Cross-spectral recognition method of bridge deck aerodynamic admittance function
NASA Astrophysics Data System (ADS)
Zhao, Lin; Ge, Yaojun
2015-12-01
This study proposes a new identification algorithm about the admittance function, which can estimate the full set of six aerodynamic admittance functions considering cross power spectral density functions about the forces and the turbulence components. The method was first numerically validated through Monte Carlo simulations, and then adopted to estimate the aerodynamic admittance of a streamlined bridge deck. The identification method was further validated through a comparison between the numerical calculation and wind tunnel tests on a moving bridge section.
Derivation of aerodynamic kernel functions
NASA Technical Reports Server (NTRS)
Dowell, E. H.; Ventres, C. S.
1973-01-01
The method of Fourier transforms is used to determine the kernel function which relates the pressure on a lifting surface to the prescribed downwash within the framework of Dowell's (1971) shear flow model. This model is intended to improve upon the potential flow aerodynamic model by allowing for the aerodynamic boundary layer effects neglected in the potential flow model. For simplicity, incompressible, steady flow is considered. The proposed method is illustrated by deriving known results from potential flow theory.
Structures that Contribute to Middle-Ear Admittance in Chinchilla
Rosowski, John J.; Ravicz, Michael E.; Songer, Jocelyn E.
2009-01-01
We describe measurements of middle-ear input admittance in chinchillas (Chinchilla lanigera) before and after various manipulations that define the contributions of different middle-ear components to function. The chinchilla’s middle-ear air spaces have a large effect on the low-frequency compliance of the middle ear, and removing the influences of these spaces reveals a highly admittant tympanic membrane and ossicular chain. Measurements of the admittance of the air spaces reveal that the high-degree of segmentation of these spaces has only a small effect on the admittance. Draining the cochlea further increases the middle-ear admittance at low frequencies and removes a low-frequency (less than 300 Hz) level dependence in the admittance. Spontaneous or sound-driven contractions of the middle-ear muscles in deeply anesthetized animals were associated with significant changes in middle-ear admittance. PMID:16944166
Fourier functional analysis for unsteady aerodynamic modeling
NASA Technical Reports Server (NTRS)
Lan, C. Edward; Chin, Suei
1991-01-01
A method based on Fourier analysis is developed to analyze the force and moment data obtained in large amplitude forced oscillation tests at high angles of attack. The aerodynamic models for normal force, lift, drag, and pitching moment coefficients are built up from a set of aerodynamic responses to harmonic motions at different frequencies. Based on the aerodynamic models of harmonic data, the indicial responses are formed. The final expressions for the models involve time integrals of the indicial type advocated by Tobak and Schiff. Results from linear two- and three-dimensional unsteady aerodynamic theories as well as test data for a 70-degree delta wing are used to verify the models. It is shown that the present modeling method is accurate in producing the aerodynamic responses to harmonic motions and the ramp type motions. The model also produces correct trend for a 70-degree delta wing in harmonic motion with different mean angles-of-attack. However, the current model cannot be used to extrapolate data to higher angles-of-attack than that of the harmonic motions which form the aerodynamic model. For linear ramp motions, a special method is used to calculate the corresponding frequency and phase angle at a given time. The calculated results from modeling show a higher lift peak for linear ramp motion than for harmonic ramp motion. The current model also shows reasonably good results for the lift responses at different angles of attack.
Song, Yi-lin; Gao, Shu-mei; Ikarashi, Akira; Yamakoshi, Ken-ichi
2009-03-01
A handy-type monitoring system for cardiovascular haemodynamic functions based on the volume-compensation and electrical admittance method is developed. In this system, the inconvenient and discomfort due to cuff occlusion of the biological segment for BP measurement is improved by developing a new device using a local pressurization method, the stability for the physiological information detection is improved by developing a new detecting system, and the noise during detection using the system is greatly reduced by using a newly developed nozzle-flapper type electro-pneumatic converter. Also, for electrical admittance cardiography to estimate CO, the applicability of a two-compartment coaxial cylindrical model and the optimal position of a spot-electrode array that is used to replace the conventional band-electrode are discussed in this research. Experimental result shows that the monitoring system should satisfy non-invasive BP and CO measurement on beat by beat, and the comfort of measurement is significantly improved. PMID:19771888
Basis Function Approximation of Transonic Aerodynamic Influence Coefficient Matrix
NASA Technical Reports Server (NTRS)
Li, Wesley W.; Pak, Chan-gi
2011-01-01
A technique for approximating the modal aerodynamic influence coefficients matrices by using basis functions has been developed and validated. An application of the resulting approximated modal aerodynamic influence coefficients matrix for a flutter analysis in transonic speed regime has been demonstrated. This methodology can be applied to the unsteady subsonic, transonic, and supersonic aerodynamics. The method requires the unsteady aerodynamics in frequency-domain. The flutter solution can be found by the classic methods, such as rational function approximation, k, p-k, p, root-locus et cetera. The unsteady aeroelastic analysis for design optimization using unsteady transonic aerodynamic approximation is being demonstrated using the ZAERO flutter solver (ZONA Technology Incorporated, Scottsdale, Arizona). The technique presented has been shown to offer consistent flutter speed prediction on an aerostructures test wing 2 configuration with negligible loss in precision in transonic speed regime. These results may have practical significance in the analysis of aircraft aeroelastic calculation and could lead to a more efficient design optimization cycle.
Tevatron admittance measurement
Zhang, X.L.; Shiltsev, V.; Tan, C.Y.; /Fermilab
2005-05-01
We measured the Tevatron beam admittance by the means of exciting the beam with noise and causing emittance growth. The noise power was about 3W with a bandwidth of 100Hz and centered either in the horizontal betatron frequency or vertical betatron frequency. We were able to controllably blow the beam emittance up quickly. From the point where the beam emittance stopped growing, we measured the beam acceptance of the Tevatron.
Basis Function Approximation of Transonic Aerodynamic Influence Coefficient Matrix
NASA Technical Reports Server (NTRS)
Li, Wesley Waisang; Pak, Chan-Gi
2010-01-01
A technique for approximating the modal aerodynamic influence coefficients [AIC] matrices by using basis functions has been developed and validated. An application of the resulting approximated modal AIC matrix for a flutter analysis in transonic speed regime has been demonstrated. This methodology can be applied to the unsteady subsonic, transonic and supersonic aerodynamics. The method requires the unsteady aerodynamics in frequency-domain. The flutter solution can be found by the classic methods, such as rational function approximation, k, p-k, p, root-locus et cetera. The unsteady aeroelastic analysis for design optimization using unsteady transonic aerodynamic approximation is being demonstrated using the ZAERO(TradeMark) flutter solver (ZONA Technology Incorporated, Scottsdale, Arizona). The technique presented has been shown to offer consistent flutter speed prediction on an aerostructures test wing [ATW] 2 configuration with negligible loss in precision in transonic speed regime. These results may have practical significance in the analysis of aircraft aeroelastic calculation and could lead to a more efficient design optimization cycle
Experimental determination of three dimensional liquid rocket nozzle admittances.
NASA Technical Reports Server (NTRS)
Zinn, B. T.; Bell, W. A.; Daniel, B. R.; Smith, A. J., Jr.
1972-01-01
The three dimensional nozzle admittance, an important parameter in combustion instability studies, was experimentally measured for several nozzle configurations. The admittance values were obtained using a modification of the classical impedance tube technique. The modified impedance tube method measures the admittance of a duct termination in the presence of one dimensional mean flow and three dimensional oscillations. Values of the nozzle admittance were obtained from pressure amplitude measurements taken at discrete points along the length of the tube. To determine the effects of nozzle geometry, nozzles were tested with half-angles of 15, 30, and 45 degrees and entrance Mach numbers of 0.08, 0.16, and 0.20. The admittance results are presented as functions of nondimensional frequency for mixed first tangential-longitudinal modes. These results are compared with available theoretical predictions and favorable agreement between theory and experiment is shown.
Introduction to Generalized Functions with Applications in Aerodynamics and Aeroacoustics
NASA Technical Reports Server (NTRS)
Farassat, F.
1994-01-01
Generalized functions have many applications in science and engineering. One useful aspect is that discontinuous functions can be handled as easily as continuous or differentiable functions and provide a powerful tool in formulating and solving many problems of aerodynamics and acoustics. Furthermore, generalized function theory elucidates and unifies many ad hoc mathematical approaches used by engineers and scientists. We define generalized functions as continuous linear functionals on the space of infinitely differentiable functions with compact support, then introduce the concept of generalized differentiation. Generalized differentiation is the most important concept in generalized function theory and the applications we present utilize mainly this concept. First, some results of classical analysis, are derived with the generalized function theory. Other applications of the generalized function theory in aerodynamics discussed here are the derivations of general transport theorems for deriving governing equations of fluid mechanics, the interpretation of the finite part of divergent integrals, the derivation of the Oswatitsch integral equation of transonic flow, and the analysis of velocity field discontinuities as sources of vorticity. Applications in aeroacoustics include the derivation of the Kirchhoff formula for moving surfaces, the noise from moving surfaces, and shock noise source strength based on the Ffowcs Williams-Hawkings equation.
A creatinine biosensor based on admittance measurement
NASA Astrophysics Data System (ADS)
Ching, Congo Tak-Shing; Sun, Tai-Ping; Jheng, Deng-Yun; Tsai, Hou-Wei; Shieh, Hsiu-Li
2015-08-01
Regular check of blood creatinine level is very important as it is a measurement of renal function. Therefore, the objective of this study is to develop a simple and reliable creatinine biosensor based on admittance measurement for precise determination of creatinine. The creatinine biosensor was fabricated with creatinine deiminase immobilized on screen-printed carbon electrodes. Admittance measurement at a specific frequency ranges (22.80 - 84.71 Hz) showed that the biosensor has an excellent linear (r2 > 0.95) response range (50 - 250 uM), which covers the normal physiological and pathological ranges of blood creatinine levels. Intraclass correlation coefficient (ICC) showed that the biosensor has excellent reliability and validity (ICC = 0.98). In conclusion, a simple and reliable creatinine biosensor was developed and it is capable of precisely determining blood creatinine levels in both the normal physiological and pathological ranges.
Acoustic-Liner Admittance in a Duct
NASA Technical Reports Server (NTRS)
Watson, W. R.
1986-01-01
Method calculates admittance from easily obtainable values. New method for calculating acoustic-liner admittance in rectangular duct with grazing flow based on finite-element discretization of acoustic field and reposing of unknown admittance value as linear eigenvalue problem on admittance value. Problem solved by Gaussian elimination. Unlike existing methods, present method extendable to mean flows with two-dimensional boundary layers as well. In presence of shear, results of method compared well with results of Runge-Kutta integration technique.
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
Aerodynamic Indicial Functions and Their Use in Aeroelastic Formulation of Lifting Surfaces
NASA Technical Reports Server (NTRS)
Marzocca, Piergiovanni; Librescu, Liviu; Silva, Walter A.
2000-01-01
An investigation related to the use of linear indicial functions in the time and frequency domains, enabling one to derive the proper aerodynamic loads as to study the subcritical response and flutter of swept lifting surfaces, respectively, of the open/closed loop aeroelastic system is presented. The expressions of the lift and aerodynamic moment in the frequency domain are given in terms of the Theodorsen's function, while, in the time domain, these are obtained directly with the help of the Wagner's function. Closed form solutions of aerodynamic derivatives are obtained, graphical representations are supplied and conclusions and prospects for further developments are outlined.
Improved multimodal admittance method in varying cross section waveguides.
Maurel, Agnès; Mercier, Jean-François; Pagneux, Vincent
2014-04-01
An improved version of the multimodal admittance method in acoustic waveguides with varying cross sections is presented. This method aims at a better convergence with respect to the number of transverse modes that are taken into account. It is based on an enriched modal expansion of the pressure: the N first modes are the local transverse modes and a supplementary (N+1)th mode, called boundary mode, is a well-chosen transverse function orthogonal to the N first modes. This expansion leads to the classical form of the coupled mode equations where the component of the boundary mode is of evanescent character. Under this form, the multimodal admittance method based on the Riccati equation on the admittance matrix (the Dirichlet-to-Neumann operator) is straightforwardly implemented. With this supplementary mode, in addition to the improvement of the convergence of the pressure field, results show a superconvergence of the scattered field outside of the varying cross sections region. PMID:24711716
NASA Technical Reports Server (NTRS)
Morelli, E. A.; Proffitt, M. S.
1999-01-01
The data for longitudinal non-dimensional, aerodynamic coefficients in the High Speed Research Cycle 2B aerodynamic database were modeled using polynomial expressions identified with an orthogonal function modeling technique. The discrepancy between the tabular aerodynamic data and the polynomial models was tested and shown to be less than 15 percent for drag, lift, and pitching moment coefficients over the entire flight envelope. Most of this discrepancy was traced to smoothing local measurement noise and to the omission of mass case 5 data in the modeling process. A simulation check case showed that the polynomial models provided a compact and accurate representation of the nonlinear aerodynamic dependencies contained in the HSR Cycle 2B tabular aerodynamic database.
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.
Analytical admittance characterization of high mobility channel
Mammeri, A. M.; Mahi, F. Z.; Varani, L.
2015-03-30
In this contribution, we investigate the small-signal admittance of the high electron mobility transistors field-effect channels under a continuation branching of the current between channel and gate by using an analytical model. The analytical approach takes into account the linearization of the 2D Poisson equation and the drift current along the channel. The analytical equations discuss the frequency dependence of the admittance at source and drain terminals on the geometrical transistor parameters.
NASA Astrophysics Data System (ADS)
Cheung, Perry; Fairweather, Joseph D.; Schwartz, Daniel T.
2012-09-01
Simple laboratory methods for determining liquid water distribution in polymer electrolyte membrane fuel cell gas diffusion layers (GDLs) are needed to engineer better GDL materials. Capillary pressure vs. liquid saturation measurements are attractive, but lack the ability to probe the hydraulic interconnectivity and distribution within the pore structure. Hydraulic admittance measurements of simple capillary bundles have recently been shown to nicely measure characteristics of the free-interfaces and hydraulic path. Here we examine the use of hydraulic admittance with a succession of increasingly complex porous media, starting with a laser-drilled sample with 154 asymmetric pores and progress to the behavior of Toray TGP-H090 carbon papers. The asymmetric laser-drilled sample clearly shows hydraulic admittance measurements are sensitive to sample orientation, especially when examined as a function of saturation state. Finite element modeling of the hydraulic admittance is consistent with experimental measurements. The hydraulic admittance spectra from GDL samples are complex, so we examine trends in the spectra as a function of wet proofing (0% and 40% Teflon loadings) as well as saturation state of the GDL. The presence of clear peaks in the admittance spectra for both GDL samples suggests a few pore types are largely responsible for transporting liquid water.
Aerodynamic parameter estimation via Fourier modulating function techniques
NASA Technical Reports Server (NTRS)
Pearson, A. E.
1995-01-01
Parameter estimation algorithms are developed in the frequency domain for systems modeled by input/output ordinary differential equations. The approach is based on Shinbrot's method of moment functionals utilizing Fourier based modulating functions. Assuming white measurement noises for linear multivariable system models, an adaptive weighted least squares algorithm is developed which approximates a maximum likelihood estimate and cannot be biased by unknown initial or boundary conditions in the data owing to a special property attending Shinbrot-type modulating functions. Application is made to perturbation equation modeling of the longitudinal and lateral dynamics of a high performance aircraft using flight-test data. Comparative studies are included which demonstrate potential advantages of the algorithm relative to some well established techniques for parameter identification. Deterministic least squares extensions of the approach are made to the frequency transfer function identification problem for linear systems and to the parameter identification problem for a class of nonlinear-time-varying differential system models.
NASA Technical Reports Server (NTRS)
Arian, Eyal; Salas, Manuel D.
1997-01-01
We derive the adjoint equations for problems in aerodynamic optimization which are improperly considered as "inadmissible." For example, a cost functional which depends on the density, rather than on the pressure, is considered "inadmissible" for an optimization problem governed by the Euler equations. We show that for such problems additional terms should be included in the Lagrangian functional when deriving the adjoint equations. These terms are obtained from the restriction of the interior PDE to the control surface. Demonstrations of the explicit derivation of the adjoint equations for "inadmissible" cost functionals are given for the potential, Euler, and Navier-Stokes equations.
Aerodynamic interference effects on tilting proprotor aircraft. [using the Green function method
NASA Technical Reports Server (NTRS)
Soohoo, P.; Morino, L.; Noll, R. B.; Ham, N. D.
1977-01-01
The Green's function method was used to study tilting proprotor aircraft aerodynamics with particular application to the problem of the mutual interference of the wing-fuselage-tail-rotor wake configuration. While the formulation is valid for fully unsteady rotor aerodynamics, attention was directed to steady state aerodynamics, which was achieved by replacing the rotor with the actuator disk approximation. The use of an actuator disk analysis introduced a mathematical singularity into the formulation; this problem was studied and resolved. The pressure distribution, lift, and pitching moment were obtained for an XV-15 wing-fuselage-tail rotor configuration at various flight conditions. For the flight configurations explored, the effects of the rotor wake interference on the XV-15 tilt rotor aircraft yielded a reduction in the total lift and an increase in the nose-down pitching moment. This method provides an analytical capability that is simple to apply and can be used to investigate fuselage-tail rotor wake interference as well as to explore other rotor design problem areas.
NASA Astrophysics Data System (ADS)
Diallo, O.; Clezio, E. Le; Delaunay, T.; Bavencoffe, M.; Feuillard, G.
2014-01-01
This work deals with the characterization of functional properties, including determination of mechanical and electrical losses, of piezoelectric materials using only one sample and one measurement. First, the natural resonant frequencies of a piezoelectric parallelepiped are calculated and the electrical admittance is determined from calculations of the charge quantity on both electrodes of the parallelepiped. A first validation of the model is performed using a comparison with Mason's model. Results are reported for a PMN-34.5PT ceramic cube and a good agreement is found between experimental admittance measurements and their modeling. The functional properties of the PMN-34.5PT are then extracted.
Diallo, O.; Bavencoffe, M.; Feuillard, G.; Clezio, E. Le; Delaunay, T.
2014-01-15
This work deals with the characterization of functional properties, including determination of mechanical and electrical losses, of piezoelectric materials using only one sample and one measurement. First, the natural resonant frequencies of a piezoelectric parallelepiped are calculated and the electrical admittance is determined from calculations of the charge quantity on both electrodes of the parallelepiped. A first validation of the model is performed using a comparison with Mason's model. Results are reported for a PMN-34.5PT ceramic cube and a good agreement is found between experimental admittance measurements and their modeling. The functional properties of the PMN-34.5PT are then extracted.
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.
A study of the ionic conduction of mica surface by admittance spectroscopy
NASA Astrophysics Data System (ADS)
Dolci, D.; Aloisi, G.; Lanzi, L.; Carlà, M.
2007-08-01
The ionic conduction on the surface of humid mica has been analyzed by admittance spectroscopy as a function of relative humidity for different surface treatments. Measurements at low frequency indicate that water adsorption proceeds first in the form of a strongly adsorbed uniform thin layer, then with the formation of highly inhomogeneous thick aggregates.
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.
An introduction to generalized functions with some applications in aerodynamics and aeroacoustics
NASA Technical Reports Server (NTRS)
Farassat, F.
1994-01-01
In this paper, we start with the definition of generalized functions as continuous linear functionals on the space of infinitely differentiable functions with compact support. The concept of generalization differentiation is introduced next. This is the most important concept in generalized function theory and the applications we present utilize mainly this concept. First, some of the results of classical analysis, such as Leibniz rule of differentiation under the integral sign and the divergence theorem, are derived using the generalized function theory. It is shown that the divergence theorem remains valid for discontinuous vector fields provided that the derivatives are all viewed as generalized derivatives. This implies that all conservation laws of fluid mechanics are valid as they stand for discontinuous fields with all derivatives treated as generalized deriatives. Once these derivatives are written as ordinary derivatives and jumps in the field parameters across discontinuities, the jump conditions can be easily found. For example, the unsteady shock jump conditions can be derived from mass and momentum conservation laws. By using a generalized function theory, this derivative becomes trivial. Other applications of the generalized function theory in aerodynamics discussed in this paper are derivation of general transport theorems for deriving governing equations of fluid mechanics, the interpretation of finite part of divergent integrals, derivation of Oswatiitsch integral equation of transonic flow, and analysis of velocity field discontinuities as sources of vorticity. Applications in aeroacoustics presented here include the derivation of the Kirchoff formula for moving surfaces,the noise from moving surfaces, and shock noise source strength based on the Ffowcs Williams-Hawkings equation.
Chen, Sheng Hwa; Hsiao, Tzu-Yu; Hsiao, Li-Chun; Chung, Yu-Mei; Chiang, Shu-Chiung
2007-07-01
Teachers have a high percentage of voice problems. For voice disordered teachers, resonant voice therapy is hypothesized to reduce voice problems. No research has been done on the physiological, acoustic, and aerodynamic effects of resonant voice therapy for school teachers. The purpose of this study is to investigate resonant voice therapy outcome from perceptual, physiological, acoustic, aerodynamic, and functional aspects for female teachers with voice disorders. A prospective study was designed for this research. The research subjects were 24 female teachers in Taipei. All subjects received resonant voice therapy in groups of 4 subjects, 90 minutes per session, and 1 session per week for 8 weeks. The outcome of resonant voice therapy was assessed from auditory perceptual judgment, videostroboscopic examination, acoustic measurements, aerodynamic measurements, and functional measurements before and after therapy. After therapy the severity of roughness, strain, monotone, resonance, hard attack, and glottal fry in auditory perceptual judgments, the severity of vocal fold pathology, mucosal wave, amplitude, and vocal fold closure in videostroboscopic examinations, phonation threshold pressure, and the score of physical scale in the Voice Handicap Index were significantly reduced. The speaking Fo, maximum range of speaking Fo, and maximum range of speaking intensity were significantly increased after therapy. No significant change was found in perturbation and breathiness measurements after therapy. Resonant voice therapy is effective for school teachers and is suggested as one of the therapy approaches in clinics for this population. PMID:16581227
Increasing Immunization Compliance by Reducing Provisional Admittance.
Davis, Wendy S; Varni, Susan E; Barry, Sara E; Frankowski, Barbara L; Harder, Valerie S
2016-08-01
Students in Vermont with incomplete or undocumented immunization status are provisionally admitted to schools and historically had a calendar year to resolve their immunization status. The process of resolving these students' immunization status was challenging for school nurses. We conducted a school-based quality improvement effort to increase student compliance with Vermont immunization regulations using a collaborative learning approach with public health school liaisons and school nurses from public schools to reduce provisional admittance in 2011-2012. Strategies included using a tracking system, accessing the immunization registry, promoting immunization importance, tracking immunization plans, and working with medical homes to update records. Participating school nurses observed decreases in the number of provisionally admitted students, although this reduction was not significantly different than matched comparison schools. We also found the number of provisionally admitted students fluctuated throughout the year and resolving the immunization status of New Americans and exchange students required special attention. Our approach supports the coordinated school health model and demonstrates the critical role school nurses play in improving population health outcomes. PMID:26699951
NASA Astrophysics Data System (ADS)
Zhang, Tingting; Lee, Eunjung; Seo, Jin Keun
2014-04-01
Trans-admittance mammography (TAM) is a bioimpedance technique for breast cancer detection. It is based on the comparison of tissue conductivity: cancerous tissue is identified by its higher conductivity in comparison with the surrounding normal tissue. In TAM, the breast is compressed between two electrical plates (in a similar architecture to x-ray mammography). The bottom plate has many sensing point electrodes that provide two-dimensional images (trans-admittance maps) that are induced by voltage differences between the two plates. Multi-frequency admittance data (Neumann data) are measured over the range 50 Hz-500 kHz. TAM aims to determine the location and size of any anomaly from the multi-frequency admittance data. Various anomaly detection algorithms can be used to process TAM data to determine the transverse positions of anomalies. However, existing methods cannot reliably determine the depth or size of an anomaly. Breast cancer detection using TAM would be improved if the depth or size of an anomaly could also be estimated, properties that are independent of the admittivity contrast. A formula is proposed here that can estimate the depth of an anomaly independent of its size and the admittivity contrast. This depth estimation can also be used to derive an estimation of the size of the anomaly. The proposed estimations are verified rigorously under a simplified model. Numerical simulation shows that the proposed method also works well in general settings.
NASA Technical Reports Server (NTRS)
Kana, D. D.; Vargas, L. M.
1977-01-01
Transient excitation forces were applied separately to simple beam-and-mass launch vehicle and payload models to develop complex admittance functions for the interface and other appropriate points on the structures. These measured admittances were then analytically combined by a matrix representation to obtain a description of the coupled system dynamic characteristics. Response of the payload model to excitation of the launch vehicle model was predicted and compared with results measured on the combined models. These results are also compared with results of earlier work in which a similar procedure was employed except that steady-state sinusoidal excitation techniques were included. It is found that the method employing transient tests produces results that are better overall than the steady state methods. Furthermore, the transient method requires far less time to implement, and provides far better resolution in the data. However, the data acquisition and handling problem is more complex for this method. It is concluded that the transient test and admittance matrix prediction method can be a valuable tool for development of payload vibration tests.
Details of insect wing design and deformation enhance aerodynamic function and flight efficiency.
Young, John; Walker, Simon M; Bomphrey, Richard J; Taylor, Graham K; Thomas, Adrian L R
2009-09-18
Insect wings are complex structures that deform dramatically in flight. We analyzed the aerodynamic consequences of wing deformation in locusts using a three-dimensional computational fluid dynamics simulation based on detailed wing kinematics. We validated the simulation against smoke visualizations and digital particle image velocimetry on real locusts. We then used the validated model to explore the effects of wing topography and deformation, first by removing camber while keeping the same time-varying twist distribution, and second by removing camber and spanwise twist. The full-fidelity model achieved greater power economy than the uncambered model, which performed better than the untwisted model, showing that the details of insect wing topography and deformation are important aerodynamically. Such details are likely to be important in engineering applications of flapping flight. PMID:19762645
Online Stability in Human-Robot Cooperation with Admittance Control.
Dimeas, Fotios; Aspragathos, Nikos
2016-01-01
In the design of a compliant admittance controller for physical human-robot interaction, it is necessary to ensure stable and effective cooperation. The stability of the admittance controller is mainly threatened by a stiff environment. Many methods that guarantee stability in arbitrary environments, impose conservative control gains that limit the effectiveness of the cooperation. Inspired by previous work in frequency domain stability observers, a method is proposed in this paper to detect unstable behavior and stabilize the robot with online adaptation of the admittance control gains. The introduced instability index is based on frequency domain analysis, which very quickly detects unstable behavior by monitoring high frequency oscillation in the force signal. To treat the instability, an adaptation scheme of the admittance parameters is proposed, that relaxes conservative gains and improves the cooperation by considering the effect of variable admittance on the operators' effort. We investigate two human-robot co-manipulation tasks; cooperation within a zero stiffness environment and cooperation in contact with a stiff double-wall virtual environment. The proposed methods are validated experimentally with a number of subjects in cooperation with an LWR manipulator. PMID:26780819
NASA Technical Reports Server (NTRS)
Nielsen, Jack N.
1988-01-01
The fundamental aerodynamics of slender bodies is examined in the reprint edition of an introductory textbook originally published in 1960. Chapters are devoted to the formulas commonly used in missile aerodynamics; slender-body theory at supersonic and subsonic speeds; vortices in viscid and inviscid flow; wing-body interference; downwash, sidewash, and the wake; wing-tail interference; aerodynamic controls; pressure foredrag, base drag, and skin friction; and stability derivatives. Diagrams, graphs, tables of terms and formulas are provided.
Characterizing the eardrum admittance: Comparisons of tympanometry and reflectance
NASA Astrophysics Data System (ADS)
Robinson, Sarah; Thompson, Suzanne; Allen, Jont B.
2015-12-01
The residual ear canal (REC) between the probe and tympanic membrane (TM) is a significant source of non-pathological variability for acoustic measurements made in the ear canal. Tympanometry and reflectance, which seek to characterize the middle ear based on the TM admittance, must account for unknown REC dimensions. In tympanometry, the REC volume and 226 Hz TM admittance are estimated by varying the canal static pressure. Using a reflectance parametrization developed by the authors, typical assumptions for removing the REC effect are extended, and methods to estimate the REC volume and TM admittance are presented and compared to tympanometry. Results of this method are shown for reflectance measurements of human ears with varying static middle ear pressures (MEPs). The data show that the 226 Hz TM compliance is non-zero at tympanometric pressure extremes, and that acoustic parameters of the middle ear have highly variable, nonlinear dependence on the MEP level.
Admittance of multiterminal quantum Hall conductors at kilohertz frequencies
Hernández, C.; Consejo, C.; Chaubet, C.; Degiovanni, P.
2014-03-28
We present an experimental study of the low frequency admittance of quantum Hall conductors in the [100 Hz, 1 MHz] frequency range. We show that the frequency dependence of the admittance of the sample strongly depends on the topology of the contacts connections. Our experimental results are well explained within the Christen and Büttiker approach for finite frequency transport in quantum Hall edge channels taking into account the influence of the coaxial cables capacitance. In the Hall bar geometry, we demonstrate that there exists a configuration in which the cable capacitance does not influence the admittance measurement of the sample. In this case, we measure the electrochemical capacitance of the sample and observe its dependence on the filling factor.
Not Available
1993-01-01
In this article two integral computational fluid dynamics methods for steady-state and transient vehicle aerodynamic simulations are described using a Chevrolet Corvette ZR-1 surface panel model. In the last decade, road-vehicle aerodynamics have become an important design consideration. Originally, the design of low-drag shapes was given high priority due to worldwide fuel shortages that occurred in the mid-seventies. More recently, there has been increased interest in the role aerodynamics play in vehicle stability and passenger safety. Consequently, transient aerodynamics and the aerodynamics of vehicle in yaw have become important issues at the design stage. While there has been tremendous progress in Navier-Stokes methodology in the last few years, the physics of bluff-body aerodynamics are still very difficult to model correctly. Moreover, the computational effort to perform Navier-Stokes simulations from the geometric stage to complete flow solutions requires much computer time and impacts the design cycle time. In the short run, therefore, simpler methods must be used for such complicated problems. Here, two methods are described for the simulation of steady-state and transient vehicle aerodynamics.
NASA Astrophysics Data System (ADS)
Bol'basov, E. N.; Lapin, I. N.; Tverdokhlebov, S. I.; Svetlichnyi, V. A.
2014-07-01
For applications in tissue engineering, three-dimensional biodegradable polymeric matrices, whose surface is functionalized by nanoparticles obtained in the liquid phase by the method of laser ablation from bulk metal (Ag or Zn) targets, are synthesized by the method of aerodynamic synthesis from a solution of poly-l-lactide acid. Their properties are investigated. It is demonstrated that the matrices represent a very porous spatial fibrous structure consisting of polymorphic fibers with diameters from 0.25 to 2.5 μm. It is established that functional coatings consisting of agglomerates of semiconductor (ZnO) or metal (Ag) nanoparticles can be produced on the surface of structural matrix elements by repeated matrix impregnation.
9 CFR 117.3 - Admittance of animals.
Code of Federal Regulations, 2013 CFR
2013-01-01
... 9 Animals and Animal Products 1 2013-01-01 2013-01-01 false Admittance of animals. 117.3 Section 117.3 Animals and Animal Products ANIMAL AND PLANT HEALTH INSPECTION SERVICE, DEPARTMENT OF AGRICULTURE VIRUSES, SERUMS, TOXINS, AND ANALOGOUS PRODUCTS; ORGANISMS AND VECTORS ANIMALS AT...
9 CFR 117.3 - Admittance of animals.
Code of Federal Regulations, 2014 CFR
2014-01-01
... 9 Animals and Animal Products 1 2014-01-01 2014-01-01 false Admittance of animals. 117.3 Section 117.3 Animals and Animal Products ANIMAL AND PLANT HEALTH INSPECTION SERVICE, DEPARTMENT OF AGRICULTURE VIRUSES, SERUMS, TOXINS, AND ANALOGOUS PRODUCTS; ORGANISMS AND VECTORS ANIMALS AT...
9 CFR 117.3 - Admittance of animals.
Code of Federal Regulations, 2011 CFR
2011-01-01
... 9 Animals and Animal Products 1 2011-01-01 2011-01-01 false Admittance of animals. 117.3 Section 117.3 Animals and Animal Products ANIMAL AND PLANT HEALTH INSPECTION SERVICE, DEPARTMENT OF AGRICULTURE VIRUSES, SERUMS, TOXINS, AND ANALOGOUS PRODUCTS; ORGANISMS AND VECTORS ANIMALS AT...
9 CFR 117.3 - Admittance of animals.
Code of Federal Regulations, 2010 CFR
2010-01-01
... 9 Animals and Animal Products 1 2010-01-01 2010-01-01 false Admittance of animals. 117.3 Section 117.3 Animals and Animal Products ANIMAL AND PLANT HEALTH INSPECTION SERVICE, DEPARTMENT OF AGRICULTURE VIRUSES, SERUMS, TOXINS, AND ANALOGOUS PRODUCTS; ORGANISMS AND VECTORS ANIMALS AT...
9 CFR 117.3 - Admittance of animals.
Code of Federal Regulations, 2012 CFR
2012-01-01
... 9 Animals and Animal Products 1 2012-01-01 2012-01-01 false Admittance of animals. 117.3 Section 117.3 Animals and Animal Products ANIMAL AND PLANT HEALTH INSPECTION SERVICE, DEPARTMENT OF AGRICULTURE VIRUSES, SERUMS, TOXINS, AND ANALOGOUS PRODUCTS; ORGANISMS AND VECTORS ANIMALS AT...
Abdala, Carolina; Keefe, Douglas H.; Oba, Sandra I.
2009-01-01
Previous work has reported non-adultlike distortion product otoacoustic emission (DPOAE) suppression in human newborns at f2 =6000 Hz, indicating an immaturity in peripheral auditory function. In this study, DPOAE suppression tuning curves (STCs) were recorded as a measure of cochlear function and acoustic admittance/reflectance (YR) in the ear canal recorded as a measure of middle-ear function, in the same 20 infants at birth and through 6 months of age. DPOAE STCs changed little from birth through 6 months, showing excessively narrow and sharp tuning throughout the test period. In contrast, several middle-ear indices at corresponding frequencies shifted systematically with increasing age, although they also remained non-adultlike at 6 months. Linear correlations were conducted between YR and DPOAE suppression features. Only two correlations out of 76 were significant, and all but three YR variables accounted for <10% of the variance in DPOAE suppression tuning. The strongest correlation was noted between admittance phase at 5700 Hz and STC tip-to-tail (R=0.49). The association between middle-ear variables and DPOAE suppression may be stronger during other developmental time periods. Study of older infants and children is needed to fully define postnatal immaturity of human peripheral auditory function. PMID:17552713
Entrainment of radio frequency chaff by wind as a function of surface aerodynamic roughness.
Gillies, John A; Nickling, William G
2003-02-01
Radio frequency (RF) chaff (approximately 2-cm x 25-microm diameter aluminum-coated glass silicate cylinders) released by military aircraft during testing and training activities has the potential to become entrained by wind upon settling to the Earth's surface. Once entrained from the surface there is the potential for RF chaff to be abraded and produce PM10 and PM2.5, which are regulated pollutants and pose health concerns. A series of portable wind tunnel tests were carried out to examine the propensity of RF chaff to become entrained by wind by defining the relationship between the threshold friction velocity of RF chaff (u(*t RF chaff)) and aerodynamic roughness (z(o)) of surfaces onto which it may deposit. The test surfaces were of varying roughness including types near the Naval Air Station (NAS), Fallon, NV, where RF chaff is released. The u(*t) of this fibrous material ranged from 0.14 m/sec for a smooth playa to 0.82 m/sec for a rough crusted playa surface with larger cobble-sized (approximately 6-26-cm diameter) rocks rising above the surface. The u(*t RF chaff) is dependent on the z(o) of the surface onto which it falls as well as the physical characteristics of the roughness. The wind regime of Fallon would allow for chaff suspension events to occur should it settle on typical surfaces in the area. However, the wind climatology of this area makes the probability of such events relatively low. PMID:12617294
Impact and admittance modeling of the Isidis Planitia, Mars
NASA Astrophysics Data System (ADS)
Mancinelli, Paolo; Mondini, Alessandro C.; Pauselli, Cristina; Federico, Costanzo
2015-11-01
In this study, the impact event that produced the Martian Isidis basin (0-20°N and 70-100°E) was modeled using the iSALE hydrocode, and the current lithospheric structure was obtained comparing the calculated admittance from topography and gravity data, with the admittance from top-load and bottom-load flexure models. The best-fit admittance model was obtained using a bottom-load flexure with a thinned crust of 10 km, likely formed by cooling of the surficial melt pool after the impact, and an elastic thickness of 36 km. We found that the impact produced crustal excavation and thickening, surficial melt pool and temperatures >1500 K beneath the area where the free-air maxima is observed. The geometry resulting from the impact modeling is compatible with the radius of the Isidis basin. Derived thermal gradient and heat flux are in agreement with an early-Noachian epoch for the Isidis impact event and with the intense volcanic activity that followed the impact.
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.
Unsteady aerodynamics modeling for flight dynamics application
NASA Astrophysics Data System (ADS)
Wang, Qing; He, Kai-Feng; Qian, Wei-Qi; Zhang, Tian-Jiao; Cheng, Yan-Qing; Wu, Kai-Yuan
2012-02-01
In view of engineering application, it is practicable to decompose the aerodynamics into three components: the static aerodynamics, the aerodynamic increment due to steady rotations, and the aerodynamic increment due to unsteady separated and vortical flow. The first and the second components can be presented in conventional forms, while the third is described using a one-order differential equation and a radial-basis-function (RBF) network. For an aircraft configuration, the mathematical models of 6-component aerodynamic coefficients are set up from the wind tunnel test data of pitch, yaw, roll, and coupled yawroll large-amplitude oscillations. The flight dynamics of an aircraft is studied by the bifurcation analysis technique in the case of quasi-steady aerodynamics and unsteady aerodynamics, respectively. The results show that: (1) unsteady aerodynamics has no effect upon the existence of trim points, but affects their stability; (2) unsteady aerodynamics has great effects upon the existence, stability, and amplitudes of periodic solutions; and (3) unsteady aerodynamics changes the stable regions of trim points obviously. Furthermore, the dynamic responses of the aircraft to elevator deflections are inspected. It is shown that the unsteady aerodynamics is beneficial to dynamic stability for the present aircraft. Finally, the effects of unsteady aerodynamics on the post-stall maneuverability are analyzed by numerical simulation.
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
Quality control of dairy products using single frequency admittance measurements
NASA Astrophysics Data System (ADS)
Mabrook, M. F.; Darbyshire, A. M.; Petty, M. C.
2006-02-01
A reusable device for the detection of adulteration in dairy products such as milk and cream has been developed. The ac electrical admittance spectra of different samples have been studied using both uncoated and alkyl mercaptan-coated gold electrodes. Uncoated gold electrodes exhibited a polarization at around 250 Hz for full fat milk, while mercaptan-coated gold electrodes showed a similar effect at around 2 kHz. The characteristics at 100 kHz and 8 °C for all skimmed milk samples revealed a linear decrease in conductance with increasing water content over the entire range of water concentration. In contrast, the conductance of full fat milk, single and double cream, showed a linear decrease only at added water concentration higher than 6%. At lower concentrations, these dairy products exhibited anomalous conductivity maxima.
Computer code for the prediction of nozzle admittance
NASA Technical Reports Server (NTRS)
Nguyen, Thong V.
1988-01-01
A procedure which can accurately characterize injector designs for large thrust (0.5 to 1.5 million pounds), high pressure (500 to 3000 psia) LOX/hydrocarbon engines is currently under development. In this procedure, a rectangular cross-sectional combustion chamber is to be used to simulate the lower traverse frequency modes of the large scale chamber. The chamber will be sized so that the first width mode of the rectangular chamber corresponds to the first tangential mode of the full-scale chamber. Test data to be obtained from the rectangular chamber will be used to assess the full scale engine stability. This requires the development of combustion stability models for rectangular chambers. As part of the combustion stability model development, a computer code, NOAD based on existing theory was developed to calculate the nozzle admittances for both rectangular and axisymmetric nozzles. This code is detailed.
Automatically calibrating admittances in KATE's autonomous launch operations model
NASA Astrophysics Data System (ADS)
Morgan, Steve
1992-09-01
This report documents a 1000-line Symbolics LISP program that automatically calibrates all 15 fluid admittances in KATE's Autonomous Launch Operations (ALO) model. (KATE is Kennedy Space Center's Knowledge-based Autonomous Test Engineer, a diagnosis and repair expert system created for use on the Space Shuttle's various fluid flow systems.) As a new KATE application, the calibrator described here breaks new ground for KSC's Artificial Intelligence Lab by allowing KATE to both control and measure the hardware she supervises. By automating a formerly manual process, the calibrator: (1) saves the ALO model builder untold amounts of labor; (2) enables quick repairs after workmen accidently adjust ALO's hand valves; and (3) frees the modeler to pursue new KATE applications that previously were too complicated. Also reported are suggestions for enhancing the program: (1) to calibrate ALO's TV cameras, pumps, and sensor tolerances; and (2) to calibrate devices in other KATE models, such as the shuttle's LOX and Environment Control System (ECS).
Automatically calibrating admittances in KATE's autonomous launch operations model
NASA Technical Reports Server (NTRS)
Morgan, Steve
1992-01-01
This report documents a 1000-line Symbolics LISP program that automatically calibrates all 15 fluid admittances in KATE's Autonomous Launch Operations (ALO) model. (KATE is Kennedy Space Center's Knowledge-based Autonomous Test Engineer, a diagnosis and repair expert system created for use on the Space Shuttle's various fluid flow systems.) As a new KATE application, the calibrator described here breaks new ground for KSC's Artificial Intelligence Lab by allowing KATE to both control and measure the hardware she supervises. By automating a formerly manual process, the calibrator: (1) saves the ALO model builder untold amounts of labor; (2) enables quick repairs after workmen accidently adjust ALO's hand valves; and (3) frees the modeler to pursue new KATE applications that previously were too complicated. Also reported are suggestions for enhancing the program: (1) to calibrate ALO's TV cameras, pumps, and sensor tolerances; and (2) to calibrate devices in other KATE models, such as the shuttle's LOX and Environment Control System (ECS).
Use of paravascular admittance waveforms to monitor relative change in arterial blood pressure
NASA Astrophysics Data System (ADS)
Zielinski, Todd M.; Hettrick, Doug; Cho, Yong
2010-04-01
Non-invasive methods to monitor ambulatory blood pressure often have limitations that can affect measurement accuracy and patient adherence [1]. Minimally invasive measurement of a relative blood pressure surrogate with an implantable device may provide a useful chronic diagnostic and monitoring tool. We assessed a technique that uses electrocardiogram and paravascular admittance waveform morphology analysis to one, measure a time duration (vascular tone index, VTI in milliseconds) change from the electrocardiogram R-wave to admittance waveform peak and two, measure the admittance waveform minimum, maximum and magnitude as indicators of change in arterial compliance/distensibility or pulse pressure secondary to change in afterload. Methods: Five anesthetized domestic pigs (32 ± 4.2 kg) were used to study the effects of phenylephrine (1-5 ug/kg/min) on femoral artery pressure and admittance waveform morphology measured with a quadrapolar electrode array catheter placed next to the femoral artery to assess the relative change in arterial compliance due to change in peripheral vascular tone. Results: Statistical difference was observed (p < 0.05) comparing baseline VTI to phenylephrine VTI (246 ± .05 ms to 320 ± .07 ms) and baseline admittance waveform maximum to phenylephrine admittance waveform maximum (0.0148 ± .002 siemens to 0.0151 ± .002 siemens). Conclusion: Chronic minimally invasive admittance measurement techniques that monitor relative change in blood pressure may be suitable for implantable devices to detect progression of cardiovascular disease such as hypertension.
Panaretos, Anastasios H; Werner, Douglas H
2015-02-23
In this paper we demonstrate the feasibility of using multiport network theory to describe the admittance properties of a longitudinally loaded plasmonic nanorod antenna. Our analysis reveals that if the appropriate terminal ports are defined across the nanorod geometry then the corresponding voltage and current quantities can be probed and thus it becomes feasible to extract the admittance matrix of the structure. Furthermore, it is demonstrated that by utilizing cylindrical dielectric waveguide theory, closed form expressions can be derived that uniquely characterize the loading material in terms of its admittance. The combination of the admittance matrix information along with the load admittance expressions provides an effective methodology for computing the nanorod's input admittance/impedance for arbitrary loading scenarios. This is important because the admittance resonances are associated with the structure's scattering peaks which are excited by a plane wave polarized parallel to its long dimension. Subsequently, the proposed approach provides a fast and computationally efficient circuit-based methodology to predict and custom engineer the scattering properties of a loaded plasmonic nanorod without having to rely on repetitive lengthy full wave simulations. PMID:25836483
Surface acoustic admittance of highly porous open-cell, elastic foams
NASA Technical Reports Server (NTRS)
Lambert, R. F.
1983-01-01
This work presents a comprehensive study of the surface acoustic admittance properties of graded sizes of open-cell foams that are highly porous and elastic. The intrinsic admittance as well as properties of samples of finite depth were predicted and then measured for sound at normal incidence over a frequency range extending from about 35-3500 Hz. The agreement between theory and experiment for a range of mean pore size and volume porosity is excellent. The implications of fibrous structure on the admittance of open-cell foams is quite evident from the results.
Localized Gravity/Topography Correlation and Admittance Spectra one the Moon
NASA Astrophysics Data System (ADS)
Ishihara, Y.; Namiki, N.; Sugita, S.; Matsumoto, K.; Goossens, S.; Araki, H.; Noda, H.; Sasaki, S.; Iwata, T.; Hanada, H.
2009-04-01
attempt localized spectral analysis of the Moon first and then apply possible compensation mechanisms to explain the observed admittance. Kaguya mission has been yielding representation of lunar gravity and topography (shape) substantially superior in resolution and accuracy to earlier solutions. For global lunar gravity field, an accurate spherical harmonic model of gravitational potential up to degree and order 100 (SGM100g) was derived from one year tracking (including 4-way Doppler) data [3]. For topography, LALT has obtained more than 6 million altitude measurements with 5 m precision, from which a spherical harmonic expansion of topography to degree and order 359 (STM359_grid-02) has been determined [4]. In this study, we use those new models. We employ the spatio-spectral localization technique [5] to obtain gravity/shape correlation and admittance spectra as function of position on the Moon. In this analysis, we localize harmonic field with axisymmetric windows of constant diameter, described by Lwin zonal harmonic coefficients. This restricts the permissible range of l in the windowed fields at both the low- (l > Lwin) and high-wave number ends (l < Lobs-Lwin, ; Lobs is the maximum degree of observation) . We chose four fixed windows with Lwin = 5, 10, 17, 26 (equivalent to spatial scales 2200, 1100, 640 and 420 km, respectively). These window sizes correspond to huge-, large-, middle-, and small-size of impact basins. For up to degree 50 with Lwin = 5 scale, it is clearly shown that the near-side contains distinct anti-correlation regions whereas the far-side is mostly occupied by high correlation regions. This difference is mainly due to large mascon basins in near-side, such as mare Imbrium. For Lwin = 10 and 17 scales, we can see anti-correlation regions at not only near-side but also far-side. Locations of anti-correlation regions in the far-side correspond to impact basins (Type II basin [6]). However, lots of far side basins (Type I basin [6]) are not
Li, J. V.; Crandall, R. S.; Repins, I. L.; Nardes, A. M.; Levi, D. H.; Sulima, O.
2011-07-01
Admittance spectroscopy is commonly used to characterize majority-carrier trapping defects. In today's practical photovoltaic devices, however, a number of other physical mechanisms may contribute to the admittance measurement and interfere with the data interpretation. Such challenges arise due to the violation of basic assumptions of conventional admittance spectroscopy such as single-junction, ohmic contact, highly conductive absorbers, and measurement in reverse bias. We exploit such violations to devise admittance spectroscopy-based methods for studying the respective origins of 'interference': majority-carrier mobility, non-ohmic contact potential barrier, minority-carrier inversion at hetero-interface, and minority-carrier lifetime in a device environment. These methods are applied to a variety of photovoltaic technologies: CdTe, Cu(In,Ga)Se2, Si HIT cells, and organic photovoltaic materials.
NASA Astrophysics Data System (ADS)
Zhang, Maomao; Soleimani, Manuchehr
2016-02-01
Electrical capacitance tomography (ECT) is an imaging method mainly capable of reconstructing dielectric permittivity. Generally, the reactance part of complex admittance is measured in a selected frequency. This paper presents for the first time an in depth and systematic analysis of complex admittance data for simultaneous reconstruction of both electrical conductivity and dielectric permittivity. A complex-valued forward model, Jacobian matrix and inverse solution are developed in the time harmonic excitation mode to allow for multi-frequency measurements. Realistic noise models are used to evaluate the performance of complex admittance ECT in a range of excitation frequencies. This paper demonstrates far greater potential for ECT as a versatile imaging tool through novel analysis of complex admittance imaging using a dual conductivity permittivity inversion method. The paper demonstrates that various classes of contactless capacitance based measurement devices can be analysed through complex multi-frequency ECT.
48 CFR 3022.101-70 - Admittance of union representatives to DHS installations.
Code of Federal Regulations, 2012 CFR
2012-10-01
... APPLICATION OF LABOR LAWS TO GOVERNMENT ACQUISITIONS Basic Labor Policies 3022.101-70 Admittance of union... Administration or United States Secret Service installations and work sites is not governed by this rule, but...
48 CFR 3022.101-70 - Admittance of union representatives to DHS installations.
Code of Federal Regulations, 2013 CFR
2013-10-01
... APPLICATION OF LABOR LAWS TO GOVERNMENT ACQUISITIONS Basic Labor Policies 3022.101-70 Admittance of union... Administration or United States Secret Service installations and work sites is not governed by this rule, but...
48 CFR 3022.101-70 - Admittance of union representatives to DHS installations.
Code of Federal Regulations, 2014 CFR
2014-10-01
... APPLICATION OF LABOR LAWS TO GOVERNMENT ACQUISITIONS Basic Labor Policies 3022.101-70 Admittance of union... Administration or United States Secret Service installations and work sites is not governed by this rule, but...
48 CFR 3022.101-70 - Admittance of union representatives to DHS installations.
Code of Federal Regulations, 2011 CFR
2011-10-01
... APPLICATION OF LABOR LAWS TO GOVERNMENT ACQUISITIONS Basic Labor Policies 3022.101-70 Admittance of union... Administration or United States Secret Service installations and work sites is not governed by this rule, but...
Aerodynamics via acoustics - Application of acoustic formulas for aerodynamic calculations
NASA Technical Reports Server (NTRS)
Farassat, F.; Myers, M. K.
1986-01-01
Prediction of aerodynamic loads on bodies in arbitrary motion is considered from an acoustic point of view, i.e., in a frame of reference fixed in the undisturbed medium. An inhomogeneous wave equation which governs the disturbance pressure is constructed and solved formally using generalized function theory. When the observer is located on the moving body surface there results a singular linear integral equation for surface pressure. Two different methods for obtaining such equations are discussed. Both steady and unsteady aerodynamic calculations are considered. Two examples are presented, the more important being an application to propeller aerodynamics. Of particular interest for numerical applications is the analytical behavior of the kernel functions in the various integral equations.
Aerodynamics Via Acoustics: Application of Acoustic Formulas for Aerodynamic Calculations
NASA Technical Reports Server (NTRS)
Farassat, F.; Myers, M. K.
1986-01-01
Prediction of aerodynamic loads on bodies in arbitrary motion is considered from an acoustic point of view, i.e., in a frame of reference fixed in the undisturbed medium. An inhomogeneous wave equation which governs the disturbance pressure is constructed and solved formally using generalized function theory. When the observer is located on the moving body surface there results a singular linear integral equation for surface pressure. Two different methods for obtaining such equations are discussed. Both steady and unsteady aerodynamic calculations are considered. Two examples are presented, the more important being an application to propeller aerodynamics. Of particular interest for numerical applications is the analytical behavior of the kernel functions in the various integral equations.
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.
Temperature admittance spectroscopy of boron doped chemical vapor deposition diamond
NASA Astrophysics Data System (ADS)
Zubkov, V. I.; Kucherova, O. V.; Bogdanov, S. A.; Zubkova, A. V.; Butler, J. E.; Ilyin, V. A.; Afanas'ev, A. V.; Vikharev, A. L.
2015-10-01
Precision admittance spectroscopy measurements over wide temperature and frequency ranges were carried out for chemical vapor deposition epitaxial diamond samples doped with various concentrations of boron. It was found that the experimentally detected boron activation energy in the samples decreased from 314 meV down to 101 meV with an increase of B/C ratio from 600 to 18000 ppm in the gas reactants. For the heavily doped samples, a transition from thermally activated valence band conduction to hopping within the impurity band (with apparent activation energy 20 meV) was detected at temperatures 120-150 K. Numerical simulation was used to estimate the impurity DOS broadening. Accurate determination of continuously altering activation energy, which takes place during the transformation of conduction mechanisms, was proposed by numerical differentiation of the Arrhenius plot. With increase of boron doping level the gradual decreasing of capture cross section from 3 × 10-13 down to 2 × 10-17 cm2 was noticed. Moreover, for the hopping conduction the capture cross section becomes 4 orders of magnitude less (˜2 × 10-20 cm2). At T > Troom in doped samples the birth of the second conductance peak was observed. We attribute it to a defect, related to the boron doping of the material.
Temperature admittance spectroscopy of boron doped chemical vapor deposition diamond
Zubkov, V. I. Kucherova, O. V.; Zubkova, A. V.; Ilyin, V. A.; Afanas'ev, A. V.; Bogdanov, S. A.; Vikharev, A. L.; Butler, J. E.
2015-10-14
Precision admittance spectroscopy measurements over wide temperature and frequency ranges were carried out for chemical vapor deposition epitaxial diamond samples doped with various concentrations of boron. It was found that the experimentally detected boron activation energy in the samples decreased from 314 meV down to 101 meV with an increase of B/C ratio from 600 to 18000 ppm in the gas reactants. For the heavily doped samples, a transition from thermally activated valence band conduction to hopping within the impurity band (with apparent activation energy 20 meV) was detected at temperatures 120–150 K. Numerical simulation was used to estimate the impurity DOS broadening. Accurate determination of continuously altering activation energy, which takes place during the transformation of conduction mechanisms, was proposed by numerical differentiation of the Arrhenius plot. With increase of boron doping level the gradual decreasing of capture cross section from 3 × 10{sup −13} down to 2 × 10{sup −17} cm{sup 2} was noticed. Moreover, for the hopping conduction the capture cross section becomes 4 orders of magnitude less (∼2 × 10{sup −20} cm{sup 2}). At T > T{sub room} in doped samples the birth of the second conductance peak was observed. We attribute it to a defect, related to the boron doping of the material.
NASA Technical Reports Server (NTRS)
Jones, R. T. (Compiler)
1979-01-01
A collection of papers on modern theoretical aerodynamics is presented. Included are theories of incompressible potential flow and research on the aerodynamic forces on wing and wing sections of aircraft and on airship hulls.
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.
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.
NASA Technical Reports Server (NTRS)
Smrekar, S. E.; Anderson, F. S.
2005-01-01
We have calculated admittance spectra using the spatio-spectral method [14] for Venus by moving the central location of the spectrum over a 1 grid, create 360x180 admittance spectra. We invert the observed admittance using top-loading (TL), hot spot (HS), and bottom loading (BL) models, resulting in elastic, crustal, and lithospheric thickness estimates (Te, Zc, and Zl) [0]. The result is a global map for interpreting subsurface structure. Estimated values of Te and Zc concur with previous TL local admittance results, but BL estimates indicate larger values than previously suspected.
Use of Admittance-Wall Models in Analysis of Radiating Line Antennas
NASA Astrophysics Data System (ADS)
Tammen, David John
This thesis describes the development of analytical models for two radiating line antenna structures: the traveling -wave microstrip antenna and the Annular Sector Radiating Line (ANSERLIN) antenna. The models provide data and insights into the operation of the antennas without requiring large amounts of computation. It was shown that the general characteristics of the radiation patterns of ANSERLIN elements can be obtained using only a small number of circularly polarized spherical modes in the field expansion. A first -order model is obtained by solving for the fields of a closed waveguide with perfect electric conducting (PEC) top and bottom walls and perfect magnetic conducting (PMC) side walls. The propagation constant obtained from these fields of the closed waveguide is then used in the equivalent magnetic current filaments to obtain the radiated fields. Use of the propagation constant of the closed waveguide fields does not include the fringing and radiation behavior. A second-order model was developed in which the radiation loss and fringing fields are included by putting a small complex admittance on the side walls rather than having PMC side walls. Two formulations were developed to include the radiation loss in the representation: a coupled-mode formulation and an eigenvalue formulation. The coupled -mode formulation, which is similar to that described by Schelkunoff for a waveguide with lossy conductors, is used to obtain the complex-valued propagation constant. In the eigenvalue formulation, the eigenvalues obtained from the solution of the characteristic equation of the waveguide with admittance side walls are used to obtain the complex -valued propagation constant. This complex-valued propagation constant, which includes the fringing and radiation behavior, is then used in the equivalent magnetic current filaments to obtain the radiated fields. Good agreement was found between measured results and results computed using the eigenvalue formulation
Inconsistent Definitions of the Pressure-Coupled Response and the Admittance of Solid Propellants
NASA Technical Reports Server (NTRS)
Cardiff, Eric H.
2003-01-01
When an acoustic wave is present in a solid propellant combustion environment, the mass flux from the combustion zone oscillates at the same frequency as the acoustics. The acoustic wave is either amplified or attenuated by the response of the combustion to the acoustic disturbance. When the acoustic wave is amplified, this process is called combustion instability. The amplification is quantitatively measured by a response function. The ability to predict combustion stability for a solid propellant formulation is essential to the formulator to prevent or minimize the effects of instabilities, such as an oscillatory thrust. Unfortunately, the prediction of response values for a particular propellant remains a technical challenge. Most predictions of the response of propellants are based on test data, but there are a number of questions about the reliability of the standard test method, the T-burner. Alternate methods have been developed to measure the response of a propellant, including the ultrasound burner, the magnetic flowmeter and the rotating valve burner, but there are still inconsistencies between the results obtained by these different methods. Aside from the experimental differences, the values of the pressure-coupled responses obtained by different researchers are often compared erroneously, for the simple reason that inconsistencies in the definitions of the responses and admittances are not considered. The use of different definitions has led to substantial confusion since the first theoretical treatments of the problem by Hart and McClure in 1959. The definitions and relations derived here seek to alleviate this problem.
Universal Impedance, Admittance and Scattering Fluctuations in Quantum-chaotic Systems
NASA Astrophysics Data System (ADS)
Hemmady, Sameer
2006-03-01
We experimentally investigate fluctuations in the eigenvalues of the impedance, admittance and scattering matrices of wave chaotic systems using a microwave analog of a quantum chaotic infinite square well potential. We consider a 2-D, time-reversal symmetric chaotic microwave resonator driven by two non-ideally coupled ports. The system-specific coupling effects are removed using the measured radiation impedance matrix (3pt<->Z Rad) [1] of the two ports. A normalized impedance matrix (3pt<->z ) is thus obtained, and the Probability Density Function (PDF) of its eigenvalues is predicted to be universal depending only on the cavity loss. We observe remarkable agreement between the statistical properties of 3pt<->z and 3pt<->y =3pt<->z -1 for all degrees of loss, which is in accordance with [1, 2] and Random Matrix Theory (RMT). We compare the joint PDF of the eigenphases of the normalized scattering matrix (3pt<->s ) with that obtained from RMT for varying degrees of loss. We study the joint PDF of the eigenvalues of 3pt<->s 3pt<->s ^ and find good agreement with [3]. [1] X. Zheng, et al., -- Electromagnetics (in press); condmat/0408317; S. Hemmady, et al., Phys. Rev. Lett. 94, 014102 (2005).[2] Y. V. Fyodorov, et al.,-- condmat/0507016.[3] P. W. Brouwer and C. W. J Beenakker -- PRB 55, 4695 (1997). Work supported by DOD MURI AFOSR Grant F496200110374, DURIP Grants FA95500410295 and FA95500510240.
Universal Impedance, Admittance and Scattering Fluctuations in Quantum-chaotic Systems.
NASA Astrophysics Data System (ADS)
Hemmady, Sameer; Zheng, Xing; Antonsen, Thomas; Ott, Edward; Anlage, Steven M.
2006-03-01
We experimentally investigate fluctuations in the eigenvalues of the impedance, admittance and scattering matrices of wave chaotic systems using a microwave analog of a quantum chaotic infinite square well potential. We consider a 2-D, time-reversal symmetric chaotic microwave resonator driven by two non-ideally coupled ports. The system-specific coupling effects are removed using the measured radiation impedance matrix (3pt<->Z Rad) [1] of the two ports. A normalized impedance matrix (3pt<->z ) is thus obtained, and the Probability Density Function (PDF) of its eigenvalues is predicted to be universal depending only on the cavity loss. We observe remarkable agreement between the statistical properties of 3pt<->z and 3pt<->y =3pt<->z -1 for all degrees of loss, which is in accordance with [1, 2] and Random Matrix Theory (RMT). We compare the joint PDF of the eigenphases of the normalized scattering matrix (3pt<->s ) with that obtained from RMT for varying degrees of loss. We study the joint PDF of the eigenvalues of 3pt<->s 3pt<->s ^ and find good agreement with [3]. [1] X. Zheng, et al., -- Electromagnetics (in press); condmat/0408317; S. Hemmady, et al., Phys. Rev. Lett. 94, 014102 (2005).[2] Y. V. Fyodorov, et al.,-- condmat/0507016.[3] P. W. Brouwer and C. W. J Beenakker -- PRB 55, 4695 (1997). Work supported by DOD MURI AFOSR Grant F496200110374, DURIP Grants FA95500410295 and FA95500510240.
Effect of nonzero surface admittance on receptivity and stability of compressible boundary layer
NASA Technical Reports Server (NTRS)
Choudhari, Meelan
1994-01-01
The effect of small-amplitude short-scale variations in surface admittance on the acoustic receptivity and stability of two-dimensional compressible boundary layers is examined. In the linearized limit, the two problems are shown to be related both physically and mathematically. This connection between the two problems is used, in conjunction with some previously reported receptivity results, to infer the modification of stability properties due to surface permeability. Numerical calculations are carried out for a self-similar flat-plate boundary layer at subsonic and low supersonic speeds. Variations in mean suction velocity at the perforated admittance surface can also induce receptivity to an acoustic wave. For a subsonic boundary layer, the dependence of admittance-induced receptivity on the acoustic-wave orientation is significantly different from that of the receptivity produced via mean suction variation. The admittance-induced receptivity is generally independent of the angle of acoustic incidence, except in a relatively narrow range of upstream-traveling waves for which the receptivity becomes weaker. However, this range of angles is precisely that for which the suction-induced receptivity tends to be large. At supersonic Mach numbers, the admittance-induced receptivity to slow acoustic models is relatively weaker than that in the case of the fast acoustic modes. We also find that purely real values for the surface admittance tend to have a destabilizing effect on the evolution of an instability wave over a slightly permeable surface. The limits on the validity of the linearized approximation are also assessed in one specific case.
Admittance of Au/1,4-benzenedithiol/Au single-molecule junctions
NASA Astrophysics Data System (ADS)
Yamauchi, Kazumasa; Kurokawa, Shu; Sakai, Akira
2012-12-01
Employing the admittance formula for double-barrier junctions [Fu and Dudley, Phys. Rev. Lett. 70, 65 (1993)], we have estimated an ac susceptance (imaginary part of admittance) of Au/1,4-benzenedithiol/Au single-molecule junctions from their current-voltage characteristics. In the MHz regime, we find that the junction susceptance shows a very small (˜0.1 aF) capacitive component that can be entirely masked by a larger electrode capacitance. Direct ac signal transmission measurements up to 1 GHz reveal no molecular signals and confirm the smallness of the molecular capacitance in the MHz regime.
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
Admittance model for the shuttle remote manipulator system in four configurations. M.S. Thesis
NASA Technical Reports Server (NTRS)
Papadopoulos, Loukas; Tolson, Robert H.
1993-01-01
A possible scenario for robot task performance in space is to mount two small, dexterous arms to the end of the Shuttle Remote Manipulator System (SRMS). As these small robots perform tasks, the flexibility of the SRMS may cause unsuccessful task executions. In order to simulate the dynamic coupling between the SRMS and the arms, admittance models of the SRMS in four brakes locked configurations were developed. The admittance model permits calculation of the SRMS end-effector response due to end-effector disturbing forces. The model will then be used in conjunction with a Stewart Platform, a vehicle emulation system. An application of the admittance model was shown by simulating the disturbing forces using two SRMS payloads, the Dextrous Orbital Servicing System (DOSS) manipulator and DOSS carrying a 1000 lb. cylinder. Mode by mode comparisons were conducted to determine the minimum number of modes required in the admittance model while retaining dynamic fidelity. It was determined that for all four SRMS configurations studied, between 4 and 6 modes of the SRMS structure (depending on the excitation loads) were sufficient to retain tolerance of 0.01 inches and 0.01 deg. These tolerances correspond to the DOSS manipulator carrying no object. When the DOSS carries the 1000 lb. cylinder, between 15 and 20 modes were sufficient, approximately three or four times as many modes as for the unloaded case.
Damage detection on the joint of steel frame through high-frequency admittance signals
NASA Astrophysics Data System (ADS)
Wang, Dansheng; Zhu, Hongping; Zhou, Huaqiang; Yang, Haiping
2008-11-01
The basic idea of a piezoelectric admittance (reciprocal of impedance) technique for structural health monitoring is presented in this paper. An experimental study on damage detection of a steel frame structure is operated by the use of the high-frequency piezoelectric admittance signals. In this experiment, three PZT active sensors are bonded to three different components around a joint of the steel frame separately, and the looseness of bolts is identified by monitoring the variations of piezoelectric admittance measurements. From the experimental results it is found that the PZT active sensors hold the ability to detect structural local damage, i.e. they are insensitive to the damage in far fields. Subsequently, two damage indexes, the covariance and the cross correlation coefficient between two real admittance data sets are defined respectively, by which the extent of damage of the frame structure is evaluated. It is found that the cross correlation coefficient index can correctly reflect the damage extent of the frame structure qualitatively in different frequency ranges, but the covariance index can not.
48 CFR 1222.101-70 - Admittance of union representatives to DOT installations.
Code of Federal Regulations, 2013 CFR
2013-10-01
... Basic Labor Policies 1222.101-70 Admittance of union representatives to DOT installations. (a) It is DOT policy to admit labor union representatives of contractor employees to DOT installations to visit work sites and transact labor union business with contractors, their employees, or union stewards pursuant...
48 CFR 1222.101-70 - Admittance of union representatives to DOT installations.
Code of Federal Regulations, 2011 CFR
2011-10-01
... Basic Labor Policies 1222.101-70 Admittance of union representatives to DOT installations. (a) It is DOT policy to admit labor union representatives of contractor employees to DOT installations to visit work sites and transact labor union business with contractors, their employees, or union stewards pursuant...
48 CFR 1222.101-70 - Admittance of union representatives to DOT installations.
Code of Federal Regulations, 2012 CFR
2012-10-01
... Basic Labor Policies 1222.101-70 Admittance of union representatives to DOT installations. (a) It is DOT policy to admit labor union representatives of contractor employees to DOT installations to visit work sites and transact labor union business with contractors, their employees, or union stewards pursuant...
48 CFR 1222.101-70 - Admittance of union representatives to DOT installations.
Code of Federal Regulations, 2014 CFR
2014-10-01
... 48 Federal Acquisition Regulations System 5 2014-10-01 2014-10-01 false Admittance of union representatives to DOT installations. 1222.101-70 Section 1222.101-70 Federal Acquisition Regulations System DEPARTMENT OF TRANSPORTATION SOCIOECONOMIC PROGRAMS APPLICATION OF LABOR LAWS TO GOVERNMENT ACQUISITIONS Basic Labor Policies...
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.
Uncertainty in Computational Aerodynamics
NASA Technical Reports Server (NTRS)
Luckring, J. M.; Hemsch, M. J.; Morrison, J. H.
2003-01-01
An approach is presented to treat computational aerodynamics as a process, subject to the fundamental quality assurance principles of process control and process improvement. We consider several aspects affecting uncertainty for the computational aerodynamic process and present a set of stages to determine the level of management required to meet risk assumptions desired by the customer of the predictions.
Computation of dragonfly aerodynamics
NASA Astrophysics Data System (ADS)
Gustafson, Karl; Leben, Robert
1991-04-01
Dragonflies are seen to hover and dart, seemingly at will and in remarkably nimble fashion, with great bursts of speed and effectively discontinuous changes of direction. In their short lives, their gossamer flight provides us with glimpses of an aerodynamics of almost extraterrestrial quality. Here we present the first computer simulations of such aerodynamics.
An analysis of light-induced admittance changes in rod outer segments
Falk, G.; Fatt, P.
1973-01-01
1. Measurements were made of the time course and amplitude of the change in real part of admittance, ΔG, of a suspension of frog rod outer segments, following a flash of light bleaching about 1% of the rhodopsin content of the rods. The measurements, based on the use of a specially designed marginal oscillator, covered the frequency range between 500 Hz and 17 MHz. 2. The components of response, previously described for rods prepared by a method involving exposure to strongly hypertonic sucrose solutions, are present in similar form when rods are isolated and maintained in isotonic solutions made up with equi-osmotic concentrations of NaCl and sucrose or with Na2SO4. 3. Component I, identified as a slowly developing positive ΔG apparent at very low frequencies, is frequency-independent up to the characteristic frequency of admittance for the suspension, fY (about 2 MHz for rods suspended in a solution having the conductivity of Ringer solution), but decreases at still higher frequencies. 4. Component II, identified as a rapidly developing positive ΔG which appears only above a critical frequency about 2·5 decades below fY, increases approximately logarithmically with frequency to reach a limiting amplitude in the region of fY. 5. The amplitude of component II, ΔGII, measured in the region of fY, varies linearly with the conductivity of the suspending medium, Go, under conditions in which the conductivity of the rod interior is also a linear function of the external conductivity. The relation for a flash bleaching 1% of the rhodopsin content of the dark-adapted rod is [Formula: see text] 6. Measurements made on rods suspended in a low-conductivity solution, which has the effect of reducing the conductivity of the rod interior to about one ninth its value for rods suspended in Ringer solution, reveal a decline in component II for frequencies above 8 MHz. 7. To explain the frequency dependence of component II and its dependence on conductivity, it is proposed
The aerodynamics of propellers
NASA Astrophysics Data System (ADS)
Wald, Quentin R.
2006-02-01
The theory and the design of propellers of minimum induced loss is treated. The pioneer analysis of this problem was presented more than half a century ago by Theodorsen, but obscurities in his treatment and inaccuracies and limited coverage in his tables of the Goldstein circulation function for helicoidal vortex sheets have not been remedied until the present work which clarifies and extends his work. The inverse problem, the prediction of the performance of a given propeller of arbitrary form, is also treated. The theory of propellers of minimum energy loss is dependent on considerations of a regular helicoidal trailing vortex sheet; consequently, a more detailed discussion of the dynamics of vortex sheets and the consequences of their instability and roll up is presented than is usually found in treatments of propeller aerodynamics. Complete and accurate tables of the circulation function are presented. Interference effects between a fuselage or a nacelle and the propeller are considered. The regimes of propeller, vortex ring, and windmill operation are characterized.
Mathematical modeling of the aerodynamic characteristics in flight dynamics
NASA Technical Reports Server (NTRS)
Tobak, M.; Chapman, G. T.; Schiff, L. B.
1984-01-01
Basic concepts involved in the mathematical modeling of the aerodynamic response of an aircraft to arbitrary maneuvers are reviewed. The original formulation of an aerodynamic response in terms of nonlinear functionals is shown to be compatible with a derivation based on the use of nonlinear functional expansions. Extensions of the analysis through its natural connection with ideas from bifurcation theory are indicated.
Admittance spectroscopy of copper indium diselenide/cadmium sulfide solar cells
NASA Astrophysics Data System (ADS)
Strifler, Walter A.
This dissertation concentrates on admittance spectroscopy of CuInSe2/CdS heterojunction solar cells prepared by chemical spray pyrolysis (CSP) and by multiple-source evaporation (MSE). The primary goal is to examine some of the more important electrical characteristics of these heterojunctions and determine if the spray-pyrolyzed cells behave similar, albeit at a lower efficiency, to higher quality cells prepared by other techniques. The primary analytical tool used in this study is admittance spectroscopy. The theory of admittance spectroscopy is developed using the concept of equivalent circuits. The traditional temperature-swept technique for admittance spectroscopy is shown to be inadequate for measuring most heterojunction samples examined in this study because of the large parallel leakage conductance found in these devices. Instead, a frequency-swept admittance technique is developed and employed to correct for the parallel conductance effect and reveal the true nature of slow charge in the depletion layer. In addition to admittance spectroscopy, the two sets of solar cell diodes are characterized using a variety of measurement techniques including capacitance-voltage, current-voltage over spectral response, capacitance dispersion over wavelength, and solar efficiency. The different pieces of experimental data are discussed to form a self-consistent physical model of the polycrystalline solar cells. Charge transport across the diode junction is dominated by recombination processes within the CuInSe2 depletion layer for both sets of diodes although the large parallel conductance in the CSP diodes often masks this characteristic. The CSP solar cells exhibit a pronounced blue peak in the spectral response indicating that electron collection is the limiting factor in the overall short-circuit quantum efficiency. A large degree of capacitance dispersion is found in both sets of diodes. Supporting measurements indicate that the majority of this dispersion is due
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)
NASA Astrophysics Data System (ADS)
Köhler, K.; Pletschen, W.; Godejohann, B.; Müller, S.; Menner, H. P.; Ambacher, O.
2015-11-01
Admittance-voltage profiling of AlxGa1-xN/GaN heterostructures was used to determine the frequency dependent capacitance and conductance of FET devices in the frequency range from 50 Hz to 1 MHz. The nominally undoped low pressure metal-organic vapor-phase epitaxy structures were grown with an Al-content of 30%. An additional 1 nm thick AlN interlayer was placed in one structure before the Al0.3Ga0.7N layer growth. For frequencies below 108 Hz it is convenient to use equivalent circuits to represent electric or dielectric properties of a material, a method widely used, for example, in impedance spectroscopy. We want to emphasize the relation between frequency dependent admittance-voltage profiling and the corresponding equivalent circuits to the complex dielectric function. Debye and Drude models are used for the description of the frequency dependent admittance profiles in a range of depletion onset of the two-dimensional electron gas. Capacitance- and conductance-frequency profiles are fitted in the entire measured range by combining both models. Based on our results, we see contributions to the two-dimensional electron gas for our samples from surface states (80%) as well as from background doping in the Al0.3Ga0.7N barriers (20%). The specific resistance of the layers below the gate is above 105 Ω cm for both samples and increases with increasing negative bias, i.e., the layers below the gate are essentially depleted. We propose that the resistance due to free charge carriers, determined by the Drude model, is located between gate and drain and, because of the AlN interlayer, the resistance is lowered by a factor of about 30 if compared to the sample without an AlN layer.
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.
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.
Aerodynamic Decelerators for Planetary Exploration: Past, Present, and Future
NASA Technical Reports Server (NTRS)
Cruz, Juna R.; Lingard, J. Stephen
2006-01-01
In this paper, aerodynamic decelerators are defined as textile devices intended to be deployed at Mach numbers below five. Such aerodynamic decelerators include parachutes and inflatable aerodynamic decelerators (often known as ballutes). Aerodynamic decelerators play a key role in the Entry, Descent, and Landing (EDL) of planetary exploration vehicles. Among the functions performed by aerodynamic decelerators for such vehicles are deceleration (often from supersonic to subsonic speeds), minimization of descent rate, providing specific descent rates (so that scientific measurements can be obtained), providing stability (drogue function - either to prevent aeroshell tumbling or to meet instrumentation requirements), effecting further aerodynamic decelerator system deployment (pilot function), providing differences in ballistic coefficients of components to enable separation events, and providing height and timeline to allow for completion of the EDL sequence. Challenging aspects in the development of aerodynamic decelerators for planetary exploration missions include: deployment in the unusual combination of high Mach numbers and low dynamic pressures, deployment in the wake behind a blunt-body entry vehicle, stringent mass and volume constraints, and the requirement for high drag and stability. Furthermore, these aerodynamic decelerators must be qualified for flight without access to the exotic operating environment where they are expected to operate. This paper is an introduction to the development and application of aerodynamic decelerators for robotic planetary exploration missions (including Earth sample return missions) from the earliest work in the 1960s to new ideas and technologies with possible application to future missions. An extensive list of references is provided for additional study.
Aerodynamic Design Using Neural Networks
NASA Technical Reports Server (NTRS)
Rai, Man Mohan; Madavan, Nateri K.
2003-01-01
The design of aerodynamic components of aircraft, such as wings or engines, involves a process of obtaining the most optimal component shape that can deliver the desired level of component performance, subject to various constraints, e.g., total weight or cost, that the component must satisfy. Aerodynamic design can thus be formulated as an optimization problem that involves the minimization of an objective function subject to constraints. A new aerodynamic design optimization procedure based on neural networks and response surface methodology (RSM) incorporates the advantages of both traditional RSM and neural networks. The procedure uses a strategy, denoted parameter-based partitioning of the design space, to construct a sequence of response surfaces based on both neural networks and polynomial fits to traverse the design space in search of the optimal solution. Some desirable characteristics of the new design optimization procedure include the ability to handle a variety of design objectives, easily impose constraints, and incorporate design guidelines and rules of thumb. It provides an infrastructure for variable fidelity analysis and reduces the cost of computation by using less-expensive, lower fidelity simulations in the early stages of the design evolution. The initial or starting design can be far from optimal. The procedure is easy and economical to use in large-dimensional design space and can be used to perform design tradeoff studies rapidly. Designs involving multiple disciplines can also be optimized. Some practical applications of the design procedure that have demonstrated some of its capabilities include the inverse design of an optimal turbine airfoil starting from a generic shape and the redesign of transonic turbines to improve their unsteady aerodynamic characteristics.
NASA Astrophysics Data System (ADS)
Dvořák, Rudolf
2016-03-01
Unlike airplanes birds must have either flapping or oscillating wings (the hummingbird). Only such wings can produce both lift and thrust - two sine qua non attributes of flying.The bird wings have several possibilities how to obtain the same functions as airplane wings. All are realized by the system of flight feathers. Birds have also the capabilities of adjusting the shape of the wing according to what the immediate flight situation demands, as well as of responding almost immediately to conditions the flow environment dictates, such as wind gusts, object avoidance, target tracking, etc. In bird aerodynamics also the tail plays an important role. To fly, wings impart downward momentum to the surrounding air and obtain lift by reaction. How this is achieved under various flight situations (cruise flight, hovering, landing, etc.), and what the role is of the wing-generated vortices in producing lift and thrust is discussed.The issue of studying bird flight experimentally from in vivo or in vitro experiments is also briefly discussed.
NASA Astrophysics Data System (ADS)
Dardé, Jérémi; Hyvönen, Nuutti; Seppänen, Aku; Staboulis, Stratos
2013-08-01
In this paper, the simultaneous retrieval of the exterior boundary shape and the interior admittivity distribution of an examined body in electrical impedance tomography is considered. The reconstruction method is built for the complete electrode model and it is based on the Fréchet derivative of the corresponding current-to-voltage map with respect to the body shape. The reconstruction problem is cast into the Bayesian framework, and maximum a posteriori estimates for the admittivity and the boundary geometry are computed. The feasibility of the approach is evaluated by experimental data from water tank measurements. The results demonstrate that the proposed method has potential for handling an unknown body shape in a practical setting.
NASA Astrophysics Data System (ADS)
Kalia, Sameer; Mahajan, Aman; Neerja, Sharma, Anshul Kumar; Kumar, Sanjeev; Bedi, R. K.
2016-05-01
The dielectric properties of Boron Sub Phthalocyanine Chloride (Cl-SubPc) thermally deposited on ITO substrate have been studied using admittance spectroscopic techniques. The I-V and capacitance -frequency (C-F) studies at various bias voltages reveal that the mobility of charge carriers decrease with bias voltage, however the conduction phenomenon still remain hopping in nature. From the differential susceptance curve, the contribution of the Schottky barrier contact in the charge carrier concentration was found to be absent. The mobility of charge carriers have been determined using differential susceptance variation and from the phase of admittance curve. The values obtained in two cases have been found to be in agreement with each other.
Characterisation of defects in p-GaN by admittance spectroscopy
NASA Astrophysics Data System (ADS)
Elsherif, O. S.; Vernon-Parry, K. D.; Evans-Freeman, J. H.; Airey, R. J.; Kappers, M.; Humphreys, C. J.
2012-08-01
Mg-doped GaN films have been grown on (0 0 0 1) sapphire using metal organic vapour phase epitaxy. Use of different buffer layer strategies caused the threading dislocation density (TDD) in the GaN to be either approximately 2×109 cm-2 or 1×1010 cm-2. Frequency-dependent capacitance and conductance measurements at temperatures up to 450 K have been used to study the electronic states associated with the Mg doping, and to determine how these are affected by the TDD. Admittance spectroscopy of the films finds a single impurity-related acceptor level with an activation energy of 160±10 meV for [Mg] of about 1×1019 cm-3, and 120±10 eV as the Mg precursor flux decreased. This level is thought to be associated with the Mg acceptor state. The TDD has no discernible effect on the trap detected by admittance spectroscopy. We compare these results with cathodoluminescence measurements reported in the literature, which reveal that most threading dislocations are non-radiative recombination centres, and discuss possible reasons why our admittance spectroscopy have not detected electrically active defects associated with threading dislocations.
Norouzi, Parviz; Gupta, Vinod Kumar; Larijani, Bagher; Rasoolipour, Solmaz; Faridbod, Farnoush; Ganjali, Mohammad R
2015-01-01
An electrochemical detection technique based on combination of was coulometric differential fast Fourier transformation admittance voltammetry (CDFFTAV) and nano-composite film modified glassy carbon electrode was successfully applied for sensitive determination of Amlodipine. The nano-composite film was made by a mixture of ionic liquid, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4), multiwall carbon nanotube and Au nanoparticles as electrochemical mediators. Studies reveal that the irreversible oxidation of Amlodipine was highly facile on the electrode surface. The electrochemical response was established on calculation of the charge under the admittance peak, which was obtained by discrete integration of the admittance response in a selected potential range, obtained in a flow injection analysis. Once established the best operative optimum conditions, the resulting nano-composite film electrode showed a catalytic effect on the oxidation of the analyte. The response is linear in the Amlodipine concentration range of 1.0 × 10(-9) to 2.0 × 10(-7)M with a detection limit of 1.25 × 10(-10)M. Moreover, the proposed technique exhibited high sensitivity, fast response time (less than 6s) and long-term stability and reproducibility around 96%, and it was successfully used to the determination of Amlodipine content in the pharmaceutical formulation. PMID:25281143
Left ventricular epicardial admittance measurement for detection of acute LV dilation
Porterfield, John E.; Larson, Erik R.; Jenkins, James T.; Escobedo, Daniel; Valvano, Jonathan W.; Pearce, John A.
2011-01-01
There are two implanted heart failure warning systems incorporated into biventricular pacemakers/automatic implantable cardiac defibrillators and tested in clinical trials: right heart pressures, and lung conductance measurements. However, both warning systems postdate measures of the earliest indicator of impending heart failure: left ventricular (LV) volume. There are currently no proposed implanted technologies that can perform LV blood volume measurements in humans. We propose to solve this problem by incorporating an admittance measurement system onto currently deployed biventricular and automatic implantable cardiac defibrillator leads. This study will demonstrate that an admittance measurement system can detect LV blood conductance from the epicardial position, despite the current generating and sensing electrodes being in constant motion with the heart, and with dynamic removal of the myocardial component of the returning voltage signal. Specifically, in 11 pigs, it will be demonstrated that 1) a physiological LV blood conductance signal can be derived; 2) LV dilation in response to dose-response intravenous neosynephrine can be detected by blood conductance in a similar fashion to the standard of endocardial crystals when admittance is used, but not when only traditional conductance is used; 3) the physiological impact of acute left anterior descending coronary artery occlusion and resultant LV dilation can be detected by blood conductance, before the anticipated secondary rise in right ventricular systolic pressure; and 4) a pleural effusion simulated by placing saline outside the pericardium does not serve as a source of artifact for blood conductance measurements. PMID:21148342
NASA Technical Reports Server (NTRS)
Hemsch, Michael J. (Editor); Nielsen, Jack N. (Editor)
1986-01-01
The present conference on tactical missile aerodynamics discusses autopilot-related aerodynamic design considerations, flow visualization methods' role in the study of high angle-of-attack aerodynamics, low aspect ratio wing behavior at high angle-of-attack, supersonic airbreathing propulsion system inlet design, missile bodies with noncircular cross section and bank-to-turn maneuvering capabilities, 'waverider' supersonic cruise missile concepts and design methods, asymmetric vortex sheding phenomena from bodies-of-revolution, and swept shock wave/boundary layer interaction phenomena. Also discussed are the assessment of aerodynamic drag in tactical missiles, the analysis of supersonic missile aerodynamic heating, the 'equivalent angle-of-attack' concept for engineering analysis, the vortex cloud model for body vortex shedding and tracking, paneling methods with vorticity effects and corrections for nonlinear compressibility, the application of supersonic full potential method to missile bodies, Euler space marching methods for missiles, three-dimensional missile boundary layers, and an analysis of exhaust plumes and their interaction with missile airframes.
Applied computational aerodynamics
Henne, P.A.
1990-01-01
The present volume discusses the original development of the panel method, the mapping solutions and singularity distributions of linear potential schemes, the capabilities of full-potential, Euler, and Navier-Stokes schemes, the use of the grid-generation methodology in applied aerodynamics, subsonic airfoil design, inverse airfoil design for transonic applications, the divergent trailing-edge airfoil innovation in CFD, Euler and potential computational results for selected aerodynamic configurations, and the application of CFD to wing high-lift systems. Also discussed are high-lift wing modifications for an advanced-capability EA-6B aircraft, Navier-Stokes methods for internal and integrated propulsion system flow predictions, the use of zonal techniques for analysis of rotor-stator interaction, CFD applications to complex configurations, CFD applications in component aerodynamic design of the V-22, Navier-Stokes computations of a complete F-16, CFD at supersonic/hypersonic speeds, and future CFD developments.
Powered-Lift Aerodynamics and Acoustics. [conferences
NASA Technical Reports Server (NTRS)
1976-01-01
Powered lift technology is reviewed. Topics covered include: (1) high lift aerodynamics; (2) high speed and cruise aerodynamics; (3) acoustics; (4) propulsion aerodynamics and acoustics; (5) aerodynamic and acoustic loads; and (6) full-scale and flight research.
Aerodynamics of thrust vectoring
NASA Technical Reports Server (NTRS)
Tseng, J. B.; Lan, C. Edward
1989-01-01
Thrust vectoring as a means to enhance maneuverability and aerodynamic performane of a tactical aircraft is discussed. This concept usually involves the installation of a multifunction nozzle. With the nozzle, the engine thrust can be changed in direction without changing the attitude of the aircraft. Change in the direction of thrust induces a significant change in the aerodynamic forces on the aircraft. Therefore, this device can be used for lift-augmenting as well as stability and control purposes. When the thrust is deflected in the longitudinal direction, the lift force and the pitching stability can be manipulated, while the yawing stability can be controlled by directing the thrust in the lateral direction.
Modeling of aircraft unsteady aerodynamic characteristics. Part 1: Postulated models
NASA Technical Reports Server (NTRS)
Klein, Vladislav; Noderer, Keith D.
1994-01-01
A short theoretical study of aircraft aerodynamic model equations with unsteady effects is presented. The aerodynamic forces and moments are expressed in terms of indicial functions or internal state variables. The first representation leads to aircraft integro-differential equations of motion; the second preserves the state-space form of the model equations. The formulations of unsteady aerodynamics is applied in two examples. The first example deals with a one-degree-of-freedom harmonic motion about one of the aircraft body axes. In the second example, the equations for longitudinal short-period motion are developed. In these examples, only linear aerodynamic terms are considered. The indicial functions are postulated as simple exponentials and the internal state variables are governed by linear, time-invariant, first-order differential equations. It is shown that both approaches to the modeling of unsteady aerodynamics lead to identical models.
Computer graphics in aerodynamic analysis
NASA Technical Reports Server (NTRS)
Cozzolongo, J. V.
1984-01-01
The use of computer graphics and its application to aerodynamic analyses on a routine basis is outlined. The mathematical modelling of the aircraft geometries and the shading technique implemented are discussed. Examples of computer graphics used to display aerodynamic flow field data and aircraft geometries are shown. A future need in computer graphics for aerodynamic analyses is addressed.
Bat flight: aerodynamics, kinematics and flight morphology.
Hedenström, Anders; Johansson, L Christoffer
2015-03-01
Bats evolved the ability of powered flight more than 50 million years ago. The modern bat is an efficient flyer and recent research on bat flight has revealed many intriguing facts. By using particle image velocimetry to visualize wake vortices, both the magnitude and time-history of aerodynamic forces can be estimated. At most speeds the downstroke generates both lift and thrust, whereas the function of the upstroke changes with forward flight speed. At hovering and slow speed bats use a leading edge vortex to enhance the lift beyond that allowed by steady aerodynamics and an inverted wing during the upstroke to further aid weight support. The bat wing and its skeleton exhibit many features and control mechanisms that are presumed to improve flight performance. Whereas bats appear aerodynamically less efficient than birds when it comes to cruising flight, they have the edge over birds when it comes to manoeuvring. There is a direct relationship between kinematics and the aerodynamic performance, but there is still a lack of knowledge about how (and if) the bat controls the movements and shape (planform and camber) of the wing. Considering the relatively few bat species whose aerodynamic tracks have been characterized, there is scope for new discoveries and a need to study species representing more extreme positions in the bat morphospace. PMID:25740899
Unsteady Aerodynamics - Subsonic Compressible Inviscid Case
NASA Technical Reports Server (NTRS)
Balakrishnan, A. V.
1999-01-01
This paper presents a new analytical treatment of Unsteady Aerodynamics - the linear theory covering the subsonic compressible (inviscid) case - drawing on some recent work in Operator Theory and Functional Analysis. The specific new results are: (a) An existence and uniqueness proof for the Laplace transform version of the Possio integral equation as well as a new closed form solution approximation thereof. (b) A new representation for the time-domain solution of the subsonic compressible aerodynamic equations emphasizing in particular the role of the initial conditions.
Prediction of Aerodynamic Coefficients using Neural Networks for Sparse Data
NASA Technical Reports Server (NTRS)
Rajkumar, T.; Bardina, Jorge; Clancy, Daniel (Technical Monitor)
2002-01-01
Basic aerodynamic coefficients are modeled as functions of angles of attack and sideslip with vehicle lateral symmetry and compressibility effects. Most of the aerodynamic parameters can be well-fitted using polynomial functions. In this paper a fast, reliable way of predicting aerodynamic coefficients is produced using a neural network. The training data for the neural network is derived from wind tunnel test and numerical simulations. The coefficients of lift, drag, pitching moment are expressed as a function of alpha (angle of attack) and Mach number. The results produced from preliminary neural network analysis are very good.
Summary analysis of the Gemini entry aerodynamics
NASA Technical Reports Server (NTRS)
Whitnah, A. M.; Howes, D. B.
1972-01-01
The aerodynamic data that were derived in 1967 from the analysis of flight-generated data for the Gemini entry module are presented. These data represent the aerodynamic characteristics exhibited by the vehicle during the entry portion of Gemini 2, 3, 5, 8, 10, 11, and 12 missions. For the Gemini, 5, 8, 10, 11, and 12 missions, the flight-generated lift-to-drag ratios and corresponding angles of attack are compared with the wind tunnel data. These comparisons show that the flight generated lift-to-drag ratios are consistently lower than were anticipated from the tunnel data. Numerous data uncertainties are cited that provide an insight into the problems that are related to an analysis of flight data developed from instrumentation systems, the primary functions of which are other than the evaluation of flight aerodynamic performance.
Identification of aerodynamic models for maneuvering aircraft
NASA Technical Reports Server (NTRS)
Lan, C. Edward; Hu, C. C.
1992-01-01
A Fourier analysis method was developed to analyze harmonic forced-oscillation data at high angles of attack as functions of the angle of attack and its time rate of change. The resulting aerodynamic responses at different frequencies are used to build up the aerodynamic models involving time integrals of the indicial type. An efficient numerical method was also developed to evaluate these time integrals for arbitrary motions based on a concept of equivalent harmonic motion. The method was verified by first using results from two-dimensional and three-dimensional linear theories. The developed models for C sub L, C sub D, and C sub M based on high-alpha data for a 70 deg delta wing in harmonic motions showed accurate results in reproducing hysteresis. The aerodynamic models are further verified by comparing with test data using ramp-type motions.
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.
Aerodynamics Improve Wind Wheel
NASA Technical Reports Server (NTRS)
Ramsey, V. W.
1982-01-01
Modifications based on aerodynamic concepts would raise efficiency of wind-wheel electric-power generator. Changes smooth airflow, to increase power output, without increasing size of wheel. Significant improvements in efficiency anticipated without any increase in size or number of moving parts and without departing from simplicity of original design.
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).
Xiao, Haosu; Zuo, Baojun; Tian, Yi; Zhang, Wang; Hao, Chenglong; Liu, Chaofeng; Li, Qi; Li, Fan; Zhang, Li; Fan, Zhigang
2012-12-20
We investigated the joint influences exerted by the nonuniform aerodynamic flow field surrounding the optical dome and the aerodynamic heating of the dome on imaging quality degradation of an airborne optical system. The Spalart-Allmaras model provided by FLUENT was used for flow computations. The fourth-order Runge-Kutta algorithm based ray tracing program was used to simulate optical transmission through the aerodynamic flow field and the dome. Four kinds of imaging quality evaluation parameters were presented: wave aberration of the exit pupil, point spread function, encircled energy, and modulation transfer function. The results show that the aero-optical disturbance of the aerodynamic flow field and the aerodynamic heating of the dome significantly affect the imaging quality of an airborne optical system. PMID:23262604
In vivo recording of aerodynamic force with an aerodynamic force platform: from drones to birds.
Lentink, David; Haselsteiner, Andreas F; Ingersoll, Rivers
2015-03-01
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
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
NASA Astrophysics Data System (ADS)
Motuzko, F. Y.; Trubitsyn, A. V.
1985-04-01
The electric current I sub h through a human body touching one phase of a 3-0 network is calculated on the basis of the conventional equivalent circuit for the general case of unequal insulation admittances in all three phases. The two extreme cases here are all three insulation admittances approaching zero or infinity respectively. The theoretical relation in the latter case is not consistent with reality, in which an infinitely large insulation admittance presents a short circuit across the 3-0 source and a fully effective shunt across the human body. The equivalent circuit is modified, accordingly, to include the internal source resistance in series with the insulation admittance in each phase. Calculations pertaining to the method of personnel protection are continued, to establish the dependence of current on the insulation resistance of the touched phase and thus establish the safe range of this resistance when the resistance as well as the insulation admittance of this phase are different from those of the other two phases and those of the other two phases are equal.
Real time pressure-volume loops in mice using complex admittance: measurement and implications.
Kottam, Anil T G; Porterfield, John; Raghavan, Karthik; Fernandez, Daniel; Feldman, Marc D; Valvano, Jonathan W; Pearce, John A
2006-01-01
Real time left ventricular (LV) pressure-volume (P-V) loops have provided a framework for understanding cardiac mechanics in experimental animals and humans. Conductance measurements have been used for the past 25 years to generate an instantaneous left ventricular (LV) volume signal. The standard conductance method yields a combination of blood and ventricular muscle conductance; however, only the blood signal is used to estimate LV volume. The state of the art techniques like hypertonic saline injection and IVC occlusion, determine only a single steady-state value of the parallel conductance of the cardiac muscle. This is inaccurate, since the cardiac muscle component should vary instantaneously throughout the cardiac cycle as the LV contracts and fills, because the distance from the catheter to the muscle changes. The capacitive nature of cardiac muscle can be used to identify its contribution to the combined conductance signal. This method, in contrast to existing techniques, yields an instantaneous estimate of the parallel admittance of cardiac muscle that can be used to correct the measurement in real time. The corrected signal consists of blood conductance alone. We present the results of real time in vivo measurements of pressure-admittance and pressure-phase loops inside the murine left ventricle. We then use the magnitude and phase angle of the measured admittance to determine pressure volume loops inside the LV on a beat by beat basis. These results may be used to achieve a substantial improvement in the state of the art in this measurement method by eliminating the need for hypertonic saline injection. PMID:17946238
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.
Admittance Test and Conceptual Study of a CW Positron Source for CEBAF
Golge, Serkan; Hyde, Charles E.; Freyberger, Arne
2009-09-02
A conceptual study of a Continuous Wave (CW) positron production is presented in this paper. The Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab (JLAB) operates with a CW electron beam with a well-defined emittance, time structure and energy spread. Positrons created via bremsstrahlung photons in a high-Z target emerge with a large emittance compared to incoming electron beam. An admittance study has been performed at CEBAF to estimate the maximum beam phase space area that can be transported in the LINAC and in the Arcs. A positron source is described utilizing the CEBAF injector electron beam, and directly injecting the positrons into the CEBAF LINAC.
Measuring the complex admittance of a nearly isolated graphene quantum dot
Zhang, Miao-Lei; Wei, Da; Deng, Guang-Wei; Li, Shu-Xiao; Li, Hai-Ou; Cao, Gang; Tu, Tao; Xiao, Ming; Guo, Guang-Can; Guo, Guo-Ping; Jiang, Hong-Wen
2014-08-18
We measured the radio-frequency reflection spectrum of an on-chip reflection line resonator coupled to a graphene double quantum dot (DQD), which was etched almost isolated from the reservoir and reached the low tunnel rate region. The charge stability diagram of DQD was investigated via dispersive phase and magnitude shift of the resonator with a high quality factor. Its complex admittance and low tunnel rate to the reservoir was also determined from the reflected signal of the on-chip resonator. Our method may provide a non-invasive and sensitive way of charge state readout in isolated quantum dots.
2014-01-01
Background In a deforming anatomic environment, the motion of an instrument suffers from complex geometrical and dynamic constraints, robot assisted minimally invasive surgery therefore requires more sophisticated skills for surgeons. This paper proposes a novel dynamic virtual fixture (DVF) to enhance the surgical operation accuracy of admittance-type medical robotics in the deforming environment. Methods A framework for DVF on the Euclidean Group SE(3) is presented, which unites rotation and translation in a compact form. First, we constructed the holonomic/non-holonomic constraints, and then searched for the corresponded reference to make a distinction between preferred and non-preferred directions. Second, different control strategies are employed to deal with the tasks along the distinguished directions. The desired spatial compliance matrix is synthesized from an allowable motion screw set to filter out the task unrelated components from manual input, the operator has complete control over the preferred directions; while the relative motion between the surgical instrument and the anatomy structures is actively tracked and cancelled, the deviation relative to the reference is compensated jointly by the operator and DVF controllers. The operator, haptic device, admittance-type proxy and virtual deforming environment are involved in a hardware-in-the-loop experiment, human-robot cooperation with the assistance of DVF controller is carried out on a deforming sphere to simulate beating heart surgery, performance of the proposed DVF on admittance-type proxy is evaluated, and both human factors and control parameters are analyzed. Results The DVF can improve the dynamic properties of human-robot cooperation in a low-frequency (0 ~ 40 rad/sec) deforming environment, and maintain synergy of orientation and translation during the operation. Statistical analysis reveals that the operator has intuitive control over the preferred directions, human and the DVF
NASA Astrophysics Data System (ADS)
Zhao, Mingkang; Wi, Hun; Lee, Eun Jung; Woo, Eung Je; In Oh, Tong
2014-10-01
Electrical impedance imaging has the potential to detect an early stage of breast cancer due to higher admittivity values compared with those of normal breast tissues. The tumor size and extent of axillary lymph node involvement are important parameters to evaluate the breast cancer survival rate. Additionally, the anomaly characterization is required to distinguish a malignant tumor from a benign tumor. In order to overcome the limitation of breast cancer detection using impedance measurement probes, we developed the high density trans-admittance mammography (TAM) system with 60 × 60 electrode array and produced trans-admittance maps obtained at several frequency pairs. We applied the anomaly detection algorithm to the high density TAM system for estimating the volume and position of breast tumor. We tested four different sizes of anomaly with three different conductivity contrasts at four different depths. From multifrequency trans-admittance maps, we can readily observe the transversal position and estimate its volume and depth. Specially, the depth estimated values were obtained accurately, which were independent to the size and conductivity contrast when applying the new formula using Laplacian of trans-admittance map. The volume estimation was dependent on the conductivity contrast between anomaly and background in the breast phantom. We characterized two testing anomalies using frequency difference trans-admittance data to eliminate the dependency of anomaly position and size. We confirmed the anomaly detection and characterization algorithm with the high density TAM system on bovine breast tissue. Both results showed the feasibility of detecting the size and position of anomaly and tissue characterization for screening the breast cancer.
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.
Advanced Aerodynamic Control Effectors
NASA Technical Reports Server (NTRS)
Wood, Richard M.; Bauer, Steven X. S.
1999-01-01
A 1990 research program that focused on the development of advanced aerodynamic control effectors (AACE) for military aircraft has been reviewed and summarized. Data are presented for advanced planform, flow control, and surface contouring technologies. The data show significant increases in lift, reductions in drag, and increased control power, compared to typical aerodynamic designs. The results presented also highlighted the importance of planform selection in the design of a control effector suite. Planform data showed that dramatic increases in lift (greater than 25%) can be achieved with multiple wings and a sawtooth forebody. Passive porosity and micro drag generator control effector data showed control power levels exceeding that available from typical effectors (moving surfaces). Application of an advanced planform to a tailless concept showed benefits of similar magnitude as those observed in the generic studies.
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.
NASA Technical Reports Server (NTRS)
McGovern, Patrick J.; Solomon, Sean C.; Smith, David E.; Zuber, Maria T.; Simons, Mark; Wieczorek, Mark A.; Phillips, Roger J.; Neumann, Gregory A.; Aharonson, Oded; Head, James W.
2002-01-01
[i] From gravity and topography data collected by the Mars Global Surveyor spacecraft we calculate gravity/topography admittances and correlations in the spectral domain and compare them to those predicted from models of lithospheric flexure. On the basis of these comparisons we estimate the thickness of the Martian elastic lithosphere (T(sub e)) required to support the observed topographic load since the time of loading. We convert T(sub e) to estimates of heat flux and thermal gradient in the lithosphere through a consideration of the response of an elastic/plastic shell. In regions of high topography on Mars (e.g., the Tharsis rise and associated shield volcanoes), the mass-sheet (small-amplitude) approximation for the calculation of gravity from topography is inadequate. A correction that accounts for finite-amplitude topography tends to increase the amplitude of the predicted gravity signal at spacecraft altitudes. Proper implementation of this correction requires the use of radii from the center of mass (collectively known as the planetary shape ) in lieu of topography referenced to a gravitational equipotential. Anomalously dense surface layers or buried excess masses are not required to explain the observed admittances for the Tharsis Montes or Olympus Mons volcanoes when this correction is applied. Derived T, values generally decrease with increasing age of the lithospheric load, in a manner consistent with a rapid decline of mantle heat flux during the Noachian and more modest rates of decline during subsequent epochs.
The long-wavelength admittance and effective elastic thickness of the Canadian Shield
NASA Astrophysics Data System (ADS)
Kirby, J. F.; Swain, C. J.
2014-06-01
The strength of the cratonic lithosphere has been controversial. On the one hand, many estimates of effective elastic thickness (Te) greatly exceed the crustal thickness, but on the other the great majority of cratonic earthquakes occur in the upper crust. This implies that the seismogenic thickness of cratons is much smaller than Te, whereas in the ocean basins they are approximately the same, leading to suspicions about the large Te estimates. One region where such estimates have been questioned is the Canadian Shield, where glacial isostatic adjustment (GIA) and mantle convection are thought to contribute to the long-wavelength undulations of the topography and gravity. To date these have not been included in models used to estimate Te from topography and gravity which conventionally are based only on loading and flexure. Here we devise a theoretical expression for the free-air (gravity/topography) admittance that includes the effects of GIA and convection as well as flexure and use it to estimate Te over the Canadian Shield. We use wavelet transforms for estimating the observed admittances, after showing that multitaper estimates, which have hitherto been popular for Te studies, have poor resolution at the long wavelengths where GIA and convection predominate, compared to wavelets. Our results suggest that Te over most of the shield exceeds 80 km, with a higher-Te core near the southwest shore of Hudson Bay. This means that the lack of mantle earthquakes in this craton is simply due to its high strength compared to the applied stresses.
Hole transport characteristics in phosphorescent dye-doped NPB films by admittance spectroscopy
NASA Astrophysics Data System (ADS)
Wang, Ying; Chen, Jiangshan; Huang, Jinying; Dai, Yanfeng; Zhang, Zhiqiang; Liu, Su; Ma, Dongge
2014-05-01
Admittance spectroscopy is a powerful tool to determine the carrier mobility. The carrier mobility is a significant parameter to understand the behavior or to optimize the organic light-emitting diode or other organic semiconductor devices. Hole transport in phosphorescent dye, bis[2-(9,9-diethyl-9H-fluoren-2-yl)-1-phenyl-1Hbenzoimidazol-N,C3] iridium(acetylacetonate [(fbi)2Ir(acac)]) doped into N,N-diphenyl-N,N-bis(1-naphthylphenyl)-1,1-biphenyl-4,4-diamine (NPB) films was investigated by admittance spectroscopy. The results show that doped (fbi)2Ir(acac) molecules behave as hole traps in NPB, and lower the hole mobility. For thicker films(≳300 nm), the electric field dependence of hole mobility is as expected positive, i.e., the mobility increases exponentially with the electric field. However, for thinner films (≲300 nm), the electric field dependence of hole mobility is negative, i.e., the hole mobility decreases exponentially with the electric field. Physical mechanisms behind the negative field dependence of hole mobility are discussed. In addition, three frequency regions were divided to analyze the behaviors of the capacitance in the hole-only device and the physical mechanism was explained by trap theory and the parasitic capacitance effect.
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.
Rarefield-Flow Shuttle Aerodynamics Flight Model
NASA Technical Reports Server (NTRS)
Blanchard, Robert C.; Larman, Kevin T.; Moats, Christina D.
1994-01-01
A model of the Shuttle Orbiter rarefied-flow aerodynamic force coefficients has been derived from the ratio of flight acceleration measurements. The in-situ, low-frequency (less than 1Hz), low-level (approximately 1 x 10(exp -6) g) acceleration measurements are made during atmospheric re-entry. The experiment equipment designed and used for this task is the High Resolution Accelerometer Package (HiRAP), one of the sensor packages in the Orbiter Experiments Program. To date, 12 HiRAP re-entry mission data sets spanning a period of about 10 years have been processed. The HiRAP-derived aerodynamics model is described in detail. The model includes normal and axial hypersonic continuum coefficient equations as function of angle of attack, body-flap deflection, and elevon deflection. Normal and axial free molecule flow coefficient equations as a function of angle of attack are also presented, along with flight-derived rarefied-flow transition bridging formulae. Comparisons are made between the aerodynamics model, data from the latest Orbiter Operational Aerodynamic Design Data Book, applicable computer simulations, and wind-tunnel data.
A Generic Nonlinear Aerodynamic Model for Aircraft
NASA Technical Reports Server (NTRS)
Grauer, Jared A.; Morelli, Eugene A.
2014-01-01
A generic model of the aerodynamic coefficients was developed using wind tunnel databases for eight different aircraft and multivariate orthogonal functions. For each database and each coefficient, models were determined using polynomials expanded about the state and control variables, and an othgonalization procedure. A predicted squared-error criterion was used to automatically select the model terms. Modeling terms picked in at least half of the analyses, which totalled 45 terms, were retained to form the generic nonlinear aerodynamic (GNA) model. Least squares was then used to estimate the model parameters and associated uncertainty that best fit the GNA model to each database. Nonlinear flight simulations were used to demonstrate that the GNA model produces accurate trim solutions, local behavior (modal frequencies and damping ratios), and global dynamic behavior (91% accurate state histories and 80% accurate aerodynamic coefficient histories) under large-amplitude excitation. This compact aerodynamics model can be used to decrease on-board memory storage requirements, quickly change conceptual aircraft models, provide smooth analytical functions for control and optimization applications, and facilitate real-time parametric system identification.
Aerodynamic shape optimization using control theory
NASA Technical Reports Server (NTRS)
Reuther, James
1996-01-01
Aerodynamic shape design has long persisted as a difficult scientific challenge due its highly nonlinear flow physics and daunting geometric complexity. However, with the emergence of Computational Fluid Dynamics (CFD) it has become possible to make accurate predictions of flows which are not dominated by viscous effects. It is thus worthwhile to explore the extension of CFD methods for flow analysis to the treatment of aerodynamic shape design. Two new aerodynamic shape design methods are developed which combine existing CFD technology, optimal control theory, and numerical optimization techniques. Flow analysis methods for the potential flow equation and the Euler equations form the basis of the two respective design methods. In each case, optimal control theory is used to derive the adjoint differential equations, the solution of which provides the necessary gradient information to a numerical optimization method much more efficiently then by conventional finite differencing. Each technique uses a quasi-Newton numerical optimization algorithm to drive an aerodynamic objective function toward a minimum. An analytic grid perturbation method is developed to modify body fitted meshes to accommodate shape changes during the design process. Both Hicks-Henne perturbation functions and B-spline control points are explored as suitable design variables. The new methods prove to be computationally efficient and robust, and can be used for practical airfoil design including geometric and aerodynamic constraints. Objective functions are chosen to allow both inverse design to a target pressure distribution and wave drag minimization. Several design cases are presented for each method illustrating its practicality and efficiency. These include non-lifting and lifting airfoils operating at both subsonic and transonic conditions.
Nozzle Aerodynamic Stability During a Throat Shift
NASA Technical Reports Server (NTRS)
Kawecki, Edwin J.; Ribeiro, Gregg L.
2005-01-01
An experimental investigation was conducted on the internal aerodynamic stability of a family of two-dimensional (2-D) High Speed Civil Transport (HSCT) nozzle concepts. These nozzles function during takeoff as mixer-ejectors to meet acoustic requirements, and then convert to conventional high-performance convergent-divergent (CD) nozzles at cruise. The transition between takeoff mode and cruise mode results in the aerodynamic throat and the minimum cross-sectional area that controls the engine backpressure shifting location within the nozzle. The stability and steadiness of the nozzle aerodynamics during this so called throat shift process can directly affect the engine aerodynamic stability, and the mechanical design of the nozzle. The objective of the study was to determine if pressure spikes or other perturbations occurred during the throat shift process and, if so, identify the caused mechanisms for the perturbations. The two nozzle concepts modeled in the test program were the fixed chute (FC) and downstream mixer (DSM). These 2-D nozzles differ principally in that the FC has a large over-area between the forward throat and aft throat locations, while the DSM has an over-area of only about 10 percent. The conclusions were that engine mass flow and backpressure can be held constant simultaneously during nozzle throat shifts on this class of nozzles, and mode shifts can be accomplished at a constant mass flow and engine backpressure without upstream pressure perturbations.
Aerodynamics of a Cryogenic Semi-Tanker
NASA Astrophysics Data System (ADS)
Ortega, Jason; Salari, Kambiz
2009-11-01
The design of a modern cryogenic semi-tanker is based primarily upon functionality with little consideration given to aerodynamic drag. As a result, these tankers have maintained the appearance of a wheeled cylinder for several decades. To reduce the fuel usage of these vehicles, this study investigates their aerodynamics. A detailed understanding of the flow field about the vehicle and its influence on aerodynamic drag is obtained by performing Reynolds-Averaged Navier-Stokes simulations of a full-scale tractor and cryogenic tanker-trailer operating at highway speed within a crosswind. The tanker-trailer has a length to diameter ratio of 6.3. The Reynolds number, based upon the tanker diameter, is 4.0x10^6, while the effective vehicle yaw angle is 6.1 . The flow field about the vehicle is characterized by large flow separation regions at the tanker underbody and base. In addition, the relatively large gap between the tractor and the tanker-trailer allows the free-stream flow to be entrained into the tractor-tanker gap. By mitigating these drag-producing phenomena through the use of simple geometry modifications, it may be possible to reduce the aerodynamic drag of cryogenic semi-tankers and, thereby, improve their fuel economy. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
ERIC Educational Resources Information Center
Nondahl, David M.; Cruickshanks, Karen J.; Wiley, Terry L.; Tweed, Ted S.; Dalton, Dayna S.
2013-01-01
Purpose: The primary purpose of this study was to measure the 16-year change in peak compensated static acoustic admittance (Peak Y[subscript tm]) in a population-based cohort of older adults, and to determine whether age was associated with any observed change in Peak Y[subscript tm]. Other tympanometric measures also were taken and analyzed.…
Ravicz, Michael E.; Rosowski, John J.
2012-01-01
The middle-ear input admittance relates sound power into the middle ear (ME) and sound pressure at the tympanic membrane (TM). ME input admittance was measured in the chinchilla ear canal as part of a larger study of sound power transmission through the ME into the inner ear. The middle ear was open, and the inner ear was intact or modified with small sensors inserted into the vestibule near the cochlear base. A simple model of the chinchilla ear canal, based on ear canal sound pressure measurements at two points along the canal and an assumption of plane-wave propagation, enables reliable estimates of YTM, the ME input admittance at the TM, from the admittance measured relatively far from the TM. YTM appears valid at frequencies as high as 17 kHz, a much higher frequency than previously reported. The real part of YTM decreases with frequency above 2 kHz. Effects of the inner-ear sensors (necessary for inner ear power computation) were small and generally limited to frequencies below 3 kHz. Computed power reflectance was ∼0.1 below 3.5 kHz, lower than with an intact ME below 2.5 kHz, and nearly 1 above 16 kHz. PMID:23039439
Freight Wing Trailer Aerodynamics
Graham, Sean; Bigatel, Patrick
2004-10-17
Freight Wing Incorporated utilized the opportunity presented by this DOE category one Inventions and Innovations grant to successfully research, develop, test, patent, market, and sell innovative fuel and emissions saving aerodynamic attachments for the trucking industry. A great deal of past scientific research has demonstrated that streamlining box shaped semi-trailers can significantly reduce a truck's fuel consumption. However, significant design challenges have prevented past concepts from meeting industry needs. Market research early in this project revealed the demands of truck fleet operators regarding aerodynamic attachments. Products must not only save fuel, but cannot interfere with the operation of the truck, require significant maintenance, add significant weight, and must be extremely durable. Furthermore, SAE/TMC J1321 tests performed by a respected independent laboratory are necessary for large fleets to even consider purchase. Freight Wing used this information to create a system of three practical aerodynamic attachments for the front, rear and undercarriage of standard semi trailers. SAE/TMC J1321 Type II tests preformed by the Transportation Research Center (TRC) demonstrated a 7% improvement to fuel economy with all three products. If Freight Wing is successful in its continued efforts to gain market penetration, the energy and environmental savings would be considerable. Each truck outfitted saves approximately 1,100 gallons of fuel every 100,000 miles, which prevents over 12 tons of CO2 from entering the atmosphere. If all applicable trailers used the technology, the country could save approximately 1.8 billion gallons of diesel fuel, 18 million tons of emissions and 3.6 billion dollars annually.
Morse, Robert Peter
2013-10-01
Many passengers experience discomfort during flight because of the effect of low humidity on the skin, eyes, throat, and nose. In this physiological study, we have investigated whether flight and low humidity also affect the tympanic membrane. From previous studies, a decrease in admittance of the tympanic membrane through drying might be expected to affect the buffering capacity of the middle ear and to disrupt automatic pressure regulation. This investigation involved an observational study onboard an aircraft combined with experiments in an environmental chamber, where the humidity could be controlled but could not be made to be as low as during flight. For the flight study, there was a linear relationship between the peak compensated static admittance of the tympanic membrane and relative humidity with a constant of proportionality of 0.00315 mmho/% relative humidity. The low humidity at cruise altitude (minimum 22.7 %) was associated with a mean decrease in admittance of about 20 % compared with measures in the airport. From the chamber study, we further found that a mean decrease in relative humidity of 23.4 % led to a significant decrease in mean admittance by 0.11 mmho [F(1,8) = 18.95, P = 0.002], a decrease of 9.4 %. The order of magnitude for the effect of humidity was similar for the flight and environmental chamber studies. We conclude that admittance changes during flight were likely to have been caused by the low humidity in the aircraft cabin and that these changes may affect the automatic pressure regulation of the middle ear during descent. PMID:23887775
Admittance Investigation of MIS Structures with HgTe-Based Single Quantum Wells
NASA Astrophysics Data System (ADS)
Izhnin, Ihor I.; Nesmelov, Sergey N.; Dzyadukh, Stanislav M.; Voitsekhovskii, Alexander V.; Gorn, Dmitry I.; Dvoretsky, Sergey A.; Mikhailov, Nikolaj N.
2016-02-01
This work presents results of the investigation of admittance of metal-insulator-semiconductor structure based on Hg1 - x Cd x Te grown by molecular beam epitaxy. The structure contains a single quantum well Hg0.35Cd0.65Te/HgTe/Hg0.35Cd0.65Te with thickness of 5.6 nm in the sub-surface layer of the semiconductor. Both the conductance-voltage and capacitance-voltage characteristics show strong oscillations when the metal-insulator-semiconductor (MIS) structure with a single quantum well based on HgTe is biased into the strong inversion mode. Also, oscillations on the voltage dependencies of differential resistance of the space charge region were observed. These oscillations were related to the recharging of quantum levels in HgTe.
Quantum dot admittance probed at microwave frequencies with an on-chip resonator
NASA Astrophysics Data System (ADS)
Frey, T.; Leek, P. J.; Beck, M.; Faist, J.; Wallraff, A.; Ensslin, K.; Ihn, T.; Büttiker, M.
2012-09-01
We present microwave frequency measurements of the dynamic admittance of a quantum dot tunnel-coupled to a two-dimensional electron gas. The measurements are made via a high-quality 6.75 GHz on-chip resonator capacitively coupled to the dot. The resonator frequency is found to shift both down and up close to conductance resonance of the dot corresponding to a change of sign of the reactance of the system from capacitive to inductive. The observations are consistent with a scattering matrix model. The sign of the reactance depends on the detuning of the dot from conductance resonance and on the magnitude of the tunnel rate to the lead with respect to the resonator frequency. Inductive response is observed on a conductance resonance when tunnel coupling and temperature are sufficiently small compared to the resonator frequency.
Three-dimensional admittance analysis of lithospheric elastic thickness over the Louisville Ridge
NASA Astrophysics Data System (ADS)
Hu, Minzhang; Li, Hui; Shen, Chongyang; Xing, Lelin; Hao, Hongtao
2016-04-01
Using bathymetry and altimetric gravity anomalies, a 1° × 1° lithospheric effective elastic thickness ( T e) model over the Louisville Ridge and its adjacent regions is calculated using the moving window admittance technique. For comparison, three bathymetry models are used: general bathymetric charts of the oceans, SIO V15.1, and BAT_VGG. The results show that BAT_VGG is more suitable for calculating T e than the other two models. T e along the Louisville Ridge was re-evaluated. The southeast of the ridge has a medium T e of 10-20 km, while T e increases dramatically seaward of the Tonga-Kermadec trench as a result of the collision of the Pacific and Indo-Australian plates.
Admittance Investigation of MIS Structures with HgTe-Based Single Quantum Wells.
Izhnin, Ihor I; Nesmelov, Sergey N; Dzyadukh, Stanislav M; Voitsekhovskii, Alexander V; Gorn, Dmitry I; Dvoretsky, Sergey A; Mikhailov, Nikolaj N
2016-12-01
This work presents results of the investigation of admittance of metal-insulator-semiconductor structure based on Hg1 - x Cd x Te grown by molecular beam epitaxy. The structure contains a single quantum well Hg0.35Cd0.65Te/HgTe/Hg0.35Cd0.65Te with thickness of 5.6 nm in the sub-surface layer of the semiconductor. Both the conductance-voltage and capacitance-voltage characteristics show strong oscillations when the metal-insulator-semiconductor (MIS) structure with a single quantum well based on HgTe is biased into the strong inversion mode. Also, oscillations on the voltage dependencies of differential resistance of the space charge region were observed. These oscillations were related to the recharging of quantum levels in HgTe. PMID:26831691
Incremental Aerodynamic Coefficient Database for the USA2
NASA Technical Reports Server (NTRS)
Richardson, Annie Catherine
2016-01-01
In March through May of 2016, a wind tunnel test was conducted by the Aerosciences Branch (EV33) to visually study the unsteady aerodynamic behavior over multiple transition geometries for the Universal Stage Adapter 2 (USA2) in the MSFC Aerodynamic Research Facility's Trisonic Wind Tunnel (TWT). The purpose of the test was to make a qualitative comparison of the transonic flow field in order to provide a recommended minimum transition radius for manufacturing. Additionally, 6 Degree of Freedom force and moment data for each configuration tested was acquired in order to determine the geometric effects on the longitudinal aerodynamic coefficients (Normal Force, Axial Force, and Pitching Moment). In order to make a quantitative comparison of the aerodynamic effects of the USA2 transition geometry, the aerodynamic coefficient data collected during the test was parsed and incorporated into a database for each USA2 configuration tested. An incremental aerodynamic coefficient database was then developed using the generated databases for each USA2 geometry as a function of Mach number and angle of attack. The final USA2 coefficient increments will be applied to the aerodynamic coefficients of the baseline geometry to adjust the Space Launch System (SLS) integrated launch vehicle force and moment database based on the transition geometry of the USA2.
NASA Astrophysics Data System (ADS)
Mehta, R. D.
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)
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)
Hooks, I.; Homan, D.; Romere, P. O.
1985-01-01
The approach and landing test (ALT) of the Space Shuttle Orbiter presented a number of unique challenges in the area of aerodynamics. The purpose of the ALT program was both to confirm the use of the Boeing 747 as a transport vehicle for ferrying the Orbiter across the country and to demonstrate the flight characteristics of the Orbiter in its approach and landing phase. Concerns for structural fatigue and performance dictated a tailcone be attached to the Orbiter for ferry and for the initial landing tests. The Orbiter with a tailcone attached presented additional challenges to the normal aft sting concept of wind tunnel testing. The landing tests required that the Orbiter be separated from the 747 at approximately 20,000 feet using aerodynamic forces to fly the vehicles apart. The concept required a complex test program to determine the relative effects of the two vehicles on each other. Also of concern, and tested, was the vortex wake created by the 747 and the means for the Orbiter to avoid it following separation.
Aerodynamic design using numerical optimization
NASA Technical Reports Server (NTRS)
Murman, E. M.; Chapman, G. T.
1983-01-01
The procedure of using numerical optimization methods coupled with computational fluid dynamic (CFD) codes for the development of an aerodynamic design is examined. Several approaches that replace wind tunnel tests, develop pressure distributions and derive designs, or fulfill preset design criteria are presented. The method of Aerodynamic Design by Numerical Optimization (ADNO) is described and illustrated with examples.
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)
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…
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.
The design of missile's dome that fits both optical and aerodynamic needs
NASA Astrophysics Data System (ADS)
Wei, Qun; Zhang, Xin; Jia, Hongguang
2010-10-01
Optical guidance missiles requires a dome which fits both optical and aerodynamic needs when they attack at 3 Ma. In this study, ellipse is the figure chosen to be the dome's shape. The ellipticity ɛ is the main variable should to be decided. The optimized function was built by optical and aerodynamic performance function multiply by their weights. The optical and aerodynamic functions were all obtained by computational fluid dynamic (CFD) simulation's results after normalization. In this study, the optical and aerodynamic performances have equal weights, after optimzing the ellipticity ɛis 2 for the missile.
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 aerodynamic modeling for arbitrary motions
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.
Nash equilibrium and multi criterion aerodynamic optimization
NASA Astrophysics Data System (ADS)
Tang, Zhili; Zhang, Lianhe
2016-06-01
Game theory and its particular Nash Equilibrium (NE) are gaining importance in solving Multi Criterion Optimization (MCO) in engineering problems over the past decade. The solution of a MCO problem can be viewed as a NE under the concept of competitive games. This paper surveyed/proposed four efficient algorithms for calculating a NE of a MCO problem. Existence and equivalence of the solution are analyzed and proved in the paper based on fixed point theorem. Specific virtual symmetric Nash game is also presented to set up an optimization strategy for single objective optimization problems. Two numerical examples are presented to verify proposed algorithms. One is mathematical functions' optimization to illustrate detailed numerical procedures of algorithms, the other is aerodynamic drag reduction of civil transport wing fuselage configuration by using virtual game. The successful application validates efficiency of algorithms in solving complex aerodynamic optimization problem.
Rarefied-flow Shuttle aerodynamics model
NASA Technical Reports Server (NTRS)
Blanchard, Robert C.; Larman, Kevin T.; Moats, Christina D.
1993-01-01
A rarefied-flow shuttle aerodynamic model spanning the hypersonic continuum to the free molecule-flow regime was formulated. The model development has evolved from the High Resolution Accelerometer Package (HiRAP) experiment conducted on the Orbiter since 1983. The complete model is described in detail. The model includes normal and axial hypersonic continuum coefficient equations as functions of angle-of-attack, body flap deflection, and elevon deflection. Normal and axial free molecule flow coefficient equations as a function of angle-of-attack are presented, along with flight derived rarefied-flow transition bridging formulae. Comparisons are made with data from the Operational Aerodynamic Design Data Book (OADDB), applicable wind-tunnel data, and recent flight data from STS-35 and STS-40. The flight-derived model aerodynamic force coefficient ratio is in good agreement with the wind-tunnel data and predicts the flight measured force coefficient ratios on STS-35 and STS-40. The model is not, however, in good agreement with the OADDB. But, the current OADDB does not predict the flight data force coefficient ratios of either STS-35 or STS-40 as accurately as the flight-derived model. Also, the OADDB differs with the wind-tunnel force coefficient ratio data.
Freight Wing Trailer Aerodynamics Final Technical Report
Sean Graham
2007-10-31
Freight Wing Incorporated utilized the opportunity presented by a DOE category two Inventions and Innovations grant to commercialize and improve upon aerodynamic technology for semi-tuck trailers, capable of decreasing heavy vehicle fuel consumption, related environmental damage, and U.S. consumption of foreign oil. Major project goals included the demonstration of aerodynamic trailer technology in trucking fleet operations, and the development and testing of second generation products. A great deal of past scientific research has demonstrated that streamlining box shaped semi-trailers can significantly reduce a truck’s fuel consumption. However, significant design challenges have prevented past concepts from meeting industry needs. Freight Wing utilized a 2003 category one Inventions and Innovations grant to develop practical solutions to trailer aerodynamics. Fairings developed for the front, rear, and bottom of standard semi-trailers together demonstrated a 7% improvement to fuel economy in scientific tests conducted by the Transportation Research Center (TRC). Operational tests with major trucking fleets proved the functionality of the products, which were subsequently brought to market. This category two grant enabled Freight Wing to further develop, test and commercialize its products, resulting in greatly increased understanding and acceptance of aerodynamic trailer technology. Commercialization was stimulated by offering trucking fleets 50% cost sharing on trial implementations of Freight Wing products for testing and evaluation purposes. Over 230 fairings were implemented through the program with 35 trucking fleets including industry leaders such as Wal-Mart, Frito Lay and Whole Foods. The feedback from these testing partnerships was quite positive with product performance exceeding fleet expectations in many cases. Fleet feedback also was also valuable from a product development standpoint and assisted the design of several second generation products
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.
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.
Dynamic soaring: aerodynamics for albatrosses
NASA Astrophysics Data System (ADS)
Denny, Mark
2009-01-01
Albatrosses have evolved to soar and glide efficiently. By maximizing their lift-to-drag ratio L/D, albatrosses can gain energy from the wind and can travel long distances with little effort. We simplify the difficult aerodynamic equations of motion by assuming that albatrosses maintain a constant L/D. Analytic solutions to the simplified equations provide an instructive and appealing example of fixed-wing aerodynamics suitable for undergraduate demonstration.
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.
Aerodynamics for the Mars Phoenix Entry Capsule
NASA Technical Reports Server (NTRS)
Edquist, Karl T.; Desai, Prasun N.; Schoenenberger, Mark
2008-01-01
Pre-flight aerodynamics data for the Mars Phoenix entry capsule are presented. The aerodynamic coefficients were generated as a function of total angle-of-attack and either Knudsen number, velocity, or Mach number, depending on the flight regime. The database was constructed using continuum flowfield computations and data from the Mars Exploration Rover and Viking programs. Hypersonic and supersonic static coefficients were derived from Navier-Stokes solutions on a pre-flight design trajectory. High-altitude data (free-molecular and transitional regimes) and dynamic pitch damping characteristics were taken from Mars Exploration Rover analysis and testing. Transonic static coefficients from Viking wind tunnel tests were used for capsule aerodynamics under the parachute. Static instabilities were predicted at two points along the reference trajectory and were verified by reconstructed flight data. During the hypersonic instability, the capsule was predicted to trim at angles as high as 2.5 deg with an on-axis center-of-gravity. Trim angles were predicted for off-nominal pitching moment (4.2 deg peak) and a 5 mm off-axis center-ofgravity (4.8 deg peak). Finally, hypersonic static coefficient sensitivities to atmospheric density were predicted to be within uncertainty bounds.
Aerodynamic sampling for landmine trace detection
NASA Astrophysics Data System (ADS)
Settles, Gary S.; Kester, Douglas A.
2001-10-01
Electronic noses and similar sensors show promise for detecting buried landmines through the explosive trace signals they emit. A key step in this detection is the sampler or sniffer, which acquires the airborne trace signal and presents it to the detector. Practicality demands no physical contact with the ground. Further, both airborne particulates and molecular traces must be sampled. Given a complicated minefield terrain and microclimate, this becomes a daunting chore. Our prior research on canine olfactory aerodynamics revealed several ways that evolution has dealt with such problems: 1) proximity of the sniffer to the scent source is important, 2) avoid exhaling back into the scent source, 3) use an aerodynamic collar on the sniffer inlet, 4) use auxiliary airjets to stir up surface particles, and 5) manage the 'impedance mismatch' between sniffer and sensor airflows carefully. Unfortunately, even basic data on aerodynamic sniffer performance as a function of inlet-tube and scent-source diameters, standoff distance, etc., have not been previously obtained. A laboratory-prototype sniffer was thus developed to provide guidance for landmine trace detectors. Initial experiments with this device are the subject of this paper. For example, a spike in the trace signal is observed upon starting the sniffer airflow, apparently due to rapid depletion of the available signal-laden air. Further, shielding the sniffer from disruptive ambient airflows arises as a key issue in sampling efficiency.
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 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.
The aerodynamics of supersonic parachutes
Peterson, C.W.
1987-06-01
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 wind tunnel data on hemisflo and 20-degree conical ribbon parachutes behind several forebody shapes and diameters are discussed. Test techniques were derived which avoided many of the opportunities to obtain erroneous supersonic parachute drag data in wind tunnels. Preliminary correlations of supersonic parachute drag with Mach number, forebody shape and diameter, canopy porosity, inflated canopy diameter and stability are presented. Supersonic parachute design considerations are discussed and applied to a M = 2 parachute system designed and tested at Sandia. It is shown that the performance of parachutes in supersonic flows is a strong function of parachute design parameters and their interactions with the payload wake.
An Admittance Survey of Large Volcanoes on Venus: Implications for Volcano Growth
NASA Technical Reports Server (NTRS)
Brian, A. W.; Smrekar, S. E.; Stofan, E. R.
2004-01-01
Estimates of the thickness of the venusian crust and elastic lithosphere are important in determining the rheological and thermal properties of Venus. These estimates offer insights into what conditions are needed for certain features, such as large volcanoes and coronae, to form. Lithospheric properties for much of the large volcano population on Venus are not well known. Previous studies of elastic thickness (Te) have concentrated on individual or small groups of edifices, or have used volcano models and fixed values of Te to match with observations of volcano morphologies. In addition, previous studies use different methods to estimate lithospheric parameters meaning it is difficult to compare their results. Following recent global studies of the admittance signatures exhibited by the venusian corona population, we performed a similar survey into large volcanoes in an effort to determine the range of lithospheric parameters shown by these features. This survey of the entire large volcano population used the same method throughout so that all estimates could be directly compared. By analysing a large number of edifices and comparing our results to observations of their morphology and models of volcano formation, we can help determine the controlling parameters that govern volcano growth on Venus.
Admittance spectroscopy of solar cells based on GaPNAs layers
Baranov, A. I. Gudovskikh, A. S.; Zelentsov, K. S.; Nikitina, E. V.; Egorov, A. Yu.
2015-04-15
Admittance spectroscopy is used to study defect levels in the layers of a GaPNAs quaternary solid solution. Centers with an activation energy of 0.22 eV and a capture cross section of ∼2.4 × 10{sup −15} cm{sup 2} are found in doped n-GaPNAs layers grown on GaP substrates. These centers correspond to already known Si{sub Ga} + V{sub P} defects in n-GaP; annealing decreases their concentration by several times. A level with an activation energy of 0.23–0.24 eV and capture cross section of ∼9.0 × 10{sup −20} cm{sup 2} is found in undoped GaPNAs layers grown on Si and GaP substrates. The concentration of these centers substantially decreases upon annealing, and, at annealing temperatures exceeding 600°C, there is absolutely no response from these defects. For undoped GaPNAs layers grown on GaP substrates, a level with an activation energy of 0.18 eV and capture cross section of ∼1.1 × 10{sup −16} cm{sup 2} is also found. The concentration of these centers remains unchanged upon annealing.
Global Nonlinear Parametric Modeling with Application to F-16 Aerodynamics
NASA Technical Reports Server (NTRS)
Morelli, Eugene A.
1997-01-01
A global nonlinear parametric modeling technique is described and demonstrated. The technique uses multivariate orthogonal modeling functions generated from the data to determine nonlinear model structure, then expands each retained modeling function into an ordinary multivariate polynomial. The final model form is a finite multivariate power series expansion for the dependent variable in terms of the independent variables. Partial derivatives of the identified models can be used to assemble globally valid linear parameter varying models. The technique is demonstrated by identifying global nonlinear parametric models for nondimensional aerodynamic force and moment coefficients from a subsonic wind tunnel database for the F-16 fighter aircraft. Results show less than 10% difference between wind tunnel aerodynamic data and the nonlinear parameterized model for a simulated doublet maneuver at moderate angle of attack. Analysis indicated that the global nonlinear parametric models adequately captured the multivariate nonlinear aerodynamic functional dependence.
Global Nonlinear Parametric Modeling with Application to F-16 Aerodynamics
NASA Technical Reports Server (NTRS)
Morelli, Eugene A.
1998-01-01
A global nonlinear parametric modeling technique is described and demonstrated. The technique uses multivariate orthogonal modeling functions generated from the data to determine nonlinear model structure, then expands each retained modeling function into an ordinary multivariate polynomial. The final model form is a finite multivariate power series expansion for the dependent variable in terms of the independent variables. Partial derivatives of the identified models can be used to assemble globally valid linear parameter varying models. The technique is demonstrated by identifying global nonlinear parametric models for nondimensional aerodynamic force and moment coefficients from a subsonic wind tunnel database for the F-16 fighter aircraft. Results show less than 10% difference between wind tunnel aerodynamic data and the nonlinear parameterized model for a simulated doublet maneuver at moderate angle of attack. Analysis indicated that the global nonlinear parametric models adequately captured the multivariate nonlinear aerodynamic functional dependence.
NASA Technical Reports Server (NTRS)
Nissim, E.
1977-01-01
Control laws are derived, by using realizable transfer functions, which permit relaxation of the stability requirements of the aerodynamic energy concept. The resulting aerodynamic eigenvalues indicate that both the trailing edge and the leading edge-trailing edge control systems can be made more effective. These control laws permit the introduction of aerodynamic damping and stiffness terms in accordance with the requirements of any specific system. Flutter suppression and gust alleviation problems can now be treated by either a trailing edge control system or by a leading edge-trailing edge control system by using the aerodynamic energy concept. Results are applicable to a wide class of aircraft operating at subsonic Mach numbers.
Parameter identification for nonlinear aerodynamic systems
NASA Technical Reports Server (NTRS)
Pearson, Allan E.
1990-01-01
Parameter identification for nonlinear aerodynamic systems is examined. It is presumed that the underlying model can be arranged into an input/output (I/O) differential operator equation of a generic form. The algorithm estimation is especially efficient since the equation error can be integrated exactly given any I/O pair to obtain an algebraic function of the parameters. The algorithm for parameter identification was extended to the order determination problem for linear differential system. The degeneracy in a least squares estimate caused by feedback was addressed. A method of frequency analysis for determining the transfer function G(j omega) from transient I/O data was formulated using complex valued Fourier based modulating functions in contrast with the trigonometric modulating functions for the parameter estimation problem. A simulation result of applying the algorithm is given under noise-free conditions for a system with a low pass transfer function.
Configuration Aerodynamics: Past - Present - Future
NASA Technical Reports Server (NTRS)
Wood, Richard M.; Agrawal, Shreekant; Bencze, Daniel P.; Kulfan, Robert M.; Wilson, Douglas L.
1999-01-01
The Configuration Aerodynamics (CA) element of the High Speed Research (HSR) program is managed by a joint NASA and Industry team, referred to as the Technology Integration Development (ITD) team. This team is responsible for the development of a broad range of technologies for improved aerodynamic performance and stability and control characteristics at subsonic to supersonic flight conditions. These objectives are pursued through the aggressive use of advanced experimental test techniques and state of the art computational methods. As the HSR program matures and transitions into the next phase the objectives of the Configuration Aerodynamics ITD are being refined to address the drag reduction needs and stability and control requirements of High Speed Civil Transport (HSCT) aircraft. In addition, the experimental and computational tools are being refined and improved to meet these challenges. The presentation will review the work performed within the Configuration Aerodynamics element in 1994 and 1995 and then discuss the plans for the 1996-1998 time period. The final portion of the presentation will review several observations of the HSR program and the design activity within Configuration Aerodynamics.
Aerodynamic drag on intermodal railcars
NASA Astrophysics Data System (ADS)
Kinghorn, Philip; Maynes, Daniel
2014-11-01
The aerodynamic drag associated with transport of commodities by rail is becoming increasingly important as the cost of diesel fuel increases. This study aims to increase the efficiency of intermodal cargo trains by reducing the aerodynamic drag on the load carrying cars. For intermodal railcars a significant amount of aerodynamic drag is a result of the large distance between loads that often occurs and the resulting pressure drag resulting from the separated flow. In the present study aerodynamic drag data have been obtained through wind tunnel testing on 1/29 scale models to understand the savings that may be realized by judicious modification to the size of the intermodal containers. The experiments were performed in the BYU low speed wind tunnel and the test track utilizes two leading locomotives followed by a set of five articulated well cars with double stacked containers. The drag on a representative mid-train car is measured using an isolated load cell balance and the wind tunnel speed is varied from 20 to 100 mph. We characterize the effect that the gap distance between the containers and the container size has on the aerodynamic drag of this representative rail car and investigate methods to reduce the gap distance.
New technology in turbine aerodynamics.
NASA Technical Reports Server (NTRS)
Glassman, A. J.; Moffitt, T. P.
1972-01-01
Cursory review of some recent work that has been done in turbine aerodynamic research. Topics discussed include the aerodynamic effect of turbine coolant, high work-factor (ratio of stage work to square of blade speed) turbines, and computer methods for turbine design and performance prediction. Experimental cooled-turbine aerodynamics programs using two-dimensional cascades, full annular cascades, and cold rotating turbine stage tests are discussed with some typical results presented. Analytically predicted results for cooled blade performance are compared to experimental results. The problems and some of the current programs associated with the use of very high work factors for fan-drive turbines of high-bypass-ratio engines are discussed. Computer programs have been developed for turbine design-point performance, off-design performance, supersonic blade profile design, and the calculation of channel velocities for subsonic and transonic flowfields. The use of these programs for the design and analysis of axial and radial turbines is discussed.
Recent advances in computational aerodynamics
NASA Astrophysics Data System (ADS)
Agarwal, Ramesh K.; Desse, Jerry E.
1991-04-01
The current state of the art in computational aerodynamics is described. Recent advances in the discretization of surface geometry, grid generation, and flow simulation algorithms have led to flowfield predictions for increasingly complex and realistic configurations. As a result, computational aerodynamics is emerging as a crucial enabling technology for the development and design of flight vehicles. Examples illustrating the current capability for the prediction of aircraft, launch vehicle and helicopter flowfields are presented. Unfortunately, accurate modeling of turbulence remains a major difficulty in the analysis of viscosity-dominated flows. In the future inverse design methods, multidisciplinary design optimization methods, artificial intelligence technology and massively parallel computer technology will be incorporated into computational aerodynamics, opening up greater opportunities for improved product design at substantially reduced costs.
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.
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.
Aerodynamics Of Missiles: Present And Future
NASA Technical Reports Server (NTRS)
Nielsen, Jack N.
1991-01-01
Paper reviews variety of topics in aerodynamics of missiles. Describes recent developments and suggests areas in which future research fruitful. Emphasis on stability and control of tactical missiles. Aerodynamic problems discussed in general terms without reference to particular missiles.
Application Program Interface for the Orion Aerodynamics Database
NASA Technical Reports Server (NTRS)
Robinson, Philip E.; Thompson, James
2013-01-01
The Application Programming Interface (API) for the Crew Exploration Vehicle (CEV) Aerodynamic Database has been developed to provide the developers of software an easily implemented, fully self-contained method of accessing the CEV Aerodynamic Database for use in their analysis and simulation tools. The API is programmed in C and provides a series of functions to interact with the database, such as initialization, selecting various options, and calculating the aerodynamic data. No special functions (file read/write, table lookup) are required on the host system other than those included with a standard ANSI C installation. It reads one or more files of aero data tables. Previous releases of aerodynamic databases for space vehicles have only included data tables and a document of the algorithm and equations to combine them for the total aerodynamic forces and moments. This process required each software tool to have a unique implementation of the database code. Errors or omissions in the documentation, or errors in the implementation, led to a lengthy and burdensome process of having to debug each instance of the code. Additionally, input file formats differ for each space vehicle simulation tool, requiring the aero database tables to be reformatted to meet the tool s input file structure requirements. Finally, the capabilities for built-in table lookup routines vary for each simulation tool. Implementation of a new database may require an update to and verification of the table lookup routines. This may be required if the number of dimensions of a data table exceeds the capability of the simulation tools built-in lookup routines. A single software solution was created to provide an aerodynamics software model that could be integrated into other simulation and analysis tools. The highly complex Orion aerodynamics model can then be quickly included in a wide variety of tools. The API code is written in ANSI C for ease of portability to a wide variety of systems. The
NASA Technical Reports Server (NTRS)
Hakkinen, Raimo J; Richardson, A S , Jr
1957-01-01
Sinusoidally oscillating downwash and lift produced on a simple rigid airfoil were measured and compared with calculated values. Statistically stationary random downwash and the corresponding lift on a simple rigid airfoil were also measured and the transfer functions between their power spectra determined. The random experimental values are compared with theoretically approximated values. Limitations of the experimental technique and the need for more extensive experimental data are discussed.
Langley Symposium on Aerodynamics, volume 1
NASA Technical Reports Server (NTRS)
Stack, Sharon H. (Compiler)
1986-01-01
The purpose of this work was to present current work and results of the Langley Aeronautics Directorate covering the areas of computational fluid dynamics, viscous flows, airfoil aerodynamics, propulsion integration, test techniques, and low-speed, high-speed, and transonic aerodynamics. The following sessions are included in this volume: theoretical aerodynamics, test techniques, fluid physics, and viscous drag reduction.
An Investigation into the Admittance of MIS-Structures Based on MBE HgCdTe with Quantum Wells
NASA Astrophysics Data System (ADS)
Dzyadukh, S. M.; Voitsekhovskii, A. V.; Nesmelov, S. N.; Dvoretskii, S. A.; N. Mikhailov, N.; Gorn, D. I.
2013-12-01
The results of investigations into the complex admittance of the MIS-structures based on heteroepitaxial MBE Hg1- x Cd x Te with quantum wells (QW) in the test-signal frequency range 1 kHz - 2 МHz at temperatures 8-300 K are reported. The thickness of single HgTe QWs was 5.6 and 7.1 nm, the content in the 35-nm thick barrier layers - 0.65 and 0.62, respectively.
Advanced Aerodynamic Design of Passive Porosity Control Effectors
NASA Technical Reports Server (NTRS)
Hunter, Craig A.; Viken, Sally A.; Wood, Richard M.; Bauer, Steven X. S.
2001-01-01
This paper describes aerodynamic design work aimed at developing a passive porosity control effector system for a generic tailless fighter aircraft. As part of this work, a computational design tool was developed and used to layout passive porosity effector systems for longitudinal and lateral-directional control at a low-speed, high angle of attack condition. Aerodynamic analysis was conducted using the NASA Langley computational fluid dynamics code USM3D, in conjunction with a newly formulated surface boundary condition for passive porosity. Results indicate that passive porosity effectors can provide maneuver control increments that equal and exceed those of conventional aerodynamic effectors for low-speed, high-alpha flight, with control levels that are a linear function of porous area. This work demonstrates the tremendous potential of passive porosity to yield simple control effector systems that have no external moving parts and will preserve an aircraft's fixed outer mold line.
Atmospheric testing of wind turbine trailing edge aerodynamic brakes
Miller, L.S.; Migliore, P.G.; Quandt, G.A.
1997-12-31
An experimental investigation was conducted using an instrumented horizontal-axis wind turbine that incorporated variable span trailing-edge aerodynamic brakes. A primary goal was to directly compare study results with (infinite-span) wind tunnel data and to provide information on how to account for device span effects during turbine design or analysis. Comprehensive measurements were utilized to define effective changes in the aerodynamic coefficients, as a function of angle of attack and control deflection, for three device spans and configurations. Differences in the lift and drag behavior are most pronounced near stall and for device spans of less than 15%. Drag performance is affected only minimally (<70%) for 15% or larger span devices. Interestingly, aerodynamic controls with characteristic vents or openings appear most affected by span reductions and three-dimensional flow.
Sensitivity analysis in computational aerodynamics
NASA Technical Reports Server (NTRS)
Bristow, D. R.
1984-01-01
Information on sensitivity analysis in computational aerodynamics is given in outline, graphical, and chart form. The prediction accuracy if the MCAERO program, a perturbation analysis method, is discussed. A procedure for calculating perturbation matrix, baseline wing paneling for perturbation analysis test cases and applications of an inviscid sensitivity matrix are among the topics covered.
Semianalytic modeling of aerodynamic shapes
NASA Technical Reports Server (NTRS)
Barger, R. L.; Adams, M. S.
1985-01-01
Equations for the semianalytic representation of a class of surfaces that vary smoothly in cross-sectional shape are presented. Some methods of fitting together and superimposing such surfaces are described. A brief discussion is also included of the application of the theory in various contexts such as computerized lofting of aerodynamic surfaces and grid generation.
Aerodynamic laboratory at Cuatro Vientos
NASA Technical Reports Server (NTRS)
JUBERA
1922-01-01
This report presents a listing of the many experiments in aerodynamics taking place at Cuatro Vientos. Some of the studies include: testing spheres, in order to determine coefficients; mechanical and chemical tests of materials; and various tests of propeller strength and flexibility.
New technology in turbine aerodynamics
NASA Technical Reports Server (NTRS)
Glassman, A. J.; Moffitt, T. P.
1972-01-01
A cursory review is presented of some of the recent work that has been done in turbine aerodynamic research at NASA-Lewis Research Center. Topics discussed include the aerodynamic effect of turbine coolant, high work-factor (ratio of stage work to square of blade speed) turbines, and computer methods for turbine design and performance prediction. An extensive bibliography is included. Experimental cooled-turbine aerodynamics programs using two-dimensional cascades, full annular cascades, and cold rotating turbine stage tests are discussed with some typical results presented. Analytically predicted results for cooled blade performance are compared to experimental results. The problems and some of the current programs associated with the use of very high work factors for fan-drive turbines of high-bypass-ratio engines are discussed. Turbines currently being investigated make use of advanced blading concepts designed to maintain high efficiency under conditions of high aerodynamic loading. Computer programs have been developed for turbine design-point performance, off-design performance, supersonic blade profile design, and the calculation of channel velocities for subsonic and transonic flow fields. The use of these programs for the design and analysis of axial and radial turbines is discussed.
Dynamic Soaring: Aerodynamics for Albatrosses
ERIC Educational Resources Information Center
Denny, Mark
2009-01-01
Albatrosses have evolved to soar and glide efficiently. By maximizing their lift-to-drag ratio "L/D", albatrosses can gain energy from the wind and can travel long distances with little effort. We simplify the difficult aerodynamic equations of motion by assuming that albatrosses maintain a constant "L/D". Analytic solutions to the simplified…
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…
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.
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.
Nostril Aerodynamics of Scenting Animals
NASA Astrophysics Data System (ADS)
Settles, G. S.
1997-11-01
Dogs and other scenting animals detect airborne odors with extraordinary sensitivity. Aerodynamic sampling plays a key role, but the literature on olfaction contains little on the external aerodynamics thereof. To shed some light on this, the airflows generated by a scenting dog were visualized using the schlieren technique. It was seen that the dog stops panting in order to scent, since panting produces a turbulent jet which disturbs scent-bearing air currents. Inspiratory airflow enters the nostrils from straight ahead, while expiration is directed to the sides of the nose and downward, as was found elsewhere in the case of rats and rabbits. The musculature and geometry of the dog's nose thus modulates the airflow during scenting. The aerodynamics of a nostril which must act reversibly as both inlet and outlet is briefly discussed. The eventual practical goal of this preliminary work is to achieve a level of understanding of the aerodynamics of canine olfaction sufficient for the design of a mimicking device. (Research supported by the DARPA Unexploded Ordnance Detection and Neutralization Program.)
Aerodynamics of a linear oscillating cascade
NASA Technical Reports Server (NTRS)
Buffum, Daniel H.; Fleeter, Sanford
1990-01-01
The steady and unsteady aerodynamics of a linear oscillating cascade are investigated using experimental and computational methods. Experiments are performed to quantify the torsion mode oscillating cascade aerodynamics of the NASA Lewis Transonic Oscillating Cascade for subsonic inlet flowfields using two methods: simultaneous oscillation of all the cascaded airfoils at various values of interblade phase angle, and the unsteady aerodynamic influence coefficient technique. Analysis of these data and correlation with classical linearized unsteady aerodynamic analysis predictions indicate that the wind tunnel walls enclosing the cascade have, in some cases, a detrimental effect on the cascade unsteady aerodynamics. An Euler code for oscillating cascade aerodynamics is modified to incorporate improved upstream and downstream boundary conditions and also the unsteady aerodynamic influence coefficient technique. The new boundary conditions are shown to improve the unsteady aerodynamic influence coefficient technique. The new boundary conditions are shown to improve the unsteady aerodynamic predictions of the code, and the computational unsteady aerodynamic influence coefficient technique is shown to be a viable alternative for calculation of oscillating cascade aerodynamics.
Interdisciplinary optimization combining electromagnetic and aerodynamic methods
NASA Astrophysics Data System (ADS)
Sullivan, Anders James
The design of missile body shapes often requires a compromise between aero-dynamic and electromagnetic performance goals. In general, the missile shape producing the lowest radar signature will be different from the preferred aero-dynamic shape. Interdisciplinary shape optimization is utilized to combine multiple disciplines to determine the best possible shape for a hybrid aerodynamic-electromagnetic problem. A composite missile body consisting of an axisymmetric body of revolution (BOR) and two thin flat plate attachments is considered. The goal is to minimize the drag and backscatter associated with this composite shape. The body is assumed to be perfectly conducting, and flying at zero degrees angle of attack. The variable nose shape serves as the optimization design parameter. To characterize the system performance, a cost function is defined which is comprised of weighted values of the drag and backscatter. To solve the electromagnetic problem, methods to treat electrically large complex bodies are investigated. Hybrid methods which combine the method of moments (MoM) with physical optics (PO) are developed to calculate the scattering from simple two-dimensional bodies. A surface-wave hybrid approach is shown to effectively approximate the traveling wave currents on the smooth interior portions of a BOR. Asymptotic methods are used to solve the resulting integral equations more efficiently. The hybrid methods are shown to produce MoM-quality results, while requiring less computational resources. To solve the composite body problem, an iterative technique is developed that preserves the simplicity of the original BOR scheme. In this formulation, the current over each part of the composite body is solved independently. The results from one part of the body are used to update the fields incident on the other part of the body. This procedure is repeated until the solution converges. To solve the aerodynamic problem, slender body theory is used to calculate the
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.
Anthony L. Crawford
2012-08-01
Natural movements and force feedback are important elements in using teleoperated equipment if complex and speedy manipulation tasks are to be accomplished in remote and/or hazardous environments, such as hot cells, glove boxes, decommissioning, explosives disarmament, and space to name a few. In order to achieve this end the research presented in this paper has developed an admittance type exoskeleton like multi-fingered haptic hand user interface that secures the user’s palm and provides 3-dimensional force feedback to the user’s fingertips. Atypical to conventional haptic hand user interfaces that limit themselves to integrating the human hand’s characteristics just into the system’s mechanical design this system also perpetuates that inspiration into the designed user interface’s controller. This is achieved by manifesting the property differences of manipulation and grasping activities as they pertain to the human hand into a nonlinear master-slave force relationship. The results presented in this paper show that the admittance-type system has sufficient bandwidth that it appears nearly transparent to the user when the user is in free motion and when the system is subjected to a manipulation task, increased performance is achieved using the nonlinear force relationship compared to the traditional linear scaling techniques implemented in the vast majority of systems.
AERODYNAMIC AND BLADING DESIGN OF MULTISTAGE AXIAL FLOW COMPRESSORS
NASA Technical Reports Server (NTRS)
Crouse, J. E.
1994-01-01
The axial-flow compressor is used for aircraft engines because it has distinct configuration and performance advantages over other compressor types. However, good potential performance is not easily obtained. The designer must be able to model the actual flows well enough to adequately predict aerodynamic performance. This computer program has been developed for computing the aerodynamic design of a multistage axial-flow compressor and, if desired, the associated blading geometry input for internal flow analysis. The aerodynamic solution gives velocity diagrams on selected streamlines of revolution at the blade row edges. The program yields aerodynamic and blading design results that can be directly used by flow and mechanical analysis codes. Two such codes are TSONIC, a blade-to-blade channel flow analysis code (COSMIC program LEW-10977), and MERIDL, a more detailed hub-to-shroud flow analysis code (COSMIC program LEW-12966). The aerodynamic and blading design program can reduce the time and effort required to obtain acceptable multistage axial-flow compressor configurations by generating good initial solutions and by being compatible with available analysis codes. The aerodynamic solution assumes steady, axisymmetric flow so that the problem is reduced to solving the two-dimensional flow field in the meridional plane. The streamline curvature method is used for the iterative aerodynamic solution at stations outside of the blade rows. If a blade design is desired, the blade elements are defined and stacked within the aerodynamic solution iteration. The blade element inlet and outlet angles are established by empirical incidence and deviation angles to the relative flow angles of the velocity diagrams. The blade element centerline is composed of two segments tangentially joined at a transition point. The local blade angle variation of each element can be specified as a fourth-degree polynomial function of path distance. Blade element thickness can also be specified
NASA Technical Reports Server (NTRS)
Tseng, K.; Morino, L.
1975-01-01
A general formulation is presented for the analysis of steady and unsteady, subsonic and supersonic aerodynamics for complex aircraft configurations. The theoretical formulation, the numerical procedure, the description of the program SOUSSA (steady, oscillatory and unsteady, subsonic and supersonic aerodynamics) and numerical results are included. In particular, generalized forces for fully unsteady (complex frequency) aerodynamics for a wing-body configuration, AGARD wing-tail interference in both subsonic and supersonic flows as well as flutter analysis results are included. The theoretical formulation is based upon an integral equation, which includes completely arbitrary motion. Steady and oscillatory aerodynamic flows are considered. Here small-amplitude, fully transient response in the time domain is considered. This yields the aerodynamic transfer function (Laplace transform of the fully unsteady operator) for frequency domain analysis. This is particularly convenient for the linear systems analysis of the whole aircraft.
(Aerodynamic focusing of particles and heavy molecules)
de la Mora, J.F.
1990-01-08
By accelerating a gas containing suspended particles or large molecules through a converging nozzle, the suspended species may be focused and therefore used to write fine lines on a surface. Our objective was to study the limits on how narrow this focal region could be as a function of particle size. We find that, for monodisperse particles with masses m{sub p} some 3.6 {times} 10{sup 5} times larger than the molecular mass m of the carrier gas (diameters above some 100{angstrom}), there is no fundamental obstacle to directly write submicron features. However, this conclusion has been verified experimentally only with particles larger than 0.1 {mu}m. Experimental, theoretical and numerical studies on the defocusing role of Brownian motion for very small particles or heavy molecules have shown that high resolution (purely aerodynamic) focusing is impossible with volatile molecules whose masses are typically smaller than 1000 Dalton. For these, the minimal focal diameter after optimization appears to be 5{radical}(m/m{sub p}) times the nozzle diameter d{sub n}. But combinations of focused lasers and aerodynamic focusing appear as promising for direct writing with molecular precursors. Theoretical and numerical schemes capable of predicting the evolution of the focusing beam, including Brownian motion effects, have been developed, although further numerical work would be desirable. 11 refs.
The interference aerodynamics caused by the wing elasticity during store separation
NASA Astrophysics Data System (ADS)
Lei, Yang; Zheng-yin, Ye
2016-04-01
Air-launch-to-orbit is the technology that has stores carried aloft and launched the store from the plane to the orbit. The separation between the aircraft and store is one of the most important and difficult phases in air-launch-to-orbit technology. There exists strong aerodynamic interference between the aircraft and the store in store separation. When the aspect ratio of the aircraft is large, the elastic deformations of the wing must be considered. The main purpose of this article is to study the influence of the interference aerodynamics caused by the elastic deformations of the wing to the unsteady aerodynamics of the store. By solving the coupled functions of unsteady Navier-Stokes equations, six degrees of freedom dynamic equations and structural dynamic equations simultaneously, the store separation with the elastic deformation of the aircraft considered is simulated numerically. And the interactive aerodynamic forces are analyzed. The study shows that the interference aerodynamics is obvious at earlier time during the separation, and the dominant frequency of the elastic wing determines the aerodynamic forces frequencies of the store. Because of the effect of the interference aerodynamics, the roll angle response and pitch angle response increase. When the store is mounted under the wingtip, the additional aerodynamics caused by the wingtip vortex is obvious, which accelerate the divergence of the lateral force and the lateral-directional attitude angle of the store. This study supports some beneficial conclusions to the engineering application of the air-launch-to-orbit.
Control of helicopter rotorblade aerodynamics
NASA Technical Reports Server (NTRS)
Fabunmi, James A.
1991-01-01
The results of a feasibility study of a method for controlling the aerodynamics of helicopter rotorblades using stacks of piezoelectric ceramic plates are presented. A resonant mechanism is proposed for the amplification of the displacements produced by the stack. This motion is then converted into linear displacement for the actuation of the servoflap of the blades. A design which emulates the actuation of the servoflap on the Kaman SH-2F is used to demonstrate the fact that such a system can be designed to produce the necessary forces and velocities needed to control the aerodynamics of the rotorblades of such a helicopter. Estimates of the electrical power requirements are also presented. A Small Business Innovation Research (SBIR) Phase 2 Program is suggested, whereby a bench-top prototype of the device can be built and tested. A collaborative effort between AEDAR Corporation and Kaman Aerospace Corporation is anticipated for future effort on this project.
Computer Simulation of Aircraft Aerodynamics
NASA Technical Reports Server (NTRS)
Inouye, Mamoru
1989-01-01
The role of Ames Research Center in conducting basic aerodynamics research through computer simulations is described. The computer facilities, including supercomputers and peripheral equipment that represent the state of the art, are described. The methodology of computational fluid dynamics is explained briefly. Fundamental studies of turbulence and transition are being pursued to understand these phenomena and to develop models that can be used in the solution of the Reynolds-averaged Navier-Stokes equations. Four applications of computer simulations for aerodynamics problems are described: subsonic flow around a fuselage at high angle of attack, subsonic flow through a turbine stator-rotor stage, transonic flow around a flexible swept wing, and transonic flow around a wing-body configuration that includes an inlet and a tail.
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.
Aerodynamic instability: A case history
NASA Technical Reports Server (NTRS)
Eisenmann, R. C.
1985-01-01
The identification, diagnosis, and final correction of complex machinery malfunctions typically require the correlation of many parameters such as mechanical construction, process influence, maintenance history, and vibration response characteristics. The progression is reviewed of field testing, diagnosis, and final correction of a specific machinery instability problem. The case history presented addresses a unique low frequency instability problem on a high pressure barrel compressor. The malfunction was eventually diagnosed as a fluidic mechanism that manifested as an aerodynamic disturbance to the rotor assembly.
Applied aerodynamics: Challenges and expectations
NASA Technical Reports Server (NTRS)
Peterson, Victor L.; Smith, Charles A.
1993-01-01
Aerospace is the leading positive contributor to this country's balance of trade, derived largely from the sale of U.S. commercial aircraft around the world. This powerfully favorable economic situation is being threatened in two ways: (1) the U.S. portion of the commercial transport market is decreasing, even though the worldwide market is projected to increase substantially; and (2) expenditures are decreasing for military aircraft, which often serve as proving grounds for advanced aircraft technology. To retain a major share of the world market for commercial aircraft and continue to provide military aircraft with unsurpassed performance, the U.S. aerospace industry faces many technological challenges. The field of applied aerodynamics is necessarily a major contributor to efforts aimed at meeting these technological challenges. A number of emerging research results that will provide new opportunities for applied aerodynamicists are discussed. Some of these have great potential for maintaining the high value of contributions from applied aerodynamics in the relatively near future. Over time, however, the value of these contributions will diminish greatly unless substantial investments continue to be made in basic and applied research efforts. The focus: to increase understanding of fluid dynamic phenomena, identify new aerodynamic concepts, and provide validated advanced technology for future aircraft.
X-34 Vehicle Aerodynamic Characteristics
NASA Technical Reports Server (NTRS)
Brauckmann, Gregory J.
1998-01-01
The X-34, being designed and built by the Orbital Sciences Corporation, is an unmanned sub-orbital vehicle designed to be used as a flying test bed to demonstrate key vehicle and operational technologies applicable to future reusable launch vehicles. The X-34 will be air-launched from an L-1011 carrier aircraft at approximately Mach 0.7 and 38,000 feet altitude, where an onboard engine will accelerate the vehicle to speeds above Mach 7 and altitudes to 250,000 feet. An unpowered entry will follow, including an autonomous landing. The X-34 will demonstrate the ability to fly through inclement weather, land horizontally at a designated site, and have a rapid turn-around capability. A series of wind tunnel tests on scaled models was conducted in four facilities at the NASA Langley Research Center to determine the aerodynamic characteristics of the X-34. Analysis of these test results revealed that longitudinal trim could be achieved throughout the design trajectory. The maximum elevon deflection required to trim was only half of that available, leaving a margin for gust alleviation and aerodynamic coefficient uncertainty. Directional control can be achieved aerodynamically except at combined high Mach numbers and high angles of attack, where reaction control jets must be used. The X-34 landing speed, between 184 and 206 knots, is within the capabilities of the gear and tires, and the vehicle has sufficient rudder authority to control the required 30-knot crosswind.
Yoshii, Masayoshi; Minami, Junichi; Ishimitsu, Toshihiko; Yamakoshi, Ken-ichi; Matsuoka, Hiroaki
2005-04-01
Only a little information is available for the evaluation of the complex hemodynamic changes that occur during hemodialysis. Recently, we developed the transthoracic electrical admittance cardiograph for repeated measurements of cardiac output, and monitored hemodynamic changes during hemodialysis by the use of this device. We measured cardiovascular hemodynamic and autonomic parameters non-invasively during 210 min of hemodialysis in 19 chronic hemodialysis patients who for more than 2 months had no history of cardiovascular collapses during hemodialysis. Blood pressure was monitored every 10 min using a cuff-oscillometric device (TM-2425; A & D, Tokyo, Japan). Cardiac output was monitored on a beat-by-beat basis by a newly developed electrical admittance cardiograph (NICOVIEW PA1100; NEC, Tokyo, Japan). Electrocardiogram R-R intervals were also monitored by the TM-2425. Power spectral analysis of R-R intervals was performed to obtain the low-frequency (LF; 0.05-0.15 Hz) and the high-frequency (HF; 0.15-0.40 Hz) components based on an autoregressive model. Change in circulatory blood volume was also monitored by a CRIT-LINE (In-Line Diagnostics, Riverdale, UT, USA). Although blood volume declined significantly by 16.3 +/- 1.4% (mean +/- SE) during hemodialysis (P < 0.0001), mean blood pressure did not change significantly. Heart rate increased significantly from the initial values of 76.3 +/- 3.4-86.4 +/- 4.9 beats/min (P = 0.03). Cardiac output and stroke volume decreased significantly from 4.47 +/- 0.30 to 2.91 +/- 0.32 L/min (P < 0.0001), and from 57.0 +/- 3.7 to 33.9 +/- 3.1 mL (P < 0.0001), respectively. Total peripheral vascular resistance increased significantly from 1940 +/- 146 to 3117 +/- 280 dyne x s x cm(5) (P < 0.0001). The LF component did not show significant change, while the HF component decreased significantly (P = 0.007), and the LF/HF ratio increased significantly (P = 0.03). These results suggest that a reduction in parasympathetic nerve
Raghavan, Karthik; Feldman, Marc D; Porterfield, John E; Larson, Erik R; Jenkins, J Travis; Escobedo, Daniel; Pearce, John A
2011-01-01
This paper presents the design, construction and testing of a device to measure pressure volume loops in the left ventricle of conscious, ambulatory rats. Pressure is measured with a standard sensor, but volume is derived from data collected from a tetrapolar electrode catheter using a novel admittance technique. There are two main advantages of the admittance technique to measure volume. First, the contribution from the adjacent muscle can be instantaneously removed. Second, the admittance technique incorporates the nonlinear relationship between the electric field generated by the catheter and the blood volume. A low power instrument weighing 27 g was designed, which takes pressure-volume loops every 2 minutes and runs for 24 hours. Pressure-volume data are transmitted wirelessly to a base station. The device was first validated in thirteen rats with an acute preparation with 2-D echocardiography used to measure true volume. From an accuracy standpoint, the admittance technique is superior to both the conductance technique calibrated with hypertonic saline injections, and calibrated with cuvettes. The device was then tested in six rats with a 24-hour chronic preparation. Stability of the animal preparation and careful calibration are important factors affecting the success of the device. PMID:21606560
Investigation of the transient aerodynamic phenomena associated with passing manoeuvres
NASA Astrophysics Data System (ADS)
Noger, C.; Regardin, C.; Széchényi, E.
2005-11-01
Passing manoeuvres and crosswind can have significant effects on the stability of road vehicles. The transient aerodynamics, which interacts with suspension, steering geometry and driver reaction is not well understood. When two vehicles overtake or cross, they mutually influence the flow field around each other, and under certain conditions, can generate severe gust loads that act as additional forces on both vehicles. The transient forces acting on them are a function of the longitudinal and transverse spacings and of the relative velocity between the two vehicles. Wind tunnel experiments have been conducted in one of the automotive wind tunnels of the Institut Aérotechnique of Saint-Cyr l’École to simulate the transient overtaking process between two models of a simple generic automobile shape. The tests were designed to study the effects of various parameters such as the longitudinal and transverse spacing, the relative velocity and the crosswind on the aerodynamic forces and moments generated on the overtaken and overtaking vehicles. Test results characterize the transient aerodynamic side force as well as the yawing moment coefficients in terms of these parameters. Measurements of the drag force coefficient as well as the static pressure distribution around the overtaken vehicle complete the understanding. The main results indicate the aerodynamic coefficients of the overtaken vehicle to be velocity independent within the limit of the test parameters, while unsteady aerodynamic effects appear in the case of an overtaking vehicle. The mutual interference effects between the vehicles vary as a linear function of the transverse spacing and the crosswind does not really generate any new unsteady behaviour.
The role of unsteady aerodynamics in aeroacoustics
NASA Technical Reports Server (NTRS)
Pao, S. Paul
1988-01-01
The role of acoustics and unsteady aerodynamics research in understanding the fundamental physics of time-dependent fluid phenomena is reviewed. The key issues are illustrated by considering the sound radiation of turbulent jets and the aeroacoustics of rotating bodies such as helicopter rotors. The importance of computational methods as a link between aerodynamics and acoustics is also discussed. It is noted that where acoustic analogy techniques are sufficiently accurate, unsteady aerodynamics can be used for acoustic prediction. In supersonic problems where acoustics and aerodynamics are coupled, an integrated nonlinear analysis can provide an accurate problem solution.
HIAD-2 (Hypersonic Inflatable Aerodynamic Decelerator)
The Hypersonic Inflatable Aerodynamic Decelerator (HIAD) project is a disruptive technology that will accommodate the atmospheric entry of heavy payloads to planetary bodies such as Mars. HIAD over...
Computational aerodynamics applications to transport aircraft design
NASA Technical Reports Server (NTRS)
Henne, P. A.
1983-01-01
Examples are cited in assessing the effect that computational aerodynamics has had on the design of transport aircraft. The application of computational potential flow methods to wing design and to high-lift system design is discussed. The benefits offered by computational aerodynamics in reducing design cost, time, and risk are shown to be substantial.These aerodynamic methods have proved to be particularly effective in exposing inferior or poor aerodynamic designs. Particular attention is given to wing design, where the results have been dramatic.
Orion Aerodynamics for Hypersonic Free Molecular to Continuum Conditions
NASA Technical Reports Server (NTRS)
Moss, James N.; Greene, Francis A.; Boyles, Katie A.
2006-01-01
Numerical simulations are performed for the Orion Crew Module, previously known as the Crew Exploration Vehicle (CEV) Command Module, to characterize its aerodynamics during the high altitude portion of its reentry into the Earth's atmosphere, that is, from free molecular to continuum hypersonic conditions. The focus is on flow conditions similar to those that the Orion Crew Module would experience during a return from the International Space Station. The bulk of the calculations are performed with two direct simulation Monte Carlo (DSMC) codes, and these data are anchored with results from both free molecular and Navier-Stokes calculations. Results for aerodynamic forces and moments are presented that demonstrate their sensitivity to rarefaction, that is, for free molecular to continuum conditions (Knudsen numbers of 111 to 0.0003). Also included are aerodynamic data as a function of angle of attack for different levels of rarefaction and results that demonstrate the aerodynamic sensitivity of the Orion CM to a range of reentry velocities (7.6 to 15 km/s).
Evaluation and modeling of aerodynamic properties of mung bean seeds
NASA Astrophysics Data System (ADS)
Shahbazi, Feizollah
2015-01-01
Aerodynamic properties of solid materials have long been used to convey and separate seeds and grains during post harvest operations. The objective of this study was the evaluation of the aerodynamic properties of mung bean seeds as a function of moisture content and two grades referred to above and below a cut point of 4.8 mm in length. The results showed that as the moisture content increased from 7.8 to 25% (w.b.), the terminal velocity of seeds increased following a polynomial relationship, from 7.28 to 8.79 and 6.02 to 7.12 m s-1, for grades A and B, respectively. Seeds at grade A had terminal velocities with a mean value of 8.05 m s-1, while at grade B had a mean value of 6.46 m s-1. The Reynolds number of both grades increased linearly with the increase of seeds moisture content, while the drag coefficient decreased with the increase of moisture content. Mathematical relationships were developed to relate the change in seeds moisture content with the obtained values of aerodynamic properties. The analysis of variance showed that moisture content had a significant effect, at 1% probability level, on all the aerodynamics properties of mung beans.
NASA Astrophysics Data System (ADS)
Maheshwari, Muneesh; Annamdas, Venu Gopal Madhav; Pang, John H. L.; Tjin, Swee Chuan; Asundi, Anand
2015-04-01
Structural health monitoring techniques using smart materials are on rise to meet the ever ending demand due to increased construction and manufacturing activities worldwide. The civil-structural components such as slabs, beams and columns and aero-components such as wings are constantly subjected to some or the other forms of external loading. This article thus focuses on condition monitoring due to loading/unloading cycle for a simply supported aluminum beam using multiple smart materials. On the specimen, fibre optic polarimetric sensor (FOPS) and fibre Bragg grating (FBG) sensors were glued. Piezoelectric wafer active sensor (PWAS) was also bonded at the centre of the specimen. FOPS and FBG provided the global and local strain measurements respectively whereas, PWAS predicted boundary condition variations by electromechanical admittance signatures. Thus these multiple smart materials together successfully assessed the condition of structure for loading and unloading tests.
3-D Navier-Stokes Analysis of Blade Root Aerodynamics for a Tiltrotor Aircraft In Cruise
NASA Technical Reports Server (NTRS)
Romander, Ethan
2006-01-01
The blade root area of a tiltrotor aircraft's rotor is constrained by a great many factors, not the least of which is aerodynamic performance in cruise. For this study, Navier-Stokes CFD techniques are used to study the aerodynamic performance in cruise of a rotor design as a function of airfoil thickness along the blade and spinner shape. Reducing airfoil thickness along the entire blade will be shown to have the greatest effect followed by smaller but still significant improvements achieved by reducing the thickness of root airfoils only. Furthermore, altering the shape of the spinner will be illustrated as a tool to tune the aerodynamic performance very near the blade root.
NASA Astrophysics Data System (ADS)
Mannequin, C.; Gonon, P.; Vallée, C.; Bsiesy, A.; Grampeix, H.; Jousseaume, V.
2011-11-01
Dielectric relaxation is studied in 10 nm HfO2 thin films which are deposited by atomic layer deposition on TiN and Pt electrodes. Transient currents are recorded from 10-3 s to 10 s, as a function of bias (0.1 V to 1 V) and temperature (20 °C to 180 °C). A Curie-von Schweidler law is observed, I = Q0/tα. The power law exponent α is constant with bias and strongly depends on the temperature (varying in the 0.65-1.05 range, with a peak at 75 °C). The amplitude Q0 is described by a relation of the form Q0 = C0Vβ, where the factor C0 is weakly activated and the exponent β varies with temperature (in the 0.9-1.5 range as T varies). Transient currents are discussed along with tunneling based models from the literature. To complement transient current experiments, admittance spectroscopy (conductance G and capacitance C) is performed at low frequencies, from 0.01 Hz to 10 kHz. The dispersion law of the conductance is of the form G ˜ ωs. The capacitance is the sum of two terms, a non-dispersive term (C∞) and a low-frequency dispersive term, CLF ˜ ω-n. The critical exponents s and n verify s ≈ α and n ≈ 1-α. At room temperature, the dielectric constant is expressed as ɛ' = Δɛ' f-n+ ɛ'∞, where ɛ'∞ = 11.1, n ≈ 0.2/0.3 (Pt/TiN), and Δɛ' ≈ 1.5/0.7 (Pt/TiN).
Inner workings of aerodynamic sweep
Wadia, A.R.; Szucs, P.N.; Crall, D.W.
1998-10-01
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 two aft-swept rotors with varying degree and type of aerodynamic sweep and one swept forward rotor. On a back-to-back test basis, the results are compared with an unswept rotor with excellent performance and adequate stall margin. Although designed to satisfy identical design speed requirements as the unswept rotor, the experimental results reveal significant variations in efficiency and stall margin with the swept rotors. At design speed, all the swept rotors demonstrated a peak stage efficiency level that was equal to that of the unswept rotor. However, the forward-swept rotor achieved the highest rotor-alone peak efficiency. At the same time, the forward-swept rotor demonstrated a significant improvement in stall margin relative to the already satisfactory level achieved by the unswept rotor. Increasing the level of aft sweep adversely affected the stall margin. A three-dimensional viscous flow analysis was used to assist in the interpretation of the data. The reduced shock/boundary layer interaction, resulting from reduced axial flow diffusion and less accumulation of centrifuged blade surface boundary layer at the tip, was identified as the prime contributor to the enhanced performance with forward sweep. The impact of tip clearance on the performance and stability for one of the aft-swept rotors was also assessed.
Progress in computational unsteady aerodynamics
NASA Technical Reports Server (NTRS)
Obayashi, Shigeru
1993-01-01
After vigorous development for over twenty years, Computational Fluid Dynamics (CFD) in the field of aerospace engineering has arrived at a turning point toward maturity. This paper discusses issues related to algorithm development for the Euler/Navier Stokes equations, code validation and recent applications of CFD for unsteady aerodynamics. Algorithm development is a fundamental element for a good CFD program. Code validation tries to bridge the reliability gap between CFD and experiment. Many of the recent applications also take a multidisciplinary approach, which is a future trend for CFD applications. As computers become more affordable, CFD is expected to be a better scientific and engineering tool.
Simulation of iced wing aerodynamics
NASA Technical Reports Server (NTRS)
Potapczuk, M. G.; Bragg, M. B.; Kwon, O. J.; Sankar, L. N.
1991-01-01
The sectional and total aerodynamic load characteristics of moderate aspect ratio wings with and without simulated glaze leading edge ice were studied both computationally, using a three dimensional, compressible Navier-Stokes solver, and experimentally. The wing has an untwisted, untapered planform shape with NACA 0012 airfoil section. The wing has an unswept and swept configuration with aspect ratios of 4.06 and 5.0. Comparisons of computed surface pressures and sectional loads with experimental data for identical configurations are given. The abrupt decrease in stall angle of attack for the wing, as a result of the leading edge ice formation, was demonstrated numerically and experimentally.
The basic aerodynamics of floatation
Davies, M.J.; Wood, D.H.
1983-09-01
The original derivation of the basic theory governing the aerodynamics of both hovercraft and modern floatation ovens, requires the validity of some extremely crude assumptions. However, the basic theory is surprisingly accurate. It is shown that this accuracy occurs because the final expression of the basic theory can be derived by approximating the full Navier-Stokes equations in a manner that clearly shows the limitations of the theory. These limitations are used in discussing the relatively small discrepancies between the theory and experiment, which may not be significant for practical purposes.
Aerodynamics. [Numerical simulation using supercomputers
Graves, R.A. Jr.
1988-01-01
A projection is made of likely improvements in the economics of commercial aircraft operation due to developments in aerodynamics in the next half-century. Notable among these improvements are active laminar flow control techniques' application to third-generation SSTs, in order to achieve an L/D value of about 20; this is comparable to current subsonic transports, and has the further consequence of reducing cabin noise. Wave-cancellation systems may also be used to eliminate sonic boom overpressures, and rapid-combustion systems may be able to eliminate all pollutants from jet exhausts other than CO/sub 2/.
Aerodynamic applications of infrared thermography
NASA Technical Reports Server (NTRS)
Daryabeigi, Kamran; Alderfer, David W.
1989-01-01
A series of wind tunnel experiments were conducted as part of a systematic study for evaluation of infrared thermography as a viable non-intrusive thermal measurement technique for aerodynamic applications. The experiments consisted of obtaining steady-state surface temperature and convective heat transfer rates for a uniformly heated cylinder in transverse flow with a Reynolds number range of 46,000 to 250,000. The calculated convective heat transfer rates were in general agreement with classical data. Furthermore, IR thermography provided valuable real-time fluid dynamic information such as visualization of flow separation, transition and vortices.
General Theory of Aerodynamic Instability and the Mechanism of Flutter
NASA Technical Reports Server (NTRS)
Theodorsen, Theodore
1979-01-01
The aerodynamic forces on an oscillating airfoil or airfoil-aileron combination of three independent degrees of freedom were determined. The problem resolves itself into the solution of certain definite integrals, which were identified as Bessel functions of the first and second kind, and of zero and first order. The theory, based on potential flow and the Kutta condition, is fundamentally equivalent to the conventional wing section theory relating to the steady case. The air forces being known, the mechanism of aerodynamic instability was analyzed. An exact solution, involving potential flow and the adoption of the Kutta condition, was derived. The solution is of a simple form and is expressed by means of an auxiliary parameter k. The flutter velocity, treated as the unknown quantity, was determined as a function of a certain ratio of the frequencies in the separate degrees of freedom for any magnitudes and combinations of the airfoil-aileron parameters.
Orion Crew Module Aerodynamic Testing
NASA Technical Reports Server (NTRS)
Murphy, Kelly J.; Bibb, Karen L.; Brauckmann, Gregory J.; Rhode, Matthew N.; Owens, Bruce; Chan, David T.; Walker, Eric L.; Bell, James H.; Wilson, Thomas M.
2011-01-01
The Apollo-derived Orion Crew Exploration Vehicle (CEV), part of NASA s now-cancelled Constellation Program, has become the reference design for the new Multi-Purpose Crew Vehicle (MPCV). The MPCV will serve as the exploration vehicle for all near-term human space missions. A strategic wind-tunnel test program has been executed at numerous facilities throughout the country to support several phases of aerodynamic database development for the Orion spacecraft. This paper presents a summary of the experimental static aerodynamic data collected to-date for the Orion Crew Module (CM) capsule. The test program described herein involved personnel and resources from NASA Langley Research Center, NASA Ames Research Center, NASA Johnson Space Flight Center, Arnold Engineering and Development Center, Lockheed Martin Space Sciences, and Orbital Sciences. Data has been compiled from eight different wind tunnel tests in the CEV Aerosciences Program. Comparisons are made as appropriate to highlight effects of angle of attack, Mach number, Reynolds number, and model support system effects.
X-33 Hypersonic Aerodynamic Characteristics
NASA Technical Reports Server (NTRS)
Murphy, Kelly J.; Nowak, Robert J.; Thompson, Richard A.; Hollis, Brian R.; Prabhu, Ramadas K.
1999-01-01
Lockheed Martin Skunk Works, under a cooperative agreement with NASA, will design, build, and fly the X-33, a half-scale prototype of a rocket-based, single-stage-to-orbit (SSTO), reusable launch vehicle (RLV). A 0.007-scale model of the X-33 604BOO02G configuration was tested in four hypersonic facilities at the NASA Langley Research Center to examine vehicle stability and control characteristics and to populate the aerodynamic flight database for the hypersonic regime. The vehicle was found to be longitudinally controllable with less than half of the total body flap deflection capability across the angle of attack range at both Mach 6 and Mach 10. Al these Mach numbers, the vehicle also was shown to be longitudinally stable or neutrally stable for typical (greater than 20 degrees) hypersonic flight attitudes. This configuration was directionally unstable and the use of reaction control jets (RCS) will be necessary to control the vehicle at high angles of attack in the hypersonic flight regime. Mach number and real gas effects on longitudinal aerodynamics were shown to be small relative to X-33 control authority.
X-33 Hypersonic Aerodynamic Characteristics
NASA Technical Reports Server (NTRS)
Murphy, Kelly J.; Nowak, Robert J.; Thompson, Richard A.; Hollis, Brian R.; Prabhu, Ramadas K.
1999-01-01
Lockheed Martin Skunk Works, under a cooperative agreement with NASA, will build and fly the X-33, a half-scale prototype of a rocket-based, single-stage-to-orbit (SSTO), reusable launch vehicle (RLV). A 0.007-scale model of the X-33 604B0002G configuration was tested in four hypersonic facilities at the NASA Langley Research Center to examine vehicle stability and control characteristics and to populate an aerodynamic flight database in the hypersonic regime. The vehicle was found to be longitudinally controllable with less than half of the total body flap deflection capability across the angle of attack range at both Mach 6 and Mach 10. At these Mach numbers, the vehicle also was shown to be longitudinally stable or neutrally stable for typical (greater than 20 degrees) hypersonic flight attitudes. This configuration was directionally unstable and the use of reaction control jets (RCS) will be necessary to control the vehicle at high angles of attack in the hypersonic flight regime. Mach number and real gas effects on longitudinal aerodynamics were shown to be small relative to X-33 control authority.
X-33 Hypersonic Aerodynamic Characteristics
NASA Technical Reports Server (NTRS)
Murphy, Kelly J.; Nowak, Robert J.; Thompson, Richard A.; Hollis, Brian R.; Prabhu, Ramadas K.
1999-01-01
Lockheed Martin Skunk Works, under a cooperative agreement with NASA, will build and fly the X-33, a half-scale prototype of a rocket-based, single-stage-to-orbit (SSTO), reusable launch vehicle (RLV). A 0.007-scale model of the X-33 604B0002G configuration was tested in four hypersonic facilities at the NASA Langley Research Center to examine vehicle stability and control characteristics and to populate an aerodynamic flight database i n the hypersonic regime. The vehicle was found to be longitudinally controllable with less than half of the total body flap deflection capability across the angle of attack range at both Mach 6 and Mach 10. At these Mach numbers, the vehicle also was shown to be longitudinally stable or neutrally stable for typical (greater than 20 degrees) hypersonic flight attitudes. This configuration was directionally unstable and the use of reaction control jets (RCS) will be necessary to control the vehicle at high angles of attack in the hypersonic flight regime. Mach number and real gas effects on longitudinal aerodynamics were shown to be small relative to X-33 control authority.
X-33 Hypersonic Aerodynamic Characteristics
NASA Technical Reports Server (NTRS)
Murphy, Kelly J.; Nowak, Robert J.; Thompson, Richard A.; Hollis, Brian R.; Prabhu, Ramadas K.
1999-01-01
Lockheed Martin Skunk Works, under a cooperative agreement with NASA, will build and fly the X-33, a half-scale prototype of a rocket-based, single-stage-to-orbit (SSTO), reusable launch vehicle (RLV). A 0.007-scale model of the X-33 604B0002G configuration was tested in four hypersonic facilities at the NASA Langley Research Center to examine vehicle stability and control characteristics and to populate an aerodynamic flight database in the hypersonic regime, The vehicle was found to be longitudinally controllable with less than half of the total body flap deflection capability across the angle of attack range at both Mach 6 and Mach 10. At these Mach numbers, the vehicle also was shown to be longitudinally stable or neutrally stable for typical (greater than 20 degrees) hypersonic flight attitudes. This configuration was directionally unstable and the use of reaction control jets (RCS) will be necessary to control the vehicle at high angles of attack in the hypersonic flight regime. Mach number and real gas effects on longitudinal aerodynamics were shown to be small relative to X-33 control authority.
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.
Aerodynamic design on high-speed trains
NASA Astrophysics Data System (ADS)
Ding, San-San; Li, Qiang; Tian, Ai-Qin; Du, Jian; Liu, Jia-Li
2016-01-01
Compared with the traditional train, the operational speed of the high-speed train has largely improved, and the dynamic environment of the train has changed from one of mechanical domination to one of aerodynamic domination. The aerodynamic problem has become the key technological challenge of high-speed trains and significantly affects the economy, environment, safety, and comfort. In this paper, the relationships among the aerodynamic design principle, aerodynamic performance indexes, and design variables are first studied, and the research methods of train aerodynamics are proposed, including numerical simulation, a reduced-scale test, and a full-scale test. Technological schemes of train aerodynamics involve the optimization design of the streamlined head and the smooth design of the body surface. Optimization design of the streamlined head includes conception design, project design, numerical simulation, and a reduced-scale test. Smooth design of the body surface is mainly used for the key parts, such as electric-current collecting system, wheel truck compartment, and windshield. The aerodynamic design method established in this paper has been successfully applied to various high-speed trains (CRH380A, CRH380AM, CRH6, CRH2G, and the Standard electric multiple unit (EMU)) that have met expected design objectives. The research results can provide an effective guideline for the aerodynamic design of high-speed trains.
The aerodynamics of small Reynolds numbers
NASA Technical Reports Server (NTRS)
Schmitz, F. W.
1980-01-01
Aerodynamic characteristics of wing model gliders and bird wings in particular are discussed. Wind tunnel measurements and aerodynamics of small Reynolds numbers are enumerated. Airfoil behavior in the critical transition from laminar to turbulent boundary layer, which is more important to bird wing models than to large airplanes, was observed. Experimental results are provided, and an artificial bird wing is described.
Future Computer Requirements for Computational Aerodynamics
NASA Technical Reports Server (NTRS)
1978-01-01
Recent advances in computational aerodynamics are discussed as well as motivations for and potential benefits of a National Aerodynamic Simulation Facility having the capability to solve fluid dynamic equations at speeds two to three orders of magnitude faster than presently possible with general computers. Two contracted efforts to define processor architectures for such a facility are summarized.
Aerodynamic seal assemblies for turbo-machinery
Bidkar, Rahul Anil; Wolfe, Christopher; Fang, Biao
2015-09-29
The present application provides an aerodynamic seal assembly for use with a turbo-machine. The aerodynamic seal assembly may include a number of springs, a shoe connected to the springs, and a secondary seal positioned about the springs and the shoe.
Aerodynamic design on high-speed trains
NASA Astrophysics Data System (ADS)
Ding, San-San; Li, Qiang; Tian, Ai-Qin; Du, Jian; Liu, Jia-Li
2016-04-01
Compared with the traditional train, the operational speed of the high-speed train has largely improved, and the dynamic environment of the train has changed from one of mechanical domination to one of aerodynamic domination. The aerodynamic problem has become the key technological challenge of high-speed trains and significantly affects the economy, environment, safety, and comfort. In this paper, the relationships among the aerodynamic design principle, aerodynamic performance indexes, and design variables are first studied, and the research methods of train aerodynamics are proposed, including numerical simulation, a reduced-scale test, and a full-scale test. Technological schemes of train aerodynamics involve the optimization design of the streamlined head and the smooth design of the body surface. Optimization design of the streamlined head includes conception design, project design, numerical simulation, and a reduced-scale test. Smooth design of the body surface is mainly used for the key parts, such as electric-current collecting system, wheel truck compartment, and windshield. The aerodynamic design method established in this paper has been successfully applied to various high-speed trains (CRH380A, CRH380AM, CRH6, CRH2G, and the Standard electric multiple unit (EMU)) that have met expected design objectives. The research results can provide an effective guideline for the aerodynamic design of high-speed trains.
Review of aerodynamic design in the Netherlands
NASA Technical Reports Server (NTRS)
Labrujere, Th. E.
1991-01-01
Aerodynamic design activities in the Netherlands, which take place mainly at Fokker, the National Aerospace Laboratory (NLR), and Delft University of Technology (TUD), are discussed. The survey concentrates on the development of the Fokker 100 wing, glider design at TUD, and research at NLR in the field of aerodynamic design. Results are shown to illustrate these activities.
Image processing of aerodynamic data
NASA Technical Reports Server (NTRS)
Faulcon, N. D.
1985-01-01
The use of digital image processing techniques in analyzing and evaluating aerodynamic data is discussed. An image processing system that converts images derived from digital data or from transparent film into black and white, full color, or false color pictures is described. Applications to black and white images of a model wing with a NACA 64-210 section in simulated rain and to computed low properties for transonic flow past a NACA 0012 airfoil are presented. Image processing techniques are used to visualize the variations of water film thicknesses on the wing model and to illustrate the contours of computed Mach numbers for the flow past the NACA 0012 airfoil. Since the computed data for the NACA 0012 airfoil are available only at discrete spatial locations, an interpolation method is used to provide values of the Mach number over the entire field.
The basic aerodynamics of floatation
NASA Astrophysics Data System (ADS)
Davies, M. J.; Wood, D. H.
1983-09-01
It is pointed out that the basic aerodynamics of modern floatation ovens, in which the continuous, freshly painted metal strip is floated, dried, and cured, is the two-dimensional analog of that of hovercraft. The basic theory for the static lift considered in connection with the study of hovercraft has had spectacular success in describing the experimental results. This appears surprising in view of the crudity of the theory. The present investigation represents an attempt to explore the reasons for this success. An outline of the basic theory is presented and an approach is shown for deriving the resulting expressions for the lift from the full Navier-Stokes equations in a manner that clearly indicates the limitations on the validity of the expressions. Attention is given to the generally good agreement between the theory and the axisymmetric (about the centerline) results reported by Jaumotte and Kiedrzynski (1965).
Rarefaction Effects in Hypersonic Aerodynamics
NASA Astrophysics Data System (ADS)
Riabov, Vladimir V.
2011-05-01
The Direct Simulation Monte-Carlo (DSMC) technique is used for numerical analysis of rarefied-gas hypersonic flows near a blunt plate, wedge, two side-by-side plates, disk, torus, and rotating cylinder. The role of various similarity parameters (Knudsen and Mach numbers, geometrical and temperature factors, specific heat ratios, and others) in aerodynamics of the probes is studied. Important kinetic effects that are specific for the transition flow regime have been found: non-monotonic lift and drag of plates, strong repulsive force between side-by-side plates and cylinders, dependence of drag on torus radii ratio, and the reverse Magnus effect on the lift of a rotating cylinder. The numerical results are in a good agreement with experimental data, which were obtained in a vacuum chamber at low and moderate Knudsen numbers from 0.01 to 10.
Aerodynamic research on tipvane windturbines
NASA Astrophysics Data System (ADS)
Vanbussel, G. J. W.; Vanholten, T.; Vankuik, G. A. M.
1982-09-01
Tipvanes are small auxiliary wings mounted at the tips of windturbine blades in such a way that a diffuser effect is generated, resulting in a mass flow augmentation through the turbine disc. For predicting aerodynamic loads on the tipvane wind turbine, the acceleration potential is used and an expansion method is applied. In its simplest form, this method can essentially be classified as a lifting line approach, however, with a proper choice of the basis load distributions of the lifting line, the numerical integration of the pressurefield becomes one dimensional. the integration of the other variable can be performed analytically. The complete analytical expression for the pressure field consists of two series of basic pressure fields. One series is related to the basic load distributions over the turbineblade, and the other series to the basic load distribution over the tipvane.
Aerodynamic seals for rotary machine
Bidkar, Rahul Anil; Cirri, Massimiliano; Thatte, Azam Mihir; Williams, John Robert
2016-02-09
An aerodynamic seal assembly for a rotary machine includes multiple sealing device segments disposed circumferentially intermediate to a stationary housing and a rotor. Each of the segments includes a shoe plate with a forward-shoe section and an aft-shoe section having multiple labyrinth teeth therebetween facing the rotor. The sealing device segment also includes multiple flexures connected to the shoe plate and to a top interface element, wherein the multiple flexures are configured to allow the high pressure fluid to occupy a forward cavity and the low pressure fluid to occupy an aft cavity. Further, the sealing device segments include a secondary seal attached to the top interface element at one first end and positioned about the flexures and the shoe plate at one second end.
Aerodynamic characteristics of aerofoils I
NASA Technical Reports Server (NTRS)
1921-01-01
The object of this report is to bring together the investigations of the various aerodynamic laboratories in this country and Europe upon the subject of aerofoils suitable for use as lifting or control surfaces on aircraft. The data have been so arranged as to be of most use to designing engineers and for the purposes of general reference. The absolute system of coefficients has been used, since it is thought by the National Advisory Committee for Aeronautics that this system is the one most suited for international use, and yet is one for which a desired transformation can be easily made. For this purpose a set of transformation constants is included in this report.
On Cup Anemometer Rotor Aerodynamics
Pindado, Santiago; Pérez, Javier; Avila-Sanchez, Sergio
2012-01-01
The influence of anemometer rotor shape parameters, such as the cups' front area or their center rotation radius on the anemometer's performance was analyzed. This analysis was based on calibrations performed on two different anemometers (one based on magnet system output signal, and the other one based on an opto-electronic system output signal), tested with 21 different rotors. The results were compared to the ones resulting from classical analytical models. The results clearly showed a linear dependency of both calibration constants, the slope and the offset, on the cups' center rotation radius, the influence of the front area of the cups also being observed. The analytical model of Kondo et al. was proved to be accurate if it is based on precise data related to the aerodynamic behavior of a rotor's cup. PMID:22778638
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.
Aerodynamic Noise Generated by Shinkansen Cars
NASA Astrophysics Data System (ADS)
KITAGAWA, T.; NAGAKURA, K.
2000-03-01
The noise value (A -weighted sound pressure level, SLOW) generated by Shinkansen trains, now running at 220-300 km/h, should be less than 75 dB(A) at the trackside. Shinkansen noise, such as rolling noise, concrete support structure noise, and aerodynamic noise are generated by various parts of Shinkansen trains. Among these aerodynamic noise is important because it is the major contribution to the noise generated by the coaches running at high speed. In order to reduce the aerodynamic noise, a number of improvements to coaches have been made. As a result, the aerodynamic noise has been reduced, but it still remains significant. In addition, some aerodynamic noise generated from the lower parts of cars remains. In order to investigate the contributions of these noises, a method of analyzing Shinkansen noise has been developed and applied to the measured data of Shinkansen noise at speeds between 120 and 315 km/h. As a result, the following conclusions have been drawn: (1) Aerodynamic noise generated from the upper parts of cars was reduced considerably by smoothing car surfaces. (2) Aerodynamic noise generated from the lower parts of cars has a major influence upon the wayside noise.
Training Data Requirement for a Neural Network to Predict Aerodynamic Coefficients
NASA Technical Reports Server (NTRS)
Korsmeyer, David (Technical Monitor); Rajkumar, T.; Bardina, Jorge
2003-01-01
Basic aerodynamic coefficients are modeled as functions of angle of attack, speed brake deflection angle, Mach number, and side slip angle. Most of the aerodynamic parameters can be well-fitted using polynomial functions. We previously demonstrated that a neural network is a fast, reliable way of predicting aerodynamic coefficients. We encountered few under fitted and/or over fitted results during prediction. The training data for the neural network are derived from wind tunnel test measurements and numerical simulations. The basic questions that arise are: how many training data points are required to produce an efficient neural network prediction, and which type of transfer functions should be used between the input-hidden layer and hidden-output layer. In this paper, a comparative study of the efficiency of neural network prediction based on different transfer functions and training dataset sizes is presented. The results of the neural network prediction reflect the sensitivity of the architecture, transfer functions, and training dataset size.
NASA Technical Reports Server (NTRS)
Batterson, J. G.
1986-01-01
The successful parametric modeling of the aerodynamics for an airplane operating at high angles of attack or sideslip is performed in two phases. First the aerodynamic model structure must be determined and second the associated aerodynamic parameters (stability and control derivatives) must be estimated for that model. The purpose of this paper is to document two versions of a stepwise regression computer program which were developed for the determination of airplane aerodynamic model structure and to provide two examples of their use on computer generated data. References are provided for the application of the programs to real flight data. The two computer programs that are the subject of this report, STEP and STEPSPL, are written in FORTRAN IV (ANSI l966) compatible with a CDC FTN4 compiler. Both programs are adaptations of a standard forward stepwise regression algorithm. The purpose of the adaptation is to facilitate the selection of a adequate mathematical model of the aerodynamic force and moment coefficients of an airplane from flight test data. The major difference between STEP and STEPSPL is in the basis for the model. The basis for the model in STEP is the standard polynomial Taylor's series expansion of the aerodynamic function about some steady-state trim condition. Program STEPSPL utilizes a set of spline basis functions.
Influence of a humidor on the aerodynamics of baseballs
NASA Astrophysics Data System (ADS)
Meyer, Edmund R.; Bohn, John L.
2008-11-01
We investigate whether storing baseballs in a controlled humidity environment significantly affects their aerodynamic properties. We measure the change in diameter and weight of baseballs as a function of relative humidity in which the balls are stored. The trajectories of pitched and batted baseballs are modeled to assess the difference between those stored at 30% relative humidity versus 50% relative humidity. We find that a drier baseball will curve slightly more than a humidified one for a given pitch velocity and rotation rate. We also find that aerodynamics alone would add 2ft to the distance a wetter baseball ball is hit. This increased distance is compensated by a 6ft reduction in the batted distance due to the change in the coefficient of restitution of the ball. We discuss consequences of these results for baseball played at Coors Field in Denver, where baseballs have been stored in a humidor at 50% relative humidity since 2002.
General Theory of Aerodynamic Instability and the Mechanism of Flutter
NASA Technical Reports Server (NTRS)
Theodorsen, Theodore
1949-01-01
The aerodynamic forces on an oscillating airfoil or airfoil-aileron combination of three independent degrees of freedom have been determined. The problem resolves itself into the solution of certain definite integrals, which have been identified as Bessel functions of the first and second kind and of zero and first order. The theory, being based on potential flow and the Kutta condition, is fundamentally equivalent to the conventional wing-section theory relating to the steady case. The air forces being known, the mechanism of aerodynamic instability has been analyzed in detail. An exact solution, involving potential flow and the adoption of the Kutta condition, has been analyzed in detail. An exact solution, involving potential flow and the adoption of the Kutta condition, has been arrived at. The solution is of a simple form and is expressed by means of an auxiliary parameter K.
Grid Sensitivity and Aerodynamic Optimization of Generic Airfoils
NASA Technical Reports Server (NTRS)
Sadrehaghighi, Ideen; Smith, Robert E.; Tiwari, Surendra N.
1995-01-01
An algorithm is developed to obtain the grid sensitivity with respect to design parameters for aerodynamic optimization. The procedure is advocating a novel (geometrical) parameterization using spline functions such as NURBS (Non-Uniform Rational B- Splines) for defining the airfoil geometry. An interactive algebraic grid generation technique is employed to generate C-type grids around airfoils. The grid sensitivity of the domain with respect to geometric design parameters has been obtained by direct differentiation of the grid equations. A hybrid approach is proposed for more geometrically complex configurations such as a wing or fuselage. The aerodynamic sensitivity coefficients are obtained by direct differentiation of the compressible two-dimensional thin-layer Navier-Stokes equations. An optimization package has been introduced into the algorithm in order to optimize the airfoil surface. Results demonstrate a substantially improved design due to maximized lift/drag ratio of the airfoil.
Active Control of Aerodynamic Noise Sources
NASA Technical Reports Server (NTRS)
Reynolds, Gregory A.
2001-01-01
Aerodynamic noise sources become important when propulsion noise is relatively low, as during aircraft landing. Under these conditions, aerodynamic noise from high-lift systems can be significant. The research program and accomplishments described here are directed toward reduction of this aerodynamic noise. Progress toward this objective include correction of flow quality in the Low Turbulence Water Channel flow facility, development of a test model and traversing mechanism, and improvement of the data acquisition and flow visualization capabilities in the Aero. & Fluid Dynamics Laboratory. These developments are described in this report.
Transpiration Control Of Aerodynamics Via Porous Surfaces
NASA Technical Reports Server (NTRS)
Banks, Daniel W.; Wood, Richard M.; Bauer, Steven X. S.
1993-01-01
Quasi-active porous surface used to control pressure loading on aerodynamic surface of aircraft or other vehicle, according to proposal. In transpiration control, one makes small additions of pressure and/or mass to cavity beneath surface of porous skin on aerodynamic surface, thereby affecting rate of transpiration through porous surface. Porous skin located on forebody or any other suitable aerodynamic surface, with cavity just below surface. Device based on concept extremely lightweight, mechanically simple, occupies little volume in vehicle, and extremely adaptable.
Identification of aerodynamic models for maneuvering aircraft
NASA Technical Reports Server (NTRS)
Lan, C. Edward; Hu, C. C.
1992-01-01
The method based on Fourier functional analysis and indicial formulation for aerodynamic modeling as proposed by Chin and Lan is extensively examined and improved for the purpose of general applications to realistic airplane configurations. Improvement is made to automate the calculation of model coefficients, and to evaluate more accurately the indicial integral. Test data of large angle-of-attack ranges for two different models, a 70 deg. delta wing and an F-18 model, are used to further verify the applicability of Fourier functional analysis and validate the indicial formulation. The results show that the general expression for harmonic motions throughout a range of k is capable of accurately modeling the nonlinear responses with large phase lag except in the region where an inconsistent hysteresis behavior from one frequency to the other occurs. The results by the indicial formulation indicate that more accurate results can be obtained when the motion starts from a low angle of attack where hysteresis effect is not important.
NASA Technical Reports Server (NTRS)
Baize, Daniel G. (Editor)
1999-01-01
The High-Speed Research Program and NASA Langley Research Center sponsored the NASA High-Speed Research Program Aerodynamic Performance Workshop on February 25-28, 1997. The workshop was designed to bring together NASA and industry High-Speed Civil Transport (HSCT) Aerodynamic Performance technology development participants in areas of Configuration Aerodynamics (transonic and supersonic cruise drag prediction and minimization), High-Lift, Flight Controls, Supersonic Laminar Flow Control, and Sonic Boom Prediction. The workshop objectives were to (1) report the progress and status of HSCT aerodynamic performance technology development; (2) disseminate this technology within the appropriate technical communities; and (3) promote synergy among the scientist and engineers working HSCT aerodynamics. In particular, single- and multi-point optimized HSCT configurations, HSCT high-lift system performance predictions, and HSCT Motion Simulator results were presented along with executive summaries for all the Aerodynamic Performance technology areas.
NASA Astrophysics Data System (ADS)
Kirby, J. F.; Swain, C. J.
2013-12-01
The flexural rigidity of the Earth's cratonic regions is a topic of much controversy. While many studies have suggested that cratons possess high elastic strength, others maintain that the continental lithosphere is everywhere weak. In this study we focus on the Canadian shield, and show that perceived evidence for weak cratonic lithosphere is compromised by shortcomings of the spectral analysis technique. Here we compare estimates of the admittance between free-air gravity and topography in the spectral domain from wavelet and multitaper methods. We apply particular attention to their long wavelength values, since it is here that the signals from mantle convection, glacial isostatic adjustment (GIA) and flexure are often present together. Our results show that, when used with certain parameter values, the multitaper method has a comparatively poor resolution at long wavelengths, and hence is not always able to distinguish between the harmonics due to convection and flexural processes. This renders it unreliable for estimating the flexural rigidity. We then show that the wavelet method does have the requisite properties to make this distinction, since it is able to correctly resolve a low-admittance dip at long wavelengths in both synthetic and real data. When the observed wavelet admittance of the Canadian shield is inverted against the predictions of a combined flexural, convection and GIA model, we find that the shield possesses a core of high effective elastic thickness (Te), greater than 118 km to 95% confidence, located to the immediate south-west of Hudson Bay.
NASA Technical Reports Server (NTRS)
Messina, Michael D.
1995-01-01
The method described in this report is intended to present an overview of a process developed to extract the forebody aerodynamic increments from flight tests. The process to determine the aerodynamic increments (rolling pitching, and yawing moments, Cl, Cm, Cn, respectively) for the forebody strake controllers added to the F/A - 18 High Alpha Research Vehicle (HARV) aircraft was developed to validate the forebody strake aerodynamic model used in simulation.
NASA Technical Reports Server (NTRS)
Hahne, David E. (Editor)
1999-01-01
NASA's High-Speed Research Program sponsored the 1999 Aerodynamic Performance Technical Review on February 8-12, 1999 in Anaheim, California. The review was designed to bring together NASA and industry High-Speed Civil Transport (HSCT) Aerodynamic Performance technology development participants in the areas of Configuration Aerodynamics (transonic and supersonic cruise drag prediction and minimization), High Lift, and Flight Controls. The review objectives were to: (1) report the progress and status of HSCT aerodynamic performance technology development; (2) disseminate this technology within the appropriate technical communities; and (3) promote synergy among the scientists and engineers working on HSCT aerodynamics. In particular, single and midpoint optimized HSCT configurations, HSCT high-lift system performance predictions, and HSCT simulation results were presented, along with executive summaries for all the Aerodynamic Performance technology areas. The HSR Aerodynamic Performance Technical Review was held simultaneously with the annual review of the following airframe technology areas: Materials and Structures, Environmental Impact, Flight Deck, and Technology Integration. Thus, a fourth objective of the Review was to promote synergy between the Aerodynamic Performance technology area and the other technology areas of the HSR Program. This Volume 1/Part 1 publication covers configuration aerodynamics.
NASA Technical Reports Server (NTRS)
Pamadi , Bandu N.; Brauckmann, Gregory J.
1999-01-01
An overview of the aerodynamic characteristics and the process of developing the preflight aerodynamic database of the NASA/ Orbital X-34 reusable launch vehicle is presented in this paper. Wind tunnel tests from subsonic to hypersonic Mach numbers including ground effect tests at low subsonic speeds were conducted in various facilities at the NASA Langley Research Center. The APAS (Aerodynamic Preliminary Analysis System) code was used for engineering level analysis and to fill the gaps in the wind tunnel test data. This aerodynamic database covers the range of Mach numbers, angles of attack, sideslip and control surface deflections anticipated in the complete flight envelope.
NASA Astrophysics Data System (ADS)
Brahmachari, Kaushik; Ray, Mina
2015-02-01
A theoretical design of surface plasmon resonance (SPR) structure operating in attenuated total reflection (ATR) mode and comprising of silicon or chalcogenide (2S2G) prism material coated with gold film having different nanoparticle sizes has been reported along with some interesting performance related simulation results at the operating wavelength of 1200 nm in infrared. The admittance loci based technique has been employed for the appropriate choice of the metal layer thickness. The sensitivity and other performance parameters of the structure based on the choice of the high index prism material and correct gold nanoparticle size have also been presented. In comparison to other conventional prism based plasmonic structures, the proposed model provides the extra degree of freedom, i.e., variations of nanoparticle size in addition to the variation in layer thickness and the use of different high index prism materials like silicon, 2S2G materials, etc. Moreover, the width of the SPR curve can be controlled by using different high index prism materials as well as by changing gold nanoparticle size. Higher sensitivity can be achieved with 2S2G while higher detection accuracy is provided by silicon as prism material.
Meuleman, Jos; van Asseldonk, Edwin; van Oort, Gijs; Rietman, Hans; van der Kooij, Herman
2016-03-01
Robotic gait training is gaining ground in rehabilitation. Room for improvement lies in reducing donning and doffing time, making training more task specific and facilitating active balance control, and by allowing movement in more degrees of freedom. Our goal was to design and evaluate a robot that incorporates these improvements. LOPES II uses an end-effector approach with parallel actuation and a minimum amount of clamps. LOPES II has eight powered degrees of freedom (hip flexion/extension, hip abduction/adduction, knee flexion/extension, pelvis forward/aft and pelvis mediolateral). All other degrees of freedom can be left free and pelvis frontal- and transversal rotation can be constrained. Furthermore arm swing is unhindered. The end-effector approach eliminates the need for exact alignment, which results in a donning time of 10-14 min for first-time training and 5-8 min for recurring training. LOPES II is admittance controlled, which allows for the control over the complete spectrum from low to high impedance. When the powered degrees of freedom are set to minimal impedance, walking in the device resembles free walking, which is an important requisite to allow task-specific training. We demonstrated that LOPES II can provide sufficient support to let severely affected patients walk and that we can provide selective support to impaired aspects of gait of mildly affected patients. PMID:26731771
NASA Astrophysics Data System (ADS)
Maheshwari, Muneesh; Annamdas, Venu Gopal M.; Pang, John Hock Lye; Tjin, Swee C.; Asundi, Anand
2015-12-01
Damage monitoring is the need of the hour in this age of infrastructure. Many methods are being used for damage monitoring in different mechanical and civil structures. Some of them are strain based methods in which abruptly increased strain signifies the presence of damage in the structure. This article focuses on crack monitoring of a fixedfixed beam using fiber optic sensors which can measure strain locally or globally. The two types of fiber optic sensors used in this research are fiber Bragg grating (FBG) and fiber optic polarimetric sensors (FOPS). FBG and FOPS are used for local strain monitoring (at one point only) and global strain monitoring (in the entire specimen) respectively. At the centre of the specimen, a piezoelectric wafer active sensor (PWAS) is also attached. PWAS is used to obtain electromechanical admittance (EMA) signatures. Further, these EMA signatures are analysed to access the damage state in the beam. These multiple smart materials together provide improved information on damages in the specimen which is very valuable for the structural health monitoring (SHM) of the specimen.
Observation of lower defect density in CH3NH3Pb(I,Cl)3 solar cells by admittance spectroscopy
NASA Astrophysics Data System (ADS)
Jiang, Minlin; Lan, Fei; Zhao, Bingxin; Tao, Quan; Wu, Jiamin; Gao, Di; Li, Guangyong
2016-06-01
The introduction of Cl into CH3NH3PbI3 precursors is reported to enhance the performance of CH3NH3PbI3 solar cell, which is attributed to the significantly increased diffusion lengths of carriers in CH3NH3Pb(I,Cl)3 solar cell. It has been assumed but never experimentally approved that the defect density in CH3NH3Pb(I,Cl)3 solar cell should be reduced according to the higher carrier lifetime observed from photoluminescence (PL) measurement. We have fabricated CH3NH3Pb(I,Cl)3 solar cell by adding a small amount of Cl source into CH3NH3PbI3 precursor. The performance of CH3NH3Pb(I,Cl)3 solar cell is significantly improved from 15.39% to 18.60%. Results from scanning electron microscopy and X-ray diffraction indicate that the morphologies and crystal structures of CH3NH3PbI3 and CH3NH3Pb(I,Cl)3 thin films remain unchanged. Open circuit voltage decay and admittance spectroscopy characterization jointly approve that Cl plays an extremely important role in suppressing the formation of defects in perovskite solar cells.
NASA Astrophysics Data System (ADS)
Keefe, Douglas H.; Zhao, Fei; Neely, Stephen T.; Gorga, Michael P.; Vohr, Betty R.
2003-01-01
This report describes the extent to which ear-canal acoustic admittance and energy reflectance (YR) in human neonates (1) predict otoacoustic emission (OAE) levels and auditory brainstem response (ABR) latencies, and (2) classify OAE and ABR responses as present or absent. Analyses are reported on a subset of ears in which hearing screening measurements were obtained previously [Norton et al., Ear. Hear. 21, 348-356 (2000a)]. Tests on 1405 ears included YR, distortion-product OAEs, transient-evoked OAEs, and ABR. Principal components analysis reduced the 33 YR variables to 5-7 factors. OAE levels decreased and ABR latencies increased with increasing high-frequency energy reflectance. Up to 28% of the variance in OAE levels and 12% of the variance in ABR wave-V latencies were explained by these factors. Thus, the YR response indirectly encodes information on inter-ear variations in forward and reverse middle-ear transmission. The YR factors classify OAEs with an area under the relative operating characteristic (ROC) curve as high as 0.79, suggesting that middle-ear dysfunction is partly responsible for the inability to record OAEs in some ears. The YR factors classified ABR responses less well, with ROC areas of 0.64 for predicting wave-V latency and 0.56 for predicting Fsp.
NASA Astrophysics Data System (ADS)
Heller, Daniel A.; Marquart, Gabriele
2002-01-01
The North Atlantic between the Charlie-Gibbs and Senja Fracture Zones shows a number of oceanic plateaux, continental fragments and unusual mid-oceanic ridges, the Reykjanes Ridges and the Iceland Plateau being the most prominent ones. While rifted continental fragments and marginal volcanic plateaux have been formed during the initial formation process of the North Atlantic, others, such as the Reykjanes Ridge and plume-related plateaux such as Iceland and possibly also Jan Mayen, are still under development. By studying the ratio of geoid to topography in the long-wavelength range for these regions of elevated topography and comparing the results with theoretical models of crustal loading and subsurface thermal uplift we can show that the Rockall Bank and the Vøring Plateau are compensated by a thick crust alone, while the Iceland Plateau, the outer Faeroe Plateau and the Jan Mayen Block have a strong component of deeply situated mass anomalies. The admittance, the spectral ratio of geoid to topography, for a number of profiles across the Reykjanes Ridge clearly indicates a decrease in compensation depth with distance from Iceland. This strengthens the argument for a mass flux from the Iceland Plume into the Reykjanes Ridge.
HSR Aerodynamic Performance Status and Challenges
NASA Technical Reports Server (NTRS)
Gilbert, William P.; Antani, Tony; Ball, Doug; Calloway, Robert L.; Snyder, Phil
1999-01-01
This paper describes HSR (High Speed Research) Aerodynamic Performance Status and Challenges. The topics include: 1) Aero impact on HSR; 2) Goals and Targets; 3) Progress and Status; and 4) Remaining Challenges. This paper is presented in viewgraph form.
Aerodynamic analysis of Pegasus - Computations vs reality
NASA Technical Reports Server (NTRS)
Mendenhall, Michael R.; Lesieutre, Daniel J.; Whittaker, C. H.; Curry, Robert E.; Moulton, Bryan
1993-01-01
Pegasus, a three-stage, air-launched, winged space booster was developed to provide fast and efficient commercial launch services for small satellites. The aerodynamic design and analysis of Pegasus was conducted without benefit of wind tunnel tests using only computational aerodynamic and fluid dynamic methods. Flight test data from the first two operational flights of Pegasus are now available, and they provide an opportunity to validate the accuracy of the predicted pre-flight aerodynamic characteristics. Comparisons of measured and predicted flight characteristics are presented and discussed. Results show that the computational methods provide reasonable aerodynamic design information with acceptable margins. Post-flight analyses illustrate certain areas in which improvements are desired.
Switchable and Tunable Aerodynamic Drag on Cylinders
NASA Astrophysics Data System (ADS)
Guttag, Mark; Lopez Jimenez, Francisco; Reis, Pedro
2015-11-01
We report results on the performance of Smart Morphable Surfaces (Smporhs) that can be mounted onto cylindrical structures to actively reduce their aerodynamic drag. Our system comprises of an elastomeric thin shell with a series of carefully designed subsurface cavities that, once depressurized, lead to a dramatic deformation of the surface topography, on demand. Our design is inspired by the morphology of the giant cactus (Carnegiea gigantea) which possesses an array of axial grooves, which are thought to help reduce aerodynamic drag, thereby enhancing the structural robustness of the plant under wind loading. We perform systematic wind tunnel tests on cylinders covered with our Smorphs and characterize their aerodynamic performance. The switchable and tunable nature of our system offers substantial advantages for aerodynamic performance when compared to static topographies, due to their operation over a wider range of flow conditions.
Switchable and Tunable Aerodynamic Drag on Cylinders
NASA Astrophysics Data System (ADS)
Guttag, Mark; Lopéz Jiménez, Francisco; Upadhyaya, Priyank; Kumar, Shanmugam; Reis, Pedro
We report results on the performance of Smart Morphable Surfaces (Smporhs) that can be mounted onto cylindrical structures to actively reduce their aerodynamic drag. Our system comprises of an elastomeric thin shell with a series of carefully designed subsurface cavities that, once depressurized, lead to a dramatic deformation of the surface topography, on demand. Our design is inspired by the morphology of the giant cactus (Carnegiea gigantea) which possesses an array of axial grooves, thought to help reduce aerodynamic drag, thereby enhancing the structural robustness of the plant under wind loading. We perform systematic wind tunnel tests on cylinders covered with our Smorphs and characterize their aerodynamic performance. The switchable and tunable nature of our system offers substantial advantages for aerodynamic performance when compared to static topographies, due to their operation over a wider range of flow conditions.
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.
Aerodynamic Characterization of a Modern Launch Vehicle
NASA Technical Reports Server (NTRS)
Hall, Robert M.; Holland, Scott D.; Blevins, John A.
2011-01-01
A modern launch vehicle is by necessity an extremely integrated design. The accurate characterization of its aerodynamic characteristics is essential to determine design loads, to design flight control laws, and to establish performance. The NASA Ares Aerodynamics Panel has been responsible for technical planning, execution, and vetting of the aerodynamic characterization of the Ares I vehicle. An aerodynamics team supporting the Panel consists of wind tunnel engineers, computational engineers, database engineers, and other analysts that address topics such as uncertainty quantification. The team resides at three NASA centers: Langley Research Center, Marshall Space Flight Center, and Ames Research Center. The Panel has developed strategies to synergistically combine both the wind tunnel efforts and the computational efforts with the goal of validating the computations. Selected examples highlight key flow physics and, where possible, the fidelity of the comparisons between wind tunnel results and the computations. Lessons learned summarize what has been gleaned during the project and can be useful for other vehicle development projects.
Aerodynamic Analyses Requiring Advanced Computers, Part 1
NASA Technical Reports Server (NTRS)
1975-01-01
Papers are presented which deal with results of theoretical research on aerodynamic flow problems requiring the use of advanced computers. Topics discussed include: viscous flows, boundary layer equations, turbulence modeling and Navier-Stokes equations, and internal flows.
Hypervelocity Free-Flight Aerodynamic Facility (HFFAF)
The HFFAF is the only aeroballistic range the nation currently capable of testing in gases other than air and at sub-atmospheric pressures. It is used primarily to study the aerodynamics, Aerotherm...
Aerodynamic Analyses Requiring Advanced Computers, part 2
NASA Technical Reports Server (NTRS)
1975-01-01
Papers given at the conference present the results of theoretical research on aerodynamic flow problems requiring the use of advanced computers. Topics discussed include two-dimensional configurations, three-dimensional configurations, transonic aircraft, and the space shuttle.
NASA Technical Reports Server (NTRS)
Armstrong, Wilbur C.
1992-01-01
The piping in a liquid rocket can assume complex configurations due to multiple tanks, multiple engines, and structures that must be piped around. The capability to handle some of these complex configurations have been incorporated into the ADMIT code. The capability to modify the input on line has been implemented. The configurations allowed include multiple tanks, multiple engines, the splitting of a pipe into unequal segments going to different (or the same) engines. This program will handle the following type elements: straight pipes, bends, inline accumulators, tuned stub accumulators, Helmholtz resonators, parallel resonators, pumps, split pipes, multiple tanks, and multiple engines.
The oscillating wing with aerodynamically balanced elevator
NASA Technical Reports Server (NTRS)
Kussner, H G; Schwartz, I
1941-01-01
The two-dimensional problem of the oscillating wing with aerodynamically balanced elevator is treated in the manner that the wing is replaced by a plate with bends and stages and the airfoil section by a mean line consisting of one or more straights. The computed formulas and tables permit, on these premises, the prediction of the pressure distribution and of the aerodynamic reactions of oscillating elevators and tabs with any position of elevator hinge in respect to elevator leading edge.
Means for controlling aerodynamically induced twist
NASA Technical Reports Server (NTRS)
Elber, W. (Inventor)
1982-01-01
A control mechanism which provides active compensation for aerodynamically induced twist deformation of high aspect ratio wings consists of a torque tube, internal to each wing and rigidly attached near the tip of each wing, which is moved by an actuator located in the aircraft fuselage. As changes in the aerodynamic loads on the wings occur the torque tube is rotated to compensate for the induced wing twist.
Bayesian inference of nonlinear unsteady aerodynamics from aeroelastic limit cycle oscillations
NASA Astrophysics Data System (ADS)
Sandhu, Rimple; Poirel, Dominique; Pettit, Chris; Khalil, Mohammad; Sarkar, Abhijit
2016-07-01
A Bayesian model selection and parameter estimation algorithm is applied to investigate the influence of nonlinear and unsteady aerodynamic loads on the limit cycle oscillation (LCO) of a pitching airfoil in the transitional Reynolds number regime. At small angles of attack, laminar boundary layer trailing edge separation causes negative aerodynamic damping leading to the LCO. The fluid-structure interaction of the rigid, but elastically mounted, airfoil and nonlinear unsteady aerodynamics is represented by two coupled nonlinear stochastic ordinary differential equations containing uncertain parameters and model approximation errors. Several plausible aerodynamic models with increasing complexity are proposed to describe the aeroelastic system leading to LCO. The likelihood in the posterior parameter probability density function (pdf) is available semi-analytically using the extended Kalman filter for the state estimation of the coupled nonlinear structural and unsteady aerodynamic model. The posterior parameter pdf is sampled using a parallel and adaptive Markov Chain Monte Carlo (MCMC) algorithm. The posterior probability of each model is estimated using the Chib-Jeliazkov method that directly uses the posterior MCMC samples for evidence (marginal likelihood) computation. The Bayesian algorithm is validated through a numerical study and then applied to model the nonlinear unsteady aerodynamic loads using wind-tunnel test data at various Reynolds numbers.
Sensitivity Analysis and Optimization of Aerodynamic Configurations with Blend Surfaces
NASA Technical Reports Server (NTRS)
Thomas, A. M.; Tiwari, S. N.
1997-01-01
A novel (geometrical) parametrization procedure using solutions to a suitably chosen fourth order partial differential equation is used to define a class of airplane configurations. Inclusive in this definition are surface grids, volume grids, and grid sensitivity. The general airplane configuration has wing, fuselage, vertical tail and horizontal tail. The design variables are incorporated into the boundary conditions, and the solution is expressed as a Fourier series. The fuselage has circular cross section, and the radius is an algebraic function of four design parameters and an independent computational variable. Volume grids are obtained through an application of the Control Point Form method. A graphic interface software is developed which dynamically changes the surface of the airplane configuration with the change in input design variable. The software is made user friendly and is targeted towards the initial conceptual development of any aerodynamic configurations. Grid sensitivity with respect to surface design parameters and aerodynamic sensitivity coefficients based on potential flow is obtained using an Automatic Differentiation precompiler software tool ADIFOR. Aerodynamic shape optimization of the complete aircraft with twenty four design variables is performed. Unstructured and structured volume grids and Euler solutions are obtained with standard software to demonstrate the feasibility of the new surface definition.
Aerodynamic design optimization by using a continuous adjoint method
NASA Astrophysics Data System (ADS)
Luo, JiaQi; Xiong, JunTao; Liu, Feng
2014-07-01
This paper presents the fundamentals of a continuous adjoint method and the applications of this method to the aerodynamic design optimization of both external and internal flows. General formulation of the continuous adjoint equations and the corresponding boundary conditions are derived. With the adjoint method, the complete gradient information needed in the design optimization can be obtained by solving the governing flow equations and the corresponding adjoint equations only once for each cost function, regardless of the number of design parameters. An inverse design of airfoil is firstly performed to study the accuracy of the adjoint gradient and the effectiveness of the adjoint method as an inverse design method. Then the method is used to perform a series of single and multiple point design optimization problems involving the drag reduction of airfoil, wing, and wing-body configuration, and the aerodynamic performance improvement of turbine and compressor blade rows. The results demonstrate that the continuous adjoint method can efficiently and significantly improve the aerodynamic performance of the design in a shape optimization problem.
Atmospheric tests of trailing-edge aerodynamic devices
Miller, L S; Huang, S; Quandt, G A
1998-01-01
An experiment was conducted at the National Renewable Energy Laboratory`s (NREL`s) National Wind Technology Center (NWTC) using an instrumented horizontal-axis wind turbine that incorporated variable-span, trailing-edge aerodynamic brakes. The goal of the investigation was to directly compare results with (infinite-span) wind tunnel data and to provide information on how to account for device span effects during turbine design or analysis. Comprehensive measurements were used to define effective changes in the aerodynamic and hinge-moment coefficients, as a function of angle of attack and control deflection, for three device spans (7.5%, 15%, and 22.5%) and configurations (Spoiler-Flap, vented sileron, and unvented aileron). Differences in the lift and drag behavior are most pronounced near stall and for device spans of less than 15%. Drag performance is affected only minimally (about a 30% reduction from infinite-span) for 15% or larger span devices. Interestingly, aerodynamic controls with vents or openings appear most affected by span reductions and three-dimensional flow.
Aerodynamic characteristics of sixteen electric, hybrid, and subcompact vehicles
NASA Technical Reports Server (NTRS)
Kurtz, D. W.
1979-01-01
An elementary electric and hybrid vehicle aerodynamic data base was developed using data obtained on sixteen electric, hybrid, and sub-compact production vehicles tested in the Lockheed-Georgia low-speed wind tunnel. Zero-yaw drag coefficients ranged from a high of 0.58 for a boxey delivery van and an open roadster to a low of about 0.34 for a current four-passenger proto-type automobile which was designed with aerodynamics as an integrated parameter. Vehicles were tested at yaw angles up to 40 degrees and a wing weighting analysis is presented which yields a vehicle's effective drag coefficient as a function of wing velocity and driving cycle. Other parameters investigated included the effects of windows open and closed, radiators open and sealed, and pop-up headlights. Complete six-component force and moment data are presented in both tabular and graphical formats. Only limited commentary is offered since, by its very nature, a data base should consist of unrefined reference material. A justification for pursuing efficient aerodynamic design of EHVs is presented.
Darrieus rotor aerodynamics in turbulent wind
Brahimi, M.T.; Paraschivoiu, I.
1995-05-01
The earlier aerodynamic models for studying vertical axis wind turbines (VAWT`s) are based on constant incident wind conditions and are thus capable of predicting only periodic variations in the loads. The purpose of the present study is to develop a model capable of predicting the aerodynamic loads on the Darrieus rotor in a turbulent wind. This model is based on the double-multiple streamtube method (DMS) and incorporates a stochastic wind model. The method used to simulate turbulent velocity fluctuations is based on the power spectral density. The problem consists in generating a region of turbulent flow with a relevant spectrum and spatial correlation. The first aerodynamic code developed is based on a one-dimensional turbulent wind model. However, since this model ignores the structure of the turbulence in the crossflow plane, an extension to three dimensions has been made. The computer code developed, CARDAAS, has been used to predict aerodynamic loads for the Sandia-17m rotor and compared to CARDAAV results and experimental data. Results have shown that the computed aerodynamic loads have been improved by including stochastic wind into the aerodynamic model.
Sharp Hypervelocity Aerodynamic Research Probe
NASA Technical Reports Server (NTRS)
Bull, Jeffrey; Kolodziej, Paul; Rasky, Daniel J. (Technical Monitor)
1996-01-01
The objective of this flight demonstration is to deploy a slender-body hypervelocity aerodynamic research probe (SHARP) from an orbiting platform using a tether, deorbit and fly it along its aerothermal performance constraint, and recover it intact in mid-air. To accomplish this objective, two flight demonstrations are proposed. The first flight uses a blunt-body, tethered reentry experiment vehicle (TREV) to prove out tethered deployment technology for accurate entries, a complete SHARP electronics suite, and a new soft mid-air helicopter recovery technique. The second flight takes advantage of this launch and recovery capability to demonstrate revolutionary sharp body concepts for hypervelocity vehicles, enabled by new Ultra-High Temperature Ceramics (UHTCs) recently developed by Ames Research Center. Successful demonstration of sharp body hypersonic vehicle technologies could have radical impact on space flight capabilities, including: enabling global reentry cross range capability from Station, eliminating reentry communications blackout, and allowing new highly efficient launch systems incorporating air breathing propulsion and zeroth staging.
Aerodynamic characteristics of French consonants
NASA Astrophysics Data System (ADS)
Demolin, Didier; Hassid, Sergio; Soquet, Alain
2001-05-01
This paper reports some aerodynamic measurements made on French consonants with a group of ten speakers. Speakers were recorded while saying nonsense words in phrases such as papa, dis papa encore. The nonsense words in the study combined each of the French consonants with three vowels /i, a, u/ to from two syllables words with the first syllable being the same as the second. In addition to the audio signal, recordings were made of the oral airflow, the pressure of the air in the pharynx above the vocal folds and the pressure of the air in the trachea just below the vocal folds. The pharyngeal pressure was recorded via a catheter (i.d. 5 mm) passed through the nose so that its open end could be seen in the pharynx below the uvula. The subglottal pressure was recorded via a tracheal puncture between the first and the second rings of the trachea or between the cricoid cartilage and the first tracheal ring. Results compare subglottal presssure, pharyngeal pressure, and airflow values. Comparisons are made between values obtained with male and female subjects and various types of consonants (voiced versus voiceless at the same place of articulation, stops, fricatives, and nasals).
Parachute Aerodynamics From Video Data
NASA Technical Reports Server (NTRS)
Schoenenberger, Mark; Queen, Eric M.; Cruz, Juan R.
2005-01-01
A new data analysis technique for the identification of static and dynamic aerodynamic stability coefficients from wind tunnel test video data is presented. This new technique was applied to video data obtained during a parachute wind tunnel test program conducted in support of the Mars Exploration Rover Mission. Total angle-of-attack data obtained from video images were used to determine the static pitching moment curve of the parachute. During the original wind tunnel test program the static pitching moment curve had been determined by forcing the parachute to a specific total angle-of -attack and measuring the forces generated. It is shown with the new technique that this parachute, when free to rotate, trims at an angle-of-attack two degrees lower than was measured during the forced-angle tests. An attempt was also made to extract pitch damping information from the video data. Results suggest that the parachute is dynamically unstable at the static trim point and tends to become dynamically stable away from the trim point. These trends are in agreement with limit-cycle-like behavior observed in the video. However, the chaotic motion of the parachute produced results with large uncertainty bands.
Skylon Aerodynamics and SABRE Plumes
NASA Technical Reports Server (NTRS)
Mehta, Unmeel; Afosmis, Michael; Bowles, Jeffrey; Pandya, Shishir
2015-01-01
An independent partial assessment is provided of the technical viability of the Skylon aerospace plane concept, developed by Reaction Engines Limited (REL). The objectives are to verify REL's engineering estimates of airframe aerodynamics during powered flight and to assess the impact of Synergetic Air-Breathing Rocket Engine (SABRE) plumes on the aft fuselage. Pressure lift and drag coefficients derived from simulations conducted with Euler equations for unpowered flight compare very well with those REL computed with engineering methods. The REL coefficients for powered flight are increasingly less acceptable as the freestream Mach number is increased beyond 8.5, because the engineering estimates did not account for the increasing favorable (in terms of drag and lift coefficients) effect of underexpanded rocket engine plumes on the aft fuselage. At Mach numbers greater than 8.5, the thermal environment around the aft fuselage is a known unknown-a potential design and/or performance risk issue. The adverse effects of shock waves on the aft fuselage and plumeinduced flow separation are other potential risks. The development of an operational reusable launcher from the Skylon concept necessitates the judicious use of a combination of engineering methods, advanced methods based on required physics or analytical fidelity, test data, and independent assessments.
Aerodynamics of a hybrid airship
NASA Astrophysics Data System (ADS)
Andan, Amelda Dianne; Asrar, Waqar; Omar, Ashraf A.
2012-06-01
The objective of this paper is to present the results of a numerical study of the aerodynamic parameters of a wingless and a winged-hull airship. The total forces and moment coefficients of the airships have been computed over a range of angles. The results obtained show that addition of a wing to a conventional airship increases the lift has three times the lifting force at positive angle of attack as compared to a wingless airship whereas the drag increases in the range of 19% to 58%. The longitudinal and directional stabilities were found to be statically stable, however, both the conventional airship and the hybrid or winged airships were found to have poor rolling stability. Wingless airship has slightly higher longitudinal stability than a winged airship. The winged airship has better directional stability than the wingless airship. The wingless airship only possesses static rolling stability in the range of yaw angles of -5° to 5°. On the contrary, the winged airship initially tested does not possess rolling stability at all. Computational fluid dynamics (CFD) simulations show that modifications to the wing placement and its dihedral have strong positive effect on the rolling stability. Raising the wings to the center of gravity and introducing a dihedral angle of 5° stabilizes the rolling motion of the winged airship.
Aerodynamics of Unsteady Sailing Kinetics
NASA Astrophysics Data System (ADS)
Keil, Colin; Schutt, Riley; Borshoff, Jennifer; Alley, Philip; de Zegher, Maximilien; Williamson, Chk
2015-11-01
In small sailboats, the bodyweight of the sailor is proportionately large enough to induce significant unsteady motion of the boat and sail. Sailors use a variety of kinetic techniques to create sail dynamics which can provide an increment in thrust, thereby increasing the boatspeed. In this study, we experimentally investigate the unsteady aerodynamics associated with two techniques, ``upwind leech flicking'' and ``downwind S-turns''. We explore the dynamics of an Olympic class Laser sailboat equipped with a GPS, IMU, wind sensor, and camera array, sailed expertly by a member of the US Olympic team. The velocity heading of a sailing boat is oriented at an apparent wind angle to the flow. In contrast to classic flapping propulsion, the heaving of the sail section is not perpendicular to the sail's motion through the air. This leads to heave with components parallel and perpendicular to the incident flow. The characteristic motion is recreated in a towing tank where the vortex structures generated by a representative 2-D sail section are observed using Particle Image Velocimetry and the measurement of thrust and lift forces. Amongst other results, we show that the increase in driving force, generated due to heave, is larger for greater apparent wind angles.
Aerodynamics of puffball mushroom spore dispersal
NASA Astrophysics Data System (ADS)
Amador, Guillermo; Barberie, Alex; Hu, David
2012-11-01
Puffball mushrooms Lycoperdon are spherical fungi that release a cloud of spores in response to raindrop impacts. In this combined experimental and theoretical study, we elucidate the aerodynamics of this unique impact-based spore-dispersal. We characterize live puffball ejections by high speed video, the geometry and elasticity of their shells by cantilever experiments, and the packing fraction and size of their spores by scanning electron microscope. We build a dynamically similar puffball mimic composed of a tied-off latex balloon filled with baby powder and topped with a 1-cm slit. A jet of powder is elicited by steady lateral compression of the mimic between two plates. The jet height is a bell-shaped function of force applied, with a peak of 18 cm at loads of 45 N. We rationalize the increase in jet height with force using Darcy's Law: the applied force generates an overpressure maintained by the air-tight elastic membrane. Pressure is relieved as the air travels through the spore interstitial spaces, entrains spores, and exits through the puffball orifice. This mechanism demonstrates how powder-filled elastic shells can generate high-speed jets using energy harvested from rain.
Ferroelectric Liquid Crystals In Aerodynamic Testing
NASA Technical Reports Server (NTRS)
Parmar, Devendra S.; Holmes, Harlan K.
1994-01-01
The process of simultaneous optical visualization and quantitative measurement of aerodynamic boundary layer parameters requires new concepts, materials and utilization methods. Measurement of shear stress in terms of the transmitted or the reflected light intensity from an aligned ferroelectric liquid crystal (FLC) thin (approx. 1 micron) film deposited on a glass substrate has been the first step in this direction. In this paper, recent progress in utilization of FLC thin films for skin friction measurement and for studying the state of the boundary layer in a wind tunnel environment is reviewed. The switching characteristics of FLCs have been used to measure pressure from the newly devised system of partially exposed polymer dispersed ferroelectric liquid crystals (PEPDFLCs). In this configuration, a PEPDFLC thin film (approx. 10-25 microns) is sandwiched between two transparent conducting electrodes, one a rigid surface and the other a flexible sheet such as polyvinylidene fluoride or mylar. The switching characteristics of the film are a function of the pressure applied to the flexible transparent electrode and a predetermined bias voltage across the two electrodes. The results, considering the dielectrics of composite media, are discussed.
Unsteady aerodynamic models for maneuvering aircraft
NASA Technical Reports Server (NTRS)
Hu, Chien-Chung; Lan, C. E.; Brandon, Jay
1993-01-01
Forced oscillation tests over a large angle-of-attack range for an F-18 model are conducted in the NASA Langley 12-foot low-speed tunnel. The resulting dynamic longitudinal data are analyzed with an unsteady aerodynamic modeling method based on Fourier functional analysis and the indicial formulation. The method is extensively examined and improved to automate the calculation of model coefficients, and to evaluate more accurately the indicial integral. The results indicate that the general model equation obtained from harmonic test data in a range of reduced frequency is capable of accurately modeling the nonlinear responses with large hysteresis effect, except in the region where a delayed flow reattachment occurs at low angles of attack in down strokes. The indicial formulation is used to calculate the response to harmonic motion, harmonic ramp motion, constant-rate pitching motion and smaller-amplitude harmonic motion. The results show that more accurate results can be obtained when the motion starts from a low angle of attack where hysteresis effect is not important.
Modeling Powered Aerodynamics for the Orion Launch Abort Vehicle Aerodynamic Database
NASA Technical Reports Server (NTRS)
Chan, David T.; Walker, Eric L.; Robinson, Philip E.; Wilson, Thomas M.
2011-01-01
Modeling the aerodynamics of the Orion Launch Abort Vehicle (LAV) has presented many technical challenges to the developers of the Orion aerodynamic database. During a launch abort event, the aerodynamic environment around the LAV is very complex as multiple solid rocket plumes interact with each other and the vehicle. It is further complicated by vehicle separation events such as between the LAV and the launch vehicle stack or between the launch abort tower and the crew module. The aerodynamic database for the LAV was developed mainly from wind tunnel tests involving powered jet simulations of the rocket exhaust plumes, supported by computational fluid dynamic simulations. However, limitations in both methods have made it difficult to properly capture the aerodynamics of the LAV in experimental and numerical simulations. These limitations have also influenced decisions regarding the modeling and structure of the aerodynamic database for the LAV and led to compromises and creative solutions. Two database modeling approaches are presented in this paper (incremental aerodynamics and total aerodynamics), with examples showing strengths and weaknesses of each approach. In addition, the unique problems presented to the database developers by the large data space required for modeling a launch abort event illustrate the complexities of working with multi-dimensional data.
NASA Technical Reports Server (NTRS)
McMillin, S. Naomi (Editor)
1999-01-01
NASA's High-Speed Research Program sponsored the 1998 Aerodynamic Performance Technical Review on February 9-13, in Los Angeles, California. The review was designed to bring together NASA and industry High-Speed Civil Transport (HSCT) Aerodynamic Performance technology development participants in areas of Configuration Aerodynamics (transonic and supersonic cruise drag prediction and minimization), High-Lift, and Flight Controls. The review objectives were to (1) report the progress and status of HSCT aerodynamic performance technology development; (2) disseminate this technology within the appropriate technical communities; and (3) promote synergy among the scientists and engineers working HSCT aerodynamics. In particular, single and multi-point optimized HSCT configurations, HSCT high-lift system performance predictions, and HSCT simulation results were presented along with executive summaries for all the Aerodynamic Performance technology areas. The HSR Aerodynamic Performance Technical Review was held simultaneously with the annual review of the following airframe technology areas: Materials and Structures, Environmental Impact, Flight Deck, and Technology Integration. Thus, a fourth objective of the Review was to promote synergy between the Aerodynamic Performance technology area and the other technology areas of the HSR Program.
NASA Technical Reports Server (NTRS)
Hahne, David E. (Editor)
1999-01-01
NASA's High-Speed Research Program sponsored the 1999 Aerodynamic Performance Technical Review on February 8-12, 1999 in Anaheim, California. The review was designed to bring together NASA and industry High-Speed Civil Transport (HSCT) Aerodynamic Performance technology development participants in the areas of Configuration Aerodynamics (transonic and supersonic cruise drag prediction and minimization), High Lift, and Flight Controls. The review objectives were to (1) report the progress and status of HSCT aerodynamic performance technology development; (2) disseminate this technology within the appropriate technical communities; and (3) promote synergy among the scientists and engineers working on HSCT aerodynamics. In particular, single and midpoint optimized HSCT configurations, HSCT high-lift system performance predictions, and HSCT simulation results were presented, along with executive summaries for all the Aerodynamic Performance technology areas. The HSR Aerodynamic Performance Technical Review was held simultaneously with the annual review of the following airframe technology areas: Materials and Structures, Environmental Impact, Flight Deck, and Technology Integration. Thus, a fourth objective of the Review was to promote synergy between the Aerodynamic Performance technology area and the other technology areas of the HSR Program. This Volume 1/Part 2 publication covers the design optimization and testing sessions.
NASA Technical Reports Server (NTRS)
McMillin, S. Naomi (Editor)
1999-01-01
NASA's High-Speed Research Program sponsored the 1998 Aerodynamic Performance Technical Review on February 9-13, in Los Angeles, California. The review was designed to bring together NASA and industry HighSpeed Civil Transport (HSCT) Aerodynamic Performance technology development participants in areas of. Configuration Aerodynamics (transonic and supersonic cruise drag prediction and minimization), High-Lift, and Flight Controls. The review objectives were to: (1) report the progress and status of HSCT aerodynamic performance technology development; (2) disseminate this technology within the appropriate technical communities; and (3) promote synergy among the scientists and engineers working HSCT aerodynamics. In particular, single and multi-point optimized HSCT configurations, HSCT high-lift system performance predictions, and HSCT simulation results were presented along with executive summaries for all the Aerodynamic Performance technology areas. The HSR Aerodynamic Performance Technical Review was held simultaneously with the annual review of the following airframe technology areas: Materials and Structures, Environmental Impact, Flight Deck, and Technology Integration. Thus, a fourth objective of the Review was to promote synergy between the Aerodynamic Performance technology area and the other technology areas of the HSR Program.
A 3-D Admittance-Level Computational Model of a Rat Hippocampus for Improving Prosthetic Design
Gilbert, Andrew; Loizos, Kyle; RamRakhyani, Anil Kumar; Hendrickson, Phillip; Lazzi, Gianluca; Berger, Theodore W.
2016-01-01
Hippocampal prosthetic devices have been developed to bridge the gap between functioning portions of the hippocampus, in order to restore lost memory functionality in those suffering from brain injury or diseases. One approach taken in recent neuroprosthetic design is to use a multi-input, multi-output device that reads data from the CA3 in the hippocampus and electrically stimulates the CA1 in an attempt to mimic the appropriate firing pattern that would occur naturally between the two areas. However, further study needs to be conducted in order to optimize electrode placement, pulse magnitude, and shape for creating the appropriate firing pattern. This paper describes the creation and implementation of an anatomically correct 3D model of the hippocampus to simulate the electric field patterns and axonal activation from electrical stimulation due to an implanted electrode array. The activating function was applied to the voltage results to determine the firing patterns in possible axon locations within the CA1. PMID:26736751
A 3-D admittance-level computational model of a rat hippocampus for improving prosthetic design.
Gilbert, Andrew; Loizos, Kyle; RamRakhyani, Anil Kumar; Hendrickson, Phillip; Lazzi, Gianluca; Berger, Theodore W
2015-01-01
Hippocampal prosthetic devices have been developed to bridge the gap between functioning portions of the hippocampus, in order to restore lost memory functionality in those suffering from brain injury or diseases. One approach taken in recent neuroprosthetic design is to use a multi-input, multi-output device that reads data from the CA3 in the hippocampus and electrically stimulates the CA1 in an attempt to mimic the appropriate firing pattern that would occur naturally between the two areas. However, further study needs to be conducted in order to optimize electrode placement, pulse magnitude, and shape for creating the appropriate firing pattern. This paper describes the creation and implementation of an anatomically correct 3D model of the hippocampus to simulate the electric field patterns and axonal activation from electrical stimulation due to an implanted electrode array. The activating function was applied to the voltage results to determine the firing patterns in possible axon locations within the CA1. PMID:26736751
Aerodynamic Parameter Identification of a Venus Lander
NASA Astrophysics Data System (ADS)
Sykes, Robert A.
An analysis was conducted to identify the parameters of an aerodynamic model for a Venus lander based on experimental free-flight data. The experimental free-flight data were collected in the NASA Langley 20-ft Vertical Spin Tunnel with a 25-percent Froude-scaled model. The experimental data were classified based on the wind tunnel run type: runs where the lander model was unperturbed over the course of the run, and runs were the model was perturbed (principally in pitch, yaw, and roll) by the wind tunnel operator. The perturbations allow for data to be obtained at higher wind angles and rotation rates than those available from the unperturbed data. The model properties and equations of motion were used to determine experimental values for the aerodynamic coefficients. An aerodynamic model was selected using a priori knowledge of axisymmetric blunt entry vehicles. The least squares method was used to estimate the aerodynamic parameters. Three sets of results were obtained from the following data sets: perturbed, unperturbed, and the combination of both. The combined data set was selected for the final set of aerodynamic parameters based on the quality of the results. The identified aerodynamic parameters are consistent with that of the static wind tunnel data. Reconstructions, of experimental data not used in the parameter identification analyses, achieved similar residuals as those with data used to identify the parameters. Simulations of the experimental data, using the identified parameters, indicate that the aerodynamic model used is incapable of replicating the limit cycle oscillations with stochastic peak amplitudes observed during the test.
NASA Technical Reports Server (NTRS)
Baize, Daniel G. (Editor)
1999-01-01
The High-Speed Research Program and NASA Langley Research Center sponsored the NASA High-Speed Research Program Aerodynamic Performance Workshop on February 25-28, 1997. The workshop was designed to bring together NASA and industry High-Speed Civil Transport (HSCT) Aerodynamic Performance technology development participants in area of Configuration Aerodynamics (transonic and supersonic cruise drag prediction and minimization), High-Lift, Flight Controls, Supersonic Laminar Flow Control, and Sonic Boom Prediction. The workshop objectives were to (1) report the progress and status of HSCT aerodyamic performance technology development; (2) disseminate this technology within the appropriate technical communities; and (3) promote synergy among the scientist and engineers working HSCT aerodynamics. In particular, single- and multi-point optimized HSCT configurations, HSCT high-lift system performance predictions, and HSCT Motion Simulator results were presented along with executive summaries for all the Aerodynamic Performance technology areas.
Aerodynamic heating in hypersonic flows
NASA Technical Reports Server (NTRS)
Reddy, C. Subba
1993-01-01
Aerodynamic heating in hypersonic space vehicles is an important factor to be considered in their design. Therefore the designers of such vehicles need reliable heat transfer data in this respect for a successful design. Such data is usually produced by testing the models of hypersonic surfaces in wind tunnels. Most of the hypersonic test facilities at present are conventional blow-down tunnels whose run times are of the order of several seconds. The surface temperatures on such models are obtained using standard techniques such as thin-film resistance gages, thin-skin transient calorimeter gages and coaxial thermocouple or video acquisition systems such as phosphor thermography and infrared thermography. The data are usually reduced assuming that the model behaves like a semi-infinite solid (SIS) with constant properties and that heat transfer is by one-dimensional conduction only. This simplifying assumption may be valid in cases where models are thick, run-times short, and thermal diffusivities small. In many instances, however, when these conditions are not met, the assumption may lead to significant errors in the heat transfer results. The purpose of the present paper is to investigate this aspect. Specifically, the objectives are as follows: (1) to determine the limiting conditions under which a model can be considered a semi-infinite body; (2) to estimate the extent of errors involved in the reduction of the data if the models violate the assumption; and (3) to come up with correlation factors which when multiplied by the results obtained under the SIS assumption will provide the results under the actual conditions.
The aerodynamics of insect flight.
Sane, Sanjay P
2003-12-01
The flight of insects has fascinated physicists and biologists for more than a century. Yet, until recently, researchers were unable to rigorously quantify the complex wing motions of flapping insects or measure the forces and flows around their wings. However, recent developments in high-speed videography and tools for computational and mechanical modeling have allowed researchers to make rapid progress in advancing our understanding of insect flight. These mechanical and computational fluid dynamic models, combined with modern flow visualization techniques, have revealed that the fluid dynamic phenomena underlying flapping flight are different from those of non-flapping, 2-D wings on which most previous models were based. In particular, even at high angles of attack, a prominent leading edge vortex remains stably attached on the insect wing and does not shed into an unsteady wake, as would be expected from non-flapping 2-D wings. Its presence greatly enhances the forces generated by the wing, thus enabling insects to hover or maneuver. In addition, flight forces are further enhanced by other mechanisms acting during changes in angle of attack, especially at stroke reversal, the mutual interaction of the two wings at dorsal stroke reversal or wing-wake interactions following stroke reversal. This progress has enabled the development of simple analytical and empirical models that allow us to calculate the instantaneous forces on flapping insect wings more accurately than was previously possible. It also promises to foster new and exciting multi-disciplinary collaborations between physicists who seek to explain the phenomenology, biologists who seek to understand its relevance to insect physiology and evolution, and engineers who are inspired to build micro-robotic insects using these principles. This review covers the basic physical principles underlying flapping flight in insects, results of recent experiments concerning the aerodynamics of insect flight, as well
NASA Astrophysics Data System (ADS)
Sekine, Katsuhisa; Yamada, Ayumi; Kageyama, Hitomi; Igarashi, Takahiro; Yamamoto, Nana; Asami, Koji
2015-06-01
Numerical calculations were carried out by the finite difference method using three-dimensional models to examine effects of the structure of skeletal muscle on the frequency-dependence of its electrical admittance Y and impedance Z in transversal and longitudinal directions. In the models, the muscle cell was represented by a rectangular solid surrounded by a smooth surface membrane, and the cells were assumed to be distributed periodically. The width of the cross section of the cell, thickness of the intercellular medium, and the relative permittivities and the conductivities of the cell interior, the intercellular medium and the surface membrane were changed. Based on the results of the calculations, reported changes in Y and Z of the muscles from 1 kHz to 1 MHz were analyzed. The analyses revealed that a decreased cell radius was reasonable to explain the Y and Z of the muscles of immature rats, rats subjected to sciatic nerve crush at chronic stage and the amyotrophic lateral sclerosis (ALS) mice. Changes in Y and Z due to the sciatic nerve crush at acute stage were attributable to the decreased cell radius, the increased space between the cells, the increased permittivity of the surface membrane and the increased conductivity of the cell interior. The changes in Z due to contraction were explained by the changes in the cell radius, and the conductivities of the cell interior and the intercellular medium. The changes in Z of meat due to aging were compared with the effects of the increase in the conductivity of the surface membrane.
NASA Technical Reports Server (NTRS)
Rizk, Magdi H.
1988-01-01
This user's manual is presented for an aerodynamic optimization program that updates flow variables and design parameters simultaneously. The program was developed for solving constrained optimization problems in which the objective function and the constraint function are dependent on the solution of the nonlinear flow equations. The program was tested by applying it to the problem of optimizing propeller designs. Some reference to this particular application is therefore made in the manual. However, the optimization scheme is suitable for application to general aerodynamic design problems. A description of the approach used in the optimization scheme is first presented, followed by a description of the use of the program.
Aerodynamic Loads Induced by a Rotor on a Body of Revolution
NASA Technical Reports Server (NTRS)
Smith, Charles A.; Betzina, Mark D.
1986-01-01
A wind-tunnel investigation was conducted in which aerodynamic loads were measured on a small-scale helicopter rotor and a body of revolution located close to it as an idealized model of a fuselage. The objective was to study the aerodynamic interactions as a function of forward speed, rotor thrust, and rotor/body position. Results show that body loads, normalized by rotor thrust, are functions of the ratio between free-stream velocity and the hover-induced velocity predicted by momentum theory.
Missile Aerodynamics for Ascent and Re-entry
NASA Technical Reports Server (NTRS)
Watts, Gaines L.; McCarter, James W.
2012-01-01
Aerodynamic force and moment equations are developed for 6-DOF missile simulations of both the ascent phase of flight and a tumbling re-entry. The missile coordinate frame (M frame) and a frame parallel to the M frame were used for formulating the aerodynamic equations. The missile configuration chosen as an example is a cylinder with fixed fins and a nose cone. The equations include both the static aerodynamic coefficients and the aerodynamic damping derivatives. The inclusion of aerodynamic damping is essential for simulating a tumbling re-entry. Appended information provides insight into aerodynamic damping.
Aerodynamic Simulation of Ice Accretion on Airfoils
NASA Technical Reports Server (NTRS)
Broeren, Andy P.; Addy, Harold E., Jr.; Bragg, Michael B.; Busch, Greg T.; Montreuil, Emmanuel
2011-01-01
This report describes recent improvements in aerodynamic scaling and simulation of ice accretion on airfoils. Ice accretions were classified into four types on the basis of aerodynamic effects: roughness, horn, streamwise, and spanwise ridge. The NASA Icing Research Tunnel (IRT) was used to generate ice accretions within these four types using both subscale and full-scale models. Large-scale, pressurized windtunnel testing was performed using a 72-in.- (1.83-m-) chord, NACA 23012 airfoil model with high-fidelity, three-dimensional castings of the IRT ice accretions. Performance data were recorded over Reynolds numbers from 4.5 x 10(exp 6) to 15.9 x 10(exp 6) and Mach numbers from 0.10 to 0.28. Lower fidelity ice-accretion simulation methods were developed and tested on an 18-in.- (0.46-m-) chord NACA 23012 airfoil model in a small-scale wind tunnel at a lower Reynolds number. The aerodynamic accuracy of the lower fidelity, subscale ice simulations was validated against the full-scale results for a factor of 4 reduction in model scale and a factor of 8 reduction in Reynolds number. This research has defined the level of geometric fidelity required for artificial ice shapes to yield aerodynamic performance results to within a known level of uncertainty and has culminated in a proposed methodology for subscale iced-airfoil aerodynamic simulation.
NASA Technical Reports Server (NTRS)
Schiff, L. B.
1974-01-01
Concepts from the theory of functionals are used to develop nonlinear formulations of the aerodynamic force and moment systems acting on bodies in large-amplitude, arbitrary motions. The analysis, which proceeds formally once the functional dependence of the aerodynamic reactions upon the motion variables is established, ensures the inclusion, within the resulting formulation, of pertinent aerodynamic terms that normally are excluded in the classical treatment. Applied to the large-amplitude, slowly varying, nonplanar motion of a body, the formulation suggests that the aerodynamic moment can be compounded of the moments acting on the body in four basic motions: steady angle of attack, pitch oscillations, either roll or yaw oscillations, and coning motion. Coning, where the nose of the body describes a circle around the velocity vector, characterizes the nonplanar nature of the general motion.
NASA Technical Reports Server (NTRS)
Rajkumar, T.; Aragon, Cecilia; Bardina, Jorge; Britten, Roy
2002-01-01
A fast, reliable way of predicting aerodynamic coefficients is produced using a neural network optimized by a genetic algorithm. Basic aerodynamic coefficients (e.g. lift, drag, pitching moment) are modelled as functions of angle of attack and Mach number. The neural network is first trained on a relatively rich set of data from wind tunnel tests of numerical simulations to learn an overall model. Most of the aerodynamic parameters can be well-fitted using polynomial functions. A new set of data, which can be relatively sparse, is then supplied to the network to produce a new model consistent with the previous model and the new data. Because the new model interpolates realistically between the sparse test data points, it is suitable for use in piloted simulations. The genetic algorithm is used to choose a neural network architecture to give best results, avoiding over-and under-fitting of the test data.
Moisture-dependent frictional and aerodynamic properties of safflower seeds
NASA Astrophysics Data System (ADS)
Kara, M.; Bastaban, S.; Öztürk, I.; Kalkan, F.; Yildiz, C.
2012-04-01
The seeds of two safflower cultivars were investigated in order to determine their frictional and aerodynamic properties as a function of moisture content. The coefficients of dynamic friction of cultivars on aluminium, plywood, fibreglass and steel surfaces increased by 87, 56, 78, and 129% for cv. Remzibey-05 seed, and by 91, 31, 71, and 131% for cv. Dinçer seed, respectively, between the initial and final moisture content levels. The terminal velocities of the Remzibey-05 and Dinçer seeds increased by 15 and 11%, respectively, with increase in moisture content between the initial and final levels.
Genetic Evolution of Shape-Altering Programs for Supersonic Aerodynamics
NASA Technical Reports Server (NTRS)
Kennelly, Robert A., Jr.; Bencze, Daniel P. (Technical Monitor)
2002-01-01
Two constrained shape optimization problems relevant to aerodynamics are solved by genetic programming, in which a population of computer programs evolves automatically under pressure of fitness-driven reproduction and genetic crossover. Known optimal solutions are recovered using a small, naive set of elementary operations. Effectiveness is improved through use of automatically defined functions, especially when one of them is capable of a variable number of iterations, even though the test problems lack obvious exploitable regularities. An attempt at evolving new elementary operations was only partially successful.
Aerodynamic optimum design of transonic turbine cascades using Genetic Algorithms
NASA Astrophysics Data System (ADS)
Li, Jun; Feng, Zhenping; Chang, Jianzhong; Shen, Zuda
1997-06-01
This paper presents an aerodynamic optimum design method for transonic turbine cascades based on the Genetic Algorithms coupled to the inviscid flow Euler solver and the boundary-layer calculation. The Genetic Algorithms control the evolution of a population of cascades towards an optimum design. The fitness value of each string is evaluated using the flow solver. The design procedure has been developed and the behavior of the genetic algorithms has been tested. The objective functions of the design examples are the minimum mean-square deviation between the aimed pressure and computed pressure and the minimum amount of user expertise.
Aerodynamic Design on Unstructured Grids for Turbulent Flows
NASA Technical Reports Server (NTRS)
Anderson, W. Kyle; Bonhaus, Daryl L.
1997-01-01
An aerodynamic design algorithm for turbulent flows using unstructured grids is described. The current approach uses adjoint (costate) variables for obtaining derivatives of the cost function. The solution of the adjoint equations is obtained using an implicit formulation in which the turbulence model is fully coupled with the flow equations when solving for the costate variables. The accuracy of the derivatives is demonstrated by comparison with finite-difference gradients and a few example computations are shown. In addition, a user interface is described which significantly reduces the time required for setting up the design problems. Recommendations on directions of further research into the Navier Stokes design process are made.
Position control optimization of aerodynamic brake device for high-speed trains
NASA Astrophysics Data System (ADS)
Zuo, Jianyong; Luo, Zhuojun; Chen, Zhongkai
2014-03-01
The aerodynamic braking is a clean and non-adhesion braking, and can be used to provide extra braking force during high-speed emergency braking. The research of aerodynamic braking has attracted more and more attentions in recent years. However, most researchers in this field focus on aerodynamic effects and seldom on issues of position control of the aerodynamic braking board. The purpose of this paper is to explore position control optimization of the braking board in an aerodynamic braking prototype. The mathematical models of the hydraulic drive unit in the aerodynamic braking system are analyzed in detail, and the simulation models are established. Three control functions—constant, linear, and quadratic—are explored. Two kinds of criteria, including the position steady-state error and the acceleration of the piston rod, are used to evaluate system performance. Simulation results show that the position steady state-error is reduced from around 12-2 mm by applying a linear instead of a constant function, while the acceleration is reduced from 25.71-3.70 m/s2 with a quadratic control function. Use of the quadratic control function is shown to improve system performance. Experimental results obtained by measuring the position response of the piston rod on a test-bench also suggest a reduced position error and smooth movement of the piston rod. This implies that the acceleration is smaller when using the quadratic function, thus verifying the effectiveness of control schemes to improve to system performance. This paper proposes an effective and easily implemented control scheme that improves the position response of hydraulic cylinders during position control.
Turbine disk cavity aerodynamics and heat transfer
NASA Astrophysics Data System (ADS)
Johnson, B. V.; Daniels, W. A.
1992-07-01
Experiments were conducted to define the nature of the aerodynamics and heat transfer for the flow within the disk cavities and blade attachments of a large-scale model, simulating the Space Shuttle Main Engine (SSME) turbopump drive turbines. These experiments of the aerodynamic driving mechanisms explored the following: (1) flow between the main gas path and the disk cavities; (2) coolant flow injected into the disk cavities; (3) coolant density; (4) leakage flows through the seal between blades; and (5) the role that each of these various flows has in determining the adiabatic recovery temperature at all of the critical locations within the cavities. The model and the test apparatus provide close geometrical and aerodynamic simulation of all the two-stage cavity flow regions for the SSME High Pressure Fuel Turbopump and the ability to simulate the sources and sinks for each cavity flow.
Aerodynamics of magnetic levitation (MAGLEV) trains
NASA Technical Reports Server (NTRS)
Schetz, Joseph A.; Marchman, James F., III
1996-01-01
High-speed (500 kph) trains using magnetic forces for levitation, propulsion and control offer many advantages for the nation and a good opportunity for the aerospace community to apply 'high tech' methods to the domestic sector. One area of many that will need advanced research is the aerodynamics of such MAGLEV (Magnetic Levitation) vehicles. There are important issues with regard to wind tunnel testing and the application of CFD to these devices. This talk will deal with the aerodynamic design of MAGLEV vehicles with emphasis on wind tunnel testing. The moving track facility designed and constructed in the 6 ft. Stability Wind Tunnel at Virginia Tech will be described. Test results for a variety of MAGLEV vehicle configurations will be presented. The last topic to be discussed is a Multi-disciplinary Design approach that is being applied to MAGLEV vehicle configuration design including aerodynamics, structures, manufacturability and life-cycle cost.
Physics of badminton shuttlecocks. Part 1 : aerodynamics
NASA Astrophysics Data System (ADS)
Cohen, Caroline; Darbois Texier, Baptiste; Quéré, David; Clanet, Christophe
2011-11-01
We study experimentally shuttlecocks dynamics. In this part we show that shuttlecock trajectory is highly different from classical parabola. When one takes into account the aerodynamic drag, the flight of the shuttlecock quickly curves downwards and almost reaches a vertical asymptote. We solve the equation of motion with gravity and drag at high Reynolds number and find an analytical expression of the reach. At high velocity, this reach does not depend on velocity anymore. Even if you develop your muscles you will not manage to launch the shuttlecock very far because of the ``aerodynamic wall.'' As a consequence you can predict the length of the field. We then discuss the extend of the aerodynamic wall to other projectiles like sports balls and its importance.
Miniature Trailing Edge Effector for Aerodynamic Control
NASA Technical Reports Server (NTRS)
Lee, Hak-Tae (Inventor); Bieniawski, Stefan R. (Inventor); Kroo, Ilan M. (Inventor)
2008-01-01
Improved miniature trailing edge effectors for aerodynamic control are provided. Three types of devices having aerodynamic housings integrated to the trailing edge of an aerodynamic shape are presented, which vary in details of how the control surface can move. A bucket type device has a control surface which is the back part of a C-shaped member having two arms connected by the back section. The C-shaped section is attached to a housing at the ends of the arms, and is rotatable about an axis parallel to the wing trailing edge to provide up, down and neutral states. A flip-up type device has a control surface which rotates about an axis parallel to the wing trailing edge to provide up, down, neutral and brake states. A rotating type device has a control surface which rotates about an axis parallel to the chord line to provide up, down and neutral states.
Aerodynamic tests of Darrieus wind turbine blades
Migliore, P.G.; Walters, R.E.; Wolfe, W.P.
1983-03-01
An indoor facility for the aerodynamic testing of Darrieus turbine blades was developed. Lift, drag, and moment coefficients were measured for two blades whose angle of attack and chord-to-radius ratio were varied. The first blade used an NACA 0015 airfoil section; the second used a 15% elliptical cross section with a modified circular arc trailing edge. Blade aerodynamic coefficients were corrected to section coefficients for comparison to published rectilinear flow data. Although the airfoil sections were symmetrical, moment coefficients were not zero and the lift and drag curves were asymmetrical about zero lift coefficient and angle of attack. These features verified the predicted virtual camber and incidence phenomena. Boundary-layer centrifugal effects were manifested by discontinuous lift curves and large differences in the angle of zero lift between th NACA 0015 and elliptical airfoils. It was concluded that rectilinear flow aerodynamic data are not applicable to Darrieus turbine blades, even for small chord-to-radius ratios.
History of the numerical aerodynamic simulation program
NASA Technical Reports Server (NTRS)
Peterson, Victor L.; Ballhaus, William F., Jr.
1987-01-01
The Numerical Aerodynamic Simulation (NAS) program has reached a milestone with the completion of the initial operating configuration of the NAS Processing System Network. This achievement is the first major milestone in the continuing effort to provide a state-of-the-art supercomputer facility for the national aerospace community and to serve as a pathfinder for the development and use of future supercomputer systems. The underlying factors that motivated the initiation of the program are first identified and then discussed. These include the emergence and evolution of computational aerodynamics as a powerful new capability in aerodynamics research and development, the computer power required for advances in the discipline, the complementary nature of computation and wind tunnel testing, and the need for the government to play a pathfinding role in the development and use of large-scale scientific computing systems. Finally, the history of the NAS program is traced from its inception in 1975 to the present time.
Wind turbine aerodynamics research needs assessment
NASA Astrophysics Data System (ADS)
Stoddard, F. S.; Porter, B. K.
1986-01-01
A prioritized list is developed for wind turbine aerodynamic research needs and opportunities which could be used by the Department of Energy program management team in detailing the DOE Five-Year Wind Turbine Research Plan. The focus of the Assessment was the basic science of aerodynamics as applied to wind turbines, including all relevant phenomena, such as turbulence, dynamic stall, three-dimensional effects, viscosity, wake geometry, and others which influence aerodynamic understanding and design. The study was restricted to wind turbines that provide electrical energy compatible with the utility grid, and included both horizontal axis wind turbines (HAWT) and vertical axis wind turbines (VAWT). Also, no economic constraints were imposed on the design concepts or recommendations since the focus of the investigation was purely scientific.
Photogrammetry of a Hypersonic Inflatable Aerodynamic Decelerator
NASA Technical Reports Server (NTRS)
Kushner, Laura Kathryn; Littell, Justin D.; Cassell, Alan M.
2013-01-01
In 2012, two large-scale models of a Hypersonic Inflatable Aerodynamic decelerator were tested in the National Full-Scale Aerodynamic Complex at NASA Ames Research Center. One of the objectives of this test was to measure model deflections under aerodynamic loading that approximated expected flight conditions. The measurements were acquired using stereo photogrammetry. Four pairs of stereo cameras were mounted inside the NFAC test section, each imaging a particular section of the HIAD. The views were then stitched together post-test to create a surface deformation profile. The data from the photogram- metry system will largely be used for comparisons to and refinement of Fluid Structure Interaction models. This paper describes how a commercial photogrammetry system was adapted to make the measurements and presents some preliminary results.
Aerodynamic optimization studies on advanced architecture computers
NASA Technical Reports Server (NTRS)
Chawla, Kalpana
1995-01-01
The approach to carrying out multi-discipline aerospace design studies in the future, especially in massively parallel computing environments, comprises of choosing (1) suitable solvers to compute solutions to equations characterizing a discipline, and (2) efficient optimization methods. In addition, for aerodynamic optimization problems, (3) smart methodologies must be selected to modify the surface shape. In this research effort, a 'direct' optimization method is implemented on the Cray C-90 to improve aerodynamic design. It is coupled with an existing implicit Navier-Stokes solver, OVERFLOW, to compute flow solutions. The optimization method is chosen such that it can accomodate multi-discipline optimization in future computations. In the work , however, only single discipline aerodynamic optimization will be included.
NASA Astrophysics Data System (ADS)
Lee, J. H.; Timmermans, J.; Su, Z.; Mancini, M.
2012-04-01
Aerodynamic roughness height (Zom) is a key parameter required in land surface hydrological model, since errors in heat flux estimations are largely dependent on accurate optimization of this parameter. Despite its significance, it remains an uncertain parameter that is not easily determined. This is mostly because of non-linear relationship in Monin-Obukhov Similarity (MOS) and unknown vertical characteristic of vegetation. Previous studies determined aerodynamic roughness using traditional wind profile method, remotely sensed vegetation index, minimization of cost function over MOS relationship or linear regression. However, these are complicated procedures that presume high accuracy for several other related parameters embedded in MOS equations. In order to simplify a procedure and reduce the number of parameters in need, this study suggests a new approach to extract aerodynamic roughness parameter via Ensemble Kalman Filter (EnKF) that affords non-linearity and that requires only single or two heat flux measurement. So far, to our knowledge, no previous study has applied EnKF to aerodynamic roughness estimation, while a majority of data assimilation study has paid attention to land surface state variables such as soil moisture or land surface temperature. This approach was applied to grassland in semi-arid Tibetan area and maize on moderately wet condition in Italy. It was demonstrated that aerodynamic roughness parameter can inversely be tracked from data assimilated heat flux analysis. The aerodynamic roughness height estimated in this approach was consistent with eddy covariance result and literature value. Consequently, this newly estimated input adjusted the sensible heat overestimated and latent heat flux underestimated by the original Surface Energy Balance System (SEBS) model, suggesting better heat flux estimation especially during the summer Monsoon period. The advantage of this approach over other methodologies is that aerodynamic roughness height
Airfoil Ice-Accretion Aerodynamics Simulation
NASA Technical Reports Server (NTRS)
Bragg, Michael B.; Broeren, Andy P.; Addy, Harold E.; Potapczuk, Mark G.; Guffond, Didier; Montreuil, E.
2007-01-01
NASA Glenn Research Center, ONERA, and the University of Illinois are conducting a major research program whose goal is to improve our understanding of the aerodynamic scaling of ice accretions on airfoils. The program when it is completed will result in validated scaled simulation methods that produce the essential aerodynamic features of the full-scale iced-airfoil. This research will provide some of the first, high-fidelity, full-scale, iced-airfoil aerodynamic data. An initial study classified ice accretions based on their aerodynamics into four types: roughness, streamwise ice, horn ice, and spanwise-ridge ice. Subscale testing using a NACA 23012 airfoil was performed in the NASA IRT and University of Illinois wind tunnel to better understand the aerodynamics of these ice types and to test various levels of ice simulation fidelity. These studies are briefly reviewed here and have been presented in more detail in other papers. Based on these results, full-scale testing at the ONERA F1 tunnel using cast ice shapes obtained from molds taken in the IRT will provide full-scale iced airfoil data from full-scale ice accretions. Using these data as a baseline, the final step is to validate the simulation methods in scale in the Illinois wind tunnel. Computational ice accretion methods including LEWICE and ONICE have been used to guide the experiments and are briefly described and results shown. When full-scale and simulation aerodynamic results are available, these data will be used to further develop computational tools. Thus the purpose of the paper is to present an overview of the program and key results to date.
Method of reducing drag in aerodynamic systems
NASA Technical Reports Server (NTRS)
Hrach, Frank J. (Inventor)
1993-01-01
In the present method, boundary layer thickening is combined with laminar flow control to reduce drag. An aerodynamic body is accelerated enabling a ram turbine on the body to receive air at velocity V sub 0. The discharge air is directed over an aft portion of the aerodynamic body producing boundary layer thickening. The ram turbine also drives a compressor by applying torque to a shaft connected between the ram turbine and the compressor. The compressor sucks in lower boundary layer air through inlets in the shell of the aircraft producing laminar flow control and reducing drag. The discharge from the compressor is expanded in a nozzle to produce thrust.
Air flow testing on aerodynamic truck
NASA Technical Reports Server (NTRS)
1975-01-01
After leasing a cab-over tractor-trailer from a Southern California firm, Dryden researchers added sheet metal modifications like those shown here. They rounded the front corners and edges, and placed a smooth fairing on the cab's roofs and sides extending back to the trailer. During the investigation of truck aerodynamics, the techniques honed in flight research proved highly applicable. By closing the gap between the cab and the trailer, for example, researchers discovered a significant reduction in aerodynamic drag, one resulting in 20 to 25 percent less fuel consumption than the standard design. Many truck manufacturers subsequently incorporated similar modifications on their products.
Unstructured mesh algorithms for aerodynamic calculations
NASA Technical Reports Server (NTRS)
Mavriplis, D. J.
1992-01-01
The use of unstructured mesh techniques for solving complex aerodynamic flows is discussed. The principle advantages of unstructured mesh strategies, as they relate to complex geometries, adaptive meshing capabilities, and parallel processing are emphasized. The various aspects required for the efficient and accurate solution of aerodynamic flows are addressed. These include mesh generation, mesh adaptivity, solution algorithms, convergence acceleration, and turbulence modeling. Computations of viscous turbulent two-dimensional flows and inviscid three-dimensional flows about complex configurations are demonstrated. Remaining obstacles and directions for future research are also outlined.
Techniques for estimating Space Station aerodynamic characteristics
NASA Technical Reports Server (NTRS)
Thomas, Richard E.
1993-01-01
A method was devised and calculations were performed to determine the effects of reflected molecules on the aerodynamic force and moment coefficients for a body in free molecule flow. A procedure was developed for determining the velocity and temperature distributions of molecules reflected from a surface of arbitrary momentum and energy accommodation. A system of equations, based on momentum and energy balances for the surface, incident, and reflected molecules, was solved by a numerical optimization technique. The minimization of a 'cost' function, developed from the set of equations, resulted in the determination of the defining properties of the flow reflected from the arbitrary surface. The properties used to define both the incident and reflected flows were: average temperature of the molecules in the flow, angle of the flow with respect to a vector normal to the surface, and the molecular speed ratio. The properties of the reflected flow were used to calculate the contribution of multiply reflected molecules to the force and moments on a test body in the flow. The test configuration consisted of two flat plates joined along one edge at a right angle to each other. When force and moment coefficients of this 90 deg concave wedge were compared to results that did not include multiple reflections, it was found that multiple reflections could nearly double lift and drag coefficients, with nearly a 50 percent increase in pitching moment for cases with specular or nearly specular accommodation. The cases of diffuse or nearly diffuse accommodation often had minor reductions in axial and normal forces when multiple reflections were included. There were several cases of intermediate accommodation where the addition of multiple reflection effects more than tripled the lift coefficient over the convex technique.
Aerodynamic Modeling for Aircraft in Unsteady Flight Conditions
NASA Technical Reports Server (NTRS)
Lan, C. Edward
2000-01-01
This report summarizes the activities in unsteady aerodynamic modeling and application of unsteady aerodynamic models to flight dynamics. A public on briefing was presented on July 21, 1999 at Langley Research Center.
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.
Nonlinear problems in flight dynamics involving aerodynamic bifurcations
NASA Technical Reports Server (NTRS)
Tobak, M.; Chapman, G. T.
1985-01-01
Aerodynamic bifurcation is defined as the replacement of an unstable equilibrium flow by a new stable equilibrium flow at a critical value of a parameter. A mathematical model of the aerodynamic contribution to the aircraft's equations of motion is amended to accommodate aerodynamic bifurcations. Important bifurcations such as, the onset of large-scale vortex-shedding are defined. The amended mathematical model is capable of incorporating various forms of aerodynamic responses, including those associated with dynamic stall of airfoils.
Index for aerodynamic data from the Bumblebee program
NASA Technical Reports Server (NTRS)
Cronvich, L. L.; Barnes, G. A.
1978-01-01
The Bumblebee program, was designed to provide a supersonic guided missile. The aerodynamics program included a fundamental research effort in supersonic aerodynamics as well as a design task in developing both test vehicles and prototypes of tactical missiles. An index of aerodynamic missile data developed in this program is presented.
14 CFR 25.445 - Auxiliary aerodynamic surfaces.
Code of Federal Regulations, 2010 CFR
2010-01-01
... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Auxiliary aerodynamic surfaces. 25.445... AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Structure Control Surface and System Loads § 25.445 Auxiliary aerodynamic surfaces. (a) When significant, the aerodynamic influence...
14 CFR 25.445 - Auxiliary aerodynamic surfaces.
Code of Federal Regulations, 2011 CFR
2011-01-01
... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Auxiliary aerodynamic surfaces. 25.445... AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Structure Control Surface and System Loads § 25.445 Auxiliary aerodynamic surfaces. (a) When significant, the aerodynamic influence...
Identification of Linear and Nonlinear Aerodynamic Impulse Responses Using Digital Filter Techniques
NASA Technical Reports Server (NTRS)
Silva, Walter A.
1997-01-01
This paper discusses the mathematical existence and the numerically-correct identification of linear and nonlinear aerodynamic impulse response functions. Differences between continuous-time and discrete-time system theories, which permit the identification and efficient use of these functions, will be detailed. Important input/output definitions and the concept of linear and nonlinear systems with memory will also be discussed. It will be shown that indicial (step or steady) responses (such as Wagner's function), forced harmonic responses (such as Tbeodorsen's function or those from doublet lattice theory), and responses to random inputs (such as gusts) can all be obtained from an aerodynamic impulse response function. This paper establishes the aerodynamic impulse response function as the most fundamental, and, therefore, the most computationally efficient, aerodynamic function that can be extracted from any given discrete-time, aerodynamic system. The results presented in this paper help to unify the understanding of classical two-dimensional continuous-time theories with modem three-dimensional, discrete-time theories. First, the method is applied to the nonlinear viscous Burger's equation as an example. Next the method is applied to a three-dimensional aeroelastic model using the CAP-TSD (Computational Aeroelasticity Program - Transonic Small Disturbance) code and then to a two-dimensional model using the CFL3D Navier-Stokes code. Comparisons of accuracy and computational cost savings are presented. Because of its mathematical generality, an important attribute of this methodology is that it is applicable to a wide range of nonlinear, discrete-time problems.
Identification of Linear and Nonlinear Aerodynamic Impulse Responses Using Digital Filter Techniques
NASA Technical Reports Server (NTRS)
Silva, Walter A.
1997-01-01
This paper discusses the mathematical existence and the numerically-correct identification of linear and nonlinear aerodynamic impulse response functions. Differences between continuous-time and discrete-time system theories, which permit the identification and efficient use of these functions, will be detailed. Important input/output definitions and the concept of linear and nonlinear systems with memory will also be discussed. It will be shown that indicial (step or steady) responses (such as Wagner's function), forced harmonic responses (such as Theodorsen's function or those from doublet lattice theory), and responses to random inputs (such as gusts) can all be obtained from an aerodynamic impulse response function. This paper establishes the aerodynamic impulse response function as the most fundamental, and, therefore, the most computationally efficient, aerodynamic function that can be extracted from any given discrete-time, aerodynamic system. The results presented in this paper help to unify the understanding of classical two-dimensional continuous-time theories with modern three-dimensional, discrete-time theories. First, the method is applied to the nonlinear viscous Burger's equation as an example. Next the method is applied to a three-dimensional aeroelastic model using the CAP-TSD (Computational Aeroelasticity Program - Transonic Small Disturbance) code and then to a two-dimensional model using the CFL3D Navier-Stokes code. Comparisons of accuracy and computational cost savings are presented. Because of its mathematical generality, an important attribute of this methodology is that it is applicable to a wide range of nonlinear, discrete-time problems.
The linear and non-linear aerodynamics of three-surface aircraft concepts
NASA Technical Reports Server (NTRS)
Agnew, J. W.; Lyerla, G. W.; Grafton, S. B.
1980-01-01
It is noted that most modern fighter aircraft rely on vortex interaction to provide lift enhancement at maneuvering angles of attack. It is shown that the close-coupled horizontal canard in a three-surface configuration provides a control surface which in addition to its other control functions, can be used to optimize this vortex interaction. Attention is given to a study intended to provide a detailed understanding of the aerodynamics of this type of configuration. The discussion examines the results of this investigation and hypotheses are presented to explain the linear and nonlinear aerodynamic phenomena observed.
Real-time estimation of aerodynamic features for ambulatory voice biofeedback
Llico, Andrés F.; Zañartu, Matías; González, Agustín J.; Wodicka, George R.; Mehta, Daryush D.; Van Stan, Jarrad H.; Hillman, Robert E.
2015-01-01
The development of ambulatory voice monitoring devices has the potential to improve the diagnosis and treatment of voice disorders. In this proof-of-concept study, real-time biofeedback is incorporated into a smartphone-based platform that records and processes neck surface acceleration. The focus is on utilizing aerodynamic measures of vocal function as a basis for biofeedback. This is done using regressed Z-scores to compare recorded values to normative estimates based on sound pressure level and fundamental frequency. Initial results from the analysis of different voice qualities suggest that accelerometer-based estimates of aerodynamic parameters can be used for real-time ambulatory biofeedback. PMID:26233054
NASA Technical Reports Server (NTRS)
Green, F. M.; Resnick, D. R.
1979-01-01
An FMP (Flow Model Processor) was designed for use in the Numerical Aerodynamic Simulation Facility (NASF). The NASF was developed to simulate fluid flow over three-dimensional bodies in wind tunnel environments and in free space. The facility is applicable to studying aerodynamic and aircraft body designs. The following general topics are discussed in this volume: (1) FMP functional computer specifications; (2) FMP instruction specification; (3) standard product system components; (4) loosely coupled network (LCN) specifications/description; and (5) three appendices: performance of trunk allocation contention elimination (trace) method, LCN channel protocol and proposed LCN unified second level protocol.
NASA Astrophysics Data System (ADS)
Wang, Z. Jane; Russell, David
2007-10-01
Dragonflies are four-winged insects that have the ability to control aerodynamic performance by modulating the phase lag (ϕ) between forewings and hindwings. We film the wing motion of a tethered dragonfly and compute the aerodynamic force and power as a function of the phase. We find that the out-of-phase motion as seen in steady hovering uses nearly minimal power to generate the required force to balance the weight, and the in-phase motion seen in takeoffs provides an additional force to accelerate. We explain the main hydrodynamic interaction that causes this phase dependence.
Wind Tunnel Measurements and Calculations of Aerodynamic Interactions Between Tiltrotor Aircraft
NASA Technical Reports Server (NTRS)
Johnson, Wayne; Yamauchi, Gloria K.; Derby, Michael R.; Wadcock, Alan J.
2002-01-01
Wind tunnel measurements and calculations of the aerodynamic interactions between two tiltrotor aircraft in helicopter mode are presented. The measured results include the roll moment and thrust change on the downwind aircraft, as a function of the upwind aircraft position (longitudinal, lateral, and vertical). Magnitudes and locations of the largest interactions are identified. The calculated interactions generally match the measurements, with discrepancies attributed to the unsteadiness of the wake and aerodynamic forces on the airframe. To interpret the interactions in terms of control and power changes on the aircraft, additional calculations are presented for trimmed aircraft with gimballed rotors.
NWTC Aerodynamics Studies Improve Energy Capture and Lower Costs of Wind-Generated Electricity
2015-08-01
Researchers at the National Wind Technology Center (NWTC) at the National Renewable Energy Laboratory (NREL) have expanded wind turbine aerodynamic research from blade and rotor aerodynamics to wind plant and atmospheric inflow effects. The energy capture from wind plants is dependent on all of these aerodynamic interactions. Research at the NWTC is crucial to understanding how wind turbines function in large, multiple-row wind plants. These conditions impact the cumulative fatigue damage of turbine structural components that ultimately effect the useful lifetime of wind turbines. This work also is essential for understanding and maximizing turbine and wind plant energy production. Both turbine lifetime and wind plant energy production are key determinants of the cost of wind-generated electricity.
Real-Time Onboard Global Nonlinear Aerodynamic Modeling from Flight Data
NASA Technical Reports Server (NTRS)
Brandon, Jay M.; Morelli, Eugene A.
2014-01-01
Flight test and modeling techniques were developed to accurately identify global nonlinear aerodynamic models onboard an aircraft. The techniques were developed and demonstrated during piloted flight testing of an Aermacchi MB-326M Impala jet aircraft. Advanced piloting techniques and nonlinear modeling techniques based on fuzzy logic and multivariate orthogonal function methods were implemented with efficient onboard calculations and flight operations to achieve real-time maneuver monitoring and analysis, and near-real-time global nonlinear aerodynamic modeling and prediction validation testing in flight. Results demonstrated that global nonlinear aerodynamic models for a large portion of the flight envelope were identified rapidly and accurately using piloted flight test maneuvers during a single flight, with the final identified and validated models available before the aircraft landed.
Development of the Orion Crew Module Static Aerodynamic Database. Par 2; Supersonic/Subsonic
NASA Technical Reports Server (NTRS)
Bibb, Karen L.; Walker, Eric L.; Brauckmann, Gregory J.; Robinson, Phil
2011-01-01
This work describes the process of developing the nominal static aerodynamic coefficients and associated uncertainties for the Orion Crew Module for Mach 8 and below. The database was developed from wind tunnel test data and computational simulations of the smooth Crew Module geometry, with no asymmetries or protuberances. The database covers the full range of Reynolds numbers seen in both entry and ascent abort scenarios. The basic uncertainties were developed as functions of Mach number and total angle of attack from variations in the primary data as well as computations at lower Reynolds numbers, on the baseline geometry, and using different flow solvers. The resulting aerodynamic database represents the Crew Exploration Vehicle Aerosciences Project's best estimate of the nominal aerodynamics for the current Crew Module vehicle.
An analytical technique for approximating unsteady aerodynamics in the time domain
NASA Technical Reports Server (NTRS)
Dunn, H. J.
1980-01-01
An analytical technique is presented for approximating unsteady aerodynamic forces in the time domain. The order of elements of a matrix Pade approximation was postulated, and the resulting polynomial coefficients were determined through a combination of least squares estimates for the numerator coefficients and a constrained gradient search for the denominator coefficients which insures stable approximating functions. The number of differential equations required to represent the aerodynamic forces to a given accuracy tends to be smaller than that employed in certain existing techniques where the denominator coefficients are chosen a priori. Results are shown for an aeroelastic, cantilevered, semispan wing which indicate a good fit to the aerodynamic forces for oscillatory motion can be achieved with a matrix Pade approximation having fourth order numerator and second order denominator polynomials.
AERODYNAMIC CLASSIFICATION OF FIBERS WITH AEROSOL CENTRIFUGES
The constituent particles of many ambient and workplace aerosols of health effects concerns are of fibrous and aggregate geometric shapes. he sites of deposition in the human respiratory system are primarily related to the mass median aerodynamic diameters of inhaled particle siz...
AWT aerodynamic design status. [Altitude Wind Tunnel
NASA Technical Reports Server (NTRS)
Davis, Milt W.
1984-01-01
The aerodynamic design of the NASA Altitude Wind Tunnel is presented in viewgraph format. The main topics covered are: analysis of a plenum evacuation system; airline definition and pressure loss code development; contraction geometry and code analysis; and design of the two stage fan. Flow characteristics such as pressure ratio, mach number distribution, adiabatic efficiency, and losses are shown.
An aerodynamic load criterion for airships
NASA Technical Reports Server (NTRS)
Woodward, D. E.
1975-01-01
A simple aerodynamic bending moment envelope is derived for conventionally shaped airships. This criterion is intended to be used, much like the Naval Architect's standard wave, for preliminary estimates of longitudinal strength requirements. It should be useful in tradeoff studies between speed, fineness ratio, block coefficient, structure weight, and other such general parameters of airship design.
Aerodynamics of high frequency flapping wings
NASA Astrophysics Data System (ADS)
Hu, Zheng; Roll, Jesse; Cheng, Bo; Deng, Xinyan
2010-11-01
We investigated the aerodynamic performance of high frequency flapping wings using a 2.5 gram robotic insect mechanism developed in our lab. The mechanism flaps up to 65Hz with a pair of man-made wing mounted with 10cm wingtip-to-wingtip span. The mean aerodynamic lift force was measured by a lever platform, and the flow velocity and vorticity were measured using a stereo DPIV system in the frontal, parasagittal, and horizontal planes. Both near field (leading edge vortex) and far field flow (induced flow) were measured with instantaneous and phase-averaged results. Systematic experiments were performed on the man-made wings, cicada and hawk moth wings due to their similar size, frequency and Reynolds number. For insect wings, we used both dry and freshly-cut wings. The aerodynamic force increase with flapping frequency and the man-made wing generates more than 4 grams of lift at 35Hz with 3 volt input. Here we present the experimental results and the major differences in their aerodynamic performances.
User's guide to program FLEXSTAB. [aerodynamics
NASA Technical Reports Server (NTRS)
Cavin, R. K., III; Colunga, D.
1975-01-01
A manual is presented for correctly submitting program runs in aerodynamics on the UNIVAC 1108 computer system. All major program modules are included. Control cards are documented for the user's convenience, and card parameters are included in order to provide some idea as to reasonable time estimates for the program modules.
Aerodynamic analysis of an isolated vehicle wheel
NASA Astrophysics Data System (ADS)
Leśniewicz, P.; Kulak, M.; Karczewski, M.
2014-08-01
Increasing fuel prices force the manufacturers to look into all aspects of car aerodynamics including wheels, tyres and rims in order to minimize their drag. By diminishing the aerodynamic drag of vehicle the fuel consumption will decrease, while driving safety and comfort will improve. In order to properly illustrate the impact of a rotating wheel aerodynamics on the car body, precise analysis of an isolated wheel should be performed beforehand. In order to represent wheel rotation in contact with the ground, presented CFD simulations included Moving Wall boundary as well as Multiple Reference Frame should be performed. Sliding mesh approach is favoured but too costly at the moment. Global and local flow quantities obtained during simulations were compared to an experiment in order to assess the validity of the numerical model. Results of investigation illustrates dependency between type of simulation and coefficients (drag and lift). MRF approach proved to be a better solution giving result closer to experiment. Investigation of the model with contact area between the wheel and the ground helps to illustrate the impact of rotating wheel aerodynamics on the car body.
Structural evaluation of deployable aerodynamic spike booms
NASA Technical Reports Server (NTRS)
Richter, B. J.
1975-01-01
An extendable boom consisting of a series of telescopic cylindrical tube segments and overlapping lock joints developed for use as an aerodynamic spike mounted atop a missile is described. Two candidate design concepts differing mainly in the particular overlapping lock joint designs are undergoing a combined analytical/experimental evaluation. Some of the results of this evaluation are presented.
Efficient Global Aerodynamic Modeling from Flight Data
NASA Technical Reports Server (NTRS)
Morelli, Eugene A.
2012-01-01
A method for identifying global aerodynamic models from flight data in an efficient manner is explained and demonstrated. A novel experiment design technique was used to obtain dynamic flight data over a range of flight conditions with a single flight maneuver. Multivariate polynomials and polynomial splines were used with orthogonalization techniques and statistical modeling metrics to synthesize global nonlinear aerodynamic models directly and completely from flight data alone. Simulation data and flight data from a subscale twin-engine jet transport aircraft were used to demonstrate the techniques. Results showed that global multivariate nonlinear aerodynamic dependencies could be accurately identified using flight data from a single maneuver. Flight-derived global aerodynamic model structures, model parameter estimates, and associated uncertainties were provided for all six nondimensional force and moment coefficients for the test aircraft. These models were combined with a propulsion model identified from engine ground test data to produce a high-fidelity nonlinear flight simulation very efficiently. Prediction testing using a multi-axis maneuver showed that the identified global model accurately predicted aircraft responses.
Aerodynamic drag in cycling: methods of assessment.
Debraux, Pierre; Grappe, Frederic; Manolova, Aneliya V; Bertucci, William
2011-09-01
When cycling on level ground at a speed greater than 14 m/s, aerodynamic drag is the most important resistive force. About 90% of the total mechanical power output is necessary to overcome it. Aerodynamic drag is mainly affected by the effective frontal area which is the product of the projected frontal area and the coefficient of drag. The effective frontal area represents the position of the cyclist on the bicycle and the aerodynamics of the cyclist-bicycle system in this position. In order to optimise performance, estimation of these parameters is necessary. The aim of this study is to describe and comment on the methods used during the last 30 years for the evaluation of the effective frontal area and the projected frontal area in cycling, in both laboratory and actual conditions. Most of the field methods are not expensive and can be realised with few materials, providing valid results in comparison with the reference method in aerodynamics, the wind tunnel. Finally, knowledge of these parameters can be useful in practice or to create theoretical models of cycling performance. PMID:21936289
Aerodynamic Design of Axial Flow Compressors
NASA Technical Reports Server (NTRS)
Bullock, R. O. (Editor); Johnsen, I. A.
1965-01-01
An overview of 'Aerodynamic systems design of axial flow compressors' is presented. Numerous chapters cover topics such as compressor design, ptotential and viscous flow in two dimensional cascades, compressor stall and blade vibration, and compressor flow theory. Theoretical aspects of flow are also covered.
Aerodynamic beam generator for large particles
Brockmann, John E.; Torczynski, John R.; Dykhuizen, Ronald C.; Neiser, Richard A.; Smith, Mark F.
2002-01-01
A new type of aerodynamic particle beam generator is disclosed. This generator produces a tightly focused beam of large material particles at velocities ranging from a few feet per second to supersonic speeds, depending on the exact configuration and operating conditions. Such generators are of particular interest for use in additive fabrication techniques.
Design Exploration of Aerodynamic Wing Shape for RLV Flyback Booster
NASA Astrophysics Data System (ADS)
Chiba, Kazuhisa; Obayashi, Shigeru; Nakahashi, Kazuhiro
The wing shape of flyback booster for a Two-Stage-To-Orbit reusable launch vehicle has been optimized considering four objectives. The objectives are to minimize the shift of aerodynamic center between supersonic and transonic conditions, transonic pitching moment and transonic drag coefficient, as well as to maximize subsonic lift coefficient. The three-dimensional Reynolds-averaged Navier-Stokes computation using the modified Spalart-Allmaras one-equation model is used in aerodynamic evaluation accounting for possible flow separations. Adaptive range multi-objective genetic algorithm is used for the present study because tradeoff can be obtained using a smaller number of individuals than conventional multi-objective genetic algorithms. Consequently, four-objective optimization has produced 102 non-dominated solutions, which represent tradeoff information among four objective functions. Moreover, Self-Organizing Maps have been used to analyze the present non-dominated solutions and to visualize tradeoffs and influence of design variables to the four objectives. Self-Organizing Maps contoured by the four objective functions and design variables are found to visualize tradeoffs and effects of each design variable.
Preliminary subsonic aerodynamic model for simulation studies of the HL-20 lifting body
NASA Technical Reports Server (NTRS)
Jackson, E. Bruce; Cruz, Christopher I.
1992-01-01
A nonlinear, six-degree-of-freedom aerodynamic model for an early version of the HL-20 lifting body is described and compared with wind tunnel data upon which it is based. Polynomial functions describing most of the aerodynamic parameters are given and tables of these functions are presented. Techniques used to arrive at these functions are described. Basic aerodynamic coefficients were modeled as functions of angles of attack and sideslip. Vehicle lateral symmetry was assumed. Compressibility (Mach) effects were ignored. Control-surface effectiveness was assumed to vary linearly with angle of deflection and was assumed to be invariant with the angle of sideslip. Dynamic derivatives were obtained from predictive aerodynamic codes. Landing-gear and ground effects were scaled from Space Shuttle data. The model described is provided to support pilot-in-the-loop simulation studies of the HL-20. By providing the data in tabular format, the model is suitable for the data interpolation architecture of many existing engineering simulation facilities. Because of the preliminary nature of the data, however, this model is not recommended for study of the absolute performance of the HL-20.
Aerodynamic and Nonlinear Dynamic Acoustic Analysis of Tension Asymmetry in Excised Canine Larynges
ERIC Educational Resources Information Center
Devine, Erin E.; Bulleit, Erin E.; Hoffman, Matthew R.; McCulloch, Timothy M.; Jiang, Jack J.
2012-01-01
Purpose: To model tension asymmetry caused by superior laryngeal nerve paralysis (SLNP) in excised larynges and apply perturbation, nonlinear dynamic, and aerodynamic analyses. Method: SLNP was modeled in 8 excised larynges using sutures and weights to mimic cricothyroid (CT) muscle function. Weights were removed from one side to create tension…
Preliminary study for a numerical aerodynamic simulation facility. Phase 1: Extension
NASA Technical Reports Server (NTRS)
Lincoln, N. R.
1978-01-01
Functional requirements and preliminary design data were identified for use in the design of all system components and in the construction of a facility to perform aerodynamic simulation for airframe design. A skeleton structure of specifications for the flow model processor and monitor, the operating system, and the language and its compiler is presented.
NASA Astrophysics Data System (ADS)
Mert, Yıldırım; Perihan, Durmuş; Şemsettin, Altındal
2013-10-01
In this study, Al/p—Si and Al/Bi4Ti3O12/p—Si structures are fabricated and their interface states (Nss), the values of series resistance (Rs), and AC electrical conductivity (σac) are obtained each as a function of temperature using admittance spectroscopy method which includes capacitance—voltage (C—V) and conductance—voltage (G—V) measurements. In addition, the effect of interfacial Bi4Ti3O12 (BTO) layer on the performance of the structure is investigated. The voltage-dependent profiles of Nss and Rs are obtained from the high-low frequency capacitance method and the Nicollian method, respectively. Experimental results show that Nss and Rs, as strong functions of temperature and applied bias voltage, each exhibit a peak, whose position shifts towards the reverse bias region, in the depletion region. Such a peak behavior is attributed to the particular distribution of Nss and the reordering and restructuring of Nss under the effect of temperature. The values of activation energy (Ea), obtained from the slope of the Arrhenius plot, of both structures are obtained to be bias voltage-independent, and the Ea of the metal-ferroelectric-semiconductor (MFS) structure is found to be half that of the metal—semiconductor (MS) structure. Furthermore, other main electrical parameters, such as carrier concentration of acceptor atoms (NA), built-in potential (Vbi), Fermi energy (EF), image force barrier lowering (Δ Φb), and barrier height (Φb), are extracted using reverse bias C-2—V characteristics as a function of temperature.
Fullwave coupling to a 3D antenna code using Green's function formulation of wave-particle response
NASA Astrophysics Data System (ADS)
Wright, John; Bonoli, P. T.; Bilato, R.; Brambilla, M.; Maggiora, R.; Lancellotti, V.
2006-10-01
Using the fullwave code, TORIC, and the 3D antenna code, TOPICA, we construct a complete linear system for the RF driven plasma. The 3D finite element antenna code, TOPICA, requires an admittance, Y, for the plasma, where B=YE. In this work, TORIC was modified to allow excitation of the (Eη, Eζ) electric field components at the plasma surface, corresponding to a single poloidal and toroidal mode number combination (m,n). This leads to the tensor response: Yn= ( ll Yηη& YηζYζη& Yζζ), where each of the Yn submatrices is Nm in size. It is shown that the admittance matrix is equivalent to a Green's function calculation for the fullwave system and the net work done is less than twice a single fullwave calculation. The admittance calculation is used with loading calculation from TOPICA to construct self consistent plasma and antenna currents.
NASA Technical Reports Server (NTRS)
Erickson, Gary E.; Deloach, Richard
2008-01-01
A collection of statistical and mathematical techniques referred to as response surface methodology was used to estimate the longitudinal stage separation aerodynamic characteristics of a generic, bimese, winged multi-stage launch vehicle configuration using data obtained on small-scale models at supersonic speeds in the NASA Langley Research Center Unitary Plan Wind Tunnel. The simulated Mach 3 staging was dominated by multiple shock wave interactions between the orbiter and booster vehicles throughout the relative spatial locations of interest. This motivated a partitioning of the overall inference space into several contiguous regions within which the separation aerodynamics were presumed to be well-behaved and estimable using cuboidal and spherical central composite designs capable of fitting full second-order response functions. The primary goal was to approximate the underlying overall aerodynamic response surfaces of the booster vehicle in belly-to-belly proximity to the orbiter vehicle using relatively simple, lower-order polynomial functions that were piecewise-continuous across the full independent variable ranges of interest. The quality of fit and prediction capabilities of the empirical models were assessed in detail, and the issue of subspace boundary discontinuities was addressed. The potential benefits of augmenting the central composite designs to full third order using computer-generated D-optimality criteria were also evaluated. The usefulness of central composite designs, the subspace sizing, and the practicality of fitting low-order response functions over a partitioned inference space dominated by highly nonlinear and possibly discontinuous shock-induced aerodynamics are discussed.
NASA Technical Reports Server (NTRS)
Erickson, Gary E.
2010-01-01
Response surface methodology was used to estimate the longitudinal stage separation aerodynamic characteristics of a generic, bimese, winged multi-stage launch vehicle configuration at supersonic speeds in the NASA LaRC Unitary Plan Wind Tunnel. The Mach 3 staging was dominated by shock wave interactions between the orbiter and booster vehicles throughout the relative spatial locations of interest. The inference space was partitioned into several contiguous regions within which the separation aerodynamics were presumed to be well-behaved and estimable using central composite designs capable of fitting full second-order response functions. The underlying aerodynamic response surfaces of the booster vehicle in belly-to-belly proximity to the orbiter vehicle were estimated using piecewise-continuous lower-order polynomial functions. The quality of fit and prediction capabilities of the empirical models were assessed in detail, and the issue of subspace boundary discontinuities was addressed. Augmenting the central composite designs to full third-order using computer-generated D-optimality criteria was evaluated. The usefulness of central composite designs, the subspace sizing, and the practicality of fitting lower-order response functions over a partitioned inference space dominated by highly nonlinear and possibly discontinuous shock-induced aerodynamics are discussed.
Aerodynamic Simulation of Runback Ice Accretion
NASA Technical Reports Server (NTRS)
Broeren, Andy P.; Whalen, Edward A.; Busch, Greg T.; Bragg, Michael B.
2010-01-01
This report presents the results of recent investigations into the aerodynamics of simulated runback ice accretion on airfoils. Aerodynamic tests were performed on a full-scale model using a high-fidelity, ice-casting simulation at near-flight Reynolds (Re) number. The ice-casting simulation was attached to the leading edge of a 72-in. (1828.8-mm ) chord NACA 23012 airfoil model. Aerodynamic performance tests were conducted at the ONERA F1 pressurized wind tunnel over a Reynolds number range of 4.7?10(exp 6) to 16.0?10(exp 6) and a Mach (M) number ran ge of 0.10 to 0.28. For Re = 16.0?10(exp 6) and M = 0.20, the simulated runback ice accretion on the airfoil decreased the maximum lift coe fficient from 1.82 to 1.51 and decreased the stalling angle of attack from 18.1deg to 15.0deg. The pitching-moment slope was also increased and the drag coefficient was increased by more than a factor of two. In general, the performance effects were insensitive to Reynolds numb er and Mach number changes over the range tested. Follow-on, subscale aerodynamic tests were conducted on a quarter-scale NACA 23012 model (18-in. (457.2-mm) chord) at Re = 1.8?10(exp 6) and M = 0.18, using low-fidelity, geometrically scaled simulations of the full-scale castin g. It was found that simple, two-dimensional simulations of the upper- and lower-surface runback ridges provided the best representation of the full-scale, high Reynolds number iced-airfoil aerodynamics, whereas higher-fidelity simulations resulted in larger performance degrada tions. The experimental results were used to define a new subclassification of spanwise ridge ice that distinguishes between short and tall ridges. This subclassification is based upon the flow field and resulting aerodynamic characteristics, regardless of the physical size of the ridge and the ice-accretion mechanism.
NASA Technical Reports Server (NTRS)
Rajkumar, T.; Bardina, Jorge; Clancy, Daniel (Technical Monitor)
2002-01-01
Wind tunnels use scale models to characterize aerodynamic coefficients, Wind tunnel testing can be slow and costly due to high personnel overhead and intensive power utilization. Although manual curve fitting can be done, it is highly efficient to use a neural network to define the complex relationship between variables. Numerical simulation of complex vehicles on the wide range of conditions required for flight simulation requires static and dynamic data. Static data at low Mach numbers and angles of attack may be obtained with simpler Euler codes. Static data of stalled vehicles where zones of flow separation are usually present at higher angles of attack require Navier-Stokes simulations which are costly due to the large processing time required to attain convergence. Preliminary dynamic data may be obtained with simpler methods based on correlations and vortex methods; however, accurate prediction of the dynamic coefficients requires complex and costly numerical simulations. A reliable and fast method of predicting complex aerodynamic coefficients for flight simulation I'S presented using a neural network. The training data for the neural network are derived from numerical simulations and wind-tunnel experiments. The aerodynamic coefficients are modeled as functions of the flow characteristics and the control surfaces of the vehicle. The basic coefficients of lift, drag and pitching moment are expressed as functions of angles of attack and Mach number. The modeled and training aerodynamic coefficients show good agreement. This method shows excellent potential for rapid development of aerodynamic models for flight simulation. Genetic Algorithms (GA) are used to optimize a previously built Artificial Neural Network (ANN) that reliably predicts aerodynamic coefficients. Results indicate that the GA provided an efficient method of optimizing the ANN model to predict aerodynamic coefficients. The reliability of the ANN using the GA includes prediction of aerodynamic
Kinematics and aerodynamics of the velocity vector roll
NASA Technical Reports Server (NTRS)
Durham, Wayne C.; Lutze, Frederick H.; Mason, W.
1993-01-01
The velocity vector roll is an angular rotation of an aircraft about its instantaneous velocity vector, constrained to be performed at constant angle-of-attack (AOA), no sideslip, and constant velocity. Consideration of the aerodynamic force equations leads to requirements for body-axis yawing and pitching rotations that satisfy these constraints. Here, the body axis rotations, and the constraints, are used in the moment equations to determine the aerodynamic moments required to perform the velocity vector roll. For representative tactical aircraft, the conditions for maximum pitching moment are a function of orientation, occurring at about 90 deg of bank in a level trajectory. Maximum required pitching moment occurs at peak roll rate, and is achieved at AOA above 45 deg. The conditions for maximum rolling moment depend on the value of the roll mode time constant. For a small time constant (fast response) the maximum rolling moment occurs at maximum roll acceleration and zero AOA, largely independent of aircraft orientation; for a large time constant, maximum required rolling moment occurs at maximum roll rate, at maximum AOA, and at 180 deg of bank in level flight. Maximum yawing moment occurs at maximum roll acceleration, maximum AOA, and is largely independent of airplane orientation.
Grid and aerodynamic sensitivity analyses of airplane components
NASA Technical Reports Server (NTRS)
Sadrehaghighi, Ideen; Smith, Robert E.; Tiwari, Surendra N.
1993-01-01
An algorithm is developed to obtain the grid sensitivity with respect to design parameters for aerodynamic optimization. The procedure is advocating a novel (geometrical) parameterization using spline functions such as NURBS (Non-Uniform Rational B-Splines) for defining the wing-section geometry. An interactive algebraic grid generation technique, known as Two-Boundary Grid Generation (TBGG) is employed to generate C-type grids around wing-sections. The grid sensitivity of the domain with respect to geometric design parameters has been obtained by direct differentiation of the grid equations. A hybrid approach is proposed for more geometrically complex configurations such as a wing or fuselage. The aerodynamic sensitivity coefficients are obtained by direct differentiation of the compressible two-dimensional thin-layer Navier-Stokes equations. An optimization package has been introduced into the algorithm in order to optimize the wing-section surface. Results demonstrate a substantially improved design due to maximized lift/drag ratio of the wing-section.
Fully integrated aerodynamic/dynamic optimization of helicopter rotor blades
NASA Technical Reports Server (NTRS)
Walsh, Joanne L.; Lamarsh, William J., II; Adelman, Howard M.
1992-01-01
A fully integrated aerodynamic/dynamic optimization procedure is described for helicopter rotor blades. The procedure combines performance and dynamic analyses with a general purpose optimizer. The procedure minimizes a linear combination of power required (in hover, forward flight, and maneuver) and vibratory hub shear. The design variables include pretwist, taper initiation, taper ratio, root chord, blade stiffnesses, tuning masses, and tuning mass locations. Aerodynamic constraints consist of limits on power required in hover, forward flight and maneuvers; airfoil section stall; drag divergence Mach number; minimum tip chord; and trim. Dynamic constraints are on frequencies, minimum autorotational inertia, and maximum blade weight. The procedure is demonstrated for two cases. In the first case, the objective function involves power required (in hover, forward flight and maneuver) and dynamics. The second case involves only hover power and dynamics. The designs from the integrated procedure are compared with designs from a sequential optimization approach in which the blade is first optimized for performance and then for dynamics. In both cases, the integrated approach is superior.
A smoke generator system for aerodynamic flight research
NASA Technical Reports Server (NTRS)
Richwine, David M.; Curry, Robert E.; Tracy, Gene V.
1989-01-01
A smoke generator system was developed for in-flight vortex flow studies on the F-18 high alpha research vehicle (HARV). The development process included conceptual design, a survey of existing systems, component testing, detailed design, fabrication, and functional flight testing. Housed in the forebody of the aircraft, the final system consists of multiple pyrotechnic smoke cartridges which can be fired simultaneously or in sequence. The smoke produced is ducted to desired locations on the aircraft surface. The smoke generator system (SGS) has been used successfully to identify vortex core and core breakdown locations as functions of flight condition. Although developed for a specific vehicle, this concept may be useful for other aerodynamic flight research which requires the visualization of local flows.
A Rapid Aerodynamic Design Procedure Based on Artificial Neural Networks
NASA Technical Reports Server (NTRS)
Rai, Man Mohan
2001-01-01
An aerodynamic design procedure that uses neural networks to model the functional behavior of the objective function in design space has been developed. This method incorporates several improvements to an earlier method that employed a strategy called parameter-based partitioning of the design space in order to reduce the computational costs associated with design optimization. As with the earlier method, the current method uses a sequence of response surfaces to traverse the design space in search of the optimal solution. The new method yields significant reductions in computational costs by using composite response surfaces with better generalization capabilities and by exploiting synergies between the optimization method and the simulation codes used to generate the training data. These reductions in design optimization costs are demonstrated for a turbine airfoil design study where a generic shape is evolved into an optimal airfoil.
Multi-objective aerodynamic shape optimization of small livestock trailers
NASA Astrophysics Data System (ADS)
Gilkeson, C. A.; Toropov, V. V.; Thompson, H. M.; Wilson, M. C. T.; Foxley, N. A.; Gaskell, P. H.
2013-11-01
This article presents a formal optimization study of the design of small livestock trailers, within which the majority of animals are transported to market in the UK. The benefits of employing a headboard fairing to reduce aerodynamic drag without compromising the ventilation of the animals' microclimate are investigated using a multi-stage process involving computational fluid dynamics (CFD), optimal Latin hypercube (OLH) design of experiments (DoE) and moving least squares (MLS) metamodels. Fairings are parameterized in terms of three design variables and CFD solutions are obtained at 50 permutations of design variables. Both global and local search methods are employed to locate the global minimum from metamodels of the objective functions and a Pareto front is generated. The importance of carefully selecting an objective function is demonstrated and optimal fairing designs, offering drag reductions in excess of 5% without compromising animal ventilation, are presented.
Team Software Development for Aerothermodynamic and Aerodynamic Analysis and Design
NASA Technical Reports Server (NTRS)
Alexandrov, N.; Atkins, H. L.; Bibb, K. L.; Biedron, R. T.; Carpenter, M. H.; Gnoffo, P. A.; Hammond, D. P.; Jones, W. T.; Kleb, W. L.; Lee-Rausch, E. M.
2003-01-01
A collaborative approach to software development is described. The approach employs the agile development techniques: project retrospectives, Scrum status meetings, and elements of Extreme Programming to efficiently develop a cohesive and extensible software suite. The software product under development is a fluid dynamics simulator for performing aerodynamic and aerothermodynamic analysis and design. The functionality of the software product is achieved both through the merging, with substantial rewrite, of separate legacy codes and the authorship of new routines. Examples of rapid implementation of new functionality demonstrate the benefits obtained with this agile software development process. The appendix contains a discussion of coding issues encountered while porting legacy Fortran 77 code to Fortran 95, software design principles, and a Fortran 95 coding standard.
Experimental Investigation of the Aerodynamic Forces on a Curveball
NASA Astrophysics Data System (ADS)
Jemmott, Colin; Utvich, Alexis; Logan, Sheldon; Rossmann, Jenn
2003-11-01
The physics of baseball has fascinated researchers nearly as long as the game has existed, yet research into aerodynamic forces on curveballs has often been conflicting and incomplete. A team of undergraduates used the newly completed Harvey Mudd College wind tunnel with a specially designed apparatus to quantify these forces. The coefficient of lift was found to be a non-linear function of both the dimensionless spin number and the Reynolds number, suggesting a stronger Reynolds number dependence than previously reported. The coefficient of drag was found to be primarily a function of spin number over the range of Reynolds numbers investigated and is significantly higher than that for a static baseball over the same Reynolds number range. While these findings help to quantify and interpret what pitchers know intuitively, they also motivate further investigations of both forces and the resulting flow field over a wider parameter range.
CFD research, parallel computation and aerodynamic optimization
NASA Technical Reports Server (NTRS)
Ryan, James S.
1995-01-01
Over five years of research in Computational Fluid Dynamics and its applications are covered in this report. Using CFD as an established tool, aerodynamic optimization on parallel architectures is explored. The objective of this work is to provide better tools to vehicle designers. Submarine design requires accurate force and moment calculations in flow with thick boundary layers and large separated vortices. Low noise production is critical, so flow into the propulsor region must be predicted accurately. The High Speed Civil Transport (HSCT) has been the subject of recent work. This vehicle is to be a passenger vehicle with the capability of cutting overseas flight times by more than half. A successful design must surpass the performance of comparable planes. Fuel economy, other operational costs, environmental impact, and range must all be improved substantially. For all these reasons, improved design tools are required, and these tools must eventually integrate optimization, external aerodynamics, propulsion, structures, heat transfer and other disciplines.
High speed civil transport aerodynamic optimization
NASA Technical Reports Server (NTRS)
Ryan, James S.
1994-01-01
This is a report of work in support of the Computational Aerosciences (CAS) element of the Federal HPCC program. Specifically, CFD and aerodynamic optimization are being performed on parallel computers. The long-range goal of this work is to facilitate teraflops-rate multidisciplinary optimization of aerospace vehicles. This year's work is targeted for application to the High Speed Civil Transport (HSCT), one of four CAS grand challenges identified in the HPCC FY 1995 Blue Book. This vehicle is to be a passenger aircraft, with the promise of cutting overseas flight time by more than half. To meet fuel economy, operational costs, environmental impact, noise production, and range requirements, improved design tools are required, and these tools must eventually integrate optimization, external aerodynamics, propulsion, structures, heat transfer, controls, and perhaps other disciplines. The fundamental goal of this project is to contribute to improved design tools for U.S. industry, and thus to the nation's economic competitiveness.
Flight Test Maneuvers for Efficient Aerodynamic Modeling
NASA Technical Reports Server (NTRS)
Morelli, Eugene A.
2011-01-01
Novel flight test maneuvers for efficient aerodynamic modeling were developed and demonstrated in flight. Orthogonal optimized multi-sine inputs were applied to aircraft control surfaces to excite aircraft dynamic response in all six degrees of freedom simultaneously while keeping the aircraft close to chosen reference flight conditions. Each maneuver was designed for a specific modeling task that cannot be adequately or efficiently accomplished using conventional flight test maneuvers. All of the new maneuvers were first described and explained, then demonstrated on a subscale jet transport aircraft in flight. Real-time and post-flight modeling results obtained using equation-error parameter estimation in the frequency domain were used to show the effectiveness and efficiency of the new maneuvers, as well as the quality of the aerodynamic models that can be identified from the resultant flight data.
Aerodynamic control with passively pitching wings
NASA Astrophysics Data System (ADS)
Gravish, Nick; Wood, Robert
Flapping wings may pitch passively under aerodynamic and inertial loads. Such passive pitching is observed in flapping wing insect and robot flight. The effect of passive wing pitch on the control dynamics of flapping wing flight are unexplored. Here we demonstrate in simulation and experiment the critical role wing pitching plays in yaw control of a flapping wing robot. We study yaw torque generation by a flapping wing allowed to passively rotate in the pitch axis through a rotational spring. Yaw torque is generated through alternating fast and slow upstroke and and downstroke. Yaw torque sensitively depends on both the rotational spring force law and spring stiffness, and at a critical spring stiffness a bifurcation in the yaw torque control relationship occurs. Simulation and experiment reveal the dynamics of this bifurcation and demonstrate that anomalous yaw torque from passively pitching wings is the result of aerodynamic and inertial coupling between the pitching and stroke-plane dynamics.
An Interactive Educational Tool for Compressible Aerodynamics
NASA Technical Reports Server (NTRS)
Benson, Thomas J.
1994-01-01
A workstation-based interactive educational tool was developed to aid in the teaching of undergraduate compressible aerodynamics. The tool solves for the supersonic flow past a wedge using the equations found in NACA 1135. The student varies the geometry or flow conditions through a graphical user interface and the new conditions are calculated immediately. Various graphical formats present the variation of flow results to the student. One such format leads the student to the generation of some of the graphs found in NACA-1135. The tool includes interactive questions and answers to aid in both the use of the tool and to develop an understanding of some of the complexities of compressible aerodynamics. A series of help screens make the simulator easy to learn and use. This paper will detail the numerical methods used in the tool and describe how it can be used and modified.
Mimicking the humpback whale: An aerodynamic perspective
NASA Astrophysics Data System (ADS)
Aftab, S. M. A.; Razak, N. A.; Mohd Rafie, A. S.; Ahmad, K. A.
2016-07-01
This comprehensive review aims to provide a critical overview of the work on tubercles in the past decade. The humpback whale is of interest to aerodynamic/hydrodynamic researchers, as it performs manoeuvres that baffle the imagination. Researchers have attributed these capabilities to the presence of lumps, known as tubercles, on the leading edge of the flipper. Tubercles generate a unique flow control mechanism, offering the humpback exceptional manoeuverability. Experimental and numerical studies have shown that the flow pattern over the tubercle wing is quite different from conventional wings. Research on the Tubercle Leading Edge (TLE) concept has helped to clarify aerodynamic issues such as flow separation, tonal noise and dynamic stall. TLE shows increased lift by delaying and restricting spanwise separation. A summary of studies on different airfoils and reported improvement in performance is outlined. The major contributions and limitations of previous work are also reported.
Aerodynamic enhancement of space transportation systems
NASA Technical Reports Server (NTRS)
Walberg, G. D.
1981-01-01
The results of a number of recent investigations are reviewed and used to demonstrate gains in launch, orbital transfer, and planetary vehicle performance and economy that can result from the proper exploitation of aerodynamic phenomena. For launch vehicles, application of control-configured design is shown to allow substantial reduction in wing and vertical fin area (and hence, weight) while maintaining acceptable vehicle performance and control. For orbital transfer and planetary vehicles, the use of aerodynamic lift and drag to reduce retropropulsion requirements is shown to produce payload increases of up to 100 percent and to enable some planetary missions that are not feasible with all-propulsive vehicles. Finally, the application of various advanced technologies to a complete set of launch and orbit transfer vehicles in an early space industrialization mission scenario is considered.
Aerodynamic interference between two Darrieus wind turbines
Schatzle, P.R.; Klimas, P.C.; Spahr, H.R.
1981-04-01
The effect of aerodynamic interference on the performance of two curved bladed Darrieus-type vertical axis wind turbines has been calculated using a vortex/lifting line aerodynamic model. The turbines have a tower-to-tower separation distance of 1.5 turbine diameters, with the line of turbine centers varying with respect to the ambient wind direction. The effects of freestream turbulence were neglected. For the cases examined, the calculations showed that the downwind turbine power decrement (1) was significant only when the line of turbine centers was coincident with the ambient wind direction, (2) increased with increasing tipspeed ratio, and (3) is due more to induced flow angularities downstream than to speed deficits near the downstream turbine.
Aerodynamic Shape Optimization Using Hybridized Differential Evolution
NASA Technical Reports Server (NTRS)
Madavan, Nateri K.
2003-01-01
An aerodynamic shape optimization method that uses an evolutionary algorithm known at Differential Evolution (DE) in conjunction with various hybridization strategies is described. DE is a simple and robust evolutionary strategy that has been proven effective in determining the global optimum for several difficult optimization problems. Various hybridization strategies for DE are explored, including the use of neural networks as well as traditional local search methods. A Navier-Stokes solver is used to evaluate the various intermediate designs and provide inputs to the hybrid DE optimizer. The method is implemented on distributed parallel computers so that new designs can be obtained within reasonable turnaround times. Results are presented for the inverse design of a turbine airfoil from a modern jet engine. (The final paper will include at least one other aerodynamic design application). The capability of the method to search large design spaces and obtain the optimal airfoils in an automatic fashion is demonstrated.
Wind turbine trailing edge aerodynamic brakes
Migliore, P G; Miller, L S; Quandt, G A
1995-04-01
Five trailing-edge devices were investigated to determine their potential as wind-turbine aerodynamic brakes, and for power modulation and load alleviation. Several promising configurations were identified. A new device, called the spoiler-flap, appears to be the best alternative. It is a simple device that is effective at all angles of attack. It is not structurally intrusive, and it has the potential for small actuating loads. It is shown that simultaneous achievement of a low lift/drag ratio and high drag is the determinant of device effectiveness, and that these attributes must persist up to an angle of attack of 45{degree}. It is also argued that aerodynamic brakes must be designed for a wind speed of at least 45 m/s (100 mph).
The aerodynamic challenges of SRB recovery
NASA Technical Reports Server (NTRS)
Bacchus, D. L.; Kross, D. A.; Moog, R. D.
1985-01-01
Recovery and reuse of the Space Shuttle solid rocket boosters was baselined to support the primary goal to develop a low cost space transportation system. The recovery system required for the 170,000-lb boosters was for the largest and heaviest object yet to be retrieved from exoatmospheric conditions. State-of-the-art design procedures were ground-ruled and development testing minimized to produce both a reliable and cost effective system. The ability to utilize the inherent drag of the boosters during the initial phase of reentry was a key factor in minimizing the parachute loads, size and weight. A wind tunnel test program was devised to enable the accurate prediction of booster aerodynamic characteristics. Concurrently, wind tunnel, rocket sled and air drop tests were performed to develop and verify the performance of the parachute decelerator subsystem. Aerodynamic problems encountered during the overall recovery system development and the respective solutions are emphasized.
Integrated structural-aerodynamic design optimization
NASA Technical Reports Server (NTRS)
Haftka, R. T.; Kao, P. J.; Grossman, B.; Polen, D.; Sobieszczanski-Sobieski, J.
1988-01-01
This paper focuses on the processes of simultaneous aerodynamic and structural wing design as a prototype for design integration, with emphasis on the major difficulty associated with multidisciplinary design optimization processes, their enormous computational costs. Methods are presented for reducing this computational burden through the development of efficient methods for cross-sensitivity calculations and the implementation of approximate optimization procedures. Utilizing a modular sensitivity analysis approach, it is shown that the sensitivities can be computed without the expensive calculation of the derivatives of the aerodynamic influence coefficient matrix, and the derivatives of the structural flexibility matrix. The same process is used to efficiently evaluate the sensitivities of the wing divergence constraint, which should be particularly useful, not only in problems of complete integrated aircraft design, but also in aeroelastic tailoring applications.
Device for reducing vehicle aerodynamic resistance
Graham, Sean C.
2006-03-07
A device for reducing vehicle aerodynamic resistance for vehicles having a generally rectangular flat front face comprising a plurality of load bearing struts of a predetermined size attached to the flat front face adjacent the sides and top thereof, a pair of pliable opposing flat sheets having an outside edge portion attached to the flat front face adjacent the sides thereof and an upper edge with a predetermined curve; the opposing flat sheets being bent and attached to the struts to form effective curved airfoil shapes, and a top pliable flat sheet disposed adjacent the top of the flat front face and having predetermined curved side edges, which, when the top sheet is bent and attached to the struts to form an effective curved airfoil shape, mate with the curved upper edges of the opposing sheets to complete the aerodynamic device.
Aerodynamics of the Mars Microprobe Entry Vehicles
NASA Technical Reports Server (NTRS)
Mitcheltree, R. A.; Moss, J. N.; Cheatwood, F. M.; Greene, F. A.; Braun, R. D.
1997-01-01
The selection of the unique aeroshell shape for the Mars Microprobes is discussed. A description of its aerodynamics in hypersonic rarefied, hypersonic continuum, supersonic and transonic flow regimes is then presented. This description is based on Direct Simulation Monte Carlo analyses in the rarefied-flow regime, thermochemical nonequilibrium Computational Fluid Dynamics in the hypersonic regime, existing wind tunnel data in the supersonic and transonic regime, additional computational work in the transonic regime, and finally, ballistic range data. The aeroshell is shown to possess the correct combination of aerodynamic stability and drag to convert the probe's initial tumbling attitude and high velocity at atmospheric-interface into the desired surface-impact orientation and velocity.
Device for reducing vehicle aerodynamic resistance
Graham, Sean C.
2006-08-22
A device for reducing vehicle aerodynamic resistance for vehicles having a generally rectangular body disposed above rear wheels, comprising a plurality of load bearing struts attached to the bottom of the rectangular body adjacent its sides, a plurality of opposing flat sheets attached to the load bearing struts, and angled flaps attached to the lower edge of the opposing sheets defining an obtuse angle with the opposing flat sheets extending inwardly with respect to the sides of the rectangular body to a predetermined height above the ground, which, stiffen the opposing flat sheets, bend to resist damage when struck by the ground, and guide airflow around the rear wheels of the vehicle to reduce its aerodynamic resistance when moving.
Transonic and supersonic ground effect aerodynamics
NASA Astrophysics Data System (ADS)
Doig, G.
2014-08-01
A review of recent and historical work in the field of transonic and supersonic ground effect aerodynamics has been conducted, focussing on applied research on wings and aircraft, present and future ground transportation, projectiles, rocket sleds and other related bodies which travel in close ground proximity in the compressible regime. Methods for ground testing are described and evaluated, noting that wind tunnel testing is best performed with a symmetry model in the absence of a moving ground; sled or rail testing is ultimately preferable, though considerably more expensive. Findings are reported on shock-related ground influence on aerodynamic forces and moments in and accelerating through the transonic regime - where force reversals and the early onset of local supersonic flow is prevalent - as well as more predictable behaviours in fully supersonic to hypersonic ground effect flows.
Performance of an aerodynamic particle separator
Ragland, K.; Han, J.; Aerts, D.
1996-12-31
This compact, high-flow device aerodynamically separates small particles from a gas stream by a series of annular truncated airfoils. The operating concept, design and performance of this novel particle separator are described. Tests results using corn starch and post-cyclone coal fly ash are presented. Particle collection efficiencies of 90% for corn starch and 70% for coal fly ash were measured at inlet velocities of 80 ft s{sup {minus}1} (2,700 cfm) and (6 inches) water pressure drop with particle loading up to 4 gr ft{sup {minus}3} in air at standard conditions. Results from computer modeling using FLUENT are presented and compared to the tests. The aerodynamic particle separator is an attractive alternative to a cyclone collector.
Aerodynamic design lowers truck fuel consumption
NASA Technical Reports Server (NTRS)
Steers, L.
1978-01-01
Energy-saving concepts in truck design are emerging from developing new shapes with improved aerodynamic flow properties that can reduce air-drag coefficient of conventional tractor-trailers without requiring severe design changes or compromising load-carrying capability. Improvements are expected to decrease somewhat with increased wind velocities and would be affected by factors such as terrain, driving techniques, and mechanical condition.
New aspects of subsonic aerodynamic noise theory
NASA Technical Reports Server (NTRS)
Goldstein, M. E.; Howes, W. L.
1973-01-01
A theory of aerodynamic noise is presented which differs from Lighthill's theory primarily in the way in which convection of the noise sources is treated. The sound directivity pattern obtained from the present theory agrees better with jet-noise directivity data than does that obtained from Lighthill's theory. The results imply that the shear-noise contribution to jet noise is smaller than previously expected.
Shuttle system ascent aerodynamic and plume heating
NASA Technical Reports Server (NTRS)
Foster, L. D.; Greenwood, T. F.; Lee, D. B.
1985-01-01
The shuttle program provided a challenge to the aerothermodynamicist due to the complexity of the flow field around the vehicle during ascent, since the configuration causes multiple shock interactions between the elements. Wind tunnel tests provided data for the prediction of the ascent design heating environment which involves both plume and aerodynamic heating phenomena. The approach for the heating methodology based on ground test firings and the use of the wind tunnel data to formulate the math models is discussed.
Aerodynamic measurement techniques. [laser based diagnostic techniques
NASA Technical Reports Server (NTRS)
Hunter, W. W., Jr.
1976-01-01
Laser characteristics of intensity, monochromatic, spatial coherence, and temporal coherence were developed to advance laser based diagnostic techniques for aerodynamic related research. Two broad categories of visualization and optical measurements were considered, and three techniques received significant attention. These are holography, laser velocimetry, and Raman scattering. Examples of the quantitative laser velocimeter and Raman scattering measurements of velocity, temperature, and density indicated the potential of these nonintrusive techniques.
Device for reducing vehicle aerodynamic resistance
Graham, Sean C.
2005-02-15
A device for a vehicle with a pair of swinging rear doors, which converts flat sheets of pliable material hinged to the sides of the vehicle adjacent the rear thereof into effective curved airfoils that reduce the aerodynamic resistance of the vehicle, when the doors are closed by hand, utilizing a plurality of stiffeners disposed generally parallel to the doors and affixed to the sheets and a plurality of collapsible tension bearings struts attached to each stiffener and the adjacent door.
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.
Integrated aerodynamic-structural-control wing design
NASA Technical Reports Server (NTRS)
Rais-Rohani, M.; Haftka, R. T.; Grossman, B.; Unger, E. R.
1992-01-01
The aerodynamic-structural-control design of a forward-swept composite wing for a high subsonic transport aircraft is considered. The structural analysis is based on a finite-element method. The aerodynamic calculations are based on a vortex-lattice method, and the control calculations are based on an output feedback control. The wing is designed for minimum weight subject to structural, performance/aerodynamic and control constraints. Efficient methods are used to calculate the control-deflection and control-effectiveness sensitivities which appear as second-order derivatives in the control constraint equations. To suppress the aeroelastic divergence of the forward-swept wing, and to reduce the gross weight of the design aircraft, two separate cases are studied: (1) combined application of aeroelastic tailoring and active controls; and (2) aeroelastic tailoring alone. The results of this study indicated that, for this particular example, aeroelastic tailoring is sufficient for suppressing the aeroelastic divergence, and the use of active controls was not necessary.
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.
Flapping wing aerodynamics: from insects to vertebrates.
Chin, Diana D; Lentink, David
2016-04-01
More than a million insects and approximately 11,000 vertebrates utilize flapping wings to fly. However, flapping flight has only been studied in a few of these species, so many challenges remain in understanding this form of locomotion. Five key aerodynamic mechanisms have been identified for insect flight. Among these is the leading edge vortex, which is a convergent solution to avoid stall for insects, bats and birds. The roles of the other mechanisms - added mass, clap and fling, rotational circulation and wing-wake interactions - have not yet been thoroughly studied in the context of vertebrate flight. Further challenges to understanding bat and bird flight are posed by the complex, dynamic wing morphologies of these species and the more turbulent airflow generated by their wings compared with that observed during insect flight. Nevertheless, three dimensionless numbers that combine key flow, morphological and kinematic parameters - the Reynolds number, Rossby number and advance ratio - govern flapping wing aerodynamics for both insects and vertebrates. These numbers can thus be used to organize an integrative framework for studying and comparing animal flapping flight. Here, we provide a roadmap for developing such a framework, highlighting the aerodynamic mechanisms that remain to be quantified and compared across species. Ultimately, incorporating complex flight maneuvers, environmental effects and developmental stages into this framework will also be essential to advancing our understanding of the biomechanics, movement ecology and evolution of animal flight. PMID:27030773
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.
Aerodynamic Design Opportunities for Future Supersonic Aircraft
NASA Technical Reports Server (NTRS)
Wood, Richard M.; Bauer, Steven X. S.; Flamm, Jeffrey D.
2002-01-01
A discussion of a diverse set of aerodynamic opportunities to improve the aerodynamic performance of future supersonic aircraft has been presented and discussed. These ideas are offered to the community in a hope that future supersonic vehicle development activities will not be hindered by past efforts. A number of nonlinear flow based drag reduction technologies are presented and discussed. The subject technologies are related to the areas of interference flows, vehicle concepts, vortex flows, wing design, advanced control effectors, and planform design. The authors also discussed the importance of improving the aerodynamic design environment to allow creativity and knowledge greater influence. A review of all of the data presented show that pressure drag reductions on the order of 50 to 60 counts are achievable, compared to a conventional supersonic cruise vehicle, with the application of several of the discussed technologies. These drag reductions would correlate to a 30 to 40% increase in cruise L/D (lift-to-drag ratio) for a commercial supersonic transport.
The aerodynamics of smoke particle sampling
NASA Astrophysics Data System (ADS)
Hedin, J.; Gumbel, J.; Rapp, M.
2005-08-01
There is a great interest in nanometer-sized particles in the mesosphere at the moment with the recent launches of the MAGIC and ECOMA payloads. However, rocket-borne measurements of these particles are far from trivial. Since rocket payloads move through the measurement volume with supersonic speeds they can introduce aerodynamic perturbations that complicate the collection of e.g. smoke particle measurements in this region. Nanometer-sized particles tend to follow the gas flow around the payload and do not reach the detector if the aerodynamic design of the instrument has not been considered carefully. The analysis is further complicated by the fact that the payload moves from continuum flow conditions to free molecular flow conditions via the transition regime. Therefore, aerodynamics simulations are of critical importance for the success of these projects. To simulate the gas flow around the rocket payload a Direct Simulation Monte Carlo program is used. A simple model has been developed to introduce smoke particles in the gas flow and determine their trajectories. The result from this is a specific lower limit to the size of smoke particles detectable by various detector designs.
NASA Technical Reports Server (NTRS)
Tang, Chun; Muppidi, Suman; Bose, Deepak; Van Norman, John W.; Tanimoto, Rebekah; Clark, Ian
2015-01-01
NASA's Low Density Supersonic Decelerator Program is developing new technologies that will enable the landing of heavier payloads in low density environments, such as Mars. A recent flight experiment conducted high above the Hawaiian Islands has demonstrated the performance of several decelerator technologies. In particular, the deployment of the Robotic class Supersonic Inflatable Aerodynamic Decelerator (SIAD-R) was highly successful, and valuable data were collected during the test flight. This paper outlines the Computational Fluid Dynamics (CFD) analysis used to estimate the aerodynamic and aerothermal characteristics of the SIAD-R. Pre-flight and post-flight predictions are compared with the flight data, and a very good agreement in aerodynamic force and moment coefficients is observed between the CFD solutions and the reconstructed flight data.
NASA Astrophysics Data System (ADS)
Marin, Andrew T.; Musselman, Kevin P.; MacManus-Driscoll, Judith L.
2013-04-01
This work shows that when a Schottky barrier is present in a photovoltaic device, such as in a device with an ITO/ZnO contact, equivalent circuit analysis must be performed with admittance spectroscopy to accurately determine the pn junction interface recombination parameters (i.e., capture cross section and density of trap states). Without equivalent circuit analysis, a Schottky barrier can produce an error of ˜4-orders of magnitude in the capture cross section and ˜50% error in the measured density of trap states. Using a solution processed ZnO/Cu2O photovoltaic test system, we apply our analysis to clearly separate the contributions of interface states at the pn junction from the Schottky barrier at the ITO/ZnO contact so that the interface state recombination parameters can be accurately characterized. This work is widely applicable to the multitude of photovoltaic devices, which use ZnO adjacent to ITO.
NASA Astrophysics Data System (ADS)
Ghezzi, Carlo; Magnanini, Renato; Parisini, Antonella; Tarricone, Luciano; Gombia, Enos; Longo, Massimo
2008-03-01
The valence band discontinuity of the lattice matched In0.48Ga0.52P/GaAs heterostructure was determined through a careful analysis of the temperature and frequency dependence of the admittance of p+/MQW/n+ structures, formed by a nominally undoped InGaP/GaAs multiple quantum well region, interposed between p+ and n+ GaAs layers. The heterostructures were grown through metal organic vapor phase epitaxy by using tertiary butyl arsine and tertiary butyl phosphine as alternative precursors for the V-group elements. The growth conditions were optimized for obtaining sharp interfaces and negligible ordering effects in the cation sublattice. Accounting for the temperature dependence of the Fermi energy and the calculated confining energy (10meV) of the heavy holes in the wells, a valence band offset ΔEV=(356±5)meV was derived from the temperature variation of the resonance frequency at which the isothermal conductance over frequency G(ω)/ω curves show a maximum. The experimental uncertainty of this result is significantly low if compared with the wide range (240-400meV) of the previously reported ΔEV values. By considering the band gap difference between InGaP and GaAs, a conduction band offset ΔEC=119meV was estimated. The accuracy of the experimental procedure and the reliability of the main assumptions of the admittance spectroscopy measurements were accurately checked. The obtained results were discussed in light of the large and growing amount of literature data by taking into account the influence of the growth conditions on the physical properties of the InGaP/GaAs quantum wells.
Aerodynamic characteristics of airplanes at high angles of attack
NASA Technical Reports Server (NTRS)
Chambers, J. R.; Grafton, S. B.
1977-01-01
An introduction to, and a broad overiew of, the aerodynamic characteristics of airplanes at high angles of attack are provided. Items include: (1) some important fundamental phenomena which determine the aerodynamic characteristics of airplanes at high angles of attack; (2) static and dynamic aerodynamic characteristics near the stall; (3) aerodynamics of the spin; (4) test techniques used in stall/spin studies; (5) applications of aerodynamic data to problems in flight dynamics in the stall/spin area; and (6) the outlook for future research in the area. Although stalling and spinning are flight dynamic problems of importance to all aircraft, including general aviation aircraft, commercial transports, and military airplanes, emphasis is placed on military configurations and the principle aerodynamic factors which influence the stability and control of such vehicles at high angles of attack.
Aerodynamics model for a generic ASTOVL lift-fan aircraft
NASA Technical Reports Server (NTRS)
Birckelbaw, Lourdes G.; Mcneil, Walter E.; Wardwell, Douglas A.
1995-01-01
This report describes the aerodynamics model used in a simulation model of an advanced short takeoff and vertical landing (ASTOVL) lift-fan fighter aircraft. The simulation model was developed for use in piloted evaluations of transition and hover flight regimes, so that only low speed (M approximately 0.2) aerodynamics are included in the mathematical model. The aerodynamic model includes the power-off aerodynamic forces and moments and the propulsion system induced aerodynamic effects, including ground effects. The power-off aerodynamics data were generated using the U.S. Air Force Stability and Control Digital DATCOM program and a NASA Ames in-house graphics program called VORVIEW which allows the user to easily analyze arbitrary conceptual aircraft configurations using the VORLAX program. The jet-induced data were generated using the prediction methods of R. E. Kuhn et al., as referenced in this report.
Unsteady aerodynamic load estimates on turning vanes in the national full-scale aerodynamic complex
NASA Technical Reports Server (NTRS)
Norman, Thomas R.
1986-01-01
Unsteady aerodynamic design loads have been estimated for each of the vane sets in the National Full-Scale Aerodynamic Complex (NFAC). These loads include estimates of local loads over one vane section and global loads over an entire vane set. The analytical methods and computer programs used to estimate these loads are discussed. In addition, the important computer input parameters are defined and the rationale used to estimate them is discussed. Finally, numerical values are presented for both the computer input parameters and the calculated design loads for each vane set.
System Identification of a Vortex Lattice Aerodynamic Model
NASA Technical Reports Server (NTRS)
Juang, Jer-Nan; Kholodar, Denis; Dowell, Earl H.
2001-01-01
The state-space presentation of an aerodynamic vortex model is considered from a classical and system identification perspective. Using an aerodynamic vortex model as a numerical simulator of a wing tunnel experiment, both full state and limited state data or measurements are considered. Two possible approaches for system identification are presented and modal controllability and observability are also considered. The theory then is applied to the system identification of a flow over an aerodynamic delta wing and typical results are presented.
Estimation of Unsteady Aerodynamic Models from Flight Test Data
NASA Technical Reports Server (NTRS)
Lan, C. Edward
2003-01-01
This report summarizes the activities in aerodynamic model estimation from flight data. In addition to public presentations at the AIAA Atmospheric Flight Mechanics Conferences, two presentations at Boeing-Seattle were made during personal trips. These are discussed in the following: 1. Methodology of Aerodynamic Model Estimation from Flight Data. 2. Applications of F-16XL aerodynamic modeling. 3. Modeling of turbulence response. 5. Presentations at Boeing-Seattle. 6. Recommendations. and 7. References.
Analysis of the Hessian for Aerodynamic Optimization: Inviscid Flow
NASA Technical Reports Server (NTRS)
Arian, Eyal; Ta'asan, Shlomo
1996-01-01
In this paper we analyze inviscid aerodynamic shape optimization problems governed by the full potential and the Euler equations in two and three dimensions. The analysis indicates that minimization of pressure dependent cost functions results in Hessians whose eigenvalue distributions are identical for the full potential and the Euler equations. However the optimization problems in two and three dimensions are inherently different. While the two dimensional optimization problems are well-posed the three dimensional ones are ill-posed. Oscillations in the shape up to the smallest scale allowed by the design space can develop in the direction perpendicular to the flow, implying that a regularization is required. A natural choice of such a regularization is derived. The analysis also gives an estimate of the Hessian's condition number which implies that the problems at hand are ill-conditioned. Infinite dimensional approximations for the Hessians are constructed and preconditioners for gradient based methods are derived from these approximate Hessians.
Domain decomposition for aerodynamic and aeroacoustic analyses, and optimization
NASA Technical Reports Server (NTRS)
Baysal, Oktay
1995-01-01
The overarching theme was the domain decomposition, which intended to improve the numerical solution technique for the partial differential equations at hand; in the present study, those that governed either the fluid flow, or the aeroacoustic wave propagation, or the sensitivity analysis for a gradient-based optimization. The role of the domain decomposition extended beyond the original impetus of discretizing geometrical complex regions or writing modular software for distributed-hardware computers. It induced function-space decompositions and operator decompositions that offered the valuable property of near independence of operator evaluation tasks. The objectives have gravitated about the extensions and implementations of either the previously developed or concurrently being developed methodologies: (1) aerodynamic sensitivity analysis with domain decomposition (SADD); (2) computational aeroacoustics of cavities; and (3) dynamic, multibody computational fluid dynamics using unstructured meshes.
High altitude aerodynamic platform concept evaluation and prototype engine testing
NASA Technical Reports Server (NTRS)
Akkerman, J. W.
1984-01-01
A design concept has been developed for maintaining a 150-pound payload at 60,000 feet altitude for about 50 hours. A 600-pound liftoff weight aerodynamic vehicle is used which operates at sufficient speeds to withstand prevailing winds. It is powered by a turbocharged four-stoke cycle gasoline fueled engine. Endurance time of 100 hours or more appears to be feasible with hydrogen fuel and a lighter payload. A prototype engine has been tested to 40,000 feet simulated altitude. Mismatch of the engine and the turbocharger system flow and problems with fuel/air mixture ratio control characteristics prohibited operation beyond 40,000 feet. But there seems to be no reason why the concept cannot be developed to function as analytically predicted.
Aerodynamic fairing/brake for high-speed trains
Ende, R.E.
1993-06-29
A dual aerodynamic function assembly for high speed MAGLEV trains having adjacent in-line cars is described comprising: a series of flaps pivotally mounted by means of a hinge to a circumferential segment of a car end, each flap displaceable to a first position covering a gap existing between the car end and a confronting end of an adjacent car thereby serving as a fairing; a second position at an oblique angle to the path of travel thereby creating drag on the train resulting in braking; and means for actuating the flaps to one or the other position; wherein the flaps have rectangular shapes along those lengths of the circumferential segment which are linear; and further wherein the flaps have contoured edges along those lengths of the circumferential segment which are curved so as to create a close edgewise fit to create a more continuous drag braking surface.
On Improving Efficiency of Differential Evolution for Aerodynamic Shape Optimization Applications
NASA Technical Reports Server (NTRS)
Madavan, Nateri K.
2004-01-01
Differential Evolution (DE) is a simple and robust evolutionary strategy that has been provEn effective in determining the global optimum for several difficult optimization problems. Although DE offers several advantages over traditional optimization approaches, its use in applications such as aerodynamic shape optimization where the objective function evaluations are computationally expensive is limited by the large number of function evaluations often required. In this paper various approaches for improving the efficiency of DE are reviewed and discussed. Several approaches that have proven effective for other evolutionary algorithms are modified and implemented in a DE-based aerodynamic shape optimization method that uses a Navier-Stokes solver for the objective function evaluations. Parallelization techniques on distributed computers are used to reduce turnaround times. Results are presented for standard test optimization problems and for the inverse design of a turbine airfoil. The efficiency improvements achieved by the different approaches are evaluated and compared.
On Improving Efficiency of Differential Evolution for Aerodynamic Shape Optimization Applications
NASA Technical Reports Server (NTRS)
Madavan, Nateri K.
2004-01-01
Differential Evolution (DE) is a simple and robust evolutionary strategy that has been proven effective in determining the global optimum for several difficult optimization problems. Although DE offers several advantages over traditional optimization approaches, its use in applications such as aerodynamic shape optimization where the objective function evaluations are computationally expensive is limited by the large number of function evaluations often required. In this paper various approaches for improving the efficiency of DE are reviewed and discussed. These approaches are implemented in a DE-based aerodynamic shape optimization method that uses a Navier-Stokes solver for the objective function evaluations. Parallelization techniques on distributed computers are used to reduce turnaround times. Results are presented for the inverse design of a turbine airfoil. The efficiency improvements achieved by the different approaches are evaluated and compared.
Integrated aerodynamic/structural design of a sailplane wing
NASA Technical Reports Server (NTRS)
Grossman, B.; Gurdal, Z.; Haftka, R. T.; Strauch, G. J.; Eppard, W. M.
1986-01-01
Using lifting-line theory and beam analysis, the geometry (planiform and twist) and composite material structural sizes (skin thickness, spar cap, and web thickness) were designed for a sailplane wing, subject to both structural and aerodynamic constraints. For all elements, the integrated design (simultaneously designing the aerodynamics and the structure) was superior in terms of performance and weight to the sequential design (where the aerodynamic geometry is designed to maximize the performance, following which a structural/aeroelastic design minimizes the weight). Integrated designs produced less rigid, higher aspect ratio wings with favorable aerodynamic/structural interactions.
Workshop on Aircraft Surface Representation for Aerodynamic Computation
NASA Technical Reports Server (NTRS)
Gregory, T. J. (Editor); Ashbaugh, J. (Editor)
1980-01-01
Papers and discussions on surface representation and its integration with aerodynamics, computers, graphics, wind tunnel model fabrication, and flow field grid generation are presented. Surface definition is emphasized.
Reference values and improvement of aerodynamic drag in professional cyclists.
García-López, Juan; Rodríguez-Marroyo, José Antonio; Juneau, Carl-Etienne; Peleteiro, José; Martínez, Alfredo Córdova; Villa, José Gerardo
2008-02-01
The aims of this study were to measure the aerodynamic drag in professional cyclists, to obtain aerodynamic drag reference values in static and effort positions, to improve the cyclists' aerodynamic drag by modifying their position and cycle equipment, and to evaluate the advantages and disadvantages of these modifications. The study was performed in a wind tunnel with five professional cyclists. Four positions were assessed with a time-trial bike and one position with a standard racing bike. In all positions, aerodynamic drag and kinematic variables were recorded. The drag area for the time-trial bike was 31% higher in the effort than static position, and lower than for the standard racing bike. Changes in the cyclists' position decreased the aerodynamic drag by 14%. The aero-helmet was not favourable for all cyclists. The reliability of aerodynamic drag measures in the wind tunnel was high (r > 0.96, coefficient of variation < 2%). In conclusion, we measured and improved the aerodynamic drag in professional cyclists. Our results were better than those of other researchers who did not assess aerodynamic drag during effort at race pace and who employed different wheels. The efficiency of the aero-helmet, and the validity, reliability, and sensitivity of the wind tunnel and aerodynamic field testing were addressed. PMID:17943597
A climatology of formation conditions for aerodynamic contrails
NASA Astrophysics Data System (ADS)
Gierens, K.; Dilger, F.
2013-06-01
Aerodynamic contrails are defined in this paper as line shaped ice clouds caused by aerodynamically triggered cooling over the wings of an aircraft in cruise which become visible immediately at the trailing edge of the wing or close to it. Effects at low altitudes like condensation to liquid droplets and their potential heterogeneous freezing are excluded from our definition. We study atmospheric conditions that allow formation of aerodynamic contrails. These conditions are stated and then applied to atmospheric data, first to a special case where an aerodynamic contrail was actually observed and then to a full year of global reanalysis data. We show where, when (seasonal variation), and how frequently (probability) aerodynamic contrails can form, and how this relates to actual patterns of air traffic. We study the formation of persistent aerodynamic contrails as well. Finally we check whether aerodynamic and exhaust contrails can coexist in the atmosphere. We show that visible aerodynamic contrails are possible only in an altitude range between roughly 540 and 250 hPa, and that the ambient temperature is the most important parameter, not the relative humidity. Finally we give an argument for our believe that currently aerodynamic contrails have a much smaller climate effect than exhaust contrails, which may however change in future with more air traffic in the tropics.
NASA Technical Reports Server (NTRS)
Periaux, J.
1979-01-01
The numerical simulation of the transonic flows of idealized fluids and of incompressible viscous fluids, by the nonlinear least squares methods is presented. The nonlinear equations, the boundary conditions, and the various constraints controlling the two types of flow are described. The standard iterative methods for solving a quasi elliptical nonlinear equation with partial derivatives are reviewed with emphasis placed on two examples: the fixed point method applied to the Gelder functional in the case of compressible subsonic flows and the Newton method used in the technique of decomposition of the lifting potential. The new abstract least squares method is discussed. It consists of substituting the nonlinear equation by a problem of minimization in a H to the minus 1 type Sobolev functional space.
Effects of ice accretions on aircraft aerodynamics
NASA Astrophysics Data System (ADS)
Lynch, Frank T.; Khodadoust, Abdollah
2001-11-01
This article is a systematic and comprehensive review, correlation, and assessment of test results available in the public domain which address the aerodynamic performance and control degradations caused by various types of ice accretions on the lifting surfaces of fixed wing aircraft. To help put the various test results in perspective, overviews are provided first of the important factors and limitations involved in computational and experimental icing simulation techniques, as well as key aerodynamic testing simulation variables and governing flow physics issues. Following these are the actual reviews, assessments, and correlations of a large number of experimental measurements of various forms of mostly simulated in-flight and ground ice accretions, augmented where appropriate by similar measurements for other analogous forms of surface contamination and/or disruptions. In-flight icing categories reviewed include the initial and inter-cycle ice accretions inherent in the use of de-icing systems which are of particular concern because of widespread misconceptions about the thickness of such accretions which can be allowed before any serious consequences occur, and the runback/ridge ice accretions typically associated with larger-than-normal water droplet encounters which are of major concern because of the possible potential for catastrophic reductions in aerodynamic effectiveness. The other in-flight ice accretion category considered includes the more familiar large rime and glaze ice accretions, including ice shapes with rather grotesque features, where the concern is that, in spite of all the research conducted to date, the upper limit of penalties possible has probably not been defined. Lastly, the effects of various possible ground frost/ice accretions are considered. The concern with some of these is that for some types of configurations, all of the normally available operating margins to stall at takeoff may be erased if these accretions are not
MEMS Applications in Aerodynamic Measurement Technology
NASA Technical Reports Server (NTRS)
Reshotko, E.; Mehregany, M.; Bang, C.
1998-01-01
Microelectromechanical systems (MEMS) embodies the integration of sensors, actuators, and electronics on a single substrate using integrated circuit fabrication techniques and compatible bulk and surface micromachining processes. Silicon and its derivatives form the material base for the MEMS technology. MEMS devices, including microsensors and microactuators, are attractive because they can be made small (characteristic dimension about 100 microns), be produced in large numbers with uniform performance, include electronics for high performance and sophisticated functionality, and be inexpensive. For aerodynamic measurements, it is preferred that sensors be small so as to approximate measurement at a point, and in fact, MEMS pressure sensors, wall shear-stress sensors, heat flux sensors and micromachined hot wires are nearing application. For the envisioned application to wind tunnel models, MEMS sensors can be placed on the surface or in very shallow grooves. MEMS devices have often been fabricated on stiff, flat silicon substrates, about 0.5 mm thick, and therefore were not easily mounted on curved surfaces. However, flexible substrates are now available and heat-flux sensor arrays have been wrapped around a curved turbine blade. Electrical leads can also be built into the flexible substrate. Thus MEMS instrumented wind tunnel models do not require deep spanwise grooves for tubes and leads that compromise the strength of conventionally instrumented models. With MEMS, even the electrical leads can potentially be eliminated if telemetry of the signals to an appropriate receiver can be implemented. While semiconductor silicon is well known for its electronic properties, it is also an excellent mechanical material for MEMS applications. However, silicon electronics are limited to operations below about 200 C, and silicon's mechanical properties start to diminish above 400 C. In recent years, silicon carbide (SiC) has emerged as the leading material candidate for
NASA Technical Reports Server (NTRS)
Haviland, J. K.; Yoo, Y. S.
1976-01-01
Expressions for calculation of subsonic and supersonic, steady and unsteady aerodynamic forces are derived, using the concept of aerodynamic elements applied to the downwash velocity potential method. Aerodynamic elements can be of arbitrary out of plane polygon shape, although numerical calculations are restricted to rectangular elements, and to the steady state case in the supersonic examples. It is suggested that the use of conforming, in place of rectangular elements, would give better results. Agreement with results for subsonic oscillating T tails is fair, but results do not converge as the number of collocation points is increased. This appears to be due to the form of expression used in the calculations. The methods derived are expected to facilitate automated flutter analysis on the computer. In particular, the aerodynamic element concept is consistent with finite element methods already used for structural analysis. The method is universal for the complete Mach number range, and, finally, the calculations can be arranged so that they do not have to be repeated completely for every reduced frequency.
Unsteady aerodynamics of conventional and supercritical airfoils
NASA Technical Reports Server (NTRS)
Davis, S. S.; Malcolm, G. N.
1980-01-01
The unsteady aerodynamics of a conventional and a supercritical airfoil are compared by examining measured chordwise unsteady pressure time-histories from four selected flow conditions. Although an oscillating supercritical airfoil excites more harmonics, the strength of the airfoil's shock wave is the more important parameter governing the complexity of the unsteady flow. Whether they are conventional or supercritical, airfoils that support weak shock waves induce unsteady loads that are qualitatively predictable with classical theories; flows with strong shock waves are sensitive to details of the shock-wave and boundary-layer interaction and cannot be adequately predicted.
Aerodynamic design trends for commercial aircraft
NASA Technical Reports Server (NTRS)
Hilbig, R.; Koerner, H.
1986-01-01
Recent research on advanced-configuration commercial aircraft at DFVLR is surveyed, with a focus on aerodynamic approaches to improved performance. Topics examined include transonic wings with variable camber or shock/boundary-layer control, wings with reduced friction drag or laminarized flow, prop-fan propulsion, and unusual configurations or wing profiles. Drawings, diagrams, and graphs of predicted performance are provided, and the need for extensive development efforts using powerful computer facilities, high-speed and low-speed wind tunnels, and flight tests of models (mounted on specially designed carrier aircraft) is indicated.
Dual nozzle aerodynamic and cooling analysis study
NASA Technical Reports Server (NTRS)
Meagher, G. M.
1981-01-01
Analytical models to predict performance and operating characteristics of dual nozzle concepts were developed and improved. Aerodynamic models are available to define flow characteristics and bleed requirements for both the dual throat and dual expander concepts. Advanced analytical techniques were utilized to provide quantitative estimates of the bleed flow, boundary layer, and shock effects within dual nozzle engines. Thermal analyses were performed to define cooling requirements for baseline configurations, and special studies of unique dual nozzle cooling problems defined feasible means of achieving adequate cooling.
Aerodynamics of High-Speed Trains
NASA Astrophysics Data System (ADS)
Schetz, Joseph A.
This review highlights the differences between the aerodynamics of high-speed trains and other types of transportation vehicles. The emphasis is on modern, high-speed trains, including magnetic levitation (Maglev) trains. Some of the key differences are derived from the fact that trains operate near the ground or a track, have much greater length-to-diameter ratios than other vehicles, pass close to each other and to trackside structures, are more subject to crosswinds, and operate in tunnels with entry and exit events. The coverage includes experimental techniques and results and analytical and numerical methods, concentrating on the most recent information available.
Insect Flight: Aerodynamics, Efficiency, and Evolution
NASA Astrophysics Data System (ADS)
Wang, Z. Jane
2007-11-01
Insects, like birds and fish, locomote via interactions between fluids and flapping wings. Their motion is governed by the Navier-Stokes equation coupled to moving boundaries. In this talk, I will first describe how dragonflies fly: their wing motions and the flows and forces they generate. I will then consider insects in several species and discuss three questions: 1) Is insect flight optimal? 2) How does the efficiency of flapping flight compare to classical fixed-wing flight? 3) How might aerodynamic effects have influenced the evolution of insect flight?
Coupled Aerodynamic-Thermal-Structural (CATS) Analysis
NASA Technical Reports Server (NTRS)
1995-01-01
Coupled Aerodynamic-Thermal-Structural (CATS) Analysis is a focused effort within the Numerical Propulsion System Simulation (NPSS) program to streamline multidisciplinary analysis of aeropropulsion components and assemblies. Multidisciplinary analysis of axial-flow compressor performance has been selected for the initial focus of this project. CATS will permit more accurate compressor system analysis by enabling users to include thermal and mechanical effects as an integral part of the aerodynamic analysis of the compressor primary flowpath. Thus, critical details, such as the variation of blade tip clearances and the deformation of the flowpath geometry, can be more accurately modeled and included in the aerodynamic analyses. The benefits of this coupled analysis capability are (1) performance and stall line predictions are improved by the inclusion of tip clearances and hot geometries, (2) design alternatives can be readily analyzed, and (3) higher fidelity analysis by researchers in various disciplines is possible. The goals for this project are a 10-percent improvement in stall margin predictions and a 2:1 speed-up in multidisciplinary analysis times. Working cooperatively with Pratt & Whitney, the Lewis CATS team defined the engineering processes and identified the software products necessary for streamlining these processes. The basic approach is to integrate the aerodynamic, thermal, and structural computational analyses by using data management and Non-Uniform Rational B-Splines (NURBS) based data mapping. Five software products have been defined for this task: (1) a primary flowpath data mapper, (2) a two-dimensional data mapper, (3) a database interface, (4) a blade structural pre- and post-processor, and (5) a computational fluid dynamics code for aerothermal analysis of the drum rotor. Thus far (1) a cooperative agreement has been established with Pratt & Whitney, (2) a Primary Flowpath Data Mapper has been prototyped and delivered to General Electric
Aerodynamics/ACEE: Aircraft energy efficiency
NASA Technical Reports Server (NTRS)
1981-01-01
An overview is presented of a 10 year program managed by NASA which seeks to make possible the most efficient use of energy for aircraft propulsion and lift as well as provide a technology that can be used by U.S. manufacturers of air transports and engines. Supercritical wings, winglets, vortex drag reduction, high lift, active control, laminar flow control, and aerodynamics by computer are among the topics discussed. Wind tunnel models in flight verification of advanced technology, and the design, construction and testing of various aircraft structures are also described.
Aerodynamic Focusing Of High-Density Aerosols
Ruiz, D. E.; Fisch, Nathaniel
2014-02-24
High-density micron-sized particle aerosols might form the basis for a number of applications in which a material target with a particular shape might be quickly ionized to form a cylindrical or sheet shaped plasma. A simple experimental device was built in order to study the properties of high-density aerosol focusing for 1 m silica spheres. Preliminary results recover previous findings on aerodynamic focusing at low densities. At higher densities, it is demonstrated that the focusing properties change in a way which is consistent with a density dependent Stokes number.
Aerodynamic performance measurements at moderate Re
NASA Astrophysics Data System (ADS)
Rosen, M.; McArthur, J.; Spedding, G. R.
2004-11-01
There has been renewed interest in the aerodynamics of lifting wings at Reynolds numbers from 10^4 to 10^5, partly due to engineering requirements of small-scale, remotely piloted aircraft, and partly because birds and bats operate in this regime. Even when the wings do not flap or pitch or plunge, the flow over the small aspect ratio wings is likely to be three-dimensional and unsteady. Wind tunnel test results are described where force measurements are combined with DPIV studies. Some problems and principles of such measurement programs will also be discussed.
Fitting aerodynamics and propulsion into the puzzle
NASA Technical Reports Server (NTRS)
Johnston, Patrick J.; Whitehead, Allen H., Jr.; Chapman, Gary T.
1987-01-01
The development of an airbreathing single-stage-to-orbit vehicle, in particular the problems of aerodynamics and propulsion integration, is examined. The boundary layer transition on constant pressure surfaces at hypersonic velocities, and the effects of noise on the transition are investigated. The importance of viscosity, real-gas effects, and drag at hypersonic speeds is discussed. A propulsion system with sufficient propulsive lift to enhance the performance of the vehicle is being developed. The difficulties of engine-airframe integration are analyzed.
Some aerodynamic considerations for advanced aircraft configurations
NASA Technical Reports Server (NTRS)
Williams, L. J.; Johnson, J. L., Jr.; Yip, L. P.
1984-01-01
Recent NASA wind-tunnel investigations of advanced unconventional configurations are surveyed, with an emphasis on those applicable to general-aviation aircraft. Photographs of typical models and graphs of aerodynamic parameters are provided. The designs discussed include aft installation of tractor or pusher-propellor engines; forward-swept wings; canards; combinations of canard, wing, and horizontal tail; and propeller-over-the-wing configurations. Consideration is given to canard-wing flow-field interactions, natural laminar flow, the choice of canard airfoil, directional stability and control, and propulsion-system location.
Sensor Systems Collect Critical Aerodynamics Data
NASA Technical Reports Server (NTRS)
2010-01-01
With the support of Small Business Innovation Research (SBIR) contracts with Dryden Flight Research Center, Tao of Systems Integration Inc. developed sensors and other components that will ultimately form a first-of-its-kind, closed-loop system for detecting, measuring, and controlling aerodynamic forces and moments in flight. The Hampton, Virginia-based company commercialized three of the four planned components, which provide sensing solutions for customers such as Boeing, General Electric, and BMW and are used for applications such as improving wind turbine operation and optimizing air flow from air conditioning systems. The completed system may one day enable flexible-wing aircraft with flight capabilities like those of birds.
Reduced order models for nonlinear aerodynamics
NASA Technical Reports Server (NTRS)
Mahajan, Aparajit J.; Dowell, Earl H.; Bliss, Donald B.
1988-01-01
Reduced order models are needed for reliable, efficient and accurate prediction of aerodynamic forces to analyze fluid structure interaction problems in turbomachinery, including propfans. Here, a finite difference, time marching Navier-Stokes code is validated for unsteady airfoil motion by comparing results with those from classical potential flow. The Navier-Stokes code is then analyzed for calculation of primitive and exact estimates of eigenvalues and eigenvectors associated with fluid-airfoil interaction. A variational formulation for the Euler equations and Navier-Stokes equations will be the basis for reduction of order through an eigenvector transformation.
A climatology of formation conditions for aerodynamic contrails
NASA Astrophysics Data System (ADS)
Gierens, K.; Dilger, F.
2013-11-01
Aircraft at cruise levels can cause two kinds of contrails, the well known exhaust contrails and the less well-known aerodynamic contrails. While the possible climate impact of exhaust contrails has been studied for many years, research on aerodynamic contrails began only a few years ago and nothing is known about a possible contribution of these ice clouds to climate impact. In order to make progress in this respect, we first need a climatology of their formation conditions and this is given in the present paper. Aerodynamic contrails are defined here as line shaped ice clouds caused by aerodynamically triggered cooling over the wings of an aircraft in cruise which become visible immediately at the trailing edge of the wing or close to it. Effects at low altitudes like condensation to liquid droplets and their potential heterogeneous freezing are excluded from our definition. We study atmospheric conditions that allow formation of aerodynamic contrails. These conditions are stated and then applied to atmospheric data: first to a special case where an aerodynamic contrail was actually observed and then to a full year of global reanalysis data. We show where, when (seasonal variation), and how frequently (probability) aerodynamic contrails can form, and how this relates to actual patterns of air traffic. We study the formation of persistent aerodynamic contrails as well. Furthermore, we check whether aerodynamic and exhaust contrails can coexist in the atmosphere. We show that visible aerodynamic contrails are possible only in an altitude range between roughly 540 and 250 hPa, and that the ambient temperature is the most important parameter, not the relative humidity. Finally, we argue that currently aerodynamic contrails have a much smaller climate effect than exhaust contrails, which may however change in future with more air traffic in the tropics.
Relevance of aerodynamic modelling for load reduction control strategies of two-bladed wind turbines
NASA Astrophysics Data System (ADS)
Luhmann, B.; Cheng, P. W.
2014-06-01
A new load reduction concept is being developed for the two-bladed prototype of the Skywind 3.5MW wind turbine. Due to transport and installation advantages both offshore and in complex terrain two-bladed turbine designs are potentially more cost-effective than comparable three-bladed configurations. A disadvantage of two-bladed wind turbines is the increased fatigue loading, which is a result of asymmetrically distributed rotor forces. The innovative load reduction concept of the Skywind prototype consists of a combination of cyclic pitch control and tumbling rotor kinematics to mitigate periodic structural loading. Aerodynamic design tools must be able to model correctly the advanced dynamics of the rotor. In this paper the impact of the aerodynamic modelling approach is investigated for critical operational modes of a two-bladed wind turbine. Using a lifting line free wake vortex code (FVM) the physical limitations of the classical blade element momentum theory (BEM) can be evaluated. During regular operation vertical shear and yawed inflow are the main contributors to periodic blade load asymmetry. It is shown that the near wake interaction of the blades under such conditions is not fully captured by the correction models of BEM approach. The differing prediction of local induction causes a high fatigue load uncertainty especially for two-bladed turbines. The implementation of both cyclic pitch control and a tumbling rotor can mitigate the fatigue loading by increasing the aerodynamic and structural damping. The influence of the time and space variant vorticity distribution in the near wake is evaluated in detail for different cyclic pitch control functions and tumble dynamics respectively. It is demonstrated that dynamic inflow as well as wake blade interaction have a significant impact on the calculated blade forces and need to be accounted for by the aerodynamic modelling approach. Aeroelastic simulations are carried out using the high fidelity multi body
Supersonic airplane design optimization method for aerodynamic performance and low sonic boom
NASA Technical Reports Server (NTRS)
Cheung, Samson H.; Edwards, Thomas A.
1992-01-01
This paper presents a new methodology for the optimization of supersonic airplane designs to meet the dual design objectives of low sonic boom and high aerodynamic performance. Two sets of design parameters are used on an existing High Speed Civil Transport (HSCT) configuration to maximize the aerodynamic performance and minimize the sonic boom under the flight track. One set of the parameters perturbs the camber line of the wing sections to maximize the lift-over-drag ratio (L/D). A preliminary optimization run yielded a 3.75 percent improvement in L/D over a baseline low-boom configuration. The other set of parameters modifies the fuselage area to achieve a target F-function. Starting from an initial configuration with strong bow, wing, and tail shocks, a modified design with a flat-top signature is obtained. The methods presented can easily incorporate other design variables and objective functions. Extensions to the present capability in progress are described.
Aerodynamic optimization of supersonic compressor cascade using differential evolution on GPU
NASA Astrophysics Data System (ADS)
Aissa, Mohamed Hasanine; Verstraete, Tom; Vuik, Cornelis
2016-06-01
Differential Evolution (DE) is a powerful stochastic optimization method. Compared to gradient-based algorithms, DE is able to avoid local minima but requires at the same time more function evaluations. In turbomachinery applications, function evaluations are performed with time-consuming CFD simulation, which results in a long, non affordable, design cycle. Modern High Performance Computing systems, especially Graphic Processing Units (GPUs), are able to alleviate this inconvenience by accelerating the design evaluation itself. In this work we present a validated CFD Solver running on GPUs, able to accelerate the design evaluation and thus the entire design process. An achieved speedup of 20x to 30x enabled the DE algorithm to run on a high-end computer instead of a costly large cluster. The GPU-enhanced DE was used to optimize the aerodynamics of a supersonic compressor cascade, achieving an aerodynamic loss minimization of 20%.
Aerodynamics inside a rapid compression machine
Mittal, Gaurav; Sung, Chih-Jen
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)
Rotor/wing aerodynamic interactions in hover
NASA Technical Reports Server (NTRS)
Felker, F. F.; Light, J. S.
1986-01-01
An experimental and theoretical investigation of rotor/wing aerodynamic interactions in hover is described. The experimental investigation consisted of both a large-scale and small-scale test. A 0.658-scale, V-22 rotor and wing was used in the large-scale test. Wind download, wing surface pressure, rotor performance, and rotor downwash data from the large-scale test are presented. A small-scale experiment was conducted to determine how changes in the rotor/wing geometry affected the aerodynamic interactions. These geometry variations included the distance between the rotor and wing, wing incidence angle, and configurations both with the rotor axis at the tip of the wing (tilt rotor configuration) and with the rotor axis at the center of the wing (compound helicopter configuration). A wing with boundary-layer control was also tested to evaluate the effect of leading and trailing edge upper surface blowing on the wing download. A computationally efficient, semi-empirical theory was developed to predict the download on the wing. Finally, correlations between the theoretical predictions and test data are presented.
Experimental aerodynamics research on a hypersonic vehicle
Oberkampf, W.L.; Aeschliman, D.P.; Tate, R.E.; Henfling, J.F.
1993-04-01
Aerodynamic force and moment measurements and flow visualization results are presented for a hypersonic vehicle configuration at Mach 8. The basic vehicle configuration is a spherically blunted 10[degree] half-angle cone with a slice parallel with the axis of the vehicle. On the slice portion of the vehicle, a flap could be attached so that deflection angles of 10[degree], 20[degree] and 30[degree] could be obtained. All of the experimental results were obtained in the Sandia Mach 8 hypersonic wind tunnel for laminar boundary layer conditions. Flow visualization results include shear stress sensitive liquid crystal photographs, surface streak flow photographs (using liquid crystals), and spark schlieren photographs and video. The liquid crystals were used as an aid in verifying that a laminar boundary layer existed over the entire body. The surface flow photo-graphs show attached and separated flow on both the leeside of the vehicle and near the flap. A detailed uncertainty analysis was conducted to estimate the contributors to body force and moment measurement uncertainty. Comparisons are made with computational results to evaluate both the experimental and numerical results. This extensive set of high-quality experimental force and moment measurements is recommended for use in the calibration and validation of relevant computational aerodynamics codes.
Experimental aerodynamics research on a hypersonic vehicle
Oberkampf, W.L.; Aeschliman, D.P.; Tate, R.E.; Henfling, J.F.
1993-04-01
Aerodynamic force and moment measurements and flow visualization results are presented for a hypersonic vehicle configuration at Mach 8. The basic vehicle configuration is a spherically blunted 10{degree} half-angle cone with a slice parallel with the axis of the vehicle. On the slice portion of the vehicle, a flap could be attached so that deflection angles of 10{degree}, 20{degree} and 30{degree} could be obtained. All of the experimental results were obtained in the Sandia Mach 8 hypersonic wind tunnel for laminar boundary layer conditions. Flow visualization results include shear stress sensitive liquid crystal photographs, surface streak flow photographs (using liquid crystals), and spark schlieren photographs and video. The liquid crystals were used as an aid in verifying that a laminar boundary layer existed over the entire body. The surface flow photo-graphs show attached and separated flow on both the leeside of the vehicle and near the flap. A detailed uncertainty analysis was conducted to estimate the contributors to body force and moment measurement uncertainty. Comparisons are made with computational results to evaluate both the experimental and numerical results. This extensive set of high-quality experimental force and moment measurements is recommended for use in the calibration and validation of relevant computational aerodynamics codes.
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.
Aerodynamic Simulation of the MEXICO Rotor
NASA Astrophysics Data System (ADS)
Herraez, I.; Medjroubi, W.; Stoevesandt, B.; Peinke, J.
2014-12-01
CFD (Computational Fluid Dynamics) simulations are a very promising method for predicting the aerodynamic behavior of wind turbines in an inexpensive and accurate way. One of the major drawbacks of this method is the lack of validated models. As a consequence, the reliability of numerical results is often difficult to assess. The MEXICO project aimed at solving this problem by providing the project partners with high quality measurements of a 4.5 meters rotor diameter wind turbine operating under controlled conditions. The large measurement data-set allows the validation of all kind of aerodynamic models. This work summarizes our efforts for validating a CFD model based on the open source software OpenFoam. Both steady- state and time-accurate simulations have been performed with the Spalart-Allmaras turbulence model for several operating conditions. In this paper we will concentrate on axisymmetric inflow for 3 different wind speeds. The numerical results are compared with pressure distributions from several blade sections and PIV-flow data from the near wake region. In general, a reasonable agreement between measurements the and our simulations exists. Some discrepancies, which require further research, are also discussed.
Cricket Ball Aerodynamics: Myth Versus Science
NASA Technical Reports Server (NTRS)
Mehta, Rabindra D.; Koga, Demmis J. (Technical Monitor)
2000-01-01
Aerodynamics plays a prominent role in the flight of a cricket ball released by a bowler. The main interest is in the fact that the ball can follow a curved flight path that is not always under the control of the bowler. ne basic aerodynamic principles responsible for the nonlinear flight or "swing" of a cricket ball were identified several years ago and many papers have been published on the subject. In the last 20 years or so, several experimental investigations have been conducted on cricket ball swing, which revealed the amount of attainable swing, and the parameters that affect it. A general overview of these findings is presented with emphasis on the concept of late swing and the effects of meteorological conditions on swing. In addition, the relatively new concept of "reverse" swing, how it can be achieved in practice and the role in it of ball "tampering", are discussed in detail. A discussion of the "white" cricket ball used in last year's World Cup, which supposedly possesses different swing properties compared to a conventional red ball, is also presented.
Aerodynamic Control using Distributed Active Bleed
NASA Astrophysics Data System (ADS)
Kearney, John; Glezer, Ari
2015-11-01
The global aerodynamic loads on a stationary and pitching airfoil at angles of attack beyond the static and dynamic stall margins, respectively are controlled in wind tunnel experiments using regulated distributed bleed driven by surface pressure differences. High-speed PIV and proper orthogonal decomposition of the vorticity flux on the static airfoil show that the bleed engenders trains of discrete vortices that advect along the surface and are associated with a local instability that is manifested by a time-averaged bifurcation of the vorticity layer near the bleed outlets and alters the vorticity flux over the airfoil and thereby the aerodynamic loads. Active bleed is used on a dynamically pitching airfoil (at reduced frequencies up to k = 0.42) to modulate the evolution of vorticity concentrations during dynamic stall. Time-periodic bleed improved the pitch stability by reducing adverse pitching moment (``negative damping'') that can precipitate structural instabilities. At the same time, the maintains the cycle-average loads to within 5% of the base flow levels by segmenting the vorticity layer during upstroke and promoting early flow attachment during downstroke segments of the pitch cycle. Supported by Georgia Tech VLRCOE.
Aerodynamics of Stardust Sample Return Capsule
NASA Technical Reports Server (NTRS)
Mitcheltree, R. A.; Wilmoth, R. G.; Cheatwood, F. M.; Brauckmann, G. J.; Greene, F. A.
1997-01-01
Successful return of interstellar dust and cometary material by the Stardust Sample Return Capsule requires an accurate description of the Earth entry vehicle's aerodynamics. This description must span the hypersonic-rarefied, hypersonic-continuum, supersonic, transonic, and subsonic flow regimes. Data from numerous sources are compiled to accomplish this objective. These include Direct Simulation Monte Carlo analyses, thermochemical nonequilibrium computational fluid dynamics, transonic computational fluid dynamics, existing wind tunnel data, and new wind tunnel data. Four observations are highlighted: 1) a static instability is revealed in the free-molecular and early transitional-flow regime due to aft location of the vehicle s center-of-gravity, 2) the aerodynamics across the hypersonic regime are compared with the Newtonian flow approximation and a correlation between the accuracy of the Newtonian flow assumption and the sonic line position is noted, 3) the primary effect of shape change due to ablation is shown to be a reduction in drag, and 4) a subsonic dynamic instability is revealed which will necessitate either a change in the vehicle s center-of-gravity location or the use of a stabilizing drogue parachute.
Aerodynamic characteristics of popcorn ash particles
Cherkaduvasala, V.; Murphy, D.W.; Ban, H.; Harrison, K.E.; Monroe, L.S.
2007-07-01
Popcorn ash particles are fragments of sintered coal fly ash masses that resemble popcorn in low apparent density. They can travel with the flow in the furnace and settle on key places such as catalyst surfaces. Computational fluid dynamics (CFD) models are often used in the design process to prevent the carryover and settling of these particles on catalysts. Particle size, density, and drag coefficient are the most important aerodynamic parameters needed in CFD modeling of particle flow. The objective of this study was to experimentally determine particle size, shape, apparent density, and drag characteristics for popcorn ash particles from a coal-fired power plant. Particle size and shape were characterized by digital photography in three orthogonal directions and by computer image analysis. Particle apparent density was determined by volume and mass measurements. Particle terminal velocities in three directions were measured in water and each particle was also weighed in air and in water. The experimental data were analyzed and models were developed for equivalent sphere and equivalent ellipsoid with apparent density and drag coefficient distributions. The method developed in this study can be used to characterize the aerodynamic properties of popcorn-like particles.
Cascade flutter analysis with transient response aerodynamics
NASA Technical Reports Server (NTRS)
Bakhle, M. A.; Mahajan, A. J.; Keith, T. G., Jr.; Stefko, G. L.
1991-01-01
Two methods for calculating linear frequency domain aerodynamic coefficients from a time marching Full Potential cascade solver are developed and verified. In the first method, the Influence Coefficient, solutions to elemental problems are superposed to obtain the solutions for a cascade in which all blades are vibrating with a constant interblade phase angle. The elemental problem consists of a single blade in the cascade oscillating while the other blades remain stationary. In the second method, the Pulse Response, the response to the transient motion of a blade is used to calculate influence coefficients. This is done by calculating the Fourier Transforms of the blade motion and the response. Both methods are validated by comparison with the Harmonic Oscillation method and give accurate results. The aerodynamic coefficients obtained from these methods are used for frequency domain flutter calculations involving a typical section blade structural model. An eigenvalue problem is solved for each interblade phase angle mode and the eigenvalues are used to determine aeroelastic stability. Flutter calculations are performed for two examples over a range of subsonic Mach numbers.
Cascade flutter analysis with transient response aerodynamics
NASA Technical Reports Server (NTRS)
Bakhle, Milind A.; Mahajan, Aparajit J.; Keith, Theo G., Jr.; Stefko, George L.
1991-01-01
Two methods for calculating linear frequency domain aerodynamic coefficients from a time-marching Full-Potential cascade solver are developed and verified. In the first method, the Influence Coefficient method, solutions to elemental problems are superposed to obtain the solutions for a cascade in which all blades are vibrating with a constant interblade phase angle. The elemental problem consists of a single blade in the cascade oscillating while the other blades remain stationary. In the second method, the Pulse Response method, the response to the transient motion of a blade is used to calculate influence coefficients. This is done by calculating the Fourier transforms of the blade motion and the response. Both methods are validated by comparison with the Harmonic Oscillation method and give accurate results. The aerodynamic coefficients obtained from these methods are used for frequency domain flutter calculations involving a typical section blade structural model. An eigenvalue problem is solved for each interblade phase angle mode and the eigenvalues are used to determine aeroelastic stability. Flutter calculations are performed for two examples over a range of subsonic Mach numbers using both flat plates and actual airfoils.
Advanced aerodynamics and active controls. Selected NASA research
NASA Technical Reports Server (NTRS)
1981-01-01
Aerodynamic and active control concepts for application to commercial transport aircraft are discussed. Selected topics include in flight direct strike lightning research, triply redundant digital fly by wire control systems, tail configurations, winglets, and the drones for aerodynamic and structural testing (DAST) program.
Exploring the Aerodynamic Drag of a Moving Cyclist
ERIC Educational Resources Information Center
Theilmann, Florian; Reinhard, Christopher
2016-01-01
Although the physics of cycling itself is a complex mixture of aerodynamics, physiology, mechanics, and heuristics, using cycling as a context for teaching physics has a tradition of certainly more than 30 years. Here, a possible feature is the discussion of the noticeable resistant forces such as aerodynamic drag and the associated power…
Survey of Unsteady Computational Aerodynamics for Horizontal Axis Wind Turbines
NASA Astrophysics Data System (ADS)
Frunzulicǎ, F.; Dumitrescu, H.; Cardoş, V.
2010-09-01
We present a short review of aerodynamic computational models for horizontal axis wind turbines (HAWT). Models presented have a various level of complexity to calculate aerodynamic loads on rotor of HAWT, starting with the simplest blade element momentum (BEM) and ending with the complex model of Navier-Stokes equations. Also, we present some computational aspects of these models.
Reliability and Applicability of Aerodynamic Measures in Dysphonia Assessment
ERIC Educational Resources Information Center
Yiu, Edwin M.-L.; Yuen, Yuet-Ming; Whitehill, Tara; Winkworth, Alison
2004-01-01
Aerodynamic measures are frequently used to analyse and document pathological voices. Some normative data are available for speakers from the English-speaking population. However, no data are available yet for Chinese speakers despite the fact that they are one of the largest populations in the world. The high variability of aerodynamic measures…
Launch vehicle aerodynamic data base development comparison with flight data
NASA Technical Reports Server (NTRS)
Hamilton, J. T.; Wallace, R. O.; Dill, C. C.
1983-01-01
The aerodynamic development plan for the Space Shuttle integrated vehicle had three major objectives. The first objective was to support the evolution of the basic configuration by establishing aerodynamic impacts to various candidate configurations. The second objective was to provide continuing evaluation of the basic aerodynamic characteristics in order to bring about a mature data base. The third task was development of the element and component aerodynamic characteristics and distributed air loads data to support structural loads analyses. The complexity of the configurations rendered conventional analytic methods of little use and therefore required extensive wind tunnel testing of detailed complex models. However, the ground testing and analyses did not predict the aerodynamic characteristics that were extracted from the Space Shuttle flight test program. Future programs that involve the use of vehicles similar to the Space Shuttle should be concerned with the complex flow fields characteristics of these types of complex configurations.
Unsteady Nonlinear Aerodynamic Response Modeling: A Data-Priven Perspective
NASA Astrophysics Data System (ADS)
Hemati, Maziar; Dawson, Scott; Rowley, Clarence
2014-11-01
Current real-time-capable aerodynamic modeling strategies are greatly challenged in the face of aggressive flight maneuvers, such as rapid pitching motions that lead to pronounced leading-edge vortex shedding and aerodynamic stall. The inability to accurately and robustly predict, in a low-dimensional manner, the nonlinear aerodynamic force/moment response of an aircraft to sharp maneuvers puts practical approaches for aerodynamic optimization and control out of reach. Here, we propose a parameter-varying model to approximate the response of an airfoil to arbitrarily prescribed rapid pitching kinematics. An output-minimization procedure is invoked to identify the nonlinear model from input-output data gathered from direct numerical fluid dynamics simulations. The resulting nonlinear models have noteworthy predictive capabilities for arbitrary pitching maneuvers that span a broad range of operating regimes, thus making the models especially useful for aerodynamic optimization and real-time control and simulation.
Evaluation of aerodynamic derivatives from a magnetic balance system
NASA Technical Reports Server (NTRS)
Raghunath, B. S.; Parker, H. M.
1972-01-01
The dynamic testing of a model in the University of Virginia cold magnetic balance wind-tunnel facility is expected to consist of measurements of the balance forces and moments, and the observation of the essentially six degree of freedom motion of the model. The aerodynamic derivatives of the model are to be evaluated from these observations. The basic feasibility of extracting aerodynamic information from the observation of a model which is executing transient, complex, multi-degree of freedom motion is demonstrated. It is considered significant that, though the problem treated here involves only linear aerodynamics, the methods used are capable of handling a very large class of aerodynamic nonlinearities. The basic considerations include the effect of noise in the data on the accuracy of the extracted information. Relationships between noise level and the accuracy of the evaluated aerodynamic derivatives are presented.
Fundamental investigation of road vehicle aerodynamics
NASA Astrophysics Data System (ADS)
Al-Garni, Abdullah Mohammed
The present investigation focuses on the aerodynamics of pickup trucks and SUVs. The flow about generic pickup truck and SUV models and a much simpler bluff body model known as the Square Back (SB) model has been documented experimentally. The main objective of the present research is to gain a better understanding of the pickup truck and SUV aerodynamics through mean and unsteady pressure measurements as well as detailed flow field measurements using PIV. The mean pressure results of the pickup truck show that the pressure outside the tailgate is higher than inside the tailgate suggesting that the tailgate reduces aerodynamic drag. Pressure fluctuation spectra indicate a spectral peak at a Strouhal number of ˜0.094 for the SB model and ˜0.07 for the SUV and pickup truck models. Velocity field measurements in horizontal planes behind the SUV and SB models show a similar flow pattern characterized by a recirculation region at the base of the model with length about 1.15 times the width of the model. The flow in the symmetry plane varies considerably between models. For the SUV there is strong upwash while for the pickup truck, there is a recirculation region inside the bed and a strong downwash behind the tailgate. For the present pickup truck model the bed recirculation region is bounded by a shear layer which does not interact directly with the tailgate. Proper Orthogonal Decomposition (POD) analysis was applied to the PIV data at selected planes in order to identify the most energetic structures in the wake of these models. It is shown that the first two modes contain almost 20% of the total fluctuation energy while 70% of energy is captured by the first twenty modes. When the most energetic modes were used in reconstruction of the flow field in the wake of SB and SUV, flapping and breathing like motions resulted. For the pickup truck it is shown that some modes capture the energy in the underbody shear layer while other modes seem to contribute more to the cab
NASA Technical Reports Server (NTRS)
Andrisani, D., II; Daughaday, H.; Dittenhauser, J.; Rynaski, E.
1978-01-01
The aerodynamics, control system, instrumentation complement and recording system of the USAF Total In/Flight Simulator (TIFS) airplane are described. A control system that would allow the ailerons to be operated collectively, as well as, differentially to entrance the ability of the vehicle to perform the dual function of maneuver load control and gust alleviation is emphasized. Mathematical prediction of the rigid body and the flexible equations of longitudinal motion using the level 2.01 FLEXSTAB program are included along with a definition of the vehicle geometry, the mass and stiffness distribution, the calculated mode frequencies and mode shapes, and the resulting aerodynamic equations of motion of the flexible vehicle. A complete description of the control and instrumentation system of the aircraft is presented, including analysis, ground test and flight data comparisons of the performance and bandwidth of the aerodynamic surface servos. Proposed modification for improved performance of the servos are also presented.
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.
NASA Astrophysics Data System (ADS)
Paterson, G. W.; Bentley, S. J.; Holland, M. C.; Thayne, I. G.; Long, A. R.
2011-09-01
The admittances and subthreshold characteristics of capacitors and MOSFETs on buried InxGa1-xAs channel wafers with a dielectric stack of Gd0.25Ga0.15O0.6/Ga2O3 deposited on GaAs and In0.53Ga0.47As are reported. Both the GaAs and InGaAs interface samples show admittance characteristics indicative of the presence of defect states within the oxide, in agreement with previously reported data from the same oxides on n+ substrates. The interface state model is applied to the admittance data to extract an apparent interface state density (Dit) that includes interface and oxide states. The Dit profiles are very different and have pronounced effects on the device performance. The device subthreshold swings (SS) at low source-drain voltages are also used to extract an apparent Dit. A simple method is used to estimate the Fermi-level position within the bandgap (Et) at threshold, and the resulting Dit(Et) are found to be in good agreement with the admittance data. The importance of proper interpretation of SS and Dit in general and in GaAs interface devices in particular is emphasized. A model that accounts for the logarithmic sweep rate dependence of the extracted Dit due to the presence of oxide states is reported and used to estimate their density from SS measurements. The implications of the band parameters of an oxide with defect states within it for the comparison of different oxides on the same substrate and the issues around the comparison of results in general are discussed.
Harloff, G.J.
1985-09-01
A theoretical aerodynamic model of lift and drag forces on a flat plate at angle of attack and at hypersonic speeds is presented. Real gas effects and friction drag are accounted for. Theoretical results are presented as a function of the viscous interaction parameter. The performance for two geometries is presented. 3 refs., 8 figs., 4 tabs.
NASA Technical Reports Server (NTRS)
Karpel, M.
1994-01-01
Various control analysis, design, and simulation techniques of aeroservoelastic systems require the equations of motion to be cast in a linear, time-invariant state-space form. In order to account for unsteady aerodynamics, rational function approximations must be obtained to represent them in the first order equations of the state-space formulation. A computer program, MIST, has been developed which determines minimum-state approximations of the coefficient matrices of the unsteady aerodynamic forces. The Minimum-State Method facilitates the design of lower-order control systems, analysis of control system performance, and near real-time simulation of aeroservoelastic phenomena such as the outboard-wing acceleration response to gust velocity. Engineers using this program will be able to calculate minimum-state rational approximations of the generalized unsteady aerodynamic forces. Using the Minimum-State formulation of the state-space equations, they will be able to obtain state-space models with good open-loop characteristics while reducing the number of aerodynamic equations by an order of magnitude more than traditional approaches. These low-order state-space mathematical models are good for design and simulation of aeroservoelastic systems. The computer program, MIST, accepts tabular values of the generalized aerodynamic forces over a set of reduced frequencies. It then determines approximations to these tabular data in the LaPlace domain using rational functions. MIST provides the capability to select the denominator coefficients in the rational approximations, to selectably constrain the approximations without increasing the problem size, and to determine and emphasize critical frequency ranges in determining the approximations. MIST has been written to allow two types data weighting options. The first weighting is a traditional normalization of the aerodynamic data to the maximum unit value of each aerodynamic coefficient. The second allows weighting the
Multiprocessing on supercomputers for computational aerodynamics
NASA Technical Reports Server (NTRS)
Yarrow, Maurice; Mehta, Unmeel B.
1991-01-01
Little use is made of multiple processors available on current supercomputers (computers with a theoretical peak performance capability equal to 100 MFLOPS or more) to improve turnaround time in computational aerodynamics. The productivity of a computer user is directly related to this turnaround time. In a time-sharing environment, such improvement in this speed is achieved when multiple processors are used efficiently to execute an algorithm. The concept of multiple instructions and multiple data (MIMD) is applied through multitasking via a strategy that requires relatively minor modifications to an existing code for a single processor. This approach maps the available memory to multiple processors, exploiting the C-Fortran-Unix interface. The existing code is mapped without the need for developing a new algorithm. The procedure for building a code utilizing this approach is automated with the Unix stream editor.
Transonic Blunt Body Aerodynamic Coefficients Computation
NASA Astrophysics Data System (ADS)
Sancho, Jorge; Vargas, M.; Gonzalez, Ezequiel; Rodriguez, Manuel
2011-05-01
In the framework of EXPERT (European Experimental Re-entry Test-bed) accurate transonic aerodynamic coefficients are of paramount importance for the correct trajectory assessment and parachute deployment. A combined CFD (Computational Fluid Dynamics) modelling and experimental campaign strategy was selected to obtain accurate coefficients. A preliminary set of coefficients were obtained by CFD Euler inviscid computation. Then experimental campaign was performed at DNW facilities at NLR. A profound review of the CFD modelling was done lighten up by WTT results, aimed to obtain reliable values of the coefficients in the future (specially the pitching moment). Study includes different turbulence modelling and mesh sensitivity analysis. Comparison with the WTT results is explored, and lessons learnt are collected.
Methods of reducing vehicle aerodynamic drag
Sirenko V.; Rohatgi U.
2012-07-08
A small scale model (length 1710 mm) of General Motor SUV was built and tested in the wind tunnel for expected wind conditions and road clearance. Two passive devices, rear screen which is plate behind the car and rear fairing where the end of the car is aerodynamically extended, were incorporated in the model and tested in the wind tunnel for different wind conditions. The conclusion is that rear screen could reduce drag up to 6.5% and rear fairing can reduce the drag by 26%. There were additional tests for front edging and rear vortex generators. The results for drag reduction were mixed. It should be noted that there are aesthetic and practical considerations that may allow only partial implementation of these or any drag reduction options.
Aerodynamics of seeing on large transport aircraft
NASA Technical Reports Server (NTRS)
Rose, W. C.
1986-01-01
Data were obtained in the full scale flight environment of the Kuiper Airborne Observatory (KAO) on the nature of turbulent shear layer over the open cavity. These data were used to verify proposed aerodynamic scaling relationships to describe the behavior of the turbulent layers and to estimate the optical performance of systems of various wavelengths operating within the KAO environment. These data and wind tunnel data are used to scale the expected optical effects for a potential stratospheric observatory for infrared astronomy (SOFIA) in which a telescope approximately 3.5 times larger than that on the KAO is envisioned. It appears that the use of combinations of active and passive aeromechanical flow control techniques can improve the optical behavior of systems in the SOFIA environment. Experiments to verify these potential improvements can be performed on the KAO with sufficient modifications to the cavity and aero-mechanical technique installations.
CFD calculations of S809 aerodynamic characteristics
Wolfe, W.P.; Ochs, S.S.
1997-01-01
Steady-state, two-dimensional CFD calculations were made for the S809 laminar-flow, wind-turbine airfoil using the commercial code CFD-ACE. Comparisons of the computed pressure and aerodynamic coefficients were made with wind tunnel data from the Delft University 1.8 m x 1.25 m low-turbulence wind tunnel. This work highlights two areas in CFD that require further investigation and development in order to enable accurate numerical simulations of flow about current generation wind-turbine airfoils: transition prediction and turbulence modeling. The results show that the laminar-to-turbulent transition point must be modeled correctly to get accurate simulations for attached flow. Calculations also show that the standard turbulence model used in most commercial CFD codes, the k-{epsilon} model, is not appropriate at angles of attack with flow separation.
Beyond robins: aerodynamic analyses of animal flight
Hedenström, Anders; Spedding, Geoffrey
2008-01-01
Recent progress in studies of animal flight mechanics is reviewed. A range of birds, and now bats, has been studied in wind tunnel facilities, revealing an array of wake patterns caused by the beating wings and also by the drag on the body. Nevertheless, the quantitative analysis of these complex wake structures shows a degree of similarity among all the different wake patterns and a close agreement with standard quasi-steady aerodynamic models and predictions. At the same time, new data on the flow over a bat wing in mid-downstroke show that, at least in this case, such simplifications cannot be useful in describing in detail either the wing properties or control prospects. The reasons for these apparently divergent results are discussed and prospects for future advances are considered. PMID:18397865
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.
Upper surface blowing aerodynamic and acoustic characteristics
NASA Technical Reports Server (NTRS)
Ryle, D. M., Jr.; Braden, J. A.; Gibson, J. S.
1977-01-01
Aerodynamic performance at cruise, and noise effects due to variations in nacelle and wing geometry and mode of operation are studied using small aircraft models that simulate upper surface blowing (USB). At cruise speeds ranging from Mach .50 to Mach .82, the key determinants of drag/thrust penalties are found to be nozzle aspect ratio, boattailing angle, and chordwise position; number of nacelles; and streamlined versus symmetric configuration. Recommendations are made for obtaining favorable cruise configurations. The acoustic studies, which concentrate on the noise created by the jet exhaust flow and its interaction with wing and flap surfaces, isolate several important sources of USB noise, including nozzle shape, exit velocity, and impingement angle; flow pathlength; and flap angle and radius of curvature. Suggestions for lessening noise due to trailing edge flow velocity, flow pathlength, and flow spreading are given, though compromises between some design options may be necessary.
Aerodynamic analysis of hypersonic waverider aircraft
NASA Technical Reports Server (NTRS)
Sandlin, Doral R.; Pessin, David N.
1993-01-01
The purpose of this study is to validate two existing codes used by the Systems Analysis Branch at NASA ARC, and to modify the codes so they can be used to generate and analyze waverider aircraft at on-design and off-design conditions. To generate waverider configurations and perform the on-design analysis, the appropriately named Waverider code is used. The Waverider code is based on the Taylor-Maccoll equations. Validation is accomplished via a comparison with previously published results. The Waverider code is modified to incorporate a fairing to close off the base area of the waverider configuration. This creates a more realistic waverider. The Hypersonic Aircraft Vehicle Optimization Code (HAVOC) is used to perform the off-design analysis of waverider configurations generated by the Waverider code. Various approximate analysis methods are used by HAVOC to predict the aerodynamic characteristics, which are validated via a comparison with experimental results from a hypersonic test model.
Aerodynamic characteristics of the Fiat UNO car
Costelli, A.F.
1984-01-01
The purpose of this article is to describe the work conducted in the aerodynamic field throughout the 4-year development and engineering time span required by the project of the UNO car. A description is given of all the parametric studies carried out. Through these studies two types of cars at present in production were defined and the characteristics of a possible future sports version laid down. A movable device, to be fitted in the back window, was also set up and patented. When actuated it reduces soiling of back window. A description is also provided of the measurements made in the car flow field and some considerations are outlined about the method applied. This method is still in development phase but it already permits some considerations and in-depth investigations to be made on the vehicle wake.
Numerical aerodynamic simulation facility feasibility study
NASA Technical Reports Server (NTRS)
1979-01-01
There were three major issues examined in the feasibility study. First, the ability of the proposed system architecture to support the anticipated workload was evaluated. Second, the throughput of the computational engine (the flow model processor) was studied using real application programs. Third, the availability reliability, and maintainability of the system were modeled. The evaluations were based on the baseline systems. The results show that the implementation of the Numerical Aerodynamic Simulation Facility, in the form considered, would indeed be a feasible project with an acceptable level of risk. The technology required (both hardware and software) either already exists or, in the case of a few parts, is expected to be announced this year. Facets of the work described include the hardware configuration, software, user language, and fault tolerance.
Aerodynamic levitation : an approach to microgravity.
Glorieux, B.; Saboungi, M.-L.; Millot, F.; Enderby, J.; Rifflet, J.-C.
2000-12-05
Measurements of the thermophysical and structural properties of liquid materials at high temperature have undergone considerable development in the past few years. Following improvements in electromagnetic levitation, aerodynamic levitation associated with laser heating has shown promise for assessing properties of different molten materials (metals, oxides, and semiconductors), preserving sample purity over a wide range of temperatures and under different gas environments. The density, surface tension and viscosity are measured with a high-speed video camera and an image analysis system. Results on nickel and alumina show that small droplets can be considered in the first approximation to be under microgravity conditions. Using a non-invasive contactless technique recently developed to measure electrical conductivity, results have been extended to variety of materials ranging from liquid metals and liquid semiconductors to ionically conducting materials. The advantage of this technique is the feasibility of monitoring changes in transport occurring during phase transitions and in deeply undercooled states.
Aerodynamic and Aerothermal TPS Instrumentation Reference Guide
NASA Technical Reports Server (NTRS)
Woollard, Bryce A.; Braun, Robert D.; Bose, Deepack
2016-01-01
The hypersonic regime of planetary entry combines the most severe environments that an entry vehicle will encounter with the greatest amount of uncertainty as to the events unfolding during that time period. This combination generally leads to conservatism in the design of an entry vehicle, specifically that of the thermal protection system (TPS). Each planetary entry provides a valuable aerodynamic and aerothermal testing opportunity; the utilization of this opportunity is paramount in better understanding how a specific entry vehicle responds to the demands of the hypersonic entry environment. Previous efforts have been made to instrument entry vehicles in order to collect data during the entry period and reconstruct the corresponding vehicle response. The purpose of this paper is to cumulatively document past TPS instrumentation designs for applicable planetary missions, as well as to list pertinent results and any explainable shortcomings.
Aerodynamics of a golf ball with grooves
NASA Astrophysics Data System (ADS)
Kim, Jooha; Son, Kwangmin; Choi, Haecheon
2009-11-01
It is well known that the drag on a dimpled ball is much lower than that on smooth ball. Choi et al. (Phys. Fluids, 2006) showed that turbulence is generated through the instability of shear layer separating from the edge of dimples and delays flow separation. Based on this mechanism, we devise a new golf ball with grooves on the surface but without any dimples. To investigate the aerodynamic performance of this new golf ball, an experiment is conducted in a wind tunnel at the Reynolds numbers of 0.5 x10^5 - 2.7 x10^5 and the spin ratios (ratio of surface velocity to the free-stream velocity) of α=0 - 0.5, which are within the ranges of real golf-ball velocity and spin rate. We measure the drag and lift forces on the grooved ball and compare them with those of smooth ball. At zero spin, the drag coefficient on the grooved ball shows a rapid fall-off at a critical Reynolds number and maintains a minimum value which is lower by 50% than that on smooth ball. At non-zero α, the drag coefficient on the grooved ball increases with increasing α, but is still lower by 40% than that on smooth ball. The lift coefficient on the grooved ball increases with increasing α, and is 100% larger than that on smooth ball. The aerodynamic characteristics of grooved ball is in general quite similar to that of dimpled ball. Some more details will be discussed in the presentation.
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.
Dynamic stability of an aerodynamically efficient motorcycle
NASA Astrophysics Data System (ADS)
Sharma, Amrit; Limebeer, David J. N.
2012-08-01
Motorcycles exhibit two potentially dangerous oscillatory modes known as 'wobble' and 'weave'. The former is reminiscent of supermarket castor shimmy, while the latter is a low frequency 'fish-tailing' motion that involves a combination of rolling, yawing, steering and side-slipping motions. These unwanted dynamic features, which can occur when two-wheeled vehicles are operated at speed, have been studied extensively. The aim of this paper is to use mathematical analysis to identify important stability trends in the on-going design of a novel aerodynamically efficient motorcycle known as the ECOSSE Spirit ES1. A mathematical model of the ES1 is developed using a multi-body dynamics software package called VehicleSim [Anon, VehicleSim Lisp Reference Manual Version 1.0, Mechanical Simulation Corporation, 2008. Available at http://www.carsim.com]. This high-fidelity motorcycle model includes realistic tyre-road contact geometry, a comprehensive tyre model, tyre relaxation and a flexible frame. A parameter set representative of a modern high-performance machine and rider is used. Local stability is investigated via the eigenvalues of the linearised models that are associated with equilibrium points of interest. A comprehensive study of the effects of frame flexibilities, acceleration, aerodynamics and tyre variations is presented, and an optimal passive steering compensator is derived. It is shown that the traditional steering damper cannot be used to stabilise the ES1 over its entire operating speed range. A simple passive compensator, involving an inerter is proposed. Flexibility can be introduced deliberately into various chassis components to change the stability characteristics of the vehicle; the implications of this idea are studied.
Aerodynamic properties of turbulent combustion fields
NASA Technical Reports Server (NTRS)
Hsiao, C. C.; Oppenheim, A. K.
1985-01-01
Flow fields involving turbulent flames in premixed gases under a variety of conditions are modeled by the use of a numerical technique based on the random vortex method to solve the Navier-Stokes equations and a flame propagation algorithm to trace the motion of the front and implement the Huygens principle, both due to Chorin. A successive over-relaxation hybrid method is applied to solve the Euler equation for flows in an arbitrarily shaped domain. The method of images, conformal transformation, and the integral-equation technique are also used to treat flows in special cases, according to their particular requirements. Salient features of turbulent flame propagation in premixed gases are interpreted by relating them to the aerodynamic properties of the flow field. Included among them is the well-known cellular structure of flames stabilized by bluff bodies, as well as the formation of the characteristic tulip shape of flames propagating in ducts. In its rudimentary form, the mechanism of propagation of a turbulent flame is shown to consist of: (1) rotary motion of eddies at the flame front, (2) self-advancement of the front at an appropriate normal burning speed, and (3) dynamic effects of expansion due to exothermicity of the combustion reaction. An idealized model is used to illustrate these fundamental mechanisms and to investigate basic aerodynamic features of flames in premixed gases. The case of a confined flame stabilized behind a rearward-facing step is given particular care and attention. Solutions are shown to be in satisfactory agreement with experimental results, especially with respect to global properties such as the average velocity profiles and reattachment length.
Aerodynamics modeling of towed-cable dynamics
Kang, S.W.; Latorre, V.R.
1991-01-17
The dynamics of a cable/drogue system being towed by an orbiting aircraft has been investigated as a part of an LTWA project for the Naval Air Systems Command. We present here a status report on the tasks performed under Phase 1. We have accomplished the following tasks under Phase 1: A literature survey on the towed-cable motion problem has been conducted. While both static (steady-state) and dynamic (transient) analyses exist in the literature, no single, comprehensive analysis exists that directly addresses the present problem. However, the survey also reveals that, when judiciously applied, these past analyses can serve as useful building blocks for approaching the present problem. A numerical model that addresses several aspects of the towed-cable dynamic problem has been adapted from a Canadian underwater code for the present aerodynamic situation. This modified code, called TOWDYN, analyzes the effects of gravity, tension, aerodynamic drag, and wind. Preliminary results from this code demonstrate that the wind effects alone CAN generate the drogue oscillation behavior, i.e., the yo-yo'' phenomenon. This code also will serve as a benchmark code for checking the accuracy of a more general and complete R D'' model code. We have initiated efforts to develop a general R D model supercomputer code that also takes into account other physical factors, such as induced oscillations and bending stiffness. This general code will be able to evaluate the relative impacts of the various physical parameters, which may become important under certain conditions. This R D code will also enable development of a simpler operational code that can be used by the Naval Air personnel in the field.
Ares I Aerodynamic Testing at the Boeing Polysonic Wind Tunnel
NASA Technical Reports Server (NTRS)
Pinier, Jeremy T.; Niskey, Charles J.; Hanke, Jeremy L.; Tomek, William G.
2011-01-01
Throughout three full design analysis cycles, the Ares I project within the Constellation program has consistently relied on the Boeing Polysonic Wind Tunnel (PSWT) for aerodynamic testing of the subsonic, transonic and supersonic portions of the atmospheric flight envelope (Mach=0.5 to 4.5). Each design cycle required the development of aerodynamic databases for the 6 degree-of-freedom (DOF) forces and moments, as well as distributed line-loads databases covering the full range of Mach number, total angle-of-attack, and aerodynamic roll angle. The high fidelity data collected in this facility has been consistent with the data collected in NASA Langley s Unitary Plan Wind Tunnel (UPWT) at the overlapping condition ofMach=1.6. Much insight into the aerodynamic behavior of the launch vehicle during all phases of flight was gained through wind tunnel testing. Important knowledge pertaining to slender launch vehicle aerodynamics in particular was accumulated. In conducting these wind tunnel tests and developing experimental aerodynamic databases, some challenges were encountered and are reported as lessons learned in this paper for the benefit of future crew launch vehicle aerodynamic developments.
Variational Methods in Sensitivity Analysis and Optimization for Aerodynamic Applications
NASA Technical Reports Server (NTRS)
Ibrahim, A. H.; Hou, G. J.-W.; Tiwari, S. N. (Principal Investigator)
1996-01-01
Variational methods (VM) sensitivity analysis, which is the continuous alternative to the discrete sensitivity analysis, is employed to derive the costate (adjoint) equations, the transversality conditions, and the functional sensitivity derivatives. In the derivation of the sensitivity equations, the variational methods use the generalized calculus of variations, in which the variable boundary is considered as the design function. The converged solution of the state equations together with the converged solution of the costate equations are integrated along the domain boundary to uniquely determine the functional sensitivity derivatives with respect to the design function. The determination of the sensitivity derivatives of the performance index or functional entails the coupled solutions of the state and costate equations. As the stable and converged numerical solution of the costate equations with their boundary conditions are a priori unknown, numerical stability analysis is performed on both the state and costate equations. Thereafter, based on the amplification factors obtained by solving the generalized eigenvalue equations, the stability behavior of the costate equations is discussed and compared with the state (Euler) equations. The stability analysis of the costate equations suggests that the converged and stable solution of the costate equation is possible only if the computational domain of the costate equations is transformed to take into account the reverse flow nature of the costate equations. The application of the variational methods to aerodynamic shape optimization problems is demonstrated for internal flow problems at supersonic Mach number range. The study shows, that while maintaining the accuracy of the functional sensitivity derivatives within the reasonable range for engineering prediction purposes, the variational methods show a substantial gain in computational efficiency, i.e., computer time and memory, when compared with the finite
Aerodynamic shape optimization of a HSCT type configuration with improved surface definition
NASA Technical Reports Server (NTRS)
Thomas, Almuttil M.; Tiwari, Surendra N.
1994-01-01
Two distinct parametrization procedures of generating free-form surfaces to represent aerospace vehicles are presented. The first procedure is the representation using spline functions such as nonuniform rational b-splines (NURBS) and the second is a novel (geometrical) parametrization using solutions to a suitably chosen partial differential equation. The main idea is to develop a surface which is more versatile and can be used in an optimization process. Unstructured volume grid is generated by an advancing front algorithm and solutions obtained using an Euler solver. Grid sensitivity with respect to surface design parameters and aerodynamic sensitivity coefficients based on potential flow is obtained using an automatic differentiator precompiler software tool. Aerodynamic shape optimization of a complete aircraft with twenty four design variables is performed. High speed civil transport aircraft (HSCT) configurations are targeted to demonstrate the process.
Incompressible lifting-surface aerodynamics for a rotor-stator combination
NASA Technical Reports Server (NTRS)
Ramachandra, S. M.
1984-01-01
Current literature on the three dimensional flow through compressor cascades deals with a row of rotor blades in isolation. Since the distance between the rotor and stator is usually 10 to 20 percent of the blade chord, the aerodynamic interference between them has to be considered for a proper evaluation of the aerothermodynamic performance of the stage. A unified approach to the aerodynamics of the incompressible flow through a stage is presented that uses the lifting surface theory for a compressor cascade of arbitrary camber and thickness distribution. The effects of rotor stator interference are represented as a linear function of the rotor and stator flows separately. The loading distribution on the rotor and stator flows separately. The loading distribution on the rotor and stator blades and the interference factor are determined concurrently through a matrix iteration process.
Using High Resolution Design Spaces for Aerodynamic Shape Optimization Under Uncertainty
NASA Technical Reports Server (NTRS)
Li, Wu; Padula, Sharon
2004-01-01
This paper explains why high resolution design spaces encourage traditional airfoil optimization algorithms to generate noisy shape modifications, which lead to inaccurate linear predictions of aerodynamic coefficients and potential failure of descent methods. By using auxiliary drag constraints for a simultaneous drag reduction at all design points and the least shape distortion to achieve the targeted drag reduction, an improved algorithm generates relatively smooth optimal airfoils with no severe off-design performance degradation over a range of flight conditions, in high resolution design spaces parameterized by cubic B-spline functions. Simulation results using FUN2D in Euler flows are included to show the capability of the robust aerodynamic shape optimization method over a range of flight conditions.
NASA Technical Reports Server (NTRS)
Klein, Vladislav; Noderer, Keith D.
1995-01-01
Aerodynamic equations with unsteady effects were formulated for an aircraft in one-degree-of-freedom, small-amplitude, harmonic motion. These equations were used as a model for aerodynamic parameter estimation from wind tunnel oscillatory data. The estimation algorithm was based on nonlinear least squares and was applied in three examples to the oscillatory data in pitch and roll of 70 deg triangular wing and an X-31 model, and in-sideslip oscillatory data of the High Incidence Research Model 2 (HIRM 2). All three examples indicated that a model using a simple indicial function can explain unsteady effects observed in measured data. The accuracy of the estimated parameters and model verification were strongly influenced by the number of data points with respect to the number of unknown parameters.