For comprehensive and current results, perform a real-time search at Science.gov.

1

Unsteady Aerodynamic Validation Experiences From the Aeroelastic Prediction Workshop

NASA Technical Reports Server (NTRS)

The AIAA Aeroelastic Prediction Workshop (AePW) was held in April 2012, bringing together communities of aeroelasticians, computational fluid dynamicists and experimentalists. The extended objective was to assess the state of the art in computational aeroelastic methods as practical tools for the prediction of static and dynamic aeroelastic phenomena. As a step in this process, workshop participants analyzed unsteady aerodynamic and weakly-coupled aeroelastic cases. Forced oscillation and unforced system experiments and computations have been compared for three configurations. This paper emphasizes interpretation of the experimental data, computational results and their comparisons from the perspective of validation of unsteady system predictions. The issues examined in detail are variability introduced by input choices for the computations, post-processing, and static aeroelastic modeling. The final issue addressed is interpreting unsteady information that is present in experimental data that is assumed to be steady, and the resulting consequences on the comparison data sets.

Heeg, Jennifer; Chawlowski, Pawel

2014-01-01

2

Unsteady transonic aerodynamics

Various papers on unsteady transonic aerodynamics are presented. The topics addressed include: physical phenomena associated with unsteady transonic flows, basic equations for unsteady transonic flow, practical problems concerning aircraft, basic numerical methods, computational methods for unsteady transonic flows, application of transonic flow analysis to helicopter rotor problems, unsteady aerodynamics for turbomachinery aeroelastic applications, alternative methods for modeling unsteady transonic flows.

Nixon, D.

1989-01-01

3

NREL Unsteady Aerodynamics Experiment phase 3 test objectives and preliminary results

The United States Department of Energy and the National Renewable Energy Laboratory (NREL) are conducting research to improve a wind turbine technology. One program, the Combined Experiment, has focused on making measurements needed to understand aerodynamic and structural responses of horizontal-axis wind turbines (HAWT). A new phase of this program, the Unsteady Aerodynamics Experiment, will focus on quantifying unsteady aerodynamic phenomena prevalent install controlled HAWTs. Optimally twisted blades and innovative data acquisition systems will be used in these tests. data can now be acquired and viewed interactively during turbine operations. This paper describes the Unsteady Aerodynamics Experiment and highlights planned future research activities.

Simms, D.A.; Fingersh, L.J.; Butterfield, C.P. [National Renewable Energy Laboratory, Golden, CO (United States). Wind Technology Division

1995-09-01

4

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

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

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

2001-08-30

5

Unsteady Aerodynamics Experiment Phases II-IV Test Configurations and Available Data Campaigns

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

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

1999-08-19

6

Fundamentals of Modern Unsteady Aerodynamics

Fundamentals of Modern Unsteady Aerodynamics U. Gulcat Springer, Tiergartenstrasse 17, D-69121 covers the modern topics on unsteady aerodynamics. The classical chapters mostly refer to the aerodynamic, different sorts of wing rock and flapping wing aerodynamics. The so-called classical topics can be found

Nagurka, Mark L.

7

Unsteady aerodynamics of blade rows

NASA Technical Reports Server (NTRS)

The requirements placed on an unsteady aerodynamic theory intended for turbomachinery aeroelastic or aeroacoustic applications are discussed along with a brief description of the various theoretical models that are available to address these requirements. The major emphasis is placed on the description of a linearized inviscid theory which fully accounts for the affects of a nonuniform mean or steady flow on unsteady aerodynamic response. Although this linearization was 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 prescribed blade motions. The motivation for this linearized unsteady aerodynamic theory is focused on, its physical and mathematical formulation is outlined and examples are presented to illustrate the status of numerical solution procedures and several effects of mean flow nonuniformity on unsteady aerodynamic response.

Verdon, Joseph M.

1989-01-01

8

Conversion of Phase II Unsteady Aerodynamics Experiment Data to Common Format

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

M. Maureen Hand.

1999-07-19

9

The purpose of this paper is to describe the instrumentation and data systems utilized in the NREL Unsteady Aerodynamics Experiment (formerly the ``Combined Experiment``) Phase 3 with special emphasis on the new capabilities of the Phase 3 system. The Phase 3 system has been designed to improve on the capabilities of the Phase 1 and 2 data systems and to add new functionality. The new system provides the capability to test more turbine parameters in a more controlled and reliable way and to allow relatively easy reconfiguration as needed for specialized tests. In addition, rapidly improving personal computer (PC) technology allows these data to be directly stored onto optical disk and postprocessed in a matter of minutes. Finally, PCs are now able to overlay real-time data and pressure distributions on the video images of the turbine in operation. This video information can then be stored on conventional videotape.

Fingersh, L.J.; Simms, D.A.; Butterfield, C.P.; Jenks, M.D. [National Renewable Energy Laboratory, Golden, CO (United States). Wind Technology Division

1995-09-01

10

NASA Technical Reports Server (NTRS)

As computational fluid dynamics methods mature, code development is rapidly transitioning from prediction of steady flowfields to unsteady flows. This change in emphasis offers a number of new challenges to the research community, not the least of which is obtaining detailed, accurate unsteady experimental data with which to evaluate new methods. Researchers at NASA Langley Research Center (LaRC) have been actively measuring unsteady pressure distributions for nearly 40 years. Over the last 20 years, these measurements have focused on developing high-quality datasets for use in code evaluation. This paper provides a sample of unsteady pressure measurements obtained by LaRC and available for government, university, and industry researchers to evaluate new and existing unsteady aerodynamic analysis methods. A number of cases are highlighted and discussed with attention focused on the unique character of the individual datasets and their perceived usefulness for code evaluation. Ongoing LaRC research in this area is also presented.

Schuster, David M.; Scott, Robert C.; Bartels, Robert E.; Edwards, John W.; Bennett, Robert M.

2000-01-01

11

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

12

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

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

2001-12-01

13

Linearized unsteady aerodynamics for turbomachinery aeroelastic applications

The unsteady aerodynamic analyses developed for turbomachinery aeroelastic predictions must be appliable to the moderate through high frequency unsteady flows that are excited by structural motions and aerodynamic interactions between adjacent blade rows and occur over a wide range of operating conditions. In addition, because of the large number of controlling parameters involved, there is a stringent requirement on computational

Joseph M. Verdon

1992-01-01

14

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

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

2001-06-22

15

Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachines

NASA Astrophysics Data System (ADS)

This textbook is a collection of technical papers that were presented at the 10th International Symposium on Unsteady Aerodynamics, Aeroacoustics, and Aeroelasticity of Turbomachines held September 8-11, 2003 at Duke University in Durham, North Carolina. The papers represent the latest in state of the art research in the areas of aeroacoustics, aerothermodynamics, computational methods, experimental testing related to flow instabilities, flutter, forced response, multistage, and rotor-stator effects for turbomachinery.

Hall, Kenneth C.; Kielb, Robert E.; Thomas, Jeffrey P.

16

Ris-PhD-Report Wind Turbines: Unsteady Aerodynamics and

RisÃ¸-PhD-Report Wind Turbines: Unsteady Aerodynamics and Inflow Noise Brian Riget Broe RisÃ¸-PhD-47 Title: Wind Turbines: Unsteady Aerodynamics and Inflow Noise Division: Wind Energy Division RisÃ¸-PhD-47(EN) December 2009 Abstract (max. 2000 char.): Aerodynamical noise from wind turbines due

17

Unsteady aerodynamics and gust response in compressors and turbines

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

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

1993-10-01

18

Unsteady aerodynamic analyses for turbomachinery aeroelastic predictions

NASA Technical Reports Server (NTRS)

Applications for unsteady aerodynamics analysis in this report are: (1) aeroelastic: blade flutter and forced vibration; (2) aeroacoustic: noise generation; (3) vibration and noise control; and (4) effects of unsteadiness on performance. This requires that the numerical simulations and analytical modeling be accurate and efficient and contain realistic operating conditions and arbitrary modes of unsteady excitation. The assumptions of this application contend that: (1) turbulence and transition can be modeled with the Reynolds averaged and using Navier-Stokes equations; (2) 'attached' flow with high Reynolds number will require thin-layer Navier-Stokes equations, or inviscid/viscid interaction analyses; (3) small-amplitude unsteady excitations will need nonlinear steady and linearized unsteady analyses; and (4) Re to infinity will concern inviscid flow. Several computer programs (LINFLO, CLT, UNSVIS, AND SFLOW-IVI) are utilized for these analyses. Results and computerized grid examples are shown. This report was given during NASA LeRC Workshop on Forced Response in Turbomachinery in August of 1993.

Verdon, Joseph M.; Barnett, M.; Ayer, T. C.

1994-01-01

19

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

20

Unsteady aerodynamics applied to the horizontal axis wind turbine disk

NASA Astrophysics Data System (ADS)

A calculation method to yield external forces in the equations of motion for a complete elastic structure horizontal axis wind turbine elastic model, which includes unsteady effects for improved time history (simulation) and force calculation, and limits the volume of the unsteady method to reduce computer runs was developed. Standard aerodynamic methods are implemented as a part of the complete method. The unsteady effects are applied to the aerodynamic induction factor, to allow easy addition and inclusion of the unsteady effects in an existing method for aerodynamic force calculation.

Montgomerie, B.

1985-03-01

21

Bifurcations in unsteady aerodynamics-implications for testing

NASA Technical Reports Server (NTRS)

The various forms of bifurcations that can occur between steady and unsteady aerodynamic flows are reviewed. Examples are provided to illustrate the various ways in which bifurcations may intervene to influence the outcome of dynamics tests involving unsteady aerodynamics. The presence of bifurcation phenomena in such tests must be taken into consideration to ensure the proper interpretation of results, and some recommendations are made to that end.

Chapman, Gary T.; Tobak, Murray

1988-01-01

22

Unsteady aerodynamics applied to the horizontal axis wind turbine disk

A calculation method to yield external forces in the equations of motion for a complete elastic structure horizontal axis wind turbine elastic model, which includes unsteady effects for improved time history (simulation) and force calculation, and limits the volume of the unsteady method to reduce computer runs was developed. Standard aerodynamic methods are implemented as a part of the complete

B. Montgomerie

1985-01-01

23

A linear aerodynamic analysis for unsteady transonic cascades

NASA Technical Reports Server (NTRS)

A potential flow analysis to predict unsteady airloads produced by the vibrations of turbomachinery blades operating at transonic Mach numbers is presented. The unsteady aerodynamic model includes the effects of blade geometry, finite mean pressure variation across the blade row, high frequency blade motion, and shock motion within the framework of a linearized, frequency domain formulation. The unsteady equations are solved implicit, least squares, finite difference approximation which is applicable on arbitrary grids. A numerical solution for the entire unsteady field is determined by matching a solution determined on a rectilinear type cascade mesh, which covers an extended blade passage region, to a solution determined on a detailed polar type local mesh, which covers and extends well beyond the supersonic region(s) adjacent to a blade surface. Cascades of double circular arc and flat plate blades demonstrate the unsteady analysis, and partially illustrate the effects of blade geometry, inlet Mach number, blade vibration frequency and shock motion on unsteady response.

Verdon, J. M.; Caspar, J. R.

1984-01-01

24

Algorithmic Enhancements for Unsteady Aerodynamics and Combustion Applications

NASA Technical Reports Server (NTRS)

Research in the FY01 focused on the analysis and development of enhanced algorithms for unsteady aerodynamics and chemically reacting flowfields. The research was performed in support of NASA Ames' efforts to improve the capabilities of the in-house computational fluid dynamics code, OVERFLOW. Specifically, the research was focused on the four areas: (1) investigation of stagnation region effects; (2) unsteady preconditioning dual-time procedures; (3) dissipation formulation for combustion; and (4) time-stepping methods for combustion.

Venkateswaran, Sankaran; Olsen, Michael (Technical Monitor)

2001-01-01

25

The influence of unsteady aerodynamics on hingeless rotor ground resonance

NASA Technical Reports Server (NTRS)

Calculations of the model frequency and damping for a hingeless rotor on a gimballed support in hover are compared with measured results for two configurations (differing in blade flap stiffness). Good correlation is obtaned when an inflow dynamics model is used to account for the influence of the unsteady aerodynamics. The effect of the unsteady aerodynamics is significant for this rotor system. The inflow dynamics model introduces additional states corresponding to perturbations of the wake-induced velocity at the rotor disk. The calculations confirm the experimental observation that the inflow mode introduced by these additional states is measurable for one configuration but not for the other.

Johnson, W.

1981-01-01

26

Role of computational fluid dynamics in unsteady aerodynamics for aeroelasticity

NASA Astrophysics Data System (ADS)

In the last two decades there have been extensive developments in computational unsteady transonic aerodynamics. Such developments are essential since the transonic regime plays an important role in the design of modern aircraft. Therefore, there has been a large effort to develop computational tools with which to accurately perform flutter analysis at transonic speeds. In the area of Computational Fluid Dynamics (CFD), unsteady transonic aerodynamics are characterized by the feature of modeling the motion of shock waves over aerodynamic bodies, such as wings. This modeling requires the solution of nonlinear partial differential equations. Most advanced codes such as XTRAN3S use the transonic small perturbation equation. Currently, XTRAN3S is being used for generic research in unsteady aerodynamics and aeroelasticity of almost full aircraft configurations. Use of Euler/Navier Stokes equations for simple typical sections has just begun. A brief history of the development of CFD for aeroelastic applications is summarized. The development of unsteady transonic aerodynamics and aeroelasticity are also summarized.

Guruswamy, Guru P.; Goorjian, Peter M.

1989-02-01

27

Unsteady aerodynamic models for agile flight at low Reynolds numbers

NASA Astrophysics Data System (ADS)

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

Brunton, Steven L.

28

Effects of unsteady aerodynamics on rotor aeroelastic stability

NASA Technical Reports Server (NTRS)

The effects of unsteady aerodynamics on the stability characteristics of helicopter rotor blades were studied. A simple physical model of each blade was used together with Theodorsen, Loewy, and quasi-steady aerodynamics to derive the equations of motion. The stability analysis comparing the effects of using each of the three theories revealed some significant differences between the Loewy and Theodorsen results. These included increases and decreases in lead-lag damping, localized around integer lead-lag frequencies. It was also shown that the standard method of multi-blade coordinates must be modified for use in conjunction with Loewy aerodynamics.

Kunz, D. L.

1977-01-01

29

Unsteady Cascade Aerodynamic Response Using a Multiphysics Simulation Code

NASA Technical Reports Server (NTRS)

The multiphysics code Spectrum(TM) is applied to calculate the unsteady aerodynamic pressures of oscillating cascade of airfoils representing a blade row of a turbomachinery component. Multiphysics simulation is based on a single computational framework for the modeling of multiple interacting physical phenomena, in the present case being between fluids and structures. Interaction constraints are enforced in a fully coupled manner using the augmented-Lagrangian method. The arbitrary Lagrangian-Eulerian method is utilized to account for deformable fluid domains resulting from blade motions. Unsteady pressures are calculated for a cascade designated as the tenth standard, and undergoing plunging and pitching oscillations. The predicted unsteady pressures are compared with those obtained from an unsteady Euler co-de refer-red in the literature. The Spectrum(TM) code predictions showed good correlation for the cases considered.

Lawrence, C.; Reddy, T. S. R.; Spyropoulos, E.

2000-01-01

30

Currently, the NREL Unsteady Aerodynamics Experiment (UAE) research turbine is scheduled to enter the NASA Ames 80-ft x 120-ft wind tunnel in early 2000. To prepare for this 3-week test, a Science Panel meeting was convened at the National Wind Technology Center (NWTC) in October 1998. During this meeting, the Science Panel and representatives from the wind energy community provided numerous detailed recommendations regarding test activities and priorities. The Unsteady Aerodynamics team of the NWTC condensed this guidance and drafted a detailed test plan. This test plan represents an attempt to balance diverse recommendations received from the Science Panel meeting, while taking into account multiple constraints imposed by the UAE research turbine, the NASA Ames 80-ft x 120-ft wind tunnel, and other sources. The NREL-NASA Ames wind tunnel tests will primarily be focused on obtaining rotating blade pressure data. NREL has been making these types of measurements since 1987 and has considerable experience in doing so. The purpose of this wind tunnel test is to acquire accurate quantitative aerodynamic and structural measurements, on a wind turbine that is geometrically and dynamically representative of full-scale machines, in an environment free from pronounced inflow anomalies. These data will be exploited to develop and validate enhanced engineering models for designing and analyzing advanced wind energy machines.

Simms, D.; Schreck, S.; Hand, M.; Fingersh, L.; Cotrell, J.; Pierce, K.; Robinson, M.

2000-08-28

31

Unsteady transonic aerodynamics during wing flutter

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

32

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

33

Unsteady aerodynamic simulation of multiple bodies in relative motion

NASA Technical Reports Server (NTRS)

A prototype method for time-accurate simulation of multiple aerodynamic bodies in relative motion is presented. The method is general and features unsteady chimera domain decomposition techniques and an implicit approximately factored finite-difference procedure to solve the time-dependent thin-layer Navier-Stokes equations. The method is applied to a set of two- and three-dimensional test problems to establish spatial and temporal accuracy, quantify computational efficiency, and begin to test overall code robustness.

Meakin, Robert L.; Suhs, Norman E.

1989-01-01

34

Unsteady aerodynamics of an oscillating cascade in a compressible flow field

NASA Technical Reports Server (NTRS)

Fundamental experiments were performed in the NASA Lewis Transonic Oscillating Cascade Facility to investigate and quantify the unsteady aerodynamics of a cascade of biconvex airfoils executing torsion-mode oscillations at realistic reduced frequencies. Flush-mounted, high-response miniature pressure transducers were used to measure the unsteady airfoil surface pressures. The pressures were measured for three interblade phase angles at two inlet Mach numbers, 0.65 and 0.80, and two incidence angles, 0 and 7 deg. The time-variant pressures were analyzed by means of discrete Fourier transform techniques, and these unique data were then compared with predictions from a linearized unsteady cascade model. The experimental results indicate that the interblade phase angle had a major effect on the chordwise distributions of the airfoil surface unsteady pressure, and that reduced frequency, incidence angle, and Mach number had a somewhat less significant effect.

Buffum, Daniel H.; Boldman, Donald R.; Fleeter, Sanford

1987-01-01

35

NASA Technical Reports Server (NTRS)

An analysis of the steady and unsteady aerodynamics of sharp-edged slender wings has been performed. The results show that slender wing theory can be modified to give the potential flow static and dynamic characteristics in incompressible flow. A semiempirical approximation is developed for the vortex-induced loads, and it is shown that the analytic approximation for sharp-edged slender wings gives good prediction of experimentally determined steady and unsteady aerodynamics at M = 0 and M = 1. The predictions are good not only for delta wings but also for so-called arrow and diamond wings. The results indicate that the effects of delta planform lifting surfaces can be included in a simple manner when determining elastic launch vehicle dynamic characteristics. For Part 1 see (N73-32763).

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

1973-01-01

36

Unsteady Aerodynamics Effected by Controlled Trapped Vorticity Concentrations

NASA Astrophysics Data System (ADS)

The transitory response of the flow-about a free-moving airfoil to time-dependent fluidic actuation that yields aerodynamic forces and moments in the absence of conventional control surfaces is investigated in wind tunnel experiments. Desired maneuvers are achieved using a 2-DOF feedback-controlled traverse that is programmed for trim and dynamic characteristics. Bi-directional changes in the pitching moment are effected by controllable, nominally-symmetric trapped vorticity concentrations on both the suction and pressure surfaces near the trailing edge. Actuation is independently applied on each surface by hybrid actuators that are each comprised of a miniature [O(0.01c)] obstruction integrated with synthetic jets which manipulate and regulate vorticity flux near the surface. Simultaneous measurements of the unsteady forces and moments and of the associated velocity field above and in the near wake of the airfoil are used to asses the coupling between the flow and vehicle dynamics with emphasis on control authority and optimal actuator placement and operating parameters. Flow control effectiveness is demonstrated by closed-loop response to a momentary force disturbance analogous to the response to a sudden gust in free flight.

Brzozowski, Daniel; Glezer, Ari

2008-11-01

37

Transonic adaptive flutter suppression using approximate unsteady time domain aerodynamics

NASA Technical Reports Server (NTRS)

A digital adaptive controller is applied to the active flutter suppression problem of a wing under time varying flight conditions in subsonic and transonic flow. Linear quadratic controller gain at each time step is obtained using an iterative Riccati solver. The digital adaptive optimal controller is robust with respect to the unknown external loads. Flutter and divergence instabilities are simultaneously suppressed using a trailing-edge control surface and displacement sensing. A new transonic unsteady aerodynamic approximation methodology is developed which enables one to carry out the rapid calculation required for transonic aeroservoelastic applications. This approximation is based on a combination of unsteady subsonic aerodynamics combined with a transonic correction procedure. Aeroservoelastic transient time response is obtained using Roger's approximation, state transition matrices and an iterative time marching algorithm. The aeroservoelastic system in the time domain is modeled using a deterministic ARMA model together with a parameter estimator. Transonic flutter boundaries of a wing structure are computed, in the time domain, using an estimated aeroelastic system matrix and are in good agreement with experimental data for the low transonic Mach number range.

Pak, Chan-Gi; Friedmann, Peretz P.; Livne, Eli

1991-01-01

38

NASA Technical Reports Server (NTRS)

Over the past three years, the National Aeronautics and Space Administration (NASA) has initiated design, development, and testing of a new human-rated space exploration system under the Constellation Program. Initial designs within the Constellation Program are scheduled to replace the present Space Shuttle, which is slated for retirement within the next three years. The development of vehicles for the Constellation system has encountered several unsteady aerodynamics challenges that have bearing on more traditional unsteady aerodynamic and aeroelastic analysis. This paper focuses on the synergy between the present NASA challenges and the ongoing challenges that have historically been the subject of research and method development. There are specific similarities in the flows required to be analyzed for the space exploration problems and those required for some of the more nonlinear unsteady aerodynamic and aeroelastic problems encountered on aircraft. The aggressive schedule, significant technical challenge, and high-priority status of the exploration system development is forcing engineers to implement existing tools and techniques in a design and application environment that is significantly stretching the capability of their methods. While these methods afford the users with the ability to rapidly turn around designs and analyses, their aggressive implementation comes at a price. The relative immaturity of the techniques for specific flow problems and the inexperience with their broad application to them, particularly on manned spacecraft flight system, has resulted in the implementation of an extensive wind tunnel and flight test program to reduce uncertainty and improve the experience base in the application of these methods. This provides a unique opportunity for unsteady aerodynamics and aeroelastic method developers to test and evaluate new analysis techniques on problems with high potential for acquisition of test and even flight data against which they can be evaluated. However, researchers may be required to alter the geometries typically used in their analyses, the types of flows analyzed, and even the techniques by which computational tools are verified and validated. This paper discusses these issues and provides some perspective on the potential for new and innovative approaches to the development of methods to attack problems in nonlinear unsteady aerodynamics.

Schuster, David M.

2008-01-01

39

Unsteady transonic aerodynamic and aeroelastic calculations about airfoils and wings

NASA Technical Reports Server (NTRS)

The development and application of transonic small disturbance codes for computing two dimensional flows, using the code ATRAN2, and for computing three dimensional flows, using the code ATRAN3S, are described. Calculated and experimental results are compared for unsteady flows about airfoils and wings, including several of the cases from the AGARD Standard Aeroelastic Configurations. In two dimensions, the results include AGARD priority cases for the NACA 54A006, NACA 64A010, NACA 0012, and MBB-A3 airfoils. In three dimensions, the results include flow about the F-5 wing, a typical wing, and the AGARD rectangular wings. Viscous corrections are included in some calculations, including those for the AGARD rectangular wing. For several cases, the aerodynamic and aeroelastic calculations are compared with experimental results.

Goorjian, P. M.; Guruswamy, G. P.

1985-01-01

40

Unstructured-grid methods development for unsteady aerodynamic and aeroelastic analyses

NASA Technical Reports Server (NTRS)

The current status of unstructured grid methods development in the Unsteady Aerodynamics Branch at NASA-Langley is described. These methods are being developed for unsteady aerodynamic and aeroelastic analyses. The flow solvers are highlighted which were developed for the solution of the unsteady Euler equations and selected results are given which show various features of the capability. The results demonstrate 2-D and 3-D applications for both steady and unsteady flows. Comparisons are also made with solutions obtained using a structured grid code and with experimental data to determine the accuracy of the unstructured grid methodology. These comparisons show good agreement which thus verifies the accuracy.

Batina, John T.; Lee, Elizabeth M.; Kleb, William L.; Rausch, Russ D.

1991-01-01

41

NASA Technical Reports Server (NTRS)

Expressions for calculation of subsonic and supersonic, steady and unsteady aerodynamic forces are derived, using the concept of aerodynamic elements applied to the downwash velocity potential method. Aerodynamic elements can be of arbitrary out of plane polygon shape, although numerical calculations are restricted to rectangular elements, and to the steady state case in the supersonic examples. It is suggested that the use of conforming, in place of rectangular elements, would give better results. Agreement with results for subsonic oscillating T tails is fair, but results do not converge as the number of collocation points is increased. This appears to be due to the form of expression used in the calculations. The methods derived are expected to facilitate automated flutter analysis on the computer. In particular, the aerodynamic element concept is consistent with finite element methods already used for structural analysis. The method is universal for the complete Mach number range, and, finally, the calculations can be arranged so that they do not have to be repeated completely for every reduced frequency.

Haviland, J. K.; Yoo, Y. S.

1976-01-01

42

Unsteady Aerodynamic and Dynamic Analysis of the Meridian UAS in a Rolling-Yawing Motion

The nonlinear and unsteady aerodynamic effects of operating the Meridian unmanned aerial system (UAS) in crosswinds and at high angular rates is investigated in this work. The Meridian UAS is a large autonomous aircraft, ...

Lykins, Ryan

2014-05-31

43

Application of a linearized unsteady aerodynamic analysis to standard cascade configurations

NASA Technical Reports Server (NTRS)

A linearized potential flow analysis, which accounts for the effects of nonuniform steady flow phenomena on the linearized unsteady aerodynamic response to prescribed blade motions, has been applied to five cascade configurations. These include the first, fifth, eighth and ninth standard configurations proposed as a result of the Second International Symposium on Aeroelasticity in Turbomachines and a NASA Lewis flutter cascade. Selected results from this study, including comparisons between analytical predictions and the experimental measurements submitted for three of the foregoing configurations, are described. The correlation between theory and experiment for the first standard configuration (a compressor cascade operating at low Mach number and frequency) is quite good. Moreover, the predictions and measurements for the NASA Lewis cascade of symmetric biconvex airfoils show good qualitative agreement. However, wide discrepancies exist between the theoretical predictions and the experimental measurements for the fifth standard configuration (a subsonic transonic fan tip cascade). These can be partially attributed to conditions being imposed in the experiment which differ from those commonly used in unsteady aerodynamic analyses.

Verdon, J. M.; Usab, W. J., Jr.

1986-01-01

44

NASA Technical Reports Server (NTRS)

The analytical development of unsteady supersonic aerodynamic influence coefficients for isolated and nearly parallel interfering coplanar and noncoplanar wings is described. Numerical formulations based on triangular discretizations of wings and diaphragms are handled in a kinematically consistent manner. Examples of isolated wing cases are compared with respect to aerodynamic influence coefficients and flutter boundaries. Aerodynamic influence coefficients for interfering wings are compared where corresponding results are available.

Appa, K.; Smith, G. C. C.

1973-01-01

45

Estimation of Unsteady Aerodynamic Models from Dynamic Wind Tunnel Data

NASA Technical Reports Server (NTRS)

Demanding aerodynamic modelling requirements for military and civilian aircraft have motivated researchers to improve computational and experimental techniques and to pursue closer collaboration in these areas. Model identification and validation techniques are key components for this research. This paper presents mathematical model structures and identification techniques that have been used successfully to model more general aerodynamic behaviours in single-degree-of-freedom dynamic testing. Model parameters, characterizing aerodynamic properties, are estimated using linear and nonlinear regression methods in both time and frequency domains. Steps in identification including model structure determination, parameter estimation, and model validation, are addressed in this paper with examples using data from one-degree-of-freedom dynamic wind tunnel and water tunnel experiments. These techniques offer a methodology for expanding the utility of computational methods in application to flight dynamics, stability, and control problems. Since flight test is not always an option for early model validation, time history comparisons are commonly made between computational and experimental results and model adequacy is inferred by corroborating results. An extension is offered to this conventional approach where more general model parameter estimates and their standard errors are compared.

Murphy, Patrick; Klein, Vladislav

2011-01-01

46

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

47

Surface pressure data from the National Renewable Energy Laboratory's ''Unsteady Aerodynamics Experiment'' were analyzed to characterize the impact of three-dimensionality, unsteadiness, and flow separation effects observed to occur on downwind horizontal axis wind turbines (HAWT). Surface pressure and strain gage data were collected from two rectangular planform blades with S809 airfoil cross-sections, one flat and one twisted. Both blades were characterized by the maximum leading edge suction pressure and by the azimuth, velocity, and yaw at which it occurred. The occurrence of dynamic stall at all but the inboard station (30% span) shows good quantitative agreement with the theoretical limits on inflow velocity and yaw that should yield dynamic stall events. A full three-dimensional characterization of the surface pressure topographies combined with flow visualization data from surface mounted tufts offer key insights into the three-dimensional processes involved in the unsteady separation process and may help to explain the discrepancies observed with force measurements at 30% span. The results suggest that quasi-static separation and dynamic stall analysis methods relying on purely two-dimensional flow characterizations may not be capable of simulating the complex three-dimensional flows observed with these data.

Robinson, M. C.; Hand, M. M.; Simms, D. A.; Schreck, S. J.

1999-04-05

48

NASA Astrophysics Data System (ADS)

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

Shimada, Kenji; Ishihara, Takeshi

2012-01-01

49

The capability to control unsteady separated flow fields could dramatically enhance aircraft agility. To enable control, however, real-time prediction of these flow fields over a broad parameter range must be realized. The present work describes real-time predictions of three-dimensional unsteady separated flow fields and aerodynamic coefficients using neural networks. Unsteady surface-pressure readings were obtained from an airfoil pitched at a constant rate through the static stall angle. All data sets were comprised of 15 simultaneously acquired pressure records and one pitch angle record. Five such records and the associated pitch angle histories were used to train the neural network using a time-series algorithm. Post-training, the input to the network was the pitch angle (alpha), the angular velocity (dalpha/dt), and the initial 15 recorded surface pressures at time (t (0)). Subsequently, the time (t+Deltat) network predictions, for each of the surface pressures, were fed back as the input to the network throughout the pitch history. The results indicated that the neural network accurately predicted the unsteady separated flow fields as well as the aerodynamic coefficients to within 5% of the experimental data. Consistent results were obtained both for the training set as well as for generalization to both other constant pitch rates and to sinusoidal pitch motions. The results clearly indicated that the neural-network model could predict the unsteady surface-pressure distributions and aerodynamic coefficients based solely on angle of attack information. The capability for real-time prediction of both unsteady separated flow fields and aerodynamic coefficients across a wide range of parameters in turn provides a critical step towards the development of control systems targeted at exploiting unsteady aerodynamics for aircraft manoeuvrability enhancement. PMID:18263439

Faller, W E; Schreck, S J

1995-01-01

50

NASA Technical Reports Server (NTRS)

Unsteady aerodynamic methods adopted for the study of aeroelasticity in helicopters are considered with focus on the development of a semiempirical model of unsteady aerodynamic forces acting on an oscillating profile at high incidence. The successive smoothing algorithm described leads to the model's coefficients in a very satisfactory manner.

Petot, D.; Loiseau, H.

1982-01-01

51

Development of a linearized unsteady aerodynamic analysis for cascade gust response predictions

NASA Technical Reports Server (NTRS)

A method for predicting the unsteady aerodynamic response of a cascade of airfoils to entropic, vortical, and acoustic gust excitations is being developed. Here, the unsteady flow is regarded as a small perturbation of a nonuniform isentropic and irrotational steady background flow. A splitting technique is used to decompose the linearized unsteady velocity into rotational and irrotational parts leading to equations for the complex amplitudes of the linearized unsteady entropy, rotational velocity, and velocity potential that are coupled only sequentially. The entropic and rotational velocity fluctuations are described by transport equations for which closed-form solutions in terms of the mean-flow drift and stream functions can be determined. The potential fluctuation is described by an inhomogeneous convected wave equation in which the source term depends on the rotational velocity field, and is determined using finite-difference procedures. The analytical and numerical techniques used to determine the linearized unsteady flow are outlined. Results are presented to indicate the status of the solution procedure and to demonstrate the impact of blade geometry and mean blade loading on the aerodynamic response of cascades to vortical gust excitations. The analysis described herein leads to very efficient predictions of cascade unsteady aerodynamic response phenomena making it useful for turbomachinery aeroelastic and aeroacoustic design applications.

Verdon, Joseph M.; Hall, Kenneth C.

1990-01-01

52

Unsteady Aerodynamic and Dynamic Analysis of the Meridian UAS in a Rolling-Yawing Motion

NASA Astrophysics Data System (ADS)

The nonlinear and unsteady aerodynamic effects of operating the Meridian unmanned aerial system (UAS) in crosswinds and at high angular rates is investigated in this work. The Meridian UAS is a large autonomous aircraft, with a V-tail configuration, operated in Polar Regions for the purpose of remotely measuring ice sheet thickness. The inherent nonlinear coupling produced by the V-tail, along with the strong atmospheric disturbances, has made classical model identification methods inadequate for proper model development. As such, a powerful tool known as Fuzzy Logic Modeling (FLM) was implemented to generate time-dependent, nonlinear, and unsteady aerodynamic models using flight test data collected in Greenland in 2011. Prior to performing FLM, compatibility analysis is performed on the data, for the purpose of systematic bias removal and airflow angle estimation. As one of the advantages of FLM is the ability to model unsteady aerodynamics, the reduced frequency for both longitudinal and lateral-directional motions is determined from the unbiased data, using Theodorsen's theory of unsteadiness, which serves as an input parameter in modeling. These models have been used in this work to identify pilot induced oscillations, unsteady coupling motions, unsteady motion due to the slipstream and cross wind interaction, and destabilizing motions and orientations. This work also assesses the accuracy of preliminary aircraft dynamic models developed using engineering level software, and addresses the autopilot Extended Kalman Filter state estimations.

Lykins, Ryan

53

NASA Technical Reports Server (NTRS)

A basic problem in flight dynamics is the mathematical formulation of the aerodynamic model for aircraft. This study is part of an ongoing effort at NASA Langley to develop a more general formulation of the aerodynamic model for aircraft that includes nonlinear unsteady aerodynamics and to develop appropriate test techniques that facilitate identification of these models. A methodology for modeling and testing using wide-band inputs to estimate the unsteady form of the aircraft aerodynamic model was developed previously but advanced test facilities were not available at that time to allow complete validation of the methodology. The new model formulation retained the conventional static and rotary dynamic terms but replaced conventional acceleration terms with more general indicial functions. In this study advanced testing techniques were utilized to validate the new methodology for modeling. Results of static, conventional forced oscillation, wide-band forced oscillation, oscillatory coning, and ramp tests are presented.

Murphy, Patrick C.; Klein, Vladislav

2003-01-01

54

NASA Astrophysics Data System (ADS)

This paper reports experimental results on using steady and unsteady plasma aerodynamic actuation to control the corner separation, which forms over the suction surface and end wall corner of a compressor cascade blade passage. Total pressure recovery coefficient distribution was adopted to evaluate the corner separation. Corner separation causes significant total pressure loss even when the angle of attack is 0°. Both steady and unsteady plasma aerodynamic actuations suppress the corner separation effectively. The control effect obtained by the electrode pair at 25% chord length is as effective as that obtained by all four electrode pairs. Increasing the applied voltage improves the control effect while it augments the power requirement. Increasing the Reynolds number or the angle of attack makes the corner separation more difficult to control. The unsteady actuation is much more effective and requires less power due to the coupling between the unsteady actuation and the separated flow. Duty cycle and excitation frequency are key parameters in unsteady plasma flow control. There are thresholds in both the duty cycle and the excitation frequency, above which the control effect saturates. The maximum relative reduction in total pressure loss coefficient achieved is up to 28% at 70% blade span. The obvious difference between steady and unsteady actuation may be that wall jet governs the flow control effect of steady actuation, while much more vortex induced by unsteady actuation is the reason for better control effect.

Li, Ying-Hong; Wu, Yun; Zhou, Min; Su, Chang-Bing; Zhang, Xiong-Wei; Zhu, Jun-Qiang

2010-06-01

55

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

56

Rotor-generated unsteady aerodynamic interactions in a 1½ stage compressor

NASA Astrophysics Data System (ADS)

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

Papalia, John J.

57

Estimation of Aircraft Unsteady Aerodynamic Parameters from Dynamic Wind Tunnel Testing

NASA Technical Reports Server (NTRS)

Improved aerodynamic mathematical models, for use in aircraft simulation or flight control design, are required when representing nonlinear unsteady aerodynamics. A key limitation of conventional aerodynamic models is the inability to map frequency and amplitude dependent data into the equations of motion directly. In an effort to obtain a more general formulation of the aerodynamic model, researchers have been led to a parallel requirement for more general testing methods. Testing for a more comprehensive model can lead to a very time consuming number of tests especially if traditional single frequency harmonic testing is attempted. This paper presents an alternative to traditional single frequency forced-oscillation testing by utilizing Schroeder sweeps to efficiently obtain the frequency response of the unsteady aerodynamic model. Schroeder inputs provide signals with a flat power spectrum over a specified frequency band. For comparison, experimental results using the traditional single-frequency inputs are also considered. A method for data analysis to determine an adequate unsteady aerodynamic model is presented. Discussion of associated issues that arise during this type of analysis and comparison of results using traditional single frequency analysis are provided.

Murphy, Patrick C.; Klein, Vladislav

2001-01-01

58

NASA Technical Reports Server (NTRS)

The theoretical basis of flexible-aircraft modeling techniques encompassing aerodynamic, control, and elastic-structure effects is investigated analytically, with a focus on methods which employ minimum-state approximations for the unsteady aerodynamics. Rational-function approximations to generalized aerodynamic forces are reviewed; constraints and lag-coefficient optimization are explained; the problem of physical weighting in the minimum-state equations of motion is examined; and results of typical analyses from the NASA Active Flexible Wing project (Perry et al., 1988) are presented in extensive tables and graphs and discussed in detail. The minimum-state approach is shown to produce accurate models at significantly reduced computation costs.

Tiffany, Sherwood H.; Karpel, Mordechay

1989-01-01

59

Wing flapping is one of the most widespread propulsion methods found in nature; however, the current understanding of the aerodynamics in bird wakes is incomplete. The role of the unsteady motion in the flow and its contribution to the aerodynamics is still an open question. In the current study, the wake of a freely flying European starling has been investigated using long-duration high-speed Particle Image Velocimetry (PIV) in the near wake. Kinematic analysis of the wings and body of the bird has been performed using additional high-speed cameras that recorded the bird movement simultaneously with the PIV measurements. The wake evolution of four complete wingbeats has been characterized through reconstruction of the time-resolved data, and the aerodynamics in the wake have been analyzed in terms of the streamwise forces acting on the bird. The profile drag from classical aerodynamics was found to be positive during most of the wingbeat cycle, yet kinematic images show that the bird does not decelerate. It is shown that unsteady aerodynamics are necessary to satisfy the drag/thrust balance by approximating the unsteady drag term. These findings may shed light on the flight efficiency of birds by providing a partial answer to how they minimize drag during flapping flight. PMID:24278243

Ben-Gida, Hadar; Kirchhefer, Adam; Taylor, Zachary J.; Bezner-Kerr, Wayne; Guglielmo, Christopher G.; Kopp, Gregory A.; Gurka, Roi

2013-01-01

60

Wing flapping is one of the most widespread propulsion methods found in nature; however, the current understanding of the aerodynamics in bird wakes is incomplete. The role of the unsteady motion in the flow and its contribution to the aerodynamics is still an open question. In the current study, the wake of a freely flying European starling has been investigated using long-duration high-speed Particle Image Velocimetry (PIV) in the near wake. Kinematic analysis of the wings and body of the bird has been performed using additional high-speed cameras that recorded the bird movement simultaneously with the PIV measurements. The wake evolution of four complete wingbeats has been characterized through reconstruction of the time-resolved data, and the aerodynamics in the wake have been analyzed in terms of the streamwise forces acting on the bird. The profile drag from classical aerodynamics was found to be positive during most of the wingbeat cycle, yet kinematic images show that the bird does not decelerate. It is shown that unsteady aerodynamics are necessary to satisfy the drag/thrust balance by approximating the unsteady drag term. These findings may shed light on the flight efficiency of birds by providing a partial answer to how they minimize drag during flapping flight. PMID:24278243

Ben-Gida, Hadar; Kirchhefer, Adam; Taylor, Zachary J; Bezner-Kerr, Wayne; Guglielmo, Christopher G; Kopp, Gregory A; Gurka, Roi

2013-01-01

61

NASA Technical Reports Server (NTRS)

A major challenge in the design and development of turbomachine airfoils for gas turbine engines is high cycle fatigue failures due to flutter and aerodynamically induced forced vibrations. In order to predict the aeroelastic response of gas turbine airfoils early in the design phase, accurate unsteady aerodynamic models are required. However, accurate predictions of flutter and forced vibration stress at all operating conditions have remained elusive. The overall objectives of this research program are to develop a transition model suitable for unsteady separated flow and quantify the effects of transition on airfoil steady and unsteady aerodynamics for attached and separated flow using this model. Furthermore, the capability of current state-of-the-art unsteady aerodynamic models to predict the oscillating airfoil response of compressor airfoils over a range of realistic reduced frequencies, Mach numbers, and loading levels will be evaluated through correlation with benchmark data. This comprehensive evaluation will assess the assumptions used in unsteady aerodynamic models. The results of this evaluation can be used to direct improvement of current models and the development of future models. The transition modeling effort will also make strides in improving predictions of steady flow performance of fan and compressor blades at off-design conditions. This report summarizes the progress and results obtained in the first year of this program. These include: installation and verification of the operation of the parallel version of TURBO; the grid generation and initiation of steady flow simulations of the NASA/Pratt&Whitney airfoil at a Mach number of 0.5 and chordal incidence angles of 0 and 10 deg.; and the investigation of the prediction of laminar separation bubbles on a NACA 0012 airfoil.

Capece, Vincent R.; Platzer, Max F.

2003-01-01

62

An exploratory study of finite difference grids for transonic unsteady aerodynamics

NASA Technical Reports Server (NTRS)

Unsteady aerodynamic forces are calculated by the XTRAN2L finite difference program which solves the complete two dimensional unsteady transonic small perturbation equation. The unsteady forces are obtained using a pulse transfer function technique which assumes the flow field behaves in a locally linear fashion about a mean condition. Forces are calculated for a linear flat plate using the default grids from the LTRAN2-NLR, LTRAN2-HI, and XTRAN3S programs. The forces are compared to the exact theoretical values for flat plate, and grid generated boundary and internal numerical reflections are observed to cause significant errors in the unsteady airloads. Grids are presented that alleviate the reflections while reducing computational time up to fifty-three percent and program size up to twenty-eight percent. Forces are presented for a six percent thick parabolic arc airfoil which demonstrate that the transform technique may be successfully applied to nonlinear transonic flows.

Seidel, D. A.; Bennett, R. M.; Whitlow, W., Jr.

1982-01-01

63

A linearized unsteady aerodynamic analysis for real blade supersonic cascades

The prediction capabilities of a linearized unsteady potential analysis have been extended to include supersonic cascades with subsonic axial flow. The numerical analysis of this type of flow presents several difficulties. First, complex oblique shock patterns exist within the cascade passage. Second, the acoustic response is discontinuous and propagates upstream and downstream of the blade row. Finally, a numerical scheme

M. D. Montgomery; J. M. Verdon; S. Fleeter

1997-01-01

64

UNSTEADY AERODYNAMIC PERFORMANCE OF MODEL WINGS AT LOW REYNOLDS NUMBERS

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

MICHAEL H. DICKINSON; KARL G. GÖTZ

1993-01-01

65

Numerical Computations of Unsteady Aerodynamics of Maneuvering Projectiles

This paper describes a multidisciplinary computational study undertaken to model the flight trajectories and the free-flight aerodynamics of finned projectiles both with and without control maneuvers. Advanced computational capabilities in computational fluid dynamics (CFD), rigid body dynamics (RBD) and flight control system (FCS) have been successfully fully coupled on high performance computing (HPC) platforms for physics-based “Virtual Fly-Outs” of munitions.

Jubaraj Sahu; James DeSpirito; Karen Heavey; Mark Costello; Jenna Stahl

2009-01-01

66

State-space model identification and feedback control of unsteady aerodynamic forces

Unsteady aerodynamic models are necessary to accurately simulate forces and develop feedback controllers for wings in agile motion; however, these models are often high dimensional or incompatible with modern control techniques. Recently, reduced-order unsteady aerodynamic models have been developed for a pitching and plunging airfoil by linearizing the discretized Navier-Stokes equation with lift-force output. In this work, we extend these reduced-order models to include multiple inputs (pitch, plunge, and surge) and explicit parameterization by the pitch-axis location, inspired by Theodorsen's model. Next, we investigate the na\\"{\\i}ve application of system identification techniques to input--output data and the resulting pitfalls, such as unstable or inaccurate models. Finally, robust feedback controllers are constructed based on these low-dimensional state-space models for simulations of a rigid flat plate at Reynolds number 100. Various controllers are implemented for models linearized at base angles of ...

Brunton, Steven L; Rowley, Clarence W

2014-01-01

67

NASA Technical Reports Server (NTRS)

The status of computational methods for unsteady aerodynamics and aeroelasticity is reviewed. The key features of challenging aeroelastic applications is discussed in terms of the flowfield state - low angle high speed flows and high angle vortex dominated flows. The critical role played by viscous effects in determining aeroelastic stability for conditions of incipient flow separation is stressed. The need for a variety of flow modeling tools, from linear formulations to implementations of the Navier-Stokes equations, is emphasized. Estimates of computer run times for flutter calculations using several computational methods are given. Applications of these methods for unsteady aerodynamic and transonic flutter calculations for airfoils, wings, and configurations are summarized. Finally, recommendations are made concerning future research directions.

Edwards, John W.; Malone, John B.

1992-01-01

68

NASA Technical Reports Server (NTRS)

The current status of computational methods for unsteady aerodynamics and aeroelasticity is reviewed. The key features of challenging aeroelastic applications are discussed in terms of the flowfield state: low-angle high speed flows and high-angle vortex-dominated flows. The critical role played by viscous effects in determining aeroelastic stability for conditions of incipient flow separation is stressed. The need for a variety of flow modeling tools, from linear formulations to implementations of the Navier-Stokes equations, is emphasized. Estimates of computer run times for flutter calculations using several computational methods are given. Applications of these methods for unsteady aerodynamic and transonic flutter calculations for airfoils, wings, and configurations are summarized. Finally, recommendations are made concerning future research directions.

Edwards, John W.; Malone, John B.

1992-01-01

69

Wing flutter boundary prediction using an unsteady Euler aerodynamic method

NASA Technical Reports Server (NTRS)

Modifications to an existing three-dimensional, implicit, upwind Euler/Navier-Stokes code (CFL3D Version 2.1) for the aeroelastic analysis of wings are described. These modifications, which were previously added to CFL3D Version 1.0, include the incorporation of a deforming mesh algorithm and the addition of the structural equations of motion for their simultaneous time-integration with the government flow equations. The paper gives a brief description of these modifications and presents unsteady calculations which check the modifications to the code. Euler flutter results for an isolated 45 degree swept-back wing are compared with experimental data for seven freestream Mach numbers which define the flutter boundary over a range of Mach number from 0.499 to 1.14. These comparisons show good agreement in flutter characteristics for freestream Mach numbers below unity. For freestream Mach numbers above unity, the computed aeroelastic results predict a premature rise in the flutter boundary as compared with the experimental boundary. Steady and unsteady contours of surface Mach number and pressure are included to illustrate the basic flow characteristics of the time-marching flutter calculations and to aid in identifying possible causes for the premature rise in the computational flutter boundary.

Lee-Rausch, Elizabeth M.; Batina, John T.

1993-01-01

70

Wing flutter boundary prediction using unsteady Euler aerodynamic method

NASA Technical Reports Server (NTRS)

Modifications to an existing 3D implicit upwind Euler/Navier-Stokes code for the aeroelastic analysis of wings are described. These modifications include the incorporation of a deforming mesh algorithm and the addition of the structural equations of motion for their simultaneous time-integration with the governing flow equations. The paper gives a brief description of these modifications and presents unsteady calculations which check the modifications to the code. Euler flutter results for an isolated 45 deg swept-back wing are compared with experimental data for seven freestream Mach numbers which define the flutter boundary over a range of Mach number from 0.499 to 1.14. These comparisons show good agreement in flutter characteristics for freestream Mach numbers below unity. For freestream Mach numbers above unity, the computed aeroelastic results predict a premature rise in the flutter boundary as compared with the experimental boundary. Steady and unsteady contours of surface Mach number and pressure are included to illustrate the basic flow characteristics of the time-marching flutter calculations and to aid in identifying possible causes for the premature rise in the computational flutter boundary.

Lee-Rausch, Elizabeth M.; Batina, John T.

1993-01-01

71

Measurement of aerodynamic noise and unsteady flow field around a symmetrical airfoil

The purpose of this paper is to study the physics of aerodynamic noise generation from the symmetrical airfoil of NACA 0018\\u000a in a uniform flow. The relationship between the noise spectrum and the unsteady flow field around the airfoil is studied in\\u000a an acoustic wind tunnel using flow visualization and PIV analysis. The discrete frequency noise was generated from the

N. Fujisawa

2002-01-01

72

Unsteady aerodynamic simulation of multiple bodies in relative motion: A prototype method

NASA Technical Reports Server (NTRS)

A prototype method for time-accurate simulation of multiple aerodynamic bodies in relative motion is presented. The method is general and features unsteady chimera domain decomposition techniques and an implicit approximately factored finite-difference procedure to solve the time-dependent thin-layer Navier-Stokes equations. The method is applied to a set of two- and three- dimensional test problems to establish spatial and temporal accuracy, quantify computational efficiency, and begin to test overall code robustness.

Meakin, Robert L.

1989-01-01

73

Development of computational methods for unsteady aerodynamics at the NASA Langley Research Center

NASA Technical Reports Server (NTRS)

The current scope, recent progress, and plans for research and development of computational methods for unsteady aerodynamics at the NASA Langley Research Center are reviewed. Both integral equations and finite difference methods for inviscid and viscous flows are discussed. Although the great bulk of the effort has focused on finite difference solution of the transonic small perturbation equation, the integral equation program is given primary emphasis here because it is less well known.

Yates, E. Carson, Jr.; Whitlow, Woodrow, Jr.

1987-01-01

74

Development of computational methods for unsteady aerodynamics at the NASA Langley Research Center

NASA Technical Reports Server (NTRS)

The current scope, recent progress, and plans for research and development of computational methods for unsteady aerodynamics at the NASA Langley Research Center are reviewed. Both integral-equations and finite-difference method for inviscid and viscous flows are discussed. Although the great bulk of the effort has focused on finite-difference solution of the transonic small-perturbation equation, the integral-equation program is given primary emphasis here because it is less well known.

Yates, E. Carson, Jr.; Whitlow, Woodrow, Jr.

1987-01-01

75

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

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

Azuma, Akira; Okamoto, Masato

2005-05-01

76

NASA Technical Reports Server (NTRS)

This paper presents recent results in the unsteady aerodynamics and computational aeroelasticity research programs at the NASA Langley Research Center. These programs include development of two types of computational methods: methods that use structured computational meshes and those that use unstructured meshes. Results show that an aeroelastic analysis method that uses unsteady transonic small disturbance (TSD) potential aerodynamics and structured, Cartesian meshes is capable of accurate analysis of complex aircraft configurations. The paper describes recent enhancements to the TSD method that allow analysis of vehicles with swept, flexible vertical surfaces and flexible fuselages and presents selected results that verify the accuracy of the new capabilities. Modifications to a structured-mesh Euler/Navier-Stokes method to allow aeroelastic analysis are described, and a wing flutter analysis using the resulting method is presented. Advantages of using unstructured meshes for the analysis of complex configurations are discussed. The paper presents development of unstructured-mesh Euler/Navier-Stokes methods for unsteady aerodynamics and aeroelastic analysis. Spatial and temporal adaption methods on unstructured meshes are described, and selected results are presented.

Whitlow, Woodrow, Jr.

1993-01-01

77

Influence of transition on steady and unsteady wind-turbine airfoil aerodynamics

NASA Astrophysics Data System (ADS)

Laminar--flow airfoils for large stall--regulated horizontal--axis wind turbines are designed to achieve a restrained maximum lift coefficient and a broad laminar low- drag bucket under steady flow conditions and at specific Reynolds numbers. Blind- comparisons of the 2000 NREL Unsteady Aerodynamics Experiment showed large discrepancies and illustrated the need for improved physics modeling. We have studied the S809 airfoil under static and dynamic (ramp-up, ramp-down, and oscillatory) conditions, using the four-equation transition model of Langtry and Menter (2009), which has been implemented as a library accessible by an OpenFOAM RANS solver. Model validation is performed using surface--pressure and lift/drag data from U. Glasgow (2009) and OSU (1995) wind tunnel experiments. Performance of the transition model is assessed by analyzing integrated performance metrics, as well as detailed surface pressure and pressure gradient, wall--shear stress, and boundary--layer profiles and separation points. Demonstration of model performance in the light-- and deep--stall regimes of dynamic stall is an important step in reducing uncertainties in full 3D simulations of turbines operating in the atmospheric boundary layer.

Paterson, Eric; Lavely, Adam; Vijayakumar, Ganesh; Brasseur, James

2011-11-01

78

Unsteady Aerodynamic Modeling in Roll for the NASA Generic Transport Model

NASA Technical Reports Server (NTRS)

Reducing the impact of loss-of-control conditions on commercial transport aircraft is a primary goal of the NASA Aviation Safety Program. One aspect in developing the supporting technologies is to improve the aerodynamic models that represent these adverse conditions. Aerodynamic models appropriate for loss of control conditions require a more general mathematical representation to predict nonlinear unsteady behaviors. In this paper, a more general mathematical model is proposed for the subscale NASA Generic Transport Model (GTM) that covers both low and high angles of attack. Particular attention is devoted to the stall region where full-scale transports have demonstrated a tendency for roll instability. The complete aerodynamic model was estimated from dynamic wind-tunnel data. Advanced computational methods are used to improve understanding and visualize the flow physics within the region where roll instability is a factor.

Murphy, Patrick C.; Klein, Vladislav; Frink, Neal T.

2012-01-01

79

Physically weighted approximations of unsteady aerodynamic forces using the minimum-state method

NASA Technical Reports Server (NTRS)

The Minimum-State Method for rational approximation of unsteady aerodynamic force coefficient matrices, modified to allow physical weighting of the tabulated aerodynamic data, is presented. The approximation formula and the associated time-domain, state-space, open-loop equations of motion are given, and the numerical procedure for calculating the approximation matrices, with weighted data and with various equality constraints are described. Two data weighting options are presented. The first weighting is for normalizing the aerodynamic data to maximum unit value of each aerodynamic coefficient. The second weighting is one in which each tabulated coefficient, at each reduced frequency value, is weighted according to the effect of an incremental error of this coefficient on aeroelastic characteristics of the system. This weighting yields a better fit of the more important terms, at the expense of less important ones. The resulting approximate yields a relatively low number of aerodynamic lag states in the subsequent state-space model. The formulation forms the basis of the MIST computer program which is written in FORTRAN for use on the MicroVAX computer and interfaces with NASA's Interaction of Structures, Aerodynamics and Controls (ISAC) computer program. The program structure, capabilities and interfaces are outlined in the appendices, and a numerical example which utilizes Rockwell's Active Flexible Wing (AFW) model is given and discussed.

Karpel, Mordechay; Hoadley, Sherwood Tiffany

1991-01-01

80

NASA Astrophysics Data System (ADS)

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

Lin, Guofeng

81

A General Theory of Unsteady Compressible Potential Aerodynamics

NASA Technical Reports Server (NTRS)

The general theory of potential aerodynamic flow around a lifting body having arbitrary shape and motion is presented. By using the Green function method, an integral representation for the potential is obtained for both supersonic and subsonic flow. Under small perturbation assumption, the potential at any point, P, in the field depends only upon the values of the potential and its normal derivative on the surface, sigma, of the body. Hence, if the point P approaches the surface of the body, the representation reduces to an integro-differential equation relating the potential and its normal derivative (which is known from the boundary conditions) on the surface sigma. For the important practical case of small harmonic oscillation around a rest position, the equation reduces to a two-dimensional Fredholm integral equation of second-type. It is shown that this equation reduces properly to the lifting surface theories as well as other classical mathematical formulas. The question of uniqueness is examined and it is shown that, for thin wings, the operator becomes singular as the thickness approaches zero. This fact may yield numerical problems for very thin wings.

Morino, L.

1974-01-01

82

A New Compendium of Unsteady Aerodynamic Test Cases for CFD: Summary of AVT WG-003 Activities

NASA Technical Reports Server (NTRS)

With the continuous progress in hardware and numerical schemes, Computational Unsteady Aerodynamics (CUA), that is, the application of Computational Fluid Dynamics (CFD) to unsteady flowfields, is slowly finding its way as a useful and reliable tool (turbulence and transition modeling permitting) in the aircraft, helicopter, engine and missile design and development process. Before a specific code may be used with confidence it is essential to validate its capability to describe the physics of the flow correctly, or at least to the level of approximation required, for which purpose a comparison with accurate experimental data is needed. Unsteady wind tunnel testing is difficult and expensive; two factors which dramatically limit the number of organizations with the capability and/or resources to perform it. Thus, unsteady experimental data is scarce, often classified and scattered in diverse documents. Additionally, access to the reports does not necessarily assure access to the data itself. The collaborative effort described in this paper was conceived with the aim of collecting into a single easily accessible document as much quality data as possible. The idea is not new. In the early 80's NATO's AGARD (Advisory Group for Aerospace Research & Development) Structures and Material Panel (SMP) produced AGARD Report No. 702 "Compendium of Unsteady Aerodynamic Measurements", which has found and continues to find extensive use within the CUA Community. In 1995 AGARD's Fluid Dynamics Panel (FDP) decided to update and expand the former database with new geometries and physical phenomena, and launched Working Group WG-22 on "Validation Data for Computational Unsteady Aerodynamic Codes". Shortly afterwards AGARD was reorganized as the RTO (Research and Technology Organization) and the WG was renamed as AVT (Applied Vehicle Technolology) WG-003. Contributions were received from AEDC, BAe, DLR, DERA, Glasgow University, IAR, NAL, NASA, NLR, and ONERA. The final publication with the results of the exercise is expected in the second part of 1999. The aim of the present paper is to announce and present the new database to the Aeroelasticity community. It is also intended to identify, together with one of the groups of end users it targets, deficiencies in the compendium that should be addressed by means of new wind tunnel tests or by obtaining access to additionally existing data.

Ruiz-Calavera, Luis P.; Bennett, Robert; Fox, John H.; Galbraith, Robert W.; Geurts, Evert; Henshaw, Micahel J. deC.; Huang, XingZhong; Kaynes, Ian W.; Loeser, Thomas; Naudin, Pierre; Tamayama, Masato

1999-01-01

83

Bifurcations In Unsteady Flows

NASA Technical Reports Server (NTRS)

Report discusses various types of bifurcations occurring between steady and unsteady aerodynamic flows. Provides examples to illustrate ways bifurcations influence results of experiments. Recommends experimenters take bifurcation phenomena into account in interpretation of measurements.

Chapman, Gary T.; Tobak, Murray

1992-01-01

84

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

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

Hartin, J.R.

1989-01-01

85

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

86

Development of a steady potential solver for use with linearized, unsteady aerodynamic analyses

NASA Technical Reports Server (NTRS)

A full potential steady flow solver (SFLOW) developed explicitly for use with an inviscid unsteady aerodynamic analysis (LINFLO) is described. The steady solver uses the nonconservative form of the nonlinear potential flow equations together with an implicit, least squares, finite difference approximation to solve for the steady flow field. The difference equations were developed on a composite mesh which consists of a C grid embedded in a rectilinear (H grid) cascade mesh. The composite mesh is capable of resolving blade to blade and far field phenomena on the H grid, while accurately resolving local phenomena on the C grid. The resulting system of algebraic equations is arranged in matrix form using a sparse matrix package and solved by Newton's method. Steady and unsteady results are presented for two cascade configurations: a high speed compressor and a turbine with high exit Mach number.

Hoyniak, Daniel; Verdon, Joseph M.

1991-01-01

87

NASA Astrophysics Data System (ADS)

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

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

2005-09-01

88

Development of an unsteady aerodynamic analysis for finite-deflection subsonic cascades

NASA Technical Reports Server (NTRS)

An unsteady potential flow analysis, which accounts for the effects of blade geometry and steady turning, was developed to predict aerodynamic forces and moments associated with free vibration or flutter phenomena in the fan, compressor, or turbine stages of modern jet engines. Based on the assumption of small amplitude blade motions, the unsteady flow is governed by linear equations with variable coefficients which depend on the underlying steady low. These equations were approximated using difference expressions determined from an implicit least squares development and applicable on arbitrary grids. The resulting linear system of algebraic equations is block tridiagonal, which permits an efficient, direct (i.e., noniterative) solution. The solution procedure was extended to treat blades with rounded or blunt edges at incidence relative to the inlet flow.

Verdon, J. M.; Caspar, J. R.

1981-01-01

89

NASA Technical Reports Server (NTRS)

Various control analysis, design, and simulation techniques for aeroelastic applications require the equations of motion to be cast in a linear time-invariant state-space form. Unsteady aerodynamics forces have to be approximated as rational functions of the Laplace variable in order to put them in this framework. For the minimum-state method, the number of denominator roots in the rational approximation. Results are shown of applying various approximation enhancements (including optimization, frequency dependent weighting of the tabular data, and constraint selection) with the minimum-state formulation to the active flexible wing wind-tunnel model. The results demonstrate that good models can be developed which have an order of magnitude fewer augmenting aerodynamic equations more than traditional approaches. This reduction facilitates the design of lower order control systems, analysis of control system performance, and near real-time simulation of aeroservoelastic phenomena.

Tiffany, Sherwood H.; Karpel, Mordechay

1989-01-01

90

Characterization and Control of Unsteady Aerodynamics on Wind Turbine Aerofoils

NASA Astrophysics Data System (ADS)

An experimental capability developed for testing two-dimensional aerofoils while dynamically pitching is discussed. Key to the approach are a dynamic pitch system, the rapid prototyping of aerofoils, inexpensive time-resolved pressure measurements, the ability to capture flow-field structure, and the ability to add compliance to the system. In addition to describing the system components, examples of typical results for characterization and control studies are given. Use of the data is also demonstrated through comparison of the results from a simulation with those from an experiment under the same conditions. Future uses of this experimental capability are also discussed.

Naughton, J.; Strike, J.; Hind, M.; Babbitt, A.; Magstadt, A.; Nikoueeyan, P.; Davidson, P.; Shareman, J.

2014-06-01

91

Estimation of unsteady aerodynamics in the wake of a freely flying European starling

Wing flapping is one of the most widespread propulsion methods found in nature; however, the current understanding of the aerodynamics in bird wakes is incomplete. The role of the unsteady motion in the flow and its contribution to the aerodynamics is still an open question. In the current study, the wake of a freely flying European starling has been investigated using long-duration high-speed Particle Image Velocimetry (PIV) in the near wake. Kinematic analysis of the wings and body of the bird has been performed using additional high-speed cameras that recorded the bird movement simultaneously with the PIV measurements. The wake evolution of four complete wingbeats has been characterized through reconstruction of the time resolved data, and the aerodynamics in the wake have been analyzed in terms of the streamwise forces acting on the bird. The profile drag from classical aerodynamics was found to be positive during most of the wingbeat cycle, yet kinematic images show that the bird does not decelerate. It ...

Ben-Gida, Hadar; Taylor, Zachary J; Bezner-Kerr, Wayne; Guglielmo, Christopher G; Kopp, Gregory A; Gurka, Roi

2013-01-01

92

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

93

State-space model identification and feedback control of unsteady aerodynamic forces

NASA Astrophysics Data System (ADS)

Unsteady aerodynamic models are necessary to accurately simulate forces and develop feedback controllers for wings in agile motion; however, these models are often high dimensional or incompatible with modern control techniques. Recently, reduced-order unsteady aerodynamic models have been developed for a pitching and plunging airfoil by linearizing the discretized Navier-Stokes equation with lift-force output. In this work, we extend these reduced-order models to include multiple inputs (pitch, plunge, and surge) and explicit parameterization by the pitch-axis location, inspired by Theodorsen's model. Next, we investigate the na\\"{\\i}ve application of system identification techniques to input--output data and the resulting pitfalls, such as unstable or inaccurate models. Finally, robust feedback controllers are constructed based on these low-dimensional state-space models for simulations of a rigid flat plate at Reynolds number 100. Various controllers are implemented for models linearized at base angles of attack $\\alpha_0=0^\\circ, \\alpha_0=10^\\circ$, and $\\alpha_0=20^\\circ$. The resulting control laws are able to track an aggressive reference lift trajectory while attenuating sensor noise and compensating for strong nonlinearities.

Brunton, Steven L.; Dawson, Scott T. M.; Rowley, Clarence W.

2014-10-01

94

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

Ramamurti, Ravi; Sandberg, William C

2007-03-01

95

NSDL National Science Digital Library

Access to the article is free, however registration and sign-in are required. Why are flies and birds much more maneuverable than airplanes? In his Perspective, Dudley explains current thinking about the biomechanics of insect flight. He highlights a report in this issue (Dickinson et al.) of a robotic fly that reproduces many of the flight characteristics of its living counterpart and reveals unexpected force generation at the ends of the up- and downstrokes.

Robert Dudley (University of Texas at Austin;Integrative Biology)

1999-06-18

96

In this paper the double linearization theory applied to lightly loaded two-dimensional subsonic and supersonic cascades undergoing oscillation with chordwise displacement or flexible deformation is presented. Numerical computation based on this theory have been conducted to demonstrate parametric dependence of the unsteady aerodynamic work on blades. The translational oscillation can be destabilized by chordwise displacement for both subsonic and supersonic

M. Namba; K. Toshimitsu

1993-01-01

97

unsteady aerodynamic and hydrodynamic forces and structural dynamics such as power take (Figure 1) and tidal turbine projects with a higher degree of accuracy than current models. The wind plant such as frontal passages through a wind plant and their effect on turbine power production and mechanical loading

98

Unsteady Analysis of Separated Aerodynamic Flows Using an Unstructured Multigrid Algorithm

NASA Technical Reports Server (NTRS)

An implicit method for the computation of unsteady flows on unstructured grids is presented. The resulting nonlinear system of equations is solved at each time step using an agglomeration multigrid procedure. The method allows for arbitrarily large time steps and is efficient in terms of computational effort and storage. Validation of the code using a one-equation turbulence model is performed for the well-known case of flow over a cylinder. A Detached Eddy Simulation model is also implemented and its performance compared to the one equation Spalart-Allmaras Reynolds Averaged Navier-Stokes (RANS) turbulence model. Validation cases using DES and RANS include flow over a sphere and flow over a NACA 0012 wing including massive stall regimes. The project was driven by the ultimate goal of computing separated flows of aerodynamic interest, such as massive stall or flows over complex non-streamlined geometries.

Pelaez, Juan; Mavriplis, Dimitri J.; Kandil, Osama

2001-01-01

99

UNAERO: A package of FORTRAN subroutines for approximating unsteady aerodynamics in the time domain

NASA Technical Reports Server (NTRS)

This report serves as an instruction and maintenance manual for a collection of CDC CYBER FORTRAN IV subroutines for approximating the unsteady aerodynamic forces in the time domain. The result is a set of constant-coefficient first-order differential equations that approximate the dynamics of the vehicle. Provisions are included for adjusting the number of modes used for calculating the approximations so that an accurate approximation is generated. The number of data points at different values of reduced frequency can also be varied to adjust the accuracy of the approximation over the reduced-frequency range. The denominator coefficients of the approximation may be calculated by means of a gradient method or a least-squares approximation technique. Both the approximation methods use weights on the residual error. A new set of system equations, at a different dynamic pressure, can be generated without the approximations being recalculated.

Dunn, H. J.

1985-01-01

100

Feasibility investigation of general time-domain unsteady aerodynamics of rotors

NASA Technical Reports Server (NTRS)

The feasibility of a general theory for the time-domain unsteady aerodynamics of helicopter rotors is investigated. The wake theory gives a linearized relation between the downwash and the wing bound circulation, in terms of the impulse response obtained directly in the time domain. This approach makes it possible to treat general wake configurations, including discrete wake vorticity with rolled-up and distorted geometry. The investigation establishes the approach for model order reduction; determines when a constrained identification method is needed; verifies the formulation of the theory for rolled-up, distorted trim wake geometry; and verifies the formulation of the theory for wake geometry perturbations. The basic soundness of the approach is demonstrated by the results presented. A research program to complete the development of the method is outlined. The result of this activity will be an approach for analyzing the aeroelastic stability and response of helicopter rotors, while retaining the important influence of the complicated rotor wake configuration.

Johnson, Wayne

1990-01-01

101

NASA Technical Reports Server (NTRS)

The input data required to execute the computer program ISCON are described. The program generates a numerical procedure for the determination of unsteady aerodynamic forces on arbitrarily interacting wings and tails in supersonic flow. A velocity potential gradient method is used. Constant Mach number is assumed throughout the flow field. Lifting surfaces are represented by trapezoidal elements which can be generated automatically by the program. The wake field is represented by rectangular strip elements. The formulation is reviewed as well as input overview and input format. Instruction on how to use ISCON, a sample problem, and the restart feature are discussed. Program size limitations, computer program flow, and error messages are also included along with a description of the SS31 program used to compute the coefficients of surface spline.

Crill, W.; Dale, B.

1977-01-01

102

NASA Technical Reports Server (NTRS)

An experimental influence coefficient technique was used to obtain unsteady aerodynamic influence coefficients and, consequently, unsteady pressures for a cascade of symmetric airfoils oscillating in pitch about mid-chord. Stagger angles of 0 deg and 10 deg were investigated for a cascade with a gap-to-chord ratio of 0.417 operating at an axial Mach number of 1.9, resulting in a supersonic leading-edge locus. Reduced frequencies ranged from 0.056 to 0.2. The influence coefficients obtained determine the unsteady pressures for any interblade phase angle. The unsteady pressures were compared with those predicted by several algorithms for interblade phase angles of 0 deg and 180 deg.

Ramsey, John K.; Erwin, Dan

2004-01-01

103

Modeling of Longitudinal Unsteady Aerodynamics of a Wing-Tail Combination

NASA Technical Reports Server (NTRS)

Aerodynamic equations for the longitudinal motion of an aircraft with a horizontal tail were developed. In this development emphasis was given on obtaining model structure suitable for model identification from experimental data. The resulting aerodynamic models included unsteady effects in the form of linear indicial functions. These functions represented responses in the lift on the wing and tail alone, and interference between those two lifting surfaces. The effect of the wing on the tail was formulated for two different expressions concerning the downwash angle at the tail. The first expression used the Cowley-Glauert approximation known-as "lag-in-downwash," the second took into account growth of the wing circulation and delay in the development of the lift on the tail. Both approaches were demonstrated in two examples using the geometry of a fighter aircraft and a large transport. It was shown that the differences in the two downwash formulations would increase for an aircraft with long tail arm performing low-speed, rapid maneuvers.

Klein, Vladislav

1999-01-01

104

Recent Experiments at the Gottingen Aerodynamic Institute

NASA Technical Reports Server (NTRS)

This report presents the results of various experiments carried out at the Gottingen Aerodynamic Institute. These include: experiments with Joukowski wing profiles; experiments on an airplane model with a built-in motor and functioning propeller; and the rotating cylinder (Magnus Effect).

Ackeret, J

1925-01-01

105

NASA Technical Reports Server (NTRS)

A simple vortex system, used to model unsteady aerodynamic effects into the rigid body longitudinal equations of motion of an aircraft, is described. The equations are used in the development of a parameter extraction algorithm. Use of the two parameter-estimation modes, one including and the other omitting unsteady aerodynamic modeling, is discussed as a means of estimating some acceleration derivatives. Computer generated data and flight data, used to demonstrate the use of the parameter-extraction algorithm are studied.

Queijo, M. J.; Wells, W. R.; Keskar, D. A.

1979-01-01

106

Transonic Unsteady Aerodynamics of the F/A-18E at Conditions Promoting Abrupt Wing Stall

NASA Technical Reports Server (NTRS)

A transonic wind tunnel test of an 8% F/A-18E model was conducted in the NASA Langley Research Center (LaRC) 16-Foot Transonic Tunnel (16-Ft TT) to investigate the Abrupt Wing Stall (AWS) characteristics of this aircraft. During this test, both steady and unsteady measurements of balance loads, wing surface pressures, wing root bending moments, and outer wing accelerations were performed. The test was conducted with a wide range of model configurations and test conditions in an attempt to reproduce behavior indicative of the AWS phenomenon experienced on full-scale aircraft during flight tests. This paper focuses on the analysis of the unsteady data acquired during this test. Though the test apparatus was designed to be effectively rigid. model motions due to sting and balance flexibility were observed during the testing, particularly when the model was operating in the AWS flight regime. Correlation between observed aerodynamic frequencies and model structural frequencies are analyzed and presented. Significant shock motion and separated flow is observed as the aircraft pitches through the AWS region. A shock tracking strategy has been formulated to observe this phenomenon. Using this technique, the range of shock motion is readily determined as the aircraft encounters AWS conditions. Spectral analysis of the shock motion shows the frequencies at which the shock oscillates in the AWS region, and probability density function analysis of the shock location shows the propensity of the shock to take on a bi-stable and even tri-stable character in the AWS flight regime.

Schuster, David M.; Byrd, James E.

2003-01-01

107

NASA Technical Reports Server (NTRS)

Experimental data were obtained to help validate analytical and computational fluid dynamics (CFD) codes used to compute unsteady cascade aerodynamics in a supersonicaxial- flow regime. Results from two analytical codes and one CFD code were compared with experimental data. One analytical code did not account for airfoil thickness or camber; another, using piston theory (piston code), accounted for thickness and camber upstream of the first shockwave/airfoil impingement locations. The Euler CFD code accounted fully for airfoil shape.

Ramsey, John K.; Erwin, Dan

2005-01-01

108

Wind turbine blade aerodynamics: The combined experiment

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 such machines. The analysis showed that inflow conditions were extremely variable and that these inflows yielded three different operational regimes. Each regime produces very different aerodynamic loading conditions that must be tolerated by the turbine. The two conditions not predicted from wind tunnel data are being subjected to further analyses to provide new guidelines for both designers and operators.

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

1994-08-01

109

NASA Technical Reports Server (NTRS)

The program DuctE3D is used for steady or unsteady aerodynamic and aeroelastic analysis of ducted fans. This guide describes the input data required and the output files generated, in using DuctE3D. The analysis solves three dimensional unsteady, compressible Euler equations to obtain the aerodynamic forces. A normal mode structural analysis is used to obtain the aeroelastic equations, which are solved using either the time domain or the frequency domain solution method. Sample input and output files are included in this guide for steady aerodynamic analysis and aeroelastic analysis of an isolated fan row.

Srivastava, R.; Reddy, T. S. R.

1997-01-01

110

NASA Technical Reports Server (NTRS)

This guide describes the input data required, for steady or unsteady aerodynamic and aeroelastic analysis of propellers and the output files generated, in using PROP3D. The aerodynamic forces are obtained by solving three dimensional unsteady, compressible Euler equations. A normal mode structural analysis is used to obtain the aeroelastic equations, which are solved using either time domain or frequency domain solution method. Sample input and output files are included in this guide for steady aerodynamic analysis of single and counter-rotation propellers, and aeroelastic analysis of single-rotation propeller.

Srivastava, R.; Reddy, T. S. R.

1996-01-01

111

A review of unsteady turbulent boundary-layer experiments

NASA Technical Reports Server (NTRS)

The essential results of a comprehensive review of existing unsteady turbulent boundary-layer experiments are presented. Different types of unsteady flow facilities are described, and the related unsteady turbulent boundary-layer experiments are cataloged and discussed. The measurements that were obtained in the various experiments are described, and a complete list of experimental results is presented. All the experiments that measured instantaneous values of velocity, turbulence intensity, or turbulent shear stress are identified, and the availability of digital data is indicated. The results of the experiments are analyzed, and several significant trends are identified. An assessment of the available data is presented, delineating gaps in the existing data, and indicating where new or extended information is needed. Guidelines for future experiments are included.

Carr, L. W.

1981-01-01

112

NASA Astrophysics Data System (ADS)

The growing applications of low Reynolds number (LRN) operating vehicles impose the need for accurate LRN flow solutions. These applications usually involve complex unsteady phenomena, which depend on the kinematics of the vehicle such as pitching, plunging, and flapping of a wing. The objective of the present study is to address the issues related to LRN aerodynamics of a harmonically pitching NACA0012 airfoil. To this end, the influence of unsteady parameters, namely, amplitude of oscillation, d, reduced frequency, k, and Reynolds number, Re, on the aerodynamic performance of the model is investigated. Computational fluid dynamics (CFD) is utilized to solve Navier-Stokes (N-S) equations discretized based on the Finite Volume Method (FVM). The resulting instantaneous lift coefficients are compared with analytical data from Theodorsen’s method. The simulation results reveal that d, k, and Re are of great importance in the aerodynamic performance of the system, as they affect the maximum lift coefficients, hysteresis loops, strength, and number of the generated vortices within the harmonic motion, and the extent of the so-called figure-of-eight phenomenon region. Thus, achieving the optimum lift coefficients demands a careful selection of these parameters.

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

2010-08-01

113

NASA Technical Reports Server (NTRS)

The aeromechanical stability of a helicopter in ground resonance was analyzed, by incorporating five different aerodynamic models in the coupled rotor/fuselage analysis. The sensitivity of the results to changes in aerodynamic modelling was carefully examined. The theoretical results were compared with experimental data and useful conclusions are drawn regarding the role of aerodynamic modeling on this aeromechanical stability problem. The aerodynamic model which provided the best all around correlation with the experimental data was identified.

Friedmann, P. P.; Venkatesan, C.

1985-01-01

114

NASA Technical Reports Server (NTRS)

Theoretical analyses and computer codes are being developed for predicting compressible unsteady inviscid and viscous flows through blade rows. Such analyses are needed to determine the impact of unsteady flow phenomena on the structural durability and noise generation characteristics of turbomachinery blading. Emphasis is being placed on developing analyses based on asymptotic representations of unsteady flow phenomena. Thus, flow driven by small-amplitude unsteady excitations in which viscous effects are concentrated in thin layers are being considered. The resulting analyses should apply in many practical situations, lead to a better understanding of the relevent physics, and they will be efficient computationally, and therefore, appropriate for aeroelastic and aeroacoustic design applications. Under the present phase (Task 3), the effort was focused on providing inviscid and viscid prediction capabilities for subsonic unsteady cascade flows.

Verdon, Joseph M.; Barnett, Mark; Hall, Kenneth C.; Ayer, Timothy C.

1991-01-01

115

Estimation of Longitudinal Unsteady Aerodynamics of a Wing-Tail Combination From Wind Tunnel Data

NASA Technical Reports Server (NTRS)

This paper presents an initial step toward model identification from wind tunnel data for an airliner configuration. Two approaches to modeling a transport configuration are considered and applied to both steady and large-amplitude forced-oscillation wind tunnel data taken over a wide range of angles of attack. Only limited conclusions could be drawn from this initial data set. Although model estimated time histories of normal force and pitching moment agree reasonably well with the corresponding measured values, model damping parameters did not, for some cases, have values consistent with small amplitude oscillatory data. In addition, large parameter standard errors implied poor information content for model structure determination and parameter estimation. Further investigation of the modeling problem for more general aerodynamic models is recommended with close attention to experiment design for obtaining parameters with high accuracy.

Murphy, Patrick C.; Klein, Vladislav

2006-01-01

116

NASA Technical Reports Server (NTRS)

The computer program written in support of the problem to determine aerodynamic influence coefficients on parallel interfering wings is described. The information is geared to the programmer. It is sufficient to describe the program logic and the required peripheral storage.

Paine, A. A.

1972-01-01

117

NASA Technical Reports Server (NTRS)

At the wake of the Columbia (STS-107) accident it was decided to remove the Protuberance Aerodynamic Load (PAL) Ramp that was originally intended to protect various protuberances outside of the Space Shuttle External Tank from high buffet load induced by cross-flows at transonic speed. In order to establish the buffet load without the PAL ramp, a wind tunnel test was conducted where segments of the protuberances were instrumented with dynamic pressure transducers; and power-spectra of sectional lift and drag forces at various span-wise locations between two adjacent support brackets were measured under different cross flow angles, Mach number and other conditions. Additionally, frequency-dependent spatial correlations between the sectional forces were also established. The sectional forces were then adjusted by the correlation length to establish span-averaged spectra of normal and lateral forces that can be suitably "added" to various other unsteady forces encountered by the protuberance. This paper describes the methodology used for calculating the correlation-adjusted power spectrum of the buffet load. A second part of the paper describes wind-tunnel results on the difference in the buffet load on the protuberances with and without the PAL ramp. In general when the ramp height is the same as that of the protuberance height, such as that found on the liquid Oxygen part of the tank, the ramp is found to cause significant reduction of the unsteady aerodynamic load. However, on the liquid Hydrogen part of the tank, where the Oxygen feed-line is far larger in diameter than the height of the PAL ramp, little protection is found to be available to all but the Cable Tray.

Panda, Jayatana; Martin, Fred W.; Sutliff, Daniel L.

2008-01-01

118

Spatial adaptation procedures on tetrahedral meshes for unsteady aerodynamic flow calculations

NASA Technical Reports Server (NTRS)

Spatial adaptation procedures for the accurate and efficient solution of steady and unsteady inviscid flow problems are described. The adaptation procedures were developed and implemented within a three-dimensional, unstructured-grid, upwind-type Euler code. These procedures involve mesh enrichment and mesh coarsening to either add points in high gradient regions of the flow or remove points where they are not needed, respectively, to produce solutions of high spatial accuracy at minimal computational cost. The paper gives a detailed description of the enrichment and coarsening procedures and presents comparisons with experimental data for an ONERA M6 wing and an exact solution for a shock-tube problem to provide an assessment of the accuracy and efficiency of the capability. Steady and unsteady results, obtained using spatial adaptation procedures, are shown to be of high spatial accuracy, primarily in that discontinuities such as shock waves are captured very sharply.

Rausch, Russ D.; Batina, John T.; Yang, Henry T. Y.

1993-01-01

119

Spatial adaptation procedures on tetrahedral meshes for unsteady aerodynamic flow calculations

NASA Technical Reports Server (NTRS)

Spatial adaptation procedures for the accurate and efficient solution of steady and unsteady inviscid flow problems are described. The adaptation procedures were developed and implemented within a three-dimensional, unstructured-grid, upwind-type Euler code. These procedures involve mesh enrichment and mesh coarsening to either add points in high gradient regions of the flow or remove points where they are not needed, respectively, to produce solutions of high spatial accuracy at minimal computational cost. A detailed description of the enrichment and coarsening procedures are presented and comparisons with experimental data for an ONERA M6 wing and an exact solution for a shock-tube problem are presented to provide an assessment of the accuracy and efficiency of the capability. Steady and unsteady results, obtained using spatial adaptation procedures, are shown to be of high spatial accuracy, primarily in that discontinuities such as shock waves are captured very sharply.

Rausch, Russ D.; Batina, John T.; Yang, Henry T. Y.

1993-01-01

120

This paper describes the design, calibration and application of an instrument that measures the effects of unsteady air flow (airwake) on a helicopter in flight. The instrument is a 1\\/54th-scale model helicopter that is mounted on a six-component dynamic force balance to measure the forces and moments that an airwake imposes onto the helicopter; it is therefore an 'Airwake Dynamometer'

Y. Wang; J. Curran; G. D. Padfield; I. Owen

2011-01-01

121

NASA Technical Reports Server (NTRS)

A linearized Euler solver for calculating unsteady flows in turbomachinery blade rows due to both incident gusts and blade motion is presented. Using the linearized Euler technique, one decomposes the flow into a mean (or steady) flow plus an unsteady, harmonically varying, small disturbance flow. Linear variable coefficient equations describe the small disturbance behavior of the flow, and are solved using a pseudo-time marching Lax-Wendroff scheme. For the blade motion problem, a harmonically deforming computational rid that conforms to the motion of vibrating blades eliminates large error producing mean flow gradient terms that would otherwise appear in the unsteady flow tangency boundary condition. The paper also presents a new, numerically exact, nonreflecting far-field boundary condition based on an eigenanalysis of the discretized equations. Computed flow solutions demonstrate the computational accuracy and efficiency of the present method. The solution of the linearized Euler equations requires one to two orders of magnitude less computer time than solution of the nonlinear Euler equations using traditional time-accurate time-marching techniques. In addition, the deformable grid significantly improves the accuracy of the solution.

Hall, Kenneth C.; Clark, William S.

1991-01-01

122

NASA Technical Reports Server (NTRS)

Spatial adaption procedures for the accurate and efficient solution of steady and unsteady inviscid flow problems are described. The adaption procedures were developed and implemented within a two-dimensional unstructured-grid upwind-type Euler code. These procedures involve mesh enrichment and mesh coarsening to either add points in high gradient regions of the flow or remove points where they are not needed, respectively, to produce solutions of high spatial accuracy at minimal computational cost. The paper gives a detailed description of the enrichment and coarsening procedures and presents comparisons with alternative results and experimental data to provide an assessment of the accuracy and efficiency of the capability. Steady and unsteady transonic results, obtained using spatial adaption for the NACA 0012 airfoil, are shown to be of high spatial accuracy, primarily in that the shock waves are very sharply captured. The results were obtained with a computational savings of a factor of approximately fifty-three for a steady case and as much as twenty-five for the unsteady cases.

Rausch, Russ D.; Yang, Henry T. Y.; Batina, John T.

1991-01-01

123

The double linearization concept is applied to a rotating annular cascade model operating at supersonic axial velocity. It is assumed that each blade vibrates with infinitesimal displacement amplitude under small but non-zero mean loading. Vibration modes normal and parallel to the blade chord are considered. Numerical results indicate that the mean loading effects play a crucial role on the aerodynamic

T. Hanada; M. Namba

1996-01-01

124

Large-amplitude forced oscillation data for an F-18 configuration are analyzed with two modeling methods: Fourier functional analysis to form the indicial integrals, and a generalized dynamic aerodynamic model for stability and control analysis. The indicial integral is first applied to calculate the pitch damping parameter for comparison with the conventional forced oscillation test. It is shown that the reduced frequency

Guofeng Lin

1997-01-01

125

Aerodynamic Characteristics of Hypersonic Flight Experiment (HYFLEX) Vehicle.

National Technical Information Service (NTIS)

The Hypersonic Flight Experiment (HYFLEX) vehicle successfully performed a hypersonic lifting flight. The vehicle was developed to establish the basic technologies necessary for an unmanned shuttle vehicle. In this report, the primary aerodynamic characte...

1997-01-01

126

NASA Technical Reports Server (NTRS)

The technique of implicit differentiation has been used in combination with linearized lifting-surface theory to derive analytical expressions for aerodynamic sensitivities (i.e., rates of change of lifting pressures with respect to general changes in aircraft geometry, including planform variations) for steady or oscillating planar or nonplanar lifting surfaces in subsonic, sonic, or supersonic flow. The geometric perturbation is defined in terms of a single variable, and the user need only provide simple expressions or similar means for defining the continuous or discontinuous global or local perturbation of interest. Example expressions are given for perturbations of the sweep, taper, and aspect ratio of a wing with trapezoidal semispan planform. In addition to direct computational use, the analytical method presented here should provide benchmark criteria for assessing the accuracy of aerodynamic sensitivities obtained by approximate methods such as finite geometry perturbation and differencing. The present process appears to be readily adaptable to more general surface-panel methods.

Yates, E. Carson, Jr.

1987-01-01

127

NASA Technical Reports Server (NTRS)

This guide describes the input data required for using ECAP2D (Euler Cascade Aeroelastic Program-Two Dimensional). ECAP2D can be used for steady or unsteady aerodynamic and aeroelastic analysis of two dimensional cascades. Euler equations are used to obtain aerodynamic forces. The structural dynamic equations are written for a rigid typical section undergoing pitching (torsion) and plunging (bending) motion. The solution methods include harmonic oscillation method, influence coefficient method, pulse response method, and time integration method. For harmonic oscillation method, example inputs and outputs are provided for pitching motion and plunging motion. For the rest of the methods, input and output for pitching motion only are given.

Reddy, T. S. R.

1995-01-01

128

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

129

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. 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. This topic in depth highlights some fun websites on the science of aerodynamics.The first site (1) provides some general information on aerodynamics. For those wanting a little more on the theory of aerodynamics, the University of Sydney has published this web textbook, Aerodynamics for Students (2). When people think of aerodynamics, they generally think of aviation and flight, which is explained on this site (3). Aerodynamics also has applications in sports, such as tennis, sailing and cycling. This website provides explanations for sports applications whether you are a beginner in the study of aerodynamics or an instructor (4). The next website reviews the aerodynamics of cycling and has a form that lets you Calculate the Aerodynamic Drag and Propulsive Power of a Bicyclist (5). The last site, AeroNet (6), is an interactive site designed to provide information about topics involved with aviation in a fun way for anyone casually interested in flight, someone thinking about aviation as a profession, or a student doing research for physics class.

130

NASA Technical Reports Server (NTRS)

A nonlinear least squares algorithm for aircraft parameter estimation from flight data was developed. The postulated model for the analysis represented longitudinal, short period motion of an aircraft. The corresponding aerodynamic model equations included indicial functions (unsteady terms) and conventional stability and control derivatives. The indicial functions were modeled as simple exponential functions. The estimation procedure was applied in five examples. Four of the examples used simulated and flight data from small amplitude maneuvers to the F-18 HARV and X-31A aircraft. In the fifth example a rapid, large amplitude maneuver of the X-31 drop model was analyzed. From data analysis of small amplitude maneuvers ft was found that the model with conventional stability and control derivatives was adequate. Also, parameter estimation from a rapid, large amplitude maneuver did not reveal any noticeable presence of unsteady aerodynamics.

Klein, Vladislav; Noderer, Keith D.

1996-01-01

131

NASA Technical Reports Server (NTRS)

A two dimensional cascade of harmonically oscillating airfoils was designed to model a near tip section from a rotor which was known to have experienced supersonic torsional flutter. This five bladed cascade had a solidity of 1.17 and a setting angle of 1.07 rad. Graphite epoxy airfoils were fabricated to achieve the realistically high reduced frequency level of 0.44. The cascade was tested over a range of static pressure ratios approximating the blade element operating conditions of the rotor along a constant speed line which penetrated the flutter boundary. The time-steady and time-unsteady flow field surrounding the center cascade airfoil were investigated. The effects of reduced solidity and decreased setting angle on the flow field were also evaluated.

Riffel, R. E.; Rothrock, M. D.

1980-01-01

132

NASA Technical Reports Server (NTRS)

This guide describes the input data required for using MSAP2D (Multi Stage Aeroelastic analysis Program - Two Dimensional) computer code. MSAP2D can be used for steady, unsteady aerodynamic, and aeroelastic (flutter and forced response) analysis of bladed disks arranged in multiple blade rows such as those found in compressors, turbines, counter rotating propellers or propfans. The code can also be run for single blade row. MSAP2D code is an extension of the original NPHASE code for multiblade row aerodynamic and aeroelastic analysis. Euler equations are used to obtain aerodynamic forces. The structural dynamic equations are written for a rigid typical section undergoing pitching (torsion) and plunging (bending) motion. The aeroelastic equations are solved in time domain. For single blade row analysis, frequency domain analysis is also provided to obtain unsteady aerodynamic coefficients required in an eigen analysis for flutter. In this manual, sample input and output are provided for a single blade row example, two blade row example with equal and unequal number of blades in the blade rows.

Reddy, T. S. R.; Srivastava, R.

1996-01-01

133

NASA Technical Reports Server (NTRS)

A quasi-steady analysis of the aeroelastic stability of the lateral (antisymmetric) modes of the 747/orbiter vehicle was accomplished. The interference effect of the orbiter wake on the 747 tail furnishes an aerodynamic undamping contribution to the elastic modes. Likewise, the upstream influence of the 747 tail and aft fuselage on the orbiter beaver-tail rail fairing also is undamping. Fortunately these undamping effects cannot overpower the large damping contribution of the 747 tail and the modes are damped for the configurations analyzed. However, significant interference effects of the orbiter on the 747 tail have been observed in the pitch plane. The high response of the 747 vertical tail in the orbiter wave was also considered. Wind tunnel data points to flapping of the OMS pod wakes as the source of the wake resonance phenomenon.

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

1976-01-01

134

Flexible Launch Vehicle Stability Analysis Using Steady and Unsteady Computational Fluid Dynamics

NASA Technical Reports Server (NTRS)

Launch vehicles frequently experience a reduced stability margin through the transonic Mach number range. This reduced stability margin can be caused by the aerodynamic undamping one of the lower-frequency flexible or rigid body modes. Analysis of the behavior of a flexible vehicle is routinely performed with quasi-steady aerodynamic line loads derived from steady rigid aerodynamics. However, a quasi-steady aeroelastic stability analysis can be unconservative at the critical Mach numbers, where experiment or unsteady computational aeroelastic analysis show a reduced or even negative aerodynamic damping.Amethod of enhancing the quasi-steady aeroelastic stability analysis of a launch vehicle with unsteady aerodynamics is developed that uses unsteady computational fluid dynamics to compute the response of selected lower-frequency modes. The response is contained in a time history of the vehicle line loads. A proper orthogonal decomposition of the unsteady aerodynamic line-load response is used to reduce the scale of data volume and system identification is used to derive the aerodynamic stiffness, damping, and mass matrices. The results are compared with the damping and frequency computed from unsteady computational aeroelasticity and from a quasi-steady analysis. The results show that incorporating unsteady aerodynamics in this way brings the enhanced quasi-steady aeroelastic stability analysis into close agreement with the unsteady computational aeroelastic results.

Bartels, Robert E.

2012-01-01

135

Flow visualization and unsteady aerodynamics in the flight of the hawkmoth, Manduca sexta

The aerodynamic mechanisms employed durng the flight of the hawkmoth, Manduca sexta, have been investigated through smoke visualization studies with tethered moths. Details of the flow around the wings and of the overall wake structure were recorded as stereophotographs and high-speed video sequences. The changes in flow which accompanied increases in flight speed from 0.4 to 5.7 m s-1 were analysed. The wake consists of an alternating series of horizontal and vertical vortex rings which are generated by successive down- and upstrokes, respectively. The downstroke produces significantly more lift than the upstroke due to a leading-edge vortex which is stabilized by a radia flow moving out towards the wingtip. The leading-edge vortex grew in size with increasing forward flight velocity. Such a phenomenon is proposed as a likely mechanism for lift enhancement in many insect groups. During supination, vorticity is shed from the leading edge as postulated in the 'flex' mechanism. This vorticity would enhance upstroke lift if it was recaptured diring subsequent translation, but it is not. Instead, the vorticity is left behind and the upstroke circulation builds up slowly. A small jet provides additional thrust as the trailing edges approach at the end of the upstroke. The stereophotographs also suggest that the bound circulation may not be reversed between half strokes at the fastest flight speeds.

Willmott, A. P.; Ellington, C. P.; Thomas, A. L. R.

1997-01-01

136

NASA Technical Reports Server (NTRS)

The aerodynamic characteristics of a Circulation Control Wing (CCW) airfoil have been numerically investigated, and comparisons with experimental data have been made. The configuration chosen was a supercritical airfoil with a 30 degree dual-radius CCW flap. Steady and pulsed jet calculations were performed. It was found that the use of steady jets, even at very small mass flow rates, yielded a lift coefficient that is comparable or superior to conventional high-lift systems. The attached flow over the flap also gave rise to lower drag coefficients, and high L/D ratios. Pulsed jets with a 50% duty cycle were also studied. It was found that they were effective in generating lift at lower reduced mass flow rates compared to a steady jet, provided the pulse frequency was sufficiently high. This benefit was attributable to the fact that the momentum coefficient of the pulsed jet, during the portions of the cycle when the jet was on, was typically twice as much as that of a steady jet.

Liu, Yi; Sankar, Lakshmi N.; Englar, Robert J.; Ahuja, Krishan K.

2003-01-01

137

Research on unsteady transonic flow theory

Contents: Unsteady Transonic Aerodynamics - An Aeronautics Challenge; Unsteady Local Linearization Solution for Pulsating Bodies at M sub infinity = 1; and Unsteady Local Linearization Solution for Pitching Bodies of Revolution at M sub infinity = 1: Stability Derivative Analysis.

S. S. Stahara; J. R. Spreiter

1976-01-01

138

Full-scale wind turbine rotor aerodynamics research

The United States Department of Energy and the National Renewable Energy Laboratory (NREL) are conducting research to improve wind turbine technology at the NREL National Wind Technology Center (NWTC). One program, the Combined Experiment, has focused on making measurements needed to understand aerodynamic and structural responses of horizontal-axis wind turbines (HAWT). A new phase of this program, the Unsteady Aerodynamics Experiment, will focus on quantifying unsteady aerodynamic phenomena prevalent in stall-controlled HAWTs. Optimally twisted blades and innovative instrumentation and data acquisition systems will be used in these tests. Data can now be acquired and viewed interactively during turbine operations. This paper describes the NREL Unsteady Aerodynamics Experiment and highlights planned future research activities.

Simms, D A; Butterfield, C P

1994-11-01

139

NASA Technical Reports Server (NTRS)

Tests were conducted a linear cascade of airfoils oscillating in pitch to measure the unsteady pressure response on selected blade along the leading edge plane of the cascade, over the chord of the center blade, and on the sidewall in the plane of the leading edge. The tests were conducted for all 96 combinations 2 mean camberline incidence angles 2 pitching amplitudes 3 reduced frequencies and 8 interblade phase angles. The pressure data were reduced to Fourier coefficient form for direct comparison, and were also processed to yield integrated loads and particularly, the aerodynamic damping coefficient. Data obtained during the test program, reproduced from the printout of the data reduction program are complied. A further description of the contents of this report is found in the text that follows.

Carta, F. O.

1981-01-01

140

Aerodynamic and Aerothermodynamic Layout of the Hypersonic Flight Experiment Shefex

NASA Astrophysics Data System (ADS)

The purpose of the SHarp Edge Flight EXperiment SHEFEX is the investigation of possible new shapes for future launcher or reentry vehicles [1]. The main focus is the improvement of common space vehicle shapes by application of facetted surfaces and sharp edges. The experiment will enable the time accurate investigation of the flow effects and their structural answer during the hypersonic flight from 90 km down to an altitude of 20 km. The project, being performed under responsibility of the German Aerospace Center (DLR) is scheduled to fly on top of a two-stage solid propellant sounding rocket for the first half of 2005. The paper contains a survey of the aerodynamic and aerothermodynamic layout of the experimental vehicle. The results are inputs for the definition of the structural layout, the TPS and the flight instrumentation as well as for the preparation of the flight test performed by the Mobile Rocket Base of DLR.

Eggers, Th.

2005-02-01

141

Interaction between reflected shock wave and unsteady jet in a shock tube experiment

Few shock tube experiments have been conducted for the integration of unsteady jets with propagating normal shock waves. Attention is presently given to the details of the shock structure behind the shock front during the interaction period. It is found that, when the unstable reflected shock wave of the hemispherical front recovers to the stable normal plane shock front, it

Yoshimi Ishii; Fumio Higashino; Akira Sakurai

1988-01-01

142

NASA Technical Reports Server (NTRS)

The design-point and off-design performance of an embedded 1.5-stage portion of a variable-speed power turbine (VSPT) was assessed using Reynolds-Averaged Navier-Stokes (RANS) analyses with mixing-planes and sector-periodic, unsteady RANS analyses. The VSPT provides one means by which to effect the nearly 50 percent main-rotor speed change required for the NASA Large Civil Tilt-Rotor (LCTR) application. The change in VSPT shaft-speed during the LCTR mission results in blade-row incidence angle changes of as high as 55 . Negative incidence levels of this magnitude at takeoff operation give rise to a vortical flow structure in the pressure-side cove of a high-turn rotor that transports low-momentum flow toward the casing endwall. The intent of the effort was to assess the impact of unsteadiness of blade-row interaction on the time-mean flow and, specifically, to identify potential departure from the predicted trend of efficiency with shaft-speed change of meanline and 3-D RANS/mixing-plane analyses used for design.

Welch, Gerard E.

2012-01-01

143

NASA Technical Reports Server (NTRS)

The first objective of the program is to introduce the meritorious counterflow methodology in microgravity in order to quantify the steady and unsteady characteristics of weakly-burning premixed and diffusion flames for a wide variety of conditions including elevated pressures. Subsequently, through detailed modeling and comparisons with the experimental data, to provide physical insight into the elementary mechanisms controlling the flame response. The configuration offers good control over the parameters of interest and can be modelled closely. The knowledge which will be gained from the counterflow flames will be subsequently used to analyze near-limit phenomena related to other configurations by conducting detailed numerical simulations including multidimensional ones. Among the problems to be analyzed are the downward and upward propagation of near-limit flames in tubes and phenomena observed in spherical and cylindrical geometries.

Egolfopoulos, Fokion N.

1995-01-01

144

NASA Astrophysics Data System (ADS)

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

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

2009-11-01

145

Modeling of Unsteady Three-dimensional Flows in Multistage Machines

NASA Technical Reports Server (NTRS)

Despite many years of development, the accurate and reliable prediction of unsteady aerodynamic forces acting on turbomachinery blades remains less than satisfactory, especially when viewed next to the great success investigators have had in predicting steady flows. Hall and Silkowski (1997) have proposed that one of the main reasons for the discrepancy between theory and experiment and/or industrial experience is that many of the current unsteady aerodynamic theories model a single blade row in an infinitely long duct, ignoring potentially important multistage effects. However, unsteady flows are made up of acoustic, vortical, and entropic waves. These waves provide a mechanism for the rotors and stators of multistage machines to communicate with one another. In other words, wave behavior makes unsteady flows fundamentally a multistage (and three-dimensional) phenomenon. In this research program, we have has as goals (1) the development of computationally efficient computer models of the unsteady aerodynamic response of blade rows embedded in a multistage machine (these models will ultimately be capable of analyzing three-dimensional viscous transonic flows), and (2) the use of these computer codes to study a number of important multistage phenomena.

Hall, Kenneth C.; Pratt, Edmund T., Jr.; Kurkov, Anatole (Technical Monitor)

2003-01-01

146

Unsteady separation experiments on 2-D airfoils, 3-D wings, and model helicopter rotors

NASA Technical Reports Server (NTRS)

Information on unsteady separation and dynamic stall is being obtained from two experimental programs that have been underway at United Technologies Research Center since 1984. The first program is designed to obtain detailed surface pressure and boundary layer condition information during high amplitude pitching oscillations of a large (17.3 in. chord) model wing in a wind tunnel. The second program involves the construction and testing of a pressure-instrumented model helicopter rotor. This presentation describes some of the results of these experiments, and in particular compares the detailed dynamic stall inception information obtained from the oscillating wing with the unsteady separation and reverse flow results measured on the retreating blade side of the model rotor during wind tunnel testing.

Lorber, Peter F.; Carta, Franklin O.

1992-01-01

147

Unsteady separation process and vorticity balance on unsteady airfoils

NASA Technical Reports Server (NTRS)

Low momentum fluid erupts at the unsteady separation region and forms a local shear layer at the viscous-inviscid interface. At the shear layer, the vorticity lumps into a vortex and protrudes into the inviscid region. This process initiates the separation process. The response of airfoils in unsteady free stream was investigated based on this vortex generation and convection concept. This approach enabled us to understand the complicated unsteady aerodynamics from a fundamental point of view.

Ho, Chih-Ming; Gursul, Ismet; Shih, Chiang; Lin, Hank

1992-01-01

148

Some unsteady separation problems for slender bodies

NASA Technical Reports Server (NTRS)

The unsteady Kutta-Joukowski condition, dynamic stall on oscillating airfoils, and unsteady shock wave-boundary layer interaction are discussed. Emphasis is placed on developing reliable prediction techniques and suppression of unsteady separation on oscillating control surfaces, wings, and rotating blades to improve aerodynamic stability.

Mccroskey, W. J.

1978-01-01

149

The measured hydraulic data collected in the Flood Plain Simulation Facility located at the Gulf Coast Hydroscience Center, near Bay St. Louis, Miss., are summarized for a series of experiments designed to study steady and unsteady flow over uniform grass roughness. All experiments were conducted during the 1973 and 1974 test seasons. Tables of measured ground-surface elevations, water-surface elevations, and point velocities are included for all experiments. A total of 19 steady flow experiments and 7 unsteady flow experiments for varying grass heights are included. The tabulated point velocities and water-surface elevations for the unsteady flow experiments were selected to represent the general changes in the flow variables as the flood wave passed through the facility but do not include all collected data. However, all data that were collected have been stored on computer disk storage and may be retrieved using the listing programs and memory locations. (Woodard-USGS)

Collins, Dannie L.; Flynn, Kathleen M.

1978-01-01

150

Aerodynamics and performance testing of the VAWT

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

Klimas, P.C.

1981-01-01

151

TIMEINTEGRATION METHODS IN COMPUTATIONAL AERODYNAMICS

' $ TIMEÂINTEGRATION METHODS IN COMPUTATIONAL AERODYNAMICS Antony Jameson Department of Aeronautics methods for unsteady problems 4. Conclusions & % #12;' $ Some Examples of Aerodynamic Calculations flow & % #12;' $ Aerodynamic Flow computations AIRPLANE DENSITY from 0.6250 to 1.1000 AIRPLANE CP from

Stanford University

152

Vortical flow management for improved configuration aerodynamics: Recent experiences

NASA Technical Reports Server (NTRS)

Recent progress in vortex-control applications for alleviating the adverse consequences of three dimensional separation and vortical interactions on slender body/swept wing configurations is reported. Examples include helical separation trip to alleviate the side force due to forebody vortex asymmetry; hinged strakes to avoid vortex breakdown effects; compartmentation of swept leading edge separation to delay the pitch-up instability; under wing vortex trip and vortex trip and vortex flaps for drag reduction at high lift; and an apex-flap trimmer to fully utilize the lift capability of trailing-edge flaps for take off and landing of delta wings. Experimental results on generic wind-tunnel models are presented to illustrate the vortex-management concepts involved and to indicate their potential for enhancing the subsonic aerodynamics of supersonic-cruise type vehicles.

Rao, D. M.

1983-01-01

153

INTRODUCTION Volant insects employ a variety of unsteady fluid-mechanic

4299 INTRODUCTION Volant insects employ a variety of unsteady fluid-mechanic phenomena to remain understanding of these phenomena has been significantly improved by studies exploring the flow field over insect models (for reviews, see Sane, 2003; Wang, 2005). Nearly all experiments on insect flight aerodynamics

Combes, Stacey A.

154

This report summarizes and makes available to other investigators the measured hydraulic data collected during a series of experiments designed to study the effect of patterned bed roughness on steady and unsteady open-channel flow. The patterned effect of the roughness was obtained by clear-cut mowing of designated areas of an otherwise fairly dense coverage of coastal Bermuda grass approximately 250 mm high. All experiments were conducted in the Flood Plain Simulation Facility during the period of October 7 through December 12, 1974. Data from 18 steady flow experiments and 10 unsteady flow experiments are summarized. Measured data included are ground-surface elevations, grass heights and densities, water-surface elevations and point velocities for all experiments. Additional tables of water-surface elevations and measured point velocities are included for the clear-cut areas for most experiments. One complete set of average water-surface elevations and one complete set of measured point velocities are tabulated for each steady flow experiment. Time series data, on a 2-minute time interval, are tabulated for both water-surface elevations and point velocities for each unsteady flow experiment. All data collected, including individual records of water-surface elevations for the steady flow experiments, have been stored on computer disk storage and can be retrieved using the computer programs listed in the attachment to this report. (Kosco-USGS)

Collins, Dannie L.; Flynn, Kathleen M.

1979-01-01

155

Journal of Wind Engineering and Industrial Aerodynamics 89 (2001) 13351350

Journal of Wind Engineering and Industrial Aerodynamics 89 (2001) 1335Â1350 Nonlinear response. The nonlinear unsteady aerodynamic forces are modeled based on static force coefficients, flutter derivatives incorporates frequency dependent parameters of unsteady aerodynamic forces by utilizing a rational function

Chen, Xinzhong

156

NASA Technical Reports Server (NTRS)

Computer data are provided for tests conducted on a linear cascade of airfoils oscillating in pitch to measure the unsteady pressure response on selected blades along the leading edge plane of the cascade, over the chord of the center blade, and on the sidewall in the plane of the leading edge.

Carta, F. O.

1981-01-01

157

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

158

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

159

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

NASA Astrophysics Data System (ADS)

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

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

2010-06-01

160

The Modern Design of Experiments for Configuration Aerodynamics: A Case Study

NASA Technical Reports Server (NTRS)

The effects of slowly varying and persisting covariate effects on the accuracy and precision of experimental result is reviewed, as is the rationale for run-order randomization as a quality assurance tactic employed in the Modern Design of Experiments (MDOE) to defend against such effects. Considerable analytical complexity is introduced by restrictions on randomization in configuration aerodynamics tests because they involve hard-to-change configuration variables that cannot be randomized conveniently. Tradeoffs are examined between quality and productivity associated with varying degrees of rigor in accounting for such randomization restrictions. Certain characteristics of a configuration aerodynamics test are considered that may justify a relaxed accounting for randomization restrictions to achieve a significant reduction in analytical complexity with a comparably negligible adverse impact on the validity of the experimental results.

DeLoach, Richard

2006-01-01

161

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

162

Aerodynamic Database Development for the Hyper-X Airframe Integrated Scramjet Propulsion Experiments

NASA Technical Reports Server (NTRS)

This paper provides an overview of the activities associated with the aerodynamic database which is being developed in support of NASA's Hyper-X scramjet flight experiments. Three flight tests are planned as part of the Hyper-X program. Each will utilize a small, nonrecoverable research vehicle with an airframe integrated scramjet propulsion engine. The research vehicles will be individually rocket boosted to the scramjet engine test points at Mach 7 and Mach 10. The research vehicles will then separate from the first stage booster vehicle and the scramjet engine test will be conducted prior to the terminal decent phase of the flight. An overview is provided of the activities associated with the development of the Hyper-X aerodynamic database, including wind tunnel test activities and parallel CFD analysis efforts for all phases of the Hyper-X flight tests. A brief summary of the Hyper-X research vehicle aerodynamic characteristics is provided, including the direct and indirect effects of the airframe integrated scramjet propulsion system operation on the basic airframe stability and control characteristics. Brief comments on the planned post flight data analysis efforts are also included.

Engelund, Walter C.; Holland, Scott D.; Cockrell, Charles E., Jr.; Bittner, Robert D.

2000-01-01

163

NASA Technical Reports Server (NTRS)

A theoretical analysis and computer program was developed for the prediction of unsteady lifting surface loadings caused by motions of leading edge and trailing edge control surfaces having sealed gaps. The final form of the downwash integral equation was formulated by isolating the singularities from the nonsingular terms and using a preferred solution process to remove and evaluate the downwash discontinuities in a systematic manner. Comparisons of theoretical and experimental pressure data are made for several control surface configurations. The comparisons indicate that reasonably accurate theoretical pressure distributions and generalized forces may be obtained for a wide variety of control surface configurations. Spanwise symmetry or antisymmetry of motion, and up to six control surfaces on each half span can be accommodated.

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

1975-01-01

164

Numerical experiments using high-resolution schemes for unsteady, inviscid, compressible flows

The performance of seven high-resolution schemes is investigated in various unsteady, inviscid, compressible flows. We employ the Roe, HLL (Harten, Lax and van Leer), and HLLC (Toro et al.) Riemann solvers, two variants of the van Leer and Steger–Warming flux vector splitting (FVS) schemes, Rusanov's scheme, and a hybrid total variation diminishing (TVD) scheme that combines a high-order Riemann solver

A. Bagabir; D. Drikakis

2004-01-01

165

SHEFEX II - Aerodynamic Re-Entry Controlled Sharp Edge Flight Experiment

NASA Astrophysics Data System (ADS)

In this paper the basic goals and architecture of the SHEFEX II mission is presented. Also launched by a two staged sounding rocket system SHEFEX II is a consequent next step in technology test and demonstration. Considering all experience and collected flight data obtained during the SHEFEX I Mission, the test vehicle has been re-designed and extended by an active control system, which allows active aerodynamic control during the re-entry phase. Thus, ceramic based aerodynamic control elements like rudders, ailerons and flaps, mechanical actuators and an automatic electronic control unit has been implemented. Special focus is taken on improved GNC Elements. In addition, some other experiments including an actively cooled thermal protection element, advanced sensor equipment, high temperature antenna inserts etc. are part of the SHEFEX II experimental payload. A final 2 stage configuration has been selected considering Brazilian solid rocket boosters derived from the S 40 family. During the experiment phase a maximum entry velocity of Mach around 10 is expected for 50 seconds. Considering these flight conditions, the heat loads are not representative for a RLV re-entry, however, it allows to investigate the principal behaviour of such a facetted ceramic TPS, a sharp leading edge at the canards and fins and all associated gas flow effects and their structural response.

Longo, J. M. A.; Turner, J.; Weihs, H.

2009-01-01

166

Unsteady Transonic Fluid - Structure - Interaction at the BAC 3-11 High Aspect Ratio Swept Wing

\\u000a A comprehensive analysis of experimental results from several wind tunnel test campaigns is presented. The experiments were\\u000a conducted in the subproject B6 of the Collaborative Research Center SFB 401. The main focus of this research is the interaction\\u000a of unsteady aerodynamic phenomena in transonic flow over a supercritical BAC 3-11\\/RES\\/30\\/21 high aspect ratio swept wing configuration\\u000a in the context of

P. C. Steimle; W. Schröder; M. Klaas

167

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

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

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

1995-10-01

168

Lattice of plates in an unsteady supersonic flow

The supersonic unsteady flow of a gas past a lattice of thin, slightly curved profiles has been investigated in several studies. The paper [1] is devoted to an evaluation of the effect of wind tunnel walls on the unsteady aerodynamic characteristics of a profile, and [2] investigates the effects of the boundaries of a free jet. These cases are equivalent

D. N. Gorelov

1966-01-01

169

International collaborative research in wind turbine rotor aerodynamics

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

D. A. Simms; C. P. Butterfield

1993-01-01

170

Unsteady transonic flow in cascades

NASA Technical Reports Server (NTRS)

There is a need for methods to predict the unsteady air loads associated with flutter of turbomachinery blading at transonic speeds. The results of such an analysis in which the steady relative flow approaching a cascade of thin airfoils is assumed to be transonic, irrotational, and isentropic is presented. The blades in the cascade are allowed to undergo a small amplitude harmonic oscillation which generates a small unsteady flow superimposed on the existing steady flow. The blades are assumed to oscillate with a prescribed motion of constant amplitude and interblade phase angle. The equations of motion are obtained by linearizing about a uniform flow the inviscid nonheat conducting continuity and momentum equations. The resulting equations are solved by employing the Weiner Hopf technique. The solution yields the unsteady aerodynamic forces acting on the cascade at Mach number equal to 1. Making use of an unsteady transonic similarity law, these results are compared with the results obtained from linear unsteady subsonic and supersonic cascade theories. A parametric study is conducted to find the effects of reduced frequency, solidity, stagger angle, and position of pitching axis on the flutter.

Surampudi, S. P.; Adamczyk, J. J.

1984-01-01

171

Aerodynamic detuning analysis of an unstalled supersonic turbofan cascade

NASA Technical Reports Server (NTRS)

An approach to passive flutter control is aerodynamic detuning, defined as designed passage-to-passage differences in the unsteady aerodynamic flow field of a rotor blade row. Thus, aerodynamic detuning directly affects the fundamental driving mechanism for flutter. A model to demonstrate the enhanced supersonic aeroelastic stability associated with aerodynamic detuning is developed. The stability of an aerodynamically detuned cascade operating in a supersonic inlet flow field with a subsonic leading edge locus is analyzed, with the aerodynamic detuning accomplished by means of nonuniform circumferential spacing of adjacent rotor blades. The unsteady aerodynamic forces and moments on the blading are defined in terms of influence coefficients in a manner that permits the stability of both a conventional uniformally spaced rotor configuration as well as the detuned nonuniform circumferentially spaced rotor to be determined. With Verdon's uniformly spaced Cascade B as a baseline, this analysis is then utilized to demonstrate the potential enhanced aeroelastic stability associated with this particular type of aerodynamic detuning.

Hoyniak, D.; Fleeter, S.

1985-01-01

172

Spectral content and spatial scales in unsteady rotationally augmented flow fields

NASA Astrophysics Data System (ADS)

Frequency spectra were computed from Cntime series acquired during the NASA Ames wind tunnel experiment, for rotationally augmented flow field conditions at zero yaw. Prominent peaks were present in the frequency spectra, corresponding to dominant aerodynamic shedding modes. These shedding modes were well correlated with flow field mean structure, and Strouhal number analyses furnished information regarding time varying flow field kinematics. Specifically, Strouhal number analyses implied that one of two distinct shedding modes was present, depending upon test section speed and local inflow angle. Information regarding these shedding kinematics will help provide understanding of the aerodynamics responsible for unsteady load production during rotationally augmented conditions. This, in turn, will aid in establishing a reliable physical basis for accurately predicting the time varying aerodynamic forces responsible for wind turbine fatigue loads and damage.

Schreck, Scott

2007-07-01

173

Low Speed Unsteady Aerodynamics Soumitra Banerjee*

and flying insects. In the research, a 2-D airfoil is subjected to pitch and plunge. Vortices are shed strength of vortices in the wake of the airfoil h0 = amplitude of plunge c = chord length dt = time step of attack and plunge wi = downwash velocity induced by vortices on airfoil Wi = downwash velocity induced

Patil, Mayuresh

174

Computational unsteady aerodynamics for lifting surfaces

NASA Technical Reports Server (NTRS)

Two dimensional problems are solved using numerical techniques. Navier-Stokes equations are studied both in the vorticity-stream function formulation which appears to be the optimal choice for two dimensional problems, using a storage approach, and in the velocity pressure formulation which minimizes the number of unknowns in three dimensional problems. Analysis shows that compact centered conservative second order schemes for the vorticity equation are the most robust for high Reynolds number flows. Serious difficulties remain in the choice of turbulent models, to keep reasonable CPU efficiency.

Edwards, John W.

1988-01-01

175

Algorithm and code development for unsteady three-dimensional Navier-Stokes equations

NASA Technical Reports Server (NTRS)

Aeroelastic tests require extensive cost and risk. An aeroelastic wind-tunnel experiment is an order of magnitude more expensive than a parallel experiment involving only aerodynamics. By complementing the wind-tunnel experiments with numerical simulations, the overall cost of the development of aircraft can be considerably reduced. In order to accurately compute aeroelastic phenomenon it is necessary to solve the unsteady Euler/Navier-Stokes equations simultaneously with the structural equations of motion. These equations accurately describe the flow phenomena for aeroelastic applications. At ARC a code, ENSAERO, is being developed for computing the unsteady aerodynamics and aeroelasticity of aircraft, and it solves the Euler/Navier-Stokes equations. The purpose of this cooperative agreement was to enhance ENSAERO in both algorithm and geometric capabilities. During the last five years, the algorithms of the code have been enhanced extensively by using high-resolution upwind algorithms and efficient implicit solvers. The zonal capability of the code has been extended from a one-to-one grid interface to a mismatching unsteady zonal interface. The geometric capability of the code has been extended from a single oscillating wing case to a full-span wing-body configuration with oscillating control surfaces. Each time a new capability was added, a proper validation case was simulated, and the capability of the code was demonstrated.

Obayashi, Shigeru

1994-01-01

176

NASA Technical Reports Server (NTRS)

Unsteady transonic flow calculations for aerodynamically interfering airfoil configurations are performed as a first step toward solving the three dimensional canard wing interaction problem. These calculations are performed by extending the XTRAN2L two dimensional unsteady transonic small disturbance code to include an additional airfoil. Unsteady transonic forces due to plunge and pitch motions of a two dimensional canard and wing are presented. Results for a variety of canard wing separation distances reveal the effects of aerodynamic interference on unsteady transonic airloads. Aeroelastic analyses employing these unsteady airloads demonstrate the effects of aerodynamic interference on aeroelastic stability and flutter. For the configurations studied, increases in wing flutter speed result with the inclusion of the aerodynamically interfering canard.

Batina, J. T.

1985-01-01

177

Real-Time Unsteady Loads Measurements Using Hot-Film Sensors

NASA Technical Reports Server (NTRS)

Several flight-critical aerodynamic problems such as buffet, flutter, stall, and wing rock are strongly affected or caused by abrupt changes in unsteady aerodynamic loads and moments. Advanced sensing and flow diagnostic techniques have made possible simultaneous identification and tracking, in realtime, of the critical surface, viscosity-related aerodynamic phenomena under both steady and unsteady flight conditions. The wind tunnel study reported here correlates surface hot-film measurements of leading edge stagnation point and separation point, with unsteady aerodynamic loads on a NACA 0015 airfoil. Lift predicted from the correlation model matches lift obtained from pressure sensors for an airfoil undergoing harmonic pitchup and pitchdown motions. An analytical model was developed that demonstrates expected stall trends for pitchup and pitchdown motions. This report demonstrates an ability to obtain unsteady aerodynamic loads in real time, which could lead to advances in air vehicle safety, performance, ride-quality, control, and health management.

Mangalam, Arun S.; Moes, Timothy R.

2004-01-01

178

Real-Time Unsteady Loads Measurements Using Hot-Film Sensors

NASA Technical Reports Server (NTRS)

Several flight-critical aerodynamic problems such as buffet, flutter, stall, and wing rock are strongly affected or caused by abrupt changes in unsteady aerodynamic loads and moments. Advanced sensing and flow diagnostic techniques have made possible simultaneous identification and tracking, in real-time, of the critical surface, viscosity-related aerodynamic phenomena under both steady and unsteady flight conditions. The wind tunnel study reported here correlates surface hot-film measurements of leading edge stagnation point and separation point, with unsteady aerodynamic loads on a NACA 0015 airfoil. Lift predicted from the correlation model matches lift obtained from pressure sensors for an airfoil undergoing harmonic pitchup and pitchdown motions. An analytical model was developed that demonstrates expected stall trends for pitchup and pitchdown motions. This report demonstrates an ability to obtain unsteady aerodynamic loads in real-time, which could lead to advances in air vehicle safety, performance, ride-quality, control, and health management.

Mangalam, Arun S.; Moes, Timothy R.

2004-01-01

179

We study the chaotic motion of a small rigid sphere, lighter than the fluid in a three-dimensional vortex of finite height. Based on the results of Eulerian and Lagrangian measurements, a sequence of models is set up. The time-independent model is a generalization of the Burgers vortex. In this case, there are two types of attractors for the particle: a fixed point on the vortex axis and a limit cycle around the vortex axis. Time dependence might combine these regular attractors into a single chaotic attractor, however its robustness is much weaker than what the experiments suggest. To construct an aperiodically time-dependent advection dynamics in a simple way, Gaussian noise is added to the particle velocity in the numerical simulation. With an appropriate choice of the noise properties, mimicking the effect of local turbulence, a reasonable agreement with the experimentally observed particle statistics is found. PMID:25122364

Vanyó, József; Vincze, Miklós; Jánosi, Imre M; Tél, Tamás

2014-07-01

180

Characterization of unsteady flow processes in a centrifugal compressor stage

Numerical experiments have been implemented to characterize the unsteady loading on the rotating impeller blades in a modem centrifugal compressor. These consist of unsteady Reynolds-averaged Navier Stokes simulations of ...

Gould, Kenneth A. (Kenneth Arthur)

2006-01-01

181

Distributed Aerodynamic Sensing and Processing Toolbox

NASA Technical Reports Server (NTRS)

A Distributed Aerodynamic Sensing and Processing (DASP) toolbox was designed and fabricated for flight test applications with an Aerostructures Test Wing (ATW) mounted under the fuselage of an F-15B on the Flight Test Fixture (FTF). DASP monitors and processes the aerodynamics with the structural dynamics using nonintrusive, surface-mounted, hot-film sensing. This aerodynamic measurement tool benefits programs devoted to static/dynamic load alleviation, body freedom flutter suppression, buffet control, improvement of aerodynamic efficiency through cruise control, supersonic wave drag reduction through shock control, etc. This DASP toolbox measures local and global unsteady aerodynamic load distribution with distributed sensing. It determines correlation between aerodynamic observables (aero forces) and structural dynamics, and allows control authority increase through aeroelastic shaping and active flow control. It offers improvements in flutter suppression and, in particular, body freedom flutter suppression, as well as aerodynamic performance of wings for increased range/endurance of manned/ unmanned flight vehicles. Other improvements include inlet performance with closed-loop active flow control, and development and validation of advanced analytical and computational tools for unsteady aerodynamics.

Brenner, Martin; Jutte, Christine; Mangalam, Arun

2011-01-01

182

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

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

Chang, I C

1981-03-01

183

NASA Technical Reports Server (NTRS)

A flight experiment was conducted to evaluate a pressure measurement system which uses pneumatic tubing and remotely located electronically scanned pressure transducer modules for in-flight unsteady aerodynamic studies. A parametric study of tubing length and diameter on the attenuation and lag of the measured signals was conducted. The hardware was found to operate satisfactorily at rates of up to 500 samples/sec per port in flight. The signal attenuation and lag due to tubing were shown to increase with tubing length, decrease with tubing diameter, and increase with altitude over the ranges tested. Measurable signal levels were obtained for even the longest tubing length tested, 4 ft, at frequencies up to 100 Hz. This instrumentation system approach provides a practical means of conducting detailed unsteady pressure surveys in flight.

Curry, Robert E.; Gilyard, Glenn B.

1989-01-01

184

Compensations during Unsteady Locomotion.

Locomotion in a complex environment is often not steady, but the mechanisms used by animals to power and control unsteady locomotion (stability and maneuverability) are not well understood. We use behavioral, morphological, and impulsive perturbations to determine the compensations used during unsteady locomotion. At the level both of the whole-body and of joints, quasi-stiffness models are useful for describing adjustments to the functioning of legs and joints during maneuvers. However, alterations to the mechanics of legs and joints often are distinct for different phases of the step cycle or for specific joints. For example, negotiating steps involves independent changes of leg stiffness during compression and thrust phases of stance. Unsteady locomotion also involves parameters that are not part of the simplest reduced-parameter models of locomotion (e.g., the spring-loaded inverted pendulum) such as moments of the hip joint. Extensive coupling among translational and rotational parameters must be taken into account to stabilize locomotion or maneuver. For example, maneuvers with morphological perturbations (increased rotational inertial turns) involve changes to several aspects of movement, including the initial conditions of rotation and ground-reaction forces. Coupled changes to several parameters may be employed to control maneuvers on a trial-by-trial basis. Compensating for increased rotational inertia of the body during turns is facilitated by the opposing effects of several mechanical and behavioral parameters. However, the specific rules used by animals to control translation and rotation of the body to maintain stability or maneuver have not been fully characterized. We initiated direct-perturbation experiments to investigate the strategies used by humans to maintain stability following center-of-mass (COM) perturbations. When walking, humans showed more resistance to medio-lateral perturbations (lower COM displacement). However, when running, humans could recover from the point of maximum COM displacement faster than when walking. Consequently, the total time necessary for recovery was not significantly different between walking and running. Future experiments will determine the mechanisms used for compensations during unsteady locomotion at the behavioral, joint, and muscle levels. Using reduced-parameter models will allow common experimental and analytical frameworks for the study of both stability and maneuverability and the determination of general control strategies for unsteady locomotion. PMID:24948138

Qiao, Mu; Jindrich, Devin L

2014-12-01

185

Numerical calculations of two dimensional, unsteady transonic flows with circulation

NASA Technical Reports Server (NTRS)

The feasibility of obtaining two-dimensional, unsteady transonic aerodynamic data by numerically integrating the Euler equations is investigated. An explicit, third-order-accurate, noncentered, finite-difference scheme is used to compute unsteady flows about airfoils. Solutions for lifting and nonlifting airfoils are presented and compared with subsonic linear theory. The applicability and efficiency of the numerical indicial function method are outlined. Numerically computed subsonic and transonic oscillatory aerodynamic coefficients are presented and compared with those obtained from subsonic linear theory and transonic wind-tunnel data.

Beam, R. M.; Warming, R. F.

1974-01-01

186

Research on unsteady transonic flow theory

NASA Technical Reports Server (NTRS)

A two-dimensional theory is considered for the unsteady flow disturbances caused by aeroelastic deformations of a thick wing at high subsonic freestream Mach numbers, having a single, internally embedded supercritical (locally supersonic) steady flow region adjacent to the low pressure side of the wing. The theory develops a matrix of unsteady aerodynamic influence coefficients (AICs) suitable as a strip theory for aeroelastic analysis of large aspect ratio thick wings of moderate sweep, typical of a wide class of current and future aircraft. The theory derives the linearized unsteady flow solutions separately for both the subcritical and supercritical regions. These solutions are coupled together to give the requisite (wing pressure-downwash) AICs by the intermediate step of defining flow disturbances on the sonic line, and at the shock wave; these intermediate quantities are then algebraically eliminated by expressing them in terms of the wing surface downwash.

Revell, J. D.

1973-01-01

187

NASA Astrophysics Data System (ADS)

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

Mettler, B. F.

2010-09-01

188

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

Unsteady separated flow is one of research frontiers in current aerodynamic. Great accomplishments have been acquired; however, most studies are on single body in a stream, such as studies on unsteady separated flows over airfoils. There are typical cases in the nature and engineering applications, in which several interacting bodies with relative motions are within the same flow field. These

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

2005-01-01

189

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

NASA Astrophysics Data System (ADS)

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

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

190

Fluid mechanics of dynamic stall. I - Unsteady flow concepts

NASA Technical Reports Server (NTRS)

Advanced military aircraft 'supermaneuverability' requirements entail the sustained operation of airfoils at stalled flow conditions. The present work addresses the effects of separated flow on vehicle dynamics; an analytic method is presented which employs static experimental data to predict the separated flow effect on incompressible unsteady aerodynamics. The key parameters in the analytic relationship between steady and nonsteady aerodynamics are the time-lag before a change of flow conditions can affect the separation-induced aerodynamic loads, the accelerated flow effect, and the moving wall effect.

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

1988-01-01

191

Comparison of aerodynamic theory and experiment for jet-flap wings

NASA Technical Reports Server (NTRS)

Aerodynamic theory predictions made for a jet flapped wing were compared with experimental data obtained in a fairly extensive series of tests in the Langley V/STOL tunnel. The tests were made on a straight, rectangular wing and investigated two types of jet flap concepts: a pure jet flap with high jet deflection and a wing with blowing at the knee of a plain trailing edge flap. The tests investigated full and partial span blowing for wing aspect ratios of 8.0 and 5.5 and momentum coefficients from 0 to about 4. The total lift, drag, and pitching moment coefficients predicted by the theory were in excellent agreement with experimental values for the pure jet flap, even with the high jet deflection. The pressure coefficients on the wing, and hence the circulation lift coefficients, were underpredicted, however, because of the linearizing assumptions of the planar theory. The lift, drag, and pitching moment coefficients, as well as pressure coefficients, were underpredicted for the wing with blowing over the flap because of the failure of the theory to account for the interaction effect of the high velocity jet passing over the flap.

Gainer, T. G.; Yip, L. P.; Vogler, R. P.

1976-01-01

192

NASA Technical Reports Server (NTRS)

The vibration and buckling characteristics of a series of 140 deg ring-supported conical shells have been investigated experimentally and analytically. Experimental results were obtained from 14 conical shells, each attached to a solid nose cap at the small end. The large (base) end was either free or attached to a solid ring of rectangular cross section. The size of the solid base rings of rectangular cross section was systematically varied to provide a wide range of edge restraint. Shell buckling was induced by aerodynamic loading at a Mach number of 3; the vibration data were obtained prior to the wind tunnel tests. The experimental vibration data indicated that the size of the base rings had a pronounced effect on the magnitude of the frequencies and on the frequency spectrum. For vibration modes having less than two circumferential waves, the frequencies descreased with increasing ring size; whereas, for modes with several circumferential waves, the frequencies initially increased rapidly with ring size and then became relatively insensitive to further increases in ring size. This latter behavior was similar to the trend exhibited by the variation of buckling pressure with ring size. The experimental results were in excellent qualitative agreement with theoretical results and indicated that current shell-of-revolution analyses are adequate for predicting the vibration and buckling behavior of ring-supported shells, at least for the simple isotropic shells considered in this investigation.

Miserentino, R.; Dixon, S. C.

1972-01-01

193

Direct use of linear time-domain aerodynamics in aeroservoelastic analysis: Aerodynamic model

NASA Technical Reports Server (NTRS)

The work presented here is the first part of a continuing effort to expand existing capabilities in aeroelasticity by developing the methodology which is necessary to utilize unsteady time-domain aerodynamics directly in aeroservoelastic design and analysis. The ultimate objective is to define a fully integrated state-space model of an aeroelastic vehicle's aerodynamics, structure and controls which may be used to efficiently determine the vehicle's aeroservoelastic stability. Here, the current status of developing a state-space model for linear or near-linear time-domain indicial aerodynamic forces is presented.

Woods, J. A.; Gilbert, Michael G.

1990-01-01

194

Unsteady transonic flow calculations for realistic aircraft configurations

NASA Technical Reports Server (NTRS)

A transonic unsteady aerodynamic and aeroelasticity code has been developed for application to realistic aircraft configurations. The new code is called CAP-TSD which is an acronym for Computational Aeroelasticity Program - Transonic Small Disturbance. The CAP-TSD code uses a time-accurate approximate factorization (AF) algorithm for solution of the unsteady transonic small-disturbance equation. The AF algorithm is very efficient for solution of steady and unsteady transonic flow problems. It can provide accurate solutions in only several hundred time steps yielding a significant computational cost savings when compared to alternative methods. The new code can treat complete aircraft geometries with multiple lifting surfaces and bodies including canard, wing, tail, control surfaces, launchers, pylons, fuselage, stores, and nacelles. Applications are presented for a series of five configurations of increasing complexity to demonstrate the wide range of geometrical applicability of CAP-TSD. These results are in good agreement with available experimental steady and unsteady pressure data. Calculations for the General Dynamics one-ninth scale F-16C aircraft model are presented to demonstrate application to a realistic configuration. Unsteady results for the entire F-16C aircraft undergoing a rigid pitching motion illustrated the capability required to perform transonic unsteady aerodynamic and aeroelastic analyses for such configurations.

Batina, John T.; Seidel, David A.; Bland, Samuel R.; Bennett, Robert M.

1987-01-01

195

NASA Technical Reports Server (NTRS)

On August 5 , 2012, the Mars Science Laboratory (MSL) entry capsule successfully entered Mars' atmosphere and landed the Curiosity rover in Gale Crater. The capsule used a reaction control system (RCS) consisting of four pairs of hydrazine thrusters to fly a guided entry. The RCS provided bank control to fly along a flight path commanded by an onboard computer and also damped unwanted rates due to atmospheric disturbances and any dynamic instabilities of the capsule. A preliminary assessment of the MSL's flight data from entry showed that the capsule flew much as predicted. This paper will describe how the MSL aerodynamics team used engineering analyses, computational codes and wind tunnel testing in concert to develop the RCS system and certify it for flight. Over the course of MSL's development, the RCS configuration underwent a number of design iterations to accommodate mechanical constraints, aeroheating concerns and excessive aero/RCS interactions. A brief overview of the MSL RCS configuration design evolution is provided. Then, a brief description is presented of how the computational predictions of RCS jet interactions were validated. The primary work to certify that the RCS interactions were acceptable for flight was centered on validating computational predictions at hypersonic speeds. A comparison of computational fluid dynamics (CFD) predictions to wind tunnel force and moment data gathered in the NASA Langley 31-Inch Mach 10 Tunnel was the lynch pin to validating the CFD codes used to predict aero/RCS interactions. Using the CFD predictions and experimental data, an interaction model was developed for Monte Carlo analyses using 6-degree-of-freedom trajectory simulation. The interaction model used in the flight simulation is presented.

Schoenenberger, Mark; VanNorman, John; Rhode, Matthew; Paulson, John

2013-01-01

196

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.

197

NASA Technical Reports Server (NTRS)

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.

1985-01-01

198

Flow volumes are extended for use in unsteady (time-dependent) flows. The resulting unsteady flow volumes are the 3 dimensional analog of streamlines. There are few examples where methods other than particle tracing have been used to visualize time varying flows. Since particle paths can become convoluted in time there are additional considerations to be made when extending any visualization technique to unsteady flows. We will present some solutions to the problems which occur in subdivision, rendering, and system design. We will apply the unsteady flow volumes to a variety of field types including moving multi-zoned curvilinear grids.

Becker, B.G.; Lane, D.A.; Max, N.L.

1995-03-01

199

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

200

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

201

The nonuniform unsteady mixing process in the compressed high-temperature field generated by an unsteady jet of fuel gas is clarified, expanding on the study of Ishii et al. (1984). The results confirm the previously calculated values of the back of the apex of the hemispherical reflected shock wave. An unstable hemispherical shock wave reconverting to a stable normal shock wave

Yoshimi Ishii

1987-01-01

202

NASA Technical Reports Server (NTRS)

Research conducted at the Institute for Computer Applications in Science and Engineering in applied mathematics, numerical analysis, fluid mechanics including fluid dynamics, acoustics, and combustion, aerodynamics, and computer science during the period 1 Apr. 1992 - 30 Sep. 1992 is summarized.

1992-01-01

203

Assessment of the derivative-moment transformation method for unsteady-load estimation

NASA Astrophysics Data System (ADS)

It is often difficult, if not impossible, to measure the aerodynamic or hydrodynamic forces on a moving body. For this reason, a classical control-volume technique is typically applied to extract the unsteady forces. However, measuring the acceleration term within the volume of interest using particle image velocimetry (PIV) can be limited by optical access, reflections, as well as shadows. Therefore, in this study, an alternative approach, termed the derivative-moment transformation (DMT) method, is introduced and tested on a synthetic data set produced using numerical simulations. The test case involves the unsteady loading of a flat plate in a two-dimensional, laminar periodic gust. The results suggest that the DMT method can accurately predict the acceleration term so long as appropriate spatial and temporal resolutions are maintained. The major deficiency, which is more dominant for the direction of drag, was found to be the determination of pressure and unsteady terms in the wake. The effect of control-volume size was investigated, suggesting that larger domains work best by minimizing the associated error in the determination of the pressure field. When decreasing the control-volume size, wake vortices, which produce high gradients across the control surfaces, are found to substantially increase the level of error. On the other hand, it was shown that for large control volumes, and with realistic spatial resolution, the accuracy of the DMT method would also suffer. Therefore, a delicate compromise is required when selecting control-volume size in future experiments.

Mohebbian, Ali; Rival, David E.

2012-08-01

204

Design and Predictions for High-Altitude (Low Reynolds Number) Aerodynamic Flight Experiment

NASA Technical Reports Server (NTRS)

A sailplane being developed at NASA Dryden Flight Research Center will support a high-altitude flight experiment. The experiment will measure the performance parameters or an airfoil at high altitudes (70,000 - 100,000 ft), low Reynolds numbers (2 x 10(exp 5) - 7 x 10(exp 5)), and high subsonic Mach numbers (0.5 and 0.65). The airfoil section lift and drag are determined from pilot and static pressure measurements. The locations of the separation bubble, Tollmien-Schlichting boundary-layer instability frequencies, and vortex shedding are measured from a hot-film strip. The details of the planned flight experiment are presented as well as several predictions of the airfoil performance.

Greer, Donald; Harmory, Phil; Krake, Keith; Drela, Mark

2000-01-01

205

NASA Technical Reports Server (NTRS)

Building block experiments and companion numerical simulations intended to verify and guide turbulence modeling are described. A series of experiments and computations being used to enhance modeling development for the shock wave turbulent boundary layer interaction problem is emphasized. Results are given for transonic flow over a circular arc airfoil undergoing shock wave induced, boundary layer separation for supersonic flow along a tube wall undergoing normal shock wave induced, boundary layer separation. Experimental data which use the complete Navier-Stokes equations are discussed.

Marvin, J. G.

1976-01-01

206

NASA Technical Reports Server (NTRS)

The SOUSSA (steady, oscillatory, and unsteady subsonic and supersonic aerodynamics) program is the computational implementation of a general potential flow analysis (by the Green's function method) that can generate pressure distributions on complete aircraft having arbitrary shapes, motions and deformations. Some applications of the initial release version of this program to several wings in steady and oscillatory motion, including flutter are presented. The results are validated by comparisons with other calculations and experiments. Experiences in using the program as well as some recent improvements are described.

Yates, E. C., Jr.; Cunningham, H. J.; Desmarais, R. N.; Silva, W. A.; Drobenko, B.

1982-01-01

207

Basis Function Approximation of Transonic Aerodynamic Influence Coefficient Matrix

NASA Technical Reports Server (NTRS)

A technique for approximating the modal aerodynamic influence coefficients matrices by using basis functions has been developed and validated. An application of the resulting approximated modal aerodynamic influence coefficients matrix for a flutter analysis in transonic speed regime has been demonstrated. This methodology can be applied to the unsteady subsonic, transonic, and supersonic aerodynamics. The method requires the unsteady aerodynamics in frequency-domain. The flutter solution can be found by the classic methods, such as rational function approximation, k, p-k, p, root-locus et cetera. The unsteady aeroelastic analysis for design optimization using unsteady transonic aerodynamic approximation is being demonstrated using the ZAERO flutter solver (ZONA Technology Incorporated, Scottsdale, Arizona). The technique presented has been shown to offer consistent flutter speed prediction on an aerostructures test wing 2 configuration with negligible loss in precision in transonic speed regime. These results may have practical significance in the analysis of aircraft aeroelastic calculation and could lead to a more efficient design optimization cycle.

Li, Wesley W.; Pak, Chan-gi

2011-01-01

208

The aerodynamics of insect flight.

The flight of insects has fascinated physicists and biologists for more than a century. Yet, until recently, researchers were unable to rigorously quantify the complex wing motions of flapping insects or measure the forces and flows around their wings. However, recent developments in high-speed videography and tools for computational and mechanical modeling have allowed researchers to make rapid progress in advancing our understanding of insect flight. These mechanical and computational fluid dynamic models, combined with modern flow visualization techniques, have revealed that the fluid dynamic phenomena underlying flapping flight are different from those of non-flapping, 2-D wings on which most previous models were based. In particular, even at high angles of attack, a prominent leading edge vortex remains stably attached on the insect wing and does not shed into an unsteady wake, as would be expected from non-flapping 2-D wings. Its presence greatly enhances the forces generated by the wing, thus enabling insects to hover or maneuver. In addition, flight forces are further enhanced by other mechanisms acting during changes in angle of attack, especially at stroke reversal, the mutual interaction of the two wings at dorsal stroke reversal or wing-wake interactions following stroke reversal. This progress has enabled the development of simple analytical and empirical models that allow us to calculate the instantaneous forces on flapping insect wings more accurately than was previously possible. It also promises to foster new and exciting multi-disciplinary collaborations between physicists who seek to explain the phenomenology, biologists who seek to understand its relevance to insect physiology and evolution, and engineers who are inspired to build micro-robotic insects using these principles. This review covers the basic physical principles underlying flapping flight in insects, results of recent experiments concerning the aerodynamics of insect flight, as well as the different approaches used to model these phenomena. PMID:14581590

Sane, Sanjay P

2003-12-01

209

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

NASA Astrophysics Data System (ADS)

Recent years have witnessed a successful model of unsteady vortex lattice to predict the limit cycle oscillations of an airfoil section. The aerodynamic model is usually in the form of discrete time, and hence, is not convenient for the analysis of non-linear aeroelastic systems. In this paper, the aerodynamic model of unsteady vortex lattice is formulated in continuous time domain and expressed in a dimensionless form. The order of aerodynamic model is greatly reduced in terms of a few aerodynamic eigenmodes to describe the unsteady vortex. Meanwhile, a static correction is included in the modal reduction to take the effects of truncated higher aerodynamic modes into account. The accuracy of the reduced-order model of aerodynamics is compared with Theodorsen's model. Using the modified aerodynamic model, the aeroelastic analysis of a two-dimensional airfoil section with combined non-linearity of freeplay and cubic stiffening in pitch is made. The numerical results indicate that the modified aerodynamic model is capable of predicting the flow about airfoil accurately and detecting the complex non-linear aeroelastic behaviors.

Zhao, Y. H.; Hu, H. Y.

2004-09-01

210

Aerodynamic Measurements of a Gulfstream Aircraft Model With and Without Noise Reduction Concepts

NASA Technical Reports Server (NTRS)

Steady and unsteady aerodynamic measurements of a high-fidelity, semi-span 18% scale Gulfstream aircraft model are presented. The aerodynamic data were collected concurrently with acoustic measurements as part of a larger aeroacoustic study targeting airframe noise associated with main landing gear/flap components, gear-flap interaction noise, and the viability of related noise mitigation technologies. The aeroacoustic tests were conducted in the NASA Langley Research Center 14- by 22-Foot Subsonic Wind Tunnel with the facility in the acoustically treated open-wall (jet) mode. Most of the measurements were obtained with the model in landing configuration with the flap deflected at 39º and the main landing gear on and off. Data were acquired at Mach numbers of 0.16, 0.20, and 0.24. Global forces (lift and drag) and extensive steady and unsteady surface pressure measurements were obtained. Comparison of the present results with those acquired during a previous test shows a significant reduction in the lift experienced by the model. The underlying cause was traced to the likely presence of a much thicker boundary layer on the tunnel floor, which was acoustically treated for the present test. The steady and unsteady pressure fields on the flap, particularly in the regions of predominant noise sources such as the inboard and outboard tips, remained unaffected. It is shown that the changes in lift and drag coefficients for model configurations fitted with gear/flap noise abatement technologies fall within the repeatability of the baseline configuration. Therefore, the noise abatement technologies evaluated in this experiment have no detrimental impact on the aerodynamic performance of the aircraft model.

Neuhart, Dan H.; Hannon, Judith A.; Khorrami, Mehdi R.

2014-01-01

211

A Three-Dimensional Linearized Unsteady Euler Analysis for Turbomachinery Blade Rows

NASA Technical Reports Server (NTRS)

A three-dimensional, linearized, Euler analysis is being developed to provide an efficient unsteady aerodynamic analysis that can be used to predict the aeroelastic and aeroacoustic response characteristics of axial-flow turbomachinery blading. The field equations and boundary conditions needed to describe nonlinear and linearized inviscid unsteady flows through a blade row operating within a cylindrical annular duct are presented. In addition, a numerical model for linearized inviscid unsteady flow, which is based upon an existing nonlinear, implicit, wave-split, finite volume analysis, is described. These aerodynamic and numerical models have been implemented into an unsteady flow code, called LINFLUX. A preliminary version of the LINFLUX code is applied herein to selected, benchmark three-dimensional, subsonic, unsteady flows, to illustrate its current capabilities and to uncover existing problems and deficiencies. The numerical results indicate that good progress has been made toward developing a reliable and useful three-dimensional prediction capability. However, some problems, associated with the implementation of an unsteady displacement field and numerical errors near solid boundaries, still exist. Also, accurate far-field conditions must be incorporated into the FINFLUX analysis, so that this analysis can be applied to unsteady flows driven be external aerodynamic excitations.

Montgomery, Matthew D.; Verdon, Joseph M.

1996-01-01

212

Shock unsteadiness creation and propagation: experimental analysis

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

213

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

Jakub Wejchert; David R. Haumann

1991-01-01

214

Computational Sports Aerodynamics of a Moving Sphere: Simulating a Ping Pong Ball in Free Flight

, baseball, soccer ball, ping pong ball, golf ball and cricket ball is concerned with aerodynamics as muchComputational Sports Aerodynamics of a Moving Sphere: Simulating a Ping Pong Ball in Free Flight such as tennis, golf and ping pong balls tends to be very unsteady and viscous, with occasionally transitional

Jameson, Antony

215

WIND-TUNNEL STUDY ON AERODYNAMIC PERFORMANCE OF SMALL VERTICAL-AXIS WIND TURBINES

1 WIND-TUNNEL STUDY ON AERODYNAMIC PERFORMANCE OF SMALL VERTICAL-AXIS WIND TURBINES J. J. Miau*1 were carried out to study the aerodynamic performance of three vertical axis wind turbines (VAWTs. On the other hand, the characteristics of unsteady flow around the helical wind turbine were studied with a hot

Leu, Tzong-Shyng "Jeremy"

216

Aerodynamic and flowfield hysteresis of slender wing aircraft undergoing large-amplitude motions

NASA Technical Reports Server (NTRS)

The implication of maneuvers through large angles of incidence is discussed by examining the unsteady aerodynamic loads, surface pressures, vortical position, and breakdown on slender, flat plate delta wings. Two examples of large amplitude unsteady motions are presented. First, the unsteady characteristics of a 70 degree swept delta wing undergoing pitch oscillation from 0 to 60 degrees is examined. Data is presented that shows the relationship between vortex breakdown and the overshoot and undershoot of the aerodynamic loads and surface pressure distribution. The second example examines the leading edge vortical flow over an 80 degree swept wing undergoing a limit cycle roll oscillation commonly called wing rock.

Nelson, Robert C.; Arena, Andrew S., Jr.; Thompson, Scott A.

1991-01-01

217

NASA Technical Reports Server (NTRS)

Free-to-roll tests were conducted in water and wind tunnels in an effort to investigate the mechanisms of wing rock on a NASP-type vehicle. The configuration tested consisted of a highly-slender forebody and a 78 deg swept delta wing. In the water tunnel test, extensive flow visualization was performed and roll angle histories were obtained. In the wind tunnel test, the roll angle, forces and moments, and limited forebody and wing surface pressures were measured during the wing rock motion. A limit cycle oscillation was observed for angles of attack between 22 deg and 30 deg. In general, the experiments confirmed that the main flow phenomena responsible for the wing-body-tail wing rock are the interactions between the forebody and the wing vortices. The variation of roll acceleration (determined from the second derivative of the roll angle time history) with roll angle clearly slowed the energy balance necessary to sustain the limit cycle oscillation. Different means of suppressing wing rock by controlling the forebody vortices using small blowing jets were also explored. Steady blowing was found to be capable of suppressing wing rock, but significant vortex asymmetrices are created, causing the model to stop at a non-zero roll angle. On the other hand, alternating pulsed blowing on the left and right sides of the fore body was demonstrated to be a potentially effective means of suppressing wing rock and eliminating large asymmetric moments at high angles of attack.

Suarez, Carlos J.; Smith, Brooke C.; Kramer, Brian R.; Ng, T. Terry; Ong, Lih-Yenn; Malcolm, Gerald N.

1993-01-01

218

The External Aerodynamics of Canine Olfaction Gary S. Settles*

The External Aerodynamics of Canine Olfaction Gary S. Settles* , Douglas A. Kester** , Lori J Literature on the External Aerodynamics of Olfaction B. Precedent Literature on Aerodynamic Sampling Technology III. Canine Olfaction Experiments IV. The Design of an Aerodynamic Sniffer A. Background B

Settles, Gary S.

219

NASA Technical Reports Server (NTRS)

This paper discusses the capabilities of the Interaction of Structures, Aerodynamics, and Controls (ISAC) system of program modules. The major modeling, analysis, and data management components of ISAC are identified. Equations of motion are displayed for a Laplace-domain representation of the unsteady aerodynamic forces. Options for approximating a frequency-domain representation of unsteady aerodynamic forces with rational functions of the Laplace variable are shown. Linear time invariant state-space equations of motion that result are discussed. Model generation and analyses of stability and dynamic response characteristics are shown for an aeroelastic vehicle which illustrate some of the capabilities of ISAC as a modeling and analysis tool for aeroelastic applications.

Adams, William M., Jr.; Hoadley, Sherwood T.

1993-01-01

220

GENERATION OF AERODYNAMICS VIA PHYSICS-BASED VIRTUAL FLIGHT SIMULATIONS

A method to efficiently generate a complete aerodynamic description for projectile flight dynamic modeling is described. At the core of the method is an unsteady, time accurate computational fluid dynamics simulation that is tightly coupled to a rigid projectile flight dynamic simulation. This coupled multidisciplinary technique allows \\

J. Sahu; M. Costello

221

Basis Function Approximation of Transonic Aerodynamic Influence Coefficient Matrix

NASA Technical Reports Server (NTRS)

A technique for approximating the modal aerodynamic influence coefficients [AIC] matrices by using basis functions has been developed and validated. An application of the resulting approximated modal AIC matrix for a flutter analysis in transonic speed regime has been demonstrated. This methodology can be applied to the unsteady subsonic, transonic and supersonic aerodynamics. The method requires the unsteady aerodynamics in frequency-domain. The flutter solution can be found by the classic methods, such as rational function approximation, k, p-k, p, root-locus et cetera. The unsteady aeroelastic analysis for design optimization using unsteady transonic aerodynamic approximation is being demonstrated using the ZAERO(TradeMark) flutter solver (ZONA Technology Incorporated, Scottsdale, Arizona). The technique presented has been shown to offer consistent flutter speed prediction on an aerostructures test wing [ATW] 2 configuration with negligible loss in precision in transonic speed regime. These results may have practical significance in the analysis of aircraft aeroelastic calculation and could lead to a more efficient design optimization cycle

Li, Wesley Waisang; Pak, Chan-Gi

2010-01-01

222

Estimation of Aircraft Nonlinear Unsteady Parameters From Wind Tunnel Data

NASA Technical Reports Server (NTRS)

Aerodynamic equations were formulated for an aircraft in one-degree-of-freedom large amplitude motion about each of its body axes. The model formulation based on indicial functions separated the resulting aerodynamic forces and moments into static terms, purely rotary terms and unsteady terms. Model identification from experimental data combined stepwise regression and maximum likelihood estimation in a two-stage optimization algorithm that can identify the unsteady term and rotary term if necessary. The identification scheme was applied to oscillatory data in two examples. The model identified from experimental data fit the data well, however, some parameters were estimated with limited accuracy. The resulting model was a good predictor for oscillatory and ramp input data.

Klein, Vladislav; Murphy, Patrick C.

1998-01-01

223

Unsteady transonic flow calculations for interfering lifting surface configurations

NASA Technical Reports Server (NTRS)

Unsteady transonic flow calculations are presented for aerodynamically interfering lifting surface configurations. Calculations are performed by extending the XTRAN3S (Version 1.5) unsteady transonic small-disturbance code to allow the treatment of an additional lifting surface. The research was conducted as a first-step toward developing the capability to treat a complete flight vehicle. Grid generation procedures for swept tapered interfering lifting surface applications of XTRAN3S are described. Transonic calculations are presented for wing-tail and canard-wing configurations for several values of mean angle of attack. The effects of aerodynamic interference on transonic steady pressure distributions and steady and oscillatory spanwise lift distributions are demonstrated. Results due to wing, tail, or canard pitching motions are presented and discussed in detail.

Batina, J. T.

1985-01-01

224

Full potential unsteady computations including aeroelastic effects

NASA Technical Reports Server (NTRS)

A unified formulation is presented based on the full potential framework coupled with an appropriate structural model to compute steady and unsteady flows over rigid and flexible configurations across the Mach number range. The unsteady form of the full potential equation in conservation form is solved using an implicit scheme maintaining time accuracy through internal Newton iterations. A flux biasing procedure based on the unsteady sonic reference conditions is implemented to compute hyperbolic regions with moving sonic and shock surfaces. The wake behind a trailing edge is modeled using a mathematical cut across which the pressure is satisfied to be continuous by solving an appropriate vorticity convection equation. An aeroelastic model based on the generalized modal deflection approach interacts with the nonlinear aerodynamics and includes both static as well as dynamic structural analyses capability. Results are presented for rigid and flexible configurations at different Mach numbers ranging from subsonic to supersonic conditions. The dynamic response of a flexible wing below and above its flutter point is demonstrated.

Shankar, Vijaya; Ide, Hiroshi

1989-01-01

225

Simulation of self-induced unsteady motion in the near wake of a Joukowski airfoil

NASA Technical Reports Server (NTRS)

The unsteady Navier-Stokes analysis is shown to be capable of analyzing the massively separated, persistently unsteady flow in the post-stall regime of a Joukowski airfoil for an angle of attack as high as 53 degrees. The analysis has provided the detailed flow structure, showing the complex vortex interaction for this configuration. The aerodynamic coefficients for lift, drag, and moment were calculated. So far only the spatial structure of the vortex interaction was computed. It is now important to potentially use the large-scale vortex interactions, an additional energy source, to improve the aerodynamic performance.

Ghia, K. N.; Osswald, G. A.; Ghia, U.

1986-01-01

226

LIMIT CYCLE FLUTTER OF AIRFOILS IN STEADY AND UNSTEADY FLOWS

The limit cycle flutter of a two-dimensional wing with non-linear pitching stiffness is investigated. For modelling the aerodynamic forces of the wing steady linear and non-linear models as well as an unsteady model were used. The flutter speed was calculated using the harmonic balance method and by predicting Hopf bifurcation. Analytical solutions based on the centre manifold theory and normal

P. Shahrzad; M. Mahzoon

2002-01-01

227

Recent German Research on Periodical Unsteady Flow in Turbomachinery

The main source of flow unsteadiness in turbomachinery is the aerodynamical interaction of the rotor and stator blade rows.\\u000a The blades and vanes, moving relatively to each other, interact because of the viscous wakes and the potential effects of\\u000a the blades. In addition, the wakes and potential effects superimpose with other flow patterns, for instance the tip clearance\\u000a vortices and

Ronald Mailach; Konrad Vogeler

2009-01-01

228

Interaction between shock wave and unsteady jet in shock tube

We have observed the interaction between a shock wave and an unsteady jet in shock tube. From the results of the experiment, we have reported that the interaction between the shock wave and the unsteady jet in a shock tube was very strong, and it temporarily generated a hemispherical reflected shock wave. However, we could not clarify the cause of

Yoshimi Ishii; Fumio Takayama

1990-01-01

229

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 of numerous jet configurations occurring in aerospace are discussed along with aeroelasticity for aeroengine and external aerodynamics, design optimization, unsteady flow modelling and aeroengine internal and external flows. It is concluded that there is a lack of detailed measurements (for both canonical and complex geometry flows) to provide validation and even, in some cases, basic understanding of flow physics. Not surprisingly, turbulence modelling is still the weak link along with, as ever, a pressing need for improved (in terms of robustness, speed and accuracy) solver technology, grid generation and geometry handling. Hence, CFD, as a truly predictive and creative design tool, seems a long way off. Meanwhile, extreme practitioner expertise is still required and the triad of computation, measurement and analytic solution must be judiciously used. PMID:17519203

Tucker, Paul G

2007-10-15

230

Simulations of the unsteady flow through the Fastrac Supersonic Turbine

Analysis of the unsteady aerodynamic environment in the Fastrac supersonic turbine is presented. Modal analysis of the turbine blades indicated possible resonance in crucial operating ranges of the turbopump. Unsteady computational fluid dynamics (CFD) analysis was conducted to support the aerodynamic and structural dynamic assessments of the turbine. Before beginning the analysis, two major problems with current unsteady analytical capabilities had to be addressed: modeling a straight centerline nozzle with the turbine blades and exit guide vanes (EGVs), and reducing run times significantly while maintaining physical accuracy. Modifications were made to the CFD code used in this study to allow the coupled nozzle/blade/EGV analysis and to incorporate Message Passing Interface (MPI) software. Because unsteadiness is a key issue for the Fastrac turbine [and future rocket engine turbines such as the Reusable Launch Vehicle (RLV)], calculations were performed for two nozzle-to-blade axial gaps. Calculations were also performed for the nozzle alone, and the results were imposed as an inlet boundary condition for a blade/EGV calculation for the large gap case. These results are compared to the nozzle/blade/EGV results.

Griffin, L.W.; Dorney, D.J.

2000-04-01

231

Simulations of the Unsteady Flow through the Fastrac Supersonic Turbine

NASA Technical Reports Server (NTRS)

Analysis of the unsteady aerodynamic environment in the Fastrac supersonic turbine is presented. Modal analysis of the turbine blades indicated possible resonance in crucial operating ranges of the turbopump. Unsteady computational fluid dynamics (CFD) analysis was conducted to support the aerodynamic and structural dynamic assessments of the turbine. Before beginning the analysis, two major problems with current unsteady analytical capabilities had to be addressed: modeling a straight centerline nozzle with the turbine blades and exit guide vanes (EGVs), and reducing run times significantly while maintaining physical accuracy. Modifications were made to the CFD code used in this study to allow the coupled nozzle/blade/EGV analysis and to incorporate Message Passing Interface (MPI) software. Because unsteadiness is a key issue for the Fastrac turbine [and future rocket engine turbines such as for the Reusable Launch Vehicle (RI.V)], calculations were performed for two nozzle-to-blade axial gaps. Calculations were also performed for the nozzle alone, and the results were imposed as an inlet boundary condition for a blade/EGV calculation for the large gap case. These results are compared to the nozzle/blade/EGV results.

Griffin, Lisa W.; Dorney, Daniel J.

1999-01-01

232

PREFACE: Aerodynamic sound Aerodynamic sound

NASA Astrophysics Data System (ADS)

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

Akishita, Sadao

2010-02-01

233

We discuss a new approach for the measurement of the surfaces of free aerosol particles with diameters from 50 to 1000 nm. Particles in this size range have significant influence on the heterogeneous chemistry in the atmosphere and affect human health. Interfacing an aerodynamic lens to an ambient pressure x-ray photoelectron spectrometer permits measurement of the surface chemical composition of unsupported aerosol particles in real time. We discuss the basic considerations for the design of such an instrument, its current limitations and potentials for improvement. Results from a proof-of-principle experiment on silicon oxide particles with average diameters of 270 nm are shown.

Mysak, Erin R.; Starr, David E.; Wilson, Kevin R.; Bluhm, Hendrik [Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

2010-01-15

234

Numerical simulations of unsteady flows in turbomachines

NASA Astrophysics Data System (ADS)

The performance of axial and centrifugal turbomachines is significantly affected by the presence of unsteady and viscous flow mechanisms. Most contemporary design systems, however, use steady or linearized unsteady inviscid flow analyses to generate new blade shapes. In an effort to increase the understanding of unsteady viscous flows in turbomachinery blade rows, and to determine the limitations of linearized inviscid flow analyses, a two-part investigation was conducted. In the first portion of this investigation, a nonlinear viscous flow analysis was developed for the prediction of unsteady flows in two dimensional axial turbomachinery blade rows. The boundary conditions were formulated to allow the specification of vortical, entropic and acoustic excitations at the inlet, and acoustic excitations at exit, of a cascade. Numerical simulations were performed for flat plate and compressor exit guide vane cascades, and the predicted results were compared with solutions from classical linearized theory and linearized inviscid flow analysis. The unsteady pressure fields predicted with the current analysis showed close agreement with the linearized solutions for low to moderate temporal frequency vortical and acoustic excitations. As the temporal frequency of the excitations was increased, nonlinear effects caused discrepancies to develop between the linearized and Navier-Stokes solution sets. The inclusion of viscosity had a significant impact on the unsteady vorticity field, but only a minimal effect on the unsteady pressure field. In the second part of this investigation, a quasi-three-dimensional Navier-Stokes analysis was modified and applied to flows in centrifugal turbomachinery blade rows. Inviscid and viscous flow simulations were performed for a centrifugal impeller at three operating conditions. By comparing the predicted and experimental circumferential distributions of the relative frame velocity and flow angle downstream of the impeller, it was hypothesized that in the experiments the end secondary flows energize the impeller suction surface boundary making the local flow behave like an inviscid fluid. The performance curve generated from the viscous calculations showed close agreement with the experimental data.

Dorney, Daniel Joseph

235

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

236

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

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

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

2011-12-01

237

NASA Technical Reports Server (NTRS)

The unsteady aerodynamic lifting surface theory, the Doublet Lattice method, with experimental steady and unsteady pressure measurements of a high aspect ratio supercritical wing model at a Mach number of 0.78 were compared. The steady pressure data comparisons were made for incremental changes in angle of attack and control surface deflection. The unsteady pressure data comparisons were made at set angle of attack positions with oscillating control surface deflections. Significant viscous and transonic effects in the experimental aerodynamics which cannot be predicted by the Doublet Lattice method are shown. This study should assist development of empirical correction methods that may be applied to improve Doublet Lattice calculations of lifting surface aerodynamics.

Mccain, W. E.

1984-01-01

238

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

239

Aeroelastic control of stability and forced response of supersonic rotors by aerodynamic detuning

NASA Technical Reports Server (NTRS)

Aerodynamic detuning, defined as designed passage-to-passage differences in the unsteady aerodynamic flow field of a rotor blade row, is a new approach to passive flutter and forced response control. In this paper, a mathematical model for aerodynamic detuning is developed and utilized to demonstrate the aeroelastic stability enhancement due to aerodynamic detuning of supersonic blade rows. In particular, a model is developed to analyze both the torsion mode and the coupled bending-torsion mode unstalled supersonic flutter and torsion mode aerodynamically forced response characteristics of an aerodynamically detuned rotor operating in a supersonic inlet flow field with a subsonic leading edge locus. As small solidity variations do not have a dominant effect on the steady-state performance of a rotor, the aerodynamic detuning mechanism considered is nonuniform circumferential spacing of adjacent blades.

Hoyniak, Daniel; Fleeter, Sanford

1987-01-01

240

A Numerical Model of Unsteady, Subsonic Aeroelastic Behavior. Ph.D Thesis

NASA Technical Reports Server (NTRS)

A method for predicting unsteady, subsonic aeroelastic responses was developed. The technique accounts for aerodynamic nonlinearities associated with angles of attack, vortex-dominated flow, static deformations, and unsteady behavior. The fluid and the wing together are treated as a single dynamical system, and the equations of motion for the structure and flow field are integrated simultaneously and interactively in the time domain. The method employs an iterative scheme based on a predictor-corrector technique. The aerodynamic loads are computed by the general unsteady vortex-lattice method and are determined simultaneously with the motion of the wing. Because the unsteady vortex-lattice method predicts the wake as part of the solution, the history of the motion is taken into account; hysteresis is predicted. Two models are used to demonstrate the technique: a rigid wing on an elastic support experiencing plunge and pitch about the elastic axis, and an elastic wing rigidly supported at the root chord experiencing spanwise bending and twisting. The method can be readily extended to account for structural nonlinearities and/or substitute aerodynamic load models. The time domain solution coupled with the unsteady vortex-lattice method provides the capability of graphically depicting wing and wake motion.

Strganac, Thomas W.

1987-01-01

241

Algorithm and code development for unsteady three-dimensional Navier-Stokes equations

NASA Technical Reports Server (NTRS)

In the last two decades, there have been extensive developments in computational aerodynamics, which constitutes a major part of the general area of computational fluid dynamics. Such developments are essential to advance the understanding of the physics of complex flows, to complement expensive wind-tunnel tests, and to reduce the overall design cost of an aircraft, particularly in the area of aeroelasticity. Aeroelasticity plays an important role in the design and development of aircraft, particularly modern aircraft, which tend to be more flexible. Several phenomena that can be dangerous and limit the performance of an aircraft occur because of the interaction of the flow with flexible components. For example, an aircraft with highly swept wings may experience vortex-induced aeroelastic oscillations. Also, undesirable aeroelastic phenomena due to the presence and movement of shock waves occur in the transonic range. Aeroelastically critical phenomena, such as a low transonic flutter speed, have been known to occur through limited wind-tunnel tests and flight tests. Aeroelastic tests require extensive cost and risk. An aeroelastic wind-tunnel experiment is an order of magnitude more expensive than a parallel experiment involving only aerodynamics. By complementing the wind-tunnel experiments with numerical simulations the overall cost of the development of aircraft can be considerably reduced. In order to accurately compute aeroelastic phenomenon it is necessary to solve the unsteady Euler/Navier-Stokes equations simultaneously with the structural equations of motion. These equations accurately describe the flow phenomena for aeroelastic applications. At Ames a code, ENSAERO, is being developed for computing the unsteady aerodynamics and aeroelasticity of aircraft and it solves the Euler/Navier-Stokes equations. The purpose of this contract is to continue the algorithm enhancements of ENSAERO and to apply the code to complicated geometries. During the last year, the geometric capability of the code was extended to simulate transonic flows, a wing with oscillating control surface. Single-grid and zonal approaches were tested. For the zonal approach, a new interpolation technique was introduced. The key development of the algorithm was an interface treatment between moving zones for a control surface using the virtual-zone concept. The work performed during the period, 1 Apr. 1992 through 31 Mar. 1993 is summarized. Additional details on the various aspects of the study are given in the Appendices.

Obayashi, Shigeru

1993-01-01

242

Algorithm and code development for unsteady three-dimensional Navier-Stokes equations

NASA Astrophysics Data System (ADS)

In the last two decades, there have been extensive developments in computational aerodynamics, which constitutes a major part of the general area of computational fluid dynamics. Such developments are essential to advance the understanding of the physics of complex flows, to complement expensive wind-tunnel tests, and to reduce the overall design cost of an aircraft, particularly in the area of aeroelasticity. Aeroelasticity plays an important role in the design and development of aircraft, particularly modern aircraft, which tend to be more flexible. Several phenomena that can be dangerous and limit the performance of an aircraft occur because of the interaction of the flow with flexible components. For example, an aircraft with highly swept wings may experience vortex-induced aeroelastic oscillations. Also, undesirable aeroelastic phenomena due to the presence and movement of shock waves occur in the transonic range. Aeroelastically critical phenomena, such as a low transonic flutter speed, have been known to occur through limited wind-tunnel tests and flight tests. Aeroelastic tests require extensive cost and risk. An aeroelastic wind-tunnel experiment is an order of magnitude more expensive than a parallel experiment involving only aerodynamics. By complementing the wind-tunnel experiments with numerical simulations the overall cost of the development of aircraft can be considerably reduced. In order to accurately compute aeroelastic phenomenon it is necessary to solve the unsteady Euler/Navier-Stokes equations simultaneously with the structural equations of motion. These equations accurately describe the flow phenomena for aeroelastic applications. At Ames a code, ENSAERO, is being developed for computing the unsteady aerodynamics and aeroelasticity of aircraft and it solves the Euler/Navier-Stokes equations. The purpose of this contract is to continue the algorithm enhancements of ENSAERO and to apply the code to complicated geometries. During the last year, the geometric capability of the code was extended to simulate transonic flows, a wing with oscillating control surface. Single-grid and zonal approaches were tested. For the zonal approach, a new interpolation technique was introduced. The key development of the algorithm was an interface treatment between moving zones for a control surface using the virtual-zone concept.

Obayashi, Shigeru

1993-03-01

243

Unsteady aerodynamic characterization of a military aircraft in vertical gusts

NASA Technical Reports Server (NTRS)

The effects of 2.5-m/sec vertical gusts on the flight characteristics of a 1:8.6 scale model of a Mirage 2000 aircraft in free flight at 35 m/sec over a distance of 30 m are investigated. The wind-tunnel setup and instrumentation are described; the impulse-response and local-coefficient-identification analysis methods applied are discussed in detail; and the modification and calibration of the gust-detection probes are reviewed. The results are presented in graphs, and good general agreement is obtained between model calculations using the two analysis methods and the experimental measurements.

Lebozec, A.; Cocquerez, J. L.

1985-01-01

244

Transonic Unsteady Aerodynamics and Aeroelasticity 1987, part 2

NASA Technical Reports Server (NTRS)

This two part document contains copies of the text and figures for the papers presented at the symposium held at NASA Langley on 20 to 22 May, 1987. The papers are grouped in five subject areas. The areas covered by this part includes the following: Methods for vortex and viscous flows; Aeroelastic applications, and Experimental results and cascade flows.

Bland, Samuel R. (compiler)

1989-01-01

245

Transonic Unsteady Aerodynamics and Aeroelasticity 1987, part 1

NASA Technical Reports Server (NTRS)

Computational fluid dynamics methods have been widely accepted for transonic aeroelastic analysis. Previously, calculations with the TSD methods were used for 2-D airfoils, but now the TSD methods are applied to the aeroelastic analysis of the complete aircraft. The Symposium papers are grouped into five subject areas, two of which are covered in this part: (1) Transonic Small Disturbance (TSD) theory for complete aircraft configurations; and (2) Full potential and Euler equation methods.

Bland, Samuel R. (compiler)

1989-01-01

246

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

NASA Technical Reports Server (NTRS)

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

Smith, Todd E.; Kadambi, Jaikrishnan R.

1990-01-01

247

Flutter and forced response of turbomachinery with frequency mistuning and aerodynamic asymmetry

NASA Astrophysics Data System (ADS)

This dissertation provides numerical studies to improve bladed disk assembly design for preventing blade high cycle fatigue failures. The analyses are divided into two major subjects. For the first subject presented in Chapter 2, the mechanisms of transonic fan flutter for tuned systems are studied to improve the shortcoming of traditional method for modern fans using a 3D time-linearized Navier-Stokes solver. Steady and unsteady flow parameters including local work on the blade surfaces are investigated. It was found that global local work monotonically became more unstable on the pressure side due to the flow rollback effect. The local work on the suction side significantly varied due to nodal diameter and flow rollback effect. Thus, the total local work for the least stable mode is dominant by the suction side. Local work on the pressure side appears to be affected by the shock on the suction side. For the second subject presented in Chapter 3, sensitivity studies are conducted on flutter and forced response due to frequency mistuning and aerodynamic asymmetry using the single family of modes approach by assuming manufacturing tolerance. The unsteady aerodynamic forces are computed using CFD methods assuming aerodynamic symmetry. The aerodynamic asymmetry is applied by perturbing the influence coefficient matrix. These aerodynamic perturbations influence both stiffness and damping while traditional frequency mistuning analysis only perturbs the stiffness. Flutter results from random aerodynamic perturbations of all blades showed that manufacturing variations that effect blade unsteady aerodynamics may cause a stable, perfectly symmetric engine to flutter. For forced response, maximum blade amplitudes are significantly influenced by the aerodynamic perturbation of the imaginary part (damping) of unsteady aerodynamic modal forces. This is contrary to blade frequency mistuning where the stiffness perturbation dominates.

Miyakozawa, Tomokazu

248

Applications of the unsteady vortex-lattice method in aircraft aeroelasticity and flight dynamics

NASA Astrophysics Data System (ADS)

The unsteady vortex-lattice method provides a medium-fidelity tool for the prediction of non-stationary aerodynamic loads in low-speed, but high-Reynolds-number, attached flow conditions. Despite a proven track record in applications where free-wake modelling is critical, other less-computationally expensive potential-flow models, such as the doublet-lattice method and strip theory, have long been favoured in fixed-wing aircraft aeroelasticity and flight dynamics. This paper presents how the unsteady vortex-lattice method can be implemented as an enhanced alternative to those techniques for diverse situations that arise in flexible-aircraft dynamics. A historical review of the methodology is included, with latest developments and practical applications. Different formulations of the aerodynamic equations are outlined, and they are integrated with a nonlinear beam model for the full description of the dynamics of a free-flying flexible vehicle. Nonlinear time-marching solutions capture large wing excursions and wake roll-up, and the linearisation of the equations lends itself to a seamless, monolithic state-space assembly, particularly convenient for stability analysis and flight control system design. The numerical studies emphasise scenarios where the unsteady vortex-lattice method can provide an advantage over other state-of-the-art approaches. Examples of this include unsteady aerodynamics in vehicles with coupled aeroelasticity and flight dynamics, and in lifting surfaces undergoing complex kinematics, large deformations, or in-plane motions. Geometric nonlinearities are shown to play an instrumental, and often counter-intuitive, role in the aircraft dynamics. The unsteady vortex-lattice method is unveiled as a remarkable tool that can successfully incorporate all those effects in the unsteady aerodynamics modelling.

Murua, Joseba; Palacios, Rafael; Graham, J. Michael R.

2012-11-01

249

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

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

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

1995-12-31

250

Unsteady Velocity Measurements Taken Behind a Model Helicopter Rotor Hub in Forward Flight

NASA Technical Reports Server (NTRS)

Drag caused by separated flow behind the hub of a helicopter has an adverse effect on aerodynamic performance of the aircraft. To determine the effect of separated flow on a configuration used extensively for helicopter aerodynamic investigations, an experiment was conducted using a laser velocimeter to measure velocities in the wake of a model helicopter hub operating at Mach-scaled conditions in forward flight. Velocity measurements were taken using a laser velocimeter with components in the vertical and downstream directions. Measurements were taken at 13 stations downstream from the rotor hub. At each station, measurements were taken in both a horizontal and vertical row of locations. These measurements were analyzed for harmonic content based on the rotor period of revolution. After accounting for these periodic velocities, the remaining unsteady velocities were treated as turbulence. Turbulence intensity distributions are presented. Average turbulent intensities ranged from approximately 2 percent of free stream to over 15 percent of free stream at specific locations and azimuths. The maximum average value of turbulence was located near the rear-facing region of the fuselage.

Berry, John D.

1997-01-01

251

This introduction to aerodynamic aspects of motor vehicle design will be of use both to vehicle designers and students of automobile engineering. Content covers vehicle systems, ventilation and aerodynamic design to reduce drag and increase stability of cars, commercial vehicles and PSVs. Topics considered include automobile aerodynamics; some fundamentals of fluid mechanics; performance of cars and light vans; aerodynamic drag of passenger cars; driving stability in sidewinds; operation, safety and comfort; high-performance vehicle aerodynamics; commercial vehicles; engine cooling systems; heating, ventilation and air conditioning of motor vehicles; wind tunnels for automobile aerodynamics; measuring and testing techniques; and numerical methods for computation of flow around road vehicles.

Hucho, W.H.

1987-01-01

252

NASA Astrophysics Data System (ADS)

The counter-rotating axial flow fan shows that the complex flow characteristics with three-dimensional, viscous, and unsteady flow fields. For the understanding of the entire core flow in counter-rotating axial flow fan, it is necessary to investigate the three-dimensional unsteady flow field between the rotors. This information is also essential for the improvement of the aerodynamic characteristics, the reduction of the aerodynamic noise level and vibration characteristics of the counter-rotating axial flow fan. The purpose of this study is, therefore, to present the periodic characteristics of the blade passage flow, the wake and the tip vortex, which are utilized for the blade design data for the improvement of the aerodynamic characteristics, the reduction of the aerodynamic noise level and vibration characteristics of the counter-rotating axial flow fan. In this paper, the three-dimensional unsteady flow by the rotor-rotor interaction of the CRF were investigated at the design point(peak efficiency operating point). Unsteady flow fields in the CRF are measured at the cross-sectional planes of the upstream, between and downstream of each rotor using the 45° inclined hot-wire probe. The stationary hot-wire technique used the 45° inclined hot-wire probe, which rotates successively with 120 degrees increments about its own axis. And, the sampling data of unsteady flow fields were phase-locked averaged to remove the random components.

Cho, Lee-Sang; Cha, Bong-Jun; Cho, Jin-Soo

253

NASA Technical Reports Server (NTRS)

A linearized unsteady aerodynamic analysis is presented for unsteady, subsonic vortical flows around lifting airfoils. The analysis fully accounts for the distortion effects of the nonuniform mean flow on the imposed vortical disturbances. A frequency domain numerical scheme which implements this linearized approach is described, and numerical results are presented for a large variety of flow configurations. The results demonstrate the effects of airfoil thickness, angle of attack, camber, and Mach number on the unsteady lift and moment of airfoils subjected to periodic vortical gusts. The results show that mean flow distortion can have a very strong effect on the airfoil unsteady response, and that the effect depends strongly upon the reduced frequency, Mach number, and gust wave numbers.

Scott, James R.; Atassi, Hafiz M.

1990-01-01

254

NASA Technical Reports Server (NTRS)

The effects of airfoil shape, thickness, camber, and mean angle of attack on transonic unsteady airloads were investigated as calculated by the transonic small-disturbance computer code XTRAN2L. Shape effects were investigated by examining the pressure distributions, shock locations, and unsteady airloads for three 10 percent thick airfoils. NACA 0010, NACA 64A010, and parabolic arc. Thickness effects were determined by studying a single airfoil shape with three different thicknesses: NACA 0008, NACA 0010, and NACA 0012. Angle of attack and camber effects were studied by including mean angle of attack or by adding a simple parabolic camber distribution to the originally symmetric airfoils. Comparisons of unsteady airloads for different airfoil configurations show similar results caused by variations in airfoil shape, thickness, camber, or mean angle of attack. Computer costs can be reduced by limiting the number of transonic unsteady aerodynamic calculations for small changes in airfoil geometry or angle of attack.

Batina, J. T.

1985-01-01

255

Aeroacoustics. [analysis of properties of sound generated by aerodynamic forces

NASA Technical Reports Server (NTRS)

An analysis was conducted to determine the properties of sound generated by aerodynamic forces or motions originating in a flow, such as the unsteady aerodynamic forces on propellers or by turbulent flows around an aircraft. The acoustics of moving media are reviewed and mathematical models are developed. Lighthill's acoustic analogy and the application to turbulent flows are analyzed. The effects of solid boundaries are calculated. Theories based on the solution of linearized vorticity and acoustic field equations are explained. The effects of nonuniform mean flow on the generation of sound are reported.

Goldstein, M., E.

1974-01-01

256

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

257

NASA Technical Reports Server (NTRS)

A collection of papers on modern theoretical aerodynamics is presented. Included are theories of incompressible potential flow and research on the aerodynamic forces on wing and wing sections of aircraft and on airship hulls.

Jones, R. T. (compiler)

1979-01-01

258

NASA Technical Reports Server (NTRS)

The annual accomplishments is reviewed for the Aerodynamics Division during FY 1991. The program includes both fundamental and applied research directed at the full spectrum of aerospace vehicles, from rotorcraft to planetary entry probes. A comprehensive review is presented of the following aerodynamics elements: computational methods and applications; CFD validation; transition and turbulence physics; numerical aerodynamic simulation; test techniques and instrumentation; configuration aerodynamics; aeroacoustics; aerothermodynamics; hypersonics; subsonics; fighter/attack aircraft and rotorcraft.

Williams, Louis J.; Hessenius, Kristin A.; Corsiglia, Victor R.; Hicks, Gary; Richardson, Pamela F.; Unger, George; Neumann, Benjamin; Moss, Jim

1992-01-01

259

Chapter 11 Aerodynamics Antony Jameson Stanford University, Stanford, CA, USA 1 Focus Multidimensional Domains 359 6 Time-stepping Schemes 365 7 Aerodynamic Shape Optimization 379 8 Related Chapters 400 Acknowledgment 400 References 400 1 FOCUS AND HISTORICAL BACKGROUND 1.1 Classical aerodynamics

Jameson, Antony

260

Unsteady flow phenomena in industrial centrifugal compressor stage

NASA Technical Reports Server (NTRS)

The results of an experimental investigation on a typical centrifugal compressor stage running on an atmospheric pressure test rig are shown. Unsteady flow was invariably observed at low flow well before surge. In order to determine the influence of the statoric components, the same impeller was repeatedly tested with the same vaneless diffuser, but varying return channel geometry. Experimental results show the strong effect exerted by the return channel, both on onset and on the behavior of unsteady flow. Observed phenomena have been found to confirm well the observed dynamic behavior of full load tested machines when gas density is high enough to cause appreciable mechanical vibrations. Therefore, testing of single stages at atmospheric pressure may provide a fairly accurate prediction of this kind of aerodynamic excitation.

Bonciani, L.; Terrinoni, L.; Tesei, A.

1982-01-01

261

NASA Astrophysics Data System (ADS)

This issue of Measurement Science and Technology contains a special feature section with selected papers from the EWA International workshop on Advanced Measurement Techniques in Aerodynamics, which was held at the Delft University of Technology, Delft, The Netherlands, 31 March-1 April 2008. The workshop was funded by the European Windtunnel Association (EWA, www.eu-ewa.aero), which is an EU-funded network established in 2004 under the European Sixth Framework Programme with the goal of integrating and standardizing the different capabilities of European wind tunnels and related flow measurement techniques. The workshop was organized with the objective of stimulating discussion among leading European universities, research institutes and industry in the field of advanced aerodynamics measurement techniques, in order to provide a transfer of new ideas from upstream research centres to wind tunnel operators and industrial users. Non-intrusive flow diagnostic techniques nowadays offer renewed capabilities for industrial wind-tunnel applications. Particle image velocimetry (PIV) plays a leading role for particular applications (unsteady and complex flows, rotorcraft aerodynamics, turbulent separated flows) and can provide solutions that cannot be achieved with conventional techniques (e.g. in the analysis of vortex flows). This formed the main motivation to revise the state-of-the-art of PIV along with other non-intrusive optical techniques such as PSP, DGV and BOS. The two-day workshop contained sessions dedicated to several specific topics: rotorcraft aerodynamics applications; state-of-the-art of high-speed PIV and configurations for time-resolved measurements; three-dimensional PIV; non-intrusive load characterization by PSP and PIV. The main conclusion emerging from the closing discussion was that the new capabilities offered by time-resolved PIV are of great scientific and industrial interest for application to unsteady flows and in particular to the determination of unsteady aerodynamic forces and loads. We believe that this workshop provided a useful framework facilitating the transfer of new ideas from developer to the user communities. At the same time the workshop provided the upstream research community with important feedback about the areas of relevance for industrial aerodynamics.

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

2009-07-01

262

NASA Technical Reports Server (NTRS)

Recent experience in the application of an optimized, second-order, backward-difference (BDF2OPT) temporal scheme is reported. The primary focus of the work is on obtaining accurate solutions of the unsteady Reynolds-averaged Navier-Stokes equations over long periods of time for aerodynamic problems of interest. The baseline flow solver under consideration uses a particular BDF2OPT temporal scheme with a dual-time-stepping algorithm for advancing the flow solutions in time. Numerical difficulties are encountered with this scheme when the flow code is run for a large number of time steps, a behavior not seen with the standard second-order, backward-difference, temporal scheme. Based on a stability analysis, slight modifications to the BDF2OPT scheme are suggested. The performance and accuracy of this modified scheme is assessed by comparing the computational results with other numerical schemes and experimental data.

Vatsa, Veer N.; Carpenter, Mark H.; Lockard, David P.

2009-01-01

263

Calculation and Correlation of the Unsteady Flowfield in a High Pressure Turbine

NASA Technical Reports Server (NTRS)

Forced vibrations in turbomachinery components can cause blades to crack or fail due to high-cycle fatigue. Such forced response problems will become more pronounced in newer engines with higher pressure ratios and smaller axial gap between blade rows. An accurate numerical prediction of the unsteady aerodynamics phenomena that cause resonant forced vibrations is increasingly important to designers. Validation of the computational fluid dynamics (CFD) codes used to model the unsteady aerodynamic excitations is necessary before these codes can be used with confidence. Recently published benchmark data, including unsteady pressures and vibratory strains, for a high-pressure turbine stage makes such code validation possible. In the present work, a three dimensional, unsteady, multi blade-row, Reynolds-Averaged Navier Stokes code is applied to a turbine stage that was recently tested in a short duration test facility. Two configurations with three operating conditions corresponding to modes 2, 3, and 4 crossings on the Campbell diagram are analyzed. Unsteady pressures on the rotor surface are compared with data.

Bakhle, Milind A.; Liu, Jong S.; Panovsky, Josef; Keith, Theo G., Jr.; Mehmed, Oral

2002-01-01

264

The present conference on aplied aerodynamics encompasses computational fluid dynamics, drag prediction/analysis, experimental aerodynamics, high angles of attack, rotor/propeller aerodynamics, super/hypersonic aerodynamics, unsteady aerodynamics, vortex physics, high-speed civil-transport aeroacoustics, and airfoil/wing aerodynamics. Specific issues addressed include high-speed civil-transport air-breathing propulsion, generic hypersonic inlet-module analysis, an investigation on spoiler effects, high-alpha vehicle dynamics, space-station resource node flow-field analysis, a numerical simulation of sabot discard aerodynamics, and vortex control using pneumatic blowing. Also addressed are Navier-Stokes solutions for the F/A-18 Wing-LEX fuselage, tail venting for enhanced yaw damping at spinning conditions, an investigation of rotor wake interactions with a body in low-speed forward flight, and multigrid calculations of 3D viscous cascade flows.

Not Available

1991-01-01

265

Examination of forced unsteady separated flow fields on a rotating wind turbine blade

The wind turbine industry faces many problems regarding the construction of efficient and predictable wind turbine machines. Steady state, two-dimensional wind tunnel data are generally used to predict aerodynamic loads on wind turbine blades. Preliminary experimental evidence indicates that some of the underlying fluid dynamic phenomena could be attributed to dynamic stall, or more specifically to generation of forced unsteady separated flow fields. A collaborative research effort between the University of Colorado and the National Renewable Energy Laboratory was conducted to systematically categorize the local and global effects of three- dimensional forced unsteady flow fields.

Huyer, S. [Univ. of Colorado, Boulder, CO (US)] [Univ. of Colorado, Boulder, CO (US)

1993-04-01

266

NASA Technical Reports Server (NTRS)

The present study, which is the first of a series of investigations of low pressure turbine (LPT) boundary layer aerodynamics, is aimed at providing detailed unsteady boundary layer flow information to understand the underlying physics of the inception, onset, and extent of the separation zone. A detailed experimental study on the behavior of the separation zone on the suction surface of a highly loaded LPT-blade under periodic unsteady wake flow is presented. Experimental investigations were performed on a large-scale, high-subsonic unsteady turbine cascade research facility with an integrated wake generator and test section unit. Blade Pak B geometry was used in the cascade. The wakes were generated by continuously moving cylindrical bars device. Boundary layer investigations were performed using hot wire anemometry at Reynolds number of 110,000, based on the blade suction surface length and the exit velocity, for one steady and two unsteady inlet flow conditions, with the corresponding passing frequencies, wake velocities, and turbulence intensities. The reduced frequencies cover the entire operation range of LP-turbines. In addition to the unsteady boundary layer measurements, blade surface pressure measurements were performed at Re = 50,000, 75,000, 100,000, 110,000, and 125,000. For each Reynolds number, surface pressure measurements are carried out at one steady and two periodic unsteady inlet flow conditions. Detailed unsteady boundary layer measurement identifies the onset and extension of the separation zone as well as its behavior under unsteady wake flow. The results, presented in ensemble-averaged and contour plot forms, help to understand the physics of the separation phenomenon under periodic unsteady wake flow.

Ozturk, Burak; Schobeiri, Meinhard T.

2009-01-01

267

The Aerodynamics of Deforming Wings at Low Reynolds Number

NASA Astrophysics Data System (ADS)

Flapping flight has gained much attention in the past decade driven by the desire to understand capabilities observed in nature and the desire to develop agile small-scale aerial vehicles. Advancing our current understanding of unsteady aerodynamics is an essential component in the development of micro-air vehicles (MAV) intended to utilize flight mechanics akin to insect flight. Thus the efforts undertaken that of bio-mimicry. The complexities of insect wing motion are dissected and simplified to more tractable problems to elucidate the fundamentals of unsteady aerodynamics in biologically inspired kinematics. The MAV's fruition would satisfy long established needs in both the military and civilian sectors. Although recent studies have provided great insight into the lift generating mechanisms of flapping wings the deflection response of such wings remains poorly understood. This dissertation numerically and experimentally investigates the aerodynamic performance of passively and actively deflected wings in hover and rotary kinematics. Flexibility is distilled to discrete lines of flexion which acknowledging major flexion lines in insect wings to be the primary avenue for deformation. Of primary concern is the development of the leading-edge vortex (LEV), a high circulation region of low pressure above the wing to which much of the wing's lift generation is attributed. Two-dimensional simulations of wings with chord-wise flexibility in a freestream reveal a lift generating mechanism unavailable to rigid wings with origins in vortical symmetry breaking. The inclusion of flexibility in translating wings accelerated from rest revealed the formation time of the initial LEV was very weakly dependent on the flexible stiffness of the wing, maintaining a universal time scale of four to five chords of travel before shedding. The frequency of oscillatory shedding of the leading and trailing-edge vortices that develops after the initial vortex shedding was shown to be responsive to flexibility satisfying an inverse proportionality to stiffness. In hover, an effective pitch angle can be defined in a flexible wing that accounts for deflection which shifts results toward trend lines of rigid wings. Three-dimensional simulations examining the effects of two distinct deformation modes undergoing prescribed deformation associated with root and tip deflection demonstrated a greater aerodynamic response to tip deflection in hover. Efficiency gains in flexion wings over rigid wing counterpart were shown to be dependent on Reynolds number with efficiency in both modes increasing with increased Reynolds number. Additionally, while the leading-edge vortex axis proved insensitive to deformation, the shape and orientation of the LEV core is modified. Experiments on three-dimensional dynamically-scaled fruit fly wings with passive deformation operating in the bursting limit Reynolds number regime revealed enhanced leading-edge vortex bursting with tip deflection promoting greater LEV core flow deceleration in stroke. Experimental studies on rotary wings highlights a universal formation time of the leading-edge vortex independent of Reynolds number, acceleration profile and aspect ratio. Efforts to replicate LEV bursting phenomena of higher aspect ratio wings in a unity aspect ratio wing such that LEV growth is no limited by span but by the LEV traversing the chord revealed a flow regime of oscillatory lift generation reminiscent of behavior exhibited in translating wings that also maintains magnitude peak to peak.

Medina, Albert

268

The study of unsteady boundary layer flows with self-induced pressure is of great theoretical and practical interest in modern aerodynamics. The use of matched asymptotic expansions for the analysis of such flows [I-8] made it possible to establish the asymptotic nature of the flow as the characteristic Reynolds number tends to infinity, similarity laws, and also the momentum laws which

A. V. Kazakov

1983-01-01

269

Prediction of aerodynamic forces on horizontal axis wind turbines in free yaw and turbulence

A free vortex lattice model is used to stimulate the flow field of a rotor at either a steady yaw angle to the wind or undergoing a changing yaw angle, for which cases the flow field itself and the aerodynamic forces on the rotor are unsteady. The model is run from an impulsive start and continues until an asymptotic (typically

Stylianos D Pesmajoglou; J. M. R Graham

2000-01-01

270

Generation of Aerodynamic Coefficients Using Time-Accurate CFD and Virtual FLy-Out Simulations

This paper describes a multidisciplinary computational study undertaken to compute the unsteady free-flight aerodynamics of spinning and finned projectiles. Advanced computational fluid dynamics (CFD), rigid body dynamics (RBD), and flight control systems have been successfully coupled on high performance computing platforms for \\

Jubaraj Sahu; Sidra Silton; James DeSpirito; Karen R. Heavey; Mark Costello

2008-01-01

271

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

272

Introduction to unsteady thermofluid mechanics

NASA Astrophysics Data System (ADS)

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

Moody, Frederick J.

273

Aerodynamic Characteristics of Water Rocket and Stabilization of Flight Trajectory

NASA Astrophysics Data System (ADS)

The aerodynamic characteristics of water rockets are analyzed experimentally by wind tunnel testing. Aerodynamic devices such as vortex generators and dimples are tested and their effectiveness to the flight performance of water rocket is discussed. Attaching vortex generators suppresses the unsteady body fluttering. Dimpling the nose reduces the drag coefficient in high angles of attack. Robust design approach is applied to water rocket design for flight stability and optimum water rocket configuration is determined. Semi-sphere nose is found to be effective for flight stability and it is desirable for the safety of landing point. Stiffed fin attachment is required for fins to work properly as aerodynamic device and it enhances the flight stability of water rockets.

Watanabe, Rikio; Tomita, Nobuyuki; Takemae, Toshiaki

274

Accurate measurement of streamwise vortices in low speed aerodynamic flows

NASA Astrophysics Data System (ADS)

Low Reynolds number experiments with flapping animals (such as bats and small birds) are of current interest in understanding biological flight mechanics, and due to their application to Micro Air Vehicles (MAVs) which operate in a similar parameter space. Previous PIV wake measurements have described the structures left by bats and birds, and provided insight to the time history of their aerodynamic force generation; however, these studies have faced difficulty drawing quantitative conclusions due to significant experimental challenges associated with the highly three-dimensional and unsteady nature of the flows, and the low wake velocities associated with lifting bodies that only weigh a few grams. This requires the high-speed resolution of small flow features in a large field of view using limited laser energy and finite camera resolution. Cross-stream measurements are further complicated by the high out-of-plane flow which requires thick laser sheets and short interframe times. To quantify and address these challenges we present data from a model study on the wake behind a fixed wing at conditions comparable to those found in biological flight. We present a detailed analysis of the PIV wake measurements, discuss the criteria necessary for accurate measurements, and present a new dual-plane PIV configuration to resolve these issues.

Waldman, Rye M.; Kudo, Jun; Breuer, Kenneth S.

2010-11-01

275

Beginner's Guide to Aerodynamics

NSDL National Science Digital Library

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

2007-12-07

276

NSDL National Science Digital Library

For those wanting a little more on the theory of aerodynamics, the University of Sydney has published this web textbook, "Aerodynamics for Students". In addition to information on fluid dynamics, flight theory, gas dynamics, propulsion, aircraft performance, and aeroelasticity, the textbook also includes data tables, computer programs, and simulations to aid in the study and understanding of aerodynamics. This textbook is a great resource for undergraduates studying engineering.

2007-12-10

277

Asymmetric Uncertainty Expression for High Gradient Aerodynamics

NASA Technical Reports Server (NTRS)

When the physics of the flow around an aircraft changes very abruptly either in time or space (e.g., flow separation/reattachment, boundary layer transition, unsteadiness, shocks, etc), the measurements that are performed in a simulated environment like a wind tunnel test or a computational simulation will most likely incorrectly predict the exact location of where (or when) the change in physics happens. There are many reasons for this, includ- ing the error introduced by simulating a real system at a smaller scale and at non-ideal conditions, or the error due to turbulence models in a computational simulation. The un- certainty analysis principles that have been developed and are being implemented today do not fully account for uncertainty in the knowledge of the location of abrupt physics changes or sharp gradients, leading to a potentially underestimated uncertainty in those areas. To address this problem, a new asymmetric aerodynamic uncertainty expression containing an extra term to account for a phase-uncertainty, the magnitude of which is emphasized in the high-gradient aerodynamic regions is proposed in this paper. Additionally, based on previous work, a method for dispersing aerodynamic data within asymmetric uncer- tainty bounds in a more realistic way has been developed for use within Monte Carlo-type analyses.

Pinier, Jeremy T

2012-01-01

278

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

279

Unsteady turbulent boundary layer analysis

NASA Technical Reports Server (NTRS)

The governing equations for an unsteady turbulent boundary layer on a swept infinite cylinder, composed of a continuity equation, a pair of momentum equations and a pair of turbulent energy equations which include upstream history efforts, are solved numerically. An explicit finite difference analog to the partial differential equations is formulated and developed into a computer program. Calculations were made for a variety of unsteady flows in both two and three dimensions but primarily for two dimensional flow fields in order to first understand some of the fundamental physical aspects of unsteady turbulent boundary layers. Oscillating free stream flows without pressure gradient, oscillating retarded free stream flows and monotonically time-varying flows have all been studied for a wide frequency range. It was found that to the lowest frequency considered, the lower frequency bound being determined by economic considerations (machine time), there were significant unsteady effects on the turbulent boundary layer.

Singleton, R. E.; Nash, J. F.; Carl, L. W.; Patel, V. C.

1973-01-01

280

In vivo recording of aerodynamic force with an aerodynamic force platform

Flapping wings enable flying animals and biomimetic robots to generate elevated aerodynamic forces. Measurements that demonstrate this capability are based on tethered experiments with robots and animals, and indirect force calculations based on measured kinematics or airflow during free flight. Remarkably, there exists no method to measure these forces directly during free flight. Such in vivo recordings in freely behaving animals are essential to better understand the precise aerodynamic function of their flapping wings, in particular during the downstroke versus upstroke. Here we demonstrate a new aerodynamic force platform (AFP) for nonintrusive aerodynamic force measurement in freely flying animals and robots. The platform encloses the animal or object that generates fluid force with a physical control surface, which mechanically integrates the net aerodynamic force that is transferred to the earth. Using a straightforward analytical solution of the Navier-Stokes equation, we verified that the method is ...

Lentink, David; Ingersoll, Rivers

2014-01-01

281

Unsteady Newton-Busemann flow theory. III - Frequency dependence and indicial response

NASA Technical Reports Server (NTRS)

Hui and Tobak applied the complete unsteady Newton-Busemann flow theory to the study of dynamic stability of oscillating aerofoils and bodies in revolution. The present article extends the results to general frequencies that may be applicable to flutter analysis. The results are likewise applied to the indicial response fluctuations in unsteady flow at very high Mach numbers. The study shows that for a group of body shapes in Newtonian flow (including the cone and wedge), the aerodynamic response to a step change in angle of attack or pitching velocity contains an initial-instant impulse followed by a rapid adjustment to the new steady-flow conditions. The impulse component is in effect an apparent mass term analogous to that which occurs initially in the aerodynamic indicial response at the zero Mach number limit.

Hui, W. H.

1982-01-01

282

Preconditioning Methods for Multidimensional Aerodynamics

Preconditioning Methods for Multidimensional Aerodynamics E. Turkel School of Mathematical Sciences of Design Aerodynamics Braunschweig, Germany 1 #12; Contents 1 Introduction 5 1.1 General requirements

Turkel, Eli

283

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

284

NASA: Beginner's Guide to Aerodynamics - Aerodynamics Index

NSDL National Science Digital Library

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

2008-12-16

285

STUDY OF SHOCK MOVEMENT AND UNSTEADY PRESSURE ON 2D GENERIC MODEL

A flexible generic model has been developed at the Chair of Heat and Power Technology in order to perform flutter experiments in a more fundamental fashion. It is made of engineered flexible material and oscillate in a controlled way at non-uniform amplitude and variable frequencies. Time-resolved measurements of the unsteady surface pressures, the instantaneous model geometry as well as unsteady

Davy Allegret-Bourdon; Torsten H. Fransson

286

The aerodynamics of hovering flight in Drosophila.

Using 3D infrared high-speed video, we captured the continuous wing and body kinematics of free-flying fruit flies, Drosophila melanogaster, during hovering and slow forward flight. We then 'replayed' the wing kinematics on a dynamically scaled robotic model to measure the aerodynamic forces produced by the wings. Hovering animals generate a U-shaped wing trajectory, in which large drag forces during a downward plunge at the start of each stroke create peak vertical forces. Quasi-steady mechanisms could account for nearly all of the mean measured force required to hover, although temporal discrepancies between instantaneous measured forces and model predictions indicate that unsteady mechanisms also play a significant role. We analyzed the requirements for hovering from an analysis of the time history of forces and moments in all six degrees of freedom. The wing kinematics necessary to generate sufficient lift are highly constrained by the requirement to balance thrust and pitch torque over the stroke cycle. We also compare the wing motion and aerodynamic forces of free and tethered flies. Tethering causes a strong distortion of the stroke pattern that results in a reduction of translational forces and a prominent nose-down pitch moment. The stereotyped distortion under tethered conditions is most likely due to a disruption of sensory feedback. Finally, we calculated flight power based directly on the measurements of wing motion and aerodynamic forces, which yielded a higher estimate of muscle power during free hovering flight than prior estimates based on time-averaged parameters. This discrepancy is mostly due to a two- to threefold underestimate of the mean profile drag coefficient in prior studies. We also compared our values with the predictions of the same time-averaged models using more accurate kinematic and aerodynamic input parameters based on our high-speed videography measurements. In this case, the time-averaged models tended to overestimate flight costs. PMID:15939772

Fry, Steven N; Sayaman, Rosalyn; Dickinson, Michael H

2005-06-01

287

An experimental study of airfoil-spoiler aerodynamics

NASA Technical Reports Server (NTRS)

The steady/unsteady flow field generated by a typical two dimensional airfoil with a statically deflected flap type spoiler was investigated. Subsonic wind tunnel tests were made over a range of parameters: spoiler deflection, angle of attack, and two Reynolds numbers; and comprehensive measurements of the mean and fluctuating surface pressures, velocities in the boundary layer, and velocities in the wake. Schlieren flow visualization of the near wake structure was performed. The mean lift, moment, and surface pressure characteristics are in agreement with previous investigations of spoiler aerodynamics. At large spoiler deflections, boundary layer character affects the static pressure distribution in the spoiler hingeline region; and, the wake mean velocity fields reveals a closed region of reversed flow aft of the spoiler. It is shown that the unsteady flow field characteristics are as follows: (1) the unsteady nature of the wake is characterized by vortex shedding; (2) the character of the vortex shedding changes with spoiler deflection; (3) the vortex shedding characteristics are in agreement with other bluff body investigations; and (4) the vortex shedding frequency component of the fluctuating surface pressure field is of appreciable magnitude at large spoiler deflections. The flow past an airfoil with deflected spoiler is a particular problem in bluff body aerodynamics is considered.

Mclachlan, B. G.; Karamcheti, K.

1985-01-01

288

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

Not Available

1992-01-01

289

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

290

Flow Fields Over Unsteady Three Dimensional Dunes

NASA Astrophysics Data System (ADS)

The flow field over dunes has been extensively measured in laboratory conditions and there is general understanding on the nature of the flow over dunes formed under equilibrium flow conditions. However, fluvial systems typically experience unsteady flow and therefore the sediment-water interface is constantly responding and reorganizing to these unsteady flows, over a range of both spatial and temporal scales. This is primarily through adjustment of bed forms (including ripples, dunes and bar forms) which then subsequently alter the flow field. This paper investigates, through the application of a numerical model, the influence of these roughness elements on the overall flow and the increase in flow resistance. A series of experiments were undertaken in a flume, 16m long and 2m wide, where a fine sand (D50 of 239?m) mobile bed was water worked under a range of unsteady hydraulic conditions to generate a series of quasi-equilibrium three dimensional bed forms. During the experiments flow was measured with acoustic Doppler velocimeters, (aDv's). On four occasions the flume was drained and the bed topography measured with terrestrial LiDAR to create digital elevation models. This data provide the necessary boundary conditions and validation data for a Large Eddy Simulation (LES) model, which provided a three dimensional time dependent prediction of flow over the four static beds. The numerical predicted flow is analyzed through a series of approaches, and included: i) standard Reynolds decomposition to the flow fields; ii) Eulerian coherent structure detection methods based on the invariants of the velocity gradient tensor; iii) Lagrangian coherent structure identification methods based upon direct Lyapunov exponents (DLE). The results show that superimposed bed forms can cause changes in the nature of the classical separated flow region in particularly the number of locations where vortices are shed and the point of flow reattachment, which may be important for sediment entrainment and sediment transport dynamics during bed form adjustment. Finally, the flow predictions enable a reassessment of the drag caused by the superimposed bed forms generated by unsteady flow.

Hardy, R. J.; Reesink, A.; Parsons, D. R.; Ashworth, P. J.; Best, J.

2013-12-01

291

Unsteady potential flow past a propeller blade section

NASA Technical Reports Server (NTRS)

An analytical study was conducted to predict the effect of an oscillating stream on the time dependent sectional pressure and lift coefficients of a model propeller blade. The assumption is that as the blade sections encounter a wake, the actual angles of attack vary in a sinusoidal manner through the wake, thus each blade is exposed to an unsteady stream oscillating about a mean value at a certain reduced frequency. On the other hand, an isolated propeller at some angle of attack can experience periodic changes in the value of the flow angle causing unsteady loads on the blades. Such a flow condition requires the inclusion of new expressions in the formulation of the unsteady potential flow around the blade sections. These expressions account for time variation of angle of attack and total shed vortices in the wake of each airfoil section. It was found that the final expressions for the unsteady pressure distribution on each blade section are periodic and that the unsteady circulation and lift coefficients exhibit a hysteresis loop.

Takallu, M. A.

1990-01-01

292

Calculation of Unsteady Transonic Flow Over an Airfoil

NASA Technical Reports Server (NTRS)

An implicit finite-difference solver for either the Euler equations or the "thin-layer" Navier-Stokes equations was used to calculate a transonic flow over the NACA 64A010 airfoil pitching about its one-quarter chord. An unsteady automatic grid-generation procedure that will improve significantly the computational efficiency of various unsteady flow problems is described. The calculated results for both inviscid and viscous flows at Mach number 0.8 over the airfoil oscillating with reduced frequency referenced to one-half chord, 0.2, are compared with experimental data measured in the Ames 11 x 11 ft Transonic Wind Tunnel. Nonlinear, unsteady effects of the flow on the surface pressure variations, shock-wave excursions, and overall airloads are examined. Good agreements between the results of computations and experiments were obtained. In the shock-wave region, however, the results of the viscous-flow computations showed closer agreement with the experimental data.

Chyu, W. J.; Davis, S. S.; Chang, K. S.

1981-01-01

293

A turbulent approach to unsteady friction

This paper discusses the existing approaches to unsteady friction and presents some new ideas on the modelling of unsteady friction in turbulent pipe flows. This paper aims to contribute to a physically-based unsteady friction model that captures the known physical characteristics of friction phenomena in transient turbulent pipe flows. For practical applicability, a new model should not require extensive computer

Ivo Pothof

2008-01-01

294

Science of Cycling: Aerodynamics

NSDL National Science Digital Library

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

2007-12-26

295

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

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

Chen, Zhifeng; Fang, Haisheng

2011-09-01

296

Spatial Characteristics of the Unsteady Differential Pressures on 16 percent F/A-18 Vertical Tails

NASA Technical Reports Server (NTRS)

Buffeting is an aeroelastic phenomenon which plagues high performance aircraft at high angles of attack. For the F/A-18 at high angles of attack, vortices emanating from wing/fuselage leading edge extensions burst, immersing the vertical tails in their turbulent wake. The resulting buffeting of the vertical tails is a concern from fatigue and inspection points of view. Previous flight and wind-tunnel investigations to determine the buffet loads on the tail did not provide a complete description of the spatial characteristics of the unsteady differential pressures. Consequently, the unsteady differential pressures were considered to be fully correlated in the analyses of buffet and buffeting. The use of fully correlated pressures in estimating the generalized aerodynamic forces for the analysis of buffeting yielded responses that exceeded those measured in flight and in the wind tunnel. To learn more about the spatial characteristics of the unsteady differential pressures, an available 16%, sting-mounted, F-18 wind-tunnel model was modified and tested in the Transonic Dynamics Tunnel (TDT) at the NASA Langley Research Center as part of the ACROBAT (Actively Controlled Response Of Buffet-Affected Tails) program. Surface pressures were measured at high angles of attack on flexible and rigid tails. Cross-correlation and cross-spectral analyses of the pressure time histories indicate that the unsteady differential pressures are not fully correlated. In fact, the unsteady differential pressure resemble a wave that travels along the tail. At constant angle of attack, the pressure correlation varies with flight speed.

Moses, Robert W.; Ashley, Holt

1998-01-01

297

Computer simulation of unsteady wall impinging gas jet

The development and wall impinging process of an axis-sysmmetric unsteady helium jet was studied by using computer simulation. The position of the jet tip, with diffusion ignored, was visualized by the particle track method, based on which the penetration was defined. The method used here proves to be valid, for the calculation results coincide with experiment data in the literature.

Yunyi Gong; Kang Li; Chuntao Shi

1992-01-01

298

Aerodynamic: Applications of Force and Flow

NSDL National Science Digital Library

This resource guide from the Middle School Portal 2 project, written specifically for teachers, provides links to exemplary resources including background information, lessons, career information, and related national science education standards. Although there is a great deal of historical information about aerodynamics that could be discussed here, we purposely narrowed the stream of resources to those that encourage students to experiment with technological design and function. Given these learning experiences, student should be prepared to articulate preferences in vehicle design and understand how the principles of aerodynamics influence vehicle performance.

Briggs, Quentin

2005-03-01

299

A method to efficiently generate a complete aerodynamic description for projectile flight dynamic modelling is described. At the core of the method is an unsteady, time accurate computational fluid dynamic simulation that is tightly coupled to a rigid projectile flight dynamic simulation. A set of short time snippets of simulated projectile motion at different Mach numbers is computed and employed

M Costello; J Sahu

2008-01-01

300

Calculation of AGARD Wing 445.6 flutter using Navier-Stokes aerodynamics

NASA Technical Reports Server (NTRS)

An unsteady, 3D, implicit upwind Euler/Navier-Stokes algorithm is here used to compute the flutter characteristics of Wing 445.6, the AGARD standard aeroelastic configuration for dynamic response, with a view to the discrepancy between Euler characteristics and experimental data. Attention is given to effects of fluid viscosity, structural damping, and number of structural model nodes. The flutter characteristics of the wing are determined using these unsteady generalized aerodynamic forces in a traditional V-g analysis. The V-g analysis indicates that fluid viscosity has a significant effect on the supersonic flutter boundary for this wing.

Lee-Rausch, Elizabeth M.; Batina, John T.

1993-01-01

301

Mechanics and aerodynamics of insect flight control.

Insects have evolved sophisticated fight control mechanisms permitting a remarkable range of manoeuvres. Here, I present a qualitative analysis of insect flight control from the perspective of flight mechanics, drawing upon both the neurophysiology and biomechanics literatures. The current literature does not permit a formal, quantitative analysis of flight control, because the aerodynamic force systems that biologists have measured have rarely been complete and the position of the centre of gravity has only been recorded in a few studies. Treating the two best-known insect orders (Diptera and Orthoptera) separately from other insects, I discuss the control mechanisms of different insects in detail. Recent experimental studies suggest that the helicopter model of flight control proposed for Drosophila spp. may be better thought of as a facultative strategy for flight control, rather than the fixed (albeit selected) constraint that it is usually interpreted to be. On the other hand, the so-called 'constant-lift reaction' of locusts appears not to be a reflex for maintaining constant lift at varying angles of attack, as is usually assumed, but rather a mechanism to restore the insect to pitch equilibrium following a disturbance. Differences in the kinematic control mechanisms used by the various insect orders are related to differences in the arrangement of the wings, the construction of the flight motor and the unsteady mechanisms of lift production that are used. Since the evolution of insect flight control is likely to have paralleled the evolutionary refinement of these unsteady aerodynamic mechanisms, taxonomic differences in the kinematics of control could provide an assay of the relative importance of different unsteady mechanisms. Although the control kinematics vary widely between orders, the number of degrees of freedom that different insects can control will always be limited by the number of independent control inputs that they use. Control of the moments about all three axes (as used by most conventional aircraft) has only been proven for larger flies and dragonflies, but is likely to be widespread in insects given the number of independent control inputs available to them. Unlike in conventional aircraft, however, insects' control inputs are likely to be highly non-orthogonal, and this will tend to complicate the neural processing required to separate the various motions. PMID:11762490

Taylor, G K

2001-11-01

302

This book presents the papers given at a conference on fluid flow and hydraulics. Topics considered at the conference included a numerical study of pressure transients in a borehole due to pipe movement, laminar fluid transients in conduits of unconventional shape, water hammer analysis needs in nuclear power plant design, modeling blockage in unsteady slurry flow in conduits, and check

1985-01-01

303

Unsteady flow and dynamic response analyses for helicopter rotor blades

NASA Technical Reports Server (NTRS)

Research is presented on helicopter rotor blade vibration and on two and three dimensional analyses of unsteady incompressible viscous flow past oscillating helicopter rotor blades. A summary is presented of the two international research collaborations which resulted from the NASA project: the collaboration under the auspices of NATO between the University of Wisconsin-Milwaukee, University of Brussels, Belgium and the Aerodynamics Research Establishment in Goettingen, West Germany, and the collaboration under the auspices of the National Science Foundation between UWM and the University of Hamburg and the Ship Research Establishment in Hamburg, West Germany. A summary is given of the benefits from the NASA project to UWM, the College of Engineering and Applied Science, and the participants on the project.

Bratanow, T.

1979-01-01

304

Viscous effect on airfoils for unsteady transonic flows

NASA Technical Reports Server (NTRS)

The viscous effect on aerodynamic performance of an arbitrary airfoil executing low frequency maneuvers during transonic flight was investigated. The small disturbance code, LTRAN2, was modified by using a conventional integral method, BLAYER, for the boundary layer and an empirical relation, viscous wedge, for simulating the suddenly thickened boundary layer behind the shock. Before the shock, only the boundary layer displacement thickness was evaluated. After the shock, the empirical wedge thickness was superimposed on the boundary layer thickness along the surface as well as in the wake region. The pressure coefficients were calculated for both steady and unsteady states. The viscous solution takes fewer iterations to obtain the converged steady state solution. Comparisons made with experimental data and the inviscid solution show that the viscous solution agrees better with the experimental data with about the same (or slightly less) amount of computational time.

Lee, S. C.

1982-01-01

305

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

306

Darrieus wind turbines are relatively simple devices. Fixed geometry blades, usually only two or three in number, rotate about a vertical axis providing power to ground mounted power conversion or absorption machinery. No yaw control or power regulation systems are required. This simplicity, however, does not extend to the rotor's aerodynamics. The blade elements travel along circular paths through air whose relative speed and direction are constantly changing. The blade elements operate both unstalled and stalled with aerodynamic stall providing the rotor's inherent power regulation. The blade elements encounter their own wakes and those generated by other elements. These features combine to cause the thorough analysis of Darrieus rotor aerodynamics to be a challenging undertaking.

Klimas, P.C.

1981-01-01

307

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

NASA Astrophysics Data System (ADS)

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

Song, Arnold; Breuer, Kenneth

2007-11-01

308

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

309

A compilation of unsteady turbulent boundary-layer experimental data

NASA Technical Reports Server (NTRS)

An extensive literature search was conducted and those experiments related to unsteady boundary layer behavior were cataloged. In addition, an international survey of industrial, university, and governmental research laboratories was made in which new and ongoing experimental programs associated with unsteady turbulent boundary layer research were identified. Pertinent references were reviewed and classified based on the technical emphasis of the various experiments. Experiments that include instantaneous or ensemble averaged profiles of boundary layer variables are stressed. The experimental apparatus and flow conditions are described and summaries of acquired data and significant conclusions are summarized. Measurements obtained from the experiments which exist in digital form were stored on magnetic tape. Instructions are given for accessing these data sets for further analysis.

Carr, L. W.

1981-01-01

310

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

311

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

312

Dynamic stall and aerodynamic damping

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

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

1999-08-01

313

Physics of Forced Unsteady Separation

NASA Technical Reports Server (NTRS)

This report contains the proceedings of a workshop held at NASA Ames Research Center in April 1990. This workshop was jointly organized by NASA, the Air Force Office of Scientific Research (AFOSR), and the Army Research Office (ARO), and was directed toward improved understanding of the physical processes that cause unsteady separation to occur. The proceedings contain the written contributions for the workshop, and include selected viewgraphs used in the various presentations.

Carr, Lawrence W. (editor)

1992-01-01

314

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

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

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

2004-04-13

315

NASA Technical Reports Server (NTRS)

The results of an integrated study of structures, aerodynamics, and controls using the STARS program on two advanced airplane configurations are presented. Results for the X-29A include finite element modeling, free vibration analyses, unsteady aerodynamic calculations, flutter/divergence analyses, and an aeroservoelastic controls analysis. Good correlation is shown between STARS results and various other verified results. The tasks performed on the Oblique Wing Research Aircraft include finite element modeling and free vibration analyses.

Dawson, Kenneth S.; Fortin, Paul E.

1987-01-01

316

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

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

Richard W. Johnson

2006-09-01

317

A collection of flow visualization techniques used in the Aerodynamic Research Branch

NASA Technical Reports Server (NTRS)

Theoretical and experimental research on unsteady aerodynamic flows is discussed. Complex flow fields that involve separations, vortex interactions, and transonic flow effects were investigated. Flow visualization techniques are used to obtain a global picture of the flow phenomena before detailed quantitative studies are undertaken. A wide variety of methods are used to visualize fluid flow and a sampling of these methods is presented. It is emphasized that the visualization technique is a thorough quantitative analysis and subsequent physical understanding of these flow fields.

1984-01-01

318

The Fifth Symposium on Numerical and Physical Aspects of Aerodynamic Flows

NASA Technical Reports Server (NTRS)

This volume contains the papers presented at the Fifth Symposium on Numerical and Physical Aspects of Aerodynamic Flows, held at the California State University, Long Beach, from 13 to 15 January 1992. The symposium, like its immediate predecessors, considers the calculation of flows of relevance to aircraft, ships, and missiles with emphasis on the solution of two-dimensional unsteady and three-dimensional equations.

1992-01-01

319

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

NASA Astrophysics Data System (ADS)

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

Hu, Hui; Clemons, Lucas; Igarashi, Hirofumi

2011-08-01

320

NASA Astrophysics Data System (ADS)

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

Katz, Joseph

2006-01-01

321

AEROSPACE SCIENCES Applied aerodynamics

was made in the application of plasma flow-control concepts to practical actu- ators. Under an Air Force labs, and academia in the development of flow-control concepts, novel configuration aerodynamic and the Air Force Research Laboratory (AFRL) to gather information on stability and flight control

Xu, Kun

322

Advanced propeller aerodynamic analysis

NASA Technical Reports Server (NTRS)

The analytical approaches as well as the capabilities of three advanced analyses for predicting propeller aerodynamic performance are presented. It is shown that two of these analyses use a lifting line representation for the propeller blades, and the third uses a lifting surface representation.

Bober, L. J.

1980-01-01

323

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

324

Computational analysis of high resolution unsteady airloads for rotor aeroacoustics

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

325

Unsteady Climate, Groundwater Recharge, and Human Influence

NASA Astrophysics Data System (ADS)

Recharge is arguably the starting point of the groundwater hydrologic cycle. It marries above-ground hydrologic and climatic processes -runoff, precipitation, evapotranspiration- with groundwater flow and biochemical dynamics. This paper focuses on unsteady climate and ground water recharge linkages. Unsteady climate by virtue of its seasonal and inter-annual fluctuations or by shifts in the earth-atmosphere's radiative budget caused by secular forcing. Recharge is primarily caused by spatially diffuse percolation or by streamflow seepage. These two mechanisms are briefly reviewed. Examples of regional recharge governed by unsteady climate and affected by unsteady population are presented. Questions are raised about climate-recharge-human feebacks, and adaptation possibilities are proposed.

Loaiciga, H. A.

2007-12-01

326

NASA Astrophysics Data System (ADS)

For convenience of both measurement and adjusting the clearance size and incidence, the current research is mainly conducted by experiments on an axial compressor linear cascade. The characteristics and the condition under which the unsteadiness of tip leakage flow would occur were investigated by dynamic measuring in different clearances, inlet velocities and incidences. From the experiment it is found that increasing tip clearance size or reducing rotor tip incidence can affect the strength of the tip clearance flow. Then the experimental results also indicate the tip leakage shows instability in certain conditions, and the frequency of unsteadiness is great influenced by inflow angle. The condition of occurrence of tip leakage flow unsteadiness is when the leakage flow is strong enough to reach the pressure side of the adjacent blade. The main cause of tip leakage flow unsteadiness is the tip blade loading.

Li, Chengqing; Ke, Tingfeng; Zhang, Jingxuan; Zhang, Hongwu; Huang, Weiguang

2013-04-01

327

Aeroacoustic Study of a High-Fidelity Aircraft Model. Part 2; Unsteady Surface Pressures

NASA Technical Reports Server (NTRS)

In this paper, we present unsteady surface pressure measurements for an 18%-scale, semi-span Gulfstream aircraft model. This high-fidelity model is being used to perform detailed studies of airframe noise associated with main landing gear, flap components, and gear-flap interaction noise, as well as to evaluate novel noise reduction concepts. The aerodynamic segment of the tests, conducted in the NASA Langley Research Center 14- by 22-Foot Subsonic Tunnel, was completed in November 2010. To discern the characteristics of the surface pressure fluctuations in the vicinity of the prominent noise sources, unsteady sensors were installed on the inboard and outboard flap edges, and on the main gear wheels, struts, and door. Various configurations were tested, including flap deflections of 0?, 20?, and 39?, with and without the main landing gear. The majority of unsteady surface pressure measurements were acquired for the nominal landing configuration where the main gear was deployed and the flap was deflected 39?. To assess the Mach number variation of the surface pressure amplitudes, measurements were obtained at Mach numbers of 0.16, 0.20, and 0.24. Comparison of the unsteady surface pressures with the main gear on and off shows significant interaction between the gear wake and the inboard flap edge, resulting in higher amplitude fluctuations when the gear is present.

Khorrami, Mehdi R.; Neuhart, Danny H.

2012-01-01

328

Preliminary results of unsteady blade surface pressure measurements for the SR-3 propeller

NASA Technical Reports Server (NTRS)

Unsteady blade surface pressures were measured on an advanced, highly swept propeller known as SR-3. These measurements were obtained because the unsteady aerodynamics of these highly loaded transonic blades is important to noise generation and aeroelastic response. Specifically, the response to periodic angle-of-attack change was measured for both two- and eight-bladed configurations over a range of flight Mach numbers from 0.4 to 0.85. The periodic angle-of-attack change was obtained by placing the propeller axis at angles up to 4 deg to the flow. Most of the results are presented in terms of the unsteady pressure coefficient variation with Mach number. Both cascade and Mach number effects were largest on the suction surface near the leading edge. The results of a three-dimensional Euler code applied in a quasi-steady fashion were compared to measured data at the reduced frequency of 0.1 and showed relatively poor agreement. Pressure waveforms are shown that suggest shock phenomena may play an important part in the unsteady pressure response at some blade locations.

Heidelberg, L. J.; Clark, B. J.

1986-01-01

329

An analysis of blade vortex interaction aerodynamics and acoustics

NASA Technical Reports Server (NTRS)

The impulsive noise associated with helicopter flight due to Blade-Vortex Interaction, sometimes called blade slap is analyzed especially for the case of a close encounter of the blade-tip vortex with a following blade. Three parts of the phenomena are considered: the tip-vortex structure generated by the rotating blade, the unsteady pressure produced on the following blade during the interaction, and the acoustic radiation due to the unsteady pressure field. To simplify the problem, the analysis was confined to the situation where the vortex is aligned parallel to the blade span in which case the maximum acoustic pressure results. Acoustic radiation due to the interaction is analyzed in space-fixed coordinates and in the time domain with the unsteady pressure on the blade surface as the source of chordwise compact, but spanwise non-compact radiation. Maximum acoustic pressure is related to the vortex core size and Reynolds number which are in turn functions of the blade-tip aerodynamic parameters. Finally noise reduction and performance are considered.

Lee, D. J.

1985-01-01

330

Aerodynamic analysis of an isolated vehicle wheel

NASA Astrophysics Data System (ADS)

Increasing fuel prices force the manufacturers to look into all aspects of car aerodynamics including wheels, tyres and rims in order to minimize their drag. By diminishing the aerodynamic drag of vehicle the fuel consumption will decrease, while driving safety and comfort will improve. In order to properly illustrate the impact of a rotating wheel aerodynamics on the car body, precise analysis of an isolated wheel should be performed beforehand. In order to represent wheel rotation in contact with the ground, presented CFD simulations included Moving Wall boundary as well as Multiple Reference Frame should be performed. Sliding mesh approach is favoured but too costly at the moment. Global and local flow quantities obtained during simulations were compared to an experiment in order to assess the validity of the numerical model. Results of investigation illustrates dependency between type of simulation and coefficients (drag and lift). MRF approach proved to be a better solution giving result closer to experiment. Investigation of the model with contact area between the wheel and the ground helps to illustrate the impact of rotating wheel aerodynamics on the car body.

Le?niewicz, P.; Kulak, M.; Karczewski, M.

2014-08-01

331

Evaluation of the constant pressure panel method (CPM) for unsteady air loads prediction

NASA Technical Reports Server (NTRS)

This paper evaluates the capability of the constant pressure panel method (CPM) code to predict unsteady aerodynamic pressures, lift and moment distributions, and generalized forces for general wing-body configurations in supersonic flow. Stability derivatives are computed and correlated for the X-29 and an Oblique Wing Research Aircraft, and a flutter analysis is carried out for a wing wind tunnel test example. Most results are shown to correlate well with test or published data. Although the emphasis of this paper is on evaluation, an improvement in the CPM code's handling of intersecting lifting surfaces is briefly discussed. An attractive feature of the CPM code is that it shares the basic data requirements and computational arrangements of the doublet lattice method. A unified code to predict unsteady subsonic or supersonic airloads is therefore possible.

Appa, Kari; Smith, Michael J. C.

1988-01-01

332

Perturbation dynamics in unsteady pipe flows

NASA Astrophysics Data System (ADS)

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

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

333

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

334

Unsteady three-dimensional simulation of VTOL upwash fountain turbulence

NASA Technical Reports Server (NTRS)

Numerical simulations of a planar turbulent wall jet and a planar VTOL upwash fountain were performed. These are three dimensional simulations which resolve large scale unsteady motions in the flows. The wall jet simulation shows good agreement with experimental data and is presented to verify the simulation methodology. Simulation of the upwash fountain predicts elevated shear stress and a half velocity width spreading rate of 33% which agrees well with experiment. Turbulence mechanisms which contribute to the enhanced spreading rate are examined.

Childs, Robert E.; Nixon, David

1987-01-01

335

Developments in unsteady pipe flow friction modelling

This paper reviews a number of unsteady friction models for transient pipe flow. Two distinct unsteady friction models, the Zielke and the Brunone models, are investigated in detail. The Zielke model, originally developed for transient laminar flow, has been selected to verify its effectiveness for \\

Anton Bergant; Angus Ross Simpson; John Vìtkovsk

2001-01-01

336

AIAA 950048 Multigrid Unsteady Navier-Stokes

AIAA 95Â0048 Multigrid Unsteady Navier-Stokes Calculations with Aeroelastic Applications Juan JÂ4344 #12;AIAA 95Â0048 Multigrid Unsteady Navier-Stokes Calculations with Aeroelastic Applications Juan J for cell i,j p static pressure qi heat flux component R(wij ) total flux residual for cell i,j R modified

Jameson, Antony

337

Compendium of NASA Langley reports on hypersonic aerodynamics

NASA Technical Reports Server (NTRS)

Reference is made to papers published by the Langley Research Center in various areas of hypersonic aerodynamics for the period 1950 to 1986. The research work was performed either in-house by the Center staff or by other personnel supported entirely or in part by grants or contracts. Abstracts have been included with the references when available. The references are listed chronologically and are grouped under the following general headings: (1) Aerodynamic Measurements - Single Shapes; (2) Aerodynamic Measurements - Configurations; (3) Aero-Heating; (4) Configuration Studies; (5) Propulsion Integration Experiment; (6) Propulsion Integration - Study; (7) Analysis Methods; (8) Test Techniques; and (9) Airframe Active Cooling Systems.

Sabo, Frances E.; Cary, Aubrey M.; Lawson, Shirley W.

1987-01-01

338

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

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

1991-01-01

339

Efficient Global Aerodynamic Modeling from Flight Data

NASA Technical Reports Server (NTRS)

A method for identifying global aerodynamic models from flight data in an efficient manner is explained and demonstrated. A novel experiment design technique was used to obtain dynamic flight data over a range of flight conditions with a single flight maneuver. Multivariate polynomials and polynomial splines were used with orthogonalization techniques and statistical modeling metrics to synthesize global nonlinear aerodynamic models directly and completely from flight data alone. Simulation data and flight data from a subscale twin-engine jet transport aircraft were used to demonstrate the techniques. Results showed that global multivariate nonlinear aerodynamic dependencies could be accurately identified using flight data from a single maneuver. Flight-derived global aerodynamic model structures, model parameter estimates, and associated uncertainties were provided for all six nondimensional force and moment coefficients for the test aircraft. These models were combined with a propulsion model identified from engine ground test data to produce a high-fidelity nonlinear flight simulation very efficiently. Prediction testing using a multi-axis maneuver showed that the identified global model accurately predicted aircraft responses.

Morelli, Eugene A.

2012-01-01

340

Size effects on insect hovering aerodynamics: an integrated computational study.

Hovering is a miracle of insects that is observed for all sizes of flying insects. Sizing effect in insect hovering on flapping-wing aerodynamics is of interest to both the micro-air-vehicle (MAV) community and also of importance to comparative morphologists. In this study, we present an integrated computational study of such size effects on insect hovering aerodynamics, which is performed using a biology-inspired dynamic flight simulator that integrates the modelling of realistic wing-body morphology, the modelling of flapping-wing and body kinematics and an in-house Navier-Stokes solver. Results of four typical insect hovering flights including a hawkmoth, a honeybee, a fruit fly and a thrips, over a wide range of Reynolds numbers from O(10(4)) to O(10(1)) are presented, which demonstrate the feasibility of the present integrated computational methods in quantitatively modelling and evaluating the unsteady aerodynamics in insect flapping flight. Our results based on realistically modelling of insect hovering therefore offer an integrated understanding of the near-field vortex dynamics, the far-field wake and downwash structures, and their correlation with the force production in terms of sizing and Reynolds number as well as wing kinematics. Our results not only give an integrated interpretation on the similarity and discrepancy of the near- and far-field vortex structures in insect hovering but also demonstrate that our methods can be an effective tool in the MAVs design. PMID:19258688

Liu, H; Aono, H

2009-03-01

341

On the acoustic and aerodynamic performance of serrated airfoils.

This paper is concerned with the aerodynamic and aeroacoustic performance of airfoils with serrated trailing edges. Although a great deal of research has been directed toward the application of serrations for reducing the trailing-edge noise, the aerodynamic performance of such airfoils has received very little research attention. Sawtooth and slitted-sawtooth trailing edges with specific geometrical characteristics have been shown to be effective in reducing the trailing edge noise over a wide range of frequencies. It has, however, also been shown that they can alter the flow characteristics near the trailing edge, namely the boundary layer thickness and surface-pressure fluctuations, and the wake formation. To better understand the effects of serrations, we shall carry out various acoustic and wind tunnel tests for a NACA6512-10 airfoil with various sawtooth, slitted and slitted-sawtooth trailing edge profiles. Flow measurements are carried out using PIV, LDV and hot-wire anemometry and the steady and unsteady forces on the airfoil are obtained using a three-component force balance system. Results are presented for a wide range of Reynolds numbers and angles of attack. The results have shown that the use of sharp serrations can significantly change the aerodynamic performance and wake characteristics of the airfoil. PMID:25235897

Liu, Xiao; Azarpeyvand, Mahdi; Joseph, Phillip

2014-04-01

342

Aerodynamic database development of the ESA intermediate experimental vehicle

NASA Astrophysics Data System (ADS)

This work deals with the aerodynamic database development of the Intermediate Experiment Vehicle. The aerodynamic analysis, carried out for the whole flight scenario, relies on computational fluid dynamics, wind tunnel test, and engineering-based design data generated during the project phases, from rarefied flow conditions, to hypersonic continuum flow up to reach subsonic speeds regime. Therefore, the vehicle aerodynamic database covers the range of Mach number, angle of attack, sideslip and control surface deflections foreseen for the vehicle nominal re-entry. In particular, the databasing activities are developed in the light of build-up approach. This means that all aerodynamic force and moment coefficients are provided by means of a linear summation over certain number of incremental contributions such as, for example, effect of sideslip angle, aerodynamic control surface effectiveness, etc. Each force and moment coefficient is treated separately and appropriate equation is provided, in which all the pertinent contributions for obtaining the total coefficient for any selected flight conditions appear. To this aim, all the available numerical and experimental aerodynamic data are gathered in order to explicit the functional dependencies from each aerodynamic model addend through polynomial expressions obtained with the least squares method. These polynomials are function of the primary variable that drives the phenomenon whereas secondary dependencies are introduced directly into its unknown coefficients which are determined by means of best-fitting algorithms.

Pezzella, Giuseppe; Marino, Giuliano; Rufolo, Giuseppe C.

2014-01-01

343

Vortex scale of unsteady separation on a pitching airfoil.

The streaklines of unsteady separation on two kinds of pitching airfoils, the NACA65-0910 and a blunt trailing edge airfoil, were studied by dye flow visualization and by the Schlieren method. The latter visualized the discrete vortices shed from the leading edge. The results of these visualization studies allow a comparison between the dynamic behavior of the streakline of unsteady separation and that of the discrete vortices shed from the leading edge. The influence of the airfoil configuration on the flow characteristics was also examined. Furthermore, the scale of a discrete vortex forming the recirculation region was investigated. The non-dimensional pitching rate was k = 0.377, the angle of attack alpha(m) = 16 degrees and the pitching amplitude was fixed to A = +/-6 degrees for Re = 4.0 x 10(3) in this experiment. PMID:12495998

Fuchiwaki, Masaki; Tanaka, Kazuhiro

2002-10-01

344

Boundary layer receptivity to unsteady free-stream pressure gradients

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

345

Robustness of de Saint Venant equations for simulating unsteady flows

Long-wave motion in open channels can be expressed mathematically by the one-dimensional de Saint Venant equations describing conservation of fluid mass and momentum. Numerical simulation models, based on either depth/velocity or water-level/discharge dependent-variable formulations of these equations, are typically used to simulate unsteady open-channel flow. However, the implications and significance of selecting either dependent-variable form - on model development, discretization and numerical solution processes, and ultimately on the range-of-application and simulation utility of resulting models - are not well known. Results obtained from a set of numerical experiments employing two models - one based on depth/velocity and the other on water-level/discharge equation formulations - reveal the sensitivity of the two equation sets to various channel properties and dynamic flow conditions. In particular, the effects of channel gradient, channel width-to-depth ratio, flow-resistance coefficient, and flow unsteadiness are analyzed and discussed.

Baltzer, Robert, A.; Schaffranek, Raymond, W.; Lai, Chintu

1995-01-01

346

Unsteady Full Annulus Simulations of a Transonic Axial Compressor Stage

NASA Technical Reports Server (NTRS)

Two recent research endeavors in turbomachinery at NASA Glenn Research Center have focused on compression system stall inception and compression system aerothermodynamic performance. Physical experiment and computational research are ongoing in support of these research objectives. TURBO, an unsteady, three-dimensional, Navier-Stokes computational fluid dynamics code commissioned and developed by NASA, has been utilized, enhanced, and validated in support of these endeavors. In the research which follows, TURBO is shown to accurately capture compression system flow range-from choke to stall inception-and also to accurately calculate fundamental aerothermodynamic performance parameters. Rigorous full-annulus calculations are performed to validate TURBO s ability to simulate the unstable, unsteady, chaotic stall inception process; as part of these efforts, full-annulus calculations are also performed at a condition approaching choke to further document TURBO s capabilities to compute aerothermodynamic performance data and support a NASA code assessment effort.

Herrick, Gregory P.; Hathaway, Michael D.; Chen, Jen-Ping

2009-01-01

347

Oscillating cascade aerodynamics at large mean incidence

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

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

1998-01-01

348

Aerodynamic measurements concerned with a turret model

NASA Technical Reports Server (NTRS)

An experimental investigation was carried out in the 14 by 14 ft Ames transonic wind tunnel on a turret model. The aerodynamic parameters measured were steady and unsteady pressures (static and total fluid pressures), local mean velocities, and local mean densities at selected locations along the optical beam path for the azimuth look angles of 90, 120, and 150 degrees from the turret. The test stream Mach numbers considered are 0.55, 0.65 and 0.75, and the Reynolds number per meter is in the range of 10 million. The results indicate that severe optical degradation can be expected at aft look azimuth, angles, this degradation in optical performance increases as the azimuth angle is increased. The ratio of rms static pressure to the local mean static pressure peaks in the range of 0.07 to 0.12 and the ratio of rms total pressure to the local mean total pressure peaks in the range of 0.02 to 0.04. These values depend on the Mach number and the aft look azimuth angle. The scale lengths obtained from correlation considerations are also presented.

Raman, K. R.

1981-01-01

349

Oscillating cascade aerodynamics at large mean incidence

NASA Technical Reports Server (NTRS)

The aerodynamics of a cascade of airfoils oscillating in torsion about the midchord is investigated experimentally at a large mean incidence angle and, for reference, at a low mean incidence angle. The airfoil section is representative of a modern, low aspect ratio, fan blade tip section. Time-dependent airfoil surface pressure measurements were made for reduced frequencies of up to 1.2 for out-of-phase oscillations at a Mach number of 0.5 and chordal incidence angles of 0 deg and 10 deg; the Reynolds number was 0.9 x l0(exp 6). For the 10 deg chordal incidence angle, a separation bubble formed at the leading edge of the suction surface. The separated flow field was found to have a dramatic effect on the chordwise distribution of the unsteady pressure. In this region, substantial deviations from the attached flow data were found with the deviations becoming less apparent in the aft region of the airfoil for all reduced frequencies. In particular, near the leading edge the separated flow had a strong destabilizing influence while the attached flow had a strong stabilizing influence.

Buffum, Daniel H.; King, Aaron J.; El-Aini, Yehia M.; Capece, Vincent R.

1996-01-01

350

Nonlinear slender wing aerodynamics. [delta wing

NASA Technical Reports Server (NTRS)

On present day high performance aircraft, a large portion of the lift is generated by leading edge vortices generated by flow separation off the highly swept leading edges of the lifting surfaces employed. It has been shown in an earlier paper how the vortex effects can be superimposed on a modified slender wing theory to give the unsteady longitudinal characteristics of sharp-edged delta wings up to very high angles of attack. The present paper extends the previous analysis to include the effects of leading edge roundness and trailing edge sweep on the aerodynamic characteristics. The paper also derives analytic means for prediction of the yaw stability of slender wings and the first order effects of Mach number. Universal scaling laws are defined for rapid preliminary design estimates of the slender wing lift and rolling moment. The results indicate that simple analytic tools can be developed to predict the aeroelastic characteristics of the space shuttle ascent configuration with its complicated flow field and aeroelastic cross-couplings.

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

1976-01-01

351

Aerodynamic Shape Optimization Using the Adjoint Method

Aerodynamic Shape Optimization Using the Adjoint Method Antony Jameson Department of Aeronautics techniques based on control theory for aerodynamic shape design in both inviscid and viscous compressible optimization of transonic wing-body combinations. 1 Introduction: Aerodynamic Design The definition

Jameson, Antony

352

Freight Wing Trailer Aerodynamics

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

Graham, Sean (Primary Investigator); Bigatel, Patrick

2004-10-17

353

A linearized Euler analysis of unsteady transonic flows in turbomachinery

A computational method for efficiently predicting unsteady transonic flows in two- and three-dimensional cascades is presented. The unsteady flow is modeled using a linearized Euler analysis whereby the unsteady flow field is decomposed into a nonlinear mean flow plus a linear harmonically varying unsteady flow. The equations that govern the perturbation flow, the linearized Euler equations, are linear variable coefficient

K. C. Hall; W. S. Clark; C. B. Lorence

1994-01-01

354

Numerical Aerodynamic Simulation (NAS)

NASA Technical Reports Server (NTRS)

The history of the Numerical Aerodynamic Simulation Program, which is designed to provide a leading-edge capability to computational aerodynamicists, is traced back to its origin in 1975. Factors motivating its development and examples of solutions to successively refined forms of the governing equations are presented. The NAS Processing System Network and each of its eight subsystems are described in terms of function and initial performance goals. A proposed usage allocation policy is discussed and some initial problems being readied for solution on the NAS system are identified.

Peterson, V. L.; Ballhaus, W. F., Jr.; Bailey, F. R.

1983-01-01

355

Unsteady tip clearance flow in an isolated axial compressor rotor

NASA Astrophysics Data System (ADS)

The paper investigates effects of operating conditions, tip clearance sizes and external unsteady excitations on the unsteady tip clearance flow in an isolated axial compressor rotor by unsteady 3D Navier-Stokes simulations. The results show that the unsteady tip clearance vortex takes a periodic flow behavior in the rotor tip region. With the decrease of the flow coefficient, the unsteady tip clearance vortex is enhanced and its frequency becomes lower. A larger tip clearance size can cause bigger unsteady fluctuation amplitude and a lower fluctuation frequency of the tip clearance vortex at the near stall operating condition. The unsteady excitation with the natural frequency of the tip clearance vortex can enhance the unsteadiness of the tip clearance vortex and improve the overall rotor performance. The frequency of the unsteady tip clearance vortex is independent of external unsteady excitations with different frequencies.

Zhang, Hongwu; Deng, Xiangyang; Chen, Jingyi; Huang, Weiguang

2005-09-01

356

Measurements of aerodynamic forces on unsteadily moving bluff parachute canopies

Equations which describe the unsteady motion of bluff bodies through fluids contain certain components, termed added mass coefficients, which can only be determined by experiment. From the solutions to such equations the ways in which the shapes of parachute canopies influence the frequency of their oscillatory motion in pitch and their corresponding damping rates are required. Although a full-scale parachute

D. J. Cockrell; R. J. Harwood; C. Q. Shen

1987-01-01

357

Aerodynamic design using numerical optimization

NASA Technical Reports Server (NTRS)

The procedure of using numerical optimization methods coupled with computational fluid dynamic (CFD) codes for the development of an aerodynamic design is examined. Several approaches that replace wind tunnel tests, develop pressure distributions and derive designs, or fulfill preset design criteria are presented. The method of Aerodynamic Design by Numerical Optimization (ADNO) is described and illustrated with examples.

Murman, E. M.; Chapman, G. T.

1983-01-01

358

Aerodynamic design via control theory

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

Antony Jameson

1988-01-01

359

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

360

Aerodynamics of a Party Balloon

ERIC Educational Resources Information Center

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

Cross, Rod

2007-01-01

361

Unsteady tip clearance flow in an isolated axial compressor rotor

The paper investigates effects of operating conditions, tip clearance sizes and external unsteady excitations on the unsteady\\u000a tip clearance flow in an isolated axial compressor rotor by unsteady 3D Navier-Stokes simulations. The results show that the\\u000a unsteady tip clearance vortex takes a periodic flow behavior in the rotor tip region. With the decrease of the flow coefficient,\\u000a the unsteady tip

Hongwu Zhang; Xiangyang Deng; Jingyi Chen; Weiguang Huang

2005-01-01

362

Aerodynamics of flapping wings with fluttering trailing edges

NASA Astrophysics Data System (ADS)

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

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

2010-11-01

363

Study of Aerodynamic Design Procedure of a Large-Scale Aircraft Noise Suppression Facility

The aerodynamic design procedure of a large-scale aircraft noise suppression facility has been developed. Flow quality required for the engine inlet flow has been determined through basic experiment. Aerodynamic design of the facility has been performed by using wind tunnel experiment and CFD. Important relationship between the length of the facility and the inlet flow quality has been found. The

Masafumi Kawai; Kiyoyuki Nagai; Shigeru Aso

2008-01-01

364

Unsteady wind loads for TMT: replacing parametric models with CFD

NASA Astrophysics Data System (ADS)

Unsteady wind loads due to turbulence inside the telescope enclosure result in image jitter and higher-order image degradation due to M1 segment motion. Advances in computational fluid dynamics (CFD) allow unsteady simulations of the flow around realistic telescope geometry, in order to compute the unsteady forces due to wind turbulence. These simulations can then be used to understand the characteristics of the wind loads. Previous estimates used a parametric model based on a number of assumptions about the wind characteristics, such as a von Karman spectrum and frozen-flow turbulence across M1, and relied on CFD only to estimate parameters such as mean wind speed and turbulent kinetic energy. Using the CFD-computed forces avoids the need for assumptions regarding the flow. We discuss here both the loads on the telescope that lead to image jitter, and the spatially-varying force distribution across the primary mirror, using simulations with the Thirty Meter Telescope (TMT) geometry. The amplitude, temporal spectrum, and spatial distribution of wind disturbances are all estimated; these are then used to compute the resulting image motion and degradation. There are several key differences relative to our earlier parametric model. First, the TMT enclosure provides sufficient wind reduction at the top end (near M2) to render the larger cross-sectional structural areas further inside the enclosure (including M1) significant in determining the overall image jitter. Second, the temporal spectrum is not von Karman as the turbulence is not fully developed; this applies both in predicting image jitter and M1 segment motion. And third, for loads on M1, the spatial characteristics are not consistent with propagating a frozen-flow turbulence screen across the mirror: Frozen flow would result in a relationship between temporal frequency content and spatial frequency content that does not hold in the CFD predictions. Incorporating the new estimates of wind load characteristics into TMT response predictions leads to revised estimates of the response of TMT to wind turbulence, and validates the aerodynamic design of the enclosure.

MacMartin, Douglas G.; Vogiatzis, Konstantinos

2014-08-01

365

Ground/Flight Correlation of Aerodynamic Loads with Structural Response

NASA Technical Reports Server (NTRS)

Ground and flight tests provide a basis and methodology for in-flight characterization of the aerodynamic and structural performance through the monitoring of the fluid-structure interaction. The NF-15B flight tests of the Intelligent Flight Control System program provided a unique opportunity to test the correlation of aerodynamic loads with points of flow attaching and detaching from the surface, which are also known as flow bifurcation points, as observed in a previous wind tunnel test performed at the U.S. Air Force Academy (Colorado Springs, Colorado). Moreover, flight tests, along with the subsequent unsteady aerodynamic tests in the NASA Transonic Dynamics Tunnel (TDT), provide a basis using surface flow sensors as means of assessing the aeroelastic performance of flight vehicles. For the flight tests, the NF-15B tail was instrumented with hot-film sensors and strain gages for measuring root-bending strains. This data were gathered via selected sideslip maneuvers performed at level flight and subsonic speeds. The aerodynamic loads generated by the sideslip maneuver resulted in a structural response, which were then compared with the hot-film sensor signals. The hot-film sensor signals near the stagnation region were found to be highly correlated with the root-bending strains. For the TDT tests, a flexible wing section developed under the U.S. Air Force Research Lab SensorCraft program was instrumented with strain gages, accelerometers, and hot-film sensors at two span stations. The TDT tests confirmed the correlation between flow bifurcation points and the wing structural response to tunnel-generated gusts. Furthermore, as the wings structural modes were excited by the gusts, a gradual phase change between the flow bifurcation point and the structural mode occurred during a resonant condition.

Mangalam, Arun S.; Davis, Mark C.

2009-01-01

366

Unsteady lifting-line theory with applications

NASA Technical Reports Server (NTRS)

Unsteady lifting-line theory is developed for a flexible unswept wing of large aspect ratio oscillating at low frequency in inviscid incompressible flow. The theory is formulated in terms of the acceleration potential and treated by the method of matched asymptotic expansions. The wing displacements are prescribed and the pressure field, airloads, and unsteady induced downwash are obtained in closed form. Sample numerical calculations are presented. The present work identifies and resolves errors in the unsteady lifting-line theory of James and points out a limitation in that of Van Holten. Comparison of the results of Reissner's approximate unsteady lifting-surface theory with those of the present work shows favorable agreement. The present work thus provides some formal justification for Reissner's ad hoc theory. For engineering purposes, the region of applicability of the theory in the reduced frequency-aspect ratio domain is identified approximately and found to cover most cases of practical interest.

Ahmadi, A. R.; Widnall, S. E.

1982-01-01

367

Calculation of AGARD Wing 445.6 Flutter Using Navier-Stokes Aerodynamics

NASA Technical Reports Server (NTRS)

The flutter characteristics of the first AGARD standard aeroelastic configuration for dynamic response, Wing 445.6, are studied using an unsteady Navier-Stokes algorithm in order to investigate a previously noted discrepancy between Euler flutter characteristics and the experimental data. The algorithm, which is a three-dimensional, implicit, upwind Euler/Navier-Stokes code (CFL3D Version 2.1), was previously modified for the time-marching, aeroelastic analysis of wings using the unsteady Euler equations. These modifications include the incorporation of a deforming mesh algorithm and the addition of the structural equations of motion for their simultaneous time integration with the governing flow equations. In this paper, the aeroelastic method is extended and evaluated for applications that use the Navier- Stokes aerodynamics. The paper presents a brief description of the aeroelastic method and presents unsteady calculations which verify this method for Navier-Stokes calculations. A linear stability analysis and a time-marching aeroelastic analysis are used to determine the flutter characteristics of the isolated 45 deg. swept-back wing. Effects of fluid viscosity, structural damping, and number of modes in the structural model are investigated. For the linear stability analysis, the unsteady generalized aerodynamic forces of the wing are computed for a range of reduced frequencies using the pulse transfer-function approach. The flutter characteristics of the wing are determined using these unsteady generalized aerodynamic forces in a traditional V-g analysis. This stability analysis is used to determine the flutter characteristics of the wing at free-stream Mach numbers of 0.96 and 1.141 using the generalized aerodynamic forces generated by solving the Euler equations and the Navier-Stokes equations. Time-marching aeroelastic calculations are performed at a free-stream Mach number of 1.141 using the Euler and Navier-Stokes equations to compare with the linear V-g flutter analysis method. The V-g analysis, which is used in conjunction with the time-marching analysis, indicates that the fluid viscosity has a significant effect on the supersonic flutter boundary for this wing while the structural damping and number of modes in the structural model have a lesser effect.

Lee-Rausch, Elizabeth M.; Batina, John T.

1993-01-01

368

The present conference discusses topics in CFD methods and their validation, vortices and vortical flows, STOL/VSTOL aerodynamics, boundary layer transition and separation, wing airfoil aerodynamics, laminar flow, supersonic and hypersonic aerodynamics, CFD for wing airfoil and nacelle applications, wind tunnel testing, flight testing, missile aerodynamics, unsteady flow, configuration aerodynamics, and multiple body/interference flows. Attention is given to the numerical simulation of vortical flows over close-coupled canard-wing configuration, propulsive lift augmentation by side fences, road-vehicle aerodynamics, a shock-capturing method for multidimensional flow, transition-detection studies in a cryogenic environment, a three-dimensional Euler analysis of ducted propfan flowfields, multiple vortex and shock interaction at subsonic and supersonic speeds, and a Navier-Stokes simulation of waverider flowfields. Also discussed are the induced drag of crescent-shaped wings, the preliminary design aerodynamics of missile inlets, finite wing lift prediction at high angles-of-attack, optimal supersonic/hypersonic bodies, and adaptive grid embedding for the two-dimensional Euler equations.

Not Available

1990-01-01

369

NASA Technical Reports Server (NTRS)

The rapid increase in available computational power over the last decade has enabled higher resolution flow simulations and more widespread use of unstructured grid methods for complex geometries. While much of this effort has been focused on steady-state calculations in the aerodynamics community, the need to accurately predict off-design conditions, which may involve substantial amounts of flow separation, points to the need to efficiently simulate unsteady flow fields. Accurate unsteady flow simulations can easily require several orders of magnitude more computational effort than a corresponding steady-state simulation. For this reason, techniques for improving the efficiency of unsteady flow simulations are required in order to make such calculations feasible in the foreseeable future. The purpose of this work is to investigate possible reductions in computer time due to the choice of an efficient time-integration scheme from a series of schemes differing in the order of time-accuracy, and by the use of more efficient techniques to solve the nonlinear equations which arise while using implicit time-integration schemes. This investigation is carried out in the context of a two-dimensional unstructured mesh laminar Navier-Stokes solver.

Jothiprasad, Giridhar; Mavriplis, Dimitri J.; Caughey, David A.

2002-01-01

370

NASA Technical Reports Server (NTRS)

The principal emphasis of the meeting was to be on the understanding and prediction of separation-induced vortex flows and their effects on vehicle performance, stability, control, and structural design loads. This report shows that a substantial amount of the papers covering this area were received from a wide range of countries, together with an attendance that was even more diverse. In itself, this testifies to the current interest in the subject and to the appropriateness of the Panel's choice of topic and approach. An attempt is made to summarize each paper delivered, and to relate the contributions made in the papers and in the discussions to some of the important aspects of vortex flow aerodynamics. This reveals significant progress and important clarifications, but also brings out remaining weaknesses in predictive capability and gaps in understanding. Where possible, conclusions are drawn and areas of continuing concern are identified.

Smith, J. H. B.; Campbell, J. F.; Young, A. D. (editor)

1992-01-01

371

Three sorts of wave equations, i.e., (1) wave equations taking into account viscosity and radial velocity, (2) wave equations assuming Hagen-Poiseuille flow and (3) water hammer equations, are compared for unsteady flow in uniform lines. Both frequency and transient response experiments are carried out with use of a rotary sinusoidal flow generator and a quick closing valve, respectively. Experimental and

S. Washio; T. Konishi; K. Okamura

1974-01-01

372

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

373

AIAA Applied Aerodynamics Conference, 7th, Seattle, WA, July 31-Aug. 2, 1989, Technical Papers

The present conference discusses the comparative aerodynamic behavior of half-span and full-span delta wings, TRANAIR applications to engine/airframe integration, a zonal approach to V/STOL vehicle aerodynamics, an aerodynamic analysis of segmented aircraft configurations in high-speed flight, unstructured grid generation and FEM flow solvers, surface grid generation for flowfields using B-spline surfaces, the use of chimera in supersonic viscous calculations for the F-15, and hypersonic vehicle forebody design studies. Also discussed are the aerothermodynamics of projectiles at hypersonic speeds, flow visualization of wing-rock motion in delta wings, vortex interaction over delta wings at high alpha, the analysis and design of dual-rotation propellers, unsteady pressure loads from plunging airfoils, the effects of riblets on the wake of an airfoil, inverse airfoil design with Navier-Stokes methods, flight testing for a 155-mm base-burn projectile, experimental results on rotor/fuselage aerodynamic interactions, the high-alpha aerodynamic characteristics of crescent and elliptic wings, and the effects of free vortices on lifting surfaces.

Not Available

1989-01-01

374

Unsteady thermocapillary migration of bubbles

NASA Technical Reports Server (NTRS)

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

Dill, Loren H.; Balasubramaniam, R.

1988-01-01

375

Computation of rotor aerodynamic loads in forward flight using a full-span free wake analysis

NASA Technical Reports Server (NTRS)

The development of an advanced computational analysis of unsteady aerodynamic loads on isolated helicopter rotors in forward flight is described. The primary technical focus of the development was the implementation of a freely distorting filamentary wake model composed of curved vortex elements laid out along contours of constant vortex sheet strength in the wake. This model captures the wake generated by the full span of each rotor blade and makes possible a unified treatment of the shed and trailed vorticity in the wake. This wake model was coupled to a modal analysis of the rotor blade dynamics and a vortex lattice treatment of the aerodynamic loads to produce a comprehensive model for rotor performance and air loads in forward flight dubbed RotorCRAFT (Computation of Rotor Aerodynamics in Forward Flight). The technical background on the major components of this analysis are discussed and the correlation of predictions of performance, trim, and unsteady air loads with experimental data from several representative rotor configurations is examined. The primary conclusions of this study are that the RotorCRAFT analysis correlates well with measured loads on a variety of configurations and that application of the full span free wake model is required to capture several important features of the vibratory loading on rotor blades in forward flight.

Quackenbush, Todd R.; Bliss, Donald B.; Wachspress, Daniel A.; Boschitsch, Alexander H.; Chua, Kiat

1990-01-01

376

Short-amplitude high-frequency wing strokes determine the aerodynamics of honeybee flight

Most insects are thought to fly by creating a leading-edge vortex that remains attached to the wing as it translates through a stroke. In the species examined so far, stroke amplitude is large, and most of the aerodynamic force is produced halfway through a stroke when translation velocities are highest. Here we demonstrate that honeybees use an alternative strategy, hovering with relatively low stroke amplitude (?90°) and high wingbeat frequency (?230 Hz). When measured on a dynamically scaled robot, the kinematics of honeybee wings generate prominent force peaks during the beginning, middle, and end of each stroke, indicating the importance of additional unsteady mechanisms at stroke reversal. When challenged to fly in low-density heliox, bees responded by maintaining nearly constant wingbeat frequency while increasing stroke amplitude by nearly 50%. We examined the aerodynamic consequences of this change in wing motion by using artificial kinematic patterns in which amplitude was systematically increased in 5° increments. To separate the aerodynamic effects of stroke velocity from those due to amplitude, we performed this analysis under both constant frequency and constant velocity conditions. The results indicate that unsteady forces during stroke reversal make a large contribution to net upward force during hovering but play a diminished role as the animal increases stroke amplitude and flight power. We suggest that the peculiar kinematics of bees may reflect either a specialization for increasing load capacity or a physiological limitation of their flight muscles. PMID:16330767

Altshuler, Douglas L.; Dickson, William B.; Vance, Jason T.; Roberts, Stephen P.; Dickinson, Michael H.

2005-01-01

377

Short-amplitude high-frequency wing strokes determine the aerodynamics of honeybee flight.

Most insects are thought to fly by creating a leading-edge vortex that remains attached to the wing as it translates through a stroke. In the species examined so far, stroke amplitude is large, and most of the aerodynamic force is produced halfway through a stroke when translation velocities are highest. Here we demonstrate that honeybees use an alternative strategy, hovering with relatively low stroke amplitude (approximately 90 degrees) and high wingbeat frequency (approximately 230 Hz). When measured on a dynamically scaled robot, the kinematics of honeybee wings generate prominent force peaks during the beginning, middle, and end of each stroke, indicating the importance of additional unsteady mechanisms at stroke reversal. When challenged to fly in low-density heliox, bees responded by maintaining nearly constant wingbeat frequency while increasing stroke amplitude by nearly 50%. We examined the aerodynamic consequences of this change in wing motion by using artificial kinematic patterns in which amplitude was systematically increased in 5 degrees increments. To separate the aerodynamic effects of stroke velocity from those due to amplitude, we performed this analysis under both constant frequency and constant velocity conditions. The results indicate that unsteady forces during stroke reversal make a large contribution to net upward force during hovering but play a diminished role as the animal increases stroke amplitude and flight power. We suggest that the peculiar kinematics of bees may reflect either a specialization for increasing load capacity or a physiological limitation of their flight muscles. PMID:16330767

Altshuler, Douglas L; Dickson, William B; Vance, Jason T; Roberts, Stephen P; Dickinson, Michael H

2005-12-13

378

Efficient Helicopter Aerodynamic and Aeroacoustic Predictions on Parallel Computers

NASA Technical Reports Server (NTRS)

This paper presents parallel implementations of two codes used in a combined CFD/Kirchhoff methodology to predict the aerodynamics and aeroacoustics properties of helicopters. The rotorcraft Navier-Stokes code, TURNS, computes the aerodynamic flowfield near the helicopter blades and the Kirchhoff acoustics code computes the noise in the far field, using the TURNS solution as input. The overall parallel strategy adds MPI message passing calls to the existing serial codes to allow for communication between processors. As a result, the total code modifications required for parallel execution are relatively small. The biggest bottleneck in running the TURNS code in parallel comes from the LU-SGS algorithm that solves the implicit system of equations. We use a new hybrid domain decomposition implementation of LU-SGS to obtain good parallel performance on the SP-2. TURNS demonstrates excellent parallel speedups for quasi-steady and unsteady three-dimensional calculations of a helicopter blade in forward flight. The execution rate attained by the code on 114 processors is six times faster than the same cases run on one processor of the Cray C-90. The parallel Kirchhoff code also shows excellent parallel speedups and fast execution rates. As a performance demonstration, unsteady acoustic pressures are computed at 1886 far-field observer locations for a sample acoustics problem. The calculation requires over two hundred hours of CPU time on one C-90 processor but takes only a few hours on 80 processors of the SP2. The resultant far-field acoustic field is analyzed with state of-the-art audio and video rendering of the propagating acoustic signals.

Wissink, Andrew M.; Lyrintzis, Anastasios S.; Strawn, Roger C.; Oliker, Leonid; Biswas, Rupak

1996-01-01

379

Aerodynamic Performances of Corrugated Dragonfly Wings at Low Reynolds Numbers

NASA Astrophysics Data System (ADS)

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

Tamai, Masatoshi; He, Guowei; Hu, Hui

2006-11-01

380

An unsteady lifting surface method for single rotation propellers

NASA Technical Reports Server (NTRS)

The mathematical formulation of a lifting surface method for evaluating the steady and unsteady loads induced on single rotation propellers by blade vibration and inflow distortion is described. The scheme is based on 3-D linearized compressible aerodynamics and presumes that all disturbances are simple harmonic in time. This approximation leads to a direct linear integral relation between the normal velocity on the blade (which is determined from the blade geometry and motion) and the distribution of pressure difference across the blade. This linear relation is discretized by breaking the blade up into subareas (panels) on which the pressure difference is treated as approximately constant, and constraining the normal velocity at one (control) point on each panel. The piece-wise constant loads can then be determined by Gaussian elimination. The resulting blade loads can be used in performance, stability and forced response predictions for the rotor. Mathematical and numerical aspects of the method are examined. A selection of results obtained from the method is presented. The appendices include various details of the derivation that were felt to be secondary to the main development in Section 1.

Williams, Marc H.

1990-01-01

381

Survey of lift-fan aerodynamic technology

NASA Technical Reports Server (NTRS)

Representatives of NASA Ames Research Center asked that a summary of technology appropriate for lift-fan powered short takeoff/vertical landing (STOVL) aircraft be prepared so that new programs could more easily benefit from past research efforts. This paper represents one of six prepared for that purpose. The authors have conducted or supervised the conduct of research on lift-fan powered STOVL designs and some of their important components for decades. This paper will first address aerodynamic modeling requirements for experimental programs to assure realistic, trustworthy results. It will next summarize the results or efforts to develop satisfactory specialized STOVL components such as inlets and flow deflectors. It will also discuss problems with operation near the ground, aerodynamics while under lift-fan power, and aerodynamic prediction techniques. Finally, results of studies to reduce lift-fan noise will be presented. The paper will emphasize results from large scale experiments, where available, for reasons that will be brought out in the discussion. Some work with lift-engine powered STOVL aircraft is also applicable to lift-fan technology and will be presented herein. Small-scale data will be used where necessary to fill gaps.

Hickey, David H.; Kirk, Jerry V.

1993-01-01

382

Straight-line climbing flight aerodynamics of a fruit bat

NASA Astrophysics Data System (ADS)

From flight data obtained on a fruit bat, Cynopterus brachyotis, a kinematic model for straight-line flapping motion is extracted and analyzed in a computational fluid dynamics (CFD) framework to gain insight into the complexity of bat flight. The intricate functional mechanics and architecture of the bat wings set it apart from other vertebrate flight. The extracted kinematic model is simulated for a range of Reynolds numbers, to observe the effect these phenomena have on the unsteady transient mechanisms of the flow produced by the flapping wings. The Strouhal number calculated from the data is high indicating that the oscillatory motion dominates the flow physics. From the obtained data, the bat exhibits fine control of its mechanics by actively varying wing camber, wing area, torsional rotation of the wing, forward and backward translational sweep of the wing, and wing conformation to dictate the fluid dynamics. As is common in flapping flight, the primary force generation is through the attached unsteady vortices on the wing surface. The bat through varying the wing camber and the wing area modulates this force output. The power requirement for the kinematics is analyzed and correlated with the aerodynamic performance.

Viswanath, K.; Nagendra, K.; Cotter, J.; Frauenthal, M.; Tafti, D. K.

2014-02-01

383

Large eddy simulation for aerodynamics: status and perspectives.

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

Sagaut, Pierre; Deck, Sébastien

2009-07-28

384

Aerodynamic loading on a cylinder behind an airfoil

NASA Astrophysics Data System (ADS)

The interaction between the wake of a rotor blade and a downstream cylinder holds the key to the understanding and control of electronic cooling fan noise. In this paper, the aerodynamic characteristics of a circular cylinder are experimentally studied in the presence of an upstream NACA 4412 airfoil for the cylinder-diameter-based Reynolds numbers of Red=2,100 20,000, and the airfoil chord-length-based Reynolds numbers of Rec=14,700 140,000. Lift and drag fluctuations on the cylinder, and the longitudinal velocity fluctuations of the flow behind the cylinder were measured simultaneously using a load cell and two hot wires, respectively. Data analysis shows that unsteady forces on the cylinder increase significantly in the presence of the airfoil wake. The dependence of the forces on two parameters is investigated, that is, the lateral distance (T) between the airfoil and the cylinder, and the Reynolds number. The forces decline quickly as T increases. For Rec<60,000, the vortices shed from the upstream airfoil make a major contribution to the unsteady forces on the cylinder compared to the vortex shedding from the cylinder itself. For Rec>60,000, no vortices are generated from the airfoil, and the fluctuating forces on the cylinder are caused by its own vortex shedding.

Zhang, H. J.; Huang, L.; Zhou, Y.

2005-05-01

385

Modeling Unsteady Cavitation and Dynamic Loads in Turbopumps

NASA Technical Reports Server (NTRS)

A computational fluid dynamics (CFD) model that includes representations of effects of unsteady cavitation and associated dynamic loads has been developed to increase the accuracy of simulations of the performances of turbopumps. Although the model was originally intended to serve as a means of analyzing preliminary designs of turbopumps that supply cryogenic propellant liquids to rocket engines, the model could also be applied to turbopumping of other liquids: this can be considered to have been already demonstrated, in that the validation of the model was performed by comparing results of simulations performed by use of the model with results of sub-scale experiments in water. The need for this or a similar model arises as follows: Cavitation instabilities in a turbopump are generated as inlet pressure drops and vapor cavities grow on inducer blades, eventually becoming unsteady. The unsteady vapor cavities lead to rotation cavitation, in which the cavities detach from the blades and become part of a fluid mass that rotates relative to the inducer, thereby generating a fluctuating load. Other instabilities (e.g., surge instabilities) can couple with cavitation instabilities, thereby compounding the deleterious effects of unsteadiness on other components of the fluid-handling system of which the turbopump is a part and thereby, further, adversely affecting the mechanical integrity and safety of the system. Therefore, an ability to predict cavitation- instability-induced dynamic pressure loads on the blades, the shaft, and other pump parts would be valuable in helping to quantify safe margins of inducer operation and in contributing to understanding of design compromises. Prior CFD models do not afford this ability. Heretofore, the primary parameter used in quantifying cavitation performance of a turbopump inducer has been the critical suction specific speed at which head breakdown occurs. This parameter is a mean quantity calculated on the basis of assumed steady-state operation of the inducer; it does not account for dynamic pressure loads associated with unsteady flow caused by instabilities. Because cavitation instabilities occur well before mean breakdown in inducers, engineers have, until now, found it necessary to use conservative factors of safety when analyzing the results of numerical simulations of flows in turbopumps.

Hosangadi, Ashvin; Ahuja, Vineet; Ungewitter, Ronald; Dash, Sanford M.

2009-01-01

386

Aerodynamics at the Particle Level

This paper is intended to clarify some of the rather well-known aerodynamic phenomena. It is also intended to pique the interest of the layman as well as the professional. All aerodynamic forces on a surface are caused by collisions of fluid particles with the surface. While the standard approach to fluid dynamics, which is founded on the fluid approximation, is effective in providing a means of calculating various behavior and properties, it begs the question of causality. The determination of the causes of many of the most important aerodynamic effects requires a microscopic examination of the fluid and of the surface with which it interacts. The Kutta-Joukowski theorem is investigated from first physical principles. It is noted that the circulation does not arise as a physical phenomenon. Various aerodynamic devices are discussed, e.g. rocket engine exhaust diffuser and the perfume atomizer.

Charles A. Crummer

2005-07-15

387

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

388

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

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

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

2011-03-01

389

Explanation and discovery in aerodynamics

The purpose of this paper is to discuss and clarify the explanations commonly cited for the aerodynamic lift generated by a wing, and to then analyse, as a case study of engineering discovery, the aerodynamic revolutions which have taken place within Formula 1 in the past 40 years. The paper begins with an introduction that provides a succinct summary of the mathematics of fluid mechanics.

McCabe, G

2005-01-01

390

Explanation and discovery in aerodynamics

The purpose of this paper is to discuss and clarify the explanations commonly cited for the aerodynamic lift generated by a wing, and to then analyse, as a case study of engineering discovery, the aerodynamic revolutions which have taken place within Formula 1 in the past 40 years. The paper begins with an introduction that provides a succinct summary of the mathematics of fluid mechanics.

Gordon McCabe

2005-12-22

391

Differential Evolution in Aerodynamic Optimization

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

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

1999-01-01

392

Aerodynamics of a Party Balloon

NASA Astrophysics Data System (ADS)

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

Cross, Rod

2007-09-01

393

Effect of pre-strain and excess length on unsteady fluid-structure interactions of membrane airfoils

NASA Astrophysics Data System (ADS)

Aerodynamic characteristics of two-dimensional membrane airfoils were experimentally investigated in a wind tunnel. The effects of the membrane pre-strain and excess length on the unsteady aspects of the fluid-structure interaction were studied. The deformation of the membrane as a function of angle of attack and free-stream velocity was measured using a high-speed camera. These measurements were complemented by the measurements of unsteady velocity field with a high frame-rate Particle Image Velocimetry (PIV) system as well as smoke visualization. Membrane airfoils with excess length exhibit higher vibration modes, earlier roll-up of vortices, and smaller separated flow regions, whereas the membranes with pre-strain generally behave more similarly to a rigid airfoil. Measured frequencies of the membrane vibrations suggest a possible coupling with the wake instabilities at high incidences for all airfoils.

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

2010-04-01

394

NASA Technical Reports Server (NTRS)

A low frequency unsteady lifting-line theory is developed for a harmonically oscillating wing of large aspect ratio. The wing is assumed to be chordwise rigid but completely flexible in the span direction. The theory is developed by use of the method of matched asymptotic expansions which reduces the problem from a singular integral equation to quadrature. The wing displacements are prescribed and the pressure field, airloads, and unsteady induced downwash are obtained in closed form. The influence of reduced frequency, aspect ratio, planform shape, and mode of oscillation on wing aerodynamics is demonstrated through numerical examples. Compared with lifting-surface theory, computation time is reduced significantly. Using the present theory, the energetic quantities associated with the propulsive performance of a finite wing oscillating in combined pitch and heave are obtained in closed form. Numerical examples are presented for an elliptic wing.

Ahmadi, A. R.

1981-01-01

395

Prediction of the aerodynamic environment and heat transfer for rotor-stator configurations

NASA Astrophysics Data System (ADS)

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 viscous code, ROTORI, and an improved version of the 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 ROTORI predictions of unsteady pressure envelopes and instantaneous contour plots are also presented. Relative merits of the two computational approaches are discussed.

Griffin, L. W.; McConnaughey, H. V.

1989-06-01

396

NASA Astrophysics Data System (ADS)

In this article, we propose a high order method for solving steady and unsteady two-dimensional laminar boundary-layer equations. This method is convergent of sixth-order of accuracy. It is shown that this method is unconditionally stable. The unsteady separated stagnation point flow, the Falkner-Skan equation and Blasius equation are considered as special cases of these equations. Numerical experiments are given to illustrate our method and its convergence.

Salama, A. A.; Mansour, A. A.

397

Current Issues in Unsteady Turbomachinery Flows (Images)

NASA Technical Reports Server (NTRS)

Among the numerous causes for unsteadiness in turbo machinery flows are turbulence and flow environment, wakes from stationary and rotating vanes, boundary layer separation, boundary layer/shear layer instabilities, presence of shock waves and deliberate unsteadiness for flow control purposes. These unsteady phenomena may lead to flow-structure interactions such as flutter and forced vibration as well as system instabilities such as stall and surge. A major issue of unsteadiness relates to the fact that a fundamental understanding of unsteady flow physics is lacking and requires continued attention. Accurate simulations and sufficient high fidelity experimental data are not available. The Glenn Research Center plan for Engine Component Flow Physics Modeling is part of the NASA 21st Century Aircraft Program. The main components of the plan include Low Pressure Turbine National Combustor Code. The goals, technical output and benefits/impacts of each element are described in the presentation. The specific areas selected for discussion in this presentation are blade wake interactions, flow control, and combustor exit turbulence and modeling.

Povinelli, Louis

2004-01-01

398

Numerical simulation of unsteady rotational flow over propfan configurations

NASA Technical Reports Server (NTRS)

The objective is to develop efficient numerical techniques for the study of aeroelastic response of a propfan in an unsteady transonic flow. A three dimensional unsteady Euler solver is being modified to address this problem.

Srivastava, R.; Sankar, L. N.

1989-01-01

399

Unsteady flow in turbomachinery: An overview

NASA Technical Reports Server (NTRS)

The importance of understanding and modeling the unsteady flow phenomena in turbomachinery is discussed. Historical events in the application and development of gas turbines for aircraft propulsion are traced. Technology advancements over the years are highlighted with focus on the compression system components. Trends in compressor research within the National Advisory Committee for Aeronautics (NACA)/National Aeronautics and Space Administration (NASA) are noted. The impact of technology advancements on the increased occurrences of unsteady flow related problems in advanced engine development programs is discussed. The impact of the new and more demanding requirements being imposed on the propulsion system to meet advanced aircraft mission needs are also noted. Brief discussions on the present day understanding and modeling capability of the unsteady flow phenomena are presented to include discussions on rotating stall, surge, flutter, forced response and noise generation.

1984-01-01

400

Unsteady penetration of a target by a liquid jet.

It is widely acknowledged that ceramic armor experiences an unsteady penetration response: an impacting projectile may erode on the surface of a ceramic target without substantial penetration for a significant amount of time and then suddenly start to penetrate the target. Although known for more than four decades, this phenomenon, commonly referred to as dwell, remains largely unexplained. Here, we use scaled analog experiments with a low-speed water jet and a soft, translucent target material to investigate dwell. The transient target response, in terms of depth of penetration and impact force, is captured using a high-speed camera in combination with a piezoelectric force sensor. We observe the phenomenon of dwell using a soft (noncracking) target material. The results show that the penetration rate increases when the flow of the impacting water jet is reversed due to the deformation of the jet-target interface--this reversal is also associated with an increase in the force exerted by the jet on the target. Creep penetration experiments with a constant indentation force did not show an increase in the penetration rate, confirming that flow reversal is the cause of the unsteady penetration rate. Our results suggest that dwell can occur in a ductile noncracking target due to flow reversal. This phenomenon of flow reversal is rather widespread and present in a wide range of impact situations, including water-jet cutting, needleless injection, and deposit removal via a fluid jet. PMID:24277818

Uth, Tobias; Deshpande, Vikram S

2013-12-10

401

NASA Astrophysics Data System (ADS)

Acoustic characteristics of the external upper surface blowing (USB) concept of a propulsive lift configuration were studied by full scale model static experiments. Test components included an FJR710 turbofan engine with an acoustically treated nacelle and a USB wing/flap assembly. These were utilized in conjunction with the ground verification testing of the propulsive systems of the National Aerospace Laboratory Quiet STOL Research Aircraft. Results were compared with the previous 8% scale cold flow model data. The defect of shielding provided by the wing/flap surface on aftradiated turbofan engine noise was studied and some attempts were made to reduce USB noise.

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

1981-10-01

402

Prediction of oscillating thick cambered aerofoil aerodynamics by a locally analytic method

NASA Technical Reports Server (NTRS)

The effects of mean-flow incidence, airfoil camber, and airfoil thickness on the incompressible aerodynamics of an oscillating airfoil are investigated theoretically, developing and applying a first-order FEM based on locally analytical solutions (LASs). Laplace equations are used to describe the steady and unsteady harmonic velocity potentials; a body-fitted computational grid is employed; grid-element solutions for both potentials are determined using a numerical LAS method; and the LASs are then assembled to obtain a complete solution. Results for a series of flat-plate and Joukowski airfoils are presented in extensive graphs and discussed in detail.

Chiang, Hsiao-Wei D.; Fleeter, Sanford

1988-01-01

403

Unsteady Newton-Busemann flow theory. Part 2: Bodies of revolution

NASA Technical Reports Server (NTRS)

Newtonian flow theory for unsteady flow past oscillating bodies of revolution at very high Mach numbers is completed by adding a centrifugal force correction to the impact pressures. Exact formulas for the unsteady pressure and the stability derivatives are obtained in closed form and are applicable to bodies of revolution that have arbitrary shapes, arbitrary thicknesses, and either sharp or blunt noses. The centrifugal force correction arising from the curved trajectories followed by the fluid particles in unsteady flow cannot be neglected even for the case of a circular cone. With this correction, the present theory is in excellent agreement with experimental results for sharp cones and for cones with small nose bluntness; gives poor agreement with the results of experiments in air for bodies with moderate or large nose bluntness. The pitching motions of slender power-law bodies of revulution are shown to be always dynamically stable according to Newton-Busemann theory.

Hui, W. H.; Tobak, M.

1981-01-01

404

A linearized Euler analysis of unsteady flows in turbomachinery

A method for calculating unsteady flows in cascades is presented. The model, which is based on the linearized unsteady Euler equations, accounts for blade loading shock motion, wake motion, and blade geometry. The mean flow through the cascade is determined by solving the full nonlinear Euler equations. Assuming the unsteadiness in the flow is small, then the Euler equations are

Kenneth C. Hall; Edward F. Crawley

1987-01-01

405

Supersonic unstalled flutter. [aerodynamic loading of thin airfoils induced by cascade motion

NASA Technical Reports Server (NTRS)

Flutter analyses were developed to predict the onset of supersonic unstalled flutter of a cascade of two-dimensional airfoils. The first of these analyzes the onset of supersonic flutter at low levels of aerodynamic loading (i.e., backpressure), while the second examines the occurrence of supersonic flutter at moderate levels of aerodynamic loading. Both of these analyses are based on the linearized unsteady inviscid equations of gas dynamics to model the flow field surrounding the cascade. These analyses are utilized in a parametric study to show the effects of cascade geometry, inlet Mach number, and backpressure on the onset of single and multi degree of freedom unstalled supersonic flutter. Several of the results are correlated against experimental qualitative observation to validate the models.

Adamczyk, J. J.; Goldstein, M. E.; Hartmann, M. J.

1978-01-01

406

Steady and unsteady flow computation in an elbow dr aft tube with experimental validation

Steady state computations are routinely used by design engineers to evaluate and compare losses in hydraulic components. In the case of the draft tube diffuser, however, experiments have shown that while a significant number of operating conditions can adequately be evaluated using steady state computations, a few operating conditions require unsteady simulations to accurately evaluate losses. This paper presents a

T. C. Vu; C. Devals; Y. Zhang; B. Nennemann; F. Guibault

2010-01-01

407

Analysis of Wind Tunnel Wall Interference Effects on Subsonic Unsteady Airfoil Flows

well-known fact, most computational fluid dynamics (CFD) simulations of wind tunnel experiments (forAnalysis of Wind Tunnel Wall Interference Effects on Subsonic Unsteady Airfoil Flows Karthikeyan interference on steady and oscillating airfoils in a subsonic wind tunnel is studied. A variety of approaches

Alonso, Juan J.

408

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

409

Two general methods for the unsteady aerodynamic analysis of horizontal-axis windmills

The problem of a horizontal-axis windmill embedded in incompressible, inviscid flow is considered. The vorticity field present in the undisturbed flow is assumed to be unperturbed by the presence of the windmill, enabling the use of a potential formulation. Two integral equation methods (for finite thickness and zero thickness blades) are presented. Both methods are formulated in a frame of

R. D. Preuss; E. O. Suciu; L. Morino

1977-01-01

410

Experimental and numerical research on the aerodynamics of unsteady moving aircraft

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

Andreas Bergmann; Andreas Huebner; Thomas Loeser

2008-01-01

411

The oblique-wing research aircraft: A test bed for unsteady aerodynamic and aeroelastic research

NASA Technical Reports Server (NTRS)

The advantages of oblique wings have been the subject of numerous theoretical studies, wind tunnel tests, low speed flight models, and finally a low speed manned demonstrator, the AD-1. The specific objectives of the OWRA program are: (1) to establish the necessary technology base required to translate theoretical and experimental results into practical mission oriented designs; (2) to design, fabricate and flight test an oblique wing aircraft throughout a realistic flight envelope, and (3) to develop and validate design and analysis tools for asymmetric aircraft configurations. The preliminary design phase of the project is complete and has resulted in a wing configuration for which construction is ready to be initiated.

Gilyard, Glenn B.

1989-01-01

412

NASA Astrophysics Data System (ADS)

Electricity is an indispensable commodity to modern society, yet it is delivered via a grid architecture that remains largely unchanged over the past century. A host of factors are conspiring to topple this dated yet venerated design: developments in renewable electricity generation technology, policies to reduce greenhouse gas emissions, and advances in information technology for managing energy systems. Modern electric grids are emerging as complex distributed systems in which a portfolio of power generation resources, often incorporating fluctuating renewable resources such as wind and solar, must be managed dynamically to meet uncontrolled, time-varying demand. Uncertainty in both supply and demand makes control of modern electric grids fundamentally more challenging, and growing portfolios of renewables exacerbate the challenge. We study three electricity grids: the state of California, the province of Ontario, and the country of Germany. To understand the effects of increasing renewables, we develop a methodology to scale renewables penetration. Analyzing these grids yields key insights about rigid limits to renewables penetration and their implications in meeting long-term emissions targets. We argue that to achieve deep penetration of renewables, the operational model of the grid must be inverted, changing the paradigm from load-following supplies to supply-following loads. To alleviate the challenge of supply-demand matching on deeply renewable grids, we first examine well-known techniques, including altering management of existing supply resources, employing utility-scale energy storage, targeting energy efficiency improvements, and exercising basic demand-side management. Then, we create several instantiations of supply-following loads -- including refrigerators, heating and cooling systems, and laptop computers -- by employing a combination of sensor networks, advanced control techniques, and enhanced energy storage. We examine the capacity of each load for supply-following and study the behaviors of populations of these loads, assessing their potential at various levels of deployment throughout the California electricity grid. Using combinations of supply-following strategies, we can reduce peak natural gas generation by 19% on a model of the California grid with 60% renewables. We then assess remaining variability on this deeply renewable grid incorporating supply-following loads, characterizing additional capabilities needed to ensure supply-demand matching in future sustainable electricity grids.

Taneja, Jayant Kumar

413

Inflow/Outflow Conditions for Unsteady Aerodynamics and Aeroacoustics in Nonuniform Flow

NASA Technical Reports Server (NTRS)

The effect of a nonuniform mean flow on the normal modes; the inflow/outflow nonreflecting boundary conditions; and the sound power are studied. The normal modes in an annular duct are computed using a spectral method in combination with a shooting method. The swirl causes force imbalance which couples the acoustic and vortical modes. The acoustic modes are distinguished from the vortical modes by their large pressure and small vorticity content. The mean swirl also produces a Doppler shift in frequency. This results in more counter-spinning modes cut-on at a given frequency than modes spinning with the swirl. Nonreflecting boundary conditions are formulated using the normal mode solutions. The inflow/outflow boundary conditions are implemented in a linearized Euler scheme and validated by computing the propagation of acoustic and vortical waves in a duct for a variety of swirling mean flows. Numerical results show that the evolution of the vortical disturbances is sensitive to the inflow conditions and the details of the wake excitations. All three components of the wake velocity must be considered to correctly compute the wake evolution and the blade upwash. For high frequencies, the acoustic-vortical mode coupling is weak and a conservation equation for the acoustic energy can be derived. Sound power calculations show significant mean flow swirl effects, but mode interference effects are small.

Atassi, Oliver V.; Grady, Joseph E. (Technical Monitor)

2003-01-01

414

NASA Astrophysics Data System (ADS)

Aerodynamic performance of low-Reynolds number flyers, for a chord-based Reynolds number of 10 5 or below, is sensitive to wind gusts and flow separation. Active flow control offers insight into fluid physics as well as possible improvements in vehicle performance. While facilitating flow control by introducing feedback control and fluidic devices, major challenges of achieving a target aerodynamic performance under unsteady flow conditions lie on the high-dimensional nonlinear dynamics of the flow system. Therefore, a successful flow control framework requires a viable as well as accessible control scheme and understanding of underlying flow dynamics as key information of the flow system. On the other hand, promising devices have been developed recently to facilitate flow control in this flow regime. The dielectric barrier discharge (DBD) actuator is such an example; it does not have moving parts and provides fast impact on the flow field locally. In this paper, recent feedback flow control studies, especially those focusing on unsteady low-Reynolds number aerodynamics, are reviewed. As an example of an effective flow control framework, it is demonstrated that aerodynamic lift of a high angle-of-attack wing under fluctuating free-stream conditions can be stabilized using the DBD actuator and an adaptive algorithm based on general input-output models. System nonlinearities and control challenges are discussed by assessing control performance and the variation of the system parameters under various flow and actuation conditions. Other fundamental issues from the flow dynamics view point, such as the lift stabilization mechanism and the influence on drag fluctuation are also explored. Both potentiality and limitation of the linear modeling approach are discussed. In addition, guidelines on system identification and the controller and actuator setups are suggested.

Cho, Young-Chang; Shyy, Wei

2011-10-01

415

Aeroelastic Analysis of Bridges: Effects of Turbulence and Aerodynamic Nonlinearities

by utilizing an example of a long span suspension bridge with aerodynamic characteristics sensitiveAeroelastic Analysis of Bridges: Effects of Turbulence and Aerodynamic Nonlinearities Xinzhong Chen for capturing the emerging concerns in bridge aerodynamics introduced by aerodynamic nonlinearities

Kareem, Ahsan

416

Unsteadiness of transonic convex-corner flows

An experimental investigation was conducted to study the transonic convex-corner flow in a turbulent boundary layer. The unsteadiness of the interaction was characterized by a local peak pressure fluctuation and the deviation of higher order moments from an effective Gaussian. The peak pressure fluctuations are correlated and compared with results from other studies.

Kung-Ming Chung

2004-01-01

417

Chaotic solute advection by unsteady groundwater flow

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

Garrison Sposito

2006-01-01

418

Unsteady heat transfer in heat pipes

The purpose was to investigate the unsteady heat transfer associated with a heat pipe during start up operation. Initial studies were conducted with a variety of heat pipe screen wick configurations in order to develop a mathematical expression for the flow velocity of a fluid inducted by the capillary structure of the wick. This mathematical model was solved first numerically

J. E. Beam

1985-01-01

419

Steady\\/unsteady gas turbine combustion simulator

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

Pratikash Prakash Panda

2011-01-01

420

Perturbation dynamics in unsteady pipe flows

This paper deals with perturbed unsteady laminar flows in a pipe. Three types of flows are considered: a flow accelerated from rest; a flow in a pipe generated by the controlled motion of a piston; and a water hammer flow where the transient is generated by the instantaneous closure of a valve. Methods of linear stability theory are used to

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

2007-01-01