of the space transportation system (STS) Space Shuttle orbiter were estimated by a simplified approach called the elevon torsional stiffness (ETS) method. This method employs rigid model wind tunnel test results to predict aeroelastic effects. Lateral/directional stability and rudder effectiveness were based on results of a wind tunnel test in which a flexible tail model was used. Comparisons with selective flight data are made in this paper. Results of correlations with flight data (although limited at the present time) verify the predicted aeroelastic effects for the orbiter. The orbiter's structural characteristics are such that the effects of aeroelasticity, whether estimated using analytical techniques or simplified methods, do not appear to affect the vehicle performance to any great extent. The large amount of scatter in the flight-extracted data made verification of the aeroelastic corrections very difficult. Generally, the simplified elevon torsional stiffness method provided better correlation with flight test results than he analytical method and reduced the verification effort and cost.

Schlosser, D. C.; Dominik, D. F.

1983-01-01

41

Comparison of taut-strip and section-model-based approaches in long-span bridge aerodynamics

This paper describes an attempt to predict the behavior of a taut-tube model of a bridge of the Golden Gate type, using the flutter derivatives for the deck section, the steady aerodynamic coefficients, information about the wind tunnel turbulence, and the mechanical properties of the taut-tube model.

Robert H. Scanlan; Nicholas P. Jones; Olivier Lorendeaux

1997-01-01

42

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

43

Horizontal Axis Wind Turbine Blade Aerodynamics in Experiments and Modeling

Turbine aerodynamics remains a challenging and crucial research area for wind energy. Blade aerodynamic forces responsible for power production must be augmented to maximize energy capture. At the same time, adverse aerodynamic loads that fatigue turbine components need to be mitigated to extend machine service life. Successful resolution of these conflicting demands and continued cost of energy reduction require accurate

Scott J. Schreck; Michael C. Robinson

2007-01-01

44

NSDL National Science Digital Library

This web page describes current research about insect flight dynamics. It focuses on the work of biologist R. McNeill Alexander of the University of Leeds, whose research team has built large-scale models of insects to test their flight aerodynamics in wind tunnels. At the bottom of the page is a small (160 x 120) QuickTime video of a Morpho butterfly (Order Lepidoptera, Family Nymphalidae) with detailed views of its wing scales. It is an excerpt from the Alien Empire miniseries of the Public Broadcasting Service's Nature series. The video requires QuickTime and may not be accessible to those with older or slow computers. The link to the "enhanced multimedia video clip" did not work at the time of this review.

0002-11-30

45

Aerodynamic design of electric and hybrid vehicles: A guidebook

NASA Technical Reports Server (NTRS)

A typical present-day subcompact electric hybrid vehicle (EHV), operating on an SAE J227a D driving cycle, consumes up to 35% of its road energy requirement overcoming aerodynamic resistance. The application of an integrated system design approach, where drag reduction is an important design parameter, can increase the cycle range by more than 15%. This guidebook highlights a logic strategy for including aerodynamic drag reduction in the design of electric and hybrid vehicles to the degree appropriate to the mission requirements. Backup information and procedures are included in order to implement the strategy. Elements of the procedure are based on extensive wind tunnel tests involving generic subscale models and full-scale prototype EHVs. The user need not have any previous aerodynamic background. By necessity, the procedure utilizes many generic approximations and assumptions resulting in various levels of uncertainty. Dealing with these uncertainties, however, is a key feature of the strategy.

Kurtz, D. W.

1980-01-01

46

Aerodynamics of Horizontal Axis Wind Turbines

\\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

47

Development in aerodynamic calculations

NASA Astrophysics Data System (ADS)

An unsteady aerodynamics models for simulating large wind energy converters is described. For the attached flow region the loads are calculated via a generalized indicial lift function based on the Wagner function. The angle of attack is defined at the 3/4 chord location and thus pitching velocity and virtual mass terms are included. Leading edge stall is incorporated by a simple time delay based on distance travelled in semichord. Trailing edge stall is incorporated via Kirchhoff's law and two first order lags. Time domain simulation of single point power spectra of velocity fluctuations, and coherence function estimates are compared with measurements.

Anderson, M. B.

1985-03-01

48

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

2010-08-26

49

NASA Technical Reports Server (NTRS)

Presented here is a comprehensive review of the following aerodynamics elements: computational methods and applications, computational fluid dynamics (CFD) validation, transition and turbulence physics, numerical aerodynamic simulation, drag reduction, test techniques and instrumentation, configuration aerodynamics, aeroacoustics, aerothermodynamics, hypersonics, subsonic transport/commuter aviation, fighter/attack aircraft and rotorcraft.

Holmes, Bruce J.; Schairer, Edward; Hicks, Gary; Wander, Stephen; Blankson, Isiaiah; Rose, Raymond; Olson, Lawrence; Unger, George

1990-01-01

50

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

51

Bifurcations in unsteady aerodynamics

NASA Technical Reports Server (NTRS)

Nonlinear algebraic functional expansions are used to create a form for the unsteady aerodynamic response that is consistent with solutions of the time dependent Navier-Stokes equations. An enumeration of means of invalidating Frechet differentiability of the aerodynamic response, one of which is aerodynamic bifurcation, is proposed as a way of classifying steady and unsteady aerodynamic phenomena that are important in flight dynamics applications. Accomodating bifurcation phenomena involving time dependent equilibrium states within a mathematical model of the aerodynamic response raises an issue of memory effects that becomes more important with each successive bifurcation.

Tobak, M.; Unal, A.

1986-01-01

52

Supersonic aerodynamic performance of truncated cones with repetitive laser pulse energy depositions

NASA Astrophysics Data System (ADS)

We investigate the drag characteristics of truncated cones in Mach 1.94 flow with repetitive laser pulse energy depositions with a frequency of up to 80 kHz. The drag decrement is almost in proportion to the laser pulse repetition frequency, and scales with a greater-than-square power of the truncation diameter. The performance of the latter is associated with the effective area of pressure modulation and the effective residence time of vortices which are baroclinically generated after the interaction between laser-heated gas bubbles and the bow shock wave. With employing a concave head, the drag decrement is enhanced. With increasing the truncation diameter, the efficiency of energy deposition becomes higher; yet, within the operation range of this study the drag coefficient still remains high.

Sasoh, A.; Kim, J.-H.; Yamashita, K.; Sakai, T.

2014-01-01

53

Effect of concentrated energy deposition on the aerodynamic drag of a blunt body in hypersonic flow

NASA Astrophysics Data System (ADS)

Experimental results on the effect of energy deposition using an electric arc discharge, upstream of a 60° half angle blunt cone configuration in a hypersonic flow stream is reported. Investigations involving drag measurements and high speed Schlieren flow visualization have been carried out in a hypersonic shock tunnel using air and argon as the test gases; and an unsteady drag reduction of about 50% (maximum reduction) has been observed in the energy deposition experiments done in argon environment. These studies also show that the effect of discharge on the flow field is more pronounced in argon environment as compared to air, which confirms that thermal effects are mainly responsible for flow alteration with discharge. It has also been observed that the interaction of the hypersonic flow with the discharge filament results in the development of an unsteady flow field.

Satheesh, K.; Jagadeesh, G.

2007-03-01

54

Nonpotential Aerodynamics for Windmills in Shear Wind.

National Technical Information Service (NTIS)

Several project goals are included in this report: (1) development of a formulation and computer program for a lifting surface aerodynamic analysis of Wind Energy Conversion Systems (WECS); (2) development of a formulation and computer program for a compl...

L. Morino

1975-01-01

55

Aerodynamic response analysis of wind turbines

Wind energy has received increasing attention in the same way as energy crisis and environmental deterioration. The aerodynamic\\u000a response of wind turbines is the major problem in wind turbine design. Blade element momentum theory was used to study the\\u000a aerodynamic thrusts of the blades on the tower. Iterative solutions were used to calculate the axial flow induction factor\\u000a for each

Jing Li; Jianyun Chen; Xiaobo Chen

2011-01-01

56

Reciprocity relations in aerodynamics

NASA Technical Reports Server (NTRS)

Reverse flow theorems in aerodynamics are shown to be based on the same general concepts involved in many reciprocity theorems in the physical sciences. Reciprocal theorems for both steady and unsteady motion are found as a logical consequence of this approach. No restrictions on wing plan form or flight Mach number are made beyond those required in linearized compressible-flow analysis. A number of examples are listed, including general integral theorems for lifting, rolling, and pitching wings and for wings in nonuniform downwash fields. Correspondence is also established between the buildup of circulation with time of a wing starting impulsively from rest and the buildup of lift of the same wing moving in the reverse direction into a sharp-edged gust.

Heaslet, Max A; Spreiter, John R

1953-01-01

57

Modeling Powered Aerodynamics for the Orion Launch Abort Vehicle Aerodynamic Database

NASA Technical Reports Server (NTRS)

Modeling the aerodynamics of the Orion Launch Abort Vehicle (LAV) has presented many technical challenges to the developers of the Orion aerodynamic database. During a launch abort event, the aerodynamic environment around the LAV is very complex as multiple solid rocket plumes interact with each other and the vehicle. It is further complicated by vehicle separation events such as between the LAV and the launch vehicle stack or between the launch abort tower and the crew module. The aerodynamic database for the LAV was developed mainly from wind tunnel tests involving powered jet simulations of the rocket exhaust plumes, supported by computational fluid dynamic simulations. However, limitations in both methods have made it difficult to properly capture the aerodynamics of the LAV in experimental and numerical simulations. These limitations have also influenced decisions regarding the modeling and structure of the aerodynamic database for the LAV and led to compromises and creative solutions. Two database modeling approaches are presented in this paper (incremental aerodynamics and total aerodynamics), with examples showing strengths and weaknesses of each approach. In addition, the unique problems presented to the database developers by the large data space required for modeling a launch abort event illustrate the complexities of working with multi-dimensional data.

Chan, David T.; Walker, Eric L.; Robinson, Philip E.; Wilson, Thomas M.

2011-01-01

58

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

R. D. Mehta

1985-01-01

59

System Identification of a Vortex Lattice Aerodynamic Model

NASA Technical Reports Server (NTRS)

The state-space presentation of an aerodynamic vortex model is considered from a classical and system identification perspective. Using an aerodynamic vortex model as a numerical simulator of a wing tunnel experiment, both full state and limited state data or measurements are considered. Two possible approaches for system identification are presented and modal controllability and observability are also considered. The theory then is applied to the system identification of a flow over an aerodynamic delta wing and typical results are presented.

Juang, Jer-Nan; Kholodar, Denis; Dowell, Earl H.

2001-01-01

60

Response of aerospace structures to reentry aerodynamic excitation

NASA Technical Reports Server (NTRS)

A bibliography on aerodynamic excitation and associated structural response is presented. Very little applicable data under actual reentry conditions was found, but many wind tunnel tests and some in-flight data were. Aerodynamic excitation and proposed space shuttle configurations and reentry trajectories were studied. Attached turbulent boundary layer, separated turbulent boundary layer, and base pressure fluctuations are the region of aerodynamic excitation most applicable to exterior panels of space shuttle-type vehicles; prediction techniques are presented for these environments. Methods for predicting the response of panel structures to acoustic excitation were investigated. A normal mode approach was developed for the low frequency response and a statistical energy approach was utilized for the high frequency response. A finite element model was made of a thermal protective system test panel. Computer programs were used to determine the natural frequencies and mode shapes of the panel and to calculate the response of the panel to a reverberant acoustic field. Power spectral densities of response displacement and acceleration are presented.

Carlin, D., Jr.

1971-01-01

61

Aerodynamic characteristics in ground proximity

NASA Technical Reports Server (NTRS)

Results from recent investigations in the Langley V/STOL tunnel of an externally blown flap and an upper surface blown flap configuration in ground proximity are presented. Comparisons of longitudinal aerodynamic characteristics indicate that in ground proximity, drag is reduced for both configurations, but changes in lift are configuration dependent. Steady state analyses of the landing approach indicate an increase in flight path angle for both configurations in ground proximity because of the drag reduction. Dynamic analyses with a fixed-base simulator indicate that the resultant flight path during landing approach is dependent on the initial flight path angle and the control technique used.

Thomas, J. L.; Hassell, J. L., Jr.; Nguyen, L. T.

1976-01-01

62

NASA Astrophysics Data System (ADS)

The execution of the first phase agreement on wind energy projects, covering the period from 1986 to 1992, is summarized. The following are addressed: wind tunnel tests of a 2.2 m and 2.8 m diameter turbine, a 5.35 m turbine in stationary yaw operation, pressure measurements, wall interference correction, a 5.35 m diameter turbine under yaw control, visualization of the flow on the rotating blade. It was concluded that the yaw characteristics (including aerodynamic performance and control characteristics) and three dimensional flow of the wind turbine chosen as cooperation items have significant engineering application background and academic value. The results are applicable for medium as well as large size wind turbines and has a positive effect on the development of wind energy technology.

Dexin, He; Thor, Sven-Erik

1993-06-01

63

NSDL National Science Digital Library

Aerodynamics is the study of what makes things go fast, right? More specifically, itÃ¢ÂÂs 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 youÃ¢ÂÂve 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

64

Alternative approaches to energy modeling

The paper evaluates a number of models for the analysis of regional impacts of energy policies, which consider production and transportation costs, the location of reserves, and the demands for energy and nonenergy goods. The energy models, all of which consider more than one fuel and sector (i.e., residential, utility, etc.) are evaluated on the basis of three sets of

A. S. Cohen; K. W. Costello

1976-01-01

65

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.

Yaste, David M (NASA Ames Research Center, Moffet Field, CA); Salari, Kambiz (Lawrence Livermore National Laboratory, Livermore, CA); Hammache, Mustapha (University of Southern California, Los Angeles, CA); Browand, Fred (University of Southern California, Los Angeles, CA); Pointer, W. David (Argonne National Laboratory, Argonne, IL); Ortega, Jason M. (Lawrence Livermore National Laboratory, Livermore, CA); McCallen, Rose (Lawrence Livermore National Laboratory, Livermore, CA); Walker, Stephen M (NASA Ames Research Center, Moffet Field, CA); Heineck, James T (NASA Ames Research Center, Moffet Field, CA); Hassan, Basil; Roy, Christopher John (Auburn University, Auburn, AL); Storms, B. (NASA Ames Research Center, Moffet Field, CA); Satran, D. (NASA Ames Research Center, Moffet Field, CA); Ross, James (NASA Ames Research Center, Moffet Field, CA); Englar, Robert (Georgia Tech Research Institute, Atlanta, GA); Chatalain, Philippe (Caltech, Pasadena, CA); Rubel, Mike (Caltech, Pasadena, CA); Leonard, Anthony (Caltech, Pasadena, CA); Hsu, Tsu-Ya (University of Southern California, Los Angeles, CA); DeChant, Lawrence Justin.

2004-06-01

66

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

67

National Technical Information Service (NTIS)

Direct Simulation Monte Carlo and free-molecular analyses were used to provide aerothermodynamic characteristics of the Mars Odyssey spacecraft. The results of these analyses were used to develop an aerodynamic database that was used extensively for the p...

N. Takashima R. G. Wilmoth

2002-01-01

68

National Technical Information Service (NTIS)

This slide presentation reviews some of the basic principles of aerodynamics. Included in the presentation are: a few demonstrations of the principles, an explanation of the concepts of lift, drag, thrust and weight, a description of Bernoulli's principle...

J. H. Cole

2010-01-01

69

Wind Turbine Blade Flow Fields and Prospects for Active Aerodynamic Control.

National Technical Information Service (NTIS)

As wind turbines continue to grow larger, problems associated with adverse aerodynamic loads will grow more critical. Thus, the wind energy technical community has begun to seriously consider the potential of aerodynamic control methodologies for mitigati...

M. Robinson S. Schreck

2007-01-01

70

Transonic aerodynamic design experience

NASA Technical Reports Server (NTRS)

Advancements have occurred in transonic numerical simulation that place aerodynamic performance design into a relatively well developed status. Efficient broad band operating characteristics can be reliably developed at the conceptual design level. Recent aeroelastic and separated flow simulation results indicate that systematic consideration of an increased range of design problems appears promising. This emerging capability addresses static and dynamic structural/aerodynamic coupling and nonlinearities associated with viscous dominated flows.

Bonner, E.

1989-01-01

71

NASA Technical Reports Server (NTRS)

Aerodynamic flow achieved by adding fixed fairings to butterfly valve. When valve fully open, fairings align with butterfly and reduce wake. Butterfly free to turn, so valve can be closed, while fairings remain fixed. Design reduces turbulence in flow of air in internal suction system. Valve aids in development of improved porous-surface boundary-layer control system to reduce aerodynamic drag. Applications primarily aerospace. System adapted to boundary-layer control on high-speed land vehicles.

Horstman, Raymond H.

1992-01-01

72

Development of aerodynamics for a solar race car

The dominant factor of a solar car is running resistance, especially aerodynamic drag; and the reduction of the CD (drag coefficient)× A (frontal projected area) value is a crucial task to maximize the performance of a solar car. This paper will introduce the aerodynamic approach of the '96 Honda solar car which participated in the World Solar Challenge, the world's

Hiroyuki Ozawa; Sumio Nishikawa; Dai Higashida

1998-01-01

73

The aerodynamics of propellers

NASA Astrophysics Data System (ADS)

The theory and the design of propellers of minimum induced loss is treated. The pioneer analysis of this problem was presented more than half a century ago by Theodorsen, but obscurities in his treatment and inaccuracies and limited coverage in his tables of the Goldstein circulation function for helicoidal vortex sheets have not been remedied until the present work which clarifies and extends his work. The inverse problem, the prediction of the performance of a given propeller of arbitrary form, is also treated. The theory of propellers of minimum energy loss is dependent on considerations of a regular helicoidal trailing vortex sheet; consequently, a more detailed discussion of the dynamics of vortex sheets and the consequences of their instability and roll up is presented than is usually found in treatments of propeller aerodynamics. Complete and accurate tables of the circulation function are presented. Interference effects between a fuselage or a nacelle and the propeller are considered. The regimes of propeller, vortex ring, and windmill operation are characterized.

Wald, Quentin R.

2006-02-01

74

Progress in computational unsteady aerodynamics

NASA Technical Reports Server (NTRS)

After vigorous development for over twenty years, Computational Fluid Dynamics (CFD) in the field of aerospace engineering has arrived at a turning point toward maturity. This paper discusses issues related to algorithm development for the Euler/Navier Stokes equations, code validation and recent applications of CFD for unsteady aerodynamics. Algorithm development is a fundamental element for a good CFD program. Code validation tries to bridge the reliability gap between CFD and experiment. Many of the recent applications also take a multidisciplinary approach, which is a future trend for CFD applications. As computers become more affordable, CFD is expected to be a better scientific and engineering tool.

Obayashi, Shigeru

1993-01-01

75

An Energy First Approach to Introductory Physics

NASA Astrophysics Data System (ADS)

While introductory physics texts and curricula vary in scope and sequence, there is one aspect that is particularly stable: the progression that begins with equations of motion, continues through Newton's Laws, and finally leads to work and energy. While this approach seems reasonable, it can lead to student misconceptions, and is not necessitated by the physics. In particular, it implies that energy is dependent on forces, rather than both being independently definable. In this paper, we discuss taking an Energy First approach, that begins with energy, and utilizes it as the core concept. We address both the pedagogical and conceptual reasons for this approach. Finally, we discuss its use in two introductory courses, one designed for elementary teachers and one designed for architecture majors. In each, we have focused on defining a scope and sequence that is appropriate and meaningful for that audience, rather than continue with a standard, generic approach to introductory physics.

White, Christopher; Meyer, Daniel; Fluet, Kimberly

2009-11-01

76

Wind turbine design codes: A preliminary comparison of the aerodynamics

The National Wind Technology Center of the National Renewable Energy Laboratory is comparing several computer codes used to design and analyze wind turbines. The first part of this comparison is to determine how well the programs predict the aerodynamic behavior of turbines with no structural degrees of freedom. Without general agreement on the aerodynamics, it is futile to try to

Marshall L. Buhl; Alan D. Wright; James L. Tangler

1997-01-01

77

Aerodynamics of high-speed railway train

NASA Astrophysics Data System (ADS)

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 are more disturbed due to turbulence of the increased speed of the train, and consequently the flow energies are converted to aerodynamic drag, noise and vibrations. With the speed-up of train, many engineering problems which have been neglected at low train speeds, are being raised with regard to aerodynamic noise and vibrations, impulse forces occurring as two trains intersect each other, impulse wave at the exit of tunnel, ear discomfort of passengers inside train, etc. These are of major limitation factors to the speed-up of train system. The present review addresses the state of the art on the aerodynamic and aeroacoustic problems of high-speed railway train and highlights proper control strategies to alleviate undesirable aerodynamic problems of high-speed railway train system.

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

2002-10-01

78

Systems Approach to Energy Planning.

National Technical Information Service (NTIS)

Many developing countries are embarking on a petroleum-intensive path of development just at a time in history when petroleum is about to become scarce and expensive. At the same time the use of traditional forms of energy--wood, crop residues, and animal...

P. F. Palmedo R. Nathans

1978-01-01

79

Powered-Lift Aerodynamics and Acoustics. [conferences

NASA Technical Reports Server (NTRS)

Powered lift technology is reviewed. Topics covered include: (1) high lift aerodynamics; (2) high speed and cruise aerodynamics; (3) acoustics; (4) propulsion aerodynamics and acoustics; (5) aerodynamic and acoustic loads; and (6) full-scale and flight research.

1976-01-01

80

Aerodynamic optimization studies on advanced architecture computers

NASA Technical Reports Server (NTRS)

The approach to carrying out multi-discipline aerospace design studies in the future, especially in massively parallel computing environments, comprises of choosing (1) suitable solvers to compute solutions to equations characterizing a discipline, and (2) efficient optimization methods. In addition, for aerodynamic optimization problems, (3) smart methodologies must be selected to modify the surface shape. In this research effort, a 'direct' optimization method is implemented on the Cray C-90 to improve aerodynamic design. It is coupled with an existing implicit Navier-Stokes solver, OVERFLOW, to compute flow solutions. The optimization method is chosen such that it can accomodate multi-discipline optimization in future computations. In the work , however, only single discipline aerodynamic optimization will be included.

Chawla, Kalpana

1995-01-01

81

Aerodynamics of magnetic levitation (MAGLEV) trains

NASA Technical Reports Server (NTRS)

High-speed (500 kph) trains using magnetic forces for levitation, propulsion and control offer many advantages for the nation and a good opportunity for the aerospace community to apply 'high tech' methods to the domestic sector. One area of many that will need advanced research is the aerodynamics of such MAGLEV (Magnetic Levitation) vehicles. There are important issues with regard to wind tunnel testing and the application of CFD to these devices. This talk will deal with the aerodynamic design of MAGLEV vehicles with emphasis on wind tunnel testing. The moving track facility designed and constructed in the 6 ft. Stability Wind Tunnel at Virginia Tech will be described. Test results for a variety of MAGLEV vehicle configurations will be presented. The last topic to be discussed is a Multi-disciplinary Design approach that is being applied to MAGLEV vehicle configuration design including aerodynamics, structures, manufacturability and life-cycle cost.

Schetz, Joseph A.; Marchman, James F., III

1996-01-01

82

Applied computational aerodynamics

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

83

A Value Conscious Approach to Energy Education.

ERIC Educational Resources Information Center

The paper presents background information, rationale, description, and evaluation of an energy education program used with preschool and kindergarten children and their families. The objective is to describe the use of combined concepts of education, economics, and early childhood in developing a value conscious approach to energy education. The…

Braun, Bonnie; Wilson, Elaine

84

NSDL National Science Digital Library

This Web site serves as an online aerodynamics textbook for college students. Offered by the department of Aerospace, Mechanical, and Mechatronic Engineering at the University of Sydney, the material is divided into several main categories. These include fluid mechanics, aerodynamics, gasdynamics, aircraft performance, and propulsion. Each of these sections has many specific topics that are discussed in detail. There are MATLAB, Excel, and FORTRAN files and data sheets that accompany the reading, but they are best used as reference and are not needed to understand most of the material.

1995-01-01

85

An Aerodynamic Analysis of a Spinning Missile with Dithering Canards

NASA Technical Reports Server (NTRS)

A generic spinning missile with dithering canards is used to demonstrate the utility of an overset structured grid approach for simulating the aerodynamics of rolling airframe missile systems. The approach is used to generate a modest aerodynamic database for the generic missile. The database is populated with solutions to the Euler and Navier-Stokes equations. It is used to evaluate grid resolution requirements for accurate prediction of instantaneous missile loads and the relative aerodynamic significance of angle-of-attack, canard pitching sequence, viscous effects, and roll-rate effects. A novel analytical method for inter- and extrapolation of database results is also given.

Meakin, Robert L.; Nygaard, Tor A.

2003-01-01

86

ENPEP: An integrated approach to energy planning

Many models have been developed to analyze various aspects of the energy system. The Energy and Power Evaluation Program (ENPEP) is a set of microcomputer-based energy planning tools that are designed to provide an integrated analysis capability. ENPEP begins with a macroeconomic analysis, develops an energy demand forecast based on this analysis, carries out an integrated supply/demand analysis for the entire energy system, evaluates the electric system component of the energy system in detail, and determines the impacts of alternative configurations. This approach is an enhancement of existing techniques in that it places emphasis on looking at the electric system as an integral part of the entire energy supply system. Also, it explicitly considers the impacts the power system has on the rest of the energy system and on the economy as a whole.

Hamilton, B.P.; Cirillo, R.R.; Buehring, W.A.

1992-01-01

87

ENPEP: An integrated approach to energy planning

Many models have been developed to analyze various aspects of the energy system. The Energy and Power Evaluation Program (ENPEP) is a set of microcomputer-based energy planning tools that are designed to provide an integrated analysis capability. ENPEP begins with a macroeconomic analysis, develops an energy demand forecast based on this analysis, carries out an integrated supply/demand analysis for the entire energy system, evaluates the electric system component of the energy system in detail, and determines the impacts of alternative configurations. This approach is an enhancement of existing techniques in that it places emphasis on looking at the electric system as an integral part of the entire energy supply system. Also, it explicitly considers the impacts the power system has on the rest of the energy system and on the economy as a whole.

Hamilton, B.P.; Cirillo, R.R.; Buehring, W.A.

1992-09-01

88

Computer graphics in aerodynamic analysis

NASA Technical Reports Server (NTRS)

The use of computer graphics and its application to aerodynamic analyses on a routine basis is outlined. The mathematical modelling of the aircraft geometries and the shading technique implemented are discussed. Examples of computer graphics used to display aerodynamic flow field data and aircraft geometries are shown. A future need in computer graphics for aerodynamic analyses is addressed.

Cozzolongo, J. V.

1984-01-01

89

Baseball is one of the popular games in America, North Asia and some parts of Europe and Africa. Despite being a popular game, scan data is not available on aerodynamic properties of baseball. Having over 108 curved stitches, complex seams and their orientation, the airflow around the ball is significantly complex and little understood. The primary objectives of this study

Firoz Alam; Huy Ho; Harun Chowdhury; Aleksandar Subic

2011-01-01

90

Projectiles and aerodynamic forces

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

H L Armstrong

1984-01-01

91

Wind turbine wake aerodynamics

The aerodynamics of horizontal axis wind turbine wakes is studied. The contents is directed towards the physics of power extraction by wind turbines and reviews both the near and the far wake region. For the near wake, the survey is restricted to uniform, steady and parallel flow conditions, thereby excluding wind shear, wind speed and rotor setting changes and yawed

L. J. Vermeer; J. N. Sørensen; A. Crespo

2003-01-01

92

Nonlinear aerodynamic forces on thin flat plate: Numerical study

NASA Astrophysics Data System (ADS)

This paper first presents a numerical simulation of nonlinear aerodynamic forces on a thin flat plate through an integration of the computational fluid dynamics (CFD) method and the forced asymptotic oscillation method. The thin flat plate is forced to have either asymptotic torsional oscillation or asymptotic vertical oscillation of increasing amplitude. A multiple-domain mesh technique together with unstructured dynamic meshes is used in the CFD simulation to accommodate large amplitude oscillations of the plate. The instantaneous frequencies and amplitudes of the aerodynamic forces are then identified from the simulated asymptotic aerodynamic force time histories using the continuous wavelet transform (CWT) in terms of the CWT ridges. Extensive numerical studies are finally performed to examine the feasibility of the proposed approach. The results show that the CFD method used in this study can properly simulate nonlinear aerodynamic forces on the plate. The amplitude of the aerodynamic force depends on the amplitude of the forced oscillation and there are high-order harmonic aerodynamic forces of higher frequency than the forced oscillation frequency, both indicating the nonlinearity of aerodynamic forces. The results also show the flutter derivatives associated with self-excited aerodynamic forces depend on the amplitude of forced oscillation in addition to reduced velocity.

Huang, Lin; Xu, You-Lin; Liao, Haili

2014-01-01

93

An Institutional Approach to Understanding Energy Transitions

NASA Astrophysics Data System (ADS)

Energy is a central concern of sustainability because how we produce and consume energy affects society, economy, and the environment. Sustainability scientists are interested in energy transitions away from fossil fuels because they are nonrenewable, increasingly expensive, have adverse health effects, and may be the main driver of climate change. They see an opportunity for developing countries to avoid the negative consequences fossil-fuel-based energy systems, and also to increase resilience, by leap-frogging-over the centralized energy grid systems that dominate the developed world. Energy transitions pose both challenges and opportunities. Obstacles to transitions include 1) an existing, centralized, complex energy-grid system, whose function is invisible to most users, 2) coordination and collective-action problems that are path dependent, and 3) difficulty in scaling up RE technologies. Because energy transitions rely on technological and social innovations, I am interested in how institutional factors can be leveraged to surmount these obstacles. The overarching question that underlies my research is: What constellation of institutional, biophysical, and social factors are essential for an energy transition? My objective is to derive a set of "design principles," that I term institutional drivers, for energy transitions analogous to Ostrom's institutional design principles. My dissertation research will analyze energy transitions using two approaches: applying the Institutional Analysis and Development Framework and a comparative case study analysis comprised of both primary and secondary sources. This dissertation includes: 1) an analysis of the world's energy portfolio; 2) a case study analysis of five countries; 3) a description of the institutional factors likely to promote a transition to renewable-energy use; and 4) an in-depth case study of Thailand's progress in replacing nonrenewable energy sources with renewable energy sources. My research will contribute to our understanding of how energy transitions at different scales can be accomplished in developing countries and what it takes for innovation to spread in a society.

Koster, Auriane Magdalena

94

Development of Aerodynamic Design System for Centrifugal Compressors,

National Technical Information Service (NTIS)

An improvement of the aerodynamic performance of centrifugal compressors for industrial use is necessary to achieve high efficiency and low energy consumption. The compressor is usually composed of many stages with different flow coefficients and the perf...

N. Nojima B. Nagata H. Kawasaki S. Sugitani

1988-01-01

95

Advanced Aerodynamic Control Effectors

NASA Technical Reports Server (NTRS)

A 1990 research program that focused on the development of advanced aerodynamic control effectors (AACE) for military aircraft has been reviewed and summarized. Data are presented for advanced planform, flow control, and surface contouring technologies. The data show significant increases in lift, reductions in drag, and increased control power, compared to typical aerodynamic designs. The results presented also highlighted the importance of planform selection in the design of a control effector suite. Planform data showed that dramatic increases in lift (greater than 25%) can be achieved with multiple wings and a sawtooth forebody. Passive porosity and micro drag generator control effector data showed control power levels exceeding that available from typical effectors (moving surfaces). Application of an advanced planform to a tailless concept showed benefits of similar magnitude as those observed in the generic studies.

Wood, Richard M.; Bauer, Steven X. S.

1999-01-01

96

Aerodynamics plays a prominent role in defining the flight of a ball that is struck or thrown through the air in almost all\\u000a ball sports. The main interest is in the fact that the ball can often deviate from its initial straight path, resulting in\\u000a a curved, or sometimes an unpredictable, flight path. It is particularly fascinating that not all

Rabindra D. Mehta

97

NASA Technical Reports Server (NTRS)

This slide presentation reviews some of the basic principles of aerodynamics. Included in the presentation are: a few demonstrations of the principles, an explanation of the concepts of lift, drag, thrust and weight, a description of Bernoulli's principle, the concept of the airfoil (i.e., the shape of the wing) and how that effects lift, and the method of controlling an aircraft by manipulating the four forces using control surfaces.

Cole, Jennifer Hansen

2010-01-01

98

The basic aerodynamics of floatation

NASA Astrophysics Data System (ADS)

It is pointed out that the basic aerodynamics of modern floatation ovens, in which the continuous, freshly painted metal strip is floated, dried, and cured, is the two-dimensional analog of that of hovercraft. The basic theory for the static lift considered in connection with the study of hovercraft has had spectacular success in describing the experimental results. This appears surprising in view of the crudity of the theory. The present investigation represents an attempt to explore the reasons for this success. An outline of the basic theory is presented and an approach is shown for deriving the resulting expressions for the lift from the full Navier-Stokes equations in a manner that clearly indicates the limitations on the validity of the expressions. Attention is given to the generally good agreement between the theory and the axisymmetric (about the centerline) results reported by Jaumotte and Kiedrzynski (1965).

Davies, M. J.; Wood, D. H.

1983-09-01

99

Identification of aerodynamic models for maneuvering aircraft

NASA Technical Reports Server (NTRS)

Due to the requirement of increased performance and maneuverability, the flight envelope of a modern fighter is frequently extended to the high angle-of-attack regime. Vehicles maneuvering in this regime are subjected to nonlinear aerodynamic loads. The nonlinearities are due mainly to three-dimensional separated flow and concentrated vortex flow that occur at large angles of attack. Accurate prediction of these nonlinear airloads is of great importance in the analysis of a vehicle's flight motion and in the design of its flight control system. A satisfactory evaluation of the performance envelope of the aircraft may require a large number of coupled computations, one for each change in initial conditions. To avoid the disadvantage of solving the coupled flow-field equations and aircraft's motion equations, an alternate approach is to use a mathematical modeling to describe the steady and unsteady aerodynamics for the aircraft equations of motion. Aerodynamic forces and moments acting on a rapidly maneuvering aircraft are, in general, nonlinear functions of motion variables, their time rate of change, and the history of maneuvering. A numerical method was developed to analyze the nonlinear and time-dependent aerodynamic response to establish the generalized indicial function in terms of motion variables and their time rates of change.

Chin, Suei; Lan, C. Edward

1990-01-01

100

An analysis of prop-fan/airframe aerodynamic integration

NASA Technical Reports Server (NTRS)

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 with advanced, subsonic, commercial transport airframes. Three basic configurations were defined and analyzed: wing mounted prop fan at a cruise Mach number of 0.8, wing mounted prop fan in a low speed configuration, and aft mounted prop fan at a cruise Mach number of 0.8.

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

1978-01-01

101

Aerodynamic mathematical modeling - basic concepts

NASA Technical Reports Server (NTRS)

The mathematical modeling of the aerodynamic response of an aircraft to arbitrary maneuvers is reviewed. Bryan's original formulation, linear aerodynamic indicial functions, and superposition are considered. These concepts are extended into the nonlinear regime. The nonlinear generalization yields a form for the aerodynamic response that can be built up from the responses to a limited number of well defined characteristic motions, reproducible in principle either in wind tunnel experiments or flow field computations. A further generalization leads to a form accommodating the discontinuous and double valued behavior characteristics of hysteresis in the steady state aerodynamic response.

Tobak, M.; Schiff, L. B.

1981-01-01

102

TAD- THEORETICAL AERODYNAMICS PROGRAM

NASA Technical Reports Server (NTRS)

This theoretical aerodynamics program, TAD, was developed to predict the aerodynamic characteristics of vehicles with sounding rocket configurations. These slender, axisymmetric finned vehicle configurations have a wide range of aeronautical applications from rockets to high speed armament. Over a given range of Mach numbers, TAD will compute the normal force coefficient derivative, the center-of-pressure, the roll forcing moment coefficient derivative, the roll damping moment coefficient derivative, and the pitch damping moment coefficient derivative of a sounding rocket configured vehicle. The vehicle may consist of a sharp pointed nose of cone or tangent ogive shape, up to nine other body divisions of conical shoulder, conical boattail, or circular cylinder shape, and fins of trapezoid planform shape with constant cross section and either three or four fins per fin set. The characteristics computed by TAD have been shown to be accurate to within ten percent of experimental data in the supersonic region. The TAD program calculates the characteristics of separate portions of the vehicle, calculates the interference between separate portions of the vehicle, and then combines the results to form a total vehicle solution. Also, TAD can be used to calculate the characteristics of the body or fins separately as an aid in the design process. Input to the TAD program consists of simple descriptions of the body and fin geometries and the Mach range of interest. Output includes the aerodynamic characteristics of the total vehicle, or user-selected portions, at specified points over the mach range. The TAD program is written in FORTRAN IV for batch execution and has been implemented on an IBM 360 computer with a central memory requirement of approximately 123K of 8 bit bytes. The TAD program was originally developed in 1967 and last updated in 1972.

Barrowman, J.

1994-01-01

103

Aerodynamic Performance of Scarf Inlets.

National Technical Information Service (NTIS)

A scarf inlet is characterized by having a longer lower lip than upper lip leading to both aerodynamic and acoustic advantages. Aerodynamically, a scarf inlet has higher angle of attack capability and is less likely to ingest foreign objects while the air...

J. M. Abbott

1979-01-01

104

Aerodynamic coefficients and transformation tables

NASA Technical Reports Server (NTRS)

The problem of the transformation of numerical values expressed in one system of units into another set or system of units frequently arises in connection with aerodynamic problems. Report contains aerodynamic coefficients and conversion tables needed to facilitate such transformation. (author)

Ames, Joseph S

1918-01-01

105

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

106

Aerodynamic design lowers truck fuel consumption

NASA Technical Reports Server (NTRS)

Energy-saving concepts in truck design are emerging from developing new shapes with improved aerodynamic flow properties that can reduce air-drag coefficient of conventional tractor-trailers without requiring severe design changes or compromising load-carrying capability. Improvements are expected to decrease somewhat with increased wind velocities and would be affected by factors such as terrain, driving techniques, and mechanical condition.

Steers, L.

1978-01-01

107

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.

108

NASA Technical Reports Server (NTRS)

Direct Simulation Monte Carlo and free-molecular analyses were used to provide aerothermodynamic characteristics of the Mars Odyssey spacecraft. The results of these analyses were used to develop an aerodynamic database that was used extensively for the pre-flight planning and in-flight execution for the aerobraking phase of the Mars Odyssey mission. During aerobraking operations, the database was used to reconstruct atmospheric density profiles during each pass. The reconstructed data was used to update the atmospheric model, which was used to determine the strategy for subsequent aerobraking maneuvers. The aerodynamic database was also used together with data obtained from on-board accelerometers to reconstruct the spacecraft attitudes throughout each aerobraking pass. The reconstructed spacecraft attitudes are in good agreement with those determined by independent on-board inertial measurements for all aerobraking passes. The differences in the pitch attitudes are significantly less than the preflight uncertainties of +/-2.9%. The differences in the yaw attitudes are influenced by zonal winds. When latitudinal gradients of density are small, the differences in the yaw attitudes are significantly less than the preflight uncertainties.

Takashima, Naruhisa; Wilmoth, Richard G.

2002-01-01

109

NASA Technical Reports Server (NTRS)

This report gives the description and the use of a specially designed aerodynamic plane table. For the accurate and expeditious geometrical measurement of models in an aerodynamic laboratory, and for miscellaneous truing operations, there is frequent need for a specially equipped plan table. For example, one may have to measure truly to 0.001 inch the offsets of an airfoil at many parts of its surface. Or the offsets of a strut, airship hull, or other carefully formed figure may require exact calipering. Again, a complete airplane model may have to be adjusted for correct incidence at all parts of its surfaces or verified in those parts for conformance to specifications. Such work, if but occasional, may be done on a planing or milling machine; but if frequent, justifies the provision of a special table. For this reason it was found desirable in 1918 to make the table described in this report and to equip it with such gauges and measures as the work should require.

Zahm, A F

1924-01-01

110

Plasma flow control, based on plasma aerodynamic actuation, has become a newly-rising research focus in international aerodynamic field. Sliding discharge is a novel approach to generate plasma aerodynamic actuation. In this paper, a three-electrode plasma sheet actuator driven by repetitive nanosecond pulses with negative DC component is used to generate sliding discharge, which can be called nanosecond-pulse sliding discharge. The

Song Huimin; Jia Min; Liang Hua; Wu Yun

2011-01-01

111

Wind turbine blade aerodynamics: The analysis of field test data

Data obtained from the National Renewable Energy Laboratory site test of a wind turbine (The Combined Experiment) was analyzed specifically to capture information regarding the aerodynamic loading experienced by the machine rotor blades. The inflow conditions were shown to be extremely variable. These inflows yielded three different operational regimes about the blades. Each regime produced very different aerodynamic loading conditions. Two of these regimes could not have been readily predicted from wind tunnel data. These conditions are being subjected to further analyses to provide new guidelines for both designers and operators. The roles of unsteady aerodynamics effects are highlighted since periods of dynamic stall were shown to be associated with brief episodes of high aerodynamic forces.

Luttges, M.W.; Miller, M.S.; Robinson, M.C.; Shipley, D.E.; Young, T.S. [Colorado Univ., Boulder, CO (United States). Dept. of Aerospace Engineering Sciences

1994-08-01

112

Wind turbine design codes: A preliminary comparison of the aerodynamics

The National Wind Technology Center of the National Renewable Energy Laboratory is comparing several computer codes used to design and analyze wind turbines. The first part of this comparison is to determine how well the programs predict the aerodynamic behavior of turbines with no structural degrees of freedom. Without general agreement on the aerodynamics, it is futile to try to compare the structural response due to the aerodynamic input. In this paper, the authors compare the aerodynamic loads for three programs: Garrad Hassan`s BLADED, their own WT-PERF, and the University of Utah`s YawDyn. This report documents a work in progress and compares only two-bladed, downwind turbines.

Buhl, M.L. Jr.; Wright, A.D.; Tangler, J.L.

1997-12-01

113

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

114

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

115

Launch vehicle aerodynamic flight test results

NASA Technical Reports Server (NTRS)

The aerodynamic flight test procedures and results for the Space Shuttle orbiter are presented. The aerodynamic characteristics used in testing were determined from flights STS-1 and through STS-4. Normal force and pitching moment were different than predicted, suggesting an unanticipated aerodynamic force acting upward on the end of the orbiter. However, lateral-directional aerodynamic characteristics were in good management with good predictions. The flight measured aerodynamics are repeatable and show good correlation with angle of attack and angle of sideslip.

Gaines, L. M.; Osborn, W. L.; Wiltse, P. D.

1983-01-01

116

Computational aerodynamics and artificial intelligence

NASA Technical Reports Server (NTRS)

Some aspects of artificial intelligence are considered and questions are speculated on, including how knowledge-based systems can accelerate the process of acquiring new knowledge in aerodynamics, how computational fluid dynamics may use 'expert' systems and how expert systems may speed the design and development process. The anatomy of an idealized expert system called AERODYNAMICIST is discussed. Resource requirements are examined for using artificial intelligence in computational fluid dynamics and aerodynamics. Considering two of the essentials of computational aerodynamics - reasoniing and calculating - it is believed that a substantial part of the reasoning can be achieved with artificial intelligence, with computers being used as reasoning machines to set the stage for calculating. Expert systems will probably be new assets of institutions involved in aeronautics for various tasks of computational aerodynamics.

Kutler, P.; Mehta, U. B.

1984-01-01

117

Computational aerodynamics and artificial intelligence

NASA Technical Reports Server (NTRS)

The general principles of artificial intelligence are reviewed and speculations are made concerning how knowledge based systems can accelerate the process of acquiring new knowledge in aerodynamics, how computational fluid dynamics may use expert systems, and how expert systems may speed the design and development process. In addition, the anatomy of an idealized expert system called AERODYNAMICIST is discussed. Resource requirements for using artificial intelligence in computational fluid dynamics and aerodynamics are examined. Three main conclusions are presented. First, there are two related aspects of computational aerodynamics: reasoning and calculating. Second, a substantial portion of reasoning can be achieved with artificial intelligence. It offers the opportunity of using computers as reasoning machines to set the stage for efficient calculating. Third, expert systems are likely to be new assets of institutions involved in aeronautics for various tasks of computational aerodynamics.

Mehta, U. B.; Kutler, P.

1984-01-01

118

Tennis Ball Aerodynamics and Dynamics

\\u000a The detailed aerodynamics and dynamics of a tennis ball have only recently been uncovered with the help of a series of experimental\\u000a studies (Mehta and Pallis, 2001, Cislunar Aerospace, Inc., 1998). Intuitively, one would expect the (rough) fabric covering on the ball to have an effect on the aerodynamics, but the extent\\u000a of the effect turned out to be much

Rabindra D. Mehtal; Jani Macari Pallis

119

\\u000a The aerodynamics of golf balls is still not well understood, primarily because the aerodynamic performance of the golf ball\\u000a depends crucially on the details of the airflow over the ball, and those details are controlled by many factors. As the ball\\u000a flies through the air, it develops lift and drag forces that depend on its velocity, spin rate, the atmospheric

Smits J. Alexander; Steven Ogg

120

Progress in reducing aerodynamic drag for higher efficiency of heavy duty trucks (class 7-8)

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. In addition, greater use of newly developed computational tools holds promise for reducing the number of prototype tests, for cutting manufacturing costs, and for reducing overall time to market. Experimental verification and validation

M Brady; F Browand; M Hammache; J T Heineck; A Leonard; R McCallen; J Ross; W Rutledge; K Salari; B Storms

1999-01-01

121

Progress in Reducing Aerodynamic Drag for Higher Efficiency of Heavy Duty Trucks (Class 7-8)

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. In addition, greater use of newly developed computational tools holds promise for reducing the number of prototype tests, for cutting manufacturing costs, and for reducing overall time to market. Experimental verification and validation

Rose McCallen; Richard Couch; Juliana Hsu; Fred Browand; Mustapha Hammache; Anthony Leonard; Mark Brady; Kambiz Salari; Walter Rutledge; James Ross; Bruce Storms; J. T. Heineck; David Driver; James Bell; Gregory Zilliac

1999-01-01

122

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

123

Aerodynamics of badminton shuttlecocks

NASA Astrophysics Data System (ADS)

A computational study is carried out to understand the aerodynamics of shuttlecocks used in the sport of badminton. The speed of the shuttlecock considered is in the range of 25-50 m/s. The relative contribution of various parts of the shuttlecock to the overall drag is studied. It is found that the feathers, and the net in the case of a synthetic shuttlecock, contribute the maximum. The gaps, in the lower section of the skirt, play a major role in entraining the surrounding fluid and causing a difference between the pressure inside and outside the skirt. This pressure difference leads to drag. This is confirmed via computations for a shuttlecock with no gaps. The synthetic shuttle experiences more drag than the feather model. Unlike the synthetic model, the feather shuttlecock is associated with a swirling flow towards the end of the skirt. The effect of the twist angle of the feathers on the drag as well as the flow has also been studied.

Verma, Aekaansh; Desai, Ajinkya; Mittal, Sanjay

2013-08-01

124

Aerodynamic design trends for commercial aircraft

NASA Technical Reports Server (NTRS)

Recent research on advanced-configuration commercial aircraft at DFVLR is surveyed, with a focus on aerodynamic approaches to improved performance. Topics examined include transonic wings with variable camber or shock/boundary-layer control, wings with reduced friction drag or laminarized flow, prop-fan propulsion, and unusual configurations or wing profiles. Drawings, diagrams, and graphs of predicted performance are provided, and the need for extensive development efforts using powerful computer facilities, high-speed and low-speed wind tunnels, and flight tests of models (mounted on specially designed carrier aircraft) is indicated.

Hilbig, R.; Koerner, H.

1986-01-01

125

Wind farm control: Addressing the aerodynamic interaction among wind turbines

Wind farms help reduce the average wind cost of energy due to many economies of scale compared to individual turbines located far from each other. However, these groupings introduce the problem of aerodynamic interaction among turbines, which can decrease the total energy converted to electricity compared to the same number of isolated turbines operating under the same wind inflow conditions.

Kathryn E. Johnson; Naveen Thomas

2009-01-01

126

An energy landscape approach to protein aggregation

NASA Astrophysics Data System (ADS)

Protein aggregation into ordered fibrillar structures is the hallmark of a class of diseases, the most prominent examples of which are Alzheimer's and Parkinson's disease. Recent results (e.g. Baldwin et al. J. Am. Chem. Soc. 2011) suggest that the aggregated state of a protein is in many cases thermodynamically more stable than the soluble state. Therefore the solubility of proteins in a cellular context appears to be to a large extent under kinetic control. Here, we first present a conceptual framework for the description of protein aggregation ( see AK Buell et al., Phys. Rev. Lett. 2010) that is an extension to the generally accepted energy landscape model for protein folding. Then we apply this model to analyse and interpret a large set of experimental data on the kinetics of protein aggregation, acquired mainly with a novel biosensing approach (see TPJK Knowles et al, Proc. Nat. Acad. Sc. 2007). We show how for example the effect of sequence modifications on the kinetics and thermodynamics of human lysozyme aggregation can be understood and quantified (see AK Buell et al., J. Am. Chem. Soc. 2011). These results have important implications for therapeutic strategies against protein aggregation disorders, in this case lysozyme systemic amyloidosis.

Buell, Alexander; Knowles, Tuomas

2012-02-01

127

NASA Technical Reports Server (NTRS)

An analysis of the steady and unsteady aerodynamics of the space shuttle orbiter has been performed. It is shown that slender wing theory can be modified to account for the effect of Mach number and leading edge roundness on both attached and separated flow loads. The orbiter unsteady aerodynamics can be computed by defining two equivalent slender wings, one for attached flow loads and another for the vortex-induced loads. It is found that the orbiter is in the transonic speed region subject to vortex-shock-boundary layer interactions that cause highly nonlinear or discontinuous load changes which can endanger the structural integrity of the orbiter wing and possibly cause snap roll problems. It is presently impossible to simulate these interactions in a wind tunnel test even in the static case. Thus, a well planned combined analytic and experimental approach is needed to solve the problem.

Ericsson, L. E.; Reding, J. P.

1976-01-01

128

Aerodynamics Via Acoustics: Application of Acoustic Formulas for Aerodynamic Calculations

NASA Technical Reports Server (NTRS)

Prediction of aerodynamic loads on bodies in arbitrary motion is considered from an acoustic point of view, i.e., in a frame of reference fixed in the undisturbed medium. An inhomogeneous wave equation which governs the disturbance pressure is constructed and solved formally using generalized function theory. When the observer is located on the moving body surface there results a singular linear integral equation for surface pressure. Two different methods for obtaining such equations are discussed. Both steady and unsteady aerodynamic calculations are considered. Two examples are presented, the more important being an application to propeller aerodynamics. Of particular interest for numerical applications is the analytical behavior of the kernel functions in the various integral equations.

Farassat, F.; Myers, M. K.

1986-01-01

129

Electric arc furnace fume control: an alternative energy saving approach

The traditional approaches practiced in North America, Japan and Europe are briefly reviewed and compared to a system which has been engineered to reduce energy consumption. Calculated energy costs for conventional systems are compared to actual costs.

R. A. Walli; J. A. Mulcahy; K. H. Chen

1981-01-01

130

Configuration Aerodynamics: Past - Present - Future

NASA Technical Reports Server (NTRS)

The Configuration Aerodynamics (CA) element of the High Speed Research (HSR) program is managed by a joint NASA and Industry team, referred to as the Technology Integration Development (ITD) team. This team is responsible for the development of a broad range of technologies for improved aerodynamic performance and stability and control characteristics at subsonic to supersonic flight conditions. These objectives are pursued through the aggressive use of advanced experimental test techniques and state of the art computational methods. As the HSR program matures and transitions into the next phase the objectives of the Configuration Aerodynamics ITD are being refined to address the drag reduction needs and stability and control requirements of High Speed Civil Transport (HSCT) aircraft. In addition, the experimental and computational tools are being refined and improved to meet these challenges. The presentation will review the work performed within the Configuration Aerodynamics element in 1994 and 1995 and then discuss the plans for the 1996-1998 time period. The final portion of the presentation will review several observations of the HSR program and the design activity within Configuration Aerodynamics.

Wood, Richard M.; Agrawal, Shreekant; Bencze, Daniel P.; Kulfan, Robert M.; Wilson, Douglas L.

1999-01-01

131

Feasibility study for a numerical aerodynamic simulation facility. Volume 1

NASA Technical Reports Server (NTRS)

A Numerical Aerodynamic Simulation Facility (NASF) was designed for the simulation of fluid flow around three-dimensional bodies, both in wind tunnel environments and in free space. The application of numerical simulation to this field of endeavor promised to yield economies in aerodynamic and aircraft body designs. A model for a NASF/FMP (Flow Model Processor) ensemble using a possible approach to meeting NASF goals is presented. The computer hardware and software are presented, along with the entire design and performance analysis and evaluation.

Lincoln, N. R.; Bergman, R. O.; Bonstrom, D. B.; Brinkman, T. W.; Chiu, S. H. J.; Green, S. S.; Hansen, S. D.; Klein, D. L.; Krohn, H. E.; Prow, R. P.

1979-01-01

132

Static Aerodynamics of the Mars Exploration Rover Entry Capsule

NASA Technical Reports Server (NTRS)

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 pre- entry analysis for determining the MER entry design requirements for development of the MER entry system, as well as targeting the MER landing sites. The database was constructed using the same approach used for Mars Pathfinder (MPF). However, the MER aerodynamic database is of much higher fidelity and tailored to the MER entry trajectories. This set of data includes direct simulation Monte Carlo calculations covering the transitional regime of the entry trajectory and computational fluid dynamics calculations describing the aerodynamics in the hypersonic and supersonic continuum regimes. An overview of the methodology used to generate the data is given along with comparisons to important features in the MPF aerodynamics and related heritage data. The MER and MPF comparison indicates that trajectory specific data is required to properly model the flight characteristics of a.blunt entry capsule at Mars.

Schoenenberger, Mark; Cheatwood, F. McNeil; Desai, Prasun

2005-01-01

133

Low Dimensional Modeling And Computational Analysis of Dragonfly Wing Aerodynamics

NASA Astrophysics Data System (ADS)

High-fidelity numerical simulations are being used to examine the key aerodynamic features and lift production of insect wings. However, the kinematics of the insect's wing and the resulting aerodynamics is highly complex, and does not lend itself easily to analysis based on simple notions of pitching/heaving kinematics or lift/drag based propulsive mechanisms. A more inventive approach is therefore needed to dissect the wing gait and gain insight into the remarkable aerodynamic performance of the insect's wing. The focus of the current investigation is on the aerodynamics of the wing of a dragonfly (Erythemis Simplicicollis) in hovering motion. The three-dimensional, time-dependent wing kinematics is obtained via a high-speed photogrammetry system. Singular Value Decomposition (SVD) is then applied to extract the essential features of the wing gait. The SVD spectrum shows that the first four modes capture more than 80% of the motion. Aerodynamics of wings flapping with kinematics synthesized from SVD modes will be discussed in detail.

Ren, Yan; Wan, Hui; Dong, Haibo

2011-11-01

134

Aerodynamic performance of scarf inlets

NASA Technical Reports Server (NTRS)

A scarf inlet is characterized by having a longer lower lip than upper lip leading to both aerodynamic and acoustic advantages. Aerodynamically, a scarf inlet has higher angle of attack capability and is less likely to ingest foreign objects while the aircraft is on the ground. Acoustically, a scarf inlet provides for reduced inlet radiated noise levels below the engine as a result of upward reflection and refraction of inlet radiated noise. Results of a wind tunnel test program are presented which illustrate the aerodynamic performance of two different scarf inlet designs. Based on these results, scarf inlet performance is summarized in a way to illustrate the advantages and limitations of a scarf inlet compared to an axisymmetric inlet.

Abbott, J. M.

1979-01-01

135

FAST AERODYNAMIC MODEL FOR DESIGN TECHNOLOGY

An innovative IT-based technique of Fast Aerodynamic Computations is offered for the analysis of airliner aerodynamic characteristics in cruise flight, which is crucial from the effectiveness standpoint. A typical airliner configuration \\

Alexander V. Bernstein; Alexander P. Kouleshov; Yuri N. Sviridenko; Victor V. Vyshinsky

136

Aerodynamic analysis of horizontal axis wind turbines

Axial momentum theory, vortex theory and inviscid flow, viscous flow and aerodynamic loads, derivatives of the aerodynamic load, maximum tip speed ratio, turbine design for maximum power, optimization, and turbines in rotationally unsymmetric flow are discussed.

O. A. M. Holme

1981-01-01

137

Aerodynamics Research Revolutionizes Truck Design

NASA Technical Reports Server (NTRS)

During the 1970s and 1980s, researchers at Dryden Flight Research Center conducted numerous tests to refine the shape of trucks to reduce aerodynamic drag and improved efficiency. During the 1980s and 1990s, a team based at Langley Research Center explored controlling drag and the flow of air around a moving body. Aeroserve Technologies Ltd., of Ottawa, Canada, with its subsidiary, Airtab LLC, in Loveland, Colorado, applied the research from Dryden and Langley to the development of the Airtab vortex generator. Airtabs create two counter-rotating vortices to reduce wind resistance and aerodynamic drag of trucks, trailers, recreational vehicles, and many other vehicles.

2008-01-01

138

Langley Symposium on Aerodynamics, volume 1

NASA Technical Reports Server (NTRS)

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.

Stack, Sharon H. (compiler)

1986-01-01

139

Langley Symposium on Aerodynamics, volume 1

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

140

Rotorcraft Aerodynamics Models for a Comprehensive Analysis

Recent developments of the aerodynamics models for the comprehensive analysis CAMRAD II are described, particularly the unsteady aerodynamic models and dynamic stall models, and the free wake geometry calculation. Three models for the unsteady aerodynamic loads in attached flow are implemented: from incompressible thin-airfoil theory, from ONERA EDLIN, and from Leishman-Beddoes. Five dynamic stall models are implemented: from Johnson, Boeing,

Wayne Johnson

1998-01-01

141

Fuel Savings and Aerodynamic Drag Reduction from Rail Car Covers

NASA Technical Reports Server (NTRS)

The potential for energy savings by reducing the aerodynamic drag of rail cars is significant. A previous study of aerodynamic drag of coal cars suggests that a 25% reduction in drag of empty cars would correspond to a 5% fuel savings for a round trip [1]. Rail statistics for the United States [2] report that approximately 5.7 billion liters of diesel fuel were consumed for coal transportation in 2002, so a 5% fuel savings would total 284 million liters. This corresponds to 2% of Class I railroad fuel consumption nationwide. As part of a DOE-sponsored study, the aerodynamic drag of scale rail cars was measured in a wind tunnel. The goal of the study was to measure the drag reduction of various rail-car cover designs. The cover designs tested yielded an average drag reduction of 43% relative to empty cars corresponding to an estimated round-trip fuel savings of 9%.

Storms, Bruce; Salari, Kambiz; Babb, Alex

2008-01-01

142

Hydrodynamics and aerodynamics - Cross fertilisation in research and design

Areas of intersection between theory and applications in hydrodynamics and aerodynamics are investigated. Fluid mechanics principles involve the minimization of drag and considers the energy exchange between a craft and its wake, which leads to boundary layer examinations. The effects of surface roughness and of turbulent boundary layers are applicable to both seagoing and airborne craft, as are flow separation

H. H. Pearcey

1982-01-01

143

Aerodynamic Optimization of a Solar - Bio Diesel Hybrid Vehicle

Energy efficiency is the most critical aspect for a successful solar powered automobile and much can be gained from the reduction of aer odynamic drag on such a vehicle. Yet, for a solar car to be practical to the everyday driver, it has to be ergonomically feasible, financially sensible, and aesthetically pleasing. This research compares aerodynamic drag calculations produced by

Neal A. Allgood

144

Rotary wing aerodynamically generated noise

NASA Technical Reports Server (NTRS)

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.

Schmitz, F. J.; Morse, H. A.

1982-01-01

145

The Aerodynamics of Golf Balls

The aerodynamic forces on golf balls were studied by dropping spinning balls through the horizontal wind stream of the B. F. Goodrich wind tunnel. The lift, L, and drag, D, were calculated from the drift of the balls, rotating at speeds, N, up to 8000 r.p.m. while falling through a wind stream having a velocity of 105 feet per second.

John M. Davies

1949-01-01

146

Review of tennis ball aerodynamics

The aerodynamics of a tennis ball are reviewed here with reference to several wind tunnel measurement efforts. Measurements for a wide variety of tennis balls, including the ‘oversized’ balls, are presented. Flow visualization results have shown that the separation location on a non?spinning tennis ball occurred relatively early, near the apex, and appeared very similar to a laminar separation in

Rabindra Mehta; Firoz Alam; Aleksandar Subic

2008-01-01

147

AERODYNAMIC PROPERTIES OF SOCCER BALL

In this paper, the authors analyse the aerodynamic properties of soccer ball. Using ADVENTURE System, the finite element flow\\u000a analysis around soccer ball is performed to figure out the coefficient of drag of soccer ball, the critical Reynolds number\\u000a of drag crisis, the track of curveball.

Y. Nakabayashi; S. Yoshimura

148

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

149

Compressor Research Facility Aerodynamics Analysis.

National Technical Information Service (NTIS)

This report documents a series of aerodynamic studies carried out jointly by AFAPL and ICFAR personnel in support of the design and development of the AF Aero Propulsion Laboratory Compressor Research Facility (CRF). The CRF is a non-return compressor tes...

G. D. Huffman

1979-01-01

150

Unsteady aerodynamics of blade rows

NASA Technical Reports Server (NTRS)

The requirements placed on an unsteady aerodynamic theory intended for turbomachinery aeroelastic applications are discussed along with a brief description of the various theoretical models that are available to address these requirements. The main emphasis is placed on the description of a linearized inviscid theory which fully accounts for the effects of a nonuniform mean or steady flow on unsteady aerodynamic response. Although this theory has been developed primarily for blade flutter prediction, more general equations are presented which account for unsteady excitations due to incident external aerodynamic disturbances as well as those due to blade motions. The resulting equations consist of a system of three field equations along with conditions imposed at blade, wake and shock surfaces and in the far field. These equations can be solved to determine the fluctuations in all fluid dynamic properties throughout the required solution domain. Example solutions are presented to demonstrate several effects associated with nonuniform steady flows on the linearized unsteady aerodynamic response to prescribed blade motions.

Verdon, J. M.

1987-01-01

151

Aerodynamic features of turbulent flames

The paper provides an interpretation for a variety of turbulent flame phenomena relating them to the aerodynamic properties of the flow field. This includes the classical notion of the breakdown of laminar flames propagation in ducts, the characteristic features of turbulent flame-fronts recorded by schlieren photography, as well as flame instabilities leading to flashback occurring in a combustion chamber behind

A. K. Oppenheim; A. F. Ghoniem

1983-01-01

152

Aerodynamics of a Dimpled Vehicle

NASA Astrophysics Data System (ADS)

Automobiles consume approximately two billion barrels of fuel each year throughout the United States. A significant portion of this fuel is used to overcome aerodynamic drag at highway speeds. As a result, even small improvements made to the aerodynamics of automobiles can result in sizeable fuel savings. Since the shape of a vehicle is often dictated by design, economics, and function, aerodynamic improvements by means of obvious body streamlining are not always possible. However, minor modifications can be made to the vehicle, such as changing the behavior of the boundary layer to delay flow separation or installing small components either to reduce underbody flow or to mitigate induced drag. In this study, we examine the effect that dimples have upon the aerodynamics of a simplified vehicle. Reynolds-averaged Navier-Stokes simulations are performed on a full-scale Ahmed body at a Reynolds number of 9.5e6 based upon the vehicle length. The dimples, which have a uniform diameter of 0.1 m and a dimple depth-to-diameter ratio of 0.14, are distributed across the vehicle surface. The results of the simulations demonstrate that the dimples modify both the recirculation zone and the strength and location of the counter-rotating vortex pair in the vehicle wake. Although an increase in base pressure can occur for a dimpled configuration, the net drag change is sensitive to both the number and placement of the dimples on the vehicle body.

Ortega, Jason; Salari, Kambiz

2010-11-01

153

Aerodynamic effects of Nacelle position

NASA Technical Reports Server (NTRS)

An engineer in the PRT test the aerodynamic effects of nacelle position with respect to the wing, May 1930. Photograph published in Engineer in Charge: A History of the Langley Aeronautical Laboratory, 1917-1958 by James R. Hansen. Page 132.

1932-01-01

154

Energy planning for development - needs and approaches

The capability of developing countries to carry out comprehensive national energy planning is examined. The analytical methods or models constructed for analyzing the energy system have to take into account the specific context in which they are built to address issues of interest to development planners. Issues discussed are resource development and technology research, energy equity considerations to all peoples in a nation, the pricing policy, and the balance of payments considerations. The impartance of the availability of adequate skilled personnel and training programs to impart the requisite skill necessary to carry out the planning is discussed. Various surveys were conducted to determine the training needs for energy planners in developing countries. (MCW)

Mubayi, V

1981-01-01

155

Determination of aerodynamic sensitivity coefficients for wings in transonic flow

NASA Technical Reports Server (NTRS)

The quasianalytical approach is applied to the 3-D full potential equation to compute wing aerodynamic sensitivity coefficients in the transonic regime. Symbolic manipulation is used to reduce the effort associated with obtaining the sensitivity equations, and the large sensitivity system is solved using 'state of the art' routines. The quasianalytical approach is believed to be reasonably accurate and computationally efficient for 3-D problems.

Carlson, Leland A.; El-Banna, Hesham M.

1992-01-01

156

Aerodynamics of a linear oscillating cascade

NASA Technical Reports Server (NTRS)

The steady and unsteady aerodynamics of a linear oscillating cascade are investigated using experimental and computational methods. Experiments are performed to quantify the torsion mode oscillating cascade aerodynamics of the NASA Lewis Transonic Oscillating Cascade for subsonic inlet flowfields using two methods: simultaneous oscillation of all the cascaded airfoils at various values of interblade phase angle, and the unsteady aerodynamic influence coefficient technique. Analysis of these data and correlation with classical linearized unsteady aerodynamic analysis predictions indicate that the wind tunnel walls enclosing the cascade have, in some cases, a detrimental effect on the cascade unsteady aerodynamics. An Euler code for oscillating cascade aerodynamics is modified to incorporate improved upstream and downstream boundary conditions and also the unsteady aerodynamic influence coefficient technique. The new boundary conditions are shown to improve the unsteady aerodynamic influence coefficient technique. The new boundary conditions are shown to improve the unsteady aerodynamic predictions of the code, and the computational unsteady aerodynamic influence coefficient technique is shown to be a viable alternative for calculation of oscillating cascade aerodynamics.

Buffum, Daniel H.; Fleeter, Sanford

1990-01-01

157

Introduction. Computational aerodynamics

The wide range of uses of computational fluid dynamics (CFD) for aircraft design is discussed along with its role in dealing with the environmental impact of flight. Enabling technologies, such as grid generation and turbulence models, are also considered along with flow\\/turbulence control. The large eddy simulation, Reynolds-averaged Navier- Stokes and hybrid turbulence modelling approaches are contrasted. The CFD prediction

Paul G. Tucker

2007-01-01

158

Hypersonic Aerodynamics Fellowships.

National Technical Information Service (NTIS)

This work resulted in: (1) a new approach to hypersonic waverider vehicles, which has lead to a family of waveriders with exceptionally promising characteristics, and (2) the first data on the interaction of a vortex with a shock wave at hypersonic speeds...

J. D. Anderson

1991-01-01

159

An electrical approach to wave energy conversion

Motions in nature, for example ocean waves, can play a significant role in tomorrow's electricity production, but the constructions require adaptations to its media. Engineers planning hydropower plants have always taken natural conditions, such as fall height, speed of flow, and geometry, as basic design parameters and constraints in the design. The present paper describes a novel approach for electric

M. Leijon; O. Danielsson; M. Eriksson; K. Thorburn; H. Bernhoff; J. Isberg; J. Sundberg; I. Ivanova; E. Sjöstedt; O. Ågren; K. E. Karlsson; A. Wolfbrandt

2006-01-01

160

Energy approach to considering multicomponent powder systems

NASA Astrophysics Data System (ADS)

The problems of formation of the structure of a dispersed multicomponent powder mixture in mixing are considered from an energy standpoint. The homogeneous state of a powder mixture is shown to be energetically more favorable than the state of its separation, since it has a lower free energy margin and a higher configurational entropy. Depending on external conditions, a mixture of homogeneous regions with different component concentrations can have a more stable state.

Minaev, A. M.; Mordasov, D. M.; Tyalina, L. N.

2013-11-01

161

Formulation for Simultaneous Aerodynamic Analysis and Design Optimization

NASA Technical Reports Server (NTRS)

An efficient approach for simultaneous aerodynamic analysis and design optimization is presented. This approach does not require the performance of many flow analyses at each design optimization step, which can be an expensive procedure. Thus, this approach brings us one step closer to meeting the challenge of incorporating computational fluid dynamic codes into gradient-based optimization techniques for aerodynamic design. An adjoint-variable method is introduced to nullify the effect of the increased number of design variables in the problem formulation. The method has been successfully tested on one-dimensional nozzle flow problems, including a sample problem with a normal shock. Implementations of the above algorithm are also presented that incorporate Newton iterations to secure a high-quality flow solution at the end of the design process. Implementations with iterative flow solvers are possible and will be required for large, multidimensional flow problems.

Hou, G. W.; Taylor, A. C., III; Mani, S. V.; Newman, P. A.

1993-01-01

162

Aeroassist flight experiment aerodynamics and aerothermodynamics

NASA Technical Reports Server (NTRS)

The problem is to determine the transitional flow aerodynamics and aerothermodynamics, including the base flow characteristics, of the Aeroassist Flight Experiment (AFE). The justification for the computational fluid dynamic (CFD) Application stems from MSFC's system integration responsibility for the AFE. To insure that the AFE objectives are met, MSFC must understand the limitations and uncertainties of the design data. Perhaps the only method capable of handling the complex physics of the rarefied high energy AFE trajectory is Bird's Direct Simulation Monte Carlo (DSMC) technique. The 3-D code used in this analysis is applicable only to the AFE geometry. It uses the Variable Hard Sphere (VHS) collision model and five specie chemistry model available from Langley Research Center. The code is benchmarked against the AFE flight data and used as an Aeroassisted Space Transfer Vehicle (ASTV) design tool. The code is being used to understand the AFE flow field and verify or modify existing design data. Continued application to lower altitudes is testing the capability of the Numerical Aerodynamic Simulation Facility (NASF) to handle 3-D DSMC and its practicality as an ASTV/AFE design tool.

Brewer, Edwin B.

1989-01-01

163

Improved Aerodynamic Influence Coefficients for Dynamic Aeroelastic Analyses

NASA Astrophysics Data System (ADS)

Currently at Bombardier Aerospace, aeroelastic analyses are performed using the Doublet Lattice Method (DLM) incorporated in the NASTRAN solver. This method proves to be very reliable and fast in preliminary design stages where wind tunnel experimental results are often not available. Unfortunately, the geometric simplifications and limitations of the DLM, based on the lifting surfaces theory, reduce the ability of this method to give reliable results for all flow conditions, particularly in transonic flow. Therefore, a new method has been developed involving aerodynamic data from high-fidelity CFD codes which solve the Euler or Navier-Stokes equations. These new aerodynamic loads are transmitted to the NASTRAN aeroelastic module through improved aerodynamic influence coefficients (AIC). A cantilevered wing model is created from the Global Express structural model and a set of natural modes is calculated for a baseline configuration of the structure. The baseline mode shapes are then combined with an interpolation scheme to deform the 3-D CFD mesh necessary for Euler and Navier-Stokes analyses. An uncoupled approach is preferred to allow aerodynamic information from different CFD codes. Following the steady state CFD analyses, pressure differences ( DeltaCp), calculated between the deformed models and the original geometry, lead to aerodynamic loads which are transferred to the DLM model. A modal-based AIC method is applied to the aerodynamic matrices of NASTRAN based on a least-square approximation to evaluate aerodynamic loads of a different wing configuration which displays similar types of mode shapes. The methodology developed in this research creates weighting factors based on steady CFD analyses which have an equivalent reduced frequency of zero. These factors are applied to both the real and imaginary part of the aerodynamic matrices as well as all reduced frequencies used in the PK-Method which solves flutter problems. The modal-based AIC method's evaluation, performed with CFD data calculated by the DLM, is essential to find the natural modes which are most influential on the flutter solutions of the different configurations. Finally, Euler and Navier-Stokes results are used to obtain improved flutter solutions for a subsonic case at Mach 0.7 and dispositions are made to accomplish the same exercise for transonic speeds.

Gratton, Patrice

164

Approaches for biological and biomimetic energy conversion

This article highlights areas of research at the interface of nanotechnology, the physical sciences, and biology that are related to energy conversion: specifically, those related to photovoltaic applications. Although much ongoing work is seeking to understand basic processes of photosynthesis and chemical conversion, such as light harvesting, electron transfer, and ion transport, application of this knowledge to the development of fully synthetic and/or hybrid devices is still in its infancy. To develop systems that produce energy in an efficient manner, it is important both to understand the biological mechanisms of energy flow for optimization of primary structure and to appreciate the roles of architecture and assembly. Whether devices are completely synthetic and mimic biological processes or devices use natural biomolecules, much of the research for future power systems will happen at the intersection of disciplines.

LaVan, David A.; Cha, Jennifer N.

2006-01-01

165

Buckling of Braced Monosymmetric Cantilevers: Timoshenko Energy Approach.

National Technical Information Service (NTIS)

The paper examines the elastic lateral buckling of monosymmetric cantilevers with a discrete intermediate brace. On the basis of the Timoshenko energy approach, the buckling capacities are determined by direct minimization of the Rayleigh quotient. The in...

S. Kitipornchai C. M. Wang V. Thevendran

1986-01-01

166

Biomimetic Approach to Solar Energy Conversion.

National Technical Information Service (NTIS)

A biomimetic process is carried out in vitro by an inanimate system or apparatus and is based on methods used by living organisms. Specifically, the prospects for using the methods of plant photosynthesis for solar energy conversion are considered. The di...

J. J. Katz T. R. Janson M. R. Wasielewski

1977-01-01

167

Resistor Emulation Approach to Low-Power Energy Harvesting

This paper presents an approach and associated circuitry for harvesting near maximum output from low power sources in the 100 muW range for miniature wireless devices. A set of converter topologies and control approaches are presented together with detailed efficiency analysis and a design example for a buck-boost based energy harvesting converter using commercially available discrete circuitry. Experimental results are

Thurein S. Paing; Regan Zane

2006-01-01

168

Computing bounds on greenhouse energy requirements using bounded error approach

The paper presents an approach, based on a linear, time-varying model to compute bounds on future energy requirements for greenhouse heating. Modelling errors and model parameter variations are bounded while no assumptions are necessary about their distributions. Bounds on model parameters are computed using an ellipsoidal parameter bounding approach. Wind speed is considered as the main external disturbance. Results forecasting

D. Maksarov; Z. S. Chalabi

1998-01-01

169

Measuring energy efficiency in economics: Shadow value approach

NASA Astrophysics Data System (ADS)

For decades, academic scholars and policy makers have commonly applied a simple average measure, energy intensity, for studying energy efficiency. In contrast, we introduce a distinctive marginal measure called energy shadow value (SV) for modeling energy efficiency drawn on economic theory. This thesis demonstrates energy SV advantages, conceptually and empirically, over the average measure recognizing marginal technical energy efficiency and unveiling allocative energy efficiency (energy SV to energy price). Using a dual profit function, the study illustrates how treating energy as quasi-fixed factor called quasi-fixed approach offers modeling advantages and is appropriate in developing an explicit model for energy efficiency. We address fallacies and misleading results using average measure and demonstrate energy SV advantage in inter- and intra-country energy efficiency comparison. Energy efficiency dynamics and determination of efficient allocation of energy use are shown through factors impacting energy SV: capital, technology, and environmental obligations. To validate the energy SV, we applied a dual restricted cost model using KLEM dataset for the 35 US sectors stretching from 1958 to 2000 and selected a sample of the four sectors. Following the empirical results, predicted wedges between energy price and the SV growth indicate a misallocation of energy use in stone, clay and glass (SCG) and communications (Com) sectors with more evidence in the SCG compared to the Com sector, showing overshoot in energy use relative to optimal paths and cost increases from sub-optimal energy use. The results show that energy productivity is a measure of technical efficiency and is void of information on the economic efficiency of energy use. Decomposing energy SV reveals that energy, capital and technology played key roles in energy SV increases helping to consider and analyze policy implications of energy efficiency improvement. Applying the marginal measure, we also contributed to energy efficiency convergence analysis employing the delta-convergence and unconditional & conditional beta-convergence concepts, investigating economic energy efficiency differences across the four US sectors using panel data models. The results show that, in terms of technical and allocative energy efficiency, the energy-intensive sectors, SCG and textile mill products, tend to catch the energy extensive sectors, the Com and furniture & fixtures, being conditional on sector-specific characteristics. Conditional convergence results indicate that technology, capital and energy are crucial factors in determining energy efficiency differences across the US sectors, implying that environmental or energy policies, and technological changes should be industry specific across the US sectors. The main finding is that the marginal value measure conveys information on both technical and allocative energy efficiency and accounts for all costs and benefits of energy consumption including environmental and externality costs.

Khademvatani, Asgar

170

Aerodynamics of a cricket ball

This paper describes experiments performed on stationary and rotating cricket balls to determine the aerodynamic forces acting on the ball over a range of bowling speeds and seam angles. Lift, drag and side forces were measured directly and it was found they exhibited magnitudes in the order of 1.4, 1 and 0.4N, respectively, for the stationary ball. At air velocities

A. T Sayers; A Hill

1999-01-01

171

Aerodynamic Design Using Neural Networks

NASA Technical Reports Server (NTRS)

The design of aerodynamic components of aircraft, such as wings or engines, involves a process of obtaining the most optimal component shape that can deliver the desired level of component performance, subject to various constraints, e.g., total weight or cost, that the component must satisfy. Aerodynamic design can thus be formulated as an optimization problem that involves the minimization of an objective function subject to constraints. A new aerodynamic design optimization procedure based on neural networks and response surface methodology (RSM) incorporates the advantages of both traditional RSM and neural networks. The procedure uses a strategy, denoted parameter-based partitioning of the design space, to construct a sequence of response surfaces based on both neural networks and polynomial fits to traverse the design space in search of the optimal solution. Some desirable characteristics of the new design optimization procedure include the ability to handle a variety of design objectives, easily impose constraints, and incorporate design guidelines and rules of thumb. It provides an infrastructure for variable fidelity analysis and reduces the cost of computation by using less-expensive, lower fidelity simulations in the early stages of the design evolution. The initial or starting design can be far from optimal. The procedure is easy and economical to use in large-dimensional design space and can be used to perform design tradeoff studies rapidly. Designs involving multiple disciplines can also be optimized. Some practical applications of the design procedure that have demonstrated some of its capabilities include the inverse design of an optimal turbine airfoil starting from a generic shape and the redesign of transonic turbines to improve their unsteady aerodynamic characteristics.

Rai, Man Mohan; Madavan, Nateri K.

2003-01-01

172

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

173

X-34 Vehicle Aerodynamic Characteristics

NASA Technical Reports Server (NTRS)

The X-34, being designed and built by the Orbital Sciences Corporation, is an unmanned sub-orbital vehicle designed to be used as a flying test bed to demonstrate key vehicle and operational technologies applicable to future reusable launch vehicles. The X-34 will be air-launched from an L-1011 carrier aircraft at approximately Mach 0.7 and 38,000 feet altitude, where an onboard engine will accelerate the vehicle to speeds above Mach 7 and altitudes to 250,000 feet. An unpowered entry will follow, including an autonomous landing. The X-34 will demonstrate the ability to fly through inclement weather, land horizontally at a designated site, and have a rapid turn-around capability. A series of wind tunnel tests on scaled models was conducted in four facilities at the NASA Langley Research Center to determine the aerodynamic characteristics of the X-34. Analysis of these test results revealed that longitudinal trim could be achieved throughout the design trajectory. The maximum elevon deflection required to trim was only half of that available, leaving a margin for gust alleviation and aerodynamic coefficient uncertainty. Directional control can be achieved aerodynamically except at combined high Mach numbers and high angles of attack, where reaction control jets must be used. The X-34 landing speed, between 184 and 206 knots, is within the capabilities of the gear and tires, and the vehicle has sufficient rudder authority to control the required 30-knot crosswind.

Brauckmann, Gregory J.

1998-01-01

174

Applied aerodynamics: Challenges and expectations

NASA Technical Reports Server (NTRS)

Aerospace is the leading positive contributor to this country's balance of trade, derived largely from the sale of U.S. commercial aircraft around the world. This powerfully favorable economic situation is being threatened in two ways: (1) the U.S. portion of the commercial transport market is decreasing, even though the worldwide market is projected to increase substantially; and (2) expenditures are decreasing for military aircraft, which often serve as proving grounds for advanced aircraft technology. To retain a major share of the world market for commercial aircraft and continue to provide military aircraft with unsurpassed performance, the U.S. aerospace industry faces many technological challenges. The field of applied aerodynamics is necessarily a major contributor to efforts aimed at meeting these technological challenges. A number of emerging research results that will provide new opportunities for applied aerodynamicists are discussed. Some of these have great potential for maintaining the high value of contributions from applied aerodynamics in the relatively near future. Over time, however, the value of these contributions will diminish greatly unless substantial investments continue to be made in basic and applied research efforts. The focus: to increase understanding of fluid dynamic phenomena, identify new aerodynamic concepts, and provide validated advanced technology for future aircraft.

Peterson, Victor L.; Smith, Charles A.

1993-01-01

175

A New Aerodynamic Data Dispersion Method for Launch Vehicle Design

NASA Technical Reports Server (NTRS)

A novel method for implementing aerodynamic data dispersion analysis is herein introduced. A general mathematical approach combined with physical modeling tailored to the aerodynamic quantity of interest enables the generation of more realistically relevant dispersed data and, in turn, more reasonable flight simulation results. The method simultaneously allows for the aerodynamic quantities and their derivatives to be dispersed given a set of non-arbitrary constraints, which stresses the controls model in more ways than with the traditional bias up or down of the nominal data within the uncertainty bounds. The adoption and implementation of this new method within the NASA Ares I Crew Launch Vehicle Project has resulted in significant increases in predicted roll control authority, and lowered the induced risks for flight test operations. One direct impact on launch vehicles is a reduced size for auxiliary control systems, and the possibility of an increased payload. This technique has the potential of being applied to problems in multiple areas where nominal data together with uncertainties are used to produce simulations using Monte Carlo type random sampling methods. It is recommended that a tailored physics-based dispersion model be delivered with any aerodynamic product that includes nominal data and uncertainties, in order to make flight simulations more realistic and allow for leaner spacecraft designs.

Pinier, Jeremy T.

2011-01-01

176

Aerodynamic modelling of insect-like flapping flight for micro air vehicles

NASA Astrophysics Data System (ADS)

Insect-like flapping flight offers a power-efficient and highly manoeuvrable basis for a micro air vehicle capable of indoor flight. The development of such a vehicle requires a careful wing aerodynamic design. This is particularly true since the flapping wings will be responsible for lift, propulsion and manoeuvres, all at the same time. It sets the requirement for an aerodynamic tool that will enable study of the parametric design space and converge on one (or more) preferred configurations. In this respect, aerodynamic modelling approaches are the most attractive, principally due to their ability to iterate rapidly through various design configurations. In this article, we review the main approaches found in the literature, categorising them into steady-state, quasi-steady, semi-empirical and fully unsteady methods. The unsteady aerodynamic model of Ansari et al. seems to be the most satisfactory to date and is considered in some detail. Finally, avenues for further research in this field are suggested.

Ansari, S. A.; ?bikowski, R.; Knowles, K.

2006-02-01

177

A Systemic Approach to Addressing the Complexity of Energy Problems

This paper presents a conceptual framework for using energy as a vehicle for holistic development to address: poverty, gender discrimination, community involvement in decision making on social, economic, and environmental issues. The approach is systemic and participatory ironically, energy is always seen or considered in fragmentation from other areas and as a technical subject, without considering it in less literal

Janet McIntyre; Merina Pradhan

2003-01-01

178

New Approach to Testing Dark Energy Models by Observations.

National Technical Information Service (NTIS)

We propose a new approach to the consistency test of dark energy models with observations. To test a category of dark energy models, we suggest introducing a characteristic Q(z) that in general varies with the redshift z but in those models plays the role...

L. E. Strigari

2013-01-01

179

Refrigeration principles and systems: An energy approach

The book presents the fundamental principles, systems, and practices of refrigeration. Emphasizing energy conservation, it offers applications of the refrigeration systems and equipment. Topics covered include: physical principles; the vapor compression refrigeration system: Pressure-enthalpy diagrams; thermodynamics of the vapor compression refrigeration cycle; reciprocating, rotary and screw compressors; heat transfer in refrigeration: Evaporators; condensers and cooling towers; refrigerant flow control (expansion) devices; refrigerants, brines, oils, and contaminants; centrifugal compressors and systems; the refrigerant piping system; low temperature refrigeration; absorption refrigeration; the refrigeration load: Component balancing; electrical service systems; and Motor Controls and Protection.

Pita, E.G.

1984-01-01

180

A Lyapunov based approach to energy maximization in renewable energy technologies

NASA Astrophysics Data System (ADS)

This dissertation describes the design and implementation of Lyapunov-based control strategies for the maximization of the power captured by renewable energy harnessing technologies such as (i) a variable speed, variable pitch wind turbine, (ii) a variable speed wind turbine coupled to a doubly fed induction generator, and (iii) a solar power generating system charging a constant voltage battery. First, a torque control strategy is presented to maximize wind energy captured in variable speed, variable pitch wind turbines at low to medium wind speeds. The proposed strategy applies control torque to the wind turbine pitch and rotor subsystems to simultaneously control the blade pitch and tip speed ratio, via the rotor angular speed, to an optimum point at which the capture efficiency is maximum. The control method allows for aerodynamic rotor power maximization without exact knowledge of the wind turbine model. A series of numerical results show that the wind turbine can be controlled to achieve maximum energy capture. Next, a control strategy is proposed to maximize the wind energy captured in a variable speed wind turbine, with an internal induction generator, at low to medium wind speeds. The proposed strategy controls the tip speed ratio, via the rotor angular speed, to an optimum point at which the efficiency constant (or power coefficient) is maximal for a particular blade pitch angle and wind speed by using the generator rotor voltage as a control input. This control method allows for aerodynamic rotor power maximization without exact wind turbine model knowledge. Representative numerical results demonstrate that the wind turbine can be controlled to achieve near maximum energy capture. Finally, a power system consisting of a photovoltaic (PV) array panel, dc-to-dc switching converter, charging a battery is considered wherein the environmental conditions are time-varying. A backstepping PWM controller is developed to maximize the power of the solar generating system. The controller tracks a desired array voltage, designed online using an incremental conductance extremum-seeking algorithm, by varying the duty cycle of the switching converter. The stability of the control algorithm is demonstrated by means of Lyapunov analysis. Representative numerical results demonstrate that the grid power system can be controlled to track the maximum power point of the photovoltaic array panel in varying atmospheric conditions. Additionally, the performance of the proposed strategy is compared to the typical maximum power point tracking (MPPT) method of perturb and observe (P&O), where the converter dynamics are ignored, and is shown to yield better results.

Iyasere, Erhun

181

The problem with the “portfolio approach” in American energy policy

One predominant theme in American energy and electricity policy is the idea of a “portfolio approach,” or that society must\\u000a embrace an assortment of different energy technologies simultaneously. This article argues that such a strategy, in practice,\\u000a is (a) biased, since fossil fuel and nuclear technologies have been heavily favored; (b) opaque, obscuring the different full\\u000a social costs of energy

Benjamin K. Sovacool

2008-01-01

182

Aerodynamic characteristics of a hybrid trimaran model

Ultra fast marine vehicles can substantially benefit from aerodynamic unloading. The subject of this study is aerodynamics of a hybrid trimaran that comprises three wave-piercing planing hulls and a wing-shaped superstructure. This configuration is characterized by high efficiency and good seaworthiness at speeds about twice those of contemporary fast ferries and combat ships. Aerodynamic coefficients of the above-water structure of

Konstantin I. Matveev; Victor A. Dubrovsky

2007-01-01

183

Two-Stage Axial Compressor Rig Designed To Develop and Validate Advanced Aerodynamic Technologies

NASA Technical Reports Server (NTRS)

Future aeropropulsion gas turbine engines must be affordable in addition to being energy efficient and environmentally benign. Progress in aerodynamic design capability is required not only to maximize the specific thrust of next-generation engines without sacrificing fuel consumption, but also to reduce parts count by increasing the aerodynamic loading of the compression system. To meet future compressor requirements, the NASA Glenn Research Center is investigating advanced aerodynamic design concepts that will lead to more compact, higher efficiency, and wider operability configurations than are currently in operation.

Larosiliere, Louis M.

2003-01-01

184

The role of unsteady aerodynamics in aeroacoustics

NASA Technical Reports Server (NTRS)

The role of acoustics and unsteady aerodynamics research in understanding the fundamental physics of time-dependent fluid phenomena is reviewed. The key issues are illustrated by considering the sound radiation of turbulent jets and the aeroacoustics of rotating bodies such as helicopter rotors. The importance of computational methods as a link between aerodynamics and acoustics is also discussed. It is noted that where acoustic analogy techniques are sufficiently accurate, unsteady aerodynamics can be used for acoustic prediction. In supersonic problems where acoustics and aerodynamics are coupled, an integrated nonlinear analysis can provide an accurate problem solution.

Pao, S. Paul

1988-01-01

185

Study on aerodynamic design optimization of turbomachinery blades

This paper describes the study on aerodynamics design optimization of turbomachinery blading developed by the authors at the\\u000a Institute of Engineering Thermophysics, Chinese Academy of Sciences, during the recent few years. The present paper describes\\u000a the aspects mainly on how to use a rapid approach of profiling a 3D blading and of grid generation for computation, a fast\\u000a and accurate

Naixing Chen; Hongwu Zhang; Weiguang Huang; Yanji Xu

2005-01-01

186

Analysis and optimization of aerodynamic noise in a centrifugal compressor

The numerical methods for the performance analysis and the noise prediction of the centrifugal compressor impeller are developed, which are coupled with the optimization design methodology consisting of response surface method, statistical approach, and genetic algorithm. Navier–Stokes equations with the two-equation (k–?) turbulence model are applied to calculate impeller aerodynamic characteristics, and Ffowcs Williams–Hawkings formulation and boundary element method are

Hyosung Sun; Hyungki Shin; Soogab Lee

2006-01-01

187

The alleviation of the aerodynamic drag and wave effects of high-speed trains in very long tunnels

The design of new high-speed railway lines requires longer and more numerous tunnel sections, where aerodynamic effects limit the maximum allowed train velocity for a given tunnel cross-section area. These effects influence the train power requirement, the traction energy costs and the pressure wave amplitude: the knowledge of the unsteady aerodynamic field around the train is therefore essential to the

Arturo Baron; Michele Mossi; Stefano Sibilla

2001-01-01

188

Towards a 3d Spatial Urban Energy Modelling Approach

NASA Astrophysics Data System (ADS)

Today's needs to reduce the environmental impact of energy use impose dramatic changes for energy infrastructure and existing demand patterns (e.g. buildings) corresponding to their specific context. In addition, future energy systems are expected to integrate a considerable share of fluctuating power sources and equally a high share of distributed generation of electricity. Energy system models capable of describing such future systems and allowing the simulation of the impact of these developments thus require a spatial representation in order to reflect the local context and the boundary conditions. This paper describes two recent research approaches developed at EIFER in the fields of (a) geo-localised simulation of heat energy demand in cities based on 3D morphological data and (b) spatially explicit Agent-Based Models (ABM) for the simulation of smart grids. 3D city models were used to assess solar potential and heat energy demand of residential buildings which enable cities to target the building refurbishment potentials. Distributed energy systems require innovative modelling techniques where individual components are represented and can interact. With this approach, several smart grid demonstrators were simulated, where heterogeneous models are spatially represented. Coupling 3D geodata with energy system ABMs holds different advantages for both approaches. On one hand, energy system models can be enhanced with high resolution data from 3D city models and their semantic relations. Furthermore, they allow for spatial analysis and visualisation of the results, with emphasis on spatially and structurally correlations among the different layers (e.g. infrastructure, buildings, administrative zones) to provide an integrated approach. On the other hand, 3D models can benefit from more detailed system description of energy infrastructure, representing dynamic phenomena and high resolution models for energy use at component level. The proposed modelling strategies conceptually and practically integrate urban spatial and energy planning approaches. The combined modelling approach that will be developed based on the described sectorial models holds the potential to represent hybrid energy systems coupling distributed generation of electricity with thermal conversion systems.

Bahu, J.-M.; Koch, A.; Kremers, E.; Murshed, S. M.

2013-09-01

189

Aerodynamic Parameters of a UK City Derived from Morphological Data

NASA Astrophysics Data System (ADS)

Detailed three-dimensional building data and a morphometric model are used to estimate the aerodynamic roughness length z 0 and displacement height d over a major UK city (Leeds). Firstly, using an adaptive grid, the city is divided into neighbourhood regions that are each of a relatively consistent geometry throughout. Secondly, for each neighbourhood, a number of geometric parameters are calculated. Finally, these are used as input into a morphometric model that considers the influence of height variability to predict aerodynamic roughness length and displacement height. Predictions are compared with estimations made using standard tables of aerodynamic parameters. The comparison suggests that the accuracy of plan-area-density based tables is likely to be limited, and that height-based tables of aerodynamic parameters may be more accurate for UK cities. The displacement heights in the standard tables are shown to be lower than the current predictions. The importance of geometric details in determining z 0 and d is then explored. Height variability is observed to greatly increase the predicted values. However, building footprint shape only has a significant influence upon the predictions when height variability is not considered. Finally, we develop simple relations to quantify the influence of height variation upon predicted z 0 and d via the standard deviation of building heights. The difference in these predictions compared to the more complex approach highlights the importance of considering the specific shape of the building-height distributions. Collectively, these results suggest that to accurately predict aerodynamic parameters of real urban areas, height variability must be considered in detail, but it may be acceptable to make simple assumptions about building layout and footprint shape.

Millward-Hopkins, J. T.; Tomlin, A. S.; Ma, L.; Ingham, D. B.; Pourkashanian, M.

2013-03-01

190

The Wisconsin Regional Energy Model - A dynamic approach to regional energy analysis

The Wisconsin Regional Energy Model (WISE) combines an engineering and economic approach to model the State's energy system. WISE is essentially a massive computerized information system which describes energy demand, conversion, transport, and use, explicitly accounting for technological, economic, and environmental interactions. The WISE model has been employed to analyze a variety of energy related problems for Wisconsin. Among the

W. K. Foell; J. W. Mitchell; J. L. Pappas

1975-01-01

191

Inner workings of aerodynamic sweep

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

192

Aerodynamics. [numerical simulation using supercomputers

NASA Technical Reports Server (NTRS)

A projection is made of likely improvements in the economics of commercial aircraft operation due to developments in aerodynamics in the next half-century. Notable among these improvements are active laminar flow control techniques' application to third-generation SSTs, in order to achieve an L/D value of about 20; this is comparable to current subsonic transports, and has the further consequence of reducing cabin noise. Wave-cancellation systems may also be used to eliminate sonic boom overpressures, and rapid-combustion systems may be able to eliminate all pollutants from jet exhausts other than CO2.

Graves, Randolph A., Jr.

1988-01-01

193

The basic aerodynamics of floatation

The original derivation of the basic theory governing the aerodynamics of both hovercraft and modern floatation ovens, requires the validity of some extremely crude assumptions. However, the basic theory is surprisingly accurate. It is shown that this accuracy occurs because the final expression of the basic theory can be derived by approximating the full Navier-Stokes equations in a manner that clearly shows the limitations of the theory. These limitations are used in discussing the relatively small discrepancies between the theory and experiment, which may not be significant for practical purposes.

Davies, M.J.; Wood, D.H.

1983-09-01

194

Simulation of iced wing aerodynamics

NASA Technical Reports Server (NTRS)

The sectional and total aerodynamic load characteristics of moderate aspect ratio wings with and without simulated glaze leading edge ice were studied both computationally, using a three dimensional, compressible Navier-Stokes solver, and experimentally. The wing has an untwisted, untapered planform shape with NACA 0012 airfoil section. The wing has an unswept and swept configuration with aspect ratios of 4.06 and 5.0. Comparisons of computed surface pressures and sectional loads with experimental data for identical configurations are given. The abrupt decrease in stall angle of attack for the wing, as a result of the leading edge ice formation, was demonstrated numerically and experimentally.

Potapczuk, M. G.; Bragg, M. B.; Kwon, O. J.; Sankar, L. N.

1991-01-01

195

Recent progress in flapping wing aerodynamics and aeroelasticity

NASA Astrophysics Data System (ADS)

Micro air vehicles (MAVs) have the potential to revolutionize our sensing and information gathering capabilities in areas such as environmental monitoring and homeland security. Flapping wings with suitable wing kinematics, wing shapes, and flexible structures can enhance lift as well as thrust by exploiting large-scale vortical flow structures under various conditions. However, the scaling invariance of both fluid dynamics and structural dynamics as the size changes is fundamentally difficult. The focus of this review is to assess the recent progress in flapping wing aerodynamics and aeroelasticity. It is realized that a variation of the Reynolds number (wing sizing, flapping frequency, etc.) leads to a change in the leading edge vortex (LEV) and spanwise flow structures, which impacts the aerodynamic force generation. While in classical stationary wing theory, the tip vortices (TiVs) are seen as wasted energy, in flapping flight, they can interact with the LEV to enhance lift without increasing the power requirements. Surrogate modeling techniques can assess the aerodynamic outcomes between two- and three-dimensional wing. The combined effect of the TiVs, the LEV, and jet can improve the aerodynamics of a flapping wing. Regarding aeroelasticity, chordwise flexibility in the forward flight can substantially adjust the projected area normal to the flight trajectory via shape deformation, hence redistributing thrust and lift. Spanwise flexibility in the forward flight creates shape deformation from the wing root to the wing tip resulting in varied phase shift and effective angle of attack distribution along the wing span. Numerous open issues in flapping wing aerodynamics are highlighted.

Shyy, W.; Aono, H.; Chimakurthi, S. K.; Trizila, P.; Kang, C.-K.; Cesnik, C. E. S.; Liu, H.

2010-10-01

196

Estimating Aerodynamic Parameters of Urban-Like Surfaces with Heterogeneous Building Heights

There are many geometrical factors than can influence the aerodynamic parameters of urban surfaces and hence the vertical\\u000a wind profiles found above. The knowledge of these parameters has applications in numerous fields, such as dispersion modelling,\\u000a wind loading calculations, and estimating the wind energy resource at urban locations. Using quasi-empirical modelling, we\\u000a estimate the dependence of the aerodynamic roughness length

J. T. Millward-Hopkins; A. S. Tomlin; L. Ma; D. Ingham; M. Pourkashanian

197

Constrained-substructure approach to optimal strain energy analysis

NASA Astrophysics Data System (ADS)

The chief tool for design of viscoelastic-based damping treatments over the past 20 years has been the modal strain energy (MSE) approach. This approach to damping design traditionally has involved a practitioner to vary placement and stiffness of add-on elements using experience and trial and error so as to maximize the add-on element's share of system MSE in modes of interest. In this paper we develop a new technique for maximizing strain energy as a function of stiffness for add-on structural elements modeled as rank r perturbations to the original stiffness matrix. The techniques is based on a constrained substructure approach allowing us to parameterize strain energy in terms of the eigenvalues of the perturbed structure. An optimality condition is derived that relates the input-output response at the attachment location of the add-on elements to the maximum achievable strain energy. A realizability condition is also derived which indicates whether or not the optimal solution is achievable with passive structural elements. This method has applications in the design of structural treatments for controlling sound and vibration and promises an efficient means of determining the limits of performance of passive structural treatments. An advantage of our approach over existing methods is that the maximum achievable strain energy fraction in the add-on elements is directly computable with the realizability condition then indicating whether the optimal solution is achievable.

Leo, Donald J.; Austin, Eric M.; Beattie, Christopher A.

2000-04-01

198

Rarefaction Effects on Galileo Probe Aerodynamics.

National Technical Information Service (NTIS)

Solutions of aerodynamic characteristics are presented for the Galileo Probe entering Jupiter's hydrogen-helium atmosphere at a nominal relative velocity of 47.4 km/s. Focus is on predicting the aerodynamic drag coefficient during the transitional flow re...

J. N. Moss G. J. Lebeau R. C. Blanchard J. M. Price

1996-01-01

199

An experimental study of Wiffle ball aerodynamics

We measure the aerodynamic forces on a Wiffle ball as a function of the Reynolds number and ball orientation. The effects of asymmetric flow outside the ball and flow within the ball are considered, and are both associated with the ball's tendency to curve without pitcher-imparted spin. The problem of Wiffle ball aerodynamics is an accessible way to introduce topics

Jenn Rossmann; Andrew Rau

2007-01-01

200

A study of golf ball aerodynamic drag

The aerodynamics of golf balls is considerably more complex than that of many other spherical balls. The surface roughness in the form of dimples intensifies the level of complexity and three-dimensionality of air flow around the golf ball. Prior studies have revealed that golf ball aerodynamics is still not fully understood due to the varied dimple size, shape, depth and

Firoz Alam; Tom Steiner; Harun Chowdhury; Hazim Moria; Iftekhar Khan; Fayez Aldawi; Aleksandar Subic

2011-01-01

201

Numerical Analysis of Flapping Wing Aerodynamics

Flapping-wing aerodynamics recently has generated a great deal of interest and increasing research effort because of the potential application in micro-air vehicles. The objective of this study is to critically review the recent progress of CFD analysis of flapping- wing aerodynamics. Critical parameters like flapping modes, frequency and amplitude for optimal thrust generation and propulsive efficiency are identified. Current gaps

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

202

The aerodynamics of small Reynolds numbers

NASA Technical Reports Server (NTRS)

Aerodynamic characteristics of wing model gliders and bird wings in particular are discussed. Wind tunnel measurements and aerodynamics of small Reynolds numbers are enumerated. Airfoil behavior in the critical transition from laminar to turbulent boundary layer, which is more important to bird wing models than to large airplanes, was observed. Experimental results are provided, and an artificial bird wing is described.

Schmitz, F. W.

1980-01-01

203

Future Computer Requirements for Computational Aerodynamics

NASA Technical Reports Server (NTRS)

Recent advances in computational aerodynamics are discussed as well as motivations for and potential benefits of a National Aerodynamic Simulation Facility having the capability to solve fluid dynamic equations at speeds two to three orders of magnitude faster than presently possible with general computers. Two contracted efforts to define processor architectures for such a facility are summarized.

1978-01-01

204

Aerodynamics of Sounding-Rocket Geometries

NASA Technical Reports Server (NTRS)

Theoretical aerodynamics program TAD predicts aerodynamic characteristics of vehicles with sounding-rocket configurations. These slender, Axisymmetric finned vehicles have a wide range of aeronautical applications from rockets to high-speed armament. TAD calculates characteristics of separate portions of vehicle, calculates interference between portions, and combines results to form total vehicle solution.

Barrowman, J.

1982-01-01

205

CFD MODELLING OF WIND TURBINE AIRFOIL AERODYNAMICS

SUMMARY This paper reports the first findings of an ongoing research programme on wind turbine computational aerodynamics at the University of Glasgow. Several modeling aspects of wind turbine airfoil aerodynamics based on the solution of the Reynolds- averaged Navier-Stokes (RANS) equations are addressed. One of these is the effect of an a priori method for structured grid adaptation aimed at

M. S. Campobasso; A. Zanon; M. Foerster; F. Fraysse; A. Bonfiglioli

206

Energy Efficiency in Future Home Environments: A Distributed Approach

In this paper, a new architecture for sharing resources amongst home environments is proposed. Our approach goes far beyond\\u000a traditional systems for distributed virtualization like PlanetLab or Grid computing, since it relies on complete decentralization\\u000a in a peer-to-peer like manner, and above all, aims at energy efficiency. Energy metrics are defined, which have to be optimized\\u000a by the system. The

Helmut Hlavacs; Karin A. Hummel; Roman Weidlich; Amine Houyou; Andreas Berl; Hermann de Meer

207

Orion Crew Module Aerodynamic Testing

NASA Technical Reports Server (NTRS)

The Apollo-derived Orion Crew Exploration Vehicle (CEV), part of NASA s now-cancelled Constellation Program, has become the reference design for the new Multi-Purpose Crew Vehicle (MPCV). The MPCV will serve as the exploration vehicle for all near-term human space missions. A strategic wind-tunnel test program has been executed at numerous facilities throughout the country to support several phases of aerodynamic database development for the Orion spacecraft. This paper presents a summary of the experimental static aerodynamic data collected to-date for the Orion Crew Module (CM) capsule. The test program described herein involved personnel and resources from NASA Langley Research Center, NASA Ames Research Center, NASA Johnson Space Flight Center, Arnold Engineering and Development Center, Lockheed Martin Space Sciences, and Orbital Sciences. Data has been compiled from eight different wind tunnel tests in the CEV Aerosciences Program. Comparisons are made as appropriate to highlight effects of angle of attack, Mach number, Reynolds number, and model support system effects.

Murphy, Kelly J.; Bibb, Karen L.; Brauckmann, Gregory J.; Rhode, Matthew N.; Owens, Bruce; Chan, David T.; Walker, Eric L.; Bell, James H.; Wilson, Thomas M.

2011-01-01

208

X-33 Hypersonic Aerodynamic Characteristics

NASA Technical Reports Server (NTRS)

Lockheed Martin Skunk Works, under a cooperative agreement with NASA, will build and fly the X-33, a half-scale prototype of a rocket-based, single-stage-to-orbit (SSTO), reusable launch vehicle (RLV). A 0.007-scale model of the X-33 604B0002G configuration was tested in four hypersonic facilities at the NASA Langley Research Center to examine vehicle stability and control characteristics and to populate an aerodynamic flight database i n the hypersonic regime. The vehicle was found to be longitudinally controllable with less than half of the total body flap deflection capability across the angle of attack range at both Mach 6 and Mach 10. At these Mach numbers, the vehicle also was shown to be longitudinally stable or neutrally stable for typical (greater than 20 degrees) hypersonic flight attitudes. This configuration was directionally unstable and the use of reaction control jets (RCS) will be necessary to control the vehicle at high angles of attack in the hypersonic flight regime. Mach number and real gas effects on longitudinal aerodynamics were shown to be small relative to X-33 control authority.

Murphy, Kelly J.; Nowak, Robert J.; Thompson, Richard A.; Hollis, Brian R.; Prabhu, Ramadas K.

1999-01-01

209

Aerodynamic optimization by simultaneously updating flow variables and design parameters

NASA Technical Reports Server (NTRS)

The application of conventional optimization schemes to aerodynamic design problems leads to inner-outer iterative procedures that are very costly. An alternative approach is presented based on the idea of updating the flow variable iterative solutions and the design parameter iterative solutions simultaneously. Two schemes based on this idea are applied to problems of correcting wind tunnel wall interference and optimizing advanced propeller designs. The first of these schemes is applicable to a limited class of two-design-parameter problems with an equality constraint. It requires the computation of a single flow solution. The second scheme is suitable for application to general aerodynamic problems. It requires the computation of several flow solutions in parallel. In both schemes, the design parameters are updated as the iterative flow solutions evolve. Computations are performed to test the schemes' efficiency, accuracy, and sensitivity to variations in the computational parameters.

Rizk, M. H.

1990-01-01

210

Grid Sensitivity and Aerodynamic Optimization of Generic Airfoils

NASA Technical Reports Server (NTRS)

An algorithm is developed to obtain the grid sensitivity with respect to design parameters for aerodynamic optimization. The procedure is advocating a novel (geometrical) parameterization using spline functions such as NURBS (Non-Uniform Rational B- Splines) for defining the airfoil geometry. An interactive algebraic grid generation technique is employed to generate C-type grids around airfoils. The grid sensitivity of the domain with respect to geometric design parameters has been obtained by direct differentiation of the grid equations. A hybrid approach is proposed for more geometrically complex configurations such as a wing or fuselage. The aerodynamic sensitivity coefficients are obtained by direct differentiation of the compressible two-dimensional thin-layer Navier-Stokes equations. An optimization package has been introduced into the algorithm in order to optimize the airfoil surface. Results demonstrate a substantially improved design due to maximized lift/drag ratio of the airfoil.

Sadrehaghighi, Ideen; Smith, Robert E.; Tiwari, Surendra N.

1995-01-01

211

NASA Technical Reports Server (NTRS)

The quasi-analytical approach is applied to the three-dimensional full potential equation to compute wing aerodynamic sensitivity coefficients in the transonic regime. Symbolic manipulation is used to reduce the effort associated with obtaining the sensitivity equations, and the large sensitivity system is solved using 'state of the art' routines. Results are compared to those obtained by the direct finite difference approach and both methods are evaluated to determine their computational accuracy and efficiency. The quasi-analytical approach is shown to be accurate and efficient for large aerodynamic systems.

Elbanna, Hesham M.; Carlson, Leland A.

1992-01-01

212

Aerodynamic effects of flexibility in flapping wings.

Recent work on the aerodynamics of flapping flight reveals fundamental differences in the mechanisms of aerodynamic force generation between fixed and flapping wings. When fixed wings translate at high angles of attack, they periodically generate and shed leading and trailing edge vortices as reflected in their fluctuating aerodynamic force traces and associated flow visualization. In contrast, wings flapping at high angles of attack generate stable leading edge vorticity, which persists throughout the duration of the stroke and enhances mean aerodynamic forces. Here, we show that aerodynamic forces can be controlled by altering the trailing edge flexibility of a flapping wing. We used a dynamically scaled mechanical model of flapping flight (Re approximately 2000) to measure the aerodynamic forces on flapping wings of variable flexural stiffness (EI). For low to medium angles of attack, as flexibility of the wing increases, its ability to generate aerodynamic forces decreases monotonically but its lift-to-drag ratios remain approximately constant. The instantaneous force traces reveal no major differences in the underlying modes of force generation for flexible and rigid wings, but the magnitude of force, the angle of net force vector and centre of pressure all vary systematically with wing flexibility. Even a rudimentary framework of wing veins is sufficient to restore the ability of flexible wings to generate forces at near-rigid values. Thus, the magnitude of force generation can be controlled by modulating the trailing edge flexibility and thereby controlling the magnitude of the leading edge vorticity. To characterize this, we have generated a detailed database of aerodynamic forces as a function of several variables including material properties, kinematics, aerodynamic forces and centre of pressure, which can also be used to help validate computational models of aeroelastic flapping wings. These experiments will also be useful for wing design for small robotic insects and, to a limited extent, in understanding the aerodynamics of flapping insect wings. PMID:19692394

Zhao, Liang; Huang, Qingfeng; Deng, Xinyan; Sane, Sanjay P

2010-03-01

213

Reduced density matrix hybrid approach: Application to electronic energy transfer

NASA Astrophysics Data System (ADS)

Electronic energy transfer in the condensed phase, such as that occurring in photosynthetic complexes, frequently occurs in regimes where the energy scales of the system and environment are similar. This situation provides a challenge to theoretical investigation since most approaches are accurate only when a certain energetic parameter is small compared to others in the problem. Here we show that in these difficult regimes, the Ehrenfest approach provides a good starting point for a dynamical description of the energy transfer process due to its ability to accurately treat coupling to slow environmental modes. To further improve on the accuracy of the Ehrenfest approach, we use our reduced density matrix hybrid framework to treat the faster environmental modes quantum mechanically, at the level of a perturbative master equation. This combined approach is shown to provide an efficient and quantitative description of electronic energy transfer in a model dimer and the Fenna-Matthews-Olson complex and is used to investigate the effect of environmental preparation on the resulting dynamics.

Berkelbach, Timothy C.; Markland, Thomas E.; Reichman, David R.

2012-02-01

214

Estimating the Energy Gap Among US Children: A Counterfactual Approach

OBJECTIVE. Our goal was to quantify the magnitude of energy imbalance responsible for the increase in body weight among US children during the periods 1988 -1994 and 1999 -2002. METHODS. We adopted a counterfactual approach to estimate weight gains in excess of normal growth and the implicit \\

Y. Claire Wang; Steven L. Gortmaker; Arthur M. Sobol; Karen M. Kuntz

2010-01-01

215

Buffering approach for energy saving in video sensors

Networked video sensors need to execute two dependent periodic tasks: video encoding and transmission. The dependency and periodicity often result in small idle intervals of CPU and wireless network interface card (WNIC). In this paper, we present a sender-buffering approach to exploit such idle intervals for energy saving. Specifically, a video sensor encodes frames in a timely fashion, but buffers

Wanghong Yuan; Klara Nahrstedt

2003-01-01

216

Progress in high-lift aerodynamic calculations

NASA Technical Reports Server (NTRS)

The current work presents progress in the effort to numerically simulate the flow over high-lift aerodynamic components, namely, multi-element airfoils and wings in either a take-off or a landing configuration. The computational approach utilizes an incompressible flow solver and an overlaid chimera grid approach. A detailed grid resolution study is presented for flow over a three-element airfoil. Two turbulence models, a one-equation Baldwin-Barth model and a two equation k-omega model are compared. Excellent agreement with experiment is obtained for the lift coefficient at all angles of attack, including the prediction of maximum lift when using the two-equation model. Results for two other flap riggings are shown. Three-dimensional results are presented for a wing with a square wing-tip as a validation case. Grid generation and topology is discussed for computing the flow over a T-39 Sabreliner wing with flap deployed and the initial calculations for this geometry are presented.

Rogers, Stuart E.

1993-01-01

217

An approach to modeling impact energy absorption by surfaces.

The energy return characteristics of an impacted surface are important for human impacts such as a child falling onto a play surface or an athlete landing on a gymnastic mat. The amount of energy dissipated or returned to the impacting body will contribute to the surface's injury-minimizing or performance-enhancing potential. We describe a simple approach for selecting a rheological computer model to simulate a human-surface impact. The situation analyzed was of a head form impact onto gymnastic tumbling mats. The approach can be used to characterize other surfaces and impacts. The force-time-displacement characteristics of the mats were determined from laboratory drop tests. Various spring-damper models were evaluated for their ability to reproduce the experimental acceleration-time and force-displacement impact curves. An exponential spring and depth damper combination was found to best replicate the surface characteristics of the mats tested here, and to demonstrate their energy flow and exchange properties. Rheological modeling is less complex than finite element modeling but still accounted for the depth, velocity, and energy characteristics of the impacted surfaces. This approach will be useful for reproducing the characteristics of surfaces when the impacting body cannot be instrumented, and for predicting force and energy flow in nonrigid impacts. PMID:20095456

Davidson, Peter L; Wilson, Suzanne J; Wilson, Barry D; Chalmers, David J

2009-11-01

218

Zeta-function approach to Casimir energy with singular potentials

In the framework of zeta-function approach the Casimir energy for three simple model system: single delta potential, step function potential and three delta potentials are analyzed. It is shown that the energy contains contributions which are peculiar to the potentials. It is suggested to renormalize the energy using the condition that the energy of infinitely separated potentials is zero which corresponds to subtraction all terms of asymptotic expansion of zeta-function. The energy obtained in this way obeys all physically reasonable conditions. It is finite in the Dirichlet limit, and it may be attractive or repulsive depending on the strength of potential. The effective action is calculated, and it is shown that the surface contribution appears. The renormalization of the effective action is discussed.

Khusnutdinov, Nail R. [Departamento de Fisica, Universidade Federal da Paraiba, Caixa Postal 5008, CEP 58051-970 Joao Pessoa, Pb (Brazil)

2006-01-15

219

Analyzing mistuned multi-stage turbomachinery rotors with aerodynamic effects

NASA Astrophysics Data System (ADS)

A great deal of research has been conducted on accurately modeling large cyclic structures such as turbomachinery rotors. Accurate modeling of realistic industrial turbomachinery requires overcoming several challenges. The first is the excessively large size of the finite element models (FEMs) needed, which can contain millions of degrees of freedom per stage of the rotor. The second challenge is the presence of small random variations in the structural properties known as mistuning, which arise from operational wear and/or manufacturing tolerances, and destroy the cyclic symmetry of the FEMs. The third is the complexity of turbomachinery models, which often include multiple stages that often have a mismatched computational grid at the interface between stages. The fourth challenge is associated with modeling the aerodynamic loads on the turbomachinery rotor. Much research has been conducted to overcome the first two challenges. By combining cyclic symmetry analysis and component mode mistuning (CMM), compact single-stage reduced order models (ROMs) can be created to accurately capture the free and forced response of these systems. These highly efficient ROMs can be developed from single sector calculations and can be of the order of the number of sectors in the stage. Recently, the third challenge associated with the complexity of modeling multiple stages has been addressed by the authors. Their method uses cyclic symmetry and CMM to form single-stage ROMs (using only single sector models and single sector calculations), and then combines these single-stage ROMs by projecting the motion along the interface between stages along a set of harmonic shape functions. This method allows for the creation of compact ROMs of multi-stage systems with mistuning using sector only calculations. The fourth challenge has been addressed only for single-stage systems by computing a complex aerodynamic matrix (which contains stiffness and damping terms) using an iterative approach. In this work, some of the effects of the aerodynamics on multi-stage systems are explored. The methodology consists of first creating efficient structural ROMs of a multi-stage rotor using the method previously developed, and then iteratively calculating the complex aerodynamic matrices for each stage. A new way to account for the effects of a shift in frequency due to mistuning on the complex aerodynamic matrix is also proposed. Additionally, a new classification of complex multi-stage aeroelastic modes is introduced. The presented results focus on exploring the influences of the aerodynamics and mistuning on the multi-stage response. A variety of numerical results are analyzed for two stages of an industrial rotor.

D'Souza, Kiran; Jung, Chulwoo; Epureanu, Bogdan I.

2013-10-01

220

System for determining aerodynamic imbalance

NASA Technical Reports Server (NTRS)

A system is provided for determining tracking error in a propeller or rotor driven aircraft by determining differences in the aerodynamic loading on the propeller or rotor blades of the aircraft. The system includes a microphone disposed relative to the blades during the rotation thereof so as to receive separate pressure pulses produced by each of the blades during the passage thereof by the microphone. A low pass filter filters the output signal produced by the microphone, the low pass filter having an upper cut-off frequency set below the frequency at which the blades pass by the microphone. A sensor produces an output signal after each complete revolution of the blades, and a recording display device displays the outputs of the low pass filter and sensor so as to enable evaluation of the relative magnitudes of the pressure pulses produced by passage of the blades by the microphone during each complete revolution of the blades.

Churchill, Gary B. (inventor); Cheung, Benny K. (inventor)

1994-01-01

221

Aerodynamic characteristics of aerofoils I

NASA Technical Reports Server (NTRS)

The object of this report is to bring together the investigations of the various aerodynamic laboratories in this country and Europe upon the subject of aerofoils suitable for use as lifting or control surfaces on aircraft. The data have been so arranged as to be of most use to designing engineers and for the purposes of general reference. The absolute system of coefficients has been used, since it is thought by the National Advisory Committee for Aeronautics that this system is the one most suited for international use, and yet is one for which a desired transformation can be easily made. For this purpose a set of transformation constants is included in this report.

1921-01-01

222

High angle of attack: Aerodynamics

NASA Technical Reports Server (NTRS)

The ability to predict high angle of attack, nonlinear, aerodynamic characteristics of flight vehicles, including aircraft, has made significant progress in the last 25 years using computational tools and analyses. The key technological element which has made these analyses possible is the ability to account for the influence of the shed vortical flow, prevalent in this angle of attack range, on geometries of interest. Using selected analysis techniques, applications have also been made to wing design in order to improve their high speed maneuver performance. Various techniques, associated with different levels of accuracy, exist to model this vortical flow influence. The ones included in this paper cover: suction analogy with extensions; free vortex filaments; free vortex sheet modeling; and Euler and Navier-Stokes solutions. Associated relevant features of vortices are also addressed, including: the wing and flow conditions which cause vortex formation; and how the vortex strength varies with angle of attack and wing sweep.

Lamar, John E.

1992-01-01

223

Aerodynamic features of turbulent flames

NASA Technical Reports Server (NTRS)

The paper provides an interpretation for a variety of turbulent flame phenomena relating them to the aerodynamic properties of the flow field. This includes the classical notion of the breakdown of laminar flames propagation in ducts, the characteristic features of turbulent flame-fronts recorded by schlieren photography, as well as flame instabilities leading to flashback occurring in a combustion chamber behind a bluff-body flame holder. The rudimentary nature of turbulent flame propagation is shown to be associated with (1) vortex motion of a large-scale turbulent eddy, combined with (2) self-advancement of the flame at the appropriate normal burning speed and (3) the concomitant action of distributed sources of specific volume. The results furnish an insight into the macroscopic properties of the mechanism of turbulent flame propagation, rationalizing in particular its capability to sustain high flow velocities at relatively low normal burning speeds.

Oppenheim, A. K.; Ghoniem, A. F.

1983-01-01

224

Aerodynamic force by Lamb vector integrals in compressible flow

NASA Astrophysics Data System (ADS)

A new exact expression of the aerodynamic force acting on a body in steady high Reynolds number (laminar and turbulent) compressible flow is proposed. The aerodynamic force is obtained by integration of the Lamb vector field given by the cross product of vorticity times velocity. The result is obtained extending a theory developed for the incompressible case. A decomposition in lift and drag contribution is obtained in the two-dimensional case. The theory links the force generation to local flow properties, in particular to the Lamb vector field and to the kinetic energy. The theoretical results are confirmed analyzing numerical solutions obtained by a standard Reynolds Averaged Navier-Stokes solver. Results are discussed for the case of a two-dimensional airfoil in subsonic, transonic, and supersonic free stream conditions.

Mele, Benedetto; Tognaccini, Renato

2014-05-01

225

Post-Stall Aerodynamic Modeling and Gain-Scheduled Control Design

NASA Technical Reports Server (NTRS)

A multidisciplinary research e.ort that combines aerodynamic modeling and gain-scheduled control design for aircraft flight at post-stall conditions is described. The aerodynamic modeling uses a decambering approach for rapid prediction of post-stall aerodynamic characteristics of multiple-wing con.gurations using known section data. The approach is successful in bringing to light multiple solutions at post-stall angles of attack right during the iteration process. The predictions agree fairly well with experimental results from wind tunnel tests. The control research was focused on actuator saturation and .ight transition between low and high angles of attack regions for near- and post-stall aircraft using advanced LPV control techniques. The new control approaches maintain adequate control capability to handle high angle of attack aircraft control with stability and performance guarantee.

Wu, Fen; Gopalarathnam, Ashok; Kim, Sungwan

2005-01-01

226

National Technical Information Service (NTIS)

The execution of the first phase agreement on wind energy projects, covering the period from 1986 to 1992, is summarized. The following are addressed: wind tunnel tests of a 2.2 m and 2.8 m diameter turbine, a 5.35 m turbine in stationary yaw operation, p...

H. Dexin S. Thor

1993-01-01

227

Hypersonic aerodynamics at North Carolina State University

NASA Technical Reports Server (NTRS)

Hypersonic Aerodynamics has attracted outstanding graduate students and faculty at NCSU. It has grown to 6 faculty and 32 graduate students for fall, 1988. A significant feature of the program is that students and faculty spend time at government laboratories which currently include NASA Langley Research Center, Naval Surface Warfare Center at Silver Spring, and the Wright Aeronautical Laboratories. Research projects include analysis, computational and experimental aerodynamics. The combined program produces graduates with the background needed to perform aerodynamics investigations of hypersonic aircraft and spacecraft. The research performed helps advance the state of the art as well as assist government laboratories in meeting their goals.

Dejarnette, Fred R.

1988-01-01

228

Active Control of Aerodynamic Noise Sources

NASA Technical Reports Server (NTRS)

Aerodynamic noise sources become important when propulsion noise is relatively low, as during aircraft landing. Under these conditions, aerodynamic noise from high-lift systems can be significant. The research program and accomplishments described here are directed toward reduction of this aerodynamic noise. Progress toward this objective include correction of flow quality in the Low Turbulence Water Channel flow facility, development of a test model and traversing mechanism, and improvement of the data acquisition and flow visualization capabilities in the Aero. & Fluid Dynamics Laboratory. These developments are described in this report.

Reynolds, Gregory A.

2001-01-01

229

The importance of aerodynamics on dynamics

NASA Technical Reports Server (NTRS)

The effects of aerodynamic phenomena on helicopter structural dynamics are examined, reviewing the results of recent theoretical and experimental investigations. A schematic diagram of a dynamic analysis is presented and discussed, noting the numerous aerodynamic inputs, and numerical data are presented in graphs. Consideration is given to forcing functions, aerodynamic damping, aeroelastic coupling, negative damping, apparent coriolis coupling, periodic coefficients, inverse damping, additional degrees of freedom, flap-lag stability, and dynamic inflow. The need for theoretical models which account for the dynamic loop between blade lift and induced flow (permitting blade motion to dynamically alter the flowfield during transients) is indicated.

Peters, David A.

1987-01-01

230

A modeling approach to energy savings of flying Canada geese using computational fluid dynamics.

A flapping flight mechanism of the Canada goose (Branta canadensis) was estimated using a two-jointed arm model in unsteady aerodynamic performance to examine how much energy can be saved in migration. Computational fluid dynamics (CFD) was used to evaluate airflow fields around the wing and in the wake. From the distributions of velocity and pressure on the wing, it was found that about 15% of goose flight energy could be saved by drag reduction from changing the morphology of the wing. From the airflow field in the wake, it was found that a pair of three-dimensional spiral flapping advantage vortices (FAV) was alternately generated. We quantitatively deduced that the optimal depth (the distance along the flight path between birds) was around 4m from the wing tip of a goose ahead, and optimal wing tip spacing (WTS, the distance between wing tips of adjacent birds perpendicular to the flight path) ranged between 0 and -0.40m in the spanwise section. It was found that a goose behind can save about 16% of its energy by induced power from FAV in V-formation. The phase difference of flapping between the goose ahead and behind was estimated at around 90.7° to take full aerodynamic benefit caused by FAV. PMID:23261397

Maeng, Joo-Sung; Park, Jae-Hyung; Jang, Seong-Min; Han, Seog-Young

2013-03-01

231

Wind Turbine Blade Design System - Aerodynamic and Structural Analysis

NASA Astrophysics Data System (ADS)

The ever increasing need for energy and the depletion of non-renewable energy resources has led to more advancement in the "Green Energy" field, including wind energy. An improvement in performance of a Wind Turbine will enhance its economic viability, which can be achieved by better aerodynamic designs. In the present study, a design system that has been under development for gas turbine turbomachinery has been modified for designing wind turbine blades. This is a very different approach for wind turbine blade design, but will allow it to benefit from the features inherent in the geometry flexibility and broad design space of the presented system. It starts with key overall design parameters and a low-fidelity model that is used to create the initial geometry parameters. The low-fidelity system includes the axisymmetric solver with loss models, T-Axi (Turbomachinery-AXIsymmetric), MISES blade-to-blade solver and 2D wing analysis code XFLR5. The geometry parameters are used to define sections along the span of the blade and connected to the CAD model of the wind turbine blade through CAPRI (Computational Analysis PRogramming Interface), a CAD neutral API that facilitates the use of parametric geometry definition with CAD. Either the sections or the CAD geometry is then available for CFD and Finite Element Analysis. The GE 1.5sle MW wind turbine and NERL NASA Phase VI wind turbine have been used as test cases. Details of the design system application are described, and the resulting wind turbine geometry and conditions are compared to the published results of the GE and NREL wind turbines. A 2D wing analysis code XFLR5, is used for to compare results from 2D analysis to blade-to-blade analysis and the 3D CFD analysis. This kind of comparison concludes that, from hub to 25% of the span blade to blade effects or the cascade effect has to be considered, from 25% to 75%, the blade acts as a 2d wing and from 75% to the tip 3D and tip effects have to be taken into account for design considerations. In addition, the benefits of this approach for wind turbine design and future efforts are discussed.

Dey, Soumitr

232

NASA Technical Reports Server (NTRS)

The High-Speed Research Program and NASA Langley Research Center sponsored the NASA High-Speed Research Program Aerodynamic Performance Workshop on February 25-28, 1997. The workshop was designed to bring together NASA and industry High-Speed Civil Transport (HSCT) Aerodynamic Performance technology development participants in areas of Configuration Aerodynamics (transonic and supersonic cruise drag prediction and minimization), High-Lift, Flight Controls, Supersonic Laminar Flow Control, and Sonic Boom Prediction. The workshop objectives were to (1) report the progress and status of HSCT aerodynamic performance technology development; (2) disseminate this technology within the appropriate technical communities; and (3) promote synergy among the scientist and engineers working HSCT aerodynamics. In particular, single- and multi-point optimized HSCT configurations, HSCT high-lift system performance predictions, and HSCT Motion Simulator results were presented along with executive summaries for all the Aerodynamic Performance technology areas.

Baize, Daniel G. (Editor)

1999-01-01

233

?-Meta Dynamics Approach To Compute Absolute Solvation Free Energy

We present a new approach to combine ? dynamics with meta-dynamics (named ?-meta dynamics) to compute free energy surface with respect to ?. Particularly, the ?-meta dynamics method extends meta-dynamics to a single virtual variable ?, i.e., the coupling parameter between solute and solvent, to compute absolute solvation free energy as an exemplary application. We demonstrate that ?-meta dynamics simulations can recover the accurate potential of mean force surface with respect to ? compared to the benchmark results from traditional ?-dynamics with umbrella sampling. The solvation free energy results for five small organic molecules from ?-meta dynamics simulations using the same filling scheme show that the statistical errors are within ±0.5 kcal/mol. The new ?-meta dynamics method is general and other variables such as order parameters to describe conformational changes can be easily combined with ?-meta dynamics. This should allow for efficient samplings on high-dimension free energy landscapes.

Wu, Pan

2013-01-01

234

The execution of the first phase agreement on wind energy projects, covering the period from 1986 to 1992, is summarized. The following are addressed: wind tunnel tests of a 2.2 m and 2.8 m diameter turbine, a 5.35 m turbine in stationary yaw operation, pressure measurements, wall interference correction, a 5.35 m diameter turbine under yaw control, visualization of the

He Dexin; Sven-Erik Thor

1993-01-01

235

Nonlinear programming extensions to rational function approximations of unsteady aerodynamics

NASA Technical Reports Server (NTRS)

This paper deals with approximating unsteady generalized aerodynamic forces in the equations of motion of a flexible aircraft. Two methods of formulating these approximations are extended to include both the same flexibility in constraining them and the same methodology in optimizing nonlinear parameters as another currently used 'extended least-squares' method. Optimal selection of 'nonlinear' parameters is made in each of the three methods by use of the same nonlinear (nongradient) optimizer. The objective of the nonlinear optimization is to obtain rational approximations to the unsteady aerodynamics whose state-space realization is of lower order than that required when no optimization of the nonlinear terms is performed. The free 'linear' parameters are determined using least-squares matrix techniques on a Lagrange multiplier formulation of an objective function which incorporates selected linear equality constraints. State-space mathematical models resulting from the different approaches are described, and results are presented which show comparative evaluations from application of each of the extended methods to a numerical example. The results obtained for the example problem show a significant (up to 63 percent) reduction in the number of differential equations used to represent the unsteady aerodynamic forces in linear time-invariant equations of motion as compared to a conventional method in which nonlinear terms are not optimized.

Tiffany, Sherwood H.; Adams, William M., Jr.

1987-01-01

236

Aerodynamic Design of AN Ariane 5 Reusable Booster STAGE*

NASA Astrophysics Data System (ADS)

A the winged liquid fly-back booster (LFBB) is one of the partially reusable space transportation systems considered within the German future space launcher technology research program ASTRA. The regarded system consists of two booster stages, which are attached to the expendable Ariane 5 core stage at an upgraded future technology level. The main area of interest of the presented aerodynamic study is the return flight after the staging procedure which dominates the layout of the LFBB. The present paper discusses the aerodynamic refinement of an existing LFBB design, focussing on its longitudinal stability and trim. Detailed aerodynamic parameter CL? CL ???? studies are performed based on Euler calculations. Force measurements and selected Navier-Stokes simulations confirm this approach. They point out that a LFBB configuration may be designed primarily based on Euler simulations. The discussion of the numerical results and their comparison with experimental results shows that it is possible to adapt the originally given LFBB proposal in a way that it allows a nearly indifferent flight along the complete return trajectory and that it additionally enables a very robust trim behaviour.

Eggers, Th.

2005-02-01

237

Integrated aerodynamic/dynamic optimization of helicopter rotor blades

NASA Technical Reports Server (NTRS)

An integrated aerodynamic/dynamic optimization procedure is used to minimize blade weight and 4 per rev vertical hub shear for a rotor blade in forward flight. The coupling of aerodynamics and dynamics is accomplished through the inclusion of airloads which vary with the design variables during the optimization process. Both single and multiple objective functions are used in the optimization formulation. The Global Criteria Approach is used to formulate the multiple objective optimization and results are compared with those obtained by using single objective function formulations. Constraints are imposed on natural frequencies, autorotational inertia, and centrifugal stress. The program CAMRAD is used for the blade aerodynamic and dynamic analyses, and the program CONMIN is used for the optimization. Since the spanwise and the azimuthal variations of loading are responsible for most rotor vibration and noise, the vertical airload distributions on the blade, before and after optimization, are compared. The total power required by the rotor to produce the same amount of thrust for a given area is also calculated before and after optimization. Results indicate that integrated optimization can significantly reduce the blade weight, the hub shear and the amplitude of the vertical airload distributions on the blade and the total power required by the rotor.

Chattopadhyay, Aditi; Walsh, Joanne L.; Riley, Michael F.

1989-01-01

238

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

239

An object-oriented approach to energy-economic modeling

In this paper, the authors discuss the experiences in creating an object-oriented economic model of the U.S. energy and agriculture markets. After a discussion of some central concepts, they provide an overview of the model, focusing on the methodology of designing an object-oriented class hierarchy specification based on standard microeconomic production functions. The evolution of the model from the class definition stage to programming it in C++, a standard object-oriented programming language, will be detailed. The authors then discuss the main differences between writing the object-oriented program versus a procedure-oriented program of the same model. Finally, they conclude with a discussion of the advantages and limitations of the object-oriented approach based on the experience in building energy-economic models with procedure-oriented approaches and languages.

Wise, M.A.; Fox, J.A.; Sands, R.D.

1993-12-01

240

New Approaches to Conjugated Polymer Electrodes for Organic Energy Storage

NASA Astrophysics Data System (ADS)

Conjugated polymers have been explored as electrodes in batteries and pseudocapacitors for over 30 years. Yet, their widespread implementation has been hindered for several reasons such as oxidative stability, low capacity, and rate limitations associated with ionic mobility relative to current state-of-the-art. On the other hand, conjugated polymers have much to offer because of their good electronic conductivity, high Coulombic efficiency, and theoretical capacities comparable to those of metal oxides. Our lab's current goal is to overcome the aforementioned challenges, so that conjugated polymeric electrodes can be suitable used in energy storage for applications such as mechanically flexible energy storage and structural power system. This talk will present several approaches towards synthesis and processing of polyaniline that achieve oxidatively stable, high capacity, ionically mobile electrodes. These approaches include template polymerization, synthesis of nanofibers, and layer-by-layer assembly.

Lutkenhaus, Jodie

2013-03-01

241

Multiprocessing on supercomputers for computational aerodynamics

NASA Technical Reports Server (NTRS)

Very little use is made of multiple processors available on current supercomputers (computers with a theoretical peak performance capability equal to 100 MFLOPs or more) in computational aerodynamics to significantly improve turnaround time. The productivity of a computer user is directly related to this turnaround time. In a time-sharing environment, the improvement in this speed is achieved when multiple processors are used efficiently to execute an algorithm. The concept of multiple instructions and multiple data (MIMD) through multi-tasking is applied via a strategy which requires relatively minor modifications to an existing code for a single processor. Essentially, this approach maps the available memory to multiple processors, exploiting the C-FORTRAN-Unix interface. The existing single processor code is mapped without the need for developing a new algorithm. The procedure for building a code utilizing this approach is automated with the Unix stream editor. As a demonstration of this approach, a Multiple Processor Multiple Grid (MPMG) code is developed. It is capable of using nine processors, and can be easily extended to a larger number of processors. This code solves the three-dimensional, Reynolds averaged, thin-layer and slender-layer Navier-Stokes equations with an implicit, approximately factored and diagonalized method. The solver is applied to generic oblique-wing aircraft problem on a four processor Cray-2 computer. A tricubic interpolation scheme is developed to increase the accuracy of coupling of overlapped grids. For the oblique-wing aircraft problem, a speedup of two in elapsed (turnaround) time is observed in a saturated time-sharing environment.

Yarrow, Maurice; Mehta, Unmeel B.

1990-01-01

242

NASA Technical Reports Server (NTRS)

NASA's High-Speed Research Program sponsored the 1999 Aerodynamic Performance Technical Review on February 8-12, 1999 in Anaheim, California. The review was designed to bring together NASA and industry High-Speed Civil Transport (HSCT) Aerodynamic Performance technology development participants in the areas of Configuration Aerodynamics (transonic and supersonic cruise drag prediction and minimization), High Lift, and Flight Controls. The review objectives were to: (1) report the progress and status of HSCT aerodynamic performance technology development; (2) disseminate this technology within the appropriate technical communities; and (3) promote synergy among the scientists and engineers working on HSCT aerodynamics. In particular, single and midpoint optimized HSCT configurations, HSCT high-lift system performance predictions, and HSCT simulation results were presented, along with executive summaries for all the Aerodynamic Performance technology areas. The HSR Aerodynamic Performance Technical Review was held simultaneously with the annual review of the following airframe technology areas: Materials and Structures, Environmental Impact, Flight Deck, and Technology Integration. Thus, a fourth objective of the Review was to promote synergy between the Aerodynamic Performance technology area and the other technology areas of the HSR Program. This Volume 1/Part 1 publication covers configuration aerodynamics.

Hahne, David E. (Editor)

1999-01-01

243

Rudolf Hermann, wind tunnels and aerodynamics

NASA Astrophysics Data System (ADS)

Rudolf Hermann was born on December 15, 1904 in Leipzig, Germany. He studied at the University of Leipzig and at the Aachen Institute of Technology. His involvement with wind tunnels began in 1934 when Professor Carl Wieselsberger engaged him to work at Aachen on the development of a supersonic wind tunnel. On January 6, 1936, Dr. Wernher von Braun visited Dr. Hermann to arrange for use of the Aachen supersonic wind tunnel for Army problems. On April 1, 1937, Dr. Hermann became Director of the Supersonic Wind Tunnel at the Army installation at Peenemunde. Results from the Aachen and Peenemunde wind tunnels were crucial in achieving aerodynamic stability for the A-4 rocket, later designated as the V-2. Plans to build a Mach 10 'hypersonic' wind tunnel facility at Kochel were accelerated after the Allied air raid on Peenemunde on August 17, 1943. Dr. Hermann was director of the new facility. Ignoring destruction orders from Hitler as WWII approached an end in Europe, Dr. Hermann and his associates hid documents and preserved wind tunnel components that were acquired by the advancing American forces. Dr. Hermann became a consultant to the Air Force at its Wright Field in November 1945. In 1951, he was named professor of Aeronautical Engineering at the University of Minnesota. In 1962, Dr. Hermann became the first Director of the Research Institute at the University of Alabama in Huntsville (UAH), a position he held until he retired in 1970.

Lundquist, Charles A.; Coleman, Anne M.

2008-04-01

244

Turbine stage aerodynamics and heat transfer prediction

NASA Technical Reports Server (NTRS)

A numerical study of the aerodynamic and thermal environment associated with axial turbine stages is presented. Computations were performed using a modification of the unsteady NASA Ames viscous code, ROTOR1, and an improved version of the NASA Lewis steady inviscid cascade system MERIDL-TSONIC coupled with boundary layer codes BLAYER and STAN5. Two different turbine stages were analyzed: the first stage of the United Technologies Research Center Large Scale Rotating Rig (LSRR) and the first stage of the Space Shuttle Main Engine (SSME) high pressure fuel turbopump turbine. The time-averaged airfoil midspan pressure and heat transfer profiles were predicted for numerous thermal boundary conditions including adiabatic wall, prescribed surface temperature, and prescribed heat flux. Computed solutions are compared with each other and with experimental data in the case of the LSRR calculations. Modified ROTOR1 predictions of unsteady pressure envelopes and instantaneous contour plots are also presented for the SSME geometry. Relative merits of the two computational approaches are discussed.

Griffin, Lisa W.; Mcconnaughey, H. V.

1989-01-01

245

Aerodynamic analysis of Pegasus - Computations vs reality

NASA Technical Reports Server (NTRS)

Pegasus, a three-stage, air-launched, winged space booster was developed to provide fast and efficient commercial launch services for small satellites. The aerodynamic design and analysis of Pegasus was conducted without benefit of wind tunnel tests using only computational aerodynamic and fluid dynamic methods. Flight test data from the first two operational flights of Pegasus are now available, and they provide an opportunity to validate the accuracy of the predicted pre-flight aerodynamic characteristics. Comparisons of measured and predicted flight characteristics are presented and discussed. Results show that the computational methods provide reasonable aerodynamic design information with acceptable margins. Post-flight analyses illustrate certain areas in which improvements are desired.

Mendenhall, Michael R.; Lesieutre, Daniel J.; Whittaker, C. H.; Curry, Robert E.; Moulton, Bryan

1993-01-01

246

Uniaxial aerodynamic attitude control of artificial satellites

NASA Technical Reports Server (NTRS)

Within the context of a simple mechanical model the paper examines the movement of a satellite with respect to the center of masses under conditions of uniaxial aerodynamic attitude control. The equations of motion of the satellite take account of the gravitational and restorative aerodynamic moments. It is presumed that the aerodynamic moment is much larger than the gravitational, and the motion equations contain a large parameter. A two-parameter integrated surface of these equations is constructed in the form of formal series in terms of negative powers of the large parameter, describing the oscillations and rotations of the satellite about its lengthwise axis, approximately oriented along the orbital tangent. It is proposed to treat such movements as nominal undisturbed motions of the satellite under conditions of aerodynamic attitude control. A numerical investigation is made for the above integrated surface.

Sazonov, V. V.

1983-01-01

247

MATLAB/Aerodynamic Analyzer System Tool.

National Technical Information Service (NTIS)

A MATLAB script has been developed that interfaces with the U. S. Army Aviation and Missile Command's Aerodynamic Analyzer System (AAS). This tool has the capability of automatically removing data biases, forcing delta symmetry, and plotting 3-Dimensional...

L. M. Auman J. Newby

2003-01-01

248

Aerodynamic Focusing of Nanoparticle or Cluster Beams.

National Technical Information Service (NTIS)

Guidelines for designing lenses or systems for aerodynamic focusing of nanoparticle or cluster beams. The design process may involve obtaining a relationship between particle size, operating pressure and aperture size, and selecting the operating pressure...

F. E. Kruis P. H. McMurry X. Wang

2005-01-01

249

Aerodynamic Performance of Hand Launch Glider

NASA Astrophysics Data System (ADS)

In recent years Micro Air Vehicles (MAV) for disaster aerial video are developed vigorously. In order to improve aerodynamic performance of MAV wing performance in low Reynolds numbers (Re) need to be improved, but research on the theme are very rare. In category of Hand Launch Glider, a kind of model aircraft, glide performance are competed, as a result high performance airfoils in Re is around 20,000 are developed. Therefore for MAV's aerodynamic performance improvement airfoils of Hand Launch Gliders should be referred and aerodynamic characteristics of the airfoils desired to be studied. So in this research, aerodynamic characteristics of the gliders are measured in wind tunnel. And also consistency between wind tunnel test and glide test in calm air is examined to confirm reliability of wind tunnel test. Comparison of different airfoils and flow visualization are also performed.

Koike, Masaru; Ishii, Mitsuru

250

Parameter Identification and Modeling of Longitudinal Aerodynamics.

National Technical Information Service (NTIS)

Using a comprehensive flight test database and a parameter identification software program produced at NASA Ames Research Center, a math model of the longitudinal aerodynamics of the Harrier aircraft was formulated. The identification program employed the...

J. W. Aksteter E. K. Parks R. E. Bach

1995-01-01

251

Aerodynamic Characterization of a Modern Launch Vehicle

NASA Technical Reports Server (NTRS)

A modern launch vehicle is by necessity an extremely integrated design. The accurate characterization of its aerodynamic characteristics is essential to determine design loads, to design flight control laws, and to establish performance. The NASA Ares Aerodynamics Panel has been responsible for technical planning, execution, and vetting of the aerodynamic characterization of the Ares I vehicle. An aerodynamics team supporting the Panel consists of wind tunnel engineers, computational engineers, database engineers, and other analysts that address topics such as uncertainty quantification. The team resides at three NASA centers: Langley Research Center, Marshall Space Flight Center, and Ames Research Center. The Panel has developed strategies to synergistically combine both the wind tunnel efforts and the computational efforts with the goal of validating the computations. Selected examples highlight key flow physics and, where possible, the fidelity of the comparisons between wind tunnel results and the computations. Lessons learned summarize what has been gleaned during the project and can be useful for other vehicle development projects.

Hall, Robert M.; Holland, Scott D.; Blevins, Jhn A.

2011-01-01

252

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

253

An Investigation of Rooftop Stolport Aerodynamics.

National Technical Information Service (NTIS)

An investigation into aerodynamic problems associated with large building rooftop STOLports was performed. Initially, a qualitative flow visualization study indicated two essential problems: (1) the establishment of smooth, steady, attached flow over the ...

J. N. Blanton H. M. Parker

1972-01-01

254

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

255

Aerodynamics of Advanced Axial-Flow Turbomachinery.

National Technical Information Service (NTIS)

A multi-task research program on aerodynamic problems in advanced axial-flow turbomachine configurations is being carried on at Iowa State University. The elements of this program are intended to contribute directly to the improvement of compressor, fan, ...

G. K. Serovy P. Kavanagh T. H. Okiishi E. C. Hansen

1979-01-01

256

Aerodynamic and Aeroelastic Insights using Eigenanalysis

NASA Technical Reports Server (NTRS)

This paper presents novel analytical results for eigenvalues and eigenvectors produced using discrete time aerodynamic and aeroelastic models. An unsteady, incompressible vortex lattice aerodynamic model is formulated in discrete time; the importance of several modeling parameters is examined. A detailed study is made of the behavior of the aerodynamic eigenvalues both in discrete and continuous time. The aerodynamic model is then incorporated into aeroelastic equations of motion. Eigenanalyses of the coupled equations produce stability results and modal characteristics which are valid for critical and non-critical velocities. Insight into the modeling and physics associated with aeroelastic system behavior is gained by examining both the eigenvalues and the eigenvectors. Potential pitfalls in discrete time model construction and analysis are examined.

Heeg, Jennifer; Dowell, Earl H.

2004-01-01

257

Aerodynamic and Aeroelastic Insights using Eigenanalysis

NASA Technical Reports Server (NTRS)

This paper presents novel analytical results for eigenvalues and eigenvectors produced using discrete time aerodynamic and aeroelastic models. An unsteady, incompressible vortex lattice aerodynamic model is formulated in discrete time; the importance of several modeling parameters is examined. A detailed study is made of the behavior of the aerodynamic eigenvalues both in discrete and continuous time. The aerodynamic model is then incorporated into aeroelastic equations of motion. Eigenanalyses of the coupled equations produce stability results and modal characteristics which are valid for critical and non-critical velocities. Insight into the modeling and physics associated with aeroelastic system behavior is gained by examining both the eigenvalues and the eigenvectors. Potential pitfalls in discrete time model construction and analysis are examined.

Heeg, Jennifer; Dowell, Earl H.

1999-01-01

258

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

259

Determination of aerodynamic sensitivity coefficients in the transonic and supersonic regimes

NASA Technical Reports Server (NTRS)

The quasi-analytical approach is developed to compute airfoil aerodynamic sensitivity coefficients in the transonic and supersonic flight regimes. Initial investigation verifies the feasibility of this approach as applied to the transonic small perturbation residual expression. Results are compared to those obtained by the direct (finite difference) approach and both methods are evaluated to determine their computational accuracies and efficiencies. The quasi-analytical approach is shown to be superior and worth further investigation.

Elbanna, Hesham M.; Carlson, Leland A.

1989-01-01

260

Fundamental aerodynamics of a new volleyball

This study compared the basic aerodynamic characteristics of conventional volleyballs with those of new designs in a wind tunnel. Furthermore, to examine the aerodynamic instability near the critical Reynolds regime (14 m\\/s), balls were propelled with an impact-type ball ejection device and the variation in the coordinates of the landing point was measured. It was found that the critical Reynolds number

Takeshi Asai; Shinichiro Ito; Kazuya Seo; Akihiro Hitotsubashi

2010-01-01

261

An experimental study of Wiffle ball aerodynamics

NASA Astrophysics Data System (ADS)

We measure the aerodynamic forces on a Wiffle ball as a function of the Reynolds number and ball orientation. The effects of asymmetric flow outside the ball and flow within the ball are considered, and are both associated with the ball's tendency to curve without pitcher-imparted spin. The problem of Wiffle ball aerodynamics is an accessible way to introduce topics such as boundary layer separation and transition to turbulence.

Rossmann, Jenn; Rau, Andrew

2007-12-01

262

Fundamental aerodynamics of a new volleyball

This study compared the basic aerodynamic characteristics of conventional volleyballs with those of new designs in a wind tunnel. Furthermore, to examine the aerodynamic instability near the critical Reynolds regime (14 m\\/s), balls were propelled with an impact-type ball ejection device and the variation in the coordinates of the landing point was measured. It was found that the critical Reynolds number

Takeshi Asai; Shinichiro Ito; Kazuya Seo; Akihiro Hitotsubashi

2012-01-01

263

Some aerodynamic problems of satellite launch vehicles

A Satellite Launch Vehicle, during its atmospheric flight, presents a variety of aerodynamic problems for which solutions\\u000a are to be obtained through analytical and experimental techniques. Generally, the problems are complex and three-dimensional\\u000a in nature and quite often involve multibody interactions, interactions between the free stream and propulsive jet etc.\\u000a \\u000a In this paper, attention is confined to the current aerodynamic

T S Prahlad

1987-01-01

264

Atmospheric tests of trailing-edge aerodynamic devices

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)] [Wichita State Univ., KS (United States); Quandt, G.A.

1998-01-01

265

Fourier functional analysis for unsteady aerodynamic modeling

NASA Technical Reports Server (NTRS)

A method based on Fourier analysis is developed to analyze the force and moment data obtained in large amplitude forced oscillation tests at high angles of attack. The aerodynamic models for normal force, lift, drag, and pitching moment coefficients are built up from a set of aerodynamic responses to harmonic motions at different frequencies. Based on the aerodynamic models of harmonic data, the indicial responses are formed. The final expressions for the models involve time integrals of the indicial type advocated by Tobak and Schiff. Results from linear two- and three-dimensional unsteady aerodynamic theories as well as test data for a 70-degree delta wing are used to verify the models. It is shown that the present modeling method is accurate in producing the aerodynamic responses to harmonic motions and the ramp type motions. The model also produces correct trend for a 70-degree delta wing in harmonic motion with different mean angles-of-attack. However, the current model cannot be used to extrapolate data to higher angles-of-attack than that of the harmonic motions which form the aerodynamic model. For linear ramp motions, a special method is used to calculate the corresponding frequency and phase angle at a given time. The calculated results from modeling show a higher lift peak for linear ramp motion than for harmonic ramp motion. The current model also shows reasonably good results for the lift responses at different angles of attack.

Lan, C. Edward; Chin, Suei

1991-01-01

266

Measurement and estimation of the aerodynamic resistance

NASA Astrophysics Data System (ADS)

Using two methods of eddy correlation system and evaporation pan to measure respectively the aerodynamic resistance over bare soil surface and maize field, this paper analyses the diurnal variation of the aerodynamic resistance and its relationship with wind speed. Based on direct measurements by eddy correlation system, an evaluation of the aerodynamic resistance models is made. These models include Thom model, Verma-Ronsenberg model, Monteith-Hatfield model, XieXianqun model, Mahrt-Ek model, Choudhury-1 model and Choudhury-2 model. The results show that: the distribution of the aerodynamic resistance takes a "U" type in the daytime and inverse "V" type at night. The aerodynamic resistance is a power function of wind speed. The aerodynamic resistances measured by eddy correlation system are in agreement with those measured by evaporation pan, but big differences occur when the evaporation rate is very small at night or rainy day. Choudhury-1 model, XieXianqun model and Thom model give the better agreement with the measurements by eddy correlation system both over bare soil surface and the maize field, while Mahrt-Ek Model and Monteith-Hatfield model perform worse.

Liu, S.; Mao, D.; Lu, L.

2006-05-01

267

NASA Technical Reports Server (NTRS)

An approximate solution is reported for the unsteady aerodynamic response of an infinite swept wing encountering a vertical oblique gust in a compressible stream. The approximate expressions are of closed form and do not require excessive computer storage or computation time, and further, they are in good agreement with the results of exact theory. This analysis is used to predict the unsteady aerodynamic response of a helicopter rotor blade encountering the trailing vortex from a previous blade. Significant effects of three dimensionality and compressibility are evident in the results obtained. In addition, an approximate solution for the unsteady aerodynamic forces associated with the pitching or plunging motion of a two dimensional airfoil in a subsonic stream is presented. The mathematical form of this solution approaches the incompressible solution as the Mach number vanishes, the linear transonic solution as the Mach number approaches one, and the solution predicted by piston theory as the reduced frequency becomes large.

Adamczyk, J. L.

1974-01-01

268

Aerodynamics of a hybrid airship

NASA Astrophysics Data System (ADS)

The objective of this paper is to present the results of a numerical study of the aerodynamic parameters of a wingless and a winged-hull airship. The total forces and moment coefficients of the airships have been computed over a range of angles. The results obtained show that addition of a wing to a conventional airship increases the lift has three times the lifting force at positive angle of attack as compared to a wingless airship whereas the drag increases in the range of 19% to 58%. The longitudinal and directional stabilities were found to be statically stable, however, both the conventional airship and the hybrid or winged airships were found to have poor rolling stability. Wingless airship has slightly higher longitudinal stability than a winged airship. The winged airship has better directional stability than the wingless airship. The wingless airship only possesses static rolling stability in the range of yaw angles of -5° to 5°. On the contrary, the winged airship initially tested does not possess rolling stability at all. Computational fluid dynamics (CFD) simulations show that modifications to the wing placement and its dihedral have strong positive effect on the rolling stability. Raising the wings to the center of gravity and introducing a dihedral angle of 5° stabilizes the rolling motion of the winged airship.

Andan, Amelda Dianne; Asrar, Waqar; Omar, Ashraf A.

2012-06-01

269

Estimating aerodynamic roughness over complex surface terrain

NASA Astrophysics Data System (ADS)

roughness plays a key role in determining aerodynamic roughness length (zo) and shear velocity, both of which are fundamental for determining wind erosion threshold and potential. While zo can be quantified from wind measurements, large proportions of wind erosion prone surfaces remain too remote for this to be a viable approach. Alternative approaches therefore seek to relate zo to morphological roughness metrics. However, dust-emitting landscapes typically consist of complex small-scale surface roughness patterns and few metrics exist for these surfaces which can be used to predict zo for modeling wind erosion potential. In this study terrestrial laser scanning was used to characterize the roughness of typical dust-emitting surfaces (playa and sandar) where element protrusion heights ranged from 1 to 199 mm, over which vertical wind velocity profiles were collected to enable estimation of zo. Our data suggest that, although a reasonable relationship (R2 > 0.79) is apparent between 3-D roughness density and zo, the spacing of morphological elements is far less powerful in explaining variations in zo than metrics based on surface roughness height (R2 > 0.92). This finding is in juxtaposition to wind erosion models that assume the spacing of larger-scale isolated roughness elements is most important in determining zo. Rather, our data show that any metric based on element protrusion height has a higher likelihood of successfully predicting zo. This finding has important implications for the development of wind erosion and dust emission models that seek to predict the efficiency of aeolian processes in remote terrestrial and planetary environments.

Nield, Joanna M.; King, James; Wiggs, Giles F. S.; Leyland, Julian; Bryant, Robert G.; Chiverrell, Richard C.; Darby, Stephen E.; Eckardt, Frank D.; Thomas, David S. G.; Vircavs, Larisa H.; Washington, Richard

2013-12-01

270

Scientific Approach to Renewable Energy Through Solar Cells

NASA Astrophysics Data System (ADS)

Renewable energy is increasingly viewed as critically important globally. Solar cells convert the energy of the sun into electricity. The method of converting solar energy to electricity is pollution free, and appears a good practical solution to the global energy problems. Energy policies have pushed for different technologies to decrease pollutant emissions and reduce global climate change. Photovoltaic technology, which utilizes sunlight to generate energy, is an attractive alternate energy source because it is renewable, harmless and domestically secure. Transparent conducting metal oxides, being n-type were used extensively in the production of heterojunction cells using p-type Cu2O. The long held consensus is that the best approach to improve cell efficiency in Cu2O-based photovoltaic devices is to achieve both p- and n-type Cu2O and thus p-n homojunction of Cu2O solar cells. Silicon, which, next to oxygen, is the most represented element in the earth's crust, is used for the production of monocrystalline silicon solar cells. Silicon is easily obtained and processed and it is not toxic and does not form compounds that would be environmentally harmful. In contemporary electronic industry silicon is the main semiconducting element. Thin-film cadmium telluride (CdTe) solar cells are the basis of a significant technology with major commercial impact on solar energy production. Polycrystalline thin-film solar cells such as CuInSe2 (CIS), Cu (In, Ga) Se2 (CIGS) and CdTe compound semiconductors are important for terrestrial applications because of their high efficiency, long-term stable performance and potential for low-cost production. Highest record efficiencies of 19.2% for CIGS and 16.5% for CdTe have been achieved.

Rao, M. C.

271

Integrated aerodynamic/dynamic optimization of helicopter rotor blades

NASA Technical Reports Server (NTRS)

An integrated aerodynamic/dynamic optimization procedure is used to minimize blade weight and 4/rev vertical shear of a rotor blade in forward flight. Both single and multiple objective functions are used, with constraints imposed on the first four coupled natural frequencies (elastic modes only), the blade aerorotational inertia, and the centrifugal stress. The global criteria approach is used for the multiple objective formulation, and the results are compared with those obtained from single objective function formulations. Optimum designs are compared against a reference blade, and it is shown that optimum results can be obtained in 7-10 cycles.

Chattopadhyay, Aditi; Walsh, Joanne L.; Riley, Michael F.

1989-01-01

272

NASA Technical Reports Server (NTRS)

NASA's High-Speed Research Program sponsored the 1998 Aerodynamic Performance Technical Review on February 9-13, in Los Angeles, California. The review was designed to bring together NASA and industry High-Speed Civil Transport (HSCT) Aerodynamic Performance technology development participants in areas of Configuration Aerodynamics (transonic and supersonic cruise drag prediction and minimization), High-Lift, and Flight Controls. The review objectives were to (1) report the progress and status of HSCT aerodynamic performance technology development; (2) disseminate this technology within the appropriate technical communities; and (3) promote synergy among the scientists and engineers working HSCT aerodynamics. In particular, single and multi-point optimized HSCT configurations, HSCT high-lift system performance predictions, and HSCT simulation results were presented along with executive summaries for all the Aerodynamic Performance technology areas. The HSR Aerodynamic Performance Technical Review was held simultaneously with the annual review of the following airframe technology areas: Materials and Structures, Environmental Impact, Flight Deck, and Technology Integration. Thus, a fourth objective of the Review was to promote synergy between the Aerodynamic Performance technology area and the other technology areas of the HSR Program.

McMillin, S. Naomi (Editor)

1999-01-01

273

NASA Technical Reports Server (NTRS)

NASA's High-Speed Research Program sponsored the 1998 Aerodynamic Performance Technical Review on February 9-13, in Los Angeles, California. The review was designed to bring together NASA and industry HighSpeed Civil Transport (HSCT) Aerodynamic Performance technology development participants in areas of. Configuration Aerodynamics (transonic and supersonic cruise drag prediction and minimization), High-Lift, and Flight Controls. The review objectives were to: (1) report the progress and status of HSCT aerodynamic performance technology development; (2) disseminate this technology within the appropriate technical communities; and (3) promote synergy among the scientists and engineers working HSCT aerodynamics. In particular, single and multi-point optimized HSCT configurations, HSCT high-lift system performance predictions, and HSCT simulation results were presented along with executive summaries for all the Aerodynamic Performance technology areas. The HSR Aerodynamic Performance Technical Review was held simultaneously with the annual review of the following airframe technology areas: Materials and Structures, Environmental Impact, Flight Deck, and Technology Integration. Thus, a fourth objective of the Review was to promote synergy between the Aerodynamic Performance technology area and the other technology areas of the HSR Program.

McMillin, S. Naomi (Editor)

1999-01-01

274

NASA Technical Reports Server (NTRS)

NASA's High-Speed Research Program sponsored the 1999 Aerodynamic Performance Technical Review on February 8-12, 1999 in Anaheim, California. The review was designed to bring together NASA and industry High-Speed Civil Transport (HSCT) Aerodynamic Performance technology development participants in the areas of Configuration Aerodynamics (transonic and supersonic cruise drag prediction and minimization), High Lift, and Flight Controls. The review objectives were to (1) report the progress and status of HSCT aerodynamic performance technology development; (2) disseminate this technology within the appropriate technical communities; and (3) promote synergy among the scientists and engineers working on HSCT aerodynamics. In particular, single and midpoint optimized HSCT configurations, HSCT high-lift system performance predictions, and HSCT simulation results were presented, along with executive summaries for all the Aerodynamic Performance technology areas. The HSR Aerodynamic Performance Technical Review was held simultaneously with the annual review of the following airframe technology areas: Materials and Structures, Environmental Impact, Flight Deck, and Technology Integration. Thus, a fourth objective of the Review was to promote synergy between the Aerodynamic Performance technology area and the other technology areas of the HSR Program. This Volume 1/Part 2 publication covers the design optimization and testing sessions.

Hahne, David E. (Editor)

1999-01-01

275

Aerodynamic Parameter Identification of a Venus Lander

NASA Astrophysics Data System (ADS)

An analysis was conducted to identify the parameters of an aerodynamic model for a Venus lander based on experimental free-flight data. The experimental free-flight data were collected in the NASA Langley 20-ft Vertical Spin Tunnel with a 25-percent Froude-scaled model. The experimental data were classified based on the wind tunnel run type: runs where the lander model was unperturbed over the course of the run, and runs were the model was perturbed (principally in pitch, yaw, and roll) by the wind tunnel operator. The perturbations allow for data to be obtained at higher wind angles and rotation rates than those available from the unperturbed data. The model properties and equations of motion were used to determine experimental values for the aerodynamic coefficients. An aerodynamic model was selected using a priori knowledge of axisymmetric blunt entry vehicles. The least squares method was used to estimate the aerodynamic parameters. Three sets of results were obtained from the following data sets: perturbed, unperturbed, and the combination of both. The combined data set was selected for the final set of aerodynamic parameters based on the quality of the results. The identified aerodynamic parameters are consistent with that of the static wind tunnel data. Reconstructions, of experimental data not used in the parameter identification analyses, achieved similar residuals as those with data used to identify the parameters. Simulations of the experimental data, using the identified parameters, indicate that the aerodynamic model used is incapable of replicating the limit cycle oscillations with stochastic peak amplitudes observed during the test.

Sykes, Robert A.

276

NASA Technical Reports Server (NTRS)

The High-Speed Research Program and NASA Langley Research Center sponsored the NASA High-Speed Research Program Aerodynamic Performance Workshop on February 25-28, 1997. The workshop was designed to bring together NASA and industry High-Speed Civil Transport (HSCT) Aerodynamic Performance technology development participants in area of Configuration Aerodynamics (transonic and supersonic cruise drag prediction and minimization), High-Lift, Flight Controls, Supersonic Laminar Flow Control, and Sonic Boom Prediction. The workshop objectives were to (1) report the progress and status of HSCT aerodyamic performance technology development; (2) disseminate this technology within the appropriate technical communities; and (3) promote synergy among the scientist and engineers working HSCT aerodynamics. In particular, single- and multi-point optimized HSCT configurations, HSCT high-lift system performance predictions, and HSCT Motion Simulator results were presented along with executive summaries for all the Aerodynamic Performance technology areas.

Baize, Daniel G. (Editor)

1999-01-01

277

Exploring Discretization Error in Simulation-Based Aerodynamic Databases

NASA Technical Reports Server (NTRS)

This work examines the level of discretization error in simulation-based aerodynamic databases and introduces strategies for error control. Simulations are performed using a parallel, multi-level Euler solver on embedded-boundary Cartesian meshes. Discretization errors in user-selected outputs are estimated using the method of adjoint-weighted residuals and we use adaptive mesh refinement to reduce these errors to specified tolerances. Using this framework, we examine the behavior of discretization error throughout a token database computed for a NACA 0012 airfoil consisting of 120 cases. We compare the cost and accuracy of two approaches for aerodynamic database generation. In the first approach, mesh adaptation is used to compute all cases in the database to a prescribed level of accuracy. The second approach conducts all simulations using the same computational mesh without adaptation. We quantitatively assess the error landscape and computational costs in both databases. This investigation highlights sensitivities of the database under a variety of conditions. The presence of transonic shocks or the stiffness in the governing equations near the incompressible limit are shown to dramatically increase discretization error requiring additional mesh resolution to control. Results show that such pathologies lead to error levels that vary by over factor of 40 when using a fixed mesh throughout the database. Alternatively, controlling this sensitivity through mesh adaptation leads to mesh sizes which span two orders of magnitude. We propose strategies to minimize simulation cost in sensitive regions and discuss the role of error-estimation in database quality.

Aftosmis, Michael J.; Nemec, Marian

2010-01-01

278

Aerospace Energy Systems Laboratory - Requirements and design approach

NASA Technical Reports Server (NTRS)

The NASA Ames/Dryden Flight Research Facility operates a mixed fleet of research aircraft employing NiCd batteries in a variety of flight-critical applications. Dryden's Battery Systems Laboratory (BSL), a computerized facility for battery maintenance servicing, has evolved over two decades into one of the most advanced facilities of its kind in the world. Recently a major BSL upgrade was initiated with the goal of modernization to provide flexibility in meeting the needs of future advanced projects. The new facility will be called the Aerospace Energy Systems Laboratory (AESL) and will employ distributed processing linked to a centralized data base. AESL will be both a multistation servicing facility and a research laboratory for the advancement of energy storage system maintenance techniques. This paper describes the baseline requirements for the AESL and the design approach being taken for its mechanization.

Glover, Richard D.

1988-01-01

279

Aerospace energy systems laboratory: Requirements and design approach

NASA Technical Reports Server (NTRS)

The NASA Ames-Dryden Flight Research Facility at Edwards, California, operates a mixed fleet of research aircraft employing nickel-cadmium (NiCd) batteries in a variety of flight-critical applications. Dryden's Battery Systems Laboratory (BSL), a computerized facility for battery maintenance servicing, has developed over two decades into one of the most advanced facilities of its kind in the world. Recently a major BSL upgrade was initiated with the goal of modernization to provide flexibility in meeting the needs of future advanced projects. The new facility will be called the Aerospace Energy Systems Laboratory (AESL) and will employ distributed processing linked to a centralized data base. AESL will be both a multistation servicing facility and a research laboratory for the advancement of energy storage system maintenance techniques. This paper describes the baseline requirements for the AESL and the design approach being taken for its mechanization.

Glover, Richard D.

1988-01-01

280

Complex energy approaches for calculating isobaric analogue states

NASA Astrophysics Data System (ADS)

Parameters of isobaric analog resonance (IAR) are calculated in the framework of the Lane model using different methods. In the standard method, the direct numerical solution of the coupled channel (CC) Lane equations served as a reference for checking two complex energy methods, namely the complex energy shell model (CXSM) and the complex scaling (CS) approaches. The IAR parameters calculated by the CXSM and the CS methods agree with that of the CC results within 1 keV for all partial waves considered. Although the CXSM and the CS methods have similarities, an important difference is that only the CXSM method offers a direct way for studying the configurations of the IAR wave function.

Betan, R. Id; Kruppa, A. T.; Vertse, T.

2008-10-01

281

Complex energy approaches for calculating isobaric analogue states

Parameters of isobaric analog resonance (IAR) are calculated in the framework of the Lane model using different methods. In the standard method, the direct numerical solution of the coupled channel (CC) Lane equations served as a reference for checking two complex energy methods, namely the complex energy shell model (CXSM) and the complex scaling (CS) approaches. The IAR parameters calculated by the CXSM and the CS methods agree with that of the CC results within 1 keV for all partial waves considered. Although the CXSM and the CS methods have similarities, an important difference is that only the CXSM method offers a direct way for studying the configurations of the IAR wave function.

Betan, R. Id; Kruppa, A. T.; Vertse, T. [Departamento de Quimica y Fisica, FCEIA(UNR)-Instituto de Fisica Rosario (CONICET), Avenida Pellegrini 250, 2000 Rosario (Argentina); Institute of Nuclear Research of the Hungarian Academy of Sciences, Post Office Box 51, H-4001 Debrecen (Hungary); Institute of Nuclear Research of the Hungarian Academy of Sciences, Post Office Box 51, H-4001 Debrecen, Hungary and University of Debrecen, Faculty of Informatics, Post Office Box 12, H-4010 Debrecen (Hungary)

2008-10-15

282

Techniques for estimating Space Station aerodynamic characteristics

NASA Technical Reports Server (NTRS)

A method was devised and calculations were performed to determine the effects of reflected molecules on the aerodynamic force and moment coefficients for a body in free molecule flow. A procedure was developed for determining the velocity and temperature distributions of molecules reflected from a surface of arbitrary momentum and energy accommodation. A system of equations, based on momentum and energy balances for the surface, incident, and reflected molecules, was solved by a numerical optimization technique. The minimization of a 'cost' function, developed from the set of equations, resulted in the determination of the defining properties of the flow reflected from the arbitrary surface. The properties used to define both the incident and reflected flows were: average temperature of the molecules in the flow, angle of the flow with respect to a vector normal to the surface, and the molecular speed ratio. The properties of the reflected flow were used to calculate the contribution of multiply reflected molecules to the force and moments on a test body in the flow. The test configuration consisted of two flat plates joined along one edge at a right angle to each other. When force and moment coefficients of this 90 deg concave wedge were compared to results that did not include multiple reflections, it was found that multiple reflections could nearly double lift and drag coefficients, with nearly a 50 percent increase in pitching moment for cases with specular or nearly specular accommodation. The cases of diffuse or nearly diffuse accommodation often had minor reductions in axial and normal forces when multiple reflections were included. There were several cases of intermediate accommodation where the addition of multiple reflection effects more than tripled the lift coefficient over the convex technique.

Thomas, Richard E.

1993-01-01

283

A systematic listing is made of several dozen possible combinations of plants which a spacecraft can encounter in flights to the asteroids, passing near Venus up to four times and near the other planets up to twice. Taking the orbits of the planets as circular at first, and allowing only for the inclination of the asteroids' orbit, they analyze the individual impulses (for departure from Earth orbit, intermediate impulses, for reducing the velocity of approach to the asteroid, and for the velocity of launch toward earth) and their sum, and the total duration of flight to the asteroid for the best courses, as function of the semimajor axis and inclination of the asteroid's orbit. Courses with twofold perturbational or aerodynamic maneuvers near Mars are more advantageous for reaching asteroids closer to the Earth and to the ecliptic plane. Several courses are advantageous for reaching both closer and more distant asteroids, including an Earth-Mars (four-impulse bielliptic maneuver)-asteroid course, and courses with perturbational maneuvers: Earth-Venus-Earth-asteroid, Earth-Mars-Earth-Earth-asteroid, and Earth-Venus-Earth-Mars-asteroid courses, if the orbital inclinations of the targets are small. When the inclinations are more than 10/sup 0/, Earth-impulse at aphelion-Earth (about two years later)-Jupiter-asteroid, Earth-Mars-Earth (about two years later)-Jupiter-asteroid, and Earth-Venus-Earth-Mars-Jupiter-asteroid courses are more advantageous. The approximate calculations are compared with calculations for elliptical noncoplanar orbits in the period of 1970-2000 as applied to Earth-Mars-asteroids Nos. 4, 8, and 20 courses with perturbational or aerodynamic maneuvers, and the correctness of the approximate calculation is shown. Methods of calculating the energy consumed in the perturbational maneuver, choosing the frequently visited asteroids, and calculating the aerodynamic maneuver are described.

Livanov, L.B.

1987-01-01

284

Dynamic energy budget approaches for modelling organismal ageing

Ageing is a complex multifactorial process involving a progressive physiological decline that, ultimately, leads to the death of an organism. It involves multiple changes in many components that play fundamental roles under healthy and pathological conditions. Simultaneously, every organism undergoes accumulative ‘wear and tear’ during its lifespan, which confounds the effects of the ageing process. The scenario is complicated even further by the presence of both age-dependent and age-independent competing causes of death. Various manipulations have been shown to interfere with the ageing process. Calorie restriction, for example, has been reported to increase the lifespan of a wide range of organisms, which suggests a strong relation between energy metabolism and ageing. Such a link is also supported within the main theories for ageing: the free radical hypothesis, for instance, links oxidative damage production directly to energy metabolism. The Dynamic Energy Budgets (DEB) theory, which characterizes the uptake and use of energy by living organisms, therefore constitutes a useful tool for gaining insight into the ageing process. Here we compare the existing DEB-based modelling approaches and, then, discuss how new biological evidence could be incorporated within a DEB framework.

van Leeuwen, Ingeborg M. M.; Vera, Julio; Wolkenhauer, Olaf

2010-01-01

285

Using Performance-Based Approach in Building Energy Standards and Codes

This paper investigates the nature and concept of performance -based approach in building design control with particular focus on building energy efficiency. The meaning of performance-based approach is explained and the current developments of performance - based building energy codes in some representative countries are described. Experience in these countries indicates that performance-based approach in building energy code is important

SAM C. M. HUI

2002-01-01

286

Aerodynamic Simulation of Ice Accretion on Airfoils

NASA Technical Reports Server (NTRS)

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 Icing Research Tunnel (IRT) was used to generate ice accretions within these four types using both subscale and full-scale models. Large-scale, pressurized windtunnel testing was performed using a 72-in.- (1.83-m-) chord, NACA 23012 airfoil model with high-fidelity, three-dimensional castings of the IRT ice accretions. Performance data were recorded over Reynolds numbers from 4.5 x 10(exp 6) to 15.9 x 10(exp 6) and Mach numbers from 0.10 to 0.28. Lower fidelity ice-accretion simulation methods were developed and tested on an 18-in.- (0.46-m-) chord NACA 23012 airfoil model in a small-scale wind tunnel at a lower Reynolds number. The aerodynamic accuracy of the lower fidelity, subscale ice simulations was validated against the full-scale results for a factor of 4 reduction in model scale and a factor of 8 reduction in Reynolds number. This research has defined the level of geometric fidelity required for artificial ice shapes to yield aerodynamic performance results to within a known level of uncertainty and has culminated in a proposed methodology for subscale iced-airfoil aerodynamic simulation.

Broeren, Andy P.; Addy, Harold E., Jr.; Bragg, Michael B.; Busch, Greg T.; Montreuil, Emmanuel

2011-01-01

287

NASA Technical Reports Server (NTRS)

This user's manual is presented for an aerodynamic optimization program that updates flow variables and design parameters simultaneously. The program was developed for solving constrained optimization problems in which the objective function and the constraint function are dependent on the solution of the nonlinear flow equations. The program was tested by applying it to the problem of optimizing propeller designs. Some reference to this particular application is therefore made in the manual. However, the optimization scheme is suitable for application to general aerodynamic design problems. A description of the approach used in the optimization scheme is first presented, followed by a description of the use of the program.

Rizk, Magdi H.

1988-01-01

288

Helicopter rotor blade aerodynamic optimization by mathematical programming

NASA Technical Reports Server (NTRS)

Formal mathematical programing was applied to the aerodynamic rotor blade design process. The approach is to couple hover and forward flight analysis programs with the general-purpose optimization program CONMIN to determine the blade taper ratio, percent taper, twist distribution, and solidity which minimize the horsepower required at hover while meeting constraints on forward flight performance. Designs obtained using this approach for the blade of a representative Army helicopter compare well with those obtained using a conventional approach involving personnel-intensive parametric studies. Results from the present method can be obtained in 2 days as compared to 5 weeks required by the conventional procedure. Also the systematic manipulation of the design variables by the optimization procedure minimizes the need for the researcher to have a vast body of past experience and data in determining the influence of a design change on the performance.

Walsh, J. L.; Bingham, G. J.; Riley, M. F.

1984-01-01

289

High-speed aerodynamic design of space vehicle and required hypersonic wind tunnel facilities

NASA Astrophysics Data System (ADS)

Problems associated with the aerodynamic design of space vehicles with emphasis of the role of hypersonic wind tunnel facilities in the development of the vehicle are considered. At first, to identify wind tunnel and computational fluid dynamics (CFD) requirements, operational environments are postulated for hypervelocity vehicles. Typical flight corridors are shown with the associated flow density: real gas effects, low density flow, and non-equilibrium flow. Based on an evaluation of these flight regimes and consideration of the operational requirements, the wind tunnel testing requirements for the aerodynamic design are examined. Then, the aerodynamic design logic and optimization techniques to develop and refine the configurations in a traditional phased approach based on the programmatic design of space vehicle are considered. Current design methodology for the determination of aerodynamic characteristics for designing the space vehicle, i.e., (1) ground test data, (2) numerical flow field solutions and (3) flight test data, are also discussed. Based on these considerations and by identifying capabilities and limits of experimental and computational methods, the role of a large conventional hypersonic wind tunnel and the high enthalpy tunnel and the interrelationship of the wind tunnels and CFD methods in actual aerodynamic design and analysis are discussed.

Sakakibara, Seizou; Hozumi, Kouichi; Soga, Kunio; Nomura, Shigeaki

290

Computation of External Aerodynamics for a Canard Rotor/Wing Aircraft

NASA Technical Reports Server (NTRS)

The aerodynamic loads on a Canard Rotor/Wing vehicle are investigated using inviscid numerical simulations in order to understand the flight characteristics of the vehicle during conversion from rotor craft to fixed-wing flight. A series of numerical simulations at seven azimuthal rotor indices are presented covering a quarter turn of the rotor With symmetry arguments, these simulations produce 25 data points for a complete rotation. A Cartesian mesh approach is used to compute the flow field about a configuration with faired-over engine inlet and exhaust that matches the wind tunnel geometry. These simulations were performed using meshes with approximately nine Million Cartesian cells. To better understand the aerodynamic effects of the rotor hub on the configuration, the same set of simulations were repeated for a hub-less geometry. Overall loads for both configurations are similar but are due to somewhat different aerodynamic mechanisms.

Pandya, S. A.; Aftosmis, M. J.

2001-01-01

291

NASA Technical Reports Server (NTRS)

An overview is given of selected measurement techniques used in the NASA Langley Research Center (LaRC) Unitary Plan Wind Tunnel (UPWT) to determine the aerodynamic characteristics of aerospace vehicles operating at supersonic speeds. A broad definition of a measurement technique is adopted in this paper and is any qualitative or quantitative experimental approach that provides information leading to the improved understanding of the supersonic aerodynamic characteristics. On surface and off-surface measurement techniques used to obtain discrete (point) and global (field) measurements and planar and global flow visualizations are described, and examples of all methods are included. The discussion is limited to recent experiences in the UPWT and is. therefore, not an exhaustive review of existing experimental techniques. The diversity and high quality of the measurement techniques and the resultant data illustrate the capabilities of a around-based experimental facility and the key role that it plays in the advancement of our understanding, prediction, and control of supersonic aerodynamics.

Erickson, Gary E.

2000-01-01

292

Transitory Aerodynamic Forces on a Body of Revolution using Synthetic Jet Actuation

NASA Astrophysics Data System (ADS)

The aerodynamic forces and moments on axisymmetric bodies at subsonic speeds are controlled by exploiting local flow attachment using fluidic (synthetic jet) actuation and thereby altering the apparent aerodynamic shape of the surface. Control is effected upstream of the base of the body by an azimuthal array of individually-controlled, aft-facing synthetic jets emanating along an azimuthal Coanda surface. Actuation produces asymmetric aerodynamic forces and moments, with ratios of lift to average jet momentum approaching values typical of conventional jet-based circulation control on two-dimensional airfoils. Momentary forces are achieved using transient (pulsed) actuation and are accompanied by the formation and shedding of vorticity concentrations as a precursor to the turning of the outer flow into the wake region.

Rinehart, Christopher; McMichael, James; Glezer, Ari

2002-11-01

293

Physics of badminton shuttlecocks. Part 1 : aerodynamics

NASA Astrophysics Data System (ADS)

We study experimentally shuttlecocks dynamics. In this part we show that shuttlecock trajectory is highly different from classical parabola. When one takes into account the aerodynamic drag, the flight of the shuttlecock quickly curves downwards and almost reaches a vertical asymptote. We solve the equation of motion with gravity and drag at high Reynolds number and find an analytical expression of the reach. At high velocity, this reach does not depend on velocity anymore. Even if you develop your muscles you will not manage to launch the shuttlecock very far because of the ``aerodynamic wall.'' As a consequence you can predict the length of the field. We then discuss the extend of the aerodynamic wall to other projectiles like sports balls and its importance.

Cohen, Caroline; Darbois Texier, Baptiste; Quéré, David; Clanet, Christophe

2011-11-01

294

Aerodynamic tests of Darrieus wind turbine blades

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

295

Status of Nozzle Aerodynamic Technology at MSFC

NASA Technical Reports Server (NTRS)

This viewgraph presentation provides information on the status of nozzle aerodynamic technology at MSFC (Marshall Space Flight Center). The objectives of this presentation were to provide insight into MSFC in-house nozzle aerodynamic technology, design, analysis, and testing. Under CDDF (Center Director's Discretionary Fund), 'Altitude Compensating Nozzle Technology', are the following tasks: Development of in-house ACN (Altitude Compensating Nozzle) aerodynamic design capability; Building in-house experience for all aspects of ACN via End-to-End Nozzle Test Program; Obtaining Experimental Data for Annular Aerospike: Thrust eta, TVC (thrust vector control) capability and surface pressures. To support selection/optimization of future Launch Vehicle propulsion we needed a parametric design and performance tool for ACN. We chose to start with the ACN Aerospike Nozzles.

Ruf, Joseph H.; McDaniels, David M.; Smith, Bud; Owens, Zachary

2002-01-01

296

Identification of aerodynamic models for maneuvering aircraft

NASA Technical Reports Server (NTRS)

A Fourier analysis method was developed to analyze harmonic forced-oscillation data at high angles of attack as functions of the angle of attack and its time rate of change. The resulting aerodynamic responses at different frequencies are used to build up the aerodynamic models involving time integrals of the indicial type. An efficient numerical method was also developed to evaluate these time integrals for arbitrary motions based on a concept of equivalent harmonic motion. The method was verified by first using results from two-dimensional and three-dimensional linear theories. The developed models for C sub L, C sub D, and C sub M based on high-alpha data for a 70 deg delta wing in harmonic motions showed accurate results in reproducing hysteresis. The aerodynamic models are further verified by comparing with test data using ramp-type motions.

Lan, C. Edward; Hu, C. C.

1992-01-01

297

Fully integrated aerodynamic/dynamic optimization of helicopter rotor blades

NASA Technical Reports Server (NTRS)

A fully integrated aerodynamic/dynamic optimization procedure is described for helicopter rotor blades. The procedure combines performance and dynamic analyses with a general purpose optimizer. The procedure minimizes a linear combination of power required (in hover, forward flight, and maneuver) and vibratory hub shear. The design variables include pretwist, taper initiation, taper ratio, root chord, blade stiffnesses, tuning masses, and tuning mass locations. Aerodynamic constraints consist of limits on power required in hover, forward flight and maneuvers; airfoil section stall; drag divergence Mach number; minimum tip chord; and trim. Dynamic constraints are on frequencies, minimum autorotational inertia, and maximum blade weight. The procedure is demonstrated for two cases. In the first case, the objective function involves power required (in hover, forward flight and maneuver) and dynamics. The second case involves only hover power and dynamics. The designs from the integrated procedure are compared with designs from a sequential optimization approach in which the blade is first optimized for performance and then for dynamics. In both cases, the integrated approach is superior.

Walsh, Joanne L.; Lamarsh, William J., II; Adelman, Howard M.

1992-01-01

298

Fully integrated aerodynamic/dynamic optimization of helicopter rotor blades

NASA Technical Reports Server (NTRS)

This paper describes a fully integrated aerodynamic/dynamic optimization procedure for helicopter rotor blades. The procedure combines performance and dynamics analyses with a general purpose optimizer. The procedure minimizes a linear combination of power required (in hover, forward flight, and maneuver) and vibratory hub shear. The design variables include pretwist, taper initiation, taper ratio, root chord, blade stiffnesses, tuning masses, and tuning mass locations. Aerodynamic constraints consist of limits on power required in hover, forward flight and maneuver; airfoil section stall; drag divergence Mach number; minimum tip chord; and trim. Dynamic constraints are on frequencies, minimum autorotational inertia, and maximum blade weight. The procedure is demonstrated for two cases. In the first case the objective function involves power required (in hover, forward flight, and maneuver) and dynamics. The second case involves only hover power and dynamics. The designs from the integrated procedure are compared with designs from a sequential optimization approach in which the blade is first optimized for performance and then for dynamics. In both cases, the integrated approach is superior.

Walsh, Joanne L.; Lamarsh, William J., II; Adelman, Howard M.

1992-01-01

299

As one of the measures to achieve the reduction in greenhouse gas emissions agreed to in the"Kyoto Protocol," an institutional scheme for determining energy efficiency standards for energy-consuming appliances, called the"Top-Runner Approach," was developed by the Japanese government. Its goal is to strengthen the legal underpinnings of various energy conservation measures. Particularly in Japan's residential sector, where energy demand has grown vigorously so far, this efficiency standard is expected to play a key role in mitigating both energy demand growth and the associated CO2 emissions. This paper presents an outlook of Japan's residential energy demand, developed by a stochastic econometric model for the purpose of analyzing the impacts of the Japan's energy efficiency standards, as well as the future stochastic behavior of income growth, demography, energy prices, and climate on the future energy demand growth to 2030. In this analysis, we attempt to explicitly take into consideration more than 30 kinds of electricity uses, heating, cooling and hot water appliances in order to comprehensively capture the progress of energy efficiency in residential energy end-use equipment. Since electricity demand, is projected to exhibit astonishing growth in Japan's residential sector due to universal increasing ownership of electric and other appliances, it is important to implement an elaborate efficiency standards policy for these appliances.

Lacommare, Kristina S H; Komiyama, Ryoichi; Marnay, Chris

2008-05-15

300

Aerodynamic Heating Measurements on Hypersonic Flight Exoerunebt (HYFLEX) Vehicle.

National Technical Information Service (NTIS)

Aerodynamic heating on the Hypersonic Flight Experiment vehicle was measured using newly developed sensors, calibrated by lamp heating tests. These sensors were shown to be of sue for flight measurement purposes. The results of the aerodynamic heating mea...

K. Fujii S. Watanabe M. Shirouzu Y. Inoue T. Kurotaki T. Koyama S. Tsuda N. Hirabayashi

2000-01-01

301

International collaborative research in wind turbine rotor aerodynamics.

National Technical Information Service (NTIS)

Five organizations from four countries are collaborating to conduct detailed wind turbine aerodynamic test programs. Fullscale atmospheric testing will be conducted on turbines configured to measure aerodynamic forces on rotating airfoils. The purpose of ...

D. A. Simms C. P. Butterfield

1993-01-01

302

Prediction of Aerodynamic Coefficients using Neural Networks for Sparse Data.

National Technical Information Service (NTIS)

Basic aerodynamic coefficients are modeled as functions of angles of attack and sideslip with vehicle lateral symmetry and compressibility effects. Most of the aerodynamic parameters can be well-fitted using polynomial functions. In this paper a fast, rel...

T. Rajkumar J. Bardina

2002-01-01

303

Nonlinear Aerodynamics of Bodies in Coning Motion

NASA Technical Reports Server (NTRS)

A numerical method for computing the nonlinear inviscid flowfield surrounding a body performing coning motion is described. The method permits accurate computation of the aerodynamic moment due to one of the four motions characterizing an arbitrary nonplanar motion. Results of computations for a slender circular cone in coning motion are presented, and show good agreement with experiment for angles of attack up to twice the cone half-angle. The computational results display significant departure of the side moment from the linear theory value with increasing angle of attack, but agree well with experimental measurements. This indicates that the initial nonlinear behavior of the aerodynamic moment is determined primarily by the inviscid flow.

Schiff, Lewis B.

1972-01-01

304

Air flow testing on aerodynamic truck

NASA Technical Reports Server (NTRS)

After leasing a cab-over tractor-trailer from a Southern California firm, Dryden researchers added sheet metal modifications like those shown here. They rounded the front corners and edges, and placed a smooth fairing on the cab's roofs and sides extending back to the trailer. During the investigation of truck aerodynamics, the techniques honed in flight research proved highly applicable. By closing the gap between the cab and the trailer, for example, researchers discovered a significant reduction in aerodynamic drag, one resulting in 20 to 25 percent less fuel consumption than the standard design. Many truck manufacturers subsequently incorporated similar modifications on their products.

1975-01-01

305

Unstructured mesh algorithms for aerodynamic calculations

NASA Technical Reports Server (NTRS)

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 emphasized. The various aspects required for the efficient and accurate solution of aerodynamic flows are addressed. These include mesh generation, mesh adaptivity, solution algorithms, convergence acceleration, and turbulence modeling. Computations of viscous turbulent two-dimensional flows and inviscid three-dimensional flows about complex configurations are demonstrated. Remaining obstacles and directions for future research are also outlined.

Mavriplis, D. J.

1992-01-01

306

Method of reducing drag in aerodynamic systems

NASA Technical Reports Server (NTRS)

In the present method, boundary layer thickening is combined with laminar flow control to reduce drag. An aerodynamic body is accelerated enabling a ram turbine on the body to receive air at velocity V sub 0. The discharge air is directed over an aft portion of the aerodynamic body producing boundary layer thickening. The ram turbine also drives a compressor by applying torque to a shaft connected between the ram turbine and the compressor. The compressor sucks in lower boundary layer air through inlets in the shell of the aircraft producing laminar flow control and reducing drag. The discharge from the compressor is expanded in a nozzle to produce thrust.

Hrach, Frank J. (inventor)

1993-01-01

307

Numerical Simulation of Unsteady Aerodynamic Models

NASA Technical Reports Server (NTRS)

This report documents the results of the numerical simulations of unsteady aerodynamic models. The results focus on numerical accuracy and efficiency, and the robustness of the numerical methods. The aerodynamic models includes the classical Wagner and Kussner functions and the Leishman-Beddoes dynamic stall model. The simulations includes the numerical approximations of the Duhamel's integrals using both indicial (step) and impulse responses, the numerical integrations of the state-space models, and the exact solutions. The report also presents the conversion among different model representations.

Nguyen, Khanh Q.; Warmbrodt, William (Technical Monitor)

1997-01-01

308

Aerodynamics of the upper surface blow flap

NASA Technical Reports Server (NTRS)

The results of some preliminary wind-tunnel investigations made to provide fundamental aerodynamic information on the upper surface blown jet-flap concept incorporating high-bypass-ratio turbofan engines are summarized. The results of the investigation have shown the concept to have aerodynamic performance generally similar to that of other externally blown high-lift systems. A few of the more critical problems associated with this concept have been identified and preliminary solutions to some of these problems have been found. These results have proven to be sufficiently encouraging to warrant continuation of fundamental research efforts on the concept.

Phelps, A. E., III

1972-01-01

309

Advanced High-Temperature Flexible TPS for Inflatable Aerodynamic Decelerators

NASA Technical Reports Server (NTRS)

Typical entry vehicle aeroshells are limited in size by the launch vehicle shroud. Inflatable aerodynamic decelerators allow larger aeroshell diameters for entry vehicles because they are not constrained to the launch vehicle shroud diameter. During launch, the hypersonic inflatable aerodynamic decelerator (HIAD) is packed in a stowed configuration. Prior to atmospheric entry, the HIAD is deployed to produce a drag device many times larger than the launch shroud diameter. The large surface area of the inflatable aeroshell provides deceleration of high-mass entry vehicles at relatively low ballistic coefficients. Even for these low ballistic coefficients there is still appreciable heating, requiring the HIAD to employ a thermal protection system (TPS). This TPS must be capable of surviving the heat pulse, and the rigors of fabrication handling, high density packing, deployment, and aerodynamic loading. This paper provides a comprehensive overview of flexible TPS tests and results, conducted over the last three years. This paper also includes an overview of each test facility, the general approach for testing flexible TPS, the thermal analysis methodology and results, and a comparison with 8-foot High Temperature Tunnel, Laser-Hardened Materials Evaluation Laboratory, and Panel Test Facility test data. Results are presented for a baseline TPS layup that can withstand a 20 W/cm2 heat flux, silicon carbide (SiC) based TPS layup, and polyimide insulator TPS layup. Recent work has focused on developing material layups expected to survive heat flux loads up to 50 W/cm2 (which is adequate for many potential applications), future work will consider concepts capable of withstanding more than 100 W/cm2 incident radiant heat flux. This paper provides an overview of the experimental setup, material layup configurations, facility conditions, and planned future flexible TPS activities.

DelCorso, Joseph A.; Cheatwood, F. McNeil; Bruce, Walter E., III; Hughes, Stephen J.; Calomino, Anthony M.

2011-01-01

310

Enhanced ground-based vibration testing for aerodynamic environments

NASA Astrophysics Data System (ADS)

Typical methods of replicating aerodynamic environments in the laboratory are generally poor. A structure which flies "freely" in its normal operating environment, excited over its entire external surface by aerodynamic forces and in all directions simultaneously, is then subjected to a vibration test in the laboratory whilst rigidly attached to a high impedance shaker and excited by forces applied through a few attachment points and in one direction only. The two environments could hardly be more different. The majority of vibration testing is carried out at commercial establishments and it is understandable that little has been published which demonstrates the limitations with the status quo. The primary objective of this research is to do just that with a view to identifying significant improvements in vibration testing in light of modern technology. In this paper, case studies are presented which highlight some of the limitations with typical vibration tests showing that they can lead to significant overtests, sometimes by many orders of magnitude, with the level of overtest varying considerably across a wide range of frequencies. This research shows that substantial benefits can be gained by "freely" suspending the structure in the laboratory and exciting it with a relatively small number of electrodynamic shakers using Multi-Input-Multi-Output (MIMO) control technology. The shaker configuration can be designed to excite the modes within the bandwidth utilising the inherent amplification of the resonances to achieve the desired response levels. This free-free MIMO vibration test approach is shown to result in substantial benefits that include extremely good replication of the aerodynamic environment and significant savings in time as all axes are excited simultaneously instead of the sequential X, Y and Z testing required with traditional vibration tests. In addition, substantial cost savings can be achieved by replacing some expensive large shaker systems with a few relatively small shaker systems.

Daborn, P. M.; Ind, P. R.; Ewins, D. J.

2014-12-01

311

NASA Technical Reports Server (NTRS)

Advances in inverse design and optimization theory in engineering fields in China are presented. Two original approaches, the image-space approach and the variational approach, are discussed in terms of turbomachine aerodynamic inverse design. Other areas of research in turbomachine aerodynamic inverse design include the improved mean-streamline (stream surface) method and optimization theory based on optimal control. Among the additional engineering fields discussed are the following: the inverse problem of heat conduction, free-surface flow, variational cogeneration of optimal grid and flow field, and optimal meshing theory of gears.

Liu, Gao-Lian

1991-01-01

312

Quantum microscopic approach to low-energy heavy ion collisions

NASA Astrophysics Data System (ADS)

The Time-dependent Hartree-Fock (TDHF) theory is applied to the study of heavy ion collisions at energies around the Coulomb barrier. The competition between fusion and nucleon transfer mechanisms is investigated. For intermediate mass systems such as 16O+208Pb, proton transfer favors fusion by reducing the Coulomb repulsion. A comparison with sub-barrier transfer experimental data shows that pairing correlations are playing an important role in enhancing proton pair transfer. For heavier and more symmetric systems, a fusion hindrance is observed due to the dominance of the quasi-fission process. Typical quasi-fission time of few zeptoseconds are obtained. Actinide collisions are also investigated both within the TDHF approach and with the Ballian-Vénéroni prescription for fluctuation and correlation of one-body observables. The possible formation of new heavy neutron-rich nuclei in actinide collisions is discussed.

Simenel, Cédric; Wakhle, Aditya; Avez, Benoît

2013-03-01

313

Circular plate analysis by finite differences; Energy approach

A numerical method of elastic analysis of thin circular plates under various axisymmetric loading and support conditions is presented. The method of analysis is based on the finite-difference procedure in the variational formulation (energy approach) and can be regarded as being equivalent to the finite-element method. A simple computer program was developed and tested on a number of illustrative examples. In most cases the obtained results exhibited a much higher level of accuracy as compared to those obtained from the finite-element analysis. And, most importantly, in each of the cases considered the number of unknowns involved is only half of that employed in the particular finite-element procedure (using the simplest finite element).

Melerski, E. (Univ. of Tasmania, Hobart (AU))

1989-06-01

314

Predictions of unsteady hawt aerodynamics by lifting line theory

A numerical engineering method for the prediction of unsteady wind turbine aerodynamics is presented. The formulation is based on lifting line theory and a semiempirical dynamic stall model of Leishman and Beddoes. The unsteady aerodynamic response of the blade aerodynamics to the sharp blade-pitch changes or unsteady wind conditions is achieved by superposition of the above methods. Comparisons between computed

H. Dumitrescu; V. Cardo?

2001-01-01

315

NASA Astrophysics Data System (ADS)

Hydropower with pumped storage is a proven technology with very high efficiency that offers a unique large-scale energy buffer. Energy storage is employed by pumping water upstream to take advantage of the excess of produced energy (e.g. during night) and next retrieving this water to generate hydro-power during demand peaks. Excess energy occurs due to other renewables (wind, solar) whose power fluctuates in an uncontrollable manner. By integrating these with hydroelectric plants with pumped storage facilities we can form autonomous hybrid renewable energy systems. The optimal planning and management thereof requires a holistic approach, where uncertainty is properly represented. In this context, a novel framework is proposed, based on stochastic simulation and optimization. This is tested in an existing hydrosystem of Greece, considering its combined operation with a hypothetical wind power system, for which we seek the optimal design to ensure the most beneficial performance of the overall scheme.

Dimas, Panagiotis; Bouziotas, Dimitris; Efstratiadis, Andreas; Koutsoyiannis, Demetris

2014-05-01

316

National Technical Information Service (NTIS)

The more important helicopter fuselage aerodynamic design issues and also interactional problems faced by the helicopter airframe aerodynamicist, including performance and handling optimization and special effects caused by rotor downwash impingement on t...

F. T. Wilson

1990-01-01

317

On Improving Efficiency of Differential Evolution for Aerodynamic Shape Optimization Applications

NASA Technical Reports Server (NTRS)

Differential Evolution (DE) is a simple and robust evolutionary strategy that has been proven effective in determining the global optimum for several difficult optimization problems. Although DE offers several advantages over traditional optimization approaches, its use in applications such as aerodynamic shape optimization where the objective function evaluations are computationally expensive is limited by the large number of function evaluations often required. In this paper various approaches for improving the efficiency of DE are reviewed and discussed. These approaches are implemented in a DE-based aerodynamic shape optimization method that uses a Navier-Stokes solver for the objective function evaluations. Parallelization techniques on distributed computers are used to reduce turnaround times. Results are presented for the inverse design of a turbine airfoil. The efficiency improvements achieved by the different approaches are evaluated and compared.

Madavan, Nateri K.

2004-01-01

318

On Improving Efficiency of Differential Evolution for Aerodynamic Shape Optimization Applications

NASA Technical Reports Server (NTRS)

Differential Evolution (DE) is a simple and robust evolutionary strategy that has been provEn effective in determining the global optimum for several difficult optimization problems. Although DE offers several advantages over traditional optimization approaches, its use in applications such as aerodynamic shape optimization where the objective function evaluations are computationally expensive is limited by the large number of function evaluations often required. In this paper various approaches for improving the efficiency of DE are reviewed and discussed. Several approaches that have proven effective for other evolutionary algorithms are modified and implemented in a DE-based aerodynamic shape optimization method that uses a Navier-Stokes solver for the objective function evaluations. Parallelization techniques on distributed computers are used to reduce turnaround times. Results are presented for standard test optimization problems and for the inverse design of a turbine airfoil. The efficiency improvements achieved by the different approaches are evaluated and compared.

Madavan, Nateri K.

2004-01-01

319

Studies in a transonic rotor aerodynamics and noise facility

NASA Technical Reports Server (NTRS)

The design, construction and testing of a transonic rotor aerodynamics and noise facility was undertaken, using a rotating arm blade element support technique. This approach provides a research capability intermediate between that of a stationary element in a moving flow and that of a complete rotating blade system, and permits the acoustic properties of blade tip elements to be studied in isolation. This approach is an inexpensive means of obtaining data at high subsonic and transonic tip speeds on the effect of variations in tip geometry. The facility may be suitable for research on broad band noise and discrete noise in addition to high-speed noise. Initial tests were conducted over the Mach number range 0.3 to 0.93 and confirmed the adequacy of the acoustic treatment used in the facility to avoid reflection from the enclosure.

Wright, S. E.; Lee, D. J.; Crosby, W.

1984-01-01

320

Genetic Algorithms Applied to Multi-Objective Aerodynamic Shape Optimization

NASA Technical Reports Server (NTRS)

A genetic algorithm approach suitable for solving multi-objective problems is described and evaluated using a series of aerodynamic shape optimization problems. Several new features including two variations of a binning selection algorithm and a gene-space transformation procedure are included. The genetic algorithm is suitable for finding Pareto optimal solutions in search spaces that are defined by any number of genes and that contain any number of local extrema. A new masking array capability is included allowing any gene or gene subset to be eliminated as decision variables from the design space. This allows determination of the effect of a single gene or gene subset on the Pareto optimal solution. Results indicate that the genetic algorithm optimization approach is flexible in application and reliable. The binning selection algorithms generally provide Pareto front quality enhancements and moderate convergence efficiency improvements for most of the problems solved.

Holst, Terry L.

2005-01-01

321

Genetic Algorithms Applied to Multi-Objective Aerodynamic Shape Optimization

NASA Technical Reports Server (NTRS)

A genetic algorithm approach suitable for solving multi-objective optimization problems is described and evaluated using a series of aerodynamic shape optimization problems. Several new features including two variations of a binning selection algorithm and a gene-space transformation procedure are included. The genetic algorithm is suitable for finding pareto optimal solutions in search spaces that are defined by any number of genes and that contain any number of local extrema. A new masking array capability is included allowing any gene or gene subset to be eliminated as decision variables from the design space. This allows determination of the effect of a single gene or gene subset on the pareto optimal solution. Results indicate that the genetic algorithm optimization approach is flexible in application and reliable. The binning selection algorithms generally provide pareto front quality enhancements and moderate convergence efficiency improvements for most of the problems solved.

Holst, Terry L.

2004-01-01

322

Nozzle Aerodynamic Stability During a Throat Shift

NASA Technical Reports Server (NTRS)

An experimental investigation was conducted on the internal aerodynamic stability of a family of two-dimensional (2-D) High Speed Civil Transport (HSCT) nozzle concepts. These nozzles function during takeoff as mixer-ejectors to meet acoustic requirements, and then convert to conventional high-performance convergent-divergent (CD) nozzles at cruise. The transition between takeoff mode and cruise mode results in the aerodynamic throat and the minimum cross-sectional area that controls the engine backpressure shifting location within the nozzle. The stability and steadiness of the nozzle aerodynamics during this so called throat shift process can directly affect the engine aerodynamic stability, and the mechanical design of the nozzle. The objective of the study was to determine if pressure spikes or other perturbations occurred during the throat shift process and, if so, identify the caused mechanisms for the perturbations. The two nozzle concepts modeled in the test program were the fixed chute (FC) and downstream mixer (DSM). These 2-D nozzles differ principally in that the FC has a large over-area between the forward throat and aft throat locations, while the DSM has an over-area of only about 10 percent. The conclusions were that engine mass flow and backpressure can be held constant simultaneously during nozzle throat shifts on this class of nozzles, and mode shifts can be accomplished at a constant mass flow and engine backpressure without upstream pressure perturbations.

Kawecki, Edwin J.; Ribeiro, Gregg L.

2005-01-01

323

Trends and pacing items in computational aerodynamics

A perspective is presented of trends in computational aerodynamics, and of important technology development items that pace future advanced applications. From a survey of AIAA Journal papers published during the past two decades, the growth trends and the progressively increasing emphasis on code development for viscous, compressible, turbulent flow are illustrated. These trends are reflected in the chronology of introduction

Dean R. Chapman

324

Aerodynamic Design of Axial Flow Compressors

NASA Technical Reports Server (NTRS)

An overview of 'Aerodynamic systems design of axial flow compressors' is presented. Numerous chapters cover topics such as compressor design, ptotential and viscous flow in two dimensional cascades, compressor stall and blade vibration, and compressor flow theory. Theoretical aspects of flow are also covered.

Bullock, R. O. (Editor); Johnsen, I. A.

1965-01-01

325

Measured Aerodynamic Interaction of Two Tiltrotors

The aerodynamic interaction of two model tiltrotors in helicopter-mode formation flight is investigated. Three scenarios representing tandem level flight, tandem operations near the ground, and a single tiltrotor operating above the ground for varying winds are examined. The effect of aircraft separation distance on the thrust and rolling moment of the trailing aircraft with and without the presence of a

Gloria K. Yamauchi; Alan J. Wadcock; Michael R. Derby

2003-01-01

326

Aerodynamic Optimization of an UAV Design

The Maracaibo Lake, Venezuela, is an important petroleum extraction region and besides it is a source of constant pollution. However, the early detection of the oil leakages minimizes the environment impact. In 2003 an UAV for the special mission of patrolling that region in search for oil leakages was designed. The purpose of this research is to optimize the aerodynamic

Pedro J. Boschetti; Andrea Amerio

327

Optimization of transition maneuvers through aerodynamic vectoring

This paper discusses the optimization of transition maneuvers between hover and cruise for small aircraft using a novel aerodynamic vectoring feature, which is achieved by allowing the wing to have variable incidence angle with respect to the fuselage. Compared to the fixed-wing aircraft case, the angle of incidence of the wing provides an additional independent control variable in the optimization

Adnan Maqsood; Tiauw Hiong Go

328

Aerodynamics of high frequency flapping wings

NASA Astrophysics Data System (ADS)

We investigated the aerodynamic performance of high frequency flapping wings using a 2.5 gram robotic insect mechanism developed in our lab. The mechanism flaps up to 65Hz with a pair of man-made wing mounted with 10cm wingtip-to-wingtip span. The mean aerodynamic lift force was measured by a lever platform, and the flow velocity and vorticity were measured using a stereo DPIV system in the frontal, parasagittal, and horizontal planes. Both near field (leading edge vortex) and far field flow (induced flow) were measured with instantaneous and phase-averaged results. Systematic experiments were performed on the man-made wings, cicada and hawk moth wings due to their similar size, frequency and Reynolds number. For insect wings, we used both dry and freshly-cut wings. The aerodynamic force increase with flapping frequency and the man-made wing generates more than 4 grams of lift at 35Hz with 3 volt input. Here we present the experimental results and the major differences in their aerodynamic performances.

Hu, Zheng; Roll, Jesse; Cheng, Bo; Deng, Xinyan

2010-11-01

329

Unsteady aerodynamics - Physical issues and numerical predictions

NASA Technical Reports Server (NTRS)

The current status of computational methods for unsteady aerodynamics is reviewed. The need to match the fluid dynamic flow equation level to the complexity of the type of unsteady flow under consideration is discussed. Comparisons of computational predictions with experimental unsteady pressures and flutter boundaries are presented. The treatment of complex aircraft geometries is also described.

Edwards, John W.

1990-01-01

330

Plane Aerodynamics Chamber (Ploskaya Aerodinamicheskaya Kamera).

National Technical Information Service (NTIS)

A description is given of a patent for a plane aerodynamics chamber for blowing through sections of the type of flat gratings consisting of plane vertical and horizontal movable walls, a parallelogrammic mechanism for changing the section of the working p...

N. N. Chernov V. G. Korneev

1967-01-01

331

AN ELECTROMAGNETIC SHOCK TUBE FOR AERODYNAMIC RESEARCH

An electromagnetically driven shock tube was studied as a possible new ; tool for aerodynamic research in which velocities of up to 41,000 fps are ; obtainable in air. At these high velocities stagnation temperatures of about ; 35,000 deg K are produced. The simple construction and operation of the shock ; tube is described and an evaluation is made

Ziemer

1958-01-01

332

Aerodynamic beam generator for large particles

A new type of aerodynamic particle beam generator is disclosed. This generator produces a tightly focused beam of large material particles at velocities ranging from a few feet per second to supersonic speeds, depending on the exact configuration and operating conditions. Such generators are of particular interest for use in additive fabrication techniques.

Brockmann, John E. (Albuquerque, NM); Torczynski, John R. (Albuquerque, NM); Dykhuizen, Ronald C. (Albuquerque, NM); Neiser, Richard A. (Albuquerque, NM); Smith, Mark F. (Albuquerque, NM)

2002-01-01

333

Aerodynamic Performance of Hand Launch Glider

In recent years Micro Air Vehicles (MAV) for disaster aerial video are developed vigorously. In order to improve aerodynamic performance of MAV wing performance in low Reynolds numbers (Re) need to be improved, but research on the theme are very rare. In category of Hand Launch Glider, a kind of model aircraft, glide performance are competed, as a result high

Masaru Koike; Mitsuru Ishii

2009-01-01

334

Aerodynamic characteristics of an oscillating airfoil

Results are reported from wind tunnel tests to study the effects of dynamic aerodynamics on the efficiency of a NACA 0018 airfoil used on a Darreius vertical axis wind turbine (VAWT). The topic is of interest because of uncontrolled pitching which occurs during operation and which produces stall, turbulence and separation effects that reduce efficiency. Present stream-tube theory and axial

R. H. Wickens

1986-01-01

335

Unsteady aerodynamics of advanced ducted fan

A three-dimensional linear frequency domain panel method has been extended to study the unsteady aerodynamics, aeroelasticity, and aeroacoustics of advanced ducted fans. Additional contributions are to extend and improve previous lifting surface theory to include for stator rows and planar supersonic tip Mach numbers, and radiated noise estimation. A two-dimensional viscous wake model is incorporated to account for the influence

Wen-Liang Huang

1996-01-01

336

Energy gradient line approach for direct hydraulic calculation in drip irrigation design

Direct calculations can be made for all emitter flows along a lateral line and in a submain unit based on an Energy Gradient Line (EGL) approach. Errors caused by the EGL approach were evaluated by a computer simulation. A Revised Energy Gradient Line (REGL) approach, developed using a mean discharge approximation, can reduce the errors and match with the results

I. P. Wu

1992-01-01

337

Aerodynamic shape optimization using control theory

NASA Technical Reports Server (NTRS)

Aerodynamic shape design has long persisted as a difficult scientific challenge due its highly nonlinear flow physics and daunting geometric complexity. However, with the emergence of Computational Fluid Dynamics (CFD) it has become possible to make accurate predictions of flows which are not dominated by viscous effects. It is thus worthwhile to explore the extension of CFD methods for flow analysis to the treatment of aerodynamic shape design. Two new aerodynamic shape design methods are developed which combine existing CFD technology, optimal control theory, and numerical optimization techniques. Flow analysis methods for the potential flow equation and the Euler equations form the basis of the two respective design methods. In each case, optimal control theory is used to derive the adjoint differential equations, the solution of which provides the necessary gradient information to a numerical optimization method much more efficiently then by conventional finite differencing. Each technique uses a quasi-Newton numerical optimization algorithm to drive an aerodynamic objective function toward a minimum. An analytic grid perturbation method is developed to modify body fitted meshes to accommodate shape changes during the design process. Both Hicks-Henne perturbation functions and B-spline control points are explored as suitable design variables. The new methods prove to be computationally efficient and robust, and can be used for practical airfoil design including geometric and aerodynamic constraints. Objective functions are chosen to allow both inverse design to a target pressure distribution and wave drag minimization. Several design cases are presented for each method illustrating its practicality and efficiency. These include non-lifting and lifting airfoils operating at both subsonic and transonic conditions.

Reuther, James

1996-01-01

338

Policy approaches to renewable energy investment in the Mediterranean region

NASA Astrophysics Data System (ADS)

Europe's climate policy objective of 20% renewable energy by 2020, and the call by the IPCC to reduce greenhouse gas emissions by 80% by 2050, pose major challenges for the European Union. Several policy options are available to move towards these objectives. In this paper, we will address the most critical policy and governance issues associated with one particular approach to scaling up renewable energy resources: reliance on large-scale energy generation facilities outside the European continent, such as onshore and offshore wind farms and concentrating solar power (CSP) facilities in the Mediterranean region. Several feasibility studies completed over the past three years (German Aerospace Center 2006; German Aerospace Center 2005; Czisch, Elektrotechnik 2005, p. 488; Lorenz, Pinner, Seitz, McKinsey Quarterly 2008, p.10; German Aerospace Center 2005; Knies 2008, The Club of Rome; Khosla, Breaking the Climate Deadlock Briefing Papers, 2008, p.19) have convincingly demonstrated that large-scale wind and CSP projects ought to be very attractive for a number of reasons, including cost, reliability of power supply, and technological maturity. According to these studies it would be technically possible for Europe to rely on large-scale wind and CSP for the majority of its power needs by 2050—indeed enough to completely replace its reliance on fossil fuels for power generation—at competitive cost over its current, carbon intensive system. While it has been shown to be technically feasible to develop renewable resources in North Africa to account for a large share of Europe's energy needs, doing so would require sustained double digit rates of growth in generating and long-distance transmission capacity, and would potentially require a very different high voltage grid architecture within Europe. Doing so at a large scale could require enormous up-front investments in technical capacity, financial instruments and human resources. What are the policy instruments best suited to achieving such growth quickly and smoothly? What bottlenecks—in terms of supply chains, human capital, finance, and transmission capacity—need to be anticipated and addressed if the rate of capacity growth is to be sustained over several decades? What model of governance would create a safe investment climate in consistence with new EU legislation (i.e. EU Renewable Energy Directive) as well as expected post-Kyoto targets and mechanisms? The material that we present here is based on a series of workshops held between November 2008 and January 2009, in which a wide range of stakeholders expressed their views about the fundamental needs for policy intervention. Supplementing the results from these workshops have been additional expert interviews, and basic financial modeling. One of the interesting results from this research is the need for a multi-pronged approach. First, there is a need for a support scheme, potentially compatible with in all cases supplementing the EU REN Directive, that would create a stable market for North African electricity in Europe. Second, there is a need for policies that facilitate the formation of public private partnerships in North Africa, as the specific investment vehicle, as a way to manage some of the uncertainties associated with large-scale investments in the region. Third, attention has to be paid to the development of supply chains within the Mediterranean region, as a way of ensuring the compatibility of such investments with sustainable development.

Patt, A.; Komendantova, N.; Battaglini, A.; Lilliestam, J.; Williges, K.

2009-04-01

339

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

340

Structural optimization of rotor blades with integrated dynamics and aerodynamics

NASA Technical Reports Server (NTRS)

The problem of structural optimization of helicopter rotor blades with integrated dynamic and aerodynamic design considerations is addressed. Results of recent optimization work on rotor blades for minimum weight with constraints on multiple coupled natural flap-lag frequencies, blade autorotational inertia and centrifugal stress has been reviewed. A strategy has been defined for the ongoing activities in the integrated dynamic/aerodynamic optimization of rotor blades. As a first step, the integrated dynamic/airload optimization problem has been formulated. To calculate system sensitivity derivatives necessary for the optimization recently developed, Global Sensitivity Equations (GSE) are being investigated. A need for multiple objective functions for the integrated optimization problem has been demonstrated and various techniques for solving the multiple objective function optimization are being investigated. The method called the Global Criteria Approach has been applied to a test problem with the blade in vacuum and the blade weight and the centrifugal stress as the multiple objectives. The results indicate that the method is quite effective in solving optimization problems with conflicting objective functions.

Chattopadhyay, Aditi; Walsh, Joanne L.

1989-01-01

341

Structural optimization of rotor blades with integrated dynamics and aerodynamics

NASA Technical Reports Server (NTRS)

The problem of structural optimization of helicopter rotor blades with integrated dynamic and aerodynamic design considerations is addressed. Results of recent optimization work on rotor blades for minimum weight with constraints on multiple coupled natural flap-lag frequencies, blade autorotational inertia and centrifugal stress has been reviewed. A strategy has been defined for the ongoing activities in the integrated dynamic/aerodynamic optimization of rotor blades. As a first step, the integrated dynamic/airload optimization problem has been formulated. To calculate system sensitivity derivatives necessary for the optimization recently developed, Global Sensitivity Equations (GSE) are being investigated. A need for multiple objective functions for the integrated optimization problem has been demonstrated and various techniques for solving the multiple objective function optimization are being investigated. The method called the Global Criteria Approach has been applied to a test problem with the blade in vacuum and the blade weight and the centrifugal stress as the multiple objectives. The results indicate that the method is quite effective in solving optimization problems with conflicting objective functions.

Chattopadhyay, Aditi; Walsh, Joanne L.

1988-01-01

342

Grid and aerodynamic sensitivity analyses of airplane components

NASA Technical Reports Server (NTRS)

An algorithm is developed to obtain the grid sensitivity with respect to design parameters for aerodynamic optimization. The procedure is advocating a novel (geometrical) parameterization using spline functions such as NURBS (Non-Uniform Rational B-Splines) for defining the wing-section geometry. An interactive algebraic grid generation technique, known as Two-Boundary Grid Generation (TBGG) is employed to generate C-type grids around wing-sections. The grid sensitivity of the domain with respect to geometric design parameters has been obtained by direct differentiation of the grid equations. A hybrid approach is proposed for more geometrically complex configurations such as a wing or fuselage. The aerodynamic sensitivity coefficients are obtained by direct differentiation of the compressible two-dimensional thin-layer Navier-Stokes equations. An optimization package has been introduced into the algorithm in order to optimize the wing-section surface. Results demonstrate a substantially improved design due to maximized lift/drag ratio of the wing-section.

Sadrehaghighi, Ideen; Smith, Robert E.; Tiwari, Surendra N.

1993-01-01

343

Introduction to Generalized Functions with Applications in Aerodynamics and Aeroacoustics

NASA Technical Reports Server (NTRS)

Generalized functions have many applications in science and engineering. One useful aspect is that discontinuous functions can be handled as easily as continuous or differentiable functions and provide a powerful tool in formulating and solving many problems of aerodynamics and acoustics. Furthermore, generalized function theory elucidates and unifies many ad hoc mathematical approaches used by engineers and scientists. We define generalized functions as continuous linear functionals on the space of infinitely differentiable functions with compact support, then introduce the concept of generalized differentiation. Generalized differentiation is the most important concept in generalized function theory and the applications we present utilize mainly this concept. First, some results of classical analysis, are derived with the generalized function theory. Other applications of the generalized function theory in aerodynamics discussed here are the derivations of general transport theorems for deriving governing equations of fluid mechanics, the interpretation of the finite part of divergent integrals, the derivation of the Oswatitsch integral equation of transonic flow, and the analysis of velocity field discontinuities as sources of vorticity. Applications in aeroacoustics include the derivation of the Kirchhoff formula for moving surfaces, the noise from moving surfaces, and shock noise source strength based on the Ffowcs Williams-Hawkings equation.

Farassat, F.

1994-01-01

344

Analysis and optimization of aerodynamic noise in a centrifugal compressor

NASA Astrophysics Data System (ADS)

The numerical methods for the performance analysis and the noise prediction of the centrifugal compressor impeller are developed, which are coupled with the optimization design methodology consisting of response surface method, statistical approach, and genetic algorithm. Navier-Stokes equations with the two-equation ( k- ?) turbulence model are applied to calculate impeller aerodynamic characteristics, and Ffowcs Williams-Hawkings formulation and boundary element method are used to predict the impeller aerodynamic noise on the basis of impeller flow field results. The computational codes are verified through the comparison of measured data. The quadratic response surface model with D-optimal three-level factorial experimental design points is constructed to optimize the impeller geometry for the advanced centrifugal compressor, and it is shown that the quadratic model exhibits a reasonable fitting quality resulting in the impeller blade design with the high performance and the low far-field noise level. The influences of selected design variables and their mutual interactions as well as the effects of various objective functions and constraints on the impeller performance and the impeller noise are also examined as a result of the optimization process.

Sun, Hyosung; Shin, Hyungki; Lee, Soogab

2006-02-01

345

Conserving the Circus? An Alternative Approach to Teaching and Learning about Energy.

ERIC Educational Resources Information Center

Critiques the "energy circus," an approach to the introduction of ideas of energy transformation and conservation which is in common use in secondary schools. Identifies some practical and conceptual difficulties and outlines an alternative approach used in introducing ideas about energy using real devices and arrow notation. (CW)

Brook, Angela J.; Wells, Peter

1988-01-01

346

International collaborative research in wind turbine rotor aerodynamics

NASA Astrophysics Data System (ADS)

Five organizations from four countries are collaborating to conduct detailed wind turbine aerodynamic test programs. Fullscale atmospheric testing will be conducted on turbines configured to measure aerodynamic forces on rotating airfoils. The purpose of these test programs is to come to a better understanding of the steady and unsteady aerodynamic behavior of wind turbine rotors, and provide information needed to build accurate aerodynamic models for design codes. Stall, dynamic inflow, yaw conditions, and tower effects all contribute to unknown aerodynamic responses. These unknown responses make it extremely difficult to produce cost-effective wind turbine designs. Turbines behave unexpectedly, experiencing power surges and higher fatigue loads than predicted. In order to evolve state-of-the-art wind turbine designs, these aerodynamic effects must be quantified and understood. This paper describes a coordinated international research effort that is underway to accelerate this key research area, and help develop a more thorough understanding of wind turbine aerodynamics.

Simms, D. A.; Butterfield, C. P.

1993-12-01

347

ERIC Educational Resources Information Center

During the period 1984-1986, over 30 teachers from the Yorkshire (England) region have worked in collaboration with the Children's Learning in Science Project (CLIS) developing and testing teaching schemes in the areas of energy, particle theory, and plant nutrition. The project is based upon the constructivist approach to teaching. This guide…

Leeds Univ. (England). Centre for Studies in Science and Mathematics Education.

348

Robust handling of non-linear constraints for GA optimization of aerodynamic shapes

NASA Astrophysics Data System (ADS)

A new approach to the robust handling of non-linear constraints for GAs (genetic algorithms) optimization is proposed. A specific feature of the approach consists of the change in the conventional search strategy by employing search paths which pass through both feasible and infeasible points (contrary to the traditional approach where only feasible points may be included in a path). The method (driven by full Navier-Stokes computations) was applied to the problem of multiobjective optimization of aerodynamic shapes subject to various geometrical and aerodynamic constraints. The results demonstrated that the method retains high robustness of conventional GAs while keeping CFD computational volume to an acceptable level, which allowed the algorithm to be used in a demanding engineering environment.

Peigin, S.; Epstein, B.

2004-08-01

349

Aerodynamic Simulation of Runback Ice Accretion

NASA Technical Reports Server (NTRS)

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 (Re) number. The ice-casting simulation was attached to the leading edge of a 72-in. (1828.8-mm ) chord NACA 23012 airfoil model. Aerodynamic performance tests were conducted at the ONERA F1 pressurized wind tunnel over a Reynolds number range of 4.7?10(exp 6) to 16.0?10(exp 6) and a Mach (M) number ran ge of 0.10 to 0.28. For Re = 16.0?10(exp 6) and M = 0.20, the simulated runback ice accretion on the airfoil decreased the maximum lift coe fficient from 1.82 to 1.51 and decreased the stalling angle of attack from 18.1deg to 15.0deg. The pitching-moment slope was also increased and the drag coefficient was increased by more than a factor of two. In general, the performance effects were insensitive to Reynolds numb er and Mach number changes over the range tested. Follow-on, subscale aerodynamic tests were conducted on a quarter-scale NACA 23012 model (18-in. (457.2-mm) chord) at Re = 1.8?10(exp 6) and M = 0.18, using low-fidelity, geometrically scaled simulations of the full-scale castin g. It was found that simple, two-dimensional simulations of the upper- and lower-surface runback ridges provided the best representation of the full-scale, high Reynolds number iced-airfoil aerodynamics, whereas higher-fidelity simulations resulted in larger performance degrada tions. The experimental results were used to define a new subclassification of spanwise ridge ice that distinguishes between short and tall ridges. This subclassification is based upon the flow field and resulting aerodynamic characteristics, regardless of the physical size of the ridge and the ice-accretion mechanism.

Broeren, Andy P.; Whalen, Edward A.; Busch, Greg T.; Bragg, Michael B.

2010-01-01

350

Multiscale approaches for studying energy transduction in dynein

Cytoplasmic dynein is an important motor that drives all minus-end directed movement along microtubules. Dynein is a complex motor whose processive motion is driven by ATP-hydrolysis. Dynein's run length has been measured to be several millimetres with typical velocities in the order of a few nanometres per second. Therefore, the average time between steps is a fraction of a second. When this time scale is compared with typical time scales for protein side chain and backbone movements (~10?9 s and ~10?5 s, respectively), it becomes clear that a multi-timescale modelling approach is required to understand energy transduction in this protein. Here, we review recent efforts to use computational and mathematical modelling to understand various aspects of dynein's chemomechanical cycle. First, we describe a structural model of dynein's motor unit showing a heptameric organization of the motor subunits. Second, we describe our molecular dynamics simulations of the motor unit that are used to investigate the dynamics of the various motor domains. Third, we present a kinetic model of the coordination between the two dynein heads. Lastly, we investigate the various potential geometries of the dimer during its hydrolytic and stepping cycle.

Serohijos, Adrian W. R.; Tsygankov, Denis; Liu, Shubin; Elston, Timothy C.; Dokholyan, Nikolay V.

2010-01-01

351

Hydrodynamics and aerodynamics - Cross fertilisation in research and design

NASA Astrophysics Data System (ADS)

Areas of intersection between theory and applications in hydrodynamics and aerodynamics are investigated. Fluid mechanics principles involve the minimization of drag and considers the energy exchange between a craft and its wake, which leads to boundary layer examinations. The effects of surface roughness and of turbulent boundary layers are applicable to both seagoing and airborne craft, as are flow separation and vortical flows. Boundary layer control and reenergizing of the boundary layer with redirected vortex energy are discussed. Vortex interaction studies are prominent in the design of offshore oil rig platforms, where orbital wave motion is equivalent to vortex occurrence, and interaction is modelled as flow over a cylinder. Descriptions are given of the design of foil-like shapes, wind-propelled commercial ships, and other applications are presented.

Pearcey, H. H.

1982-01-01

352

Aerodynamic Self Excitation of a Taut Elastic Ribbon

NASA Astrophysics Data System (ADS)

The investigators analyzed, both theoretically and experimentally, the motion of a taut ribbon of elastic material in an air stream to show that the resulting standing-wave motion is a manifestation of self excitation. Self excitation is a phenomenon in which the oscillatory motion of the object extracts energy from a steady energy source. Such a ribbon simulates the motion of the human vocal folds as well as that of unstable bridge ``galloping,'' such as is famously exemplified in the Tacoma Narrows bridge collapse. The phenomenon discussed in this talk is also relevant to aerodynamic flutter and the ``quaking'' of leaves of trees in the breeze. Chief among the findings of this work is the origin of inharmonic modes of oscillation of a self excited ribbon.

Matteson, Sam; Lambert, David

2011-10-01

353

Dynamic Gas-Surface Interaction Modeling for Satellite Aerodynamic Computations

NASA Astrophysics Data System (ADS)

Drag coefficients are a large source of uncertainty when predicting the aerodynamic forces on orbiting satellites. Accordingly, the focus of this research is to improve the fidelity of drag modeling by investigating the nature of gas-surface interactions in low earth orbit. The author has investigated to what extent oxygen adsorption can influence the parameters of drag coefficient models, most notably the energy accommodation coefficient. To accomplish this, several analysis techniques are applied. Fitted drag coefficients for 68 objects were provided by Air Force Space Command Drag Analysis Office and are analyzed using analytical and numerical aerodynamic models. Gas-surface parameters are estimated by comparing the model results to the observed coefficients. The results indicate that a successful and predictive relationship of the energy accommodation coefficient can be obtained with gas-surface models incorporating Langmuir adsorption. Good agreement with data has been obtained by using a cosine reflection model below 500 km. Furthermore, it is found that satellite accommodation coefficients can be explained by a model in which atomic oxygen binds to the surface with an energy of approximately 5.7 eV. Multi-axis accelerometer data from the CHAMP and GRACE satellites has also been analyzed to derive measurements of lift and drag which are compared to model predictions given different gas-surface assumptions. The results indicate that diffuse reflection is appropriate for CHAMP near 400 km and that the accommodation coefficient before 2008 ranges between 0.86 and 0.89. CHAMP accelerometer data is also combined with remote sensing estimates of density to arrive at values of drag coefficient which do not depend on empirical atmospheric models alone. This dataset confirms the predicted drop in accommodation with decreasing atomic oxygen pressure. The culmination of this work is an enhanced energy accommodation and drag coefficient model applicable between 100 km and 500 km altitudes for satellites in both circular and elliptical orbits.

Pilinski, M. D.

354

National Technical Information Service (NTIS)

A reference building approach to building energy performance standards (BEPS) is described in this report which could serve as a framework for the further development of energy standards for new single-family residences. Each proposed new building design ...

S. R. Petersen J. L. Heldenbrand

1980-01-01

355

The evaluation of emissions from new energy sources has stimulated the development of new comparative approaches to health assessment studies. All energy sources that result in incomplete combustion are known to emit carcinogenic and mutagenic polynuclear aromatic compounds. Ther...

356

Rarefaction effects on Galileo probe aerodynamics

NASA Technical Reports Server (NTRS)

Solutions of aerodynamic characteristics are presented for the Galileo Probe entering Jupiter's hydrogen-helium atmosphere at a nominal relative velocity of 47.4 km/s. Focus is on predicting the aerodynamic drag coefficient during the transitional flow regime using the direct simulation Monte Carlo (DSMC) method. Accuracy of the probe's drag coefficient directly impacts the inferred atmospheric properties that are being extracted from the deceleration measurements made by onboard accelerometers as part of the Atmospheric Structure Experiment. The range of rarefaction considered in the present study extends from the free molecular limit to continuum conditions. Comparisons made with previous calculations and experimental measurements show the present results for drag to merge well with Navier-Stokes and experimental results for the least rarefied conditions considered.

Moss, James N.; LeBeau, Gerald J.; Blanchard, Robert C.; Price, Joseph M.

1996-01-01

357

Parameter identification and modeling of longitudinal aerodynamics

NASA Technical Reports Server (NTRS)

Using a comprehensive flight test database and a parameter identification software program produced at NASA Ames Research Center, a math model of the longitudinal aerodynamics of the Harrier aircraft was formulated. The identification program employed the equation error method using multiple linear regression to estimate the nonlinear parameters. The formulated math model structure adhered closely to aerodynamic and stability/control theory, particularly with regard to compressibility and dynamic manoeuvring. Validation was accomplished by using a three degree-of-freedom nonlinear flight simulator with pilot inputs from flight test data. The simulation models agreed quite well with the measured states. It is important to note that the flight test data used for the validation of the model was not used in the model identification.

Aksteter, J. W.; Parks, E. K.; Bach, R. E., Jr.

1995-01-01

358

Aerodynamic enhancement of space transportation systems

NASA Technical Reports Server (NTRS)

The results of a number of recent investigations are reviewed and used to demonstrate gains in launch, orbital transfer, and planetary vehicle performance and economy that can result from the proper exploitation of aerodynamic phenomena. For launch vehicles, application of control-configured design is shown to allow substantial reduction in wing and vertical fin area (and hence, weight) while maintaining acceptable vehicle performance and control. For orbital transfer and planetary vehicles, the use of aerodynamic lift and drag to reduce retropropulsion requirements is shown to produce payload increases of up to 100 percent and to enable some planetary missions that are not feasible with all-propulsive vehicles. Finally, the application of various advanced technologies to a complete set of launch and orbit transfer vehicles in an early space industrialization mission scenario is considered.

Walberg, G. D.

1981-01-01

359

High speed civil transport aerodynamic optimization

NASA Technical Reports Server (NTRS)

This is a report of work in support of the Computational Aerosciences (CAS) element of the Federal HPCC program. Specifically, CFD and aerodynamic optimization are being performed on parallel computers. The long-range goal of this work is to facilitate teraflops-rate multidisciplinary optimization of aerospace vehicles. This year's work is targeted for application to the High Speed Civil Transport (HSCT), one of four CAS grand challenges identified in the HPCC FY 1995 Blue Book. This vehicle is to be a passenger aircraft, with the promise of cutting overseas flight time by more than half. To meet fuel economy, operational costs, environmental impact, noise production, and range requirements, improved design tools are required, and these tools must eventually integrate optimization, external aerodynamics, propulsion, structures, heat transfer, controls, and perhaps other disciplines. The fundamental goal of this project is to contribute to improved design tools for U.S. industry, and thus to the nation's economic competitiveness.

Ryan, James S.

1994-01-01

360

CFD research, parallel computation and aerodynamic optimization

NASA Technical Reports Server (NTRS)

Over five years of research in Computational Fluid Dynamics and its applications are covered in this report. Using CFD as an established tool, aerodynamic optimization on parallel architectures is explored. The objective of this work is to provide better tools to vehicle designers. Submarine design requires accurate force and moment calculations in flow with thick boundary layers and large separated vortices. Low noise production is critical, so flow into the propulsor region must be predicted accurately. The High Speed Civil Transport (HSCT) has been the subject of recent work. This vehicle is to be a passenger vehicle with the capability of cutting overseas flight times by more than half. A successful design must surpass the performance of comparable planes. Fuel economy, other operational costs, environmental impact, and range must all be improved substantially. For all these reasons, improved design tools are required, and these tools must eventually integrate optimization, external aerodynamics, propulsion, structures, heat transfer and other disciplines.

Ryan, James S.

1995-01-01

361

Using Satellite Aerodynamics to Sense Thermospheric Winds

NASA Astrophysics Data System (ADS)

It is well known that even in the rarified space environment satellite aerodynamics still play a role in determining parameters such as drag and attitude, and if the aerodynamics are well understood, satellite deceleration can be used to determine the in-track neutral momentum flux or density if a wind velocity is assumed, as clearly demonstrated with the CHAMP and GRACE satellites. In addition to measurement of the neutral density, these satellites have demonstrated how the cross winds can influence the satellite attitude. In this work, it is shown how if the satellite geometry is taken to the extreme of adding a simple long rigid gossamer tail, as with a dart, sufficient sensitivity can be achieved to measure the cross track winds with precision comparable to the in-track density determination.

Cooke, D. L.; Jackson, D.

2010-12-01

362

Wind turbine trailing edge aerodynamic brakes

Five trailing-edge devices were investigated to determine their potential as wind-turbine aerodynamic brakes, and for power modulation and load alleviation. Several promising configurations were identified. A new device, called the spoiler-flap, appears to be the best alternative. It is a simple device that is effective at all angles of attack. It is not structurally intrusive, and it has the potential for small actuating loads. It is shown that simultaneous achievement of a low lift/drag ratio and high drag is the determinant of device effectiveness, and that these attributes must persist up to an angle of attack of 45{degree}. It is also argued that aerodynamic brakes must be designed for a wind speed of at least 45 m/s (100 mph).

Migliore, P G [National Renewable Energy Lab., Golden, CO (United States); Miller, L S [Wichita State Univ., KS (United States). Dept. of Aerospace Engineering; Quandt, G A

1995-04-01

363

Aerodynamic Shape Optimization Using Hybridized Differential Evolution

NASA Technical Reports Server (NTRS)

An aerodynamic shape optimization method that uses an evolutionary algorithm known at Differential Evolution (DE) in conjunction with various hybridization strategies is described. DE is a simple and robust evolutionary strategy that has been proven effective in determining the global optimum for several difficult optimization problems. Various hybridization strategies for DE are explored, including the use of neural networks as well as traditional local search methods. A Navier-Stokes solver is used to evaluate the various intermediate designs and provide inputs to the hybrid DE optimizer. The method is implemented on distributed parallel computers so that new designs can be obtained within reasonable turnaround times. Results are presented for the inverse design of a turbine airfoil from a modern jet engine. (The final paper will include at least one other aerodynamic design application). The capability of the method to search large design spaces and obtain the optimal airfoils in an automatic fashion is demonstrated.

Madavan, Nateri K.

2003-01-01

364

Aerodynamics of Seeing on Large Transport Aircraft

NASA Technical Reports Server (NTRS)

Efforts were undertaken to obtain a set of data that examined the level of turbulence and the scale sizes in the shear layer existing over the fence quieted cavity on the NASA-Ames Kuiper Airborne Observatory (KAO). These data were to be taken during the present study and compared with data taken from previous wind tunnel experiments, for which both aerodynamic and direct optical measurements were made. The data obtained during the present study were presented and discussed in light of their impact on the quality of optical images, that is, seeing through the shear layer. In addition, scaling relationships were presented that allow optical data obtained in one aerodynamic environment to be estimated for another one at perhaps different Mach numbers, scale sizes, or aircraft configurations.

Rose, William C.

1988-01-01

365

An Interactive Educational Tool for Compressible Aerodynamics

NASA Technical Reports Server (NTRS)

A workstation-based interactive educational tool was developed to aid in the teaching of undergraduate compressible aerodynamics. The tool solves for the supersonic flow past a wedge using the equations found in NACA 1135. The student varies the geometry or flow conditions through a graphical user interface and the new conditions are calculated immediately. Various graphical formats present the variation of flow results to the student. One such format leads the student to the generation of some of the graphs found in NACA-1135. The tool includes interactive questions and answers to aid in both the use of the tool and to develop an understanding of some of the complexities of compressible aerodynamics. A series of help screens make the simulator easy to learn and use. This paper will detail the numerical methods used in the tool and describe how it can be used and modified.

Benson, Thomas J.

1994-01-01

366

Aerodynamic shape optimization of arbitrary hypersonic vehicles

NASA Technical Reports Server (NTRS)

A new method was developed to optimize, in terms of aerodynamic wave drag minimization, arbitrary (nonaxisymmetric) hypersonic vehicles in modified Newtonian flow, while maintaining the initial volume and length of the vehicle. This new method uses either a surface fitted Fourier series to represent the vehicle's geometry or an independent point motion algorithm. In either case, the coefficients of the Fourier series or the spatial locations of the points defining each cross section were varied and a numerical optimization algorithm based on a quasi-Newton gradient search concept was used to determine the new optimal configuration. Results indicate a significant decrease in aerodynamic wave drag for simple and complex geometries at relatively low CPU costs. In the case of a cone, the results agreed well with known analytical optimum ogive shapes. The procedure is capable of accepting more complex flow field analysis codes.

Dulikravich, George S.; Sheffer, Scott G.

1991-01-01

367

Remarks on the theory of aerodynamic noise

NASA Technical Reports Server (NTRS)

The accuracy of approximations employed in the Lighthill theory in current aerodynamic noise research is critically evaluated. Based on the method of matched asymptotic expansions, the full Navier-Stokes equations are expanded for small Mach numbers. To the first order, the near-field is generally nonisentropic. The pressure field (pseudo-sound) is generated by the incompressible Reynolds stresses in the turbulent flow and the velocity, pressure perturbation, and their derivatives on the boundaries. In the far-field, the first-order pressure (acoustic) field satisfying a linear wave equation is obtained by matching with the pseudo-sound field. A uniformly valid solution for the pressure field in a stationary or uniformly moving medium is obtained. The solution shows that the generation of the first-order aerodynamic noise does not depend on the viscous, thermal, or entropy effects in the adiabatic flow nor on the shear stress on a smooth rigid boundary.

Pan, Y. S.

1975-01-01

368

Fundamental aerodynamics of the soccer ball

When the boundary layer of a sports ball undergoes the transition from laminar to turbulent flow, a drag crisis occurs whereby\\u000a the drag coefficient (C\\u000a d) rapidly decreases. However, the aerodynamic properties and boundary-layer dynamics of a soccer ball are not yet well understood.\\u000a In this study we showed that the critical Reynolds number (Re\\u000a crit) of soccer balls ranged

T. Asai; K. Seo; O. Kobayashi; R. Sakashita

2007-01-01

369

Aerodynamics of intermittent bounds in flying birds

Flap-bounding is a common flight style in small birds in which flapping phases alternate with flexed-wing bounds. Body lift\\u000a is predicted to be essential to making this flight style an aerodynamically attractive flight strategy. To elucidate the contributions\\u000a of the body and tail to lift and drag during the flexed-wing bound phase, we used particle image velocimetry (PIV) and measured

Bret W. Tobalske; Jason W. D. Hearn; Douglas R. Warrick

2009-01-01

370

Unsteady aerodynamics of fluttering and tumbling plates

We investigate the aerodynamics of freely falling plates in a quasi-two-dimensional flow at Reynolds number of 10(3) , 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

A. Andersen; U. Pesavento; Z. Jane Wang

2005-01-01

371

Unsteady aerodynamics of fluttering and tumbling plates

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

372

Aerodynamic characteristics of flapping motion in hover

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

373

Experimental aerodynamics research on a hypersonic vehicle

Aerodynamic force and moment measurements and flow visualization results are presented for a hypersonic vehicle configuration at Mach 8. The basic vehicle configuration is a spherically blunted 10Â° half-angle cone with a slice parallel with the axis of the vehicle. On the slice portion of the vehicle, a flap could be attached so that deflection angles of 10Â°, 20Â° and

W. L. Oberkampf; D. P. Aeschliman; R. E. Tate; J. F. Henfling

1993-01-01

374

Experimental aerodynamics research on a hypersonic vehicle

Aerodynamic force and moment measurements and flow visualization results are presented for a hypersonic vehicle configuration at Mach 8. The basic vehicle configuration is a spherically blunted 10[degree] half-angle cone with a slice parallel with the axis of the vehicle. On the slice portion of the vehicle, a flap could be attached so that deflection angles of 10[degree], 20[degree] and

W. L. Oberkampf; D. P. Aeschliman; R. E. Tate; J. F. Henfling

1993-01-01

375

Opportunities for aerodynamic-drag reduction

NASA Technical Reports Server (NTRS)

Methods for reducing aerodynamic drag to improve aircraft performance and reduce fuel consumption are discussed. The techniques considered are: (1) pressure drag reduction, (2) supercritical airfoils, (3) subcritical airfoils, (4) induced drag reduction by over-the-wing blowing and increased aspect ratio, and (5) friction drag reduction by laminar flow control and slot injection. It is stated that a 50 percent reduction from current drag values is expected through the application of these techniques.

Bower, R. E.

1975-01-01

376

New aspects of subsonic aerodynamic noise theory

NASA Technical Reports Server (NTRS)

A theory of aerodynamic noise is presented which differs from Lighthill's theory primarily in the way in which convection of the noise sources is treated. The sound directivity pattern obtained from the present theory agrees better with jet-noise directivity data than does that obtained from Lighthill's theory. The results imply that the shear-noise contribution to jet noise is smaller than previously expected.

Goldstein, M. E.; Howes, W. L.

1973-01-01

377

Hydrodynamic and aerodynamic breakup of liquid sheets

NASA Technical Reports Server (NTRS)

The effect of hydrodynamic, aerodynamic and liquid surface forces on the mean drop diameter of water sprays that are produced by the breakup of nonswirling and swirling water sheets in quiescent air and in airflows similar to those encountered in gas turbine combustors is investigated. The mean drop diameter is used to characterize fuel sprays and it is a very important factor in determining the performance and exhaust emissions of gas turbine combustors.

Ingebo, R.

1982-01-01

378

Recent progress in circulation control aerodynamics

NASA Technical Reports Server (NTRS)

A workshop on circulation control aerodynamics was held on February 19-21, 1986 at NASA Ames Research Center, Moffett Field, CA. The subjects covered were viscosity and turbulence of Coanda jets, circulation control airfoils, airfoil theory, circulation control airfoil and wing experiments, circulation control rotor theory, X-Wing technology, and fixed-wing technology. The unclassified papers of the Workshop are reviewed in this paper, and Workshop recommendations for future research and development on circulation control are presented.

Nielsen, Jack N.; Biggers, James C.

1987-01-01

379

Aerodynamic considerations in open shelters. Final report

Aerodynamic factors are addressed bearing on the suitability of open structures as blast shelters. Blast closures and attenuator designs are discussed. The research on shelter filling is reviewed; this includes both experimental and theoretical work on scale models and full-scale structures of large dimensions. Shock-dominated and pressure-gradient-dominated shelter-filling mechanisms are described and their potential effects on people are discussed.

Hickman, R.G.

1984-11-01

380

Windbreak Aerodynamics: Is Computational Fluid Dynamics Reliable?

To investigate the suitability of computational fluid dynamics (CFD) with regard to windbreak aerodynamics, simulations are\\u000a performed with a state-of-the-art numerical scheme (Fluent) and compared against experimental data for two- and three-dimensional\\u000a disturbances, namely the case of a long straight porous shelter fence and the case of a shelter fence erected in a square\\u000a about an enclosed plot. A thorough

P. Bourdin; John D. Wilson

2008-01-01

381

Variable-Fidelity Aerodynamic Shape Optimization

\\u000a Aerodynamic shape optimization (ASO) plays an important role in the design of aircraft, turbomachinery and other fluid machinery.\\u000a Simulation-driven ASO involves the coupling of computational fluid dynamics (CFD) solvers with numerical optimization methods.\\u000a Although being relatively mature and widely used, ASO is still being improved and numerous challenges remain. This chapter\\u000a provides an overview of simulation-driven ASO methods, with an

Leifur Leifsson; Slawomir Koziel

382

Application of strand meshes to complex aerodynamic flow fields

NASA Astrophysics Data System (ADS)

We explore a new approach for viscous computational fluid dynamics calculations for external aerodynamics around geometrically complex bodies that incorporates nearly automatic mesh generation and efficient flow solution methods. A prismatic-like grid using "strands" is grown a short distance from the body surface to capture the viscous boundary layer, and adaptive Cartesian grids are used throughout the rest of the domain. The approach presents several advantages over established methods: nearly automatic grid generation from triangular or quadrilateral surface tessellations, very low memory overhead, automatic mesh adaptivity for time-dependent problems, and fast and efficient solvers from structured data in both the strand and Cartesian grids.The approach is evaluated for complex geometries and flow fields. We investigate the effects of strand length and strand vector smoothing to understand the effects on computed solutions. Results of three applications using the strand-adaptive Cartesian approach are given, including a NACA wing, isolated V-22 (TRAM) rotor in hover, and the DLR-F6 wing-body transport. The results from these cases show that the strand approach can successfully resolve near-body and off-body features as well as or better than established methods.

Katz, Aaron; Wissink, Andrew M.; Sankaran, Venkateswaran; Meakin, Robert L.; Chan, William M.

2011-07-01

383

Progress in design optimization using evolutionary algorithms for aerodynamic problems

NASA Astrophysics Data System (ADS)

Evolutionary algorithms (EAs) are useful tools in design optimization. Due to their simplicity, ease of use, and suitability for multi-objective design optimization problems, EAs have been applied to design optimization problems from various areas. In this paper we review the recent progress in design optimization using evolutionary algorithms to solve real-world aerodynamic problems. Examples are given in the design of turbo pump, compressor, and micro-air vehicles. The paper covers the following topics that are deemed important to solve a large optimization problem from a practical viewpoint: (1) hybridized approaches to speed up the convergence rate of EAs; (2) the use of surrogate model to reduce the computational cost stemmed from EAs; (3) reliability based design optimization using EAs; and (4) data mining of Pareto-optimal solutions.

Lian, Yongsheng; Oyama, Akira; Liou, Meng-Sing

2010-07-01

384

Recent Improvements in Aerodynamic Design Optimization on Unstructured Meshes

NASA Technical Reports Server (NTRS)

Recent improvements in an unstructured-grid method for large-scale aerodynamic design are presented. Previous work had shown such computations to be prohibitively long in a sequential processing environment. Also, robust adjoint solutions and mesh movement procedures were difficult to realize, particularly for viscous flows. To overcome these limiting factors, a set of design codes based on a discrete adjoint method is extended to a multiprocessor environment using a shared memory approach. A nearly linear speedup is demonstrated, and the consistency of the linearizations is shown to remain valid. The full linearization of the residual is used to precondition the adjoint system, and a significantly improved convergence rate is obtained. A new mesh movement algorithm is implemented and several advantages over an existing technique are presented. Several design cases are shown for turbulent flows in two and three dimensions.

Nielsen, Eric J.; Anderson, W. Kyle

2000-01-01

385

Lawrence Livermore National Laboratory (LLNL) as part of its Department of Energy (DOE), Energy Efficiency and Renewable Energy (EERE), and Vehicle Technologies Program (VTP) effort has investigated class 8 tractor-trailer aerodynamics for many years. This effort has identified many drag producing flow structures around the heavy vehicles and also has designed and tested many new active and passive drag reduction techniques and concepts for significant on the road fuel economy improvements. As part of this effort a database of experimental, computational, and conceptual design for aerodynamic drag reduction devices has been established. The objective of this report is to provide design guidance for trailer base devices to improve their aerodynamic performance. These devices are commonly referred to as boattails, base flaps, tail devices, and etc. The information provided here is based on past research and our most recent full-scale experimental investigations in collaboration with Navistar Inc. Additional supporting data from LLNL/Navistar wind tunnel, track test, and on the road test will be published soon. The trailer base devices can be identified by 4 flat panels that are attached to the rear edges of the trailer base to form a closed cavity. These devices have been engineered in many different forms such as, inflatable and non-inflatable, 3 and 4-sided, closed and open cavity, and etc. The following is an in-depth discussion with some recommendations, based on existing data and current research activities, of changes that could be made to these devices to improve their aerodynamic performance. There are 6 primary factors that could influence the aerodynamic performance of trailer base devices: (1) Deflection angle; (2) Boattail length; (3) Sealing of edges and corners; (4) 3 versus 4-sided, Position of the 4th plate; (5) Boattail vertical extension, Skirt - boattail transition; and (6) Closed versus open cavity.

Salari, K; Ortega, J

2010-12-13

386

The Aerodynamics of a Flying Sports Disc

NASA Astrophysics Data System (ADS)

The flying sports disc is a spin-stabilised axi-symmetric wing of quite remarkable design. A typical disc has an approximate elliptical cross-section and hollowed out under-side cavity, such as the Frisbee(TM) disc. An experimental study of flying disc aerodynamics, including both spinning and non-spinning tests, has been carried out in the wind tunnel. Load measurements, pressure data and flow visualisation techniques have enabled an explanation of the flow physics and provided data for free-flight simulations. A computer simulation that predicts free-flight trajectories from a given set of initial conditions was used to investigate the dynamics of a flying disc. This includes a six-degree of freedom mathematical model of disc flight mechanics, with aerodynamic coefficients derived from experimental data. A flying sports disc generates lift through forward velocity just like a conventional wing. The lift contributed by spin is insignificant and does not provide nearly enough down force to support hover. Without spin, the disc tumbles ground-ward under the influence of an unstable aerodynamic pitching moment. From a backhand throw however, spin is naturally given to the disc. The unchanged pitching moment now results in roll, due to gyroscopic precession, stabilising the disc in free-flight.

Potts, Jonathan R.; Crowther, William J.

2001-11-01

387

Aerodynamics for the Mars Phoenix Entry Capsule

NASA Technical Reports Server (NTRS)

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 database was constructed using continuum flowfield computations and data from the Mars Exploration Rover and Viking programs. Hypersonic and supersonic static coefficients were derived from Navier-Stokes solutions on a pre-flight design trajectory. High-altitude data (free-molecular and transitional regimes) and dynamic pitch damping characteristics were taken from Mars Exploration Rover analysis and testing. Transonic static coefficients from Viking wind tunnel tests were used for capsule aerodynamics under the parachute. Static instabilities were predicted at two points along the reference trajectory and were verified by reconstructed flight data. During the hypersonic instability, the capsule was predicted to trim at angles as high as 2.5 deg with an on-axis center-of-gravity. Trim angles were predicted for off-nominal pitching moment (4.2 deg peak) and a 5 mm off-axis center-ofgravity (4.8 deg peak). Finally, hypersonic static coefficient sensitivities to atmospheric density were predicted to be within uncertainty bounds.

Edquist, Karl T.; Desai, Prasun N.; Schoenenberger, Mark

2008-01-01

388

Aerodynamically balanced ailerons for a commuter aircraft

NASA Astrophysics Data System (ADS)

This review paper describes the state of designing aerodynamically balanced ailerons with a practical application to commuter aircraft, with Saab 2000 being used as an example. A modern design method is presented based on the application of CFD computations to determine the aileron aerodynamic data combined with flight mechanical simulations to study the impact on airplane rolling maneuvers and aileron dynamics. Dynamic response of aileron deflection, airplane roll rate and roll acceleration to the applied wheel force is determined by frequency analysis. A review on the design requirements on ailerons and practical design considerations is presented. The CFD computations are described in detail with comparisons against wind tunnel experiments and flight tests for validation of the methodology. Description of the flight mechanical simulation system includes the modeling of the aileron control system. The frequency analysis summarizes the equations of the employed Fourier analysis, spectrum analysis and system identification. Numerical results are presented on aileron hinge moment coefficient, airplane rolling moment coefficient, wheel force in sideslip and rolling maneuvers and gain and phase lag in frequency analysis results to highlight the key discussion points including the effects of aileron control system and aileron and tab gap sizes. Overall, aerodynamically balanced ailerons, together with a mechanical control system, offer large cost savings on small- and medium-sized airplanes.

Soinne, Erkki

2001-08-01

389

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

390

Future Challenges and Opportunities in Aerodynamics

NASA Technical Reports Server (NTRS)

Investments in aeronautics research and technology have declined substantially over the last decade, in part due to the perception that technologies required in aircraft design are fairly mature and readily available. This perception is being driven by the fact that aircraft configurations, particularly the transport aircraft, have evolved only incrementally, over last several decades. If however, one considers that the growth in air travel is expected to triple in the next 20 years, it becomes quickly obvious that the evolutionary development of technologies is not going to meet the increased demands for safety, environmental compatibility, capacity, and economic viability. Instead, breakthrough technologies will he required both in traditional disciplines of aerodynamics, propulsion, structures, materials, controls, and avionics as well as in the multidisciplinary integration of these technologies into the design of future aerospace vehicles concepts. The paper discusses challenges and opportunities in the field of aerodynamics over the next decade. Future technology advancements in aerodynamics will hinge on our ability, to understand, model, and control complex, three-dimensional, unsteady viscous flow across the speed range. This understanding is critical for developing innovative flow and noise control technologies and advanced design tools that will revolutionize future aerospace vehicle systems and concepts. Specifically, the paper focuses on advanced vehicle concepts, flow and noise control technologies, and advanced design and analysis tools.

Kumar, Ajay; Hefner, Jerry N.

2000-01-01

391

High angle of attack hypersonic aerodynamics

NASA Technical Reports Server (NTRS)

A new aerodynamics force model is presented which is based on modified Newtonian theory and empirical correlations. The algebraic model was developed for complete vehicles from take off to orbital speeds and for large angles of attack. Predictions are compared to results for a wind tunnel model at a Mach number of 20, and the full scale Shuttle Orbiter for Mach numbers from 0.25 to 20 for angles of attack from 0 to 50 deg. The maximum shuttle orbiter lift/drag at Mach 10 and 20 is 1.85 at 20-deg angle-of-attack. Aerodynamic force predictions are made for a transatmospheric vehicle, which is a derivative of the Shuttle Orbiter, for Mach numbers from 4 to 27 at angles of attack from 5 to 40 deg. Predicted aerodynamic force data indicate that lift/drag ratios of 5.2 at Mach number 10 and 3.6 at Mach number 26 are obtainable. Changes in force coefficients with changes in: nose angle, sweep angle, and (volume exp 2/3)/planform area are quantified for Mach numbers of 10 and 26. Lift/drag ratios increase with decreasing nose angle and (volume exp 2/3)/planform area and increasing wing sweep angle. Lift/drag ratios are independent of these variables for angles of attack in excess of 20 deg at Mach 10 and 30 deg at Mach 26.

Harloff, Gary J.

1987-01-01

392

NASA Technical Reports Server (NTRS)

A simulation study was conducted to investigate aerodynamic modeling methods for prediction of post-stall flight dynamics of large transport airplanes. The research approach involved integrating dynamic wind tunnel data from rotary balance and forced oscillation testing with static wind tunnel data to predict aerodynamic forces and moments during highly dynamic departure and spin motions. Several state-of-the-art aerodynamic modeling methods were evaluated and predicted flight dynamics using these various approaches were compared. Results showed the different modeling methods had varying effects on the predicted flight dynamics and the differences were most significant during uncoordinated maneuvers. Preliminary wind tunnel validation data indicated the potential of the various methods for predicting steady spin motions.

Murch, Austin M.; Foster, John V.

2007-01-01

393

Research on gray decision-making approach for the evaluation of the energy efficiency

There are many factors affecting Unit GDP energy consumption, including industrial structure, living habits, energy consuming structure, physical energy efficiency, energy prices and so on. Aggregation approach for interval gray utility value and gray preference order in the group decision-making is studied. This paper first introduced interval gray utility value and interval gray preference order. The weight model for interval

Yu Wei; Zhu Jian-jun; Wu Yang-yun

2007-01-01

394

An integrated renewable energy park approach for algal biofuel production in United States

Algal biomass provides viable third generation feedstock for liquid transportation fuel that does not compete with food crops for cropland. However, fossil energy inputs and intensive water usage diminishes the positive aspects of algal energy production. An integrated renewable energy park (IREP) approach is proposed for aligning renewable energy industries in resource-specific regions in United States for synergistic electricity and

Bobban Subhadra; Mark Edwards

2010-01-01

395

Numerical and experimental investigations on unsteady aerodynamics of flapping wings

NASA Astrophysics Data System (ADS)

The development of a dynamic unstructured grid high-order accurate spectral difference (SD) method for the three dimensional compressible Navier-Stokes (N-S) equations and its applications in flapping-wing aerodynamics are carried out in this work. Grid deformation is achieved via an algebraic blending strategy to save computational cost. The Geometric Conservation Law (GCL) is imposed to ensure that grid deformation will not contaminate the flow physics. A low Mach number preconditioning procedure is conducted in the developed solver to handle the bio-inspired flow. The capability of the low Mach number preconditioned SD solver is demonstrated by a series of two dimensional (2D) and three dimensional (3D) simulations of the unsteady vortex dominated flow. Several topics in the flapping wing aerodynamics are numerically and experimentally investigated in this work. These topics cover some of the cutting-edge issues in flapping wing aerodynamics, including the wake structure analysis, airfoil thickness and kinematics effects on the aerodynamic performances, vortex structure analysis around 3D flapping wings and the kinematics optimization. Wake structures behind a sinusoidally pitching NACA0012 airfoil are studied with both experimental and numerical approaches. The experiments are carried out with Particle Image Velocimetry (PIV) and two types of wake transition processes, namely the transition from a drag-indicative wake to a thrust-indicative wake and that from the symmetric wake to the asymmetric wake are distinguished. The numerical results from the developed SD solver agree well with the experimental results. It is numerically found that the deflective direction of the asymmetric wake is determined by the initial conditions, e.g. initial phase angle. As most insects use thin wings (i. e., wing thickness is only a few percent of the chord length) in flapping flight, the effects of airfoil thickness on thrust generation are numerically investigated by simulating the flow fields around a series of plunging NACA symmetric airfoils with thickness ratio ranging from 4.0% to 20.0% of the airfoil chord length. The contribution of viscous force to flapping propulsion is accessed and it is found that viscous force becomes thrust producing, instead of drag producing, and plays a non-negligible role in thrust generation for thin airfoils. This is closely related to the variations of the dynamics of the unsteady vortex structures around the plunging airfoils. As nature flyers use complex wing kinematics in flapping flight, kinematics effects on the aerodynamic performance with different airfoil thicknesses are numerically studied by using a series of NACA symmetric airfoils. It is found that the combined plunging and pitching motion can outperform the pure plunging or pitching motion by sophisticatedly adjusting the airfoil gestures during the oscillation stroke. The thin airfoil better manipulates leading edge vortices (LEVs) than the thick airfoil (NACA0030) does in studied cases, and there exists an optimal thickness for large thrust generation with reasonable propulsive efficiency. With the present kinematics and dynamic parameters, relatively low reduced frequency is conducive for thrust production and propulsive efficiency for all tested airfoil thicknesses. In order to obtain the optimal kinematics parameters of flapping flight, a kinematics optimization is then performed. A gradient-based optimization algorithm is coupled with a second-order SD Navier-Stokes solver to search for the optimal kinematics of a certain airfoil undergoing a combined plunging and pitching motion. Then a high-order SD scheme is used to verify the optimization results and reveal the detailed vortex structures associated with the optimal kinematics of the flapping flight. It is found that for the case with maximum propulsive efficiency, there exists no leading edge separation during most of the oscillation cycle. In order to provide constructive suggestions to the design of micro-air-vehicles (MAVs), 3D simulations of the flapping wings are carrie

Yu, Meilin

396

Aerodynamic effects of trees on pollutant concentration in street canyons.

This paper deals with aerodynamic effects of avenue-like tree planting on flow and traffic-originated pollutant dispersion in urban street canyons by means of wind tunnel experiments and numerical simulations. Several parameters affecting pedestrian level concentration are investigated, namely plant morphology, positioning and arrangement. We extend our previous work in this novel aspect of research to new configurations which comprise tree planting of different crown porosity and stand density, planted in two rows within a canyon of street width to building height ratio W/H=2 with perpendicular approaching wind. Sulfur hexafluoride was used as tracer gas to model the traffic emissions. Complementary to wind tunnel experiments, 3D numerical simulations were performed with the Computational Fluid Dynamics (CFD) code FLUENT using a Reynolds Stress turbulence closure for flow and the advection-diffusion method for concentration calculations. In the presence of trees, both measurements and simulations showed considerable larger pollutant concentrations near the leeward wall and slightly lower concentrations near the windward wall in comparison with the tree-less case. Tree stand density and crown porosity were found to be of minor importance in affecting pollutant concentration. On the other hand, the analysis indicated that W/H is a more crucial parameter. The larger the value of W/H the smaller is the effect of trees on pedestrian level concentration regardless of tree morphology and arrangement. A preliminary analysis of approaching flow velocities showed that at low wind speed the effect of trees on concentrations is worst than at higher speed. The investigations carried out in this work allowed us to set up an appropriate CFD modelling methodology for the study of the aerodynamic effects of tree planting in street canyons. The results obtained can be used by city planners for the design of tree planting in the urban environment with regard to air quality issues. PMID:19596394

Buccolieri, Riccardo; Gromke, Christof; Di Sabatino, Silvana; Ruck, Bodo

2009-09-15

397

Aerodynamics model for a generic ASTOVL lift-fan aircraft

NASA Technical Reports Server (NTRS)

This report describes the aerodynamics model used in a simulation model of an advanced short takeoff and vertical landing (ASTOVL) lift-fan fighter aircraft. The simulation model was developed for use in piloted evaluations of transition and hover flight regimes, so that only low speed (M approximately 0.2) aerodynamics are included in the mathematical model. The aerodynamic model includes the power-off aerodynamic forces and moments and the propulsion system induced aerodynamic effects, including ground effects. The power-off aerodynamics data were generated using the U.S. Air Force Stability and Control Digital DATCOM program and a NASA Ames in-house graphics program called VORVIEW which allows the user to easily analyze arbitrary conceptual aircraft configurations using the VORLAX program. The jet-induced data were generated using the prediction methods of R. E. Kuhn et al., as referenced in this report.

Birckelbaw, Lourdes G.; Mcneil, Walter E.; Wardwell, Douglas A.

1995-01-01

398

Some applications of aerodynamic formulations to problems in aircraft dynamics

NASA Technical Reports Server (NTRS)

Two applications of mathematical modeling to aerodynamic problems are cussed. The first application is an investigation of the capacity of a nonlinear aerodynamic mathematical model to describe the aerodynamic reactions on an airfoil with a deflecting flap in transonic flow. Flow field computational methods are used to evaluate the nonlinear, unsteady aerodynamic data in terms of characteristic motions called for by the model. Histories of unconstrained motions of the flap are generated from the flap equations of motion, with the aerodynamic reactions specified by the mathematical model. In the second application wing rock is investigated. The most recent model accommodates experimental results wing rock by admitting the existence of aerodynamic hysteresis in the variation of the steady state rolling moment coefficient with roll angle is described.

Schiff, L. B.; Tobak, M.

1981-01-01

399

Several approaches have been developed to restore energy in distribution systems after the interruption of services for part of the system. In order to achieve the energy restoration plan, these approaches usually perform the restoration for circuits with specific features. Additionally, they are not able to deal with large outage zones. This paper develops a method using Genetic algorithms for

A. C. B. Delbem; A. de Carvalho; N. G. Bretas

2003-01-01

400

Unsteady aerodynamic load estimates on turning vanes in the national full-scale aerodynamic complex

NASA Technical Reports Server (NTRS)

Unsteady aerodynamic design loads have been estimated for each of the vane sets in the National Full-Scale Aerodynamic Complex (NFAC). These loads include estimates of local loads over one vane section and global loads over an entire vane set. The analytical methods and computer programs used to estimate these loads are discussed. In addition, the important computer input parameters are defined and the rationale used to estimate them is discussed. Finally, numerical values are presented for both the computer input parameters and the calculated design loads for each vane set.

Norman, Thomas R.

1986-01-01

401

Propulsion and airframe aerodynamic interactions of supersonic V/STOL configurations, phase 1

NASA Technical Reports Server (NTRS)

A wind tunnel model of a supersonic V/STOL fighter configuration has been tested to measure the aerodynamic interaction effects which can result from geometrically close-coupled propulsion system/airframe components. The approach was to configure the model to present two different test techniques. One was a coventional test technique composed of two test modes. In the Flow-Through mode, absolute configuration aerodynamics are measured, including inlet/airframe interactions. In the Jet-Effects mode, incremental nozzle/airframe interactions are measured. The other test technique is a propulsion simulator approach, where a subscale, externally powered engine is mounted in the model. This allows proper measurement of inlet/airframe and nozzle/airframe interactions simultaneously.

Mraz, M. R.; Hiley, P. E.

1985-01-01

402

Estimation of Unsteady Aerodynamic Models from Flight Test Data

NASA Technical Reports Server (NTRS)

This report summarizes the activities in aerodynamic model estimation from flight data. In addition to public presentations at the AIAA Atmospheric Flight Mechanics Conferences, two presentations at Boeing-Seattle were made during personal trips. These are discussed in the following: 1. Methodology of Aerodynamic Model Estimation from Flight Data. 2. Applications of F-16XL aerodynamic modeling. 3. Modeling of turbulence response. 5. Presentations at Boeing-Seattle. 6. Recommendations. and 7. References.

Lan, C. Edward

2003-01-01

403

Non-propulsive aerodynamic noise

NASA Technical Reports Server (NTRS)

In the first part of the paper, the contribution of airframe noise to total aircraft noise on approach is assessed for a large current technology transport and for the same airframe powered with bypass ratio 10 engines with an additional 5 dB noise suppression applied to the fan and turbine noise sources. The airframe noise of the envisioned advanced subsonic transport is 2 EPNdB less than the largest contributor to the total aircraft noise, the fan inlet. The noise impact of the airframe noise, as measured by noise contour area, is 1/4 that of fan noise. Further fan noise reduction efforts should not view airframe noise as an absolute noise floor. In the second part of the paper, the results from one recent cavity noise wind tunnel experiment is reported. A cavity of dimensions 11.25 in. (28.58 cm) long, 2.5 in. (6.35 cm) wide, and variable depth was tested in the Mach number range of .20 through .90. Reynolds number varied from 5 to 100 million per foot (16 to 328 million per meter). The 1/d ratio was varied from 4.4 to 20.0. The model was tested at yaw angles from 0 to 15 degrees. In general, the deeper the cavity, the greater the amplitude of the acoustic tones. Reynolds number appeared to have little effect on acoustic tone amplitudes. Tone amplitude and bandwidth changed with Mach number. The effect of yaw on acoustic tones varied with Reynolds number, Mach number, 1/h, and mode number. At Mach number 0.90, increased yaw shifted the tone frequencies of the higher modal frequencies to lower frequencies. As cavity depth decreased, the effect of yaw decreased.

Willshire, William L., Jr.; Tracy, Maureen B.

1992-01-01

404

Regulatory and voluntary approaches for enhancing building energy efficiency

Buildings are the dominant energy consumers in modern cities but their consumption can be largely cut back through improving efficiency, which is an effective means to lessen greenhouse gas emissions and slow down depletion of non-renewable energy resources. However, the potential energy cost saving alone is hardly a sufficient incentive to investing into improvement measures, unless the cost of using

W. L. Lee; F. W. H. Yik

2004-01-01

405

Biomimetic approach to solar energy conversion - Artificial photosynthesis

Green plants and certain bacteria use the energy of sunlight to drive chemical reactions that require an energy input to proceed in the desired manner. Thus, green plants use solar energy to convert carbon dioxide and water to carbohydrates, proteins, and lipids that are the nutrients for all other living organisms. Plants also produce natural fibers, such as cotton and

J. J. Katz

1978-01-01

406

Advanced Unstructured Grid Generation for Complex Aerodynamic Applications

NASA Technical Reports Server (NTRS)

A new approach for distribution of grid points on the surface and in the volume has been developed. In addition to the point and line sources of prior work, the new approach utilizes surface and volume sources for automatic curvature-based grid sizing and convenient point distribution in the volume. A new exponential growth function produces smoother and more efficient grids and provides superior control over distribution of grid points in the field. All types of sources support anisotropic grid stretching which not only improves the grid economy but also provides more accurate solutions for certain aerodynamic applications. The new approach does not require a three-dimensional background grid as in the previous methods. Instead, it makes use of an efficient bounding-box auxiliary medium for storing grid parameters defined by surface sources. The new approach is less memory-intensive and more efficient computationally. The grids generated with the new method either eliminate the need for adaptive grid refinement for certain class of problems or provide high quality initial grids that would enhance the performance of many adaptation methods.

Pirzadeh, Shahyar

2010-01-01

407

Advanced Unstructured Grid Generation for Complex Aerodynamic Applications

NASA Technical Reports Server (NTRS)

A new approach for distribution of grid points on the surface and in the volume has been developed and implemented in the NASA unstructured grid generation code VGRID. In addition to the point and line sources of prior work, the new approach utilizes surface and volume sources for automatic curvature-based grid sizing and convenient point distribution in the volume. A new exponential growth function produces smoother and more efficient grids and provides superior control over distribution of grid points in the field. All types of sources support anisotropic grid stretching which not only improves the grid economy but also provides more accurate solutions for certain aerodynamic applications. The new approach does not require a three-dimensional background grid as in the previous methods. Instead, it makes use of an efficient bounding-box auxiliary medium for storing grid parameters defined by surface sources. The new approach is less memory-intensive and more efficient computationally. The grids generated with the new method either eliminate the need for adaptive grid refinement for certain class of problems or provide high quality initial grids that would enhance the performance of many adaptation methods.

Pirzadeh, Shahyar Z.

2008-01-01

408

A PDE Sensitivity Equation Method for Optimal Aerodynamic Design

NASA Technical Reports Server (NTRS)

The use of gradient based optimization algorithms in inverse design is well established as a practical approach to aerodynamic design. A typical procedure uses a simulation scheme to evaluate the objective function (from the approximate states) and its gradient, then passes this information to an optimization algorithm. Once the simulation scheme (CFD flow solver) has been selected and used to provide approximate function evaluations, there are several possible approaches to the problem of computing gradients. One popular method is to differentiate the simulation scheme and compute design sensitivities that are then used to obtain gradients. Although this black-box approach has many advantages in shape optimization problems, one must compute mesh sensitivities in order to compute the design sensitivity. In this paper, we present an alternative approach using the PDE sensitivity equation to develop algorithms for computing gradients. This approach has the advantage that mesh sensitivities need not be computed. Moreover, when it is possible to use the CFD scheme for both the forward problem and the sensitivity equation, then there are computational advantages. An apparent disadvantage of this approach is that it does not always produce consistent derivatives. However, for a proper combination of discretization schemes, one can show asymptotic consistency under mesh refinement, which is often sufficient to guarantee convergence of the optimal design algorithm. In particular, we show that when asymptotically consistent schemes are combined with a trust-region optimization algorithm, the resulting optimal design method converges. We denote this approach as the sensitivity equation method. The sensitivity equation method is presented, convergence results are given and the approach is illustrated on two optimal design problems involving shocks.

Borggaard, Jeff; Burns, John

1996-01-01

409

Experimental Investigation of Hypersonic Flow and Plasma Aerodynamic Actuation Interaction

NASA Astrophysics Data System (ADS)

For hypersonic flow, it was found that the most effective plasma actuator is derived from an electromagnetic perturbation. An experimental study was performed between hypersonic flow and plasma aerodynamic actuation interaction in a hypersonic shock tunnel, in which a Mach number of 7 was reached. The plasma discharging characteristic was acquired in static flows. In a hypersonic flow, the flow field can affect the plasma discharging characteristics. DC discharging without magnetic force is unstable, and the discharge channel cannot be maintained. When there is a magnetic field, the energy consumption of the plasma source is approximately three to four times larger than that without a magnetic field, and at the same time plasma discharge can also affect the hypersonic flow field. Through schlieren pictures and pressure measurement, it was found that plasma discharging could induce shockwaves and change the total pressure and wall pressure of the flow field.

Sun, Quan; Cheng, Bangqin; Li, Yinghong; Cui, Wei; Yu, Yonggui; Jie, Junhun

2013-09-01

410

Estimating Aerodynamic Parameters of Urban-Like Surfaces with Heterogeneous Building Heights

NASA Astrophysics Data System (ADS)

There are many geometrical factors than can influence the aerodynamic parameters of urban surfaces and hence the vertical wind profiles found above. The knowledge of these parameters has applications in numerous fields, such as dispersion modelling, wind loading calculations, and estimating the wind energy resource at urban locations. Using quasi-empirical modelling, we estimate the dependence of the aerodynamic roughness length and zero-plane displacement for idealized urban surfaces, on the two most significant geometrical characteristics; surface area density and building height variability. A validation of the spatially-averaged, logarithmic wind profiles predicted by the model is carried out, via comparisons with available wind-tunnel and numerical data for arrays of square based blocks of uniform and heterogeneous heights. The model predicts two important properties of the aerodynamic parameters of surfaces of heterogeneous heights that have been suggested by experiments. Firstly, the zero-plane displacement of a heterogeneous array can exceed the surface mean building height significantly. Secondly, the characteristic peak in roughness length with respect to surface area density becomes much softer for heterogeneous arrays compared to uniform arrays, since a variation in building height can prevent a skimming flow regime from occurring. Overall the simple model performs well against available experimental data and may offer more accurate estimates of surface aerodynamic parameters for complex urban surfaces compared to models that do not include height variability.

Millward-Hopkins, J. T.; Tomlin, A. S.; Ma, L.; Ingham, D.; Pourkashanian, M.

2011-12-01

411

Workshop on Aircraft Surface Representation for Aerodynamic Computation

NASA Technical Reports Server (NTRS)

Papers and discussions on surface representation and its integration with aerodynamics, computers, graphics, wind tunnel model fabrication, and flow field grid generation are presented. Surface definition is emphasized.

Gregory, T. J. (editor); Ashbaugh, J. (editor)

1980-01-01

412

Aerodynamic Decelerators for Planetary Exploration: Past, Present, and Future

NASA Technical Reports Server (NTRS)

In this paper, aerodynamic decelerators are defined as textile devices intended to be deployed at Mach numbers below five. Such aerodynamic decelerators include parachutes and inflatable aerodynamic decelerators (often known as ballutes). Aerodynamic decelerators play a key role in the Entry, Descent, and Landing (EDL) of planetary exploration vehicles. Among the functions performed by aerodynamic decelerators for such vehicles are deceleration (often from supersonic to subsonic speeds), minimization of descent rate, providing specific descent rates (so that scientific measurements can be obtained), providing stability (drogue function - either to prevent aeroshell tumbling or to meet instrumentation requirements), effecting further aerodynamic decelerator system deployment (pilot function), providing differences in ballistic coefficients of components to enable separation events, and providing height and timeline to allow for completion of the EDL sequence. Challenging aspects in the development of aerodynamic decelerators for planetary exploration missions include: deployment in the unusual combination of high Mach numbers and low dynamic pressures, deployment in the wake behind a blunt-body entry vehicle, stringent mass and volume constraints, and the requirement for high drag and stability. Furthermore, these aerodynamic decelerators must be qualified for flight without access to the exotic operating environment where they are expected to operate. This paper is an introduction to the development and application of aerodynamic decelerators for robotic planetary exploration missions (including Earth sample return missions) from the earliest work in the 1960s to new ideas and technologies with possible application to future missions. An extensive list of references is provided for additional study.

Cruz, Juna R.; Lingard, J. Stephen

2006-01-01

413

Integrated aerodynamic/structural design of a sailplane wing

NASA Technical Reports Server (NTRS)

Using lifting-line theory and beam analysis, the geometry (planiform and twist) and composite material structural sizes (skin thickness, spar cap, and web thickness) were designed for a sailplane wing, subject to both structural and aerodynamic constraints. For all elements, the integrated design (simultaneously designing the aerodynamics and the structure) was superior in terms of performance and weight to the sequential design (where the aerodynamic geometry is designed to maximize the performance, following which a structural/aeroelastic design minimizes the weight). Integrated designs produced less rigid, higher aspect ratio wings with favorable aerodynamic/structural interactions.

Grossman, B.; Gurdal, Z.; Haftka, R. T.; Strauch, G. J.; Eppard, W. M.

1986-01-01

414

A climatology of formation conditions for aerodynamic contrails

NASA Astrophysics Data System (ADS)

Aerodynamic contrails are defined in this paper as line shaped ice clouds caused by aerodynamically triggered cooling over the wings of an aircraft in cruise which become visible immediately at the trailing edge of the wing or close to it. Effects at low altitudes like condensation to liquid droplets and their potential heterogeneous freezing are excluded from our definition. We study atmospheric conditions that allow formation of aerodynamic contrails. These conditions are stated and then applied to atmospheric data, first to a special case where an aerodynamic contrail was actually observed and then to a full year of global reanalysis data. We show where, when (seasonal variation), and how frequently (probability) aerodynamic contrails can form, and how this relates to actual patterns of air traffic. We study the formation of persistent aerodynamic contrails as well. Finally we check whether aerodynamic and exhaust contrails can coexist in the atmosphere. We show that visible aerodynamic contrails are possible only in an altitude range between roughly 540 and 250 hPa, and that the ambient temperature is the most important parameter, not the relative humidity. Finally we give an argument for our believe that currently aerodynamic contrails have a much smaller climate effect than exhaust contrails, which may however change in future with more air traffic in the tropics.

Gierens, K.; Dilger, F.

2013-06-01

415

14 CFR 25.445 - Auxiliary aerodynamic surfaces.

Code of Federal Regulations, 2013 CFR

...AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Structure Control Surface and System Loads Â§ 25.445 Auxiliary aerodynamic surfaces. (a) When...

2014-01-01

416

On the formulation of the aerodynamic characteristics in aircraft dynamics

NASA Technical Reports Server (NTRS)

The theory of functionals is used to reformulate the notions of aerodynamic indicial functions and superposition. Integral forms for the aerodynamic response to arbitrary motions are derived that are free of dependence on a linearity assumption. Simplifications of the integral forms lead to practicable nonlinear generalizations of the linear superpositions and stability derivative formulations. Applied to arbitrary nonplanar motions, the generalization yields a form for the aerodynamic response that can be compounded of the contributions from a limited number of well-defined characteristic motions, in principle reproducible in the wind tunnel. Further generalizations that would enable the consideration of random fluctuations and multivalued aerodynamic responses are indicated.

Tobak, M.; Schiff, L. B.

1976-01-01

417

A simplified method for predicting the stability of aerodynamically excited turbomachinery

NASA Technical Reports Server (NTRS)

A method is presented for the quick and accurate prediction of the stability of aerodynamically excited turbomachinery using real eigenvalue/eigenvector data obtained from a rotordynamics model. An expression is presented which uses the modal data and the transmitted torque to provide a numerical value of the relative stability of the system. This approach provides a powerful design tool to quickly ascertain the effects of squeeze-film damper bearings, bearing location, and support changes on system stability.

Storace, Albert F.

1991-01-01

418

On the generation of flight dynamics aerodynamic tables by computational fluid dynamics

An approach for the generation of aerodynamic tables using computational fluid dynamics is discussed. For aircraft flight dynamics, forces and moments are often tabulated in multi-dimensional look-up tables, requiring a large number of calculations to fill the tables. A method to efficiently reduce the number of high-fidelity analyses is reviewed. The method uses a kriging-based surrogate model. Low-fidelity (computationally cheap)

A. Da Ronch; M. Ghoreyshi; K. J. Badcock

419

MEMS Applications in Aerodynamic Measurement Technology

NASA Technical Reports Server (NTRS)

Microelectromechanical systems (MEMS) embodies the integration of sensors, actuators, and electronics on a single substrate using integrated circuit fabrication techniques and compatible bulk and surface micromachining processes. Silicon and its derivatives form the material base for the MEMS technology. MEMS devices, including microsensors and microactuators, are attractive because they can be made small (characteristic dimension about 100 microns), be produced in large numbers with uniform performance, include electronics for high performance and sophisticated functionality, and be inexpensive. For aerodynamic measurements, it is preferred that sensors be small so as to approximate measurement at a point, and in fact, MEMS pressure sensors, wall shear-stress sensors, heat flux sensors and micromachined hot wires are nearing application. For the envisioned application to wind tunnel models, MEMS sensors can be placed on the surface or in very shallow grooves. MEMS devices have often been fabricated on stiff, flat silicon substrates, about 0.5 mm thick, and therefore were not easily mounted on curved surfaces. However, flexible substrates are now available and heat-flux sensor arrays have been wrapped around a curved turbine blade. Electrical leads can also be built into the flexible substrate. Thus MEMS instrumented wind tunnel models do not require deep spanwise grooves for tubes and leads that compromise the strength of conventionally instrumented models. With MEMS, even the electrical leads can potentially be eliminated if telemetry of the signals to an appropriate receiver can be implemented. While semiconductor silicon is well known for its electronic properties, it is also an excellent mechanical material for MEMS applications. However, silicon electronics are limited to operations below about 200 C, and silicon's mechanical properties start to diminish above 400 C. In recent years, silicon carbide (SiC) has emerged as the leading material candidate for applications in high temperature environments and can be used for high-temperature MEMS applications. With SiC, diodes and more complex electronics have been shown to operate to about 600 C, while the mechanical properties of SiC are maintained to much higher temperatures. Even when MEMS devices show benefits in the laboratory, there are many packaging challenges for any aeronautics application. Incorporating MEMS into these applications requires new approaches to packaging that goes beyond traditional integrated circuit (IC) packaging technologies. MEMS must interact mechanically, as well as electrically with their environment, making most traditional chip packaging and mounting techniques inadequate. Wind tunnels operate over wide temperature ranges in an environment that is far from being a 'clean-room.' In flight, aircraft are exposed to natural elements (e.g. rain, sun, ice, insects and dirt) and operational interferences(e.g. cleaning and deicing fluids, and maintenance crews). In propulsion systems applications, MEMS devices will have to operate in environments containing gases with very high temperatures, abrasive particles and combustion products. Hence deployment and packaging that maintains the integrity of the MEMS system is crucial. This paper presents an overview of MEMS fabrication and materials, descriptions of available sensors with more details on those being developed in our laboratories, and a discussion of sensor deployment options for wind tunnel and flight applications.

Reshotko, E.; Mehregany, M.; Bang, C.

1998-01-01

420

Aerodynamic performance of osculating-cones waveriders at high altitudes

NASA Astrophysics Data System (ADS)

The steady-state aerodynamic characteristics of three-dimensional waverider configurations immersed in hypersonic rarefied flows are investigated. Representative geometries are generated using an inverse design procedure, the method of osculating cones, which defines an exit plane shock shape and approximates the flow properties of the compression surface by assuming that each spanwise station along the shock profile lies within a region of locally conical flow. Vehicle surface and flow field properties are predicted using the direct simulation Monte Carlo method, a probabilistic numerical scheme in which simulated molecules are followed through representative collisions with each other and solid surfaces, and subsequent deterministic displacement. The aerodynamic properties of high- and low-Reynolds number waverider geometries, optimized for maximum lift-to-drag ratio and subject to mission-oriented constraints, are contrasted with results from reference caret and delta wings with similar internal volumes to quantify the relevance and advantage of the waverider concept at high altitudes. The high-Reynolds number waverider, optimized for the continuum regime at Minfinity = 4 and Reinfinity = 250 million, was the focus of recent wind tunnel testing for near on-design and off-design conditions, including low subsonic speeds. The present work extends the previous analyses into the high-altitude regime. The low-Reynolds number waverider, optimized at Minfinity = 20 and Reinfinity = 2.5 million, is studied to determine if optimization potential exists for a high-Mach number waverider at high altitudes. A characteristic length of 5 m is assumed for both waverider configurations, representative of a hypersonic missile concept. The geometries are aerodynamically evaluated over a parametric space consisting of an altitude variation of 95 km to 150 km and an angle of attack range of --5° to 10°. The effect of off-design Mach number on the performance of the high-Reynolds number waverider is also considered. At Minfinity = 4 in level flight, from 95 km to 105 km, the lift-to-drag ratio of the volume-matched caret wing is superior to that of the osculating-cones waverider optimized for Minfinity = 4 and Re infinity = 250 million. From 105 km to 150 km, the performance of the osculating-cones waverider is slightly superior to that of caret and delta wings due to the degree of concavity of its lower surface. At off-design conditions, the performance of the three configurations approaches a common free-molecular limit. At Minfinity = 20 in level flight, the lift-to-drag ratio of the osculating-cones waverider optimized for Minfinity = 20 and Reinfinity = 2.5 million is similar to a volume-matched caret wing, due to the caret wing's enhanced lift coefficient. At higher angles of attack, the superior drag characteristics of the osculating-cones waverider produces an increased lift-to-drag ratio over that of the reference configurations from 95 km to 120 km. At higher altitudes, the performance of the three configurations approaches a common free-molecular limit. Maximum lift-to-drag ratio does not exceed unity for the configurations studied over the chosen high-altitude parametric space, which is consistent with previous investigations. Results support the hypothesis that potential for aerodynamic optimization exists at high altitudes for realistic, volume-oriented waverider configurations.

Graves, Rick Evan

421

An initial investigation into methods of computing transonic aerodynamic sensitivity coefficients

NASA Technical Reports Server (NTRS)

The primary accomplishments of the project are as follows: (1) Using the transonic small perturbation equation as a flowfield model, the project demonstrated that the quasi-analytical method could be used to obtain aerodynamic sensitivity coefficients for airfoils at subsonic, transonic, and supersonic conditions for design variables such as Mach number, airfoil thickness, maximum camber, angle of attack, and location of maximum camber. It was established that the quasi-analytical approach was an accurate method for obtaining aerodynamic sensitivity derivatives for airfoils at transonic conditions and usually more efficient than the finite difference approach. (2) The usage of symbolic manipulation software to determine the appropriate expressions and computer coding associated with the quasi-analytical method for sensitivity derivatives was investigated. Using the three dimensional fully conservative full potential flowfield model, it was determined that symbolic manipulation along with a chain rule approach was extremely useful in developing a combined flowfield and quasi-analytical sensitivity derivative code capable of considering a large number of realistic design variables. (3) Using the three dimensional fully conservative full potential flowfield model, the quasi-analytical method was applied to swept wings (i.e. three dimensional) at transonic flow conditions. (4) The incremental iterative technique has been applied to the three dimensional transonic nonlinear small perturbation flowfield formulation, an equivalent plate deflection model, and the associated aerodynamic and structural discipline sensitivity equations; and coupled aeroelastic results for an aspect ratio three wing in transonic flow have been obtained.

Carlson, Leland A.

1994-01-01

422

Analysis of Mechanical Milling in Simoloyer: An Energy Modeling Approach

NASA Astrophysics Data System (ADS)

A model was developed to estimate the energy transfer from milling media to the powder during milling carried out in Simoloyer CM 01 (Zoz GmbH, Wenden, Germany), a horizontal attritor high-energy ball mill. The model was then used to estimate the energy transfer in milling of iron at 1000 rpm. Furthermore, the time required to achieve a particular grain size was formulated as a function of milling speed, using the model developed for the energy transfer. The results were verified at 500 rpm and 1500 rpm for iron and aluminum.

Karthik, B.; Sai Gautam, G.; Karthikeyan, N. R.; Murty, B. S.

2012-04-01

423

Running hot water: A systems approach to energy conservation

NASA Astrophysics Data System (ADS)

Ways to conserve energy in domestic hot water systems are discussed. Examination of the Swedish situation shows that centralized systems, where water heating is a subsidiary of space heating, waste energy because water cools in the pipes after use, and the entire system must operate in summer. Also, water temperature is often much higher than required. Solar panels, individual water heaters, heat pumps, and heat exchangers could contribute to energy conservation, but changes in consumer behavior can also be extremely effective. For example, dish washing energy requirements were reduced by 80% in one neighborhood by giving each apartment a plastic bowl for washing up.

Wulff, P.

1982-03-01

424

Within the next few years, numerical shape optimization based on high fidelity methods is likely to play a strategic role in future aircraft design. In this context, suitable tools have to be developed for solving aerodynamic shape optimization problems, and the adjoint approach - which allows fast and accurate evaluations of the gradients with respect to the design parameters -

Joël Brezillon; Richard P. Dwight

2009-01-01

425

Energy use and emissions from marine vessels: a total fuel life cycle approach.

Regional and global air pollution from marine transportation is a growing concern. In discerning the sources of such pollution, researchers have become interested in tracking where along the total fuel life cycle these emissions occur. In addition, new efforts to introduce alternative fuels in marine vessels have raised questions about the energy use and environmental impacts of such fuels. To address these issues, this paper presents the Total Energy and Emissions Analysis for Marine Systems (TEAMS) model. TEAMS can be used to analyze total fuel life cycle emissions and energy use from marine vessels. TEAMS captures "well-to-hull" emissions, that is, emissions along the entire fuel pathway, including extraction, processing, distribution, and use in vessels. TEAMS conducts analyses for six fuel pathways: (1) petroleum to residual oil, (2) petroleum to conventional diesel, (3) petroleum to low-sulfur diesel, (4) natural gas to compressed natural gas, (5) natural gas to Fischer-Tropsch diesel, and (6) soybeans to biodiesel. TEAMS calculates total fuel-cycle emissions of three greenhouse gases (carbon dioxide, nitrous oxide, and methane) and five criteria pollutants (volatile organic compounds, carbon monoxide, nitrogen oxides, particulate matter with aerodynamic diameters of 10 microm or less, and sulfur oxides). TEAMS also calculates total energy consumption, fossil fuel consumption, and petroleum consumption associated with each of its six fuel cycles. TEAMS can be used to study emissions from a variety of user-defined vessels. This paper presents TEAMS and provides example modeling results for three case studies using alternative fuels: a passenger ferry, a tanker vessel, and a container ship. PMID:17269235

Winebrake, James J; Corbett, James J; Meyer, Patrick E

2007-01-01

426

Aerodynamic drag of modern soccer balls.

Soccer balls such as the Adidas Roteiro that have been used in soccer tournaments thus far had 32 pentagonal and hexagonal panels. Recently, the Adidas Teamgeist II and Adidas Jabulani, respectively having 14 and 8 panels, have been used at tournaments; the aerodynamic characteristics of these balls have not yet been verified. Now, the Adidas Tango 12, having 32 panels, has been developed for use at tournaments; therefore, it is necessary to understand its aerodynamic characteristics. Through a wind tunnel test and ball trajectory simulations, this study shows that the aerodynamic resistance of the new 32-panel soccer ball is larger in the high-speed region and lower in the middle-speed region than that of the previous 14- and 8-panel balls. The critical Reynolds number of the Roteiro, Teamgeist II, Jabulani, and Tango 12 was ~2.2?×?10(5) (drag coefficient, C d ???0.12), ~2.8?×?10(5) (C d ???0.13), ~3.3?×?10(5) (C d ???0.13), and ~2.4?×?10(5) (C d ???0.15), respectively. The flight trajectory simulation suggested that the Tango 12, one of the newest soccer balls, has less air resistance in the medium-speed region than the Jabulani and can thus easily acquire large initial velocity in this region. It is considered that the critical Reynolds number of a soccer ball, as considered within the scope of this experiment, depends on the extended total distance of the panel bonds rather than the small designs on the panel surfaces. PMID:23705104

Asai, Takeshi; Seo, Kazuya

2013-12-01

427

Effects of ice accretions on aircraft aerodynamics

NASA Astrophysics Data System (ADS)

This article is a systematic and comprehensive review, correlation, and assessment of test results available in the public domain which address the aerodynamic performance and control degradations caused by various types of ice accretions on the lifting surfaces of fixed wing aircraft. To help put the various test results in perspective, overviews are provided first of the important factors and limitations involved in computational and experimental icing simulation techniques, as well as key aerodynamic testing simulation variables and governing flow physics issues. Following these are the actual reviews, assessments, and correlations of a large number of experimental measurements of various forms of mostly simulated in-flight and ground ice accretions, augmented where appropriate by similar measurements for other analogous forms of surface contamination and/or disruptions. In-flight icing categories reviewed include the initial and inter-cycle ice accretions inherent in the use of de-icing systems which are of particular concern because of widespread misconceptions about the thickness of such accretions which can be allowed before any serious consequences occur, and the runback/ridge ice accretions typically associated with larger-than-normal water droplet encounters which are of major concern because of the possible potential for catastrophic reductions in aerodynamic effectiveness. The other in-flight ice accretion category considered includes the more familiar large rime and glaze ice accretions, including ice shapes with rather grotesque features, where the concern is that, in spite of all the research conducted to date, the upper limit of penalties possible has probably not been defined. Lastly, the effects of various possible ground frost/ice accretions are considered. The concern with some of these is that for some types of configurations, all of the normally available operating margins to stall at takeoff may be erased if these accretions are not adequately removed prior to takeoff. Throughout this review, important voids in the available database are highlighted, as are instances where previous lessons learned have tended to be overlooked.

Lynch, Frank T.; Khodadoust, Abdollah

2001-11-01

428

NASA Technical Reports Server (NTRS)

The approach and takeoff performance was evaluated of a contracting cowl variable geometry design inlet installed on a high-bypass-ratio turbofan engine. The design was finalized after consideration of aerodynamic, acoustic, and mechanical factors which would lead to a viable flight worthy concept. The aerodynamic results are presented in terms of inlet recovery and distortion parameter as functions of throat Mach number, and acoustic results in terms of Perceived Noise Level. The contracting cowl high throat Mach number inlet is shown to be an attractive means to reduce forward radiated noise from a high bypass ratio turbofan engine.

Blommer, H. E.; Schaefer, J. W.

1976-01-01

429

Aerodynamic assessment of prosthetic speech aids.

The primary function of a speech aid prosthesis is to provide adequate palatopharyngeal function by preventing nasal emission and hypernasality during oral speech production and permitting sufficient nasal air escape during nasal consonant production. The adequacy of speech aids is often judged subjectively by speech-language pathologists and prosthodontists. However, when oral and laryngeal function are also affected, additional information may be needed for accurate assessment of palatopharyngeal function and optimal prosthetic management. In these instances, aerodynamic measurements can provide information about palatopharyngeal function and guide fabrication and modification of speech aid prostheses to provide adequate palatopharyngeal function for speech. PMID:3863945

Reisberg, D J; Smith, B E

1985-11-01

430

Aerodynamic Size Classification of Glass Fibers.

NASA Astrophysics Data System (ADS)

The objective of this research was to examine a technique by which fibers may be aerodynamically classified by diameter and/or length. In this study a system for fiber preparation and generation as well as an in situ fiber classifier were constructed and evaluated. A recently developed technique, the size classification of particles by opposing jets, was modified. The research set-up consisted of (1) a vibrating bed fiber generator, which also functioned as a preselector, (2) an opposing-jet classifier equipped with electrodes and high voltage power supplies to create fiber-aligning electric fields inside the classifier and (3) an optoelectric fiber sensor to measure the concentration and length of fibers. The classified fibers were also collected on filters for the counting and dimensional analysis of the fibers. Some flow instability problems were found during the initial tests of the classifier. They were attributed to random flow fluctuations in the nozzles caused by very small perturbations upstream of the nozzles. Within a critical range of flow Reynolds numbers the flow becomes "intermittent", i.e. it alternates in time between being laminar and turbulent in a random sequence. Small disturbances upstream of the point of consideration can "trigger" the changes from laminar to turbulent flow and the initial disturbance may be "amplified", sending a turbulent flash through the flow system. The classifier performed well with test aerosols after the nozzle flowrate had been decreased to correspond to a lower and less critical Reynolds number and after some modifications had been made to smooth the flow inside the classifier inlet chambers. The cut-off of test aerosols was sharp, but the loss of particles greater than 2.5 (mu)m in aerodynamic diameter was unsatisfactorily high. The classifier was able to classify fibers by aerodynamic diameter, but not as predicted through calculations. The results were difficult to interpret because of the high loss of fibers with large or very small aerodynamic diameters. Fiber separation by diameter was far more distinct than by length.

Laosmaa, Pekka J. J.

431

Aerodynamic characteristics of horizontal tail surfaces

NASA Technical Reports Server (NTRS)

Collected data are presented on the aerodynamic characteristics of 17 horizontal tail surfaces including several with balanced elevators and two with end plates. Curves are given for coefficients of normal force, drag, and elevator hinge moment. A limited analysis of the results has been made. The normal-force coefficients are in better agreement with the lifting-surface theory of Prandtl and Blenk for airfoils of low aspect ratio than with the usual lifting-line theory. Only partial agreement exists between the elevator hinge-moment coefficients and those predicted by Glauert's thin-airfoil theory.

Silverstein, Abe; Katzoff, S

1940-01-01

432

The Aerodynamic Forces on Airship Hulls

NASA Technical Reports Server (NTRS)

This report describes the new method for making computations in connection with the study of rigid airship, which was used in the investigation of the navy's ZR-1 by the special subcommittee of the National Advisory Committee for Aeronautics appointed for this purpose. It presents the general theory of the air forces on airship hulls of the type mentioned, and an attempt has been made to develop the results from the very fundamentals of mechanics without reference to some of the modern highly developed conceptions, which may not yet be thoroughly known to readers uninitiated into modern aerodynamics, and which may, perhaps, for all time remain restricted to a small number of specialists.

Munk, Max M

1924-01-01

433

Aerodynamic noise emission from turbulent shear layers.

NASA Technical Reports Server (NTRS)

The Phillips (1960) convected wave equation is employed in this paper to study aerodynamic noise emission processes in subsonic and supersonic shear layers. The wave equation in three spatial dimensions is first reduced to an ordinary differential equation by Fourier transformation and then solved via the WKBJ method. Three typical solutions are required for discussions in this paper. The current results are different from the classical conclusions. The effects of refraction, convection, Mach-number dependence and temperature dependence of turbulent noise emission are analyzed in the light of solutions to the Phillips equation.

Pao, S. P.

1973-01-01

434

Aerodynamics of High-Speed Trains

NASA Astrophysics Data System (ADS)

This review highlights the differences between the aerodynamics of high-speed trains and other types of transportation vehicles. The emphasis is on modern, high-speed trains, including magnetic levitation (Maglev) trains. Some of the key differences are derived from the fact that trains operate near the ground or a track, have much greater length-to-diameter ratios than other vehicles, pass close to each other and to trackside structures, are more subject to crosswinds, and operate in tunnels with entry and exit events. The coverage includes experimental techniques and results and analytical and numerical methods, concentrating on the most recent information available.

Schetz, Joseph A.

435

Generic Wing-Body Aerodynamics Data Base

NASA Technical Reports Server (NTRS)

The wing-body aerodynamics data base consists of a series of CFD (Computational Fluid Dynamics) simulations about a generic wing body configuration consisting of a ogive-circular-cylinder fuselage and a simple symmetric wing mid-mounted on the fuselage. Solutions have been obtained for Nonlinear Potential (P), Euler (E) and Navier-Stokes (N) solvers over a range of subsonic and transonic Mach numbers and angles of attack. In addition, each solution has been computed on a series of grids, coarse, medium and fine to permit an assessment of grid refinement errors.

Holst, Terry L.; Olsen, Thomas H.; Kwak, Dochan (Technical Monitor)

2001-01-01

436

Fluidization technologies: Aerodynamic principles and process engineering.

The concept of fluidization has been adapted to different unit processes of pharmaceutical product development. Till date a lot of improvements have been made in the engineering design to achieve superior process performance. This review is focused on the fundamental principles of aerodynamics and hydrodynamics associated with the fluidization technologies. Fluid-bed coating, fluidized bed granulation, rotor processing, hot melt granulation, electrostatic coating, supercritical fluid based fluidized bed technology are highlighted. Developments in the design of processing equipments have been explicitly elucidated. This article also discusses processing problems from the operator's perspective along with latest developments in the application of these principles. PMID:19340888

Dixit, Rahul; Puthli, Shivanand

2009-11-01

437

Aerodynamic Optimization of a Winglet Design

NASA Astrophysics Data System (ADS)

In the present study, an experimental study is presented for a flow around an isolated wing equipped by a winglet and profiled with Naca 0012. Several cases of winglets were tested according to the angle ß: 0°, 55°, 65°and 75°. For all these cases at a velocity of 20, 30 and 40 meters per second, wind tunnel tests are performed and compared for different angles of incidence. It is observed that the aerodynamic performance of the winglet with ?= 55° differ favorably for positive angle of incidence compared for other cases.

Belferhat, S.; Meftah, S. M. A.; Yahiaoui, T.; Imine, B.

2013-04-01

438

Fitting aerodynamics and propulsion into the puzzle

NASA Technical Reports Server (NTRS)

The development of an airbreathing single-stage-to-orbit vehicle, in particular the problems of aerodynamics and propulsion integration, is examined. The boundary layer transition on constant pressure surfaces at hypersonic velocities, and the effects of noise on the transition are investigated. The importance of viscosity, real-gas effects, and drag at hypersonic speeds is discussed. A propulsion system with sufficient propulsive lift to enhance the performance of the vehicle is being developed. The difficulties of engine-airframe integration are analyzed.

Johnston, Patrick J.; Whitehead, Allen H., Jr.; Chapman, Gary T.

1987-01-01

439

Dual nozzle aerodynamic and cooling analysis study

NASA Technical Reports Server (NTRS)

Analytical models to predict performance and operating characteristics of dual nozzle concepts were developed and improved. Aerodynamic models are available to define flow characteristics and bleed requirements for both the dual throat and dual expander concepts. Advanced analytical techniques were utilized to provide quantitative estimates of the bleed flow, boundary layer, and shock effects within dual nozzle engines. Thermal analyses were performed to define cooling requirements for baseline configurations, and special studies of unique dual nozzle cooling problems defined feasible means of achieving adequate cooling.

Meagher, G. M.

1981-01-01

440

Insect Flight: Aerodynamics, Efficiency, and Evolution

NASA Astrophysics Data System (ADS)

Insects, like birds and fish, locomote via interactions between fluids and flapping wings. Their motion is governed by the Navier-Stokes equation coupled to moving boundaries. In this talk, I will first describe how dragonflies fly: their wing motions and the flows and forces they generate. I will then consider insects in several species and discuss three questions: 1) Is insect flight optimal? 2) How does the efficiency of flapping flight compare to classical fixed-wing flight? 3) How might aerodynamic effects have influenced the evolution of insect flight?

Wang, Z. Jane

2007-11-01

441

A climatology of formation conditions for aerodynamic contrails

NASA Astrophysics Data System (ADS)

Aircraft at cruise levels can cause two kinds of contrails, the well known exhaust contrails and the less well-known aerodynamic contrails. While the possible climate impact of exhaust contrails has been studied for many years, research on aerodynamic contrails began only a few years ago and nothing is known about a possible contribution of these ice clouds to climate impact. In order to make progress in this respect, we first need a climatology of their formation conditions and this is given in the present paper. Aerodynamic contrails are defined here as line shaped ice clouds caused by aerodynamically triggered cooling over the wings of an aircraft in cruise which become visible immediately at the trailing edge of the wing or close to it. Effects at low altitudes like condensation to liquid droplets and their potential heterogeneous freezing are excluded from our definition. We study atmospheric conditions that allow formation of aerodynamic contrails. These conditions are stated and then applied to atmospheric data: first to a special case where an aerodynamic contrail was actually observed and then to a full year of global reanalysis data. We show where, when (seasonal variation), and how frequently (probability) aerodynamic contrails can form, and how this relates to actual patterns of air traffic. We study the formation of persistent aerodynamic contrails as well. Furthermore, we check whether aerodynamic and exhaust contrails can coexist in the atmosphere. We show that visible aerodynamic contrails are possible only in an altitude range between roughly 540 and 250 hPa, and that the ambient temperature is the most important parameter, not the relative humidity. Finally, we argue that currently aerodynamic contrails have a much smaller climate effect than exhaust contrails, which may however change in future with more air traffic in the tropics.

Gierens, K.; Dilger, F.

2013-11-01

442

Possible Approaches to the Development of Photo-catalytic Solar Energy Converters

NASA Astrophysics Data System (ADS)

Possible approaches to the development of photo-catalytic solar energy converters, and their perspectives, are discussed with special reference to the conversion of solar energy into chemical energy by the photo-catalytic decomposition of water into hydrogen and oxygen. 408 references.

Zamaraev, Kirill I.; Parmon, Valentin N.

1980-08-01

443

An integrated approach to optimization of energy supply mix in smart buildings

In recent years we have witnessed an increased interest for installations of hybrid energy supply systems in buildings, designed specifically to meet their diverse energy demand (cooling, heating and electricity). This paper proposes a new algorithm that generates the optimal hybrid energy system mix and suggests the ways for the system normal operation. The integrated approach analyzes simultaneously the end-use

T. Gafurov; M. B. Tellez; M. Prodanovic

2011-01-01

444

Computational Approach in Determination of 233U and 233Th Fermi Energy

NASA Astrophysics Data System (ADS)

There are several methods to get Fermi energy such as hermit polynomial expansion and Wigner-Kirkwood expansion, these are analytical method. In this paper will be discussed numerical approach of calculating Fermi energy of 233Th and 233U nuclei. Our work demonstrates the simple technique of determining Fermi energy.

Kurniadi, R.; Perkasa, Y. S.; Waris, A.

2010-12-01

445

Energy Conservation Education. An Action Approach. Grades 4-9.

ERIC Educational Resources Information Center

Seventeen lessons are provided in this curriculum designed to involve students (grades 4-9) in energy conservation. The lessons are presented in four parts. The three lessons in part I are intended to give students a preliminary conceptual framework for energy conservation and to motivate them to participate in the conservation-action projects…

Zamm, Michael; Samuel, Barry C.