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Sample records for abrupt wing stall

  1. Recommended Experimental Procedures for Evaluation of Abrupt Wing Stall Characteristics

    NASA Technical Reports Server (NTRS)

    Capone, F. J.; Hall, R. M.; Owens, D. B.; Lamar, J. E.; McMillin, S. N.

    2003-01-01

    This paper presents a review of the experimental program under the Abrupt Wing Stall (AWS) Program. Candidate figures of merit from conventional static tunnel tests are summarized and correlated with data obtained in unique free-to-roll tests. Where possible, free-to-roll results are also correlated with flight data. Based on extensive studies of static experimental figures of merit in the Abrupt Wing Stall Program for four different aircraft configurations, no one specific figure of merit consistently flagged a warning of potential lateral activity when actual activity was seen to occur in the free-to-roll experiments. However, these studies pointed out the importance of measuring and recording the root mean square signals of the force balance.

  2. Free-To-Roll Analysis of Abrupt Wing Stall on Military Aircraft at Transonic Speeds

    NASA Technical Reports Server (NTRS)

    Owens, D. Bruce; Capone, Francis J.; Brandon, Jay M.; Cunningham, Kevin; Chambers, Joseph R.

    2003-01-01

    Transonic free-to-roll and static wind tunnel tests for four military aircraft - the AV-8B, the F/A-18C, the preproduction F/A-18E, and the F-16C - have been analyzed. These tests were conducted in the NASA Langley 16-Foot Transonic Tunnel as a part of the NASA/Navy/Air Force Abrupt Wing Stall Program. The objectives were to evaluate the utility of the free-to-roll test technique as a tool for predicting areas of significant uncommanded lateral motions and for gaining insight into the wing-drop and wing-rock behavior of military aircraft at transonic conditions. The analysis indicated that the free-to-roll results had good agreement with flight data on all four models. A wide range of motions - limit cycle wing rock, occasional and frequent damped wing drop/rock and wing rock divergence - were observed. The analysis shows the effects that the static and dynamic lateral stability can have on the wing drop/rock behavior. In addition, a free-to-roll figure of merit was developed to assist in the interpretation of results and assessment of the severity of the motions.

  3. Accomplishments of the Abrupt Wing Stall (AWS) Program and Future Research Requirements

    NASA Technical Reports Server (NTRS)

    Hall, Robert M.; Woodson, Shawn H.; Chambers, Joseph R.

    2003-01-01

    The Abrupt Wing Stall (AWS) Program has addressed the problem of uncommanded lateral motions, such as wing drop and wing rock, at transonic speeds. The genesis of this Program was the experience of the F/A-18E/F Program in the late 199O's, when wing drop was discovered in the heart of the maneuver envelope for the pre-production aircraft. While the F/A-18E/F problem was subsequently corrected by a leading-edge flap scheduling change and the addition of a porous door to the wing fold fairing, the AWS Program was initiated as a national response to the lack of technology readiness available at the time of the F/A-18E/F Development Program. The AWS Program objectives were to define causal factors for the F/A-18E/F experience, to gain insights into the flow physics associated with wing drop, and to develop methods and analytical tools so that future programs could identify this type of problem before going to flight test. The paper reviews, for the major goals of the AWS Program, the status of the technology before the program began, the program objectives, accomplishments, and impacts. Lessons learned are presented for the benefit of future programs that must assess whether a vehicle will have uncommanded lateral motions before going to flight test. Finally, recommended future research needs are presented in light of the AWS Program experience.

  4. Accomplishments of the Abrupt Wing Stall (AWS) Program and Future Research Requirements

    NASA Technical Reports Server (NTRS)

    Hall, Robert M.; Woodson, Shawn H.; Chambers, Joseph R.

    2003-01-01

    The Abrupt Wing Stall (AWS) Program has addressed the problem of uncommanded lateral motions, such as wing drop and wing rock, at transonic speeds. The genesis of this Program was the experience of the F/A-1 8E/F Program in the late 1990's, when wing drop was discovered in the heart of the maneuver envelope for the pre-production aircraft. While the F/A-1 8E/F problem was subsequently corrected by a leading-edge flap scheduling change and the addition of a porous door to the wing fold fairing, the AWS Program was initiated as a national response to the lack of technology readiness available at the time of the F/A-18E/F Development Program. The AWS Program objectives were to define causal factors for the F/A-18E/F experience, to gain insights into the flow physics associated with wing drop, and to develop methods and analytical tools so that future programs could identify this type of problem before going to flight test. The paper reviews, for the major goals of the AWS Program, the status of the technology before the

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

    NASA Technical Reports Server (NTRS)

    Schuster, David M.; Byrd, James E.

    2003-01-01

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

  6. 14 CFR 23.201 - Wings level stall.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Wings level stall. 23.201 Section 23.201... STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Flight Stalls § 23.201 Wings level... airplane stalls. (b) The wings level stall characteristics must be demonstrated in flight as follows...

  7. The effects of leading edge modifications on the post-stall characteristics of wings

    NASA Technical Reports Server (NTRS)

    Winkelmann, A. E.; Barlow, J. B.; Saini, J. K.; Anderson, J. D., Jr.; Jones, E.

    1980-01-01

    An investigation of the effects of leading edge modifications on the post-stall characteristics of two rectangular planform wings in a series of low speed wind tunnel tests is presented. Abrupt discontinuities in the leading edge shape of the wings were produced by placing a nose glove over a portion of the span or by deflecting sections of a segmented leading edge flap. Six component balance data, oil flow visualization photographs, and pressure distribution measurements were obtained, and tests made to study the development of flow separation at stall on small scale planform wing models. Results of oil flow visualization tests at and beyond stall showed the formation of counter-rotating swirl patterns on the upper surface of the '2-D' and '3-D' wings, and results of a numerical lifting line technique applied to wings with leading edge modifications are included.

  8. 14 CFR 23.201 - Wings level stall.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... produce and to correct roll by unreversed use of the rolling control and to produce and to correct yaw by unreversed use of the directional control, up to the time the airplane stalls. (b) The wings level stall... speed, the elevator control must be pulled back so that the rate of speed reduction will not exceed one...

  9. Study of the Unsteady Flow Features on a Stalled Wing

    NASA Technical Reports Server (NTRS)

    Yon, Steven A.; Katz, Joseph

    1997-01-01

    The occurrence of large scale structures in the post stall flow over a rectangular wing at high angles of attack was investigated in a small-scale subsonic wind tunnel. Mean and time dependent measurements within the separated flow field suggest the existence of two distinct angle of attack regimes beyond wing stall. The shallow stall regime occurs over a narrow range of incidence angles (2-3 deg.) immediately following the inception of leading edge separation. In this regime, the principal mean flow structures, termed stall cells, are manifested as a distinct spanwise periodicity in the chordwise extent of the separated region on the model surface with possible lateral mobility not previously reported. Within the stall cells and on the wing surface, large amplitude pressure fluctuations occur with a frequency much lower than anticipated for bluff body shedding, and with minimum effect in the far wake. In the deep stall regime, stall cells are not observed and the separated region near the model is relatively free of large amplitude pressure disturbances.

  10. Vorticity Transport on a Flexible Wing in Stall Flutter

    NASA Astrophysics Data System (ADS)

    Akkala, James; Buchholz, James; Farnsworth, John; McLaughlin, Thomas

    2014-11-01

    The circulation budget within dynamic stall vortices was investigated on a flexible NACA 0018 wing model of aspect ratio 6 undergoing stall flutter. The wing had an initial angle of attack of 6 degrees, Reynolds number of 1 . 5 ×105 and large-amplitude, primarily torsional, limit cycle oscillations were observed at a reduced frequency of k = πfc / U = 0 . 1 . Phase-locked stereo PIV measurements were obtained at multiple chordwise planes around the 62.5% and 75% spanwise locations to characterize the flow field within thin volumetric regions over the suction surface. Transient surface pressure measurements were used to estimate boundary vorticity flux. Recent analyses on plunging and rotating wings indicates that the magnitude of the pressure-gradient-driven boundary flux of secondary vorticity is a significant fraction of the magnitude of the convective flux from the separated leading-edge shear layer, suggesting that the secondary vorticity plays a significant role in regulating the strength of the primary vortex. This phenomenon is examined in the present case, and the physical mechanisms governing the growth and evolution of the dynamic stall vortices are explored. This work was supported by the Air Force Office of Scientific Research through the Flow Interactions and Control Program monitored by Dr. Douglas Smith, and through the 2014 AFOSR/ASEE Summer Faculty Fellowship Program (JA and JB).

  11. Analysis of Low-Speed Stall Aerodynamics of a Swept Wing with Laminar-Flow Glove

    NASA Technical Reports Server (NTRS)

    Bui, Trong T.

    2014-01-01

    Reynolds-Averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) analysis was conducted to study the low-speed stall aerodynamics of a GIII aircraft's swept wing modified with a laminar-flow wing glove. The stall aerodynamics of the gloved wing were analyzed and compared with the unmodified wing for the flight speed of 120 knots and altitude of 2300 ft above mean sea level (MSL). The Star-CCM+ polyhedral unstructured CFD code was first validated for wing stall predictions using the wing-body geometry from the First American Institute of Aeronautics and Astronautics (AIAA) CFD High-Lift Prediction Workshop. It was found that the Star-CCM+ CFD code can produce results that are within the scattering of other CFD codes considered at the workshop. In particular, the Star-CCM+ CFD code was able to predict wing stall for the AIAA wing-body geometry to within 1 degree of angle of attack as compared to benchmark wind-tunnel test data. Current results show that the addition of the laminar-flow wing glove causes the gloved wing to stall much earlier than the unmodified wing. Furthermore, the gloved wing has a different stall characteristic than the clean wing, with no sharp lift drop-off at stall for the gloved wing.

  12. Analysis of Low Speed Stall Aerodynamics of a Swept Wing with Laminar Flow Glove

    NASA Technical Reports Server (NTRS)

    Bui, Trong T.

    2014-01-01

    Reynolds-Averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) analysis was conducted to study the low-speed stall aerodynamics of a GIII aircraft's swept wing modified with a laminar-flow wing glove. The stall aerodynamics of the gloved wing were analyzed and compared with the unmodified wing for the flight speed of 120 knots and altitude of 2300 ft above mean sea level (MSL). The Star-CCM+ polyhedral unstructured CFD code was first validated for wing stall predictions using the wing-body geometry from the First American Institute of Aeronautics and Astronautics (AIAA) CFD High-Lift Prediction Workshop. It was found that the Star-CCM+ CFD code can produce results that are within the scattering of other CFD codes considered at the workshop. In particular, the Star-CCM+ CFD code was able to predict wing stall for the AIAA wing-body geometry to within 1 degree of angle of attack as compared to benchmark wind-tunnel test data. Current results show that the addition of the laminar-flow wing glove causes the gloved wing to stall much earlier than the unmodified wing. Furthermore, the gloved wing has a different stall characteristic than the clean wing, with no sharp lift drop-off at stall for the gloved wing.

  13. A CFD Database for Airfoils and Wings at Post-Stall Angles of Attack

    NASA Technical Reports Server (NTRS)

    Petrilli, Justin; Paul, Ryan; Gopalarathnam, Ashok; Frink, Neal T.

    2013-01-01

    This paper presents selected results from an ongoing effort to develop an aerodynamic database from Reynolds-Averaged Navier-Stokes (RANS) computational analysis of airfoils and wings at stall and post-stall angles of attack. The data obtained from this effort will be used for validation and refinement of a low-order post-stall prediction method developed at NCSU, and to fill existing gaps in high angle of attack data in the literature. Such data could have potential applications in post-stall flight dynamics, helicopter aerodynamics and wind turbine aerodynamics. An overview of the NASA TetrUSS CFD package used for the RANS computational approach is presented. Detailed results for three airfoils are presented to compare their stall and post-stall behavior. The results for finite wings at stall and post-stall conditions focus on the effects of taper-ratio and sweep angle, with particular attention to whether the sectional flows can be approximated using two-dimensional flow over a stalled airfoil. While this approximation seems reasonable for unswept wings even at post-stall conditions, significant spanwise flow on stalled swept wings preclude the use of two-dimensional data to model sectional flows on swept wings. Thus, further effort is needed in low-order aerodynamic modeling of swept wings at stalled conditions.

  14. Analysis of Low-Speed Stall Aerodynamics of a Business Jets Wing Using STAR-CCM+

    NASA Technical Reports Server (NTRS)

    Bui, Trong

    2016-01-01

    Reynolds-Averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) analysis was conducted: to study the low-speed stall aerodynamics of a GIII aircrafts swept wing modified with (1) a laminar-flow wing glove, or (2) a seamless flap. The stall aerodynamics of these two different wing configurations were analyzed and compared with the unmodified baseline wing for low-speed flight. The Star-CCM+ polyhedral unstructured CFD code was first validated for wing stall predictions using the wing-body geometry from the First AIAA CFD High-Lift Prediction Workshop.

  15. Pitching effect on transonic wing stall of a blended flying wing with low aspect ratio

    NASA Astrophysics Data System (ADS)

    Tao, Yang; Zhao, Zhongliang; Wu, Junqiang; Fan, Zhaolin; Zhang, Yi

    2018-05-01

    Numerical simulation of the pitching effect on transonic wing stall of a blended flying wing with low aspect ratio was performed using improved delayed detached eddy simulation (IDDES). To capture the discontinuity caused by shock wave, a second-order upwind scheme with Roe’s flux-difference splitting is introduced into the inviscid flux. The artificial dissipation is also turned off in the region where the upwind scheme is applied. To reveal the pitching effect, the implicit approximate-factorization method with sub-iterations and second-order temporal accuracy is employed to avoid the time integration of the unsteady Navier-Stokes equations solved by finite volume method at Arbitrary Lagrange-Euler (ALE) form. The leading edge vortex (LEV) development and LEV circulation of pitch-up wings at a free-stream Mach number M = 0.9 and a Reynolds number Re = 9.6 × 106 is studied. The Q-criterion is used to capture the LEV structure from shear layer. The result shows that a shock wave/vortex interaction is responsible for the vortex breakdown which eventually causes the wing stall. The balance of the vortex strength and axial flow, and the shock strength, is examined to provide an explanation of the sensitivity of the breakdown location. Pitching motion has great influence on shock wave and shock wave/vortex interactions, which can significantly affect the vortex breakdown behavior and wing stall onset of low aspect ratio blended flying wing.

  16. Power reduction and the radial limit of stall delay in revolving wings of different aspect ratio

    PubMed Central

    Kruyt, Jan W.; van Heijst, GertJan F.; Altshuler, Douglas L.; Lentink, David

    2015-01-01

    Airplanes and helicopters use high aspect ratio wings to reduce the power required to fly, but must operate at low angle of attack to prevent flow separation and stall. Animals capable of slow sustained flight, such as hummingbirds, have low aspect ratio wings and flap their wings at high angle of attack without stalling. Instead, they generate an attached vortex along the leading edge of the wing that elevates lift. Previous studies have demonstrated that this vortex and high lift can be reproduced by revolving the animal wing at the same angle of attack. How do flapping and revolving animal wings delay stall and reduce power? It has been hypothesized that stall delay derives from having a short radial distance between the shoulder joint and wing tip, measured in chord lengths. This non-dimensional measure of wing length represents the relative magnitude of inertial forces versus rotational accelerations operating in the boundary layer of revolving and flapping wings. Here we show for a suite of aspect ratios, which represent both animal and aircraft wings, that the attachment of the leading edge vortex on a revolving wing is determined by wing aspect ratio, defined with respect to the centre of revolution. At high angle of attack, the vortex remains attached when the local radius is shorter than four chord lengths and separates outboard on higher aspect ratio wings. This radial stall limit explains why revolving high aspect ratio wings (of helicopters) require less power compared with low aspect ratio wings (of hummingbirds) at low angle of attack and vice versa at high angle of attack. PMID:25788539

  17. Short revolving wings enable hovering animals to avoid stall and reduce drag

    NASA Astrophysics Data System (ADS)

    Lentink, David; Kruyt, Jan W.; Heijst, Gertjan F.; Altshuler, Douglas L.

    2014-11-01

    Long and slender wings reduce the drag of airplanes, helicopters, and gliding animals, which operate at low angle of attack (incidence). Remarkably, there is no evidence for such influence of wing aspect ratio on the energetics of hovering animals that operate their wings at much higher incidence. High incidence causes aircraft wings to stall, hovering animals avoid stall by generating an attached vortex along the leading edge of their wings that elevates lift. Hypotheses that explain this capability include the necessity for a short radial distance between the shoulder joint and wing tip, measured in chord lengths, instead of the long tip-to-tip distance that elevates aircraft performance. This stems from how hovering animals revolve their wings around a joint, a condition for which the precise effect of aspect ratio on stall performance is unknown. Here we show that the attachment of the leading edge vortex is determined by wing aspect ratio with respect to the center of rotation-for a suite of aspect ratios that represent both animal and aircraft wings. The vortex remains attached when the local radius is shorter than 4 chord lengths, and separates outboard on more slender wings. Like most other hovering animals, hummingbirds have wing aspect ratios between 3 and 4, much stubbier than helicopters. Our results show this makes their wings robust against flow separation, which reduces drag below values obtained with more slender wings. This revises our understanding of how aspect ratio improves performance at low Reynolds numbers.

  18. 14 CFR 23.201 - Wings level stall.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... stall. (a) It must be possible to produce and to correct roll by unreversed use of the rolling control and to produce and to correct yaw by unreversed use of the directional control, up to the time the.... Starting from a speed at least 10 knots above the stall speed, the elevator control must be pulled back so...

  19. 14 CFR 23.201 - Wings level stall.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... stall. (a) It must be possible to produce and to correct roll by unreversed use of the rolling control and to produce and to correct yaw by unreversed use of the directional control, up to the time the.... Starting from a speed at least 10 knots above the stall speed, the elevator control must be pulled back so...

  20. 14 CFR 23.201 - Wings level stall.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... stall. (a) It must be possible to produce and to correct roll by unreversed use of the rolling control and to produce and to correct yaw by unreversed use of the directional control, up to the time the.... Starting from a speed at least 10 knots above the stall speed, the elevator control must be pulled back so...

  1. Analysis of Low-Speed Stall Aerodynamics of a Swept Wing with Seamless Flaps

    NASA Technical Reports Server (NTRS)

    Bui, Trong T.

    2016-01-01

    Computational fluid dynamics (CFD) analysis was conducted to study the low-speed stall aerodynamics of a Gulfstream G-III airplane (Gulfstream Aerospace Corporation, Savannah, Georgia) swept wing modified with an experimental seamless, compliant flap called the Adaptive Compliant Trailing Edge (ACTE) flap. The stall characteristics of the modified ACTE wing were analyzed and compared with the unmodified, clean wing at the flight speed of 120 knots and altitude of 2300 feet above mean sea level, in free air as well as in ground effect. A polyhedral finite-volume unstructured full Navier-Stokes CFD code, STAR-CCM (registered trademark) plus (CD-adapco [Computational Dynamics Limited, United Kingdom, and Analysis & Design Application Co., United States]), was used. Steady Reynolds-averaged Navier-Stokes CFD simulations were conducted for a clean wing and the ACTE wings at various ACTE deflection angles in free air (-2 degrees, 15 degrees, and 30 degrees) as well as in ground effect (15 degrees and 30 degrees). Solution sensitivities to grid densities were examined. In free air, the ACTE wings are predicted to stall at lower angles of attack than the clean wing. In ground effect, all wings are predicted to stall at lower angles of attack than the corresponding wings in free air. Even though the lift curves are higher in ground effect than in free air, the maximum lift coefficients for all wings are lower in ground effect. Finally, the lift increase due to ground effect for the ACTE wing is predicted to be less than the clean wing.

  2. Further studies of stall flutter and nonlinear divergence of two-dimensional wings

    NASA Technical Reports Server (NTRS)

    Dugundji, J.; Chopra, I.

    1975-01-01

    An experimental investigation is made of the purely torsional stall flutter of a two-dimensional wing pivoted about the midchord, and also of the bending-torsion stall flutter of a two-dimensional wing pivoted about the quarterchord. For the purely torsional flutter case, large amplitude limit cycles ranging from + or - 11 to + or - 160 degrees were observed. Nondimensional harmonic coefficients were extracted from the free transient vibration tests for amplitudes up to 80 degrees. Reasonable nondimensional correlation was obtained for several wing configurations. For the bending-torsion flutter case, large amplitude coupled limit cycles were observed with torsional amplitudes as large as + or - 40 degrees. The torsion amplitudes first increased, then decreased with increasing velocity. Additionally, a small amplitude, predominantly torsional flutter was observed when the static equilibrium angle was near the stall angle.

  3. An experimental study of mushroom shaped stall cells. [on finite wings with separated flow

    NASA Technical Reports Server (NTRS)

    Winkelmann, A. E.

    1982-01-01

    Surface patterns characterized by a pair of counter-rotating swirls have been observed in connection with the conduction of surface flow visualization experiments involving test geometries with separated flows. An example of this phenomenon occurring on a finite wing with trailing edge stall has been referred to by Winkelmann and Barlow (1980) as 'mushroom shaped'. A description is presented of a collection of experimental results which show or suggest the occurrence of mushroom shaped stall cells on a variety of test geometries. Investigations conducted with finite wings, airfoil models, and flat plates are considered, and attention is given to studies involving the use of bluff models, investigations of shock induced boundary layer separation, and mushroom shaped patterns observed in a number of miscellaneous cases. It is concluded that the mushroom shaped stall cell appears commonly in separated flow regions.

  4. Low-Frequency Flow Oscillations on Stalled Wings Exhibiting Cellular Separation Topology

    NASA Astrophysics Data System (ADS)

    Disotell, Kevin James

    One of the most pervasive threats to aircraft controllability is wing stall, a condition associated with loss of lift due to separation of air flow from the wing surface at high angles of attack. A recognized need for improved upset recovery training in extended-envelope flight simulators is a physical understanding of the post-stall aerodynamic environment, particularly key flow phenomena which influence the vehicle trajectory. Large-scale flow structures known as stall cells, which scale with the wing chord and are spatially-periodic along the span, have been previously observed on post-stall airfoils with trailing-edge separation present. Despite extensive documentation of stall cells in the literature, the physical mechanisms behind their formation and evolution have proven to be elusive. The undertaken study has sought to characterize the inherently turbulent separated flow existing above the wing surface with cell formation present. In particular, the question of how the unsteady separated flow may interact with the wing to produce time-averaged cellular surface patterns is considered. Time-resolved, two-component particle image velocimetry measurements were acquired at the plane of symmetry of a single stall cell formed on an extruded NACA 0015 airfoil model at chord Reynolds number of 560,000 to obtain insight into the time-dependent flow structure. The evolution of flow unsteadiness was analyzed over a static angle-of-attack range covering the narrow post-stall regime in which stall cells have been observed. Spectral analysis of velocity fields acquired near the stall angle confirmed a low-frequency flow oscillation previously detected in pointwise surface measurements by Yon and Katz (1998), corresponding to a Strouhal number of 0.042 based on frontal projected chord height. Probability density functions of the streamwise velocity component were used to estimate the convective speed of this mode at approximately half the free-stream velocity, in agreement

  5. An Iterative Decambering Approach for Post-Stall Prediction of Wing Characteristics using known Section Data

    NASA Technical Reports Server (NTRS)

    Mukherjee, Rinku; Gopalarathnam, Ashok; Kim, Sung Wan

    2003-01-01

    An iterative decambering approach for the post stall prediction of wings using known section data as inputs is presented. The method can currently be used for incompressible .ow and can be extended to compressible subsonic .ow using Mach number correction schemes. A detailed discussion of past work on this topic is presented first. Next, an overview of the decambering approach is presented and is illustrated by applying the approach to the prediction of the two-dimensional C(sub l) and C(sub m) curves for an airfoil. The implementation of the approach for iterative decambering of wing sections is then discussed. A novel feature of the current e.ort is the use of a multidimensional Newton iteration for taking into consideration the coupling between the di.erent sections of the wing. The approach lends itself to implementation in a variety of finite-wing analysis methods such as lifting-line theory, discrete-vortex Weissinger's method, and vortex lattice codes. Results are presented for a rectangular wing for a from 0 to 25 deg. The results are compared for both increasing and decreasing directions of a, and they show that a hysteresis loop can be predicted for post-stall angles of attack.

  6. Robust post-stall perching with a simple fixed-wing glider using LQR-Trees.

    PubMed

    Moore, Joseph; Cory, Rick; Tedrake, Russ

    2014-06-01

    Birds routinely execute post-stall maneuvers with a speed and precision far beyond the capabilities of our best aircraft control systems. One remarkable example is a bird exploiting post-stall pressure drag in order to rapidly decelerate to land on a perch. Stall is typically associated with a loss of control authority, and it is tempting to attribute this agility of birds to the intricate morphology of the wings and tail, to their precision sensing apparatus, or their ability to perform thrust vectoring. Here we ask whether an extremely simple fixed-wing glider (no propeller) with only a single actuator in the tail is capable of landing precisely on a perch from a large range of initial conditions. To answer this question, we focus on the design of the flight control system; building upon previous work which used linear feedback control design based on quadratic regulators (LQR), we develop nonlinear feedback control based on nonlinear model-predictive control and 'LQR-Trees'. Through simulation using a flat-plate model of the glider, we find that both nonlinear methods are capable of achieving an accurate bird-like perching maneuver from a large range of initial conditions; the 'LQR-Trees' algorithm is particularly useful due to its low computational burden at runtime and its inherent performance guarantees. With this in mind, we then implement the 'LQR-Trees' algorithm on real hardware and demonstrate a 95 percent perching success rate over 147 flights for a wide range of initial speeds. These results suggest that, at least in the absence of significant disturbances like wind gusts, complex wing morphology and sensing are not strictly required to achieve accurate and robust perching even in the post-stall flow regime.

  7. Kinematics and Flow Evolution of a Flexible Wing in Stall Flutter

    NASA Astrophysics Data System (ADS)

    Farnsworth, John; Akkala, James; Buchholz, James; McLaughlin, Thomas

    2014-11-01

    Large amplitude stall flutter limit cycle oscillations were observed on an aspect ratio six finite span NACA0018 flexible wing model at a free stream velocity of 23 m/s and an initial angle of attack of six degrees. The wing motion was characterized by periodic oscillations of predominately a torsional mode at a reduced frequency of k = 0.1. The kinematics were quantified via stereoscopic tracking of the wing surface with high speed camera imaging and direct linear transformation. Simultaneously acquired accelerometer measurements were used to track the wing motion and trigger the collection of two-dimensional particle image velocimetry field measurements to the phase angle of the periodic motion. Aerodynamically, the flutter motion is driven by the development and shedding of a dynamic stall vortex system, the evolution of which is characterized and discussed. This work was supported by the AFOSR Flow Interactions and Control Portfolio monitored by Dr. Douglas Smith and the AFOSR/ASEE Summer Faculty Fellowship Program (JA and JB).

  8. Formation and Development of the Dynamic Stall Vortex on a Wing with Leading Edge Tubercles

    NASA Astrophysics Data System (ADS)

    Hrynuk, John; Bohl, Douglas

    2015-11-01

    Humpback whales are unique in that their flippers have leading edge ``bumps'' or tubercles. Past work on airfoils inspired by whale flippers has centered on the static aerodynamic characteristics of these airfoils. The current study uses Molecular Tagging Velocimetry (MTV) to investigate the effects of tubercles on dynamically pitching NACA 0012 airfoils. A baseline (i.e. straight leading edge) wing and one modified with leading edge tubercles are investigated. Tracking of the Dynamic Stall Vortex (DSV) is performed to quantitatively compare the DSV formation location, path, and convective velocity for tubercled and baseline wings. The results show that there is a spanwise variation in the initial formation location and motion of the DSV on the modified wing. Once formed, the DSV aligns into a more uniform spanwise structure. As the pitching motion progresses, the DSV on the modified wing convects away from the airfoil surface later and slower than is observed for the baseline airfoil. The results indicate that the tubercles may delay stall when compared to the baseline airfoil. This work was supported by NSF Grant # 0845882.

  9. Effect of inlet ingestion of a wing tip vortex on compressor face flow and turbojet stall margin

    NASA Technical Reports Server (NTRS)

    Mitchell, G. A.

    1975-01-01

    A two-dimensional inlet was alternately mated to a coldpipe plug assembly and a J85-GE-13 turbojet engine, and placed in a Mach 0.4 stream so as to ingest the tip vortex of a forward mounted wing. Vortex properties were measured just forward of the inlet and at the compressor face. Results show that ingestion of a wing tip vortex by a turbojet engine can cause a large reduction in engine stall margin. The loss in stall compressor pressure ratio was primarily dependent on vortex location and rotational direction and not on total-pressure distortion.

  10. A Survey of Reynolds Number and Wing Geometry Effects on Lift Characteristics in the Low Speed Stall Region

    NASA Technical Reports Server (NTRS)

    Polhamus, Edward C.

    1996-01-01

    This paper presents a survey of the effects of Reynolds number on the low- speed lift characteristics of wings encountering separated flows at their leading and side edges, with emphasis on the region near the stall. The influence of leading-edge profile and Reynolds number on the stall characteristics of two- dimensional airfoils are reviewed first to provide a basis for evaluating three- dimensional effects associated with various wing planforms. This is followed by examples of the effects of Reynolds number and geometry on the lift characteristics near the stall for a series of three-dimensional wings typical of those suitable for high-speed aircraft and missiles. Included are examples of the effects of wing geometry on the onset and spanwise progression of turbulent reseparation near the leading edge and illustrations of the degree to which simplified theoretical approaches can be useful in defining the influence of the various geometric parameters. Also illustrated is the manner in which the Reynolds number and wing geometry parameters influence whether the turbulent reseparation near the leading edge results in a sudden loss of lift, as in the two-dimensional case, or the formation of a leading-edge vortex with Rs increase in lift followed by a gentle stall as in the highly swept wing case. Particular emphasis is placed on the strong influence of 'induced camber' on the development of turbulent reseparation. R is believed that the examples selected for this report may be useful in evaluating viscous flow solutions by the new computational methods based on the Navier-Stokes equations as well as defining fruitful research areas for the high-Reynolds-number wind tunnels.

  11. Flow-around modes for a rhomboid wing with a stall vortex in the shock layer

    NASA Astrophysics Data System (ADS)

    Zubin, M. A.; Maximov, F. A.; Ostapenko, N. A.

    2017-12-01

    The results of theoretical and experimental investigation of an asymmetrical hypersonic flow around a V-shaped wing with the opening angle larger than π on the modes with attached shockwaves on forward edges, when the stall flow is implemented on the leeward wing cantilever behind the kink point of the cross contour. In this case, a vortex of nonviscous nature is formed in which the velocities on the sphere exceeding the speed of sound and resulting in the occurrence of pressure shocks with an intensity sufficient for the separation of the turbulent boundary layer take place in the reverse flow according to the calculations within the framework of the ideal gas. It is experimentally established that a separation boundary layer can exist in the reverse flow, and its structure is subject to the laws inherent to the reverse flow in the separation region of the turbulent boundary layer arising in the supersonic conic flow under the action of a shockwave incident to the boundary layer.

  12. 2-D and 3-D oscillating wing aerodynamics for a range of angles of attack including stall

    NASA Technical Reports Server (NTRS)

    Piziali, R. A.

    1994-01-01

    A comprehensive experimental investigation of the pressure distribution over a semispan wing undergoing pitching motions representative of a helicopter rotor blade was conducted. Testing the wing in the nonrotating condition isolates the three-dimensional (3-D) blade aerodynamic and dynamic stall characteristics from the complications of the rotor blade environment. The test has generated a very complete, detailed, and accurate body of data. These data include static and dynamic pressure distributions, surface flow visualizations, two-dimensional (2-D) airfoil data from the same model and installation, and important supporting blockage and wall pressure distributions. This body of data is sufficiently comprehensive and accurate that it can be used for the validation of rotor blade aerodynamic models over a broad range of the important parameters including 3-D dynamic stall. This data report presents all the cycle-averaged lift, drag, and pitching moment coefficient data versus angle of attack obtained from the instantaneous pressure data for the 3-D wing and the 2-D airfoil. Also presented are examples of the following: cycle-to-cycle variations occurring for incipient or lightly stalled conditions; 3-D surface flow visualizations; supporting blockage and wall pressure distributions; and underlying detailed pressure results.

  13. A Cross-Validation Approach to Approximate Basis Function Selection of the Stall Flutter Response of a Rectangular Wing in a Wind Tunnel

    NASA Technical Reports Server (NTRS)

    Kukreja, Sunil L.; Vio, Gareth A.; Andrianne, Thomas; azak, Norizham Abudl; Dimitriadis, Grigorios

    2012-01-01

    The stall flutter response of a rectangular wing in a low speed wind tunnel is modelled using a nonlinear difference equation description. Static and dynamic tests are used to select a suitable model structure and basis function. Bifurcation criteria such as the Hopf condition and vibration amplitude variation with airspeed were used to ensure the model was representative of experimentally measured stall flutter phenomena. Dynamic test data were used to estimate model parameters and estimate an approximate basis function.

  14. Application of an airfoil stall flutter computer prediction program to a three-dimensional wing: Prediction versus experiment. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Muffoletto, A. J.

    1982-01-01

    An aerodynamic computer code, capable of predicting unsteady and C sub m values for an airfoil undergoing dynamic stall, is used to predict the amplitudes and frequencies of a wing undergoing torsional stall flutter. The code, developed at United Technologies Research Corporation (UTRC), is an empirical prediction method designed to yield unsteady values of normal force and moment, given the airfoil's static coefficient characteristics and the unsteady aerodynamic values, alpha, A and B. In this experiment, conducted in the PSU 4' x 5' subsonic wind tunnel, the wing's elastic axis, torsional spring constant and initial angle of attack are varied, and the oscillation amplitudes and frequencies of the wing, while undergoing torsional stall flutter, are recorded. These experimental values show only fair comparisons with the predicted responses. Predictions tend to be good at low velocities and rather poor at higher velocities.

  15. Exploratory study of the effects of wing-leading-edge modifications on the stall/spin behavior of a light general aviation airplane

    NASA Technical Reports Server (NTRS)

    1979-01-01

    Configurations with full-span and segmented leading-edge flaps and full-span and segmented leading-edge droop were tested. Studies were conducted with wind-tunnel models, with an outdoor radio-controlled model, and with a full-scale airplane. Results show that wing-leading-edge modifications can produce large effects on stall/spin characteristics, particularly on spin resistance. One outboard wing-leading-edge modification tested significantly improved lateral stability at stall, spin resistance, and developed spin characteristics.

  16. Wind-tunnel Investigation of High-lift and Stall-control Devices on a 37 Degree Sweptback Wing of Aspect Ratio 6 at High Reynolds Numbers

    NASA Technical Reports Server (NTRS)

    Koven, William; Graham, Robert R

    1948-01-01

    Results are presented of an investigation in the Langley 19-foot pressure tunnel of the longitudinal characteristics of a semispan model wing having 37 degrees sweepback of the leading edge, an aspect ratio of 6, and NACA 641-212 airfoil section perpendicular to the 27-percent-chord line. Several types of stall-control devices including extensible round-nose leading-edge flaps, a leading-edge slat, and a drooped leading edge were investigated; partial- and full-span trailing-edge split and double slotted flaps were also tested. In addition, various combinations of the aforementioned leading- and trailing-edge flaps were investigated. The tests covered a range of Reynolds numbers between 2.00 x 10(6) and 9.35 x 10(6). The wing with or without trailing-edge splity of double slotted flap was longitudinally unstable near maximum lift due to tip stalling. The addition of an outboard half-span leading-edge flap or a leading-edge slat to the plain wing or wing with inboard half-span split flaps eliminated tip stalling and resulted in stable moment variations at the stall. The drooped leading edge, on the other hand, was only effective when used in conjunction with an upper-surface fence. The combination of an outboard leading-edge device and inboard half-span double slotted flap resulted in an undesirable loop in the pitching-moment curve near maximum lift in spite of an inboard stall. The loop is attributed to the section characteristics of the double slotted flap. Air-flow surveys behind the wing indicated that a suitably placed horizontal tail would eliminate the loop in the moment curve.

  17. Simulator study of the stall departure characteristics of a light general aviation airplane with and without a wing-leading-edge modification

    NASA Technical Reports Server (NTRS)

    Riley, D. R.

    1985-01-01

    A six-degree-of-freedom nonlinear simulation was developed for a two-place, single-engine, low-wing general aviation airplane for the stall and initial departure regions of flight. Two configurations, one with and one without an outboard wing-leading-edge modification, were modeled. The math models developed are presented simulation predictions and flight-test data for validation purposes and simulation results for the two configurations for various maneuvers and power settings are compared to show the beneficial influence of adding the wing-leading-edge modification.

  18. Propeller swirl effect on single-engine general-aviation aircraft stall-spin tendencies

    NASA Technical Reports Server (NTRS)

    Katz, Joseph; Feistel, Terry W.

    1987-01-01

    An investigation is conducted of the effect of a single engine, untapered low wing general aviation aircraft propeller's swirl on the craft's stall pattern. The asymmetrical character of the propeller's swirl can trigger an early stall of one of the wings, aggravating the spin-entry condition. It is shown that the combination of this propeller-induced effect with adverse sideslip can result in large and abrupt changes in the rolling moment, in such conditions as uncoordinated low speed turning maneuvers where the pilot yaws the aircraft with wings level, rather than rolling it.

  19. Comparative developmental analysis of Drosophila and Tribolium reveals conserved and diverged roles of abrupt in insect wing evolution.

    PubMed

    Ravisankar, Padmapriyadarshini; Lai, Yi-Ting; Sambrani, Nagraj; Tomoyasu, Yoshinori

    2016-01-15

    Morphological innovation is a fundamental process in evolution, yet its molecular basis is still elusive. Acquisition of elytra, highly modified beetle forewings, is an important innovation that has driven the successful radiation of beetles. Our RNAi screening for candidate genes has identified abrupt (ab) as a potential key player in elytron evolution. In this study, we performed a series of RNA interference (RNAi) experiments in both Tribolium and Drosophila to understand the contributions of ab to the evolution of beetle elytra. We found that (i) ab is essential for proper wing vein patterning both in Tribolium and Drosophila, (ii) ab has gained a novel function in determining the unique elytron shape in the beetle lineage, (iii) unlike Hippo and Insulin, other shape determining pathways, the shape determining function of ab is specific to the elytron and not required in the hindwing, (iv) ab has a previously undescribed role in the Notch signal-associated wing formation processes, which appears to be conserved between beetles and flies. These data suggest that ab has gained a new function during elytron evolution in beetles without compromising the conserved wing-related functions. Gaining a new function without losing evolutionarily conserved functions may be a key theme in the evolution of morphologically novel structures. Copyright © 2015 Elsevier Inc. All rights reserved.

  20. Flight investigation of the effects of an outboard wing-leading-edge modification on stall/spin characteristics of a low-wing, single-engine, T-tail light airplane

    NASA Technical Reports Server (NTRS)

    Stough, H. Paul, III; Dicarlo, Daniel J.; Patton, James M., Jr.

    1987-01-01

    Flight tests were performed to investigate the change in stall/spin characteristics due to the addition of an outboard wing-leading-edge modification to a four-place, low-wing, single-engine, T-tail, general aviation research airplane. Stalls and attempted spins were performed for various weights, center of gravity positions, power settings, flap deflections, and landing-gear positions. Both stall behavior and wind resistance were improved compared with the baseline airplane. The latter would readily spin for all combinations of power settings, flap deflections, and aileron inputs, but the modified airplane did not spin at idle power or with flaps extended. With maximum power and flaps retracted, the modified airplane did enter spins with abused loadings or for certain combinations of maneuver and control input. The modified airplane tended to spin at a higher angle of attack than the baseline airplane.

  1. Laser velocimeter systems analysis applied to a flow survey above a stalled wing. [conducted in Langley high-speed 7 by 10 foot tunnel

    NASA Technical Reports Server (NTRS)

    Young, W. H., Jr.; Meyers, J. F.; Hepner, T. E.

    1977-01-01

    A laser velocimeter operating in the backscatter mode was used to survey the flow above a stalled wing. Polarization was used to separate the two orthogonal velocity components of the fringe-type laser velocimeter, and digital counters were used for data processing. The velocities of the kerosene seed particles were measured with less than 2 percent uncertainty. The particle velocity measurements were collected into histograms. The flow field survey was carried out above an aspect-ratio-8 stalled wing with an NACA 0012 section. The angle of attack was 19.5 deg, the Mach number was 0.49, and the Reynolds number was 1,400,000. The flow field was characterized by the periodic shedding of discrete vortices from near the crest of the airfoil.

  2. Flight investigation of the effect of tail configuration on stall, spin, and recovery characteristics of a low-wing general aviation research airplane

    NASA Technical Reports Server (NTRS)

    Stough, H. Paul, III; Patton, James M., Jr.; Sliwa, Steven M.

    1987-01-01

    Flight tests were performed to investigate the stall, spin, and recovery characteristics of a low-wing, single-engine, light airplane with four interchangeable tail configurations. The four tail configurations were evaluated for effects of varying mass distribution, center-of-gravity position, and control inputs. The airplane tended to roll-off at the stall. Variations in tail configuration produced spins ranging from 40 deg to 60 deg angle of attack and turn rates of about 145 to 208 deg/sec. Some unrecoverable flat spins were encountered which required use of the airplane spin chute for recovery. For recoverable spins, antispin rudder followed by forward wheel with ailerons centered provided the quickest spin recovery. The moderate spin modes agreed very well with those predicted from spin-tunnel model tests, however, the flat spin was at a lower angle of attack and a slower rotation rate than indicated by the model tests.

  3. Dynamic stall reattachment revisited

    NASA Astrophysics Data System (ADS)

    Mulleners, Karen

    2017-11-01

    Dynamic stall on pitching airfoils is an important practical problem that affects for example rotary wing aircraft and wind turbines. It also comprises a number of interesting fundamental fluid dynamical phenomena such as unsteady flow separation, vortex formation and shedding, unsteady flow reattachment, and dynamic hysteresis. Following up on past efforts focussing on the separation development, we now revisited the flow reattachment or stall recovery process. Experimental time-resolved velocity field and surface pressure data for a two-dimensional sinusoidally pitching airfoil with various reduced frequencies was analysed using different Eulerian, Lagrangian, and modal decomposition methods. This complementary analysis resulted in the identification of the chain of events that play a role in the flow reattachment process, a detailed description of that role, and characterisation of the individual events by the governing time-scales and flow features.

  4. Flow Visualization of Dynamic Stall on an Oscillating Airfoil

    DTIC Science & Technology

    1989-09-01

    Dynamic Stall; Dynamic lift, ’Unsteady lift; Helicopter retreating blade stall; Oscillating airfoil ; Flow visualization,’Schlieren method ;k ez.S-,’ .0...the degree of MASTER OF SCIENCE IN AERONAUTICAL ENGINEERING from the NAVAL POSTGRADUATE SCHOOL September 1989 Author...and moment behavior is quite different from the static stall associated with fixed-wing airfoils . Helicopter retreating blade stall is a dynamic

  5. MODEL TESTS AND 3D ELASTIC FINITE ELEMENT ANALYSIS FOR STEEL PIPE PILES WITH WINGS IN STALLED IN SOIL CEMENT COLUMN

    NASA Astrophysics Data System (ADS)

    Tamai, Toshiyuki; Teramoto, Shuntarou; Kimura, Makoto

    Steel pipe piles with wings installed in soil cement column is a composite foundation of pile consisting of soil improvement with cement and steel pipe with wings. This type of pile shows higher vertical bearing capacity when compared to steel pipe piles that are installed without soil cement. It is thought the wings contribute to higher bearing capacity of this type of piles. The wings are also thought to play the role of structural unification of pile foundations and load transfer. In this study, model test and 3D elastic finite element analysis was carried out in order to elucidate the effect of wings on the structural unification of pile foundation and the load transfer mechanism. Firstly, the model test was carried out in order to grasp the influence of pile with and without wings, the shape of wings of the pile and the unconfined compression strength of the soil cement on the structural unification of the pile foundation. The numerical analysis of the model test was then carried out on the intermediate part of the pile foundation with wings and mathematical model developed. Finally load tran sfer mechanism was checked for the entire length of the pile through this mathematical model and the load sharing ratio of the wings and stress distribution occurring in the soil cement clarified. In addition, the effect of the wing interval on the structural unification of the pile foundation and load transfer was also checked and clarified.

  6. The AFDD International Dynamic Stall Workshop on Correlation of Dynamic Stall Models with 3-D Dynamic Stall Data

    NASA Technical Reports Server (NTRS)

    Tan, C. M.; Carr, L. W.

    1996-01-01

    A variety of empirical and computational fluid dynamics two-dimensional (2-D) dynamic stall models were compared to recently obtained three-dimensional (3-D) dynamic stall data in a workshop on modeling of 3-D dynamic stall of an unswept, rectangular wing, of aspect ratio 10. Dynamic stall test data both below and above the static stall angle-of-attack were supplied to the participants, along with a 'blind' case where only the test conditions were supplied in advance, with results being compared to experimental data at the workshop itself. Detailed graphical comparisons are presented in the report, which also includes discussion of the methods and the results. The primary conclusion of the workshop was that the 3-D effects of dynamic stall on the oscillating wing studied in the workshop can be reasonably reproduced by existing semi-empirical models once 2-D dynamic stall data have been obtained. The participants also emphasized the need for improved quantification of 2-D dynamic stall.

  7. Wind-tunnel investigation of effects of wing-leading-edge modifications on the high angle-of-attack characteristics of a T-tail low-wing general-aviation aircraft

    NASA Technical Reports Server (NTRS)

    White, E. R.

    1982-01-01

    Exploratory tests have been conducted in the NASA-Langley Research Center's 12-Foot Low-Speed wind Tunnel to evaluate the application of wing-leading-edge devices on the stall-departure and spin resistance characteristics of a 1/6-scale model of a T-tail general-aviation aircraft. The model was force tested with an internal strain-gauge balance to obtain aerodynamic data on the complete configuration and with a separate wing balance to obtain aerodynamic data on the outer portion of the wing. The addition of the outboard leading-edge droop eliminated the abrupt stall of the windtip and maintained or increased the resultant-force coefficient up to about alpha = 32 degrees. This change in slope of the resultant-force coefficient curve with angle of attack has been shown to be important for eliminating autorotation and for providing spin resistance.

  8. Rotating Stall Suppression Using Oscillatory Blowing Actuation on Blades

    DTIC Science & Technology

    2010-06-30

    severe mechanical vibrations. Certainly, violent surge cannot be tolerated in an aircraft jet engine because of the danger of mechanical failure or...isolated airfoils increases the stall angle. Therefore, herein it was hypothesized that when a stall cell reaches a blade with jet actuation, the stall...Detailed view of the jet slot. Figure 2.30: Wing fences mounted on test blade (with the neighboring airfoils re- moved). (a) Attachment and pipe (b

  9. Large-Vortex Capture by a Wing at Very High Angles of Attack

    NASA Technical Reports Server (NTRS)

    Wu, J. M.; Wu, J. Z.; Denny, G. A.; Lu, X. Y.

    1996-01-01

    In generating the lift on a wing, the static stall is a severe barrier. As the angle of attack, alpha, increases to the stall angle, alpha(sub stall) the flow separation point on the upper surface of the wing moves to the leading edge, so that on a two-dimensional airfoil or a large-aspect-ratio wing, the lift abruptly drops to a very low level. Therefore, the first generation of aeronautical flow type, i.e., the attached steady flow, has been limited to alpha less than alpha(sub stall). Owing to the obvious importance in applications, therefore, a great effort has been made in the past two decades to enlarge the range of usable angles of attack by various flow controls for a large-aspect-ratio wing. Basically, relevant works fall into two categories. The first category is usually refereed to as separation control, which concentrates on partially separated flow at alpha less than alpha(sub stall). Since the first experimental study of Collins and Zelenevitz, there has been ample literature showing that a partially separated flow can be turned to almost fully attached by flow controls, so that the lift is recovered and the stall is delayed (for a recent work see Seifert et al.). It has been well established that, in this category, unsteady controls are much more effective than steady ones and can be realized at a very low power-input level (Wu et al.; Seifert et al.). The second and more ambitious category of relevant efforts is the post-stall lift enhancement. Its possibility roots at the existence of a second lift peak at a very high angle of attack. In fact, As alpha further increases from alpha(sub stall), the completely separated flow develops and gradually becomes a bluff-body flow. This flow gives a normal force to the airfoil with a lift component, which reaches a peak at a maximum utilizable angle of attack, alpha(sub m) approx.= 40 deg. This second peak is of the same level as the first lift peak at alpha(sub stall). Meanwhile, the drag is also quickly

  10. Dynamic Stall Patterns

    NASA Astrophysics Data System (ADS)

    Davidson, Phillip; Babbitt, Ashli; Magstadt, Andrew; Nikoueeyan, Pourya; Naughton, Jonathan; Jonathan Naughton Team

    2014-11-01

    The performance of helicopter and wind turbine blades is affected by dynamic stall. Dynamic stall has received considerable attention, but it is still difficult to simulate and not fully understood. Over the past seven years, many airfoils for helicopter and wind turbine use ranging from 9.5 to 30% thick have been experimentally tested and simulated while dynamically pitching to further characterize dynamic stall. Tests have been run at chord Reynolds number between 225,000-440,000 for various reduced frequencies, mean angles of attack, and oscillation amplitudes. Characterization of stall has been accomplished using data from previous studies as well as the unsteady pressure and flow-field data available from our own work. Where available, combined surface and flow-field data allow for clear identification of the types of stall observed and the flow structure associated with them. The results indicate that thin airfoil stall, leading edge stall, and trailing edge stall are observed in the oscillating airfoil experiments and simulations. These three main stall types are further divided into subcategories. By improving our understanding of the features of dynamic stall, it is expected that physics-based simulations can be improved. Work supported by DOE and a gift from BP.

  11. Active Control of Surge in Compressors Which Exhibit Abrupt Stall

    DTIC Science & Technology

    2001-06-01

    sensor (of pressure, flow rate, etc.) is fed to a controller which applies a proper control law to drive the actuator (valve, The present paper reports...1993), who analyzed the influence of sensor and numerical simulation shows that: t) the predictions of control acutrsltin o th mxmm sabizd opesr...a sensor of compressor face total pressure), a The present paper considers the active suppression of surge in a butterfly throttle/actuation valve

  12. Flight Measurements of the Flying Qualities of a Lockheed P-80A Airplane (Army No. 44-85099) - Stalling Characteristics

    NASA Technical Reports Server (NTRS)

    Anderson, Seth B.; Cooper, George E.

    1947-01-01

    This report contains the flight-test results of the stalling characteristics measured during the flying-qualities investigation of the Lockheed P-8OA airplane (Army No. 44-85099). The tests were conducted in straight and turning flight with and without wing-tip tanks. These tests showed satisfactory stalling characteristics and adequate stall warning for all configurations and conditions tested.

  13. The effect of leading edge tubercles on dynamic stall

    NASA Astrophysics Data System (ADS)

    Hrynuk, John

    The effect of the leading edge tubercles of humpback whales has been heavily studied for their static benefits. These studies have shown that tubercles inhibit flow separation, limit spanwise flow, and extend the operating angle of a wing beyond the static stall point while maintaining lift, all while having a comparatively low negative impact on drag. The current study extends the prior work to investigating the effect of tubercles on dynamic stall, a fundamental flow phenomenon that occurs when wings undergo dynamic pitching motions. Flow fields around the wing models tested were studied using Laser Induced Fluorescence (LIF) and Molecular Tagging Velocimetry (MTV).Resulting velocity fields show that the dynamics of the formation and separation of the leading edge vortex were fundamentally different between the straight wing and the tubercled wing. Tracking of the Dynamic Stall Vortex (DSV) and Shear Layer Vortices (SLVs), which may have a significant impact on the overall flow behavior, was done along with calculations of vortex circulation. Proximity to the wing surface and total circulation were used to evaluate potential dynamic lift increases provided by the tubercles. The effects of pitch rate on the formation process and benefits of the tubercles were also studied and were generally consistent with prior dynamic stall studies. However, tubercles were shown to affect the SLV formation and the circulation differently at higher pitch rates.

  14. Dynamic Stall Control Using Plasma Actuators

    NASA Astrophysics Data System (ADS)

    Webb, Nathan; Singhal, Achal; Castaneda, David; Samimy, Mo

    2017-11-01

    Dynamic stall occurs in many applications, including sharp maneuvers of fixed wing aircraft, wind turbines, and rotorcraft and produces large unsteady aerodynamic loads that can lead to flutter and mechanical failure. This work uses flow control to reduce the unsteady loads by excitation of instabilities in the shear layer over the separated region using nanosecond pulse driven dielectric barrier discharge (NS-DBD) plasma actuators. These actuators have been shown to effectively delay or mitigate static stall. A wide range of flow parameters were explored in the current work: Reynolds number (Re = 167,000 to 500,000), reduced frequency (k = 0.025 to 0.075), and excitation Strouhal number (Ste = 0 to 10). Based on the results, three major conclusions were drawn: (a) Low Strouhal number excitation (Ste <0.5) results in oscillatory aerodynamic loads in the stalled stage of dynamic stall; (b) All excitation resulted in earlier flow reattachment; and (c) Excitation at progressively higher Ste weakened and eventually eliminated the dynamic stall vortex (DSV), thereby dramatically reducing the unsteady loading. The decrease in the strength of the DSV is achieved by the formation of shear layer coherent structures that bleed the leading-edge vorticity prior to the ejection of the DSV.

  15. Stalling of Helicopter Blades

    NASA Technical Reports Server (NTRS)

    Gustafson, F B; Myers, G C , Jr

    1946-01-01

    Theoretical studies have predicted that operation of helicopter rotor beyond certain combinations of thrust, forward speed, and rotational speed might be prevented by rapidly increasing stalling of the retreating blade. The same studies also indicate that the efficiency of the rotor will increase until these limits are reached or closely approached, so that it is desirable to design helicopter rotors for operation close to the limits imposed by blade stalling. Inasmuch as the theoretical predictions of blade stalling involve numerous approximations and assumptions, an experimental investigation was needed to determine whether, in actual practice, the stall did occur and spread as predicted and to establish the amount of stalling that could be present without severe vibration or control difficulties being introduced. This report presents the results of such an investigation.

  16. Advance Ratio Effects on the Dynamic-stall Vortex of a Rotating Blade in Steady Forward Flight

    DTIC Science & Technology

    2014-08-06

    dependence on advance ratio is used to relate the stability of the dynamic-stall vortex to Coriolis effects . Advance ratio effects on the dynamic-stall vortex...relate the stability of the dynamic-stall vortex to Coriolis effects . Keywords: Leading-edge vortex, Dynamic stall vortex, Vortex flows, Rotating wing...Reynolds number are not decoupled. 3. Radial flow field In the rotating environment the coupled effect of centripetal and Coriolis accelerations is ex

  17. Stall Flutter Control of a Smart Blade Section Undergoing Asymmetric Limit Oscillations

    DOE PAGES

    Li, Nailu; Balas, Mark J.; Nikoueeyan, Pourya; ...

    2016-01-01

    Stall flutter is an aeroelastic phenomenon resulting in unwanted oscillatory loads on the blade, such as wind turbine blade, helicopter rotor blade, and other flexible wing blades. While the stall flutter and related aeroelastic control have been studied theoretically and experimentally, microtab control of asymmetric limit cycle oscillations (LCOs) in stall flutter cases has not been generally investigated. This paper presents an aeroservoelastic model to study the microtab control of the blade section undergoing moderate stall flutter and deep stall flutter separately. The effects of different dynamic stall conditions and the consequent asymmetric LCOs for both stall cases are simulatedmore » and analyzed. Then, for the design of the stall flutter controller, the potential sensor signal for the stall flutter, the microtab control capability of the stall flutter, and the control algorithm for the stall flutter are studied. Lastly, the improvement and the superiority of the proposed adaptive stall flutter controller are shown by comparison with a simple stall flutter controller.« less

  18. Stall-proof Airplanes

    NASA Technical Reports Server (NTRS)

    Lachmann, G

    1927-01-01

    My lecture has to do with the following questions. Is the danger of stalling necessarily inherent in the airplane in its present form and structure, or can it be diminished or eliminated by suitable means? Do we possess such means or devices and how must they operate? In this connection I will devote special attention to the exhibition of stall-proof airplanes by Fokker under the auspices of the English Air Ministry, which took place in Croyden last April.

  19. Effect of wing flexibility on the experimental aerodynamic characteristics of an oblique wing

    NASA Technical Reports Server (NTRS)

    Hopkins, E. J.; Yee, S. C.

    1977-01-01

    A solid-aluminum oblique wing was designed to deflect considerably under load so as to relieve the asymmetric spanwise stalling that is characteristic of this type of wing by creating washout on the trailing wing panel and washin on the leading wing panel. Experimental forces, and pitching, rolling and yawing moments were measured with the wing mounted on a body of revolution. In order to vary the dynamic pressure, measurements were made at several unit Reynolds numbers, and at Mach numbers. The wing was investigated when unswept (at subsonic Mach numbers only) and when swept 45 deg, 50 deg, and 60 deg. The wing was straight tapered in planform, had an aspect ratio of 7.9 (based on the unswept span), and a profile with a maximum thickness of 4 percent chord. The results substantiate the concept that an oblique wing designed with the proper amount of flexibility self relieves itself of asymmetric spanwise stalling and the associated nonlinear moment curves.

  20. Variable Camber Morphing Wings

    DTIC Science & Technology

    2016-02-02

    devices and wind turbines , but also it is present in fixed wings, which can vibrate at high frequencies during flight, and in the most fascinating...way to delay dynamic stall to control periodic vortex generation and improve the performance of rotorcrafts and wind turbines (McCroskey, 1982). As...Axis Wind Turbines , Sandia National Laboratories Energy Report, SAND80-2114. 7. RESPONSIBILITY NOTICE “The authors are the only responsible for

  1. A theory of rotating stall of multistage axial compressors

    NASA Technical Reports Server (NTRS)

    Moore, F. K.

    1983-01-01

    A theoretical analysis was made of rotating stall in axial compressors of many stages, finding conditions for a permanent, straight-through traveling disturbance, with the steady compressor characteristic assumed known, and with simple lag processes ascribed to the flows in the inlet, blade passages, and exit regions. For weak disturbances, predicted stall propagation speeds agree well with experimental results. For a locally-parabolic compressor characteristic, an exact nonlinear solution is found and discussed. For deep stall, the stall-zone boundary is most abrupt at the trailing edge, as expected. When a complete characteristic having unstalling and reverse-flow features is adopted, limit cycles governed by a Lienard's equation are found. Analysis of these cycles yields predictions of recovery from rotating stall; a relaxation oscillation is found at some limiting flow coefficient, above which no solution exists. Recovery is apparently independent of lag processes in the blade passages, but instead depends on the lags originating in the inlet and exit flows, and also on the shape of the given characteristic diagram. Small external lags and tall diagrams favor early recovery. Implications for future research are discussed.

  2. Experimental Investigation of Stall Cells on NACA0015 Airfoils

    NASA Astrophysics Data System (ADS)

    Dell'Orso, Haley

    A particular type of 3-D separation, known as a stall cell, was investigated experimentally on two NACA0015 airfoils with aspect ratios of AR = 4 and 2.67. A parametric map of the angles of attack and Reynolds number conditions under which stall cells form was created using oil flow visualization. It was observed that stalls cells form naturally under specific conditions when the Reynolds number exceeds a critical Reynolds number, Re c ≥ Recrit. Based on the work of Weihs & Katz, the formation of a stall cell requires sufficient 3-dimensionality in the flow field. Next, full and partial span trips (composed of either zig-zag tape or an artificial step) were added to the airfoil and it was found that the introduction of additional 3-dimensional disturbances reduced the value of Recrit. For full-span step trips, where no additional 3-dimensionalities were introduced to the flow field, a stall cell was not formed at conditions where one was otherwise not present. However, a partial step trip did cause the formation of a stall cell (under specific conditions) through the introduction of three dimensionalities associated with the trip's ends. These results confirm that three dimensionalities need to be present in order for a stall cell to form. Flow field data were used to explore stall cell characteristics with and without external trips. Under conditions where a stall cell was present, two recirculation regions (i.e., stall cell foci) were observed, outboard of which flow abruptly reattached due to entrainment by the foci. Within the stall cell, flow was funneled away from the middle of the stall cell and into the associated focus point. In addition, at mid-span, the separated flow rotated about the spanwise direction. Outboard, the structure also began to rotate about the chord-normal direction; near the foci, all rotation occurred about the chord-normal direction. The fluctuating flow field was also considered, and elevated levels of chordwise (u'u'/Uinfinity 2

  3. Stall flutter analysis of propfans

    NASA Technical Reports Server (NTRS)

    Reddy, T. S. R.

    1988-01-01

    Three semi-empirical aerodynamic stall models are compared with respect to their lift and moment hysteresis loop prediction, limit cycle behavior, easy implementation, and feasibility in developing the parameters required for stall flutter prediction of advanced turbines. For the comparison of aeroelastic response prediction including stall, a typical section model and a plate structural model are considered. The response analysis includes both plunging and pitching motions of the blades. In model A, a correction of the angle of attack is applied when the angle of attack exceeds the static stall angle. In model B, a synthesis procedure is used for angles of attack above static stall angles, and the time history effects are accounted for through the Wagner function.

  4. Measurement of Aerodynamic Forces for Various Mean Angles of Attack on an Airfoil Oscillating in Pitch and on Two Finite-span Wings Oscillating in Bending with Emphasis on Damping in the Stall

    NASA Technical Reports Server (NTRS)

    Rainey, A Gerald

    1957-01-01

    The oscillating air forces on a two-dimensional wing oscillating in pitch about the midchord have been measured at various mean angles of attack and at Mach numbers of 0.35 and 0.7. The magnitudes of normal-force and pitching-moment coefficients were much higher at high angles of attack than at low angles of attack for some conditions. Large regions of negative damping in pitch were found, and it was shown that the effect of increasing the Mach number 0.35 to 0.7 was to decrease the initial angle of attack at which negative damping occurred. Measurements of the aerodynamic damping of a 10-percent-thick and of a 3-percent-thick finite-span wing oscillating in the first bending mode indicate no regions of negative damping for this type of motion over the range of variables covered. The damping measured at high angles of attack was generally larger than that at low angles of attack. (author)

  5. 14 CFR 25.207 - Stall warning.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Stall warning. 25.207 Section 25.207... STANDARDS: TRANSPORT CATEGORY AIRPLANES Flight Stalls § 25.207 Stall warning. (a) Stall warning with... be clear and distinctive to the pilot in straight and turning flight. (b) The warning must be...

  6. 14 CFR 23.207 - Stall warning.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Stall warning. 23.207 Section 23.207... STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Flight Stalls § 23.207 Stall warning. (a) There must be a clear and distinctive stall warning, with the flaps and landing gear in any...

  7. 14 CFR 25.207 - Stall warning.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Stall warning. 25.207 Section 25.207... STANDARDS: TRANSPORT CATEGORY AIRPLANES Flight Stalls § 25.207 Stall warning. (a) Stall warning with... be clear and distinctive to the pilot in straight and turning flight. (b) The warning must be...

  8. 14 CFR 23.207 - Stall warning.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 1 2013-01-01 2013-01-01 false Stall warning. 23.207 Section 23.207... STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Flight Stalls § 23.207 Stall warning. (a) There must be a clear and distinctive stall warning, with the flaps and landing gear in any...

  9. 14 CFR 23.207 - Stall warning.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Stall warning. 23.207 Section 23.207... STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Flight Stalls § 23.207 Stall warning. (a) There must be a clear and distinctive stall warning, with the flaps and landing gear in any...

  10. 14 CFR 25.207 - Stall warning.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Stall warning. 25.207 Section 25.207... STANDARDS: TRANSPORT CATEGORY AIRPLANES Flight Stalls § 25.207 Stall warning. (a) Stall warning with... be clear and distinctive to the pilot in straight and turning flight. (b) The warning must be...

  11. 14 CFR 23.207 - Stall warning.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Stall warning. 23.207 Section 23.207... STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Flight Stalls § 23.207 Stall warning. (a) There must be a clear and distinctive stall warning, with the flaps and landing gear in any...

  12. 14 CFR 25.207 - Stall warning.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 1 2013-01-01 2013-01-01 false Stall warning. 25.207 Section 25.207... STANDARDS: TRANSPORT CATEGORY AIRPLANES Flight Stalls § 25.207 Stall warning. (a) Stall warning with... be clear and distinctive to the pilot in straight and turning flight. (b) The warning must be...

  13. 14 CFR 25.207 - Stall warning.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Stall warning. 25.207 Section 25.207... STANDARDS: TRANSPORT CATEGORY AIRPLANES Flight Stalls § 25.207 Stall warning. (a) Stall warning with... be clear and distinctive to the pilot in straight and turning flight. (b) The warning must be...

  14. 14 CFR 23.207 - Stall warning.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Stall warning. 23.207 Section 23.207... STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Flight Stalls § 23.207 Stall warning. (a) There must be a clear and distinctive stall warning, with the flaps and landing gear in any...

  15. 14 CFR 25.103 - Stall speed.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Stall speed. 25.103 Section 25.103... STANDARDS: TRANSPORT CATEGORY AIRPLANES Flight Performance § 25.103 Stall speed. (a) The reference stall speed, VSR, is a calibrated airspeed defined by the applicant. VSR may not be less than a 1-g stall...

  16. 14 CFR 25.103 - Stall speed.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Stall speed. 25.103 Section 25.103... STANDARDS: TRANSPORT CATEGORY AIRPLANES Flight Performance § 25.103 Stall speed. (a) The reference stall speed, VSR, is a calibrated airspeed defined by the applicant. VSR may not be less than a 1-g stall...

  17. Wing Leading Edge Concepts for Noise Reduction

    NASA Technical Reports Server (NTRS)

    Shmilovich, Arvin; Yadlin, Yoram; Pitera, David M.

    2010-01-01

    This study focuses on the development of wing leading edge concepts for noise reduction during high-lift operations, without compromising landing stall speeds, stall characteristics or cruise performance. High-lift geometries, which can be obtained by conventional mechanical systems or morphing structures have been considered. A systematic aerodynamic analysis procedure was used to arrive at several promising configurations. The aerodynamic design of new wing leading edge shapes is obtained from a robust Computational Fluid Dynamics procedure. Acoustic benefits are qualitatively established through the evaluation of the computed flow fields.

  18. An experimental study of separated flow on a finite wing

    NASA Technical Reports Server (NTRS)

    Winkelmann, A. E.

    1981-01-01

    The flow field associated with the formation of a mushroom shaped trailing edge stall cell on a low-aspect-ratio (AR = 4.0) wing was investigated in a series of low speed wind tunnel tests (Reynolds number based on 15.2 cm chord = 480,000). Flow field surveys of the separation bubble and wake of a partially stalled and fully stalled wing were completed using a hot-wire probe, a split-film probe, and a directional sensitive pressure probe. A new color video display technique was developed to display the flow field survey data. Photographs were obtained of surface oil flow patterns and smoke flow visualization

  19. 3-D Stall Cell Inducement Using Static Trips on a NACA0015 Airfoil

    NASA Astrophysics Data System (ADS)

    Dell'Orso, Haley; Amitay, Michael

    2015-11-01

    Stall cells typically occur at high angles of attack and moderate to high Reynolds numbers (105 to 106) , which are applicable to High Altitude Long Endurance (HALE) vehicles. Under certain conditions stall cells can form abruptly and have a severe and detrimental impact on flight. In order to better understand this phenomenon, stall cell formation is studied using oil flow visualization and SPIV on a NACA0015 airfoil with AR = 2.67. It was shown that there is a critical Reynolds number above which stall cells begin to form, and that Recrit varies with angle of attack. Zig-zag tape and balsa wood trips were used to induce stall cells at lower Reynolds numbers than they would otherwise be present. This will aid in understanding the formation mechanism of these cells. It was also demonstrated that, in the case of full span trips, stall cells are induced by the 3-D nature of zig-zag trips and did not appear when balsa wood trips were used. This suggests that the formation of the stall cell might be due to 3-D disturbances that are naturally present in a flow field. AFOSR Grant Number FA9550-13-1-0059.

  20. Post-Stall Aerodynamic Modeling and Gain-Scheduled Control Design

    NASA Technical Reports Server (NTRS)

    Wu, Fen; Gopalarathnam, Ashok; Kim, Sungwan

    2005-01-01

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

  1. X-31 in flight - Post Stall Maneuver

    NASA Technical Reports Server (NTRS)

    1995-01-01

    Two X-31 Enhanced Fighter Maneuverability (EFM) demonstrators were flown at the Rockwell International facility, Palmdale, California, and the NASA Dryden Flight Research Center, Edwards, California, to obtain data that may apply to the design of highly-maneuverable next-generation fighters. The program had its first flight on October 11, 1990, in Palmdale; it ended in June 1995. The X-31 program demonstrated the value of thrust vectoring (directing engine exhaust flow) coupled with advanced flight control systems, to provide controlled flight during close-in air combat at very high angles of attack. The result of this increased maneuverability is an aircraft with a significant advantage over conventional fighters. 'Angle-of-attack' (alpha) is an engineering term to describe the angle of an aircraft body and wings relative to its actual flight path. During maneuvers, pilots often fly at extreme angles of attack -- with the nose pitched up while the aircraft continues in its original direction. This can lead to loss of control and result in the loss of the aircraft, pilot or both. Three thrust vectoring paddles made of graphite epoxy mounted on the exhaust nozzle of the X-31 aircraft directed the exhaust flow to provide control in pitch (up and down) and yaw (right and left) to improve control. The paddles can sustain heat of up to 1,500 degrees centigrade for extended periods of time. In addition the X-31 aircraft were configured with movable forward canards and fixed aft strakes. The canards were small wing-like structures set on the wing line between the nose and the leading edge of the wing. The strakes were set on the same line between the trailing edge of the wing and the engine exhaust. Both supplied additional control in tight maneuvering situations. The X-31 research program produced technical data at high angles of attack. This information is giving engineers and aircraft designers a better understanding of aerodynamics, effectiveness of flight controls

  2. Effect of wing bend on the experimental force and moment characteristics of an oblique wing

    NASA Technical Reports Server (NTRS)

    Hopkins, E. J.; Nelson, E. R.

    1976-01-01

    Static longitudinal and lateral/directional force and moment characteristics are presented for an elliptical oblique wing mounted on top of a Sears-Haack body of revolution. The wing had an aspect ratio of 6 (based on the unswept span) and was tested at various sweep angles relative to the body axis ranging from 0 to 60 deg. In an attempt to create more symmetrical spanwise wing stalling characteristics, both wing panels were bent upward to produce washout on the trailing wing panel and washing on the leading wing panel. Small fluorescent tufts were attached to the wing surface to indicate the stall progression on the wing. The tests were conducted throughout a Mach number range from 0.6 to 1.4 at a constant unit Reynolds number of 8.2 x 10 per meter. The test results indicate that upward bending of the wing panels had only a small effect on the linearity of the moment curves and would require an impractical wing-pivot location at low lift to eliminate the rolling moment resulting from this bending.

  3. Helicopter gust response characteristics including unsteady aerodynamic stall effects

    NASA Technical Reports Server (NTRS)

    Arcidiacono, P. J.; Bergquist, R. R.; Alexander, W. T., Jr.

    1974-01-01

    The results of an analytical study to evaluate the general response characteristics of a helicopter subjected to various types of discrete gust encounters are presented. The analysis employed was a nonlinear coupled, multi-blade rotorfuselage analysis including the effects of blade flexibility and unsteady aerodynamic stall. Only the controls-fixed response of the basic aircraft without any aircraft stability augmentation was considered. A discussion of the basic differences between gust sensitivity of fixed and rotary wing aircraft is presented. The effects of several rotor configuration and aircraft operating parameters on initial gust-induced load factor and blade vibratory stress and pushrod loads are discussed.

  4. Simulator Studies of the Deep Stall

    NASA Technical Reports Server (NTRS)

    White, Maurice D.; Cooper, George E.

    1965-01-01

    Simulator studies of the deep-stall problem encountered with modern airplanes are discussed. The results indicate that the basic deep-stall tendencies produced by aerodynamic characteristics are augmented by operational considerations. Because of control difficulties to be anticipated in the deep stall, it is desirable that adequate safeguards be provided against inadvertent penetrations.

  5. Comparison of driven and simulated "free" stall flutter in a wind tunnel

    NASA Astrophysics Data System (ADS)

    Culler, Ethan; Farnsworth, John; Fagley, Casey; Seidel, Jurgen

    2016-11-01

    Stall flutter and dynamic stall have received a significant amount of attention over the years. To experimentally study this problem, the body undergoing stall flutter is typically driven at a characteristic, single frequency sinusoid with a prescribed pitching amplitude and mean angle of attack offset. This approach allows for testing with repeatable kinematics, however it effectively decouples the structural motion from the aerodynamic forcing. Recent results suggest that this driven approach could misrepresent the forcing observed in a "free" stall flutter scenario. Specifically, a dynamically pitched rigid NACA 0018 wing section was tested in the wind tunnel under two modes of operation: (1) Cyber-Physical where "free" stall flutter was physically simulated through a custom motor-control system modeling a torsional spring and (2) Direct Motor-Driven Dynamic Pitch at a single frequency sinusoid representative of the cyber-physical motion. The time-resolved pitch angle and moment were directly measured and compared for each case. It was found that small deviations in the pitch angle trajectory between these two operational cases generate significantly different aerodynamic pitching moments on the wing section, with the pitching moments nearly 180o out of phase in some cases. This work is supported by the Air Force Office of Scientific Research through the Flow Interactions and Control Program and by the National Defense Science and Engineering Graduate Fellowship Program.

  6. Analysis of the cycle-to-cycle pressure distribution variations in dynamic stall

    NASA Astrophysics Data System (ADS)

    Harms, Tanner; Nikoueeyan, Pourya; Naughton, Jonathan

    2017-11-01

    Dynamic stall is an unsteady flow phenomenon observed on blades and wings that, despite decades of focused study, remains a challenging problem for rotorcraft and wind turbine applications. Traditionally, dynamic stall has been studied on pitch-oscillating airfoils by measuring the unsteady pressure distribution that is phase-averaged, by which the typical flow pattern may be observed and quantified. In cases where light to deep dynamic stall are observed, pressure distributions with high levels of variance are present in regions of separation. It was recently observed that, under certain conditions, this scatter may be the result of a two-state flow solution - as if there were a bifurcation in the unsteady pressure distribution behavior on the suction side of the airfoil. This is significant since phase-averaged dynamic stall data are often used to tune dynamic stall models and for validation of simulations of dynamic stall. In order to better understand this phenomenon, statistical analysis of the pressure data using probability density functions (PDFs) and other statistical approaches has been carried out for the SC 1094R8, DU97-W-300, and NACA 0015 airfoil geometries. This work uses airfoil data acquired under Army contract W911W60160C-0021, DOE Grant DE-SC0001261, and a gift from BP Alternative Energy North America, Inc.

  7. X-31 in flight - Post Stall Maneuver

    NASA Technical Reports Server (NTRS)

    1995-01-01

    Two X-31 Enhanced Fighter Maneuverability (EFM) demonstrators were flown at Rockwell International's Palmdale, Calif., facility and the NASA Dryden Flight Research Center, Edwards, Calif., to obtain data that may apply to the design of highly-maneuverable next-generation fighters. The program had its first flight on Oct. 11, 1990, in Palmdale; it ended in June 1995. The X-31 program demonstrated the value of thrust vectoring (directing engine exhaust flow) coupled with advanced flight control systems, to provide controlled flight during close-in air combat at very high angles of attack. The result of this increased maneuverability is a significant advantage over conventional fighters. 'Angle-of-attack' (alpha) is an engineering term to describe the angle of an aircraft's body and wings relative to its actual flight path. During maneuvers, pilots often fly at extreme angles of attack -- with the nose pitched up while the aircraft continues in its original direction. This can lead to loss of control and result in the loss of the aircraft, pilot or both. Three thrust vectoring paddles made of graphite epoxy mounted on the X-31's exhaust nozzle directed the exhaust flow to provide control in pitch (up and down) and yaw (right and left) to improve control. The paddles can sustain heat of up to 1,500 degrees centigrade for extended periods of time. In addition the X-31s were configured with movable forward canards and fixed aft strakes. The canards were small wing-like structures set on the wing line between the nose and the leading edge of the wing. The strakes were set on the same line between the trailing edge of the wing and the engine exhaust. Both supplyied additional control in tight maneuvering situations. The X-31 research program produced technical data at high angles of attack. This information is giving engineers and aircraft designers a better understanding of aerodynamics, effectiveness of flight controls and thrust vectoring, and airflow phenomena at high

  8. On the Lateral Static Stability of Low-Aspect-Ratio Rectangular Wings

    NASA Astrophysics Data System (ADS)

    Linehan, Thomas; Mohseni, Kamran

    2017-11-01

    Low-aspect-ratio rectangular wings experience a reduction in lateral static stability at angles of attack distinct from that of lift stall. Stereoscopic digital particle image velocimetry is used to elucidate the flow physics behind this trend. Rectangular wings of AR = 0.75, 1, 1.5, 3 were tested at side-slip angles β = -10° and 0° with angle of attack varied in the range α =10° -40° . In side-slip, the leading-edge separation region emerges on the leeward wing where leading-edge flow reattachment is highly intermittent due to vortex shedding. The tip vortex downwash of the AR < 1.5 wings is sufficient to restrict the shedding of leading-edge vorticity, enabling sustained lift from the leading-edge separation region to high angles of attack. The windward tip vortex grows in size with increasing angle of attack, occupying an increasingly larger percentage of the windward wing. At high angles of attack pre-lift stall, the windward tip vortex lifts off the wing, resulting in separated flow underneath it. The downwash of the AR = 3 wing is insufficient to reattach the leading-edge flow at high incidence. The flow stalls on the leeward wing with stalled flow expanding upstream toward the windward wing with increasing angle of attack.

  9. Some observations of separated flow on finite wings

    NASA Technical Reports Server (NTRS)

    Winkelmann, A. E.; Ngo, H. T.; De Seife, R. C.

    1982-01-01

    Wind tunnel test results for aspects of flow over airfoils exhibiting single and multiple trailing edge stall 'mushroom' cells are reported. Rectangular wings with aspect ratios of 4.0 and 9.0 were tested at Reynolds numbers of 480,000 and 257,000, respectively. Surface flow patterns were visualized by means of a fluorescent oil flow technique, separated flow was observed with a tuft wand and a water probe, spanwise flow was studied with hot-wire anemometry, smoke flow and an Ar laser illuminated the centerplane flow, and photographs were made of the oil flow patterns. Swirl patterns on partially and fully stalled wings suggested vortex flow attachments in those regions, and a saddle point on the fully stalled AR=4.0 wing indicated a secondary vortex flow at the forward region of the separation bubble. The separation wake decayed downstream, while the tip vortex interacted with the separation bubble on the fully stalled wing. Three mushroom cells were observed on the AR=9.0 wing.

  10. Avian Wings

    NASA Technical Reports Server (NTRS)

    Liu, Tianshu; Kuykendoll, K.; Rhew, R.; Jones, S.

    2004-01-01

    This paper describes the avian wing geometry (Seagull, Merganser, Teal and Owl) extracted from non-contact surface measurements using a three-dimensional laser scanner. The geometric quantities, including the camber line and thickness distribution of airfoil, wing planform, chord distribution, and twist distribution, are given in convenient analytical expressions. Thus, the avian wing surfaces can be generated and the wing kinematics can be simulated. The aerodynamic characteristics of avian airfoils in steady inviscid flows are briefly discussed. The avian wing kinematics is recovered from videos of three level-flying birds (Crane, Seagull and Goose) based on a two-jointed arm model. A flapping seagull wing in the 3D physical space is re-constructed from the extracted wing geometry and kinematics.

  11. 14 CFR 25.203 - Stall characteristics.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... recovery and to regain control of the airplane. The maximum bank angle that occurs during the recovery may... controls, up to the time the airplane is stalled. No abnormal nose-up pitching may occur. The longitudinal control force must be positive up to and throughout the stall. In addition, it must be possible to...

  12. 14 CFR 25.203 - Stall characteristics.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... recovery and to regain control of the airplane. The maximum bank angle that occurs during the recovery may... controls, up to the time the airplane is stalled. No abnormal nose-up pitching may occur. The longitudinal control force must be positive up to and throughout the stall. In addition, it must be possible to...

  13. 14 CFR 23.49 - Stalling period.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... on the stalling speed, with engine(s) idling and throttle(s) closed; (3) The propeller(s) in the... which the airplane is controllable with— (1) For reciprocating engine-powered airplanes, the engine(s... more than 110 percent of the stalling speed; (2) For turbine engine-powered airplanes, the propulsive...

  14. Clutch-Starting Stalled Research Students

    ERIC Educational Resources Information Center

    Ahern, Kathy; Manathunga, Catherine

    2004-01-01

    Many research students go through periods where their research seems to stall, their motivation drops, and they seem unable to make any progress. As supervisors, we attempt to remain alert to signs that our student's progress has stalled. Drawing on cognitive strategies, this article explores a problem-solving model supervisors can use to identify…

  15. Wind Tunnel Pressure Distribution Tests on a Series of Biplane Wing Models

    NASA Technical Reports Server (NTRS)

    Knight, Montgomery; Noyes, Richard

    1929-01-01

    This report is on the changes in forces on each wing of a biplane cellule when either the stagger or the gap is varied. Since each test was carried up to a 90 degree angle of attack, the results may be used in the study of stalled flight and of spinning as well as in the structural design of biplane wings.

  16. Why do Cross-Flow Turbines Stall?

    NASA Astrophysics Data System (ADS)

    Cavagnaro, Robert; Strom, Benjamin; Polagye, Brian

    2015-11-01

    Hydrokinetic turbines are prone to instability and stall near their peak operating points under torque control. Understanding the physics of turbine stall may help to mitigate this undesirable occurrence and improve the robustness of torque controllers. A laboratory-scale two-bladed cross-flow turbine operating at a chord-based Reynolds number ~ 3 ×104 is shown to stall at a critical tip-speed ratio. Experiments are conducting bringing the turbine to this critical speed in a recirculating current flume by increasing resistive torque and allowing the rotor to rapidly decelerate while monitoring inflow velocity, torque, and drag. The turbine stalls probabilistically with a distribution generated from hundreds of such events. A machine learning algorithm identifies stall events and indicates the effectiveness of available measurements or combinations of measurements as predictors. Bubble flow visualization and PIV are utilized to observe fluid conditions during stall events including the formation, separation, and advection of leading-edge vortices involved in the stall process.

  17. Comfort zone-design free stalls: do they influence the stall use behavior of lame cows?

    PubMed

    Cook, N B; Marin, M J; Mentink, R L; Bennett, T B; Schaefer, M J

    2008-12-01

    The behavior of 59 cows in 4 herds, each with Comfort Zone-design free stalls with dimensions suitable for 700-kg, mature Holstein dairy cows, was filmed for a 48-h period. Comparison was made between nonlame, slightly lame, and moderately lame cows on either rubber-crumb-filled mattress stall surfaces bedded with a small amount of sawdust (2 herds) or a Pack Mat design, which consisted of a rubber-crumb-filled mattress pad installed 5 cm below a raised rear curb, bedded with 5 to 8 cm of sand bedding (2 herds). All other stall design components were similar. Despite adequate resting space and freedom to perform normal rising and lying movements, lame cows on mattresses stood in the stall for >2 h longer than nonlame cows. Although a significant increase in stall standing behavior was observed in lame cows on Pack Mat stalls, the mean (95% confidence interval) standing time in the stall was only 0.7 (0 to 3.0) h/d for nonlame cows and 1.6 (0 to 4.2) h/d for moderately lame cows, which was less than the 2.1 (0 to 4.4), 4.3 (1.6 to 6.9), and 4.9 (2.5 to 7.3) h/d spent standing in the stall for nonlame, slightly lame, and moderately lame cows on mattresses, respectively. This observation supports the hypothesis that it is the nature of the stall surface that dictates changes in stall standing behavior observed in lame cows, rather than other components of stall design. The finding that only 5 to 8 cm of sand over a mattress pad provides most of the benefits of deep sand-bedded stalls, along with other advantages related to stall maintenance and manure handling, gives farmers another useful housing alternative with which to improve cow comfort and well-being.

  18. Stalling Tropical Cyclones over the Atlantic Basin

    NASA Astrophysics Data System (ADS)

    Nielsen-Gammon, J. W.; Emanuel, K.

    2017-12-01

    Hurricane Harvey produced massive amounts of rain over southeast Texas and southwest Louisiana. Average storm total rainfall amounts over a 10,000 square mile (26,000 square km) area exceeded 30 inches (750 mm). An important aspect of the storm that contributed to the large rainfall totals was its unusual motion. The storm stalled shortly after making landfall, then moved back offshore before once again making landfall five days later. This storm motion permitted heavy rainfall to occur in the same general area for an extended period of time. The unusual nature of this event motivates an investigation into the characteristics and potential climate change influences on stalled tropical cyclones in the Atlantic basin using the HURDAT 2 storm track database for 1866-2016 and downscaled tropical cyclones driven by simulations of present and future climate. The motion of cyclones is quantified as the size of a circle circumscribing all storm locations during a given length of time. For a three-day period, Harvey remained inside a circle with a radius of 123 km. This ranks within the top 0.6% of slowest-moving historical storm instances. Among the 2% of slowest-moving storm instances prior to Harvey, only 13 involved storms that stalled near the continental United States coast, where they may have produced substantial rainfall onshore while tapping into marine moisture. Only two such storms stalled in the month of September, in contrast to 20 September stalls out of the 36 storms that stalled over the nearby open Atlantic. Just four of the stalled coastal storms were hurricanes, implying a return frequency for such storms of much less than once per decade. The synoptic setting of these storms is examined for common features, and historical and projected trends in occurrences of stalled storms near the coast and farther offshore are investigated.

  19. Compressor Stall Recovery Through Tip Injection Assessed

    NASA Technical Reports Server (NTRS)

    Suder, Ken L.

    2001-01-01

    Aerodynamic stability is a fundamental limit in the compressor design process. The development of robust techniques for increasing stability has several benefits: enabling higher loading and fewer blades, increasing safety throughout a mission, increasing tolerance to stage mismatch during part-speed operation and speed transients, and providing an opportunity to match stages at the compressor maximum efficiency point, thus reducing fuel burn. Mass injection upstream of the tip of a high-speed axial compressor rotor is a stability enhancement approach known to be effective in suppressing stall in tip-critical rotors if the injection is activated before stall occurs. This approach to stall suppression requires that a reliable stall warning system be available. Tests have recently been performed to assess whether steady injection can also be used to recover from fully developed stall. If mass injection is effective in recovering from stall quickly enough to avoid structural damage or loss of engine power, then a stall warning system may not be required. The stall recovery tests were performed on a transonic compressor rotor at its design tip speed of 1475 ft/sec using four injectors evenly spaced around the compressor case upstream of the rotor. The injectors were connected to an external air source. In an actual engine application, the injected air would be supplied with compressor bleed air. The injectors were isolated from the air source by a fast-acting butterfly valve. With the injectors turned off, the compressor was throttled into stall. Air injection was then activated with no change in throttle setting by opening the butterfly valve. The compressor recovered from stall at a fixed throttle setting with the aid of tip injection. The unsteady operating characteristic of the rotor was measured during these tests using high-response pressure sensors located upstream and downstream of the rotor. The figure shows the results, where the unsteady pressure and mass

  20. Reconfiguration control system for an aircraft wing

    NASA Technical Reports Server (NTRS)

    Wakayama, Sean R. (Inventor)

    2008-01-01

    Independently deflectable control surfaces are located on the trailing edge of the wing of a blended wing-body aircraft. The reconfiguration control system of the present invention controls the deflection of each control surface to optimize the spanwise lift distribution across the wing for each of several flight conditions, e.g., cruise, pitch maneuver, and high lift at low speed. The control surfaces are deflected and reconfigured to their predetermined optimal positions when the aircraft is in each of the aforementioned flight conditions. With respect to cruise, the reconfiguration control system will maximize the lift to drag ratio and keep the aircraft trimmed at a stable angle of attack. In a pitch maneuver, the control surfaces are deflected to pitch the aircraft and increase lift. Moreover, this increased lift has its spanwise center of pressure shifted inboard relative to its location for cruise. This inboard shifting reduces the increased bending moment about the aircraft's x-axis occasioned by the increased pitch force acting normal to the wing. To optimize high lift at low speed, during take-off and landing for example, the control surfaces are reconfigured to increase the local maximum coefficient of lift at stall-critical spanwise locations while providing pitch trim with control surfaces that are not stall critical.

  1. Airfoil Dynamic Stall and Rotorcraft Maneuverability

    NASA Technical Reports Server (NTRS)

    Bousman, William G.

    2000-01-01

    The loading of an airfoil during dynamic stall is examined in terms of the augmented lift and the associated penalties in pitching moment and drag. It is shown that once stall occurs and a leading-edge vortex is shed from the airfoil there is a unique relationship between the augmented lift, the negative pitching moment, and the increase in drag. This relationship, referred to here as the dynamic stall function, shows limited sensitivity to effects such as the airfoil section profile and Mach number, and appears to be independent of such parameters as Reynolds number, reduced frequency, and blade sweep. For single-element airfoils there is little that can be done to improve rotorcraft maneuverability except to provide good static C(l(max)) characteristics and the chord or blade number that is required to provide the necessary rotor thrust. However, multi-element airfoils or airfoils with variable geometry features can provide augmented lift in some cases that exceeds that available from a single-element airfoil. The dynamic stall function is shown to be a useful tool for the evaluation of both measured and calculated dynamic stall characteristics of single element, multi-element, and variable geometry airfoils.

  2. Plasma-based Compressor Stall Control

    NASA Astrophysics Data System (ADS)

    McGowan, Ryan; Corke, Thomas

    2017-11-01

    The use of dielectric barrier discharge (DBD) plasma actuator casing treatment to prevent or delay stall inception in an axial fan is examined. The actuators are powered by a pulsed-DC waveform which induces a larger peak velocity than a purely AC waveform such as a sine or sawtooth wave. With this system, a high-voltage DC source is supplied to both electrodes, remaining constant in time for the exposed electrode. Meanwhile, the covered electrode is periodically grounded for several microseconds and allowed to rise back to the source DC level. To test the actuators' ability to interact with and modify the formation of stall cells, a facility has been designed and constructed around nonconductive fan blades. The actuators are installed in the fan casing near the blade tips. The instrumentation allows for the measurement of rotating pressure disturbances (traveling stall cells) in this tip gap region as well as fan performance characteristics including pressure rise and flow rate. The casing plasma actuation is found to reduce the correlation of the rotating stall cells, thereby extending the stall margin of the fan. Various azimuthal arrangements of the plasma actuator casing treatment is explored, as well as input voltage levels to the actuator to determine optimum conditions. NASA SBIR Contract NNX14CC12C.

  3. Analysis of abrupt transitions in ecological systems

    USDA-ARS?s Scientific Manuscript database

    The occurrence and causes of abrupt transitions, thresholds, or regime shifts between ecosystem states are of great concern and the likelihood of such transitions is increasing for many ecological systems. General understanding of abrupt transitions has been advanced by theory, but hindered by the l...

  4. Experimental investigation of high-incidence delta-wing flow control

    NASA Astrophysics Data System (ADS)

    Buzica, Andrei; Bartasevicius, Julius; Breitsamter, Christian

    2017-09-01

    The possibility of extending the flight envelope for configurations with slender delta-shaped wings is investigated in this study by means of active flow control through pulsating jets from slot pairs distributed along the leading edge. The experiments comprise stereoscopic particle image velocimetry as well as force and moment measurements on a half-delta wing model. The analysis focuses on three high-incidence regimes: pre-stall, stall, and post-stall. This study also compares different perturbation methods: blowing with spatially constant and variable parameters, frequency and phase. At an incidence of 45°, the unison pulsed blowing facilitates the most significant flow transformation. Here, the separated shear layer reattaches on the wing's suction side, thus increasing the lift. Phase-averaged flow field measurements describe, in this particular case, the underlying physics of the flow-disturbance interaction.

  5. A low-speed wind tunnel study of vortex interaction control techniques on a chine-forebody/delta-wing configuration

    NASA Technical Reports Server (NTRS)

    Rao, Dhanvada M.; Bhat, M. K.

    1992-01-01

    A low speed wind tunnel evaluation was conducted of passive and active techniques proposed as a means to impede the interaction of forebody chine and delta wing vortices, when such interaction leads to undesirable aerodynamic characteristics particularly in the post stall regime. The passive method was based on physically disconnecting the chine/wing junction; the active technique employed deflection of inboard leading edge flaps. In either case, the intent was to forcibly shed the chine vortices before they encountered the downwash of wing vortices. Flow visualizations, wing pressures, and six component force/moment measurements confirmed the benefits of forced vortex de-coupling at post stall angles of attack and in sideslip, viz., alleviation of post stall zero beta asymmetry, lateral instability and twin tail buffet, with insignificant loss of maximum lift.

  6. Membrane wing aerodynamics for micro air vehicles

    NASA Astrophysics Data System (ADS)

    Lian, Yongsheng; Shyy, Wei; Viieru, Dragos; Zhang, Baoning

    2003-10-01

    The aerodynamic performance of a wing deteriorates considerably as the Reynolds number decreases from 10 6 to 10 4. In particular, flow separation can result in substantial change in effective airfoil shape and cause reduced aerodynamic performance. Lately, there has been growing interest in developing suitable techniques for sustained and robust flight of micro air vehicles (MAVs) with a wingspan of 15 cm or smaller, flight speed around 10 m/ s, and a corresponding Reynolds number of 10 4-10 5. This paper reviews the aerodynamics of membrane and corresponding rigid wings under the MAV flight conditions. The membrane wing is observed to yield desirable characteristics in delaying stall as well as adapting to the unsteady flight environment, which is intrinsic to the designated flight speed. Flow structures associated with the low Reynolds number and low aspect ratio wing, such as pressure distribution, separation bubble and tip vortex are reviewed. Structural dynamics in response to the surrounding flow field is presented to highlight the multiple time-scale phenomena. Based on the computational capabilities for treating moving boundary problems, wing shape optimization can be conducted in automated manners. To enhance the lift, the effect of endplates is evaluated. The proper orthogonal decomposition method is also discussed as an economic tool to describe the flow structure around a wing and to facilitate flow and vehicle control.

  7. Nonlinear analysis and control of an aircraft in the neighbourhood of deep stall

    NASA Astrophysics Data System (ADS)

    Kolb, Sébastien; Hétru, Laurent; Faure, Thierry M.; Montagnier, Olivier

    2017-01-01

    When an aircraft is locked in a stable equilibrium at high angle-of-attack, we have to do with the so-called deep stall which is a very dangerous situation. Airplanes with T-tail are mainly concerned with this phenomenon since the wake of the main wing flows over the horizontal tail and renders it ineffective but other aircrafts such as fighters can also be affected. First the phase portrait and bifurcation diagram are determined and characterized (with three equilibria in a deep stall prone configuration). It allows to diagnose the configurations of aircrafts susceptible to deep stall and also to point out the different types of time evolutions. Several techniques are used in order to determine the basin of attraction of the stable equilibrium at high angle-of-attack. They are based on the calculation of the stable manifold of the saddle-point equilibrium at medium angle-of-attack. Then several ways are explored in order to try to recover from deep stall. They exploits static features (such as curves of pitching moment versus angle-of-attack for full pitch down and full pitch up elevators) or dynamic aspects (excitation of the eigenmodes and improvement of the aerodynamic efficiency of the tail). Finally, some properties of a deep stall prone aircraft are pointed out and some control tools are also implemented. We try also to apply this mathematical results in a concrete situation by taking into account the captors specificities or by estimating the relevant variables thanks to other available information.

  8. Investigation of Rotating Stall Phenomena in Axial Flow Compressors. Volume I. Basic Studies of Rotating Stall

    DTIC Science & Technology

    1976-06-01

    rotating stall control system which was tested both on a low speed rig and a J-85-S engine. The second objective was to perform fundamental studies of the...Stator Stage 89 6 Annular Cascade Configuration Used for Rotating Stall Studies on Rotoi-Stator Stage ..... .............. ... 90 7 Static Pressure Rise...ground tests on a J-8S-S turbojet engine. The work i3 reported in three separate volumes. Volume I entitled, "Basic Studies of Rotating Stall", covers

  9. 14 CFR 23.49 - Stalling period.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... which the airplane is controllable with— (1) For reciprocating engine-powered airplanes, the engine(s... more than 110 percent of the stalling speed; (2) For turbine engine-powered airplanes, the propulsive..., VSOand VS1at maximum weight must not exceed 61 knots for— (1) Single-engine airplanes; and (2...

  10. Airfoil stall interpreted through linear stability analysis

    NASA Astrophysics Data System (ADS)

    Busquet, Denis; Juniper, Matthew; Richez, Francois; Marquet, Olivier; Sipp, Denis

    2017-11-01

    Although airfoil stall has been widely investigated, the origin of this phenomenon, which manifests as a sudden drop of lift, is still not clearly understood. In the specific case of static stall, multiple steady solutions have been identified experimentally and numerically around the stall angle. We are interested here in investigating the stability of these steady solutions so as to first model and then control the dynamics. The study is performed on a 2D helicopter blade airfoil OA209 at low Mach number, M 0.2 and high Reynolds number, Re 1.8 ×106 . Steady RANS computation using a Spalart-Allmaras model is coupled with continuation methods (pseudo-arclength and Newton's method) to obtain steady states for several angles of incidence. The results show one upper branch (high lift), one lower branch (low lift) connected by a middle branch, characterizing an hysteresis phenomenon. A linear stability analysis performed around these equilibrium states highlights a mode responsible for stall, which starts with a low frequency oscillation. A bifurcation scenario is deduced from the behaviour of this mode. To shed light on the nonlinear behavior, a low order nonlinear model is created with the same linear stability behavior as that observed for that airfoil.

  11. 14 CFR 25.201 - Stall demonstration.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ...; or (3) The pitch control reaches the aft stop and no further increase in pitch attitude occurs when... steady rate of speed reduction can be established, apply the longitudinal control so that the speed... flight stalls, apply the longitudinal control to achieve airspeed deceleration rates up to 3 knots per...

  12. 14 CFR 25.201 - Stall demonstration.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ...; or (3) The pitch control reaches the aft stop and no further increase in pitch attitude occurs when... steady rate of speed reduction can be established, apply the longitudinal control so that the speed... flight stalls, apply the longitudinal control to achieve airspeed deceleration rates up to 3 knots per...

  13. 14 CFR 25.201 - Stall demonstration.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ...; or (3) The pitch control reaches the aft stop and no further increase in pitch attitude occurs when... steady rate of speed reduction can be established, apply the longitudinal control so that the speed... flight stalls, apply the longitudinal control to achieve airspeed deceleration rates up to 3 knots per...

  14. 14 CFR 25.201 - Stall demonstration.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ...; or (3) The pitch control reaches the aft stop and no further increase in pitch attitude occurs when... steady rate of speed reduction can be established, apply the longitudinal control so that the speed... flight stalls, apply the longitudinal control to achieve airspeed deceleration rates up to 3 knots per...

  15. 14 CFR 25.201 - Stall demonstration.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ...; or (3) The pitch control reaches the aft stop and no further increase in pitch attitude occurs when... steady rate of speed reduction can be established, apply the longitudinal control so that the speed... flight stalls, apply the longitudinal control to achieve airspeed deceleration rates up to 3 knots per...

  16. 16 CFR 1505.50 - Stalled motor testing.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 16 Commercial Practices 2 2011-01-01 2011-01-01 false Stalled motor testing. 1505.50 Section 1505... USE BY CHILDREN Policies and Interpretations § 1505.50 Stalled motor testing. (a) § 1505.6(e)(4)(ii) requires that a motor-operated toy be tested with the motor stalled if the construction of the toy is such...

  17. 16 CFR 1505.50 - Stalled motor testing.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 16 Commercial Practices 2 2010-01-01 2010-01-01 false Stalled motor testing. 1505.50 Section 1505... USE BY CHILDREN Policies and Interpretations § 1505.50 Stalled motor testing. (a) § 1505.6(e)(4)(ii) requires that a motor-operated toy be tested with the motor stalled if the construction of the toy is such...

  18. Factors affecting stall use for different freestall bases.

    PubMed

    Wagner-Storch, A M; Palmer, R W; Kammel, D W

    2003-06-01

    The objective of this study was to compare stall use (stall occupancy and cow position) by barn side for factors affecting stall use. A closed circuit television system recorded stall use four times per day for a 9-mo period starting May 9, 2001. Six factors were analyzed: stall base, distance to water, stall location within stall base section, stall location within barn, inside barn temperature, and length of time cows were exposed to stall bases. Two barn sides with different stocking densities were analyzed: low (66%), with cows milked by robotic milker; and high (100%), with cows milked 2X in parlor. Six stall base types were tested: two mattresses, a waterbed, a rubber mat, concrete, and sand (high side only). The base types were grouped 3 to 7 stalls/section and randomly placed in each row. Cows spent more time in mattress-based stalls, but the highest percentage lying was in sand-based stalls. The following significant stall occupancy percentages were found: sand had the highest percentage of cows lying on the high stocking density side (69%), followed by mattress type 1 (65%) > mattress type 2 (57%) > waterbed (45%) > rubber mat (33%) > concrete (23%). Mattress type 1 had the highest percentage stalls occupied (88%), followed by mattress type 2 (84%) > sand (79%) > soft rubber mat (65%) > waterbed (62%) > concrete (39%). On the low stocking rate side, mattress type 1 had the highest percentage cows lying (45%) and occupied (59.6%), followed by mattress type 2 > waterbed > soft rubber mat > concrete. Cow lying and stalls occupied percentages were highest for stalls 1) not at the end of a section, and 2) on the outside row, and varied by base type for time cows exposed to stalls and inside barn temperature. Lying and occupied percentages were different for different mattress types. The percentage of stalls with cows standing was higher for mat and mattress-based stalls. Results show mattress type 1 and sand to be superior and rubber mats and concrete inferior

  19. A status report on NASA general aviation stall/spin flight testing

    NASA Technical Reports Server (NTRS)

    Patton, J. M., Jr.

    1980-01-01

    The NASA Langley Research Center has undertaken a comprehensive program involving spin tunnel, static and rotary balance wind tunnel, full-scale wind tunnel, free flight radio control model, flight simulation, and full-scale testing. Work underway includes aerodynamic definition of various configurations at high angles of attack, testing of stall and spin prevention concepts, definition of spin and spin recovery characteristics, and development of test techniques and emergency spin recovery systems. This paper presents some interesting results to date for the first aircraft (low-wing, single-engine) in the program, in the areas of tail design, wing leading edge design, mass distribution, center of gravity location, and small airframe changes, with associated pilot observations. The design philosophy of the spin recovery parachute system is discussed in addition to test techniques.

  20. Abrupt climate change and extinction events

    NASA Technical Reports Server (NTRS)

    Crowley, Thomas J.

    1988-01-01

    There is a growing body of theoretical and empirical support for the concept of instabilities in the climate system, and indications that abrupt climate change may in some cases contribute to abrupt extinctions. Theoretical indications of instabilities can be found in a broad spectrum of climate models (energy balance models, a thermohaline model of deep-water circulation, atmospheric general circulation models, and coupled ocean-atmosphere models). Abrupt transitions can be of several types and affect the environment in different ways. There is increasing evidence for abrupt climate change in the geologic record and involves both interglacial-glacial scale transitions and the longer-term evolution of climate over the last 100 million years. Records from the Cenozoic clearly show that the long-term trend is characterized by numerous abrupt steps where the system appears to be rapidly moving to a new equilibrium state. The long-term trend probably is due to changes associated with plate tectonic processes, but the abrupt steps most likely reflect instabilities in the climate system as the slowly changing boundary conditions caused the climate to reach some threshold critical point. A more detailed analysis of abrupt steps comes from high-resolution studies of glacial-interglacial fluctuations in the Pleistocene. Comparison of climate transitions with the extinction record indicates that many climate and biotic transitions coincide. The Cretaceous-Tertiary extinction is not a candidate for an extinction event due to instabilities in the climate system. It is quite possible that more detailed comparisons and analysis will indicate some flaws in the climate instability-extinction hypothesis, but at present it appears to be a viable candidate as an alternate mechanism for causing abrupt environmental changes and extinctions.

  1. Flapping wing aerodynamics: from insects to vertebrates.

    PubMed

    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. © 2016. Published by The Company of Biologists Ltd.

  2. Rotating stall simulation for axial and centrifugal compressors

    NASA Astrophysics Data System (ADS)

    Halawa, Taher; Gadala, Mohamed S.

    2017-05-01

    This study presents a numerical simulation of the rotating stall phenomenon in axial and centrifugal compressors with detailed descriptions of stall precursors and its development with time. Results showed that the vaneless region of the centrifugal compressor is the most critical location affected by stall. It was found that the tip leakage flow and the back flow impingement are the main cause of the stall development at the impeller exit area for centrifugal compressors. The results of the axial compressor simulations indicated that the early separated flow combined with the tip leakage flow can block the impeller passages during stall.

  3. Inflatable wing

    DOEpatents

    Priddy, Tommy G.

    1988-01-01

    An inflatable wing is formed from a pair of tapered, conical inflatable tubes in bonded tangential contact with each other. The tubes are further connected together by means of top and bottom reinforcement boards having corresponding longitudinal edges lying in the same central diametral plane passing through the associated tube. The reinforcement boards are made of a stiff reinforcement material, such as Kevlar, collapsible in a direction parallel to the spanwise wing axis upon deflation of the tubes. The stiff reinforcement material cooperates with the inflated tubes to impart structural I-beam characteristics to the composite structure for transferring inflation pressure-induced tensile stress from the tubes to the reinforcement boards. A plurality of rigid hoops shaped to provide airfoil definition are spaced from each other along the spanwise axis and are connected to the top and bottom reinforcement boards. Tension lines are employed for stabilizing the hoops along the trailing and leading edges thereof.

  4. Analysis of oscillatory pressure data including dynamic stall effects

    NASA Technical Reports Server (NTRS)

    Carta, F. O.

    1974-01-01

    The dynamic stall phenomenon was examined in detail by analyzing an existing set of unsteady pressure data obtained on an airfoil oscillating in pitch. Most of the data were for sinusoidal oscillations which penetrated the stall region in varying degrees, and here the effort was concentrated on the chordwise propagation of pressure waves associated with the dynamic stall. It was found that this phenomenon could be quantified in terms of a pressure wave velocity which is consistently much less than free-stream velocity, and which varies directly with frequency. It was also found that even when the stall region has been deeply penetrated and a substantial dynamic stall occurs during the downstroke, stall recovery near minimum incidence will occur, followed by a potential flow behavior up to stall inception.

  5. Pressure-based high-order TVD methodology for dynamic stall control

    NASA Astrophysics Data System (ADS)

    Yang, H. Q.; Przekwas, A. J.

    1992-01-01

    The quantitative prediction of the dynamics of separating unsteady flows, such as dynamic stall, is of crucial importance. This six-month SBIR Phase 1 study has developed several new pressure-based methodologies for solving 3D Navier-Stokes equations in both stationary and moving (body-comforting) coordinates. The present pressure-based algorithm is equally efficient for low speed incompressible flows and high speed compressible flows. The discretization of convective terms by the presently developed high-order TVD schemes requires no artificial dissipation and can properly resolve the concentrated vortices in the wing-body with minimum numerical diffusion. It is demonstrated that the proposed Newton's iteration technique not only increases the convergence rate but also strongly couples the iteration between pressure and velocities. The proposed hyperbolization of the pressure correction equation is shown to increase the solver's efficiency. The above proposed methodologies were implemented in an existing CFD code, REFLEQS. The modified code was used to simulate both static and dynamic stalls on two- and three-dimensional wing-body configurations. Three-dimensional effect and flow physics are discussed.

  6. Abrupt Impacts of Climate Change: Anticipating Surprises

    NASA Astrophysics Data System (ADS)

    White, James W. C.; Alley, Richard B.; Archer, David E.; Barnosky, Anthony D.; Dunlea, Edward; Foley, Jonathan; Fu, Rong; Holland, Marika M.; Lozier, M. Susan; Schmitt, Johanna; Smith, Laurence C.; Sugihara, George; Thompson, David W. J.; Weaver, Andrew J.; Wofsy, Steven C.

    2014-05-01

    Levels of carbon dioxide and other greenhouse gases in Earth's atmosphere are exceeding levels recorded in the past millions of years, and thus climate is being forced beyond the range of the recent geological era. Lacking concerted action by the world's nations, it is clear that the future climate will be warmer, sea levels will rise, global rainfall patterns will change, and ecosystems will be altered. However, there is still uncertainty about how we will arrive at that future climate state. Although many projections of future climatic conditions have predicted steadily changing conditions giving the impression that communities have time to gradually adapt, the scientific community has been paying increasing attention to the possibility that at least some changes will be abrupt, perhaps crossing a threshold or "tipping point" to change so quickly that there will be little time to react. This presentation will synopsize the new US National Research Council Report, Abrupt Impacts of Climate Change: Anticipating Surprises, highlighting areas of increased and decreased concern, as well as areas of new concern. Emphasis is placed on not only abrupt change in physical climate, but on abrupt changes in human and natural systems that can occur as a result of a slowly changing climate. The report calls for action now on an abrupt change early warning system (ACEWS) if societies are to be resilient to climate change.

  7. Quantifying the dynamic wing morphing of hovering hummingbird

    PubMed Central

    Nakata, Toshiyuki; Kitamura, Ikuo; Tanaka, Hiroto

    2017-01-01

    Animal wings are lightweight and flexible; hence, during flapping flight their shapes change. It has been known that such dynamic wing morphing reduces aerodynamic cost in insects, but the consequences in vertebrate flyers, particularly birds, are not well understood. We have developed a method to reconstruct a three-dimensional wing model of a bird from the wing outline and the feather shafts (rachides). The morphological and kinematic parameters can be obtained using the wing model, and the numerical or mechanical simulations may also be carried out. To test the effectiveness of the method, we recorded the hovering flight of a hummingbird (Amazilia amazilia) using high-speed cameras and reconstructed the right wing. The wing shape varied substantially within a stroke cycle. Specifically, the maximum and minimum wing areas differed by 18%, presumably due to feather sliding; the wing was bent near the wrist joint, towards the upward direction and opposite to the stroke direction; positive upward camber and the ‘washout’ twist (monotonic decrease in the angle of incidence from the proximal to distal wing) were observed during both half-strokes; the spanwise distribution of the twist was uniform during downstroke, but an abrupt increase near the wrist joint was found during upstroke. PMID:28989736

  8. Dynamic Stall on Advanced Airfoil Sections,

    DTIC Science & Technology

    1980-05-01

    that travel downstream from the regime, where the boundary-layer charac- leading-edge region; throughout the teristics differ the most. Before compar...largest chord lengths of travel . As we shall see value of CL, , but it also has very large in later sections, the onset of super- negative pitc-iing...or chordlengths of travel , and the or deep dynamic stall characteristics of curves are phased so that the angles of any of the helicopter sections. The

  9. A Wind Tunnel Investigation of Joined Wing Scissor Morphing

    DTIC Science & Technology

    2006-06-01

    would use the low sweep for carrier landing and subsonic cruise, and use the high sweep for 12 supersonic flight [13]. According to Raymer [19...Wright-Patterson AFB, Ohio: Air Force Institute of Technology, 2005. 12. Katz, Joseph, Shaun Byrne, and Robert Hahl. "Stall Resistance Features of...Lifting-Body Airplane Configurations." Journal of Aircraft 2nd ser. 36 (1999): 471-474. 13. Kress, Robert W. "Variable Sweep Wing Design." AIAA 83

  10. Stall dimensions and the prevalence of lameness, injury, and cleanliness on 317 tie-stall dairy farms in Ontario

    PubMed Central

    2005-01-01

    Abstract The study objectives were to provide a province-wide description of stall dimensions and the aspects of cattle welfare linked to stall design in the tie-stall industry. Data on stall design; stall dimensions; and the prevalence of lameness, injury, and hind limb and udder cleanliness in lactating dairy cattle were collected from a sample of 317 tie-stall farms across Ontario. The majority of the study farms (90%) had stalls with dimensions (length, width, tie-chain length, and tie rail height) that were less than the current recommendations. This may explain, in part, the prevalence of lameness measured as the prevalence of back arch (3.2%) and severe hind claw rotation (23%), hock lesions (44%), neck lesions (3.8%), broken tails (3%), dirty hind limbs (23%), and dirty udders (4.6%). Veterinarians and producers may use this information to compare farms with the industry averages and target areas in need of improvement. PMID:16454382

  11. The economics of abrupt climate change.

    PubMed

    Perrings, Charles

    2003-09-15

    The US National Research Council defines abrupt climate change as a change of state that is sufficiently rapid and sufficiently widespread in its effects that economies are unprepared or incapable of adapting. This may be too restrictive a definition, but abrupt climate change does have implications for the choice between the main response options: mitigation (which reduces the risks of climate change) and adaptation (which reduces the costs of climate change). The paper argues that by (i) increasing the costs of change and the potential growth of consumption, and (ii) reducing the time to change, abrupt climate change favours mitigation over adaptation. Furthermore, because the implications of change are fundamentally uncertain and potentially very high, it favours a precautionary approach in which mitigation buys time for learning. Adaptation-oriented decision tools, such as scenario planning, are inappropriate in these circumstances. Hence learning implies the use of probabilistic models that include socioeconomic feedbacks.

  12. Bacillus cereus in free-stall bedding.

    PubMed

    Magnusson, M; Svensson, B; Kolstrup, C; Christiansson, A

    2007-12-01

    To increase the understanding of how different factors affect the bacterial growth in deep sawdust beds for dairy cattle, the microbiological status of Bacillus cereus and coliforms in deep sawdust-bedded free stalls was investigated over two 14-d periods on one farm. High counts of B. cereus and coliforms were found in the entire beds. On average, 4.1 log(10) B. cereus spores, 5.5 log(10) B. cereus, and 6.7 log(10) coliforms per gram of bedding could be found in the upper layers of the sawdust likely to be in contact with the cows' udders. The highest counts of B. cereus spores, B. cereus, and coliforms were found in the bedding before fresh bedding was added, and the lowest immediately afterwards. Different factors of importance for the growth of B. cereus in the bedding material were explored in laboratory tests. These were found to be the type of bedding, pH, and the type and availability of nutrients. Alternative bedding material such as peat and mixtures of peat and sawdust inhibited the bacterial growth of B. cereus. The extent of growth of B. cereus in the sawdust was increased in a dose-dependent manner by the availability of feces. Urine added to different bedding material raised the pH and also led to bacterial growth of B. cereus in the peat. In sawdust, a dry matter content greater than 70% was needed to lower the water activity to 0.95, which is needed to inhibit the growth of B. cereus. In an attempt to reduce the bacterial growth of B. cereus and coliforms in deep sawdust beds on the farm, the effect of giving bedding daily or a full replacement of the beds was studied. The spore count of B. cereus in the back part of the free stalls before fresh bedding was added was 0.9 log units lower in stalls given daily bedding than in stalls given bedding twice weekly. No effect on coliform counts was found. Replacement of the entire sawdust bedding had an effect for a short period, but by 1 to 2 mo after replacement, the counts of B. cereus spores in the

  13. The quest for stall-free dynamic lift

    NASA Technical Reports Server (NTRS)

    Tung, C.; Mcalister, K. W.; Carr, Lawrence W.; Duque, E.; Zinner, R.

    1992-01-01

    During the past decade, numerous major effects have addressed the question of how to control or alleviate dynamic stall effects on helicopter rotors, but little concrete evidence of any significant reduction of the adverse characteristics of the dynamic stall phenomenon has been demonstrated. Nevertheless, it is important to remember that the control of dynamic stall is an achievable goal. Experiments performed at the US Army Aeroflight-dynamics Directorate more than a decade ago demonstrated that dynamic stall is not an unavoidable penalty of high amplitude motion, and that airfoils can indeed operate dynamically at angles far above the static-stall angle without necessarily forming a stall vortex. These experiments, one of them featuring a slat that was designed from static airfoil considerations, showed that unsteadiness can be a very beneficial factor in the development of high-lift devices for helicopter rotors. The experience drawn from these early experiments is now being focused on a program for the alleviation of dynamic-stall effects on helicopter rotors. The purpose of this effort is to demonstrate that rotor stall can be controlled through an improved understanding of the unsteady effects on airfoil stall and to document the role of specific means that lead to stall alleviation in the three dimensional unsteady environment of helicopter rotors in forward flight. The first concept to be addressed in this program will be a slatted airfoil. A two dimensional unsteady Navier-Stokes code has been modified to compute the flow around a two-element airfoil.

  14. Abrupt climate change: can society cope?

    PubMed

    Hulme, Mike

    2003-09-15

    Consideration of abrupt climate change has generally been incorporated neither in analyses of climate-change impacts nor in the design of climate adaptation strategies. Yet the possibility of abrupt climate change triggered by human perturbation of the climate system is used to support the position of both those who urge stronger and earlier mitigative action than is currently being contemplated and those who argue that the unknowns in the Earth system are too large to justify such early action. This paper explores the question of abrupt climate change in terms of its potential implications for society, focusing on the UK and northwest Europe in particular. The nature of abrupt climate change and the different ways in which it has been defined and perceived are examined. Using the example of the collapse of the thermohaline circulation (THC), the suggested implications for society of abrupt climate change are reviewed; previous work has been largely speculative and has generally considered the implications only from economic and ecological perspectives. Some observations about the implications from a more social and behavioural science perspective are made. If abrupt climate change simply implies changes in the occurrence or intensity of extreme weather events, or an accelerated unidirectional change in climate, the design of adaptation to climate change can proceed within the existing paradigm, with appropriate adjustments. Limits to adaptation in some sectors or regions may be reached, and the costs of appropriate adaptive behaviour may be large, but strategy can develop on the basis of a predicted long-term unidirectional change in climate. It would be more challenging, however, if abrupt climate change implied a directional change in climate, as, for example, may well occur in northwest Europe following a collapse of the THC. There are two fundamental problems for society associated with such an outcome: first, the future changes in climate currently being

  15. Detection of abrupt changes in dynamic systems

    NASA Technical Reports Server (NTRS)

    Willsky, A. S.

    1984-01-01

    Some of the basic ideas associated with the detection of abrupt changes in dynamic systems are presented. Multiple filter-based techniques and residual-based method and the multiple model and generalized likelihood ratio methods are considered. Issues such as the effect of unknown onset time on algorithm complexity and structure and robustness to model uncertainty are discussed.

  16. Abrupt tropical climate change: past and present.

    PubMed

    Thompson, Lonnie G; Mosley-Thompson, Ellen; Brecher, Henry; Davis, Mary; León, Blanca; Les, Don; Lin, Ping-Nan; Mashiotta, Tracy; Mountain, Keith

    2006-07-11

    Three lines of evidence for abrupt tropical climate change, both past and present, are presented. First, annually and decadally averaged delta(18)O and net mass-balance histories for the last 400 and 2,000 yr, respectively, demonstrate that the current warming at high elevations in the mid- to low latitudes is unprecedented for at least the last 2 millennia. Second, the continuing retreat of most mid- to low-latitude glaciers, many having persisted for thousands of years, signals a recent and abrupt change in the Earth's climate system. Finally, rooted, soft-bodied wetland plants, now exposed along the margins as the Quelccaya ice cap (Peru) retreats, have been radiocarbon dated and, when coupled with other widespread proxy evidence, provide strong evidence for an abrupt mid-Holocene climate event that marked the transition from early Holocene (pre-5,000-yr-B.P.) conditions to cooler, late Holocene (post-5,000-yr-B.P.) conditions. This abrupt event, approximately 5,200 yr ago, was widespread and spatially coherent through much of the tropics and was coincident with structural changes in several civilizations. These three lines of evidence argue that the present warming and associated glacier retreat are unprecedented in some areas for at least 5,200 yr. The ongoing global-scale, rapid retreat of mountain glaciers is not only contributing to global sea-level rise but also threatening freshwater supplies in many of the world's most populous regions.

  17. Physics based modeling of axial compressor stall

    NASA Astrophysics Data System (ADS)

    Zaki, Mina Adel

    2009-12-01

    Axial compressors are used in a wide variety of aerodynamic applications and are one of the most important components in aero-engines. However, the operability of compressors is limited at low-mass flow rates by fluid dynamic instabilities such as stall and surge. These instabilities can lead to engine failure and loss of engine power which can compromise the aircraft safety and reliability. Thus, a better understanding of how stall occurs and the causes behind its inception is extremely important. In the vicinity of the stall line, the flow field is inherently unsteady due to the interactions between adjacent rows of blades, formation of separation cells, and the viscous effects including shock-boundary layer interactions. Accurate modeling of these phenomena requires a proper set of stable and accurate boundary conditions at the rotor-stator interface that conserve mass, momentum, and energy, while eliminating false reflections. As a part of this research effort, an existing 3-D Navier-Stokes analysis for modeling single stage compressors has been modified to model multi-stage axial compressors and turbines. Several rotor-stator interface boundary conditions have been implemented. These conditions have been evaluated for the first stage (a stator and a rotor) of the two-stage fuel turbine on the space shuttle main engine (SSME). Their effectiveness in conserving global properties such as mass, momentum, and energy across the interface while yielding good performance predictions has been evaluated. While all the methods gave satisfactory results, a characteristic based approach and an unsteady sliding mesh approach are found to work best. Accurate modeling of the formation of stall cells requires the use of advanced turbulence models. As a part of this effort, a new advanced turbulence model called the Hybrid RANS/KES (HRKES) model has been developed and implemented. This model solves the Menter's k-o-SST model near walls and switches to the Kinetic Eddy

  18. Analysis of stall flutter of a helicopter radar blade

    NASA Technical Reports Server (NTRS)

    Crimi, P.

    1973-01-01

    A study of rotor blade aeroelastic stability was carried out, using an analytic model of a two-dimensional airfoil undergoing dynamic stall and an elastomechanical representation including flapping, flapwise bending and torsional degrees of freedom. Results for a hovering rotor demonstrated that the models used are capable of reproducing both classical and stall flutter. The minimum rotor speed for the occurrence of stall flutter in hover, was found to be determined from coupling between torsion and flapping. Instabilities analogous to both classical and stall flutter were found to occur in forward flight. However, the large stall-related torsional oscillations which commonly limit aircraft forward speed appear to be the response to rapid changes in aerodynamic moment which accompany stall and unstall, rather than the result of an aeroelastic instability. The severity of stall-related instabilities and response was found to depend to some extent on linear stability. Increasing linear stability lessens the susceptibility to stall flutter and reduced the magnitude of the torsional response to stall and unstall.

  19. Close-loop Dynamic Stall Control on a Pitching Airfoil

    NASA Astrophysics Data System (ADS)

    Giles, Ian; Corke, Thomas

    2017-11-01

    A closed-loop control scheme utilizing a plasma actuator to control dynamic stall is presented. The plasma actuator is located at the leading-edge of a pitching airfoil. It initially pulses at an unsteady frequency that perturbs the boundary layer flow over the suction surface of the airfoil. As the airfoil approaches and enters stall, the amplification of the unsteady disturbance is detected by an onboard pressure sensor also located near the leading edge. Once detected, the actuator is switched to a higher voltage control state that in static airfoil experiments would reattach the flow. The threshold level of the detection is a parameter in the control scheme. Three stall regimes were examined: light, medium, and deep stall, that were defined by their stall penetration angles. The results showed that in general, the closed-loop control scheme was effective at controlling dynamic stall. The cycle-integrated lift improved in all cases, and increased by as much as 15% at the lowest stall penetration angle. As important, the cycle-integrated aerodynamic damping coefficient also increased in all cases, and was made to be positive at the light stall regime where it traditionally is negative. The latter is important in applications where negative damping can lead to stall flutter.

  20. Surface temperature effect on subsonic stall.

    NASA Technical Reports Server (NTRS)

    Macha, J. M.; Norton, D. J.; Young, J. C.

    1972-01-01

    Results of an analytical and experimental study of boundary layer flow over an aerodynamic surface rejecting heat to a cool environment. This occurs following reentry of a Space Shuttle vehicle. Analytical studies revealed that a surface to freestream temperature ratio, greater than unity tended to destabilize the boundary layer, hastening transition and separation. Therefore, heat transfer accentuated the effect of an adverse pressure gradient. Wind tunnel tests of a 0012-64 NACA airfoil showed that the stall angle was significantly reduced while drag tended to increase for freestream temperature ratios up to 2.2.

  1. Stall/Spin Problems of Military Aircraft

    DTIC Science & Technology

    1976-06-01

    AVIONS DE COMBAT par C. I Burthe 15A SPIN INVESTIGATION OF THI; HANSA JET by H. Nep rt 15B METHODES D’ESSAIS DE VRILLES EN VOL par J.P. Duval 16 F-14A...General Dynamics’ Fort Worth Division F.O. Box 748, Fort Worth, Texas 16Ol SUMMARY In this paper the stall/spin problem as ,.iewed by American industry...nous pouvaI~s le constater, l’amblioratirn esp~r~o n’a Pu 9cre acquise. Les ph~norn~nes obtenus iont onicure comparables 6 ceux trouvite pr~cdemvi~ rt

  2. Stall induced instability of a teetered rotor

    NASA Astrophysics Data System (ADS)

    Glasgow, J. C.; Corrigan, R. D.

    Recent tests on the 38m Mod-0 horizontal experimental wind turbine yielded quantitative information on stall induced instability of a teetered rotor. Tests were conducted on rotor blades with NACA 230 series and NACA 643-618 airfoils at low rotor speeds to produce high angles of attack at relatively low wind speeds and power levels. The behavior of the rotor shows good agreement with predicted rotor response based on blade angle of attack calculations and airfoil section properties. The untwisted blades with the 64 series airfoil sections had a slower rate of onset of rotor instability when compared with the twisted 230 series blades, but high teeter angles and teeter stop impacts were experienced with both rotors as wind speeds increased to produce high angles of attack on the outboard portion of the blade. The relative importance of blade twist and airfoil section stall characteristics on the rate of onset of rotor unstability with increasing wind speed was not established however. Blade pitch was shown to be effective in eliminating rotor instability at the expense of some loss in rotor performance near rated wind speed.

  3. Flutter analysis of swept-wing subsonic aircraft with parameter studies of composite wings

    NASA Technical Reports Server (NTRS)

    Housner, J. M.; Stein, M.

    1974-01-01

    A computer program is presented for the flutter analysis, including the effects of rigid-body roll, pitch, and plunge of swept-wing subsonic aircraft with a flexible fuselage and engines mounted on flexible pylons. The program utilizes a direct flutter solution in which the flutter determinant is derived by using finite differences, and the root locus branches of the determinant are searched for the lowest flutter speed. In addition, a preprocessing subroutine is included which evaluates the variable bending and twisting stiffness properties of the wing by using a laminated, balanced ply, filamentary composite plate theory. The program has been substantiated by comparisons with existing flutter solutions. The program has been applied to parameter studies which examine the effect of filament orientation upon the flutter behavior of wings belonging to the following three classes: wings having different angles of sweep, wings having different mass ratios, and wings having variable skin thicknesses. These studies demonstrated that the program can perform a complete parameter study in one computer run. The program is designed to detect abrupt changes in the lowest flutter speed and mode shape as the parameters are varied.

  4. Abruptness of Cascade Failures in Power Grids

    NASA Astrophysics Data System (ADS)

    Pahwa, Sakshi; Scoglio, Caterina; Scala, Antonio

    2014-01-01

    Electric power-systems are one of the most important critical infrastructures. In recent years, they have been exposed to extreme stress due to the increasing demand, the introduction of distributed renewable energy sources, and the development of extensive interconnections. We investigate the phenomenon of abrupt breakdown of an electric power-system under two scenarios: load growth (mimicking the ever-increasing customer demand) and power fluctuations (mimicking the effects of renewable sources). Our results on real, realistic and synthetic networks indicate that increasing the system size causes breakdowns to become more abrupt; in fact, mapping the system to a solvable statistical-physics model indicates the occurrence of a first order transition in the large size limit. Such an enhancement for the systemic risk failures (black-outs) with increasing network size is an effect that should be considered in the current projects aiming to integrate national power-grids into ``super-grids''.

  5. Abruptness of Cascade Failures in Power Grids

    PubMed Central

    Pahwa, Sakshi; Scoglio, Caterina; Scala, Antonio

    2014-01-01

    Electric power-systems are one of the most important critical infrastructures. In recent years, they have been exposed to extreme stress due to the increasing demand, the introduction of distributed renewable energy sources, and the development of extensive interconnections. We investigate the phenomenon of abrupt breakdown of an electric power-system under two scenarios: load growth (mimicking the ever-increasing customer demand) and power fluctuations (mimicking the effects of renewable sources). Our results on real, realistic and synthetic networks indicate that increasing the system size causes breakdowns to become more abrupt; in fact, mapping the system to a solvable statistical-physics model indicates the occurrence of a first order transition in the large size limit. Such an enhancement for the systemic risk failures (black-outs) with increasing network size is an effect that should be considered in the current projects aiming to integrate national power-grids into “super-grids”. PMID:24424239

  6. Abruptness of cascade failures in power grids.

    PubMed

    Pahwa, Sakshi; Scoglio, Caterina; Scala, Antonio

    2014-01-15

    Electric power-systems are one of the most important critical infrastructures. In recent years, they have been exposed to extreme stress due to the increasing demand, the introduction of distributed renewable energy sources, and the development of extensive interconnections. We investigate the phenomenon of abrupt breakdown of an electric power-system under two scenarios: load growth (mimicking the ever-increasing customer demand) and power fluctuations (mimicking the effects of renewable sources). Our results on real, realistic and synthetic networks indicate that increasing the system size causes breakdowns to become more abrupt; in fact, mapping the system to a solvable statistical-physics model indicates the occurrence of a first order transition in the large size limit. Such an enhancement for the systemic risk failures (black-outs) with increasing network size is an effect that should be considered in the current projects aiming to integrate national power-grids into "super-grids".

  7. Supercritical flow characteristics at abrupt expansion structure

    NASA Astrophysics Data System (ADS)

    Lim, Jia Jun; Puay, How Tion; Zakaria, Nor Azazi

    2017-10-01

    When dealing with the design of a hydraulic structure, lateral expansion is often necessary for flow emerging at high velocity served as a cross-sectional transition. If the abrupt expansion structure is made to diverge rapidly, it will cause the major part of the flow fail to follow the boundaries. If the transition is too gradual, it will result in a waste of structural material. A preliminary study on the flow structure near the expansion and its relationship with flow parameter is carried out in this study. A two-dimensional depth-averaged model is developed to simulate the supercritical flow at the abrupt expansion structure. Constrained Interpolation Profile (CIP) scheme (which is of third order accuracy) is adopted in the numerical model. Results show that the flow structure and flow characteristics at the abrupt expansion can be reproduced numerically. The validation of numerical result is done against analytical studies. The result from numerical simulation showed good agreement with the analytical solution.

  8. The "stall barrier" as a new preventive in general aviation accidents.

    DOT National Transportation Integrated Search

    1966-09-01

    An elementary device, actuated by the conventional stall warning vane, is described which can be inexpensively installed in any aircraft. The new device, the Stall Barrier, prevents stalls through (1) warning the pilot through the 'touch sense' of th...

  9. A Comparative Study of Some Dynamic Stall Models

    NASA Technical Reports Server (NTRS)

    Reddy, T. S. R.; Kaza, K. R. V.

    1987-01-01

    Three semi-empirical aerodynamic stall models are compared with respect to their lift and moment hysteresis loop prediction, limit cycle behavior, easy implementation, and feasibility in developing the parameters required for stall flutter prediction of advanced turbines. For the comparison of aeroelastic response prediction including stall, a typical section model and a plate structural model are considered. The response analysis includes both plunging and pitching motions of the blades. In model A, a correction to the angle of attack is applied when the angle of attack exceeds the static stall angle. In model B, a synthesis procedure is used for angles of attack above static stall angles and the time history effects are accounted through the Wagner function. In both models the life and moment coefficients for angle of attack below stall are obtained from tabular data for a given Mach number and angle of attack. In model C, referred to an the ONERA model, the life and moment coefficients are given in the form of two differential equations, one for angles below stall, and the other for angles above stall. The parameters of those equations are nonlinear functions of the angle of attack.

  10. 14 CFR 23.691 - Artificial stall barrier system.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Design and Construction Control Systems § 23.691 Artificial stall barrier system. If the function of an artificial stall... downward pitching control will be provided must be established. (b) Considering the plus and minus airspeed...

  11. 14 CFR 23.691 - Artificial stall barrier system.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Design and Construction Control Systems § 23.691 Artificial stall barrier system. If the function of an artificial stall... downward pitching control will be provided must be established. (b) Considering the plus and minus airspeed...

  12. 14 CFR 23.691 - Artificial stall barrier system.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Design and Construction Control Systems § 23.691 Artificial stall barrier system. If the function of an artificial stall... downward pitching control will be provided must be established. (b) Considering the plus and minus airspeed...

  13. 14 CFR 23.691 - Artificial stall barrier system.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Design and Construction Control Systems § 23.691 Artificial stall barrier system. If the function of an artificial stall... downward pitching control will be provided must be established. (b) Considering the plus and minus airspeed...

  14. 14 CFR 23.691 - Artificial stall barrier system.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... AIRCRAFT AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Design and Construction Control Systems § 23.691 Artificial stall barrier system. If the function of an artificial stall... downward pitching control will be provided must be established. (b) Considering the plus and minus airspeed...

  15. Effects of boundary layer forcing on wing-tip vortices

    NASA Astrophysics Data System (ADS)

    Shaw-Ward, Samantha

    The nature of turbulence within wing-tip vortices has been a topic of research for decades, yet accurate measurements of Reynolds stresses within the core are inherently difficult due to the bulk motion wandering caused by initial and boundary conditions in wind tunnels. As a result, characterization of a vortex as laminar or turbulent is inconclusive and highly contradicting. This research uses several experimental techniques to study the effects of broadband turbulence, introduced within the wing boundary layer, on the development of wing-tip vortices. Two rectangular wings with a NACA 0012 profile were fabricated for the use of this research. One wing had a smooth finish and the other rough, introduced by P80 grade sandpaper. Force balance measurements showed a small reduction in wing performance due to surface roughness for both 2D and 3D configurations, although stall characteristics remained relatively unchanged. Seven-hole probes were purpose-built and used to assess the mean velocity profiles of the vortices five chord lengths downstream of the wing at multiple angles of attack. Above an incidence of 4 degrees, the vortices were nearly axisymmetric, and the wing roughness reduced both velocity gradients and peak velocity magnitudes within the vortex. Laser Doppler velocimetry was used to further assess the time-resolved vortex at an incidence of 5 degrees. Evidence of wake shedding frequencies and wing shear layer instabilities at higher frequencies were seen in power spectra within the vortex. Unlike the introduction of freestream turbulence, wing surface roughness did not appear to increase wandering amplitude. A new method for removing the effects of vortex wandering is proposed with the use of carefully selected high-pass filters. The filtered data revealed that the Reynolds stress profiles of the vortex produced by the smooth and rough wing were similar in shape, with a peak occurring away from the vortex centre but inside of the core. Single hot

  16. Temperature Distribution Measurement of The Wing Surface under Icing Conditions

    NASA Astrophysics Data System (ADS)

    Isokawa, Hiroshi; Miyazaki, Takeshi; Kimura, Shigeo; Sakaue, Hirotaka; Morita, Katsuaki; Japan Aerospace Exploration Agency Collaboration; Univ of Notre Dame Collaboration; Kanagawa Institute of Technology Collaboration; Univ of Electro-(UEC) Team, Comm

    2016-11-01

    De- or anti-icing system of an aircraft is necessary for a safe flight operation. Icing is a phenomenon which is caused by a collision of supercooled water frozen to an object. For the in-flight icing, it may cause a change in the wing cross section that causes stall, and in the worst case, the aircraft would fall. Therefore it is important to know the surface temperature of the wing for de- or anti-icing system. In aerospace field, temperature-sensitive paint (TSP) has been widely used for obtaining the surface temperature distribution on a testing article. The luminescent image from the TSP can be related to the temperature distribution. (TSP measurement system) In icing wind tunnel, we measured the surface temperature distribution of the wing model using the TSP measurement system. The effect of icing conditions on the TSP measurement system is discussed.

  17. Recent developments in rotary-wing aerodynamic theory

    NASA Technical Reports Server (NTRS)

    Johnson, W.

    1986-01-01

    Current progress in the computational analysis of rotary-wing flowfields is surveyed, and some typical results are presented in graphs. Topics examined include potential theory, rotating coordinate systems, lifting-surface theory (moving singularity, fixed wing, and rotary wing), panel methods (surface singularity representations, integral equations, and compressible flows), transonic theory (the small-disturbance equation), wake analysis (hovering rotor-wake models and transonic blade-vortex interaction), limitations on computational aerodynamics, and viscous-flow methods (dynamic-stall theories and lifting-line theory). It is suggested that the present algorithms and advanced computers make it possible to begin working toward the ultimate goal of turbulent Navier-Stokes calculations for an entire rotorcraft.

  18. Vertical Motion Simulator Experiment on Stall Recovery Guidance

    NASA Technical Reports Server (NTRS)

    Schuet, Stefan; Lombaerts, Thomas; Stepanyan, Vahram; Kaneshige, John; Shish, Kimberlee; Robinson, Peter; Hardy, Gordon H.

    2017-01-01

    A stall recovery guidance system was designed to help pilots improve their stall recovery performance when the current aircraft state may be unrecognized under various complicating operational factors. Candidate guidance algorithms were connected to the split-cue pitch and roll flight directors that are standard on large transport commercial aircraft. A new thrust guidance algorithm and cue was also developed to help pilots prevent the combination of excessive thrust and nose-up stabilizer trim. The overall system was designed to reinforce the current FAA recommended stall recovery procedure. A general transport aircraft model, similar to a Boeing 757, with an extended aerodynamic database for improved stall dynamics simulation fidelity was integrated into the Vertical Motion Simulator at NASA Ames Research Center. A detailed study of the guidance system was then conducted across four stall scenarios with 30 commercial and 10 research test pilots, and the results are reported.

  19. Experimental Aerodynamic Characteristics of a Joined-wing Research Aircraft Configuration

    NASA Technical Reports Server (NTRS)

    Smith, Stephen C.; Stonum, Ronald K.

    1989-01-01

    A wind-tunnel test was conducted at Ames Research Center to measure the aerodynamic characteristics of a joined-wing research aircraft (JWRA). This aircraft was designed to utilize the fuselage and engines of the existing NASA AD-1 aircraft. The JWRA was designed to have removable outer wing panels to represent three different configurations with the interwing joint at different fractions of the wing span. A one-sixth-scale wind-tunnel model of all three configurations of the JWRA was tested in the Ames 12-Foot Pressure Wind Tunnel to measure aerodynamic performance, stability, and control characteristics. The results of these tests are presented. Longitudinal and lateral-directional characteristics were measured over an angle of attack range of -7 to 14 deg and over an angle of sideslip range of -5 to +2.5 deg at a Mach number of 0.35 and a Reynolds number of 2.2x10(6)/ft. Various combinations of deflected control surfaces were tested to measure the effectiveness and impact on stability of several control surface arrangements. In addition, the effects on stall and post-stall aerodynamic characteristics from small leading-edge devices called vortilons were measured. The results of these tests indicate that the JWRA had very good aerodynamic performance and acceptable stability and control throughout its flight envelope. The vortilons produced a profound improvement in the stall and post-stall characteristics with no measurable effects on cruise performance.

  20. View east, showing Northwest Wing (Wing 5) and rear elevations ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    View east, showing Northwest Wing (Wing 5) and rear elevations of facade and tis flaking wings (Wings 1 and 2) - Hospital for Sick Children, 1731 Bunker Hill Road, Northeast, Washington, District of Columbia, DC

  1. Reactivation of stalled polyribosomes in synaptic plasticity

    PubMed Central

    Graber, Tyson E.; Hébert-Seropian, Sarah; Khoutorsky, Arkady; David, Alexandre; Yewdell, Jonathan W.; Lacaille, Jean-Claude; Sossin, Wayne S.

    2013-01-01

    Some forms of synaptic plasticity require rapid, local activation of protein synthesis. Although this is thought to reflect recruitment of mRNAs to free ribosomes, this would limit the speed and magnitude of translational activation. Here we provide compelling in situ evidence supporting an alternative model in which synaptic mRNAs are transported as stably paused polyribosomes. Remarkably, we show that metabotropic glutamate receptor activation allows the synthesis of proteins that lead to a functional long-term depression phenotype even when translation initiation has been greatly reduced. Thus, neurons evolved a unique mechanism to swiftly translate synaptic mRNAs into functional protein upon synaptic signaling using stalled polyribosomes to bypass the rate-limiting step of translation initiation. Because dysregulated plasticity is implicated in neurodevelopmental and psychiatric disorders such as fragile X syndrome, this work uncovers a unique translational target for therapies. PMID:24043809

  2. Experimental study of the velocity field on a delta wing

    NASA Technical Reports Server (NTRS)

    Payne, F. M.; Ng, T. T.; Nelson, R. C.

    1987-01-01

    An experimental study of the leading edge vortices on delta wings at large angles of incidence is presented. A combination of flow visualization, seven-hole pressure probe surveys and laser velocimeter measurements were used to study the leading edge vortex formation and breakdown for a set of delta wings. The delta wing models were thin flat plates with sharp leading edges having sweep angles of 70, 75, 80, and 85 degrees. The flow structure was examined for angles of incidence from 10 to 40 degrees and chord Reynolds numbers from 85,000 to 640,000. Vortex breakdown was observed on all the wings tested. Both bubble and spiral modes of breakdown were observed. The visualization and wake survey data shows that when vortex breakdown occurs the core flow transforms abruptly from a jet-like flow to a wake-like flow. The result also revealed that probe induced vortex breakdown was more steady than the natural breakdown.

  3. Canard-wing lift interference related to maneuvering aircraft at subsonic speeds

    NASA Technical Reports Server (NTRS)

    Gloss, B. B.; Mckinney, L. W.

    1973-01-01

    An investigation was conducted at Mach numbers of 0.7 and 0.9 to determine the lift interference effect of canard location on wing planforms typical of maneuvering fighter configurations. The canard had an exposed area of 16.0 percent of the wing reference area and was located in the plane of the wing or in a position 18.5 percent of the wing mean geometric chord above the wing plane. In addition, the canard could be located at two longitudinal stations. Two different wing planforms were tested: one with a leading-edge sweep angle of 60 deg and the other with a leading-edge sweep angle of 44 deg. The results indicated that although downwash from the canard reduced the wing lift at angles of attack up to approximately 16 deg, the total lift was substantially greater with the canard on than with the canard off. At angles of attack above 16 deg, the canard delayed the wing stall. Changing canard deflection had essentially no effect on the total lift, since the additional lift generated by the canard deflection was lost on the wing due to an increased downwash at the wing from the canard.

  4. Active flow control of the laminar separation bubble on a plunging airfoil near stall

    NASA Astrophysics Data System (ADS)

    Pande, Arth; Agate, Mark; Little, Jesse; Fasel, Hermann

    2017-11-01

    The effects of small amplitude (A/c = 0.048) high frequency (πfc/U∞ = 0.70) plunging motion on the X-56A airfoil are examined experimentally at Re = 200,000 for 12° angle of attack (CL,MAX = 12.25°) . The purpose of this research is to study the aerodynamic influence of structural motion when the wing is vibrating close to its eigenfrequency near static stall. Specific focus is placed on the laminar separation bubble (LSB) near the leading edge and its control via plasma actuation. In the baseline case, the leading edge bubble bursts during the oscillation cycle causing moment stall. A collaborative computational effort has shown that small amplitude forcing at a frequency that is most amplified by the primary instability of the LSB (FLSB+= 1, Fc+= 52) generates coherent spanwise vortices that entrain freestream momentum, thus reducing separation all while maintaining a laminar flow state. Results (PIV and surface pressure) indicate that a similar control mechanism is effective in the experiments. This is significant given the existence of freestream turbulence in the wind tunnel which has been shown to limit the efficacy of this active flow control technique in a model problem using Direct Numerical Simulation. The implications of these results are discussed.

  5. View east, showing Northwest Wing (Wing 5), west wall of ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    View east, showing Northwest Wing (Wing 5), west wall of the North Wing (Wing 2) and rear elevations of the facade and its flanking wings (Wings 1 and 2) - Hospital for Sick Children, 1731 Bunker Hill Road, Northeast, Washington, District of Columbia, DC

  6. Wing-Fixed PIV and force measurements of a large transverse gust encounter

    NASA Astrophysics Data System (ADS)

    Perrotta, Gino

    2015-11-01

    The unsteady aerodynamics of an aspect ratio 4 flat plate wing encountering a large-amplitude transverse gust were investigated using PIV in the wing-fixed reference frame and direct unsteady force measurements. Using a new experimental facility at the University of Maryland, the wing was towed at Reynolds number 20,000 through a 7m-long tank of nominally quiescent water containing a single cross-stream planar jet with velocity equal to the wing's towed velocity - a transverse gust ratio equal to one. The planar jet was created by pumping water through 30 cylindrical nozzles arranged in a single row. PIV confirms that the individual jets converge into a single, narrow, planar gust with a streamwise velocity profile resembling a canonical cosine-squared gust. Forces and fluid velocities of this wing-gust interaction will be presented for two pre-gust conditions: attached flow on the wing and stalled flow over the wing. In both cases, the gust encounter results in a momentary spike in lift coefficient. The peak lift coefficient was measured between 3 and 6 and varies with angle of attack. At low angle of attack, the attached flow wing produces less lift before the gust and much more (non-circulatory) lift during the gust than the stalled wing. Although the flow over the wing at low angle of attack separates during the gust and reattaches afterwards, the recovery time is similar to that of the high angle case, on the order of 10 chord lengths travelled.

  7. Oblique Wing Flights

    NASA Image and Video Library

    2018-05-09

    Flown in the mid 70's, this Oblique Wing was a large-scale R/C experimental aircraft to demonstrate the ability to pivot its wing to an oblique angle, allowing for a reduced drag penalty at transonic speeds.

  8. Theory of wing rock

    NASA Technical Reports Server (NTRS)

    Hsu, C.-H.; Lan, C. E.

    1985-01-01

    Wing rock is one type of lateral-directional instabilities at high angles of attack. To predict wing rock characteristics and to design airplanes to avoid wing rock, parameters affecting wing rock characteristics must be known. A new nonlinear aerodynamic model is developed to investigate the main aerodynamic nonlinearities causing wing rock. In the present theory, the Beecham-Titchener asymptotic method is used to derive expressions for the limit-cycle amplitude and frequency of wing rock from nonlinear flight dynamics equations. The resulting expressions are capable of explaining the existence of wing rock for all types of aircraft. Wing rock is developed by negative or weakly positive roll damping, and sustained by nonlinear aerodynamic roll damping. Good agreement between theoretical and experimental results is obtained.

  9. Abrupt climate-independent fire regime changes

    USGS Publications Warehouse

    Pausas, Juli G.; Keeley, Jon E.

    2014-01-01

    Wildfires have played a determining role in distribution, composition and structure of many ecosystems worldwide and climatic changes are widely considered to be a major driver of future fire regime changes. However, forecasting future climatic change induced impacts on fire regimes will require a clearer understanding of other drivers of abrupt fire regime changes. Here, we focus on evidence from different environmental and temporal settings of fire regimes changes that are not directly attributed to climatic changes. We review key cases of these abrupt fire regime changes at different spatial and temporal scales, including those directly driven (i) by fauna, (ii) by invasive plant species, and (iii) by socio-economic and policy changes. All these drivers might generate non-linear effects of landscape changes in fuel structure; that is, they generate fuel changes that can cross thresholds of landscape continuity, and thus drastically change fire activity. Although climatic changes might contribute to some of these changes, there are also many instances that are not primarily linked to climatic shifts. Understanding the mechanism driving fire regime changes should contribute to our ability to better assess future fire regimes.

  10. Abrupt warming of the Red Sea

    NASA Astrophysics Data System (ADS)

    Raitsos, D. E.; Hoteit, I.; Prihartato, P. K.; Chronis, T.; Triantafyllou, G.; Abualnaja, Y.

    2011-07-01

    Coral reef ecosystems, often referred to as “marine rainforests,” concentrate the most diverse life in the oceans. Red Sea reef dwellers are adapted in a very warm environment, fact that makes them vulnerable to further and rapid warming. The detection and understanding of abrupt temperature changes is an important task, as ecosystems have more chances to adapt in a slowly rather than in a rapid changing environment. Using satellite derived sea surface and ground based air temperatures, it is shown that the Red Sea is going through an intense warming initiated in the mid-90s, with evidence for an abrupt increase after 1994 (0.7°C difference pre and post the shift). The air temperature is found to be a key parameter that influences the Red Sea marine temperature. The comparisons with Northern Hemisphere temperatures revealed that the observed warming is part of global climate change trends. The hitherto results also raise additional questions regarding other broader climatic impacts over the area.

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

    PubMed

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

    2008-02-08

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

  12. Transonic Aerodynamic Loading Characteristics of a Wing-Body-Tail Combination Having a 52.5 deg. Sweptback Wing of Aspect Ratio 3 With Conical Wing Camber and Body Indentation for a Design Mach Number of Square Root of 2

    NASA Technical Reports Server (NTRS)

    Cassetti, Marlowe D.; Re, Richard J.; Igoe, William B.

    1961-01-01

    An investigation has been made of the effects of conical wing camber and body indentation according to the supersonic area rule on the aerodynamic wing loading characteristics of a wing-body-tail configuration at transonic speeds. The wing aspect ratio was 3, taper ratio was 0.1, and quarter-chord-line sweepback was 52.5 deg. with 3-percent-thick airfoil sections. The tests were conducted in the Langley 16-foot transonic tunnel at Mach numbers from 0.80 to 1.05 and at angles of attack from 0 deg. to 14 deg., with Reynolds numbers based on mean aerodynamic chord varying from 7 x 10(exp 6) to 8 x 10(exp 6). Conical camber delayed wing-tip stall and reduced the severity of the accompanying longitudinal instability but did not appreciably affect the spanwise load distribution at angles of attack below tip stall. Body indentation reduced the transonic chordwise center-of-pressure travel from about 8 percent to 5 percent of the mean aerodynamic chord.

  13. LANN wing design

    NASA Technical Reports Server (NTRS)

    Firth, G. C.

    1983-01-01

    The LANN wing is the result of a joint effort between Lockheed, the Air Force, NASA, and the Netherlands to measure unsteady pressures at transonic speeds. It is a moderate-aspect-ratio transport wing configuration. The wing was machined from NITRONIC 40 and has 12 percent thick supercritical airfoil sections.

  14. Effects of three types of free-stall surfaces on preferences and stall usage by dairy cows.

    PubMed

    Tucker, C B; Weary, D M; Fraser, D

    2003-02-01

    One important criterion in choosing appropriate housing systems for dairy cattle is that the freestall provides a comfortable surface for the cow. This paper describes two experiments testing the effects of commonly used lying surfaces on stall preference and stall usage by Holstein cows. In both experiments, 12 cows were housed individually in separate pens. Each pen contained three free stalls with a different surface: deep-bedded sawdust, deep-bedded sand, and a geotextile mattress covered with 2 to 3 cm of sawdust. The animals were restricted to each surface in turn, in a random order for either 2 (Experiment 1) or 3 d (Experiment 2). Both before and after this restriction phase, the animals were allowed access to all three surfaces, and preference was determined, based on lying times. Of the 12 cows used in Experiment 1, 10 preferred sawdust before and nine after the restriction phase. During the restriction phase, average lying times and number of lying events during the restriction phase were significantly lower for the sand-bedded stalls (P < or = 0.05), and standing times were higher on mattresses (P < or = 0.05), compared with sawdust. Although these cows had some experience with all three surfaces during the experiment, they had been housed in sawdust-bedded stalls during their previous lactation. Cows used in Experiment 2 had spent their previous lactation in sand bedded stalls. In this experiment, about half the cows preferred sand and half sawdust, after the restriction phase. During the restriction phase of experiment, lying times and number of lying events were lower, and standing times were higher when the animals were restricted to the mattresses compared to either sand or sawdust (P < or = 0.05). These results indicate that (1) free stall surface can affect both stall preferences and stall usage, and (2) mattresses are less preferred.

  15. Wing kinematics and flexibility for optimal manoeuvring and escape

    NASA Astrophysics Data System (ADS)

    Wong, Jaime Gustav

    Understanding how animals control the dynamic stall vortices in their wake is critical to developing micro-aerial vehicles and autonomous underwater vehicles, not to mention wind turbines, delta wings, and rotor craft that undergo similar dynamic stall processes. Applying this knowledge to biomimetic engineering problems requires progress in three areas: (i) understanding the flow physics of natural swimmers and flyers; (ii) developing flow measurement techniques to resolve this physics; and (iii) deriving low-cost models suitable for studying the vast parameter space observed in nature. This body of work, which consists of five research chapters, focuses on the leading-edge vortex (LEV) that forms on profiles undergoing rapid manoeuvres, delta wings, and similar devices. Lagrangian particle tracking is used throughout this thesis to track the mass and circulation transport in the LEV on manoeuvring profiles. The growth and development of the LEV is studied in relation to: flapping and plunging profile kinematics; spanwise flow from profile sweep and spanwise profile bending; and varying the angle-of-attack gradient along the profile span. Finally, scaling relationships derived from the observations above are used to develop a low-cost model for LEV growth, that is validated on a flat-plate delta wing. Together these results contribute to each of the three topics identified above, as a step towards developing robust, agile biomimetic swimmers and flyers.

  16. The phenomenon of dynamic stall. [vortex shedding phenomenon on oscillating airfoils

    NASA Technical Reports Server (NTRS)

    Mccroskey, W. J.

    1981-01-01

    The general features of dynamic stall on oscillating airfoils are explained in terms of the vortex shedding phenomenon, and the important differences between static stall, light dynamic stall, and deep stall are described. An overview of experimentation and prediction techniques is given.

  17. 6. HUBBARD TUB, SHOWING WHIRLPOOL MOTOR OUTSIDE BATH STALL. ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    6. HUBBARD TUB, SHOWING WHIRLPOOL MOTOR OUTSIDE BATH STALL. - Hot Springs National Park, Bathhouse Row, Quapaw Bathhouse: Mechanical & Piping Systems, State Highway 7, 1 mile north of U.S. Highway 70, Hot Springs, Garland County, AR

  18. 16. Oblique, guard quarters; shower stalls at left; view to ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    16. Oblique, guard quarters; shower stalls at left; view to south-southwest, 65mm lens with electronic flash illumination. - Tule Lake Project Jail, Post Mile 44.85, State Route 139, Newell, Modoc County, CA

  19. INTERIOR DETAIL, TWO TOILET STALLS, SHOWING ROUGHCUT DOORS; VIEW TO ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    INTERIOR DETAIL, TWO TOILET STALLS, SHOWING ROUGH-CUT DOORS; VIEW TO NORTH - Fort Bragg, Noncommissioned Officers' Service Club, Guest House Building, South of Butner Road, Fayetteville, Cumberland County, NC

  20. Women's toilet with marble stalls and wooden doors, east end ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Women's toilet with marble stalls and wooden doors, east end of first floor. View to southwest. - San Bernardino Valley College, Life Science Building, 701 South Mount Vernon Avenue, San Bernardino, San Bernardino County, CA

  1. Stable interior, showing center aisle, stalls, and feed troughs. View ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Stable interior, showing center aisle, stalls, and feed troughs. View looking southwest - Fort Hill Farm, Stable, West of Staunton (Roanoke) River between Turkey & Caesar's Runs, Clover, Halifax County, VA

  2. Subsonic-transonic stall flutter study

    NASA Technical Reports Server (NTRS)

    Stardter, H.

    1979-01-01

    The objective of the Subsonic/Transonic Stall Flutter Program was to obtain detailed measurements of both the steady and unsteady flow field surrounding a rotor and the mechanical state of the rotor while it was operating in both steady and flutter modes to provide a basis for future analysis and for development of theories describing the flutter phenomenon. The program revealed that while all blades flutter at the same frequency, they do not flutter at the same amplitude, and their interblade phase angles are not equal. Such a pattern represents the superposition of a number of rotating nodal diameter patterns, each characterized by a different amplitude and different phase indexing, but each rotating at a speed that results in the same flutter frequency as seen in the rotor system. Review of the steady pressure contours indicated that flutter may alter the blade passage pressure distribution. The unsteady pressure amplitude contour maps reveal regions of high unsteady pressure amplitudes near the leading edge, lower amplitudes near the trailing.

  3. Wetlands issue stalls Clean Water Act

    NASA Astrophysics Data System (ADS)

    Bush, Susan

    Although reauthorization of the Clean Water Act was scheduled for 1992, action has stalled due to debate over the contentious wetland issue and is not likely to pick up again until after the first of the year. The subject of the debate, regulation of wetlands, is found in Section 404, which makes up only a small part of the Clean Water Act.At the meeting, “New Directions in Clean Water Policy,” held in Charlottesville, Va., July 28-31, Ralph Heimlich, an economist with the Office of Policy and Planning Evaluation at the Environmental Protection Agency, said “it is unfortunate that the Section 404 Dredge and Fill permit program, our only national wetland regulation, is part of the Clean Water Act.” The controversy over wetland reform, he added, “has delayed and threatens to poison action on Clean Water Act reauthorization, provisions that may be more directly significant in improving water quality.”

  4. Parachuting with bristled wings

    NASA Astrophysics Data System (ADS)

    Kasoju, Vishwa; Santhanakrishnan, Arvind; Senter, Michael; Armel, Kristen; Miller, Laura

    2017-11-01

    Free takeoff flight recordings of thrips (body length <1 mm) show that they can intermittently cease flapping and instead float passively downwards by spreading their bristled wings. Such drag-based parachuting can lower the speed of falling and aid in long distance dispersal by minimizing energetic demands needed for active flapping flight. However, the role of bristled wings in parachuting remains unclear. In this study, we examine if using bristled wings lowers drag forces in parachuting as compared to solid (non-bristled) wings. Wing angles and settling velocities were obtained from free takeoff flight videos. A solid wing model and bristled wing model with bristle spacing to diameter ratio of 5 performing translational motion were comparatively examined using a dynamically scaled robotic model. We measured force generated under varying wing angle from 45-75 degrees across a Reynolds number (Re) range of 1 to 15. Drag experienced by the wings decreased in both wing models when varying Re from 1 to 15. Leakiness of flow through bristles, visualized using spanwise PIV, and implications for force generation will be presented. Numerical simulations will be used to investigate the stability of free fall using bristled wings.

  5. Ch-47C Fixed-System Stall-Flutter Damping

    DTIC Science & Technology

    1975-08-01

    flutter. The steady and vibratory loads in the cyclic-trim linkage are so related that motions across the control system’s mechan- ical free play could...be a significant part of the stall-flutter motion, depending on the magnitude of the free play . For this reason it is recommended that future testing...include the deter- mination of the effects of control-system free play on the stall-flutter responses. , f ,**~ - ,***,- * **4 , - - *. i

  6. Stability Analysis for Rotating Stall Dynamics in Axial Flow Compressors

    DTIC Science & Technology

    1999-01-01

    modes determines collectively local stability of the compressor model. Explicit conditions are obtained for local stability of rotating stall which...critical modes determines the stability for rotating stall collectively . We point out that although in a special case our stability condition for...strict crossing assumption implies that the zero solution changes its stability as ~, crosses ~’c. For instance, odk (yc ) > 0 implies that the zero

  7. A method for analyzing dynamic stall of helicopter rotor blades

    NASA Technical Reports Server (NTRS)

    Crimi, P.; Reeves, B. L.

    1972-01-01

    A model for each of the basic flow elements involved in the unsteady stall of a two-dimensional airfoil in incompressible flow is presented. The interaction of these elements is analyzed using a digital computer. Computations of the loading during transient and sinusoidal pitching motions are in good qualitative agreement with measured loads. The method was used to confirm that large torsional response of helicopter blades detected in flight tests can be attributed to dynamic stall.

  8. Computational Analysis of a Wing Designed for the X-57 Distributed Electric Propulsion Aircraft

    NASA Technical Reports Server (NTRS)

    Deere, Karen A.; Viken, Jeffrey K.; Viken, Sally A.; Carter, Melissa B.; Wiese, Michael R.; Farr, Norma L.

    2017-01-01

    A computational study of the wing for the distributed electric propulsion X-57 Maxwell airplane configuration at cruise and takeoff/landing conditions was completed. Two unstructured-mesh, Navier-Stokes computational fluid dynamics methods, FUN3D and USM3D, were used to predict the wing performance. The goal of the X-57 wing and distributed electric propulsion system design was to meet or exceed the required lift coefficient 3.95 for a stall speed of 58 knots, with a cruise speed of 150 knots at an altitude of 8,000 ft. The X-57 Maxwell airplane was designed with a small, high aspect ratio cruise wing that was designed for a high cruise lift coefficient (0.75) at angle of attack of 0deg. The cruise propulsors at the wingtip rotate counter to the wingtip vortex and reduce induced drag by 7.5 percent at an angle of attack of 0.6deg. The unblown maximum lift coefficient of the high-lift wing (with the 30deg flap setting) is 2.439. The stall speed goal performance metric was confirmed with a blown wing computed effective lift coefficient of 4.202. The lift augmentation from the high-lift, distributed electric propulsion system is 1.7. The predicted cruise wing drag coefficient of 0.02191 is 0.00076 above the drag allotted for the wing in the original estimate. However, the predicted drag overage for the wing would only use 10.1 percent of the original estimated drag margin, which is 0.00749.

  9. A numerical strategy for modelling rotating stall in core compressors

    NASA Astrophysics Data System (ADS)

    Vahdati, M.

    2007-03-01

    The paper will focus on one specific core-compressor instability, rotating stall, because of the pressing industrial need to improve current design methods. The determination of the blade response during rotating stall is a difficult problem for which there is no reliable procedure. During rotating stall, the blades encounter the stall cells and the excitation depends on the number, size, exact shape and rotational speed of these cells. The long-term aim is to minimize the forced response due to rotating stall excitation by avoiding potential matches between the vibration modes and the rotating stall pattern characteristics. Accurate numerical simulations of core-compressor rotating stall phenomena require the modelling of a large number of bladerows using grids containing several tens of millions of points. The time-accurate unsteady-flow computations may need to be run for several engine revolutions for rotating stall to get initiated and many more before it is fully developed. The difficulty in rotating stall initiation arises from a lack of representation of the triggering disturbances which are inherently present in aeroengines. Since the numerical model represents a symmetric assembly, the only random mechanism for rotating stall initiation is provided by numerical round-off errors. In this work, rotating stall is initiated by introducing a small amount of geometric mistuning to the rotor blades. Another major obstacle in modelling flows near stall is the specification of appropriate upstream and downstream boundary conditions. Obtaining reliable boundary conditions for such flows can be very difficult. In the present study, the low-pressure compression (LPC) domain is placed upstream of the core compressor. With such an approach, only far field atmospheric boundary conditions are specified which are obtained from aircraft speed and altitude. A chocked variable-area nozzle, placed after the last compressor bladerow in the model, is used to impose boundary

  10. Some observations on the mechanism of aircraft wing rock

    NASA Technical Reports Server (NTRS)

    Hwang, C.; Pi, W. S.

    1979-01-01

    A scale model of the Northrop F-5A was tested in NASA Ames Research Center Eleven-Foot Transonic Tunnel to simulate the wing rock oscillations in a transonic maneuver. For this purpose, a flexible model support device was designed and fabricated, which allowed the model to oscillate in roll at the scaled wing rock frequency. Two tunnel entries were performed to acquire the pressure (steady state and fluctuating) and response data when the model was held fixed and when it was excited by flow to oscillate in roll. Based on these data, a limit cycle mechanism was identified, which supplied energy to the aircraft model and caused the Dutch roll type oscillations, commonly called wing rock. The major origin of the fluctuating pressures that contributed to the limit cycle was traced to the wing surface leading edge stall and the subsequent lift recovery. For typical wing rock oscillations, the energy balance between the pressure work input and the energy consumed by the model's aerodynamic and mechanical damping was formulated and numerical data presented.

  11. Some observations on the mechanism of aircraft wing rock

    NASA Technical Reports Server (NTRS)

    Hwang, C.; Pi, W. S.

    1978-01-01

    A pressure scale model of Northrop F-5A was tested in NASA Ames Research Center Eleven-Foot Transonic Tunnel to simulate the wing rock oscillations in a transonic maneuver. For this purpose, a flexible model support device was designed and fabricated which allowed the model to oscillate in roll at the scaled wing rock frequency. Two tunnel entries were performed to acquire the pressure (steady state and fluctuating) and response data when the model was held fixed and when it was excited by flow to oscillate in roll. Based on these data, a limit cycle mechanism was identified which supplied energy to the aircraft model and caused the Dutch roll type oscillations, commonly called wing rock. The major origin of the fluctuating pressures which contributed to the limit cycle was traced to the wing surface leading edge stall and the subsequent lift recovery. For typical wing rock oscillations, the energy balance between the pressure work input and the energy consumed by the model aerodynamic and mechanical damping was formulated and numerical data presented.

  12. Hock lesions and free-stall design.

    PubMed

    Weary, D M; Taszkun, I

    2000-04-01

    We compared the prevalence and severity of skin lesions on the hocks of lactating dairy cows in southern British Columbia, comparing 20 farms using three common bedding surfaces: sawdust, sand, and geotextile mattresses. Skin lesions were scored at five positions on the hock. For each position we noted if the lesion showed inflammatory attributes, and then assigned a severity score. Of the 1752 lactating cows scored, 1267 cows (73%) had at least one hock lesion. Of those cows with lesions, 87% had lesions on both legs, 76% had lesions on more than one location on the hock, and 78% had a lesion of at least moderate severity (i.e., evidence of skin breakage or an area of hair loss >10 cm2). Lesions were most prevalent on farms that used geotextile mattresses (91% of cows) and least common on farms that used sand (24% of cows). Moreover, lesions on cows from farms using mattresses were more numerous and more severe than those on cows from sand-bedded farms. The prevalence and severity of lesions on farms using sawdust was intermediate. Lesions also varied in relation to location on the hock. For farms using geotextile mattresses, lesions were more common and more severe on the lateral surfaces of both the tuber calcis and the tarsal joint. On farms using sawdust, lesions were common on the dorsal surface of the tuber calcis and the lateral surfaces of both the tuber calcis and the tarsal joint. Lesions were rare on all five positions for cows from sand-bedded farms. Among the 10 farms sampled using sawdust, we found a significant negative relationship between the length of the stall and severity of lesions. For cows with lesions, the number and severity of lesions increased with age.

  13. The Arctic Grand Challenge: Abrupt Climate Change

    NASA Astrophysics Data System (ADS)

    Wilkniss, P. E.

    2003-12-01

    Trouble in polar paradise (Science, 08/30/02), significant changes in the Arctic environment are scientifically documented (R.E. Moritz et al. ibid.). More trouble, lots more, "abrupt climate change," (R. B. Alley, et al. Science 03/28/03). R. Corell, Arctic Climate Impact Assessment team (ACIA), "If you want to see what will happen in the rest of the world 25 years from now just look what's happening in the Arctic," (Arctic Council meeting, Iceland, 08/03). What to do? Make abrupt Arctic climate change a grand challenge for the IPY-4 and beyond! Scientifically:Describe the "state" of the Arctic climate system as succinctly as possible and accept it as the point of departure.Develop a hypothesis and criteria what constitutes "abrupt climate change," in the Arctic that can be tested with observations. Observations: Bring to bear existing observations and coordinate new investments in observations through an IPY-4 scientific management committee. Make the new Barrow, Alaska, Global Climate Change Research Facility a major U.S. contribution and focal point for the IPY-4 in the U.S Arctic. Arctic populations, Native peoples: The people of the North are living already, daily, with wrenching change, encroaching on their habitats and cultures. For them "the earth is faster now," (I. Krupnik and D. Jolly, ARCUS, 2002). From a political, economic, social and entirely realistic perspective, an Arctic grand challenge without the total integration of the Native peoples in this effort cannot succeed. Therefore: Communications must be established, and the respective Native entities must be approached with the determination to create well founded, well functioning, enduring partnerships. In the U.S. Arctic, Barrow with its long history of involvement and active support of science and with the new global climate change research facility should be the focal point of choice Private industry: Resource extraction in the Arctic followed by oil and gas consumption, return the combustion

  14. An experimental and numerical investigation on the formation of stall-cells on airfoils

    NASA Astrophysics Data System (ADS)

    Manolesos, M.; Papadakis, G.; Voutsinas, S.

    2014-12-01

    Stall Cells (SCs) are large scale three-dimensional structures of separated flow that have been observed on the suction side of airfoils designed for or used on wind turbine blades. SCs are unstable in nature but can be stabilised by means of a localized disturbance; here in the form of a zigzag tape covering 10% of the wing span. Based on extensive tuft flow visualisations, the resulting flow was found macroscopically similar to the undisturbed flow. Next a combined investigation was carried out including pressure recordings, Stereo-PIV measurements and CFD simulations. The investigation parameters were the aspect ratio, the angle of attack and the Re number. Tuft and pressure data were found in good agreement. The 3D CFD simulations reproduced the structure of the SCs in qualitative agreement with the experimental data but had a delay of ~3deg in capturing the first appearance of a SC. The error in Cl max prediction was 7% compared to 19% for the 2D cases. Tests show that SCs grow with Re number and angle of attack. Also analysis of the time averaged computational results indicated the presence of three types of vortices: (a) the trailing edge line vortex (TELV) in the wake, (b) the separation line vortex (SLV) over the wing and (c) the SC vortices. The TELV and SLV run parallel to the trailing edge and are of opposite sign, while the SC vortices start normal to the wing suction surface, then bend towards the SC centre and later extend downstream, with their vorticity parallel to the free stream.

  15. Flow Field Analysis of Fully Coupled Computations of a Flexible Wing undergoing Stall Flutter

    DTIC Science & Technology

    2016-01-01

    unsteady aerodynamic loads due to structural displacements. In terms of actuation , most, if not all, active ∗Research Associate, Department of...flutter suppression techniques, conventional trailing edge flap actuators with a bandwidth of 10 Hz5 was used. Interestingly, the frequencies associated...influence of the flow features on the aeroelastic instability are quantified. Finally, the influence of actuation through a blowing port at 75% span is

  16. Towards Greenland Glaciation: Cumulative or Abrupt Transition?

    NASA Astrophysics Data System (ADS)

    Tan, N.; Ramstein, G.; Contoux, C.; Ladant, J. B.; Dumas, C.; Donnadieu, Y.

    2014-12-01

    The insolation evolution [Laskar 2004] from 4 to 2.5 Ma depicts a series of three summer solstice insolation minima between 2.7 and 2.6 Ma, but there are other more important summer solstice minima notably around 3.82 and 3.05 Ma. On such a time span of more than 1 Ma, data shows that there are variations in the evolution of atmospheric CO2 concentration with a local maximum around 3 Ma [Seki et al.2010; Bartoli et al. 2011], before a decrease between 3 and 2.6 Ma. The latter, suggesting an abrupt ice sheet inception around 2.7 Ma, has been shown to be a major culprit for the full Greenland Glaciation [Lunt et al. 2008]. However, a recent study [Contoux et al. 2014, in review] suggests that a lowering of CO2 is not sufficient to initiate a glaciation on Greenland and must be combined to low summer insolation, with surviving ice during insolation maximum, suggesting a cumulative process in the first place, which could further lead to full glaciation at 2.7 Ma. Through a new tri-dimensional interpolation method implemented within the asynchronous coupling between an atmosphere ocean general circulation model (IPSL-CM5A) and an ice sheet model (GRISLI), we investigate the transient evolution of Greenland ice sheet during the Pliocene to diagnose whether the ice sheet inception is an abrupt event or rather a cumulative process, involving waxing and waning of the ice sheet during several orbital cycles. ReferencesBartoli, G., Hönisch, B., & Zeebe, R. E. (2011). Atmospheric CO2 decline during the Pliocene intensification of Northern Hemisphere glaciations. Paleoceanography, 26(4). Contoux C, Dumas C, Ramstein G, Jost A, Dolan A. M. (2014) Modelling Greenland Ice sheet inception and sustainability during the late Pliocene. (in review for Earth and Planetary Science Letters.).Laskar, J., Robutel, P., Joutel, F., Gastineau, M., Correia, A. C. M., & Levrard, B. (2004). A long-term numerical solution for the insolation quantities of the Earth. Astronomy & Astrophysics, 428

  17. Controlled vortical flow on delta wings through unsteady leading edge blowing

    NASA Technical Reports Server (NTRS)

    Lee, K. T.; Roberts, Leonard

    1990-01-01

    The vortical flow over a delta wing contributes an important part of the lift - the so called nonlinear lift. Controlling this vortical flow with its favorable influence would enhance aircraft maneuverability at high angle of attack. Several previous studies have shown that control of the vortical flow field is possible through the use of blowing jets. The present experimental research studies vortical flow control by applying a new blowing scheme to the rounded leading edge of a delta wing; this blowing scheme is called Tangential Leading Edge Blowing (TLEB). Vortical flow response both to steady blowing and to unsteady blowing is investigated. It is found that TLEB can redevelop stable, strong vortices even in the post-stall angle of attack regime. Analysis of the steady data shows that the effect of leading edge blowing can be interpreted as an effective change in angle of attack. The examination of the fundamental time scales for vortical flow re-organization after the application of blowing for different initial states of the flow field is studied. Different time scales for flow re-organization are shown to depend upon the effective angle of attack. A faster response time can be achieved at angles of attack beyond stall by a suitable choice of the initial blowing momentum strength. Consequently, TLEB shows the potential of controlling the vortical flow over a wide range of angles of attack; i.e., in both for pre-stall and post-stall conditions.

  18. Determination of the Stability and Control Characteristics of a Tailless All-Wing Airplane Model with Sweepback in the Langley Free-Flight Tunnel

    NASA Technical Reports Server (NTRS)

    Seacord, Charles L.; Campbell, John P.

    1945-01-01

    Force and flight tests were performance on an all-wing model with windmilling propellers. Tests were conducted with deflected and retracted flaps, with and without auxiliary vertical tail surfaces, and with different centers of gravity and trim coefficients. Results indicate serious reduction of stick-fixed longitudinal stability because of wing-tip stalling at high lift coefficient. Directional stability without vertical tail is undesirably low. Low effective dihedral should be maintained. Elevator and rudder control system is satisfactory.

  19. Wind tunnel pressure distribution tests on a series of biplane wing models Part II : effects of changes in decalage, dihedral, sweepback and overhang

    NASA Technical Reports Server (NTRS)

    Knight, Montgomery; Noyes, Richard W

    1929-01-01

    This preliminary report furnishes information on the changes in the forces on each wing of a biplane cellule when the decalage, dihedral, sweepback and overhang are separately varied. The data were obtained from pressure distribution tests made in the Atmospheric Wind Tunnel of the Langley Memorial Aeronautical Laboratory. Since each test was carried up to 90 degree angle of attack, the results may be used in the study of stalled flight and of spinning and in the structural design of biplane wings.

  20. Dynamic Stall Characteristics of Drooped Leading Edge Airfoils

    NASA Technical Reports Server (NTRS)

    Sankar, Lakshmi N.; Sahin, Mehmet; Gopal, Naveen

    2000-01-01

    Helicopters in high-speed forward flight usually experience large regions of dynamic stall over the retreating side of the rotor disk. The rapid variations in the lift and pitching moments associated with the stall process can result in vibratory loads, and can cause fatigue and failure of pitch links. In some instances, the large time lag between the aerodynamic forces and the blade motion can trigger stall flutter. A number of techniques for the alleviation of dynamic stall have been proposed and studied by researchers. Passive and active control techniques have both been explored. Passive techniques include the use of high solidity rotors that reduce the lift coefficients of individual blades, leading edge slots and leading edge slats. Active control techniques include steady and unsteady blowing, and dynamically deformable leading edge (DDLE) airfoils. Considerable amount of experimental and numerical data has been collected on the effectiveness of these concepts. One concept that has not received as much attention is the drooped-leading edge airfoil idea. It has been observed in wind tunnel studies and flight tests that drooped leading edge airfoils can have a milder dynamic stall, with a significantly milder load hysteresis. Drooped leading edge airfoils may not, however, be suitable at other conditions, e.g. in hover, or in transonic flow. Work needs to be done on the analysis and design of drooped leading edge airfoils for efficient operation in a variety of flight regimes (hover, dynamic stall, and transonic flow). One concept that is worthy of investigation is the dynamically drooping airfoil, where the leading edge shape is changed roughly once-per-rev to mitigate the dynamic stall.

  1. Cellular Structures in the Flow Over the Flap of a Two-Element Wing

    NASA Technical Reports Server (NTRS)

    Yon, Steven A.; Katz, Joseph

    1997-01-01

    Flow visualization information and time dependent pressure coefficients were recorded for the flow over a two-element wing. The investigation focused on the stall onset; particularly at a condition where the flow is attached on the main element but separated on the flap. At this condition, spanwise separation cells were visible in the flow over the flap, and time dependent pressure data was measured along the centerline of the separation cell. The flow visualizations indicated that the spanwise occurrence of the separation cells depends on the flap (and not wing) aspect ratio.

  2. The Influence of Tip Shape on the Wing Load Distribution as Determined by Flight Tests

    NASA Technical Reports Server (NTRS)

    Rhode, Richard V

    1935-01-01

    Pressure measurements were made in flight on the right upper wing of an M-3 airplane. The effects of tip plan form, washout, and transverse camber were investigated with eight tip forms in unyawed conditions through the range of positive lift coefficients from zero lift to the stall. The conclusion is that the tip plan form does not influence the span distribution of the coefficients of normal force and moment. It is shown inferentially that temperature, humidity, and the aging of the wood and fabric wing structure used on the M-3 airplane have an appreciable influence on the load distribution.

  3. Slotted Aircraft Wing

    NASA Technical Reports Server (NTRS)

    McLean, James D. (Inventor); Witkowski, David P. (Inventor); Campbell, Richard L. (Inventor)

    2006-01-01

    A swept aircraft wing includes a leading airfoil element and a trailing airfoil element. At least one full-span slot is defined by the wing during at least one transonic condition of the wing. The full-span slot allows a portion of the air flowing along the lower surface of the leading airfoil element to split and flow over the upper surface of the trailing airfoil element so as to achieve a performance improvement in the transonic condition.

  4. Development of a nonlinear switching function and its application to static lift characteristics of straight wings

    NASA Technical Reports Server (NTRS)

    Hewes, D. E.

    1978-01-01

    A mathematical modeling technique was developed for the lift characteristics of straight wings throughout a very wide angle of attack range. The technique employs a mathematical switching function that facilitates the representation of the nonlinear aerodynamic characteristics in the partially and fully stalled regions and permits matching empirical data within + or - 4 percent of maximum values. Although specifically developed for use in modeling the lift characteristics, the technique appears to have other applications in both aerodynamic and nonaerodynamic fields.

  5. Control of vortex on a non-slender delta wing by a nanosecond pulse surface dielectric barrier discharge

    NASA Astrophysics Data System (ADS)

    Zhao, Guang-yin; Li, Ying-hong; Liang, Hua; Han, Meng-hu; Hua, Wei-zhuo

    2015-01-01

    Wind tunnel experiments are conducted for improving the aerodynamic performance of delta wing using a leading-edge pulsed nanosecond dielectric barrier discharge (NS-DBD). The whole effects of pulsed NS-DBD on the aerodynamic performance of the delta wing are studied by balanced force measurements. Pressure measurements and particle image velocimetry (PIV) measurements are conducted to investigate the formation of leading-edge vortices affected by the pulsed NS-DBD, compared to completely stalled flow without actuation. Various pulsed actuation frequencies of the plasma actuator are examined with the freestream velocity up to 50 m/s. Stall has been delayed substantially and significant shifts in the aerodynamic forces can be achieved at the post-stall regions when the actuator works at the optimum reduced frequency of F + = 2. The upper surface pressure measurements show that the largest change of static pressure occurs at the forward part of the wing at the stall region. The time-averaged flow pattern obtained from the PIV measurement shows that flow reattachment is promoted with excitation, and a vortex flow pattern develops. The time-averaged locations of the secondary separation line and the center of the vortical region both move outboard with excitation.

  6. Flow structures around a flapping wing considering ground effect

    NASA Astrophysics Data System (ADS)

    Van Truong, Tien; Kim, Jihoon; Kim, Min Jun; Park, Hoon Cheol; Yoon, Kwang Joon; Byun, Doyoung

    2013-07-01

    Over the past several decades, there has been great interest in understanding the aerodynamics of flapping flight, namely the two flight modes of hovering and forward flight. However, there has been little focus on the aerodynamic characteristics during takeoff of insects. In a previous study we found that the Rhinoceros Beetle ( Trypoxylusdichotomus) takes off without jumping, which is uncommon for other insects. In this study we built a scaled-up electromechanical model of a flapping wing and investigated fluid flow around the beetle's wing model. In particular, the present dynamically scaled mechanical model has the wing kinematics pattern achieved from the real beetle's wing kinematics during takeoff. In addition, we could systematically change the three-dimensional inclined motion of the flapping model through each stroke. We used digital particle image velocimetry with high spatial resolution, and were able to qualitatively and quantitatively study the flow field around the wing at a Reynolds number of approximately 10,000. The present results provide insight into the aerodynamics and the evolution of vortical structures, as well as the ground effect experienced by a beetle's wing during takeoff. The main unsteady mechanisms of beetles have been identified and intensively analyzed as the stability of the leading edge vortex (LEV) during strokes, the delayed stall during upstroke, the rotational circulation in pronation periods, and wake capture in supination periods. Due to the ground effect, the LEV was enhanced during half downstroke, and the lift force could thus be increased to lift the beetle during takeoff. This is useful for researchers in developing a micro air vehicle that has a beetle-like flapping wing motion.

  7. Computational Modeling and Analysis of Aeroelastic Wing Flutter

    NASA Astrophysics Data System (ADS)

    Menon, Karthik; Katz, Joseph; Mittal, Rajat

    2017-11-01

    Aeroelastic flutter is ubiquitous in aeronautics; of particular relevance here is the flutter of aircraft wings, helicopter rotor blades, flexible wing MAVs and UAVs, and long-endurance aerial systems such as airships and solar powered air-vehicles. Here, we attempt to understand some fundamental aspects of this problem via immersed boundary method based numerical simulations of canonical bodies. We report findings on the effect of body geometry on the dynamics of flutter involving coupled pitch-heave oscillations. We also explore flow-induced flutter of airfoils in pre and post-stall configurations, including the effect of stiffness and pitch axis location. Finally, a novel force decomposition method is used to provide some insight into the flutter dynamics and associated unsteady flow physics. This work is supported by AFOSR Grant FA9550-16-1-0404.

  8. Hummingbird wing efficacy depends on aspect ratio and compares with helicopter rotors

    PubMed Central

    Kruyt, Jan W.; Quicazán-Rubio, Elsa M.; van Heijst, GertJan F.; Altshuler, Douglas L.; Lentink, David

    2014-01-01

    Hummingbirds are the only birds that can sustain hovering. This unique flight behaviour comes, however, at high energetic cost. Based on helicopter and aeroplane design theory, we expect that hummingbird wing aspect ratio (AR), which ranges from about 3.0 to 4.5, determines aerodynamic efficacy. Previous quasi-steady experiments with a wing spinner set-up provide no support for this prediction. To test this more carefully, we compare the quasi-steady hover performance of 26 wings, from 12 hummingbird taxa. We spun the wings at angular velocities and angles of attack that are representative for every species and measured lift and torque more precisely. The power (aerodynamic torque × angular velocity) required to lift weight depends on aerodynamic efficacy, which is measured by the power factor. Our comparative analysis shows that AR has a modest influence on lift and drag forces, as reported earlier, but interspecific differences in power factor are large. During the downstroke, the power required to hover decreases for larger AR wings at the angles of attack at which hummingbirds flap their wings (p < 0.05). Quantitative flow visualization demonstrates that variation in hover power among hummingbird wings is driven by similar stable leading edge vortices that delay stall during the down- and upstroke. A side-by-side aerodynamic performance comparison of hummingbird wings and an advanced micro helicopter rotor shows that they are remarkably similar. PMID:25079868

  9. Wing-kinematics measurement and aerodynamics in a small insect in hovering flight

    PubMed Central

    Cheng, Xin; Sun, Mao

    2016-01-01

    Wing-motion of hovering small fly Liriomyza sativae was measured using high-speed video and flows of the wings calculated numerically. The fly used high wingbeat frequency (≈265 Hz) and large stroke amplitude (≈182°); therefore, even if its wing-length (R) was small (R ≈ 1.4 mm), the mean velocity of wing reached ≈1.5 m/s, the same as that of an average-size insect (R ≈ 3 mm). But the Reynolds number (Re) of wing was still low (≈40), owing to the small wing-size. In increasing the stroke amplitude, the outer parts of the wings had a “clap and fling” motion. The mean-lift coefficient was high, ≈1.85, several times larger than that of a cruising airplane. The partial “clap and fling” motion increased the lift by ≈7%, compared with the case of no aerodynamic interaction between the wings. The fly mainly used the delayed stall mechanism to generate the high-lift. The lift-to-drag ratio is only 0.7 (for larger insects, Re being about 100 or higher, the ratio is 1–1.2); that is, although the small fly can produce enough lift to support its weight, it needs to overcome a larger drag to do so. PMID:27168523

  10. Wing-kinematics measurement and aerodynamics in a small insect in hovering flight.

    PubMed

    Cheng, Xin; Sun, Mao

    2016-05-11

    Wing-motion of hovering small fly Liriomyza sativae was measured using high-speed video and flows of the wings calculated numerically. The fly used high wingbeat frequency (≈265 Hz) and large stroke amplitude (≈182°); therefore, even if its wing-length (R) was small (R ≈ 1.4 mm), the mean velocity of wing reached ≈1.5 m/s, the same as that of an average-size insect (R ≈ 3 mm). But the Reynolds number (Re) of wing was still low (≈40), owing to the small wing-size. In increasing the stroke amplitude, the outer parts of the wings had a "clap and fling" motion. The mean-lift coefficient was high, ≈1.85, several times larger than that of a cruising airplane. The partial "clap and fling" motion increased the lift by ≈7%, compared with the case of no aerodynamic interaction between the wings. The fly mainly used the delayed stall mechanism to generate the high-lift. The lift-to-drag ratio is only 0.7 (for larger insects, Re being about 100 or higher, the ratio is 1-1.2); that is, although the small fly can produce enough lift to support its weight, it needs to overcome a larger drag to do so.

  11. Pressure Distribution Tests on PW-9 Wing Models from -18 Degree Through 90 Degree Angle of Attack

    NASA Technical Reports Server (NTRS)

    Loeser, Oscar E , Jr

    1929-01-01

    At the request of the Army Air Corps, an investigation of the pressure distribution over PW-9 wing models was conducted in the atmospheric wind tunnel of the National Advisory Committee for Aeronautics. The primary purpose of these tests was to obtain wind-tunnel data on the load distribution on the cellule to be correlated with similar information obtained in flight tests, both to be used for design purposes. Because of the importance of the conditions beyond the stall as affecting the control and stability, this investigation was extended through 90 degree angle of attack. The results for the range of normal flight have been given in NACA Technical Report No. 271. The present paper presents the same results in a different form and includes, in addition, those over the greater range of angle of attack, -18 degrees through 90 degrees. The results show that: (1) at angles of attack above maximum lift, the biplane upper wing pressures are decreased by the shielding action of the lower wing. (2) the burble of the biplane lower wing, with respect to the angle of attack, is delayed, due to the shielding action of the lower wing. (3) the center of pressure of the biplane upper wing (semispan) is, in general, displaced forward and outward with reference to that of the wing as a monoplane, while for the lower wing there is but slight difference for both conditions. (4) the overhanging portion of the upper wing is little affected by the presence of the lower wing.

  12. Dynamic Stall Suppression Using Combustion-Powered Actuation (COMPACT)

    NASA Technical Reports Server (NTRS)

    Matalanis, Claude G.; Bowles, Patrick O.; Jee, Solkeun; Min, Byung-Young; Kuczek, Andrzej E.; Croteau, Paul F.; Wake, Brian E.; Crittenden, Thomas; Glezer, Ari; Lorber, Peter F.

    2016-01-01

    Retreating blade stall is a well-known phenomenon that limits rotorcraft speed, maneuverability, and efficiency. Airfoil dynamic stall is a simpler problem, which demonstrates many of the same flow phenomena. Combustion Powered Actuation (COMPACT) is an active flow control technology, which at the outset of this work, had been shown to mitigate static and dynamic stall at low Mach numbers. The attributes of this technology suggested strong potential for success at higher Mach numbers, but such experiments had never been conducted. The work detailed in this report documents a 3-year effort focused on assessing the effectiveness of COMPACT for dynamic stall suppression at freestream conditions up to Mach 0.5. The work done has focused on implementing COMPACT on a high-lift rotorcraft airfoil: the VR-12. This selection was made in order to ensure that any measured benefits are over and above the capabilities of state-of-the-art high-lift rotorcraft airfoils. The detailed Computational Fluid Dynamics (CFD) simulations, wind-tunnel experiments, and system-level modeling conducted have shown the following: (1) COMPACT, in its current state of development, is capable of reducing the adverse effects of deep dynamic stall at Mach numbers up to 0.4; (2) The two-dimensional (2D) CFD results trend well compared to the experiments; and (3) Implementation of the CFD results into a system-level model suggest that significant rotor-level benefits are possible.

  13. Static stall alleviation using a rail plasma actuator

    NASA Astrophysics Data System (ADS)

    Choi, Young-Joon; Gray, Miles; Sirohi, Jayant; Raja, Laxminarayan L.

    2018-07-01

    An experimental study was conducted to investigate the ability of a rail plasma actuator (RailPAc) to alleviate static stall on an airfoil. The RailPAc device consists of parallel rails flush mounted on the upper surface of a VR-12 airfoil, with a high-current (∼1.3 kA) arc bridging the gap between the rails. A Lorentz force (∼0.3 N lasting  ∼1 ms) generated on the arc propels it along the airfoil chord and transfers momentum to the surrounding flow. Experiments were conducted in a low speed wind tunnel at two different Reynolds numbers ( and ) and various static angles of attack (up to  ∼30°). Particle image velocimetry (PIV) was used to measure the flow over the passive and actuated airfoil, while the airfoil lift was measured using a force balance. The experiments showed that the RailPAc promotes flow reattachment and can suppress static stall over a wide range of angles of attack. Operation of a single RailPAc resulted in  ∼40 improvement in post-stall lift and  ∼4° increase in stall angle compared to a passive airfoil with an unpowered RailPAc. The results provide insight into the actuation mechanism and demonstrate, for the first time, the ability of the RailPAc to alleviate static stall on an airfoil.

  14. A Comparative Study of Three Methodologies for Modeling Dynamic Stall

    NASA Technical Reports Server (NTRS)

    Sankar, L.; Rhee, M.; Tung, C.; ZibiBailly, J.; LeBalleur, J. C.; Blaise, D.; Rouzaud, O.

    2002-01-01

    During the past two decades, there has been an increased reliance on the use of computational fluid dynamics methods for modeling rotors in high speed forward flight. Computational methods are being developed for modeling the shock induced loads on the advancing side, first-principles based modeling of the trailing wake evolution, and for retreating blade stall. The retreating blade dynamic stall problem has received particular attention, because the large variations in lift and pitching moments encountered in dynamic stall can lead to blade vibrations and pitch link fatigue. Restricting to aerodynamics, the numerical prediction of dynamic stall is still a complex and challenging CFD problem, that, even in two dimensions at low speed, gathers the major difficulties of aerodynamics, such as the grid resolution requirements for the viscous phenomena at leading-edge bubbles or in mixing-layers, the bias of the numerical viscosity, and the major difficulties of the physical modeling, such as the turbulence models, the transition models, whose both determinant influences, already present in static maximal-lift or stall computations, are emphasized by the dynamic aspect of the phenomena.

  15. Examining Dynamic Stall for an Oscillating NACA 4412 Hydrofoil

    NASA Astrophysics Data System (ADS)

    McVay, Eric; Lang, Amy; Gamble, Lawren; Bradshaw, Michael

    2013-11-01

    Dynamic stall is unsteady separation that occurs when a hydrofoil pitches through the static stall angle while simultaneously experiencing a rapid change in angle of attack. The NACA 4412 hydrofoil was selected for this research because it has strong trailing edge turbulent boundary layer separation characteristics. General dynamic stall angle of attack for approximately symmetric airfoils has been recorded to occur at 24 degrees, with separation beginning at about 16 degrees. It is predicted that the boundary layer will stay attached at a higher angle of attack because of the cambered geometry of the hydrofoil. It is also hypothesized that the boundary layer separation occurs closer to the trailing edge and that the dynamic stall angle of attack occurs somewhere between 24 and 28 degrees for the oscillating NACA 4412 hydrofoil. This research was conducted in a water tunnel facility using Time Resolved Digital Particle Image Velocimetry (TR-DPIV). The hydrofoil was pitched up from 0 to 30 degrees at Reynolds numbers of 60,000, 80,000 and 100,000. Flow characteristics, dynamic stall angles of attack, and points of boundary layer separation were compared at each velocity with both tripped and un-tripped surfaces. Follow-on research will be conducted using flow control techniques from sharks and dolphins to examine the potential benefits of these natural designs for separation control. Support for this research by NSF REU Grant #1062611 and CBET Grant #0932352 is gratefully acknowledged.

  16. Going, Going, Gone: Localizing Abrupt Offsets of Moving Objects

    ERIC Educational Resources Information Center

    Maus, Gerrit W.; Nijhawan, Romi

    2009-01-01

    When a moving object abruptly disappears, this profoundly influences its localization by the visual system. In Experiment 1, 2 aligned objects moved across the screen, and 1 of them abruptly disappeared. Observers reported seeing the objects misaligned at the time of the offset, with the continuing object leading. Experiment 2 showed that the…

  17. The Influence of Second Harmonic Phase and Amplitude Variation in Cyclically Pitching Wings

    NASA Astrophysics Data System (ADS)

    Culler, Ethan; Farnsworth, John

    2017-11-01

    From wind tunnel testing of a cyber-physical wing model, it has been found that the pitch trajectory for stall flutter is described by an array of higher harmonic frequencies with decaying energy content. These frequencies distort the stall flutter motion from that of a pure sinusoidal oscillation in pitch and can have a significant effect on the resulting force production. In order to understand how these higher harmonic frequencies contribute to the overall pitching moment characteristics of a wing in stall flutter, a rigid finite span wing model, with aspect ratio four, was pitched in the wind tunnel. The prescribed motion of the pitch cycle was varied by changing the amplitude ratio and phase of the second harmonic of the oscillation frequency. The second harmonic represents the second highest energy mode in the pitching cycle spectra. Pitching moment and planar particle image velocimetry data was collected. From these pitching trajectories, a significant dependence of pitching moment on both the phase and amplitude of the prescribed waveforms was found. Specifically, for the same amplitude ratio, variations in the phase produced changes of approximately 30 percent in the phase averaged pitching moment.

  18. Abrupt Change in Ecological Systems: Inference and Diagnosis.

    PubMed

    Ratajczak, Zak; Carpenter, Stephen R; Ives, Anthony R; Kucharik, Christopher J; Ramiadantsoa, Tanjona; Stegner, M Allison; Williams, John W; Zhang, Jien; Turner, Monica G

    2018-05-18

    Abrupt ecological changes are, by definition, those that occur over short periods of time relative to typical rates of change for a given ecosystem. The potential for such changes is growing due to anthropogenic pressures, which challenges the resilience of societies and ecosystems. Abrupt ecological changes are difficult to diagnose because they can arise from a variety of circumstances, including rapid changes in external drivers (e.g., climate, or resource extraction), nonlinear responses to gradual changes in drivers, and interactions among multiple drivers and disturbances. We synthesize strategies for identifying causes of abrupt ecological change and highlight instances where abrupt changes are likely. Diagnosing abrupt changes and inferring causation are increasingly important as society seek to adapt to rapid, multifaceted environmental changes. Copyright © 2018 Elsevier Ltd. All rights reserved.

  19. Investigation of nonlinear inviscid and viscous flow effects in the analysis of dynamic stall. [air flow and chordwise pressure distribution on airfoil below stall condition

    NASA Technical Reports Server (NTRS)

    Crimi, P.

    1974-01-01

    A method for analyzing unsteady airfoil stall was refined by including nonlinear effects in the representation of the inviscid flow. Certain other aspects of the potential-flow model were reexamined and the effects of varying Reynolds number on stall characteristics were investigated. Refinement of the formulation improved the representation of the flow and chordwise pressure distribution below stall, but substantial quantitative differences between computed and measured results are still evident for sinusoidal pitching through stall. Agreement is substantially improved by assuming the growth rate of the dead-air region at the onset of leading-edge stall is of the order of the component of the free stream normal to the airfoil chordline. The method predicts the expected increase in the resistance to stalling with increasing Reynolds number. Results indicate that a given airfoil can undergo both trailing-edge and leading-edge stall under unsteady conditions.

  20. Abrupt contraction flow of magnetorheological fluids

    NASA Astrophysics Data System (ADS)

    Kuzhir, P.; López-López, M. T.; Bossis, G.

    2009-05-01

    Contraction and expansion flows of magnetorheological fluids occur in a variety of smart devices. It is important therefore to learn how these flows can be controlled by means of applied magnetic fields. This paper presents a first investigation into the axisymmetric flow of a magnetorheological fluid through an orifice (so-called abrupt contraction flow). The effect of an external magnetic field, longitudinal or transverse to the flow, is examined. In experiments, the pressure-flow rate curves were measured, and the excess pressure drop (associated with entrance and exit losses) was derived from experimental data through the Bagley correction procedure. The effect of the longitudinal magnetic field is manifested through a significant increase in the slope of the pressure-flow rate curves, while no discernible yield stress occurs. This behavior, observed at shear Mason numbers 10

  1. Stall Recovery Guidance Algorithms Based on Constrained Control Approaches

    NASA Technical Reports Server (NTRS)

    Stepanyan, Vahram; Krishnakumar, Kalmanje; Kaneshige, John; Acosta, Diana

    2016-01-01

    Aircraft loss-of-control, in particular approach to stall or fully developed stall, is a major factor contributing to aircraft safety risks, which emphasizes the need to develop algorithms that are capable of assisting the pilots to identify the problem and providing guidance to recover the aircraft. In this paper we present several stall recovery guidance algorithms, which are implemented in the background without interfering with flight control system and altering the pilot's actions. They are using input and state constrained control methods to generate guidance signals, which are provided to the pilot in the form of visual cues. It is the pilot's decision to follow these signals. The algorithms are validated in the pilot-in-the loop medium fidelity simulation experiment.

  2. Comparison of pitch rate history effects on dynamic stall

    NASA Technical Reports Server (NTRS)

    Chandrasekhara, M. S.; Carr, Lawrence W.; Ahmed, S.

    1992-01-01

    Dynamic stall of an airfoil is a classic case of forced unsteady separated flow. Flow separation is brought about by large incidences introduced by the large amplitude unsteady pitching motion of an airfoil. One of the parameters that affects the dynamic stall process is the history of the unsteady motion. In addition, the problem is complicated by the effects of compressibility that rapidly appear over the airfoil even at low Mach numbers at moderately high angles of attack. Consequently, it is of interest to know the effects of pitch rate history on the dynamic stall process. This abstract compares the results of a flow visualization study of the problem with two different pitch rate histories, namely, oscillating airfoil motion and a linear change in the angle of attack due to a transient pitching motion.

  3. Dynamic stall experiments on the NACA 0012 airfoil

    NASA Technical Reports Server (NTRS)

    Mcalister, K. W.; Carr, L. W.; Mccroskey, W. J.

    1978-01-01

    The flow over a NACA 0012 airfoil undergoing large oscillations in pitch was experimentally studied at a Reynolds number of and over a range of frequencies and amplitudes. Hot-wire probes and surface-pressure transducers were used to clarify the role of the laminar separation bubble, to delineate the growth and shedding of the stall vortex, and to quantify the resultant aerodynamic loads. In addition to the pressure distributions and normal force and pitching moment data that have often been obtained in previous investigations, estimates of the unsteady drag force during dynamic stall have been derived from the surface pressure measurements. Special characteristics of the pressure response, which are symptomatic of the occurrence and relative severity of moment stall, have also been examined.

  4. Adaptive wing structures

    NASA Astrophysics Data System (ADS)

    Perkins, David A.; Reed, John L., Jr.; Havens, Ernie

    2004-07-01

    Cornerstone Research Group, Inc. (CRG), with specific no-cost guidance and support from Lockheed Martin, proposed to significantly increase the capability of loitering Unmanned Air Vehicles (UAVs) by developing a unique adaptive wing structure. This technology will offer significant operational benefit to air vehicles of this type currently under development. The development of this adaptive wing structure will enable such aircraft to adapt their wing configuration to maximize efficiency in each flight regime experienced during their mission. Additionally, the benefits of this development program will enhance the agility and maneuverability of the vehicle; therefore increasing its mission capability. The specific morphing ability CRG proposed to develop was a controlled expansion and contraction of the wing chord, which increases the wing planform area and therefore the lift produced. CRG proved feasibility of this concept and developed a sub-scale prototype integrating smart materials developed at CRG.

  5. An examination of gas compressor stability and rotating stall

    NASA Technical Reports Server (NTRS)

    Fozi, Aziz A.

    1987-01-01

    The principal sources of vibration related reliability problems in high pressure centrifugal gas compressors are the re-excitation of the first critical speed or Resonant Subsynchronous Vibration (RSSV), and the forced vibration due to rotating stall in the vaneless diffusers downstream of the impellers. An example of such field problems is given elsewhere. This paper describes the results of a test program at the author's company, initiated in 1983 and completed during 1985, which studied the RSSV threshold and the rotating stall phenomenon in a high pressure gas compressor.

  6. Study of casing treatment stall margin improvement phenomena. [for compressor rotor blade tips compressor blades rotating stalls

    NASA Technical Reports Server (NTRS)

    Prince, D. C., Jr.; Wisler, D. C.; Hilvers, D. E.

    1974-01-01

    The results of a program of experimental and analytical research in casing treatments over axial compressor rotor blade tips are presented. Circumferential groove, axial-skewed slot, and blade angle slot treatments were tested. These yielded, for reduction in stalling flow and loss in peak efficiency, 5.8% and 0 points, 15.3% and 2.0 points, and 15.0% and 1.2 points, respectively. These values are consistent with other experience. The favorable stalling flow situations correlated well with observations of higher-then-normal surface pressures on the rotor blade pressure surfaces in the tip region, and with increased maximum diffusions on the suction surfaces. Annular wall pressure gradients, especially in the 50-75% chord region, are also increased and blade surface pressure loadings are shifted toward the trailing edge for treated configurations. Rotor blade wakes may be somewhat thinner in the presence of good treatments, particularly under operating conditions close to the baseline stall.

  7. Experimental Investigation of Ice Accretion Effects on a Swept Wing

    NASA Technical Reports Server (NTRS)

    Wong, S. C.; Vargas, M.; Papadakis, M.; Yeong, H. W.; Potapczuk, M.

    2005-01-01

    An experimental investigation was conducted to study the effects of 2-, 5-, 10-, and 22.5-min ice accretions on the aerodynamic performance of a swept finite wing. The ice shapes tested included castings of ice accretions obtained from icing tests at the NASA Glenn Icing Research Tunnel (IRT) and simulated ice shapes obtained with the LEWICE 2.0 ice accretion code. The conditions used for the icing tests were selected to provide five glaze ice shapes with complete and incomplete scallop features and a small rime ice shape. The LEWICE ice shapes were defined for the same conditions as those used in the icing tests. All aerodynamic performance tests were conducted in the 7- x 10-ft Low-Speed Wind Tunnel Facility at Wichita State University. Six component force and moment measurements, aileron hinge moments, and surface pressures were obtained for a Reynolds number of 1.8 million based on mean aerodynamic chord and aileron deflections in the range of -15o to 20o. Tests were performed with the clean wing, six IRT ice shape castings, seven smooth LEWICE ice shapes, and seven rough LEWICE ice shapes. Roughness for the LEWICE ice shapes was simulated with 36-size grit. The experiments conducted showed that the glaze ice castings reduced the maximum lift coefficient of the clean wing by 11.5% to 93.6%, while the 5-min rime ice casting increased maximum lift by 3.4%. Minimum iced wing drag was 133% to 3533% greater with respect to the clean case. The drag of the iced wing near the clean wing stall angle of attack was 17% to 104% higher than that of the clean case. In general, the aileron remained effective in changing the lift of the clean and iced wings for all angles of attack and aileron deflections tested. Aileron hinge moments for the iced wing cases remained within the maximum and minimum limits defined by the clean wing hinge moments. Tests conducted with the LEWICE ice shapes showed that in general the trends in aerodynamic performance degradation of the wing with

  8. Towards Greenland Glaciation: cumulative or abrupt transition?

    NASA Astrophysics Data System (ADS)

    Ramstein, Gilles; Tan, Ning; Ladant, Jean-baptiste; Dumas, Christophe; Contoux, Camille

    2017-04-01

    During the mid-Pliocene warming period (3-3.3 Ma BP), the global annual mean temperatures inferred by data and model studies were 2-3° warmer than pre-industrial values. Accordingly, Greenland ice sheet volume is supposed to reach at the most, only half of that of present-day [Haywood et al. 2010]. Around 2.7-2.6 Ma BP, just ˜ 500 kyr after the warming peak of mid-Pliocene, the Greenland ice sheet has reached its full size [Lunt et al. 2008]. A crucial question concerns the evolution of the Greenland ice sheet from half to full size during the 3 - 2.5 Ma period. Data show a decreasing trend of atmospheric CO2 concentration from 3 Ma to 2.5 Ma [Seki et al.2010; Bartoli et al. 2011; Martinez et al. 2015]. However, a recent study [Contoux et al. 2015] suggests that a lowering of CO2 is not sufficient to initiate a perennial glaciation on Greenland and must be combined with low summer insolation to preserve the ice sheet during insolation maxima. This suggests rather a cumulative process than an abrupt event. In order to diagnose the evolution of the ice sheet build-up, we carry on, for the first time, a transient simulation of climate and ice sheet evolutions from 3 Ma to 2.5 Ma. This strategy enables us to investigate the waxing and waning of the ice sheet during several orbital cycles. We use a tri-dimensional interpolation method designed by Ladant et al. (2014), which allows the evolution of CO2 concentration and of orbital parameters, and the evolution of the Greenland ice sheet size to be taken into account. By interpolating climatic snapshot simulations ran with various possible combinations of CO2, orbits and ice sheet sizes, we can build a continuous climatic forcing that is then used to provide 500 kyrs-long ice sheet simulations. With such a tool, we may offer a physically based answer to different CO2 reconstructions scenarios and analyse which one is the most consistent with Greenland ice sheet buildup.

  9. Progress has Stalled in U.S. Stroke Death Rates after Decades of Decline

    MedlinePlus

    ... Library (PHIL) Progress has stalled in US stroke death rates after decades of decline More timely stroke ... cdc.gov/vitalsigns/stroke/infographic.html#graphic) Stroke death declines have stalled in 3 out of every ...

  10. Dairy Cows Produce Less Milk and Modify Their Behaviour during the Transition between Tie-Stall to Free-Stall

    PubMed Central

    Broucek, Jan; Uhrincat, Michal; Mihina, Stefan; Soch, Miloslav; Mrekajova, Andrea; Hanus, Anton

    2017-01-01

    Simple Summary The purpose of this study was to evaluate the influence of moving cows from the barn with stanchion-stall housing to free-stall housing on their behaviour and production. Cows lay down up to ten hours after removing. The cows in their second lactation and open cows tended to lie sooner after removing than cows in their first lactation and pregnant cows. The times of total lying and rumination were increasing from the first day to the tenth day after removing. Cows produced 23.3% less milk at the first day following the transfer than at the last day prior to moving (23.76 ± 7.20 kg vs. 30.97 ± 7.26 kg, p < 0.001). Loss of milk was gradually reduced and on the 14th day, cows achieved maximum production. The difference was found in milk losses due to the shift between cows in first and second lactation. Abstract Transfer of cattle to an unknown barn may result in a reduction in its welfare. Housing and management practices can result in signs of stress that include a long-term suppression of milk efficiency. The purpose of this study was to evaluate the influence of moving cows from the stanchion-stall housing to free-stall housing on their behaviour and production. The Holstein cows were moved into the new facility with free-stall housing from the old barn with stanchion-stall housing. Cows lay down up to ten hours (596.3 ± 282.7 min) after removing. The cows in their second lactation and open cows tended to lie sooner after removing than cows in their first lactation and pregnant cows. The times of total lying and rumination were increasing from the first day to the tenth day after removing (23.76 ± 7.20 kg vs. 30.97 ± 7.26 kg, p < 0.001). Cows produced 23.3% less milk at the first day following the transfer than at the last day prior to moving (p < 0.001). Loss of milk was gradually reduced and maximum production was achieved on the 14th day. The difference was found in milk losses due to the shift between cows on the first and second lactation

  11. An Assessment of the Effect of Compressibility on Dynamic Stall

    NASA Technical Reports Server (NTRS)

    Carr, Lawrence W.; Chandrasekhara, M. S.; David, Sanford S. (Technical Monitor)

    1994-01-01

    Compressibility plays a significant role in the development of separation on airfoils experiencing unsteady motion, even at moderately compressible free-stream flow velocities. This effect can result in completely changed stall characteristics compared to those observed at incompressible speed, and can dramatically affect techniques used to control separation. There has been a significant effort in recent years directed toward better understanding; of this process, and its impact on possible techniques for control of separation in this complex environment. A review of existing research in this area will be presented, with emphasis on the physical mechanisms that play such an important role in the development of separation on airfoils. The increasing impact of compressibility on the stall process will be discussed as a function of free-stream Mach number, and an analysis of the changing flow physics will be presented. Examples of the effect of compressibility on dynamic stall will be selected from both recent and historical efforts by members of the aerospace community, as well as from the ongoing research program of the present authors. This will include a presentation of a sample of high speed filming of compressible dynamic stall which has recently been created using real-time interferometry.

  12. 14 CFR 33.65 - Surge and stall characteristics.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... Section 33.65 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: AIRCRAFT ENGINES Design and Construction; Turbine Aircraft Engines § 33.65 Surge and stall characteristics. When the engine is operated in accordance with operating instructions required by...

  13. 14 CFR 33.65 - Surge and stall characteristics.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... Section 33.65 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: AIRCRAFT ENGINES Design and Construction; Turbine Aircraft Engines § 33.65 Surge and stall characteristics. When the engine is operated in accordance with operating instructions required by...

  14. 14 CFR 33.65 - Surge and stall characteristics.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Surge and stall characteristics. 33.65 Section 33.65 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: AIRCRAFT ENGINES Design and Construction; Turbine Aircraft Engines § 33.65 Surge and...

  15. 14 CFR 33.65 - Surge and stall characteristics.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 1 2013-01-01 2013-01-01 false Surge and stall characteristics. 33.65 Section 33.65 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: AIRCRAFT ENGINES Design and Construction; Turbine Aircraft Engines § 33.65 Surge and...

  16. 14 CFR 33.65 - Surge and stall characteristics.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Surge and stall characteristics. 33.65 Section 33.65 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: AIRCRAFT ENGINES Design and Construction; Turbine Aircraft Engines § 33.65 Surge and...

  17. Prediction of active control of subsonic centrifugal compressor rotating stall

    NASA Technical Reports Server (NTRS)

    Lawless, Patrick B.; Fleeter, Sanford

    1993-01-01

    A mathematical model is developed to predict the suppression of rotating stall in a centrifugal compressor with a vaned diffuser. This model is based on the employment of a control vortical waveform generated upstream of the impeller inlet to damp weak potential disturbances that are the early stages of rotating stall. The control system is analyzed by matching the perturbation pressure in the compressor inlet and exit flow fields with a model for the unsteady behavior of the compressor. The model was effective at predicting the stalling behavior of the Purdue Low Speed Centrifugal Compressor for two distinctly different stall patterns. Predictions made for the effect of a controlled inlet vorticity wave on the stability of the compressor show that for minimum control wave magnitudes, on the order of the total inlet disturbance magnitude, significant damping of the instability can be achieved. For control waves of sufficient amplitude, the control phase angle appears to be the most important factor in maintaining a stable condition in the compressor.

  18. Building No. 392, interior overview with welding stalls and steel ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Building No. 392, interior overview with welding stalls and steel plate floor, view facing west-southwest - U.S. Naval Base, Pearl Harbor, Marine Railway No. 1 Accessories House & Apprentice Welding School, Additions, Intersection of Avenue B & Sixth Street, Pearl City, Honolulu County, HI

  19. Flying wings / flying fuselages

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

    The present paper has documented the historical relationships between various classes of all lifting vehicles, which includes the flying wing, all wing, tailless, lifting body, and lifting fuselage. The diversity in vehicle focus was to ensure that all vehicle types that map have contributed to or been influenced by the development of the classical flying wing concept was investigated. The paper has provided context and perspective for present and future aircraft design studies that may employ the all lifting vehicle concept. The paper also demonstrated the benefit of developing an understanding of the past in order to obtain the required knowledge to create future concepts with significantly improved aerodynamic performance.

  20. Slotted Aircraft Wing

    NASA Technical Reports Server (NTRS)

    Vassberg, John C. (Inventor); Gea, Lie-Mine (Inventor); McLean, James D. (Inventor); Witowski, David P. (Inventor); Krist, Steven E. (Inventor); Campbell, Richard L. (Inventor)

    2006-01-01

    An aircraft wing includes a leading airfoil element and a trailing airfoil element. At least one slot is defined by the wing during at least one transonic condition of the wing. The slot may either extend spanwise along only a portion of the wingspan, or it may extend spanwise along the entire wingspan. In either case, the slot allows a portion of the air flowing along the lower surface of the leading airfoil element to split and flow over the upper surface of the trailing airfoil element so as to achieve a performance improvement in the transonic condition.

  1. Neural network adaptive control of wing-rock motion of aircraft model mounted on three-degree-of-freedom dynamic rig in wind tunnel

    NASA Astrophysics Data System (ADS)

    Ignatyev, D. I.

    2018-06-01

    High-angles-of-attack dynamics of aircraft are complicated with dangerous phenomena such as wing rock, stall, and spin. Autonomous dynamically scaled aircraft model mounted in three-degree-of-freedom (3DoF) dynamic rig is proposed for studying aircraft dynamics and prototyping of control laws in wind tunnel. Dynamics of the scaled aircraft model in 3DoF manoeuvre rig in wind tunnel is considered. The model limit-cycle oscillations are obtained at high angles of attack. A neural network (NN) adaptive control suppressing wing rock motion is designed. The wing rock suppression with the proposed control law is validated using nonlinear time-domain simulations.

  2. Investigation in the Langley 19-foot Pressure Tunnel of Two Wings of NACA 65-210 and 64-210 Airfoil Sections with Various Type Flaps

    NASA Technical Reports Server (NTRS)

    Sivells, James C; Spooner, Stanley H

    1949-01-01

    Report presents the results of an investigation conducted in the Langley 19-foot pressure tunnel to determine the maximum lift and stalling characteristics of two thin wings equipped with several types of flaps. Split, single slotted, and double slotted flaps were tested on one wing which had NACA 65-210 airfoil sections and split and double slotted flaps were tested on the other, which had NACA 64-210 airfoil sections. Both wings were zero sweep, an aspect ratio of 9, and a taper ratio of 0.4.

  3. Leading-edge flow reattachment and the lateral static stability of low-aspect-ratio rectangular wings

    NASA Astrophysics Data System (ADS)

    Linehan, Thomas; Mohseni, Kamran

    2017-11-01

    The relationship between lateral static stability derivative, Clβ,lift coefficient, CL, and angle of attack was investigated for rectangular wings of aspect ratio A R =0.75 ,1 ,1.5 , and 3 using Stereo-Digital Particle Image Velocimetry (S-DPIV) and direct force and moment measurements. When the product Cl βA R is plotted with respect to CL, the lateral stability curves of each wing collapse to a single line for CL<0.7 . For CL>0.7 , the linearity and scaling of Clβwith respect to CL is lost. S-DPIV is used to elucidate the flow physics in this nonlinear regime. At α =10∘ , the leading-edge separation region emerges on the leeward portion of the sideslipped wing by means of vortex shedding. For the A R ≤1.5 wings at α >15∘ , the tip vortex downwash is sufficient to restrict the shedding of leading-edge vorticity thereby sustaining the lift of the leading-edge separation region at high angles of attack. Concurrently, the windward tip vortex grows in size and strength with increasing angle of attack, displacing the leading-edge separation region further toward the leeward wing. This reorganization of lift-generating vorticity results in the initial nonlinearities between Cl β and CL at angles of attack for which CL is still increasing. At angles of attack near that of maximum lift for the A R ≤1 wings, the windward tip vortex lifts off the wing, decreasing the lateral static stability of the wing prior to lift stall. For the A R =3 wing at α >10∘ , nonlinear trends in Cl β versus CL occur due to the spanwise evolution of stalled flow.

  4. High angle-of-attack aerodynamic characteristics of crescent and elliptic wings

    NASA Technical Reports Server (NTRS)

    Vandam, C. P.

    1989-01-01

    Static longitudinal and lateral-directional forces and moments were measured for elliptic- and crescent-wing models at high angles-of-attack in the NASA Langley 14 by 22-Ft Subsonic Tunnel. The forces and moments were obtained for an angle-of-attack range including stall and post-stall conditions at a Reynolds number based on the average wing chord of about 1.8 million. Flow-visualization photographs using a mixture of oil and titanium-dioxide were also taken for several incidence angles. The force and moment data and the flow-visualization results indicated that the crescent wing model with its highly swept tips produced much better high angle-of-attack aerodynamic characteristics than the elliptic model. Leading-edge separation-induced vortex flow over the highly swept tips of the crescent wing is thought to produce this improved behavior at high angles-of-attack. The unique planform design could result in safer and more efficient low-speed airplanes.

  5. Analysis of iced wings

    NASA Technical Reports Server (NTRS)

    Cebeci, T.; Chen, H. H.; Kaups, K.; Schimke, S.; Shin, J.

    1992-01-01

    A method for computing ice shapes along the leading edge of a wing and a method for predicting its aerodynamic performance degradation due to icing is described. Ice shapes are computed using an extension of the LEWICE code which was developed for airfoils. The aerodynamic properties of the iced wing are determined with an interactive scheme in which the solutions of the inviscid flow equations are obtained from a panel method and the solutions of the viscous flow equations are obtained from an inverse three-dimensional finite-difference boundary-layer method. A new interaction law is used to couple the inviscid and viscous flow solutions. The application of the LEWICE wing code to the calculation of ice shapes on a MS-317 swept wing shows good agreement with measurements. The interactive boundary-layer method is applied to a tapered ice wing in order to study the effect of icing on the aerodynamic properties of the wing at several angles of attack.

  6. Artificial insect wings with biomimetic wing morphology and mechanical properties.

    PubMed

    Liu, Zhiwei; Yan, Xiaojun; Qi, Mingjing; Zhu, Yangsheng; Huang, Dawei; Zhang, Xiaoyong; Lin, Liwei

    2017-09-26

    The pursuit of a high lift force for insect-scale flapping-wing micro aerial vehicles (FMAVs) requires that their artificial wings possess biomimetic wing features which are close to those of their natural counterpart. In this work, we present both fabrication and testing methods for artificial insect wings with biomimetic wing morphology and mechanical properties. The artificial cicada (Hyalessa maculaticollis) wing is fabricated through a high precision laser cutting technique and a bonding process of multilayer materials. Through controlling the shape of the wing venation, the fabrication method can achieve three-dimensional wing architecture, including cambers or corrugations. Besides the artificial cicada wing, the proposed fabrication method also shows a promising versatility for diverse wing types. Considering the artificial cicada wing's characteristics of small size and light weight, special mechanical testing systems are designed to investigate its mechanical properties. Flexural stiffness, maximum deformation rate and natural frequency are measured and compared with those of its natural counterpart. Test results reveal that the mechanical properties of the artificial cicada wing depend strongly on its vein thickness, which can be used to optimize an artificial cicada wing's mechanical properties in the future. As such, this work provides a new form of artificial insect wings which can be used in the field of insect-scale FMAVs.

  7. An experimental study of dynamic stall on advanced airfoil sections. Volume 1: Summary of the experiment

    NASA Technical Reports Server (NTRS)

    Mccroskey, W. J.; Mcalister, K. W.; Carr, L. W.; Pucci, S. L.

    1982-01-01

    The static and dynamic characteristics of seven helicopter sections and a fixed-wing supercritical airfoil were investigated over a wide range of nominally two dimensional flow conditions, at Mach numbers up to 0.30 and Reynolds numbers up to 4 x 10 to the 6th power. Details of the experiment, estimates of measurement accuracy, and test conditions are described in this volume (the first of three volumes). Representative results are also presented and comparisons are made with data from other sources. The complete results for pressure distributions, forces, pitching moments, and boundary-layer separation and reattachment characteristics are available in graphical form in volumes 2 and 3. The results of the experiment show important differences between airfoils, which would otherwise tend to be masked by differences in wind tunnels, particularly in steady cases. All of the airfoils tested provide significant advantages over the conventional NACA 0012 profile. In general, however, the parameters of the unsteady motion appear to be more important than airfoil shape in determining the dynamic-stall airloads.

  8. Dimension Determination of Precursive Stall Events in a Single Stage High Speed Compressor

    NASA Technical Reports Server (NTRS)

    Bright, Michelle M.; Qammar, Helen K.; Hartley, Tom T.

    1996-01-01

    This paper presents a study of the dynamics for a single-stage, axial-flow, high speed compressor core, specifically, the NASA Lewis rotor stage 37. Due to the overall blading design for this advanced core compressor, each stage has considerable tip loading and higher speed than most compressor designs, thus, the compressor operates closer to the stall margin. The onset of rotating stall is explained as bifurcations in the dynamics of axial compressors. Data taken from the compressor during a rotating stall event is analyzed. Through the use of a box-assisted correlation dimension methodology, the attractor dimension is determined during the bifurcations leading to rotating stall. The intent of this study is to examine the behavior of precursive stall events so as to predict the entrance into rotating stall. This information may provide a better means to identify, avoid or control the undesirable event of rotating stall formation in high speed compressor cores.

  9. In-flight total forces, moments and static aeroelastic characteristics of an oblique-wing research airplane

    NASA Technical Reports Server (NTRS)

    Curry, R. E.; Sim, A. G.

    1984-01-01

    A low-speed flight investigation has provided total force and moment coefficients and aeroelastic effects for the AD-1 oblique-wing research airplane. The results were interpreted and compared with predictions that were based on wind tunnel data. An assessment has been made of the aeroelastic wing bending design criteria. Lateral-directional trim requirements caused by asymmetry were determined. At angles of attack near stall, flow visualization indicated viscous flow separation and spanwise vortex flow. These effects were also apparent in the force and moment data.

  10. The role of the leading edge vortex in lift augmentation of steadily revolving wings: a change in perspective.

    PubMed

    Nabawy, Mostafa R A; Crowther, William J

    2017-07-01

    The presence of a stable leading edge vortex (LEV) on steadily revolving wings increases the maximum lift coefficient that can be generated from the wing and its role is important to understanding natural flyers and flapping wing vehicles. In this paper, the role of LEV in lift augmentation is discussed under two hypotheses referred to as 'additional lift' and 'absence of stall'. The 'additional lift' hypothesis represents the traditional view. It presumes that an additional suction/circulation from the LEV increases the lift above that of a potential flow solution. This behaviour may be represented through either the 'Polhamus leading edge suction' model or the so-called 'trapped vortex' model. The 'absence of stall' hypothesis is a more recent contender that presumes that the LEV prevents stall at high angles of attack where flow separation would normally occur. This behaviour is represented through the so-called 'normal force' model. We show that all three models can be written in the form of the same potential flow kernel with modifiers to account for the presence of a LEV. The modelling is built on previous work on quasi-steady models for hovering wings such that model parameters are determined from first principles, which allows a fair comparison between the models themselves, and the models and experimental data. We show that the two models which directly include the LEV as a lift generating component are built on a physical picture that does not represent the available experimental data. The simpler 'normal force' model, which does not explicitly model the LEV, performs best against data in the literature. We conclude that under steady conditions the LEV as an 'absence of stall' model/mechanism is the most satisfying explanation for observed aerodynamic behaviour. © 2017 The Author(s).

  11. Controls on the abruptness of gravel-sand transitions

    NASA Astrophysics Data System (ADS)

    Venditti, J. G.; Church, M. A.; Lamb, M. P.; Domarad, N.; Rennie, C. D.

    2014-12-01

    As gravel-bedded rivers fine downstream, they characteristically exhibit an abrupt transition from gravel- to sand-bed. This is the only abrupt transition in grain-size that occurs in the fluvial system and has attracted considerable attention. A number of competing theories have been proposed to account for the abruptness of the transition, including base-level control, attrition of ~10mm gravel to produce sand, and sediment sorting processes. The prevailing theory for the emergence of abrupt transitions is size selective sorting of bimodal sediment wherein gravel deposits due to downstream declining shear stress, fining the bedload until a sand-bed emerges. We explored this hypothesis by examining grain-size, shear stress, gravel mobility and sand suspension thresholds through the gravel-sand transition (GST) of the Fraser River, British Columbia. The Fraser GST is an arrested gravel wedge with patches of gravel downstream of the wedge forming a diffuse extension. There is an abrupt change in bed slope through the transition that leads to an abrupt change in shear stress. The GST, bed-slope change and backwater caused by the ocean are all coincident spatially, which enhances the sharpness of the GST. Interestingly, the bimodal reach of the river occurs downstream of the GST and exhibits no downstream gradients in shear stress, suspended sediment flux, gravel mobility or sand suspension thresholds. This calls into question the prevailing theory for the emergence of an abrupt GST by size selective sorting. We provide evidence, both empirical and theoretical, that suggests the emergence of an abrupt GST is caused by rapid deposition of sand when fine gravel deposits. We argue that the emergence of gravel-sand transitions is a consequence of gravel-bedded rivers adopting a steeper slope than sand-bedded rivers. The abruptness arises because the bed slope required to convey the gravel load fixes the distal location of a terminal gravel wedge, and once the river has

  12. Dynamic stall - The case of the vertical axis wind turbine

    NASA Astrophysics Data System (ADS)

    Laneville, A.; Vittecoq, P.

    1986-05-01

    This paper presents the results of an experimental investigation on a driven Darrieus turbine rotating at different tip speed ratios. For a Reynolds number of 3.8 x 10 to the 4th, the results indicate the presence of dynamic stall at tip speed ratio less than 4, and that helicopter blade aerodynamics can be used in order to explain some aspects of the phenomenon. It was observed that in deep stall conditions, a vortex is formed at the leading edge; this vortex moves over the airfoil surface with 1/3 of the airfoil speed and then is shed at the trailing edge. After its shedding, the vortex can interact with the airfoil surface as the blade passes downstream.

  13. Laser holographic interferometry for an unsteady airfoil in dynamic stall

    NASA Technical Reports Server (NTRS)

    Lee, G.; Buell, D. A.; Licursi, J. P.; Craig, J. E.

    1983-01-01

    Laser holographic interferometry was used to study a two-dimensional NACA 0012 airfoil undergoing dynamic stall. The airfoil, fabricated from graphite fiber and epoxy, was tested at Mach numbers of 0.3 to 0.6, at Reynolds numbers of 500,000-2,000,000, at reduced frequencies of 0.015 to 0.15, and at mean angles of attack of 0-10 deg with amplitudes of 10 deg. Density and pressure fields were obtained from dual-plate interferograms. Double-pulse interferograms, which seemed to show the wake boundaries better, were also taken. Comparisons of pressures with orifice pressures were good for the attached flow cases. For the separated flow cases, which had a vortex enbedded in the flow, the comparisons were poor. Vortices, wake structures, and the dynamic stall process can be seen by holographic interferometry.

  14. The Rise and Stall of Canada's Gender-Equity Revolution.

    PubMed

    Guppy, Neil; Luongo, Nicole

    2015-08-01

    The growing symmetry in gender roles is a revolutionary change as consequential as technological advances and globalization. We illustrate how the social world in Canada has changed for women and men over the course of the last century, both in terms of greater gender equity and of policies supporting equity. However, some of the significant changes that occurred in the last 100 years have recently stalled, while the overall progress has been uneven for certain subgroups. We suggest reasons for both the stalling and the unevenness and make policy recommendations for reigniting the march to enhanced equality between the sexes. © 2015 Canadian Sociological Association/La Société canadienne de sociologie.

  15. Development of the Larzac Engine Rig for Compressor Stall Testing

    DTIC Science & Technology

    2011-12-01

    due to high vibration levels. Most pressure and all temperature sensors were of conventional type, providing analogue output signals, but of...Must have enough thermal stability to withstand the flow temperature at the particular location. 4. Must be stable in relation to engine vibration ...Instabilities in an Aeroengine ”, ICIASF ’97 Record, IEEE Publications 1997. 7. Hoess, B., Leinhos, D., Fottner, L., 2000, “Stall Inception in the

  16. A kinesthetic-tactual display for stall deterrence

    NASA Technical Reports Server (NTRS)

    Gilson, R. D.; Ventola, R. W.; Fenton, R. E.

    1975-01-01

    A kinesthetic tactual display may be effectively used as a control aid per previous flight tests. Angle of attack information would be continuously presented to a pilot, via this display, during critical operational phases where stalls are probable. A two phase plan for evaluating this concept is presented. A first development phase would encompass: (1) display fabrication for a conventional control yoke; (2) its installation, together with other necessary instrumentation, in an experimental aircraft; and (3) preliminary flight testing by experienced pilots.

  17. 17. WEST WING, EAST SIDE, TO RIGHT: SOUTH WING NORTH ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    17. WEST WING, EAST SIDE, TO RIGHT: SOUTH WING NORTH SIDE, IN BACKGROUND - Fort Sam Houston, San Antonio Quartermaster Depot, Northwest corner of New Braunfels Avenue & Grayson Street, San Antonio, Bexar County, TX

  18. Nonplanar wing load-line and slender wing theory

    NASA Technical Reports Server (NTRS)

    Deyoung, J.

    1977-01-01

    Nonplanar load line, slender wing, elliptic wing, and infinite aspect ratio limit loading theories are developed. These are quasi two dimensional theories but satisfy wing boundary conditions at all points along the nonplanar spanwise extent of the wing. These methods are applicable for generalized configurations such as the laterally nonplanar wing, multiple nonplanar wings, or wing with multiple winglets of arbitrary shape. Two dimensional theory infers simplicity which is practical when analyzing complicated configurations. The lateral spanwise distribution of angle of attack can be that due to winglet or control surface deflection, wing twist, or induced angles due to multiwings, multiwinglets, ground, walls, jet or fuselage. In quasi two dimensional theory the induced angles due to these extra conditions are likewise determined for two dimensional flow. Equations are developed for the normal to surface induced velocity due to a nonplanar trailing vorticity distribution. Application examples are made using these methods.

  19. Comparison of High-Fidelity Computational Tools for Wing Design of a Distributed Electric Propulsion Aircraft

    NASA Technical Reports Server (NTRS)

    Deere, Karen A.; Viken, Sally A.; Carter, Melissa B.; Viken, Jeffrey K.; Derlaga, Joseph M.; Stoll, Alex M.

    2017-01-01

    A variety of tools, from fundamental to high order, have been used to better understand applications of distributed electric propulsion to aid the wing and propulsion system design of the Leading Edge Asynchronous Propulsion Technology (LEAPTech) project and the X-57 Maxwell airplane. Three high-fidelity, Navier-Stokes computational fluid dynamics codes used during the project with results presented here are FUN3D, STAR-CCM+, and OVERFLOW. These codes employ various turbulence models to predict fully turbulent and transitional flow. Results from these codes are compared for two distributed electric propulsion configurations: the wing tested at NASA Armstrong on the Hybrid-Electric Integrated Systems Testbed truck, and the wing designed for the X-57 Maxwell airplane. Results from these computational tools for the high-lift wing tested on the Hybrid-Electric Integrated Systems Testbed truck and the X-57 high-lift wing presented compare reasonably well. The goal of the X-57 wing and distributed electric propulsion system design achieving or exceeding the required ?? (sub L) = 3.95 for stall speed was confirmed with all of the computational codes.

  20. Flow and Performance Calculations of Axial Compressor near Stall Margin

    NASA Astrophysics Data System (ADS)

    Hwang, Yoojun; Kang, Shin-Hyoung

    2010-06-01

    Three-dimensional flows through a Low Speed Research Axial Compressor were numerically conducted in order to estimate the performance through unsteady and steady-state simulations. The first stage with the inlet guide vane was investigated at the design point to confirm that the rotor blade induced periodicity exists. Special attention was paid to the flow near the stall condition to inspect the flow behavior in the vicinity of the stall margin. The performance predicted under the steady-state assumption is in good agreement with the measured data. However, the steady-state calculations induce more blockage through the blade passage. Flow separations on the blade surface and end-walls are reduced when unsteady simulation is conducted. The negative jet due to the wake of the rotor blade periodically distorts the boundary layer on the surface of the stator blade and improves the performance of the compressor in terms of the pressure rise. The advantage of the unsteadiness increases as the flow rate reduces. In addition, the rotor tip leakage flow is forced downstream by the unsteadiness. Consequently, the behavior contributes to extending the range of operation by preventing the leakage flow from proceeding upstream near the stall margin.

  1. Stalled Pulsing Inertial Oscillation Model for a Tornadic Cyclone

    NASA Technical Reports Server (NTRS)

    Costen, Robert C.

    2005-01-01

    A supercell storm is a tall, rotating thunderstorm that can generate hail and tornadoes. Two models exist for the development of the storm's rotation or mesocyclone - the conventional splitting-storm model, and the more recent pulsing inertial oscillation (PIO) model, in which a nonlinear pulse represents the supercell. Although data support both models and both could operate in the same supercell, neither model has satisfactorily explained the tornadic cyclone. A tornadic cyclone is an elevated vorticity concentration of Rossby number approximately 1000 that develops within the contracting mesocyclone shortly before a major tornado appears at the surface. We now show that if the internal temperature excess due to latent energy release is limited to the realistic range of -12 K to +12 K, the PIO model can stall part way through the pulse in a state of contraction and spin-up. Should this happen, the stalled-PIO model can evolve into a tornadic cyclone with a central pressure deficit that exceeds 40 mb, which is greater than the largest measured value. This simulation uses data from a major tornadic supercell that occurred over Oklahoma City, Oklahoma, USA, on May 3, 1999. The stalled-PIO mechanism also provides a strategy for human intervention to retard or reverse the development of a tornadic cyclone and its pendant tornado.

  2. Effects of Compressibility on the Maximum Lift Characteristics and Spanwise Load Distribution of a 12-Foot-Span Fighter-Type Wing of NACA 230-Series Airfoil Sections

    NASA Technical Reports Server (NTRS)

    West, F E

    1945-01-01

    Lift characteristics and pressure distribution for a NACA 230 wing were investigated for an angle of attack range of from -10 to +24 degrees and Mach range of from 0.2 to 0.7. Maximum lift coefficient increased up to a Mach number of 0.3, decreased rapidly to a Mach number of 0.55, and then decreased moderately. At high speeds, maximum lift coefficient was reached at from 10 to 12 degrees beyond the stalling angle. In high-speed stalls, resultant load underwent a moderate shift outward.

  3. Interference of Tail Surfaces and Wing and Fuselage from Tests of 17 Combinations in the N.A.C.A. Variable-Density Tunnel

    NASA Technical Reports Server (NTRS)

    Sherman, Albert

    1939-01-01

    An investigation of the interference associated with tail surfaces added to wing-fuselage combinations was included in the interference program in progress in the NACA variable-density tunnel. The results indicate that, in aerodynamically clean combinations, the increment to the high-speed drag can be estimated from section characteristics within useful limits of accuracy. The interference appears mainly as effects on the downwash angel and as losses in the tail. An interference burble, which markedly increases the glide-path angle and the stability in pitch before the actual stall, may be considered a means of obtaining satisfactory stalling characteristics for a complete combination.

  4. Simulator study of stall/post-stall characteristics of a fighter airplane with relaxed longitudinal static stability. [F-16

    NASA Technical Reports Server (NTRS)

    Nguyen, L. T.; Ogburn, M. E.; Gilbert, W. P.; Kibler, K. S.; Brown, P. W.; Deal, P. L.

    1979-01-01

    A real-time piloted simulation was conducted to evaluate the high-angle-of-attack characteristics of a fighter configuration based on wind-tunnel testing of the F-16, with particular emphasis on the effects of various levels of relaxed longitudinal static stability. The aerodynamic data used in the simulation was conducted on the Langley differential maneuvering simulator, and the evaluation involved representative low-speed combat maneuvering. Results of the investigation show that the airplane with the basic control system was resistant to the classical yaw departure; however, it was susceptible to pitch departures induced by inertia coupling during rapid, large-amplitude rolls at low airspeed. The airplane also exhibited a deep-stall trim which could be flown into and from which it was difficult to recover. Control-system modifications were developed which greatly decreased the airplane susceptibility to the inertia-coupling departure and which provided a reliable means for recovering from the deep stall.

  5. Thyroperoxidase and thyroglobulin antibodies in early pregnancy and placental abruption.

    PubMed

    Haddow, James E; McClain, Monica R; Palomaki, Glenn E; Neveux, Louis M; Lambert-Messerlian, Geralyn; Canick, Jacob A; Malone, Fergal D; Porter, T Flint; Nyberg, David A; Bernstein, Peter S; D'Alton, Mary E

    2011-02-01

    To estimate the relationship between thyroid antibodies and placental abruption. This cohort study assesses thyroperoxidase and thyroglobulin antibodies in relation to placental abruption among 10,062 women with singleton viable pregnancies (from the First and Second Trimester Risk of Aneuploidy [FaSTER] trial). A thyroperoxidase antibody cutoff of 50 international units/mL is used for comparison with published data from another cohort. Women with elevated thyroperoxidase antibody levels in the first and second trimesters have a higher rate of placental abruption than antibody-negative women. This relationship is less strong in the first trimester (1.51% compared with 0.83%; odds ratio [OR], 1.83; 95% confidence interval [CI], 0.99-3.37) than in the second trimester (1.78% compared with 0.82%; OR, 2.20; 95% CI, 1.21-3.99). A similar, but weaker, relationship is present for thyroglobulin antibodies. Sixty-four of 782 thyroperoxidase antibody-positive pregnancies without abruption become negative by the second trimester; one pregnancy with abruption becomes antibody-positive. Odds ratios for pregnancies with both thyroperoxidase and thyroglobulin antibody elevations are also higher (first trimester: OR, 2.10; 95% CI, 0.91-4.86; second trimester: OR, 2.73; 95% CI, 1.17-6.33). The present data confirm an association between thyroid antibody elevations and placental abruption described in a recent report. These findings, however, do not provide support for recommending routine testing for thyroid antibodies during pregnancy. II.

  6. Kinetic modeling predicts a stimulatory role for ribosome collisions at elongation stall sites in bacteria

    PubMed Central

    Ferrin, Michael A; Subramaniam, Arvind R

    2017-01-01

    Ribosome stalling on mRNAs can decrease protein expression. To decipher ribosome kinetics at stall sites, we induced ribosome stalling at specific codons by starving the bacterium Escherichia coli for the cognate amino acid. We measured protein synthesis rates from a reporter library of over 100 variants that encoded systematic perturbations of translation initiation rate, the number of stall sites, and the distance between stall sites. Our measurements are quantitatively inconsistent with two widely-used kinetic models for stalled ribosomes: ribosome traffic jams that block initiation, and abortive (premature) termination of stalled ribosomes. Rather, our measurements support a model in which collision with a trailing ribosome causes abortive termination of the stalled ribosome. In our computational analysis, ribosome collisions selectively stimulate abortive termination without fine-tuning of kinetic rate parameters at ribosome stall sites. We propose that ribosome collisions serve as a robust timer for translational quality control pathways to recognize stalled ribosomes. DOI: http://dx.doi.org/10.7554/eLife.23629.001 PMID:28498106

  7. Geometric Analysis of Wing Sections

    DOT National Transportation Integrated Search

    1995-04-01

    This paper describes a new geometric analysis procedure for wing sections. This procedure is based on the normal mode analysis for continuous functions. A set of special shape functions is introduced to represent the geometry of the wing section. The...

  8. [Reversible catatonia after the abrupt discontinuation of clozapine: Case report].

    PubMed

    Jaafari, M; Bout, A; Rammouz, I; Aalouane, R

    2016-12-01

    In this paper, we report the case of a patient, aged 26, with schizophrenia who was admitted to psychiatric emergencies for catatonia, one week after abrupt discontinuation of clozapine. An improvement was seen after only two days of the reintroduction of clozapine alone. This catatonia is reversible and it responds magnificently to the reintroduction of clozapine. And we conclude that patients and their caregivers need to be educated about the effects of abrupt cessation of clozapine administration. Copyright © 2016 L’Encéphale, Paris. Published by Elsevier Masson SAS. All rights reserved.

  9. Phase Memory Preserving Harmonics from Abruptly Autofocusing Beams.

    PubMed

    Koulouklidis, Anastasios D; Papazoglou, Dimitris G; Fedorov, Vladimir Yu; Tzortzakis, Stelios

    2017-12-01

    We demonstrate both theoretically and experimentally that the harmonics from abruptly autofocusing ring-Airy beams present a surprising property: They preserve the phase distribution of the fundamental beam. Consequently, this "phase memory" imparts to the harmonics the abrupt autofocusing behavior, while, under certain conditions, their foci coincide in space with the one of the fundamental. Experiments agree well with our theoretical estimates and detailed numerical calculations. Our findings open the way for the use of such beams and their harmonics in strong field science.

  10. Status of wing flutter

    NASA Technical Reports Server (NTRS)

    Kussner, H G

    1936-01-01

    This report presents a survey of previous theoretical and experimental investigations on wing flutter covering thirteen cases of flutter observed on airplanes. The direct cause of flutter is, in the majority of cases, attributable to (mass-) unbalanced ailerons. Under the conservative assumption that the flutter with the phase angle most favorable for excitation occurs only in two degrees of freedom, the lowest critical speed can be estimated from the data obtained on the oscillation bench. Corrective measures for increasing the critical speed and for definite avoidance of wing flutter, are discussed.

  11. Theory of wing rock

    NASA Technical Reports Server (NTRS)

    Hsu, C. H.; Lan, C. E.

    1984-01-01

    A theory is developed for predicting wing rock characteristics. From available data, it can be concluded that wing rock is triggered by flow asymmetries, developed by negative or weakly positive roll damping, and sustained by nonlinear aerodynamic roll damping. A new nonlinear aerodynamic model that includes all essential aerodynamic nonlinearities is developed. The Beecham-Titchener method is applied to obtain approximate analytic solutions for the amplitude and frequency of the limit cycle based on the three degree-of-freedom equations of motion. An iterative scheme is developed to calculate the average aerodynamic derivatives and dynamic characteristics at limit cycle conditions. Good agreement between theoretical and experimental results is obtained.

  12. 167th Airlift Wing > Home

    Science.gov Websites

    encouraged to call 304-616-5127, to offer suggestions on how to improve the wing. The number goes directly to Spotlight Life saver training offered at wing proves invaluable to Airman Life saver training offered at wing proves invaluable to Airman Life saver training offered at wing proves invaluable to Airman WVANG

  13. Butterfly wing colours: scale beads make white pierid wings brighter.

    PubMed Central

    Stavenga, D. G.; Stowe, S.; Siebke, K.; Zeil, J.; Arikawa, K.

    2004-01-01

    The wing-scale morphologies of the pierid butterflies Pieris rapae (small white) and Delias nigrina (common jezabel), and the heliconine Heliconius melpomene are compared and related to the wing-reflectance spectra. Light scattering at the wing scales determines the wing reflectance, but when the scales contain an absorbing pigment, reflectance is suppressed in the absorption wavelength range of the pigment. The reflectance of the white wing areas of P. rapae, where the scales are studded with beads, is considerably higher than that of the white wing areas of H. melpomene, which has scales lacking beads. The beads presumably cause the distinct matt-white colour of the wings of pierids and function to increase the reflectance amplitude. This will improve the visual discrimination between conspecific males and females. PMID:15306303

  14. Detached-Eddy Simulations of Separated Flow Around Wings With Ice Accretions: Year One Report

    NASA Technical Reports Server (NTRS)

    Choo, Yung K. (Technical Monitor); Thompson, David; Mogili, Prasad

    2004-01-01

    A computational investigation was performed to assess the effectiveness of Detached-Eddy Simulation (DES) as a tool for predicting icing effects. The AVUS code, a public domain flow solver, was employed to compute solutions for an iced wing configuration using DES and steady Reynolds Averaged Navier-Stokes (RANS) equation methodologies. The configuration was an extruded GLC305/944-ice shape section with a rectangular planform. The model was mounted between two walls so no tip effects were considered. The numerical results were validated by comparison with experimental data for the same configuration. The time-averaged DES computations showed some improvement in lift and drag results near stall when compared to steady RANS results. However, comparisons of the flow field details did not show the level of agreement suggested by the integrated quantities. Based on our results, we believe that DES may prove useful in a limited sense to provide analysis of iced wing configurations when there is significant flow separation, e.g., near stall, where steady RANS computations are demonstrably ineffective. However, more validation is needed to determine what role DES can play as part of an overall icing effects prediction strategy. We conclude the report with an assessment of existing computational tools for application to the iced wing problem and a discussion of issues that merit further study.

  15. 144th Fighter Wing

    Science.gov Websites

    , the wing provides agile combat support, and intelligence, surveillance and reconnaissance to combatant the U.S. Air Force AF Week in Photos Senior leaders meet with industry to discuss utilizing artificial intelligence and quantum science throughout the Air Force AF announces 2018 Blacks in Government Meritorious

  16. Adaptive wing structures

    NASA Astrophysics Data System (ADS)

    Reed, John L., Jr.; Hemmelgarn, Christopher D.; Pelley, Bryan M.; Havens, Ernie

    2005-05-01

    Cornerstone Research Group, Inc. (CRG) is developing a unique adaptive wing structure intended to enhance the capability of loitering Unmanned Air Vehicles (UAVs). In order to tailor the wing design to a specific application, CRG has developed a wing structure capable of morphing in chord and increasing planform area by 80 percent. With these features, aircraft will be capable of optimizing their flight efficiency throughout the entire mission profile. The key benefit from this morphing design is increased maneuverability, resulting in improved effectiveness over the current design. During the development process CRG has overcome several challenges in the design of such a structure while incorporating advanced materials capable of maintaining aerodynamic shape and transferring aerodynamic loads while enabling crucial changes in planform shape. To overcome some of these challenges, CRG is working on integration of their shape memory polymer materials into the wing skin to enable seamless morphing. This paper will address the challenges associated with the development of a morphing aerospace structure capable of such large shape change, the materials necessary for enabling morphing capabilities, and the current status of the morphing program within CRG.

  17. Comparison of dynamic stall phenomena for pitching and vertical translation motions

    NASA Technical Reports Server (NTRS)

    Fukushima, T.; Dadone, L. U.

    1977-01-01

    Test data for vertical translation motions of the V0012 and V23010-1.58 airfoils were compared with force pitch and oscillation data to determine qualitative differences in dynamic stall behavior. Chordwise differential pressure variations were examined in detail for the test conditions displaying dynamic stall. The comparison revealed a number of differences both in the onset of stall and in the progression separation as a function of the type of motion. The evidence of secondary stall events following the recovery from initial stall were found to be dependent on the type of motion, but additional data will be needed to incorporate vertical translation effects into the empirical approximation of dynamic stall.

  18. Aerodynamic study of a stall regulated horizontal-axis wind turbine

    NASA Astrophysics Data System (ADS)

    Constantinescu, S. G.; Crunteanu, D. E.; Niculescu, M. L.

    2013-10-01

    The wind energy is deemed as one of the most durable energetic variants of the future because the wind resources are immense. Furthermore, one predicts that the small wind turbines will play a vital role in the urban environment. Unfortunately, the complexity and the price of pitch regulated small horizontal-axis wind turbines represent ones of the main obstacles to widespread the use in populated zones. Moreover, the energetic efficiency of small stall regulated wind turbines has to be high even at low and medium wind velocities because, usually the cities are not windy places. During the running stall regulated wind turbines, due to the extremely broad range of the wind velocity, the angle of attack can reach high values and some regions of the blade will show stall and post-stall behavior. This paper deals with stall and post-stall regimes because they can induce significant vibrations, fatigue and even the wind turbine failure.

  19. Investigating Flow Features Near Abrupt Topography in the Mariana Basin

    DTIC Science & Technology

    2015-09-30

    1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Investigating Flow Features Near Abrupt Topography in...waves generated by flow over topography and mesoscale eddies generated by flow past islands. Having identified the prime locations in the region for such

  20. Abrupt Depletion Layer Approximation for the Metal Insulator Semiconductor Diode.

    ERIC Educational Resources Information Center

    Jones, Kenneth

    1979-01-01

    Determines the excess surface change carrier density, surface potential, and relative capacitance of a metal insulator semiconductor diode as a function of the gate voltage, using the precise questions and the equations derived with the abrupt depletion layer approximation. (Author/GA)

  1. Preferences of dairy cows for three stall surface materials with small amounts of bedding.

    PubMed

    Norring, M; Manninen, E; de Passillé, A M; Rushen, J; Saloniemi, H

    2010-01-01

    Farmers' concerns about the economy, cost of labor, and hygiene have resulted in reduced use of organic bedding in stalls for dairy cows; however, the reduced use of organic bedding possibly impairs cow comfort. The effects of different stall surface materials were evaluated in an unheated building in which only a small amount of bedding was used. The lying time and preferences of 18 cows using 3 stall surface materials (concrete, soft rubber mat, and sand) were compared. All materials were lightly bedded with a small amount of straw, and the amount of straw added to each stall was measured. The cows only had access to stalls of one surface type while their lying time was observed. Lying times were longest on the rubber mats compared with other surfaces (rubber mat 768; concrete 727; sand 707+/-16 min/d). In a preference test, cows had access to 2 of the 3 types of stalls for 10 d and their stall preference was measured. Cows preferred stalls with rubber mats to stalls with a concrete floor (median 73 vs. 18 from a total of 160 observations per day; interquartile range was 27 and 12, respectively), but showed no preference for sand stalls compared with stalls with a concrete floor or with rubber mats. More straw was needed on sand stalls compared with concrete or mat (638+/-13 g/d on sand, 468+/-10 g/d on concrete, and 464+/-8 g/d on rubber mats). Lying times on bedded mats indicated that mats were comfortable for the cows. If availability or cost of bedding material requires limiting the amount of bedding used, rubber mats may help maintain cow comfort. Copyright 2010 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

  2. SMA actuators for morphing wings

    NASA Astrophysics Data System (ADS)

    Brailovski, V.; Terriault, P.; Georges, T.; Coutu, D.

    An experimental morphing laminar wing was developed to prove the feasibility of aircraft fuel consumption reduction through enhancement of the laminar flow regime over the wing extrados. The morphing wing prototype designed for subsonic cruise flight conditions (Mach 0.2 … 0.3; angle of attack - 1 … +2∘), combines three principal subsystems: (1) flexible extrados, (2) rigid intrados and (3) an actuator group located inside the wing box. The morphing capability of the wing relies on controlled deformation of the wing extrados under the action of shape memory alloys (SMA) actuators. A coupled fluid-structure model of the morphing wing was used to evaluate its mechanical and aerodynamic performances in different flight conditions. A 0.5 m chord and 1 m span prototype of the morphing wing was tested in a subsonic wind tunnel. In this work, SMA actuators for morphing wings were modeled using a coupled thermo-mechanical finite element model and they were windtunnel validated. If the thermo-mechanical model of SMA actuators presented in this work is coupled with the previously developed structureaerodynamic model of the morphing wing, it could serve for the optimization of the entire morphing wing system.

  3. The dynamics underlying the regeneration and stalling of Hurricane Harvey

    NASA Astrophysics Data System (ADS)

    Liang, X. S.

    2017-12-01

    The explosive regeneration and stalling make the hurricane Harvey go from a little-noticed storm to an extremely destructive behemoth in late August 2017 that incurred an estimated economic loss at 70-200 billion USD. In this study, we use a recently developed analysis tool, namely, multiscale window transform (MWT), and the MWT-based theory of canonical transfer, to investigate the dynamics underlying this regeneration and stalling. The atmospheric fields are reconstructed onto three scale ranges or windows, namely, large-scale, tropical cyclone-scale, and cumulus convection-scale windows. The intertwined cyclone-scale nonlinear energy process is uniquely separated into a transport of energy within the cyclone window and an interscale transfer through reconstructing the "atomic" energy fluxes on the multiple scale windows. The resulting transfer bears a Lie bracket form, reminiscent of the Poisson bracket in Hamiltonian mechanics, and is hence referred to as canonical. It is found that within the Gulf of Mexico, Harvey gains much energy from the cumulus convection window through an inverse energy cascade, leading to its explosive growth. In the mean time, there is a barotropic instability (positive canonical transfer) center of the mean circulation in the lower and mid troposphere which lies quasi-steadily over Houston during August 22 through early September. The northwestward propagating Harvey meets that center and then stalls for two days near the coastline, dropping torrential and unprecedented amounts of rainfall and causing catastrophic flooding. It moves out of the instability center by the end of August, and then dissipates quickly in the following days.

  4. Stalled replication forks within heterochromatin require ATRX for protection

    PubMed Central

    Huh, M S; Ivanochko, D; Hashem, L E; Curtin, M; Delorme, M; Goodall, E; Yan, K; Picketts, D J

    2016-01-01

    Expansive growth of neural progenitor cells (NPCs) is a prerequisite to the temporal waves of neuronal differentiation that generate the six-layered neocortex, while also placing a heavy burden on proteins that regulate chromatin packaging and genome integrity. This problem is further reflected by the growing number of developmental disorders caused by mutations in chromatin regulators. ATRX gene mutations cause a severe intellectual disability disorder (α-thalassemia mental retardation X-linked (ATRX) syndrome; OMIM no. 301040), characterized by microcephaly, urogenital abnormalities and α-thalassemia. Although the ATRX protein is required for the maintenance of repetitive DNA within heterochromatin, how this translates to disease pathogenesis remain poorly understood and was a focus of this study. We demonstrate that AtrxFoxG1Cre forebrain-specific conditional knockout mice display poly(ADP-ribose) polymerase-1 (Parp-1) hyperactivation during neurogenesis and generate fewer late-born Cux1- and Brn2-positive neurons that accounts for the reduced cortical size. Moreover, DNA damage, induced Parp-1 and Atm activation is elevated in progenitor cells and contributes to their increased level of cell death. ATRX-null HeLa cells are similarly sensitive to hydroxyurea-induced replication stress, accumulate DNA damage and proliferate poorly. Impaired BRCA1-RAD51 colocalization and PARP-1 hyperactivation indicated that stalled replication forks are not efficiently protected. DNA fiber assays confirmed that MRE11 degradation of stalled replication forks was rampant in the absence of ATRX or DAXX. Indeed, fork degradation in ATRX-null cells could be attenuated by treatment with the MRE11 inhibitor mirin, or exacerbated by inhibiting PARP-1 activity. Taken together, these results suggest that ATRX is required to limit replication stress during cellular proliferation, whereas upregulation of PARP-1 activity functions as a compensatory mechanism to protect stalled forks

  5. Monitoring indices of cow comfort in free-stall-housed dairy herds.

    PubMed

    Cook, N B; Bennett, T B; Nordlund, K V

    2005-11-01

    Indices of cow comfort are used widely by consultants in the dairy industry, with a general understanding that they are representative of lying behavior. This study examines the influence of stall base type (sand or a geotextile mattress filled with rubber crumbs) and time of measurement on 4 indices of comfort collected at hourly intervals in 12 herds, aligned by morning and afternoon milking. Stall base type significantly influenced all indices of comfort. For example, the least squares mean (SE) cow comfort index (proportion of cows touching a stall that are lying down) was 0.76 (0.015) in herds with mattresses compared with 0.86 (0.015) in herds with sand stalls. Significant hourly variation was also identified suggesting that timing of measurement is important. None of the indices of cow comfort derived from the high-yielding group pen was associated with the mean 24-h lying time of 10 sentinel cows whose time budgets were known in each herd. However, the cow comfort index was associated with the herd mean 24-h stall standing time, with the strongest relationships occurring 2 h before the morning and afternoon milking, when stall base type did not significantly influence the association. When measured at these times, we recommend use of the stall standing index (proportion of cows touching a stall that are standing), with values greater than 0.20 being associated with abnormally long herd mean stall standing times greater than 2 h/d.

  6. Enhancing BEM simulations of a stalled wind turbine using a 3D correction model

    NASA Astrophysics Data System (ADS)

    Bangga, Galih; Hutomo, Go; Syawitri, Taurista; Kusumadewi, Tri; Oktavia, Winda; Sabila, Ahmad; Setiadi, Herlambang; Faisal, Muhamad; Hendranata, Yongki; Lastomo, Dwi; Putra, Louis; Kristiadi, Stefanus; Bumi, Ilmi

    2018-03-01

    Nowadays wind turbine rotors are usually employed with pitch control mechanisms to avoid deep stall conditions. Despite that, wind turbines often operate under pitch fault situation causing massive flow separation to occur. Pure Blade Element Momentum (BEM) approaches are not designed for this situation and inaccurate load predictions are already expected. In the present studies, BEM predictions are improved through the inclusion of a stall delay model for a wind turbine rotor operating under pitch fault situation of -2.3° towards stall. The accuracy of the stall delay model is assessed by comparing the results with available Computational Fluid Dynamics (CFD) simulations data.

  7. An experimental investigation of compressor stall using an on-line distortion indicator and signal conditioner

    NASA Technical Reports Server (NTRS)

    Costakis, W. G.; Wenzel, L. M.

    1975-01-01

    The relation of the steady-state and dynamic distortions and the stall margin of a J85-13 turbojet engine was investigated. A distortion indicator capable of computing two distortion indices was used. A special purpose signal conditioner was also used as an interface between transducer signals and distortion indicator. A good correlation of steady-state distortion and stall margin was established. The prediction of stall by using the indices as instantaneous distortion indicators was not successful. A sensitivity factor that related the loss of stall margin to the turbulence level was found.

  8. ANALYTICAL AND EXPERIMENTAL INVESTIGATION OF ROTATING STALL PHENOMENA IN TURBINE ENGINE COMPRESSORS.

    DTIC Science & Technology

    AXIAL FLOW COMPRESSORS, STALLING), TURBOJET ENGINES , AXIAL FLOW COMPRESSOR BLADES , LIFT, HYSTERESIS, TURBULENCE, INLET GUIDE VANES , RINGS, STABILITY, THREE DIMENSIONAL FLOW, VISCOSITY, VORTICES, FLUIDICS.

  9. Experimental Investigation of Rotating Stall in a Research Multistage Axial Compressor

    NASA Technical Reports Server (NTRS)

    Lepicovsky, Jan; Braunscheidel, Edward P.; Welch, Gerard E.

    2007-01-01

    A collection of experimental data acquired in the NASA low-speed multistage axial compressor while operated in rotating stall is presented in this paper. The compressor was instrumented with high-response wall pressure modules and a static pressure disc probe for in-flow measurement, and a split-fiber probe for simultaneous measurements of velocity magnitude and flow direction. The data acquired to-date have indicated that a single fully developed stall cell rotates about the flow annulus at 50.6% of the rotor speed. The stall phenomenon is substantially periodic at a fixed frequency of 8.29 Hz. It was determined that the rotating stall cell extends throughout the entire compressor, primarily in the axial direction. Spanwise distributions of the instantaneous absolute flow angle, axial and tangential velocity components, and static pressure acquired behind the first rotor are presented in the form of contour plots to visualize different patterns in the outer (midspan to casing) and inner (hub to mid-span) flow annuli during rotating stall. In most of the cases observed, the rotating stall started with a single cell. On occasion, rotating stall started with two emerging stall cells. The root cause of the variable stall cell count is unknown, but is not attributed to operating procedures.

  10. Experimental study of dynamic stall on Darrieus wind turbine blades

    NASA Astrophysics Data System (ADS)

    Brochier, G.; Fraunie, P.; Beguier, C.; Paraschivoiu, I.

    1985-12-01

    An experimental study of periodic vortex phenomena was performed on a model of a two straight-bladed Darrieus wind turbine under controlled-rotation conditions in the IMST water tunnel. The main focus of interest was the tip-speed ratios at which dynamic stall appears. Observations of this phenomenon from dye emission and the formation of hydrogen bubbles were made in the form of photographs, film and video recordings. Velocity measurements were obtained using the Laser-Doppler Velocimeter and components of velocity fluctuations could be determined quantitatively.

  11. Miniature Rocket Motor for Aircraft Stall/Spin Recovery

    NASA Technical Reports Server (NTRS)

    Lucy, M. H.

    1985-01-01

    Design accommodates different thrust levels and burn times with minimum weight. Different thrust levels achieved by substituting other propellants of different diameter and burn-rate characteristics. Different burn times achieved by simply changing length of grain/tube assembly. Grain bond material also acts as insulator for fiberglass tube. Rocket motor attached to aircraft model and ignited from radio-controlled 4.8-volt power source. Device provides more than twice energy available in previous designs at only 60 percent of weight. Rocket motor used to identify energy requirements for aircraft stall/spin recovery positive propulsion system.

  12. Dynamic Stall Computations Using a Zonal Navier-Stokes Model

    DTIC Science & Technology

    1988-06-01

    NAVAL POSTGRADUATE SCHOOL lotMonterey ,California CD Lj STATF ,-S THESIS DYNAMIC STALL CALCULATIONS USING A ZONAL.-,_ % 0 NVETESISDE by Jack H...Conroyd, Jr. June 1988 Thesis Co-advisors: M.F. Platzer Lawrence W. Carr Approved for public release; distribution is unlimitedDOTIC , ~~~~~~~~ELECT...OINT %, Master s Thesis OM To June 212 6 SLP;’LEENTARY NOTATION ri The views expressed in this thesis are those of the author and do not reflect the

  13. Subsonic/transonic stall flutter investigation of a rotating rig

    NASA Technical Reports Server (NTRS)

    Jutras, R. R.; Fost, R. B.; Chi, R. M.; Beacher, B. F.

    1981-01-01

    Stall flutter is investigated by obtaining detailed quantitative steady and aerodynamic and aeromechanical measurements in a typical fan rotor. The experimental investigation is made with a 31.3 percent scale model of the Quiet Engine Program Fan C rotor system. Both subsonic/transonic (torsional mode) flutter and supersonic (flexural) flutter are investigated. Extensive steady and unsteady data on the blade deformations and aerodynamic properties surrounding the rotor are acquired while operating in both the steady and flutter modes. Analysis of this data shows that while there may be more than one traveling wave present during flutter, they are all forward traveling waves.

  14. Aerodynamics and Ecomorphology of Flexible Feathers and Morphing Bird Wings

    NASA Astrophysics Data System (ADS)

    Klaassen van Oorschot, Brett

    shape affected performance during flapping but not gliding flight. Extended wings outperformed swept wings by about a third in flapping flight. This finding contrasts previous work that showed wing shape didn't affect performance in flapping flight (Usherwood and Ellington, 2002a, 2002b). This work provided key insights that inspired the second and third chapters of my dissertation. The second chapter examines the significance of wing tip slots across 135 avian species, ranging from small passerines to large seabirds. This research was completed with the help of an undergraduate international researcher, Ho Kwan Tang, and is currently in press at the Journal of Morphology (Klaassen van Oorschot, in press). These slots are caused by asymmetric emarginations missing from the leading and trailing edge of the primary feathers. We used a novel metric of primary feather emargination that allowed us to show that wing tip slots are nearly ubiquitous across the avian clade. We also showed that emargination is segregated according to habitat and behavioral metrics like flight style. Finally, we showed that emargination scaled with mass. These findings illustrated that wing tip slots may be an adaptation for efficacy during vertical takeoff rather than efficiency during gliding flight. In the third chapter, I sought to better understand the function of these slotted primary feathers. In an effort to bridge biology and aeronautics, I collaborated with Richard Choroszucha, an aeronautical engineer from the University of Michigan, on this work. These feathers deflect under aerodynamic load, and it has been hypothesized that they reduce induced drag during gliding flight (Tucker, 1993, 1995). We exposed individual primary feathers to different speeds in the wind tunnel and measured deflection such as bend, twist, and sweep. We found that feather deflection reoriented force, resulting in increased lateral stability and delayed stall characteristics compared to a rigid airfoil. These

  15. Design of a new VTOL UAV by combining cycloidal blades and FanWing propellers

    NASA Astrophysics Data System (ADS)

    Li, Daizong

    Though the propelling principles of Cycloidal Blades and FanWing propellers are totally different, their structures are similar. Therefore, it is possible to develop an aircraft which combines both types of the propulsion modes of Cyclogyro and FanWing aircrafts. For this kind of aircraft, Cycloidal Blades Mode provides capabilities of Vertical Take-Off and Landing, Instantly Alterable Vector Thrusting, and Low Noise. The FanWing Mode provides capabilities of High Efficiency, Energy-Saving, and Cannot-Stall Low-Speed Cruising. Besides, because both of these propellers are observably better than conventional screw propeller in terms of efficiency, so this type of VTOL UAV could fly with Long Endurance. Furthermore, the usage of flying-wing takes advantage of high structure utilization and high aerodynamic efficiency, eliminates the interference of fuselage and tail, and overcomes flying wing's shortcomings of pitching direction instability and difficulty of control. A new magnetic suspension track-type cycloidal propulsion system is also presented in the paper to solve problems of heavy structure, high mechanical resistance, and low reliability in the traditional cycloidal propellers. The further purpose of this design is to trying to make long-endurance VTOL aircraft and Practical Flying Cars possible in reality, and to bring a new era to the aviation industry.

  16. Measurement and Analysis of Wing and Tail Buffeting Loads on a Fighter Airplane

    NASA Technical Reports Server (NTRS)

    Huston, Wilber B; Skopinski, T H

    1955-01-01

    The buffeting loads measured on the wing and tail of a fighter airplane during 194 maneuvers are given in tabular form, along with the associated flight conditions. Measurements were made at altitudes of 30,000 to 10,000 feet and at speeds up to a Mach number of 0.8. Least-squares methods have been used for a preliminary analysis of the data. The agreement between the results of this analysis and the loads measured in stalls is sufficiently good to suggest the examination of the buffeting of other airplanes on the same basis.

  17. Dynamic Stall of Finite Span Blades and its Control

    NASA Astrophysics Data System (ADS)

    Taylor, Keith; Leong, Chia; Amitay, Michael

    2013-11-01

    An experimental investigational study into a dynamically pitching s809 airfoil at a Reynolds number of 220,000 was conducted. Particle Image Velocimetry was employed to visualize and quantify the flow field around the airfoil. This investigation compares a 2-D configuration with 3-D configuration (i.e., a finite span blade). The difference in the flow field between these two configurations is explored, as the vibrations present in the 3-D configuration (due to the dynamic stall) may contribute to a different apparent flow field than classical results would suggest. In addition, a comparison between lift and drag coefficients, measured on the 2-D and 3-D configurations, is explored, demonstrating how time varying lift and drag forces oscillate at characteristic frequencies associated with the primary vibrational modes of the model. In addition, flow control is applied through the actuation of an array of synthetic jets located near the leading edge of the model, in order to effect changes in the flow field around the model, demonstrating how dynamic stall can be delayed or eliminated during dynamic conditions.

  18. Computations of Combustion-Powered Actuation for Dynamic Stall Suppression

    NASA Technical Reports Server (NTRS)

    Jee, Solkeun; Bowles, Patrick O.; Matalanis, Claude G.; Min, Byung-Young; Wake, Brian E.; Crittenden, Tom; Glezer, Ari

    2016-01-01

    A computational framework for the simulation of dynamic stall suppression with combustion-powered actuation (COMPACT) is validated against wind tunnel experimental results on a VR-12 airfoil. COMPACT slots are located at 10% chord from the leading edge of the airfoil and directed tangentially along the suction-side surface. Helicopter rotor-relevant flow conditions are used in the study. A computationally efficient two-dimensional approach, based on unsteady Reynolds-averaged Navier-Stokes (RANS), is compared in detail against the baseline and the modified airfoil with COMPACT, using aerodynamic forces, pressure profiles, and flow-field data. The two-dimensional RANS approach predicts baseline static and dynamic stall very well. Most of the differences between the computational and experimental results are within two standard deviations of the experimental data. The current framework demonstrates an ability to predict COMPACT efficacy across the experimental dataset. Enhanced aerodynamic lift on the downstroke of the pitching cycle due to COMPACT is well predicted, and the cycleaveraged lift enhancement computed is within 3% of the test data. Differences with experimental data are discussed with a focus on three-dimensional features not included in the simulations and the limited computational model for COMPACT.

  19. Wind-Tunnel Investigation of the Horizontal Motion of a Wing Near the Ground

    NASA Technical Reports Server (NTRS)

    Serebrisky, Y. M.; Biachuev, S. A.

    1946-01-01

    By the method of images the horizontal steady motion of a wing at small heights above the ground was investigated in the wind tunnel, A rectangular wing with Clark Y-H profile was tested with and without flaps. The distance from the trailing edge of the wing to the ground was varied within the limits 0.75 less than or = s/c less than or = 0.25. Measurements were made of the lift, the drag, the pitching moment, and the pressure distribution at one section. For a wing without flaps and one with flaps a considereble decrease in the lift force and a,drop in the drag was obtained at angles of attack below stalling. The flow separation near the ground occurs at smaller angles of attack than is the case for a great height above the ground. At horizontal steady flight for practical values of the height above the ground the maximum lift coefficient for the wing without flaps changes little, but markedly decreases for the wing with flaps. Analysis of these phenomena involves the investigation of the pressure distribution. The pressure distribution curves showed that the changes occurring near the ground are not equivalent to a change in the angle of attack. At the lower surface of the section a very strong increase in the pressures is observed. The pressure changes on the upper surface at angles of attack below stalling are insignificant and lead mainly to an increase in the unfavorable pressure gradient, resulting in the earlier occurrence of separation. For a wing with flaps at large angles of attack for distances from the trailing edge of the flap to the ground less than 0.5 chord, the flow between the wing end the ground is retarded so greatly that the pressure coefficient at the lower surface of the section is very near its limiting value (P = 1), and any further possibility of increase in the pressure is very small. In the application an approximate computation procedure is given of the change of certain aerodynamic characteristics for horizontal steady flight near the

  20. Wireless Internet Gateways (WINGS)

    DTIC Science & Technology

    1997-01-01

    WIRELESS INTERNET GATEWAYS (WINGS) J.J. Garcia-Luna-Aceves, Chane L. Fullmer, Ewerton Madruga Computer Engineering Department University of...rooftop.com Abstract— Today’s internetwork technology has been extremely success- ful in linking huge numbers of computers and users. However, to date...this technology has been oriented to computer interconnection in relatively stable operational environments, and thus cannot adequately support many of

  1. ACTE Wing Loads Analysis

    NASA Technical Reports Server (NTRS)

    Horn, Nicholas R.

    2015-01-01

    The Adaptive Compliant Trailing Edge (ACTE) project modified a Gulfstream III (GIII) aircraft with a new flexible flap that creates a seamless transition between the flap and the wing. As with any new modification, it is crucial to ensure that the aircraft will not become overstressed in flight. To test this, Star CCM a computational fluid dynamics (CFD) software program was used to calculate aerodynamic data for the aircraft at given flight conditions.

  2. Wing on a String

    ERIC Educational Resources Information Center

    Fitzgerald, Mike; Brand, Lance

    2004-01-01

    In this article, the authors present an activity that shows students how flight occurs. The "wing on a string" is a simple teacher-made frame that consists of PVC pipe, fishing line, and rubber bands--all readily available hardware store items. The only other materials/tools involved are a sheet of paper, some pieces of a soda straw, a stapler,…

  3. Why do magmas stall? Insights from petrologic and geodetic data

    NASA Astrophysics Data System (ADS)

    Zimmer, M. M.; Plank, T.; Freymueller, J.; Hauri, E. H.; Larsen, J. F.; Nye, C. J.

    2007-12-01

    Magmas stall at various depths in the crust due to their internal properties (magma viscosity, buoyancy) and external crustal controls (local stress regime, wallrock strength). Annen et al. (JPet 2006) propose a petrological model in which buoyant magma ascends through the crust until the depth of water saturation, after which it crystallizes catastrophically and stalls due to the large increase in magma viscosity. Magmas may erupt from this storage region, or viscous death may result in pluton formation. In order to test this model, and constrain magma storage depths, we combine petrological and geodetic data for several active volcanoes along the Aleutian-Alaska arc. We analyzed glassy, primarily olivine-hosted melt inclusions by SIMS in tephra samples for their pre-eruptive volatile contents, which can be related to the depth of entrapment via pressure-dependent H2O-CO2 solubility models (e.g., VolatileCalc). Melt inclusions are not in equilibrium with pure water vapor (all will contain S and C species), but >50% of the inclusion population are in equilibrium with a vapor containing >85% H2O. Geodetic data (InSAR, GPS) record surface deformation related to volcano inflation/deflation, and can be inverted to solve for the depths of volume change (magma storage) in the crust. In the Aleutians, we find that the maximum melt inclusion trapping depths and geodetic depths correlate, suggesting both techniques record crustal magma storage and crystallization. Melt inclusions from the 1997 Okmok eruption are trapped at ≤3 km; deformation during the eruption and subsequent inflation occurred at 3±0.5 km (Miyagi et al., EPSL 2004; Lu & Masterlark, JGR 2005). At Akutan, melt inclusions and GPS data indicate magma storage at ~5-7 km. Inclusions from flank cones of Makushin yield depths of 7 km, similar to inflation observed beneath the main edifice (6.8 km, Lu et al., JGR 2002). Pleistocene inclusions from Augustine volcano indicate magma storage at 10-18 km, in accord

  4. The Atlantic Meridional Overturning Circulation and Abrupt Climate Change.

    PubMed

    Lynch-Stieglitz, Jean

    2017-01-03

    Abrupt changes in climate have occurred in many locations around the globe over the last glacial cycle, with pronounced temperature swings on timescales of decades or less in the North Atlantic. The global pattern of these changes suggests that they reflect variability in the Atlantic meridional overturning circulation (AMOC). This review examines the evidence from ocean sediments for ocean circulation change over these abrupt events. The evidence for changes in the strength and structure of the AMOC associated with the Younger Dryas and many of the Heinrich events is strong. Although it has been difficult to directly document changes in the AMOC over the relatively short Dansgaard-Oeschger events, there is recent evidence supporting AMOC changes over most of these oscillations as well. The lack of direct evidence for circulation changes over the shortest events leaves open the possibility of other driving mechanisms for millennial-scale climate variability.

  5. Ultra-wideband horn antenna with abrupt radiator

    DOEpatents

    McEwan, T.E.

    1998-05-19

    An ultra-wideband horn antenna transmits and receives impulse waveforms for short-range radars and impulse time-of flight systems. The antenna reduces or eliminates various sources of close-in radar clutter, including pulse dispersion and ringing, sidelobe clutter, and feedline coupling into the antenna. Dispersion is minimized with an abrupt launch point radiator element; sidelobe and feedline coupling are minimized by recessing the radiator into a metallic horn. Low frequency cut-off associated with a horn is extended by configuring the radiator drive impedance to approach a short circuit at low frequencies. A tapered feed plate connects at one end to a feedline, and at the other end to a launcher plate which is mounted to an inside wall of the horn. The launcher plate and feed plate join at an abrupt edge which forms the single launch point of the antenna. 8 figs.

  6. Ultra-wideband horn antenna with abrupt radiator

    DOEpatents

    McEwan, Thomas E.

    1998-01-01

    An ultra-wideband horn antenna transmits and receives impulse waveforms for short-range radars and impulse time-of flight systems. The antenna reduces or eliminates various sources of close-in radar clutter, including pulse dispersion and ringing, sidelobe clutter, and feedline coupling into the antenna. Dispersion is minimized with an abrupt launch point radiator element; sidelobe and feedline coupling are minimized by recessing the radiator into a metallic horn. Low frequency cut-off associated with a horn is extended by configuring the radiator drive impedance to approach a short circuit at low frequencies. A tapered feed plate connects at one end to a feedline, and at the other end to a launcher plate which is mounted to an inside wall of the horn. The launcher plate and feed plate join at an abrupt edge which forms the single launch point of the antenna.

  7. Large-scale wind-tunnel investigation of a close-coupled canard-delta-wing fighter model through high angles of attack

    NASA Technical Reports Server (NTRS)

    Stoll, F.; Koenig, D. G.

    1983-01-01

    Data obtained through very high angles of attack from a large-scale, subsonic wind-tunnel test of a close-coupled canard-delta-wing fighter model are analyzed. The canard delays wing leading-edge vortex breakdown, even for angles of attack at which the canard is completely stalled. A vortex-lattice method was applied which gave good predictions of lift and pitching moment up to an angle of attack of about 20 deg, where vortex-breakdown effects on performance become significant. Pitch-control inputs generally retain full effectiveness up to the angle of attack of maximum lift, beyond which, effectiveness drops off rapidly. A high-angle-of-attack prediction method gives good estimates of lift and drag for the completely stalled aircraft. Roll asymmetry observed at zero sideslip is apparently caused by an asymmetry in the model support structure.

  8. Elucidating Dynamical Processes Relevant to Flow Encountering Abrupt Topography (FLEAT)

    DTIC Science & Technology

    2015-09-30

    Encountering Abrupt Topography (FLEAT) Bo Qiu Dept of Oceanography, University of Hawaii at Manoa 1000 Pope Rd. Honolulu, HI 96822 phone: (808) 956...c) to explore relevant dynamics by using both simplified models and OGCM output with realistic topography and surface boundary conditions...scale abyssal circulation, we propose to use the Hallberg Isopycnal Model (HIM). The HIM allows sloping isopycnals to interact with bottom topography

  9. Climate Stability: Pathway to understand abrupt glacial climate shifts

    NASA Astrophysics Data System (ADS)

    Zhang, X.; Knorr, G.; Barker, S.; Lohmann, G.

    2017-12-01

    Glacial climate is marked by abrupt, millennial-scale climate changes known as Dansgaard-Oeschger (DO) cycles that have been linked to variations in the Atlantic meridional overturning circulation (AMOC). The most pronounced stadial coolings, Heinrich Stadials (HSs), are associated with massive iceberg discharges to the North Atlantic. This motivates scientists to consider that the North Atlantic freshwater perturbations is a common trigger of the associated abrupt transitions between weak and strong AMOC states. However, recent studies suggest that the Heinrich ice-surging events are triggered by ocean subsurface warming associated with an AMOC slow-down. Furthermore, the duration of ice-rafting events does not systematically coincide with the beginning and end of the pronounced cold conditions during HSs. In this context, we show that both, changes in atmospheric CO2 and ice sheet configuration can provide important control on the stability of the AMOC, using a coupled atmosphere-ocean model. Our simulations reveal that gradual changes in Northern Hemisphere ice sheet height and atmospheric CO2 can act as a trigger of abrupt glacial/deglacial climate changes. The simulated global climate responses—including abrupt warming in the North Atlantic, a northward shift of the tropical rain belts, and Southern Hemisphere cooling related to the bipolar seesaw—are generally consistent with empirical evidence. We further find that under a delicate configuration of atmospheric CO2 and ice sheet height the AMOC can be characterized by a self-oscillation (resonance) feature (Hopf Bifucation) with a 1000-year cycle that is comparable with observed small DO events during the MIS 3. This provides an alternative explanation for millennial-scale DO variability during glacial periods.

  10. [Prelabour uterine torsion complicated by partial abruption and fetal death].

    PubMed

    Agar, N; Canis, M; Accoceberry, M; Bourdel, N; Lafaye, A-L; Gallot, D

    2014-06-01

    Uterine torsion is a rare obstetrical complication whose diagnosis remains challenging. We report a case of 180 degrees dextrogyre torsion at 36(+5) weeks of gestation complicated by partial abruption and in utero fetal death. Emergency cesarean section was performed through an unintentional posterior hysterotomy. Literature reports a few similar cases. Vertical hysterotomy should be advised in this context avoiding incision on lateral sides associated with increased risk of vascular or ureteral injury. Copyright © 2013 Elsevier Masson SAS. All rights reserved.

  11. Associations between cow hygiene, hock injuries, and free stall usage on US dairy farms.

    PubMed

    Lombard, J E; Tucker, C B; von Keyserlingk, M A G; Kopral, C A; Weary, D M

    2010-10-01

    This cross-sectional study evaluated cow comfort measures in free stall dairies across the United States as part of the National Animal Health Monitoring System's Dairy 2007 study. The study was conducted in 17 states and evaluations were completed between March 5 and September 5, 2007. Assessors recorded hygiene and hock scores, number of cows housed in the pen, the number of cows standing with only the front feet in a stall, standing fully in a stall, and lying in a stall. Facility design measures included bedding type, bedding quantity, stall length and width, presence of a neck rail or brisket locator, and relevant distances from the rear and bed of the stall. Of the 491 operations that completed the cow comfort assessment, 297 had Holstein cows housed in free stalls and were included in this analysis. Negative binomial models were constructed to evaluate the following outcomes: the number of cows that were very dirty, had severe hock injuries, stood with front feet in the stall, stood with all feet in the stall, and were lying in the stall. Hygiene was better on farms that did not tail dock cows compared with those that did (5.7 vs. 8.8% were dirty) and on farms located in the study's west region compared with those located in the east region (5.2 vs. 9.7% were dirty). Severe hock injuries were less common on farms in the west than those in the east (0.5 vs. 4.1%). In addition, severe hock injuries were less common on farms that used dirt as a stall base or sand as bedding compared with farms that did not. A higher percentage of cows was standing with front feet in the stall at higher ambient temperatures (incidence rate ratio=1.016) and as time since feeding increased (incidence rate ratio=1.030). A lower percentage of cows were standing with front feet in the stall when the stalls were shorter and when there were fewer cows per stall. Standing fully in a stall was performed by a higher percentage of cows during the summer than during the spring (13.6 vs. 8

  12. Placental abruption possibly due to parvovirus B19 infection.

    PubMed

    Kawabe, Ayaka; Takai, Yasushi; Tamaru, Jun-Ichi; Samejima, Kouki; Seki, Hiroyuki

    2016-01-01

    There is concern about the development of anemia-associated fetal hydrops associated with maternal parvovirus B19 infection. Parvovirus B19 infection occurs via the globoside (P antigen) receptor, the main glycolipid of erythroid cells, which induces apoptosis. Similar findings have been reported for the P antigen of globoside-containing placental trophoblast cells. A 32-year-old woman was infected with human parvovirus B19 at week 32 of pregnancy, and had severe anemia at week 34. At week 37, an emergency cesarean section was performed because of sudden abdominal pain and fetal bradycardia; placental abruption was found. A live male infant was delivered with no sign of fetal hydrops or fetal infection. Placental tissue was positive for parvovirus B19 according to polymerase chain reaction. Immunohistochemical analysis using caspase-related M30 CytoDEATH monoclonal antibody revealed M30 staining of the placental villous trophoblasts. Placental trophoblasts and erythroid precursor cells have been reported to express globoside (P antigen), which is necessary for parvovirus B19 infectivity, and to show apoptotic activity as a result of infection. Placentas from three other pregnancies with documented abruption showed no M30 staining. The present case strongly suggests an association between placental abruption and apoptosis resulting from parvovirus B19 infection.

  13. Response of seafloor ecosystems to abrupt global climate change

    PubMed Central

    Moffitt, Sarah E.; Hill, Tessa M.; Roopnarine, Peter D.; Kennett, James P.

    2015-01-01

    Anthropogenic climate change is predicted to decrease oceanic oxygen (O2) concentrations, with potentially significant effects on marine ecosystems. Geologically recent episodes of abrupt climatic warming provide opportunities to assess the effects of changing oxygenation on marine communities. Thus far, this knowledge has been largely restricted to investigations using Foraminifera, with little being known about ecosystem-scale responses to abrupt, climate-forced deoxygenation. We here present high-resolution records based on the first comprehensive quantitative analysis, to our knowledge, of changes in marine metazoans (Mollusca, Echinodermata, Arthropoda, and Annelida; >5,400 fossils and trace fossils) in response to the global warming associated with the last glacial to interglacial episode. The molluscan archive is dominated by extremophile taxa, including those containing endosymbiotic sulfur-oxidizing bacteria (Lucinoma aequizonatum) and those that graze on filamentous sulfur-oxidizing benthic bacterial mats (Alia permodesta). This record, from 16,100 to 3,400 y ago, demonstrates that seafloor invertebrate communities are subject to major turnover in response to relatively minor inferred changes in oxygenation (>1.5 to <0.5 mL⋅L−1 [O2]) associated with abrupt (<100 y) warming of the eastern Pacific. The biotic turnover and recovery events within the record expand known rates of marine biological recovery by an order of magnitude, from <100 to >1,000 y, and illustrate the crucial role of climate and oceanographic change in driving long-term successional changes in ocean ecosystems. PMID:25825727

  14. Anticipatory adjustments to abrupt changes of opposing forces.

    PubMed

    Rapp, Katrin; Heuer, Herbert

    2015-01-01

    Anticipatory adjustments to abrupt load changes are based on task-specific predictive information. The authors asked whether anticipatory adjustments to abrupt offsets of horizontal forces are related to expectancy. In two experiments participants held a position against an opposing force or moved against it. At force offset they had to stop rapidly. Duration of the opposing force or distance moved against it varied between blocks of trials and was constant within each block, or it varied from trial to trial. These two variations resulted in opposite changes of the expectancy of force offset with the passage of time or distance. With constant force durations or distances in each block of trials, anticipatory adjustments tended to be poorest with the longest duration or distance, but with variable force durations or distances they tended to be best with the longest duration or distance. Thus anticipatory adjustments were related to expectancy rather than time or distance per se. Anticipatory adjustments resulted in shorter peak amplitudes of the involuntary movements, accompanied by longer movement times in Experiment 1 and faster movement times in Experiment 2. Thus, for different states of the limb at abrupt dynamic changes anticipatory adjustments involve different mechanisms that modulate different mechanical characteristics.

  15. Response of seafloor ecosystems to abrupt global climate change

    NASA Astrophysics Data System (ADS)

    Moffitt, Sarah E.; Hill, Tessa M.; Roopnarine, Peter D.; Kennett, James P.

    2015-04-01

    Anthropogenic climate change is predicted to decrease oceanic oxygen (O2) concentrations, with potentially significant effects on marine ecosystems. Geologically recent episodes of abrupt climatic warming provide opportunities to assess the effects of changing oxygenation on marine communities. Thus far, this knowledge has been largely restricted to investigations using Foraminifera, with little being known about ecosystem-scale responses to abrupt, climate-forced deoxygenation. We here present high-resolution records based on the first comprehensive quantitative analysis, to our knowledge, of changes in marine metazoans (Mollusca, Echinodermata, Arthropoda, and Annelida; >5,400 fossils and trace fossils) in response to the global warming associated with the last glacial to interglacial episode. The molluscan archive is dominated by extremophile taxa, including those containing endosymbiotic sulfur-oxidizing bacteria (Lucinoma aequizonatum) and those that graze on filamentous sulfur-oxidizing benthic bacterial mats (Alia permodesta). This record, from 16,100 to 3,400 y ago, demonstrates that seafloor invertebrate communities are subject to major turnover in response to relatively minor inferred changes in oxygenation (>1.5 to <0.5 mLṡL-1 [O2]) associated with abrupt (<100 y) warming of the eastern Pacific. The biotic turnover and recovery events within the record expand known rates of marine biological recovery by an order of magnitude, from <100 to >1,000 y, and illustrate the crucial role of climate and oceanographic change in driving long-term successional changes in ocean ecosystems.

  16. Acute diabetes insipidus mediated by vasopressinase after placental abruption.

    PubMed

    Wallia, Amisha; Bizhanova, Aigerim; Huang, Wenyu; Goldsmith, Susan L; Gossett, Dana R; Kopp, Peter

    2013-03-01

    Postpartum, diabetes insipidus (DI) can be part of Sheehan's syndrome or lymphocytic hypophysitis in combination with anterior pituitary hormone deficiencies. In contrast, acute onset of isolated DI in the postpartum period is unusual. This patient presented at 33 weeks gestation with placental abruption, prompting a cesarean delivery of twins. Immediately after delivery, she developed severe DI. The DI could be controlled with the vasopressinase-resistant 1-deamino-8-D-arginine vasopressin (DDAVP), but not with arginine vasopressin (AVP), and it resolved within a few weeks. The aim of this study was to demonstrate that the postpartum DI in this patient was caused by the release of placental vasopressinase into the maternal bloodstream. Cells were transiently transfected with the AVP receptor 2 (AVPR2) and treated with either AVP or DDAVP in the presence of the patient's serum collected postpartum or 10 weeks after delivery. The response to the different treatments was evaluated by measuring the activity of a cAMP-responsive firefly luciferase reporter construct. The in vitro studies demonstrate that the patient's postpartum serum disrupts activation of the AVPR2 by AVP, but not by the vasopressinase-resistant DDAVP. Placental abruption can rarely be associated with acute postpartum DI caused by release of placental vasopressinase into the bloodstream. This clinical entity must be considered in patients with placental abruption and when evaluating patients presenting with DI after delivery.

  17. Over-the-wing propeller

    NASA Technical Reports Server (NTRS)

    Johnson, Joseph L., Jr. (Inventor); White, E. Richard (Inventor)

    1986-01-01

    This invention is an aircraft with a system for increasing the lift drag ratio over a broad range of operating conditions. The system positions the engines and nacelles over the wing in such a position that gains in propeller efficiency is achieved simultaneously with increases in wing lift and a reduction in wing drag. Adverse structural and torsional effects on the wings are avoided by fuselage mounted pylons which attach to the upper portion of the fuselage aft of the wings. Similarly, pylon-wing interference is eliminated by moving the pylons to the fuselage. Further gains are achieved by locating the pylon surface area aft of the aircraft center of gravity, thereby augmenting both directional and longitudinal stability. This augmentation has the further effect of reducing the size, weight and drag of empennage components. The combination of design changes results in improved cruise performance and increased climb performance while reducing fuel consumption and drag and weight penalties.

  18. Flexible wings in flapping flight

    NASA Astrophysics Data System (ADS)

    Moret, Lionel; Thiria, Benjamin; Zhang, Jun

    2007-11-01

    We study the effect of passive pitching and flexible deflection of wings on the forward flapping flight. The wings are flapped vertically in water and are allowed to move freely horizontally. The forward speed is chosen by the flapping wing itself by balance of drag and thrust. We show, that by allowing the wing to passively pitch or by adding a flexible extension at its trailing edge, the forward speed is significantly increased. Detailed measurements of wing deflection and passive pitching, together with flow visualization, are used to explain our observations. The advantage of having a wing with finite rigidity/flexibility is discussed as we compare the current results with our biological inspirations such as birds and fish.

  19. Both DNA Polymerases δ and ε Contact Active and Stalled Replication Forks Differently

    PubMed Central

    Yu, Chuanhe; Gan, Haiyun

    2017-01-01

    ABSTRACT Three DNA polymerases, polymerases α, δ, and ε (Pol α, Pol δ, and Pol ε), are responsible for eukaryotic genome duplication. When DNA replication stress is encountered, DNA synthesis stalls until the stress is ameliorated. However, it is not known whether there is a difference in the association of each polymerase with active and stalled replication forks. Here, we show that each DNA polymerase has a distinct pattern of association with active and stalled replication forks. Pol α is enriched at extending Okazaki fragments of active and stalled forks. In contrast, although Pol δ contacts the nascent lagging strands of active and stalled forks, it binds to only the matured (and not elongating) Okazaki fragments of stalled forks. Pol ε has greater contact with the nascent single-stranded DNA (ssDNA) of the leading strand on active forks than on stalled forks. We propose that the configuration of DNA polymerases at stalled forks facilitates the resumption of DNA synthesis after stress removal. PMID:28784720

  20. Numerical investigation of the unsteady tip leakage flow and rotating stall inception in a transonic compressor

    NASA Astrophysics Data System (ADS)

    Zhang, Yanfeng; Lu, Xingen; Chu, Wuli; Zhu, Junqiang

    2010-08-01

    It is well known that tip leakage flow has a strong effect on the compressor performance and stability. This paper reports on a numerical investigation of detailed flow structures in an isolated transonic compressor rotor-NASA Rotor 37 at near stall and stalled conditions aimed at improving understanding of changes in 3D tip leakage flow structures with rotating stall inception. Steady and unsteady 3D Navier-Stokes analyses were conducted to investigate flow structures in the same rotor. For steady analysis, the predicted results agree well with the experimental data for the estimation of compressor rotor global performance. For unsteady flow analysis, the unsteady flow nature caused by the breakdown of the tip leakage vortex in blade tip region in the transonic compressor rotor at near stall condition has been captured with a single blade passage. On the other hand, the time-accurate unsteady computations of multi-blade passage at near stall condition indicate that the unsteady breakdown of the tip leakage vortex triggered the short length-scale — spike type rotating stall inception at blade tip region. It was the forward spillage of the tip leakage flow at blade leading edge resulting in the spike stall inception. As the mass flow ratio is decreased, the rotating stall cell was further developed in the blade passage.

  1. Representative Stall Model of Regional Aircraft for Simulator Training Using a Spline Shape Prescriptive Modeling Approach

    NASA Astrophysics Data System (ADS)

    Zhang, Tony S.

    Loss-of-control following aerodynamic stall remains the largest contributor to fatal civil aviation accidents. Aerodynamic models past stall are required to train pilots on stall recovery techniques using ground-based simulators, which are safe, inexpensive, and accessible. A methodology for creating representative stall models, which capture essential stall characteristics, is being developed for classes of twin-turboprop commuter and twin-engine regional jet aircraft. Despite having lower fidelity than type specific stall models generated from wind tunnel, flight test, and/or CFD studies data, these models are configuration adjustable and significantly cheaper to construct for high angle-of-attack regimes. Baseline specific stall models are modified to capture changes in aerodynamic coefficients due to configuration variations from a baseline to a target aircraft. A Shape Prescriptive Modeling approach combining existing theory and data using least-squares splines is used to make coefficient change predictions. Initial results are satisfactory and suggest that representative models are suitable for stall training.

  2. Evaluating Classroom Interaction with the iPad®: An Updated Stalling's Tool

    ERIC Educational Resources Information Center

    MacKinnon, Gregory; Schep, Lourens; Borden, Lisa Lunney; Murray-Orr, Anne; Orr, Jeff; MacKinnon, Paula

    2016-01-01

    A large study of classrooms in the Caribbean context necessitated the use of a validated classroom observation tool. In practice, the paper-version Stalling's instrument (Stallings & Kaskowitz 1974) presented specific challenges with respect to (a) facile data collection and (b) qualitative observations of classrooms. In response to these…

  3. Wind Tunnel Pressure Distribution Tests on a Series of Biplane Wing Models. Part III Effects of Charges in Various Combinations of Stagger, Gap, Sweepback, and Decalage

    NASA Technical Reports Server (NTRS)

    Knight, Montgomery; Noyes, Richard W

    1929-01-01

    This preliminary report furnishes information on the changes in the forces on each wing of a biplane cellule for various combinations of stagger and gap, stagger and sweepback, stagger and decalage, and gap and decalage. The data were obtained from pressure distribution tests made in the atmospheric wind tunnel of the Langley Memorial Aeronautical Laboratory. Since each test was carried up to 90deg angle of attack, the results may be used in the study of stalled flight and of spinning as well as in the structural design of biplane wings.

  4. Wing flapping with minimum energy

    NASA Technical Reports Server (NTRS)

    Jones, R. T.

    1980-01-01

    A technique employed by Prandtl and Munk is adapted for the case of a wing in flapping motion to determine its lift distribution. The problem may be reduced to one of minimizing induced drag for a specified and periodically varying bending moment at the wing root. It is concluded that two wings in close tandem arrangement, moving in opposite phase, would eliminate the induced aerodynamic losses calculated

  5. 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.

  6. Quiet Clean Short-haul Experimental Engine (QCSEE): The aerodynamic and mechanical design of the QCSEE under-the-wing fan

    NASA Technical Reports Server (NTRS)

    1977-01-01

    The design, fabrication, and testing of two experimental high bypass geared turbofan engines and propulsion systems for short haul passenger aircraft are described. The aerodynamic and mechanical design of a variable pitch 1.34 pressure ratio fan for the under the wing (UTW) engine are included. The UTW fan was designed to permit rotation of the 18 composite fan blades into the reverse thrust mode of operation through both flat pitch and stall pitch directions.

  7. Atmospheric CO2 and abrupt climate change on submillennial timescales

    NASA Astrophysics Data System (ADS)

    Ahn, Jinho; Brook, Edward

    2010-05-01

    How atmospheric CO2 varies and is controlled on various time scales and under various boundary conditions is important for understanding how the carbon cycle and climate change are linked. Ancient air preserved in ice cores provides important information on past variations in atmospheric CO2. In particular, concentration records for intervals of abrupt climate change may improve understanding of mechanisms that govern atmospheric CO2. We present new multi-decadal CO2 records that cover Greenland stadial 9 (between Dansgaard-Oeschger (DO) events 8 and 9) and the abrupt cooling event at 8.2 ka. The CO2 records come from Antarctic ice cores but are well synchronized with Greenland ice core records using new high-resolution CH4 records,precisely defining the timing of CO2 change with respect to abrupt climate events in Greenland. Previous work showed that during stadial 9 (40~38 ka), CO2 rose by about 15~20 ppm over around 2,000 years, and at the same time temperatures in Antarctica increased. Dust proxies indicate a decrease in dust flux over the same period. With more detailed data and better age controls we now find that approximately half of the CO2 increase during stadial 9 occurred abruptly, over the course of decades to a century at ~39.6 ka. The step increase of CO2 is synchronous with a similar step increase of Antarctic isotopic temperature and a small abrupt change in CH4, and lags after the onset of decrease in dust flux by ~400 years. New atmospheric CO2 records at the well-known ~8.2 ka cooling event were obtained from Siple Dome ice core, Antarctica. Our preliminary CO2 data span 900 years and include 19 data points within the 8.2 ka cooling event, which persisted for ~160 years (Thomas et al., Quarternary Sci. Rev., 2007). We find that CO2 increased by 2~4 ppm during that cooling event. Further analyses will improve the resolution and better constrain the CO2 variability during other times in the early Holocene to determine if the variations observed

  8. Wider stall space affects behavior, lesion scores, and productivity of gestating sows.

    PubMed

    Salak-Johnson, J L; DeDecker, A E; Levitin, H A; McGarry, B M

    2015-10-01

    Limited space allowance within the standard gestation stall is an important welfare concern because it restricts the ability of the sow to make postural adjustments and hinders her ability to perform natural behaviors. Therefore, we evaluated the impacts of increasing stall space and/or providing sows the freedom to access a small pen area on sow well-being using multiple welfare metrics. A total of 96 primi- and multiparous crossbred sows were randomly assigned in groups of 4 sows/treatment across 8 replicates to 1 of 3 stall treatments (TRT): standard stall (CTL; dimensions: 61 by 216 cm), width-adjustable stall (flex stall [FLX]; dimensions: adjustable width of 56 to 79 cm by 216 cm), or an individual walk-in/lock-in stall with access to a small communal open-pen area at the rear of the stall (free-access stall [FAS]; dimensions: 69 by 226 cm). Lesion scores, behavior, and immune and productivity traits were measured at various gestational days throughout the study. Total lesion scores were greatest for sows in FAS and least for sows in FLX ( < 0.001). Higher-parity sows in FAS had the most severe lesion scores (TRT × parity, < 0.0001) and scores were greatest at all gestational days (TRT × day, < 0.05). Regardless of parity, sows in FLX had the least severe scores ( < 0.0001). As pregnancy progressed, lesion scores increased among sows in CTL ( < 0.05). Sow BW and backfat (BF) were greater for sows in FLX and FAS ( < 0.05), and BCS and BF were greater for parity 1 and 2 sows in FAS than the same parity sows in CTL (TRT × parity, < 0.05). Duration and frequency of some postural behaviors and sham chew behavior were affected by TRT ( < 0.05) and time of day (TRT × day, < 0.05). These data indicate that adequate stall space, especially late in gestation, may improve the well-being of higher-parity and heavier-bodied gestating sows as assessed by changes in postural behaviors, lesion severity scores, and other sow traits. Moreover, compromised welfare measures

  9. A theory of post-stall transients in axial compression systems. II - Application

    NASA Technical Reports Server (NTRS)

    Greitzer, E. M.; Moore, F. K.

    1985-01-01

    Using the theory developed in Part I, calculations have been carried out to show the evolution of the mass flow, pressure rise, and rotating-stall cell amplitude during compression system post-stall transients. In particular, it is shown that the unsteady growth or decay of the stall cell can have a significant effect on the instantaneous compressor pumping characteristic and hence on the overall system behavior. A limited parametric study is carried out to illustrate the impact of different system features on transient behavior. It is shown, for example, that the ultimate mode of system response, surge or stable rotating stall, depends not only on the B parameter, but also on the compressor length-to-radius ratio. Small values of this latter quantity tend to favor the occurrence of surge, as do large values of B. Based on the analytical and numerical results, several specific topics are suggested for future research on post-stall transients.

  10. Preliminary analysis of dynamic stall effects on a 91-meter wind turbine rotor

    NASA Technical Reports Server (NTRS)

    Wilson, Robert E.

    1995-01-01

    Analytical investigation of dynamic stall on HAWT (horizontal-axis wind turbines) rotor loads was conducted. Dynamic stall was modeled using the Gormont approach on the MOD-2 rotor, treating the blade as a rigid body teetering about a fixed axis. Blade flapwise bending moments at station 370 were determined with and without dynamic stall for spatial variations in local wind speed due to wind shear and yaw. The predicted mean flapwise bending moments were found to be in good agreement with test results. Results obtained with and without dynamic stall showed no significant difference for the mean flapwise bending moment. The cyclic bending moments calculated with and without dynamic stall effects were substantially the same. None of the calculated cyclic loads reached the level of the cyclic loads measured on the MOD-2 using the Boeing five-minute-average technique.

  11. RFWD3-Dependent Ubiquitination of RPA Regulates Repair at Stalled Replication Forks.

    PubMed

    Elia, Andrew E H; Wang, David C; Willis, Nicholas A; Boardman, Alexander P; Hajdu, Ildiko; Adeyemi, Richard O; Lowry, Elizabeth; Gygi, Steven P; Scully, Ralph; Elledge, Stephen J

    2015-10-15

    We have used quantitative proteomics to profile ubiquitination in the DNA damage response (DDR). We demonstrate that RPA, which functions as a protein scaffold in the replication stress response, is multiply ubiquitinated upon replication fork stalling. Ubiquitination of RPA occurs on chromatin, involves sites outside its DNA binding channel, does not cause proteasomal degradation, and increases under conditions of fork collapse, suggesting a role in repair at stalled forks. We demonstrate that the E3 ligase RFWD3 mediates RPA ubiquitination. RFWD3 is necessary for replication fork restart, normal repair kinetics during replication stress, and homologous recombination (HR) at stalled replication forks. Mutational analysis suggests that multisite ubiquitination of the entire RPA complex is responsible for repair at stalled forks. Multisite protein group sumoylation is known to promote HR in yeast. Our findings reveal a similar requirement for multisite protein group ubiquitination during HR at stalled forks in mammalian cells. Copyright © 2015 Elsevier Inc. All rights reserved.

  12. Numerical investigation of the aerodynamic and structural characteristics of a corrugated wing

    NASA Astrophysics Data System (ADS)

    Hord, Kyle

    Previous experimental studies on static, bio-inspired corrugated wings have shown that they produce favorable aerodynamic properties such as delayed stall compared to streamlined wings and flat plates at high Reynolds numbers (Re ≥ 4x104). The majority of studies have been carried out with scaled models of dragonfly forewings from the Aeshna Cyanea in either wind tunnels or water channels. In this thesis, the aerodynamics of a corrugated airfoil was studied using computational fluid dynamics methods at a low Reynolds number of 1000. Structural analysis was also performed using the commercial software SolidWorks 2009. The flow field is described by solving the incompressible Navier-Stokes equations on an overlapping grid using the pressure-Poisson method. The equations are discretized in space with second-order accurate central differences. Time integration is achieved through the second-order Crank-Nicolson implicit method. The complex vortex structures that form in the corrugated airfoil valleys and around the corrugated airfoil are studied in detail. Comparisons are made with experimental measurements from corrugated wings and also with simulations of a flat plate. Contrary to the studies at high Reynolds numbers, our study shows that at low Reynolds numbers the wing corrugation does not provide any aerodynamic benefit compared to a smoothed flat plate. Instead, the corrugated profile generates more pressure drag which is only partially offset by the reduction of friction drag, leading to more total drag than the flat plate. Structural analysis shows that the wing corrugation can increase the resistance to bending moments on the wing structure. A smoothed structure has to be three times thicker to provide the same stiffness. It was concluded the corrugated wing has the structural benefit to provide the same resistance to bending moments with a much reduced weight.

  13. Experimental investigation of vortices shed by various wing fin configurations. M.S. Thesis. Final Report

    NASA Technical Reports Server (NTRS)

    Iversen, J.; Moghadam, M.

    1981-01-01

    Forty-six different fins, which were members of twelve plan-form families, were tested. A two dimensional Boeing single element airfoil at an angle of attack of eight degrees and a sweepback angle of thirty-two was used to simulate a portion of the wing of a generator aircraft. Various free stream velocities were used to test any individual fin at its particular angle of attack. While the fin itself was mounted on the upper surface of the generator model, the angle of attack of each fin was varied until stall was reached and/or passed. The relative fin vortex strengths were measured in two ways. First, the maximum angular velocity of a four blade rotor placed in the fin vortex center was measured with the use of a stroboscope. Second, the maximum rolling moment on a following wing model placed in the fin vortex center was measured by a force balance.

  14. Power and efficiency analysis of a flapping wing wind energy harvester

    NASA Astrophysics Data System (ADS)

    Bryant, Matthew; Shafer, Michael W.; Garcia, Ephrahim

    2012-04-01

    Energy harvesting from flowing fluids using flapping wings and fluttering aeroelastic structures has recently gained significant research attention as a possible alternative to traditional rotary turbines, especially at and below the centimeter scale. One promising approach uses an aeroelastic flutter instability to drive limit cycle oscillations of a flexible piezoelectric energy harvesting structure. Such a system is well suited to miniaturization and could be used to create self-powered wireless sensors wherever ambient flows are available. In this paper, we examine modeling of the aerodynamic forces, power extraction, and efficiency of such a flapping wing energy harvester at a low Reynolds number on the order of 1000. Two modeling approaches are considered, a quasi-steady method generalized from existing models of insect flight and a modified model that includes terms to account to the effects of dynamic stall. The modified model is shown to provide better agreement with CFD simulations of a flapping energy harvester.

  15. Finding Intervals of Abrupt Change in Earth Science Data

    NASA Astrophysics Data System (ADS)

    Zhou, X.; Shekhar, S.; Liess, S.

    2011-12-01

    In earth science data (e.g., climate data), it is often observed that a persistently abrupt change in value occurs in a certain time-period or spatial interval. For example, abrupt climate change is defined as an unusually large shift of precipitation, temperature, etc, that occurs during a relatively short time period. A similar pattern can also be found in geographical space, representing a sharp transition of the environment (e.g., vegetation between different ecological zones). Identifying such intervals of change from earth science datasets is a crucial step for understanding and attributing the underlying phenomenon. However, inconsistencies in these noisy datasets can obstruct the major change trend, and more importantly can complicate the search of the beginning and end points of the interval of change. Also, the large volume of data makes it challenging to process the dataset reasonably fast. In earth science data (e.g., climate data), it is often observed that a persistently abrupt change in value occurs in a certain time-period or spatial interval. For example, abrupt climate change is defined as an unusually large shift of precipitation, temperature, etc, that occurs during a relatively short time period. A similar change pattern can also be found in geographical space, representing a sharp transition of the environment (e.g., vegetation between different ecological zones). Identifying such intervals of change from earth science datasets is a crucial step for understanding and attributing the underlying phenomenon. However, inconsistencies in these noisy datasets can obstruct the major change trend, and more importantly can complicate the search of the beginning and end points of the interval of change. Also, the large volume of data makes it challenging to process the dataset fast. In this work, we analyze earth science data using a novel, automated data mining approach to identify spatial/temporal intervals of persistent, abrupt change. We first

  16. Analysis of unswept and swept wing chordwise pressure data from an oscillating NACA 0012 airfoil experiment. Volume 1: Technical Report

    NASA Technical Reports Server (NTRS)

    St.hilaire, A. O.; Carta, F. O.

    1983-01-01

    The unsteady chordwise force response on the airfoil surface was investigated and its sensitivity to the various system parameters was examined. A further examination of unsteady aerodynamic data on a tunnel spanning wing (both swept and unswept), obtained in a wind tunnel, was performed. The main body of this data analysis was carried out by analyzing the propagation speed of pressure disturbances along the chord and by studying the behavior of the unsteady part of the chordwise pressure distribution at various points of the airfoil pitching cycle. It was found that Mach number effects dominate the approach to and the inception of both static and dynamic stall. The stall angle decreases as the Mach number increases. However, sweep dominates the load behavior within the stall regime. Large phase differences between unswept and swept responses, that do not exist at low lift coefficient, appear once the stall boundary is penetrated. It was also found that reduced frequency is not a reliable indicator of the unsteady aerodynamic response in the high angle of attack regime.

  17. Control of Flow Structure on Non-Slender Delta Wing: Bio-inspired Edge Modifications, Passive Bleeding, and Pulsed Blowing

    NASA Astrophysics Data System (ADS)

    Yavuz, Mehmet Metin; Celik, Alper; Cetin, Cenk

    2016-11-01

    In the present study, different flow control approaches including bio-inspired edge modifications, passive bleeding, and pulsed blowing are introduced and applied for the flow over non-slender delta wing. Experiments are conducted in a low speed wind tunnel for a 45 degree swept delta wing using qualitative and quantitative measurement techniques including laser illuminated smoke visualization, particle image velocimety (PIV), and surface pressure measurements. For the bio-inspired edge modifications, the edges of the wing are modified to dolphin fluke geometry. In addition, the concept of flexion ratio, a ratio depending on the flexible length of animal propulsors such as wings, is introduced. For passive bleeding, directing the free stream air from the pressure side of the planform to the suction side of the wing is applied. For pulsed blowing, periodic air injection through the leading edge of the wing is performed in a square waveform with 25% duty cycle at different excitation frequencies and compared with the steady and no blowing cases. The results indicate that each control approach is quite effective in terms of altering the overall flow structure on the planform. However, the success level, considering the elimination of stall or delaying the vortex breakdown, depends on the parameters in each method.

  18. Horizontal axis wind turbine post stall airfoil characteristics synthesization

    NASA Technical Reports Server (NTRS)

    Tangler, James L.; Ostowari, Cyrus

    1995-01-01

    Blade-element/momentum performance prediction codes are routinely used for wind turbine design and analysis. A weakness of these codes is their inability to consistently predict peak power upon which the machine structural design and cost are strongly dependent. The purpose of this study was to compare post-stall airfoil characteristics synthesization theory to a systematically acquired wind tunnel data set in which the effects of aspect ratio, airfoil thickness, and Reynolds number were investigated. The results of this comparison identified discrepancies between current theory and the wind tunnel data which could not be resolved. Other factors not previously investigated may account for these discrepancies and have a significant effect on peak power prediction.

  19. Dynamic stall study of a multi-element airfoil

    NASA Technical Reports Server (NTRS)

    Tung, Chee; Mcalister, Kenneth W.; Wang, Clin M.

    1992-01-01

    Unsteady flow behavior and load characteristics of a VR-7 airfoil with and without a slat were studied in the water tunnel of the Aeroflightdynamics Directorate, NASA Ames Research Center. Both airfoils were oscillated sinusoidally between 5 and 25 degrees at a Reynolds number of 200,000 to obtain the unsteady lift, drag and pitching moment data. A fluorescing dye was released from an orifice located at the leading edge of the airfoil for the purpose of visualizing the boundary layer and wake flow. The flow field and load predictions of an incompressible Navier-Stokes code based on a velocity-vorticity formulation were compared with the test data. The test and predictions both confirm that the slatted VR-7 airfoil delays both static and dynamic stall as compared to the VR-7 airfoil alone.

  20. Stall flutter experiment in a transonic oscillating linear cascade

    NASA Technical Reports Server (NTRS)

    Boldman, D. R.; Buggele, A. E.; Michalson, G. M.

    1981-01-01

    Two dimensional biconvex airfoils were oscillated at reduced frequencies up to 0.5 based on semi-chord and a free stream Mach number of 0.80 to simulate transonic stall flutter in rotors. Steady-state periodicity was confirmed through end-wall pressure measurements, exit flow traverses, and flow visualization. The initial flow visualization results from flutter tests indicated that the oscillating shock on the airfoils lagged the airfoil motion by as much as 80 deg. These initial data exhibited an appreciable amount of scatter; however, a linear fit of the results indicated that the greatest shock phase lag occurred at a positive interblade phase angle. Photographs of the steady-state and unsteady flow fields reveal some of the features of the lambda shock wave on the suction surface of the airfoils.

  1. Subsychronous vibration of multistage centrifugal compressors forced by rotating stall

    NASA Technical Reports Server (NTRS)

    Fulton, J. W.

    1987-01-01

    A multistage centrifugal compressor, in natural gas re-injection service on an offshore petroleum production platform, experienced subsynchronous vibrations which caused excessive bearing wear. Field performance testing correlated the subsynchronous amplitude with the discharge flow coefficient, demonstrating the excitation to be aerodynamic. Adding two impellers allowed an increase in the diffuser flow angle (with respect to tangential) to meet the diffuser stability criteria based on factory and field tests correlated using the theory of Senoo (for rotating stall in a vaneless diffuser). This modification eliminated all significant subsynchronous vibrations in field service, thus confirming the correctness of the solution. Other possible sources of aerodynamically induced vibrations were considered, but the judgment that those are unlikely has been confirmed by subsequent experience with other similar compressors.

  2. Freight Wing Trailer Aerodynamics

    SciTech Connect

    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,more » 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.« less

  3. Reversible stalling of transcription elongation complexes by high pressure.

    PubMed

    Erijman, L; Clegg, R M

    1998-07-01

    We have investigated the effect of high hydrostatic pressure on the stability of RNA polymerase molecules during transcription. RNA polymerase molecules participating in stalled or active ternary transcribing complexes do not dissociate from the template DNA and nascent RNA at pressures up to 180 MPa. A lower limit for the free energy of stabilization of an elongating ternary complex relative to the quaternary structure of the free RNAP molecules is estimated to be 20 kcal/mol. The rate of elongation decreases at high pressure; transcription completely halts at sufficiently high pressure. The overall rate of elongation has an apparent activation volume (DeltaVdouble dagger) of 55-65 ml . mol-1 (at 35 degrees C). The pressure-stalled transcripts are stable and resume elongation at the prepressure rate upon decompression. The efficiency of termination decreases at the rho-independent terminator tR2 after the transcription reaction has been exposed to high pressure. This suggests that high pressure modifies the ternary complex such that termination is affected in a manner different from that of elongation. The solvent and temperature dependence of the pressure-induced inhibition show evidence for major conformational changes in the core polymerase enzyme during RNA synthesis. It is proposed that the inhibition of the elongation phase of the transcription reaction at elevated pressures is related to a reduction of the partial specific volume of the RNA polymerase molecule; under high pressure, the RNA polymerase molecule does not have the necessary structural flexibility required for the protein to translocate.

  4. Pegasus ICON Wing Arrival

    NASA Image and Video Library

    2017-02-22

    The wing for the Orbital ATK Pegasus XL rocket arrives by truck at Building 1555 at Vandenberg Air Force Base in California. The Pegasus rocket is being prepared for NASA's Ionospheric Connection Explorer, or ICON, mission. ICON will launch from the Kwajalein Atoll aboard the Pegasus XL on Dec. 8, 2017. ICON will study the frontier of space - the dynamic zone high in Earth's atmosphere where terrestrial weather from below meets space weather above. The explorer will help determine the physics of Earth's space environment and pave the way for mitigating its effects on our technology, communications systems and society.

  5. Pegasus ICON Wing Arrival

    NASA Image and Video Library

    2017-02-22

    Workers unload the wing for the Orbital ATK Pegasus XL rocket from a truck at Building 1555 at Vandenberg Air Force Base in California. The rocket is being prepared for NASA's Ionospheric Connection Explorer, or ICON, mission. ICON will launch from the Kwajalein Atoll aboard the Pegasus XL on Dec. 8, 2017. ICON will study the frontier of space - the dynamic zone high in Earth's atmosphere where terrestrial weather from below meets space weather above. The explorer will help determine the physics of Earth's space environment and pave the way for mitigating its effects on our technology, communications systems and society.

  6. Pegasus ICON Wing Arrival

    NASA Image and Video Library

    2017-02-22

    Workers transfer the wing for the Orbital ATK Pegasus XL rocket from a truck to a forklift at Building 1555 at Vandenberg Air Force Base in California. The rocket is being prepared for NASA's Ionospheric Connection Explorer, or ICON, mission. ICON will launch from the Kwajalein Atoll aboard the Pegasus XL on Dec. 8, 2017. ICON will study the frontier of space - the dynamic zone high in Earth's atmosphere where terrestrial weather from below meets space weather above. The explorer will help determine the physics of Earth's space environment and pave the way for mitigating its effects on our technology, communications systems and society.

  7. Pegasus ICON Wing Arrival

    NASA Image and Video Library

    2017-02-22

    The wing for the Orbital ATK Pegasus XL rocket was offloaded from a truck and transporter to Building 1555 at Vandenberg Air Force Base in California. The rocket is being prepared for NASA's Ionospheric Connection Explorer, or ICON, mission. ICON will launch from the Kwajalein Atoll aboard the Pegasus XL on Dec. 8, 2017. ICON will study the frontier of space - the dynamic zone high in Earth's atmosphere where terrestrial weather from below meets space weather above. The explorer will help determine the physics of Earth's space environment and pave the way for mitigating its effects on our technology, communications systems and society.

  8. Nonlinear aerodynamic wing design

    NASA Technical Reports Server (NTRS)

    Bonner, Ellwood

    1985-01-01

    The applicability of new nonlinear theoretical techniques is demonstrated for supersonic wing design. The new technology was utilized to define outboard panels for an existing advanced tactical fighter model. Mach 1.6 maneuver point design and multi-operating point compromise surfaces were developed and tested. High aerodynamic efficiency was achieved at the design conditions. A corollary result was that only modest supersonic penalties were incurred to meet multiple aerodynamic requirements. The nonlinear potential analysis of a practical configuration arrangement correlated well with experimental data.

  9. Prevalence of lameness among dairy cattle in Wisconsin as a function of housing type and stall surface.

    PubMed

    Cook, Nigel B

    2003-11-01

    To determine the prevalence of lameness as a function of season (summer vs winter), housing type (free stalls vs tie stalls), and stall surface (sand vs any other surface) among lactating dairy cows in Wisconsin. Epidemiologic survey. 3,621 lactating dairy cows in 30 herds. Herds were visited once during the summer and once during the winter, and a locomotion score ranging from 1 (no gait abnormality) to 4 (severe lameness) was assigned to all lactating cows. Cows with a score of 3 or 4 were considered to be clinically lame. Mean +/- SD herd lameness prevalence was 21.1 +/- 10.5% during the summer and 23.9 +/- 10.7% during the winter; these values were significantly different. During the winter, mean prevalence of lameness in free-stall herds with non-sand stall surfaces (33.7%) was significantly higher than prevalences in free-stall herds with sand stall surfaces (21.2%), tie-stall herds with non-sand stall surfaces (21.7%), and tie-stall herds with sand stall surfaces (12.1%). Results suggest that the prevalence of lameness among dairy cattle in Wisconsin is higher than previously thought and that lameness prevalence is associated with season, housing type, and stall surface.

  10. Aeroelastic Wing Shaping Using Distributed Propulsion

    NASA Technical Reports Server (NTRS)

    Nguyen, Nhan T. (Inventor); Reynolds, Kevin Wayne (Inventor); Ting, Eric B. (Inventor)

    2017-01-01

    An aircraft has wings configured to twist during flight. Inboard and outboard propulsion devices, such as turbofans or other propulsors, are connected to each wing, and are spaced along the wing span. A flight controller independently controls thrust of the inboard and outboard propulsion devices to significantly change flight dynamics, including changing thrust of outboard propulsion devices to twist the wing, and to differentially apply thrust on each wing to change yaw and other aspects of the aircraft during various stages of a flight mission. One or more generators can be positioned upon the wing to provide power for propulsion devices on the same wing, and on an opposite wing.

  11. Butterflies regulate wing temperatures using radiative cooling

    NASA Astrophysics Data System (ADS)

    Tsai, Cheng-Chia; Shi, Norman Nan; Ren, Crystal; Pelaez, Julianne; Bernard, Gary D.; Yu, Nanfang; Pierce, Naomi

    2017-09-01

    Butterfly wings are live organs embedded with multiple sensory neurons and, in some species, with pheromoneproducing cells. The proper function of butterfly wings demands a suitable temperature range, but the wings can overheat quickly in the sun due to their small thermal capacity. We developed an infrared technique to map butterfly wing temperatures and discovered that despite the wings' diverse visible colors, regions of wings that contain live cells are the coolest, resulting from the thickness of the wings and scale nanostructures. We also demonstrated that butterflies use behavioral traits to prevent overheating of their wings.

  12. Overview: Performance Adaptive Aeroelastic Wing

    NASA Technical Reports Server (NTRS)

    Hashemi, Kelley

    2017-01-01

    An overview of recent aeroelasitc wing-shaping work at the NASA Ames Research Center is presented. The highlight focuses on activity related to the Performance Adaptive Aeroelastic Wing concept and related Variable Camber Continuous Trailing Edge Flap actuation system. Topics covered include drag-reducing configurations and online algorithms, gust and maneuver load techniques, and wind tunnel demonstrations.

  13. X-31 wing removal

    NASA Image and Video Library

    1995-05-18

    U.S. and German personnel of the X-31 Enhanced Fighter Maneuverability Technology Demonstrator aircraft program removing the right wing of the aircraft, which was ferried from Edwards Air Force Base, California, to Europe on May 22, 1995 aboard an Air Force Reserve C-5 transport. The X-31, based at the NASA Dryden Flight Research Center was ferried to Europe and flown in the Paris Air Show in June. The wing of the X-31 was removed on May 18, 1995, to allow the aircraft to fit inside the C-5 fuselage. Officials of the X-31 project used Manching, Germany, as a staging base to prepare the aircraft for the flight demonstration. At the air show, the X-31 demonstrated the value of using thrust vectoring (directing engine exhaust flow) coupled with advanced flight control systems to provide controlled flight at very high angles of attack. The aircraft arrived back at Edwards in a Air Force Reserve C-5 on June 25, 1995 and off loaded at Dryden June 27. The X-31 aircraft was developed jointly by Rockwell International's North American Aircraft Division (now part of Boeing) and Daimler-Benz Aerospace (formerly Messerschmitt-Bolkow-Blohm), under sponsorship by the U.S. Department of Defense and the German Federal Ministry of Defense.

  14. Beetle wings are inflatable origami

    NASA Astrophysics Data System (ADS)

    Chen, Rui; Ren, Jing; Ge, Siqin; Hu, David

    2015-11-01

    Beetles keep their wings folded and protected under a hard shell. In times of danger, they must unfold them rapidly in order for them to fly to escape. Moreover, they must do so across a range of body mass, from 1 mg to 10 grams. How can they unfold their wings so quickly? We use high-speed videography to record wing unfolding times, which we relate to the geometry of the network of blood vessels in the wing. Larger beetles have longer unfolding times. Modeling of the flow of blood through the veins successfully accounts for the wing unfolding speed of large beetles. However, smaller beetles have anomalously short unfolding times, suggesting they have lower blood viscosity or higher driving pressure. The use of hydraulics to unfold complex objects may have implications in the design of micro-flying air vehicles.

  15. Use of impact testing to predict softness, cow preference, and hardening over time of stall bases.

    PubMed

    Fulwider, W K; Palmer, R W

    2004-09-01

    The objective of this study was to assess the softness and durability of commercially available free-stall bases, and to determine the relationship of stall base softness to cow preference. Clegg impact values were recorded at the University of Wisconsin-Madison Arlington Agricultural Research Station on June 19, 2002, and again on July 24, 2003. The Clegg Impact Soil Tester (model 95051, Lafayette Instruments, Lafayette, IN) with a 20-kg hammer was used in this study. The impact of the hammer on the free-stall base results in a digital display based on peak deceleration of the hammer's impact with the free-stall base in tens of gravities (CIV/H). The CIV/H value, as measured by the Clegg Impact hammer, is based on peak deceleration of the 20-kg hammer's impact with the surface, from a height of 30 cm. Clegg impact measures were highly correlated with cow preference measurements. This relationship suggests that Clegg impact measures of compressibility were good indicators for predicting stall-base acceptance. A cork mattress, 4 foam mattresses, 4 rubber mattresses, 4 rubber mats, and a waterbed were evaluated in this study. Foam-based mattresses lost cushioning ability faster than rubber mattresses or rubber mats. Clegg impact values increased over the 13-mo time period for most stall base types, which indicated a tendency of stall bases to harden.

  16. A comparison of free-stall barns used by modernized Wisconsin dairies.

    PubMed

    Bewley, J; Palmer, R W; Jackson-Smith, D B

    2001-02-01

    A primary objective of the Wisconsin Dairy Modernization Survey was to compare features of free-stall barns available to dairy producers. This study used data from a large random sample of expanding dairy farms to determine whether the theoretical benefits of particular free-stall configurations bear out under on-farm conditions. Comparisons were made among herds using free-stall barns as their primary housing for new versus remodeled facilities, barn design, bedding used, feed-delivery design, manure removal strategies, animal restraint, maternity areas, overcrowding, and cooling methods. Producers who made the transition from tie-stall housing to free-stall housing were satisfied with this decision. New free-stall barns provided a more desirable environment for the herds than remodeled free-stall barns, although initial investments were higher. When new free-stall barns were compared, herds with four-row barns had higher production, lower somatic cell count, and higher stocking rates than herds with six-row barns. Respondents were more satisfied with four- and six-row barns than with two- and three-row barns. Respondents felt sand provided some advantages for cow comfort, while satisfaction with bedding cost and manure handling was higher with mattresses. Dairy Herd Improvement data showed no difference in milk production or somatic cell count for producers who chose sand or mattress-based free stalls. Respondents were more satisfied with the use of drive-through feeding than other feed-delivery designs. Most producers chose to use tractor scrapers to remove manure; however, producers who used automated systems were more satisfied with manure management. Few differences were observed when comparing self-locking head gates to palpation rails. Overcrowding did not have any adverse affect on production or user satisfaction with feed intake or cow comfort. Using supplemental cooling appeared to facilitate higher production.

  17. Experimental investigation on the effects of non-cyclical frequency and amplitude variation on dynamic stall

    NASA Astrophysics Data System (ADS)

    Heintz, Kyle C.

    An experimental study of a cambered airfoil undergoing non-cyclical, transient pitch trajectories and the resulting effects on the dynamic stall phenomenon is presented. Surface pressure measurements and airfoil incidence angle are acquired simultaneously to resolve instantaneous aerodynamic load coefficients at Mach numbers ranging from 0.2 to 0.4. Derived from these coefficients are various formulations of the aerodynamic damping factor, referred to copiously throughout. Using a two-motor mechanism, each providing independent frequency and amplitude input to the airfoil, unique pitch motions can be implemented by actively controlling the phase between inputs. This work primarily focuses on three pitch motion schemas, the first of which is a "chirp" style trajectory featuring concurrent exponential frequency growth and amplitude decay. Second, these parameters are tested separately to determine their individual contributions. Lastly, a novel dual harmonic pitch motion is devised which rapidly traverses dynamic stall regimes on an inter-cycle basis by modulating the static-stall penetration angle. Throughout all results presented, there is evidence that for consecutive pitch-cycles, the process of dynamic stall is affected when prior oscillations prior have undergone deeper stall-penetration angles. In other words when stall-penetration is descending, retreating from a regime of light or deep stall, statistics of load coefficients, such as damping coefficient, maximum lift, minimum quarter-chord moment, and their phase relationships, do not match the values seen when stall-penetration was growing. The outcomes herein suggest that the airfoil retains some memory of previous flow separation which has the potential to change the influence of the dynamic stall vortex.

  18. Control of Flow Structure on Low Swept Delta Wing with Steady Leading Edge Blowing

    NASA Astrophysics Data System (ADS)

    Ozturk, Ilhan; Zharfa, Mohammadreza; Yavuz, Mehmet Metin

    2014-11-01

    Interest in unmanned combat air vehicles (UCAVs) and micro air vehicles (MAVs) has stimulated investigation of the flow structure, as well as its control, on delta wings having low and moderate values of sweep angle. In the present study, the flow structure is characterized on a delta wing of low sweep 35-degree angle, which is subjected to steady leading edge blowing. The techniques of laser illuminated smoke visualization, laser Doppler anemometry (LDA), and surface pressure measurements are employed to investigate the steady and unsteady nature of the flow structure on delta wing, in relation to the dimensionless magnitude of the blowing coefficient. Using statistics and spectral analysis, unsteadiness of the flow structure is studied in detail. Different injection locations are utilized to apply different blowing patterns in order to identify the most efficient control, which provides the upmost change in the flow structure with the minimum energy input. The study aims to find the optimum flow control strategy to delay or to prevent the stall and possibly to reduce the buffeting on the wing surface. Since the blowing set-up is computer controlled, the unsteady blowing patterns compared to the present steady blowing patterns will be studied next. This project was supported by the Scientific and Technological Research Council of Turkey (Project Number: 3501 111M732).

  19. Pressure measurements on a rectangular wing with a NACA0012 airfoil during conventional flutter

    NASA Technical Reports Server (NTRS)

    Rivera, Jose A., Jr.; Dansberry, Bryan E.; Durham, Michael H.; Bennett, Robert M.; Silva, Walter A.

    1992-01-01

    The Structural Dynamics Division at NASA LaRC has started a wind tunnel activity referred to as the Benchmark Models Program. The primary objective of the program is to acquire measured dynamic instability and corresponding pressure data that will be useful for developing and evaluating aeroelastic type CFD codes currently in use or under development. The program is a multi-year activity that will involve testing of several different models to investigate various aeroelastic phenomena. The first model consisted of a rigid semispan wing having a rectangular planform and a NACA 0012 airfoil shape which was mounted on a flexible two degree-of-freedom mount system. Two wind-tunnel tests were conducted with the first model. Several dynamic instability boundaries were investigated such as a conventional flutter boundary, a transonic plunge instability region near Mach = 0.90, and stall flutter. In addition, wing surface unsteady pressure data were acquired along two model chords located at the 60 to 95-percent span stations during these instabilities. At this time, only the pressure data for the conventional flutter boundary is presented. The conventional flutter boundary and the wing surface unsteady pressure measurements obtained at the conventional flutter boundary test conditions in pressure coefficient form are presented. Wing surface steady pressure measurements obtained with the model mount system rigidized are also presented. These steady pressure data were acquired at essentially the same dynamic pressure at which conventional flutter had been encountered with the mount system flexible.

  20. Abrupt cooling over the North Atlantic in modern climate models

    PubMed Central

    Sgubin, Giovanni; Swingedouw, Didier; Drijfhout, Sybren; Mary, Yannick; Bennabi, Amine

    2017-01-01

    Observations over the 20th century evidence no long-term warming in the subpolar North Atlantic (SPG). This region even experienced a rapid cooling around 1970, raising a debate over its potential reoccurrence. Here we assess the risk of future abrupt SPG cooling in 40 climate models from the fifth Coupled Model Intercomparison Project (CMIP5). Contrary to the long-term SPG warming trend evidenced by most of the models, 17.5% of the models (7/40) project a rapid SPG cooling, consistent with a collapse of the local deep-ocean convection. Uncertainty in projections is associated with the models' varying capability in simulating the present-day SPG stratification, whose realistic reproduction appears a necessary condition for the onset of a convection collapse. This event occurs in 45.5% of the 11 models best able to simulate the observed SPG stratification. Thus, due to systematic model biases, the CMIP5 ensemble as a whole underestimates the chance of future abrupt SPG cooling, entailing crucial implications for observation and adaptation policy. PMID:28198383

  1. The abrupt onset of the modern South Asian Monsoon winds.

    PubMed

    Betzler, Christian; Eberli, Gregor P; Kroon, Dick; Wright, James D; Swart, Peter K; Nath, Bejugam Nagender; Alvarez-Zarikian, Carlos A; Alonso-García, Montserrat; Bialik, Or M; Blättler, Clara L; Guo, Junhua Adam; Haffen, Sébastien; Horozal, Senay; Inoue, Mayuri; Jovane, Luigi; Lanci, Luca; Laya, Juan Carlos; Mee, Anna Ling Hui; Lüdmann, Thomas; Nakakuni, Masatoshi; Niino, Kaoru; Petruny, Loren M; Pratiwi, Santi D; Reijmer, John J G; Reolid, Jesús; Slagle, Angela L; Sloss, Craig R; Su, Xiang; Yao, Zhengquan; Young, Jeremy R

    2016-07-20

    The South Asian Monson (SAM) is one of the most intense climatic elements yet its initiation and variations are not well established. Dating the deposits of SAM wind-driven currents in IODP cores from the Maldives yields an age of 12. 9 Ma indicating an abrupt SAM onset, over a short period of 300 kyrs. This coincided with the Indian Ocean Oxygen Minimum Zone expansion as revealed by geochemical tracers and the onset of upwelling reflected by the sediment's content of particulate organic matter. A weaker 'proto-monsoon' existed between 12.9 and 25 Ma, as mirrored by the sedimentary signature of dust influx. Abrupt SAM initiation favors a strong influence of climate in addition to the tectonic control, and we propose that the post Miocene Climate Optimum cooling, together with increased continentalization and establishment of the bipolar ocean circulation, i.e. the beginning of the modern world, shifted the monsoon over a threshold towards the modern system.

  2. Abrupt climate warming in East Antarctica during the early Holocene

    NASA Astrophysics Data System (ADS)

    Cremer, Holger; Heiri, Oliver; Wagner, Bernd; Wagner-Cremer, Friederike

    2007-08-01

    We report a centennial-scale warming event between 8600 and 8400 cal BP from Amery Oasis, East Antarctica, that is documented by the geochemical record in a lacustrine sediment sequence. The organic carbon content, the C/S ratio, and the sedimentation rate in this core have distinctly elevated values around 8500 y ago reflecting relatively warm and ice-free conditions that led to well-ventilated conditions in the lake and considerable sedimentation of both autochthonous and allochthonous organic matter on the lake bottom. This abrupt warming event occurred concurrently with reported warm climatic conditions in the Southern Ocean while the climate in central East Antarctic remained cold. The comparison of the spatial and temporal variability of warm climatic periods documented in various terrestrial, marine, and glacial archives from East Antarctica elucidates the uniqueness of the centennial-scale warming event in the Amery Oasis. We also discuss a possible correlation of the Amery warming event with the abrupt climatic deterioration around 8200 cal BP on the Northern Hemisphere.

  3. Abrupt climate change and collapse of deep-sea ecosystems

    USGS Publications Warehouse

    Yasuhara, Moriaki; Cronin, T. M.; Demenocal, P.B.; Okahashi, H.; Linsley, B.K.

    2008-01-01

    We investigated the deep-sea fossil record of benthic ostracodes during periods of rapid climate and oceanographic change over the past 20,000 years in a core from intermediate depth in the northwestern Atlantic. Results show that deep-sea benthic community "collapses" occur with faunal turnover of up to 50% during major climatically driven oceanographic changes. Species diversity as measured by the Shannon-Wiener index falls from 3 to as low as 1.6 during these events. Major disruptions in the benthic communities commenced with Heinrich Event 1, the Inter-Aller??d Cold Period (IACP: 13.1 ka), the Younger Dryas (YD: 12.9-11.5 ka), and several Holocene Bond events when changes in deep-water circulation occurred. The largest collapse is associated with the YD/IACP and is characterized by an abrupt two-step decrease in both the upper North Atlantic Deep Water assemblage and species diversity at 13.1 ka and at 12.2 ka. The ostracode fauna at this site did not fully recover until ???8 ka, with the establishment of Labrador Sea Water ventilation. Ecologically opportunistic slope species prospered during this community collapse. Other abrupt community collapses during the past 20 ka generally correspond to millennial climate events. These results indicate that deep-sea ecosystems are not immune to the effects of rapid climate changes occurring over centuries or less. ?? 2008 by The National Academy of Sciences of the USA.

  4. North Pacific deglacial hypoxic events linked to abrupt ocean warming

    USGS Publications Warehouse

    Praetorius, Summer K; Mix, Alan C.; Davies, Maureen H.; Wolhowe, Matthew D; Addison, Jason A.; Prahl, Frederick G

    2015-01-01

    Marine sediments from the North Pacific document two episodes of expansion and strengthening of the subsurface oxygen minimum zone (OMZ) accompanied by seafloor hypoxia during the last deglacial transition1, 2, 3, 4. The mechanisms driving this hypoxia remain under debate1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11. We present a new high-resolution alkenone palaeotemperature reconstruction from the Gulf of Alaska that reveals two abrupt warming events of 4–5 degrees Celsius at the onset of the Bølling and Holocene intervals that coincide with sudden shifts to hypoxia at intermediate depths. The presence of diatomaceous laminations and hypoxia-tolerant benthic foraminiferal species, peaks in redox-sensitive trace metals12, 13, and enhanced 15N/14N ratio of organic matter13, collectively suggest association with high export production. A decrease in 18O/16O values of benthic foraminifera accompanying the most severe deoxygenation event indicates subsurface warming of up to about 2 degrees Celsius. We infer that abrupt warming triggered expansion of the North Pacific OMZ through reduced oxygen solubility and increased marine productivity via physiological effects; following initiation of hypoxia, remobilization of iron from hypoxic sediments could have provided a positive feedback on ocean deoxygenation through increased nutrient utilization and carbon export. Such a biogeochemical amplification process implies high sensitivity of OMZ expansion to warming.

  5. Global Aerodynamic Modeling for Stall/Upset Recovery Training Using Efficient Piloted Flight Test Techniques

    NASA Technical Reports Server (NTRS)

    Morelli, Eugene A.; Cunningham, Kevin; Hill, Melissa A.

    2013-01-01

    Flight test and modeling techniques were developed for efficiently identifying global aerodynamic models that can be used to accurately simulate stall, upset, and recovery on large transport airplanes. The techniques were developed and validated in a high-fidelity fixed-base flight simulator using a wind-tunnel aerodynamic database, realistic sensor characteristics, and a realistic flight deck representative of a large transport aircraft. Results demonstrated that aerodynamic models for stall, upset, and recovery can be identified rapidly and accurately using relatively simple piloted flight test maneuvers. Stall maneuver predictions and comparisons of identified aerodynamic models with data from the underlying simulation aerodynamic database were used to validate the techniques.

  6. Control of unsteady separated flow associated with the dynamic stall of airfoils

    NASA Technical Reports Server (NTRS)

    Wilder, Michael C.

    1992-01-01

    The two principal objectives of this research were to achieve an improved understanding of the mechanisms involved in the onset and development of dynamic stall under compressible flow conditions, and to investigate the feasibility of employing adaptive airfoil geometry as an active flow control device in the dynamic stall engine. Presented here are the results of a quantitative (PDI) study of the compressibility effects on dynamic stall over the transiently pitching airfoil, as well as a discussion of a preliminary technique developed to measure the deformation produced by the adaptive geometry control device, and bench test results obtained using an airfoil equipped with the device.

  7. Rotating stall investigation of 0.72 hub-tip ratio single-stage compressor

    NASA Technical Reports Server (NTRS)

    Graham, Robert W; Prian, Vasily D

    1954-01-01

    The rotating stall characteristics of a 0.72 hub-tip ratio, single-stage compressor were investigated. The stage was a 14-inch-diameter replica of the fourth stage of an experimental multistage compressor. No similarity existed between the frequency and propagation rate of the stall patterns observed in the single-stage replica and those observed in the multistage compressor after the fourth stage. A fatigue failure of the rotor blades occurred during the testing which was attributed to a resonance between the stall frequency and the natural bending frequency of the blades.

  8. Investigation of rotor blade element airloads for a teetering rotor in the blade stall regime

    NASA Technical Reports Server (NTRS)

    Dadone, L. U.; Fukushima, T.

    1974-01-01

    A model of a teetering rotor was tested in a low speed wind tunnel. Blade element airloads measured on an articulated model rotor were compared with the teetering rotor and showed that the teetering rotor is subjected to less extensive flow separation. Retreating blade stall was studied. Results show that stall, under the influence of unsteady aerodynamic effects, consists of four separate stall events, each associated with a vortex shed from the leading edge and sweeping over the upper surface of the rotor blade. Current rotor performance prediction methodology was evaluated through computer simulation.

  9. Insect Wing Membrane Topography Is Determined by the Dorsal Wing Epithelium

    PubMed Central

    Belalcazar, Andrea D.; Doyle, Kristy; Hogan, Justin; Neff, David; Collier, Simon

    2013-01-01

    The Drosophila wing consists of a transparent wing membrane supported by a network of wing veins. Previously, we have shown that the wing membrane cuticle is not flat but is organized into ridges that are the equivalent of one wing epithelial cell in width and multiple cells in length. These cuticle ridges have an anteroposterior orientation in the anterior wing and a proximodistal orientation in the posterior wing. The precise topography of the wing membrane is remarkable because it is a fusion of two independent cuticle contributions from the dorsal and ventral wing epithelia. Here, through morphological and genetic studies, we show that it is the dorsal wing epithelium that determines wing membrane topography. Specifically, we find that wing hair location and membrane topography are coordinated on the dorsal, but not ventral, surface of the wing. In addition, we find that altering Frizzled Planar Cell Polarity (i.e., Fz PCP) signaling in the dorsal wing epithelium alone changes the membrane topography of both dorsal and ventral wing surfaces. We also examined the wing morphology of two model Hymenopterans, the honeybee Apis mellifera and the parasitic wasp Nasonia vitripennis. In both cases, wing hair location and wing membrane topography are coordinated on the dorsal, but not ventral, wing surface, suggesting that the dorsal wing epithelium also controls wing topography in these species. Because phylogenomic studies have identified the Hymenotera as basal within the Endopterygota family tree, these findings suggest that this is a primitive insect character. PMID:23316434

  10. Cessna-172R Airplane in Cruise and Landing Configurations: A Numerical Study of the Wing Loads and Wake

    NASA Astrophysics Data System (ADS)

    Jha, Pankaj

    2013-11-01

    The present work deals with the analysis of flight test data on a Cessna 172R airplane near University Park airport in Pennsylvania. Several tests pertaining to rate-of-climb, cruise, stall and landing were performed. Those of aerodynamic nature will be discussed. The wing loads for the cruise as well as landing configurations with various flap angles were computed using a vortex method considering horse-shoe and bound vortices. The stall speed and maximum lift coefficient of the airplane for these flap settings at a particular altitude were determined. The comparison against the processed flight data was generally very good. A detailed study will be presented. A CFD approach inspired by the author's work (Jha et al., 2013) to model wind turbine blades and wakes and classical aerodynamics problems was taken to model the airplane wings. The simulation results were also compared against the flight data. In addition, these simulations facilitated visualization and analysis of flow features of interest, like wing tip trailing vortices and their turbulence characterization. Graduate Research Assistant, Aerospace Engineering.

  11. Aeroelastic Analysis of Aircraft: Wing and Wing/Fuselage Configurations

    NASA Technical Reports Server (NTRS)

    Chen, H. H.; Chang, K. C.; Tzong, T.; Cebeci, T.

    1997-01-01

    A previously developed interface method for coupling aerodynamics and structures is used to evaluate the aeroelastic effects for an advanced transport wing at cruise and under-cruise conditions. The calculated results are compared with wind tunnel test data. The capability of the interface method is also investigated for an MD-90 wing/fuselage configuration. In addition, an aircraft trim analysis is described and applied to wing configurations. The accuracy of turbulence models based on the algebraic eddy viscosity formulation of Cebeci and Smith is studied for airfoil flows at low Mach numbers by using methods based on the solutions of the boundary-layer and Navier-Stokes equations.

  12. Ancient Wings: animating the evolution of butterfly wing patterns.

    PubMed

    Arbesman, Samuel; Enthoven, Leo; Monteiro, Antónia

    2003-10-01

    Character optimization methods can be used to reconstruct ancestral states at the internal nodes of phylogenetic trees. However, seldom are these ancestral states visualized collectively. Ancient Wings is a computer program that provides a novel method of visualizing the evolution of several morphological traits simultaneously. It allows users to visualize how the ventral hindwing pattern of 54 butterflies in the genus Bicyclus may have changed over time. By clicking on each of the nodes within the evolutionary tree, the user can see an animation of how wing size, eyespot size, and eyespot position relative the wing margin, have putatively evolved as a collective whole. Ancient Wings may be used as a pedagogical device as well as a research tool for hypothesis-generation in the fields of evolutionary, ecological, and developmental biology.

  13. Mechanisms of Wing Beat Sound in Flapping Wings of Beetles

    NASA Astrophysics Data System (ADS)

    Allen, John

    2017-11-01

    While the aerodynamic aspects of insect flight have received recent attention, the mechanisms of sound production by flapping wings is not well understood. Though the harmonic structure of wing beat frequency modulation has been reported with respect to biological implications, few studies have rigorously quantified it with respect directionality, phase coupling and vortex tip scattering. Moreover, the acoustic detection and classification of invasive species is both of practical as well scientific interest. In this study, the acoustics of the tethered flight of the Coconut Rhinoceros Beetle (Oryctes rhinoceros) is investigated with four element microphone array in conjunction with complementary optical sensors and high speed video. The different experimental methods for wing beat determination are compared in both the time and frequency domain. Flow visualization is used to examine the vortex and sound generation due to the torsional mode of the wing rotation. Results are compared with related experimental studies of the Oriental Flower Beetle. USDA, State of Hawaii.

  14. Effect of outer wing separation on lift and thrust generation in a flapping wing system.

    PubMed

    Mahardika, Nanang; Viet, Nguyen Quoc; Park, Hoon Cheol

    2011-09-01

    We explore the implementation of wing feather separation and lead-lagging motion to a flapping wing. A biomimetic flapping wing system with separated outer wings is designed and demonstrated. The artificial wing feather separation is implemented in the biomimetic wing by dividing the wing into inner and outer wings. The features of flapping, lead-lagging, and outer wing separation of the flapping wing system are captured by a high-speed camera for evaluation. The performance of the flapping wing system with separated outer wings is compared to that of a flapping wing system with closed outer wings in terms of forward force and downward force production. For a low flapping frequency ranging from 2.47 to 3.90 Hz, the proposed biomimetic flapping wing system shows a higher thrust and lift generation capability as demonstrated by a series of experiments. For 1.6 V application (lower frequency operation), the flapping wing system with separated wings could generate about 56% higher forward force and about 61% less downward force compared to that with closed wings, which is enough to demonstrate larger thrust and lift production capability of the separated outer wings. The experiments show that the outer parts of the separated wings are able to deform, resulting in a smaller amount of drag production during the upstroke, while still producing relatively greater lift and thrust during the downstroke.

  15. Logistics Implications of Composite Wings

    DTIC Science & Technology

    1993-12-01

    Composite Wing and Air Logistics Center Locations 33 12 F-15E Strike Eagle Aircraft 34 la F-16C Fighting Falcon Aircraft 35 14 E-3 Sentry...Structure , 12 2 366th Wing Maintenance Concept 41 vOt Foreword The US Air Force has taken the initiative to reorganize into objective wings, at...the Air Force in 1967. He began his Air Force career as an F-102 radar weapon system specialist and worked on the flight line at Ramstein Air Base

  16. Airplane wing vibrations due to atmospheric turbulence

    NASA Technical Reports Server (NTRS)

    Pastel, R. L.; Caruthers, J. E.; Frost, W.

    1981-01-01

    The magnitude of error introduced due to wing vibration when measuring atmospheric turbulence with a wind probe mounted at the wing tip was studied. It was also determined whether accelerometers mounted on the wing tip are needed to correct this error. A spectrum analysis approach is used to determine the error. Estimates of the B-57 wing characteristics are used to simulate the airplane wing, and von Karman's cross spectrum function is used to simulate atmospheric turbulence. It was found that wing vibration introduces large error in measured spectra of turbulence in the frequency's range close to the natural frequencies of the wing.

  17. Aerodynamic analysis of the Darrieus wind turbines including dynamic-stall effects

    NASA Astrophysics Data System (ADS)

    Paraschivoiu, Ion; Allet, Azeddine

    Experimental data for a 17-m wind turbine are compared with aerodynamic performance predictions obtained with two dynamic stall methods which are based on numerical correlations of the dynamic stall delay with the pitch rate parameter. Unlike the Gormont (1973) model, the MIT model predicts that dynamic stall does not occur in the downwind part of the turbine, although it does exist in the upwind zone. The Gormont model is shown to overestimate the aerodynamic coefficients relative to the MIT model. The MIT model is found to accurately predict the dynamic-stall regime, which is characterized by a plateau oscillating near values of the experimental data for the rotor power vs wind speed at the equator.

  18. An experimental and analytical investigation of stall effects on flap-lag stability in forward flight

    NASA Technical Reports Server (NTRS)

    Nagabhushanam, J.; Gaonkar, Gopal H.; Mcnulty, Michael J.

    1987-01-01

    Experiments have been performed with a 1.62 m diameter hingeless rotor in a wind tunnel to investigate flap-lag stability of isolated rotors in forward flight. The three-bladed rotor model closely approaches the simple theoretical concept of a hingeless rotor as a set of rigid, articulated flap-lag blades with offset and spring restrained flap and lag hinges. Lag regressing mode stability data was obtained for advance ratios as high as 0.55 for various combinations of collective pitch and shaft angle. The prediction includes quasi-steady stall effects on rotor trim and Floquet stability analyses. Correlation between data and prediction is presented and is compared with that of an earlier study based on a linear theory without stall effects. While the results with stall effects show marked differences from the linear theory results, the stall theory still falls short of adequate agreement with the experimental data.

  19. A theory of post-stall transients in axial compression systems. I - Development of equations

    NASA Technical Reports Server (NTRS)

    Moore, F. K.; Greitzer, E. M.

    1985-01-01

    An approximate theory is presented for post-stall transients in multistage axial compression systems. The theory leads to a set of three simultaneous nonlinear third-order partial differential equations for pressure rise, and average and disturbed values of flow coefficient, as functions of time and angle around the compressor. By a Galerkin procedure, angular dependence is averaged, and the equations become first order in time. These final equations are capable of describing the growth and possible decay of a rotating-stall cell during a compressor mass-flow transient. It is shown how rotating-stall-like and surgelike motions are coupled through these equations, and also how the instantaneous compressor pumping characteristic changes during the transient stall process.

  20. The Danger of Stalled Flight and an Analysis of the Factors which Govern It

    NASA Technical Reports Server (NTRS)

    Hopf, L

    1921-01-01

    A definition of "stalled fight" is presented as well as a detailed discussion on the how and why it occurs. Some suggestions are made to prevent its occurrence such as carrying an air speed instrument in the airplane.

  1. Computer modeling of the stalled flow of a rotating cylinder and the reverse magnus effect

    NASA Astrophysics Data System (ADS)

    Belotserkovskii, S. M.; Kotovskii, V. N.; Nisht, M. I.; Fedorov, R. M.

    1985-02-01

    Unsteady stalled flow around a rotating cylinder is investigated in a numerical experiment. Attention is mostly given to the reverse Magnus effect which was discovered in tube experiments at some critical rotational speed of the cylinder.

  2. A theory of rotating stall of multistage axial compressors. III - Limit cycles

    NASA Technical Reports Server (NTRS)

    Moore, F. K.

    1983-01-01

    A theory of rotating stall, based on single parameters for blade-passage lag and external-flow lag and a given compressor characteristic yields limit cycles in velocity space. These limit cycles are governed by Lienard's equation with the characteristic playing the role of nonlinear damping function. Cyclic integrals of the solution determine stall propagation speed and the effect of rotating stall on average performance. Solution with various line-segment characteristics and various throttle settings are found and discussed. There is generally a limiting flow coefficient beyond which no solution is possible; this probably represents stall recovery. This recovery point is independent of internal compressor lag, but does depend on external lags and on the height-to-width ratio of the diagram. Tall diagrams and small external lags (inlet and diffusor) favor recovery. Suggestions for future theoretical and experimental research are discussed.

  3. Control of unsteady separated flow associated with the dynamic stall of airfoils

    NASA Technical Reports Server (NTRS)

    Wilder, M. C.

    1994-01-01

    A unique active flow-control device is proposed for the control of unsteady separated flow associated with the dynamic stall of airfoils. The device is an adaptive-geometry leading-edge which will allow controlled, dynamic modification of the leading-edge profile of an airfoil while the airfoil is executing an angle-of-attack pitch-up maneuver. A carbon-fiber composite skin has been bench tested, and a wind tunnel model is under construction. A baseline parameter study of compressible dynamic stall was performed for flow over an NACA 0012 airfoil. Parameters included Mach number, pitch rate, pitch history, and boundary layer tripping. Dynamic stall data were recorded via point-diffraction interferometry and the interferograms were analyzed with in-house developed image processing software. A new high-speed phase-locked photographic image recording system was developed for real-time documentation of dynamic stall.

  4. Computational analysis of stall and separation control in centrifugal compressors

    NASA Astrophysics Data System (ADS)

    Stein, Alexander

    2000-10-01

    A numerical technique for simulating unsteady viscous fluid flow in turbomachinery components has been developed. In this technique, the three-dimensional form of the Reynolds averaged Navier-Stokes equations is solved in a time-accurate manner. The flow solver is used to study fluid dynamic phenomena that lead to instabilities in centrifugal compressors. The results indicate that large flow incidence angles, at reduced flow rates, can cause boundary layer separation near the blade leading edge. This mechanism is identified as the primary factor in the stall inception process. High-pressure jets upstream of the compressor face are studied as a means of controlling compressor instabilities. Steady jets are found to alter the leading edge flow pattern and effectively suppress compressor instabilities. Yawed jets are more effective than parallel jets and an optimum yaw angle exists for each compression system. Numerical simulations utilizing pulsed jets have also been done. Pulsed jets are found to yield additional performance enhancements and lead to a reduction in external air requirements for operating the jets. Jets pulsed at higher frequencies perform better than low-frequency jets. These findings suggest that air injection is a viable means of alleviating compressor instabilities and could impact gas turbine technology. Results concerning the optimization of practical air injection systems and implications for future research are discussed. The flow solver developed in this work, along with the postprocessing tools developed to interpret the results, provide a rational framework for analyzing and controlling current and next generation compression systems.

  5. Stalling HIV through social marketing: prospects in Pakistan.

    PubMed

    Husain, Sara; Shaikh, Babar T

    2005-07-01

    Over the last two decades HIV/AIDS has evolved from a series of interesting case-reports to a growing epidemic that threatens the entire world. It is feared to cause devastation among large pockets of populations and may roll back more than thirty years of public health achievements. This killer disease has been more amenable to behavioral change than by provision of curative services and attempts are being made to educate the public about this threat. Various techniques of promotion have been tried through out the world including television dramas/soaps, mass media and school curricula. Social marketing is an evolving strategy used to influence human behavior and choices. By using the principles of marketing and promoting behavior as a product, social marketers attempt to understand the dynamics of human behaviour and devise messages and products to change, modify, accept or reject unsafe behaviors or practices. Thus, social marketers provide an effective force to combat the spread of HIV and may serve to be invaluable allies in health promotion efforts. In a complex and diversified cultural milieu of Pakistan, social marketing can have a significant impact on health determinants and the conditions that will facilitate the adoption of health-oriented behaviors and practices. This paper gives an account of the elements needed for the success of a health promotion strategy adopted in a developing country and makes a case for social marketing to be adopted as the lead strategy for stalling HIV/AIDS in Pakistan.

  6. Control of VR-7 Dynamic Stall by Strong Steady Blowing

    NASA Technical Reports Server (NTRS)

    Weaver, D.; McAlister, K. W.; Tso, J.

    2004-01-01

    An experiment was performed in a water tunnel on a Boeing-Vertol VR-7 airfoil to study the effects of tangential blowing over the upper surface. Blowing was applied at the quarter-chord location during sinusoidal pitching oscillations described by alpha = alpha(sub m) + 10 deg sin omega t. Results were obtained for a Reynolds number of 1 x 10(exp 5), mean angles of 10 and 15 deg, reduced frequencies ranging from 0.005 to 0.15, and blowing rates from C(sub mu) = 0.16 to 0.66. Unsteady lift, drag, and pitching moment loads are reported, along with fluorescent-dye flow visualizations. Strong steady blowing was found to prevent the bursting of the leading-edge separation bubble at several test points. When this occurred, the lift was increased significantly, stall was averted, and the shape of the moment response showed a positive damping in pitch. In almost all cases, steady blowing reduced the hysteresis amplitudes present in the loads, but the benefits diminished as the reduced frequency and mean angle of oscillation increased. A limited number of pulsed blowing cases indicated that for low blowing rates, the greatest gains were achieved at F(sup +) = 0.9.

  7. Exploratory wind tunnel investigation of the stability and control characteristics of a three-surface, forward-swept wing advanced turboprop model

    NASA Technical Reports Server (NTRS)

    Coe, Paul L., Jr.; Perkins, John N.; Owens, D. Bruce

    1990-01-01

    The purpose of the present investigation was to parametrically study the stability and control characteristics of a forward-swept wing three-surface turboprop model through an extended angle of attack range, including the deep-stall region. As part of a joint research program between North Carolina State University and NASA Langley Research Center, a low-speed wind tunnel investigation was conducted with a three-surface, forward-swept wing, aft-mounted, twin-pusher propeller, model, representative of an advanced turboprop configuration. The tests were conducted in the NASA Langley 12-Foot Low-Speed Wind Tunnel. The model parameters varied in the test were horizontal tail location, canard size, sweep and location, and wing position. The model was equipped with air turbines, housed within the nacelles and driven by compressed air, to model turboprop power effects. A three-surface, forward-swept wing configuration that provided satisfactory static longitudinal and lateral/directional stability was identified. The three-surface configuration was found to have greater longitudinal control and increased center of gravity range relative to a conventional (two-surface) design. The test showed that power had a large favorable effect on stability and control about all three axis in the post-stall regime.

  8. An Experimental Study of Dynamic Stall on Advanced Airfoil Sections. Volume 1. Summary of the Experiment.

    DTIC Science & Technology

    1982-07-01

    Aeronautics and United States Army Space Administration Aviation Research and Ames Remrch Cente Development Command Moffett Field. California 94035 St...appear to be more important than airfoil shape in determining the dynamic- stall airloads. 1. INTRODUCTION Retreating- blade stall limits the high-speed...12.2% Thick R.A.E. Aerofoil Section. RAE Technical Report 68303, Royal Aircraft Establishment, Farnborough Hants, England, Jan. 1969. 14. Fromme, J. A

  9. Cow comfort in tie-stalls: increased depth of shavings or straw bedding increases lying time.

    PubMed

    Tucker, C B; Weary, D M; von Keyserlingk, M A G; Beauchemin, K A

    2009-06-01

    Over half of US dairy operations use tie-stalls, but these farming systems have received relatively little research attention in terms of stall design and management. The current study tested the effects of the amount of 2 bedding materials, straw and shavings, on dairy cattle lying behavior. The effects of 4 levels of shavings, 3, 9, 15, and 24 kg/stall (experiment 1, n = 12), and high and low levels of straw in 2 separate experiments: 1, 3, 5, and 7 kg/stall (experiment 2, n = 12) and 0.5, 1, 2, and 3 kg/stall (experiment 3, n = 12) were assessed. Treatments were compared using a crossover design with lactating cows housed in tie-stalls fitted with mattresses. Treatments were applied for 1 wk. Total lying time, number of lying bouts, and the length of each lying bout was recorded with data loggers. In experiment 1, cows spent 3 min more lying down for each additional kilogram of shavings (11.0, 11.7, 11.6, and 12.1 +/- 0.24 h/d for 3, 9, 15, and 24 kg/stall shavings, respectively). In experiment 2, cows increased lying time by 12 min for every additional kilogram of straw (11.2, 12.0, 11.8, and 12.4 +/- 0.24 h/d for 1, 3, 5, and 7 kg/stall of straw, respectively). There were no differences in lying behavior among the lower levels of straw tested in experiment 3 (11.7 +/- 0.32 h/d). These results indicated that additional bedding above a scant amount improves cow comfort, as measured by lying time, likely because a well-bedded surface is more compressible.

  10. Stage Effects on Stalling and Recovery of a High-Speed 10-Stage Axial- Flow Compressor

    DTIC Science & Technology

    1990-06-01

    facility C Specific heat of air at constant pressureP Cx Axial velocity DC Direct current DAC Data acquisition computer DCS Design corrected compressor ...was designed to inve3tigate the component performance of an axial -flow compressor while stalling and operating in rotating stall. No attempt was made...Temperatures were measured from a probe configuration similar to the to - pressure design . 68 Table 4.2 Compressor instrumentation RADIAL PROPERTY AXIAL

  11. Abrupt tectonics and rapid slab detachment with grain damage

    PubMed Central

    Bercovici, David; Schubert, Gerald; Ricard, Yanick

    2015-01-01

    A simple model for necking and detachment of subducting slabs is developed to include the coupling between grain-sensitive rheology and grain-size evolution with damage. Necking is triggered by thickened buoyant crust entrained into a subduction zone, in which case grain damage accelerates necking and allows for relatively rapid slab detachment, i.e., within 1 My, depending on the size of the crustal plug. Thick continental crustal plugs can cause rapid necking while smaller plugs characteristic of ocean plateaux cause slower necking; oceanic lithosphere with normal or slightly thickened crust subducts without necking. The model potentially explains how large plateaux or continental crust drawn into subduction zones can cause slab loss and rapid changes in plate motion and/or induce abrupt continental rebound. PMID:25605890

  12. Abrupt tectonics and rapid slab detachment with grain damage.

    PubMed

    Bercovici, David; Schubert, Gerald; Ricard, Yanick

    2015-02-03

    A simple model for necking and detachment of subducting slabs is developed to include the coupling between grain-sensitive rheology and grain-size evolution with damage. Necking is triggered by thickened buoyant crust entrained into a subduction zone, in which case grain damage accelerates necking and allows for relatively rapid slab detachment, i.e., within 1 My, depending on the size of the crustal plug. Thick continental crustal plugs can cause rapid necking while smaller plugs characteristic of ocean plateaux cause slower necking; oceanic lithosphere with normal or slightly thickened crust subducts without necking. The model potentially explains how large plateaux or continental crust drawn into subduction zones can cause slab loss and rapid changes in plate motion and/or induce abrupt continental rebound.

  13. Abrupt climate shift in the Western Mediterranean Sea.

    PubMed

    Schroeder, K; Chiggiato, J; Bryden, H L; Borghini, M; Ben Ismail, S

    2016-03-11

    One century of oceanographic measurements has evidenced gradual increases in temperature and salinity of western Mediterranean water masses, even though the vertical stratification has basically remained unchanged. Starting in 2005, the basic structure of the intermediate and deep layers abruptly changed. We report here evidence of reinforced thermohaline variability in the deep western basin with significant dense water formation events producing large amounts of warmer, saltier and denser water masses than ever before. We provide a detailed chronological order to these changes, giving an overview of the new water masses and following their route from the central basin interior to the east (toward the Tyrrhenian) and toward the Atlantic Ocean. As a consequence of this climate shift, new deep waters outflowing through Gibraltar will impact the North Atlantic in terms of salt and heat input. In addition, modifications in the Mediterranean abyssal ecosystems and biogeochemical cycles are to be expected.

  14. Abrupt climate shift in the Western Mediterranean Sea

    PubMed Central

    Schroeder, K.; Chiggiato, J.; Bryden, H. L.; Borghini, M.; Ben Ismail, S.

    2016-01-01

    One century of oceanographic measurements has evidenced gradual increases in temperature and salinity of western Mediterranean water masses, even though the vertical stratification has basically remained unchanged. Starting in 2005, the basic structure of the intermediate and deep layers abruptly changed. We report here evidence of reinforced thermohaline variability in the deep western basin with significant dense water formation events producing large amounts of warmer, saltier and denser water masses than ever before. We provide a detailed chronological order to these changes, giving an overview of the new water masses and following their route from the central basin interior to the east (toward the Tyrrhenian) and toward the Atlantic Ocean. As a consequence of this climate shift, new deep waters outflowing through Gibraltar will impact the North Atlantic in terms of salt and heat input. In addition, modifications in the Mediterranean abyssal ecosystems and biogeochemical cycles are to be expected. PMID:26965790

  15. Bend-imitating models of abruptly bent electron waveguides

    NASA Astrophysics Data System (ADS)

    Vakhnenko, Oleksiy O.

    2011-07-01

    The fundamentals of bend-imitating approach regarding the one-electron quantum mechanics in abruptly bent ideal electron waveguides are given. In general, the theory allows to model each particular circularlike bend of a continuous quantum wire as some effective multichannel scatterer being pointlike in longitudinal direction. Its scattering ability is determined by the bending angle, mean bending radius, lateral coordinate (or coordinates) in wire cross section, time (or electronic energy), and possibly by the applied magnetic field. In an equivalent formulation, the theory gives rise to rather simple matching rules for the electron wave function and its longitudinal derivative affecting only the straight parts of a wire and thereby permitting to bypass a detailed quantum mechanical consideration of elbow domains. The proposed technique is applicable for the analytical investigation of spectral and transport electronic properties related to the ideal abruptly bent 3D wirelike structures of fixed cross section and is adaptable to the 2D wirelike structures as well as to the wirelike structures subjected to the magnetic field perpendicular to the plane of wire bending. In the framework of bend-imitating approach, the investigation of electron scattering in a singly bent 2D quantum wire and a doubly bent 2D quantum wire with S-like bend has been made and the explicit dependences of transmission and reflection coefficients on geometrical parameters of respective structure as well as on electron energy have been obtained. The total suppression of mixing between the scattering channels of S-like bent quantum wire is predicted.

  16. Abrupt glacial climate shifts controlled by ice sheet changes.

    PubMed

    Zhang, Xu; Lohmann, Gerrit; Knorr, Gregor; Purcell, Conor

    2014-08-21

    During glacial periods of the Late Pleistocene, an abundance of proxy data demonstrates the existence of large and repeated millennial-scale warming episodes, known as Dansgaard-Oeschger (DO) events. This ubiquitous feature of rapid glacial climate change can be extended back as far as 800,000 years before present (BP) in the ice core record, and has drawn broad attention within the science and policy-making communities alike. Many studies have been dedicated to investigating the underlying causes of these changes, but no coherent mechanism has yet been identified. Here we show, by using a comprehensive fully coupled model, that gradual changes in the height of the Northern Hemisphere ice sheets (NHISs) can alter the coupled atmosphere-ocean system and cause rapid glacial climate shifts closely resembling DO events. The simulated global climate responses--including abrupt warming in the North Atlantic, a northward shift of the tropical rainbelts, and Southern Hemisphere cooling related to the bipolar seesaw--are generally consistent with empirical evidence. As a result of the coexistence of two glacial ocean circulation states at intermediate heights of the ice sheets, minor changes in the height of the NHISs and the amount of atmospheric CO2 can trigger the rapid climate transitions via a local positive atmosphere-ocean-sea-ice feedback in the North Atlantic. Our results, although based on a single model, thus provide a coherent concept for understanding the recorded millennial-scale variability and abrupt climate changes in the coupled atmosphere-ocean system, as well as their linkages to the volume of the intermediate ice sheets during glacials.

  17. Abrupt plate acceleration during rifted margin formation: Cause and effect

    NASA Astrophysics Data System (ADS)

    Brune, Sascha; Williams, Simon; Butterworth, Nathaniel; Müller, Dietmar

    2017-04-01

    Extension rate is known to control key processes during rifted margin formation such as crust-mantle coupling, decompression melting, magmatism, and serpentinisation. Here we build on recent advances in plate tectonic reconstructions by quantifying the extension velocity history of Earth's major rifted margins during the last 240 million years. We find that many successful rifts start with a slow phase of extension followed by rapid acceleration that introduces a fast phase. The transition from slow to fast rifting takes place long before crustal break-up: approximately half of the present day rifted margin area was created during the slow, and the other half during the fast rift phase. We reproduce the rapid transition from slow to fast extension using analytical and numerical modelling with constant force boundary conditions. In these models, rift velocities are not imposed but instead evolve naturally in response to the changing strength of the rift. Our results demonstrate that abrupt plate acceleration during continental rifting is controlled by a rift-intrinsic strength-velocity feedback. The abruptness of rift acceleration is thereby governed by the nonlinearity of lithospheric localization. Realistic brittle and power-law rheologies lead to a speed-up duration between two and ten million years. For successful rifts that generate a new ocean basin, the duration of rift speed-up is notably almost independent of the applied extensional force. Instead, the force controls the duration of the slow phase: higher forces shorten the slow phase while lower forces prolong it. If the force is too low, however, delocalisation processes prevent the rift from reaching the point of speed-up and produce a failed rift, even if the extensional system was active for many million years.

  18. The Effect of Split Trailing-edge Wing Flaps on the Aerodynamic Characteristics of a Parasol Monoplane

    NASA Technical Reports Server (NTRS)

    Wallace, Rudolf, N

    1933-01-01

    This paper presents the results of tests conducted in the N.A.C.A. full-scale wind tunnel on a Fairchild F-22 airplane equipped with a special wing having split trailing-edge flaps. The flaps extended over the outer 90 percent of the wing span, and were of the fixed-hinge type having a width equal to 20 percent of the wing chord. The results show that with a flap setting of 59 degrees the maximum lift of the wing was increased 42 percent, and that the flaps increased the range of available gliding angles from 2.7 degrees to 7.0 degrees. Deflection of the split flaps did not increase the stalling angle or seriously affect the longitudinal balance of the airplane. With flaps down the landing speed of the airplane is decreased, but the calculated climb and level-flight performance is inferior to that with the normal wing. Calculations indicate that the take-off distance required to clear an obstacle 100 feet high is not affected by flap settings from 0 degrees to 20 degrees but is greatly increased by larger flap angles.

  19. Design of supercritical swept wings

    NASA Technical Reports Server (NTRS)

    Garabedian, P.; Mcfadden, G.

    1982-01-01

    Computational fluid dynamics are used to discuss problems inherent to transonic three-dimensional flow past supercritical swept wings. The formulation for a boundary value problem for the flow past the wing is provided, including consideration of weak shock waves and the use of parabolic coordinates. A swept wing code is developed which requires a mesh of 152 x 10 x 12 points and 200 time cycles. A formula for wave drag is calculated, based on the idea that the conservation form of the momentum equation becomes an entropy inequality measuring the drag, expressible in terms of a small-disturbance equation for a potential function in two dimensions. The entropy inequality has been incorporated in a two-dimensional code for the analysis of transonic flow over airfoils. A method of artificial viscosity is explored for optimum pressure distributions with design, and involves a free boundary problem considering speed over only a portion of the wing.

  20. Embedded Wing Propulsion Conceptual Study

    NASA Technical Reports Server (NTRS)

    Kim, Hyun D.; Saunders, John D.

    2003-01-01

    As a part of distributed propulsion work under NASA's Revolutionary Aeropropulsion Concepts or RAC project, a new propulsion-airframe integrated vehicle concept called Embedded Wing Propulsion (EWP) is developed and examined through system and computational fluid dynamics (CFD) studies. The idea behind the concept is to fully integrate a propulsion system within a wing structure so that the aircraft takes full benefits of coupling of wing aerodynamics and the propulsion thrust stream. The objective of this study is to assess the feasibility of the EWP concept applied to large transport aircraft such as the Blended-Wing-Body aircraft. In this paper, some of early analysis and current status of the study are presented. In addition, other current activities of distributed propulsion under the RAC project are briefly discussed.

  1. Compressibility effects on dynamic stall of airfoils undergoing rapid transient pitching motion

    NASA Technical Reports Server (NTRS)

    Chandrasekhara, M. S.; Platzer, M. F.

    1992-01-01

    The research was carried out in the Compressible Dynamic Stall Facility, CDSF, at the Fluid Mechanics Laboratory (FML) of NASA Ames Research Center. The facility can produce realistic nondimensional pitch rates experienced by fighter aircraft, which on model scale could be as high as 3600/sec. Nonintrusive optical techniques were used for the measurements. The highlight of the effort was the development of a new real time interferometry method known as Point Diffraction Interferometry - PDI, for use in unsteady separated flows. This can yield instantaneous flow density information (and hence pressure distributions in isentropic flows) over the airfoil. A key finding is that the dynamic stall vortex forms just as the airfoil leading edge separation bubble opens-up. A major result is the observation and quantification of multiple shocks over the airfoil near the leading edge. A quantitative analysis of the PDI images shows that pitching airfoils produce larger suction peaks than steady airfoils at the same Mach number prior to stall. The peak suction level reached just before stall develops is the same at all unsteady rates and decreases with increase in Mach number. The suction is lost once the dynamic stall vortex or vortical structure begins to convect. Based on the knowledge gained from this preliminary analysis of the data, efforts to control dynamic stall were initiated. The focus of this work was to arrive at a dynamically changing leading edge shape that produces only 'acceptable' airfoil pressure distributions over a large angle of attack range.

  2. Measurement of Flow Pattern Within a Rotating Stall Cell in an Axial Compressor

    NASA Technical Reports Server (NTRS)

    Lepicovsky, Jan; Braunscheidel, Edward P.

    2006-01-01

    Effective active control of rotating stall in axial compressors requires detailed understanding of flow instabilities associated with this compressor regime. Newly designed miniature high frequency response total and static pressure probes as well as commercial thermoanemometric probes are suitable tools for this task. However, during the rotating stall cycle the probes are subjected to flow direction changes that are far larger than the range of probe incidence acceptance, and therefore probe data without a proper correction would misrepresent unsteady variations of flow parameters. A methodology, based on ensemble averaging, is proposed to circumvent this problem. In this approach the ensemble averaged signals acquired for various probe setting angles are segmented, and only the sections for probe setting angles close to the actual flow angle are used for signal recombination. The methodology was verified by excellent agreement between velocity distributions obtained from pressure probe data, and data measured with thermoanemometric probes. Vector plots of unsteady flow behavior during the rotating stall regime indicate reversed flow within the rotating stall cell that spreads over to adjacent rotor blade channels. Results of this study confirmed that the NASA Low Speed Axial Compressor (LSAC) while in a rotating stall regime at rotor design speed exhibits one stall cell that rotates at a speed equal to 50.6 percent of the rotor shaft speed.

  3. High-Speed Experiments on Combustion-Powered Actuation for Dynamic Stall Suppression

    NASA Technical Reports Server (NTRS)

    Matalanis, Claude; Bowles, Patrick; Lorber, Peter; Crittenden, Thomas; Glezer, Ari; Schaeffler, Norman; Min, Byung-Young; Jee, Solkeun; Kuczek, Andrzej; Wake, Brian

    2016-01-01

    This work documents high-speed wind tunnel experiments conducted on a pitching airfoil equipped with an array of combustion-powered actuators (COMPACT). The main objective of these experiments was to demonstrate the stall-suppression capability of COMPACT on a high-lift rotorcraft airfoil, the VR-12, at relevant Mach numbers. Through dynamic pressure measurements at the airfoil surface it was shown that COMPACT can positively affect the stall behavior of the VR-12 at Mach numbers up to 0.4. Static airfoil results demonstrated 25% and 50% increases in post-stall lift at Mach numbers of 0.4 and 0.3, respectively. Deep dynamic stall results showed cycle-averaged lift coefficient increases up to 11% at Mach 0.4. Furthermore, it was shown that these benefits could be achieved with relatively few pulses during down-stroke and with no need to pre-anticipate the stall event. The flow mechanisms responsible for stall suppression were investigated using particle image velocimetry.

  4. Unsteady aerodynamics of reverse flow dynamic stall on an oscillating blade section

    NASA Astrophysics Data System (ADS)

    Lind, Andrew H.; Jones, Anya R.

    2016-07-01

    Wind tunnel experiments were performed on a sinusoidally oscillating NACA 0012 blade section in reverse flow. Time-resolved particle image velocimetry and unsteady surface pressure measurements were used to characterize the evolution of reverse flow dynamic stall and its sensitivity to pitch and flow parameters. The effects of a sharp aerodynamic leading edge on the fundamental flow physics of reverse flow dynamic stall are explored in depth. Reynolds number was varied up to Re = 5 × 105, reduced frequency was varied up to k = 0.511, mean pitch angle was varied up to 15∘, and two pitch amplitudes of 5∘ and 10∘ were studied. It was found that reverse flow dynamic stall of the NACA 0012 airfoil is weakly sensitive to the Reynolds numbers tested due to flow separation at the sharp aerodynamic leading edge. Reduced frequency strongly affects the onset and persistence of dynamic stall vortices. The type of dynamic stall observed (i.e., number of vortex structures) increases with a decrease in reduced frequency and increase in maximum pitch angle. The characterization and parameter sensitivity of reverse flow dynamic stall given in the present work will enable the development of a physics-based analytical model of this unsteady aerodynamic phenomenon.

  5. Pre-Stall Behavior of a Transonic Axial Compressor Stage via Time-Accurate Numerical Simulation

    NASA Technical Reports Server (NTRS)

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

    2008-01-01

    CFD calculations using high-performance parallel computing were conducted to simulate the pre-stall flow of a transonic compressor stage, NASA compressor Stage 35. The simulations were run with a full-annulus grid that models the 3D, viscous, unsteady blade row interaction without the need for an artificial inlet distortion to induce stall. The simulation demonstrates the development of the rotating stall from the growth of instabilities. Pressure-rise performance and pressure traces are compared with published experimental data before the study of flow evolution prior to the rotating stall. Spatial FFT analysis of the flow indicates a rotating long-length disturbance of one rotor circumference, which is followed by a spike-type breakdown. The analysis also links the long-length wave disturbance with the initiation of the spike inception. The spike instabilities occur when the trajectory of the tip clearance flow becomes perpendicular to the axial direction. When approaching stall, the passage shock changes from a single oblique shock to a dual-shock, which distorts the perpendicular trajectory of the tip clearance vortex but shows no evidence of flow separation that may contribute to stall.

  6. Dynamic stall characterization using modal analysis of phase-averaged pressure distributions

    NASA Astrophysics Data System (ADS)

    Harms, Tanner; Nikoueeyan, Pourya; Naughton, Jonathan

    2017-11-01

    Dynamic stall characterization by means of surface pressure measurements can simplify the time and cost associated with experimental investigation of unsteady airfoil aerodynamics. A unique test capability has been developed at University of Wyoming over the past few years that allows for time and cost efficient measurement of dynamic stall. A variety of rotorcraft and wind turbine airfoils have been tested under a variety of pitch oscillation conditions resulting in a range of dynamic stall behavior. Formation, development and separation of different flow structures are responsible for the complex aerodynamic loading behavior experienced during dynamic stall. These structures have unique signatures on the pressure distribution over the airfoil. This work investigates the statistical behavior of phase-averaged pressure distribution for different types of dynamic stall by means of modal analysis. The use of different modes to identify specific flow structures is being investigated. The use of these modes for different types of dynamic stall can provide a new approach for understanding and categorizing these flows. This work uses airfoil data acquired under Army contract W911W60160C-0021, DOE Grant DE-SC0001261, and a gift from BP Alternative Energy North America, Inc.

  7. Central American Tactical Airlift Wing

    DTIC Science & Technology

    2017-03-17

    will examine the airlift demands for Central America. Then it will examine the success of the HAW in Europe. Next, cost analysis will illustrate the...feasibility of a collaborative airlift wing in Central America. Finally, we will offer a proposal for the construct of the Tactical Airlift Wing...been unable to perform outside of the HAW construct . In the same way that the HAW provides heavy airlift to partner nations that would otherwise be

  8. Low-Reynolds Number Aerodynamics of an 8.9 Percent Scale Semispan Swept Wing for Assessment of Icing Effects

    NASA Technical Reports Server (NTRS)

    Broeren, Andy P.; Woodard, Brian S.; Diebold, Jeffrey M.; Moens, Frederic

    2017-01-01

    Aerodynamic assessment of icing effects on swept wings is an important component of a larger effort to improve three-dimensional icing simulation capabilities. An understanding of ice-shape geometric fidelity and Reynolds and Mach number effects on the iced-wing aerodynamics is needed to guide the development and validation of ice-accretion simulation tools. To this end, wind-tunnel testing and computational flow simulations were carried out for an 8.9%-scale semispan wing based upon the Common Research Model airplane configuration. The wind-tunnel testing was conducted at the Wichita State University 7 ft x 10 ft Beech wind tunnel from Reynolds numbers of 0.8×10(exp 6) to 2.4×10(exp 6) and corresponding Mach numbers of 0.09 to 0.27. This paper presents the results of initial studies investigating the model mounting configuration, clean-wing aerodynamics and effects of artificial ice roughness. Four different model mounting configurations were considered and a circular splitter plate combined with a streamlined shroud was selected as the baseline geometry for the remainder of the experiments and computational simulations. A detailed study of the clean-wing aerodynamics and stall characteristics was made. In all cases, the flow over the outboard sections of the wing separated as the wing stalled with the inboard sections near the root maintaining attached flow. Computational flow simulations were carried out with the ONERA elsA software that solves the compressible, three-dimensional RANS equations. The computations were carried out in either fully turbulent mode or with natural transition. Better agreement between the experimental and computational results was obtained when considering computations with free transition compared to turbulent solutions. These results indicate that experimental evolution of the clean wing performance coefficients were due to the effect of three-dimensional transition location and that this must be taken into account for future data

  9. Low-Reynolds Number Aerodynamics of an 8.9 Percent Scale Semispan Swept Wing for Assessment of Icing Effects

    NASA Technical Reports Server (NTRS)

    Broeren, Andy P.; Woodard, Brian S.; Diebold, Jeffrey M.; Moens, Frederic

    2017-01-01

    Aerodynamic assessment of icing effects on swept wings is an important component of a larger effort to improve three-dimensional icing simulation capabilities. An understanding of ice-shape geometric fidelity and Reynolds and Mach number effects on the iced-wing aerodynamics is needed to guide the development and validation of ice-accretion simulation tools. To this end, wind-tunnel testing and computational flow simulations were carried out for an 8.9 percent-scale semispan wing based upon the Common Research Model airplane configuration. The wind-tunnel testing was conducted at the Wichita State University 7 by 10 ft Beech wind tunnel from Reynolds numbers of 0.8×10(exp 6) to 2.4×10(exp 6) and corresponding Mach numbers of 0.09 to 0.27. This paper presents the results of initial studies investigating the model mounting configuration, clean-wing aerodynamics and effects of artificial ice roughness. Four different model mounting configurations were considered and a circular splitter plate combined with a streamlined shroud was selected as the baseline geometry for the remainder of the experiments and computational simulations. A detailed study of the clean-wing aerodynamics and stall characteristics was made. In all cases, the flow over the outboard sections of the wing separated as the wing stalled with the inboard sections near the root maintaining attached flow. Computational flow simulations were carried out with the ONERA elsA software that solves the compressible, threedimensional RANS equations. The computations were carried out in either fully turbulent mode or with natural transition. Better agreement between the experimental and computational results was obtained when considering computations with free transition compared to turbulent solutions. These results indicate that experimental evolution of the clean wing performance coefficients were due to the effect of three-dimensional transition location and that this must be taken into account for future

  10. A Study of Wing Flutter

    NASA Technical Reports Server (NTRS)

    Zahm, A F; Bear, R M

    1929-01-01

    Part I describes vibration tests, in a wind tunnel, of simple airfoils and of the tail plane of an M0-1 airplane model; it also describes the air flow about this model. From these tests are drawn inferences as to the cause and cure of aerodynamic wing vibrations. Part II derives stability criteria for wing vibrations in pitch and roll, and gives design rules to obviate instability. Part III shows how to design spars to flex equally under a given wing loading and thereby economically minimize the twisting in pitch that permits cumulative flutter. Resonant flutter is not likely to ensue from turbulence of air flow along past wings and tail planes in usual flying conditions. To be flutterproof a wing must be void of reversible autorotation and not have its centroid far aft of its pitching axis, i. e., axis of pitching motion. Danger of flutter is minimized by so proportioning the wing's torsional resisting moment to the air pitching moment at high-speed angles that the torsional flexure is always small. (author)

  11. Evaluation of the significance of abrupt changes in precipitation and runoff process in China

    NASA Astrophysics Data System (ADS)

    Xie, Ping; Wu, Ziyi; Sang, Yan-Fang; Gu, Haiting; Zhao, Yuxi; Singh, Vijay P.

    2018-05-01

    Abrupt changes are an important manifestation of hydrological variability. How to accurately detect the abrupt changes in hydrological time series and evaluate their significance is an important issue, but methods for dealing with them effectively are lacking. In this study, we propose an approach to evaluate the significance of abrupt changes in time series at five levels: no, weak, moderate, strong, and dramatic. The approach was based on an index of correlation coefficient calculated for the original time series and its abrupt change component. A bigger value of correlation coefficient reflects a higher significance level of abrupt change. Results of Monte-Carlo experiments verified the reliability of the proposed approach, and also indicated the great influence of statistical characteristics of time series on the significance level of abrupt change. The approach was derived from the relationship between correlation coefficient index and abrupt change, and can estimate and grade the significance levels of abrupt changes in hydrological time series. Application of the proposed approach to ten major watersheds in China showed that abrupt changes mainly occurred in five watersheds in northern China, which have arid or semi-arid climate and severe shortages of water resources. Runoff processes in northern China were more sensitive to precipitation change than those in southern China. Although annual precipitation and surface water resources amount (SWRA) exhibited a harmonious relationship in most watersheds, abrupt changes in the latter were more significant. Compared with abrupt changes in annual precipitation, human activities contributed much more to the abrupt changes in the corresponding SWRA, except for the Northwest Inland River watershed.

  12. Supersonic Stall Flutter of High Speed Fans. [in turbofan engines

    NASA Technical Reports Server (NTRS)

    Adamczyk, J. J.; Stevens, W.; Jutras, R.

    1981-01-01

    An analytical model is developed for predicting the onset of supersonic stall bending flutter in axial flow compressors. The analysis is based on a modified two dimensional, compressible, unsteady actuator disk theory. It is applied to a rotor blade row by considering a cascade of airfoils whose geometry and dynamic response coincide with those of a rotor blade element at 85 percent of the span height (measured from the hub). The rotor blades are assumed to be unshrouded (i.e., free standing) and to vibrate in their first flexural mode. The effects of shock waves and flow separation are included in the model through quasi-steady, empirical, rotor total-pressure-loss and deviation-angle correlations. The actuator disk model predicts the unsteady aerodynamic force acting on the cascade blading as a function of the steady flow field entering the cascade and the geometry and dynamic response of the cascade. Calculations show that the present model predicts the existence of a bending flutter mode at supersonic inlet Mach numbers. This flutter mode is suppressed by increasing the reduced frequency of the system or by reducing the steady state aerodynamic loading on the cascade. The validity of the model for predicting flutter is demonstrated by correlating the measured flutter boundary of a high speed fan stage with its predicted boundary. This correlation uses a level of damping for the blade row (i.e., the log decrement of the rotor system) that is estimated from the experimental flutter data. The predicted flutter boundary is shown to be in good agreement with the measured boundary.

  13. Abrupt Atmospheric Methane Increases Associated With Hudson Strait Heinrich Events

    NASA Astrophysics Data System (ADS)

    Rhodes, R.; Brook, E.; Chiang, J. C. H.; Blunier, T.; Maselli, O. J.; McConnell, J. R.; Romanini, D.; Severinghaus, J. P.

    2015-12-01

    The drivers of abrupt climate change during the Last Glacial Period are not well understood. While Dansgaard-Oeschger (DO) cycles are thought to be linked to variations in the strength of the Atlantic Meridional Ocean Circulation (AMOC), it is not clear how or if Heinrich Events—extensive influxes of icebergs into the North Atlantic Ocean that impacted global climate and biogeochemistry—are related. An enduring problem is the difficultly in dating iceberg rafted debris deposits that typically lack foraminifera. Here we present an ultra-high resolution record of methane from the West Antarctic Ice Sheet Divide ice core at unprecedented, continuous temporal resolution from 67.2-9.8 ka BP, which we propose constrains the timing of Heinrich events. Our methane record essentially mirrors Greenland ice core stable isotope variability across D-O events, except during Heinrich stadials 1, 2, 4 and 5. Partway through these stadials only, methane increases abruptly and rapidly, as at the onset of a D-O event but Greenland temperature exhibits no equivalent response. Speleothem records exhibit signatures of drought in the Northern extra-tropics and intensified monsoonal activity over South America at these times. We use a simple heuristic model to propose that cold air temperatures and extensive sea ice in the North, resulting from Heinrich events, caused extreme reorganization of tropical hydroclimate. This involved curtailment of the seasonal northerly migration of tropical rain belts, leading to intensification of rainfall over Southern Hemisphere tropical wetlands, thus allowing production of excess methane relative to a 'normal' Greenland stadial. We note that this mechanism can operate if AMOC is already in a slowed state when a Heinrich event occurs, as paleo-evidence suggests it was. Heinrich events and associated sea ice cover would therefore act to prolong the duration of this AMOC state. Our findings place the big four Heinrich events of Hudson Strait origin

  14. Channel-wing System for Thrust Deflection and Force/Moment Generation

    NASA Technical Reports Server (NTRS)

    Englar, Robert J. (Inventor); Bushnell, Dennis M. (Inventor)

    2006-01-01

    An aircraft comprising a Channel Wing having blown c h - ne1 circulation control wings (CCW) for various functions. The blown channel CCW includes a channel that has a rounded or near-round trailing edge. The channel further has a trailing-edge slot that is adjacent to the rounded trailing edge of the channel. The trailing-edge slot has an inlet connected to a source of pressurized air and is capable of tangentially discharging pressurized air over the rounded trailing edge. The aircraft further has a propeller that is located in the channel and ahead of the rounded trailing edge of the channel. The propeller provides a propeller thrust exhaust stream across the channel wing to propel the aircraft through the air and to provide high lift. The pressurized air being discharged over the rounded trailing edge provides a high lift that is obtained independent of an aircraft angle of attack, thus preventing the asymmetry. separated flow, and stall experienced by the CC wing at the high angle of attack it required for high lift generation. The aircraft can further include blown outboard circulation control wings (CCW) that are synergistically connected to the blown channel CCWs. The blown outboard CCWs provide additional high lift, control thrust/drag interchange, and can provide all three aerodynamic moments when differential blowing is applied front-to-rear or left-to-right. Both the blown channel CCW and the outboard CCW also have leading-edge blowing slots to prevent flow separation or to provide aerodynamic moments for control.

  15. The aerodynamic benefit of wing-wing interaction depends on stroke trajectory in flapping insect wings.

    PubMed

    Lehmann, Fritz-Olaf; Pick, Simon

    2007-04-01

    Flying insects may enhance their flight force production by contralateral wing interaction during dorsal stroke reversal ('clap-and-fling'). In this study, we explored the forces and moments due to clap-and-fling at various wing tip trajectories, employing a dynamically scaled electromechanical flapping device. The 17 tested bio-inspired kinematic patterns were identical in stroke amplitude, stroke frequency and angle of attack with respect to the horizontal stroke plane but varied in heaving motion. Clap-and-fling induced vertical force augmentation significantly decreased with increasing vertical force production averaged over the entire stroke cycle, whereas total force augmentation was independent from changes in force produced by a single wing. Vertical force augmentation was also largely independent of forces produced due to wing rotation at the stroke reversals, the sum of rotational circulation and wake capture force. We obtained maximum (17.4%) and minimum (1.4%) vertical force augmentation in two types of figure-eight stroke kinematics whereby rate and direction of heaving motion during fling may explain 58% of the variance in vertical force augmentation. This finding suggests that vertical wing motion distinctly alters the flow regime at the beginning of the downstroke. Using an analytical model, we determined pitching moments acting on an imaginary body of the flapping device from the measured time course of forces, the changes in length of the force vector's moment arm, the position of the centre of mass and body angle. The data show that pitching moments are largely independent from mean vertical force; however, clap-and-fling reinforces mean pitching moments by approximately 21%, compared to the moments produced by a single flapping wing. Pitching moments due to clap-and-fling significantly increase with increasing vertical force augmentation and produce nose-down moments in most of the tested patterns. The analytical model, however, shows that

  16. Heat and pregnancy-related emergencies: Risk of placental abruption during hot weather.

    PubMed

    He, Siyi; Kosatsky, Tom; Smargiassi, Audrey; Bilodeau-Bertrand, Marianne; Auger, Nathalie

    2018-02-01

    Outdoor heat increases the risk of preterm birth and stillbirth, but the association with placental abruption has not been studied. Placental abruption is a medical emergency associated with major morbidity and mortality in pregnancy. We determined the relationship between ambient temperature and risk of placental abruption in warm seasons. We performed a case-crossover analysis of 17,172 women whose pregnancies were complicated by placental abruption in Quebec, Canada from May to October 1989-2012. The main exposure measure was the maximum temperature reached during the week before abruption. We computed odds ratios (OR) and 95% confidence intervals (CI) for the association of temperature with placental abruption, adjusted for humidity and public holidays. We assessed whether associations were stronger preterm or at term, or varied with maternal age, parity, comorbidity and socioeconomic status. Compared with 15°C, a maximum weekly temperature of 30°C was associated with 1.07 times the odds of abruption (95% CI 0.99-1.16). When the timing of abruption was examined, the associations were significantly stronger at term (OR 1.12, 95% CI 1.02-1.24) than preterm (OR 0.96, 95% CI 0.83-1.10). Relationships were more prominent at term for women who were younger than 35years old, nulliparous or socioeconomically disadvantaged, but did not vary with comorbidity. Associations were stronger within 1 and 5days of abruption. Temperature was not associated with preterm abruption regardless of maternal characteristics. Elevated temperatures in warm seasons may increase the risk of abruption in women whose pregnancies are near or at term. Pregnant women may be more sensitive to heat and should consider preventive measures such as air conditioning and hydration during hot weather. Copyright © 2017 Elsevier Ltd. All rights reserved.

  17. Abrupt drainage cycles of the Fennoscandian Ice Sheet

    PubMed Central

    Soulet, Guillaume; Ménot, Guillemette; Bayon, Germain; Rostek, Frauke; Ponzevera, Emmanuel; Toucanne, Samuel; Lericolais, Gilles; Bard, Edouard

    2013-01-01

    Continental ice sheets are a key component of the Earth’s climate system, but their internal dynamics need to be further studied. Since the last deglaciation, the northern Eurasian Fennoscandian Ice Sheet (FIS) has been connected to the Black Sea (BS) watershed, making this basin a suitable location to investigate former ice-sheet dynamics. Here, from a core retrieved in the BS, we combine the use of neodymium isotopes, high-resolution elemental analysis, and biomarkers to trace changes in sediment provenance and river runoff. We reveal cyclic releases of meltwater originating from Lake Disna, a proglacial lake linked to the FIS during Heinrich Stadial 1. Regional interactions within the climate–lake–FIS system, linked to changes in the availability of subglacial water, led to abrupt drainage cycles of the FIS into the BS watershed. This phenomenon raised the BS water level by ∼100 m until the sill of the Bosphorus Strait was reached, flooding the vast northwestern BS shelf and deeply affecting the hydrology and circulation of the BS and, probably, of the Marmara and Aegean Seas. PMID:23569264

  18. Modeling geologically abrupt climate changes in the Miocene

    NASA Astrophysics Data System (ADS)

    Haupt, B. J.; Seidov, D.

    2010-12-01

    The gradual cooling of the Cenozoic, including the Miocene epoch, was punctuated by many geologically abrupt warming and cooling episodes - strong deviations from the cooling trend with time span of ten to hundred thousands of years. Our working hypothesis is that some of those warming episodes at least partially might have been caused by dynamics of the emerging Antarctic Ice Sheet, which, in turn, might have caused strong changes of sea surface salinity in the Miocene Southern Ocean. Feasibility of this hypothesis is explored in a series of coupled ocean-atmosphere computer experiments. The results suggest that relatively small and geologically short-lived changes in freshwater balance in the Southern Ocean could have significantly contributed to at least two prominent warming episodes in the Miocene. Importantly, the experiments also suggest that the Southern Ocean was more sensitive to the salinity changes in the Miocene than today, which can attributed to the opening of the Central American Isthmus as a major difference between the Miocene and the present-day ocean-sea geometry.

  19. Turbulent forced convection of nanofluids downstream an abrupt expansion

    NASA Astrophysics Data System (ADS)

    Kimouche, Abdelali; Mataoui, Amina

    2018-03-01

    Turbulent forced convection of Nanofluids through an axisymmetric abrupt expansion is investigated numerically in the present study. The governing equations are solved by ANYS 14.0 CFD code based on the finite volume method by implementing the thermo-physical properties of each nanofluid. All results are analyzed through the evolutions of skin friction coefficient and Nusselt number. For each nanofluid, the effect of both volume fraction and Reynolds number on this type of flow configuration, are examined. An increase on average Nusselt number with the volume fraction and Reynolds number, are highlighted and correlated. Two relationships are proposed. The first one, determines the average Nusselt number versus Reynolds number, volume fraction and the ratio of densities of the solid particles to that of the base fluid ( \\overline{Nu}=f(\\operatorname{Re},φ, ρ_s/ρ_f) ). The second one varies according Reynolds number, volume fraction and the conductivities ratio of solid particle to that of the base fluid ( \\overline{Nu}=f(\\operatorname{Re},φ, k_s/k_f) ).

  20. Placental abruption: etiopathogenic aspects, diagnostic and therapeutic implications.

    PubMed

    Brăila, Anca Daniela; Gluhovschi, Adrian; Neacşu, Adrian; Lungulescu, Cristian Virgil; Brăila, Mihai; Vîrcan, Elena Luminiţa; Cotoi, Bogdan Virgil; Gogănău, Alexandru Marian

    2018-01-01

    The severe form of retroplacental hematoma is a serious accident in the second stage of pregnancy and at birth with frightening for the mother and fetus that often lead to death. The pathological mechanism presumes conditions for a "special ground" capital for the "efficiency" of the acute intradecidual vascular accident with the rupture of the uterus-placental arterioles. The complete clinical picture of this severe form of retroplacental hematoma - the placental abruption, observed and mentioned by the classics (vascular drama of Couvelaire) consists of five syndromes, 18 signs and symptoms, four paradoxes, phenomena not fully met in the other forms of retroplacental hematoma (minor and intermediate). The rate of incidence of retroplacental hematoma is in between 0.13-1.38% and depends on the environment, on the socio-economic and medical conditions, on the "obstetric education" and associated pathology. Our study aims at re-evaluating the clinico-paraclinical phenomenon imposed by the dramatism of the phenomenon of in utero placental apoplexy, the impact on neonatal mortality and on the functional prognosis from the point of view of surgical climax.

  1. Dynamic response of desert wetlands to abrupt climate change

    PubMed Central

    Springer, Kathleen B.; Manker, Craig R.; Pigati, Jeffrey S.

    2015-01-01

    Desert wetlands are keystone ecosystems in arid environments and are preserved in the geologic record as groundwater discharge (GWD) deposits. GWD deposits are inherently discontinuous and stratigraphically complex, which has limited our understanding of how desert wetlands responded to past episodes of rapid climate change. Previous studies have shown that wetlands responded to climate change on glacial to interglacial timescales, but their sensitivity to short-lived climate perturbations is largely unknown. Here, we show that GWD deposits in the Las Vegas Valley (southern Nevada, United States) provide a detailed and nearly complete record of dynamic hydrologic changes during the past 35 ka (thousands of calibrated 14C years before present), including cycles of wetland expansion and contraction that correlate tightly with climatic oscillations recorded in the Greenland ice cores. Cessation of discharge associated with rapid warming events resulted in the collapse of entire wetland systems in the Las Vegas Valley at multiple times during the late Quaternary. On average, drought-like conditions, as recorded by widespread erosion and the formation of desert soils, lasted for a few centuries. This record illustrates the vulnerability of desert wetland flora and fauna to abrupt climate change. It also shows that GWD deposits can be used to reconstruct paleohydrologic conditions at millennial to submillennial timescales and informs conservation efforts aimed at protecting these fragile ecosystems in the face of anthropogenic warming. PMID:26554007

  2. Abrupt climate changes during Termination III in Southern Europe.

    PubMed

    Pérez-Mejías, Carlos; Moreno, Ana; Sancho, Carlos; Bartolomé, Miguel; Stoll, Heather; Cacho, Isabel; Cheng, Hai; Edwards, R Lawrence

    2017-09-19

    The Late Quaternary glacial-interglacial transitions represent the highest amplitude climate changes over the last million years. Unraveling the sequence of events and feedbacks at Termination III (T-III), including potential abrupt climate reversals similar to those of the last Termination, has been particularly challenging due to the scarcity of well-dated records worldwide. Here, we present speleothem data from southern Europe covering the interval from 262.7 to 217.9 kyBP, including the transition from marine isotope stage (MIS) 8 to MIS 7e. High-resolution δ 13 C, δ 18 O, and Mg/Ca profiles reveal major millennial-scale changes in aridity manifested in changing water availability and vegetation productivity. uranium-thorium dates provide a solid chronology for two millennial-scale events (S8.1 and S8.2) which, compared with the last two terminations, has some common features with Heinrich 1 and Heinrich 2 in Termination I (T-I).

  3. Abrupt climate changes during Termination III in Southern Europe

    NASA Astrophysics Data System (ADS)

    Pérez-Mejías, Carlos; Moreno, Ana; Sancho, Carlos; Bartolomé, Miguel; Stoll, Heather; Cacho, Isabel; Cheng, Hai; Edwards, R. Lawrence

    2017-09-01

    The Late Quaternary glacial-interglacial transitions represent the highest amplitude climate changes over the last million years. Unraveling the sequence of events and feedbacks at Termination III (T-III), including potential abrupt climate reversals similar to those of the last Termination, has been particularly challenging due to the scarcity of well-dated records worldwide. Here, we present speleothem data from southern Europe covering the interval from 262.7 to 217.9 kyBP, including the transition from marine isotope stage (MIS) 8 to MIS 7e. High-resolution δ13C, δ18O, and Mg/Ca profiles reveal major millennial-scale changes in aridity manifested in changing water availability and vegetation productivity. uranium-thorium dates provide a solid chronology for two millennial-scale events (S8.1 and S8.2) which, compared with the last two terminations, has some common features with Heinrich 1 and Heinrich 2 in Termination I (T-I).

  4. Abrupt climate changes during Termination III in Southern Europe

    PubMed Central

    Pérez-Mejías, Carlos; Moreno, Ana; Sancho, Carlos; Bartolomé, Miguel; Stoll, Heather; Cacho, Isabel; Cheng, Hai; Edwards, R. Lawrence

    2017-01-01

    The Late Quaternary glacial–interglacial transitions represent the highest amplitude climate changes over the last million years. Unraveling the sequence of events and feedbacks at Termination III (T-III), including potential abrupt climate reversals similar to those of the last Termination, has been particularly challenging due to the scarcity of well-dated records worldwide. Here, we present speleothem data from southern Europe covering the interval from 262.7 to 217.9 kyBP, including the transition from marine isotope stage (MIS) 8 to MIS 7e. High-resolution δ13C, δ18O, and Mg/Ca profiles reveal major millennial-scale changes in aridity manifested in changing water availability and vegetation productivity. uranium–thorium dates provide a solid chronology for two millennial-scale events (S8.1 and S8.2) which, compared with the last two terminations, has some common features with Heinrich 1 and Heinrich 2 in Termination I (T-I). PMID:28874530

  5. Anticipating abrupt shifts in temporal evolution of probability of eruption

    NASA Astrophysics Data System (ADS)

    Rohmer, J.; Loschetter, A.

    2016-04-01

    Estimating the probability of eruption by jointly accounting for different sources of monitoring parameters over time is a key component for volcano risk management. In the present study, we are interested in the transition from a state of low-to-moderate probability value to a state of high probability value. By using the data of MESIMEX exercise at the Vesuvius volcano, we investigated the potential for time-varying indicators related to the correlation structure or to the variability of the probability time series for detecting in advance this critical transition. We found that changes in the power spectra and in the standard deviation estimated over a rolling time window both present an abrupt increase, which marks the approaching shift. Our numerical experiments revealed that the transition from an eruption probability of 10-15% to > 70% could be identified up to 1-3 h in advance. This additional lead time could be useful to place different key services (e.g., emergency services for vulnerable groups, commandeering additional transportation means, etc.) on a higher level of alert before the actual call for evacuation.

  6. Abrupt drainage cycles of the Fennoscandian Ice Sheet.

    PubMed

    Soulet, Guillaume; Ménot, Guillemette; Bayon, Germain; Rostek, Frauke; Ponzevera, Emmanuel; Toucanne, Samuel; Lericolais, Gilles; Bard, Edouard

    2013-04-23

    Continental ice sheets are a key component of the Earth's climate system, but their internal dynamics need to be further studied. Since the last deglaciation, the northern Eurasian Fennoscandian Ice Sheet (FIS) has been connected to the Black Sea (BS) watershed, making this basin a suitable location to investigate former ice-sheet dynamics. Here, from a core retrieved in the BS, we combine the use of neodymium isotopes, high-resolution elemental analysis, and biomarkers to trace changes in sediment provenance and river runoff. We reveal cyclic releases of meltwater originating from Lake Disna, a proglacial lake linked to the FIS during Heinrich Stadial 1. Regional interactions within the climate-lake-FIS system, linked to changes in the availability of subglacial water, led to abrupt drainage cycles of the FIS into the BS watershed. This phenomenon raised the BS water level by ∼100 m until the sill of the Bosphorus Strait was reached, flooding the vast northwestern BS shelf and deeply affecting the hydrology and circulation of the BS and, probably, of the Marmara and Aegean Seas.

  7. Dynamic response of desert wetlands to abrupt climate change

    USGS Publications Warehouse

    Springer, Kathleen; Manker, Craig; Pigati, Jeffrey S.

    2015-01-01

    Desert wetlands are keystone ecosystems in arid environments and are preserved in the geologic record as groundwater discharge (GWD) deposits. GWD deposits are inherently discontinuous and stratigraphically complex, which has limited our understanding of how desert wetlands responded to past episodes of rapid climate change. Previous studies have shown that wetlands responded to climate change on glacial to interglacial timescales, but their sensitivity to short-lived climate perturbations is largely unknown. Here, we show that GWD deposits in the Las Vegas Valley (southern Nevada, United States) provide a detailed and nearly complete record of dynamic hydrologic changes during the past 35 ka (thousands of calibrated 14C years before present), including cycles of wetland expansion and contraction that correlate tightly with climatic oscillations recorded in the Greenland ice cores. Cessation of discharge associated with rapid warming events resulted in the collapse of entire wetland systems in the Las Vegas Valley at multiple times during the late Quaternary. On average, drought-like conditions, as recorded by widespread erosion and the formation of desert soils, lasted for a few centuries. This record illustrates the vulnerability of desert wetland flora and fauna to abrupt climate change. It also shows that GWD deposits can be used to reconstruct paleohydrologic conditions at millennial to submillennial timescales and informs conservation efforts aimed at protecting these fragile ecosystems in the face of anthropogenic warming.

  8. Detecting and isolating abrupt changes in linear switching systems

    NASA Astrophysics Data System (ADS)

    Nazari, Sohail; Zhao, Qing; Huang, Biao

    2015-04-01

    In this paper, a novel fault detection and isolation (FDI) method for switching linear systems is developed. All input and output signals are assumed to be corrupted with measurement noises. In the proposed method, a 'lifted' linear model named as stochastic hybrid decoupling polynomial (SHDP) is introduced. The SHDP model governs the dynamics of the switching linear system with all different modes, and is independent of the switching sequence. The error-in-variable (EIV) representation of SHDP is derived, and is used for the fault residual generation and isolation following the well-adopted local approach. The proposed FDI method can detect and isolate the fault-induced abrupt changes in switching models' parameters without estimating the switching modes. Furthermore, in this paper, the analytical expressions of the gradient vector and Hessian matrix are obtained based on the EIV SHDP formulation, so that they can be used to implement the online fault detection scheme. The performance of the proposed method is then illustrated by simulation examples.

  9. Mechanical characterization of capsule properties using abrupt-step channels

    NASA Astrophysics Data System (ADS)

    Salsac, Anne-Virginie; Le Goff, Anne; Kaoui, Badr; Barthè-Biesel, Dominique; Biomechanics; Bioengineering Lab Team

    2017-11-01

    Capsules consisting of a liquid droplet enclosed by a thin polymerized membrane are commonly encountered in nature (cells) or in industrial process (pharmaceutical, cosmetic or food products). The mechanical properties of the capsule wall are essential to guarantee the particle integrity and release of the internal contents when and where necessary. The difficulty is to assess the mechanical properties of the thin membrane. We will show how abrupt-step channels can be used to identify the membrane viscoelastic properties and point of rupture. This can be achieved by using a channel presenting a step change in cross-section and inverting the direction of the flow of the capsule suspension within the tube. To deduce information on the viscoelasticity, we will exploit the relaxation of the capsules as they flow through the expansion. To study membrane rupture, we will instead invert the channel, block the capsules at the neck of the constriction and determine the pressure difference needed for breakup. All the experiments will be conducted on initially spherical capsules with a thin cross-linked protein membrane for a proof of concept.

  10. The role of the leading edge vortex in lift augmentation of steadily revolving wings: a change in perspective

    PubMed Central

    Crowther, William J.

    2017-01-01

    The presence of a stable leading edge vortex (LEV) on steadily revolving wings increases the maximum lift coefficient that can be generated from the wing and its role is important to understanding natural flyers and flapping wing vehicles. In this paper, the role of LEV in lift augmentation is discussed under two hypotheses referred to as ‘additional lift' and ‘absence of stall’. The ‘additional lift' hypothesis represents the traditional view. It presumes that an additional suction/circulation from the LEV increases the lift above that of a potential flow solution. This behaviour may be represented through either the ‘Polhamus leading edge suction' model or the so-called ‘trapped vortex' model. The ‘absence of stall' hypothesis is a more recent contender that presumes that the LEV prevents stall at high angles of attack where flow separation would normally occur. This behaviour is represented through the so-called ‘normal force' model. We show that all three models can be written in the form of the same potential flow kernel with modifiers to account for the presence of a LEV. The modelling is built on previous work on quasi-steady models for hovering wings such that model parameters are determined from first principles, which allows a fair comparison between the models themselves, and the models and experimental data. We show that the two models which directly include the LEV as a lift generating component are built on a physical picture that does not represent the available experimental data. The simpler ‘normal force' model, which does not explicitly model the LEV, performs best against data in the literature. We conclude that under steady conditions the LEV as an ‘absence of stall’ model/mechanism is the most satisfying explanation for observed aerodynamic behaviour. PMID:28747395

  11. Aircraft wing structural detail design (wing, aileron, flaps, and subsystems)

    NASA Technical Reports Server (NTRS)

    Downs, Robert; Zable, Mike; Hughes, James; Heiser, Terry; Adrian, Kenneth

    1993-01-01

    The goal of this project was to design, in detail, the wing, flaps, and ailerons for a primary flight trainer. Integrated in this design are provisions for the fuel system, the electrical system, and the fuselage/cabin carry-through interface structure. This conceptual design displays the general arrangement of all major components in the wing structure, taking into consideration the requirements set forth by the appropriate sections of Federal Aviation Regulation Part 23 (FAR23) as well as those established in the statement of work.

  12. Stage effects on stalling and recovery of a high-speed 10-stage axial-flow compressor

    SciTech Connect

    Copenhaver, W.W.

    1988-01-01

    Results of a high-speed 10-stage axial-flow compressor test involving overall compressor and individual stage performance while stalling and operating in quasi-steady rotating stall are described. Test procedures and data-acquisition methods used to obtain the dynamic stalling and quasi-steady in-stall data are explained. Unstalled and in-stall time-averaged data obtained from the compressor operating at five different shaft speeds and one off-schedule variable vane condition are presented. Effects of compressor speed and variable geometry on overall compressor in-stall pressure rise and hysteresis extent are illustrated through the use of quasi-steady-stage temperature rise and pressure-rise characteristics. Results indicate that individual stage performance duringmore » overall compressor rotating stall operation varies considerably throughout the length of the compressor. The measured high-speed 10-stage test compressor individual stage pressure and temperature characteristics were input into a stage-by-stage dynamic compressor performance model. Comparison of the model results and measured pressures provided the additional validation necessary to demonstrate the model's ability to predict high-speed multistage compressor stalling and in-stall performance.« less

  13. Wing flexibility improves bumblebee flight stability.

    PubMed

    Mistick, Emily A; Mountcastle, Andrew M; Combes, Stacey A

    2016-11-01

    Insect wings do not contain intrinsic musculature to change shape, but rather bend and twist passively during flight. Some insect wings feature flexible joints along their veins that contain patches of resilin, a rubber-like protein. Bumblebee wings exhibit a central resilin joint (1m-cu) that has previously been shown to improve vertical force production during hovering flight. In this study, we artificially stiffened bumblebee (Bombus impatiens) wings in vivo by applying a micro-splint to the 1m-cu joint, and measured the consequences for body stability during forward flight in both laminar and turbulent airflow. In laminar flow, bees with stiffened wings exhibited significantly higher mean rotation rates and standard deviation of orientation about the roll axis. Decreasing the wing's flexibility significantly increased its projected surface area relative to the oncoming airflow, likely increasing the drag force it experienced during particular phases of the wing stroke. We hypothesize that higher drag forces on stiffened wings decrease body stability when the left and right wings encounter different flow conditions. Wing splinting also led to a small increase in body rotation rates in turbulent airflow, but this change was not statistically significant, possibly because bees with stiffened wings changed their flight behavior in turbulent flow. Overall, we found that wing flexibility improves flight stability in bumblebees, adding to the growing appreciation that wing flexibility is not merely an inevitable liability in flapping flight, but can enhance flight performance. © 2016. Published by The Company of Biologists Ltd.

  14. An archival analysis of stall warning system effectiveness during airborne icing encounters

    NASA Astrophysics Data System (ADS)

    Maris, John Michael

    An archival study was conducted to determine the influence of stall warning system performance on aircrew decision-making outcomes during airborne icing encounters. A Conservative Icing Response Bias (CIRB) model was developed to explain the historical variability in aircrew performance in the face of airframe icing. The model combined Bayes' Theorem with Signal Detection Theory (SDT) concepts to yield testable predictions that were evaluated using a Binary Logistic Regression (BLR) multivariate technique applied to two archives: the NASA Aviation Safety Reporting System (ASRS) incident database, and the National Transportation Safety Board (NTSB) accident databases, both covering the period January 1, 1988 to October 2, 2015. The CIRB model predicted that aircrew would experience more incorrect response outcomes in the face of missed stall warnings than with stall warning False Alarms. These predicted outcomes were observed at high significance levels in the final sample of 132 NASA/NTSB cases. The CIRB model had high sensitivity and specificity, and explained 71.5% (Nagelkerke R2) of the variance of aircrew decision-making outcomes during the icing encounters. The reliability and validity metrics derived from this study suggest indicate that the findings are generalizable to the population of U.S. registered turbine-powered aircraft. These findings suggest that icing-related stall events could be reduced if the incidence of stall warning Misses could be minimized. Observed stall warning Misses stemmed from three principal causes: aerodynamic icing effects, which reduced the stall angle-of-attack (AoA) to below the stall warning calibration threshold; tail stalls, which are not monitored by contemporary protection systems; and icing-induced system issues (such as frozen pitot tubes), which compromised stall warning system effectiveness and airframe envelope protections. Each of these sources of missed stall warnings could be addressed by Aerodynamic Performance

  15. Aerodynamic optimization of aircraft wings using a coupled VLM-2.5D RANS approach

    NASA Astrophysics Data System (ADS)

    Parenteau, Matthieu

    The design process of transonic civil aircraft is complex and requires strong governance to manage the various program development phases. There is a need in the community to have numerical models in all disciplines that span the conceptual, preliminary and detail design phases in a seamless fashion so that choices made in each phase remain consistent with each other. The objective of this work is to develop an aerodynamic model suitable for conceptual multidisciplinary design optimization with low computational cost and sufficient fidelity to explore a large design space in the transonic and high-lift regimes. The physics-based reduce order model is based on the inviscid Vortex Lattice Method (VLM), selected for its low computation time. Viscous effects are modeled with two-dimensional high-fidelity RANS calculations at various sections along the span and incorporated as an angle of attack correction inside the VLM. The viscous sectional data are calculated with infinite swept wing conditions to allow viscous crossflow effects to be included for a more accurate maximum lift coefficient and spanload evaluations. These viscous corrections are coupled through a modified alpha coupling method for 2.5D RANS sectional data, stabilized in the post-stall region with artificial dissipation. The fidelity of the method is verified against 3D RANS flow solver solutions on the Bombardier Research Wing (BRW). Clean and high-lift configurations are investigated. The overall results show impressive precision of the VLM/2.5D RANS approach compared to 3D RANS solutions and in compute times in the order of seconds on a standard desktop computer. Finally, the aerodynamic solver is implemented in an optimization framework with a Covariant Matrix Adaptation Evolution Strategy (CMA-ES) optimizer to explore the design space of aerodynamic wing planform. Single-objective low-speed and high-speed optimizations are performed along with composite-objective functions for combined low

  16. Measurements and performance prediction of an adaptive wing micro air vehicle

    NASA Astrophysics Data System (ADS)

    Shkarayev, Sergey V.; Jouse, Wayne C.; Null, William R.; Wagner, Matthew G.

    2003-08-01

    The mission space requirements imposed on the design of micro air vehicles (MAVs) typically consist of several distinct flight segments that generally conflict: the transit phases of flight require high speeds, while the loiter/surveillance phase requires lower flight velocities. Maximum efficiency must be sought in order to prolong battery life and aircraft endurance. The adaptive wing MAV developed at the University of Arizona features a thin, deformable flying wing with an efficient rudder-elevator control system. The wing camber is varied to accommodate different flight speeds while maintaining a constant total lift at a relatively low angle of attack. A new airfoil was developed from the Selig 5010 that features a small negative pitching moment for pitch stability. Wind tunnel tests were performed and stall angles and best lift-to-drag ratios were analyzed from the data. The wind tunnel data was used in a performance analysis in order to determine the flight speeds and throttle settings for maximum endurance at each camber, as well as the MAV's theoretical minimum and maximum flight speeds. The effectiveness of camber change on flight speed and endurance was examined with promising results; flight speed could be reduced by 25% by increasing the camber from 3 to 9% without any increase in power consumption.

  17. Measurement of circulation around wing-tip vortices and estimation of lift forces using stereo PIV

    NASA Astrophysics Data System (ADS)

    Asano, Shinichiro; Sato, Haru; Sakakibara, Jun

    2017-11-01

    Applying the flapping flight to the development of an aircraft as Mars space probe and a small aircraft called MAV (Micro Air Vehicle) is considered. This is because Reynolds number assumed as the condition of these aircrafts is low and similar to of insects and small birds flapping on the earth. However, it is difficult to measure the flow around the airfoil in flapping flight directly because of its three-dimensional and unsteady characteristics. Hence, there is an attempt to estimate the flow field and aerodynamics by measuring the wake of the airfoil using PIV, for example the lift estimation method based on a wing-tip vortex. In this study, at the angle of attack including the angle after stall, we measured the wing-tip vortex of a NACA 0015 cross-sectional and rectangular planform airfoil using stereo PIV. The circulation of the wing-tip vortex was calculated from the obtained velocity field, and the lift force was estimated based on Kutta-Joukowski theorem. Then, the validity of this estimation method was examined by comparing the estimated lift force and the force balance data at various angles of attack. The experiment results are going to be presented in the conference.

  18. An Experimental Investigation of Flow past a Wing at high Angles of Attack

    NASA Astrophysics Data System (ADS)

    Dalela, Vipul; Mukherjee, Rinku

    2017-11-01

    The aerodynamic characteristics for post-stall angles of attack past a single and/or multiple 3D wing(s) have been studied using a novel `decambering technique' assuming the flow to be steady. It is expected that the location of separation as well as the strength of the separated flow is unsteady. The objective of this work therefore is to investigate flow at high angles of attack considering unsteady behavior. The numerical technique used for this purpose that accounts for loss in camber due to flow separation is termed as `decambering'. Two linear functions are used to define the `decambering' for the steady case, located at the leading edge and anywhere between 50%-80% chord. Wind tunnel experiments are to be conducted to study the unsteady nature of separated flow using flow visualization techniques. An estimation of the unsteady wake will be of paramount importance. It is expected to get an experimental corroboration for the numerical decambering. A NACA 4415 wing section is being tested for a range of Reynolds numbers. It is observed from the preliminary results that the drag becomes more dominant after increasing the Reynolds number from Re = 0.093 ×106 to Re = 0.128 ×106 resulting a gentle decrease in the lift coefficient, Cl.

  19. An experimental description of the flow in a centrifugal compressor from alternate stall to surge

    NASA Astrophysics Data System (ADS)

    Moënne-Loccoz, V.; Trébinjac, I.; Benichou, E.; Goguey, S.; Paoletti, B.; Laucher, P.

    2017-08-01

    The present paper gives the experimental results obtained in a centrifugal compressor stage designed and built by SAFRAN Helicopter Engines. The compressor is composed of inlet guide vanes, a backswept splittered unshrouded impeller, a splittered vaned radial diffuser and axial outlet guide vanes. Previous numerical simulations revealed a particular S-shape pressure rise characteristic at partial rotation speed and predicted an alternate flow pattern in the vaned radial diffuser at low mass flow rate. This alternate flow pattern involves two adjacent vane passages. One passage exhibits very low momentum and a low pressure recovery, whereas the adjacent passage has very high momentum in the passage inlet and diffuses efficiently. Experimental measurements confirm the S-shape of the pressure rise characteristic even if the stability limit experimentally occurs at higher mass flow than numerically predicted. At low mass flow the alternate stall pattern is confirmed thanks to the data obtained by high-frequency pressure sensors. As the compressor is throttled the path to instability has been registered and a first scenario of the surge inception is given. The compressor first experiences a steady alternate stall in the diffuser. As the mass flow decreases, the alternate stall amplifies and triggers the mild surge in the vaned diffuser. An unsteady behavior results from the interaction of the alternate stall and the mild surge. Finally, when the pressure gradient becomes too strong, the alternate stall blows away and the compressor enters into deep surge.

  20. A time-varying subjective quality model for mobile streaming videos with stalling events

    NASA Astrophysics Data System (ADS)

    Ghadiyaram, Deepti; Pan, Janice; Bovik, Alan C.

    2015-09-01

    Over-the-top mobile video streaming is invariably influenced by volatile network conditions which cause playback interruptions (stalling events), thereby impairing users' quality of experience (QoE). Developing models that can accurately predict users' QoE could enable the more efficient design of quality-control protocols for video streaming networks that reduce network operational costs while still delivering high-quality video content to the customers. Existing objective models that predict QoE are based on global video features, such as the number of stall events and their lengths, and are trained and validated on a small pool of ad hoc video datasets, most of which are not publicly available. The model we propose in this work goes beyond previous models as it also accounts for the fundamental effect that a viewer's recent level of satisfaction or dissatisfaction has on their overall viewing experience. In other words, the proposed model accounts for and adapts to the recency, or hysteresis effect caused by a stall event in addition to accounting for the lengths, frequency of occurrence, and the positions of stall events - factors that interact in a complex way to affect a user's QoE. On the recently introduced LIVE-Avvasi Mobile Video Database, which consists of 180 distorted videos of varied content that are afflicted solely with over 25 unique realistic stalling events, we trained and validated our model to accurately predict the QoE, attaining standout QoE prediction performance.

  1. Analysis of an unswept propfan blade with a semiempirical dynamic stall model

    NASA Technical Reports Server (NTRS)

    Reddy, T. S. R.; Kaza, K. R. V.

    1989-01-01

    The time history response of a propfan wind tunnel model with dynamic stall is studied analytically. The response obtained from the analysis is compared with available experimental data. The governing equations of motion are formulated in terms of blade normal modes which are calculated using the COSMIC-NASTRAN computer code. The response analysis considered the blade plunging and pitching motions. The lift, drag and moment coefficients for angles of attack below the static stall angle are obtained from a quasi-steady theory. For angles above static stall angles, a semiempirical dynamic stall model based on a correction to angle of attack is used to obtain lift, drag and moment coefficients. Using these coefficients, the aerodynamic forces are calculated at a selected number of strips, and integrated to obtain the total generalized forces. The combined momentum-blade element theory is used to calculate the induced velocity. The semiempirical stall model predicted a limit cycle oscillation near the setting angle at which large vibratory stresses were observed in an experiment. The predicted mode and frequency of oscillation also agreed with those measured in the experiment near the setting angle.

  2. Rkr1/Ltn1 Ubiquitin Ligase-mediated Degradation of Translationally Stalled Endoplasmic Reticulum Proteins*

    PubMed Central

    Crowder, Justin J.; Geigges, Marco; Gibson, Ryan T.; Fults, Eric S.; Buchanan, Bryce W.; Sachs, Nadine; Schink, Andrea; Kreft, Stefan G.; Rubenstein, Eric M.

    2015-01-01

    Aberrant nonstop proteins arise from translation of mRNA molecules beyond the coding sequence into the 3′-untranslated region. If a stop codon is not encountered, translation continues into the poly(A) tail, resulting in C-terminal appendage of a polylysine tract and a terminally stalled ribosome. In Saccharomyces cerevisiae, the ubiquitin ligase Rkr1/Ltn1 has been implicated in the proteasomal degradation of soluble cytosolic nonstop and translationally stalled proteins. Rkr1 is essential for cellular fitness under conditions associated with increased prevalence of nonstop proteins. Mutation of the mammalian homolog causes significant neurological pathology, suggesting broad physiological significance of ribosome-associated quality control. It is not known whether and how soluble or transmembrane nonstop and translationally stalled proteins targeted to the endoplasmic reticulum (ER) are detected and degraded. We generated and characterized model soluble and transmembrane ER-targeted nonstop and translationally stalled proteins. We found that these proteins are indeed subject to proteasomal degradation. We tested three candidate ubiquitin ligases (Rkr1 and ER-associated Doa10 and Hrd1) for roles in regulating abundance of these proteins. Our results indicate that Rkr1 plays the primary role in targeting the tested model ER-targeted nonstop and translationally stalled proteins for degradation. These data expand the catalog of Rkr1 substrates and highlight a previously unappreciated role for this ubiquitin ligase at the ER membrane. PMID:26055716

  3. An Experimental Investigation of Compressible Dynamic Stall on a Pitching Airfoil

    NASA Astrophysics Data System (ADS)

    Thorne, Katie; Bowles, Patrick

    2009-11-01

    A new facility has been designed and constructed at the University of Notre Dame to investigate dynamic stall on a 2-D pitching airfoil at high subsonic Mach numbers. This work is motivated by the need to investigate dynamic stall at conditions relevant to military helicopters. One focus of the experiments is to characterize the role of shock/boundary layer interactions during the pitching cycle. The new dynamic stall facility is integrated into a closed-loop, low turbulence wind tunnel capable of achieving test section Mach numbers in excess of M = 0.6. The design of the dynamic stall test section was focused on achieving reduced pitching frequencies of up to k = 0.2 and chord Reynolds numbers up to 5 x10^6. The facility has the unique ability to execute non-harmonic pitching motions through the use of an actuated pitch link mechanism. Optical access is provided to allow the use of high-speed and Schlieren imaging. Thirty-one flush mounted Kulite dynamic pressure transducers provide the instantaneous unsteady surface pressure distribution over the airfoil. Initial dynamic stall measurements obtained in the new facility will be described.

  4. Analysis of Ribosome Stalling and Translation Elongation Dynamics by Deep Learning.

    PubMed

    Zhang, Sai; Hu, Hailin; Zhou, Jingtian; He, Xuan; Jiang, Tao; Zeng, Jianyang

    2017-09-27

    Ribosome stalling is manifested by the local accumulation of ribosomes at specific codon positions of mRNAs. Here, we present ROSE, a deep learning framework to analyze high-throughput ribosome profiling data and estimate the probability of a ribosome stalling event occurring at each genomic location. Extensive validation tests on independent data demonstrated that ROSE possessed higher prediction accuracy than conventional prediction models, with an increase in the area under the receiver operating characteristic curve by up to 18.4%. In addition, genome-wide statistical analyses showed that ROSE predictions can be well correlated with diverse putative regulatory factors of ribosome stalling. Moreover, the genome-wide ribosome stalling landscapes of both human and yeast computed by ROSE recovered the functional interplays between ribosome stalling and cotranslational events in protein biogenesis, including protein targeting by the signal recognition particles and protein secondary structure formation. Overall, our study provides a novel method to complement the ribosome profiling techniques and further decipher the complex regulatory mechanisms underlying translation elongation dynamics encoded in the mRNA sequence. Copyright © 2017 Elsevier Inc. All rights reserved.

  5. Fatigue Testing of Vampire Wings,

    DTIC Science & Technology

    1979-06-01

    Fork End Upper (Threaded) Lug 2 Lower Root End Filling (R.E.F.) Through Inboard 8 mm (?4 in.) Dia . Bolt Holes. STA.747 (Fig.15) 3 Main Spar Assembl’ at...AD-AOA9 402 AERONAUTICAL RESEARCH LABS MELBOURNE (AUSTRALIA) F/G 1/ 3 FATIGUE TESTING OF VAMPIRE WINGS.(U) JUN 79 R A BRUTON. C A PATCHING...Number: (c) Summary in Isolation: ARL-Struc.-Report-378 Unclassified 3 . Title: FATIGUE TESTING OF VAMPIRE WINGS 4. Personal Author(s): 5. Document Date

  6. From Abrupt Change to the Future (Hans Oeschger Medal Lecture)

    NASA Astrophysics Data System (ADS)

    Stocker, T.

    2009-04-01

    The award of the Oeschger Medal 2009 is a particular honor and pleasure for me as I was given the chance to take over from Hans Oeschger the lead of a wonderful Institute at the University of Bern in 1993. Very apprehensive first, in front of the huge expectations and challenges, I quickly found dear colleagues, close collaborators and extremely supportive staff who all dedicated their time and creativity to work for the common goal of better understanding the Earth System, its variations in the past and its sensitivity to perturbations that man is inflicting on it today. Although met with innate skepticism first by the experimental physicists, our efforts in modelling, particularly the approach of using climate models of reduced complexity, quickly paid off and provided added value to the hard won data and measurements from polar ice cores. It is clear that modelling in such a diverse environment is so much more stimulating and enriching than working on a sophisticated parameterisation in a big modelling centre. Simple models have suggested that the Earth System may have limited stability and that rather fundamental changes could be triggered by the increase of greenhouse gases. However, it is the unique results from polar ice cores, particularly from Greenland that showed that, indeed, the Earth System has limited stability and can react in extremely abrupt ways to changes in forcing. Likewise, the Antarctic ice cores have provided one of the corner stones of our knowledge about climate change: Concentrations of CO2 are today 29% higher than ever during the last 800,000 years. These two fundamental insights from the paleoclimatic archive call for accelerated research into the sensitivity of the climate system and its components to perturbations, as well as the investigation of feedback mechanisms in the biogeochemical cycles that are disturbed by the input of CO2 into the atmosphere by burning fossil fuels and land use change. Our research has only scratched the

  7. Flexible-Wing-Based Micro Air Vehicles

    NASA Technical Reports Server (NTRS)

    Ifju, Peter G.; Jenkins, David A.; Ettinger, Scott; Lian, Yong-Sheng; Shyy, Wei; Waszak, Martin R.

    2002-01-01

    This paper documents the development and evaluation of an original flexible-wing-based Micro Air Vehicle (MAV) technology that reduces adverse effects of gusty wind conditions and unsteady aerodynamics, exhibits desirable flight stability, and enhances structural durability. The flexible wing concept has been demonstrated on aircraft with wingspans ranging from 18 inches to 5 inches. Salient features of the flexible-wing-based MAV, including the vehicle concept, flexible wing design, novel fabrication methods, aerodynamic assessment, and flight data analysis are presented.

  8. Aerodynamics of dynamic wing flexion in translating wings

    NASA Astrophysics Data System (ADS)

    Liu, Yun; Cheng, Bo; Sane, Sanjay P.; Deng, Xinyan

    2015-06-01

    We conducted a systematic experimental study to investigate the aerodynamic effects of active trailing-edge flexion on a high-aspect-ratio wing translating from rest at a high angle of attack. We varied the timing and speed of the trailing-edge flexion and measured the resulting aerodynamic effects using a combination of direct force measurements and two-dimensional PIV flow measurements. The results indicated that the force and flow characteristics depend strongly on the timing of flexion, but relatively weakly on its speed. This is because the force and vortical flow structure are more sensitive to the timing of flexion relative to the shedding of starting vortex and leading-edge vortex. When the trailing-edge flexion occurred slightly before the starting vortex was shed, the lift production was greatly improved with the instantaneous peak lift increased by 54 % and averaged lift increased by 21 % compared with the pre-flexed case where the trailing-edge flexed before wing translation. However, when the trailing-edge flexed during or slightly after the leading-edge vortex shedding, the lift was significantly reduced by the disturbed development of leading-edge vortex. The force measurement results also imply that the trailing-edge flexion prior to wing translation does not augment lift but increases drag, thus resulting in a lower lift-drag ratio as compared to the case of flat wing.

  9. An international contrast of rates of placental abruption: an age-period-cohort analysis.

    PubMed

    Ananth, Cande V; Keyes, Katherine M; Hamilton, Ava; Gissler, Mika; Wu, Chunsen; Liu, Shiliang; Luque-Fernandez, Miguel Angel; Skjærven, Rolv; Williams, Michelle A; Tikkanen, Minna; Cnattingius, Sven

    2015-01-01

    Although rare, placental abruption is implicated in disproportionately high rates of perinatal morbidity and mortality. Understanding geographic and temporal variations may provide insights into possible amenable factors of abruption. We examined abruption frequencies by maternal age, delivery year, and maternal birth cohorts over three decades across seven countries. Women that delivered in the US (n = 863,879; 1979-10), Canada (4 provinces, n = 5,407,463; 1982-11), Sweden (n = 3,266,742; 1978-10), Denmark (n = 1,773,895; 1978-08), Norway (n = 1,780,271, 1978-09), Finland (n = 1,411,867; 1987-10), and Spain (n = 6,151,508; 1999-12) were analyzed. Abruption diagnosis was based on ICD coding. Rates were modeled using Poisson regression within the framework of an age-period-cohort analysis, and multi-level models to examine the contribution of smoking in four countries. Abruption rates varied across the seven countries (3-10 per 1000), Maternal age showed a consistent J-shaped pattern with increased rates at the extremes of the age distribution. In comparison to births in 2000, births after 2000 in European countries had lower abruption rates; in the US there was an increase in rate up to 2000 and a plateau thereafter. No birth cohort effects were evident. Changes in smoking prevalence partially explained the period effect in the US (P = 0.01) and Sweden (P<0.01). There is a strong maternal age effect on abruption. While the abruption rate has plateaued since 2000 in the US, all other countries show declining rates. These findings suggest considerable variation in abruption frequencies across countries; differences in the distribution of risk factors, especially smoking, may help guide policy to reduce abruption rates.

  10. The computation of the post-stall behavior of a circulation controlled airfoil

    NASA Technical Reports Server (NTRS)

    Linton, Samuel W.

    1993-01-01

    The physics of the circulation controlled airfoil is complex and poorly understood, particularly with regards to jet stall, which is the eventual breakdown of lift augmentation by the jet at some sufficiently high blowing rate. The present paper describes the numerical simulation of stalled and unstalled flows over a two-dimensional circulation controlled airfoil using a fully implicit Navier-Stokes code, and the comparison with experimental results. Mach numbers of 0.3 and 0.5 and jet total to freestream pressure ratios of 1.4 and 1.8 are investigated. The Baldwin-Lomax and k-epsilon turbulence models are used, each modified to include the effect of strong streamline curvature. The numerical solutions of the post-stall circulation controlled airfoil show a highly regular unsteady periodic flowfield. This is the result of an alternation between adverse pressure gradient and shock induced separation of the boundary layer on the airfoil trailing edge.

  11. Dynamic Stall Measurements and Computations for a VR-12 Airfoil with a Variable Droop Leading Edge

    NASA Technical Reports Server (NTRS)

    Martin, P. B.; McAlister, K. W.; Chandrasekhara, M. S.; Geissler, W.

    2003-01-01

    High density-altitude operations of helicopters with advanced performance and maneuver capabilities have lead to fundamental research on active high-lift system concepts for rotor blades. The requirement for this type of system was to improve the sectional lift-to-drag ratio by alleviating dynamic stall on the retreating blade while simultaneously reducing the transonic drag rise of the advancing blade. Both measured and computational results showed that a Variable Droop Leading Edge (VDLE) airfoil is a viable concept for application to a rotor high-lift system. Results are presented for a series of 2D compressible dynamic stall wind tunnel tests with supporting CFD results for selected test cases. These measurements and computations show a dramatic decrease in the drag and pitching moment associated with severe dynamic stall when the VDLE concept is applied to the Boeing VR-12 airfoil. Test results also show an elimination of the negative pitch damping observed in the baseline moment hysteresis curves.

  12. Instrumentation and control system for an F-15 stall/spin

    NASA Technical Reports Server (NTRS)

    Pitts, F. L.; Holmes, D. C. E.; Zaepfel, K. P.

    1974-01-01

    An instrumentation and control system is described that was used for radio-controlled F-15 airplane model stall/spin research at the NASA-Langley Research Center. This stall/spin research technique, using scale model aircraft, provides information on the post-stall and spin-entry characteristics of full-scale aircraft. The instrumentation described provides measurements of flight parameters such as angle of attack and sideslip, airspeed, control-surface position, and three-axis rotation rates; these data are recorded on an onboard magnetic tape recorder. The proportional radio control system, which utilizes analog potentiometric signals generated from ground-based pilot inputs, and the ground-based system used in the flight operation are also described.

  13. Interference of Tail Surfaces and Wing and Fuselage from Tests of 17 Combinations in the N.A.C.A. Variable-Density Tunnel

    NASA Technical Reports Server (NTRS)

    Sherman, Albert

    1939-01-01

    An investigation of the interference associated with tail surfaces added to wing-fuselage combinations was included in the interference program in progress in the NACA variable-density tunnel. The results indicate that, in aerodynamically clean combinations, the increment of the high-speed drag can be estimated from section characteristics within useful limits of accuracy. The interference appears mainly as effects on the downwash angle and as losses in the tail effectiveness and varies with the geometry of the combination. An interference burble, which markedly increases the glide-path angle and the stability in pitch before the actual stall, may be considered a means of obtaining satisfactory stalling characteristics for complete combination.

  14. On the autorotation of animal wings

    PubMed Central

    Martín-Alcántara, Antonio; Fernandez-Feria, Ramon; Dudley, Robert

    2017-01-01

    Botanical samaras spin about their centre of mass and create vertical aerodynamic forces which slow their rate of descent. Descending autorotation of animal wings, however, has never been documented. We report here that isolated wings from Anna's hummingbirds, and also from 10 species of insects, can stably autorotate and achieve descent speeds and aerodynamic performance comparable to those of samaras. A hummingbird wing loaded at its base with the equivalent of 50% of the bird's body mass descended only twice as fast as an unloaded wing, and rotated at frequencies similar to those of the wings in flapping flight. We found that even entire dead insects could stably autorotate depending on their wing postures. Feather removal trials showed no effect on descent velocity when the secondary feathers were removed from hummingbird wings. By contrast, partial removal of wing primaries substantially improved performance, except when only the outer primary was present. A scaling law for the aerodynamic performance of autorotating wings is well supported if the wing aspect ratio and the relative position of the spinning axis from the wing base are included. Autorotation is a useful and practical method that can be used to explore the aerodynamics of wing design. PMID:28077761

  15. X-Wing Research Vehicle

    NASA Technical Reports Server (NTRS)

    1986-01-01

    One of the most unusual experimental flight vehicles appearing at NASA's Ames-Dryden Flight Research Facility (later redesignated Dryden Flight Research Center) in the 1980s was the Rotor Systems Research Aircraft (RSRA) X-Wing aircraft, seen here on the ramp. The craft was developed originally and then modified by Sikorsky Aircraft for a joint NASA-Defense Advanced Research Projects Agency (DARPA) program and was rolled out 19 August 1986. Taxi tests and initial low-altitude flight tests without the main rotor attached were carried out at Dryden before the program was terminated in 1988. The unusual aircraft that resulted from the Ames Research Center/Army X-Wing Project was flown at the Ames-Dryden Flight Research Facility (now Dryden Flight Research Center), Edwards, California, beginning in the spring of 1984, with a follow-on program beginning in 1986. The program, was conceived to provide an efficient combination of the vertical lift characteristic of conventional helicopters and the high cruise speed of fixed-wing aircraft. It consisted of a hybrid vehicle called the NASA/Army Rotor Systems Research Aircraft (RSRA), which was equipped with advanced X-wing rotor systems. The program began in the early 1970s to investigate ways to increase the speed of rotor aircraft, as well as their performance, reliability, and safety . It also sought to reduce the noise, vibration, and maintenance costs of helicopters. Sikorsky Aircraft Division of United Technologies Laboratories built two RSRA aircraft. NASA's Langley Research Center, Hampton, Virginia, did some initial testing and transferred the program to Ames Research Center, Mountain View, California, for an extensive flight research program conducted by Ames and the Army. The purpose of the 1984 tests was to demonstrate the fixed-wing capability of the helicopter/airplane hybrid research vehicle and explore its flight envelope and flying qualities. These tests, flown by Ames pilot G. Warren Hall and Army Maj (soon

  16. A vortex model for forces and moments on low-aspect-ratio wings in side-slip with experimental validation

    PubMed Central

    DeVoria, Adam C.

    2017-01-01

    This paper studies low-aspect-ratio () rectangular wings at high incidence and in side-slip. The main objective is to incorporate the effects of high angle of attack and side-slip into a simplified vortex model for the forces and moments. Experiments are also performed and are used to validate assumptions made in the model. The model asymptotes to the potential flow result of classical aerodynamics for an infinite aspect ratio. The → 0 limit of a rectangular wing is considered with slender body theory, where the side-edge vortices merge into a vortex doublet. Hence, the velocity fields transition from being dominated by a spanwise vorticity monopole ( ≫ 1) to a streamwise vorticity dipole ( ∼ 1). We theoretically derive a spanwise loading distribution that is parabolic instead of elliptic, and this physically represents the additional circulation around the wing that is associated with reattached flow. This is a fundamental feature of wings with a broad-facing leading edge. The experimental measurements of the spanwise circulation closely approximate a parabolic distribution. The vortex model yields very agreeable comparison with direct measurement of the lift and drag, and the roll moment prediction is acceptable for ≤ 1 prior to the roll stall angle and up to side-slip angles of 20°. PMID:28293139

  17. Laser velocimeter measurements of dynamic stall. [conducted in the Ames two foot wind tunnel

    NASA Technical Reports Server (NTRS)

    Owen, F. K.

    1984-01-01

    Laser velocimeter measurements were made during the study of a two-dimensional NACA 0012 airfoil undergoing conditions of dynamic stall. The measurements, which were obtained in the Ames 2 foot wind tunnel at reduced frequencies of 0.12 and 1.2, show significant flow field hysteresis around the static stall angle. Comparisons were also made with dual-plate interferograms and good agreement was found for the attached flow cases. For separated flow, characteristic vortex shedding caused poor agreement and significantly increased the measured Reynolds shear stresses.

  18. Chaotic Time Series Analysis Method Developed for Stall Precursor Identification in High-Speed Compressors

    NASA Technical Reports Server (NTRS)

    1997-01-01

    A new technique for rotating stall precursor identification in high-speed compressors has been developed at the NASA Lewis Research Center. This pseudo correlation integral method uses a mathematical algorithm based on chaos theory to identify nonlinear dynamic changes in the compressor. Through a study of four various configurations of a high-speed compressor stage, a multistage compressor rig, and an axi-centrifugal engine test, this algorithm, using only a single pressure sensor, has consistently predicted the onset of rotating stall.

  19. Dual wing, swept forward swept rearward wing, and single wing design optimization for high performance business airplanes

    NASA Technical Reports Server (NTRS)

    Rhodes, M. D.; Selberg, B. P.

    1982-01-01

    An investigation was performed to compare closely coupled dual wing and swept forward swept rearward wing aircraft to corresponding single wing 'baseline' designs to judge the advantages offered by aircraft designed with multiple wing systems. The optimum multiple wing geometry used on the multiple wing designs was determined in an analytic study which investigated the two- and three-dimensional aerodynamic behavior of a wide range of multiple wing configurations in order to find the wing geometry that created the minimum cruise drag. This analysis used a multi-element inviscid vortex panel program coupled to a momentum integral boundary layer analysis program to account for the aerodynamic coupling between the wings and to provide the two-dimensional aerodynamic data, which was then used as input for a three-dimensional vortex lattice program, which calculated the three-dimensional aerodynamic data. The low drag of the multiple wing configurations is due to a combination of two dimensional drag reductions, tailoring the three dimensional drag for the swept forward swept rearward design, and the structural advantages of the two wings that because of the structural connections permitted higher aspect ratios.

  20. Photonic Crystals on the Wing

    DTIC Science & Technology

    2011-11-01

    Giraldo MA Stavenga DG (2007) Sexual dichroism and pigment localization in the wing scales of Pieris rapae butterflies. Proc R Soc B 274:97-102 4...723 41. Stavenga DG, Arikawa K (2011) Photoreceptor spectral sensitivities of the Small White butterfly Pieris rapae crucivora interpreted with

  1. The Wings for Angels Project

    ERIC Educational Resources Information Center

    McMillan, Liberty; McMillan, Ellen; Ayers, Ann

    2012-01-01

    How can the spirits of critically ill children be raised? Alexis Weisel (co-president of the Monarch High School National Art Honor Society, 2010-2011) had this question in mind when she initiated and developed the Wings for Angels Project after hearing about the Believe in Tomorrow (BIT) organization through her art teacher, Ellen McMillan. The…

  2. Wings: Women Entrepreneurs Take Flight.

    ERIC Educational Resources Information Center

    Baldwin, Fred D.

    1997-01-01

    Women's Initiative Networking Groups (WINGS) provides low- and moderate-income women in Appalachian Kentucky with training in business skills, contacts, and other resources they need to succeed as entrepreneurs. The women form informal networks to share business know-how and support for small business startup and operations. The program plans to…

  3. Relative loading on biplane wings

    NASA Technical Reports Server (NTRS)

    Diehl, Walter S

    1934-01-01

    Recent improvements in stress analysis methods have made it necessary to revise and to extend the loading curves to cover all conditions of flight. This report is concerned with a study of existing biplane data by combining the experimental and theoretical data to derive a series of curves from which the lift curves of the individual wings of a biplane may be obtained.

  4. Wing Leading Edge Debris Analysis

    NASA Technical Reports Server (NTRS)

    Shah, Sandeep; Jerman, Gregory

    2004-01-01

    This is a slide presentation showing the Left Wing Leading Edge (WLE) heat damage observations: Heavy "slag" deposits on select RCC panels. Eroded and knife-edged RCC rib sections. Excessive overheating and slumping of carrier panel tiles. Missing or molten attachment bolts but intact bushing. Deposit mainly on "inside" RCC panel. Deposit on some fractured RCC surface

  5. Safety recommendation : right wing separation

    DOT National Transportation Integrated Search

    1999-05-28

    On April 19, 1999, at about 12:46 p.m. eastern daylight time, a Beech T-34A, N140SW, operated by Sky Warriors, Inc., collided with the ground near Rydall, Georgia, following an inflight separation of the right wing. Both the air transport pilot and t...

  6. 165th Airlift Wing > Home

    Science.gov Websites

    Questions Search 165th Airlift Wing: Featured Links Quick Contacts Organization Phone Number Base Locator Chronicle is our way of communicating with our unit members, their families and our extended fan-base. This Air Base command sgt major visits Pennsylvania ANG Oklahoma National Guard provides Joint Terminal

  7. 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)

  8. Intelligent Prediction of Fan Rotation Stall in Power Plants Based on Pressure Sensor Data Measured In-Situ

    PubMed Central

    Xu, Xiaogang; Wang, Songling; Liu, Jinlian; Liu, Xinyu

    2014-01-01

    Blower and exhaust fans consume over 30% of electricity in a thermal power plant, and faults of these fans due to rotation stalls are one of the most frequent reasons for power plant outage failures. To accurately predict the occurrence of fan rotation stalls, we propose a support vector regression machine (SVRM) model that predicts the fan internal pressures during operation, leaving ample time for rotation stall detection. We train the SVRM model using experimental data samples, and perform pressure data prediction using the trained SVRM model. To prove the feasibility of using the SVRM model for rotation stall prediction, we further process the predicted pressure data via wavelet-transform-based stall detection. By comparison of the detection results from the predicted and measured pressure data, we demonstrate that the SVRM model can accurately predict the fan pressure and guarantee reliable stall detection with a time advance of up to 0.0625 s. This superior pressure data prediction capability leaves significant time for effective control and prevention of fan rotation stall faults. This model has great potential for use in intelligent fan systems with stall prevention capability, which will ensure safe operation and improve the energy efficiency of power plants. PMID:24854057

  9. Notes on the technique of landing airplanes equipped with wing flaps

    NASA Technical Reports Server (NTRS)

    Gough, Melvin N

    1936-01-01

    The proper landing of airplanes equipped with flaps, although probably no more difficult than landing without them, requires a different technique. The effects of flaps on the aerodynamics characteristics of a wing are given and, with the aid of figures and diagrams, a detailed comparison of the glide and landing of an airplane with and without flaps is made. The dangers attending improper execution and the importance of such factors as air speed fuselage attitude, glide-path angle, and control manipulation, upon all of which a pilot bases his judgement, are emphasized. Of most importance in connection with the use of flaps are: the maintenance of a sufficient margin of speed above the stall; a decisive use of the controls at the proper time; more cautious use of power during the approach glide; and, above all, the willingness to accept the steep nose-down attitude necessary in the glide resulting from the use of flaps.

  10. The NASA supercritical-wing technology

    NASA Technical Reports Server (NTRS)

    Bartlett, D. W.; Patterson, J. C., Jr.

    1978-01-01

    A number of high aspect ratio supercritical wings in combination with a representative wide body type fuselage were tested in the Langley 8 foot transonic pressure tunnel. The wing parameters investigated include aspect ratio, sweep, thickness to chord ratio, and camber. Subsequent to these initial series of tests, a particular wing configuration was selected for further study and development. Tests on the selected wing involved the incorporation of a larger inboard trailing edge extension, an inboard leading edge extension, and flow through nacelles. Range factors for the various supercritical wing configurations are compared with those for a reference wide body transport configuration.

  11. F-8 oblique wing structural feasibility study

    NASA Technical Reports Server (NTRS)

    Koltko, E.; Katz, A.; Bell, M. A.; Smith, W. D.; Lauridia, R.; Overstreet, C. T.; Klapprott, C.; Orr, T. F.; Jobe, C. L.; Wyatt, F. G.

    1975-01-01

    The feasibility of fitting a rotating oblique wing on an F-8 aircraft to produce a full scale manned prototype capable of operating in the transonic and supersonic speed range was investigated. The strength, aeroelasticity, and fatigue life of such a prototype are analyzed. Concepts are developed for a new wing, a pivot, a skewing mechanism, control systems that operate through the pivot, and a wing support assembly that attaches in the F-8 wing cavity. The modification of the two-place NTF-8A aircraft to the oblique wing configuration is discussed.

  12. Maternal sleep duration and complaints of vital exhaustion during pregnancy is associated with placental abruption.

    PubMed

    Qiu, Chunfang; Sanchez, Sixto E; Gelaye, Bizu; Enquobahrie, Daniel A; Ananth, Cande V; Williams, Michelle A

    2015-02-01

    Sleep disorders are associated with cardiovascular complications and preterm delivery (PTD). Insufficient sleep results in metabolic alterations and increased inflammation, both known to contribute to placental abruption (abruption), a determinant of PTD. We examined associations of abruption with sleep duration and complaints of vital exhaustion. The study included 164 abruption cases and 160 controls in a multicenter study in Peru. Data on habitual sleep duration and vital exhaustion during the first 6 months of pregnancy were elicited during interviews conducted following delivery. Women were categorized according to short, normal and long sleep duration (≤6, 7-8 and ≥9 h); and frequency of feeling exhausted. Odds ratios (OR) and 95% confidence intervals (CI) were calculated. Short and long sleep durations were associated with increased odds of abruption. The ORs of abruption in relation to short (≤6 h) and long (≥9 h) sleep duration were 2.0 (95% CI 1.1-3.7) and 2.1 (95% CI 1.1-4.1), compared with normal sleep duration (7-8 h). Complaints of vital exhaustion were also associated with abruption (OR = 2.37; 95% CI 1.46-3.85), and were independent of sleep duration. We extend the existing literature and support the thesis that maternal sleep habits and disorders should be assessed among pregnant women.

  13. A laboratory scale model of abrupt ice-shelf disintegration

    NASA Astrophysics Data System (ADS)

    Macayeal, D. R.; Boghosian, A.; Styron, D. D.; Burton, J. C.; Amundson, J. M.; Cathles, L. M.; Abbot, D. S.

    2010-12-01

    An important mode of Earth’s disappearing cryosphere is the abrupt disintegration of ice shelves along the Peninsula of Antarctica. This disintegration process may be triggered by climate change, however the work needed to produce the spectacular, explosive results witnessed with the Larsen B and Wilkins ice-shelf events of the last decade comes from the large potential energy release associated with iceberg capsize and fragmentation. To gain further insight into the underlying exchanges of energy involved in massed iceberg movements, we have constructed a laboratory-scale model designed to explore the physical and hydrodynamic interactions between icebergs in a confined channel of water. The experimental apparatus consists of a 2-meter water tank that is 30 cm wide. Within the tank, we introduce fresh water and approximately 20-100 rectangular plastic ‘icebergs’ having the appropriate density contrast with water to mimic ice. The blocks are initially deployed in a tight pack, with all blocks arranged in a manner to represent the initial state of an integrated ice shelf or ice tongue. The system is allowed to evolve through time under the driving forces associated with iceberg hydrodynamics. Digitized videography is used to quantify how the system of plastic icebergs evolves between states of quiescence to states of mobilization. Initial experiments show that, after a single ‘agitator’ iceberg begins to capsize, an ‘avalanche’ of capsizing icebergs ensues which drives horizontal expansion of the massed icebergs across the water surface, and which stimulates other icebergs to capsize. A surprise initially evident in the experiments is the fact that the kinetic energy of the expanding mass of icebergs is only a small fraction of the net potential energy released by the rearrangement of mass via capsize. Approximately 85 - 90 % of the energy released by the system goes into water motion modes, including a pervasive, easily observed seich mode of the tank

  14. Full-scale semi-span tests of an advanced NLF business jet wing

    NASA Technical Reports Server (NTRS)

    Hahne, David E.; Jordan, Frank L., Jr.; Davis, Patrick J.; Muchmore, C. Byram

    1987-01-01

    An investigation has been conducted in the NASA Langley Research Center's 30- by 60-Foot Wind Tunnel on a full-scale semispan model to evaluate and document the low-speed, high-lift characteristics of a business-jet class wing utilizing the HSNLF(1)-0213 airfoil section and a single slotted flap system. In addition to the high-lift studies, evaluations of boundary layer transition effects, the effectiveness of a segmented leading-edge droop for improved stall/spin resistance, and roll control effectiveness with and without flap deflection were made. The wind-tunnel investigation showed that deployment of a single-slotted trailing-edge flap provided substantial increments in lift. Fixed transition studies indicated no adverse effects on lift and pitching-moment characteristics for either the cruise or landing configuration. Subscale roll damping tests also indicated that stall/spin resistance could be enhanced through the use of a properly designed leading-edge droop.

  15. An experimental study of the aerodynamic characteristics of planar and non-planar outboard wing planforms

    NASA Technical Reports Server (NTRS)

    Naik, D. A.; Ostowari, C.

    1987-01-01

    A series of wind tunnel experiments have been conducted to investigate the aerodynamic characteristics of several planar and nonplanar wingtip planforms. Seven different configurations: base-line rectangular, elliptical, swept and tapered, swept and tapered with dihedral, swept and tapered with anhedral, rising arc, and drooping arc, were investigated for two different spans. The data are available in terms of coefficient plots of force data, flow visualization photographs, and velocity and pressure flowfield surveys. All planforms, particularly the nonplanar, have some advantages over the baseline rectangular planform. Span efficiencies up to 20-percent greater than baseline are a possibility. However, it is suggested that the span efficiency concept might need refinement for nonplanar wings. Flow survey data show the change in effective span with vortex roll-up. The flow visualization shows the occurrence of mushroom-cell-separation flow patterns at angles of attack corresponding to stall. These grow with an increase in post-stall angle of attack. For the larger aspect ratios, the cells are observed to split into sub-cells at the higher angles of attack. For all angles of attack, some amount of secondary vortex flow is observed for the planar and nonplanar out-board planforms with sweep and taper.

  16. AST Composite Wing Program: Executive Summary

    NASA Technical Reports Server (NTRS)

    Karal, Michael

    2001-01-01

    The Boeing Company demonstrated the application of stitched/resin infused (S/RFI) composite materials on commercial transport aircraft primary wing structures under the Advanced Subsonic technology (AST) Composite Wing contract. This report describes a weight trade study utilizing a wing torque box design applicable to a 220-passenger commercial aircraft and was used to verify the weight savings a S/RFI structure would offer compared to an identical aluminum wing box design. This trade study was performed in the AST Composite Wing program, and the overall weight savings are reported. Previous program work involved the design of a S/RFI-base-line wing box structural test component and its associated testing hardware. This detail structural design effort which is known as the "semi-span" in this report, was completed under a previous NASA contract. The full-scale wing design was based on a configuration for a MD-90-40X airplane, and the objective of this structural test component was to demonstrate the maturity of the S/RFI technology through the evaluation of a full-scale wing box/fuselage section structural test. However, scope reductions of the AST Composite Wing Program pre-vented the fabrication and evaluation of this wing box structure. Results obtained from the weight trade study, the full-scale test component design effort, fabrication, design development testing, and full-scale testing of the semi-span wing box are reported.

  17. Comparison of Milk Yield and Animal Health in Turkish Farms with Differing Stall Types and Resting Surfaces

    PubMed Central

    Kara, Nurcan Karslioglu; Galic, Askin; Koyuncu, Mehmet

    2015-01-01

    The current study was carried out to determine the influence of different resting surfaces and stall types on milk yield and animal health. Study was carried out in Bursa that is one of the most important cities of Turkey in terms of dairy production. Effects of resting surfaces and stall types on milk yield were found to be important. Also influence of different resting surfaces and stall types on lactation length was examined and found that rubber mats were different from the two other options. Relationships between different resting surfaces or stall types and health problems were examined and connection between stall type and repeat breeding (RB), dystocia, retained placenta and a connection between resting surface types and RB and clinical mastitis were found to be important. Considering their economic reflections, it can be said that results are quite important to the Turkish dairy industry. PMID:25557824

  18. Design & fabrication of two seated aircraft with an advanced rotating leading edge wing

    NASA Astrophysics Data System (ADS)

    Al Ahmari, Saeed Abdullah Saeed

    The title of this thesis is "Design & Fabrication of two Seated Aircraft with an Advanced Rotating Leading Edge Wing", this gives almost a good description of the work has been done. In this research, the moving surface boundary-layer control (MSBC) concept was investigated and implemented. An experimental model was constructed and tested in wind tunnel to determine the aerodynamic characteristics using the leading edge moving surface of modified semi-symmetric airfoil NACA1214. The moving surface is provided by a high speed rotating cylinder, which replaces the leading edge of the airfoil. The angle of attack, the cylinder surfaces velocity ratio Uc/U, and the flap deflection angle effects on the lift and drag coefficients and the stall angle of attack were investigated. This new technology was applied to a 2-seat light-sport aircraft that is designed and built in the Aerospace Engineering Department at KFUPM. The project team is led by the aerospace department chairman Dr. Ahmed Z. AL-Garni and Dr. Wael G. Abdelrahman and includes graduate and under graduate student. The wing was modified to include a rotating cylinder along the leading edge of the flap portion. This produced very promising results such as the increase of the maximum lift coefficient at Uc/U=3 by 82% when flaps up and 111% when flaps down at 40° and stall was delayed by 8degrees in both cases. The laboratory results also showed that the effective range of the leading-edge rotating cylinder is at low angles of attack which reduce the need for higher angles of attack for STOL aircraft.

  19. Effects of alley and stall surfaces on indices of claw and leg health in dairy cattle housed in a free-stall barn.

    PubMed

    Vokey, F J; Guard, C L; Erb, H N; Galton, D M

    2001-12-01

    A 15-wk 2 x 3 factorial trial in a university dairy herd compared the effects of two alley surfaces and three free-stall beds on indices of lameness. Alley surfaces were grooved concrete (Ct) or 1.9-cm-thick interlocking rubber mats (R). Stalls were deep sand (S), rubber mattresses (M), or concrete (C). Mattress and concrete stalls were bedded with sawdust. At wk 1 and 15, the hind claws and hocks of 120 primi- (n = 69) and multiparous (n = 51) cows were scored for lesions and three claw measurements (dorsal wall length, heel depth, and toe angle) were recorded. Rates of lateral and medial claw growth and wear were calculated by measuring the migration of a reference mark away from the coronet. Digital photographs of claw surfaces were used to rescore claw lesions. Clinical lameness was evaluated by assigning a locomotion score from 1 to 4 to each cow during wk 1, 5, 10, and 14. Digital dermatitis (present/not present) and interdigital dermatitis (mild, moderate, or severe) were recorded at wk 15. The number of days that cows spent in a hospital barn was recorded. Before assignment, cows were professionally foot trimmed, sorted by initial claw lesion score, and then randomized in consecutive blocks of three to stall treatments. Photograph scores were highly repeatable. Nonparametric statistical techniques were used for analyses of rank data. Claw lesion score increased significantly for all treatment groups except RC and RS; however, when early lactation cows were excluded, no differences were found between treatment groups. Hock scores increased significantly more for cows in CtC than in CtS or RS. Significantly more animals from RC spent more than 10 d in the hospital pen compared with RM and RS. Groups did not significantly differ for clinical lameness. Cows in RS and RC had significantly lower rates for lateral claw net growth than those in CtM. Having moderate or severe interdigital dermatitis at wk 15 was associated with greater increases in claw lesion score

  20. Questionnaire-based study to assess the association between management practices and mastitis within tie-stall and free-stall dairy housing systems in Switzerland

    PubMed Central

    2013-01-01

    Background Prophylactic measures are key components of dairy herd mastitis control programs, but some are only relevant in specific housing systems. To assess the association between management practices and mastitis incidence, data collected in 2011 by a survey among 979 randomly selected Swiss dairy farms, and information from the regular test day recordings from 680 of these farms was analyzed. Results The median incidence of farmer-reported clinical mastitis (ICM) was 11.6 (mean 14.7) cases per 100 cows per year. The median annual proportion of milk samples with a composite somatic cell count (PSCC) above 200,000 cells/ml was 16.1 (mean 17.3) %. A multivariable negative binomial regression model was fitted for each of the mastitis indicators for farms with tie-stall and free-stall housing systems separately to study the effect of other (than housing system) management practices on the ICM and PSCC events (above 200,000 cells/ml). The results differed substantially by housing system and outcome. In tie-stall systems, clinical mastitis incidence was mainly affected by region (mountainous production zone; incidence rate ratio (IRR) = 0.73), the dairy herd replacement system (1.27) and farmers age (0.81). The proportion of high SCC was mainly associated with dry cow udder controls (IRR = 0.67), clean bedding material at calving (IRR = 1.72), using total merit values to select bulls (IRR = 1.57) and body condition scoring (IRR = 0.74). In free-stall systems, the IRR for clinical mastitis was mainly associated with stall climate/temperature (IRR = 1.65), comfort mats as resting surface (IRR = 0.75) and when no feed analysis was carried out (IRR = 1.18). The proportion of high SSC was only associated with hand and arm cleaning after calving (IRR = 0.81) and beef producing value to select bulls (IRR = 0.66). Conclusions There were substantial differences in identified risk factors in the four models. Some of the factors were in agreement with the reported literature

  1. Questionnaire-based study to assess the association between management practices and mastitis within tie-stall and free-stall dairy housing systems in Switzerland.

    PubMed

    Gordon, Paz F; van den Borne, Bart H P; Reist, Martin; Kohler, Samuel; Doherr, Marcus G

    2013-10-09

    Prophylactic measures are key components of dairy herd mastitis control programs, but some are only relevant in specific housing systems. To assess the association between management practices and mastitis incidence, data collected in 2011 by a survey among 979 randomly selected Swiss dairy farms, and information from the regular test day recordings from 680 of these farms was analyzed. The median incidence of farmer-reported clinical mastitis (ICM) was 11.6 (mean 14.7) cases per 100 cows per year. The median annual proportion of milk samples with a composite somatic cell count (PSCC) above 200,000 cells/ml was 16.1 (mean 17.3) %. A multivariable negative binomial regression model was fitted for each of the mastitis indicators for farms with tie-stall and free-stall housing systems separately to study the effect of other (than housing system) management practices on the ICM and PSCC events (above 200,000 cells/ml). The results differed substantially by housing system and outcome. In tie-stall systems, clinical mastitis incidence was mainly affected by region (mountainous production zone; incidence rate ratio (IRR) = 0.73), the dairy herd replacement system (1.27) and farmers age (0.81). The proportion of high SCC was mainly associated with dry cow udder controls (IRR = 0.67), clean bedding material at calving (IRR = 1.72), using total merit values to select bulls (IRR = 1.57) and body condition scoring (IRR = 0.74). In free-stall systems, the IRR for clinical mastitis was mainly associated with stall climate/temperature (IRR = 1.65), comfort mats as resting surface (IRR = 0.75) and when no feed analysis was carried out (IRR = 1.18). The proportion of high SSC was only associated with hand and arm cleaning after calving (IRR = 0.81) and beef producing value to select bulls (IRR = 0.66). There were substantial differences in identified risk factors in the four models. Some of the factors were in agreement with the reported literature while others were not. This

  2. The joined wing - An overview. [aircraft tandem wings in diamond configurations

    NASA Technical Reports Server (NTRS)

    Wolkovitch, J.

    1985-01-01

    The joined wing is a new type of aircraft configuration which employs tandem wings arranged to form diamond shapes in plan view and front view. Wind-tunnel tests and finite-element structural analyses have shown that the joined wing provides the following advantages over a comparable wing-plus-tail system; lighter weight and higher stiffness, higher span-efficiency factor, higher trimmed maximum lift coefficient, lower wave drag, plus built-in direct lift and direct sideforce control capability. A summary is given of research performed on the joined wing. Calculated joined wing weights are correlated with geometric parameters to provide simple weight estimation methods. The results of low-speed and transonic wind-tunnel tests are summarized, and guidelines for design of joined-wing aircraft are given. Some example joined-wing designs are presented and related configurations having connected wings are reviewed.

  3. Experimental optimization of wing shape for a hummingbird-like flapping wing micro air vehicle.

    PubMed

    Nan, Yanghai; Karásek, Matěj; Lalami, Mohamed Esseghir; Preumont, André

    2017-03-06

    Flapping wing micro air vehicles (MAVs) take inspiration from natural fliers, such as insects and hummingbirds. Existing designs manage to mimic the wing motion of natural fliers to a certain extent; nevertheless, differences will always exist due to completely different building blocks of biological and man-made systems. The same holds true for the design of the wings themselves, as biological and engineering materials differ significantly. This paper presents results of experimental optimization of wing shape of a flexible wing for a hummingbird-sized flapping wing MAV. During the experiments we varied the wing 'slackness' (defined by a camber angle), the wing shape (determined by the aspect and taper ratios) and the surface area. Apart from the generated lift, we also evaluated the overall power efficiency of the flapping wing MAV achieved with the various wing design. The results indicate that especially the camber angle and aspect ratio have a critical impact on the force production and efficiency. The best performance was obtained with a wing of trapezoidal shape with a straight leading edge and an aspect ratio of 9.3, both parameters being very similar to a typical hummingbird wing. Finally, the wing performance was demonstrated by a lift-off of a 17.2 g flapping wing robot.

  4. Wing spar stress charts and wing truss proportions

    NASA Technical Reports Server (NTRS)

    Warner, Edward P

    1926-01-01

    In order to simplify the calculation of beams continuous over three supports, a series of charts have been calculated giving the bending moments at all the critical points and the reactions at all supports for such members. Using these charts as a basis, calculations of equivalent bending moments, representing the total stresses acting in two bay-wing trusses of proportions varying over a wide range, have been determined, both with and without allowance for column effect. This leads finally to the determination of the best proportions for any particular truss or the best strut locations in any particular airplane. The ideal proportions are found to vary with the thickness of the wing section used, the aspect ratio, and the ratio of gap to chord.

  5. 76 FR 77452 - Advisory Circular for Stall and Stick Pusher Training

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-12-13

    ... a recovery from a stall or approach. Scenario-based training that includes realistic events that... training, testing, and checking recommendations designed to maximize the likelihood that pilots will... circular was developed based on a review of recommended practices developed by major aircraft manufacturers...

  6. EVALUATION OF STYRENE EMISSIONS FROM A SHOWER STALL/BATHTUB MANUFACTURING FACILITY

    EPA Science Inventory

    The report gives results of emissions measurements carried out at a representative facility (Eljer Plumbingware in Wilson, NC) that manufactures polyester-resin-reinforced shower stalls and bathtubs by spraying styrene-based resins onto molds in vented, open, spray booths. Styren...

  7. Preventing Stalled Quality Improvement Teams: A Written Test of Project Selectionability.

    ERIC Educational Resources Information Center

    Bacdayan, Paul

    2002-01-01

    Discusses organizations' use of quality improvement teams in total quality management and how they can benefit from training team personnel in how to select projects with a low risk of stalling. Describes an efficient written assessment test of project selection ability designed for those who conduct evaluations of training sessions. (Author/LRW)

  8. Experimental Investigation of Dynamic Stall on an Airfoil with Leading Edge Tubercles

    NASA Astrophysics Data System (ADS)

    Hrynuk, John; Bohl, Douglas

    2013-11-01

    Humpback whales are unique in that their flippers have leading edge ``bumps'' or tubercles. Past work on airfoils modeled after whale flippers has centered on the static aerodynamic characteristics of these airfoils. In the current work, NACA 0012 airfoils modified with leading edge tubercles are investigated to determine the effect of the tubercles on the dynamic characteristics, specifically on dynamic stall vortex formation, of the airfoils. Molecular Tagging Velocimetry (MTV) is used to measure the flow field around the modified airfoils at nondimensional pitch rates of Ω = 0.1, 0.2, and 0.4. The results show that the characteristics of the dynamics stall vortex are dependent on the location relative to the peak or valley of the leading edge bumps. These characteristics are also found to be different than those observed in dynamic stall on a smooth leading edge airfoil. In specific, the location of the dynamic stall vortex appears to form further aft on the airfoil for the tubercle case versus the smooth case. This work supported by NSF Grant # 0845882.

  9. Integrated delivery systems focus on service delivery after capitation efforts stall.

    PubMed

    2005-03-01

    Integrated delivery systems focus on service delivery after capitation efforts stall. Integrated delivery systems are going through changes that are focusing the provider organizations more on delivering care than managing risk, says Dean C. Coddington, one of the leading researchers into capitated organizations and a senior consultant with McManis Consulting in Denver.

  10. Pilot Human Factors in Stall/Spin Accidents of Supersonic Fighter Aircraft

    NASA Technical Reports Server (NTRS)

    Anderson, S. B.; Enevoldson, E. K.; Nguyen, L. T.

    1983-01-01

    A study has been made of pilot human factors related to stall/spin accidents of supersonic fighter aircraft. The military specifications for flight at high angles of attack are examined. Several pilot human factors problems related to stall/spin are discussed. These problems include (1) unsatisfactory nonvisual warning cues; (2) the inability of the pilot to quickly determine if the aircraft is spinning out of control, or to recognize the type of spin; (3) the inability of the pilot to decide on and implement the correct spin recovery technique; (4) the inability of the pilot to move, caused by high angular rotation; and (5) the tendency of pilots to wait too long in deciding to abandon the irrecoverable aircraft. Psycho-physiological phenomena influencing pilot's behavior in stall/spin situations include (1) channelization of sensory inputs, (2) limitations in precisely controlling several muscular inputs, (3) inaccurate judgment of elapsed time, and (4) disorientation of vestibulo-ocular inputs. Results are given of pilot responses to all these problems in the F14A, F16/AB, and F/A-18A aircraft. The use of departure spin resistance and automatic spin prevention systems incorporated on recent supersonic fighters are discussed. These systems should help to improve the stall/spin accident record with some compromise in maneuverability.

  11. A theory of post-stall transients in multistage axial compression systems

    NASA Technical Reports Server (NTRS)

    Moore, F. K.; Greitzer, E. M.

    1985-01-01

    A theory is presented for post stall transients in multistage axial compressors. The theory leads to a set of coupled first-order ordinary differential equations capable of describing the growth and possible decay of a rotating-stall cell during a compressor mass-flow transient. These changing flow features are shown to have a significant effect on the instantaneous compressor pumping characteristic during unsteady operation, and henace on the overall system behavior. It is also found from the theory that the ultimate mode of system response, stable rotating stall or surge, depends not only on the B parameter but also on other parameters, such as the compressor length-to-diameter ratio. Small values of this latter quantity tend to favor the occurrence of surge, as do large values of B. A limited parametric study is carried out to show the impact of the different system features on transient behavior. Based on analytical and numerical results, several specific topics are suggested for future research on post-stall transients.

  12. Numerical analysis of rotating stall instabilities of a pump- turbine in pump mode

    NASA Astrophysics Data System (ADS)

    Xia, L. S.; Cheng, Y. G.; Zhang, X. X.; Yang, J. D.

    2014-03-01

    Rotating stall may occur at part load flow of a pump-turbine in pump mode. Unstable flow structures developing under stall condition can lead to a sudden drop of efficiency, high dynamic load and even cavitation. CFD simulations on a pump-turbine model in pump mode were carried out to reveal the onset and developed mechanisms of these unstable flow phenomena at part load. The simulation results of energy-discharge and efficiency characteristics are in good agreement with those obtained by experiments. The more deviate from design conditions with decreasing flow rate, the more flow separations within the vanes. Under specific conditions, four stationary separation zones begin to progress on the circumference, rotating at a fraction of the impeller rotation rate. Rotating stalls lead to the flow in the vane diffuser channels alternating between outward jet flow and blockage. Strong jets impact the spiral casing wall causing high pressure pulsations. Severe separations of the stall cells disturb the flow inducing periodical large amplitude pressure fluctuations, of which the intensity at different span wise of the guide vanes is different. The enforced rotating nonuniform pressure distributions on the circumference lead to dynamic uniform forces on the impeller and guide vanes. The results show that the CFD simulations are capable to gain the complicated flow structure information for analysing the unstable characteristics of the pump mode at part load.

  13. Combustion-Powered Actuation for Dynamic Stall Suppression - Simulations and Low-Mach Experiments

    NASA Technical Reports Server (NTRS)

    Matalanis, Claude G.; Min, Byung-Young; Bowles, Patrick O.; Jee, Solkeun; Wake, Brian E.; Crittenden, Tom; Woo, George; Glezer, Ari

    2014-01-01

    An investigation on dynamic-stall suppression capabilities of combustion-powered actuation (COMPACT) applied to a tabbed VR-12 airfoil is presented. In the first section, results from computational fluid dynamics (CFD) simulations carried out at Mach numbers from 0.3 to 0.5 are presented. Several geometric parameters are varied including the slot chordwise location and angle. Actuation pulse amplitude, frequency, and timing are also varied. The simulations suggest that cycle-averaged lift increases of approximately 4% and 8% with respect to the baseline airfoil are possible at Mach numbers of 0.4 and 0.3 for deep and near-deep dynamic-stall conditions. In the second section, static-stall results from low-speed wind-tunnel experiments are presented. Low-speed experiments and high-speed CFD suggest that slots oriented tangential to the airfoil surface produce stronger benefits than slots oriented normal to the chordline. Low-speed experiments confirm that chordwise slot locations suitable for Mach 0.3-0.4 stall suppression (based on CFD) will also be effective at lower Mach numbers.

  14. High-resolution LES of the rotating stall in a reduced scale model pump-turbine

    NASA Astrophysics Data System (ADS)

    Pacot, Olivier; Kato, Chisachi; Avellan, François

    2014-03-01

    Extending the operating range of modern pump-turbines becomes increasingly important in the course of the integration of renewable energy sources in the existing power grid. However, at partial load condition in pumping mode, the occurrence of rotating stall is critical to the operational safety of the machine and on the grid stability. The understanding of the mechanisms behind this flow phenomenon yet remains vague and incomplete. Past numerical simulations using a RANS approach often led to inconclusive results concerning the physical background. For the first time, the rotating stall is investigated by performing a large scale LES calculation on the HYDRODYNA pump-turbine scale model featuring approximately 100 million elements. The computations were performed on the PRIMEHPC FX10 of the University of Tokyo using the overset Finite Element open source code FrontFlow/blue with the dynamic Smagorinsky turbulence model and the no-slip wall condition. The internal flow computed is the one when operating the pump-turbine at 76% of the best efficiency point in pumping mode, as previous experimental research showed the presence of four rotating cells. The rotating stall phenomenon is accurately reproduced for a reduced Reynolds number using the LES approach with acceptable computing resources. The results show an excellent agreement with available experimental data from the reduced scale model testing at the EPFL Laboratory for Hydraulic Machines. The number of stall cells as well as the propagation speed corroborates the experiment.

  15. Mechanisms of ribosome stalling by SecM at multiple elongation steps

    PubMed Central

    Zhang, Jun; Pan, Xijiang; Yan, Kaige; Sun, Shan; Gao, Ning; Sui, Sen-Fang

    2015-01-01

    Regulation of translating ribosomes is a major component of gene expression control network. In Escherichia coli, ribosome stalling by the C-terminal arrest sequence of SecM regulates the SecA-dependent secretion pathway. Previous studies reported many residues of SecM peptide and ribosome exit tunnel are critical for stalling. However, the underlying molecular mechanism is still not clear at the atomic level. Here, we present two cryo-EM structures of the SecM-stalled ribosomes at 3.3–3.7 Å resolution, which reveal two different stalling mechanisms at distinct elongation steps of the translation cycle: one is due to the inactivation of ribosomal peptidyl-transferase center which inhibits peptide bond formation with the incoming prolyl-tRNA; the other is the prolonged residence of the peptidyl-RNA at the hybrid A/P site which inhibits the full-scale tRNA translocation. These results demonstrate an elegant control of translation cycle by regulatory peptides through a continuous, dynamic reshaping of the functional center of the ribosome. DOI: http://dx.doi.org/10.7554/eLife.09684.001 PMID:26670735

  16. Accounting for biases in riboprofiling data indicates a major role for proline in stalling translation.

    PubMed

    Artieri, Carlo G; Fraser, Hunter B

    2014-12-01

    The recent advent of ribosome profiling-sequencing of short ribosome-bound fragments of mRNA-has offered an unprecedented opportunity to interrogate the sequence features responsible for modulating translational rates. Nevertheless, numerous analyses of the first riboprofiling data set have produced equivocal and often incompatible results. Here we analyze three independent yeast riboprofiling data sets, including two with much higher coverage than previously available, and find that all three show substantial technical sequence biases that confound interpretations of ribosomal occupancy. After accounting for these biases, we find no effect of previously implicated factors on ribosomal pausing. Rather, we find that incorporation of proline, whose unique side-chain stalls peptide synthesis in vitro, also slows the ribosome in vivo. We also reanalyze a method that implicated positively charged amino acids as the major determinant of ribosomal stalling and demonstrate that it produces false signals of stalling in low-coverage data. Our results suggest that any analysis of riboprofiling data should account for sequencing biases and sparse coverage. To this end, we establish a robust methodology that enables analysis of ribosome profiling data without prior assumptions regarding which positions spanned by the ribosome cause stalling. © 2014 Artieri and Fraser; Published by Cold Spring Harbor Laboratory Press.

  17. Corner separation and the onset of stall in an axial compressor

    NASA Astrophysics Data System (ADS)

    Thiam, Aicha; Whittlesey, Robert; Wark, Candace; Williams, David

    2007-11-01

    Axial compressor performance is limited by the onset of stall between the diffusing passageways of the rotors and stators. The flow physics responsible for the stall depends on the blade geometry of the machine, and in this experiment stall develops from a blade-hub corner separation. The 1.5 stage axial compressor consists of inlet guide vanes, a rotor and stator section. Separate motors drive the downstream fan and rotor, which makes it possible to change the compressor pressure ratio and flow coefficient by changing either the wheel speed or the bulk flow rate through the machine. Detailed maps of the flow behind the stators and in front of the rotors were obtained using a Kulite stagnation pressure probe. Mean pressure measurements show the growth of the corner flow separation and divergence of the ``through flow'' toward the outer casing. Spectra show a sensitivity of the separated region to small amplitude external disturbances, in this case originating from the downstream fan. The onset of rotating stall appears as the first subharmonic of the rotor frequency, 0.5 fr, then shifts to a slightly lower frequency 0.45 fr as the flow coefficient is decreased.

  18. Observations in Flight of the Region of Stalled Flow over the Blades of an Autogiro Rotor

    NASA Technical Reports Server (NTRS)

    Bailey, F J , Jr; Gustafon, F B

    1939-01-01

    The flow over the inner halves of the rotor blades on a Kellet YG-1B autogiro was investigated in flight by making camera records of the motion of silk streamers attached to the upper surfaces of the blades. These records were analyzed to determine the boundaries of the region within which the flow over the blade sections was stalled for various tip-speed ratios. For the sake of comparison, corresponding theoretical boundaries were obtained. Both the size of the stalled area and its rate of growth with increasing tip-speed ratio were found to be larger than the theory predicted, although experiment agreed with theory with regard to shape and general location of the stalled area. The stalled region may be an important factor in both the rotor lift-drag ratio and the blade flapping motion at the higher tip-speed ratios. The method of study used in this paper should be useful in further studies of the problem, including the reduction of the size of the region.

  19. Similitude relations for buffet and wing rock on delta wings

    NASA Astrophysics Data System (ADS)

    Mabey, D. G.

    1997-08-01

    Vortex flow phenomena at high angles of incidence are of great interest to the designers of advanced combat aircraft. The steady phenomena (such as steady lift and pitching moments) are understood fairly well, whereas the unsteady phenomena are still uncertain. This paper addresses two important unsteady phenomena on delta wings. With regard to the frequency parameter of the quasi-periodic excitation caused by vortex bursting, a new correlation is established covering a range of sweep back from 60 to 75°. With regard to the much lower frequency parameter of limit-cycle rigid-body wing-rock, a new experiment shows conclusively that although the motion is non-linear, the frequency parameter can be predicted by quasi-steady theory. As a consequence, for a given sweep angle, the frequency parameter is inversely proportional to the square root of the inertia in roll. This is an important observation when attempting to extrapolate from model tests in wind tunnels to predict the wing-rock characteristics of aircraft.

  20. Conical Magnetic Bearings Developed for Active Stall Control in Gas Turbine Engines

    NASA Technical Reports Server (NTRS)

    Trudell, Jeffrey J.; Kascak, Albert F.; Provenza, Andrew J.; Buccieri, Carl J.

    2004-01-01

    Active stall control is a current research area at the NASA Glenn Research Center that offers a great benefit in specific fuel consumption by allowing the gas turbine to operate beyond the onset of stall. Magnetic bearings are being investigated as a new method to perform active stall control. This enabling global aviation safety technology would result in improved fuel efficiency and decreased carbon dioxide emissions, as well as improve safety and reliability by eliminating oil-related delays and failures of engine components, which account for 40 percent of the commercial aircraft departure delays. Active stall control works by perturbing the flow in front of the compressor stage such that it cancels the pressure wave, which causes the compressor to go into stall. Radial magnetic bearings are able to whirl the shaft so that variations in blade tip leakage would flow upstream causing a perturbation wave that could cancel the rotating stall cell. Axial or thrust magnetic bearings cannot be used to cancel the surge mode in the compressor because they have a very low bandwidth and thus cannot modulate at a high enough frequency. Frequency response is limited because the thrust runner cannot be laminated. To improve the bandwidth of magnetic thrust bearings, researchers must use laminations to suppress the eddy currents. A conical magnetic bearing can be laminated, resulting in increased bandwidth in the axial direction. In addition, this design can produce both radial and thrust force in a single bearing, simplifying the installation. The proposed solution combines the radial and thrust bearing into one design that can be laminated--a conical magnetic bearing. The new conical magnetic bearing test rig, funded by a Glenn fiscal year 2002 Director's Discretionary Fund, was needed because none of the existing rigs has an axial degree of freedom. The rotor bearing configuration will simulate that of the main shaft on a gas turbine engine. One conical magnetic bearing