Unsteady Aerodynamic Validation Experiences From the Aeroelastic Prediction Workshop
NASA Technical Reports Server (NTRS)
Heeg, Jennifer; Chawlowski, Pawel
2014-01-01
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.
Unsteady Aerodynamics Experiment Phase V: Test Configuration and Available Data Campaigns
Hand, M. M.; Simms, D. A.; Fingersh, L. J.; Jager, D. W.; Cotrell, J. R.
2001-08-30
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.
Conversion of Phase II Unsteady Aerodynamics Experiment Data to Common Format
Hand, M. M.
1999-07-19
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.
NASA Technical Reports Server (NTRS)
Schuster, David M.; Scott, Robert C.; Bartels, Robert E.; Edwards, John W.; Bennett, Robert M.
2000-01-01
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.
Hand, M. M.; Simms, D. A.; Fingersh, L. J.; Jager, D. W.; Cotrell, J. R.; Schreck, S.; Larwood, S. M.
2001-12-01
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.
Forced response unsteady aerodynamics in a multistage compressor
NASA Astrophysics Data System (ADS)
Capece, Vincent Ralph
The fundamental flow physics of the unsteady aerodynamics associated with forced vibrations in turbomachinery are investigated. Unique data are obtained through a series of experiments in a three stage axial flow research compressor which quantify the unsteady harmonic gust interaction phenomena over a range of operating and geometric conditions at high values of reduced frequency. In these experiments the effects of the following on the stator vane unsteady aerodynamics were quantified: (1) the steady aerodynamic loading, (2) the detailed waveform of the aerodynamic forcing function, including the chordwise and transverse gust components, (3) multistage blade row interactions, and (4) the solidity, ranging from a design value of 1.09 to an isolated airfoil. In addition, the effect of flow separation on the unsteady aerodynamics of an isolated airfoil was also investigated.
Simms, D.; Schreck, S.; Hand, M.; Fingersh, L.J.
2001-06-22
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.
Turbine blade unsteady aerodynamic loading and heat transfer
NASA Astrophysics Data System (ADS)
Johnston, David Alan
Stator indexing to minimize the unsteady aerodynamic loading of closely spaced airfoil rows in turbomachinery is a new technique for the passive control of flow-induced vibrations. This technique, along with the effects of steady blade loading, were studied by means of experiments performed in a two-stage low-speed research turbine. With the second vane row fixed, the inlet vane row was indexed to six positions over one vane-pitch cycle for a range of stage loadings. The aerodynamic forcing function to the first-stage rotor was measured in the rotating reference frame, with the resulting rotor blade unsteady aerodynamic response quantified by rotor blades instrumented with dynamic pressure transducers. Reductions in the unsteady lift magnitude were achieved at all turbine operating conditions, with attenuation ranging from 37% to 74% of the maximum unsteady lift. Additionally, in complementary experiments, the effects of stator indexing and steady blade loading on the unsteady heat transfer of the first- and second-stage rotors was studied for the design and highest blade loading conditions using platinum-film heat gages. The attenuation of unsteady heat transfer coefficient was blade-loading dependent and location dependent along the chord and span, ranging 10% to 90% of maximum. Due to the high degree of location dependence of attenuation, stator indexing is therefore best suited to minimize unsteady heat transfer in local hot spots of the blade rather than the blade as a whole.
Unsteady aerodynamics and gust response in compressors and turbines
S. R. Manwaring; D. C. Wisler
1993-01-01
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
Unsteady aerodynamic models for agile flight at low Reynolds numbers
Rowley, Clarence W.
Unsteady aerodynamic models for agile flight at low Reynolds numbers Steven L. Brunton , Clarence W for the unsteady aerodynamic forces on a small wing in response to agile maneuvers and gusts. In a previous study, it was shown that Theodorsen's and Wagner's unsteady aerodynamic models agree with force data from DNS
Identification of Experimental Unsteady Aerodynamic Impulse Responses
NASA Technical Reports Server (NTRS)
Silva, Walter A.; Piatak, David J.; Scott, Robert C.
2003-01-01
The identification of experimental unsteady aerodynamic impulse responses using the Oscillating Turntable (OTT) at NASA Langley's Transonic Dynamics Tunnel (TDT) is described. Results are presented for two configurations: a Rigid Semispan Model (RSM) and a rectangular wing with a supercritical airfoil section. Both models were used to acquire unsteady pressure data due to pitching oscillations on the OTT. A deconvolution scheme involving a step input in pitch and the resultant step response in pressure, for several pressure transducers, is used to identify the pressure impulse responses. The identified impulse responses are then used to predict the pressure response due to pitching oscillations at several frequencies. Comparisons with the experimental data are presented.
Rotor blade unsteady aerodynamic gust response to inlet guide vane wakes
Manwaring, S.R.; Fleetner, S. (Purdue Univ., West Lafayette, IN (United States). School of Mechanical Engineering)
1993-01-01
A series of experiments is performed in an extensively instrumented axial flow research compressor to investigate the fundamental flow physics of wake-generated periodic rotor blade row unsteady aerodynamics at realistic values of the reduced frequency. Unique unsteady data are obtained that describe the fundamental unsteady aerodynamic gust interaction phenomena on the first-stage rotor blades of a research axial flow compressor generated by the wakes from the inlet guide vanes. In these experiments, the effects of steady blade aerodynamic loading and the aerodynamic forcing function, including both the transverse and chordwise gust components, and the amplitude of the gusts, are investigated and quantified.
Aerodynamic Force Modeling for Unsteady Wing Ryan Jantzen
Aerodynamic Force Modeling for Unsteady Wing Maneuvers Ryan Jantzen and Kunihiko Taira Florida, Wright-Patterson Air Force Base, OH We report on the development of an aerodynamic force model for a flat focus is placed on examining the influence of large-amplitude wing motion on the unsteady aerodynamics
Unsteady aerodynamics and gust response in compressors and turbines
Manwaring, S.R.; Wisler, D.C. (Aerodynamics Research Lab., Cincinnati, OH (United States). GE Aircraft Engines)
1993-10-01
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.
NASA Technical Reports Server (NTRS)
Bartels, Robert E.
2011-01-01
Launch vehicles frequently experience a reduced stability margin through the transonic Mach number range. This reduced stability margin is caused by an undamping of the aerodynamics in 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 lineloads derived from steady rigid computational fluid dynamics (CFD). However, a quasi-steady aeroelastic stability analysis can be unconservative at the critical Mach numbers where experiment or unsteady computational aeroelastic (CAE) analysis show a reduced or even negative aerodynamic damping. This paper will present a method of enhancing the quasi-steady aeroelastic stability analysis of a launch vehicle with unsteady aerodynamics. The enhanced formulation uses unsteady CFD to compute the response of selected lower frequency modes. The response is contained in a time history of the vehicle lineloads. A proper orthogonal decomposition of the unsteady aerodynamic lineload 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 of the enhanced quasi-static aeroelastic stability analysis are compared with the damping and frequency computed from unsteady CAE analysis 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 CAE analysis.
Unsteady aerodynamics and flow control for flapping wing flyers
NASA Astrophysics Data System (ADS)
Ho, Steven; Nassef, Hany; Pornsinsirirak, Nick; Tai, Yu-Chong; Ho, Chih-Ming
2003-11-01
The creation of micro air vehicles (MAVs) of the same general sizes and weight as natural fliers has spawned renewed interest in flapping wing flight. With a wingspan of approximately 15 cm and a flight speed of a few meters per second, MAVs experience the same low Reynolds number (10 4-10 5) flight conditions as their biological counterparts. In this flow regime, rigid fixed wings drop dramatically in aerodynamic performance while flexible flapping wings gain efficacy and are the preferred propulsion method for small natural fliers. Researchers have long realized that steady-state aerodynamics does not properly capture the physical phenomena or forces present in flapping flight at this scale. Hence, unsteady flow mechanisms must dominate this regime. Furthermore, due to the low flight speeds, any disturbance such as gusts or wind will dramatically change the aerodynamic conditions around the MAV. In response, a suitable feedback control system and actuation technology must be developed so that the wing can maintain its aerodynamic efficiency in this extremely dynamic situation; one where the unsteady separated flow field and wing structure are tightly coupled and interact nonlinearly. For instance, birds and bats control their flexible wings with muscle tissue to successfully deal with rapid changes in the flow environment. Drawing from their example, perhaps MAVs can use lightweight actuators in conjunction with adaptive feedback control to shape the wing and achieve active flow control. This article first reviews the scaling laws and unsteady flow regime constraining both biological and man-made fliers. Then a summary of vortex dominated unsteady aerodynamics follows. Next, aeroelastic coupling and its effect on lift and thrust are discussed. Afterwards, flow control strategies found in nature and devised by man to deal with separated flows are examined. Recent work is also presented in using microelectromechanical systems (MEMS) actuators and angular speed variation to achieve active flow control for MAVs. Finally, an explanation for aerodynamic gains seen in flexible versus rigid membrane wings, derived from an unsteady three-dimensional computational fluid dynamics model with an integrated distributed control algorithm, is presented.
D. Simms; S. Schreck; M. Hand; L. Fingersh; J. Cotrell; K. Pierce; M. Robinson
2000-01-01
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
Unsteady aerodynamic modeling and active aeroelastic control
NASA Technical Reports Server (NTRS)
Edwards, J. W.
1977-01-01
Unsteady aerodynamic modeling techniques are developed and applied to the study of active control of elastic vehicles. The problem of active control of a supercritical flutter mode poses a definite design goal stability, and is treated in detail. The transfer functions relating the arbitrary airfoil motions to the airloads are derived from the Laplace transforms of the linearized airload expressions for incompressible two dimensional flow. The transfer function relating the motions to the circulatory part of these loads is recognized as the Theodorsen function extended to complex values of reduced frequency, and is termed the generalized Theodorsen function. Inversion of the Laplace transforms yields exact transient airloads and airfoil motions. Exact root loci of aeroelastic modes are calculated, providing quantitative information regarding subcritical and supercritical flutter conditions.
CFD methods development considerations for unsteady aerodynamic analysis
NASA Technical Reports Server (NTRS)
Batina, John T.
1992-01-01
The development of computational fluid dynamics (CFD) methods for unsteady aerodynamic analysis is described. Special emphasis is placed on considerations that are required for application of the methods to unsteady aerodynamic flow problems. Two broad categories of topics are presented to illustrate the major points. Although primary application of these CFD methods is to relatively low frequency oscillatory phenomena such as flutter, the ideas that are presented may be of value to developers of computational aeroacoustic methods for predicting high frequency acoustics.
Unsteady aerodynamic modeling for arbitrary motions. [for active control techniques
NASA Technical Reports Server (NTRS)
Edwards, J. W.
1977-01-01
Results indicating that unsteady aerodynamic loads derived under the assumption of simple harmonic motions executed by airfoil or wing can be extended to arbitrary motions are summarized. The generalized Theodorsen (1953) function referable to loads due to simple harmonic oscillations of a wing section in incompressible flow, the Laplace inversion integral for unsteady aerodynamic loads, calculations of root loci of aeroelastic loads, and analysis of generalized compressible transient airloads are discussed.
Numerical simulation of unsteady aerodynamic heating induced by shock reflections
Shigeru Aso; Kenichi Ohyama
1992-01-01
Numerical simulations on unsteady shock reflections by a ramp have been conducted in order to investigate unsteady aerodynamic heating due to shock reflection processes at a higher incident shock Mach number. The two-dimensional Navier-Stokes equations with a thin layer approximation are solved numerically by a Total Variation Diminishing (TVD) scheme. The effect of mesh refinement to the calculated results is
Algorithmic Enhancements for Unsteady Aerodynamics and Combustion Applications
NASA Technical Reports Server (NTRS)
Venkateswaran, Sankaran; Olsen, Michael (Technical Monitor)
2001-01-01
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.
A review of scale effects in unsteady aerodynamics
NASA Astrophysics Data System (ADS)
Mabey, D. G.
The importance of scale effects is recognised generally in steady aerodynamics but is often ignored in unsteady aerodynamics. An attempt is made to remedy this situation by the compilation of a review of information on the influence of Reynolds number from a wide range of unsteady aerodynamic tests, with particular reference to wing flows. The unsteady tests considered are buffet and buffeting, dynamic tests of aerofoils and wings, pressure measurements, oscillatory control surface derivatives, and stability derivatives. The review suggests that for the usual recommended model conditions with fixed transition, scale effects are small for fully-attached or well-separated flows, but may be large close to incipient separation. With fixed transition extrapolation from model to full scale Reynolds numbers is usually possible. In contrast, with free transition scale effects can be large for both attached and separated flows. Much more research is needed into the magnitude of scale effects on unsteady flows at transonic speeds. Some test cases for the prediction of scale effects in unsteady aerodynamics are suggested. This review combines material presented by the author in Paper 3.4.1 ICAS-90 Proceedings (Stockholm) and Paper 27 AGARD CP 507 October 1991 (San Diego).
Role of computational fluid dynamics in unsteady aerodynamics for aeroelasticity
NASA Technical Reports Server (NTRS)
Guruswamy, Guru P.; Goorjian, Peter M.
1989-01-01
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.
Unsteady aerodynamic models for agile flight at low Reynolds numbers
NASA Astrophysics Data System (ADS)
Brunton, Steven L.
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.
Review of unsteady transonic aerodynamics: Theory and applications
NASA Astrophysics Data System (ADS)
Bendiksen, Oddvar O.
2011-02-01
Unsteady transonic flow theory is reviewed and classical results from the nonlinear asymptotic theory are combined with new results from computational fluid dynamics. The emphasis is on applications to the field of aeroelasticity and on clarifying the limitations of linearized theories in problems involving mixed subsonic-supersonic flows. The inherent differences between nonlinear transonic aerodynamics and linear subsonic and supersonic aerodynamics are considered from a theoretical and computational standpoint, and the practical implications of these differences in formulating suitable aerodynamic models for aeroelastic stability calculations are discussed. Transonic similarity principles are reviewed and their relevance in understanding flutter, divergence, and control reversal phenomena of transonic aircraft is illustrated through practical examples.
Role of computational fluid dynamics in unsteady aerodynamics for aeroelasticity
Guru P. Guruswamy; Peter M. Goorjian
1989-01-01
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
Unsteady Aerodynamic Force Modeling via S-BT Method
Weigang Yao; Min Xu; Tianxiang Cai; Mao Ye; Yu Qian
2009-01-01
The main goal of present paper is to construct an efficient reduced order model (ROM) for unsteady aerodynamic force modeling. Balanced Truncation (BT) is presented to address the problem. For conventional BT method, it is necessary to compute exact controllability and observability grammians. Although it is relatively straightforward to compute these matrices in a control setting where the system order
Application of Approximate Unsteady Aerodynamics for Flutter Analysis
NASA Technical Reports Server (NTRS)
Pak, Chan-gi; Li, Wesley W.
2010-01-01
A technique for approximating the modal aerodynamic influence coefficient (AIC) matrices by using basis functions has been developed. A process for using the resulting approximated modal AIC matrix in aeroelastic analysis has also been developed. The method requires the unsteady aerodynamics in frequency domain, and this methodology can be applied to the unsteady subsonic, transonic, and supersonic aerodynamics. 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 using unsteady subsonic aerodynamic approximation is demonstrated herein. The technique presented is shown to offer consistent flutter speed prediction on an aerostructures test wing (ATW) 2 and a hybrid wing body (HWB) type of vehicle configuration with negligible loss in precision. This method computes AICs that are functions of the changing parameters being studied and are generated within minutes of CPU time instead of hours. These results may have practical application in parametric flutter analyses as well as more efficient multidisciplinary design and optimization studies.
Unsteady aerodynamic modeling for arbitrary motions. [of thin wing
NASA Technical Reports Server (NTRS)
Edwards, J. W.; Ashley, H.; Breakwell, J. V.
1977-01-01
A study is presented on the unsteady aerodynamic loads due to arbitrary motions of a thin wing and their adaptation for the calculation of response and true stability of aeroelastic modes. In an Appendix, the use of Laplace transform techniques and the generalized Theodorsen function for two-dimensional incompressible flow is reviewed. New applications of the same approach are shown also to yield airloads valid for quite general small motions. Numerical results are given for the two-dimensional supersonic case. Previously proposed approximate methods, starting from simple harmonic unsteady theory, are evaluated by comparison with exact results obtained by the present approach. The Laplace inversion integral is employed to separate the loads into 'rational' and 'nonrational' parts, of which only the former are involved in aeroelastic stability of the wing. Among other suggestions for further work, it is explained how existing aerodynamic computer programs may be adapted in a fairly straightforward fashion to deal with arbitrary transients.
Unsteady aerodynamics of an oscillating cascade in a compressible flow field
NASA Technical Reports Server (NTRS)
Buffum, Daniel H.; Boldman, Donald R.; Fleeter, Sanford
1987-01-01
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.
The unsteady aerodynamics of an oscillating cascade in a compressible flow field
NASA Technical Reports Server (NTRS)
Buffum, Daniel H.; Boldman, Donald R.; Fleeter, Sanford
1988-01-01
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.
NASA Technical Reports Server (NTRS)
Ericsson, L. E.; Reding, J. P.
1973-01-01
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).
A linearized unsteady aerodynamic analysis for real blade supersonic cascades
Montgomery, M.D.; Verdon, J.M. [United Technologies Research Center, East Hartford, CT (United States); Fleeter, S. [Purdue Univ., West Lafayette, IN (United States). School of Mechanical Engineering
1997-10-01
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 based on the domain of dependence is required for numerical stability. These difficulties are addressed by developing a discontinuity capturing scheme and matching the numerical near-field solution to an analytical far-field solution. Comparisons with semi-analytic results for flat plate cascades show that reasonable predictions of the unsteady aerodynamic response at the airfoil surfaces are possible, but aeroacoustic response calculations are difficult. Comparisons between flat plate and real blade cascade results show that one effect of real blades is the impulsive loads due to motion of finite strength shocks.
Prediction of Unsteady Aerodynamic Coefficients at High Angles of Attack
NASA Technical Reports Server (NTRS)
Pamadi, Bandu N.; Murphy, Patrick C.; Klein, Vladislav; Brandon, Jay M.
2001-01-01
The nonlinear indicial response method is used to model the unsteady aerodynamic coefficients in the low speed longitudinal oscillatory wind tunnel test data of the 0.1 scale model of the F-16XL aircraft. Exponential functions are used to approximate the deficiency function in the indicial response. Using one set of oscillatory wind tunnel data and parameter identification method, the unknown parameters in the exponential functions are estimated. The genetic algorithm is used as a least square minimizing algorithm. The assumed model structures and parameter estimates are validated by comparing the predictions with other sets of available oscillatory wind tunnel test data.
NASA Technical Reports Server (NTRS)
Morino, L.
1975-01-01
The program SUSSA ACTS, steady and unsteady subsonic and supersonic aerodynamics for aerospace complex transportation system, is presented. Fully unsteady aerodynamics is discussed first, followed by developments on normal wash, pressure distribution, generalized forces, supersonic formulation, numerical results, geometry preprocessor, the user manual, control surfaces, and first order formulation. The ILSWAR program was also discussed.
Gilles Rahier; Jean Prieur; François Vuillot; Nicolas Lupoglazoff; Anthoine Biancherin
2004-01-01
The acoustic post-processing of unsteady aerodynamic jet simulations using Kirchhoff or Ffowcs Williams and Hawkings (FW–H) surface integral methods is investigated from the theoretical and practical points of view. This analysis is carried out for a supersonic hot jet, starting from the flow fields provided by an unsteady aerodynamic simulation whose characteristics are recalled. Both acoustic integral methods are first
NASA Technical Reports Server (NTRS)
Ericsson, L. E.; Reding, J. P.
1976-01-01
An analysis of the steady and unsteady aerodynamics of the space shuttle orbiter has been performed. It is shown that slender wing theory can be modified to account for the effect of Mach number and leading edge roundness on both attached and separated flow loads. The orbiter unsteady aerodynamics can be computed by defining two equivalent slender wings, one for attached flow loads and another for the vortex-induced loads. It is found that the orbiter is in the transonic speed region subject to vortex-shock-boundary layer interactions that cause highly nonlinear or discontinuous load changes which can endanger the structural integrity of the orbiter wing and possibly cause snap roll problems. It is presently impossible to simulate these interactions in a wind tunnel test even in the static case. Thus, a well planned combined analytic and experimental approach is needed to solve the problem.
Circulation methods for lift measurement in an unsteady aerodynamic flow
NASA Astrophysics Data System (ADS)
Yuan, Jiankun; Olinger, David J.
2001-11-01
Recently an ultrasonic circulation measurement technique has been developed to determine mean lift on various aerodynamic bodies, including airfoils and delta wings^1. The ultrasonic method is based on measuring transit times of acoustic pulses along paths enclosing the aerodynamic body. In the present work, the largely unstudied extension of the ultrasonic technique to determine instantaneous lift in unsteady flows is addressed. An analytical method, based on unsteady potential flow theory, is developed which properly converts the instantaneous bound circulation measured in the ultrasonic technique to instantaneous lift. The analytical method is validated using a finite element solution of flow over an oscillating flat plate at low angle of attack and Reynolds number = 100. The bound circulation within an enclosed acoustic path is determined from the numerical simulation and converted to instantaneous lift via the developed method. Comparing these values to instantaneous lift values determined from integration of the surface pressure distribution shows that the developed method provides improved results compared to a quasi-steady Kutta-Joukowski theorem used in past investigations. The improvement in the proper phase of the instantaneous lift force is nominally larger than the improvement for rms lift amplitudes. The numerical study also shows that proper selection of the enclosing acoustic path is critical for accurate lift measurement. ^1H. Johari, & W. Durgin, Expts. in Fluids 25, 1 (1998).
Computation of unsteady transonic aerodynamics with steady state fixed by truncation error injection
NASA Technical Reports Server (NTRS)
Fung, K.-Y.; Fu, J.-K.
1985-01-01
A novel technique is introduced for efficient computations of unsteady transonic aerodynamics. The steady flow corresponding to body shape is maintained by truncation error injection while the perturbed unsteady flows corresponding to unsteady body motions are being computed. This allows the use of different grids comparable to the characteristic length scales of the steady and unsteady flows and, hence, allows efficient computation of the unsteady perturbations. An example of typical unsteady computation of flow over a supercritical airfoil shows that substantial savings in computation time and storage without loss of solution accuracy can easily be achieved. This technique is easy to apply and requires very few changes to existing codes.
Nelson, Robert C.
2003-01-01
Progress in Aerospace Sciences 39 (2003) 185248 The unsteady aerodynamics of slender wings nonlinearities and flow field time lags. The aerodynamic and the vortical flow structure over simple delta wings of leading-edge vortices and their influence on delta wing aerodynamics for stationary models is presented
NASA Technical Reports Server (NTRS)
Schuster, David M.
2008-01-01
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.
Simultaneous Excitation of Multiple-Input Multiple-Output CFD-Based Unsteady Aerodynamic Systems
NASA Technical Reports Server (NTRS)
Silva, Walter A.
2007-01-01
A significant improvement to the development of CFD-based unsteady aerodynamic reduced-order models (ROMs) is presented. This improvement involves the simultaneous excitation of the structural modes of the CFD-based unsteady aerodynamic system that enables the computation of the unsteady aerodynamic state-space model using a single CFD execution, independent of the number of structural modes. Four different types of inputs are presented that can be used for the simultaneous excitation of the structural modes. Results are presented for a flexible, supersonic semi-span configuration using the CFL3Dv6.4 code.
Simultaneous Excitation of Multiple-Input Multiple-Output CFD-Based Unsteady Aerodynamic Systems
NASA Technical Reports Server (NTRS)
Silva, Walter A.
2008-01-01
A significant improvement to the development of CFD-based unsteady aerodynamic reduced-order models (ROMs) is presented. This improvement involves the simultaneous excitation of the structural modes of the CFD-based unsteady aerodynamic system that enables the computation of the unsteady aerodynamic state-space model using a single CFD execution, independent of the number of structural modes. Four different types of inputs are presented that can be used for the simultaneous excitation of the structural modes. Results are presented for a flexible, supersonic semi-span configuration using the CFL3Dv6.4 code.
Application of unsteady aerodynamic methods for transonic aeroelastic analysis
NASA Technical Reports Server (NTRS)
Whitlow, Woodrow, Jr.
1988-01-01
Aerodynamic methods for aeroelastic analysis are applied to various flow problems. These methods include those that solve the three dimensional transonic small disturbance (TSD) potential equation, the two dimensional (2-D) full potential (FP) equation, and the 2-D thin layer Navier-Stokes equations. Flutter analysis performed using TSD aerodynamics show that such methods can be used to analyze some aeroelastic phenomena. For thicker bodies and larger amplitude motions, a nonisentropic FP method is presented. The unsteady FP equation is modified to model the entropy jumps across shock waves. The conservative form of the modified equation is solved in generalized coordinates using an implicit, approximate factorization method. Pressures calculated on the NLR 7301 and NACA 64A010A airfoils using the nonisentropic FP method are presented. It is shown that modeling shock generated entropy extends the range of validity of the FP method. A Navier-Stokes code is correlated with pressures measured on a supercritical airfoil at transonic speeds. When corrections are made for wind tunnel wall effects, the calculations correlate well with the measured data.
Forcing function effects on unsteady aerodynamic gust response. I - Forcing functions
NASA Technical Reports Server (NTRS)
Henderson, Gregory H.; Fleeter, Sanford
1992-01-01
The paper investigates the fundamental gust modeling assumption on the basis of a series of experiments performed in the Purdue Annular Cascade Research Facility. The measured unsteady flow fields are compared to linear-theory gust requirements. The perforated plate forcing functions closely resemble linear-theory forcing functions, with the static pressure fluctuations small and the periodic velocity vectors parallel to the downstream mean-relative flow angle over the entire periodic cycle. The airfoil forcing functions exhibit characteristics far from linear-theory gusts, with the alignment of the velocity vectors and the static pressure fluctuation amplitudes dependent on the rotor-loading condition, rotor solidity, and the inlet mean-relative flow angle. It is shown that airfoil wakes, both compressor and turbine, cannot be modeled with the boundary conditions of current state-of-the-art linear unsteady aerodynamic theory.
Unsteady Aerodynamic and Dynamic Analysis of the Meridian UAS in a Rolling-Yawing Motion
Lykins, Ryan
2014-05-31
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...
Forcing function effects on unsteady aerodynamic gust response: Part 1--Forcing functions
Henderson, G.H.; Fleeter, S. (Purdue Univ., West Lafayette, IN (United States). School of Mechanical Engineering)
1993-10-01
The fundamental gust modeling assumption is investigated by means of a series of experiments performed in the Purdue Annular Cascade Research Facility. The unsteady periodic flow field is generated by rotating rows of perforated plates and airfoil cascades. In this paper, the measured unsteady flow fields are compared to linear-theory vortical gust requirements, with the resulting unsteady gust response of a downstream stator cascade correlated with linear theory predictions in an accompanying paper. The perforated-plate forcing functions closely resemble linear-theory forcing functions, with the static pressure fluctuations small and the periodic velocity vectors parallel to the downstream mean-relative flow angle over the entire periodic cycle. In contrast, the airfoil forcing functions exhibit characteristics far from linear-theory vortical gusts, with the alignment of the velocity vectors and the static pressure fluctuation amplitudes dependent on the rotor-loading conditions, rotor solidity, and the inlet mean-relative flow angle. Thus, these unique data clearly show that airfoil wakes, both compressor and turbine, are not able to be modeled with the boundary conditions of current state-of-the-art linear unsteady aerodynamic theory.
The vertical-axis wind turbine - Unsteady aerodynamic forces on a Darrieus rotor
B. Chezlepretre
1980-01-01
Unsteady aerodynamic forces on a Darrieus wind turbine can give rise to fatigue cracking and vibrations in the rotor blades. The present paper presents an experimental and theoretical study of aerodynamic forces during blade rotation. Measurements of pressure differences between homologous points on either side of the rotor were obtained for a two-bladed Darrieus wind turbine with NACA 0012 profiles
Large eddy simulation on the unsteady aerodynamic response of a road vehicle in transient crosswinds
Makoto Tsubokura; Takuji Nakashima; Masashi Kitayama; Yuki Ikawa; Deog Hee Doh; Toshio Kobayashi
2010-01-01
A large eddy simulation method based on a fully unstructured finite volume method was developed, and the unsteady aerodynamic response of a road vehicle subjected to transient crosswinds was investigated. First, the method was validated for a 1\\/20-scale wind-tunnel model in a static aerodynamic condition; this showed that the surface pressure distributions as well as the aerodynamic forces and moments
NASA Technical Reports Server (NTRS)
Henderson, Gregory H.; Fleeter, Sanford
1992-01-01
The paper investigates the fundamental gust modeling assumption on the basis of a series of experiments performed in the Purdue Annular Cascade Research Facility. The unsteady period flow field is generated by rotating flows of perforated plates and airfoil cascades, with the resulting unsteady periodic chordwise pressure response of a downstream low solidity stator row determined by miniature pressure transducers embedded within selected airfoils. When the forcing function exhibited the characteristics of a linear-theory gust, the resulting response on the downstream stator airfoils was in excellent agreement with the linear-theory models. When the forcing function did not exhibit linear-theory gust characteristics, the resulting unsteady aerodynamic response of the downstream stators was much more complex and correlated poorly with the linear-theory gust predictions. It is shown that the forcing function generator significantly affects the resulting gust response, with the complexity of the response characteristics increasing from the perforated-plate to the airfoil-cascade forcing functions.
Henderson, G.H.; Fleeter, S. (Purdue Univ., West Lafayette, IN (United States). School of Mechanical Engineering)
1993-10-01
The fundamental gust modeling assumption is investigated by means of series of experiments performed in the Purdue Annular Cascade Research Facility. The unsteady periodic flow field is generated by rotating rows of perforated plates and airfoil cascades, with the resulting unsteady periodic chord wise pressure response of a downstream low-solidity stator row determined by miniature pressure transducers embedded within selected airfoils. When the forcing function exhibited the characteristic of a linear-theory vortical gust, as was the case for the perforated-plate wake generators, the resulting response on the downstream stator airfoils was in excellent agreement with the linear-theory models. In contrast, when the forcing function did not exhibit linear-theory vortical gust characteristics, i.e., for the airfoil wake generators, the resulting unsteady aerodynamic responses of the downstream stators were much more complex and correlated poorly with the linear-theory gust predictions. Thus, this investigation has quantitatively shown that the forcing function generator significantly affects the resulting gust response, with the complexity of the response characteristics increasing from the perforated-plate to the airfoil-cascade forcing functions.
NASA Technical Reports Server (NTRS)
Silva, Walter A.
1993-01-01
A methodology for modeling nonlinear unsteady aerodynamic responses, for subsequent use in aeroservoelastic analysis and design, using the Volterra-Wiener theory of nonlinear systems is presented. The methodology is extended to predict nonlinear unsteady aerodynamic responses of arbitrary frequency. The Volterra-Wiener theory uses multidimensional convolution integrals to predict the response of nonlinear systems to arbitrary inputs. The CAP-TSD (Computational Aeroelasticity Program - Transonic Small Disturbance) code is used to generate linear and nonlinear unit impulse responses that correspond to each of the integrals for a rectangular wing with a NACA 0012 section with pitch and plunge degrees of freedom. The computed kernels then are used to predict linear and nonlinear unsteady aerodynamic responses via convolution and compared to responses obtained using the CAP-TSD code directly. The results indicate that the approach can be used to predict linear unsteady aerodynamic responses exactly for any input amplitude or frequency at a significant cost savings. Convolution of the nonlinear terms results in nonlinear unsteady aerodynamic responses that compare reasonably well with those computed using the CAP-TSD code directly but at significant computational cost savings.
Unsteady Aerodynamics of Static Airfoils in Reverse Flow
NASA Astrophysics Data System (ADS)
Lind, Andrew; Jones, Anya
2013-11-01
Wind tunnel experiments have been conducted on two-dimensional blunt and sharp trailing edge airfoils held at static angles of attack in reverse flow for three Reynolds numbers. The current work is aimed at advancing the understanding of fully developed reverse flow for high-speed helicopter applications, and evaluates the potential for blunt trailing edge airfoils to mitigate unsteady rotor blade airloads in this flow regime. Time-resolved particle image velocimetry measurements at post-stall angles of attack have revealed the evolution of a trailing edge vortex formed by the roll-up of vorticity generated in a separated shear layer. Proper orthogonal decomposition (POD) was applied to the flow field measurements to improve the identification and tracking of dominant flow structures. Unsteady force balance measurements have captured non-structural vibrations with frequency content which correlates well with that of the temporal coefficients for the first two POD spatial modes. These vibrations vary in frequency with angle of attack and are shown to be linked with trailing edge vortex shedding. The findings presented here give fundamental insight towards the development of efficient rotor blades for high-speed helicopters.
Unsteady Aerodynamic Models for Turbomachinery Aeroelastic and Aeroacoustic Applications
NASA Technical Reports Server (NTRS)
Verdon, Joseph M.; Barnett, Mark; Ayer, Timothy C.
1995-01-01
Theoretical analyses and computer codes are being developed for predicting compressible unsteady inviscid and viscous flows through blade rows of axial-flow turbomachines. Such analyses are needed to determine the impact of unsteady flow phenomena on the structural durability and noise generation characteristics of the blading. The emphasis has been placed on developing analyses based on asymptotic representations of unsteady flow phenomena. Thus, high Reynolds number flows driven by small amplitude unsteady excitations have been considered. The resulting analyses should apply in many practical situations and lead to a better understanding of the relevant flow physics. In addition, they will be efficient computationally, and therefore, appropriate for use in aeroelastic and aeroacoustic design studies. Under the present effort, inviscid interaction and linearized inviscid unsteady flow models have been formulated, and inviscid and viscid prediction capabilities for subsonic steady and unsteady cascade flows have been developed. In this report, we describe the linearized inviscid unsteady analysis, LINFLO, the steady inviscid/viscid interaction analysis, SFLOW-IVI, and the unsteady viscous layer analysis, UNSVIS. These analyses are demonstrated via application to unsteady flows through compressor and turbine cascades that are excited by prescribed vortical and acoustic excitations and by prescribed blade vibrations. Recommendations are also given for the future research needed for extending and improving the foregoing asymptotic analyses, and to meet the goal of providing efficient inviscid/viscid interaction capabilities for subsonic and transonic unsteady cascade flows.
Unsteady aerodynamic analysis for offshore floating wind turbines under different wind conditions.
Xu, B F; Wang, T G; Yuan, Y; Cao, J F
2015-02-28
A free-vortex wake (FVW) model is developed in this paper to analyse the unsteady aerodynamic performance of offshore floating wind turbines. A time-marching algorithm of third-order accuracy is applied in the FVW model. Owing to the complex floating platform motions, the blade inflow conditions and the positions of initial points of vortex filaments, which are different from the fixed wind turbine, are modified in the implemented model. A three-dimensional rotational effect model and a dynamic stall model are coupled into the FVW model to improve the aerodynamic performance prediction in the unsteady conditions. The effects of floating platform motions in the simulation model are validated by comparison between calculation and experiment for a small-scale rigid test wind turbine coupled with a floating tension leg platform (TLP). The dynamic inflow effect carried by the FVW method itself is confirmed and the results agree well with the experimental data of a pitching transient on another test turbine. Also, the flapping moment at the blade root in yaw on the same test turbine is calculated and compares well with the experimental data. Then, the aerodynamic performance is simulated in a yawed condition of steady wind and in an unyawed condition of turbulent wind, respectively, for a large-scale wind turbine coupled with the floating TLP motions, demonstrating obvious differences in rotor performance and blade loading from the fixed wind turbine. The non-dimensional magnitudes of loading changes due to the floating platform motions decrease from the blade root to the blade tip. PMID:25583859
NASA Astrophysics Data System (ADS)
Suzuki, Kensuke
A new analysis tool, an unsteady Hybrid Navier-Stokes/Vortex Model, for a horizontal axis wind turbine (HAWT) in yawed flow is presented, and its convergence and low cost computational performance are demonstrated. In earlier work, a steady Hybrid Navier-Stokes/Vortex Model was developed with a view to improving simulation results obtained by participants of the NASA Ames blind comparison workshop, following the NREL Unsteady Aerodynamics Experiment. The hybrid method was shown to better predict rotor torque and power over the range of wind speeds, from fully attached to separated flows. A decade has passed since the workshop was held and three dimensional unsteady Navier-Stokes analyses have become available using super computers. In the first chapter, recent results of unsteady Euler and Navier-Stokes computations are reviewed as standard references of what is currently possible and are contrasted with results of the Hybrid Navier-Stokes/Vortex Model in steady flow. In Chapter 2, the computational method for the unsteady Hybrid model is detailed. The grid generation procedure, using ICEM CFD, is presented in Chapter 3. Steady and unsteady analysis results for the NREL Phase IV rotor and for a modified "swept NREL rotor" are presented in Chapter 4-Chapter 7.
Unsteady aerodynamic analysis of space shuttle vehicles. Part 1: Summary report
NASA Technical Reports Server (NTRS)
Ericsson, L. E.; Reding, J. P.
1973-01-01
An analysis of the unsteady aerodynamics of space shuttle vehicles was performed. The results show that slender wing theory can be modified to give the potential flow static and dynamic characteristics over a large Mach number range from M = 0 to M 1. A semi-empirical analytic approximation is derived for the loads induced by the leading edge vortex; and it is shown that the developed analytic technique gives good prediction of experimentally determined steady and unsteady delta wing aerodynamics, including the effects of leading edge roundness. At supersonic speeds, attached leading edge flow is established and shock-induced flow separation effects become of concern. Analysis of experimental results for a variety of boost configurations led to a definition of the main features of the flow interference effects between orbiter (delta wing) and booster. The effects of control deflection on the unsteady aerodynamics of the delta-wing orbiter were also evaluated.
Mechanism of unsteady aerodynamic heating with sudden change in surface temperature
Hao Chen; Lin Bao
2009-01-01
The characteristics and mechanism of unsteady aerodynamic heating of a transient hypersonic boundary layer caused by a sudden\\u000a change in surface temperature are studied. The complete time history of wall heat flux is presented with both analytical and\\u000a numerical approaches. With the analytical method, the unsteady compressible boundary layer equation is solved. In the neighborhood\\u000a of the initial and final
Numerical Study of Steady and Unsteady Canard-Wing-Body Aerodynamics
NASA Technical Reports Server (NTRS)
Eugene, L. Tu
1996-01-01
The use of canards in advanced aircraft for control and improved aerodynamic performance is a topic of continued interest and research. In addition to providing maneuver control and trim, the influence of canards on wing aerodynamics can often result in increased maximum lift and decreased trim drag. In many canard-configured aircraft, the main benefits of canards are realized during maneuver or other dynamic conditions. Therefore, the detailed study and understanding of canards requires the accurate prediction of the non-linear unsteady aerodynamics of such configurations. For close-coupled canards, the unsteady aerodynamic performance associated with the canard-wing interaction is of particular interest. The presence of a canard in close proximity to the wing results in a highly coupled canard-wing aerodynamic flowfield which can include downwash/upwash effects, vortex-vortex interactions and vortex-surface interactions. For unsteady conditions, these complexities of the canard-wing flowfield are further increased. The development and integration of advanced computational technologies provide for the time-accurate Navier-Stokes simulations of the steady and unsteady canard-wing-body flox,fields. Simulation, are performed for non-linear flight regimes at transonic Mach numbers and for a wide range of angles of attack. For the static configurations, the effects of canard positioning and fixed deflection angles on aerodynamic performance and canard-wing vortex interaction are considered. For non-static configurations, the analyses of the canard-wing body flowfield includes the unsteady aerodynamics associated with pitch-up ramp and pitch oscillatory motions of the entire geometry. The unsteady flowfield associated with moving canards which are typically used as primary control surfaces are considered as well. The steady and unsteady effects of the canard on surface pressure integrated forces and moments, and canard-wing vortex interaction are presented in detail including the effects of the canard on the static and dynamic stability characteristics. The current study provides an understanding of the steady and unsteady canard-wing-body flowfield. Emphasis is placed on the effects of the canard on aerodynamic performance as well as the detailed flow physics of the canard-wing flowfield interactions. The computational tools developed to accurately predict the time-accurate flowfield of moving canards provides for the capability of coupled fluids-controls simulations desired in the detailed design and analysis of advanced aircraft.
Development of a linearized unsteady aerodynamic analysis for cascade gust response predictions
NASA Technical Reports Server (NTRS)
Verdon, Joseph M.; Hall, Kenneth C.
1990-01-01
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.
Shigeru Aso; Kenichi Oyama; Masanori Hayashi
1992-01-01
Numerical simulation of unsteady shock reflection by a ramp have been conducted. The two-dimensional thin layered Navier-Stokes equation is solved numerically by a TVD (Total Variation Diminishing) scheme in order to simulate unsteady shock reflections and an unsteady aerodynamic heating by shock reflections. The calculations have been carried out for various mesh systems. The detailed flow structure and the effect
The influence of neighboring blade rows on the unsteady aerodynamic response of cascades
Hall, K.C.; Silkowski, P.D. [Duke Univ., Durham, NC (United States). Dept. of Mechanical Engineering and Materials Science
1997-01-01
In this paper, the authors present an analysis of the unsteady aerodynamic response of cascades due to incident gusts (the forced response problem) or blade vibration (the flutter problem) when the cascade is part of a multistage fan, compressor, or turbine. Most current unsteady aerodynamic models assume the cascade to be isolated in an infinitely long duct. This assumption, however, neglects the potentially important influence of neighboring blade rows. They present an elegant and computationally efficient method to model these neighboring blade row effects. In the present method, they model the unsteady aerodynamic response due to so-called spinning modes (pressure and vorticity waves), with each mode corresponding to a different circumferential wave number and frequency. Then, for each mode, they compute the reflection and transmission coefficients for each blade row. These coefficients can be obtained from any of the currently available unsteady linearized aerodynamic models of isolated cascades. A set of linear equations is then constructed that couples together the various spinning modes, and the linear equations are solved via LU decomposition. Numerical results are presented for both the gust response and blade vibration problems. To validate the model, the authors compare their results to other analytical models, and to a multistage vortex lattice model. They show that the effect of neighboring blade rows on the aerodynamic damping of vibrating cascades is significant, but nevertheless can be modeled with a small number of modes.
NASA Technical Reports Server (NTRS)
Murphy, Patrick C.; Klein, Vladislav
2003-01-01
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.
Rotor-generated unsteady aerodynamic interactions in a 1½ stage compressor
NASA Astrophysics Data System (ADS)
Papalia, John J.
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.
Estimation of Aircraft Unsteady Aerodynamic Parameters from Dynamic Wind Tunnel Testing
NASA Technical Reports Server (NTRS)
Murphy, Patrick C.; Klein, Vladislav
2001-01-01
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.
NASA Technical Reports Server (NTRS)
Kandil, O. A.
1981-01-01
Progress is reported in the development of reliable nonlinear vortex methods for predicting the steady and unsteady aerodynamic loads of highly sweptback wings at large angles of attack. Abstracts of the papers, talks, and theses produced through this research are included. The modified nonlinear discrete vortex method and the nonlinear hybrid vortex method are highlighted.
Parametric Reduced-Order Models for Probabilistic Analysis of Unsteady Aerodynamic Applications
T. Bui-Thanh; K. Willcox; O. Ghattas
2008-01-01
Methodology is presented to derive reduced-order models for large-scale parametric applications in unsteady aerodynamics. The specific case considered in this paper is a computational fluid dynamic (CFD) model with parametric dependence that arises from geometric shape variations. The first key contribution of the methodology is the derivation of a linearized model that permits the eects of geometry variations to be
Transonic unsteady aerodynamics in the vicinity of shock-buffet instability
NASA Astrophysics Data System (ADS)
Iovnovich, M.; Raveh, D. E.
2012-02-01
A study of transonic unsteady aerodynamic responses in the vicinity of shock-buffet is presented. Navier-Stokes simulations of a NACA 0012 airfoil with a fitted 20% trailing edge flap are performed to compute the aerodynamic responses to prescribed pitch and flap motions, about mean flow conditions at shock-buffet onset, and while exhibiting shock buffet. The unsteady aerodynamic response is found to be fundamentally different from the response predicted by the linear aerodynamic theory. At mean angles of attack close to buffet onset noticeable damped resonance responses are observed at frequencies close to the buffet frequency. The responses grow as the mean angle of attack is increased towards buffet onset. Also, a phase lead is observed for the aerodynamic coefficients, for some range of frequencies. The large aerodynamic responses and phase lead appear in frequencies that are typical of structural elastic frequencies, suggesting that they may be responsible for transonic aeroelastic instabilities. At shock buffet conditions, prescribing sufficiently large pitch or flap harmonic motions results in synchronization of the buffet frequency with the excitation frequencies. At these conditions, the lift and pitching moment responses to prescribed pitch motion also result in resonance and phase lead, as in the pre-buffet case. Large prescribed flap motions eliminate the lift resonance response, and significantly reduce the lift coefficient amplitudes, indicating that the aerodynamic coefficients at these conditions can be controlled by prescribed structural motions.
NASA Technical Reports Server (NTRS)
Capece, Vincent R.; Platzer, Max F.
2003-01-01
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.
Investigation of pump hydraulic noise by unsteady aerodynamic measurements
B. Godefroi; J. Tourret; M. Bertinier; M. Pluviose
1990-01-01
An experimental method is developed to further understand the physical mechanisms of acoustic wave generation in centrifugal flow turbine engines. This method measures the complete unsteady pressure field throughout the engine and its variations with rotor position or airflow. Time pressure signals are obtained synchronously by using a large number of fixed and rotating transducers. These time signal values are
UNSTEADY AERODYNAMIC PERFORMANCE OF MODEL WINGS AT LOW REYNOLDS NUMBERS
MICHAEL H. DICKINSON; KARL G. GÖTZ
1993-01-01
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
Characteristic boundary conditions for three-dimensional transonic unsteady aerodynamics
NASA Technical Reports Server (NTRS)
Whitlow, W., Jr.
1984-01-01
Characteristic far-field boundary conditions for the three-dimensional unsteady transonic small disturbance potential equation have been developed. The boundary conditions were implemented in the XTRAN3S finite difference code and tested for a flat plate rectangular wing with a pulse in angle of attack; the freestream Mach number was 0.85. The calculated force response shows that the characteristic boundary conditions reduce disturbances that are reflected from the computational boundaries.
Identification of unsteady aerodynamics and aeroelastic integro-differential systems
NASA Technical Reports Server (NTRS)
Gupta, N. K.; Iliff, K. W.
1985-01-01
The problem of estimating integro-differential models based on test or simulation data is dealt with. The identification techniques proposed for estimating parameters in models described by differential equations need to be considerably extended to deal with the integral terms. Conditions under which the integral terms may be approximated by algebraic values are discussed. The integro-differential models discussed are related to indicial models proposed by aerodynamicists to describe unsteady flow.
Unsteady aerodynamic analysis of space shuttle vehicles. Part 3: Booster interference effects
NASA Technical Reports Server (NTRS)
Reding, J. P.; Ericsson, L. E.
1973-01-01
An investigation of the interference flow field on the space-shuttle boost configuration has been made. The results show that the interference effects can dominate the shuttle aerodynamics. Vortices shed from shock-induced flow separations on the forward portion of the vehicle affect the aerodynamic loads on the aft portion of the booster. Thus, the forebody and aft-body flow fields are coupled. This coupling and the associated time lag due to the finite convection speed of the vortices furnish a mechanism whereby the unsteady aerodynamics can cause undamping of certain low frequency elastic modes of the booster. A preliminary order-of-magnitude analysis of the aeroelastic stability of the shuttle booster indicates that negative aerodynamic damping could occur for at least one bending mode and be of sufficient magnitude to dominate the structural damping. The implication of these results, (with the possibility of undamped oscillations leading to structural failure), is serious enough to warrant further, more detailed analysis.
NASA Technical Reports Server (NTRS)
Yates, E. Carson, Jr.
1990-01-01
Progress in the development of computational methods for steady and unsteady aerodynamics has perennially paced advancements in aeroelastic analysis and design capabilities. Since these capabilities are of growing importance in the analysis and design of high-performance aircraft, considerable effort has been directed toward the development of appropriate aerodynamic methodology. The contributions to those efforts from the integral-equations research program at the NASA Langley Research Center is reviewed. Specifically, the current scope, progress, and plans for research and development for inviscid and viscous flows are discussed, and example applications are shown in order to highlight the generality, versatility, and attractive features of this methodology.
Dmytro M. Voytovych
2004-01-01
An efficient and accurate computational method for predicting unsteady flows in multistage turbomachinery is presented. Particularly, a method is developed to solve the flutter and forced response problems accounting for blade row coupling. The aerodynamic blade row coupling is provided by propagation of waves in the working fluid. A set of travelling waves is represented by multiple unsteady solutions for
Application of the ASP3D Computer Program to Unsteady Aerodynamic and Aeroelastic Analyses
NASA Technical Reports Server (NTRS)
Batina, John T.
2006-01-01
A new computer program has been developed called ASP3D (Advanced Small Perturbation - 3D), which solves the small perturbation potential flow equation in an advanced form including mass-consistent surface and trailing wake boundary conditions, and entropy, vorticity, and viscous effects. The purpose of the program is for unsteady aerodynamic and aeroelastic analyses, especially in the nonlinear transonic flight regime. The program exploits the simplicity of stationary Cartesian meshes with the movement or deformation of the configuration under consideration incorporated into the solution algorithm through a planar surface boundary condition. The paper presents unsteady aerodynamic and aeroelastic applications of ASP3D to assess the time dependent capability and demonstrate various features of the code.
NASA Technical Reports Server (NTRS)
Edwards, John W.; Malone, John B.
1992-01-01
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.
Expansion series of integral functions occurring in unsteady aerodynamics
NASA Technical Reports Server (NTRS)
Ueda, T.
1982-01-01
Attention is given to two real integral functions which occur in the kernel of singular integral equations for subsonic unsteady lifting surfaces. The arguments k, r, and X of the functions correspond to the reduced frequency, spanwise distance, and modified coordinate in the flow direction, respectively. The value of the parameter nu in the functions depends on geometrical conditions. The considered investigation has the objective to present a series for general values of the nonnegative integer nu in order to compute efficiently the integral functions. The approach makes it possible to avoid any approximation or numerical quadrature.
Development of computational methods for unsteady aerodynamics at the NASA Langley Research Center
NASA Technical Reports Server (NTRS)
Yates, E. Carson, Jr.; Whitlow, Woodrow, Jr.
1987-01-01
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.
Development of computational methods for unsteady aerodynamics at the NASA Langley Research Center
NASA Technical Reports Server (NTRS)
Yates, E. Carson, Jr.; Whitlow, Woodrow, Jr.
1987-01-01
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.
NASA Technical Reports Server (NTRS)
Peele, E. L.; Adams, W. M., Jr.
1979-01-01
A computer program, ISAC, is described which calculates the stability and response of a flexible airplane equipped with active controls. The equations of motion relative to a fixed inertial coordinate system are formulated in terms of the airplane's rigid body motion and its unrestrained normal vibration modes. Unsteady aerodynamic forces are derived from a doublet lattice lifting surface theory. The theoretical basis for the program is briefly explained together with a description of input data and output results.
Wing flutter boundary prediction using an unsteady Euler aerodynamic method
NASA Technical Reports Server (NTRS)
Lee-Rausch, Elizabeth M.; Batina, John T.
1993-01-01
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.
NASA Technical Reports Server (NTRS)
Whitlow, Woodrow, Jr.
1993-01-01
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.
Improving the Unsteady Aerodynamic Performance of Transonic Turbines using Neural Networks
NASA Technical Reports Server (NTRS)
Rai, Man Mohan; Madavan, Nateri K.; Huber, Frank W.
1999-01-01
A recently developed neural net-based aerodynamic design procedure is used in the redesign of a transonic turbine stage to improve its unsteady aerodynamic performance. The redesign procedure used incorporates the advantages of both traditional response surface methodology and neural networks by employing a strategy called parameter-based partitioning of the design space. Starting from the reference design, a sequence of response surfaces based on both neural networks and polynomial fits are constructed to traverse the design space in search of an optimal solution that exhibits improved unsteady performance. The procedure combines the power of neural networks and the economy of low-order polynomials (in terms of number of simulations required and network training requirements). A time-accurate, two-dimensional, Navier-Stokes solver is used to evaluate the various intermediate designs and provide inputs to the optimization procedure. The procedure yielded a modified design that improves the aerodynamic performance through small changes to the reference design geometry. These results demonstrate the capabilities of the neural net-based design procedure, and also show the advantages of including high-fidelity unsteady simulations that capture the relevant flow physics in the design optimization process.
NASA Technical Reports Server (NTRS)
Batina, John T.
1990-01-01
Improved algorithm for the solution of the time-dependent Euler equations are presented for unsteady aerodynamic analysis involving unstructured dynamic meshes. The improvements were developed recently to the spatial and temporal discretizations used by unstructured grid flow solvers. The spatial discretization involves a flux-split approach which is naturally dissipative and captures shock waves sharply with at most one grid point within the shock structure. The temporal discretization involves an implicit time-integration scheme using a Gauss-Seidel relaxation procedure which is computationally efficient for either steady or unsteady flow problems. For example, very large time steps may be used for rapid convergence to steady state, and the step size for unsteady cases may be selected for temporal accuracy rather than for numerical stability. Steady and unsteady flow results are presented for the NACA 0012 airfoil to demonstrate applications of the new Euler solvers. The unsteady results were obtained for the airfoil pitching harmonically about the quarter chord. The resulting instantaneous pressure distributions and lift and moment coefficients during a cycle of motion compare well with experimental data. A description of the Euler solvers is presented along with results and comparisons which assess the capability.
NASA Astrophysics Data System (ADS)
Morino, L.; Gennaretti, M.; Iemma, U.; Salvatore, F.
Recent developments on a general boundary integral formulation for the aerodynamic and aeroacoustic analyses of lifting bodies (e.g., wings and rotors) are reviewed. The emphasis is on recent numerical results, specifically on the effects of the unsteadiness, of the viscosity, and of the transonic nonlinearities. The boundary-element full-potential formulation for bodies in arbitrary motion is outlined along with the its extension to viscous/inviscid interaction. The effects of viscosity are taken into account through a coupled boundary-layer/full-potential technique similar to that used in the CFD community. Numerical results obtained with the present formulation are compared against numerical and experimental results available in literature. They include (i) aerodynamics and aeroacoustics of helicopter rotors in hover and forward flight in subsonic flows; (ii) transonic aerodynamics/acoustics results for steady potential flows around airfoils and hovering rotors, and (iii) viscous flows (subsonic and transonic) around airfoils.
Physically weighted approximations of unsteady aerodynamic forces using the minimum-state method
NASA Technical Reports Server (NTRS)
Karpel, Mordechay; Hoadley, Sherwood Tiffany
1991-01-01
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.
Unsteady rotor aerodynamics using a vortex panel method
NASA Technical Reports Server (NTRS)
Crispin, Y.
1982-01-01
The problem of the potential incompressible flow about a helicopter rotor blade is solved using an unsteady vortex-panel method where the mutual interaction between the blade and the distorting free wake is taken into account. The present method alleviates the need to rely upon measured-wake geometries or p5escribed-wake models in order to calculate the airloads. A computer program has been developed which is capable of predicting the geometry of the time-dependent three-dimensional (3-D) wake and the instantaneous loadings for a single blade in hover, climb, and forward flight. The solution is obtained by using a time-accurate step-by-step procedure. The complex-wake geometry at any time is presented graphically with a computer graphics system. Calculated results are compared with published data for a rotor blade in both hover and forward flight. The code has also been applied to the study of the effect of changing blade tip geometry.
Linearized Unsteady Aerodynamic Analysis of the Acoustic Response to Wake/Blade-Row Interaction
NASA Technical Reports Server (NTRS)
Verdon, Joseph M.; Huff, Dennis L. (Technical Monitor)
2001-01-01
The three-dimensional, linearized Euler analysis, LINFLUX, is being developed to provide a comprehensive and efficient unsteady aerodynamic scheme for predicting the aeroacoustic and aeroelastic responses of axial-flow turbomachinery blading. LINFLUX couples a near-field, implicit, wave-split, finite-volume solution to far-field acoustic eigensolutions, to predict the aerodynamic responses of a blade row to prescribed structural and aerodynamic excitations. It is applied herein to predict the acoustic responses of a fan exit guide vane (FEGV) to rotor wake excitations. The intent is to demonstrate and assess the LINFLUX analysis via application to realistic wake/blade-row interactions. Numerical results are given for the unsteady pressure responses of the FEGV, including the modal pressure responses at inlet and exit. In addition, predictions for the modal and total acoustic power levels at the FEGV exit are compared with measurements. The present results indicate that the LINFLUX analysis should be useful in the aeroacoustic design process, and for understanding the three-dimensional flow physics relevant to blade-row noise generation and propagation.
NASA Technical Reports Server (NTRS)
Pototzky, Anthony S.
2008-01-01
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.
Hugoniot experiments with unsteady waves
NASA Astrophysics Data System (ADS)
Fratanduono, D. E.; Munro, D. H.; Celliers, P. M.; Collins, G. W.
2014-07-01
Recent development of transparent shock wave standard materials, such as quartz, enables continuous tracking of shock waves using optical velocimetry, providing information on shock wave steadiness and pressure perturbations in the target. From a first order perturbation analysis, we develop a set of analytical formulas that connect the pressure perturbations at the drive surface to the shock velocity perturbations observed in measurements. With targets that incorporate a calibrated transparent witness material, such as quartz, and with the analytical formulas describing the perturbation response, it is possible to determine the sound speed and Grüneisen coefficient of an unknown sample by using evolution of the non-steady perturbations as a probe. These formulas can also be used to improve the accuracy of traditional shock wave impedance match Hugoniot experiments of opaque samples driven with non-steady waves.
Stochastic model for aerodynamic force dynamics on wind turbine blades in unsteady wind inflow
Luhur, Muhammad Ramzan; Kühn, Martin; Wächter, Matthias
2015-01-01
The paper presents a stochastic approach to estimate the aerodynamic forces with local dynamics on wind turbine blades in unsteady wind inflow. This is done by integrating a stochastic model of lift and drag dynamics for an airfoil into the aerodynamic simulation software AeroDyn. The model is added as an alternative to the static table lookup approach in blade element momentum (BEM) wake model used by AeroDyn. The stochastic forces are obtained for a rotor blade element using full field turbulence simulated wind data input and compared with the classical BEM and dynamic stall models for identical conditions. The comparison shows that the stochastic model generates additional extended dynamic response in terms of local force fluctuations. Further, the comparison of statistics between the classical BEM, dynamic stall and stochastic models' results in terms of their increment probability density functions gives consistent results.
NASA Technical Reports Server (NTRS)
Tiffany, Sherwood H.; Karpel, Mordechay
1989-01-01
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.
Estimation of unsteady aerodynamics in the wake of a freely flying European starling
Ben-Gida, Hadar; Taylor, Zachary J; Bezner-Kerr, Wayne; Guglielmo, Christopher G; Kopp, Gregory A; Gurka, Roi
2013-01-01
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 ...
Calculation of unsteady transonic aerodynamics for oscillating wings with thickness
NASA Technical Reports Server (NTRS)
Ruo, S. Y.; Theisen, J. G.
1975-01-01
An analytical approach is presented to account for some of the nonlinear characteristics of the transonic flow equation for finite thickness wings undergoing harmonic oscillation at sonic flight speed in an inviscid, shock-free fluid. The thickness effect is accounted for in the analysis through use of the steady local Mach number distribution over the wing at its mean position by employing the local linearization concept and a coordinate transformation. Computed results are compared with that of the linearized theory and experiments. Based on the local linearization concept, an alternate formulation avoiding the limitations of the coordinate transformation method is presented.
NASA Technical Reports Server (NTRS)
Tiffany, Sherwood H.; Adams, William M., Jr.
1988-01-01
The approximation of unsteady generalized aerodynamic forces in the equations of motion of a flexible aircraft are discussed. Two methods of formulating these approximations are extended to include the same flexibility in constraining the approximations and the same methodology in optimizing nonlinear parameters as another currently used extended least-squares method. Optimal selection of nonlinear parameters is made in each of the three methods by use of the same nonlinear, nongradient optimizer. The objective of the nonlinear optimization is to obtain rational approximations to the unsteady aerodynamics whose state-space realization is lower order than that required when no optimization of the nonlinear terms is performed. The free linear parameters are determined using the least-squares matrix techniques of a Lagrange multiplier formulation of an objective function which incorporates selected linear equality constraints. State-space mathematical models resulting from different approaches are described and results are presented that show comparative evaluations from application of each of the extended methods to a numerical example.
NSDL National Science Digital Library
Robert Dudley (University of Texas at Austin; Integrative Biology)
1999-06-18
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.
NASA Technical Reports Server (NTRS)
Bennett, R. M.
1972-01-01
The method of integral relations is applied in a one-strip approximation to the perturbation equations governing small motions of an inclined, sharp-edged, flat surface about the mean supersonic steady flow. Algebraic expressions for low reduced-frequency aerodynamics are obtained and a set of ordinary differential equations are obtained for general oscillatory motion. Results are presented for low reduced-frequency aerodynamics and for the variation of the unsteady forces with frequency. The method gives accurate results for the aerodynamic forces at low reduced frequency which are in good agreement with available experimental data. However, for cases in which the aerodynamic forces vary rapidly with frequency, the results are qualitatively correct, but of limited accuracy. Calculations indicate that for a range of inclination angles near shock detachment such that the flow in the shock layer is low supersonic, the aerodynamic forces vary rapidly both with inclination angle and with reduced frequency.
NASA Technical Reports Server (NTRS)
Ramsey, John K.; Erwin, Dan
2004-01-01
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.
Unsteady Analysis of Separated Aerodynamic Flows Using an Unstructured Multigrid Algorithm
NASA Technical Reports Server (NTRS)
Pelaez, Juan; Mavriplis, Dimitri J.; Kandil, Osama
2001-01-01
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.
Feasibility investigation of general time-domain unsteady aerodynamics of rotors
NASA Technical Reports Server (NTRS)
Johnson, Wayne
1990-01-01
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.
Recent Experiments at the Gottingen Aerodynamic Institute
NASA Technical Reports Server (NTRS)
Ackeret, J
1925-01-01
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).
Low dimensional state-space representations for classical unsteady aerodynamic models
NASA Astrophysics Data System (ADS)
Brunton, Steven L.; Rowley, Clarence W.
2010-11-01
This work develops reduced order models for the unsteady aerodynamic forces on a small wing in response to agile maneuvers and gusts. In particular, the classical unsteady models of Wagner and Theodorsen are cast into a low-dimensional state-space framework. Low order state-space models are more computationally efficient than the classical formulations, and are well suited for modification with nonlinear dynamics and the application of control techniques. Reduced order models are obtained using the eigensystem realization algorithm on force data from the direct numerical simulation (DNS) of a pitching or plunging 2D flat plate at Reynolds numbers between 100 and 1000. Models are tested on rapid pitch and plunge maneuvers with a range of effective angle-of-attack. We evaluate the performance of the models based on agreement with results from DNS, in particular, the ability to reproduce lift forces over a range of pitching and plunging frequencies. Bode plots of the reduced order models, Wagner's and Theodorsen's methods, and DNS provide a concise assessment.
NASA Astrophysics Data System (ADS)
Voytovych, Dmytro M.
An efficient and accurate computational method for predicting unsteady flows in multistage turbomachinery is presented. Particularly, a method is developed to solve the flutter and forced response problems accounting for blade row coupling. The aerodynamic blade row coupling is provided by propagation of waves in the working fluid. A set of travelling waves is represented by multiple unsteady solutions for each blade row. Each solution has a particular frequency and interblade phase angle defined by the scattering and frequency shifting mechanisms. The waves are allowed to propagate between the rows by exchanging the information between various unsteady solutions at the interface boundaries. Only a finite number of unsteady solutions must be retained in the model to compute accurately the unsteady aerodynamic response. The unsteady solutions are defined by solving a system of time-linearized Reynolds-averaged Navier-Stokes equations with the Spalart-Allmaras one-equation turbulence model. After linearization, the resulting system of equations consists of the non-linear steady equations and linear unsteady equations with variable coefficients. The equations are discretized on a deforming, multi-block grid and advanced in the pseudo-time domain using a finite-volume Lax-Wendroff integration technique. Using the circumferential periodicity only one blade-to-blade passage is required to model each blade row. Various acceleration techniques such as multi-grid, local time-stepping and smoothing are employed to improve the convergence rate. The steady flow solver is validated against available experimental data. Results from the unsteady flow solver are compared with a semi-analytical method for the flutter problem. The analysis of the flutter problem for a front one-and-half stage of a modern axial compressor demonstrated the capability of the method of predicting the unsteady loads on blades with complex realistic geometry. The unsteady flow calculations in the forced response problem revealed the importance of the first two blade passing frequencies for computing the unsteady load on blades in a downstream blade row. The present time-linearized method is several orders of magnitude faster than conventional non-linear time-marching methods.
NASA Technical Reports Server (NTRS)
Queijo, M. J.; Wells, W. R.; Keskar, D. A.
1979-01-01
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.
NASA Technical Reports Server (NTRS)
Mabey, D. G.; Chambers, J. R.
1986-01-01
From May 6 to 9, 1985, the Fluid Dynamics Panel and Flight Mechanics Panel of AGARD jointly arranged a Symposium on Unsteady Aerodynamics-Fundamentals and Applications to Aircraft Dynamics at the Stadthall, Goettingen, West Germany. This Symposium was organized by an international program committee chaired by Dr. K. J. Orlik-Ruckemann of the Fluid Dynamics Panel. The program consisted of five sessions grouped in two parts: (1) Fundamentals of Unsteady Aerodynamics; and (2) Applications to Aircraft Dynamics. The 35 papers presented at the 4 day meeting are published in AGARD CP 386 and listed in the Appendix. As the papers are already available and cover a very wide field, the evaluators have offered brief comments on every paper, followed by an overall evaluation of the meeting, together with some general conclusions and recommendations.
Transonic Unsteady Aerodynamics of the F/A-18E at Conditions Promoting Abrupt Wing Stall
NASA Technical Reports Server (NTRS)
Schuster, David M.; Byrd, James E.
2003-01-01
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.
Introduction of the ASP3D Computer Program for Unsteady Aerodynamic and Aeroelastic Analyses
NASA Technical Reports Server (NTRS)
Batina, John T.
2005-01-01
A new computer program has been developed called ASP3D (Advanced Small Perturbation 3D), which solves the small perturbation potential flow equation in an advanced form including mass-consistent surface and trailing wake boundary conditions, and entropy, vorticity, and viscous effects. The purpose of the program is for unsteady aerodynamic and aeroelastic analyses, especially in the nonlinear transonic flight regime. The program exploits the simplicity of stationary Cartesian meshes with the movement or deformation of the configuration under consideration incorporated into the solution algorithm through a planar surface boundary condition. The new ASP3D code is the result of a decade of developmental work on improvements to the small perturbation formulation, performed while the author was employed as a Senior Research Scientist in the Configuration Aerodynamics Branch at the NASA Langley Research Center. The ASP3D code is a significant improvement to the state-of-the-art for transonic aeroelastic analyses over the CAP-TSD code (Computational Aeroelasticity Program Transonic Small Disturbance), which was developed principally by the author in the mid-1980s. The author is in a unique position as the developer of both computer programs to compare, contrast, and ultimately make conclusions regarding the underlying formulations and utility of each code. The paper describes the salient features of the ASP3D code including the rationale for improvements in comparison with CAP-TSD. Numerous results are presented to demonstrate the ASP3D capability. The general conclusion is that the new ASP3D capability is superior to the older CAP-TSD code because of the myriad improvements developed and incorporated.
A review of unsteady turbulent boundary-layer experiments
NASA Technical Reports Server (NTRS)
Carr, L. W.
1981-01-01
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.
NASA Technical Reports Server (NTRS)
Carta, F. O.
1982-01-01
Tests were 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. 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. Results from the unsteady Verdon/Caspar theory for cascaded blades with nonzero thickness and camber were compared with the experimental measurements. The three primary results are: (1) from the leading edge plane blade data, the cascade was judged to be periodic in unsteady flow over the range of parameters tested; (2) the interblade phase angle was found to be the single most important parameter affecting the stability of the oscillating cascade blades; and (3) the real blade theory and the experiment were in excellent agreement for the several cases chosen for comparison.
Advanced Small Perturbation Potential Flow Theory for Unsteady Aerodynamic and Aeroelastic Analyses
NASA Technical Reports Server (NTRS)
Batina, John T.
2005-01-01
An advanced small perturbation (ASP) potential flow theory has been developed to improve upon the classical transonic small perturbation (TSP) theories that have been used in various computer codes. These computer codes are typically used for unsteady aerodynamic and aeroelastic analyses in the nonlinear transonic flight regime. The codes exploit the simplicity of stationary Cartesian meshes with the movement or deformation of the configuration under consideration incorporated into the solution algorithm through a planar surface boundary condition. The new ASP theory was developed methodically by first determining the essential elements required to produce full-potential-like solutions with a small perturbation approach on the requisite Cartesian grid. This level of accuracy required a higher-order streamwise mass flux and a mass conserving surface boundary condition. The ASP theory was further developed by determining the essential elements required to produce results that agreed well with Euler solutions. This level of accuracy required mass conserving entropy and vorticity effects, and second-order terms in the trailing wake boundary condition. Finally, an integral boundary layer procedure, applicable to both attached and shock-induced separated flows, was incorporated for viscous effects. The resulting ASP potential flow theory, including entropy, vorticity, and viscous effects, is shown to be mathematically more appropriate and computationally more accurate than the classical TSP theories. The formulaic details of the ASP theory are described fully and the improvements are demonstrated through careful comparisons with accepted alternative results and experimental data. The new theory has been used as the basis for a new computer code called ASP3D (Advanced Small Perturbation - 3D), which also is briefly described with representative results.
NASA Technical Reports Server (NTRS)
Vepa, R.
1976-01-01
The general behavior of unsteady airloads in the frequency domain is explained. Based on this, a systematic procedure is described whereby the airloads, produced by completely arbitrary, small, time-dependent motions of a thin lifting surface in an airstream, can be predicted. This scheme employs as raw materials any of the unsteady linearized theories that have been mechanized for simple harmonic oscillations. Each desired aerodynamic transfer function is approximated by means of an appropriate Pade approximant, that is, a rational function of finite degree polynomials in the Laplace transform variable. Although these approximations have many uses, they are proving especially valuable in the design of automatic control systems intended to modify aeroelastic behavior.
NASA Technical Reports Server (NTRS)
Petrarca, J. R.; Harrison, B. A.; Redman, M. C.; Rowe, W. S.
1979-01-01
A digital computer program was developed to calculate unsteady loadings caused by motions of lifting surfaces with leading edge and trailing edge controls based on the subsonic kernel function approach. The pressure singularities at hinge line and side edges were extracted analytically as a preliminary step to solving the integral equation of collocation. The program calculates generalized aerodynamic forces for user supplied deflection modes. Optional intermediate output includes pressure at an array of points, and sectional generalized forces. From one to six controls on the half span can be accomodated.
NASA Technical Reports Server (NTRS)
Friedmann, P. P.; Venkatesan, C.
1984-01-01
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.
Estimation of Longitudinal Unsteady Aerodynamics of a Wing-Tail Combination From Wind Tunnel Data
NASA Technical Reports Server (NTRS)
Murphy, Patrick C.; Klein, Vladislav
2006-01-01
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.
Aeroassist flight experiment aerodynamics and aerothermodynamics
NASA Technical Reports Server (NTRS)
Brewer, Edwin B.
1989-01-01
The problem is to determine the transitional flow aerodynamics and aerothermodynamics, including the base flow characteristics, of the Aeroassist Flight Experiment (AFE). The justification for the computational fluid dynamic (CFD) Application stems from MSFC's system integration responsibility for the AFE. To insure that the AFE objectives are met, MSFC must understand the limitations and uncertainties of the design data. Perhaps the only method capable of handling the complex physics of the rarefied high energy AFE trajectory is Bird's Direct Simulation Monte Carlo (DSMC) technique. The 3-D code used in this analysis is applicable only to the AFE geometry. It uses the Variable Hard Sphere (VHS) collision model and five specie chemistry model available from Langley Research Center. The code is benchmarked against the AFE flight data and used as an Aeroassisted Space Transfer Vehicle (ASTV) design tool. The code is being used to understand the AFE flow field and verify or modify existing design data. Continued application to lower altitudes is testing the capability of the Numerical Aerodynamic Simulation Facility (NASF) to handle 3-D DSMC and its practicality as an ASTV/AFE design tool.
Detached-Eddy Simulations Applied to Unsteady Crosswind Aerodynamics of Ground Vehicles
T. Favre; B. Diedrichs; G. Efraimsson
\\u000a Crosswind stability is an important safety issue for manufacturers of cars, buses and rail vehicles. Since side wind conditions\\u000a are unsteady phenomena they require time-dependent techniques to simulate the flow. In this study, a hybrid RANS-LES methods,\\u000a Detached-Eddy Simulation, is applied to evaluate headwind and unsteady crosswind situations for a simple model of car. A grid\\u000a refinement study is carried
A flight experiment to measure rarefied-flow aerodynamics
NASA Technical Reports Server (NTRS)
Blanchard, Robert C.
1990-01-01
A flight experiment to measure rarefied-flow aerodynamics of a blunt lifting body is being developed by NASA. This experiment, called the Rarefied-Flow Aerodynamic Measurement Experiment (RAME), is part of the Aeroassist Flight Experiment (AFE) mission, which is a Pathfinder design tool for aeroassisted orbital transfer vehicles. The RAME will use flight measurements from accelerometers, rate gyros, and pressure transducers, combined with knowledge of AFE in-flight mass properties and trajectory, to infer aerodynamic forces and moments in the rarefied-flow environment, including transition into the hypersonic continuum regime. Preflight estimates of the aerodynamic measurements are based upon environment models, existing computer simulations, and ground test results. Planned maneuvers at several altitudes will provide a first-time opportunity to examine gas-surface accommondation effects on aerodynamic coefficients in an environment of changing atmospheric composition. A description is given of the RAME equipment design.
NASA Technical Reports Server (NTRS)
Malcolm, G. N.; Davis, S. S.
1978-01-01
Two new wind tunnel test apparatuses were developed at NASA-Ames Research Center. The first is a rotary-balance apparatus to be used in the Ames 12-Foot Pressure Tunnel for investigating the effects of Reynolds number, spin rate, and angle of attack on the aerodynamics of fighter and general aviation aircraft in a steady spin motion. The second apparatus provides capability for oscillating a large two dimensional wing (0.5 m chord, 1.35 m span) instrumented with steady and unsteady pressure transducers in the Ames 11 x 11 ft. Transonic Wind Tunnel. A complete description of both apparatuses, their capabilities, and some typical wind tunnel results are presented.
Deck, Sébastien; Gand, Fabien; Brunet, Vincent; Ben Khelil, Saloua
2014-08-13
This paper provides an up-to-date survey of the use of zonal detached eddy simulations (ZDES) for unsteady civil aircraft applications as a reflection on the stakes and perspectives of the use of hybrid methods in the framework of industrial aerodynamics. The issue of zonal or non-zonal treatment of turbulent flows for engineering applications is discussed. The ZDES method used in this article and based on a fluid problem-dependent zonalization is briefly presented. Some recent landmark achievements for conditions all over the flight envelope are presented, including low-speed (aeroacoustics of high-lift devices and landing gear), cruising (engine-airframe interactions), propulsive jets and off-design (transonic buffet and dive manoeuvres) applications. The implications of such results and remaining challenges in a more global framework are further discussed. PMID:25024411
NASA Technical Reports Server (NTRS)
Paine, A. A.
1972-01-01
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.
Application of two-dimensional unsteady aerodynamic to a free-tip rotor response analysis
NASA Technical Reports Server (NTRS)
Yates, L.; Kumagai, H.
1985-01-01
The free-tip rotor utilizes a rotor blade tip which is structurally decoupled from the blade inboard section. The tip is free to pitch about its own pitch axis to respond to the local flow angularity changes. The tip also experiences the heaving motion due to the flapping of the rotor blade. For an airfoil in any pitching and heaving motion which can be expanded into a Fourier series, the lift and moment calculated by Theodoren's theory is simply the linear combination of the lift and moment calculated for each harmonic. These lift and moment are then used to determine the response of the free-tip rotor. A parametric study is performed to determine the effect of mechanical damping, mechanical spring, sweep, friction, and a constant control moment on the free-tip rotor response characteristics and the resulting azimuthal lift distributions. The results showed that the free-tip has the capability to suppress the oscillatory lift distribution around the azimuth and to eliminate a significant negative life peak on the advancing tip. This result agrees with the result of the previous analysis based on the steady aerodynamics.
Unsteady aerodynamic and heat transfer processes in a transonic turbine stage
D. A. Ashworth; J. E. Lagraff; D. L. Schultz; K. J. Grindrod
1985-01-01
The effect of the interaction of the wake from a nozzle guide vane with the rotor may be simulated in part by means of a stationary rotor and a moving wake system. This technique is applied to a transonic rotor blade cascade, and the unsteady measurements of surface pressure and heat transfer rate are compared with baseline data obtained without
Spatial adaptation procedures on tetrahedral meshes for unsteady aerodynamic flow calculations
NASA Technical Reports Server (NTRS)
Rausch, Russ D.; Batina, John T.; Yang, Henry T. Y.
1993-01-01
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.
Spatial adaptation procedures on tetrahedral meshes for unsteady aerodynamic flow calculations
NASA Technical Reports Server (NTRS)
Rausch, Russ D.; Batina, John T.; Yang, Henry T. Y.
1993-01-01
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.
Guofeng Lin
1997-01-01
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
Program user's manual for an unsteady helicopter rotor-fuselage aerodynamic analysis
NASA Technical Reports Server (NTRS)
Lorber, Peter F.
1988-01-01
The Rotor-Fuselage Analysis is a method of calculating the aerodynamic reaction between a helicopter rotor and fuselage. This manual describes the structure and operation of the computer programs that make up the Rotor-Fuselage Analysis, programs which prepare the input and programs which display the output.
Structural effects of unsteady aerodynamic forces on horizontal-axis wind turbines
NASA Astrophysics Data System (ADS)
Miller, M. S.; Shipley, D. E.
1994-08-01
Due to its renewable nature and abundant resources, wind energy has the potential to fulfill a large portion of this nation's energy needs. The simplest means of utilizing wind energy is through the use of downwind, horizontal-axis wind turbines (HAWT) with fixed-pitch rotors. This configuration regulates the peak power by allowing the rotor blade to aerodynamically stall. The stall point, the point of maximum coefficient of lift, is currently predicted using data obtained from wind tunnel tests. Unfortunately, these tests do not accurately simulate conditions encountered in the field. Flow around the tower and nacelle coupled with inflow turbulence and rotation of the turbine blades create unpredicted aerodynamic forces. Dynamic stall is hypothesized to occur. Such aerodynamic loads are transmitted into the rotor and tower causing structural resonance that drastically reduces the design lifetime of the wind turbine. The current method of alleviating this problem is to structurally reinforce the tower and blades. However, this adds unneeded mass and, therefore, cost to the turbines. A better understanding of the aerodynamic forces and the manner in which they affect the structure would allow for the design of more cost effective and durable wind turbines. Data compiled by the National Renewable Energy Laboratory (NREL) for a downwind HAWT with constant chord, untwisted, fixed-pitch rotors is analyzed. From these data, the actual aerodynamic characteristics of the rotor are being portrayed and the potential effects upon the structure can for the first time be fully analyzed. Based upon their understanding, solutions to the problem of structural resonance are emerging.
A comparison of baseline aerodynamic performance of optimally-twisted versus non-twisted HAWT blades
D. A. Simms; M. C. Robinson; M. M. Hand; L. J. Fingersh
1995-01-01
NREL has completed the initial twisted blade field tests of the ``Unsteady Aerodynamics Experiment.`` This test series continues systematic measurements of unsteady aerodynamic phenomena prevalent in stall-controlled horizontal axis wind turbines (HAWTs). The blade twist distribution optimizes power production at a single angle of attack along the span. Abrupt transitions into and out of stall are created due to rapid
NASA Technical Reports Server (NTRS)
Reddy, T. S. R.
1995-01-01
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.
NSDL National Science Digital Library
Aerodynamics is the study of what makes things go fast, right? More specifically, itâ??s the study of the interaction between bodies and the atmosphere. If youâ??ve 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.
NASA Technical Reports Server (NTRS)
Morino, L.
1980-01-01
Recent developments of the Green's function method and the computer program SOUSSA (Steady, Oscillatory, and Unsteady Subsonic and Supersonic Aerodynamics) are reviewed and summarized. Applying the Green's function method to the fully unsteady (transient) potential equation yields an integro-differential-delay equation. With spatial discretization by the finite-element method, this equation is approximated by a set of differential-delay equations in time. Time solution by Laplace transform yields a matrix relating the velocity potential to the normal wash. Premultiplying and postmultiplying by the matrices relating generalized forces to the potential and the normal wash to the generalized coordinates one obtains the matrix of the generalized aerodynamic forces. The frequency and mode-shape dependence of this matrix makes the program SOUSSA useful for multiple frequency and repeated mode-shape evaluations.
NASA Technical Reports Server (NTRS)
Riffel, R. E.; Rothrock, M. D.
1980-01-01
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 translational model flutter. This five bladed cascade had a solidity of 1.52 and a setting angle of 0.90 rad. Unique graphite epoxy airfoils were fabricated to achieve the realistic high reduced frequency level of 0.15. 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.
NASA Technical Reports Server (NTRS)
Hui, W. H.
1985-01-01
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.
Flexible Launch Vehicle Stability Analysis Using Steady and Unsteady Computational Fluid Dynamics
NASA Technical Reports Server (NTRS)
Bartels, Robert E.
2012-01-01
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.
NASA Technical Reports Server (NTRS)
Reding, J. P.; Ericsson, L. E.
1976-01-01
An exploratory analysis has been made of the aeroelastic stability of the Space Shuttle Launch Configuration, with the objective of defining critical flow phenomena with adverse aeroelastic effects and developing simple analytic means of describing the time-dependent flow-interference effects so that they can be incorporated into a computer program to predict the aeroelastic stability of all free-free modes of the shuttle launch configuration. Three critical flow phenomana have been identified: (1) discontinuous jump of orbiter wing shock, (2) inlet flow between orbiter and booster, and (3) H.O. tank base flow. All involve highly nonlinear and often discontinuous aerodynamics which cause limit cycle oscillations of certain critical modes. Given the appropriate static data, the dynamic effects of the wing shock jump and the HO tank bulbous base effect can be analyzed using the developed quasi-steady techniques. However, further analytic and experimental efforts are required before the dynamic effects of the inlet flow phenomenon can be predicted for the shuttle launch configuration.
Flow visualization and unsteady aerodynamics in the flight of the hawkmoth, Manduca sexta
Willmott, A. P.; Ellington, C. P.; Thomas, A. L. R.
1997-01-01
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.
Experimental investigation of transonic oscillating cascade aerodynamics
NASA Technical Reports Server (NTRS)
Buffum, Daniel H.; Fleeter, Sanford
1989-01-01
Fundamental experiments are performed in the NASA Lewis Transonic Oscillating Cascade Facility to investigate the subsonic and transonic aerodynamics of cascaded airfoils executing torsion mode oscillations at realistic values of reduced frequency. In particular, an unsteady aerodynamic influence coefficient technique is developed and utilized. In this technique, only one airfoil in the cascade is oscillated at a time, with the resulting airfoil surface unsteady pressure distribution measured on one dynamically instrumented reference airfoil. The unsteady aerodynamics of an equivalent cascade with all airfoils oscillating at any specified interblade phase angle are then determined through a vector summation of these data. These influence coefficient determined oscillating cascade data were correlated with: (1) data obtained in this cascade with all airfoils oscillating at several interblade phase angle values; and (2) predictions from a classical linearized unsteady cascade model.
Experiments on an unsteady, three-dimensional separation
NASA Technical Reports Server (NTRS)
Henk, R. W.; Reynolds, W. C.; Reed, H. L.
1992-01-01
Unsteady, three-dimensional flow separation occurs in a variety of technical situations including turbomachinery and low-speed aircraft. An experimental program at Stanford in unsteady, three-dimensional, pressure-driven laminar separation has investigated the structure and time-scaling of these flows; of particular interest is the development, washout, and control of flow separation. Results reveal that a two-dimensional, laminar boundary layer passes through several stages on its way to a quasi-steady three-dimensional separation. The quasi-steady state of the separation embodies a complex, unsteady, vortical structure.
Simms, D.A.; Robinson, M.C.; Hand, M.M.; Fingersh, L.J. [National Renewable Energy Lab., Golden, CO (United States)
1996-10-01
NREL has completed the initial twisted blade field tests of the Unsteady Aerodynamics Experiment. This test series continues systematic measurements of unsteady aerodynamic phenomena prevalent in stall-controlled horizontal axis wind turbines (HAWTs). The blade twist distribution optimizes power production at a single angle of attack along the span. Abrupt transitions into and out of stall are created due to rapid changes in inflow. Data from earlier experiments have been analyzed extensively to characterize the steady and unsteady response of untwisted blades. In this report, a characterization and comparison of the baseline aerodynamic performance of the twisted versus non-twisted blade sets will be presented for steady flow conditions.
A comparison of baseline aerodynamic performance of optimally-twisted versus non-twisted HAWT blades
Simms, D.A.; Robinson, M.C.; Hand, M.M.; Fingersh, L.J.
1995-01-01
NREL has completed the initial twisted blade field tests of the ``Unsteady Aerodynamics Experiment.`` This test series continues systematic measurements of unsteady aerodynamic phenomena prevalent in stall-controlled horizontal axis wind turbines (HAWTs). The blade twist distribution optimizes power production at a single angle of attack along the span. Abrupt transitions into and out of stall are created due to rapid changes in inflow. Data from earlier experiments have been analyzed extensively to characterize the steady and unsteady response of untwisted blades. In this report, a characterization and comparison of the baseline aerodynamic performance of the twisted versus non-twisted blade sets will be presented for steady flow conditions.
Shigeru Aso; Masanori Hayashi; Anzhong Tan; Yoshiharu Tanahashi
1990-01-01
Experimental and numerical investigations on unsteady aerodynamic heating in shock reflections have been performed. In the experiments surface heat flux changes induced by unsteady shock impingement have been measured. Remarkable characteristics of surface heat transfer change are observed. An additional increase of surface heat transfer owing to the impingement of slip layer is observed in complex Mach reflection and double
The Analysis of Underexpanded Jet Flows for Hypersonic Aerodynamic Experiments in
Riabov, Vladimir V.
The Analysis of Underexpanded Jet Flows for Hypersonic Aerodynamic Experiments in Vacuum Chambers V of rarefied-gas flows [1]- [3] and aerodynamics of hypersonic probes in wind tunnels [4]-[7]. The objective using quantum concepts [9], [10]. Aerodynamic characteristics of wedges, disks, and plates are studied
NASA Technical Reports Server (NTRS)
Rowe, W. S.; Petrarca, J. R.
1980-01-01
Changes to be made that provide increased accuracy and increased user flexibility in prediction of unsteady loadings caused by control surface motions are described. Analysis flexibility is increased by reducing the restrictions on the location of the downwash stations relative to the leading edge and the edges of the control surface boundaries. Analysis accuracy is increased in predicting unsteady loading for high Mach number analysis conditions through use of additional chordwise downwash stations. User guideline are presented to enlarge analysis capabilities of unusual wing control surface configurations. Comparative results indicate that the revised procedures provide accurate predictions of unsteady loadings as well as providing reductions of 40 to 75 percent in computer usage cost required by previous versions of this program.
Predicting Unsteady Aeroelastic Behavior
NASA Technical Reports Server (NTRS)
Strganac, Thomas W.; Mook, Dean T.
1990-01-01
New method for predicting subsonic flutter, static deflections, and aeroelastic divergence developed. Unsteady aerodynamic loads determined by unsteady-vortex-lattice method. Accounts for aspect ratio and angle of attack. Equations for motion of wing and flow field solved iteratively and simultaneously. Used to predict transient responses to initial disturbances, and to predict steady-state static and oscillatory responses. Potential application for research in such unsteady structural/flow interactions as those in windmills, turbines, and compressors.
NASA Technical Reports Server (NTRS)
Carta, F. O.
1981-01-01
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.
Standardization of computational experiments in unsteady turbulent boundary-layer flow
NASA Technical Reports Server (NTRS)
Carr, L. W.
1977-01-01
Numerical experiments are proposed as standard cases to be computed by all who plan to analyze unsteady turbulent boundary layer behavior. In this way, differences between the results obtained by various methods can be compared in a completely defined environment. The test cases range in difficulty from time relaxation study of the steady flow on a flat plate to the analysis of unsteady reversed flow. Initial and boundary conditions are fully defined for each case and representative outputs are presented. It is recommended that tabulated samples of computations of these test cases be published in a compendium of results.
Effect of Transition Aerodynamics on Aeroassist Flight Experiment Trajectories
NASA Technical Reports Server (NTRS)
Minier, Elizabeth A.; Suit, William T.
1988-01-01
Various transition methods are used here to study the viscous effects encountered in low density, hypersonic flight, through the transition from free molecular to continuum flow. Methods utilizing Viking data, Shuttle Orbiter data, a Potter number parameter, and a Shock Reynolds number were implemented in the Program to Optimize Simulated Trajectories (POST). Simulations of the Aeroassist Flight Experiment (AFE) using open loop guidance were used to assess the aerodynamic performance of the vehicle. A bank angle was found for each transition method that would result in a 200 nautical-mile apogee. Once this was done, the open loop guidance was replaced by the proposed guidance algorithm for the AFE. Simulations were again conducted using that guidance and the different transitions for comparison. For the gains used, the guidance system showed some sensitivity in apogee altitude to the transition method assumed, but the guidance was able to successfully complete the mission.
NASA Technical Reports Server (NTRS)
Welch, Gerard E.
2012-01-01
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.
Aerodynamics of ski jumping: experiments and CFD simulations
W. Meile; E. Reisenberger; M. Mayer; B. Schmölzer; W. Müller; G. Brenn
2006-01-01
The aerodynamic behaviour of a model ski jumper is investigated experimentally at full-scale Reynolds numbers and computationally applying a standard RANS code. In particular we focus on the influence of different postures on aerodynamic forces in a wide range of angles of attack. The experimental results proved to be in good agreement with full-scale measurements with athletes in much larger
Unsteady high-pressure flow experiments with applications to explosive volcanic eruptions
M. M. Orescanin; J. M. Austin; S. W. Kieffer
2010-01-01
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
Incipient torsional stall flutter aerodynamic experiments on a swept three-dimensional wing
NASA Technical Reports Server (NTRS)
Lorber, Peter F.; Carta, Franklin O.
1991-01-01
The aerodynamics of small amplitude pitching motions near stall have been studied experimentally in order to improve understanding of the torsional stall flutter problem for propeller blades. A model wing was oscillated in pitch at several small amplitudes over a wide and representative range of conditions. Unsteady surface pressures were measured and integrated to determine the aerodynamic damping at five spanwise stations. Strong negative damping was found for motions centered near static stall for all studied reduced frequencies, Mach numbers, and sweep angles. The 30-deg sweptback configuration was found to become negatively damped over the entire span nearly simultaneously, while the unswept model exhibited local regions of negative damping that moved toward the wing tip as the mean angle of attack was increased.
NASA Technical Reports Server (NTRS)
Brandon, Jay M.; Shah, Gautam H.
1990-01-01
The effects of harmonic or constant-rate-ramp pitching motions (giving angles of attack from 0 to 75 deg) on the aerodynamic performance of a fighter-aircraft model with highly swept leading-edge extensions are investigated experimentally in the NASA Langley 12-ft low-speed wind tunnel. The model configuration and experimental setup are described, and the results of force and moment measurements and flow visualizations are presented graphically and discussed in detail. Large force overshoots and hysteresis are observed and attributed to lags in vortical-flow development and breakup. The motion variables have a strong influence on the persistence of dynamic effects, which are found to affect pitch-rate capability more than flight-path turning performance.
Rotorcraft Aerodynamics Models for a Comprehensive Analysis
Wayne Johnson
1998-01-01
Recent developments of the aerodynamics models for the comprehensive analysis CAMRAD II are described, particularly the unsteady aerodynamic models and dynamic stall models, and the free wake geometry calculation. Three models for the unsteady aerodynamic loads in attached flow are implemented: from incompressible thin-airfoil theory, from ONERA EDLIN, and from Leishman-Beddoes. Five dynamic stall models are implemented: from Johnson, Boeing,
Closed-Loop Control of a Wing in an Unsteady Flow David Williams1
Dabiri, John O.
and gusting flows requires control systems that account for both the unsteady aerodynamics and the flow system changes associated with both the unsteady aerodynamics and the actuator response. In this paper the focus
Some unsteady separation problems for slender bodies
NASA Technical Reports Server (NTRS)
Mccroskey, W. J.
1978-01-01
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.
Collins, Dannie L.; Flynn, Kathleen M.
1978-01-01
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)
Aerodynamics and performance testing of the VAWT
Klimas, P.C.
1981-01-01
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.
Velocity-Dependent Hydrodynamic Dispersion During Unsteady, Unsaturated Soil Water Flow: Experiments
NASA Astrophysics Data System (ADS)
Bond, W. J.
1986-12-01
The effect of the velocity dependence of the hydrodynamic dispersion coefficient on solute movement and distribution during unsteady flow of water in unsaturated soils is described mathematically and experimentally. Approximate analytical solutions of the solute transport equation are presented for velocity-dependent dispersion during constant potential and constant flux horizontal absorption, subject to a step change in solute concentration and a pulse input of solute, respectively. Discussion is confined to the case where there is no chemical interaction between the solute and the soil and no soil water that is inaccessible to the solute. Experiments were designed to demonstrate velocity-dependent dispersion and were carried out with a fine sand for the conditions outlined above. The effect of the velocity dependence of the dispersion coefficient was to cause the spread in the concentration profile to be greater than would have been expected if there was no velocity dependence. This effect is large at small times and decreases with increasing time for constant potential absorption. During constant flux absorption the magnitude of the effect depends largely on the magnitude of the input flux, increasing as the flux increases, but it also increases slightly with increasing time. The relationship between the dispersion coefficient and pore water velocity was measured for this fine sand by means of steady, saturated breakthrough experiments. This independently measured relationship was then used in the approximate analytical solutions to predict the observed concentration profiles from the unsteady experiments. Very good agreement was found.
NASA Technical Reports Server (NTRS)
Compton, H. R.; Blanchard, R. C.; Walberg, G. D.
1978-01-01
A two-phase experiment is proposed which utilizes the Shuttle Orbiter and its unique series of repeated entries into the earth's atmosphere as an airborne in situ aerodynamic testing laboratory. The objective of the experiment is to determine static aerodynamic force coefficients, first of the orbiter, and later of various entry configurations throughout the high speed flight regime, including the transition from free molecule to continuum fluid flow. The objective will be accomplished through analysis of inflight measurements from both shuttle-borne and shuttle-launched instrumented packages. Results are presented to demonstrate the feasibility of such an experiment.
Investigation of oscillating cascade aerodynamics by an experimental influence coefficient technique
NASA Technical Reports Server (NTRS)
Buffum, Daniel H.; Fleeter, Sanford
1988-01-01
Fundamental experiments are performed in the NASA Lewis Transonic Oscillating Cascade Facility to investigate the torsion mode unsteady aerodynamics of a biconvex airfoil cascade at realistic values of the reduced frequency for all interblade phase angles at a specified mean flow condition. In particular, an unsteady aerodynamic influence coefficient technique is developed and utilized in which only one airfoil in the cascade is oscillated at a time and the resulting airfoil surface unsteady pressure distribution measured on one dynamically instrumented airfoil. The unsteady aerodynamics of an equivalent cascade with all airfoils oscillating at a specified interblade phase angle are then determined through a vector summation of these data. These influence coefficient determined oscillation cascade data are correlated with data obtained in this cascade with all airfoils oscillating at several interblade phase angle values. The influence coefficients are then utilized to determine the unsteady aerodynamics of the cascade for all interblade phase angles, with these unique data subsequently correlated with predictions from a linearized unsteady cascade model.
Investigation of oscillating cascade aerodynamics by an experimental influence coefficient technique
NASA Technical Reports Server (NTRS)
Buffum, Daniel H.; Fleeter, Sanford
1988-01-01
Fundamental experiments are performed in the NASA Lewis Transonic Oscillating Cascade Facility to investigate the torsion mode unsteady aerodynamics of a biconvex airfoil cascade at realistic values of the reduced frequency for all interblade phase angles at a specified mean flow condition. In particular, an unsteady aerodynamic influence coefficient technique is developed and utilized in which only one airfoil in the cascade is oscillated at a time and the resulting airfoil surface unsteady pressure distribution measured on one dynamically instrumented airfoil. The unsteady aerodynamics of an equivalent cascade with all airfoils oscillating at a specified interblade phase angle are then determined through a vector summation of these data. These influence coefficient determined oscillating cascade data are correlated with data obtained in this cascade with all airfoils oscillating at several interblade phase angle values. The influence coefficients are then utilized to determine the unsteady aerodynamics of the cascade for all interblade phase angles, with these unique data subsequently correlated with predictions from a linearized unsteady cascade model.
Recent darrieus Vertical-Axis Wind Turbine aerodynamical experiments at Sandia National Laboratories
NASA Astrophysics Data System (ADS)
Klimas, P. C.
The aerodynamics of airfoils operating in the vertical axis wind turbine (VAWT) environment were examined. The experiments are intended to reduce VAWT cost of energy an increase system reliability. The experiments include: (1) chordwise pressure surveys; (2) circumferential blade acceleration surveys; (3) effects of blade camber; (4) pitch and offset; (5) blade blowing; and (6) use of sections designed specifically for VAWT application.
Recent Darrieus vertical axis wind turbine aerodynamical experiments at Sandia National Laboratories
NASA Astrophysics Data System (ADS)
Klimas, P. C.
1981-05-01
Experiments contributing to the understanding of the aerodynamics of airfoils operating in the vertical axis wind turbine (VAWT) environment are described. These experiments are ultimately intended to reduce VAWT cost of energy and increase system reliability. They include chordwise pressure surveys, circumferential blade acceleration surveys, effects of blade camber, pitch and offset, blade blowing, and use of sections designed specifically for VAWT application.
Recent Darrieus vertical-axis wind turbine aerodynamical experiments at Sandia National Laboratories
Klimas, P.C.
1981-01-01
Experiments contributing to the understanding of the aerodynamics of airfoils operating in the vertical axis wind turbine (VAWT) environment are described. These experiments are ultimately intended to reduce VAWT cost of energy and increase system reliability. They include chordwise pressure surveys, circumferential blade acceleration surveys, effects of blade camber, pitch and offset, blade blowing, and use of sections designed specifically for VAWT application.
Recent darrieus Vertical-Axis Wind Turbine aerodynamical experiments at Sandia National Laboratories
P. C. Klimas
1981-01-01
The aerodynamics of airfoils operating in the vertical axis wind turbine (VAWT) environment were examined. The experiments are intended to reduce VAWT cost of energy an increase system reliability. The experiments include: (1) chordwise pressure surveys; (2) circumferential blade acceleration surveys; (3) effects of blade camber; (4) pitch and offset; (5) blade blowing; and (6) use of sections designed specifically
Claude Landron; Louis Hennet; Jean-Pierre Coutures; Tudor Jenkins; Chantal Alétru; Neville Greaves; Alan Soper; Gareth Derbyshire
2000-01-01
Conventional radiative furnaces require sample containment that encourages contamination at elevated temperatures and generally need windows which restrict the entrance and exit solid angles required for diffraction and scattering measurements. We describe a contactless windowless furnace based on aerodynamic levitation and laser heating which has been designed for high temperature neutron scattering experiments. Data from initial experiments are reported for
Panoramic diagnostics of surface temperatures and heat fluxes in an aerodynamic experiment
G. M. Zharkova; V. N. Kovrizhina
2010-01-01
The principles of visualization and measurement of surface temperatures and heat fluxes by the method of liquid-crystal tomography in an aerophysical experiment are described. The properties of polymeric liquid-crystal, heat-sensitive coatings and application of them in subsonic and hypersonic facilities for investigating the structure of a near-wall flow and aerodynamic heating are considered.
Panoramic diagnostics of surface temperatures and heat fluxes in an aerodynamic experiment
NASA Astrophysics Data System (ADS)
Zharkova, G. M.; Kovrizhina, V. N.
2010-12-01
The principles of visualization and measurement of surface temperatures and heat fluxes by the method of liquid-crystal tomography in an aerophysical experiment are described. The properties of polymeric liquid-crystal, heat-sensitive coatings and application of them in subsonic and hypersonic facilities for investigating the structure of a near-wall flow and aerodynamic heating are considered.
Collins, Dannie L.; Flynn, Kathleen M.
1979-01-01
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)
The effects of unsteady on-road flow conditions on cabin noise
NASA Astrophysics Data System (ADS)
Oettle, Nicholas Richard
On-road, a vehicle experiences unsteady flow conditions due to turbulence in the natural wind, moving through the unsteady wakes of other road vehicles and travelling through the stationary wakes generated by roadside obstacles. There is increasing concern about potential differences between steady flow conditions that are typically used for development and the transient conditions that occur on-road. This work considers whether steady techniques are able to predict the unsteady results measured on-road, the impact of this unsteadiness on the noise perceived in the cabin and whether minor changes made to the geometry of the vehicle could affect this. Both external aerodynamic and acoustic measurements were taken using a full-size vehicle combined with measurements of the noise inside the cabin. Data collection took place on-road under a range of wind conditions to accurately measure the response of the vehicle to oncoming flow unsteadiness, with steady-state measurements taking place in full-scale aeroacoustic wind tunnels.. Overall it was demonstrated that, using a variety of temporal and spectral approaches, steady techniques were able to predict unsteady on-road results well enough to assess cabin noise by correctly taking into account the varying on-road flow conditions. Aerodynamic admittance values remained less than unity in the sideglass region of the vehicle, with the exception of the the region nearest the A-pillar. The reducing unsteady energy at frequencies greater than 10 Hz, combined with the corresponding roll-off in admittance, implies that unsteady frequencies below 10 Hz affect the vehicle most, where the response remains quasi-steady. Quasi-steady cabin noise simulations allowed a subjective assessment of the predicted unsteady cabin noise, where the impact of cabin noise modulations were quantified and found to be important to perception. Minor geometry changes affected the sensitivity of cabin noise to changes in yaw angle, altering modulation and therefore having an important impact on the unsteady wind noise perceived on-road..
Aerodynamics of Heavy Vehicles
NASA Astrophysics Data System (ADS)
Choi, Haecheon; Lee, Jungil; Park, Hyungmin
2014-01-01
We present an overview of the aerodynamics of heavy vehicles, such as tractor-trailers, high-speed trains, and buses. We introduce three-dimensional flow structures around simplified model vehicles and heavy vehicles and discuss the flow-control devices used for drag reduction. Finally, we suggest important unsteady flow structures to investigate for the enhancement of aerodynamic performance and future directions for experimental and numerical approaches.
NASA Technical Reports Server (NTRS)
Carta, F. O.
1981-01-01
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.
Numerical solutions for unsteady subsonic vortical flows around loaded cascades
J. Fang; H. M. Atassi
1993-01-01
A frequency domain linearized unsteady aerodynamic analysis is presented for three-dimensional unsteady vortical flows around a cascade of loaded airfoils. The analysis fully accounts for the distortion of the impinging vortical disturbances by the mean flow. The entire unsteady flow field is calculated in response to upstream three-dimensional harmonic disturbances. Numerical results are presented for two standard cascade configurations representing
Panoramic diagnostics of surface temperatures and heat fluxes in an aerodynamic experiment
G. M. Zharkova; V. N. Kovrizhina
2010-01-01
The principles of visualization and measurement of surface temperatures and heat fluxes by the method of liquid-crystal tomography\\u000a in an aerophysical experiment are described. The properties of polymeric liquid-crystal, heat-sensitive coatings and application\\u000a of them in subsonic and hypersonic facilities for investigating the structure of a near-wall flow and aerodynamic heating\\u000a are considered.
NASA Technical Reports Server (NTRS)
Wells, William L.
1989-01-01
Two scaled models of the Aeroassist Flight Experiment (AFE) vehicle were tested in two air wind tunnels and one CF4 tunnel. The tests were to determine the static longitudinal aerodynamic characteristics, and shock shapes for the configuration in hypersonic continuum flow. The tests were conducted with a range of angle of attack to evaluate the effects of Mach number, Reynolds numbers, and normal shock density ratio.
The Modern Design of Experiments for Configuration Aerodynamics: A Case Study
NASA Technical Reports Server (NTRS)
DeLoach, Richard
2006-01-01
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.
NASA Technical Reports Server (NTRS)
Findlay, J. T.; Kelly, G. M.; Mcconnell, J. G.; Compton, H. R.
1984-01-01
Longitudinal aerodynamic performance comparisons between flight extracted and predicted values are presented for the first eight NASA Space Shuttle entry missions. Challenger results are correlated with the ensemble five flight Columbia experience and indicate effects due to differing angle-of-attack and body flap deflection profiles. An Appendix is attached showing the results of each flight using both the LaRC LAIRS and NOAA atmospheres. Discussions are presented which review apparent density anomalies observed in the flight data, with particular emphasis on the suggested shears and turbulence encountered during STS-2 and STS-4. Atmospheres derived from Shuttle data are presented which show structure different than that remotely sensed and imply regions of unstable air masses as a plausible explanation. Though additional aerodynamic investigations are warranted, an added benefit of Shuttle flight data for atmospheric research is discussed, in particular, as applicable to future NASA space vehicles such as AOTVs and tethered satellites.
Unsteady Lift Suppression with a Robust Closed Loop Controller
Dabiri, John O.
to enhance aircraft maneuverability comes from the effects of unsteady aerodynamics and the substantial time the aerodynamic loads and the response to actua- tion. For example, the time delays in the lift response flow used a controller based on a quasi-steady model of the aerodynamics and actuator response
Aerodynamic Database Development for the Hyper-X Airframe Integrated Scramjet Propulsion Experiments
NASA Technical Reports Server (NTRS)
Engelund, Walter C.; Holland, Scott D.; Cockrell, Charles E., Jr.; Bittner, Robert D.
2000-01-01
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.
In vivo recording of aerodynamic force with an aerodynamic force platform: from drones to birds
Lentink, David; Haselsteiner, Andreas F.; Ingersoll, Rivers
2015-01-01
Flapping wings enable flying animals and biomimetic robots to generate elevated aerodynamic forces. Measurements that demonstrate this capability are based on experiments with tethered 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 non-intrusive 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 accurate. We subsequently validated the method with a quadcopter that is suspended in the AFP and generates unsteady thrust profiles. These independent measurements confirm that the AFP is indeed accurate. We demonstrate the effectiveness of the AFP by studying aerodynamic weight support of a freely flying bird in vivo. These measurements confirm earlier findings based on kinematics and flow measurements, which suggest that the avian downstroke, not the upstroke, is primarily responsible for body weight support during take-off and landing. PMID:25589565
Quasi-steady aerodynamic analysis of propeller-wing interaction
NASA Astrophysics Data System (ADS)
Cho, Jinsoo; Cho, Jaeheon
1999-08-01
A quasi-steady scheme for the analysis of aerodynamic interaction between a propeller and a wing has been developed. The quasi-steady analysis uses a 3D steady vortex lattice method for the propeller and a 3D unsteady panel method for the wing. The aerodynamic coupling is represented by periodic loads, which are decomposed into harmonics and the harmonic amplitudes are found iteratively. Each stage of the iteration involves the solution of an isolated propeller or wing problem, the interaction being done through the Fourier transform of the induced velocity field. The propeller analysis code was validated by comparing the predicted velocity field about an isolated propeller with detailed laser Doppler velocimeter measurements, and the quasi-steady scheme by comparison with mean loads measured in a wing-propeller experiment. Comparisons have also been made among the fluctuating loads predicted by the present method, an unsteady panel scheme and a quasi-steady vortex lattice scheme. Copyright
NASA Astrophysics Data System (ADS)
Lee, Eun Seok
2000-10-01
An improved aerodynamics performance of a turbine cascade shape can be achieved by an understanding of the flow-field associated with the stator-rotor interaction. In this research, an axial gas turbine airfoil cascade shape is optimized for improved aerodynamic performance by using an unsteady Navier-Stokes solver and a parallel genetic algorithm. The objective of the research is twofold: (1) to develop a computational fluid dynamics code having faster convergence rate and unsteady flow simulation capabilities, and (2) to optimize a turbine airfoil cascade shape with unsteady passing wakes for improved aerodynamic performance. The computer code solves the Reynolds averaged Navier-Stokes equations. It is based on the explicit, finite difference, Runge-Kutta time marching scheme and the Diagonalized Alternating Direction Implicit (DADI) scheme, with the Baldwin-Lomax algebraic and k-epsilon turbulence modeling. Improvements in the code focused on the cascade shape design capability, convergence acceleration and unsteady formulation. First, the inverse shape design method was implemented in the code to provide the design capability, where a surface transpiration concept was employed as an inverse technique to modify the geometry satisfying the user specified pressure distribution on the airfoil surface. Second, an approximation storage multigrid method was implemented as an acceleration technique. Third, the preconditioning method was adopted to speed up the convergence rate in solving the low Mach number flows. Finally, the implicit dual time stepping method was incorporated in order to simulate the unsteady flow-fields. For the unsteady code validation, the Stokes's 2nd problem and the Poiseuille flow were chosen and compared with the computed results and analytic solutions. To test the code's ability to capture the natural unsteady flow phenomena, vortex shedding past a cylinder and the shock oscillation over a bicircular airfoil were simulated and compared with experiments and other research results. The rotor cascade shape optimization with unsteady passing wakes was performed to obtain an improved aerodynamic performance using the unsteady Navier-Stokes solver. Two objective functions were defined as minimization of total pressure loss and maximization of lift, while the mass flow rate was fixed. A parallel genetic algorithm was used as an optimizer and the penalty method was introduced. Each individual's objective function was computed simultaneously by using a 32 processor distributed memory computer. One optimization took about four days.
The aerodynamics of an oscillating cascade in a compressible flow field
NASA Technical Reports Server (NTRS)
Buffum, D. H.; Fleeter, S.
1990-01-01
Fundamental experiments are performed in the NASA Lewis Research Center Transonic Oscillating Cascade Facility to investigate and quantify the aerodynamics of a cascade of bioconvex airfoils executing torsion mode oscillations at realistic reduced frequency values. Both steady and unsteady airfoil surface pressures are measured at two inlet Mach numbers, 0.65 and 0.80, and two incidence angles, 0 and 7 deg, with the harmonic torsional airfoil cascade oscillations at realistic high reduced frequency and unsteady data obtained at several interblade phase angle values. The time-variant pressures are analyzed by means of discrete Fourier transform techniques, with these unique data compared with predictions from a linearized unsteady cascade model. The experimental results indicate that the interblade phase angle has a major effect on the chordwise distributions of the airfoil surface unsteady pressure, with the effect of reduced frequency, incidence angle, and Mach numbers somewhat less significant.
Knowledge Based Airfoil Aerodynamic and Aeroacoustic Design
B. Greschner; C. Yu; S. Zheng; M. Zhuang; Z. J. Wang; F. Thiele
A systematic investigation of the unsteady flows around a series of NACA airfoils is carried out. The main objective is to conduct manual design case studies on the connections between an airfoil shape characteristics and it s aerodynamic and aeroacoustic performance. The approach employs the unsteady CFD flow simulations in the near field of an airfoil and the FW-H integral
NASA Technical Reports Server (NTRS)
Hanson, Donald B.
1994-01-01
Typical analytical models for interaction between rotor and stator in a turbofan analyze the effect of wakes from the rotor impinging on the stator, producing unsteady loading, and thereby generating noise. Reflection/transmission characteristics of the rotor are sometimes added in a separate calculation. In those models, there is a one-to-one relationship between wake harmonics and noise harmonics; that is, the BPF (blade passing frequency) wake harmonic causes only the BPF noise harmonic, etc. This report presents a more complete model in which flow tangency boundary conditions are satisfied on two cascades in relative motion for several harmonics simultaneously. By an extension of S.N. Smith's code for two dimensional flat plate cascades, the noise generation/frequency scattering/blade row reflection problem is solved in a single matrix inversion. It is found that the BPF harmonic excitation of the stator scatters considerable energy in the higher BPF harmonics due to relative motion between the blade rows. Furthermore, when swirl between the rotor and stator is modeled, a 'mode trapping' effect occurs which explains observations on fans operating at rotational speeds below BFP cuton: the BPF mode amplifies between blade rows by multiple reflections but cannot escape to the inlet and exit ducts. However, energy scattered into higher harmonics does propagate and dominates the spectrum at two and three times BPF. This report presents the complete derivation of the theory, comparison with a previous (more limited) coupled rotor/stator interaction theory due to Kaji and Okazaki, exploration of the mode trapping phenomenon, and parametric studies showing the effects of vane/blade ratio and rotor/stator interaction. For generality, the analysis applies to stages where the rotor is either upstream or downstream of the stator and to counter rotation stages. The theory has been coded in a FORTRAN program called CUP2D, documented in Volume 2 of this report. It is concluded that the new features of this analysis - unsteady coupling, frequency scattering, and flow turning between rotor and stator - have a profound effect on noise generation caused by rotor/stator interaction. Treating rotors and stators as isolated cascades is not adequate for noise analysis and prediction.
DOE's effort to reduce truck aerodynamic drag through joint experiments and computations.
Salari, Kambiz (Lawrence Livermore National Laboratory); Browand, Fred (University of Southern California); Sreenivas, Kidambi (University of Tennessee, Chattanooga); Pointer, W. David (Argonne National Laboratory); Taylor, Lafayette (University of Tennessee, Chattanooga); Pankajakshan, Ramesh (University of Tennessee, Chattanooga); Whitfield, David (University of Tennessee, Chattanooga); Plocher, Dennis (University of Southern California); Ortega, Jason M. (Lawrence Livermore National Laboratory); Merzel, Tai (University of Southern California); McCallen, Rose (Lawrence Livermore National Laboratory); Walker, Stephen M (NASA Ames Research Center); Heineck, James T (NASA Ames Research Center); Hassan, Basil; Roy, Christopher John (Auburn University); Storms, B. (NASA Ames Research Center); Ross, James (NASA Ames Research Center); Englar, Robert (Georgia Tech Research Institute); Rubel, Mike (Caltech); Leonard, Anthony (Caltech); Radovich, Charles (University of Southern California); Eastwood, Craig (Lawrence Livermore National Laboratory); Paschkewitz, John (Lawrence Livermore National Laboratory); Castellucci, Paul (Lawrence Livermore National Laboratory); DeChant, Lawrence Justin.
2005-08-01
Class 8 tractor-trailers are responsible for 11-12% of the total US consumption of petroleum. Overcoming aero drag represents 65% of energy expenditure at highway speeds. Most of the drag results from pressure differences and reducing highway speeds is very effective. The goal is to reduce aerodynamic drag by 25% which would translate to 12% improved fuel economy or 4,200 million gal/year. Objectives are: (1) In support of DOE's mission, provide guidance to industry in the reduction of aerodynamic drag; (2) To shorten and improve design process, establish a database of experimental, computational, and conceptual design information; (3) Demonstrate new drag-reduction techniques; and (4) Get devices on the road. Some accomplishments are: (1) Concepts developed/tested that exceeded 25% drag reduction goal; (2) Insight and guidelines for drag reduction provided to industry through computations and experiments; (3) Joined with industry in getting devices on the road and providing design concepts through virtual modeling and testing; and (4) International recognition achieved through open documentation and database.
ERIC Educational Resources Information Center
Jernigan, S. R.; Fahmy, Y.; Buckner, G. D.
2009-01-01
This paper details a successful and inexpensive implementation of a remote laboratory into a distance control systems course using readily available hardware and software. The physical experiment consists of a beach ball and a dc blower; the control objective is to make the height of the aerodynamically levitated beach ball track a reference…
Experiments on the unsteady flow field and noise generation in a centrifugal pump impeller
NASA Astrophysics Data System (ADS)
Choi, Jong-Soo; McLaughlin, Dennis K.; Thompson, Donald E.
2003-06-01
This paper reports on an experimental investigation of large-scale flowfield instabilities in a pump rotor and the process of noise generation by these instabilities. Measurements of the fluctuating components of velocity and surface pressure were made with hot-wire probes and surface mounted pressure transducers on a seven bladed back swept centrifugal water pump impeller operating with air as the working fluid. The impeller was operated without a volute or scroll diffuser, thereby eliminating any sound generation from pressure fluctuations on the volute cutoff. Thus the study focused on flow field and noise components other than the blade passage frequency (and its harmonics). The primary goal of the study was to provide fundamental information on the unsteady flow processes, particularly those associated with the noise generation in the device. It was further anticipated that detailed flow measurements would be useful for the validation of future computational simulations. The measured data at the discharge show a jet-wake type of flow pattern which results in a strong vorticity field. The flow with high velocity found on the pressure side of the impeller tends to move to the low-pressure region present at the suction side of the passage as a form of roll-up around the blade trailing edge. This motion causes an unsteady flow separation at the suction side of the blade and consequently disturbs the flow in the adjacent passage. By interacting with the impeller blades near the trailing edges, this instability flow causes a periodic pressure fluctuation on the blade surface and generates noise by a trailing edge generation mechanism. The spectrum of surface pressure measured at the trailing edge of each blade reveals a cluster of peaks which were identified with azimuthal mode numbers. The correlation between the acoustic farfield pressure and the surface pressure on the impeller blade has proven that the azimuthal modes synchronized with the number of impeller blades generate noise much more efficiently than the other modes. The paper also clarifies the correlation between unsteady flowfield measurements, in both impeller and laboratory co-ordinates, with the radiated noise properties. Thus some light is shed on the noise generation mechanisms of this particular device.
ATRAN3S: An unsteady transonic code for clean wings
NASA Technical Reports Server (NTRS)
Guruswamy, G. P.; Goorjian, P. M.; Merritt, F. J.
1985-01-01
The development and applications of the unsteady transonic code ATRAN3S for clean wings are discussed. Explanations of the unsteady, transonic small-disturbance aerodynamic equations that are used and their solution procedures are discussed. A detailed user's guide, along with input and output for a sample case, is given.
An unsteady lifting surface theory for ducted fan blades
R. M. Chi
1993-01-01
A frequency domain lifting surface theory is developed to predict the unsteady aerodynamic pressure loads on oscillating blades of a ducted subsonic fan. The steady baseline flow as observed in the rotating frame of reference is the helical flow dictated by the forward flight speed and the rotational speed of the fan. The unsteady perturbation flow, which is assumed to
Unsteady laminar pipe flow of a Carbopol gel. Part I: experiment
Antoine Poumaere; Miguel Moyers-Gonzalez; Cathy Castelain; Teodor Burghelea
2013-01-21
A experimental study of low Reynolds numbers unsteady pipe flows of a yield stress shear thinning fluid (Carbopol- 980) is presented. The investigation of the solid-fluid transition in a rheometric flow in the presence and in the ab- sence of the wall slip reveals a coupling between the irreversible deformation states and the wall slip phenomenon. Particularly, the presence of wall slip nearly suppresses the scaling of the deformation power deficit associated to the rheological hysteresis with the rate at which the material is forced. The irreversible solid-fluid transition and the wall slip behaviour emerge in the same range of the applied stresses and thus, the two phenomena appear to be coupled to each other. In-situ measurements of the flow fields performed during an increasing/decreasing stepped pressure ramp reveal three distinct flow regimes: solid (pluglike), solid-fluid and fluid. The deformation power deficit associated with the hysteresis observed during the increasing/decreasing branches of the pressure ramps reveals a dependence on the rate at which the unsteady flow is driven consistent with that observed during the rheological measurements in the presence of slip. The dependence of the slip velocity on the wall shear stresses reveals a Navier-type slip behaviour only within the fluid flow regime, which indicates that the wall slip phenomenon is directly coupled to the solid-fluid transition. A universal scaling of the slip velocity with the wall velocity gradients is found and the slip length is independent on the characteristic time of forcing t0. The paper closes with a discussion of the main findings, their possible impact on our current understanding of the yielding and slip behaviour of Carbopol gels. Several steps worth being pursued by future experimental/theoretical studies are proposed.
Cascade aerodynamic gust response including steady loading effects
NASA Technical Reports Server (NTRS)
Chiang, Hsiao-Wei D.; Fleeter, Sanford
1990-01-01
To predict the unsteady convected gust aerodynamic response of a cascade comprised of arbitrary thick and cambered aerofoils in an incompressible, inviscid, flow field, a complete first-order model is formulated. The flow is analyzed by considering a periodic flow channel. The velocity potential is separated into steady and unsteady harmonic components, each described by a Laplace equation. The strong dependence of the unsteady aerodynamics on the steady effects of aerofoil and cascade geometry and incidence angle is manifested in the coupling of the unsteady and steady flow fields through the unsteady boundary conditions. Analytical solutions in individual grid elements of a body-fitted computational grid are then determined, with the complete solution obtained by assembly of these local solutions. The validity and capabilities of this model and solution technique are then demonstrated by analyzing the steady and unsteady aerodynamics of both theoretical and experimental cascade configurations.
D. Simms; S. Schreck; M. Hand; L. J. Fingersh
2001-01-01
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
Aerodynamic Interaction Effects of a Helicopter Rotor and Fuselage
NASA Technical Reports Server (NTRS)
Boyd, David D., Jr.
1999-01-01
A three year Cooperative Research Agreements made in each of the three years between the Subsonic Aerodynamics Branch of the NASA Langley Research Center and the Virginia Polytechnic Institute and State University (Va. Tech) has been completed. This document presents results from this three year endeavor. The goal of creating an efficient method to compute unsteady interactional effects between a helicopter rotor and fuselage has been accomplished. This paper also includes appendices to support these findings. The topics are: 1) Rotor-Fuselage Interactions Aerodynamics: An Unsteady Rotor Model; and 2) Rotor/Fuselage Unsteady Interactional Aerodynamics: A New Computational Model.
Theory and Low-Order Modeling of Unsteady Airfoil Flows
NASA Astrophysics Data System (ADS)
Ramesh, Kiran
Unsteady flow phenomena are prevalent in a wide range of problems in nature and engineering. These include, but are not limited to, aerodynamics of insect flight, dynamic stall in rotorcraft and wind turbines, leading-edge vortices in delta wings, micro-air vehicle (MAV) design, gust handling and flow control. The most significant characteristics of unsteady flows are rapid changes in the circulation of the airfoil, apparent-mass effects, flow separation and the leading-edge vortex (LEV) phenomenon. Although experimental techniques and computational fluid dynamics (CFD) methods have enabled the detailed study of unsteady flows and their underlying features, a reliable and inexpensive loworder method for fast prediction and for use in control and design is still required. In this research, a low-order methodology based on physical principles rather than empirical fitting is proposed. The objective of such an approach is to enable insights into unsteady phenomena while developing approaches to model them. The basis of the low-order model developed here is unsteady thin-airfoil theory. A time-stepping approach is used to solve for the vorticity on an airfoil camberline, allowing for large amplitudes and nonplanar wakes. On comparing lift coefficients from this method against data from CFD and experiments for some unsteady test cases, it is seen that the method predicts well so long as LEV formation does not occur and flow over the airfoil is attached. The formation of leading-edge vortices (LEVs) in unsteady flows is initiated by flow separation and the formation of a shear layer at the airfoil's leading edge. This phenomenon has been observed to have both detrimental (dynamic stall in helicopters) and beneficial (high-lift flight in insects) effects. To predict the formation of LEVs in unsteady flows, a Leading Edge Suction Parameter (LESP) is proposed. This parameter is calculated from inviscid theory and is a measure of the suction at the airfoil's leading edge. It is hypothesized, and verified with experimental and computational data, that LEV formation always occurs at the same critical value of LESP irrespective of motion kinematics. Further, the applicability of the LESP criterion in influencing the occurrence of LEV formation is demonstrated. To model the growth and convection of leading-edge vortices, the unsteady thin-airfoil theory is augmented with discrete-vortex shedding from the leading edge. The LESP criterion is used to predict and modulate the shedding of leading-edge vorticity. Comparisons with experiments and CFD for test-cases with different airfoils, Reynolds numbers and motion kinematics, show that the method performs remarkably well in predicting force coefficients and flowfields for unsteady flows. The use of a single empirical parameter - the critical LESP value, allows the determination of onset, growth and termination of leading-edge vortex shedding. In the final part of the research, the discrete-vortex model is extended to flows where the freestream velocity is varying or small in comparison with motion velocity. With this extension, the method is made applicable to a larger set of 2D flows such as perching and hovering maneuvers, gusts, and sinusoidally varying freestream. Abstractions of perching and hovering are designed as test cases and used to validate the low-order model's performance in highly-unsteady, vortex-dominated flows. Alongside development of the low-order methodology, several features of unsteady flows are studied and analyzed with the aid of CFD and experiments. While remaining computationally inexpensive and retaining the essential flow-physics, the method is seen to be successful in prediction of both force coefficients and flow histories.
Aerodynamic detuning analysis of an unstalled supersonic turbofan cascade
NASA Technical Reports Server (NTRS)
Hoyniak, D.; Fleeter, S.
1985-01-01
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.
NASA Technical Reports Server (NTRS)
Cassell, Alan M.
2013-01-01
The testing of 3- and 6-meter diameter Hypersonic Inflatable Aerodynamic Decelerator (HIAD) test articles was completed in the National Full-Scale Aerodynamics Complex 40 ft x 80 ft Wind Tunnel test section. Both models were stacked tori, constructed as 60 degree half-angle sphere cones. The 3-meter HIAD was tested in two configurations. The first 3-meter configuration utilized an instrumented flexible aerodynamic skin covering the inflatable aeroshell surface, while the second configuration employed a flight-like flexible thermal protection system. The 6-meter HIAD was tested in two structural configurations (with and without an aft-mounted stiffening torus near the shoulder), both utilizing an instrumented aerodynamic skin.
An aerodynamic model for one and two degree of freedom wing rock of slender delta wings
NASA Technical Reports Server (NTRS)
Hong, John
1993-01-01
The unsteady aerodynamic effects due to the separated flow around slender delta wings in motion were analyzed. By combining the unsteady flow field solution with the rigid body Euler equations of motion, self-induced wing rock motion is simulated. The aerodynamic model successfully captures the qualitative characteristics of wing rock observed in experiments. For the one degree of freedom in roll case, the model is used to look into the mechanisms of wing rock and to investigate the effects of various parameters, like angle of attack, yaw angle, displacement of the separation point, and wing inertia. To investigate the roll and yaw coupling for the delta wing, an additional degree of freedom is added. However, no limit cycle was observed in the two degree of freedom case. Nonetheless, the model can be used to apply various control laws to actively control wing rock using, for example, the displacement of the leading edge vortex separation point by inboard span wise blowing.
Numerical solutions for unsteady subsonic vortical flows around loaded cascades
NASA Technical Reports Server (NTRS)
Fang, J.; Atassi, H. M.
1992-01-01
A frequency domain linearized unsteady aerodynamic analysis is presented for three-dimensional unsteady vortical flows around a cascade of loaded airfoils. The analysis fully accounts for the distortion of the impinging vortical disturbances by the mean flow. The entire unsteady flow field is calculated in response to upstream three-dimensional harmonic disturbances. Numerical results are presented for two standard cascade configurations representing turbine and compressor bladings for a reduced frequency range from 0.1 to 5. Results show that the upstream gust conditions and blade sweep strongly affect the unsteady blade response.
Numerical solutions for unsteady subsonic vortical flows around loaded cascades
Fang, J.; Atassi, H.M. (Univ. of Notre Dame, IN (United States). Dept. of Aerospace and Mechanical Engineering)
1993-10-01
A frequency domain linearized unsteady aerodynamic analysis is presented for three-dimensional unsteady vortical flows around a cascade of loaded airfoils. The analysis fully accounts for the distortion of the impinging vortical disturbances by the mean flow. The entire unsteady flow field is calculated in response to upstream three-dimensional harmonic disturbances. Numerical results are presented for two standard cascade configurations representing turbine and compressor bladings for a reduced frequency range from 0.1 to 5. Results show that the upstream gust conditions and blade sweep strongly affect the unsteady blade response.
R. E. Wilson
1981-01-01
Aerodynamic developments for vertical axis and horizontal axis wind turbines are given that relate to the performance and aerodynamic loading of these machines. Included are: (1) a fixed wake aerodynamic model of the Darrieus vertical axis wind turbine; (2) experimental results that suggest the existence of a laminar flow Darrieus vertical axis turbine; (3) a simple aerodynamic model for the
Real-Time Unsteady Loads Measurements Using Hot-Film Sensors
NASA Technical Reports Server (NTRS)
Mangalam, Arun S.; Moes, Timothy R.
2004-01-01
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.
Real-Time Unsteady Loads Measurements Using Hot-Film Sensors
NASA Technical Reports Server (NTRS)
Mangalam, Arun S.; Moes, Timothy R.
2004-01-01
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.
Computational unsteady aerodynamics for lifting surfaces
NASA Technical Reports Server (NTRS)
Edwards, John W.
1988-01-01
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.
NASA Technical Reports Server (NTRS)
Weilmuenster, K. J.; Hamilton, H. H., II
1986-01-01
The use of experimental or computed data to evaluate the performance of aeroassist orbital transfer vehicles (AOTVs) is discussed. Aerodynamic and surface pressure data are derived from computed flowfield solutions (the HALIS inviscid flowfield code), the Newtonian theory, and ground-based, wind tunnel studies (hypersonic He tunnel, 31-inch Mach 10 tunnel, and a hypersonic CF4 tunnel). The wind tunnel and HALIS models were tested at angles-of-attack that ranged from -10 to 10 deg. The effects of the ellipticity of the nose, the radius of the circular arc, and the angle through which the arc passes on the aerodynamic characteristics of the vehicles are examined. It is observed that the HALIS and CF4 tunnel generated surface pressure on the AOTVs produced the most useful aerodynamic data. Good correlation is obtained for the experimental and computational data; however, the Newtonian results do not correspond to the tunnel/HALIS data.
NSDL National Science Digital Library
2010-01-01
The following resource is from Lessonopoly, which has created student activities and lesson plans to support the video series, Science of the Olympic Winter Games, created by NBC Learn and the National Science Foundation. Featuring exclusive footage from NBC Sports and contributions from Olympic athletes and NSF scientists, the series will help teach your students valuable scientific concepts. In this particular lesson, students will learn about the role of scientific research in the design of competition suits for athletes in the Winter Olympics. Students will also explore and research the concept of aerodynamics, and conduct their own scientific experiment to gain an understanding of this concept.
Special opportunities in helicopter aerodynamics
NASA Technical Reports Server (NTRS)
Mccroskey, W. J.
1983-01-01
Aerodynamic research relating to modern helicopters includes the study of three dimensional, unsteady, nonlinear flow fields. A selective review is made of some of the phenomenon that hamper the development of satisfactory engineering prediction techniques, but which provides a rich source of research opportunities: flow separations, compressibility effects, complex vortical wakes, and aerodynamic interference between components. Several examples of work in progress are given, including dynamic stall alleviation, the development of computational methods for transonic flow, rotor-wake predictions, and blade-vortex interactions.
Characterization of unsteady flow processes in a centrifugal compressor stage
Gould, Kenneth A. (Kenneth Arthur)
2006-01-01
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 ...
Vanyó, József; Vincze, Miklós; Jánosi, Imre M; Tél, Tamás
2014-07-01
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
NASA Astrophysics Data System (ADS)
Vanyó, József; Vincze, Miklós; Jánosi, Imre M.; Tél, Tamás
2014-07-01
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.
ERIC Educational Resources Information Center
Weltner, Klaus
1990-01-01
Describes some experiments showing both qualitatively and quantitatively that aerodynamic lift is a reaction force. Demonstrates reaction forces caused by the acceleration of an airstream and the deflection of an airstream. Provides pictures of demonstration apparatus and mathematical expressions. (YP)
Hypersonic flutter of a curved shallow panel with aerodynamic heating
T. Bein; P. Friedmann; X. Zhong; I. Nydick
1993-01-01
The general equations describing the nonlinear fluttering oscillations of shallow, curved, heated orthotropic panels have been derived. The formulation takes into account the location of the panel on the surface of a generic hypersonic vehicle, when calculating the aerodynamic loads. It is also shown that third order piston theory produces unsteady aerodynamic loading which is in close agreement with that
Distributed Aerodynamic Sensing and Processing Toolbox
NASA Technical Reports Server (NTRS)
Brenner, Martin; Jutte, Christine; Mangalam, Arun
2011-01-01
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.
Experimental characterization of high speed centrifugal compressor aerodynamic forcing functions
NASA Astrophysics Data System (ADS)
Gallier, Kirk
The most common and costly unexpected post-development gas turbine engine reliability issue is blade failure due to High Cycle Fatigue (HCF). HCF in centrifugal compressors is a coupled nonlinear fluid-structure problem for which understanding of the phenomenological root causes is incomplete. The complex physics of this problem provides significant challenges for Computational Fluid Dynamics (CFD) techniques. Furthermore, the available literature fails to address the flow field associated with the diffuser potential field, a primary cause of forced impeller vibration. Because of the serious nature of HCF, the inadequacy of current design approaches to predict HCF, and the fundamental lack of benchmark experiments to advance the design practices, there exists a need to build a database of information specific to the nature of the diffuser generated forcing function as a foundation for understanding flow induced blade vibratory failure. The specific aim of this research is to address the fundamental nature of the unsteady aerodynamic interaction phenomena inherent in high-speed centrifugal compressors wherein the impeller exit flow field is dynamically modulated by the vaned diffuser potential field or shock structure. The understanding of this unsteady aerodynamic interaction is fundamental to characterizing the impeller forcing function. Unsteady static pressure measurement at several radial and circumferential locations in the vaneless space offer a depiction of pressure field radial decay, circumferential variation and temporal fluctuation. These pressure measurements are coupled with high density, full field measurement of the velocity field within the diffuser vaneless space at multiple spanwise positions. The velocity field and unsteady pressure field are shown to be intimately linked. A strong momentum gradient exiting the impeller is shown to extend well across the vaneless space and interact with the diffuser vane leading edge. The deterministic unsteady pressure field is found to be dominated by the blade-vane interaction. HCF concerns are illuminated by persistent pressure waves extending radially across the vaneless space and impacting the impeller pressure surface. Finally, the average impeller exit flow field is found to present a highly unsteady velocity field to the downstream vane row, challenging the common design assumption of a rapid mixing model for diffuser design.
NASA Astrophysics Data System (ADS)
Mettler, B. F.
2010-09-01
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.
Hypersonic flutter of a curved shallow panel with aerodynamic heating
NASA Technical Reports Server (NTRS)
Bein, T.; Friedmann, P.; Zhong, X.; Nydick, I.
1993-01-01
The general equations describing the nonlinear fluttering oscillations of shallow, curved, heated orthotropic panels have been derived. The formulation takes into account the location of the panel on the surface of a generic hypersonic vehicle, when calculating the aerodynamic loads. It is also shown that third order piston theory produces unsteady aerodynamic loading which is in close agreement with that based upon direct solution of the Euler equations. Results, for simply supported panels, are obtained using Galerkin's method combined with direct numerical integration in time to compute stable limit cycle amplitudes. These results illustrate the sensitivity of the aeroelastic behavior to the unsteady aerodynamic assumptions, temperature, orthotropicity and flow orientation.
B. Metcalf; J. Longo; S. Ghosh; F. Stern
2006-01-01
Unsteady free-surface, wave-induced separation is documented using towing tank experiments for a surface-piercing NACA 0024 foil, which has insignificant separation, no wave effects, and 2-D flow in the deep. The test conditions are for minimal, reattaching, and nonreattaching separation: Froude numbers (Fr)=0.19, 0.37, and 0.55 and Reynolds numbers=0.822, 1.52, and 2.26×106. The measurements include mean far-field wave elevations for all
Compensations during Unsteady Locomotion.
Qiao, Mu; Jindrich, Devin L
2014-12-01
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
Research on unsteady transonic flow theory
NASA Technical Reports Server (NTRS)
Revell, J. D.
1973-01-01
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.
Interdisciplinary Aerodynamics Group INSTITUTE OF (logo)
Diggavi, Suhas
Interdisciplinary Aerodynamics Group INSTITUTE OF (logo) Mechanical Engineering Implementation,theerror on the common mesh nodes is minimized A simple coupling algorithm was implemented on an unsteady 2D heat conduction problem by imposing a temperature and heat flux exchange througha
Development of a nonlinear unsteady transonic flow theory
NASA Technical Reports Server (NTRS)
Stahara, S. S.; Spreiter, J. R.
1973-01-01
A nonlinear, unsteady, small-disturbance theory capable of predicting inviscid transonic flows about aerodynamic configurations undergoing both rigid body and elastic oscillations was developed. The theory is based on the concept of dividing the flow into steady and unsteady components and then solving, by method of local linearization, the coupled differential equation for unsteady surface pressure distribution. The equations, valid at all frequencies, were derived for two-dimensional flows, numerical results, were obtained for two classses of airfoils and two types of oscillatory motions.
Development of a linearized unsteady Euler analysis for turbomachinery blade rows
NASA Technical Reports Server (NTRS)
Verdon, Joseph M.; Montgomery, Matthew D.; Kousen, Kenneth A.
1995-01-01
A linearized unsteady aerodynamic analysis for axial-flow turbomachinery blading is described in this report. The linearization is based on the Euler equations of fluid motion and is motivated by the need for an efficient aerodynamic analysis that can be used in predicting the aeroelastic and aeroacoustic responses of blade rows. The field equations and surface conditions required for inviscid, nonlinear and linearized, unsteady aerodynamic analyses of three-dimensional flow through a single, blade row operating within a cylindrical duct, are derived. An existing numerical algorithm for determining time-accurate solutions of the nonlinear unsteady flow problem is described, and a numerical model, based upon this nonlinear flow solver, is formulated for the first-harmonic linear unsteady problem. The linearized aerodynamic and numerical models have been implemented into a first-harmonic unsteady flow code, called LINFLUX. At present this code applies only to two-dimensional flows, but an extension to three-dimensions is planned as future work. The three-dimensional aerodynamic and numerical formulations are described in this report. Numerical results for two-dimensional unsteady cascade flows, excited by prescribed blade motions and prescribed aerodynamic disturbances at inlet and exit, are also provided to illustrate the present capabilities of the LINFLUX analysis.
Supersonic flutter analysis of wings using an unsteady 3D panel method
Jinsoo Cho; Younhyuck Chang
2001-01-01
A frequency-domain flutter analysis scheme for wings is developed using an unsteady 3D panel method. The unsteady aerodynamic force calculation is based on the s-plane unsteady nonplanar lifting surface method, and a finite element method is used to structurally model the wing. The flutter analysis is done using the normal mode approach and a U–g method in frequency-domain. The U–g
Aerodynamics of biplane and tandem wings at low Reynolds numbers
NASA Astrophysics Data System (ADS)
Jones, R.; Cleaver, D. J.; Gursul, I.
2015-06-01
Experiments were performed to investigate the aerodynamic characteristics of two-wing configurations at a low Reynolds number of 100,000. The wing models were rectangular flat plates with a semi-aspect ratio of two. The stagger between the wings was varied from ? X/c = 0 to 1.5; the gap was varied from ? Y/c = 0 to 2 and ? Y/c = -1.5 to 1.5 for biplane and tandem configurations, respectively, with the decalage angle fixed at 0°. Lift, drag, aerodynamic efficiency and power efficiency ratios show that for small incidence angles, performance compared with the single wing is degraded. However, for single-wing post-stall angles of attack, lift performance improves and stall is delayed significantly for many configurations with nonzero gap, i.e., ? Y/c ? 0. For a fixed angle of attack, there are optimal gaps between the wings for which total lift becomes maximum. Particle image velocimetry measurements show that performance improvement relies heavily on the strength of the inter-wing flow and the interaction of the separated shear layers from the leading edge and trailing edge of the leading wing with the trailing wing. Unsteady forces are found to intensify for certain two-wing configurations. A switching between the stalled and unstalled states for the trailing wing as well as a switching between the merged and distinct wakes is shown to have high flow unsteadiness and large lift fluctuations.
NASA Technical Reports Server (NTRS)
Wilson, R. E.
1981-01-01
Aerodynamic developments for vertical axis and horizontal axis wind turbines are given that relate to the performance and aerodynamic loading of these machines. Included are: (1) a fixed wake aerodynamic model of the Darrieus vertical axis wind turbine; (2) experimental results that suggest the existence of a laminar flow Darrieus vertical axis turbine; (3) a simple aerodynamic model for the turbulent windmill/vortex ring state of horizontal axis rotors; and (4) a yawing moment of a rigid hub horizontal axis wind turbine that is related to blade coning.
A theoretical study on the unsteady aerothermodynamics for attached flow models
NASA Astrophysics Data System (ADS)
Chen, Hao; Bao, Lin; Tong, Binggang
2010-08-01
The principle of the unsteady aerothermodynamics was theoretically investigated for the attached flow. Firstly, two simplified models with analytic solutions to the N-S equations were selected for the research, namely the compressible unsteady flows on the infinite flat plate with both time-varying wall velocity and time-varying wall temperature boundary conditions. The unsteady temperature field and the unsteady wall heat flux (heat flow) were analytically solved for the second model. Then, the interaction characteristic of the unsteady temperature field and the unsteady velocity field in the simplified models and the effects of the interaction on the transient wall heat transfer were studied by these two analytic solutions. The unsteady heat flux, which is governed by the energy equation, is directly related to the unsteady compression work and viscous dissipation which originates from the velocity field governed by the momentum equation. The main parameters and their roles in how the unsteady velocity field affects the unsteady heat flux were discussed for the simplified models. Lastly, the similarity criteria of the unsteady aerothermodynamics were derived based on the compressible boundary layer equations. Along with the Strouhal number St u , the unsteadiness criterion of the velocity field, St T number, the unsteadiness criterion of the temperature field was proposed for the first time. Different from the traditional method used in unsteady aerodynamics which measures the flow unsteadiness only by the St u number, present results show that the flow unsteadiness in unsteady aerothermodynamics should be comprehensively estimated by comparing the relative magnitudes of the temperature field unsteadiness criterion St T number with the coefficients of other terms in the dimensionless energy equation.
NASA Technical Reports Server (NTRS)
1999-01-01
This document describes the aerodynamic design of an experimental hybrid laminar flow control (HLFC) wing panel intended for use on a Boeing 757 airplane to provide a facility for flight research on high Reynolds number HLFC and to demonstrate practical HLFC operation on a full-scale commercial transport airplane. The design consists of revised wing leading edge contour designed to produce a pressure distribution favorable to laminar flow, definition of suction flow requirements to laminarize the boundary layer, provisions at the inboard end of the test panel to prevent attachment-line boundary layer transition, and a Krueger leading edge flap that serves both as a high lift device and as a shield to prevent insect accretion on the leading edge when the airplane is taking off or landing.
Reciprocity relations in aerodynamics
NASA Technical Reports Server (NTRS)
Heaslet, Max A; Spreiter, John R
1953-01-01
Reverse flow theorems in aerodynamics are shown to be based on the same general concepts involved in many reciprocity theorems in the physical sciences. Reciprocal theorems for both steady and unsteady motion are found as a logical consequence of this approach. No restrictions on wing plan form or flight Mach number are made beyond those required in linearized compressible-flow analysis. A number of examples are listed, including general integral theorems for lifting, rolling, and pitching wings and for wings in nonuniform downwash fields. Correspondence is also established between the buildup of circulation with time of a wing starting impulsively from rest and the buildup of lift of the same wing moving in the reverse direction into a sharp-edged gust.
Unsteady transonic flow calculations for realistic aircraft configurations
NASA Technical Reports Server (NTRS)
Batina, John T.; Seidel, David A.; Bland, Samuel R.; Bennett, Robert M.
1987-01-01
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.
NASA Technical Reports Server (NTRS)
Schoenenberger, Mark; VanNorman, John; Rhode, Matthew; Paulson, John
2013-01-01
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.
Unsteady heat transfer and direct comparison to steady-state measurements in a rotor-wake experiment
NASA Technical Reports Server (NTRS)
Obrien, J. E.; Simoneau, R. J.; Lagraff, J. E.; Morehouse, K. A.
1986-01-01
Circumferentially local and time-resolved heat transfer measurements were obtained for a circular cylinder in crossflow located downstream of a rotating spoked wheel wake generator in a steady flow tunnel. The unsteady heat transfer effects were obtained by developing an extension of a thin film gauge technique employed to date exclusively in short-duration facilities. The time-average thin film results and conventional steady-state heat transfer measurements were compared. Time-averaged wake-induced stagnation heat transfer enhancement levels above the nowake case were about 10% for the four cylinder Reynolds numbers. This enhancement level was nearly independent of bar passing frequency and was related directly to the time integral of the heat transfer spikes observed at the bar passing frequency. It is observed that the wake-induced heat transfer spikes have peak magnitudes averaging 30 to 40% above the interwake heat transfer level.
An unsteady lifting surface theory for ducted fan blades
Chi, R.M. (United Technologies Research Center, East Hartford, CT (United States). Dept. of Propulsion and Flight Systems)
1993-01-01
A frequency domain lifting surface theory is developed to predict the unsteady aerodynamic pressure loads on oscillating blades of a ducted subsonic fan. The steady baseline flow as observed in the rotating frame of reference is the helical flow dictated by the forward flight speed and the rotational speed of the fan. The unsteady perturbation flow, which is assumed to be potential, is determined by solving an integral equation that relates the unknown jump in perturbation velocity potential across the lifting surface to the upwash velocity distribution prescribed by the vibratory motion of the blade. Examples of unsteady pressure distributions are given to illustrate the differences between the three-dimensional lifting surface analysis and the classical two-dimensional strip analysis. The effects of blade axial bending, bowing (i.e., circumferential bending), and sweeping on the unsteady pressure load are also discussed.
NASA Technical Reports Server (NTRS)
Mehta, R. D.
1985-01-01
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.
NASA Technical Reports Server (NTRS)
Yates, E. C., Jr.; Cunningham, H. J.; Desmarais, R. N.; Silva, W. A.; Drobenko, B.
1982-01-01
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.
Assessment of the derivative-moment transformation method for unsteady-load estimation
NASA Astrophysics Data System (ADS)
Mohebbian, Ali; Rival, David E.
2012-08-01
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.
Aerodynamic Measurements of a Gulfstream Aircraft Model With and Without Noise Reduction Concepts
NASA Technical Reports Server (NTRS)
Neuhart, Dan H.; Hannon, Judith A.; Khorrami, Mehdi R.
2014-01-01
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.
New Flutter Analysis Technique for CFD-based Unsteady Aeroelasticity
NASA Technical Reports Server (NTRS)
Pak, Chan-gi; Jutte, Christine V.
2009-01-01
This paper presents a flutter analysis technique for the transonic flight regime. The technique uses an iterative approach to determine the critical dynamic pressure for a given mach number. Unlike other CFD-based flutter analysis methods, each iteration solves for the critical dynamic pressure and uses this value in subsequent iterations until the value converges. This process reduces the iterations required to determine the critical dynamic pressure. To improve the accuracy of the analysis, the technique employs a known structural model, leaving only the aerodynamic model as the unknown. The aerodynamic model is estimated using unsteady aeroelastic CFD analysis combined with a parameter estimation routine. The technique executes as follows. The known structural model is represented as a finite element model. Modal analysis determines the frequencies and mode shapes for the structural model. At a given mach number and dynamic pressure, the unsteady CFD analysis is performed. The output time history of the surface pressure is converted to a nodal aerodynamic force vector. The forces are then normalized by the given dynamic pressure. A multi-input multi-output parameter estimation software, ERA, estimates the aerodynamic model through the use of time histories of nodal aerodynamic forces and structural deformations. The critical dynamic pressure is then calculated using the known structural model and the estimated aerodynamic model. This output is used as the dynamic pressure in subsequent iterations until the critical dynamic pressure is determined. This technique is demonstrated on the Aerostructures Test Wing-2 model at NASA's Dryden Flight Research Center.
Design and Predictions for a High-Altitude (Low-Reynolds-Number) Aerodynamic Flight Experiment
NASA Technical Reports Server (NTRS)
Greer, Donald; Hamory, Phil; Krake, Keith; Drela, Mark
1999-01-01
A sailplane being developed at NASA Dryden Flight Research Center will support a high-altitude flight experiment. The experiment will measure the performance parameters of an airfoil at high altitudes (70,000 to 100,000 ft), low Reynolds numbers (200,000 to 700,000), and high subsonic Mach numbers (0.5 and 0.65). The airfoil section lift and drag are determined from pitot 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. Several predictions of the airfoil performance are also presented. Mark Drela from the Massachusetts Institute of Technology designed the APEX-16 airfoil, using the MSES code. Two-dimensional Navier-Stokes analyses were performed by Mahidhar Tatineni and Xiaolin Zhong from the University of California, Los Angeles, and by the authors at NASA Dryden.
Design and Predictions for High-Altitude (Low Reynolds Number) Aerodynamic Flight Experiment
NASA Technical Reports Server (NTRS)
Greer, Donald; Harmory, Phil; Krake, Keith; Drela, Mark
2000-01-01
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.
Entry aerodynamics and heating
NASA Technical Reports Server (NTRS)
Olstad, W.
1974-01-01
An overview of the problems of entry aerodynamics and heating is given with emphasis on survival of the probe, predictability of performance, and reliability of performance. Technological challenges to performance prediction are considered and include: turbulent heat transfer, radiation blockage, chemical state of the shock layer, afterbody heat transfer, asymmetric ablation, and real-gas aerodynamics. It is indicated that various obstacles must be overcome in order to achieve technology readiness. These obstacles are considered to be: extrapolations from ground tests to flight; lack of flight experience; lack of parametric data; and uncertain knowledge of atmospherics.
Insight into wind turbine stall and post-stall aerodynamics
NASA Astrophysics Data System (ADS)
Tangler, James L.
2004-07-01
The objective of this study was to evaluate measured NASA Ames Unsteady Aerodynamic Experiment post-stall blade element data and to provide guidelines for developing an empirical approach that predicts post-stall aerofoil characteristics. Blade element data were analysed from the five radial stations of the baseline 5.03 m radius rotor. A lifting surface/prescribed wake performance prediction method was used to determine a reference angle of attack that corresponds to the measured blade element data. Using the measured normal and tangential force coefficients and estimated angle of attack, spanwise distributions of lift and drag performance characteristics were derived along with the circulation distributions. Guidelines for a new stall and post-stall model based on the measured trends in the aerofoil performance characteristics, along with flat plate theory, are proposed for predicting the peak and post-peak power. Copyright
Quasi-steady aerodynamic analysis of propeller-wing interaction
Jinsoo Cho; Jaeheon Cho
1999-01-01
A quasi-steady scheme for the analysis of aerodynamic interaction between a propeller and a wing has been developed. The quasi-steady analysis uses a 3D steady vortex lattice method for the propeller and a 3D unsteady panel method for the wing. The aerodynamic coupling is represented by periodic loads, which are decomposed into harmonics and the harmonic amplitudes are found iteratively.
Numerical and experimental study of unsteady flow field and vibration in radial inflow turbines
Kreuz-Ihli, T.; Filsinger, D.; Schulz, A.; Wittig, S.
2000-04-01
The blades of turbocharger impellers are exposed to unsteady aerodynamic forces, which cause blade vibrations and may lead to failures. An indispensable requirement for a safe design of radial inflow turbines is a detailed knowledge of the exciting forces. Up to now, only a few investigations relating to unsteady aerodynamic forces in radial turbines have been presented. To give a detailed insight into the complex phenomena, a comprehensive research project was initiated at the Institut fuer Thermische Stroemungsmaschinen, at the University of Karlsruhe. A turbocharger test rig was installed in the high-pressure, high-temperature laboratory of the institute. The present paper gives a description of the test rig design and the measuring techniques. The flow field in a vaneless radial inflow turbine was analyzed using laser-Doppler anemometry. First results of unsteady flow field investigations in the turbine scroll and unsteady phase-resolved measurements of the flow field in the turbine rotor will be discussed. Moreover, results from finite element calculations analyzing frequencies and mode shapes are presented. As vibrations in turbines of turbochargers are assumed to be predominantly excited by unsteady aerodynamic forces, a method to predict the actual transient flow in a radial turbine utilizing the commercial Navier-Stokes solver TASCflow3d was developed. Results of the unsteady calculations are presented and comparisons with the measured unsteady flow field are made. As a major result, the excitation effect of the tongue region in a vaneless radial inflow turbine can be demonstrated.
NASA Technical Reports Server (NTRS)
Sambamurthi, Jay; Warmbrod, John; Seaford, Mark
1989-01-01
An engineering methodology has been developed to predict the convective heating and pressure environments to the base surfaces of the Aeroassist Flight Experiment (AFE) vehicle during its earth aeropass. Data obtained from prior flight vehicles, wind tunnel tests, CFD analysis of AFE, and simple one-dimensional isentropic flow expansion relationships along with standard aeroheating methods were employed. With the exception of one corner, the AFE base surfaces are immersed in separated flow and are, therefore, exposed to heating and pressure that are small compared to the front face of the aerobrake.
WIND-TUNNEL STUDY ON AERODYNAMIC PERFORMANCE OF SMALL VERTICAL-AXIS WIND TURBINES
Leu, Tzong-Shyng "Jeremy"
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
J. M. Simmons; P. M. G. Cleary
1980-01-01
Prediction of the amplitude of vortex -induced vibration (aeolian vibration) of electrical transmission lines is based on knowledge of the aerodynamic power transferred to a circular cylinder oscilating in a cross flow. Methods for the measurement of aerodynamic power and the available data are reviewed. The paper reports new data obtained by direct measurement of the unsteady pressure distribution on
COMPUTATION OF CASCADE FLUTTER WITH A COUPLED AERODYNAMIC AND STRUCTURAL MODEL
Liu, Feng
COMPUTATION OF CASCADE FLUTTER WITH A COUPLED AERODYNAMIC AND STRUCTURAL MODEL M. SADEGHI AND F-3975, USA Abstract. A computational method for flutter simulation of turboma- chinery cascades is presented aerodynamic and structural models. The unsteady Euler/Navier-Stokes equations are solved in 2D using a second
Aerodynamic and flowfield hysteresis of slender wing aircraft undergoing large-amplitude motions
NASA Technical Reports Server (NTRS)
Nelson, Robert C.; Arena, Andrew S., Jr.; Thompson, Scott A.
1991-01-01
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.
Computational Aerodynamics of Insects' Flapping Flight
NASA Astrophysics Data System (ADS)
Yang, Kyung Dong; Kyung, Richard
2011-11-01
The kinematics of the Insects' flapping flight is modeled through mathematical and computational observations with commercial software. Recently, study on the insects' flapping flight became one of the challenging research subjects in the field of aeronautics because of its potential applicability to intelligent micro-robots capable of autonomous flight and the next generation aerial-vehicles. In order to uncover its curious unsteady characteristics, many researchers have conducted experimental and computational studies on the unsteady aerodynamics of insects' flapping flight. In the present paper, the unsteady flow physics around insect wings is carried out by utilizing computer software e-AIRS. The e-AIRS (e-Science Aerospace Integrated Research System) analyzes and models the results of computational and experimental aerodynamics, along with integrated research process of these two research activities. Stroke angles and phase angles, the important two factors in producing lift of the airfoils are set as main parameters to determine aerodynamic characteristics of the insects' flapping flight. As a result, the optimal phase angle to minimize the drag and to maximize the lift are found. Various simulations indicate that using proper value of variables produce greater thrust due to an optimal angle of attack at the initial position during down stroke motion.
Jakub Wejchert; David R. Haumann
1991-01-01
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
Prediction of Hyper-X Stage Separation Aerodynamics Using CFD
NASA Technical Reports Server (NTRS)
Buning, Pieter G.; Wong, Tin-Chee; Dilley, Arthur D.; Pao, Jenn L.
2000-01-01
The NASA X-43 "Hyper-X" hypersonic research vehicle will be boosted to a Mach 7 flight test condition mounted on the nose of an Orbital Sciences Pegasus launch vehicle. The separation of the research vehicle from the Pegasus presents some unique aerodynamic problems, for which computational fluid dynamics has played a role in the analysis. This paper describes the use of several CFD methods for investigating the aerodynamics of the research and launch vehicles in close proximity. Specifically addressed are unsteady effects, aerodynamic database extrapolation, and differences between wind tunnel and flight environments.
Evaluation of Aerodynamic Noise Generation by a Generic Side Mirror
Yiping Wang; Zhengqi Gu; Weiping Li; Xiaohui Lin
2010-01-01
The aerodynamic noise radiation from a side view mirror (SVM) in the high-speed airflow is calculated by the combination of unsteady incompressible fluid flow analysis and acoustic analysis. The transient flow past the generic SVM is simulated with variable turbulence model, namely DES Detached Eddy Simulation and LES (Large Eddy Simulation). Detailed velocity vectors and contour plots of the time-varying
Unsteady inviscid flowfields of 2D airfoils by non-linear singular integral computational analysis
E. G. Ladopoulos
2011-01-01
A two-dimensional aerodynamics representation analysis is introduced for the investigation of inviscid flowfields of unsteady airfoils. The problem of the unsteady flow of a two-dimensional NACA airfoil is therefore reduced to the solution of a non-linear multidimensional singular integral equation, when the form of the source and vortex strength distribution is dependent on the history of the above distribution on
NASA Technical Reports Server (NTRS)
Muffoletto, A. J.
1982-01-01
An aerodynamic computer code, capable of predicting unsteady and C sub m values for an airfoil undergoing dynamic stall, is used to predict the amplitudes and frequencies of a wing undergoing torsional stall flutter. The code, developed at United Technologies Research Corporation (UTRC), is an empirical prediction method designed to yield unsteady values of normal force and moment, given the airfoil's static coefficient characteristics and the unsteady aerodynamic values, alpha, A and B. In this experiment, conducted in the PSU 4' x 5' subsonic wind tunnel, the wing's elastic axis, torsional spring constant and initial angle of attack are varied, and the oscillation amplitudes and frequencies of the wing, while undergoing torsional stall flutter, are recorded. These experimental values show only fair comparisons with the predicted responses. Predictions tend to be good at low velocities and rather poor at higher velocities.
Simulation of self-induced unsteady motion in the near wake of a Joukowski airfoil
NASA Technical Reports Server (NTRS)
Ghia, K. N.; Osswald, G. A.; Ghia, U.
1986-01-01
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.
Unsteady Petschek reconnection
Helfried K. Biernat; Martin F. Heyn; Valdimir S. Semenov
1987-01-01
A model of unsteady Petschek reconnection with propagating shock waves is presented. The results depend uniquely on a prescribed, time-dependent reconnection rate. An application to flux transfer events at the dayside magnetopause is discussed.
Nonlinear Green's function method for unsteady transonic flows
NASA Technical Reports Server (NTRS)
Tseng, K.; Morino, L.
1982-01-01
Advantages to employing Green's function in describing unsteady three-dimensional transonic flows are explored. The development of the function for application to linear subsonic and supersonic unsteady aerodynamics is reviewed. It is shown that unique solutions are possible for external flows, with all functional expressions being defined in Prandtl-Glauert space. The development of methods of using the Green's function for transonic flows is traced, noting the necessity of including the effects of significant nonlinear terms. The steady-state problem is considered to demonstrate the shock-capturing ability of the method and the usefulness of the function in the incompressible, subsonic, transonic, and supersonic areas of potential unsteady three-dimensional flows around complex configurations. Computational time is asserted to be an order of magnitude less than with finite difference methods.
Unsteady transition measurements on a pitching three-dimensional wing
NASA Technical Reports Server (NTRS)
Lorber, Peter F.; Carta, Franklin O.
1992-01-01
Boundary layer transition measurements were made during an experimental study of the aerodynamics of a rectangular wing undergoing unsteady pitching motions. The wing was tested at chordwise Mach numbers between 0.2 and 0.6, at sweep angles of 0, 15, and 30 deg, and for steady state, sinusoidal, and constant pitch rate motions. The model was scaled to represent a full size helicopter rotor blade, with chord Reynolds numbers between 2 and 6 x 10(exp 6). Sixteen surface hot-film gages were located along three spanwise stations: 0.08, 0.27, and 0.70 chords from the wing tip. Qualitative heat transfer information was obtained to identify the unsteady motion of the point of transition to turbulence. In combination with simultaneous measurements of the unsteady surface pressure distributions, the results illustrate the effects of compressibility, sweep, pitch rate, and proximity to the wing tip on the transition and relaminarization locations.
Introduction. Computational aerodynamics.
Tucker, Paul G
2007-10-15
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
PREFACE: Aerodynamic sound Aerodynamic sound
NASA Astrophysics Data System (ADS)
Akishita, Sadao
2010-02-01
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.
A Computational Model for Rotor-Fuselage Interactional Aerodynamics
NASA Technical Reports Server (NTRS)
Boyd, D. Douglas, Jr.; Barnwell, Richard W.; Gorton, Susan Althoff
2000-01-01
A novel unsteady rotor-fuselage interactional aerodynamics model has been developed. This model loosely couples a Generalized Dynamic Wake Theory (GDWT) to a thin-layer Navier-Stokes solution procedure. This coupling is achieved using an unsteady pressure jump boundary condition in the Navier-Stokes model. The new unsteady pressure jump boundary condition models each rotor blade as a moving pressure jump which travels around the rotor azimuth and is applied between two adjacent planes in a cylindrical, non-rotating grid. Comparisons are made between measured and predicted time-averaged and time-accurate rotor inflow ratios. Additional comparisons are made between measured and predicted unsteady surface pressures on the top centerline and sides of the fuselage.
Adjoint sensitivity analysis of time averaged quantities for unsteady flows
NASA Astrophysics Data System (ADS)
Wang, Qiqi
2011-11-01
Sensitivity analysis is an essential gradient for data assimilation, aerodynamic design, uncertainty quantification and optimal flow control. In particular. the adjoint sensitivity analysis method has been shown to solve very high dimensional optimization problems typically found these applications. This talk focuses on recent developments in extending adjoint sensitivity analysis to unsteady flows. The adjoint equation of unsteady flows must be integrated backwards in time. Each backward time step must use the flow solution at the corresponding time. As a result, the entire time history of the flow solution must be either stored or recalculated. The invention of checkpointing schemes provides an economic solution to this challenge. In particular, the dynamic checkpointing scheme makes this solution more practical for computational fluid dynamics problems. In unsteady flows, the quantities of interest are often long time averages. We demonstrate that sensitivity analysis of these long time averaged quantities poses significant new challenge. A novel windowing scheme is developed to compute correct sensitivity for periodic unsteady flows, such as in laminar vortex shedding. Initial investigation of sensitivity analysis of chaotic unsteady flows, i.e., transitional and turbulent flows, is also discussed. This work is supported by a subcontract of PSAAP program at Stanford awarded to MIT.
Measurements of Unsteady Wake Interference Between Tandem Cylinders
NASA Technical Reports Server (NTRS)
Jenkins, Luther N.; Neuhart, Dan H.; McGinley, Cahterine B.; Choudhari, Meelan M.; Khorrami, Mehdi R.
2006-01-01
A multi-phase, experimental study in the Basic Aerodynamics Research Tunnel at the NASA Langley Research Center has provided new insight into the unsteady flow interaction around cylinders in tandem arrangement. Phase 1 of the study characterized the mean and unsteady near-field flow around two cylinders of equal diameter using 2-D Particle Image Velocimetry (PIV) and hot-wire anemometry. These measurements were performed at a Reynolds number of 1.66 x 10(exp 5), based on cylinder diameter, and spacing-to-diameter ratios, L/D, of 1.435 and 3.7. The current phase, Phase 2, augments this dataset by characterizing the surface flow on the same configurations using steady and unsteady pressure measurements and surface flow visualization. Transition strips were applied to the front cylinder during both phases to produce a turbulent boundary layer upstream of the flow separation. For these flow conditions and L/D ratios, surface pressures on both the front and rear cylinders show the effects of L/D on flow symmetry, pressure recovery, and the location of flow separation and attachment. Mean streamlines and instantaneous vorticity obtained from the PIV data are used to explain the flow structure in the gap and near-wake regions and its relationship to the unsteady surface pressures. The combination of off-body and surface measurements provides a comprehensive dataset to develop and validate computational techniques for predicting the unsteady flow field at higher Reynolds numbers.
Algorithm and code development for unsteady three-dimensional Navier-Stokes equations
NASA Technical Reports Server (NTRS)
Obayashi, Shigeru
1993-01-01
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.
A Numerical Model of Unsteady, Subsonic Aeroelastic Behavior. Ph.D Thesis
NASA Technical Reports Server (NTRS)
Strganac, Thomas W.
1987-01-01
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.
Unsteady Optimization Using a Discrete Adjoint Approach Applied to Aeroacoustic Shape Design
Rumpfkeil, Markus Peer
Unsteady Optimization Using a Discrete Adjoint Approach Applied to Aeroacoustic Shape Design Markus Street, Toronto, ON, M3H 5T6, Canada In this paper, shape optimization is used to minimize aerodynamic step n J Objective function J Y Gradient of objective function M Free stream Mach number N Total number
American Institute of Aeronautics and Astronautics Unsteady Flow Measurements for Gust Load
Patil, Mayuresh
1 American Institute of Aeronautics and Astronautics Unsteady Flow Measurements for Gust Load Gusts are common flight occurrences which can rapidly change the aerodynamic forces experienced design, making the structure heavier. Reducing the gust loads on the aircraft will result in a lighter
Algorithm development with applications to aerodynamics and aeroelasticity
NASA Technical Reports Server (NTRS)
Goorjian, P. M.; Obayashi, S.; Chaderjian, N. M.; Guruswamy, G. P.
1992-01-01
The development of a streamwise upwind algorithm is presented. Applications of this algorithm to steady flow over a delta wing and unsteady flow over an oscillating wing, respectively, are covered. An extension to higher order accuracy for upwind methods is discussed. This scheme will use the compatibility relations for the extension. The use of multiple zones in the calculation of unsteady flows is considered. Multiple zones are one way to treat complex configurations, such as complete aircraft. Aeroelastic calculations are discussed. A procedure for aeroelastic calculations is described that simultaneously solves the aerodynamic and structural equations of motion. Sample calculations are given to illustrate the above.
Flutter and forced response of turbomachinery with frequency mistuning and aerodynamic asymmetry
NASA Astrophysics Data System (ADS)
Miyakozawa, Tomokazu
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.
Unsteady analysis of rotor blade tip flow
NASA Technical Reports Server (NTRS)
Maskey, B.; Rao, B. M.
1985-01-01
The development of the VSAERO-TS and VSAERO-H computer programs for calculating the unsteady aerodynamic characteristics of arbitrarily shaped wings oscillating in pitch is presented. The effect of several wake parameters on chordwise pressure distribution in VSAERO-TS is given and the convergence characteristics of both programs are discussed. In the program, the influence coefficient for each panel is formulated for a planar surface and so a skewed panel is represented by a projected flat quadrilateral lying in the mean plane. Since panels in the extreme roll-up region of the tip vortex are highly skewed the program was modified to treat each highly skewed panel as a pair of triangles. The programs are validated by comparing the chordwise pressure distribution of several blade tip planforms with experimental data. The comparison, for the most part, is good. The triangular panel representation improved the chordwise pressure distribution near the tip region for higher mean angle of attack.
Forced response analysis of an aerodynamically detuned supersonic turbomachine rotor
NASA Technical Reports Server (NTRS)
Hoyniak, D.; Fleeter, S.
1985-01-01
The effect of aerodynamic detuning on the supersonic flow induced forced response behavior of a turbomachine blade row is analyzed using an aeroelastic model. The rotor is modeled as a flat plate airfoil cascade representing an unwrapped rotor annulus; the aerodynamic detuning is achieved by alternating the circumferential spacing of adjacent rotor blades. The total unsteady aerodynamic loading on the blading, due to the convection of the transverse gust past the airfoil cascade as well as that resulting from the motion of the cascade, is developed in terms of influence coefficients. The model developed here is then used to analyze the effect of aerodynamic detuning on the flow induced forced response behavior of a twelve-bladed rotor with Verdon's Cascade B flow geometry.
Advanced multistage turbine blade aerodynamics, performance, cooling, and heat transfer
Fleeter, S.; Lawless, P.B. [Purdue Univ., West Lafayette, IN (United States). School of Mechanical Engineering
1995-12-31
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.
Unsteady Velocity Measurements Taken Behind a Model Helicopter Rotor Hub in Forward Flight
NASA Technical Reports Server (NTRS)
Berry, John D.
1997-01-01
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.
NASA Technical Reports Server (NTRS)
Newman, P. A.; Anderson, E. C.; Peterson, J. B., Jr.
1984-01-01
An overview is presented of the entire procedure developed for the aerodynamic design of the contoured wind tunnel liner for the NASA supercritical, laminar flow control (LFC), swept wing experiment. This numerical design procedure is based upon the simple idea of streamlining and incorporates several transonic and boundary layer analysis codes. The liner, presently installed in the Langley 8 Foot Transonic Pressure Tunnel, is about 54 ft long and extends from within the existing contraction cone, through the test section, and into the diffuser. LFC model testing has begun and preliminary results indicate that the liner is performing as intended. The liner design results presented in this paper, however, are examples of the calculated requirements and the hardware implementation of them.
An unsteady helicopter rotor: Fuselage interaction analysis
NASA Technical Reports Server (NTRS)
Lorber, Peter F.; Egolf, T. Alan
1988-01-01
A computational method was developed to treat unsteady aerodynamic interactions between a helicopter rotor, wake, and fuselage and between the main and tail rotors. An existing lifting line prescribed wake rotor analysis and a source panel fuselage analysis were coupled and modified to predict unsteady fuselage surface pressures and airloads. A prescribed displacement technique is used to position the rotor wake about the fuselage. Either a rigid blade or an aeroelastic blade analysis may be used to establish rotor operating conditions. Sensitivity studies were performed to determine the influence of the wake fuselage geometry on the computation. Results are presented that describe the induced velocities, pressures, and airloads on the fuselage and on the rotor. The ability to treat arbitrary geometries is demonstrated using a simulated helicopter fuselage. The computational results are compared with fuselage surface pressure measurements at several locations. No experimental data was available to validate the primary product of the analysis: the vibratory airloads on the entire fuselage. A main rotor-tail rotor interaction analysis is also described, along with some hover and forward flight.
Unsteady aerodynamic characterization of a military aircraft in vertical gusts
NASA Technical Reports Server (NTRS)
Lebozec, A.; Cocquerez, J. L.
1985-01-01
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.
Transonic Unsteady Aerodynamics and Aeroelasticity 1987, part 2
NASA Technical Reports Server (NTRS)
Bland, Samuel R. (compiler)
1989-01-01
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.
Ris-PhD-Report Wind Turbines: Unsteady Aerodynamics and
of the lift response of a sinusoidal gust as function of reduced wave number. The black line is the 1-D sinusoidal gust on a flat aerofoil (Section 2.1.2). The absolute value of the lift response |L is the corresponding phase of the lift relative to the phase of the gust at the midpoint of the aerofoil to the gust
Subsonic steady and unsteady aerodynamic loads on missiles and aircraft
NASA Technical Reports Server (NTRS)
1983-01-01
Steady lifting flows over highly swept delta wings at large incidence were studied. After an exhaustive literature review, development of a vortex-lattice method was attempted. To demonstrate the feasibility of using such a method, an existing code was modified. A system of vortex lines to simulate the leading-edge wake was added. The coefficients predicted by the modified code were in good agreement with experimental data.
Transonic Unsteady Aerodynamics and Aeroelasticity 1987, part 1
NASA Technical Reports Server (NTRS)
Bland, Samuel R. (compiler)
1989-01-01
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.
Aeroacoustics. [analysis of properties of sound generated by aerodynamic forces
NASA Technical Reports Server (NTRS)
Goldstein, M., E.
1974-01-01
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.
Application of Hybrid Method for Aerodynamic Noise Prediction
NASA Astrophysics Data System (ADS)
Yu, L.; Song, W. P.
2011-09-01
A hybrid prediction method for aerodynamic noise is performed using high order accuracy method in this paper. The method combines a two-dimensional Unsteady Reynolds-Averaged Navier-Stokes(URANS) solver with the acoustic analogy method using Ffowcs Williams-Hawkings equation with penetrable data surface (FW-Hpds). Tandem cylinders are chosen to validate the prediction method. The computations are conducted at a Reynolds number of 1.66 × 105 based on the cylinder diameter. Both the aerodynamic and acoustic results show good agreement with the experimental data, showing a successful application of the hybrid prediction method using two-dimensional URANS simulation.
Identification of aerodynamic models for maneuvering aircraft
NASA Technical Reports Server (NTRS)
Chin, Suei; Lan, C. Edward
1990-01-01
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.
NASA Astrophysics Data System (ADS)
van Oudheusden, B. W.; Scarano, F.
2009-07-01
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.
NASA Technical Reports Server (NTRS)
Williams, Louis J.; Hessenius, Kristin A.; Corsiglia, Victor R.; Hicks, Gary; Richardson, Pamela F.; Unger, George; Neumann, Benjamin; Moss, Jim
1992-01-01
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.
Numerical study of multi-element airfoil aerodynamics
NASA Technical Reports Server (NTRS)
Wang, Clin M.; Tung, Chee
1992-01-01
Unsteady flowfields around oscillating Boeing VR7 airfoil with and without a leading-edge slat were numerically investigated by a novel zonal method using a conformal mapping technique. Numerical aero-dynamic hysteresis loops show that the leading-edge slat prevents the airfoil dynamic stall at reduced frequency of 0.15, Reynolds number of 1 million, and the oscillation range of 5 deg to 25 deg.
Heat transfer analysis of charring ablators under aerodynamic heating
J. L. Lin; C. S. Yang
2005-01-01
Purpose – This work experimentally and numerically investigates the aerodynamic heating of the charring-ablating materials. Design\\/methodology\\/approach – The experimental model is a stainless steel cone with an attached charring ablator, in which supersonic hot flow impinges. The initial numerical simulation is based on physical and mathematical models, including one-dimensional, unsteady energy transport and mass conservation equations, coupled with calculations of
NASA Technical Reports Server (NTRS)
Holmes, Bruce J.; Schairer, Edward; Hicks, Gary; Wander, Stephen; Blankson, Isiaiah; Rose, Raymond; Olson, Lawrence; Unger, George
1990-01-01
Presented here is a comprehensive review of the following aerodynamics elements: computational methods and applications, computational fluid dynamics (CFD) validation, transition and turbulence physics, numerical aerodynamic simulation, drag reduction, test techniques and instrumentation, configuration aerodynamics, aeroacoustics, aerothermodynamics, hypersonics, subsonic transport/commuter aviation, fighter/attack aircraft and rotorcraft.
Jameson, Antony
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
Aerodynamic Control of a Pitching Airfoil using Distributed Active Bleed
NASA Astrophysics Data System (ADS)
Kearney, John; Glezer, Ari
2012-11-01
Aero-effected flight control using distributed active bleed driven by pressure differences across lifting surface and regulated by integrated louver actuators is investigated in wind tunnel experiments. The interaction between unsteady bleed and the cross flows alters the apparent aerodynamic shape of the lifting surface by regulating the accumulation and shedding of vorticity concentrations, and consequently the distributions of forces and moments. The present experiments are conducted using a 2-D dynamically-pitching VR-7 airfoil model from pre- to post-stall angles of attack. The effects of leading edge bleed at high angles of attack on the formation and evolution of the dynamic stall vorticity concentrations are investigated at high reduced frequencies (k > 0.1) using PIV phase-locked to the airfoil's motion. The time-dependent bleed enables broad-range variation in lift and pitching moment with significant extension of the stall margin. In particular, bleed actuation reduces the extent of ``negative damping'' or pitching moment instability with minimal lift penalty. Supported by NTRC-VLRCOE, monitored by Dr. Mike Rutkowski.
Unsteady Flowfield in a High-Pressure Turbine Modeled by TURBO
NASA Technical Reports Server (NTRS)
Bakhle, Milind A.; Mehmed, Oral
2003-01-01
Forced response, or resonant vibrations, in turbomachinery components can cause blades to crack or fail because of the large vibratory blade stresses and subsequent high-cycle fatigue. Forced-response vibrations occur when turbomachinery blades are subjected to periodic excitation at a frequency close to their natural frequency. Rotor blades in a turbine are constantly subjected to periodic excitations when they pass through the spatially nonuniform flowfield created by upstream vanes. Accurate numerical prediction of the unsteady aerodynamics phenomena that cause forced-response vibrations can lead to an improved understanding of the problem and offer potential approaches to reduce or eliminate specific forced-response problems. The objective of the current work was to validate an unsteady aerodynamics code (named TURBO) for the modeling of the unsteady blade row interactions that can cause forced response vibrations. The three-dimensional, unsteady, multi-blade-row, Reynolds-averaged Navier-Stokes turbomachinery code named TURBO was used to model a high-pressure turbine stage for which benchmark data were recently acquired under a NASA contract by researchers at the Ohio State University. The test article was an initial design for a high-pressure turbine stage that experienced forced-response vibrations which were eliminated by increasing the axial gap. The data, acquired in a short duration or shock tunnel test facility, included unsteady blade surface pressures and vibratory strains.
Unsteady Simulation of the Viscous Flow About a V-22 Rotor and Wing in Hover
NASA Technical Reports Server (NTRS)
Meakin, Robert L.
1996-01-01
Results of an unsteady thin-layer Navier-Stokes simulation of a 0.658-scale V-22 rotor and wing configuration in hover are presented. All geometric components of the flapped-wing and rotor test rig, including rotor blades, are accurately modeled. Rotor motion and rotor/airframe interference effects are simulated directly using moving body overset grid methods. Tiltrotor hover aerodynamics are visualized via unsteady particle trace images. Wing download predictive ability is demonstrated. Simulation results are compared with experimental data.
Aerodynamic effects of flexibility in flapping wings
Zhao, Liang; Huang, Qingfeng; Deng, Xinyan; Sane, Sanjay P.
2010-01-01
Recent work on the aerodynamics of flapping flight reveals fundamental differences in the mechanisms of aerodynamic force generation between fixed and flapping wings. When fixed wings translate at high angles of attack, they periodically generate and shed leading and trailing edge vortices as reflected in their fluctuating aerodynamic force traces and associated flow visualization. In contrast, wings flapping at high angles of attack generate stable leading edge vorticity, which persists throughout the duration of the stroke and enhances mean aerodynamic forces. Here, we show that aerodynamic forces can be controlled by altering the trailing edge flexibility of a flapping wing. We used a dynamically scaled mechanical model of flapping flight (Re ? 2000) to measure the aerodynamic forces on flapping wings of variable flexural stiffness (EI). For low to medium angles of attack, as flexibility of the wing increases, its ability to generate aerodynamic forces decreases monotonically but its lift-to-drag ratios remain approximately constant. The instantaneous force traces reveal no major differences in the underlying modes of force generation for flexible and rigid wings, but the magnitude of force, the angle of net force vector and centre of pressure all vary systematically with wing flexibility. Even a rudimentary framework of wing veins is sufficient to restore the ability of flexible wings to generate forces at near-rigid values. Thus, the magnitude of force generation can be controlled by modulating the trailing edge flexibility and thereby controlling the magnitude of the leading edge vorticity. To characterize this, we have generated a detailed database of aerodynamic forces as a function of several variables including material properties, kinematics, aerodynamic forces and centre of pressure, which can also be used to help validate computational models of aeroelastic flapping wings. These experiments will also be useful for wing design for small robotic insects and, to a limited extent, in understanding the aerodynamics of flapping insect wings. PMID:19692394
The Aerodynamics of Deforming Wings at Low Reynolds Number
NASA Astrophysics Data System (ADS)
Medina, Albert
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.
Optimization of the aerodynamics of small-scale flapping aircraft in hover
Sidney Lebental
2008-01-01
Flapping flight is one of the most widespread mean of transportation. It is a complex unsteady aerodynamic problem that has been studied extensively in the past century. Nevertheless, by its complex nature, flapping flight remains a challenging subject. With the development of micro air vehicles, researchers need new computational methods to design these aircrafts efficiently. In this dissertation, I will
Prediction of the aerodynamic environment and heat transfer for rotor-stator configurations
L. W. Griffin; H. V. McConnaughey
1989-01-01
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
Recent developments in the Green's function method. [for aerodynamics computer program
NASA Technical Reports Server (NTRS)
Tseng, K.; Puglise, J. A.; Morino, L.
1977-01-01
A recent computational development on the Green's function method (the method used in the computer program SOUSSA: Steady, Oscillatory and Unsteady Subsonic and Supersonic Aerodynamics) is presented. A scheme consisting of combined numerical (Gaussian quadrature) and analytical procedures for the evaluation of the source and doublet integrals used in the program is presented. This combination results in 80 to 90% reduction in computer time.
Effects of hysteretic and aerodynamic damping on supersonic panel flutter of composite plates
Kyo-Nam Koo; Woo-Seok Hwang
2004-01-01
The governing equation for the finite element analysis of the panel flutter of composite plates including structural damping is derived from Hamilton's principle. The first order shear deformable plate theory has been applied to structural modelling so as to obtain the finite element eigenvalue equation. The unsteady aerodynamic load in a supersonic flow is computed by using the linear piston
Integrated modeling of insect flight: From morphology, kinematics to aerodynamics
NASA Astrophysics Data System (ADS)
Liu, Hao
2009-02-01
An integrated and rigorous model for the simulation of insect flapping flight is addressed. The method is very versatile, easily integrating the modeling of realistic wing-body morphology, realistic flapping-wing and body kinematics, and unsteady aerodynamics in insect flight. A morphological model is built based on an effective differential geometric method for reconstructing geometry of and a specific grid generator for the wings and body; and a kinematic model is constructed capable to mimic the realistic wing-body kinematics of flapping flight. A fortified FVM-based NS solver for dynamically moving multi-blocked, overset-grid systems is developed and verified to be self-consistent by a variety of benchmark tests; and evaluation of flapping energetics is established on inertial and aerodynamic forces, torques and powers. Validation of this integrated insect dynamic flight simulator is achieved by comparisons of aerodynamic force-production with measurements in terms of the time-varying and mean lift and drag forces. Results for three typical insect hovering flights (hawkmoth, honeybee and fruitfly) over a wide rang of Reynolds numbers from O(10 2) to O(10 4) demonstrate its feasibility in accurately modeling and quantitatively evaluating the unsteady aerodynamic mechanisms in insect flapping flight.
Accurate measurement of streamwise vortices in low speed aerodynamic flows
NASA Astrophysics Data System (ADS)
Waldman, Rye M.; Kudo, Jun; Breuer, Kenneth S.
2010-11-01
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.
Forced response analysis of an aerodynamically detuned supersonic turbomachine rotor
NASA Technical Reports Server (NTRS)
Hoyniak, D.; Fleeter, S.
1985-01-01
High performance aircraft-engine fan and compressor blades are vulnerable to aerodynamically forced vibrations generated by inlet flow distortions due to wakes from upstream blade and vane rows, atmospheric gusts, and maldistributions in inlet ducts. In this report, an analysis is developed to predict the flow-induced forced response of an aerodynamically detuned rotor operating in a supersonic flow with a subsonic axial component. The aerodynamic detuning is achieved by alternating the circumferential spacing of adjacent rotor blades. The total unsteady aerodynamic loading acting on the blading, as a result of the convection of the transverse gust past the airfoil cascade and the resulting motion of the cascade, is developed in terms of influence coefficients. This analysis is used to investigate the effect of aerodynamic detuning on the forced response of a 12-blade rotor, with Verdon's Cascade B flow geometry as a uniformly spaced baseline configuration. The results of this study indicate that, for forward traveling wave gust excitations, aerodynamic detuning is very beneficial, resulting in significantly decreased maximum-amplitude blade responses for many interblade phase angles.
Asymmetric Uncertainty Expression for High Gradient Aerodynamics
NASA Technical Reports Server (NTRS)
Pinier, Jeremy T
2012-01-01
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.
Future Challenges and Opportunities in Aerodynamics
NASA Technical Reports Server (NTRS)
Kumar, Ajay; Hefner, Jerry N.
2000-01-01
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.
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.
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.
R. E. Wilson
1980-01-01
The aerodynamics of wind turbines is reviewed starting with effects of lift and drag on translating devices and proceeding through the performance aerodynamics of the horizontal-axis and vertical-axis machines currently in service. Horizontal-axis rotor aerodynamics is outlined and the performance limits are presented along with key assumptions and problem areas. The Darrieus rotor multiple streamtube analysis is developed and compared
Semi-empirical model for prediction of unsteady forces on an airfoil with application to flutter
NASA Technical Reports Server (NTRS)
Mahajan, Aparajit J.; Kaza, Krishna Rao V.
1992-01-01
A semi-empirical model is described for predicting unsteady aerodynamic forces on arbitrary airfoils under mildly stalled and unstalled conditions. Aerodynamic forces are modeled using second order ordinary differential equations for lift and moment with airfoil motion as the input. This model is simultaneously integrated with structural dynamics equations to determine flutter characteristics for a two degrees-of-freedom system. Results for a number of cases are presented to demonstrate the suitability of this model to predict flutter. Comparison is made to the flutter characteristics determined by a Navier-Stokes solver and also the classical incompressible potential flow theory.
Status and prospects of computational fluid dynamics for unsteady transonic viscous flows
NASA Technical Reports Server (NTRS)
Mccroskey, W. J.; Kutler, P.; Bridgeman, J. O.
1984-01-01
Applications of computational aerodynamics to aeronautical research, design, and analysis have increased rapidly over the past decade, and these applications offer significant benefits to aeroelasticians. The past developments are traced by means of a number of specific examples, and the trends are projected over the next several years. The crucial factors that limit the present capabilities for unsteady analyses are identified; they include computer speed and memory, algorithm and solution methods, grid generation, turbulence modeling, vortex modeling, data processing, and coupling of the aerodynamic and structural dynamic analyses. The prospects for overcoming these limitations are presented, and many improvements appear to be readily attainable. If so, a complete and reliable numerical simulation of the unsteady, transonic viscous flow around a realistic fighter aircraft configuration could become possible within the next decade. The possibilities of using artificial intelligence concepts to hasten the achievement of this goal are also discussed.
NASA Technical Reports Server (NTRS)
Wells, William L.
1989-01-01
Thin-film resistance gages were used to measure cylinder surface heat-transfer rates in the near wake of the Aeroassist Flight Experiment vehicle configuration, while surface-streamline directions were ascertained by the oil-flow techniques under the same configuration and test conditions. Both heat transfer distributions and flow over the entire cylinder surface were influenced by impingement of that portion of the free shear layer originating at the forebody shoulder in the upper symmetry plane. Heating rate distributions predicted with a Navier-Stokes solver computer code were in general agreement with measurements.
Acoustics of unsteady transonic flow
A. S. Lyrintzis; Y. Xue
1990-01-01
Investigation of noise mechanisms due to unsteady transonic flow is important for aircraft noise reduction. In this work, the near-field impulsive noise due to transonic Blade Vortex Interaction (BVI) and oscillating flap is simulated numerically. These problems are modeled by the two-dimensional high frequency transonic small disturbance equation (VTRAN2 code). The three types of unsteady shock wave motion have been
Numerical Aerodynamic Simulation
NASA Technical Reports Server (NTRS)
1989-01-01
An overview of historical and current numerical aerodynamic simulation (NAS) is given. The capabilities and goals of the Numerical Aerodynamic Simulation Facility are outlined. Emphasis is given to numerical flow visualization and its applications to structural analysis of aircraft and spacecraft bodies. The uses of NAS in computational chemistry, engine design, and galactic evolution are mentioned.
Not Available
1992-01-01
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.
NASA Astrophysics Data System (ADS)
Bozinoski, Radoslav
Significant research has been performed over the last several years on understanding the unsteady aerodynamics of various fluid flows. Much of this work has focused on quantifying the unsteady, three-dimensional flow field effects which have proven vital to the accurate prediction of many fluid and aerodynamic problems. Up until recently, engineers have predominantly relied on steady-state simulations to analyze the inherently three-dimensional ow structures that are prevalent in many of today's "real-world" problems. Increases in computational capacity and the development of efficient numerical methods can change this and allow for the solution of the unsteady Reynolds-Averaged Navier-Stokes (RANS) equations for practical three-dimensional aerodynamic applications. An integral part of this capability has been the performance and accuracy of the turbulence models coupled with advanced parallel computing techniques. This report begins with a brief literature survey of the role fully three-dimensional, unsteady, Navier-Stokes solvers have on the current state of numerical analysis. Next, the process of creating a baseline three-dimensional Multi-Block FLOw procedure called MBFLO3 is presented. Solutions for an inviscid circular arc bump, laminar at plate, laminar cylinder, and turbulent at plate are then presented. Results show good agreement with available experimental, numerical, and theoretical data. Scalability data for the parallel version of MBFLO3 is presented and shows efficiencies of 90% and higher for processes of no less than 100,000 computational grid points. Next, the description and implementation techniques used for several turbulence models are presented. Following the successful implementation of the URANS and DES procedures, the validation data for separated, non-reattaching flows over a NACA 0012 airfoil, wall-mounted hump, and a wing-body junction geometry are presented. Results for the NACA 0012 showed significant improvement in flow predictions for the three-dimensional DES when compared to experiment. The initial results using the RANS and DES procedures compared well with experimental data for the wall-mounted hump as well. Using the RANS model, the onset of separation was accurately predicted while the reattachment point was over-predicted. The RANS procedure also over-predicted the mean pressure, skin friction, and velocity profiles in the separation zone. The DES procedure showed much better results for the secondary flow of a wing/endwall junction; the three-dimensional structures resolved in the wake of the DES improved the local flow physics in the separation region and the predictions of the mean pressure distribution, skin friction, and streamwise velocity. The DES procedure exhibited a three-dimensional ow structure in the wake, with a 13.65% shorter mean separation region compared to RANS and a mean reattachment length that is in good agreement with experimental measurements. DES predictions of the pressure coefficient in the separation region also exhibit good agreement with experiment and are more accurate than RANS predictions.
NASA Astrophysics Data System (ADS)
Utvich, Alexis; Jemmott, Colin; Logan, Sheldon; Rossmann, Jenn
2003-11-01
A team of undergraduate students has performed experiments on Wiffle balls in the Harvey Mudd College wind tunnel facility. Wiffle balls are of particular interest because they can attain a curved trajectory with little or no pitcher-imparted spin. The reasons behind this have not previously been quantified formally. A strain gauge device was designed and constructed to measure the lift and drag forces on the Wiffle ball; a second device to measure lift and drag on a spinning ball was also developed. Experiments were conducted over a range of Reynolds numbers corresponding to speeds of roughly 0-40 mph. Lift forces of up to 0.2 N were measured for a Wiffle ball at 40 mph. This is believed to be due to air flowing into the holes on the Wiffle ball in addition to the effect of the holes on external boundary layer separation. A fog-based flow visualization system was developed in order to provide a deeper qualitative understanding of what occurred in the flowfield surrounding the ball. The data and observations obtained in this study support existing assumptions about Wiffle ball aerodynamics and begin to elucidate the mechanisms involved in Wiffle ball flight.
Aerodynamics of advanced axial-flow turbomachinery
NASA Technical Reports Server (NTRS)
Serovy, G. K.; Kavanagh, P.; Kiishi, T. H.
1980-01-01
A multi-task research program on aerodynamic problems in advanced axial-flow turbomachine configurations was carried out at Iowa State University. The elements of this program were intended to contribute directly to the improvement of compressor, fan, and turbine design methods. Experimental efforts in intra-passage flow pattern measurements, unsteady blade row interaction, and control of secondary flow are included, along with computational work on inviscid-viscous interaction blade passage flow techniques. This final report summarizes the results of this program and indicates directions which might be taken in following up these results in future work. In a separate task a study was made of existing turbomachinery research programs and facilities in universities located in the United States. Some potentially significant research topics are discussed which might be successfully attacked in the university atmosphere.
NSDL National Science Digital Library
Aerodynamics is the study of what makes things go fast, right? More specifically, itâ??s 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 youâ??ve 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.
Unsteady potential flow past a propeller blade section
NASA Technical Reports Server (NTRS)
Takallu, M. A.
1990-01-01
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.
NASA Technical Reports Server (NTRS)
Pak, Chan-gi; Li, Wesley W.
2009-01-01
Supporting the Aeronautics Research Mission Directorate guidelines, the National Aeronautics and Space Administration [NASA] Dryden Flight Research Center is developing a multidisciplinary design, analysis, and optimization [MDAO] tool. This tool will leverage existing tools and practices, and allow the easy integration and adoption of new state-of-the-art software. Today s modern aircraft designs in transonic speed are a challenging task due to the computation time required for the unsteady aeroelastic analysis using a Computational Fluid Dynamics [CFD] code. Design approaches in this speed regime are mainly based on the manual trial and error. Because of the time required for unsteady CFD computations in time-domain, this will considerably slow down the whole design process. These analyses are usually performed repeatedly to optimize the final design. As a result, there is considerable motivation to be able to perform aeroelastic calculations more quickly and inexpensively. This paper will describe the development of unsteady transonic aeroelastic design methodology for design optimization using reduced modeling method and unsteady aerodynamic approximation. The method requires the unsteady transonic aerodynamics be represented in the frequency or Laplace domain. Dynamically linear assumption is used for creating Aerodynamic Influence Coefficient [AIC] matrices in transonic speed regime. Unsteady CFD computations are needed for the important columns of an AIC matrix which corresponded to the primary modes for the flutter. Order reduction techniques, such as Guyan reduction and improved reduction system, are used to reduce the size of problem transonic flutter can be found by the classic methods, such as Rational function approximation, p-k, p, root-locus etc. Such a methodology could be incorporated into MDAO tool for design optimization at a reasonable computational cost. The proposed technique is verified using the Aerostructures Test Wing 2 actually designed, built, and tested at NASA Dryden Flight Research Center. The results from the full order model and the approximate reduced order model are analyzed and compared.
Aerodynamic: Applications of Force and Flow
NSDL National Science Digital Library
Quentin Briggs
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.
Numerical and Experimental Study on Unsteady Shedding of Partial Cavitation
NASA Astrophysics Data System (ADS)
Ji, Bin; Luo, Xianwu; Wu, Yulin; Peng, Xiaoxing; Xu, Hongyuan
Periodically unsteady shedding of partial cavity and forming of cavitation cloud have a great influence on hydraulic performances and cavitation erosion for ship propellers and hydro machines. In the present study, the unsteady cavitating flow around a hydrofoil has been calculated by using the single fluid approach with a developed cavitation mass transfer expression based on the vaporization and condensation of the fluid. The numerical simulation depicted the unsteady shedding of partial cavity, such as the process of cavity developing, breaking off and collapsing in the downstream under the steady incoming flow condition. It is noted that good agreement between the numerical results and that of experiment conducted at a cavitation tunnel is achieved. The cavitating flow field indicates that the cavity shedding was mainly caused by the re-entrant jet near cavity trailing edge, which was also clearly recorded by high-speed photographing.
Numerical studies of unsteady transonic flow over an oscillating airfoil
NASA Astrophysics Data System (ADS)
Chyu, W. J.; Davis, S. S.
1984-10-01
A finite-difference solution to the Navier-Stokes equations combined with a time-varying grid-generation technique was used to compute unsteady transonic flow over an oscillating airfoil. These computations were compared with experimental data (obtained at Ames Research Center) which form part of the AGARD standard configuration for aeroelastic analysis. A variety of approximations to the full Navier-Stokes equations was used to determine the effect of frequency, shock-wave motion, flow separation, and airfoil geometry on unsteady pressures and overall air loads. Good agreement is shown between experiment and theory with the limiting factor being the lack of a reliable turbulence model for high-Reynolds-number, unsteady transonic flows.
Unsteady Aspects of an Oblique Shock Reflection over a Heated Wall
NASA Astrophysics Data System (ADS)
Jaunet, Vincent; Dupont, Pierre; Dussauge, Jean-Paul
2011-11-01
In supersonic flows, when an oblique shock wave impinges a boundary layer and makes it separate, strong aerodynamical loads at low frequency are created. This study aims at studying density effects on these structures by means of wall heating. Experiments are conducted at Mach 2.3. The temperature of the floor of the test section can be heated up to twice the recovery value. The interaction length is investigated through mean schlieren visualizations. It turns out that the interaction length increases of about 30% between the adiabatic case and the heated one, whatever the adverse pressure gradient involved. Hotwire measurements are performed in the external flow in order to characterize the unsteadiness of the reflected shock. Results show that lower frequencies are involved in the heated case, in accordance with the Strouhal number of the interaction based on the interaction length L and the external velocity Ue: St =f/* L Ue ~= 0 . 03 . The authors wish to thank the CNES for supporting this program.
M Costello; J Sahu
2008-01-01
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
Aerodynamics of badminton shuttlecocks
NASA Astrophysics Data System (ADS)
Verma, Aekaansh; Desai, Ajinkya; Mittal, Sanjay
2013-08-01
A computational study is carried out to understand the aerodynamics of shuttlecocks used in the sport of badminton. The speed of the shuttlecock considered is in the range of 25-50 m/s. The relative contribution of various parts of the shuttlecock to the overall drag is studied. It is found that the feathers, and the net in the case of a synthetic shuttlecock, contribute the maximum. The gaps, in the lower section of the skirt, play a major role in entraining the surrounding fluid and causing a difference between the pressure inside and outside the skirt. This pressure difference leads to drag. This is confirmed via computations for a shuttlecock with no gaps. The synthetic shuttle experiences more drag than the feather model. Unlike the synthetic model, the feather shuttlecock is associated with a swirling flow towards the end of the skirt. The effect of the twist angle of the feathers on the drag as well as the flow has also been studied.
Unsteady characteristics of inlet vortices
NASA Astrophysics Data System (ADS)
Wang, Z.; Gursul, I.
2012-10-01
An experimental study of the unsteady characteristics of inlet vortices has been conducted using a high-frame rate digital particle image velocimetry system. The results revealed the formation of a pair of counter-rotating inlet vortices for the no-wind configuration and one single inlet vortex when there was crosswind. In all measurement planes, from near the ground to the inlet, evidence of vortex meandering with quasi-periodicity was found. The vortex meander is dominant in the direction of the crosswind, and its amplitude increases with crosswind velocity. The proper orthogonal decomposition analysis of the instantaneous velocity field suggested that the most energetic mode was a helical displacement wave, corresponding to the first helical mode. Similarities with the meandering of the trailing vortices from wings were noted. The present results also suggest that the unsteady characteristics of the focus of separation formed on the ground might be responsible for the unsteady nature of the inlet vortex.
Numerical modeling of wind turbine aerodynamic noise in the time domain.
Lee, Seunghoon; Lee, Seungmin; Lee, Soogab
2013-02-01
Aerodynamic noise from a wind turbine is numerically modeled in the time domain. An analytic trailing edge noise model is used to determine the unsteady pressure on the blade surface. The far-field noise due to the unsteady pressure is calculated using the acoustic analogy theory. By using a strip theory approach, the two-dimensional noise model is applied to rotating wind turbine blades. The numerical results indicate that, although the operating and atmospheric conditions are identical, the acoustical characteristics of wind turbine noise can be quite different with respect to the distance and direction from the wind turbine. PMID:23363200
Calculation of AGARD Wing 445.6 flutter using Navier-Stokes aerodynamics
NASA Technical Reports Server (NTRS)
Lee-Rausch, Elizabeth M.; Batina, John T.
1993-01-01
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.
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!
NASA Technical Reports Server (NTRS)
Horstman, Raymond H.
1992-01-01
Aerodynamic flow achieved by adding fixed fairings to butterfly valve. When valve fully open, fairings align with butterfly and reduce wake. Butterfly free to turn, so valve can be closed, while fairings remain fixed. Design reduces turbulence in flow of air in internal suction system. Valve aids in development of improved porous-surface boundary-layer control system to reduce aerodynamic drag. Applications primarily aerospace. System adapted to boundary-layer control on high-speed land vehicles.
NASA Technical Reports Server (NTRS)
Batina, John T.
1992-01-01
A time-accurate approximate-factorization (AF) algorithm is described for solution of the three-dimensional unsteady transonic small-disturbance equation. The AF algorithm consists of a time-linearization procedure coupled with a subiteration technique. The algorithm is the basis for the Computational Aeroelasticity Program-Transonic Small Disturbance (CAP-TSD) computer code, which was developed for the analysis of unsteady aerodynamics and aeroelasticity of realistic aircraft configurations. The paper describes details on the governing flow equations and boundary conditions, with an emphasis on documenting the finite-difference formulas of the AF algorithm.
Experimental contribution to the determination of blade forces in unsteady cascade flow
NASA Astrophysics Data System (ADS)
Sugeng, F.
The characteristics of unsteady flows in turbomachines are very complex, and, for this reason, a complete understanding of the involved processes has not yet been possible. However, new developments, related to advances in measurement technology and electronic data processing, provide now a basis for the study of the periodically unsteady flow in a cascade. The present investigation is concerned with the study of the problems of unsteady flow by means of modern measuring procedures. A number of experimental studies conducted during the last 20 years make contributions to a better understanding of the unsteady flow effects in the turbomachine. However, data are needed for a direct comparison of experimental and computational results. In the current investigation, studies of the flow in a cascade are conducted by making use of a special wind tunnel installation. Attention is given to the experimental equipment, a description of the measuring systems, the conduction of the experiment, the measured data, and the determination of the unsteady blade forces.
Acoustics of unsteady transonic flow
NASA Astrophysics Data System (ADS)
Lyrintzis, A. S.; Xue, Y.
Investigation of noise mechanisms due to unsteady transonic flow is important for aircraft noise reduction. In this work, the near-field impulsive noise due to transonic Blade Vortex Interaction (BVI) and oscillating flap is simulated numerically. These problems are modeled by the two-dimensional high frequency transonic small disturbance equation (VTRAN2 code). The three types of unsteady shock wave motion have been identified. Two different important disturbances exist in the pressure signal. The first disturbance is related to the fluctuating lift and the second is related to the fluctuating drag. Pressure wave signatures, noise frequency spectra, and noise directivity are investigated.
The effect of aerodynamic asymmetries on turbomachinery flutter
NASA Astrophysics Data System (ADS)
Ekici, Kivanc; Kielb, Robert E.; Hall, Kenneth C.
2013-01-01
In this paper, the effect of aerodynamic asymmetries on the flutter characteristics of turbomachinery blades is investigated. Specifically, the present method is used to study the effect of leading edge blending in loaded and unloaded rotors. The unsteady aerodynamic response of the blades to self-excited vibrations is modeled using a harmonic balance method, which allows one to model the entire wheel using complex periodic boundary conditions and a computational grid spanning a single sector (symmetry group). This reduces the computational and memory requirements dramatically compared to similar time-accurate analyses. It is shown that alternate blending degrades the stability of a loaded rotor whereas it improves the stability of an unloaded rotor. On the other hand, when blends are spaced five blades apart their effect is less pronounced.
The predicted effect of aerodynamic detuning on coupled bending-torsion unstalled supersonic flutter
NASA Technical Reports Server (NTRS)
Hoyniak, D.; Fleeter, S.
1986-01-01
A mathematical model is developed to predict the enhanced coupled bending-torsion unstalled supersonic flutter stability due to alternate circumferential spacing aerodynamic detuning of a turbomachine rotor. The translational and torsional unsteady aerodynamic coefficients are developed in terms of influence coefficients, with the coupled bending-torsion stability analysis developed by considering the coupled equations of motion together with the unsteady aerodynamic loading. The effect of this aerodynamic detuning on coupled bending-torsion unstalled supersonic flutter as well as the verification of the modeling are then demonstrated by considering an unstable 12 bladed rotor, with Verdon's uniformly spaced Cascade B flow geometry as a baseline. However, with the elastic axis and center of gravity at 60 percent of the chord, this type of aerodynamic detuning has a minimal effect on stability. For both uniform and nonuniform circumferentially space rotors, a single degree of freedom torsion mode analysis was shown to be appropriate for values of the bending-torsion natural frequency ratio lower than 0.6 and higher 1.2. When the elastic axis and center of gravity are not coincident, the effect of detuning on cascade stability was found to be very sensitive to the location of the center of gravity with respect to the elastic axis. In addition, it was determined that when the center of gravity was forward of an elastic axis located at midchord, a single degree of freedom torsion model did not accurately predict cascade stability.
Doublet-point method for supersonic unsteady lifting surfaces
NASA Technical Reports Server (NTRS)
Ueda, T.; Dowell, E. H.
1984-01-01
A method to predict unsteady aerodynamic forces on lifting surfaces in supersonic flow is presented. The wing is divided into small segments in which the lift force is expressed by a single-point doublet of the acceleration potential. This is the same concept as the doublet-point method developed by the authors for subsonic flows. In order to avoid sensitiveness to the Mach number, the upwash due to the point doublet is calculated by averaging over small areas. The integration is done analyticaly so that it requires no numerical quadrature. Pressure distributions are directly obtained as the unknowns of the algebraic equation. The results are compared with those obtained by other methods for various wing geometries, including the AGARD wing-tail configuration.
Inviscid analysis of unsteady blade tip flow correlation studies
NASA Technical Reports Server (NTRS)
Rao, B. M.; Maskew, B.
1985-01-01
Two computer programs, VSAERO-TS and VSAERO-H, were used for computing the unsteady subsonic aerodynamic characteristics of arbitrarily shaped wings oscillating in pitch. Program VSAERO-TS is a time-stepping analysis capable of treating large amplitude motions while program VSAERO-H uses harmonic wake and small amplitude assumptions. A comparison between the computed (VSAERO-TS and VSAERO-H) and DFVLR test results for chordwise pressure distributions for rectangular, swept, taper and ogee blade tips is presented in this report. A wide range of angles of attack (mean) from 0 to 12 deg and reduced frequencies of 0.1, 0.2 and 0.3 are covered in this report. Also, the comparison includes several spanwise stations.
Unsteady flow and dynamic response analyses for helicopter rotor blades
NASA Technical Reports Server (NTRS)
Bratanow, T.
1979-01-01
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.
Aerodynamic Design of Heavy Vehicles Reporting Period January 15, 2004 through April 15, 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
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.
Status of Nozzle Aerodynamic Technology at MSFC
NASA Technical Reports Server (NTRS)
Ruf, Joseph H.; McDaniels, David M.; Smith, Bud; Owens, Zachary
2002-01-01
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.
Aerodynamic Flow Control using Distributed Active Bleed
NASA Astrophysics Data System (ADS)
Kearney, John M.; Glezer, Ari
2010-11-01
The aerodynamic effects of large-area air bleed that is driven through surface openings by pressure differences across a lifting airfoil and regulated by addressable, arrays of integrated louvers have been investigated in wind tunnel experiments. Time-dependent interactions between the bleed and cross flows alter the apparent aerodynamic shape of the lifting surface and consequently the distributions of aerodynamic forces and moments. The lift and pitching moment can be significantly altered over a wide range of angles of attack from pre- to post-stall by independently-controlled bleed near the leading (LE) and trailing (TE) edges. While TE bleed effects nearly-linear variation of the pitching moment with minimal changes in lift, LE bleed leads to large variations in lift and pitching moment with minimal drag penalty. Phase-locked PIV shows the effects of the bleed on the flow on the suction surface and in the near wake. Supported by AFOSR
NASA Technical Reports Server (NTRS)
Dawson, Kenneth S.; Fortin, Paul E.
1987-01-01
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.
Klimas, P.C.
1981-01-01
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.
Aerodynamic Drag and Gyroscopic Stability
Courtney, Elya R
2013-01-01
This paper describes the effects on aerodynamic drag of rifle bullets as the gyroscopic stability is lowered from 1.3 to 1.0. It is well known that a bullet can tumble for stability less than 1.0. The Sierra Loading Manuals (4th and 5th Editions) have previously reported that ballistic coefficient decreases significantly as gyroscopic stability, Sg, is lowered below 1.3. These observations are further confirmed by the experiments reported here. Measured ballistic coefficients were compared with gyroscopic stabilities computed using the Miller Twist Rule for nearly solid metal bullets with uniform density and computed using the Courtney-Miller formula for plastic-tipped bullets. The experiments reported here also demonstrate a decrease in aerodynamic drag near Sg = 1.23 +/- 0.02. It is hypothesized that this decrease in drag over a narrow band of Sg values is due to a rapid damping of coning motions (precession and nutation). Observation of this drag decrease at a consistent value of Sg demonstrates the relati...
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.
Investigation of the unsteady pressure distribution on the blade of an axial flow fan
NASA Technical Reports Server (NTRS)
Henderson, R. E.
1975-01-01
A major source of the noise generated by high bypass ratio aircraft fan engines is the unsteady pressures (forces and moments) acting on the fan blades. These unsteady pressures are the result of the interaction of the blades with the wakes of upstream blade rows, inlet flow distortions, and inlet turbulence. An experimental system was developed which will permit the measurement of the unsteady pressure distributions; a series of experiments were conducted to investigate these effects, and the results are compared with predictions from existing theoretical analyses.
The Fifth Symposium on Numerical and Physical Aspects of Aerodynamic Flows
NASA Technical Reports Server (NTRS)
1992-01-01
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.
A collection of flow visualization techniques used in the Aerodynamic Research Branch
NASA Technical Reports Server (NTRS)
1984-01-01
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.
Study of aerodynamic characteristics in hard disk drives by numerical simulation
Hayato Shimizu; Mikio Tokuyama; Satomitsu Imai; Shigeo Nakamura; Kazuo Sakai
2001-01-01
The behavior of the air flow inside a hard disk drive is evaluated by a three-dimensional unsteady-flow analysis technique called large eddy simulation (LES). The simulation shows that the fluctuation of the aerodynamic force is strongly correlated with the amplitude of the disk vibration, which causes positioning error of the read\\/write head. It also shows that the power loss caused
An experimental study of the unsteady vortex structures in the wake of a root-fixed flapping wing
NASA Astrophysics Data System (ADS)
Hu, Hui; Clemons, Lucas; Igarashi, Hirofumi
2011-08-01
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.
Aerodynamic performance of a hovering hawkmoth with flexible wings: a computational approach
Nakata, Toshiyuki; Liu, Hao
2012-01-01
Insect wings are deformable structures that change shape passively and dynamically owing to inertial and aerodynamic forces during flight. It is still unclear how the three-dimensional and passive change of wing kinematics owing to inherent wing flexibility contributes to unsteady aerodynamics and energetics in insect flapping flight. Here, we perform a systematic fluid-structure interaction based analysis on the aerodynamic performance of a hovering hawkmoth, Manduca, with an integrated computational model of a hovering insect with rigid and flexible wings. Aerodynamic performance of flapping wings with passive deformation or prescribed deformation is evaluated in terms of aerodynamic force, power and efficiency. Our results reveal that wing flexibility can increase downwash in wake and hence aerodynamic force: first, a dynamic wing bending is observed, which delays the breakdown of leading edge vortex near the wing tip, responsible for augmenting the aerodynamic force-production; second, a combination of the dynamic change of wing bending and twist favourably modifies the wing kinematics in the distal area, which leads to the aerodynamic force enhancement immediately before stroke reversal. Moreover, an increase in hovering efficiency of the flexible wing is achieved as a result of the wing twist. An extensive study of wing stiffness effect on aerodynamic performance is further conducted through a tuning of Young's modulus and thickness, indicating that insect wing structures may be optimized not only in terms of aerodynamic performance but also dependent on many factors, such as the wing strength, the circulation capability of wing veins and the control of wing movements. PMID:21831896
NASA Technical Reports Server (NTRS)
Marshall, F. J.; Deffenbaugh, F. D.
1974-01-01
A method is developed to determine the flow field of a body of revolution in separated flow. The computer was used to integrate various solutions and solution properties of the sub-flow fields which made up the entire flow field without resorting to a finite difference solution to the complete Navier-Stokes equations. The technique entails the use of the unsteady cross flow analogy and a new solution to the two-dimensional unsteady separated flow problem based upon an unsteady, discrete-vorticity wake. Data for the forces and moments on aerodynamic bodies at low speeds and high angle of attack (outside the range of linear inviscid theories) such that the flow is substantially separated are produced which compare well with experimental data. In addition, three dimensional steady separated regions and wake vortex patterns are determined. The computer program developed to perform the numerical calculations is described.
On the Physics of Flow Separation Along a Low Pressure Turbine Blade Under Unsteady Flow Conditions
NASA Technical Reports Server (NTRS)
Schobeiri, Meinhard T.; Ozturk, Burak; Ashpis, David E.
2005-01-01
The present study, which is the first of a series of investigations dealing with specific issues of low pressure turbine (LPT) boundary layer aerodynamics, is aimed at providing detailed unsteady boundary 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 at Texas A&M Turbomachinery Performance and Flow Research Laboratory using a large-scale unsteady turbine cascade research facility with an integrated wake generator and test section unit. To account for a high flow deflection of LPT-cascades at design and off-design operating points, the entire wake generator and test section unit including the traversing system is designed to allow a precise angle adjustment of the cascade relative to the incoming flow. This is done by a hydraulic platform, which simultaneously lifts and rotates the wake generator and test section unit. The unit is then attached to the tunnel exit nozzle with an angular accuracy of better than 0.05 , which is measured electronically. Utilizing a Reynolds number of 110,000 based on the blade suction surface length and the exit velocity, one steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, wake velocities and turbulence intensities are investigated using hot-wire anemometry. In addition to the unsteady boundary layer measurements, blade surface pressure measurements were performed at Re=50,000, 75,000, 100,000, and 125,000 at one steady and two periodic unsteady inlet flow conditions. Detailed unsteady boundary layer measurement identifies the onset and extent of the separation zone as well as its behavior under unsteady wake flow. The results presented in ensemble-averaged and contour plot forms contribute to understanding the physics of the separation phenomenon under periodic unsteady wake flow. Several physical mechanisms are discussed.
Airfoil optimization for unsteady flows with application to high-lift noise reduction
NASA Astrophysics Data System (ADS)
Rumpfkeil, Markus Peer
The use of steady-state aerodynamic optimization methods in the computational fluid dynamic (CFD) community is fairly well established. In particular, the use of adjoint methods has proven to be very beneficial because their cost is independent of the number of design variables. The application of numerical optimization to airframe-generated noise, however, has not received as much attention, but with the significant quieting of modern engines, airframe noise now competes with engine noise. Optimal control techniques for unsteady flows are needed in order to be able to reduce airframe-generated noise. In this thesis, a general framework is formulated to calculate the gradient of a cost function in a nonlinear unsteady flow environment via the discrete adjoint method. The unsteady optimization algorithm developed in this work utilizes a Newton-Krylov approach since the gradient-based optimizer uses the quasi-Newton method BFGS, Newton's method is applied to the nonlinear flow problem, GMRES is used to solve the resulting linear problem inexactly, and last but not least the linear adjoint problem is solved using Bi-CGSTAB. The flow is governed by the unsteady two-dimensional compressible Navier-Stokes equations in conjunction with a one-equation turbulence model, which are discretized using structured grids and a finite difference approach. The effectiveness of the unsteady optimization algorithm is demonstrated by applying it to several problems of interest including shocktubes, pulses in converging-diverging nozzles, rotating cylinders, transonic buffeting, and an unsteady trailing-edge flow. In order to address radiated far-field noise, an acoustic wave propagation program based on the Ffowcs Williams and Hawkings (FW-H) formulation is implemented and validated. The general framework is then used to derive the adjoint equations for a novel hybrid URANS/FW-H optimization algorithm in order to be able to optimize the shape of airfoils based on their calculated far-field pressure fluctuations. Validation and application results for this novel hybrid URANS/FW-H optimization algorithm show that it is possible to optimize the shape of an airfoil in an unsteady flow environment to minimize its radiated far-field noise while maintaining good aerodynamic performance.
Turbine-99 unsteady simulations - Validation
NASA Astrophysics Data System (ADS)
Cervantes, M. J.; Andersson, U.; Lövgren, H. M.
2010-08-01
The Turbine-99 test case, a Kaplan draft tube model, aimed to determine the state of the art within draft tube simulation. Three workshops were organized on the matter in 1999, 2001 and 2005 where the geometry and experimental data were provided as boundary conditions to the participants. Since the last workshop, computational power and flow modelling have been developed and the available data completed with unsteady pressure measurements and phase resolved velocity measurements in the cone. Such new set of data together with the corresponding phase resolved velocity boundary conditions offer new possibilities to validate unsteady numerical simulations in Kaplan draft tube. The present work presents simulation of the Turbine-99 test case with time dependent angular resolved inlet velocity boundary conditions. Different grids and time steps are investigated. The results are compared to experimental time dependent pressure and velocity measurements.
NASA Astrophysics Data System (ADS)
Li, Chengqing; Ke, Tingfeng; Zhang, Jingxuan; Zhang, Hongwu; Huang, Weiguang
2013-04-01
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.
NASA Astrophysics Data System (ADS)
Katz, Joseph
2006-01-01
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.
Wind turbine wake aerodynamics
L. J. Vermeer; J. N. Sørensen; A. Crespo
2003-01-01
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
D. V. Sadin
1994-01-01
The unsteady filtering flow of a gas described by the equations of motion proposed by Khristianovich in [1] is investigated.\\u000a It is shown that for the gas flow in the pores a critical regime can develop when the reduced velocity (an analog of the Mach\\u000a number in gas dynamics) is less than unity. The reduced velocity is the ratio of
Physics of Forced Unsteady Separation
NASA Technical Reports Server (NTRS)
Carr, Lawrence W. (editor)
1992-01-01
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.
Computational analysis of high resolution unsteady airloads for rotor aeroacoustics
NASA Technical Reports Server (NTRS)
Quackenbush, Todd R.; Lam, C.-M. Gordon; Wachspress, Daniel A.; Bliss, Donald B.
1994-01-01
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.
Aerodynamic heated steam generating apparatus
Kim, K.
1986-08-12
An aerodynamic heated steam generating apparatus is described which consists of: an aerodynamic heat immersion coil steam generator adapted to be located on the leading edge of an airframe of a hypersonic aircraft and being responsive to aerodynamic heating of water by a compression shock airstream to produce steam pressure; an expansion shock air-cooled condensor adapted to be located in the airframe rearward of and operatively coupled to the aerodynamic heat immersion coil steam generator to receive and condense the steam pressure; and an aerodynamic heated steam injector manifold adapted to distribute heated steam into the airstream flowing through an exterior generating channel of an air-breathing, ducted power plant.
Experimental Aerodynamics of Mesoscale Trailing Edge Actuators
Stephen Solovitz; John Eaton
2001-01-01
Experiments were performed on a wing with segmented Gurney flaps. Each of the sixteen active flaps is approximately 1.5can be actuated in only two positions: 90 degrees up or 90 degrees down. Wind tunnel experiments were conducted at chord Reynolds numbers up to 800,000. Measurements include the determination of aerodynamic forces and moments using a 6 DOF balance, surface pressure
Preliminary results of unsteady blade surface pressure measurements for the SR-3 propeller
NASA Technical Reports Server (NTRS)
Heidelberg, L. J.; Clark, B. J.
1986-01-01
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.
Aeroacoustic Study of a High-Fidelity Aircraft Model. Part 2; Unsteady Surface Pressures
NASA Technical Reports Server (NTRS)
Khorrami, Mehdi R.; Neuhart, Danny H.
2012-01-01
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.
Methodology of Blade Unsteady Pressure Measurement in the NASA Transonic Flutter Cascade
NASA Technical Reports Server (NTRS)
Lepicovsky, J.; McFarland, E. R.; Capece, V. R.; Jett, T. A.; Senyitko, R. G.
2002-01-01
In this report the methodology adopted to measure unsteady pressures on blade surfaces in the NASA Transonic Flutter Cascade under conditions of simulated blade flutter is described. The previous work done in this cascade reported that the oscillating cascade produced waves, which for some interblade phase angles reflected off the wind tunnel walls back into the cascade, interfered with the cascade unsteady aerodynamics, and contaminated the acquired data. To alleviate the problems with data contamination due to the back wall interference, a method of influence coefficients was selected for the future unsteady work in this cascade. In this approach only one blade in the cascade is oscillated at a time. The majority of the report is concerned with the experimental technique used and the experimental data generated in the facility. The report presents a list of all test conditions for the small amplitude of blade oscillations, and shows examples of some of the results achieved. The report does not discuss data analysis procedures like ensemble averaging, frequency analysis, and unsteady blade loading diagrams reconstructed using the influence coefficient method. Finally, the report presents the lessons learned from this phase of the experimental effort, and suggests the improvements and directions of the experimental work for tests to be carried out for large oscillation amplitudes.
An analysis of blade vortex interaction aerodynamics and acoustics
NASA Technical Reports Server (NTRS)
Lee, D. J.
1985-01-01
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.
Unsteady wake measurements behind an airfoil and prediction of dynamic stall from the wake
Hamed Sadeghi; Mahmoud Mani; S. M. Hossein Karimian
2010-01-01
Purpose – The primary purpose of this paper is to investigate the characteristics of the unsteady flow field in the wake of Eppler-361 airfoil undergoing harmonic pitch oscillation in both pre-stall and post-stall regimes. Design\\/methodology\\/approach – Experimental measurements were carried out to study the characteristics of the unsteady flow field within the wake of an airfoil. All of the experiments
NASA Technical Reports Server (NTRS)
Zaman, K. B. M. Q.
2004-01-01
The effect of periodic perturbation on jet in cross-flow (JICF) is reviewed. In the first part of the paper, flow visualization result from several past works are discussed. Beginning with description of the characteristic vortex systems of a JICF it is shown that specific perturbation techniques work by organizing and intensifying specific vortex systems. Oscillatory blowing works primarily through an organization of the shear layer vortices. In the second part of the paper, results of an ongoing experiment involving another mechanical perturbation technique are discussed. It involves two tabs at the orifice exit whose asymmetry in placement is reversed periodically. It directly modulates the counter-rotating vortex pair (CVP). Effects of the perturbation for an array of three adjacent orifices are exploded. The flowfield data show an improvement in mixing compared to the unperturbed case.
Aerodynamic sound generated by a wing of complex geometry
NASA Astrophysics Data System (ADS)
Wood, Trevor Howard
2002-09-01
The aerodynamic sound produced by a wing in unsteady flow is computed numerically. A boundary element method is used to calculate both the aerodynamic flow and the sound radiated in an attempt to provide a unified and computationally efficient method. This method is intended to help fill the gap between numerically expensive techniques (e.g., RANS, LES) and analytical methods which are available only for a small subset of the wing geometries of interest. The advances made in the current research are through the incorporation of several previously developed techniques in boundary element and vortex methods and their aggregate application to the present aerodynamic sound problem. The method is capable of modeling general three-dimensional wing geometries with a multiple number of wing elements (e.g., flaps) and with thin shear layer wakes that evolve freely with the unsteady flow. The passage of a vortex filament, which also evolves freely and nonlinearly, can be simulated to study the Blade-Vortex Interaction (BVI) problem. Validations with two-dimensional analytical solutions for parallel BVI show that the lift spectra are computed to within 1 dB up to nondimensional frequencies (scaled by the freestream velocity and the half-chord length) of about 10 using only 40 panels along a streamwise wing section. The parallel BVI problem was used to investigate the effects of wing geometry. These results show that the high frequency response is significantly reduced for high thickness, camber, sweep, and taper, but is increased for high angle of attack and flap deflection angle. The most important parameters affecting the BVI signal is observed to be the minimum separation distance between the vortex filament and the wing. It is shown that the correct separation distance is only achieved when the vortex is modeled as evolving freely and nonlinearly.
Compendium of NASA Langley reports on hypersonic aerodynamics
NASA Technical Reports Server (NTRS)
Sabo, Frances E.; Cary, Aubrey M.; Lawson, Shirley W.
1987-01-01
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.
Aerodynamics and vortical structures in hovering fruitflies
NASA Astrophysics Data System (ADS)
Meng, Xue Guang; Sun, Mao
2015-03-01
We measure the wing kinematics and morphological parameters of seven freely hovering fruitflies and numerically compute the flows of the flapping wings. The computed mean lift approximately equals to the measured weight and the mean horizontal force is approximately zero, validating the computational model. Because of the very small relative velocity of the wing, the mean lift coefficient required to support the weight is rather large, around 1.8, and the Reynolds number of the wing is low, around 100. How such a large lift is produced at such a low Reynolds number is explained by combining the wing motion data, the computed vortical structures, and the theory of vorticity dynamics. It has been shown that two unsteady mechanisms are responsible for the high lift. One is referred as to "fast pitching-up rotation": at the start of an up- or downstroke when the wing has very small speed, it fast pitches down to a small angle of attack, and then, when its speed is higher, it fast pitches up to the angle it normally uses. When the wing pitches up while moving forward, large vorticity is produced and sheds at the trailing edge, and vorticity of opposite sign is produced near the leading edge and on the upper surface, resulting in a large time rate of change of the first moment of vorticity (or fluid impulse), hence a large aerodynamic force. The other is the well known "delayed stall" mechanism: in the mid-portion of the up- or downstroke the wing moves at large angle of attack (about 45 deg) and the leading-edge-vortex (LEV) moves with the wing; thus, the vortex ring, formed by the LEV, the tip vortices, and the starting vortex, expands in size continuously, producing a large time rate of change of fluid impulse or a large aerodynamic force.
NASA Astrophysics Data System (ADS)
Cain, T.; Owen, R.; Walton, C.
2005-02-01
The scramjet flight test Hyshot-2, flew on the 30 July 2002. The programme, led by the University of Queensland, had the primary objective of obtaining supersonic combustion data in flight for comparison with measurements made in shock tunnels. QinetiQ was one of the sponsors, and also provided aerodynamic data and trajectory predictions for the ballistic re-entry of the spinning sounding rocket. The unconventional missile geometry created by the nose-mounted asymmetric-scramjet in conjunction with the high angle of attack during re-entry makes the problem interesting. This paper presents the wind tunnel measurements and aerodynamic calculations used as input for the trajectory prediction. Indirect comparison is made with data obtained in the Hyshot-2 flight using a 6 degree-of-freedom trajectory simulation.
NASA Astrophysics Data System (ADS)
Zhang, L. P.; Chang, X. H.; Duan, X. P.; Zhang, H. X.
For very insect such as tiny wasp Encarsaria Formosa, Weis-Fogh found that the ‘clap-fling’ mechanism of their wings is the main cause for their large lift. In this paper, we simulate the motion numerically and analyze the generation of large lift by the wings with an unsteady incompressible flow solver based on dynamic hybrid mesh. Both one wing flapping and two wings ‘clap and fling’ are considered in the Reynolds number range of 8-128, the difference on flow structures and aerodynamic forces are compared with each other, and then high lift mechanism is analyzed.
NASA Technical Reports Server (NTRS)
Hoyniak, D.; Fleeter, S.
1985-01-01
The effects of alternate-blade structural detuning and adjacent-blade alternate-circumferential-spacing aerodynamic detuning on the supersonic unstalled torsional flutter stability of a turbomachine rotor are investigated analytically. An unsteady aerodynamic model employing influence coefficients is constructed for the case of a flat-plate-airfoil cascade in torsion-mode harmonic oscillation in a supersonic inviscid isentropic adiabatic irrotational perfect-gas inlet flow with a subsonic leading-edge locus. The influence coefficients and equations of motion are derived; the model is verified by applying it to the 12-blade cascade-B flow geometry studied by Verdon and McCune (1975); and the results are presented graphically. It is found that the rotor can be stabilized over the entire reduced frequency range by applying a combination of structural and aerodynamic detuning as the passive flutter-control mechanism.
NASA Technical Reports Server (NTRS)
Cole, Jennifer Hansen
2010-01-01
This slide presentation reviews some of the basic principles of aerodynamics. Included in the presentation are: a few demonstrations of the principles, an explanation of the concepts of lift, drag, thrust and weight, a description of Bernoulli's principle, the concept of the airfoil (i.e., the shape of the wing) and how that effects lift, and the method of controlling an aircraft by manipulating the four forces using control surfaces.
Evaluation of Turbulence Models for Unsteady Flows of an Oscillating Airfoil
NASA Technical Reports Server (NTRS)
Srinivasan, G. R.; Ekaterinaris, J. A.; McCroskey, W. J.
1995-01-01
Unsteady flowfields of a two-dimensional oscillating airfoil are calculated using an implicit, finite-difference, Navier Stokes numerical scheme. Five widely used turbulence models are used with the numerical scheme to assess the accuracy and suitability of the models for simulating the retreating blade stall of helicopter rotor in forward flight. Three unsteady flow conditions corresponding to an essentially attached flow, light-stall, and deep-stall cases of an oscillating NACA 0015 wing experiment were chosen as test cases for computations. Results of unsteady airloads hysteresis curves, harmonics of unsteady pressures, and instantaneous flowfield patterns are presented. Some effects of grid density, time-step size, and numerical dissipation on the unsteady solutions relevant to the evaluation of turbulence models are examined. Comparison of unsteady airloads with experimental data show that all models tested are deficient in some sense and no single model predicts airloads consistently and in agreement with experiment for the three flow regimes. The chief findings are that the simple algebraic model based on the renormalization group theory (RNG) offers some improvement over the Baldwin Lomax model in all flow regimes with nearly same computational cost. The one-equation models provide significant improvement over the algebraic and the half-equation models but have their own limitations. The Baldwin-Barth model overpredicts separation and underpredicts reattachment. In contrast, the Spalart-Allmaras model underpredicts separation and overpredicts reattachment.
Inherently unsteady flame spread to extinction over thick fuels in microgravity
Robert A. Altenkirch; Lin Tang; Kurt Sacksteder; Subrata Bhattacharjee; Michael A. Delichatsios
1998-01-01
Results of an experiment for flame spread over thick PMMA in a quiescent, 50% O2 in N2, 1 atm, microgravity environment recently obtained aboard space shuttle mission STS 85 are described. Previous experimental results indicate that the spread process is unsteady with the spread rate decreasing with time. Although experiment time in the earlier experiments was insufficient to determine if
Aerodynamic database development of the ESA intermediate experimental vehicle
NASA Astrophysics Data System (ADS)
Pezzella, Giuseppe; Marino, Giuliano; Rufolo, Giuseppe C.
2014-01-01
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.
Aerodynamic measurements concerned with a turret model
NASA Technical Reports Server (NTRS)
Raman, K. R.
1981-01-01
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.
Oscillating cascade aerodynamics at large mean incidence
NASA Technical Reports Server (NTRS)
Buffum, Daniel H.; King, Aaron J.; El-Aini, Yehia M.; Capece, Vincent R.
1996-01-01
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.
NASA Technical Reports Server (NTRS)
Hah, Chunill
2011-01-01
The current paper reports on an investigation of steady and unsteady flow effects of circumferential grooves casing treatment in a transonic compressor rotor. Circumferential grooves casing treatment is used mainly to increase stall margin in axial compressors with a relatively small decrease in aerodynamic efficiency. It is widely believed that flow mechanisms of circumferential grooves casing treatment near stall conditions are not yet well understood even though this treatment has been used widely in real engines. Numerical analysis based on steady Reynolds-averaged Navier-Stokes (RANS) has been the primary tool used to understand flow mechanism for circumferential grooves casing treatment. Although steady RANS explains some flow effects of circumferential grooves casing treatment, it does not calculate all the measured changes in the compressor characteristics. Therefore, design optimization of circumferential grooves with steady RANS has not been very successful. As a compressor operates toward the stall condition, the flow field becomes transient. Major sources of self-generated flow unsteadiness are shock oscillation and interaction between the passage shock and the tip leakage vortex. In the present paper, an unsteady Reynolds-averaged Navier-Stokes (URANS) approach is applied to study the effects of circumferential grooves in a transonic compressor. The results from URANS are compared with the results from RANS and measured data. The current investigation shows that there are significant unsteady flow effects on the performance of the circumferential grooves casing treatment. For the currently investigated rotor, the unsteady effects are of the same magnitude as the steady effects in terms of extending the compressor stall margin.
Unsteady transonic potential flow over a flexible fuselage
NASA Technical Reports Server (NTRS)
Gibbons, Michael D.
1993-01-01
A flexible fuselage capability has been developed and implemented within version 1.2 of the CAP-TSD code. The capability required adding time dependent terms to the fuselage surface boundary conditions and the fuselage surface pressure coefficient. The new capability will allow modeling the effect of a flexible fuselage on the aeroelastic stability of complex configurations. To assess the flexible fuselage capability several steady and unsteady calculations have been performed for slender fuselages with circular cross-sections. Steady surface pressures are compared with experiment at transonic flight conditions. Unsteady cross-sectional lift is compared with other analytical results at a low subsonic speed and a transonic case has been computed. The comparisons demonstrate the accuracy of the flexible fuselage modifications.
Robustness of de Saint Venant equations for simulating unsteady flows
Baltzer, Robert A.; Schaffranek, Raymond W.; Lai, Chintu
1995-01-01
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.
Conservation-form equations of unsteady open-channel flow
Lai, C.; Baltzer, R.A.; Schaffranek, R.W.
2002-01-01
The unsteady open-channel flow equations are typically expressed in a variety of forms due to the imposition of differing assumptions, use of varied dependent variables, and inclusion of different source/sink terms. Questions often arise as to whether a particular equation set is expressed in a form consistent with the conservation-law definition. The concept of conservation form is developed to clarify the meaning mathematically. Six sets of unsteady-flow equations typically used in engineering practice are presented and their conservation properties are identified and discussed. Results of the theoretical development and analysis of the equations are substantiated in a set of numerical experiments conducted using alternate equation forms. Findings of these analytical and numerical efforts demonstrate that the choice of dependent variable is the fundamental factor determining the nature of the conservation properties of any particular equation form.
NASA Technical Reports Server (NTRS)
Singh, Kamakhya Prasad
1995-01-01
A new methodology is developed to simulate unsteady flows about prescribed and aerodynamically determined moving boundary problems. The method couples the fluid dynamics and rigid-body dynamics equations to capture the time-dependent interference between stationary and moving boundaries. The unsteady, compressible, inviscid (Euler) equations are solved on dynamic, unstructured grids by an explicit, finite-volume, upwind method. For efficiency, the grid adaptation is performed within a window around the moving object. The Eulerian equations of the rigid-body dynamics are solved by a Runge-Kutta method in a non-inertial frame of reference. The two-dimensional flow solver is validated by computing the flow past a sinusoidally-pitching airfoil and comparing these results with the experimental data. The overall methodology is used for two two-dimensional examples: the flow past an airfoil which is performing a three-degrees-of-freedom motion in a transonic freestream, and the free-fall of a store after separation from a wing-section. Then the unstructured mesh methodology is extended to three-dimensions to simulate unsteady flow past bodies in relative motion, where the trajectory is determined from the instantaneous aerodynamics. The flow solver and the adaptation scheme in three dimensions are validated by simulating the transonic, unsteady flow around a wing undergoing a forced, periodic, pitching motion, and comparing the results with the experimental data. To validate the trajectory code, the six-degrees-of-freedom motion of a store separating from a wing was computed using the experimentally determined force and moment fields, then comparing with an independently generated trajectory. Finally, the overall methodology was demonstrated by simulating the unsteady flowfield and the trajectory of a store dropped from a wing. The methodology, its computational cost notwithstanding, has proven to be accurate, automated, easy for dynamic gridding, and relatively efficient for the required man-hours.
TAD- THEORETICAL AERODYNAMICS PROGRAM
NASA Technical Reports Server (NTRS)
Barrowman, J.
1994-01-01
This theoretical aerodynamics program, TAD, was developed to predict the aerodynamic characteristics of vehicles with sounding rocket configurations. These slender, axisymmetric finned vehicle configurations have a wide range of aeronautical applications from rockets to high speed armament. Over a given range of Mach numbers, TAD will compute the normal force coefficient derivative, the center-of-pressure, the roll forcing moment coefficient derivative, the roll damping moment coefficient derivative, and the pitch damping moment coefficient derivative of a sounding rocket configured vehicle. The vehicle may consist of a sharp pointed nose of cone or tangent ogive shape, up to nine other body divisions of conical shoulder, conical boattail, or circular cylinder shape, and fins of trapezoid planform shape with constant cross section and either three or four fins per fin set. The characteristics computed by TAD have been shown to be accurate to within ten percent of experimental data in the supersonic region. The TAD program calculates the characteristics of separate portions of the vehicle, calculates the interference between separate portions of the vehicle, and then combines the results to form a total vehicle solution. Also, TAD can be used to calculate the characteristics of the body or fins separately as an aid in the design process. Input to the TAD program consists of simple descriptions of the body and fin geometries and the Mach range of interest. Output includes the aerodynamic characteristics of the total vehicle, or user-selected portions, at specified points over the mach range. The TAD program is written in FORTRAN IV for batch execution and has been implemented on an IBM 360 computer with a central memory requirement of approximately 123K of 8 bit bytes. The TAD program was originally developed in 1967 and last updated in 1972.
Gomes, Lara Elena; Loss, Jefferson Fagundes
2015-08-01
The understanding of swimming propulsion is a key factor in the improvement of performance in this sport. Propulsive forces have been quantified under steady conditions since the 1970s, but actual swimming involves unsteady conditions. Thus, the purpose of the present article was to review the effects of unsteady conditions on swimming propulsion based on studies that have compared steady and unsteady conditions while exploring their methods, their limitations and their results, as well as encouraging new studies based on the findings of this systematic review. A multiple database search was performed, and only those studies that met all eligibility criteria were included. Six studies that compared steady and unsteady conditions using physical experiments or numerical simulations were selected. The selected studies verified the effects of one or more factors that characterise a condition as unsteady on the propulsive forces. Consequently, much research is necessary to understand the effect of each individual variable that characterises a condition as unsteady on swimming propulsion, as well as the effects of these variables as a whole on swimming propulsion. PMID:25707429
Numerical Aerodynamic Simulation (NAS)
NASA Technical Reports Server (NTRS)
Peterson, V. L.; Ballhaus, W. F., Jr.; Bailey, F. R.
1983-01-01
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.
Aerodynamics: The Mathematical Implications
NSDL National Science Digital Library
Smikle, Hermine E.
2000-03-11
This unit from the Yale-New Haven Teachers Institute is "an attempt to develop a unit in mathematics that will provide topics for students interested in the aviation trades." The unit can be used to cover all areas of mathematics from areas in geometry sectors to basic addition of fraction and decimal numbers. These general math concepts will be introduced using aerodynamics and aviation language and it is hoped that students will begin "to understand the applicability of some of the mathematics concepts they have learned." This curriculum unit also includes sample lesson plans and references.
On Wings: Aerodynamics of Eagles.
ERIC Educational Resources Information Center
Millson, David
2000-01-01
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)
Aerodynamic design via control theory
Antony Jameson
1988-01-01
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
Aerodynamics of a Party Balloon
ERIC Educational Resources Information Center
Cross, Rod
2007-01-01
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…
Aerodynamics of runback ice accretions
Edward A. Whalen
2007-01-01
An experimental study of the effects of simulated runback ice accretions has been performed in order to describe their aerodynamic performance penalties and investigate their scaling for use in sub-scale aerodynamic testing. Runback ice accretions corresponding to three flight conditions, warm hold, cold hold and descent, were simulated and tested on the NACA 23012 and NACA 3415. The ice shapes
Inner workings of aerodynamic sweep
A. R. Wadia; P. N. Szucs; D. W. Crall
1998-01-01
The recent trend in using aerodynamic sweep to improve the performance of transonic blading has been one of the more significant technological evolutions for compression components in turbomachinery. This paper reports on the experimental and analytical assessment of the pay-off derived from both aft and forward sweep technology with respect to aerodynamic performance and stability. The single-stage experimental investigation includes
Not Available
1990-01-01
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.
Ground/Flight Correlation of Aerodynamic Loads with Structural Response
NASA Technical Reports Server (NTRS)
Mangalam, Arun S.; Davis, Mark C.
2009-01-01
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.
NASA Technical Reports Server (NTRS)
Zahm, A F
1924-01-01
This report gives the description and the use of a specially designed aerodynamic plane table. For the accurate and expeditious geometrical measurement of models in an aerodynamic laboratory, and for miscellaneous truing operations, there is frequent need for a specially equipped plan table. For example, one may have to measure truly to 0.001 inch the offsets of an airfoil at many parts of its surface. Or the offsets of a strut, airship hull, or other carefully formed figure may require exact calipering. Again, a complete airplane model may have to be adjusted for correct incidence at all parts of its surfaces or verified in those parts for conformance to specifications. Such work, if but occasional, may be done on a planing or milling machine; but if frequent, justifies the provision of a special table. For this reason it was found desirable in 1918 to make the table described in this report and to equip it with such gauges and measures as the work should require.
NASA Technical Reports Server (NTRS)
Takashima, Naruhisa; Wilmoth, Richard G.
2002-01-01
Direct Simulation Monte Carlo and free-molecular analyses were used to provide aerothermodynamic characteristics of the Mars Odyssey spacecraft. The results of these analyses were used to develop an aerodynamic database that was used extensively for the pre-flight planning and in-flight execution for the aerobraking phase of the Mars Odyssey mission. During aerobraking operations, the database was used to reconstruct atmospheric density profiles during each pass. The reconstructed data was used to update the atmospheric model, which was used to determine the strategy for subsequent aerobraking maneuvers. The aerodynamic database was also used together with data obtained from on-board accelerometers to reconstruct the spacecraft attitudes throughout each aerobraking pass. The reconstructed spacecraft attitudes are in good agreement with those determined by independent on-board inertial measurements for all aerobraking passes. The differences in the pitch attitudes are significantly less than the preflight uncertainties of +/-2.9%. The differences in the yaw attitudes are influenced by zonal winds. When latitudinal gradients of density are small, the differences in the yaw attitudes are significantly less than the preflight uncertainties.
Steady and unsteady transonic small disturbance analysis of realistic aircraft configurations
NASA Technical Reports Server (NTRS)
Batina, John T.; Seidel, David A.; Bennett, Robert M.; Cunningham, Herbert J.; Bland, Samuel R.
1988-01-01
A transonic unsteady aerodynamic and aeroelasticity code CAP-TSD (Computational Aeroelasticity Program-Transonic Small Disturbance) has been developed for application to realistic aircraft configurations. The code uses a time-accurate approximate factorization (AF) algorithm for solution of the unsteady transonic small-disturbance potential equation. The paper gives an overview of the CAP-TSD code development effort and reports on recent algorithm modifications. The algorithm modifications include: an Engquist-Osher (E-O) type-dependent switch to treat regions of supersonic flow, extension of the E-O switch for second-order spatial accuracy, nonisentropic effects to treat strong-shock cases, nonreflecting far field boundary conditions for unsteady applications, and several modifications to accelerate convergence to steady state. The modifications have significantly improved the stability of the AF algorithm and hence the reliability of the CAP-TSD code in general. Calculations are also presented from a flutter analysis of a 45-deg sweptback wing which agree well with experimental data. The paper present descriptions of the CAP-TSD code and algorithm details along with results.
Steady and unsteady transonic small disturbance analysis of realistic aircraft configurations
NASA Technical Reports Server (NTRS)
Batina, John T.; Seidel, David A.; Bennett, Robert M.; Cunningham, Herbert J.; Bland, Samuel R.
1989-01-01
A transonic unsteady aerodynamic and aeroelastic code called CAP-TSD (Computational Aeroelasticity Program - Transonic Small Disturbance) was developed for application to realistic aircraft configurations. It permits the calculation of steady and unsteady flows about complete aircraft configurations for aeroelastic analysis of the flutter critical transonic speed range. The CAP-TSD code uses a time accurate approximate factorization algorithm for solution of the unsteady transonic small disturbance potential equation. An overview is given of the CAP-TSD code development effort along with recent algorithm modifications which are listed and discussed. Calculations are presented for several configurations including the General Dynamics 1/9th scale F-16C aircraft model to evaluate the algorithm and hence the reliability of the CAP-TSD code in general. Calculations are also presented for a flutter analysis of a 45 deg sweptback wing which agree well with the experimental data. Descriptions are presented of the CAP-TSD code and algorithm details along with results and comparisons which demonstrate the stability, accuracy, efficiency, and utility of CAP-TSD.
Forced unsteady deceleration of a turbulent boundary layer from a temporal perspective
NASA Technical Reports Server (NTRS)
Brereton, G. J.
1992-01-01
The behavior of a turbulent boundary layer which has been subjected to a local ramp-like deceleration in the external velocity field, which leads to forced separation, has been studied experimentally. The data of this study are re-interpreted in light of more recent findings concerning the temporal nature of boundary layer turbulence in the presence of forced unsteady shear. In particular, the robustness of the near-wall turbulent motions to organized deformation is recognized. Their resilence during unsteady shearing action promotes continued efficient turbulent mixing and rapid redistribution of turbulent kinetic energy during forced transients. In aerodynamic problems, the rapid nature of the adjustment of the turbulence field to a new temporal boundary condition necessitates equally rapid remedial measures to be taken if means of control/prevention of forced unsteady separation are to be deployed to maximum effect. This requirement suggests exploration of the use of simple, real-time statistical forecasting techniques, based upon time-series analysis of easily-measurable features of the flow, to help assure timely deployment of mechanisms of boundary-layer control. This paper focuses upon the nature of turbulence in boundary layers undergoing forced deceleration which would lead to separation. A preliminary form of a forecasting model is presented and evaluated. Using observations of the previous two large eddies passing a detector, it forecasts the behavior of the future large eddy rather well.
Numerical simulation of unsteady viscous flows
NASA Technical Reports Server (NTRS)
Hankey, Wilbur L.
1987-01-01
Most unsteady viscous flows may be grouped into two categories, i.e., forced and self-sustained oscillations. Examples of forced oscillations occur in turbomachinery and in internal combustion engines while self-sustained oscillations prevail in vortex shedding, inlet buzz, and wing flutter. Numerical simulation of these phenomena was achieved due to the advancement of vector processor computers. Recent progress in the simulation of unsteady viscous flows is addressed.
Measurement of unsteady pressures in rotating systems
NASA Technical Reports Server (NTRS)
Kienappel, K.
1978-01-01
The principles of the experimental determination of unsteady periodic pressure distributions in rotating systems are reported. An indirect method is discussed, and the effects of the centrifugal force and the transmission behavior of the pressure measurement circuit were outlined. The required correction procedures are described and experimentally implemented in a test bench. Results show that the indirect method is suited to the measurement of unsteady nonharmonic pressure distributions in rotating systems.
Computation of rotor aerodynamic loads in forward flight using a full-span free wake analysis
NASA Technical Reports Server (NTRS)
Quackenbush, Todd R.; Bliss, Donald B.; Wachspress, Daniel A.; Boschitsch, Alexander H.; Chua, Kiat
1990-01-01
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.
Efficient Helicopter Aerodynamic and Aeroacoustic Predictions on Parallel Computers
NASA Technical Reports Server (NTRS)
Wissink, Andrew M.; Lyrintzis, Anastasios S.; Strawn, Roger C.; Oliker, Leonid; Biswas, Rupak
1996-01-01
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.
NASA Technical Reports Server (NTRS)
Smith, J. H. B.; Campbell, J. F.; Young, A. D. (editor)
1992-01-01
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.
Modelling and Simulation in Aerodynamic Design
Mosegaard, Klaus
Modelling and Simulation in Aerodynamic Design In different kinds of aerodynamic design elements is too complex. Aerodynamic properties of different airfoils are found from either numerical turbine blade, two design features are important. The aerodynamic design attempts to optimize the blade
Efficient aerodynamic shape optimization in MDO context
Antonio Fazzolari; Nicolas R. Gauger; Joel Brezillon
2007-01-01
Multidisciplinary analysis is necessary to reach physically meaningful optimum designs. For aero-structural shape optimization this means coupling two disciplines—aerodynamics and structural mechanics. In this paper, the sensitivity evaluation for aerodynamic shape optimization is considered, while taking into account the static aeroelastic effects introduced by the variations in the aerodynamic forces, which are associated with changes in the aerodynamic shape. Due
Survey of lift-fan aerodynamic technology
NASA Technical Reports Server (NTRS)
Hickey, David H.; Kirk, Jerry V.
1993-01-01
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.
High-order accurate, low numerical diffusion methods for aerodynamics
NASA Astrophysics Data System (ADS)
Ekaterinaris, John A.
2005-04-01
In recent years numerical methods have been widely used to effectively resolve complex flow features of aerodynamics flows with meshes that are reasonable for today's computers. High-order numerical methods were used mainly in direct numerical simulations and aeroacoustics. For many aeronautical applications, accurate computation of vortex-dominated flows is important because the vorticity in the flow field and the wake of swept wings at an incidence and rotor blades largely determines the distribution of loading. The main deficiency of widely available, second-order accurate methods for the accurate computation of these flows is the numerical diffusion of vorticity to unacceptable levels. Application of high-order accurate, low-diffusion numerical methods can significantly alleviate this deficiency of traditional second order methods. Furthermore, higher-order space discretizations have the potential to improve detached eddy simulation predictions of separated flows with significant unsteadiness. Recently developed high-order accurate finite-difference, finite-volume, and finite-element methods are reviewed. These methods can be used as an attractive alternative of traditional low-order central and upwind computational fluid dynamics methods for improved predictions of vortical and other complex, separated, unsteady flows. The main features of these methods are summarized, from a practical user's point of view, their applicability and relative strength is indicated, and examples from recent applications are presented to illustrate their performance on selected problems.
Structural dynamics and aerodynamics measurements of biologically inspired flexible flapping wings.
Wu, P; Stanford, B K; Sällström, E; Ukeiley, L; Ifju, P G
2011-03-01
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
An adjoint method for shape optimization in unsteady viscous flows
NASA Astrophysics Data System (ADS)
Srinath, D. N.; Mittal, Sanjay
2010-03-01
A new method for shape optimization for unsteady viscous flows is presented. It is based on the continuous adjoint approach using a time accurate method and is capable of handling both inverse and direct objective functions. The objective function is minimized or maximized subject to the satisfaction of flow equations. The shape of the body is parametrized via a Non-Uniform Rational B-Splines (NURBS) curve and is updated by using the gradients obtained from solving the flow and adjoint equations. A finite element method based on streamline-upwind Petrov/Galerkin (SUPG) and pressure stabilized Petrov/Galerkin (PSPG) stabilization techniques is used to solve both the flow and adjoint equations. The method has been implemented and tested for the design of airfoils, based on enhancing its time-averaged aerodynamic coefficients. Interesting shapes are obtained, especially when the objective is to produce high performance airfoils. The effect of the extent of the window of time integration of flow and adjoint equations on the design process is studied. It is found that when the window of time integration is insufficient, the gradients are most likely to be erroneous.
An unsteady lifting surface method for single rotation propellers
NASA Technical Reports Server (NTRS)
Williams, Marc H.
1990-01-01
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.
Prediction of the aerodynamic environment and heat transfer for rotor-stator configurations
NASA Astrophysics Data System (ADS)
Griffin, L. W.; McConnaughey, H. V.
1989-06-01
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.
Prediction of the aerodynamic environment and heat transfer for rotor-stator configurations
NASA Technical Reports Server (NTRS)
Griffin, L. W.; Mcconnaughey, H. V.
1989-01-01
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.
On Sound Generated Aerodynamically. II. Turbulence as a Source of Sound
M. J. Lighthill
1954-01-01
The theory of sound generated aerodynamically is extended by taking into account the statistical properties of turbulent airflows, from which the sound radiated (without the help of solid boundaries) is called aerodynamic noise. The theory is developed with special reference to the noise of jets, for which a detailed comparison with experiment is made (section 7 for subsonic jets, section
Computational aerodynamics and artificial intelligence
NASA Technical Reports Server (NTRS)
Mehta, U. B.; Kutler, P.
1984-01-01
The general principles of artificial intelligence are reviewed and speculations are made concerning how knowledge based systems can accelerate the process of acquiring new knowledge in aerodynamics, how computational fluid dynamics may use expert systems, and how expert systems may speed the design and development process. In addition, the anatomy of an idealized expert system called AERODYNAMICIST is discussed. Resource requirements for using artificial intelligence in computational fluid dynamics and aerodynamics are examined. Three main conclusions are presented. First, there are two related aspects of computational aerodynamics: reasoning and calculating. Second, a substantial portion of reasoning can be achieved with artificial intelligence. It offers the opportunity of using computers as reasoning machines to set the stage for efficient calculating. Third, expert systems are likely to be new assets of institutions involved in aeronautics for various tasks of computational aerodynamics.
Computational aerodynamics and artificial intelligence
NASA Technical Reports Server (NTRS)
Kutler, P.; Mehta, U. B.
1984-01-01
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.
Aerodynamics at the Particle Level
Charles A. Crummer
2012-09-23
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.
Aerodynamic Drag and Gyroscopic Stability
Elya R. Courtney; Michael W. Courtney
2014-10-16
This paper describes the effects on aerodynamic drag of rifle bullets as the gyroscopic stability is lowered from 1.3 to 1.0. It is well known that a bullet can tumble for stability less than 1.0. The Sierra Loading Manuals (4th and 5th Editions) have previously reported that ballistic coefficient decreases significantly as gyroscopic stability, Sg, is lowered below 1.3. These observations are further confirmed by experiments reported here. Measured ballistic coefficients were compared with gyroscopic stabilities computed using the Miller Twist Rule for nearly solid metal bullets with uniform density and computed using the Courtney-Miller formula for plastic-tipped bullets. The relationship between Sg and drag may be used to test the applicability of existing gyroscopic stability formulas for given bullet designs and to evaluate the accuracy of alternate formulas in cases where the existing stability formulas are not as accurate. The most definitive test of formulas predicting stability will always be observation of whether bullets tumble under given conditions. However, observations of drag changes provide valuable supplemental information because they suggest changes in stability as conditions change. Use of a continuous variable (drag) rather than a binary variable (tumbling) allows insight into stability over a range of conditions where the binary variable does not change.
Non-linear unsteady wing theory, part 1. Quasi two-dimensional behavior: Airfoils and slender wings
NASA Technical Reports Server (NTRS)
Mccune, J. E.
1987-01-01
The initial phases of a study of the large-amplitude unsteady aerodynamics of wings in severe maneuver are reported. The research centers on vortex flows, their initiation at wing surfaces, their subsequent convection, and interaction dynamically with wings and control surfaces. The focus is on 2D and quasi-2D aspects of the problem and features the development of an exact nonlinear unsteady airfoil theory as well as an approach to the crossflow problem for slender wing applications including leading-edge separation. The effective use of interactive on-line computing in quantifying and visualizing the nonsteady effects of severe maneuver is demonstrated. Interactive computational work is now possible, in which a maneuver can be initiated and its effects observed and analyzed immediately.
Some aspects of unsteady separation
NASA Technical Reports Server (NTRS)
Smith, C. R.; Walker, J. D. A.
1992-01-01
Unsteady separation can be forced in a variety of ways and in this presentation two fundamental means will be considered: (1) the introduction of convected vorticular disturbances into the flow; and (2) the influence of a specific type of three-dimensional geometry. In both situations a response of the viscous flow near the wall is provoked wherein the fluid near the surface abruptly focuses into a narrow region that erupts from the surface into the mainstream. In two-dimensional flows, the eruption takes the form of a narrow, explosively-growing spike, while in three-dimensional situations, examples are presented which indicate that the eruption is along a narrow zone in the shape of a crescent-shaped plume. The nature of the three-dimensional flow near a circular cylinder, which is mounted normal to a flat plate, is also examined in this study. Here the three-dimensional geometry induces complex three-dimensional separations periodically. The dynamics of the generation process is studied experimentally in a water channel using hydrogen bubble wires and a laser sheet, and the main features of the laminar regime through to transition are documented.
Plotting Program For Aerodynamical Computations
NASA Technical Reports Server (NTRS)
Wigren, L. J.; Lovely, P. K.
1992-01-01
Panel Method Aerodynamic Plotting Program (PMAPP) written to plot results of aerodynamical analyses (flow data) from PMARC (ARC-12642), program for computation of three-dimensional flow by low-order panel method. PMAPP is interactive, color-capable graphics program designed to work with variety of computer terminals and printers. Also used to plot data from other programs, provided files containing those data defined according to PMARC conventions. Written in FORTRAN 77.
Explanation and discovery in aerodynamics
Gordon McCabe
2005-12-22
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.
Differential Evolution in Aerodynamic Optimization
T. Rogalsky; R. W. Derksen; S. Kocabiyik
1999-01-01
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...
Supersonic aerodynamics of delta wings
NASA Technical Reports Server (NTRS)
Wood, Richard M.
1988-01-01
Through the empirical correlation of experimental data and theoretical analysis, a set of graphs has been developed which summarize the inviscid aerodynamics of delta wings at supersonic speeds. The various graphs which detail the aerodynamic performance of delta wings at both zero-lift and lifting conditions were then employed to define a preliminary wing design approach in which both the low-lift and high-lift design criteria were combined to define a feasible design space.
Aerodynamic transfer of energy to the vocal folds
NASA Astrophysics Data System (ADS)
Thomson, Scott L.; Mongeau, Luc; Frankel, Steven H.
2005-09-01
The aerodynamic transfer of energy from glottal airflow to vocal fold tissue during phonation was explored using complementary synthetic and numerical vocal fold models. The synthetic model was fabricated using a flexible polyurethane rubber compound. The model size, shape, and material properties were generally similar to corresponding human vocal fold characteristics. Regular, self-sustained oscillations were achieved at a frequency of approximately 120 Hz. The onset pressure was approximately 1.2 kPa. A corresponding two-dimensional finite element model was developed using geometry definitions and material properties based on the synthetic model. The finite element model upstream and downstream pressure boundary conditions were based on experimental values acquired using the synthetic model. An analysis of the fully coupled fluid and solid numerical domains included flow separation and unsteady effects. The numerical results provided detailed flow data that was used to investigate aerodynamic energy transfer mechanisms. The results support the hypothesis that a cyclic variation of the orifice profile from a convergent to a divergent shape leads to a temporal asymmetry in the average wall pressure, which is the key factor for the achievement of self-sustained vocal fold oscillations.
Aerodynamic transfer of energy to the vocal folds.
Thomson, Scott L; Mongeau, Luc; Frankel, Steven H
2005-09-01
The aerodynamic transfer of energy from glottal airflow to vocal fold tissue during phonation was explored using complementary synthetic and numerical vocal fold models. The synthetic model was fabricated using a flexible polyurethane rubber compound. The model size, shape, and material properties were generally similar to corresponding human vocal fold characteristics. Regular, self-sustained oscillations were achieved at a frequency of approximately 120 Hz. The onset pressure was approximately 1.2 kPa. A corresponding two-dimensional finite element model was developed using geometry definitions and material properties based on the synthetic model. The finite element model upstream and downstream pressure boundary conditions were based on experimental values acquired using the synthetic model. An analysis of the fully coupled fluid and solid numerical domains included flow separation and unsteady effects. The numerical results provided detailed flow data that was used to investigate aerodynamic energy transfer mechanisms. The results support the hypothesis that a cyclic variation of the orifice profile from a convergent to a divergent shape leads to a temporal asymmetry in the average wall pressure, which is the key factor for the achievement of self-sustained vocal fold oscillations. me rica. PMID:16240827
Transonic aerodynamic and aeroelastic characteristics of a variable sweep wing
NASA Technical Reports Server (NTRS)
Goorjian, P. M.; Guruswamy, G. P.; Ide, H.; Miller, G.
1985-01-01
The flow over the B-1 wing is studied computationally, including the aeroelastic response of the wing. Computed results are compared with results from wind tunnel and flight tests for both low-sweep and high-sweep cases, at 25.0 deg. and 67.5 deg., respectively, for selected transonic Mach numbers. The aerodynamic and aeroelastic computations are made by using the transonic unsteady code ATRAN3S. Steady aerodynamic computations compare well with wind tunnel results for the 25.0 deg. sweep case and also for small angles of attack at the 67.5 deg. sweep case. The aeroelastic response results show that the wing is stable at the low sweep angle for the calculation at the Mach number at which there is a shock wave. In the higher sweep case, for the higher angle of attack at which oscillations were observed in the flight and wind tunnel tests, the calculations do not show any shock waves. Their absence lends support to the hypothesis that the observed oscillations are due to the presence of leading edge separation vortices and are not due to shock wave motion as was previously proposed.
NASA Astrophysics Data System (ADS)
Caplot, M.; Haertig, J.
The aerodynamic analysis used by the present numerical and experimental study of blade-vortex interactions is based on the computation of the velocity potential in a two-dimensional, incompressible, inviscid and unsteady flow. The pressure, lift, and drag coefficients deduced from theoretical instantaneous velocity field results obtained around a lifting Joukowski airfoil under the action of an incident vortex are compared with water tunnel measurements; good agreement is noted. Two-dimensional data are transformed in order to study the case of a helicopter rotor's parallel blade-vortex interaction.
Prediction of oscillating thick cambered aerofoil aerodynamics by a locally analytic method
NASA Technical Reports Server (NTRS)
Chiang, Hsiao-Wei D.; Fleeter, Sanford
1988-01-01
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.
Unsteady specific work and isentropic efficiency of a radial turbine driven by pulsed detonations
NASA Astrophysics Data System (ADS)
Rouser, Kurt P.
There has been longstanding government and industry interest in pressure-gain combustion for use in Brayton cycle based engines. Theoretically, pressure-gain combustion allows heat addition with reduced entropy loss. The pulsed detonation combustor (PDC) is a device that can provide such pressure-gain combustion and possibly replace typical steady deflagration combustors. The PDC is inherently unsteady, however, and comparisons with conventional steady deflagration combustors must be based upon time-integrated performance variables. In this study, the radial turbine of a Garrett automotive turbocharger was coupled directly to and driven, full admission, by a PDC in experiments fueled by hydrogen or ethylene. Data included pulsed cycle time histories of turbine inlet and exit temperature, pressure, velocity, mass flow, and enthalpy. The unsteady inlet flowfield showed momentary reverse flow, and thus unsteady accumulation and expulsion of mass and enthalpy within the device. The coupled turbine-driven compressor provided a time-resolved measure of turbine power. Peak power increased with PDC fill fraction, and duty cycle increased with PDC frequency. Cycle-averaged unsteady specific work increased with fill fraction and frequency. An unsteady turbine efficiency formulation is proposed, including heat transfer effects, enthalpy flux-weighted total pressure ratio, and ensemble averaging over multiple cycles. Turbine efficiency increased with frequency but was lower than the manufacturer reported conventional steady turbine efficiency.
Current Issues in Unsteady Turbomachinery Flows (Images)
NASA Technical Reports Server (NTRS)
Povinelli, Louis
2004-01-01
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.
Unsteady penetration of a target by a liquid jet
Uth, Tobias; Deshpande, Vikram S.
2013-01-01
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
Unsteady penetration of a target by a liquid jet.
Uth, Tobias; Deshpande, Vikram S
2013-12-10
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
Supersonic unstalled flutter. [aerodynamic loading of thin airfoils induced by cascade motion
NASA Technical Reports Server (NTRS)
Adamczyk, J. J.; Goldstein, M. E.; Hartmann, M. J.
1978-01-01
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.
Unsteady PIV for regular head waves Submitted for presentation at the 26th
Gui, Lichuan
system in the Iowa Institute of Hydraulic Research towing tank of a two-dimensional, deep-water, long1 Unsteady PIV for regular head waves Submitted for presentation at the 26th American Towing Tank Phase-averaged results from a towing tank experiment of regular head waves are documented. Uniform flow
Unsteady Exact Solution for Flows of Fluids with Pressure-Dependent Viscosities
K. R. Rajagopal; G. Saccomandi
2006-01-01
Stokes recognized that the viscosity of ?uids could generally depend on their pres- sure, and this has been conflrmed by numerous experiments. In this paper we con- sider several unsteady ?ows of ?uids with pressure-dependent viscosity, and we establish explicit exact solutions for these problems that can serve as benchmarks for numerical solutions for ?ows in complicated geometries.
NASA Technical Reports Server (NTRS)
Piette, Douglas S.; Cazier, Frank W., Jr.
1989-01-01
Present flutter analysis methods do not accurately predict the flutter speeds in the transonic flow region for wings with supercritical airfoils. Aerodynamic programs using computational fluid dynamic (CFD) methods are being developed, but these programs need to be verified before they can be used with confidence. A wind tunnel test was performed to obtain all types of data necessary for correlating with CFD programs to validate them for use on high aspect ratio wings. The data include steady state and unsteady aerodynamic measurements on a nominal stiffness wing and a wing four times that stiffness. There is data during forced oscillations and during flutter at several angles of attack, Mach numbers, and tunnel densities.
Assessment of Periodic Flow Assumption for Unsteady Heat
Chung, Yongmann M.
Assessment of Periodic Flow Assumption for Unsteady Heat Transfer in Grooved Channels Yongmann M of unsteady heat transfer in grooved channel flows are made. The flows are of special relevance to electronic, Modeling, Heat Transfer, Laminar, Periodic, Unsteady 1 Introduction With increasing power densities
UNSTEADY WIND TUNNEL CONTROL OF STABILITY AND TRANSITION
UNSTEADY WIND TUNNEL CONTROL OF STABILITY AND TRANSITION IN SWEPT-WING BOUNDARY LAYERS WILLIAM.reed@asu.edu #12;UNSTEADY WIND TUNNEL Boundary-Layer Transition · Receptivity External disturbances enter instabilities #12;UNSTEADY WIND TUNNEL RICH VARIETY OF STABILITY BEHAVIOR GENERIC TO 3-D BOUNDARY LAYERS
Dynamic stall behavior from unsteady force measurements
NASA Astrophysics Data System (ADS)
Tsang, K. K. Y.; So, R. M. C.; Leung, R. C. K.; Wang, X. Q.
2008-01-01
A direct force measurement technique employing piezoelectric load cells is used to experimentally investigate a two-dimensional airfoil (NACA 0012) undergoing dynamic stall. The load cells are installed at each end of the airfoil and give the force response in two directions in the plane normal to the airfoil axis during oscillations. Experiments are carried out at a Reynolds number based on the airfoil chord equal to 7.7×104, and at four reduced frequencies, k=0.005, 0.01, 0.02, and 0.04. Phase-averaged lift of the airfoil undergoing dynamic stall is presented. It is observed that hysteresis loops of the lift occur both when the airfoil is pitched to exceed its static stall limit and when it is still within its static stall limit, and they grow in size with increasing k at the same pitching mean angle of attack and pitching amplitude. Both the lift and the drag induced by the pitching motion are further analyzed using the methods of higher order correlation analysis and continuous wavelet transforms to undercover their nonlinear and nonstationary features, in addition to classical FFT-based spectral analysis. The results are quantitatively illustrated by an energy partition analysis. It is found that the unsteady lift and drag show opposite trends when the airfoil undergoes transition from the pre-stall regime to the full-stall regime. The degree of nonlinearity of the lift increases, and the lift show a nonstationary feature in the light-stall regime, while the nonlinearity of the drag decreases, and the drag shows nonstationary feature in both the light-stall and the full-stall regimes. Furthermore, the lift and the drag have significant nonlinear interactions as shown by the correlation analysis in the light-stall regime.
The aerodynamics of ship superstructures
NASA Astrophysics Data System (ADS)
Healey, J. V.
1991-11-01
After 70 years of naval aviation, a belated understanding of the aerodynamics of ships is slowly emerging. The lack of understanding, and undoubtedly other reasons, has led to superstructure configurations that are unsuited to adjacent helicopter flight. This has resulted in severely limited safe operating envelopes, danger to pilots and ship personnel and blade strikes that occasionally result in the complete loss of a helicopter. The air flows around ships abound with recirculating zones, bounded by shear layers that emanate from the sharp edges of the superstructures. These zones vary enormously in size in an intermittent manner, giving rise to flows with extreme velocity gradients and turbulence intensity levels that are too high to be measured with hot wire anemometers. This complicates the situation because, at the present time, a data base for simulation can be established only via measurement. The essential ingredients for the aerodynamic design of new ships are proposed and some suggestions for the improvement of the aerodynamics of existing ships are made. Correcting an aerodynamically poor ship is no substitute for the incorporation of aerodynamics into the ship design process.
14 CFR 25.445 - Auxiliary aerodynamic surfaces.
Code of Federal Regulations, 2010 CFR
2010-01-01
...2010-01-01 2010-01-01 false Auxiliary aerodynamic surfaces. 25.445 Section...Surface and System Loads § 25.445 Auxiliary aerodynamic surfaces. (a) When...significant, the aerodynamic influence between auxiliary aerodynamic surfaces, such as...
Time-Varying Wing-Twist Improves Aerodynamic Efficiency of Forward Flight in Butterflies
Zheng, Lingxiao; Hedrick, Tyson L.; Mittal, Rajat
2013-01-01
Insect wings can undergo significant chordwise (camber) as well as spanwise (twist) deformation during flapping flight but the effect of these deformations is not well understood. The shape and size of butterfly wings leads to particularly large wing deformations, making them an ideal test case for investigation of these effects. Here we use computational models derived from experiments on free-flying butterflies to understand the effect of time-varying twist and camber on the aerodynamic performance of these insects. High-speed videogrammetry is used to capture the wing kinematics, including deformation, of a Painted Lady butterfly (Vanessa cardui) in untethered, forward flight. These experimental results are then analyzed computationally using a high-fidelity, three-dimensional, unsteady Navier-Stokes flow solver. For comparison to this case, a set of non-deforming, flat-plate wing (FPW) models of wing motion are synthesized and subjected to the same analysis along with a wing model that matches the time-varying wing-twist observed for the butterfly, but has no deformation in camber. The simulations show that the observed butterfly wing (OBW) outperforms all the flat-plate wings in terms of usable force production as well as the ratio of lift to power by at least 29% and 46%, respectively. This increase in efficiency of lift production is at least three-fold greater than reported for other insects. Interestingly, we also find that the twist-only-wing (TOW) model recovers much of the performance of the OBW, demonstrating that wing-twist, and not camber is key to forward flight in these insects. The implications of this on the design of flapping wing micro-aerial vehicles are discussed. PMID:23341923
Contribution to the aerodynamic study of wings and propellers
NASA Technical Reports Server (NTRS)
Menard, M.
1983-01-01
Various problems regarding the aerodynamics of lifting wings are solved. Two methods are proposed for replacing the wing, both involving "viscous" edge vortices. the applications give results which agree well with experiments. Two new methods are also proposed for calculating propellers based on the vortex model consisting of an edge vortex and a "viscous" hub vortex.
Numerical Analysis on Aerodynamic Heating in Hypersonic Shock Interacting Flow
Keiichi Kitamura; Yoshiaki Nakamura
2008-01-01
It is still challenging to predict surface heat-transfer rate in hypersonic flow computations. In this paper, we first performed numerical experiments by changing numerical flux functions and meshes for a hypersonic flow around a hemisphere. Results show that AUSM+ flux function by Liou (1996) on a carefully refined mesh can lead to a shock stable solution with an accurate aerodynamic
Aerodynamic aspects on recovery of sounding rocket payload
M. Shirouzu; H. Kubota; Y. Shibato
1980-01-01
Aerodynamic experiments for the design of a recovery system for a sounding rocket payload included wind tunnel tests of payload models at high angles of attack over Mach numbers ranging from subsonic to supersonic and airdrop tests of payload models. It was shown that (1) the magnitude of the cross-flow proportionality factor used for predicting the payload normal force coefficient
Aerodynamic and Aeroacoustic Wind Tunnel Testing of the Orion Spacecraft
NASA Technical Reports Server (NTRS)
Ross, James C.
2011-01-01
The Orion aerodynamic testing team has completed more than 40 tests as part of developing the aerodynamic and loads databases for the vehicle. These databases are key to achieving good mechanical design for the vehicle and to ensure controllable flight during all potential atmospheric phases of a mission, including launch aborts. A wide variety of wind tunnels have been used by the team to document not only the aerodynamics but the aeroacoustic environment that the Orion might experience both during nominal ascents and launch aborts. During potential abort scenarios the effects of the various rocket motor plumes on the vehicle must be accurately understood. The Abort Motor (AM) is a high-thrust, short duration motor that rapidly separates Orion from its launch vehicle. The Attitude Control Motor (ACM), located in the nose of the Orion Launch Abort Vehicle, is used for control during a potential abort. The 8 plumes from the ACM interact in a nonlinear manner with the four AM plumes which required a carefully controlled test to define the interactions and their effect on the control authority provided by the ACM. Techniques for measuring dynamic stability and for simulating rocket plume aerodynamics and acoustics were improved or developed in the course of building the aerodynamic and loads databases for Orion.
Aerodynamic Effects in Weakly Ionized Gas: Phenomenology and Applications
Popovic, S.; Vuskovic, L. [Department of Physics, Old Dominion University, Norfolk, Virginia (United States)
2006-12-01
Aerodynamic effects in ionized gases, often neglected phenomena, have been subject of a renewed interest in recent years. After a brief historical account, we discuss a selected number of effects and unresolved problems that appear to be relevant in both aeronautic and propulsion applications in subsonic, supersonic, and hypersonic flow. Interaction between acoustic shock waves and weakly ionized gas is manifested either as plasma-induced shock wave dispersion and acceleration or as shock-wave induced double electric layer in the plasma, followed by the localized increase of the average electron energy and density, as well as enhancement of optical emission. We describe the phenomenology of these effects and discuss several experiments that still do not have an adequate interpretation. Critical for application of aerodynamic effects is the energy deposition into the flow. We classify and discuss some proposed wall-free generation schemes with respect to the efficiency of energy deposition and overall generation of the aerodynamic body force.
Electromyographic responses to aerodynamic vs. drop handlebars
Layne, Donald Jodel
1996-01-01
Aerodynamic Handlebars were developed to increase the competitive cyclists aerodynamic advantage. They place the cyclist in a laid out position with the hands stretched out in front similar to a down hill skier "tuck" ...
The Current Status of Unsteady CFD Approaches for Aerodynamic Flow Control
Mark H. Carpenter; Bart A. Singer; Nail Yamaleev; Veer N. Vatsa; Sally A. Viken; Harold L. Atkins
2002-01-01
Abstract: An overview of the current status of time dependentalgorithms is presented. Special attention isgiven to algorithms used to predict fluid actuatorflows, as well as other active and passive flow controldevices. Capabilities for the next decade are predicted,and principal impediments to the progress oftime-dependent algorithms are identified.
Progress in unstructured-grid methods development for unsteady aerodynamic applications
NASA Technical Reports Server (NTRS)
Batina, John T.
1992-01-01
The development of unstructured-grid methods for the solution of the equations of fluid flow and what was learned over the course of the research are summarized. The focus of the discussion is on the solution of the time-dependent Euler equations including spatial discretizations, temporal discretizations, and boundary conditions. An example calculation with an implicit upwind method using a CFL number of infinity is presented for the Boeing 747 aircraft. The results were obtained in less than one hour CPU time on a Cray-2 computer, thus, demonstrating the speed and robustness of the capability. Additional calculations for the ONERA M6 wing demonstrate the accuracy of the method through the good agreement between calculated results and experimental data for a standard transonic flow case.
The Current Status of Unsteady CFD Approaches for Aerodynamic Flow Control
NASA Technical Reports Server (NTRS)
Carpenter, Mark H.; Singer, Bart A.; Yamaleev, Nail; Vatsa, Veer N.; Viken, Sally A.; Atkins, Harold L.
2002-01-01
An overview of the current status of time dependent algorithms is presented. Special attention is given to algorithms used to predict fluid actuator flows, as well as other active and passive flow control devices. Capabilities for the next decade are predicted, and principal impediments to the progress of time-dependent algorithms are identified.
Aerodynamics Research Revolutionizes Truck Design
NASA Technical Reports Server (NTRS)
2008-01-01
During the 1970s and 1980s, researchers at Dryden Flight Research Center conducted numerous tests to refine the shape of trucks to reduce aerodynamic drag and improved efficiency. During the 1980s and 1990s, a team based at Langley Research Center explored controlling drag and the flow of air around a moving body. Aeroserve Technologies Ltd., of Ottawa, Canada, with its subsidiary, Airtab LLC, in Loveland, Colorado, applied the research from Dryden and Langley to the development of the Airtab vortex generator. Airtabs create two counter-rotating vortices to reduce wind resistance and aerodynamic drag of trucks, trailers, recreational vehicles, and many other vehicles.
Anisotropic Delaunay Mesh Adaptation for Unsteady Simulations
Frey, Pascal
Anisotropic Delaunay Mesh Adaptation for Unsteady Simulations C. Dobrzynski1 and P. Frey2,3 1 IMB Modelamiento Matem´atico, Santiago, Chile Summary. Anisotropic mesh adaptation is a key feature in many capturing or tracking problems. In this paper, we describe a local mesh adaptation method based
Efficient uncertainty quantification in unsteady aeroelastic simulations
J. A. S. Witteveen; H. Bijl
2009-01-01
An efficient uncertainty quantification method for unsteady problems is presented in order to achieve a constant accuracy in time for a constant number of samples. The approach is applied to the aeroelastic problems of a transonic airfoil flutter system and the AGARD 445.6 wing benchmark with uncertainties in the flow and the structure.
Unsteady three-dimensional flow separation
NASA Technical Reports Server (NTRS)
Hui, W. H.
1988-01-01
A concise mathematical framework is constructed to study the topology of steady 3-D separated flows of an incompressible, or a compressible viscous fluid. Flow separation is defined by the existence of a stream surface which intersects with the body surface. The line of separation is itself a skin-friction line. Flow separation is classified as being either regular or singular, depending respectively on whether the line of separation contains only a finite number of singular points or is a singular line of the skin-friction field. The special cases of 2-D and axisymmetric flow separation are shown to be of singular type. In regular separation it is shown that a line of separation originates from a saddle point of separation of the skin-friction field and ends at nodal points of separation. Unsteady flow separation is defined relative to a coordinate system fixed to the body surface. It is shown that separation of an unsteady 3-D incompressible viscous flow at time t, when viewed from such a frame of reference, is topologically the same as that of the fictitious steady flow obtained by freezing the unsteady flow at the instant t. Examples are given showing effects of various forms of flow unsteadiness on flow separation.
Natural convection in unsteady Couette motion
A. K. Singh
1988-01-01
Unsteady free convective flow of an incompressible viscous fluid between two vertical parallel plates is considered for impulsive start of one of the plates. Expressions for velocity and temperature fields and their related quantities are obtained by the Laplace transform technique. The effect of Grashof number is to increase the velocity of both air and water and to decrease the
Schwarz Methods for the Unsteady Compressible
Cai, Xiao-Chuan
)T is the velocity vector and E is the total energy per unit volume. We are interested in unsteady, external ows equations, see e.g. CS96, DW94, SBG95]. Here we report on our preliminaryexperiences on using95, VM95]. To advance in time, a large linear system of equations must be solved. Depending
Unsteadiness of transonic convex-corner flows
Kung-Ming Chung
2004-01-01
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.
Aerodynamic yawing moment characteristics of bird wings.
Sachs, Gottfried
2005-06-21
The aerodynamic yawing moments due to sideslip are considered for wings of birds. Reference is made to the experience with aircraft wings in order to identify features which are significant for the yawing moment characteristics. Thus, it can be shown that wing sweep, aspect ratio and lift coefficient have a great impact. Focus of the paper is on wing sweep which can considerably increase the yawing moment due to sideslip when compared with unswept wings. There are many birds the wings of which employ sweep. To show the effect of sweep for birds, the aerodynamic characteristics of a gull wing which is considered as a representative example are treated in detail. For this purpose, a sophisticated aerodynamic method is used to compute results of high precision. The yawing moments of the gull wing with respect to the sideslip angle and the lift coefficient are determined. They show a significant level of yaw stability which strongly increases with the lift coefficient. It is particularly high in the lift coefficient region of best gliding flight conditions. In order to make the effect of sweep more perspicuous, a modification of the gull wing employing no sweep is considered for comparison. It turns out that the unswept wing yields yawing moments which are substantially smaller than those of the original gull wing with sweep. Another feature significant for the yawing moment characteristics concerns the fact that sweep is at the outer part of bird wings. By considering the underlying physical mechanism, it is shown that this feature is most important for the efficiency of wing sweep. To sum up, wing sweep provides a primary contribution to the yawing moments. It may be concluded that this is an essential reason why there is sweep in bird wings. PMID:15808868
CFD-based Optimization for Automotive Aerodynamics
Dumas, Laurent
Chapter 1 CFD-based Optimization for Automotive Aerodynamics Laurent Dumas Abstract The car drag- ments. An overview of the main characteristics of automotive aerodynamics and a detailed presentation.dumas@upmc.fr) 1 #12;2 Laurent Dumas 1.1 Introducing Automotive Aerodynamics 1.1.1 A Major Concern for Car
Challenges and Complexity of Aerodynamic Wing
Jameson, Antony
Chapter 1 Challenges and Complexity of Aerodynamic Wing Design Kasidit Leoviriyakit and Antony@stanford.edu and jameson@baboon.stanford.edu This paper focuses on aerodynamic design methodology. It discusses challenges and complexity of aerodynamic wing design for a transonic aircraft, which arise from the complex nature of flow
ME421. Foundations of Aerodynamics. Victor Yakhot
Lin, Xi
ME421. Foundations of Aerodynamics. Victor Yakhot Syllabus. Spring 2014 . 1/16, 21. Fluids;Books. 1. D. Wilcox, "Basic Fluid Mechanics". 2. J. Anderson, Fundamentals of aerodynamics. 3. V.Yakhot,, ME421. Fluid Mechanics and aerodynamics. My lecture notes. 4. I. Abbott and A. Doenhoff, Theory
ME421. Foundations of Aerodynamics. Victor Yakhot
ME421. Foundations of Aerodynamics. Victor Yakhot Syllabus. Spring 2013 . 1/17, 22. Fluids Mechanics". 2. J. Anderson, Fundamentals of aerodynamics. 3. V.Yakhot,, ME421. Fluid Mechanics and aerodynamics. My lecture notes. 4. I. Abbott and A. Doenhoff, Theory of wing sections, Dover Publications, NY
Toward Practical Aerodynamic Design Through Numerical Optimization
Zingg, David W.
Toward Practical Aerodynamic Design Through Numerical Optimization David W. Zingg, and Laura6, Canada A Newton-Krylov algorithm for aerodynamic optimization is applied to the multipoint design aerodynamic design. I. Introduction Beginning with the work of Hicks et al.1 and Hicks and Henne,2 numerical
Conformal Mapping in Wing Aerodynamics Thomas Johnson
Morrow, James A.
Conformal Mapping in Wing Aerodynamics Thomas Johnson June 4, 2013 Contents 1 Introduction 1 2 the first complete treatment of conformal mapping in aerodynamics. Near the beginning of the twentieth and aerodynamics. The purpose of this exposition is to give the reader an elementary intro- duction to the use
Aerodynamic Aspects of Disk Files
Eckart Lennemann
1974-01-01
Abstract: Airflows between centrally clamped, rotating, rigid disks are investigated with respect to the type of flow pattern, the parameters that influence nonuniform flow, and the effects of various flow patterns on disk stability. The experimental method uses a waterflow modeling,technique,for the airflow. The observed,flow patterns are highly unsteady. The configuration,and position of the shroud and slider arm are found
Discrete Adjoint-Based Design for Unsteady Turbulent Flows On Dynamic Overset Unstructured Grids
NASA Technical Reports Server (NTRS)
Nielsen, Eric J.; Diskin, Boris
2012-01-01
A discrete adjoint-based design methodology for unsteady turbulent flows on three-dimensional dynamic overset unstructured grids is formulated, implemented, and verified. The methodology supports both compressible and incompressible flows and is amenable to massively parallel computing environments. The approach provides a general framework for performing highly efficient and discretely consistent sensitivity analysis for problems involving arbitrary combinations of overset unstructured grids which may be static, undergoing rigid or deforming motions, or any combination thereof. General parent-child motions are also accommodated, and the accuracy of the implementation is established using an independent verification based on a complex-variable approach. The methodology is used to demonstrate aerodynamic optimizations of a wind turbine geometry, a biologically-inspired flapping wing, and a complex helicopter configuration subject to trimming constraints. The objective function for each problem is successfully reduced and all specified constraints are satisfied.
Steady and unsteady 3D interactive boundary layers
NASA Astrophysics Data System (ADS)
Smith, F. T.
The paper describes theoretical and computational research on 3D steady and unsteady flows at medium-to-high Reynolds numbers (Re), aimed at increasing understanding of 3D separation and boundary-layer transition. Concerning steady 3D flows first, an interactive-boundary-layer (IBL) formulation for 3D laminar flow of an incompressible fluid over a surface-mounted obstacle is addressed computationally and compared with other methods at various Re. The computational approach is designed deliberately to capture the extra ellipicity present due to the three-dimensionality, making use of skewed shears in linear quasi-planar sweeps of the boundary layer and local updating in the 3D interaction law. Results including separation are presented for a range of Re and obstacle heights, together with grid-effect studies, and comparisons are made, first with triple-deck predictions for high Re and, second, with an alternative IBL approach presented in a companion work. The latter and the current work together yield a broad agreement on predictions for the 3D flow, stretching from the triple-deck through the IBL to thin-layer Navier-Stokes predictions, over a wide range of Re. Second, the computational approach is extended to unsteady 3D flows, for the triple-deck limit including linear and nonlinear Tollmien-Schlichting waves. Results for small and nonsmall disturbances and comparisons are presented, showing fairly encouraging agreement between theory, computations and experiments.
CAMRAD - A COMPREHENSIVE ANALYTICAL MODEL OF ROTORCRAFT AERODYNAMICS AND DYNAMICS
NASA Technical Reports Server (NTRS)
Johnson, W.
1994-01-01
The Comprehensive Analytical Model of Rotorcraft Aerodynamics, CAMRAD, program is designed to calculate rotor performance, loads, and noise; helicopter vibration and gust response; flight dynamics and handling qualities; and system aeroelastic stability. The analysis is a consistent combination of structural, inertial, and aerodynamic models applicable to a wide range of problems and a wide class of vehicles. The CAMRAD analysis can be applied to articulated, hingeless, gimballed, and teetering rotors with an arbitrary number of blades. The rotor degrees of freedom included are blade/flap bending, rigid pitch and elastic torsion, and optionally gimbal or teeter motion. General two-rotor aircrafts can be modeled. Single main-rotor and tandem helicopter and sideby-side tilting proprotor aircraft configurations can be considered. The case of a rotor or helicopter in a wind tunnel can also be modeled. The aircraft degrees of freedom included are the six rigid body motion, elastic airframe motions, and the rotor/engine speed perturbations. CAMRAD calculates the load and motion of helicopters and airframes in two stages. First the trim solution is obtained; then the flutter, flight dynamics, and/or transient behavior can be calculated. The trim operating conditions considered include level flight, steady climb or descent, and steady turns. The analysis of the rotor includes nonlinear inertial and aerodynamic models, applicable to large blade angles and a high inflow ratio, The rotor aerodynamic model is based on two-dimensional steady airfoil characteristics with corrections for three-dimensional and unsteady flow effects, including a dynamic stall model. In the flutter analysis, the matrices are constructed that describe the linear differential equations of motion, and the equations are analyzed. In the flight dynamics analysis, the stability derivatives are calculated and the matrices are constructed that describe the linear differential equations of motion. These equations are analyzed. In the transient analysis, the rigid body equations of motion are numerically integrated, for a prescribed transient gust or control input. The CAMRAD program product is available by license for a period of ten years to domestic U.S. licensees. The licensed program product includes the CAMRAD source code, command procedures, sample applications, and one set of supporting documentation. Copies of the documentation may be purchased separately at the price indicated below. CAMRAD is written in FORTRAN 77 for the DEC VAX under VMS 4.6 with a recommended core memory of 4.04 megabytes. The DISSPLA package is necessary for graphical output. CAMRAD was developed in 1980.
Aerodynamics of a Dimpled Vehicle
NASA Astrophysics Data System (ADS)
Ortega, Jason; Salari, Kambiz
2010-11-01
Automobiles consume approximately two billion barrels of fuel each year throughout the United States. A significant portion of this fuel is used to overcome aerodynamic drag at highway speeds. As a result, even small improvements made to the aerodynamics of automobiles can result in sizeable fuel savings. Since the shape of a vehicle is often dictated by design, economics, and function, aerodynamic improvements by means of obvious body streamlining are not always possible. However, minor modifications can be made to the vehicle, such as changing the behavior of the boundary layer to delay flow separation or installing small components either to reduce underbody flow or to mitigate induced drag. In this study, we examine the effect that dimples have upon the aerodynamics of a simplified vehicle. Reynolds-averaged Navier-Stokes simulations are performed on a full-scale Ahmed body at a Reynolds number of 9.5e6 based upon the vehicle length. The dimples, which have a uniform diameter of 0.1 m and a dimple depth-to-diameter ratio of 0.14, are distributed across the vehicle surface. The results of the simulations demonstrate that the dimples modify both the recirculation zone and the strength and location of the counter-rotating vortex pair in the vehicle wake. Although an increase in base pressure can occur for a dimpled configuration, the net drag change is sensitive to both the number and placement of the dimples on the vehicle body.
POEMS in Newton's Aerodynamic Frustum
ERIC Educational Resources Information Center
Sampedro, Jaime Cruz; Tetlalmatzi-Montiel, Margarita
2010-01-01
The golden mean is often naively seen as a sign of optimal beauty but rarely does it arise as the solution of a true optimization problem. In this article we present such a problem, demonstrating a close relationship between the golden mean and a special case of Newton's aerodynamical problem for the frustum of a cone. Then, we exhibit a parallel…
AIAA 20033498 Viscous Aerodynamic Shape
Jameson, Antony
design tool, but as an aid to analyze the fluid flow. The design process has still been done by trial for aerodynamic shape design in viscous compressible flow mod- eled by the Navier-Stokes equations. It extends, a Pareto front is captured, broadening the design range of optimal shapes. INTRODUCTION CFD has played
The aerodynamics of supersonic parachutes
1987-01-01
A discussion of the aerodynamics and performance of parachutes flying at supersonic speeds is the focus of this paper. Typical performance requirements for supersonic parachute systems are presented, followed by a review of the literature on supersonic parachute configurations and their drag characteristics. Data from a recent supersonic wind tunnel test series is summarized. The value and limitations of supersonic
Rotary wing aerodynamically generated noise
NASA Technical Reports Server (NTRS)
Schmitz, F. J.; Morse, H. A.
1982-01-01
The history and methodology of aerodynamic noise reduction in rotary wing aircraft are presented. Thickness noise during hover tests and blade vortex interaction noise are determined and predicted through the use of a variety of computer codes. The use of test facilities and scale models for data acquisition are discussed.
Aerodynamic design via control theory
NASA Technical Reports Server (NTRS)
Jameson, Antony
1988-01-01
The question of how to modify aerodynamic design in order to improve performance is addressed. Representative examples are given to demonstrate the computational feasibility of using control theory for such a purpose. An introduction and historical survey of the subject is included.
Shuttle reentry aerodynamic heating test
NASA Technical Reports Server (NTRS)
Pond, J. E.; Mccormick, P. O.; Smith, S. D.
1971-01-01
The research for determining the space shuttle aerothermal environment is reported. Brief summaries of the low Reynolds number windward side heating test, and the base and leeward heating and high Reynolds number heating test are included. Also discussed are streamline divergence and the resulting effect on aerodynamic heating, and a thermal analyzer program that is used in the Thermal Environment Optimization Program.
Experimental Aerodynamics of Mesoscale Trailing Edge Actuators
NASA Astrophysics Data System (ADS)
Solovitz, Stephen; Eaton, John
2001-11-01
Experiments were performed on a wing with segmented Gurney flaps. Each of the sixteen active flaps is approximately 1.5can be actuated in only two positions: 90 degrees up or 90 degrees down. Wind tunnel experiments were conducted at chord Reynolds numbers up to 800,000. Measurements include the determination of aerodynamic forces and moments using a 6 DOF balance, surface pressure profiles, and wake surveys. Actuation of the full span of the airfoil from the up position to the down position increases the lift coefficient by approximately 0.6 for low to moderate angles of attack. The flaps have a reduced but still significant effect past stall. The overall changes in wing loads are linear with the number of flaps actuated, suggesting that simple control laws may be used. However, surface pressure measurements indicate that each flap affects the section lift over a substantial span. A study of the transient performance of the flaps is underway.
Report of the Panel on Aerodynamics
NASA Technical Reports Server (NTRS)
Bradley, Richard G.; Bushnell, Dennis
1984-01-01
Progress in aerodynamics over the past 50 years has been evidenced by the development of increasingly sophisticated and efficient flight vehicles throughout the flight spectrum. Advances have generally arisen in an evolutionary manner from experience gained in wind tunnel testing, flight testing, and improvements in analytical and computational capabilities. As a result of this evolutionary development, both military and commercial vehicles operate at a relatively high efficiency level. This observation plus the fact that airplanes have not changed appreciably in outward appearance over recent years has led some skeptics to conclude incorrectly that aerodynamics is a mature technology, with little to be gained from further developments in the field. It is of interest to note that progress in aerodynamics has occurred without a thorough understanding of the fundamental physics of flow, turbulence, vortex dynamics, and separated flow, for example. The present understanding of transition, turbulence, and boundary layer separation is actually very limited. However, these fundamental flow phenomena provide the key to reducing the viscous drag of aircraft. Drag reduction provides the greatest potential for increased flight efficiency from the standpoint of both saving energy and maximizing performance. Recent advances have led to innovative concepts for reducing turbulent friction drag by modifying the turbulent structure within the boundary layer. Further advances in this basic area should lead to methods for reducing skin friction drag significantly. The current challenges for military aircraft open entirely new fields of investigation for the aerodynamicist. The ability through very high speed information processing technology to totally integrate the flight and propulsion controls can permit an aircraft to fly with "complete abandon," avoiding departure, buffet, and other undesirable characteristics. To utilize these new control concepts, complex aerodynamic phenomena will have to be understood, predicted, and controlled. Current requirements for military aircraft include configuration optimization through a widened envelope from subsonic to supersonic and from low to high angles of attack. This task is further complicated by requirements for control of observables. These challenging new designs do not have the luxury of a large experimental data base from which to optimize for various parameter combinations. Consequently, there exists a strong need for better techniques, both experimental and computational, to permit design optimization in a complete sense.
Aerodynamics of runback ice accretions
NASA Astrophysics Data System (ADS)
Whalen, Edward A.
An experimental study of the effects of simulated runback ice accretions has been performed in order to describe their aerodynamic performance penalties and investigate their scaling for use in sub-scale aerodynamic testing. Runback ice accretions corresponding to three flight conditions, warm hold, cold hold and descent, were simulated and tested on the NACA 23012 and NACA 3415. The ice shapes were simulated on two levels of fidelity. Medium-fidelity simulations captured the chordwise location, cross-section, height distribution and chordwise extent of the ice accretion. Low-fidelity simulations captured their height and chordwise location. Two scaling methods were also employed. Each simulation was scaled based upon the ratio of the aerodynamic model chord to the full-scale icing model, called geometric scaling. The warm hold simulations were also scaled based upon the ratio of the local, clean-model boundary-layer thickness on the aerodynamic model to that of the icing model, called boundary-layer scaling. This method was employed because the geometrically-scaled simulations were found to be on the order of the boundary-layer thickness as the model approached stall. Following aerodynamic performance testing, fluorescent-oil flow visualization and hot-wire anemometry were used to investigate the flowfield resulting from the low-fidelity warm hold simulations. Results for this work have shown that runback ice accretions can cause significant aerodynamic performance penalties. In general, the NACA 23012 experienced greater aerodynamic performance penalties due to the runback simulations than did the NACA 3415. Low-fidelity simulations of the cold hold case agreed quite well with their medium fidelity counterparts. In the descent case, the level of variation in ice accretion height was too small for there to be a distinction between the low- and medium-fidelity cases. Low-fidelity simulations of the warm hold accretion did not agree well with the medium-fidelity simulation. In fact, the geometrically-scaled simulation was observed to increase the maximum lift and stalling angle-of-attack of the NACA 3415. Flowfield investigations using fluorescent-oil flow visualization and hot-wire anemometry showed that the simulations that were similar in height to the clean-model local boundary-layer thickness acted to stabilize the recovering boundary layer, delaying stall past the stalling angle-of-attack of the clean case.
A Vortex Array Model of the Unsteady Wake of a Two-dimensional Pitching Airfoil
NASA Astrophysics Data System (ADS)
Naguib, Ahmed; Koochesfahani, Manoochehr
2008-11-01
Motivated by recent interest in MAV aerodynamics, the present study is focused on obtaining a simplified, vortex-array model of the unsteady flow in the wake of an airfoil undergoing small-amplitude but high-reduced-frequency pitch oscillations. The model is used to predict the mean and unsteady velocity field in the wake of a NACA 0012 airfoil executing a sinusoidal as well as non-sinusoidal pitch oscillation. The model predictive accuracy is assessed by comparison to the LDV measurements of the streamwise velocity by Koochesfahani (AIAA J. 37, 1999) at a chord Reynolds number of 12,000 and a reduced frequency as high as 10. The results demonstrate the ability of the vortex-array model to successfully reproduce the experimentally measured mean and phase-averaged streamwise velocity profiles in the wake of the airfoil. Moreover, by using the model to reconstruct the complete velocity field in the wake, the mean streamwise force acting on the airfoil is computed for different frequencies, amplitudes and waveforms of the oscillation.
A first-order time-domain Green's function approach to supersonic unsteady flow
NASA Technical Reports Server (NTRS)
Freedman, M. I.; Tseng, K.
1985-01-01
A time-domain Green's Function Method for unsteady supersonic potential flow around complex aircraft configurations is presented. The focus is on the supersonic range wherein the linear potential flow assumption is valid. The Green's function method is employed in order to convert the potential-flow differential equation into an integral one. This integral equation is then discretized, in space through standard finite-element technique, and in time through finite-difference, to yield a linear algebraic system of equations relating the unknown potential to its prescribed co-normalwash (boundary condition) on the surface of the aircraft. The arbitrary complex aircraft configuration is discretized into hyperboloidal (twisted quadrilateral) panels. The potential and co-normalwash are assumed to vary linearly within each panel. Consistent with the spatial linear (first-order) finite-element approximations, the potential and co-normalwash are assumed to vary linearly in time. The long range goal of our research is to develop a comprehensive theory for unsteady supersonic potential aerodynamics which is capable of yielding accurate results even in the low supersonic (i.e., high transonic) range.
Aerodynamics inside a rapid compression machine
Mittal, Gaurav; Sung, Chih-Jen [Department of Mechanical and Aerospace Engineering, Case Western Reserve University, Cleveland, OH 44106 (United States)
2006-04-15
The aerodynamics inside a rapid compression machine after the end of compression is investigated using planar laser-induced fluorescence (PLIF) of acetone. To study the effect of reaction chamber configuration on the resulting aerodynamics and temperature field, experiments are conducted and compared using a creviced piston and a flat piston under varying conditions. Results show that the flat piston design leads to significant mixing of the cold vortex with the hot core region, which causes alternate hot and cold regions inside the combustion chamber. At higher pressures, the effect of the vortex is reduced. The creviced piston head configuration is demonstrated to result in drastic reduction of the effect of the vortex. Experimental conditions are also simulated using the Star-CD computational fluid dynamics package. Computed results closely match with experimental observation. Numerical results indicate that with a flat piston design, gas velocity after compression is very high and the core region shrinks quickly due to rapid entrainment of cold gases. Whereas, for a creviced piston head design, gas velocity after compression is significantly lower and the core region remains unaffected for a long duration. As a consequence, for the flat piston, adiabatic core assumption can significantly overpredict the maximum temperature after the end of compression. For the creviced piston, the adiabatic core assumption is found to be valid even up to 100 ms after compression. This work therefore experimentally and numerically substantiates the importance of piston head design for achieving a homogeneous core region inside a rapid compression machine. (author)
Visualization of unsteady computational fluid dynamics
NASA Technical Reports Server (NTRS)
Haimes, Robert
1994-01-01
A brief summary of the computer environment used for calculating three dimensional unsteady Computational Fluid Dynamic (CFD) results is presented. This environment requires a super computer as well as massively parallel processors (MPP's) and clusters of workstations acting as a single MPP (by concurrently working on the same task) provide the required computational bandwidth for CFD calculations of transient problems. The cluster of reduced instruction set computers (RISC) is a recent advent based on the low cost and high performance that workstation vendors provide. The cluster, with the proper software can act as a multiple instruction/multiple data (MIMD) machine. A new set of software tools is being designed specifically to address visualizing 3D unsteady CFD results in these environments. Three user's manuals for the parallel version of Visual3, pV3, revision 1.00 make up the bulk of this report.
NASA Astrophysics Data System (ADS)
Jiang, Y.
2005-11-01
In fully developed laminar pipe and channel flows that undergo transients from a known initial state, exact analytical solutions for the momentary velocity field as a functional of the flow rate can be determined from the Navier-Stokes equations, for arbitrary flow unsteadiness [Phys. Fluids 12, 3, 518, (2000)]. When these flows experience heat transfer at their walls, the companion thermal energy equation can be linearized and may also be solved analytically when flow transients are large. Under this restriction, solutions can be found for the instantaneous temperature field, for arbitrary time unsteadiness in both the flow and the wall heat flux. Expressions for Nusselt numbers in convective heat transfer in duct flows with arbitrary temporal flow and heat flux unsteadiness can then be found, which illustrate how the flow and heat flux transient histories determine whether the unsteadiness enhances or reduces the overall heat-transfer effectiveness. These expressions are used to show how significant enhancements or reductions in the average Nusselt number can be achieved in duct flow by applying appropriate temporal bulk-flow control.
Inviscid steady/unsteady flow calculations
NASA Technical Reports Server (NTRS)
Pordal, H. S.; Khosla, P. K.; Rubin, S. G.
1991-01-01
The solution of the Euler equations using a flux splitting procedure is considered for low subsonic to high supersonic flows. Steady and unsteady, internal and external flow fields, are computed. For transient flows, a direct sparse matrix solver is applied to compute the flow field at each instant of time. Oscillation free normal and oblique shocks are captured. Unstart and restart of a simplified two-dimensional inlet is investigated.
UNSTRUCTURED MESHES IN UNSTEADY CFD APPLICATIONS
Dmitry A. Lysenko
Four state-of-the-art applications of unstructured tetrahedral meshes (both static and dynamic- adaptive) in numerical simulations of different fluid dynamics phenomena are presented. The numerical methods are varied form simple Euler equations through unsteady Reynolds averaged equations to filtered Navie-Stokes equations. Meshes practically of all types are applied for these simulations. Special attention is devoted to the questions related to dynamic
Unsteady incompressible flow computations with quadrilateral elements
NASA Technical Reports Server (NTRS)
Tezduyar, T. E.; Shih, R.; Mittal, S.
1990-01-01
A comparative investigation, based on a series of numerical tests, of various velocity-pressure elements used for incompressible flow computations is presented. These elements are implemented in conjunction with one-step and multi-step temporal integration of unsteady Navier-Stokes equations. The test cases chosen are the standing vortex problem, the lid-driven cavity flow, and flow past a circular cylinder.
Unsteady loads due to propulsive lift configurations
NASA Technical Reports Server (NTRS)
Morton, J. B.; Haviland, J. K.; Catalano, G. D.; Herling, W. W.
1975-01-01
The flow of a jet over an airfoil representative of upper surface blowing was studied using laser techniques. Experimental techniques were developed for the investigation of unsteady pressures behind a cold model jet. Construction of a 1/4 scale model of the 'Beach' test configuration was completed along with construction of a portable detector. The portable detector is used in conjunction with a laser to measure jet flows during tests on the 'Beach' facility. The detector incorporates both optical and electronic components.
Unsteady natural convection in micropolar nanofluids
NASA Astrophysics Data System (ADS)
Rup, Kazimierz; Nering, Konrad
2014-09-01
This paper presents the analysis of momentum, angular momentum and heat transfer during unsteady natural convection in micropolar nanofluids. Selected nanofluids treated as single phase fluids contain small particles with diameter size 10-38.4 nm. In particular three water-based nanofluids were analyzed. Volume fraction of these solutions was 6%. The first of the analyzed nanofluids contained TiO2 nanoparticles, the second one contained Al2O3 nanoparticles, and the third one the Cu nanoparticles.
Unsteady Flow Simulation of a Controlled Airfoil
Sol Keun Jee; Omar Lopez; Jonathan Muse; Anthony Calise; Robert Moser
2008-01-01
An airfoil moving with two degrees of freedom (pitching and plunging) is simulated with a closed-loop flow control system. The simulation of the unsteady airfoil is computed using a Delayed Detached Eddy Simulation (DDES), a hybrid non-zonal RANS-LES turbulence model based on DES. The control system controls the airfoil in two modes, first through direct application of forces and torques,
Study of Unsteady Flow Actuation Produced by Surface Plasma Actuator on 2-D Airfoil
NASA Astrophysics Data System (ADS)
Phan, Minh Khang; Shin, Jichul
2014-10-01
Effect of flow actuation driven by low current continuous or pulsed DC surface glow discharge plasma actuator is studied. Schlieren image of induced flow on flat plate taken at a high repetition rate reveals that the actuation is mostly initiated near the cathode. Assuming that the actuation is mostly achieved by ions in the cathode sheath region, numerical model for the source of flow actuation is obtained by analytical estimation of ion pressure force created in DC plasma sheath near the cathode and added in momentum equation as a body force term. Modeled plasma flow actuator is simulated with NACA0012 airfoil oscillating over a certain range of angle of attack (AoA) at specific reduced frequencies of airfoil. By changing actuation authority according to the change in AoA, stabilization of unsteady flow field is improved and hence steady aerodynamic performance can be maintained. Computational result shows that plasma actuation is only effective in modifying aerodynamic characteristics of separated flow. It turns out that plasma pulse frequency should be tuned for optimal performance depending on phase angle and rotating speed. The actuation authority can be parameterized by a ratio between plasma pulse frequency and reduced frequency.
Axisymmetric, Ventilated Supercavitation in Unsteady, Horizontal Flow
NASA Astrophysics Data System (ADS)
Kawakami, Ellison; Lee, Seung-Jae; Arndt, Roger
2012-11-01
Drag reduction and/or speed augmentation of marine vehicles by means of supercavitation is a topic of great interest. During the initial launch of a supercavitating vehicle, an artificial supercavity is required until the vehicle can reach conditions at which a natural supercavity can be sustained. Previous studies at Saint Anthony Falls Laboratory (SAFL) focused on the behavior of ventilated supercavities in steady horizontal flows. In open waters, vehicles can encounter unsteady flows, especially when traveling under waves. A study has been carried out at SAFL to investigate the effects of unsteady flow on axisymmetric supercavities. An attempt is made to duplicate sea states seen in open waters. In an effort to track cavity dimensions throughout a wave cycle, an automated cavity tracking script has been developed. Using a high speed camera and the proper software, it is possible to synchronize cavity dimensions with pressure measurements taken inside the cavity. Results regarding supercavity shape, ventilation demand, cavitation parameters and closure methods are presented. It was found that flow unsteadiness caused a decrease in the overall length of the supercavity while having only a minimal effect on the maximum diameter. The supercavity volume varied with cavitation number and a possible relationship between the two is being explored. (Supported by ONR)
Visualization of unsteady computational fluid dynamics
NASA Technical Reports Server (NTRS)
Haimes, Robert
1995-01-01
The current computing environment that most researchers are using for the calculation of 3D unsteady Computational Fluid Dynamic (CFD) results is a super-computer class machine. The Massively Parallel Processors (MPP's) such as the 160 node IBM SP2 at NAS and clusters of workstations acting as a single MPP (like NAS's SGI Power-Challenge array) provide the required computation bandwidth for CFD calculations of transient problems. Work is in progress on a set of software tools designed specifically to address visualizing 3D unsteady CFD results in these super-computer-like environments. The visualization is concurrently executed with the CFD solver. The parallel version of Visual3, pV3 required splitting up the unsteady visualization task to allow execution across a network of workstation(s) and compute servers. In this computing model, the network is almost always the bottleneck so much of the effort involved techniques to reduce the size of the data transferred between machines.
Viking entry aerodynamics and heating
NASA Technical Reports Server (NTRS)
Polutchko, R. J.
1974-01-01
The characteristics of the Mars entry including the mission sequence of events and associated spacecraft weights are described along with the Viking spacecraft. Test data are presented for the aerodynamic characteristics of the entry vehicle showing trimmed alpha, drag coefficient, and trimmed lift to drag ratio versus Mach number; the damping characteristics of the entry configuration; the angle of attack time history of Viking entries; stagnation heating and pressure time histories; and the aeroshell heating distribution as obtained in tests run in a shock tunnel for various gases. Flight tests which demonstrate the aerodynamic separation of the full-scale aeroshell and the flying qualities of the entry configuration in an uncontrolled mode are documented. Design values selected for the heat protection system based on the test data and analysis performed are presented.