X-31 Loaded in C-5 Cargo Bay

NASA Technical Reports Server (NTRS)

1995-01-01

The X-31 Enhanced Fighter Maneuverability Technology Demonstrator Aircraft, based at the NASA Dryden Flight Research Center, Edwards Air Force Base, California, is secured inside the fuselage of an Air Force Reserve C-5 transport. The C-5 was used to ferry the X-31 from Europe back to Edwards, after being flown in the Paris Air Show in June 1995. The X-31's right wing, removed so the aircraft could fit inside the C-5, is in the shipping container in the foreground. 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 X-31 Enhanced Fighter Maneuverability (EFM) demonstrator flew at the Ames- Dryden Flight Research Facility, Edwards, California (redesignated the Dryden Flight Research Center in 1994) from February 1992 until 1995 and before that at the Air Force's Plant 42 in Palmdale, California. The goal of the project was to provide design information for the next generation of highly maneuverable fighter aircraft. This program demonstrated the value of using thrust vectoring (directing engine exhaust flow) coupled with an advanced flight control system to provide controlled flight to very high angles of attack. The result was a significant advantage over most conventional fighters in close-in combat situations. The X-31 flight program focused on agile flight within the post-stall regime, producing technical data to give aircraft designers a better understanding of aerodynamics, effectiveness of flight controls and thrust vectoring, and airflow phenomena at high angles of attack. Stall is a condition of an airplane or an airfoil in which lift decreases and drag increases due to the separation of airflow. Thrust vectoring compensates for the loss of control through normal aerodynamic surfaces that occurs during a stall. Post-stall refers to flying beyond the normal stall angle of attack, which in the X-31 was at a 30-degree angle of attack. During Dryden flight testing, the X-31 aircraft established several milestones. On November 6, 1992, the X-31 achieved controlled flight at a 70-degree angle of attack. On April 29, 1993, the second X-31 successfully executed a rapid minimum-radius, 180-degree turn using a post-stall maneuver, flying well beyond the aerodynamic limits of any conventional aircraft. This revolutionary maneuver has been called the 'Herbst Maneuver' after Wolfgang Herbst, a German proponent of using post-stall flight in air-to-air combat. It is also called a 'J Turn' when flown to an arbitrary heading change. The aircraft was flown in tactical maneuvers against an F/A-18 and other tactical aircraft as part of the test flight program. During November and December 1993, the X-31 reached a supersonic speed of Mach 1.28. In 1994, the X-31 program installed software to demonstrate quasi-tailless operation. The X-31 flight test program was conducted by an international test organization (ITO) managed by the Advanced Research Projects Office (ARPA), known as the Defense Advanced Research Projects Office (DARPA) before March 1993. The ITO included the U.S. Navy and U.S. Air Force, Rockwell Aerospace, the Federal Republic of Germany, Daimler-Benz (formerly Messerschmitt-Bolkow-Blohm and Deutsche Aerospace), and NASA. Gary Trippensee was the ITO director and NASA Project Manager. Pilots came from participating organizations. The X-31 was 43.33 feet long with a wingspan of 23.83 feet. It was powered by a single General Electric P404-GE-400 turbofan engine that produced 16,000 pounds of thrust in afterburner.

Theoretical Determination of Axial Fan Performance

NASA Technical Reports Server (NTRS)

Struve, E.

1943-01-01

The report presents a method for the computation of axial fan characteristics. The method is based on the assumption that the law of constancy of the circulation along the blade holds, approximately, for all fan conditions for which the blade elements operate at normal angles of attack (up to the stalling angles). Pressure head coefficient K(sub a) and power coefficient K(sub u) for the force components in the axial and tangential directions, respectively, and analogous to the lift and drag coefficients C(sub y) and C(sub x) are conveniently introduced.

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

Investigation of a bio-inspired lift-enhancing effector on a 2D airfoil.

PubMed

Johnston, Joe; Gopalarathnam, Ashok

2012-09-01

A flap mounted on the upper surface of an airfoil, called a 'lift-enhancing effector', has been shown in wind tunnel tests to have a similar function to a bird's covert feathers, which rise off the wing's surface in response to separated flows. The effector, fabricated from a thin Mylar sheet, is allowed to rotate freely about its leading edge. The tests were performed in the NCSU subsonic wind tunnel at a chord Reynolds number of 4 × 10(5). The maximum lift coefficient with the effector was the same as that for the clean airfoil, but was maintained over an angle-of-attack range from 12° to almost 20°, resulting in a very gentle stall behavior. To better understand the aerodynamics and to estimate the deployment angle of the free-moving effector, fixed-angle effectors fabricated out of stiff wood were also tested. A progressive increase in the stall angle of attack with increasing effector angle was observed, with diminishing returns beyond the effector angle of 60°. Drag tests on both the free-moving and fixed effectors showed a marked improvement in drag at high angles of attack. Oil flow visualization on the airfoil with and without the fixed-angle effectors proved that the effector causes the separation point to move aft on the airfoil, as compared to the clean airfoil. This is thought to be the main mechanism by which an effector improves both lift and drag. A comparison of the fixed-effector results with those from the free-effector tests shows that the free effector's deployment angle is between 30° and 45°. When operating at and beyond the clean airfoil's stall angle, the free effector automatically deploys to progressively higher angles with increasing angles of attack. This slows down the rapid upstream movement of the separation point and avoids the severe reduction in the lift coefficient and an increase in the drag coefficient that are seen on the clean airfoil at the onset of stall. Thus, the effector postpones the stall by 4-8° and makes the stall behavior more gentle. The benefits of using the effector could include care-free operations at high angles of attack during perching and maneuvering flight, especially in gusty conditions.

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.

Aerodynamic characteristics at high angles of attack

NASA Technical Reports Server (NTRS)

Chambers, J. R.

1977-01-01

An overview is presented of the aerodynamic inputs required for analysis of flight dynamics in the high-angle-of-attack regime wherein large-disturbance, nonlinear effects predominate. An outline of the presentation is presented. The discussion includes: (1) some important fundamental phenomena which determine to a large extent the aerodynamic characteristics of airplanes at high angles of attack; (2) static and dynamic aerodynamic characteristics near the stall; (3) aerodynamics of the spin; (4) test techniques used in stall/spin studies; (5) applications of aerodynamic data to problems in flight dynamics in the stall/spin area; and (6) the outlook for future research in the area.

Navier-Stokes Simulation of UH-60A Rotor/Wake Interaction Using Adaptive Mesh Refinement

NASA Technical Reports Server (NTRS)

Chaderjian, Neal M.

2017-01-01

High-resolution simulations of rotor/vortex-wake interaction for a UH60-A rotor under BVI and dynamic stallconditions were carried out with the OVERFLOW Navier-Stokes code.a. The normal force and pitching moment variation with azimuth angle were in good overall agreementwith flight-test data, similar to other CFD results reported in the literature.b. The wake-grid resolution did not have a significant effect on the rotor-blade airloads. This surprisingresult indicates that a wake grid spacing of (Delta)S=10% ctip is sufficient for engineering airloads predictionfor hover and forward flight. This assumes high-resolution body grids, high-order spatial accuracy, anda hybrid RANS/DDES turbulence model.c. Three-dimensional dynamic stall was found to occur due the presence of blade-tip vortices passing overa rotor blade on the retreating side. This changed the local airfoil angle of attack, causing stall, unlikethe 2D perspective of pure pitch oscillation of the local airfoil section.

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.

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.

Wind-tunnel investigation to determine the low speed yawing stability derivatives of a twin jet fighter model at high angles of attack

NASA Technical Reports Server (NTRS)

Coe, P. L., Jr.; Newsom, W. A., Jr.

1974-01-01

An investigation was conducted to determine the low-speed yawing stability derivatives of a twin-jet fighter airplane model at high angles of attack. Tests were performed in a low-speed tunnel utilizing variable-curvature walls to simulate pure yawing motion. The results of the study showed that at angles of attack below the stall the yawing derivatives were essentially independent of the yawing velocity and sideslip angle. However, at angles of attack above the stall some nonlinear variations were present and the derivatives were strongly dependent upon sideslip angle. The results also showed that the rolling moment due to yawing was primarily due to the wing-fuselage combination, and that at angles of attack below the stall both the vertical and horizontal tails produced significant contributions to the damping in yaw. Additionally, the tests showed that the use of the forced-oscillation data to represent the yawing stability derivatives is questionable, at high angles of attack, due to large effects arising from the acceleration in sideslip derivatives.

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.

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).

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.

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.

Theory for rates, equilibrium constants, and Brønsted slopes in F1-ATPase single molecule imaging experiments

PubMed Central

Volkán-Kacsó, Sándor; Marcus, Rudolph A.

2015-01-01

A theoretical model of elastically coupled reactions is proposed for single molecule imaging and rotor manipulation experiments on F1-ATPase. Stalling experiments are considered in which rates of individual ligand binding, ligand release, and chemical reaction steps have an exponential dependence on rotor angle. These data are treated in terms of the effect of thermodynamic driving forces on reaction rates, and lead to equations relating rate constants and free energies to the stalling angle. These relations, in turn, are modeled using a formalism originally developed to treat electron and other transfer reactions. During stalling the free energy profile of the enzymatic steps is altered by a work term due to elastic structural twisting. Using biochemical and single molecule data, the dependence of the rate constant and equilibrium constant on the stall angle, as well as the Børnsted slope are predicted and compared with experiment. Reasonable agreement is found with stalling experiments for ATP and GTP binding. The model can be applied to other torque-generating steps of reversible ligand binding, such as ADP and Pi release, when sufficient data become available. PMID:26483483

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.

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.

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.

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...

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...

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

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.

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) and spanwise (w¯'w¯'/Uinfinity 2) components of the normal stress were observed when stall cells were present, concentrated near the foci. Finally, a partial-span dynamic oscillating step trip was incorporated into the NACA0015 model with AR = 2.67. Initially, the actuator was driven by a square wave and the transitory behavior of flow field was explored as the trip moved from the extended to the flush position. It was shown that during this motion the flow was temporarily attached before settling into a state where a small cell was present. The intermediate reattachment was due to the natural oscillations of the actuator at its resonant frequency (ƒres = 100 Hz). This result suggested that actuating the trip at a frequency that is associated with the separated shear layer, which also coincided with the resonance frequency of the actuator, might enable mitigation of the stall cell. Therefore, the trip was driven using a sine wave with ƒ = 100 Hz (corresponding to a dimensionless frequency St = 0.35) when the airfoil was set at alpha = 13.4° and U infinity = 55 m/s, and it caused nearly complete reattachment of a 3-D separated region. At alpha = 16°, the size of the stall cell was very large and extended throughout most of the span when the trip was in the flush position; thus, the dynamic motion of the trip only affected the separated flow directly downstream of the actuator, which was reduced in size and magnitude. Phase-averaged data were also acquired, and it was shown that, during the periodic motion of the trip, coherent vortices were formed and advected downstream as they grew in size. This resulted, in a time average sense, in tilting of the flow towards the surface. However, the reattachment was unsteady.

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.

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.

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.

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...

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...

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...

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...

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...

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...

Two-stage fan. 4: Performance data for stator setting angle optimization

NASA Technical Reports Server (NTRS)

Burger, G. D.; Keenan, M. J.

1975-01-01

Stator setting angle optimization tests were conducted on a two-stage fan to improve efficiency at overspeed, stall margin at design speed, and both efficiency and stall margin at partspeed. The fan has a design pressure ratio of 2.8, a flow rate of 184.2 lb/sec (83.55 kg/sec) and a 1st-stage rotor tip speed of 1450 ft/sec (441.96 in/sec). Performance was obtained at 70,100, and 105 percent of design speed with different combinations of 1st-stage and 2nd-stage stator settings. One combination of settings, other than design, was common to all three speeds. At design speed, a 2.0 percentage point increase in stall margin was obtained at the expense of a 1.3 percentage point efficiency decrease. At 105 percent speed, efficiency was improved by 1.8 percentage points but stall margin decreased 4.7 percentage points. At 70 percent speed, no change in stall margin or operating line efficiency was obtained with stator resets although considerable speed-flow requlation occurred.

Prediction of Airfoil Characteristics With Higher Order Turbulence Models

NASA Technical Reports Server (NTRS)

Gatski, Thomas B.

1996-01-01

This study focuses on the prediction of airfoil characteristics, including lift and drag over a range of Reynolds numbers. Two different turbulence models, which represent two different types of models, are tested. The first is a standard isotropic eddy-viscosity two-equation model, and the second is an explicit algebraic stress model (EASM). The turbulent flow field over a general-aviation airfoil (GA(W)-2) at three Reynolds numbers is studied. At each Reynolds number, predicted lift and drag values at different angles of attack are compared with experimental results, and predicted variations of stall locations with Reynolds number are compared with experimental data. Finally, the size of the separation zone predicted by each model is analyzed, and correlated with the behavior of the lift coefficient near stall. In summary, the EASM model is able to predict the lift and drag coefficients over a wider range of angles of attack than the two-equation model for the three Reynolds numbers studied. However, both models are unable to predict the correct lift and drag behavior near the stall angle, and for the lowest Reynolds number case, the two-equation model did not predict separation on the airfoil near stall.

Fundamental Understanding of Rotor Aeromechanics at High Advance Ratio Through Wind Tunnel Testing

NASA Astrophysics Data System (ADS)

Berry, Benjamin

The purpose of this research is to further the understanding of rotor aeromechanics at advance ratios (mu) beyond the maximum of 0.5 (ratio of forward airspeed to rotor tip speed) for conventional helicopters. High advance ratio rotors have applications in high speed compound helicopters. In addition to one or more conventional main rotors, these aircraft employ either thrust compounding (propellers), lift compounding (fixed-wings), or both. An articulated 4-bladed model rotor was constructed, instrumented, and tested up to a maximum advance ratio of mu=1.6 in the Glenn L. Martin Wind Tunnel at the University of Maryland. The data set includes steady and unsteady rotor hub forces and moments, blade structural loads, blade flapping angles, swashplate control angles, and unsteady blade pressures. A collective-thrust control reversal--where increasing collective pitch results in lower rotor thrust--was observed and is a unique phenomenon to the high advance ratio flight regime. The thrust reversal is explained in a physical manner as well as through an analytical formulation. The requirements for the occurrence of the thrust reversal are enumerated. The effects of rotor geometry design on the thrust reversal onset are explored through the formulation and compared to the measured data. Reverse-flow dynamic stall was observed to extend the the lifting capability of the edgewise rotor well beyond the expected static stall behavior of the airfoil sections. Through embedded unsteady blade surface pressure transducers, the normal force, pitching moment, and shed dynamic stall vortex time histories at a blade section in strong reverse flow were analyzed. Favorable comparisons with published 2-D pitching airfoil reverse flow dynamic stall data indicate that the 3-D stall environment can likely be predicted using models developed from such 2-D experiments. Vibratory hub loads were observed to increase with advance ratio. Maximum amplitude was observed near mu=1, with a reduction in vibratory loads at higher advance ratios. Blade load 4/rev harmonics dominated due to operation near a 4/rev fanplot crossing of the 2nd flap bending mode natural frequency. Oscillatory loads sharply increase in the presence of retreating blade reverse flow dynamic stall, and are evident in blade torsion, pitch link, and hub load measurements. The blades exhibited torsion moment vibrations at the frequency of the 1st torsion mode in response to the reverse flow pitching moment loading.

High-fidelity numerical simulation of the flow field around a NACA-0012 aerofoil from the laminar separation bubble to a full stall

NASA Astrophysics Data System (ADS)

ElJack, Eltayeb

2017-05-01

In the present work, large eddy simulations of the flow field around a NACA-0012 aerofoil near stall conditions are performed at a Reynolds number of 5 × 104, Mach number of 0.4, and at various angles of attack. The results show the following: at relatively low angles of attack, the bubble is present and intact; at moderate angles of attack, the laminar separation bubble bursts and generates a global low-frequency flow oscillation; and at relatively high angles of attack, the laminar separation bubble becomes an open bubble that leads the aerofoil into a full stall. Time histories of the aerodynamic coefficients showed that the low-frequency oscillation phenomenon and its associated physics are indeed captured in the simulations. The aerodynamic coefficients compared to previous and recent experimental data with acceptable accuracy. Spectral analysis identified a dominant low-frequency mode featuring the periodic separation and reattachment of the flow field. At angles of attack α ≤ 9.3°, the low-frequency mode featured bubble shedding rather than bubble bursting and reformation. The underlying mechanism behind the quasi-periodic self-sustained low-frequency flow oscillation is discussed in detail.

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.

A comparative analysis between NACA 4412 airfoil and it's modified form with tubercles

NASA Astrophysics Data System (ADS)

Hasan, Md. Jonayed; Islam, Md. Tazul; Hassan, Md. Mehedi

2017-06-01

The effect of tubercles on the leading edge of an airfoil become more vivid at high angle of attacks. The effect of tubercles with large wavelength and small amplitude on the leading edge of a NACA 4412 airfoil section was investigated numerically and experimentally. The phenomena of improving the airfoil performance by modifying the contours drove our interest to do this analysis. The models were developed & numerical simulations were carried out with both NACA 4412 airfoil and modified airfoil model at Re=1.03×106 and angles of attack ranging from 0° to 20°. Flow separation was analyzed with vector profiles. CL, CD at different angle of attacks was developed and it gave down noticeable pre-stall & post-stall behavior. The airfoils were studied experimentally in a low speed wind tunnel. Pressure distribution over the two airfoils was obtained. It was evident from the pressure distributions that the modified airfoil exhibits significant aerodynamic performance at high angles of attack. We can infer that these effects will be advantageous for maneuverability and post-stall behavior.

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.

Prediction of unsteady airfoil flows at large angles of incidence

NASA Technical Reports Server (NTRS)

Cebeci, Tuncer; Jang, H. M.; Chen, H. H.

1992-01-01

The effect of the unsteady motion of an airfoil on its stall behavior is of considerable interest to many practical applications including the blades of helicopter rotors and of axial compressors and turbines. Experiments with oscillating airfoils, for example, have shown that the flow can remain attached for angles of attack greater than those which would cause stall to occur in a stationary system. This result appears to stem from the formation of a vortex close to the surface of the airfoil which continues to provide lift. It is also evident that the onset of dynamic stall depends strongly on the airfoil section, and as a result, great care is required in the development of a calculation method which will accurately predict this behavior.

Unsteady Thick Airfoil Aerodynamics: Experiments, Computation, and Theory

NASA Technical Reports Server (NTRS)

Strangfeld, C.; Rumsey, C. L.; Mueller-Vahl, H.; Greenblatt, D.; Nayeri, C. N.; Paschereit, C. O.

2015-01-01

An experimental, computational and theoretical investigation was carried out to study the aerodynamic loads acting on a relatively thick NACA 0018 airfoil when subjected to pitching and surging, individually and synchronously. Both pre-stall and post-stall angles of attack were considered. Experiments were carried out in a dedicated unsteady wind tunnel, with large surge amplitudes, and airfoil loads were estimated by means of unsteady surface mounted pressure measurements. Theoretical predictions were based on Theodorsen's and Isaacs' results as well as on the relatively recent generalizations of van der Wall. Both two- and three-dimensional computations were performed on structured grids employing unsteady Reynolds-averaged Navier-Stokes (URANS). For pure surging at pre-stall angles of attack, the correspondence between experiments and theory was satisfactory; this served as a validation of Isaacs theory. Discrepancies were traced to dynamic trailing-edge separation, even at low angles of attack. Excellent correspondence was found between experiments and theory for airfoil pitching as well as combined pitching and surging; the latter appears to be the first clear validation of van der Wall's theoretical results. Although qualitatively similar to experiment at low angles of attack, two-dimensional URANS computations yielded notable errors in the unsteady load effects of pitching, surging and their synchronous combination. The main reason is believed to be that the URANS equations do not resolve wake vorticity (explicitly modeled in the theory) or the resulting rolled-up un- steady flow structures because high values of eddy viscosity tend to \\smear" the wake. At post-stall angles, three-dimensional computations illustrated the importance of modeling the tunnel side walls.

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)

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.

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.

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.

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.

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.

Numerical study of delta wing leading edge blowing

NASA Technical Reports Server (NTRS)

Yeh, David; Tavella, Domingo; Roberts, Leonard

1988-01-01

Spanwise and tangential leading edge blowing as a means of controlling the position and strength of the leading edge vortices are studied by numerical solution of the three-dimensional Navier-Stokes equations. The leading edge jet is simulated by defining a permeable boundary, corresponding to the jet slot, where suitable boundary conditions are implemented. Numerical results are shown to compare favorably with experimental measurements. It is found that the use of spanwise leading edge blowing at moderate angle of attack magnifies the size and strength of the leading edge vortices, and moves the vortex cores outboard and upward. The increase in lift primarily comes from the greater nonlinear vortex lift. However, spanwise blowing causes earlier vortex breakdown, thus decreasing the stall angle. The effects of tangential blowing at low to moderate angles of attack tend to reduce the pressure peaks associated with leading edge vortices and to increase the suction peak around the leading edge, so that the integrated value of the surface pressure remains about the same. Tangential leading edge blowing in post-stall conditions is shown to re-establish vortical flow and delay vortex bursting, thus increasing C sub L sub max and stall angle.

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 with Yon and Katz. Large-amplitude streamwise Reynolds stresses in the separated shear layer were found to be manifested by the low-frequency oscillation through inspection of the spectral energy distribution. Using the method of Proper Orthogonal Decomposition to construct reduced-order models of the acquired time sequences, the low-frequency unsteadiness appeared to be linked to an interaction between the separated and trailing-edge shear layers, in contrast to a bubble-bursting mechanism which has been observed for different stall behaviors. As the static angle of attack was increased further, the separated flow structure was seen to transition to a faster eddy motion expected for bluff-body wakes. A novel scaling study was conducted to evaluate the potential role of low-frequency unsteadiness in producing the spanwise wavelengths associated with cell formation, which was found to be in favorable agreement with scaling trends in the literature. Finally, instantaneous pressure-sensitive paint measurements were demonstrated on a DU 97-W-300 wind turbine airfoil at chord Reynolds number of 225,000 with leading-edge trip applied, in which the development of spiral node structures associated with cell formation were captured in the trailing-edge separation. The contributed work suggests that further study into the influence of large-scale unsteadiness on the three-dimensional organization of stall cells is merited.

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.

Assessment of a Conceptual Flap System Intended for Enhanced General Aviation Safety

NASA Technical Reports Server (NTRS)

Campbell, Bryan A.; Carter, Melissa B.

2017-01-01

A novel multielement trailing-edge flap system for light general aviation airplanes was conceived for enhanced safety during normal and emergency landings. The system is designed to significantly reduce stall speed, and thus approach speed, with the goal of reducing maneuveringflight accidents and enhancing pilot survivability in the event of an accident. The research objectives were to assess the aerodynamic performance characteristics of the system and to evaluate the extent to which it provided both increased lift and increased drag required for the low-speed landing goal. The flap system was applied to a model of a light general aviation, high-wing trainer and tested in the Langley 12- Foot Low-Speed Wind Tunnel. Data were obtained for several device deflection angles, and component combinations at a dynamic pressure of 4 pounds per square foot. The force and moment data supports the achievement of the desired increase in lift with substantially increased drag, all at relatively shallow angles of attack. The levels of lift and drag can be varied through device deflection angles and inboard/outboard differential deflections. As such, it appears that this flap system may provide an enabling technology to allow steep, controllable glide slopes for safe rapid descent to landing with reduced stall speed. However, a simple flat-plate lower surface spoiler (LSS) provided either similar or superior lift with little impact on pitch or drag as compared to the proposed system. Higher-fidelity studies are suggested prior to use of the proposed system.

Steady Aerodynamic Characteristics of Two-Dimensional NACA0012 Airfoil for One Revolution Angle of Attack

NASA Astrophysics Data System (ADS)

Park, Byung Ho; Han, Yong Oun

2018-04-01

Steady variations in aerodynamic forces and flow behaviors of two-dimensional NACA0012 airfoil were investigated using a numerical method for One Revolution Angle of Attack (AOA) at Reynolds number of 105 . The profiles of lift coefficients, drag coefficients, and pressure coefficients were compared with those of the experimental data. The AERODAS model was used to analyze the profiles of lift and drag coefficients. Wake characteristics were given along with the deficit profiles of incoming velocity components. Both the characteristics of normal and reverse airfoil models were compared with the basic aerodynamic data for the same range of AOA. The results show that two peaks of the lift coefficients appeared at 11.5{°} and 42{°} and are in good agreement with the pre-stall and post-stall models, respectively. Counter-rotating vortex flows originated from the leading and trailing edges at a high AOA, which formed an impermeable zone over the suction surface and made reattachments in the wake. Moreover, the acceleration of inflow along the boundary of the vortex wrap appeared in the profile of the wake velocity. The drag profile was found to be independent of the airfoil mode, but the lift profile was quite sensitive to the airfoil mode.

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.

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.

14 CFR 25.481 - Tail-down landing conditions.

Code of Federal Regulations, 2010 CFR

2010-01-01

... landing conditions. (a) In the tail-down attitude, the airplane is assumed to contact the ground at... an attitude corresponding to either the stalling angle or the maximum angle allowing clearance with...

Numerical evaluations of the effect of leading-edge protuberances on the static and dynamic stall characteristics of an airfoil

NASA Astrophysics Data System (ADS)

Cai, C.; Zuo, Z. G.; Liu, S. H.; Wu, Y. L.; Wang, F. B.

2013-12-01

Wavy leading edge modifications of airfoils through imitating humpback whale flippers has been considered as a viable passive way to control flow separation. In this paper, flows around a baseline 634-021 airfoil and one with leading-edge sinusoidal protuberances were simulated using S-A turbulence model. When studying the static stall characteristics, it is found that the modified airfoil does not stall in the traditional manner, with increasing poststall lift coefficients. At high angles of attack, the flows past the wavy leading edge stayed attached for a distance, while the baseline foil is in a totally separated flow condition. On this basis, the simulations of pitch characteristic were carried out for both foils. At high angles of attack mild variations in lift and drag coefficients of the modified foil can be found, leading to a smaller area of hysteresis loop. The special structure of wavy leading edge can help maintain high consistency of the flow field in dynamic pitching station within a particular range of angles of attack.

Modeling, simulation, and flight characteristics of an aircraft designed to fly at 100,000 feet

NASA Technical Reports Server (NTRS)

Sim, Alex G.

1991-01-01

A manned real time simulation of a conceptual vehicle, the stratoplane, was developed to study the problems associated with the flight characteristics of a large, lightweight vehicle. Mathematical models of the aerodynamics, mass properties, and propulsion system were developed in support of the simulation and are presented. The simulation was at first conducted without control augmentation to determine the needs for a control system. The unaugmented flying qualities were dominated by lightly damped dutch roll oscillations. Constant pilot workloads were needed at high altitudes. Control augmentation was studied using basic feedbacks. For the longitudinal axis, flight path angle, and pitch rate feedback were sufficient to damp the phugoid mode and to provide good flying qualities. In the lateral directional axis, bank angle, roll rate, and yaw rate feedbacks were sufficient to provide a safe vehicle with acceptable handling qualities. Intentionally stalling the stratoplane to very high angles of attack (deep stall) was studied as a means of enable safe and rapid descent. It was concluded that the deep stall maneuver is viable for this class of vehicle.

Application of variable-gain output feedback for high-alpha control

NASA Technical Reports Server (NTRS)

Ostroff, Aaron J.

1990-01-01

A variable-gain, optimal, discrete, output feedback design approach that is applied to a nonlinear flight regime is described. The flight regime covers a wide angle-of-attack range that includes stall and post stall. The paper includes brief descriptions of the variable-gain formulation, the discrete-control structure and flight equations used to apply the design approach, and the high performance airplane model used in the application. Both linear and nonlinear analysis are shown for a longitudinal four-model design case with angles of attack of 5, 15, 35, and 60 deg. Linear and nonlinear simulations are compared for a single-point longitudinal design at 60 deg angle of attack. Nonlinear simulations for the four-model, multi-mode, variable-gain design include a longitudinal pitch-up and pitch-down maneuver and high angle-of-attack regulation during a lateral maneuver.

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.

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.

Wall-modeled large eddy simulation of high-lift devices from low to post-stall angle of attacks

NASA Astrophysics Data System (ADS)

Bodart, Julien; Larsson, Johan; Moin, Parviz

2013-11-01

The flow around a McDonnell-Douglas 30P/30N multi-element airfoil at the flight Reynolds number of 9 million (based on chord) is computed using LES with an equilibrium wall-model with special treatment for transitional flows. Several different angles of attack are considered, up to and including stall, challenging the wall-model in several flow regimes. The maximum lift coefficient, which is generally difficult to predict with RANS approaches, is accurately predicted, as compared to experiments performed in the NASA LPT wind-tunnel. NASA grant: NNX11AI60A.

The Role of Separation Bubbles on the Aerodynamic Characteristics of Airfoils, Including Stall and Post-Stall, at Low Reynolds Numbers

NASA Technical Reports Server (NTRS)

Chen, Hsun H.; Cebeci, Tuncer

2007-01-01

Airfoils at high Reynolds numbers, in general, have small separation bubbles that are usually confined to the leading edge. Since the Reynolds number is large, the turbulence model for the transition region between the laminar and turbulent flow is not important. Furthermore, the onset of transition occurs either at separation or prior to separation and can be predicted satisfactorily by empirical correlations when the incident angle is small and can be assumed to correspond to laminar separation when the correlations do not apply, i.e., at high incidence angles.

An experimental study of an airfoil with a bio-inspired leading edge device at high angles of attack

NASA Astrophysics Data System (ADS)

Mandadzhiev, Boris A.; Lynch, Michael K.; Chamorro, Leonardo P.; Wissa, Aimy A.

2017-09-01

Robust and predictable aerodynamic performance of unmanned aerial vehicles at the limits of their design envelope is critical for safety and mission adaptability. Deployable aerodynamic surfaces from the wing leading or trailing edges are often used to extend the aerodynamic envelope (e.g. slats and flaps). Birds have also evolved feathers at the leading edge (LE) of their wings, known as the alula, which enables them to perform high angles of attack maneuvers. In this study, a series of wind tunnel experiments are performed to quantify the effect of various deployment parameters of an alula-like LE device on the aerodynamic performance of a cambered airfoil (S1223) at stall and post stall conditions. The alula relative angle of attack, measured from the mean chord of the airfoil, is varied to modulate tip-vortex strength, while the alula deflection angle is varied to modulate the distance between the tip vortex and the wing surface. Integrated lift force measurements were collected at various alula-inspired device configurations. The effect of the alula-inspired device on the boundary layer velocity profile and turbulence intensity were investigated through hot-wire anemometer measurements. Results show that as alula deflection angle increases, the lift coefficient also increase especially at lower alula relative angles of attack. Moreover, at post stall wing angles of attack, the wake velocity deficit is reduced in the presence of alula device, confirming the mitigation of the wing adverse pressure gradient. The results are in strong agreement with measurements taken on bird wings showing delayed flow reversal and extended range of operational angles of attack. An engineered alula-inspired device has the potential to improve mission adaptability in small unmanned air vehicles during low Reynolds number flight.

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...

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...

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...

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 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...

Stator hub treatment study

NASA Technical Reports Server (NTRS)

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

1974-01-01

The results of an experimental research program to investigate the potential of improving compressor stall margin by the application of hub treatment are presented. Extensive tuft probing showed that the two-stage, 0.5 radius ratio compressor selected for the test was indeed hub critical. Circumferential groove and baffled wide blade angle slot hub treatments under the stators were tested. Performance measurements were made with total and static pressure probes, wall static pressure taps, flow angle measuring instrumentation and hot film anemometers. Stator hub treatment was not found to be effective in improving compressor stall margin by delaying the point of onset of rotating stall or in modifying compressor performance for any of the configurations tested. Extensive regions of separated flow were observed on the suction surface of the stators near the hub. However, the treatment did not delay the point where flow separation in the stator hub region becomes apparent.

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.

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.

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.

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.

An analysis method for multi-component airfoils in separated flow

NASA Technical Reports Server (NTRS)

Rao, B. M.; Duorak, F. A.; Maskew, B.

1980-01-01

The multi-component airfoil program (Langley-MCARF) for attached flow is modified to accept the free vortex sheet separation-flow model program (Analytical Methods, Inc.-CLMAX). The viscous effects are incorporated into the calculation by representing the boundary layer displacement thickness with an appropriate source distribution. The separation flow model incorporated into MCARF was applied to single component airfoils. Calculated pressure distributions for angles of attack up to the stall are in close agreement with experimental measurements. Even at higher angles of attack beyond the stall, correct trends of separation, decrease in lift coefficients, and increase in pitching moment coefficients are predicted.

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.

Lift hysteresis at stall as an unsteady boundary-layer phenomenon

NASA Technical Reports Server (NTRS)

Moore, Franklin K

1956-01-01

Analysis of rotating stall of compressor blade rows requires specification of a dynamic lift curve for the airfoil section at or near stall, presumably including the effect of lift hysteresis. Consideration of the magnus lift of a rotating cylinder suggests performing an unsteady boundary-layer calculation to find the movement of the separation points of an airfoil fixed in a stream of variable incidence. The consideration of the shedding of vorticity into the wake should yield an estimate of lift increment proportional to time rate of change of angle of attack. This increment is the amplitude of the hysteresis loop. An approximate analysis is carried out according to the foregoing ideas for a 6:1 elliptic airfoil at the angle of attack for maximum lift. The assumptions of small perturbations from maximum lift are made, permitting neglect of distributed vorticity in the wake. The calculated hysteresis loop is counterclockwise. Finally, a discussion of the forms of hysteresis loops is presented; and, for small reduced frequency of oscillation, it is concluded that the concept of a viscous "time lag" is appropriate only for harmonic variations of angle of attack with time at mean conditions other than maximum lift.

A flight investigation of the ultra-deep-stall descent and spin recovery characteristics of a 1/6 scale radiocontrolled model of the Piper PA38 Tomahawk

NASA Technical Reports Server (NTRS)

Blanchard, W. S., Jr.

1981-01-01

Ultradeep stall descent and spin recovery characteristics of a 1/6 scale radio controlled model of the Piper PA38 Tomahawk aircraft was investigated. It was shown that the full scale PA38 is a suitable aircraft for conducting ultradeep stall research. Spin recovery was accomplished satisfactorily by entry to the ultradeep stall mode, followed by the exit from the ultradeep stall mode. It is concluded that since the PA38 has excellent spin recovery characteristics using normal recovery techniques (opposite rudder and forward control colum pressure), recovery using ultradeep stall would be beneficial only if the pilot suffered from disorientation.

Unsteady Navier-Stokes computations over airfoils using both fixed and dynamic meshes

NASA Technical Reports Server (NTRS)

Rumsey, Christopher L.; Anderson, W. Kyle

1989-01-01

A finite volume implicit approximate factorization method which solves the thin layer Navier-Stokes equations was used to predict unsteady turbulent flow airfoil behavior. At a constant angle of attack of 16 deg, the NACA 0012 airfoil exhibits an unsteady periodic flow field with the lift coefficient oscillating between 0.89 and 1.60. The Strouhal number is 0.028. Results are similar at 18 deg, with a Strouhal number of 0.033. A leading edge vortex is shed periodically near maximum lift. Dynamic mesh solutions for unstalled airfoil flows show general agreement with experimental pressure coefficients. However, moment coefficients and the maximum lift value are underpredicted. The deep stall case shows some agreement with experiment for increasing angle of attack, but is only qualitatively comparable past stall and for decreasing angle of attack.

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.

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.

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).

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.

Wind tunnel research comparing lateral control devices, particularly at high angles of attack X : various control devices on a wing with a fixed auxiliary airfoil

NASA Technical Reports Server (NTRS)

Weick, Fred E; Noyes, Richard W

1933-01-01

Results are given of a series of systemic tests comparing lateral control devices with particular reference to their effectiveness at high angles of attack. These tests were made with two sizes of ordinary ailerons and different sizes of spoilers on a Clark Y wing model having a narrow auxiliary airfoil fixed ahead and above the leading edge, the chords of the main and auxiliary airfoils being parallel. In addition, the auxiliary airfoil itself was given angular deflection. The purpose was to provide rolling moments for lateral control. The tests were made in a 7 by 10 foot wind tunnel. They included both force and rotation tests to show the effect of the devices on the lift and drag characteristics of the wing and on the lateral stability characteristics, as well as lateral control. They showed that none of the aileron arrangements tried would give rolling control of an assumed satisfactory value at all angles of attack up to the stall. However, they would give satisfactory values, but at the expense of abnormally high deflections and very heavy hinge moments. The most effective combination of ailerons and spoilers gave satisfactory values of rolling moment at angles of attack below the stall, and the values did not fall off as rapidly above the stall as with ailerons alone. With an arrangement of this type having the proper relative proportions and linkage, it should be possible to obtain reasonably satisfactory yawing moments and control forces. Deflecting one-half of the auxiliary airfoil downward for the purpose of control gave strong favorable yawing moments at all angles of attack, but gave very small rolling moments at the low angles of attack.

A model for the selective amplification of spatially coherent waves in a centrifugal compressor on the verge of rotating stall

NASA Technical Reports Server (NTRS)

Lawless, Patrick B.; Fleeter, Sanford

1993-01-01

A simple model for the stability zones of a low speed centrifugal compressor is developed, with the goal of understanding the driving mechanism for the changes in stalling behavior predicted for, and observed in, the Purdue Low Speed Centrifugal Research Compressor Facility. To this end, earlier analyses of rotating stall suppression in centrifugal compressors are presented in a reduced form that preserves the essential parameters of the model that affect the stalling behavior of the compressor. The model is then used to illuminate the relationship between compressor geometry, expected mode shape, and regions of amplification for weak waves which are indicative of the susceptibility of the system to rotating stall. The results demonstrate that increasing the stagger angle of the diffuser vanes, and consequently the diffusion path length, results in the compressor moving towards a condition where higher-order spatial modes are excited during stall initiation. Similarly, flow acceleration in the diffuser section caused by an increase in the number of diffuser vanes also results in the excitation of higher modes.

Measurements in Flight of the Flying Qualities of a Chance Vought F4U-4 Airplane: TED No. NACA 2388

NASA Technical Reports Server (NTRS)

Liddell, Charles J., Jr.; Reynolds, Robert M.; Christofferson, Frank E.

1947-01-01

The results of flight tests to determine flying qualities of a Chance Vought F4U-4 airplane are presented and discussed herein. In addition to comprehensive measurements at low altitude (about 8000 ft), tests of limited scope were made at high altitude (about 25,000 ft). The more important characteristics, based on a comparison of the test results and opinions of the pilots with the Navy requirements, can be summarized as follows: 1. The short-period control-free oscillations of the elevator angle and the normal acceleration were satisfactorily damped. 2. The most rearward center-of-gravity locations for satisfactory static longitudinal stability with power on, as determined by the control-force variations, were approximately 30 and 27 percent M.A.C. with flaps and gear up and down, respectively. 3. In maneuvering flight the conditions for which control-force gradients of satisfactory magnitude were obtained were seriously limited by sizable changes in the gradient with center-of-gravity location, airspeed, altitude, acceleration factor, and direction of turn. 4. The elevator and rudder controls were satisfactory for landings and take-offs. 5. The trim tabs were sufficiently effective for all controls. 6. The directional and lateral dynamic stability was positive, but the rudder oscillation did not damp within one cycle. The airplane oscillation damped sufficiently at low altitude but not at high altitude. 7. Both rudder-fixed and rudder-free static directional stability were positive over a sideslip range of +/-15 deg. However, the rudder force tended to reverse at high angles of right sideslip with flaps and gear up, power on, at low speeds. 8. The stick-fixed static lateral stability (dihedral effect) was positive in all conditions, but the stick-free dihedral effect was neutral at low speeds with flap and gear down, power on. 9. The yaw due to abrupt full aileron deflection at low speed was mot excessive, and the rudder control was adequate to hold trim sideslip. 10. In abrupt rudder-fixed aileron rolls in the clean configuration the maximum pb/2V for full aileron deflection at low and normal speeds was only 0.064. 11. The stalling characteristics were considered unsatisfactory in all configurations in both straight and turning flight due to inadequate stall warning. The motions in the stalls were not unduly severe, and recovery could be effected promptly by normal use of the controls.

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.

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.

An experimental investigation of the helicopter rotor blade element airloads on a model rotor in the blade stall regime

NASA Technical Reports Server (NTRS)

Fisher, R. K., Jr.; Tompkins, J. E.; Bobo, C. J.; Child, R. F.

1971-01-01

A wind tunnel test program was conducted on an eight foot diameter model rotor system to determine blade element airloads characteristics in the unstalled and stalled flight regimes. The fully articulated model rotor system utilized three blades with a Vertol 23010-1.58 airfoil section, the blades being 1/7.5 scale models of the Ch-47C rotor blades. Instrumentation was incorporated at the blade 75% radial station to measure pressure and skin friction distributions, surface streamline directions and local angle of attack. The test program was conducted in three phases; non-rotating, hover and forward flight at advance ratios of 0.15, 0.35 and 0.60. Test data were analyzed with respect to providing insight to the mechanisms affecting blade stall, particularly retreating blade stall during forward flight conditions. From such data, an assessment was made as to the applicability of current theoretical analyses used for the prediction of blade element airloads in the stall regime.

Direct numerical simulation of the flow around an aerofoil in ramp-up motion

NASA Astrophysics Data System (ADS)

Rosti, Marco E.; Omidyeganeh, Mohammad; Pinelli, Alfredo

2016-02-01

A detailed analysis of the flow around a NACA0020 aerofoil at Rec = 2 × 104 undergoing a ramp up motion has been carried out by means of direct numerical simulations. During the manoeuvre, the angle of attack is linearly varied in time between 0° and 20° with a constant rate of change of α ˙ rad = 0 . 12 U ∞ / c . When the angle of incidence has reached the final value, the lift experiences a first overshoot and then suddenly decreases towards the static stall asymptotic value. The transient instantaneous flow is dominated by the generation and detachment of the dynamic stall vortex, a large scale structure formed by the merging of smaller scales vortices generated by an instability originating at the trailing edge. New insights on the vorticity dynamics leading to the lift overshoot, lift crisis, and the damped oscillatory cycle that gradually matches the steady condition are discussed using a number of post-processing techniques. These include a detailed analysis of the flow ensemble average statistics and coherent structures identification carried out using the Q -criterion and the finite-time Lyapunov exponent technique. The results are compared with the one obtained in a companion simulation considering a static stall condition at the final angle of incidence α = 20°.

Flow separation on wind turbines blades

NASA Astrophysics Data System (ADS)

Corten, G. P.

2001-01-01

In the year 2000, 15GW of wind power was installed throughout the world, producing 100PJ of energy annually. This contributes to the total electricity demand by only 0.2%. Both the installed power and the generated energy are increasing by 30% per year world-wide. If the airflow over wind turbine blades could be controlled fully, the generation efficiency and thus the energy production would increase by 9%. Power Control To avoid damage to wind turbines, they are cut out above 10 Beaufort (25 m/s) on the wind speed scale. A turbine could be designed in such a way that it converts as much power as possible in all wind speeds, but then it would have to be to heavy. The high costs of such a design would not be compensated by the extra production in high winds, since such winds are rare. Therefore turbines usually reach maximum power at a much lower wind speed: the rated wind speed, which occurs at about 6 Beaufort (12.5 m/s). Above this rated speed, the power intake is kept constant by a control mechanism. Two different mechanisms are commonly used. Active pitch control, where the blades pitch to vane if the turbine maximum is exceeded or, passive stall control, where the power control is an implicit property of the rotor. Stall Control The flow over airfoils is called "attached" when it flows over the surface from the leading edge to the trailing edge. However, when the angle of attack of the flow exceeds a certain critical angle, the flow does not reach the trailing edge, but leaves the surface at the separation line. Beyond this line the flow direction is reversed, i.e. it flows from the trailing edge backward to the separation line. A blade section extracts much less energy from the flow when it separates. This property is used for stall control. Stall controlled rotors always operate at a constant rotation speed. The angle of attack of the flow incident to the blades is determined by the blade speed and the wind speed. Since the latter is variable, it determines the angle of attack. The art of designing stall rotors is to make the separated area on the blades extend in such a way, that the extracted power remains precisely constant, independent of the wind speed, while the power in the wind at cut-out exceeds the maximum power of the turbine by a factor of 8. Since the stall behaviour is influenced by many parameters, this demand cannot be easily met. However, if it can be met, the advantage of stall control is its passive operation, which is reliable and cheap. Problem Definition In practical application, stall control is not very accurate and many stall-controlled turbines do not meet their specifications. Deviations of the design-power in the order of tens of percent are regular. In the nineties, the aerodynamic research on these deviations focussed on: profile aerodynamics, computational fluid dynamics, rotational effects on separation and pressure measurements on test turbines. However, this did not adequately solve the actual problems with stall turbines. In this thesis, we therefore formulated the following as the essential question: "Does the separated blade area really extend with the wind speed, as we predict?" To find the answer a measurement technique was required, which 1) was applicable on large commercial wind turbines, 2) could follow the dynamic changes of the stall pattern, 3) was not influenced by the centrifugal force and 4) did not disturb the flow. Such a technique was not available, therefore we decided to develop it. Stall Flag Method For this method, a few hundred indicators are fixed to the rotor blades in a special pattern. These indicators, called "stall flags" are patented by the Netherlands Energy Research Foundation (ECN). They have a retro-reflective area which, depending on the flow direction, is or is not covered. A powerful light source in the field up to 500m behind the turbine illuminates the swept rotor area. The uncovered reflectors reflect the light to the source, where a digital video camera records the dynamic stall patterns. The images are analysed by image processing software that we developed. The program extracts the stall pattern, the blade azimuth angles and the rotor speed from the stall flags. It also measures the yaw error and the wind speed from the optical signals of other sensors, which are recorded simultaneously. We subsequently characterise the statistical stall behaviour from the sequences of thousands of analysed images. For example, the delay in the stall angle by vortex generators can be measured within 1° of accuracy from the stall flag signals. Properties of the Stall Flag The new indicators are compared to the classic tufts. Stall flags are pressure driven while tufts are driven by frictional drag, which means that they have more drag. The self-excited motion of tufts, due to the Kelvin-Helmholtz instability, complicates the interpretation and gives more drag. We designed stall flags in such a way that this instability is avoided. An experiment with a 65cm diameter propeller confirms the independence of stall flags from the centrifugal force and that stall flags respond quickly to changes in the flow. We developed an optical model of the method to find an optimum set-up. With the present system, we can take measurements on turbines of all actual diameters. The stall flag responds to separated flow with an optical signal. The contrast of this signal exceeds that of tuft-signals by a factor of at least 1000. To detect the stall flag signal we need a factor of 25 fewer pixels of the CCD chip than is necessary for tufts. Stall flags applied on fast moving objects may show light tracks due to motion blur, which in fact yields even more information. In the case of tuft visualisations, even a slight motion blur is fatal. Principal Results In dealing with the fundamental theory of wind turbines, we found a new aspect of the conversion efficiency of a wind turbine, which also concerns the stall behaviour. Another new aspect concerns the effects of rotation on stall. By using the stall flag method, we were able to clear up two practical problems that seriously threatened the performance of stall turbines. These topics will be described briefly. 1. Inherent Heat Generation The classic result for an actuator disk representing a wind turbine is that the power extracted equals the kinetic power transferred. This is a consequence of disregarding the flow around the disk. When this flow is included, we need to introduce a heat generation term in the energy balance. This has the practical consequence that an actuator disk at the Lanchester-Betz limit transfers 50% more kinetic energy than it extracts. This surplus is dissipated in heat. Using this new argument, together with a classic argument on induction, we see no reason to introduce the concept of edge-forces on the tips of the rotor blades (Van Kuik, 1991). We rather recommend following the ideas of Lanchester (1915) on the edge of the actuator disk and on the wind speed at the disc. We analyse the concept induction, and show that correcting for the aspect ratio, for induced drag and application of Blade Element Momentum Theory all have the same significance for a wind turbine. Such corrections are sometimes made twice (Viterna & Corrigan, 1981). 2. Rotational Effects on Flow Separation In designing wind turbine rotors, one uses the aerodynamic characteristics measured in the wind tunnel on fixed aerodynamic profiles. These characteristics are corrected for the effects of rotation and subsequently used for wind turbine rotors. Such a correction was developed by Snel (1990-1999). This correction is based on boundary layer theory, the validity of which we question in regard to separated flow. We estimated the effects of rotation on flow separation by arguing that the separation layer is thick so the velocity gradients are small and viscosity can be neglected. We add the argument that the chord-wise speed and its derivative normal to the wall is zero at the separation line, which causes the terms with the chord-wise speed or accelerations to disappear. The conclusion is that the chord-wise pressure gradient balances the Coriolis force. By doing so we obtain a simple set of equations that can be solved analytically. Subsequently, our model predicts that the convective term with the radial velocity (vrvr/r) is dominant in the equation for the r-direction, precisely the term that was neglected in Snel's analysis. 3. Multiple Power Levels Several large commercial wind turbines demonstrate drops in maximum power levels up to 45%, under apparently equal conditions. Earlier studies attempting to explain this effect by technical malfunctioning, aerodynamic instabilities and blade contamination effects estimated with computational fluid dynamics, have not yet yielded a plausible result. We formulated many hypotheses, three of which were useful. By taking stall flag measurements and making two other crucial experiments, we could confirm one of those three hypotheses: the insect hypothesis. Insects only fly in low wind, impacting upon the blades at specific locations. In these conditions, the insectual remains are located at positions where roughness has little influence on the profile performance, so that the power is not affected. In high winds however, the flow around the blades has changed. As a result, the positions at which the insects have impacted at low winds are very sensitive to contamination. So the contamination level changes at low wind when insects fly and this level determines the power in high winds when insects do not fly. As a consequence we get discrete power levels in high winds. The other two hypotheses, which did not cause the multiple power levels for the case we studied, gave rise to two new insights. First, we expect the power to depend on the wind direction at sites where the shape of the terrain concentrates the wind. In this case the power level of all turbine types, including pitch regulated ones, will be affected. Second, we infer heuristically that the stalled area on wind turbine blades will adapt continuously to wind variations. Therefore, the occurrence of strong bi-stable stall-hysteresis, which most blade sections demonstrate in the wind tunnel, is lost. This has been confirmed by taking special stall flag measurements. 4. Deviation of Specifications The maximum power of stall controlled wind turbines often shows large systematic deviations from the design. We took stall flag measurements on a rotor, the maximum power of which was 30% too high, so that the turbine had to be cut out far below the designed cut-out wind speed. We immediately observed the blade areas with deviating stall behaviour. Some areas that should have stalled did not and caused the excessive power. We adapted those areas by shifting the vortex generators. In this way we obtained a power curve that met the design much more closely and we realised a production increase of 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

High-Lift OVERFLOW Analysis of the DLR-F11 Wind Tunnel Model

NASA Technical Reports Server (NTRS)

Pulliam, Thomas H.; Sclafani, Anthony J.

2014-01-01

In response to the 2nd AIAA CFD High Lift Prediction Workshop, the DLR-F11 wind tunnel model is analyzed using the Reynolds-averaged Navier-Stokes flow solver OVERFLOW. A series of overset grids for a bracket-off landing configuration is constructed and analyzed as part of a general grid refinement study. This high Reynolds number (15.1 million) analysis is done at multiple angles-of-attack to evaluate grid resolution effects at operational lift levels as well as near stall. A quadratic constitutive relation recently added to OVERFLOW for improved solution accuracy is utilized for side-of-body separation issues at low angles-of-attack and outboard wing separation at stall angles. The outboard wing separation occurs when the slat brackets are added to the landing configuration and is a source of discrepancy between the predictions and experimental data. A detailed flow field analysis is performed at low Reynolds number (1.35 million) after pressure tube bundles are added to the bracket-on medium grid system with the intent of better understanding bracket/bundle wake interaction with the wing's boundary layer. Localized grid refinement behind each slat bracket and pressure tube bundle coupled with a time accurate analysis are exercised in an attempt to improve stall prediction capability. The results are inconclusive and suggest the simulation is missing a key element such as boundary layer transition. The computed lift curve is under-predicted through the linear range and over-predicted near stall, and the solution from the most complete configuration analyzed shows outboard wing separation occurring behind slat bracket 6 where the experiment shows it behind bracket 5. These results are consistent with most other participants of this workshop.

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.

Handling qualities related to stall/spin accidents of supersonic fighter aircraft

NASA Technical Reports Server (NTRS)

Anderson, S. B.

1984-01-01

This paper reviews the handling qualities which influence the high angle of attack (AOA) behavior of supersonic fighter aircraft in order to obtain a clearer understanding of the causes of stall/spin accidents. The results show that, because modern fighters suffer more serious consequences when control is lost, good handling qualities are essential for safe operation at high AOA. Relaxed static stability used on some fighter aircraft can result in control problems at high AOA owing to inertia coupling and the difficulty of a recovery from a deep stall. Indications are that the use of departure/spin resistance and an automatic spin prevention system will greatly improve the safety record for modern supersonic fighters.

An experimental study of static and oscillating rotor blade sections in reverse flow

NASA Astrophysics Data System (ADS)

Lind, Andrew Hume

The rotorcraft community has a growing interest in the development of high-speed helicopters to replace outdated fleets. One barrier to the design of such helicopters is the lack of understanding of the aerodynamic behavior of retreating rotor blades in the reverse flow region. This work considers two fundamental models of this complex unsteady flow regime: static and oscillating (i.e., pitching) airfoils in reverse flow. Wind tunnel tests have been performed at the University of Maryland (UMD) and the United States Naval Academy (USNA). Four rotor blade sections are considered: two featuring a sharp geometric trailing edge (NACA 0012 and NACA 0024) and two featuring a blunt geometric trailing edge (ellipse and cambered ellipse). Static airfoil experiments were performed at angles of attack through 180 deg and Reynolds numbers up to one million, representative of the conditions found in the reverse flow region of a full-scale high-speed helicopter. Time-resolved velocity field measurements were used to identify three unsteady flow regimes: slender body vortex shedding, turbulent wake, and deep stall vortex shedding. Unsteady airloads were measured in these three regimes using unsteady pressure transducers. The magnitude of the unsteady airloads is high in the turbulent wake regime when the separated shear layer is close to the airfoil surface and in deep stall due to periodic vortex-induced flow. Oscillating airfoil experiments were performed on a NACA 0012 and cambered ellipse to investigate reverse flow dynamic stall characteristics by modeling cyclic pitching kinematics. The parameter space spanned three Reynolds numbers (165,000; 330,000; and 500,000), five reduced frequencies between 0.100 and 0.511, three mean pitch angles (5,10, and 15 deg), and two pitch amplitudes (5 deg and 10 deg). The sharp aerodynamic leading edge of the NACA 0012 airfoil forces flow separation resulting in deep dynamic stall. The number of associated vortex structures depends strongly on pitching kinematics. The cambered ellipse exhibits light reverse flow dynamic stall for a wide range of pitching kinematics. Deep dynamic stall over the cambered ellipse airfoil is observed for high mean pitch angles and pitch amplitudes. The detailed results and analysis in this work contributes to the development of a new generation of high-speed helicopters.

Flow Structure along the 1303 UCAV

NASA Astrophysics Data System (ADS)

Kosoglu, Mehmet A.; Rockwell, Donald

2007-11-01

The 1303 Unmanned Combat Air Vehicle is representative of a variety of UCAVs with blended wing-body configurations. Flow structure along a scale model of this configuration was investigated using dye visualization and particle image velocimetry for variations of Reynolds number and angle-of-attack. Both of these parameters substantially influence onset and structure of the leading-edge vortex (LEV) and a separation bubble/stall region along the tip. The onset of formation of the LEV initially occurs at a location well downstream of the apex and moves upstream for increasing values of either Reynolds number or angle-of-attack. In cases where a separation bubble or stall region exists, quantitative information on its structure was obtained via PIV imaging on a plane nearly parallel to the surface of the wing. By acquiring images on planes at successively larger elevations from the surface, it was possible to gain insight into the space-time features of the three-dimensional and highly time-dependent structure of the bubble or stall region. Time-averaged images indicate that maximum velocity defect decreases in magnitude and moves downstream with increasing elevation from the surface.

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.

Investigation of Periodic Pitching through the Static Stall Angle of Attack.

DTIC Science & Technology

1987-03-01

been completed to characterize and predict the dynamic stall process. In 1968 Ham (Ref 11) completed a study to explain the torsional oscillation of...peak values of l.:t and moment could be predicted accurately, but the model did not predict when the peaks would occur. Another problem with the...model was that it required input from experimental results to tell when leading edge vortex separation occurred. The prediction of when vortex shedding

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.

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

NASA Technical Reports Server (NTRS)

Wilder, M. C.

1995-01-01

An effort to understand and control the unsteady separated flow associated with the dynamic stall of airfoils was funded for three years through the NASA cooperative agreement program. As part of this effort a substantial data base was compiled detailing the effects various parameters have on the development of the dynamic stall flow field. Parameters studied include Mach number, pitch rate, and pitch history, as well as Reynolds number (through two different model chord lengths) and the condition of the boundary layer at the leading edge of the airfoil (through application of surface roughness). It was found for free stream Mach numbers as low as 0.4 that a region of supersonic flow forms on the leading edge of the suction surface of the airfoil at moderate angles of attack. The shocks which form in this supersonic region induce boundary-layer separation and advance the dynamic stall process. Under such conditions a supercritical airfoil profile is called for to produce a flow field having a weaker leading-edge pressure gradient and no leading-edge shocks. An airfoil having an adaptive-geometry, or dynamically deformable leading edge (DDLE), is under development as a unique active flow-control device. The DDLE, formed of carbon-fiber composite and fiberglass, can be flexed between a NACA 0012 profile and a supercritical profile in a controllable fashion while the airfoil is executing an angle-of-attack pitch-up maneuver. The dynamic stall data were recorded using point diffraction interferometry (PDI), a noninvasive measurement technique. A new high-speed cinematography system was developed for recording interferometric images. The system is capable of phase-locking with the pitching airfoil motion for real-time documentation of the development of the dynamic stall flow field. Computer-aided image analysis algorithms were developed for fast and accurate reduction of the images, improving interpretation of the results.

Suppression of dynamic stall with a leading-edge slat on a VR-7 airfoil

NASA Technical Reports Server (NTRS)

Mcalister, K. W.; Tung, C.

1993-01-01

The VR-7 airfoil was experimentally studied with and without a leading-edge slat at fixed angles of attack from 0 deg to 30 deg at Re = 200,000 and for unsteady pitching motions described by alpha equals alpha(sub m) + 10 deg(sin(wt)). The models were two dimensional, and the test was performed in a water tunnel at Ames Research Center. The unsteady conditions ranged over Re equals 100,000 to 250,000, k equals 0.001 to 0.2, and alpha(sub m) = 10 deg to 20 deg. Unsteady lift, drag, and pitching-moment measurements were obtained along with fluorescent-dye flow visualizations. The addition of the slat was found to delay the static-drag and static-moment stall by about 5 degrees and to eliminate completely the development of a dynamic-stall vortex during unsteady motions that reached angles as high as 25 degrees. In all of the unsteady cases studied, the slat caused a significant reduction in the force and moment hysteresis amplitudes. The reduced frequency was found to have the greatest effect on the results, whereas the Reynolds number had little effect on the behavior of either the basic or the slatted airfoil. The slat caused a slight drag penalty at low angles of attack, but generally increased the lift/drag ratio when averaged over the full cycle of oscillation.

Low-speed aerodynamic characteristics of a 13.1-percent-thick, high-lift airfoil

NASA Technical Reports Server (NTRS)

Sivier, K. R.; Ormsbee, A. I.; Awker, R. W.

1974-01-01

Experimental study of the low-speed, sectional characteristics of a high-lift airfoil, and comparison of these characteristics with the predictions of the theoretical methods used in the airfoil's design. The 13.1% thick UI-1720 airfoil was found to achieve the predicted maximum lift coefficient of nearly 2.0. No upper-surface flow separation was found below the stall angle of attack of 16 deg; it appeared that stall was due to an abrupt leading-edge flow separation.

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.

Experimental studies of flow separation and stalling on two-dimensional airfoils at low speeds. Phase 2: Studies with Fowler flap extended

NASA Technical Reports Server (NTRS)

Seetharam, H. C.; Wentz, W. H., Jr.

1975-01-01

Results were given on experimental studies of flow separation and stalling on a two-dimensional GA(W)-1 17 percent thick airfoil with an extended Fowler flap. Experimental velocity profiles obtained from a five tube probe survey with optimum flap gap and overlap setting (flap at 40 deg) are shown at various stations above, below, and behind the airfoil/flap combination for various angles of attack. The typical zones of steady flow, intermittent turbulence, and large scale turbulence were obtained from a hot wire anemometer survey and are depicted graphically for an angle of attack of 12.5 deg. Local skin friction distributions were obtained and are given for various angles of attack. Computer plots of the boundary layer profiles are shown for the case of the flap at 40 deg. Static pressure contours are also given. A GA(W)-2 section model was fabricated with 30 percent Fowler flaps and with pressure tabs.

40 CFR 1065.930 - Engine starting, restarting, and shutdown.

Code of Federal Regulations, 2010 CFR

2010-07-01

... cranking time as normal. (c) Respond to engine stalling with the following steps: (1) If the engine stalls... 40 Protection of Environment 32 2010-07-01 2010-07-01 false Engine starting, restarting, and...) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Field Testing and Portable Emission Measurement...

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.

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.

Aerodynamic study of a blade with sine variation of chord length along the height for Darrieus wind turbine

NASA Astrophysics Data System (ADS)

Crunteanu, D. E.; Constantinescu, S. G.; 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. In contrast to these wind turbines, the Darrieus wind turbines are simpler and their price is lower. Unfortunately, their blades run at high variations of angles of attack, in stall and post-stall regimes, which can induce significant vibrations, fatigue and even the wind turbine failure. For this reason, the present paper deals with a blade with sine variation of chord length along the height because it has better behavior in stall and post-stall regimes than the classic blade with constant chord length.

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.

Simulation Study of Flap Effects on a Commercial Transport Airplane in Upset Conditions

NASA Technical Reports Server (NTRS)

Cunningham, Kevin; Foster, John V.; Shah, Gautam H.; Stewart, Eric C.; Ventura, Robin N.; Rivers, Robert A.; Wilborn, James E.; Gato, William

2005-01-01

As part of NASA's Aviation Safety and Security Program, a simulation study of a twinjet transport airplane crew training simulation was conducted to address fidelity for upset or loss of control conditions and to study the effect of flap configuration in those regimes. Piloted and desktop simulations were used to compare the baseline crew training simulation model with an enhanced aerodynamic model that was developed for high-angle-of-attack conditions. These studies were conducted with various flap configurations and addressed the approach-to-stall, stall, and post-stall flight regimes. The enhanced simulation model showed that flap configuration had a significant effect on the character of departures that occurred during post-stall flight. Preliminary comparisons with flight test data indicate that the enhanced model is a significant improvement over the baseline. Some of the unrepresentative characteristics that are predicted by the baseline crew training simulation for flight in the post-stall regime have been identified. This paper presents preliminary results of this simulation study and discusses key issues regarding predicted flight dynamics characteristics during extreme upset and loss-of-control flight conditions with different flap configurations.

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.

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.

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 and more treatments for digital dermatitis. All claw measurements were correlated; however, toe angle was most strongly correlated with the other two. In this experiment, stall and alley configurations did not lead to significant differences in several indices of lameness.

X-31 post-stall envelope expansion and tactical utility testing

NASA Technical Reports Server (NTRS)

Canter, Dave

1994-01-01

Technical and nontechnical lessons learned from the X-31 aircraft program are described in this viewgraph presentation. The tactical utility of high angle of attack flight and thrust vector control is discussed.

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.

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.

Global surface pressure measurements of static and dynamic stall on a wind turbine airfoil at low Reynolds number

NASA Astrophysics Data System (ADS)

Disotell, Kevin J.; Nikoueeyan, Pourya; Naughton, Jonathan W.; Gregory, James W.

2016-05-01

Recognizing the need for global surface measurement techniques to characterize the time-varying, three-dimensional loading encountered on rotating wind turbine blades, fast-responding pressure-sensitive paint (PSP) has been evaluated for resolving unsteady aerodynamic effects in incompressible flow. Results of a study aimed at demonstrating the laser-based, single-shot PSP technique on a low Reynolds number wind turbine airfoil in static and dynamic stall are reported. PSP was applied to the suction side of a Delft DU97-W-300 airfoil (maximum thickness-to-chord ratio of 30 %) at a chord Reynolds number of 225,000 in the University of Wyoming open-return wind tunnel. Static and dynamic stall behaviors are presented using instantaneous and phase-averaged global pressure maps. In particular, a three-dimensional pressure topology driven by a stall cell pattern is detected near the maximum lift condition on the steady airfoil. Trends in the PSP-measured pressure topology on the steady airfoil were confirmed using surface oil visualization. The dynamic stall case was characterized by a sinusoidal pitching motion with mean angle of 15.7°, amplitude of 11.2°, and reduced frequency of 0.106 based on semichord. PSP images were acquired at selected phase positions, capturing the breakdown of nominally two-dimensional flow near lift stall, development of post-stall suction near the trailing edge, and a highly three-dimensional topology as the flow reattaches. Structural patterns in the surface pressure topologies are considered from the analysis of the individual PSP snapshots, enabled by a laser-based excitation system that achieves sufficient signal-to-noise ratio in the single-shot images. The PSP results are found to be in general agreement with observations about the steady and unsteady stall characteristics expected for the airfoil.

Heat addition to a subsonic boundary layer: A preliminary analytical study

NASA Technical Reports Server (NTRS)

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

1971-01-01

A preliminary analytical study of the effects of heat addition to the subsonic boundary layer flow over a typical airfoil shape is presented. This phenomenon becomes of interest in the space shuttle mission since heat absorbed by the wing structure during re-entry will be rejected to the boundary layer during the subsequent low speed maneuvering and landing phase. A survey of existing literature and analytical solutions for both laminar and turbulent flow indicate that a heated surface generally destabilizes the boundary layer. Specifically, the boundary layer thickness is increased, the skin friction at the surface is decreased and the point of flow separation is moved forward. In addition, limited analytical results predict that the angle of attack at which a heated airfoil will stall is significantly less than the stall angle of an unheated wing. These effects could adversely affect the lift and drag, and thus the maneuvering capabilities of booster and orbiter shuttle vehicles.

Aerodynamic Analysis of Morphing Blades

NASA Astrophysics Data System (ADS)

Harris, Caleb; Macphee, David; Carlisle, Madeline

2016-11-01

Interest in morphing blades has grown with applications for wind turbines and other aerodynamic blades. This passive control method has advantages over active control methods such as lower manufacturing and upkeep costs. This study has investigated the lift and drag forces on individual blades with experimental and computational analysis. The goal has been to show that these blades delay stall and provide larger lift-to-drag ratios at various angles of attack. Rigid and flexible airfoils were cast from polyurethane and silicone respectively, then lift and drag forces were collected from a load cell during 2-D testing in a wind tunnel. Experimental data was used to validate computational models in OpenFOAM. A finite volume fluid-structure-interaction solver was used to model the flexible blade in fluid flow. Preliminary results indicate delay in stall and larger lift-to-drag ratios by maintaining more optimal angles of attack when flexing. Funding from NSF REU site Grant EEC 1358991 is greatly appreciated.

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.

Control research in the NASA high-alpha technology program

NASA Technical Reports Server (NTRS)

Gilbert, William P.; Nguyen, Luat T.; Gera, Joseph

1990-01-01

NASA is conducting a focused technology program, known as the High-Angle-of-Attack Technology Program, to accelerate the development of flight-validated technology applicable to the design of fighters with superior stall and post-stall characteristics and agility. A carefully integrated effort is underway combining wind tunnel testing, analytical predictions, piloted simulation, and full-scale flight research. A modified F-18 aircraft has been extensively instrumented for use as the NASA High-Angle-of-Attack Research Vehicle used for flight verification of new methods and concepts. This program stresses the importance of providing improved aircraft control capabilities both by powered control (such as thrust-vectoring) and by innovative aerodynamic control concepts. The program is accomplishing extensive coordinated ground and flight testing to assess and improve available experimental and analytical methods and to develop new concepts for enhanced aerodynamics and for effective control, guidance, and cockpit displays essential for effective pilot utilization of the increased agility provided.

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.

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.

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.

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.

Exploratory low-speed wind-tunnel study of concepts designed to improve aircraft stability and control at high angles of attack. M.S. Thesis

NASA Technical Reports Server (NTRS)

Hahne, D. E.

1985-01-01

A wind tunnel investigation of concepts to improve the high angle-of-attack stability and control characteristics of a high performance aircraft was conducted. The effect of vertical tail geometry on stability and the effectiveness of several conventional and unusual control concepts was determined. These results were obtained over a large angle-of-attack range. Vertical tail location, cant angle and leading edge sweep could influence both longitudinal and lateral-directional stability. The control concepts tested were found to be effective and to provide control into the post stall angle-of-attack region.

Coriolis effect on dynamic stall in a vertical axis wind turbine

NASA Astrophysics Data System (ADS)

Tsai, Hsieh-Chen; Colonius, Tim

2013-11-01

The immersed boundary method is used to simulate the flow around a two-dimensional rotating NACA 0018 airfoil at moderate (sub-scale) Reynolds number in order to investigate separated flow occurring on a vertical-axis wind turbine (VAWT). The influence of dynamic stall on the forces is characterized as a function of tip-speed ratio. The influence of the Coriolis effect is also investigated by comparing the rotating airfoil to one undergoing a surging and pitching motion that produces an equivalent speed and angle-of-attack variation over the cycle. While the Coriolis force produces only small differences in the averaged forces, it plays an important role during dynamic stall. Due to the fact that the Coriolis force deflects the fluid and propagates the vortices differently, the wake-capturing phenomenon of the trailing edge vortex is observed in the flow around the rotating airfoil during a certain range of azimuthal angle. This wake-capturing of the trailing edge vortex leads to a large decrease in lift. However, because of the phase difference between each wake-capturing, there are only small differences in the average forces. The simulations are also compared to results from companion water-tunnel experiments at Caltech. This project is supported by the Gordon and Betty Moore Foundation.

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.

The results of a low speed wind tunnel test to investigate the effects of installing refan JT8D engines on the McDonnell Douglas DC-9-30

NASA Technical Reports Server (NTRS)

Chrisenberry, H. E.; Doss, P. G.; Kressly, A. E.; Prichard, R. D.; Thorndike, C. S.

1973-01-01

A low speed wind tunnel test was conducted to assess the effects of the larger JT8D refan nacelles on the stability and control characteristics of the DC-9-30, with emphasis on the deep stall regime. Deep stall pitching moment and elevator hinge moment data, and low angle of attack tail-on and tail-off pitching moment data are presented. The refan nacelle was tested in conjunction with various pylons of reduced span relative to the production DC-9-30 pylon. Also, a horizontal tail that was larger than the production tail was tested. The data show that the refan installation has a small detrimental effect on the DC-9-30 deep stall recovery capability, that recovery characteristics are essentially independent of pylon span, and that the larger horizontal tail significantly increases recovery margins. The deep stall characteristics with the refan installation, within the range of pylon spans tested, are acceptable with no additional design changes anticipated.

Study on casing treatment and stator matching on multistage fan

NASA Astrophysics Data System (ADS)

Wu, Chuangliang; Yuan, Wei; Deng, Zhe

2017-10-01

Casing treatments are required for expanding the stall margin of multi-stage high-load turbofans designed with high blade-tip Mach numbers and high leakage flow. In the case of a low mass flow, the casing treatment effectively reduces the blockages caused by the leakage flow and enlarges the stall margin. However, in the case of a high mass flow, the casing treatment affects the overall flow capacity of the fan, the thrust when operating at the high speeds usually required by design-point specifications. Herein, we study a two-stage high-load fan with three-dimensional numerical simulations. We use the simulation results to propose a scheme that enlarges the stall margin of multistage high-load fans without sacrificing the flow capacity when operating with a large mass flow. Furthermore, a circumferential groove casing treatment is used and adjustments are made to the upstream stator angle to match the casing treatment. The stall margin is thus increased to 16.3%, with no reduction in the maximum mass flow rate or the design thrust performance.

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.

Effects of exercise on biomechanical properties of the superficial digital flexor tendon in foals.

PubMed

Cherdchutham, W; Meershoek, L S; van Weeren, P R; Barneveld, A

2001-12-01

To determine the effects of exercise on biomechanical properties of the superficial digital flexor tendon (SDFT) in foals. 43 Dutch Warmblood foals. From 1 week until 5 months of age, 14 foals were housed in stalls and not exercised, 14 foals were housed in stalls and exercised daily, and 15 foals were maintained at pasture. Eight foals in each group were euthanatized at 5 months, and remaining foals were housed together in a stall and paddock until euthanatized at 11 months. After euthanasia, SDFT were isolated and fit in a material testing system. Mean cross-sectional area (CSA) was measured and traction forces recorded. Normalized force at rupture (force(rup)), normalized force at 4% strain, strain at rupture, stress at 4% strain (stress(4%stain)), and stress at rupture were compared among and within groups. At 5 months, mean CSA and normalized force(rup) were significantly greater and stress(4%strain) significantly less in the pastured group, compared with the other groups. At 11 months, CSA and normalized force(rup) were not significantly different among groups, because force(rup) increased significantly from 5 to 11 months in the nonexercised group and decreased significantly in the pastured group. Exercise significantly affected the biomechanical properties of the SDFT in foals. Evenly distributed moderate- and low-intensity exercise at a young age may be more effective for development of strong, flexible tendons in horses than single episodes of high-intensity exercise superimposed on stall rest. This effect may impact later susceptibility to SDFT injury.

Tail Buffeting

NASA Technical Reports Server (NTRS)

Abdrashitov, G.

1943-01-01

An approximate theory of buffeting is here presented, based on the assumption of harmonic disturbing forces. Two cases of buffeting are considered: namely, for a tail angle of attack greater and less than the stalling angle, respectively. On the basis of the tests conducted and the results of foreign investigators, a general analysis is given of the nature of the forced vibrations the possible load limits on the tail, and the methods of elimination of buffeting.

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.

Concepts and application of dynamic separation for agility and super-maneuverability of aircraft: An assessment

NASA Technical Reports Server (NTRS)

Freymuth, Peter

1992-01-01

Aims for improvement of fighter aircraft pursued by the unsteady flow community are high agility (the ability of the aircraft to make close turns in a low-speed regime) and super maneuverability (the ability of the aircraft to operate at high angles of attack in a post stall regime during quick maneuvers in a more extended speed range). High agility requires high lift coefficients at low speeds in a dynamic situation and this requirement can be met by dynamically forced separation or by quasistatic stall control. The competing methods will be assessed based on the known physics. Maneuvering into the post stall regime also involves dynamic separation but because even fast maneuvers involving the entire aircraft are 'aerodynamically slow' the resulting dynamic vortex structures should be considered 'elicited' rather than 'forced.' More work seems to be needed in this area of elicited dynamic separation.

Two-dimensional dynamic stall as simulated in a varying freestream

NASA Technical Reports Server (NTRS)

Pierce, G. A.; Kunz, D. L.; Malone, J. B.

1978-01-01

A low speed wind tunnel equipped with a axial gust generator to simulate the aerodynamic environment of a helicopter rotor was used to study the dynamic stall of a pitching blade in an effort to ascertain to what extent harmonic velocity perturbations in the freestream affect dynamic stall. The aerodynamic moment on a two dimensional, pitching blade model in both constant and pulsating airstream was measured. An operational analog computer was used to perform on-line data reduction and plots of moment versus angle of attack and work done by the moment were obtained. The data taken in the varying freestream were then compared to constant freestream data and to the results of two analytical methods. These comparisons show that the velocity perturbations have a significant effect on the pitching moment which can not be consistently predicted by the analytical methods, but had no drastic effect on the blade stability.

Longitudinal Stability and Stalling Characteristics of a 1/8.33-Scale Model of the Republic XF-12 Airplane

NASA Technical Reports Server (NTRS)

Pepper, Edward; Foster, Gerald V.

1946-01-01

The XF-12 airplane is a high performance, photo-reconnaissance aircraft designed by the Republic Aviation Corporation for Army Air Forces. A series of tests of a 1/8.33-scale powered model was conducted in the Langley 9-foot pressure tunnel to obtain information relative to the aerodynamic design of the airplane. This report presents the results of tests to determine the static longitudinal stability and stalling characteristics of the model. From this investigation it was indicated that the airplane will possess a positive static margin for all probable flight conditions. The stalling characteristics are considered satisfactory in that the stall initiates near the root section and progresses toward the tips. Early root section stalling occurs, with the flaps retracted and may cause undesirable tail buffeting and erratic elevator control in the normal flight range. From considerations of sinking speed landing flap deflections of 40 degrees may be preferable to 55 degrees of 65 degrees.

Three-Dimensional Aerodynamic Instabilities In Multi-Stage Axial Compressors

NASA Technical Reports Server (NTRS)

Tan, Choon S.; Gong, Yifang; Suder, Kenneth L. (Technical Monitor)

2001-01-01

This thesis presents the conceptualization and development of a computational model for describing three-dimensional non-linear disturbances associated with instability and inlet distortion in multistage compressors. Specifically, the model is aimed at simulating the non-linear aspects of short wavelength stall inception, part span stall cells, and compressor response to three-dimensional inlet distortions. The computed results demonstrated the first-of-a-kind capability for simulating short wavelength stall inception in multistage compressors. The adequacy of the model is demonstrated by its application to reproduce the following phenomena: (1) response of a compressor to a square-wave total pressure inlet distortion; (2) behavior of long wavelength small amplitude disturbances in compressors; (3) short wavelength stall inception in a multistage compressor and the occurrence of rotating stall inception on the negatively sloped portion of the compressor characteristic; (4) progressive stalling behavior in the first stage in a mismatched multistage compressor; (5) change of stall inception type (from modal to spike and vice versa) due to IGV stagger angle variation, and "unique rotor tip incidence" at these points where the compressor stalls through short wavelength disturbances. The model has been applied to determine the parametric dependence of instability inception behavior in terms of amplitude and spatial distribution of initial disturbance, and intra-blade-row gaps. It is found that reducing the inter-blade row gaps suppresses the growth of short wavelength disturbances. It is also concluded from these parametric investigations that each local component group (rotor and its two adjacent stators) has its own instability point (i.e. conditions at which disturbances are sustained) for short wavelength disturbances, with the instability point for the compressor set by the most unstable component group. For completeness, the methodology has been extended to describe finite amplitude disturbances in high-speed compressors. Results are presented for the response of a transonic compressor subjected to inlet distortions.

Aerodynamic performance of a fan stage utilizing Variable Inlet Guide Vanes (VIGVs) for thrust modulation. [subsonic V/STOL aircraft

NASA Technical Reports Server (NTRS)

Woollett, R. R.

1983-01-01

An experimental research program was conducted in the Lewis Research Center's 9x15-foot (2.74x4.57 m) low speed wind tunnel to evaluate the aerodynamic performance of an inlet and fan system with variable inlet guide vanes (VIGVs) for use on a subsonic V/STOL aircraft. At high VIGV blade angles (lower weight flow and thrust levels), the fan stage was stalled over a major portion of its radius. In spite of the stall, fan blade stresses only exceeded the limits at the most extreme flow conditions. It was found that inlet flow separation does not necessarily lead to poor inlet performance or adverse fan operating conditions. Generally speaking, separated inlet flow did not adversely affect the fan blade stress levels. There were some cases, however, at high VIGV angles and high inlet angles-of-attack where excessive blade stress levels were encountered. An evaluation term made up of the product of the distortion parameter, K alpha, the weight flow and the fan pressure ratio minus one, was found to correlate quite well with the observed blade stress results.

Aerodynamic performance of a fan stage utilizing variable inlet guide vanes (VIGV's) for thrust modulation. [subsonic V/STOL aircraft

NASA Technical Reports Server (NTRS)

Woollett, R. R.

1983-01-01

An experimental research program was conducted in the Lewis Research Center's 9 x 15-foot (2.74 x 4.57 m) low speed wind tunnel to evaluate the aerodynamic performance of an inlet and fan system with variable inlet guide vanes (VIGVs) for use on a subsonic V/STOL aircraft. At high VIGV blade angles (lower weight flow and thrust levels), the fan stage was stalled over a major portion of its radius. In spite of the stall, fan blade stresses only exceeded the limits at the most extreme flow conditions. It was found that inlet flow separation does not necessarily lead to poor inlet performance or adverse fan operating conditions. Generally speaking, separated inlet flow did not adversely affect the fan blade stress levels. There were some cases, however, at high VIGV angles and high inlet angles-of-attack where excessive blade stress levels were encountered. An evaluation term made up of the product of the distortion parameter, K alpha, the weight flow and the fan pressure ratio minus one, was found to correlate quite well with the observed blade stress results. Previously announced in STAR as N83-27957

Investigating locomotion of dairy cows by use of high speed cinematography.

PubMed

Herlin, A H; Drevemo, S

1997-05-01

The longterm influence of management systems on the locomotion of 17 dairy cows was investigated by high speed cinematography (100 frames/s) and kinematic analysis. Angular patterns and hoof trajectories of the left fore- and hindlimbs are presented and statistics made of occurring minimum and maximum angles. At the recording, 3 cows had been kept in tie-stalls (TI) and 6 cows in cubicles (CI) for a consecutive time of about 2.5 years while 8 cows had been kept on grass for about 3 months. Four of the grazing cows had earlier been kept in cubicles (CG) and 4 in tie-stalls (TG) during earlier off grazing seasons together with TI and CI cows. The CI cows had a smaller maximum angle of the elbow joint compared to TI, TG and CG cows. The hock joint angle of the CI cows was less flexed during the stance phase than in TI and CG cows while the minimum angle during the swing phase was greater in the TI and CI cows compared to TG and CG cows. Pastured cows (TG and CG) had a less pronounced flexion of the fetlock joint angle during the stance compared to cows kept indoors (TI and CI). The results suggest that slatted floor and lack of exercise during summer grazing may affect locomotion. This is indicated by restrictions in the movements of the elbow and hock joints and in less fetlock joint flexion at full support.

Forced Oscillation Wind Tunnel Testing for FASER Flight Research Aircraft

NASA Technical Reports Server (NTRS)

Hoe, Garrison; Owens, Donald B.; Denham, Casey

2012-01-01

As unmanned air vehicles (UAVs) continue to expand their flight envelopes into areas of high angular rate and high angle of attack, modeling the complex unsteady aerodynamics for simulation in these regimes has become more difficult using traditional methods. The goal of this experiment was to improve the current six degree-of-freedom aerodynamic model of a small UAV by replacing the analytically derived damping derivatives with experimentally derived values. The UAV is named the Free-flying Aircraft for Sub-scale Experimental Research, FASER, and was tested in the NASA Langley Research Center 12- Foot Low-Speed Tunnel. The forced oscillation wind tunnel test technique was used to measure damping in the roll and yaw axes. By imparting a variety of sinusoidal motions, the effects of non-dimensional angular rate and reduced frequency were examined over a large range of angle of attack and side-slip combinations. Tests were performed at angles of attack from -5 to 40 degrees, sideslip angles of -30 to 30 degrees, oscillation amplitudes from 5 to 30 degrees, and reduced frequencies from 0.010 to 0.133. Additionally, the effect of aileron or elevator deflection on the damping coefficients was examined. Comparisons are made of two different data reduction methods used to obtain the damping derivatives. The results show that the damping derivatives are mainly a function of angle of attack and have dependence on the non-dimensional rate and reduced frequency only in the stall/post-stall regime

An inviscid-viscous interaction approach to the calculation of dynamic stall initiation on airfoils

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cebeci, T.; Platzer, M.F.; Jang, H.M.

An interactive boundary-layer method is described for computing unsteady incompressible flow over airfoils, including the initiation of dynamic stall. The inviscid unsteady panel method developed by Platzer and Teng is extended to include viscous effects. The solutions of the boundary-layer equations are obtained with an inverse finite-difference method employing an interaction law based on the Hilbert integral, and the algebraic eddy-viscosity formulation of Cebeci and Smith. The method is applied to airfoils subject to periodic and ramp-type motions and its abilities are examined for a range of angles of attack, reduced frequency, and pitch rate.

Evaluation of range and distortion tolerance for high Mach number transonic fan stages. Task 2: Performance of a 1500-foot-per-second tip speed transonic fan stage with variable geometry inlet guide vanes and stator

NASA Technical Reports Server (NTRS)

Bilwakesh, K. R.; Koch, C. C.; Prince, D. C.

1972-01-01

A 0.5 hub/tip radius ratio compressor stage consisting of a 1500 ft/sec tip speed rotor, a variable camber inlet guide vane and a variable stagger stator was designed and tested with undistorted inlet flow, flow with tip radial distortion, and flow with 90 degrees, one-per-rev, circumferential distortion. At the design speed and design IGV and stator setting the design stage pressure ratio was achieved at a weight within 1% of the design flow. Analytical results on rotor tip shock structure, deviation angle and part-span shroud losses at different operating conditions are presented. The variable geometry blading enabled efficient operation with adequate stall margin at the design condition and at 70% speed. Closing the inlet guide vanes to 40 degrees changed the speed-versus-weight flow relationship along the stall line and thus provided the flexibility of operation at off-design conditions. Inlet flow distortion caused considerable losses in peak efficiency, efficiency on a constant throttle line through design pressure ratio at design speed, stall pressure ratio, and stall margin at the 0 degrees IGV setting and high rotative speeds. The use of the 40 degrees inlet guide vane setting enabled partial recovery of the stall margin over the standard constant throttle line.

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.

A preliminary theoretical study of double blade two-dimensional aerodynamics for applications to vertical axis wind turbines

NASA Astrophysics Data System (ADS)

Weibust, E.

1981-04-01

A NASA model for computing the subsonic, viscous, attached flow around multielement airfoils was used to determine the amount of energy lost when using double blades rather than single ones. The resulting tangential force for the double or single blade configuration used as a criterion is found. Radial spacing, toe-in toe-out angle and tangential displacement (stagger) were varied to see how tagential force is affected. The greatest tangential force values are found to be achieved for maximum allowable radial spacing, which is determined by structural considerations, and is assumed to be on the order of 1.5 c. At this rather large distance, stagger as well as toe-in toe-out angle only gives slight improvements as long as the flow separation effects (stall region) are not considered. A large part of the energy is captured at relatively high wind speeds when the flow on the blades is partly separated (stalled).

Passive control of the flow around unsteady aerofoils using a self-activated deployable flap

NASA Astrophysics Data System (ADS)

Rosti, Marco E.; Omidyeganeh, Mohammad; Pinelli, Alfredo

2018-03-01

Self-activated feathers are used by many birds to adapt their wing characteristics to the sudden change of flight incidence angle. In particular, dorsal feathers are believed to pop-up as a consequence of unsteady flow separation and to interact with the flow to palliate the sudden stall breakdown typical of dynamic stall. Inspired by the adaptive character of birds feathers, some authors have envisaged the potential benefits of using of flexible flaps mounted on aerodynamic surfaces to counteract the negative aerodynamic effects associated with dynamic stall. This contribution explores more in depth the physical mechanisms that play a role in the modification of the unsteady flow field generated by a NACA0020 aerofoil equipped with an elastically mounted flap undergoing a specific ramp-up manoeuvre. We discuss the design of flaps that limit the severity of the dynamic stall breakdown by increasing the value of the lift overshoot also smoothing its abrupt decay in time. A detailed analysis on the modification of the turbulent and unsteady vorticity field due to the flap flow interaction during the ramp-up motion is also provided to explain the more benign aerodynamic response obtained when the flap is in use.

Models of Lift and Drag Coefficients of Stalled and Unstalled Airfoils in Wind Turbines and Wind Tunnels

NASA Technical Reports Server (NTRS)

Spera, David A.

2008-01-01

Equations are developed with which to calculate lift and drag coefficients along the spans of torsionally-stiff rotating airfoils of the type used in wind turbine rotors and wind tunnel fans, at angles of attack in both the unstalled and stalled aerodynamic regimes. Explicit adjustments are made for the effects of aspect ratio (length to chord width) and airfoil thickness ratio. Calculated lift and drag parameters are compared to measured parameters for 55 airfoil data sets including 585 test points. Mean deviation was found to be -0.4 percent and standard deviation was 4.8 percent. When the proposed equations were applied to the calculation of power from a stall-controlled wind turbine tested in a NASA wind tunnel, mean deviation from 54 data points was -1.3 percent and standard deviation was 4.0 percent. Pressure-rise calculations for a large wind tunnel fan deviated by 2.7 percent (mean) and 4.4 percent (standard). The assumption that a single set of lift and drag coefficient equations can represent the stalled aerodynamic behavior of a wide variety of airfoils was found to be satisfactory.

Validation of an Actuator Line Model Coupled to a Dynamic Stall Model for Pitching Motions Characteristic to Vertical Axis Turbines

NASA Astrophysics Data System (ADS)

Mendoza, Victor; Bachant, Peter; Wosnik, Martin; Goude, Anders

2016-09-01

Vertical axis wind turbines (VAWT) can be used to extract renewable energy from wind flows. A simpler design, low cost of maintenance, and the ability to accept flow from all directions perpendicular to the rotor axis are some of the most important advantages over conventional horizontal axis wind turbines (HAWT). However, VAWT encounter complex and unsteady fluid dynamics, which present significant modeling challenges. One of the most relevant phenomena is dynamic stall, which is caused by the unsteady variation of angle of attack throughout the blade rotation, and is the focus of the present study. Dynamic stall is usually used as a passive control for VAWT operating conditions, hence the importance of predicting its effects. In this study, a coupled model is implemented with the open-source CFD toolbox OpenFOAM for solving the Navier-Stokes equations, where an actuator line model and dynamic stall model are used to compute the blade loading and body force. Force coefficients obtained from the model are validated with experimental data of pitching airfoil in similar operating conditions as an H-rotor type VAWT. Numerical results show reasonable agreement with experimental data for pitching motion.

Spanwise visualization of the flow around a three-dimensional foil with leading edge protuberances

NASA Astrophysics Data System (ADS)

Stanway, M. J.; Techet, A. H.

2006-11-01

Studies of model humpback whale fins have shown that leading edge protuberances, or tubercles, can lead to delayed stall and increased lift at higher angles of attack, compared to foils with geometrically smooth leading edges. Such enhanced performance characteristics could prove highly useful in underwater vehicles such as gliders or long range AUVs (autonomous underwater vehicles). In this work, Particle Imaging Velocimetry (PIV) is performed on two static wings in a water tunnel over a range of angles of attack. These three- dimensional, finite-aspect ratio wings are modeled after a humpback whale flipper and are identical in shape, tapered from root to tip, except for the leading edge. In one of the foils the leading edge is smooth, whereas in the other, regularly spaced leading edge bumps are machined to simulate the whale’s fin tubercles. Results from these PIV tests reveal distinct cells where coherent flow structures are destroyed as a result of the leading edge perturbations. Tests are performed at Reynolds numbers Re ˜ O(10^5), based on chordlength, in a recirculating water tunnel. An inline six-axis load cell is mounted to measure the forces on the foil over a range of static pitch angles. It is hypothesized that this spanwise breakup of coherent vortical structures is responsible for the delayed angle of stall. These quantitative experiments complement exiting qualitative studies with two dimensional foils.

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

14 CFR 25.1583 - Operating limitations.

Code of Federal Regulations, 2010 CFR

2010-01-01

... any regime of flight (climb, cruise, or descent) unless a higher speed is authorized for flight test... and aileron controls, as well as maneuvers that involve angles of attack near the stall, should be... and balance control and loading document that is incorporated by reference in the Airplane Flight...

Loads Correlation of a Full-Scale UH-60A Airloads Rotor in a Wind Tunnel

NASA Technical Reports Server (NTRS)

Yeo, Hyeonsoo; Romander, Ethan A.

2012-01-01

Wind tunnel measurements of the rotor trim, blade airloads, and structural loads of a full-scale UH-60A Black Hawk main rotor are compared with calculations obtained using the comprehensive rotorcraft analysis CAMRAD II and a coupled CAMRAD II/OVERFLOW 2 analysis. A speed sweep at constant lift up to an advance ratio of 0.4 and a thrust sweep at constant speed into deep stall are investigated. The coupled analysis shows significant improvement over comprehensive analysis. Normal force phase is better captured and pitching moment magnitudes are better predicted including the magnitude and phase of the two stall events in the fourth quadrant at the deeply stalled condition. Structural loads are, in general, improved with the coupled analysis, but the magnitude of chord bending moment is still significantly underpredicted. As there are three modes around 4 and 5/rev frequencies, the structural responses to the 5/rev airloads due to dynamic stall are magnified and thus care must be taken in the analysis of the deeply stalled condition.

Oscillating Cascade Aerodynamics at Large Mean Incidence Angles

NASA Technical Reports Server (NTRS)

Buffum, Daniel H.

1997-01-01

In a cooperative program with Pratt & Whitney, researchers obtained fundamental separated flow unsteady aerodynamic data in the NASA Lewis Research Center's Oscillating Cascade. These data fill a void that has hindered the understanding and prediction of subsonic and transonic stall flutter. For small-amplitude torsional oscillations, unsteady pressure distributions were measured on airfoils with cross sections representative of an advanced, low-aspect-ratio fan blade. Data were obtained for two mean incidence angles with a subsonic inflow. At high mean incidence angles (alpha = 10 deg), the mean flow separated at the leading edge and reattached at about 40 percent of the chord. For comparison purposes, data were also obtained for a low incidence angle (a = 0 deg) attached flow.

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.

Aeroelastic Stability of Idling Wind Turbines

NASA Astrophysics Data System (ADS)

Wang, Kai; Riziotis, Vasilis A.; Voutsinas, Spyros G.

2016-09-01

Wind turbine rotors in idling operation mode can experience high angles of attack, within the post stall region that are capable of triggering stall-induced vibrations. In the present paper rotor stability in slow idling operation is assessed on the basis of non-linear time domain and linear eigenvalue analysis. Analysis is performed for a 10 MW conceptual wind turbine designed by DTU. First the flow conditions that are likely to favour stall induced instabilities are identified through non-linear time domain aeroelastic analysis. Next, for the above specified conditions, eigenvalue stability simulations are performed aiming at identifying the low damped modes of the turbine. Finally the results of the eigenvalue analysis are evaluated through computations of the work of the aerodynamic forces by imposing harmonic vibrations following the shape and frequency of the various modes. Eigenvalue analysis indicates that the asymmetric and symmetric out-of-plane modes have the lowest damping. The results of the eigenvalue analysis agree well with those of the time domain analysis.

Stall behavior of a scaled three-dimensional wind turbine blade

NASA Astrophysics Data System (ADS)

Mulleners, Karen; Melius, Matthew; Cal, Raul Bayoan

2014-11-01

The power generation of a wind turbine is influenced by many factors including the unsteady incoming flow characteristics, pitch regulation, and the geometry of the various turbine components. Within the framework of maximizing energy extraction, it is important to understand and tailor the aerodynamics of a wind turbine. In the interest of seeking further understanding into the complex flow over wind turbine blades, a three-dimensional scaled blade model has been designed and manufactured to be dynamically similar to a rotating full-scale NREL 5MW wind turbine blade. A wind tunnel experiment has been carried out in the 2.2 m × 1.8 m cross-section closed loop wind tunnel at DLR in Göttingen by means of time-resolved stereoscopic PIV. An extensive coherent structure analysis of the time-resolved velocity field over the suction side of the blade was performed to study stall characteristics under a geometrically induced pressure gradient. In particular, the radial extent and propagation of stalled flow regions were characterized for various static angles of attack.

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.

Periodic and aperiodic flow patterns around an airfoil with leading-edge protuberances

NASA Astrophysics Data System (ADS)

Cai, Chang; Zuo, Zhigang; Maeda, Takao; Kamada, Yasunari; Li, Qing'an; Shimamoto, Kensei; Liu, Shuhong

2017-11-01

Recently leading-edge protuberances have attracted great attention as a passive method for separation control. In this paper, the effect of multiple leading-edge protuberances on the performance of a two-dimensional airfoil is investigated through experimental measurement of aerodynamic forces, surface tuft visualization, and numerical simulation. In contrast to the sharp stall of the baseline airfoil with large hysteresis effect during AOA (angle of attack) increasing and decreasing, the stall process of the modified airfoil with leading-edge protuberances is gentle and stable. Flow visualization revealed that the flow past each protuberance is periodic and symmetric at small AOAs. Streamwise vortices are generated on the shoulders of the protuberance, leading to a larger separation around the valley sections and a longer attachment along the peak sections. When some critical AOA is exceeded, aperiodic and asymmetric flow patterns occur on the protuberances at different spanwise positions, with leading-edge separation on some of the valley sections and non-stalled condition elsewhere. A combined mechanism, involving both the compartmentalization effect of the slender momentum-enhanced attached flows on the protuberance peaks and the downwash effect of the local stalled region with low circulation, is proposed to explain the generation of the aperiodic flow patterns. The influence of the number of protuberances is also investigated, which shows similar aperiodic flow patterns. The distance between the neighboring local stalled valley sections is found to be in the range of 4-7 times the protuberance wavelength. According to the proposed mechanism, it is speculated that the distance between the neighboring local stalled valley sections is inclined to increase with a smaller protuberance amplitude or at a larger AOA.

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.

Simulation Modeling Requirements for Loss-of-Control Accident Prevention of Turboprop Transport Aircraft

NASA Technical Reports Server (NTRS)

Crider, Dennis; Foster, John V.

2012-01-01

In-flight loss of control remains the leading contributor to aviation accident fatalities, with stall upsets being the leading causal factor. The February 12, 2009. Colgan Air, Inc., Continental Express flight 3407 accident outside Buffalo, New York, brought this issue to the forefront of public consciousness and resulted in recommendations from the National Transportation Safety Board to conduct training that incorporates stalls that are fully developed and develop simulator standards to support such training. In 2010, Congress responded to this accident with Public Law 11-216 (Section 208), which mandates full stall training for Part 121 flight operations. Efforts are currently in progress to develop recommendations on implementation of stall training for airline pilots. The International Committee on Aviation Training in Extended Envelopes (ICATEE) is currently defining simulator fidelity standards that will be necessary for effective stall training. These recommendations will apply to all civil transport aircraft including straight-wing turboprop aircraft. Government-funded research over the previous decade provides a strong foundation for stall/post-stall simulation for swept-wing, conventional tail jets to respond to this mandate, but turboprops present additional and unique modeling challenges. First among these challenges is the effect of power, which can provide enhanced flow attachment behind the propellers. Furthermore, turboprops tend to operate for longer periods in an environment more susceptible to ice. As a result, there have been a significant number of turboprop accidents as a result of the early (lower angle of attack) stalls in icing. The vulnerability of turboprop configurations to icing has led to studies on ice accumulation and the resulting effects on flight behavior. Piloted simulations of these effects have highlighted the important training needs for recognition and mitigation of icing effects, including the reduction of stall margins. This paper addresses simulation modeling requirements that are unique to turboprop transport aircraft and highlights the growing need for aerodynamic models suitable for stall training for these configurations. A review of prominent accidents that involved aerodynamic stall is used to illustrate various modeling features unique to turboprop configurations and the impact of stall behavior on susceptibility to loss of control that has led to new training requirements. This is followed by an overview of stability and control behavior of straight-wing turboprops, the related aerodynamic characteristics, and a summary of recent experimental studies on icing effects. In addition, differences in flight dynamics behavior between swept-wing jets and straight-wing turboprop configurations are discussed to compare and contrast modeling requirements. Specific recommendations for aerodynamic models along with further research needs and data measurements are also provided. 1

A Comparative Study Using CFD to Predict Iced Airfoil Aerodynamics

NASA Technical Reports Server (NTRS)

Chi, x.; Li, Y.; Chen, H.; Addy, H. E.; Choo, Y. K.; Shih, T. I-P.

2005-01-01

WIND, Fluent, and PowerFLOW were used to predict the lift, drag, and moment coefficients of a business-jet airfoil with a rime ice (rough and jagged, but no protruding horns) and with a glaze ice (rough and jagged end has two or more protruding horns) for angles of attack from zero to and after stall. The performance of the following turbulence models were examined by comparing predictions with available experimental data. Spalart-Allmaras (S-A), RNG k-epsilon, shear-stress transport, v(sup 2)-f, and a differential Reynolds stress model with and without non-equilibrium wall functions. For steady RANS simulations, WIND and FLUENT were found to give nearly identical results if the grid about the iced airfoil, the turbulence model, and the order of accuracy of the numerical schemes used are the same. The use of wall functions was found to be acceptable for the rime ice configuration and the flow conditions examined. For rime ice, the S-A model was found to predict accurately until near the stall angle. For glaze ice, the CFD predictions were much less satisfactory for all turbulence models and codes investigated because of the large separated region produced by the horns. For unsteady RANS, WIND and FLUENT did not provide better results. PowerFLOW, based on the Lattice Boltzmann method, gave excellent results for the lift coefficient at and near stall for the rime ice, where the flow is inherently unsteady.

Additional Testing of the DHC-6 Twin Otter Tailplane Iced Airfoil Section in the Ohio State University 7x10 Low Speed Wind Tunnel. Volume 2

NASA Technical Reports Server (NTRS)

Gregorek, Gerald; Dresse, John J.; LaNoe, Karine; Ratvasky, Thomas (Technical Monitor)

2000-01-01

The need for fundamental research in Ice Contaminated Tailplane Stall (ICTS) was established through three international conferences sponsored by the FAA. A joint NASA/FAA Tailplane Icing Program was formed in 1994 with the Ohio State University playing a critical role for wind tunnel and analytical research. Two entries of a full-scale 2-dimensional tailplane airfoil model of a DHC-6 Twin Otter were made in The Ohio State University 7x10 ft wind tunnel. This report describes the second test entry that examined additional ice shapes and roughness, as well as airfoil section differences. The addition data obtained in this test fortified the original database of aerodynamic coefficients that permit a detailed analysis of flight test results with an OSU-developed analytical program. The testing encompassed a full range of angles of attack and elevator deflections at flight Reynolds number conditions. Aerodynamic coefficients, C(L), C(M), and C(He), were obtained by integrating static pressure coefficient, C(P), values obtained from surface taps. Comparisons of clean and iced airfoil results show a significant decrease in the tailplane aeroperformance (decreased C(Lmax), decreased stall angle, increased C(He)) for all ice shapes with the grit having the lease affect and the LEWICE shape having the greatest affect. All results were consistent with observed tailplane stall phenomena and constitute an effective set of data for comprehensive analysis of ICTS.

Wind turbine generator with improved operating subassemblies

DOEpatents

Cheney, Jr., Marvin C.

1985-01-01

A wind turbine includes a yaw spring return assembly to return the nacelle from a position to which it has been rotated by yawing forces, thus preventing excessive twisting of the power cables and control cables. It also includes negative coning restrainers to limit the bending of the flexible arms of the rotor towards the tower, and stop means on the rotor shaft to orient the blades in a vertical position during periods when the unit is upwind when the wind commences. A pendulum pitch control mechanism is improved by orienting the pivot axis for the pendulum arm at an angle to the longitudinal axis of its support arm, and excessive creep is of the synthetic resin flexible beam support for the blades is prevented by a restraining cable which limits the extent of pivoting of the pendulum during normal operation but which will permit further pivoting under abnormal conditions to cause the rotor to stall.

Volume Dynamics Propulsion System Modeling for Supersonics Vehicle Research

NASA Technical Reports Server (NTRS)

Kopasakis, George; Connolly, Joseph W.; Paxson, Daniel E.; Ma, Peter

2010-01-01

Under the NASA Fundamental Aeronautics Program the Supersonics Project is working to overcome the obstacles to supersonic commercial flight. The proposed vehicles are long slim body aircraft with pronounced aero-servo-elastic modes. These modes can potentially couple with propulsion system dynamics; leading to performance challenges such as aircraft ride quality and stability. Other disturbances upstream of the engine generated from atmospheric wind gusts, angle of attack, and yaw can have similar effects. In addition, for optimal propulsion system performance, normal inlet-engine operations are required to be closer to compressor stall and inlet unstart. To study these phenomena an integrated model is needed that includes both airframe structural dynamics as well as the propulsion system dynamics. This paper covers the propulsion system component volume dynamics modeling of a turbojet engine that will be used for an integrated vehicle Aero-Propulso-Servo-Elastic model and for propulsion efficiency studies.

Volume Dynamics Propulsion System Modeling for Supersonics Vehicle Research

NASA Technical Reports Server (NTRS)

Kopasakis, George; Connolly, Joseph W.; Paxson, Daniel E.; Ma, Peter

2008-01-01

Under the NASA Fundamental Aeronautics Program, the Supersonics Project is working to overcome the obstacles to supersonic commercial flight. The proposed vehicles are long slim body aircraft with pronounced aero-servo-elastic modes. These modes can potentially couple with propulsion system dynamics; leading to performance challenges such as aircraft ride quality and stability. Other disturbances upstream of the engine generated from atmospheric wind gusts, angle of attack, and yaw can have similar effects. In addition, for optimal propulsion system performance, normal inlet-engine operations are required to be closer to compressor stall and inlet unstart. To study these phenomena an integrated model is needed that includes both airframe structural dynamics as well as the propulsion system dynamics. This paper covers the propulsion system component volume dynamics modeling of a turbojet engine that will be used for an integrated vehicle Aero-Propulso-Servo-Elastic model and for propulsion efficiency studies.

Volume Dynamics Propulsion System Modeling for Supersonics Vehicle Research

NASA Technical Reports Server (NTRS)

Kopasakis, George; Connolly, Joseph W.; Paxson, Daniel E.; Ma, Peter

2008-01-01

Under the NASA Fundamental Aeronautics Program the Supersonics Project is working to overcome the obstacles to supersonic commercial flight. The proposed vehicles are long slim body aircraft with pronounced aero-servo-elastic modes. These modes can potentially couple with propulsion system dynamics; leading to performance challenges such as aircraft ride quality and stability. Other disturbances upstream of the engine generated from atmospheric wind gusts, angle of attack, and yaw can have similar effects. In addition, for optimal propulsion system performance, normal inlet-engine operations are required to be closer to compressor stall and inlet unstart. To study these phenomena an integrated model is needed that includes both airframe structural dynamics as well as the propulsion system dynamics. This paper covers the propulsion system component volume dynamics modeling of a turbojet engine that will be used for an integrated vehicle Aero- Propulso-Servo-Elastic model and for propulsion efficiency studies.

Wind-tunnel investigation of the flow correction for a model-mounted angle of attack sensor at angles of attack from -10 deg to 110 deg. [Langley 12-foot low speed wind tunnel test

NASA Technical Reports Server (NTRS)

Moul, T. M.

1979-01-01

A preliminary wind tunnel investigation was undertaken to determine the flow correction for a vane angle of attack sensor over an angle of attack range from -10 deg to 110 deg. The sensor was mounted ahead of the wing on a 1/5 scale model of a general aviation airplane. It was shown that the flow correction was substantial, reaching about 15 deg at an angle of attack of 90 deg. The flow correction was found to increase as the sensor was moved closer to the wing or closer to the fuselage. The experimentally determined slope of the flow correction versus the measured angle of attack below the stall angle of attack agreed closely with the slope of flight data from a similar full scale airplane.

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).

Experimental study of effects of forebody geometry on high angle of attack static and dynamic stability and control

NASA Technical Reports Server (NTRS)

Brandon, J. M.; Murri, D. G.; Nguyen, L. T.

1986-01-01

A series of low-speed wind tunnel tests on a generic airplane model with a cylindrical fuselage were made to investigate the effects of forebody shape and fitness ratio, and fuselage/wing proximity on static and dynamic lateral/directional stability. In addition, some preliminary testing to determine the effectiveness of deflectable forebody strakes for high angle of attack yaw control was conducted. During the stability investigation, 11 forebodies were tested including three different cross-sectional shapes with fineness ratios of 2, 3, and 4. In addition, the wing was tested at two longitudinal positions to provide a substantial variation in forebody/wing proximity. Conventional force tests were conducted to determine static stability characteristics, and single-degree-of-freedom free-to-roll tests were conducted to study the wing rock characteristics of the model with the various forebodies. Flow visualization data were obtained to aid in the analysis of the complex flow phenomena involved. The results show that the forebody cross-sectional shape and fineness ratio and forebody/wing proximity can strongly affect both static and dynamic (roll) stability at high angles of attack. These characteristics result from the impact of these factors on forebody vortex development, the behavior of the vortices in sideslip, and their interaction with the wing flow field. Preliminary results from the deflectable strake investigation indicated that forebody flow control using this concept can provide very large yaw control moments at stall and post-stall angles of attack.

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.

Investigation of Unsteady Flow Interaction Between an Ultra-Compact Inlet and a Transonic Fan

NASA Technical Reports Server (NTRS)

Hah, Chunill; Rabe, Douglas; Scribben, Angie

2015-01-01

In the study presented, unsteady flow interaction between an ultra-compact inlet and a transonic fan stage is investigated. Future combat aircraft engines require ultra-compact inlet ducts as part of an integrated, advanced propulsion system to improve air vehicle capability and effectiveness to meet future mission needs. The main purpose of the current study is to advance the understanding of the flow interaction between a modern ultra-compact inlet and a transonic fan for future design applications. Many experimental/ analytical studies have been reported on the aerodynamics of compact inlets in aircraft engines. On the other hand, very few studies have been reported on the effects of flow distortion from these inlets on the performance of the following fan/compressor stages. The primary goal of the study presented is to investigate how flow interaction between an ultra-compact inlet and a transonic compressor influence the operating margin of the compressor. Both Unsteady Reynolds-averaged Navier-Stokes (URANS) and Large Eddy Simulation (LES) approaches are used to calculate the unsteady flow field, and the numerical results are used to study the flow interaction. The present study indicates that stall inception of the following compressor stage is affected directly based on how the distortion pattern evolves before it interacts with the fan/compressor face. For the present compressor, the stall initiates at the tip section with clean inlet flow and distortion pattern away from the casing itself seems to have limited impacts on the stall inception of the compressor. A counter-rotating swirl, which is generated due to flow separation inside the s-shaped compact duct, generates an increased flow angle near the blade tip. This increased flow angle near the rotor tip due to the secondary flow from the counter-rotating vortices is the primary reason for the reduced compressor stall margin.

14 CFR 25.533 - Hull and main float bottom pressures.

Code of Federal Regulations, 2011 CFR

2011-01-01

... AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Structure Water Loads § 25.533 Hull and main... figure 2 of appendix B; V S 1=seaplane stalling speed (Knots) at the design water takeoff weight with... design water takeoff weight with flaps extended in the appropriate takeoff position; and β=angle of dead...

14 CFR 25.533 - Hull and main float bottom pressures.

Code of Federal Regulations, 2010 CFR

2010-01-01

... AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Structure Water Loads § 25.533 Hull and main... figure 2 of appendix B; V S 1=seaplane stalling speed (Knots) at the design water takeoff weight with... design water takeoff weight with flaps extended in the appropriate takeoff position; and β=angle of dead...

Numerical simulations of the NREL S826 airfoil

NASA Astrophysics Data System (ADS)

Sagmo, KF; Bartl, J.; Sætran, L.

2016-09-01

2D and 3D steady state simulations were done using the commercial CFD package Star-CCM+ with three different RANS turbulence models. Lift and drag coefficients were simulated at different angles of attack for the NREL S826 airfoil at a Reynolds number of 100 000, and compared to experimental data obtained at NTNU and at DTU. The Spalart-Allmaras and the Realizable k-epsilon turbulence models reproduced experimental results for lift well in the 2D simulations. The 3D simulations with the Realizable two-layer k-epsilon model predicted essentially the same lift coefficients as the 2D Spalart-Allmaras simulations. A comparison between 2D and 3D simulations with the Realizable k-epsilon model showed a significantly lower prediction in drag by the 2D simulations. From the conducted 3D simulations surface pressure predictions along the wing span were presented, along with volumetric renderings of vorticity. Both showed a high degree of span wise flow variation when going into the stall region, and predicted a flow field resembling that of stall cells for angles of attack above peak lift.

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 Monitoring (APM) systems that directly measure the boundary layer airflow adjacent to the affected aerodynamic surfaces, independent of other aircraft stall protection, air data, and AoA systems. In addition to investigating APM systems, measures should also be taken to include the CIRB phenomenon in aircrew training to better prepare crews to cope with airborne icing encounters. The SDT/BLR technique would allow the forecast gains from these improved systems and training processes to be evaluated objectively and quantitatively. The SDT/BLR model developed for this study has broad application outside the realm of airborne icing. The SDT technique has been extensively validated by prior research, and the BLR is a very robust multivariate technique. Combined, they could be applied to evaluate high order constructs (such as stall awareness for this study), in complex and dynamic environments. The union of SDT and BLR reduces the modeling complexities for each variable into the four binary SDT categories of Hit, Miss, False Alarm, and Correct Rejection, which is the optimum format for the BLR. Despite this reductionist approach to complex situations, the method has demonstrated very high statistical and practical significance, as well as excellent predictive power, when applied to the airborne icing scenario.

Structural basis for translational surveillance by the large ribosomal subunit-associated protein quality control complex

PubMed Central

Lyumkis, Dmitry; Oliveira dos Passos, Dario; Tahara, Erich B.; Webb, Kristofor; Bennett, Eric J.; Vinterbo, Staal; Potter, Clinton S.; Carragher, Bridget; Joazeiro, Claudio A. P.

2014-01-01

All organisms have evolved mechanisms to manage the stalling of ribosomes upon translation of aberrant mRNA. In eukaryotes, the large ribosomal subunit-associated quality control complex (RQC), composed of the listerin/Ltn1 E3 ubiquitin ligase and cofactors, mediates the ubiquitylation and extraction of ribosome-stalled nascent polypeptide chains for proteasomal degradation. How RQC recognizes stalled ribosomes and performs its functions has not been understood. Using single-particle cryoelectron microscopy, we have determined the structure of the RQC complex bound to stalled 60S ribosomal subunits. The structure establishes how Ltn1 associates with the large ribosomal subunit and properly positions its E3-catalytic RING domain to mediate nascent chain ubiquitylation. The structure also reveals that a distinguishing feature of stalled 60S particles is an exposed, nascent chain-conjugated tRNA, and that the Tae2 subunit of RQC, which facilitates Ltn1 binding, is responsible for selective recognition of stalled 60S subunits. RQC components are engaged in interactions across a large span of the 60S subunit surface, connecting the tRNA in the peptidyl transferase center to the distally located nascent chain tunnel exit. This work provides insights into a mechanism linking translation and protein degradation that targets defective proteins immediately after synthesis, while ignoring nascent chains in normally translating ribosomes. PMID:25349383

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.

Additional flow field studies of the GA(W)-1 airfoil with 30-percent chord Fowler flap including slot-gap variations and cove shape modifications

NASA Technical Reports Server (NTRS)

Wentz, W. H., Jr.; Ostowari, C.

1983-01-01

Experimental measurements were made to determine the effects of slot gap opening and flap cove shape on flap and airfoil flow fields. Test model was the GA(W)-1 airfoil with 0.30c Fowler flap deflected 35 degrees. Tests were conducted with optimum, wide and narrow gaps, and with three cove shapes. Three test angles were selected, corresponding to pre-stall and post-stall conditions. Reynolds number was 2,200,000 and Mach number was 0.13. Force, surface pressure, total pressure, and split-film turbulence measurements were made. Results were compared with theory for those parameters for which theoretical values were available.

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.

The CF6 jet engine performance improvement: New front mount

NASA Technical Reports Server (NTRS)

Fasching, W. A.

1979-01-01

The New Front Mount was evaluated in component tests including stress, deflection/distortion and fatigue tests. The test results demonstrated a performance improvement of 0.1% in cruise sfc, 16% in compressor stall margin and 10% in compressor stator angle margin. The New Front Mount hardware successfully completed 35,000 simulated flight cycles endurance testing.

Self streamlining wind tunnel: Low speed testing and transonic test section design

NASA Technical Reports Server (NTRS)

Wolf, S. W. D.; Goodyer, M. J.

1977-01-01

Comprehensive aerodynamic data on an airfoil section were obtained through a wide range of angles of attack, both stalled and unstalled. Data were gathered using a self streamlining wind tunnel and were compared to results obtained on the same section in a conventional wind tunnel. The reduction of wall interference through streamline was demonstrated.

Departure solutions of the unsteady thin-layer and full Navier-Stokes equations solved using streamline curvature based iteration techniques

NASA Technical Reports Server (NTRS)

Barnett, M.; Turner, D.; Rothmayer, A. P.

1992-01-01

The development of a thorough understanding of the mechanisms for vortex eruptions from viscous layers, which are believed to be associated with phenomena such as dynamic stall onset and transition, is crucial if accurate models of such phenomena are to be formulated. The development of such models may, in turn, allow for the possibility that such effects could be accounted for during the design of various aerodynamic devices such as wings, helicopter rotors, and turbomachinery blading and thus lead to designs which are stall free or stall resistant and which have better stall-recovery properties. The present investigation is being conducted as part of an effort to develop analytical and numerical tools which can be used to help improve our understanding of the vortex-eruption mechanism at high Reynolds numbers. The addition of the normal-momentum equation to the classical unsteady boundary-layer equations is crucial according to recent asymptotic analyses of the vortex-eruption problem and is a key feature of the analyses being developed by the present authors. The purpose of this paper is as follows: to describe departure solution behavior observed when using unsteady, streamline-curvature based solution procedures in which nontrivial transverse pressure gradient effects are included; and to show that special treatment of the time-derivative of the normal velocity is needed to eliminate the ill-posed solution behavior, which is observed when small spatial and temporal step sizes are used.

Experimental study of flow separation control on a low- Re airfoil using leading-edge protuberance method

NASA Astrophysics Data System (ADS)

Zhang, M. M.; Wang, G. F.; Xu, J. Z.

2014-04-01

An experimental study of flow separation control on a low- Re c airfoil was presently investigated using a newly developed leading-edge protuberance method, motivated by the improvement in the hydrodynamics of the giant humpback whale through its pectoral flippers. Deploying this method, the control effectiveness of the airfoil aerodynamics was fully evaluated using a three-component force balance, leading to an effectively impaired stall phenomenon and great improvement in the performances within the wide post-stall angle range (22°-80°). To understand the flow physics behind, the vorticity field, velocity field and boundary layer flow field over the airfoil suction side were examined using a particle image velocimetry and an oil-flow surface visualization system. It was found that the leading-edge protuberance method, more like low-profile vortex generator, effectively modified the flow pattern of the airfoil boundary layer through the chordwise and spanwise evolutions of the interacting streamwise vortices generated by protuberances, where the separation of the turbulent boundary layer dominated within the stall region and the rather strong attachment of the laminar boundary layer still existed within the post-stall region. The characteristics to manipulate the flow separation mode of the original airfoil indicated the possibility to further optimize the control performance by reasonably designing the layout of the protuberances.

Modeling dynamic stall on wind turbine blades under rotationally augmented flow fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guntur, S.; Schreck, S.; Sorensen, N. N.

It is well known that airfoils under unsteady flow conditions with a periodically varying angle of attack exhibit aerodynamic characteristics different from those under steady flow conditions, a phenomenon commonly known as dynamic stall. It is also well known that the steady aerodynamic characteristics of airfoils in the inboard region of a rotating blade differ from those under steady two-dimensional (2D) flow conditions, a phenomenon commonly known as rotational augmentation. This paper presents an investigation of these two phenomena together in the inboard parts of wind turbine blades. This analysis is carried out using data from three sources: (1) themore » National Renewable Energy Laboratory’s Unsteady Aerodynamics Experiment Phase VI experimental data, including constant as well as continuously pitching blade conditions during axial operation, (2) data from unsteady Delayed Detached Eddy Simulations (DDES) carried out using the Technical University of Denmark’s in-house flow solver Ellipsys3D, and (3) data from a simplified model based on the blade element momentum method with a dynamic stall subroutine that uses rotationally augmented steady-state polars obtained from steady Phase VI experimental sequences, instead of the traditional 2D nonrotating data. The aim of this work is twofold. First, the blade loads estimated by the DDES simulations are compared to three select cases of the N sequence experimental data, which serves as a validation of the DDES method. Results show reasonable agreement between the two data in two out of three cases studied. Second, the dynamic time series of the lift and the moment polars obtained from the experiments are compared to those from the dynamic stall subroutine that uses the rotationally augmented steady polars. This allowed the differences between the stall phenomenon on the inboard parts of harmonically pitching blades on a rotating wind turbine and the classic dynamic stall representation in 2D flow to be investigated. Results from the dynamic stall subroutine indicated a good qualitative agreement between the model and the experimental data in many cases, which suggests that the current 2D dynamic stall model as used in BEM-based aeroelastic codes may provide a reasonably accurate representation of three-dimensional rotor aerodynamics when used in combination with a robust rotational augmentation model.« less

The L1-type cell adhesion molecule Neuroglian is necessary for maintenance of sensory axon advance in the Drosophila embryo.

PubMed

Martin, Veronica; Mrkusich, Eli; Steinel, Martin C; Rice, Jason; Merritt, David J; Whitington, Paul M

2008-04-08

Cell adhesion molecules have long been implicated in the regulation of axon growth, but the precise cellular roles played by individual cell adhesion molecules and the molecular basis for their action are still not well understood. We have used the sensory system of the Drosophila embryo to shed light on the mechanism by which the L1-type cell adhesion molecule Neuroglian regulates axon growth. We have found a highly penetrant sensory axon stalling phenotype in neuroglian mutant embryos. Axons stalled at a variety of positions along their normal trajectory, but most commonly in the periphery some distance along the peripheral nerve. All lateral and dorsal cluster sensory neurons examined, except for the dorsal cluster neuron dbd, showed stalling. Sensory axons were never seen to project along inappropriate pathways in neuroglian mutants and stalled axons showed normal patterns of fasciculation within nerves. The growth cones of stalled axons possessed a simple morphology, similar to their appearance in wild-type embryos when advancing along nerves. Driving expression of the wild-type form of Neuroglian in sensory neurons alone rescued the neuroglian mutant phenotype of both pioneering and follower neurons. A partial rescue was achieved by expressing the Neuroglian extracellular domain. Over/mis-expression of Neuroglian in all neurons, oenocytes or trachea had no apparent effect on sensory axon growth. We conclude that Neuroglian is necessary to maintain axon advance along axonal substrates, but is not required for initiation of axon outgrowth, axon fasciculation or recognition of correct growth substrates. Expression of Neuroglian in sensory neurons alone is sufficient to promote axon advance and the intracellular region of the molecule is largely dispensable for this function. It is unlikely, therefore, that Nrg acts as a molecular 'clutch' to couple adhesion of F-actin within the growth cone to the extracellular substrate. Rather, we suggest that Neuroglian mediates sensory axon advance by promoting adhesion of the surface of the growth cone to its substrate. Our finding that stalling of a pioneer sensory neuron is rescued by driving Neuroglian in sensory neurons alone may suggest that Neuroglian can act in a heterophilic fashion.

The L1-type cell adhesion molecule Neuroglian is necessary for maintenance of sensory axon advance in the Drosophila embryo

PubMed Central

Martin, Veronica; Mrkusich, Eli; Steinel, Martin C; Rice, Jason; Merritt, David J; Whitington, Paul M

2008-01-01

Background Cell adhesion molecules have long been implicated in the regulation of axon growth, but the precise cellular roles played by individual cell adhesion molecules and the molecular basis for their action are still not well understood. We have used the sensory system of the Drosophila embryo to shed light on the mechanism by which the L1-type cell adhesion molecule Neuroglian regulates axon growth. Results We have found a highly penetrant sensory axon stalling phenotype in neuroglian mutant embryos. Axons stalled at a variety of positions along their normal trajectory, but most commonly in the periphery some distance along the peripheral nerve. All lateral and dorsal cluster sensory neurons examined, except for the dorsal cluster neuron dbd, showed stalling. Sensory axons were never seen to project along inappropriate pathways in neuroglian mutants and stalled axons showed normal patterns of fasciculation within nerves. The growth cones of stalled axons possessed a simple morphology, similar to their appearance in wild-type embryos when advancing along nerves. Driving expression of the wild-type form of Neuroglian in sensory neurons alone rescued the neuroglian mutant phenotype of both pioneering and follower neurons. A partial rescue was achieved by expressing the Neuroglian extracellular domain. Over/mis-expression of Neuroglian in all neurons, oenocytes or trachea had no apparent effect on sensory axon growth. Conclusion We conclude that Neuroglian is necessary to maintain axon advance along axonal substrates, but is not required for initiation of axon outgrowth, axon fasciculation or recognition of correct growth substrates. Expression of Neuroglian in sensory neurons alone is sufficient to promote axon advance and the intracellular region of the molecule is largely dispensable for this function. It is unlikely, therefore, that Nrg acts as a molecular 'clutch' to couple adhesion of F-actin within the growth cone to the extracellular substrate. Rather, we suggest that Neuroglian mediates sensory axon advance by promoting adhesion of the surface of the growth cone to its substrate. Our finding that stalling of a pioneer sensory neuron is rescued by driving Neuroglian in sensory neurons alone may suggest that Neuroglian can act in a heterophilic fashion. PMID:18397531

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.

Dynamic Wind-Tunnel Testing of a Sub-Scale Iced S-3B Viking

NASA Technical Reports Server (NTRS)

Lee, Sam; Barnhart, Billy; Ratvasky, Thomas P.

2012-01-01

The effect of ice accretion on a 1/12-scale complete aircraft model of S-3B Viking was studied in a rotary-balance wind tunnel. Two types of ice accretions were considered: ice protection system failure shape and runback shapes that form downstream of the thermal ice protection system. The results showed that the ice shapes altered the stall characteristics of the aircraft. The ice shapes also reduced the control surface effectiveness, but mostly near the stall angle of attack. There were some discrepancies with the data with the flaps deflected that were attributed to the low Reynolds number of the test. Rotational and forced-oscillation studies showed that the effects of ice were mostly in the longitudinal forces, and the effects on the lateral forces were relatively minor.

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.

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.

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.

Exploratory investigation of the incipient spinning characteristics of a typical light general aviation airplane

NASA Technical Reports Server (NTRS)

Ranaudo, R. J.

1977-01-01

The incipient spinning characteristics of general aviation airplanes were studied. Angular rates in pitch, yaw, and roll were measured through the stall during the incipient spin and throughout the recovery along with control positions, angle of attack, and angle of sideslip. The characteristic incipient spinning motion was determined from a given set of entry conditions. The sequence of recovery controls were varied at two distinct points during the incipient spin, and the effect on recovery characteristics was examined. Aerodynamic phenomena associated with flow over the aft portion of the fuselage, vertical stabilizer, and rubber are described.

Mouse embryonic stem cells have increased capacity for replication fork restart driven by the specific Filia-Floped protein complex.

PubMed

Zhao, Bo; Zhang, Weidao; Cun, Yixian; Li, Jingzheng; Liu, Yan; Gao, Jing; Zhu, Hongwen; Zhou, Hu; Zhang, Rugang; Zheng, Ping

2018-01-01

Pluripotent stem cells (PSCs) harbor constitutive DNA replication stress during their rapid proliferation and the consequent genome instability hampers their applications in regenerative medicine. It is therefore important to understand the regulatory mechanisms of replication stress response in PSCs. Here, we report that mouse embryonic stem cells (ESCs) are superior to differentiated cells in resolving replication stress. Specifically, ESCs utilize a unique Filia-Floped protein complex-dependent mechanism to efficiently promote the restart of stalled replication forks, therefore maintaining genomic stability. The ESC-specific Filia-Floped complex resides on replication forks under normal conditions. Replication stress stimulates their recruitment to stalling forks and the serine 151 residue of Filia is phosphorylated in an ATR-dependent manner. This modification enables the Filia-Floped complex to act as a functional scaffold, which then promotes the stalling fork restart through a dual mechanism: both enhancing recruitment of the replication fork restart protein, Blm, and stimulating ATR kinase activation. In the Blm pathway, the scaffolds recruit the E3 ubiquitin ligase, Trim25, to the stalled replication forks, and in turn Trim25 tethers and concentrates Blm at stalled replication forks through ubiquitination. In differentiated cells, the recruitment of the Trim25-Blm complex to replication forks and the activation of ATR signaling are much less robust due to lack of the ESC-specific Filia-Floped scaffold. Thus, our study reveals that ESCs utilize an additional and unique regulatory layer to efficiently promote the stalled fork restart and maintain genomic stability.

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.

Influence of Thickness and Angle of Attack on the Dynamics of Rectangular Cylinder Wakes

NASA Astrophysics Data System (ADS)

Mohebi, Meraj

Stereoscopic Particle Image Velocimetry measurements were taken in the turbulent wake of two-dimensional rectangular cylinders. The influence of post-stall angles of attack and Reynolds number on the flow behind a thin at plate, and for the normal case, the effect of thickness to chord (t=d) ratio over a family of rectangular cylinders were investigated. At all cases, quasi-periodic vortex shedding is observed, the normal direction Reynolds stress becomes very large just downstream of the mean recirculation zone, and the spanwise motions were uncorrelated to the main vortex shedding process. The data were processed to obtain the mean velocities, Reynolds stresses, and forces on the body. All terms in the turbulent kinetic energy equations were measured with the exception of dissipation which was found by difference. The pressure-related terms were estimated from the numerical solution of the Poisson equation for the instantaneous velocity field. Proper Orthogonal Decomposition modes are related via mean-field theory to construct generalized phase-averaging and low-order models capturing coherent cycle-to-cycle variations. The advection, production and pressure diffusion were all significant and mostly coherent. It is shown that high, average, and low amplitude vortex shedding cycles are different in terms of vortex street dimensions, vortex topology, circulation, and decay rate. It is also shown that these flows experience irregular significant decreases in the shedding amplitude associated with shedding of disorganized vortices in a large wake. Reynolds number was found to have imperceptible effects on the wake of a normal thin plate. A reduction in the angle of attack caused the wake to decrease in size and increase in shedding frequency but the global characteristics vary non-linearly. An increase in thickness from thin plate (t=d=0.05), caused the wake to shrink, low cycles to diminish, and local turbulence increase to a peak at t=d=1.0, identified as a critical thickness. At t=d=1.9, however, turbulent quantities decrease, the wake grows larger and significant cycle-to-cycle variations in the ow reports of a new vortex formation process.

Navier-Stokes Simulation of UH-60A Rotor/Wake Interaction Using Adaptive Mesh Refinement

NASA Technical Reports Server (NTRS)

Chaderjian, Neal M.

2017-01-01

Time-dependent Navier-Stokes simulations have been carried out for a flexible UH-60A rotor in forward flight, where the rotor wake interacts with the rotor blades. These flow conditions involved blade vortex interaction and dynamic stall, two common conditions that occur as modern helicopter designs strive to achieve greater flight speeds and payload capacity. These numerical simulations utilized high-order spatial accuracy and delayed detached eddy simulation. Emphasis was placed on understanding how improved rotor wake resolution affects the prediction of the normal force, pitching moment, and chord force of the rotor. Adaptive mesh refinement was used to highly resolve the turbulent rotor wake in a computationally efficient manner. Moreover, blade vortex interaction was found to trigger dynamic stall. Time-dependent flow visualization was utilized to provide an improved understanding of the numerical and physical mechanisms involved with three-dimensional dynamic stall.

Influence of Finite Span and Sweep on Active Flow Control Efficacy

NASA Technical Reports Server (NTRS)

Greenblatt, David; Washburn, Anthony E.

2008-01-01

Active flow control efficacy was investigated by means of leading-edge and flap-shoulder zero mass-flux blowing slots on a semispan wing model that was tested in unswept (standard) and swept configurations. On the standard configuration, stall commenced inboard, but with sweep the wing stalled initially near the tip. On both configurations, leading-edge perturbations increased CL,max and post stall lift, both with and without deflected flaps. Without sweep, the effect of control was approximately uniform across the wing span but remained effective to high angles of attack near the tip; when sweep was introduced a significant effect was noted inboard, but this effect degraded along the span and produced virtually no meaningful lift enhancement near the tip, irrespective of the tip configuration. In the former case, control strengthened the wingtip vortex; in the latter case, a simple semi-empirical model, based on the trajectory or "streamline" of the evolving perturbation, served to explain the observations. In the absence of sweep, control on finite-span flaps did not differ significantly from their nominally twodimensional counterpart. Control from the flap produced expected lift enhancement and CL,max improvements in the absence of sweep, but these improvements degraded with the introduction of sweep.

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.

Investigation of Blade-row Flow Distributions in Axial-flow-compressor Stage Consisting of Guide Vanes and Rotor-blade Row

NASA Technical Reports Server (NTRS)

Mahoney, John J; Dugan, Paul D; Budinger, Raymond E; Goelzer, H Fred

1950-01-01

A 30-inch tip-diameter axial-flow compressor stage was investigated with and without rotor to determine individual blade-row performance, interblade-row effects, and outer-wall boundary-layer conditions. Velocity gradients at guide-vane outlet without rotor approximated design assumptions, when the measured variation of leaving angle was considered. With rotor in operation, Mach number and rotor-blade effects changed flow distribution leaving guide vanes and invalidated design assumption of radial equilibrium. Rotor-blade performance correlated interpolated two-dimensional results within 2 degrees, although tip stall was indicated in experimental and not two-dimensional results. Boundary-displacement thickness was less than 1.0 and 1.5 percent of passage height after guide vanes and after rotor, respectively, but increased rapidly after rotor when tip stall occurred.

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.

Structure-function analysis of ribonucleotide bypass by B family DNA replicases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clausen, Anders R.; Murray, Michael S.; Passer, Andrew R.

2013-11-01

Ribonucleotides are frequently incorporated into DNA during replication, they are normally removed, and failure to remove them results in replication stress. This stress correlates with DNA polymerase (Pol) stalling during bypass of ribonucleotides in DNA templates. Here we demonstrate that stalling by yeast replicative Pols δ and ε increases as the number of consecutive template ribonucleotides increases from one to four. The homologous bacteriophage RB69 Pol also stalls during ribonucleotide bypass, with a pattern most similar to that of Pol ε. Crystal structures of an exonuclease-deficient variant of RB69 Pol corresponding to multiple steps in single ribonucleotide bypass reveal thatmore » increased stalling is associated with displacement of Tyr391 and an unpreferred C2´-endo conformation for the ribose. Even less efficient bypass of two consecutive ribonucleotides in DNA correlates with similar movements of Tyr391 and displacement of one of the ribonucleotides along with the primer-strand DNA backbone. These structure–function studies have implications for cellular signaling by ribonucleotides, and they may be relevant to replication stress in cells defective in ribonucleotide excision repair, including humans suffering from autoimmune disease associated with RNase H2 defects.« less

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.

Correlation Between Geometric Similarity of Ice Shapes and the Resulting Aerodynamic Performance Degradation: A Preliminary Investigation Using WIND

NASA Technical Reports Server (NTRS)

Wright, William B.; Chung, James

1999-01-01

Aerodynamic performance calculations were performed using WIND on ten experimental ice shapes and the corresponding ten ice shapes predicted by LEWICE 2.0. The resulting data for lift coefficient and drag coefficient are presented. The difference in aerodynamic results between the experimental ice shapes and the LEWICE ice shapes were compared to the quantitative difference in ice shape geometry presented in an earlier report. Correlations were generated to determine the geometric features which have the most effect on performance degradation. Results show that maximum lift and stall angle can be correlated to the upper horn angle and the leading edge minimum thickness. Drag coefficient can be correlated to the upper horn angle and the frequency-weighted average of the Fourier coefficients. Pitching moment correlated with the upper horn angle and to a much lesser extent to the upper and lower horn thicknesses.

Comparative Flight and Full-Scale Wind-Tunnel Measurements of the Maximum Lift of an Airplane

NASA Technical Reports Server (NTRS)

Silverstein, Abe; Katzoff, S; Hootman, James A

1938-01-01

Determinations of the power-off maximum lift of a Fairchild 22 airplane were made in the NACA full-scale wind tunnel and in flight. The results from the two types of test were in satisfactory agreement. It was found that, when the airplane was rotated positively in pitch through the angle of stall at rates of the order of 0.1 degree per second, the maximum lift coefficient was considerably higher than that obtained in the standard tests, in which the forces are measured with the angles of attack fixed. Scale effect on the maximum lift coefficient was also investigated.

Stalled RNAP-II molecules bound to non-coding rDNA spacers are required for normal nucleolus architecture.

PubMed

Freire-Picos, M A; Landeira-Ameijeiras, V; Mayán, María D

2013-07-01

The correct distribution of nuclear domains is critical for the maintenance of normal cellular processes such as transcription and replication, which are regulated depending on their location and surroundings. The most well-characterized nuclear domain, the nucleolus, is essential for cell survival and metabolism. Alterations in nucleolar structure affect nuclear dynamics; however, how the nucleolus and the rest of the nuclear domains are interconnected is largely unknown. In this report, we demonstrate that RNAP-II is vital for the maintenance of the typical crescent-shaped structure of the nucleolar rDNA repeats and rRNA transcription. When stalled RNAP-II molecules are not bound to the chromatin, the nucleolus loses its typical crescent-shaped structure. However, the RNAP-II interaction with Seh1p, or cryptic transcription by RNAP-II, is not critical for morphological changes. Copyright © 2013 John Wiley & Sons, Ltd.

Effects of spanwise blowing on the pressure field and vortex-lift characteristics of a 44 deg swept trapezoidal wing. [wind tunnel stability tests - aircraft models

NASA Technical Reports Server (NTRS)

Campbell, J. F.

1975-01-01

Wind-tunnel data were obtained at a free-stream Mach number of 0.26 for a range of model angle of attack, jet thrust coefficient, and jet location. Results of this study show that the sectional effects to spanwise blowing are strongly dependent on angle of attack, jet thrust coefficient, and span location; the largest effects occur at the highest angles of attack and thrust coefficients and on the inboard portion of the wing. Full vortex lift was achieved at the inboard span station with a small blowing rate, but successively higher blowing rates were necessary to achieve full vortex lift at increased span distances. It is shown that spanwise blowing increases lift throughout the angle-of-attack range, delays wing stall to higher angles of attack, and improves the induced-drag polars. The leading-edge suction analogy can be used to estimate the section and total lifts resulting from spanwise blowing.

Aerodynamic calculational methods for curved-blade Darrieus VAWT WECS

NASA Astrophysics Data System (ADS)

Templin, R. J.

1985-03-01

Calculation of aerodynamic performance and load distributions for curved-blade wind turbines is discussed. Double multiple stream tube theory, and the uncertainties that remain in further developing adequate methods are considered. The lack of relevant airfoil data at high Reynolds numbers and high angles of attack, and doubts concerning the accuracy of models of dynamic stall are underlined. Wind tunnel tests of blade airbrake configurations are summarized.

An experimental and analytical investigation of isolated rotor flap-lag stability in forward flight

NASA Technical Reports Server (NTRS)

Gaonkar, Gopal H.; Mcnulty, Michael J.

1985-01-01

For flap-lag stability of isolated rotors, experimental and analytical investigations are conducted in hover and forward flight on the adequacy of a linear quasi-steady aerodynamics theory with dynamic inflow. Forward flight effects on lag regressing mode are emphasized. Accordingly, a soft inplane hingeless rotor with three blades is tested at advance ratios as high as 0.55 and at shaft angles as high as 20 deg. The 1.62-m model rotor is untrimmed with an essentially unrestricted tilt of the tip path plane. By computerized symbolic manipulation, an analytical model is developed in substall to predict stability margins with mode indentification. It also predicts substall and stall regions to help explain the correlation between theory and data. The correlation shows both the strengths and weaknesses of the data and theory, and promotes further insights into areas in which further study is needed in substall and stall.

Preliminary aerodynamic design considerations for advanced laminar flow aircraft configurations

NASA Technical Reports Server (NTRS)

Johnson, Joseph L., Jr.; Yip, Long P.; Jordan, Frank L., Jr.

1986-01-01

Modern composite manufacturing methods have provided the opportunity for smooth surfaces that can sustain large regions of natural laminar flow (NLF) boundary layer behavior and have stimulated interest in developing advanced NLF airfoils and improved aircraft designs. Some of the preliminary results obtained in exploratory research investigations on advanced aircraft configurations at the NASA Langley Research Center are discussed. Results of the initial studies have shown that the aerodynamic effects of configuration variables such as canard/wing arrangements, airfoils, and pusher-type and tractor-type propeller installations can be particularly significant at high angles of attack. Flow field interactions between aircraft components were shown to produce undesirable aerodynamic effects on a wing behind a heavily loaded canard, and the use of properly designed wing leading-edge modifications, such as a leading-edge droop, offset the undesirable aerodynamic effects by delaying wing stall and providing increased stall/spin resistance with minimum degradation of laminar flow behavior.

Flow-Field Measurement of Device-Induced Embedded Streamwise Vortex on a Flat Plate

NASA Technical Reports Server (NTRS)

Yao, Chung-Sheng; Lin, John C.; Allan, Brian G.

2002-01-01

Detailed flow-field measurements were performed downstream of a single vortex generator (VG) using an advanced Stereo Digital Particle Image Velocimetry system. Thc passive flow-control devices examined consisted of a low-profile VG with a device height, h, approximately equal to 20 percent of the boundary-layer thickness, sigma, and a conventional VG with h is approximately sigma. Flow-field data were taken at twelve cross-flow planes downstream of the VG to document and quantify the evolution of embedded streamwise vortex. The effects of device angle of attack on vortex development downstream were compared between the low-profile VG and the conventional VG. Key parameters including vorticity, circulation, trajectory, and half-life radius - describing concentration, strength, path, and size, respectively--of the device-induced streamwise vortex were extracted from the flow-field data. The magnitude of maximum vorticity increases as angle of attack increases for the low-profile VG, but the trend is reversed for the conventional VG, probably due to flow stalling around the larger device at higher angles of attack. Peak vorticity and circulation for the low-profile VG decays exponentially and inversely proportional to the distance downstream from the device. The device-height normalized vortex trajectories for the low-profile VG, especially in the lateral direction, follow the general trends of the conventional VG. The experimental database was used to validate the predictive capability of computational fluid dynamics (CFD). CFD accurately predicts the vortex circulation and path; however, improvements are needed for predicting the vorticity strength and vortex size.

Micro air vehicle motion tracking and aerodynamic modeling

NASA Astrophysics Data System (ADS)

Uhlig, Daniel V.

Aerodynamic performance of small-scale fixed-wing flight is not well understood, and flight data are needed to gain a better understanding of the aerodynamics of micro air vehicles (MAVs) flying at Reynolds numbers between 10,000 and 30,000. Experimental studies have shown the aerodynamic effects of low Reynolds number flow on wings and airfoils, but the amount of work that has been conducted is not extensive and mostly limited to tests in wind and water tunnels. In addition to wind and water tunnel testing, flight characteristics of aircraft can be gathered through flight testing. The small size and low weight of MAVs prevent the use of conventional on-board instrumentation systems, but motion tracking systems that use off-board triangulation can capture flight trajectories (position and attitude) of MAVs with minimal onboard instrumentation. Because captured motion trajectories include minute noise that depends on the aircraft size, the trajectory results were verified in this work using repeatability tests. From the captured glide trajectories, the aerodynamic characteristics of five unpowered aircraft were determined. Test results for the five MAVs showed the forces and moments acting on the aircraft throughout the test flights. In addition, the airspeed, angle of attack, and sideslip angle were also determined from the trajectories. Results for low angles of attack (less than approximately 20 deg) showed the lift, drag, and moment coefficients during nominal gliding flight. For the lift curve, the results showed a linear curve until stall that was generally less than finite wing predictions. The drag curve was well described by a polar. The moment coefficients during the gliding flights were used to determine longitudinal and lateral stability derivatives. The neutral point, weather-vane stability and the dihedral effect showed some variation with different trim speeds (different angles of attack). In the gliding flights, the aerodynamic characteristics exhibited quasi-steady effects caused by small variations in the angle of attack. The quasi-steady effects, or small unsteady effects, caused variations in the aerodynamic characteristics (particularly incrementing the lift curve), and the magnitude of the influence depended on the angle-of-attack rate. In addition to nominal gliding flight, MAVs in general are capable of flying over a wide flight envelope including agile maneuvers such as perching, hovering, deep stall and maneuvering in confined spaces. From the captured motion trajectories, the aerodynamic characteristics during the numerous unsteady flights were gathered without the complexity required for unsteady wind tunnel tests. Experimental results for the MAVs show large flight envelopes that included high angles of attack (on the order of 90 deg) and high angular rates, and the aerodynamic coefficients had dynamic stall hysteresis loops and large values. From the large number of unsteady high angle-of-attack flights, an aerodynamic modeling method was developed and refined for unsteady MAV flight at high angles of attack. The method was based on a separation parameter that depended on the time history of the angle of attack and angle-of-attack rate. The separation parameter accounted for the time lag inherit in the longitudinal characteristics during dynamic maneuvers. The method was applied to three MAVs and showed general agreement with unsteady experimental results and with nominal gliding flight results. The flight tests with the MAVs indicate that modern motion tracking systems are capable of capturing the flight trajectories, and the captured trajectories can be used to determine the aerodynamic characteristics. From the captured trajectories, low Reynolds number MAV flight is explored in both nominal gliding flight and unsteady high angle-of-attack flight. Building on the experimental results, a modeling method for the longitudinal characteristics is developed that is applicable to the full flight envelope.

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.

Theory of single-molecule controlled rotation experiments, predictions, tests, and comparison with stalling experiments in F1-ATPase.

PubMed

Volkán-Kacsó, Sándor; Marcus, Rudolph A

2016-10-25

A recently proposed chemomechanical group transfer theory of rotary biomolecular motors is applied to treat single-molecule controlled rotation experiments. In these experiments, single-molecule fluorescence is used to measure the binding and release rate constants of nucleotides by monitoring the occupancy of binding sites. It is shown how missed events of nucleotide binding and release in these experiments can be corrected using theory, with F 1 -ATP synthase as an example. The missed events are significant when the reverse rate is very fast. Using the theory the actual rate constants in the controlled rotation experiments and the corrections are predicted from independent data, including other single-molecule rotation and ensemble biochemical experiments. The effective torsional elastic constant is found to depend on the binding/releasing nucleotide, and it is smaller for ADP than for ATP. There is a good agreement, with no adjustable parameters, between the theoretical and experimental results of controlled rotation experiments and stalling experiments, for the range of angles where the data overlap. This agreement is perhaps all the more surprising because it occurs even though the binding and release of fluorescent nucleotides is monitored at single-site occupancy concentrations, whereas the stalling and free rotation experiments have multiple-site occupancy.

Analysis of rig test data for an axial/centrifugal compressor in the 12 kg/sec

NASA Technical Reports Server (NTRS)

Owen, A. K.

1994-01-01

Extensive testing was done on a T55-L-712 turboshaft engine compressor in a compressor test rig at TEXTRON/Lycoming. These rig tests will be followed by a series of engine tests to occur at the NASA Lewis Research Center beginning in the last quarter of 1993. The goals of the rig testing were: (1) map the steady state compressor operation from 20 percent to 100 percent design speed, (2) quantify the effects of compressor bleed on the operation of the compressor, and (3) explore and measure the operation of the compressor in the flow ranges 'beyond' the normal compressor stall line. Instrumentation consisted of 497 steady state pressure sensors, 153 temperature sensors and 34 high response transducers for transient analysis in the pre- and post-stall operating regime. These measurements allow for generation of detailed stage characteristics as well as overall mapping. Transient data is being analyzed for the existence of modal disturbances at the front face of the compression system ('stall precursors'). This paper presents some preliminary results of the ongoing analysis and a description of the current and future program plans. It will primarily address the unsteady events at the front face of the compression system that occur as the system transitions from steady state to unsteady (stall/surge) operation.

DHC-6 Twin Otter Tailplane Airfoil Section Testing in the Ohio State University 7x10 Wind Tunnel. Volume 1

NASA Technical Reports Server (NTRS)

Hiltner, Dale; McKee, Michael; LaNoe, Karine; Gregorek, Gerald; Ratvasky, Thomas (Technical Monitor)

2000-01-01

Ice contaminated tailplane stall (ICTS) has been found to be responsible for 16 accidents with 139 fatalities over the last three decades, and is suspected to have played a role in other accidents and incidents. The need for fundamental research in this area has been recognized at three international conferences sponsored by the FAA since 1991. In order to conduct such research, a joint NASA/FAA Tailplane Icing Program was formed in 1994: the Ohio State University has played an important role in this effort. The program employs icing tunnel testing, dry wind tunnel testing, flight testing, and analysis using a six-degrees-of-freedom computer code tailored to this problem. A central goal is to quantify the effect of tailplane icing on aircraft stability and control to aid in the analysis of flight test procedures to identify aircraft susceptibility to ICTS. This report contains the results ot testing of a full scale 2D model of a tailplane section of NASA's Icing Research Aircraft, with and without ice shapes, in an Ohio State University 7 x 10 Low Speed wind tunnel in 1994. The results have been integrated into a comprehensive database of aerodynamic coefficients and stability and control derivatives that will permit detailed analysis of flight test results with the analytical computer program. The testing encompassed a full range of angles of attack and elevator deflections, as well as two velocities to evaluate Reynolds number effects. Lift, drag, pitching moment, and hinge moment coefficients were obtained. In addition. instrumentation for use during flight testing was verified to be effective, all components showing acceptable fidelity. Comparison of clean and iced airfoil results show the ice shapes causing a significant decrease in the magnitude of CLmax (from -1.3 to -0.64) and associated stall angle (from -18.6 deg to -8.2 deg). Furthermore, the ice shapes caused an increase in hinge moment coefficient of approximately 0.02, the change being markedly abrupt for one of the ice shapes. A noticeable effect of elevator deflection is that magnitude of the stall angle is decreased for negative (upward) elevator deflections. All these result are consistent with observed tailplane phenomena. and constitute an effective set of data for comprehensive analysis of ICTS

Biomimetics and Tubercles on Flippers for Hydrodynamic Flow Control

NASA Astrophysics Data System (ADS)

Fish, Frank E.

2011-11-01

The biomimetic approach seeks to incorporate designs based on biological organisms into engineered technologies. Biomimetics can be used to engineer machines that emulate the performance of organisms, particularly in instances where the organism's performance exceeds current mechanical technology or provides new directions to solve existing problems. The ability to control the flow of water around the body dictates the performance of marine mammals in the aquatic environment. Morphological specializations of marine mammals afford mechanisms for passive flow control. Aside from the design of the body, which minimizes drag, the morphology of the appendages provide hydrodynamic advantages with respect to drag, lift, thrust, and stall. Of particular interest are the pectoral flippers of the humpback whale (Megaptera novaeangliae). These flippers act as wing-like structures to provide hydrodynamic lift for maneuvering. The use of any such wing-like structure in making small radius turns to enhance both agility and maneuverability is constrained by performance associated with stall. Delay of stall can be accomplished passively by modification of the flipper leading edge. The design of the flippers includes prominent leading edge bumps or tubercles. Such a design is exhibited by the leading edge tubercles on the flippers of humpback whales. These novel morphological structures induce a spanwise flow field of separated vortices alternating with regions of accelerated flow. The coupled flow regions maintain areas of attached flow and delay stall to high angles of attack. The morphological features of humpback whales for flow control can be utilized in the biomimetic design of engineered structures and commercial products for increased hydrodynamic performance. Nature retains a store of untouched knowledge, which would be beneficial in advancing technology.

X-31 high angle of attack control system performance

NASA Technical Reports Server (NTRS)

Huber, Peter; Seamount, Patricia

1994-01-01

The design goals for the X-31 flight control system were: (1) level 1 handling qualities during post-stall maneuvering (30 to 70 degrees angle-of-attack); (2) thrust vectoring to enhance performance across the flight envelope; and (3) adequate pitch-down authority at high angle-of-attack. Additional performance goals are discussed. A description of the flight control system is presented, highlighting flight control system features in the pitch and roll axes and X-31 thrust vectoring characteristics. The high angle-of-attack envelope clearance approach will be described, including a brief explanation of analysis techniques and tools. Also, problems encountered during envelope expansion will be discussed. This presentation emphasizes control system solutions to problems encountered in envelope expansion. An essentially 'care free' envelope was cleared for the close-in-combat demonstrator phase. High angle-of-attack flying qualities maneuvers are currently being flown and evaluated. These results are compared with pilot opinions expressed during the close-in-combat program and with results obtained from the F-18 HARV for identical maneuvers. The status and preliminary results of these tests are discussed.

Workshop II On Unsteady Separated Flow Proceedings

DTIC Science & Technology

1988-07-28

was static stall angle of 12 ° . achieved by injecting diluted food coloring at the apex through a 1.5 mm diameter tube placed The response of the wing...differences with uniform step size in q, and trailing -. 75 three- pront differences with uniform step size in ,, ,,as used The nonlinearity of the...flow prop- "Kutta condition." erties for slender 3D wings are addressed. To begin the The present paper emphasizes recent progress in the de- study

Transonic Free-To-Roll Analysis of the F/A-18E and F-35 Configurations

NASA Technical Reports Server (NTRS)

Owens, D. Bruce; McConnell, Jeffrey K.; Brandon, Jay M.; Hall, Robert M.

2004-01-01

The free-to-roll technique is used as a tool for predicting areas of uncommanded lateral motions. Recently, the NASA/Navy/Air Force Abrupt Wing Stall Program extended the use of this technique to the transonic speed regime. Using this technique, this paper evaluates various wing configurations on the pre-production F/A-18E aircraft and the Joint Strike Fighter (F-35) aircraft. The configurations investigated include leading and trailing edge flap deflections, fences, leading edge flap gap seals, and vortex generators. These tests were conducted in the NASA Langley 16-Foot Transonic Tunnel. The analysis used a modification of a figure-of-merit developed during the Abrupt Wing Stall Program to discern configuration effects. The results showed how the figure-of-merit can be used to schedule wing flap deflections to avoid areas of uncommanded lateral motion. The analysis also used both static and dynamic wind tunnel data to provide insight into the uncommanded lateral behavior. The dynamic data was extracted from the time history data using parameter identification techniques. In general, modifications to the pre-production F/A-18E resulted in shifts in angle-of-attack where uncommanded lateral activity occurred. Sealing the gap between the inboard and outboard leading-edge flaps on the Navy version of the F-35 eliminated uncommanded lateral activity or delayed the activity to a higher angle-of-attack.

WT - WIND TUNNEL PERFORMANCE ANALYSIS

NASA Technical Reports Server (NTRS)

Viterna, L. A.

1994-01-01

WT was developed to calculate fan rotor power requirements and output thrust for a closed loop wind tunnel. The program uses blade element theory to calculate aerodynamic forces along the blade using airfoil lift and drag characteristics at an appropriate blade aspect ratio. A tip loss model is also used which reduces the lift coefficient to zero for the outer three percent of the blade radius. The application of momentum theory is not used to determine the axial velocity at the rotor plane. Unlike a propeller, the wind tunnel rotor is prevented from producing an increase in velocity in the slipstream. Instead, velocities at the rotor plane are used as input. Other input for WT includes rotational speed, rotor geometry, and airfoil characteristics. Inputs for rotor blade geometry include blade radius, hub radius, number of blades, and pitch angle. Airfoil aerodynamic inputs include angle at zero lift coefficient, positive stall angle, drag coefficient at zero lift coefficient, and drag coefficient at stall. WT is written in APL2 using IBM's APL2 interpreter for IBM PC series and compatible computers running MS-DOS. WT requires a CGA or better color monitor for display. It also requires 640K of RAM and MS-DOS v3.1 or later for execution. Both an MS-DOS executable and the source code are provided on the distribution medium. The standard distribution medium for WT is a 5.25 inch 360K MS-DOS format diskette in PKZIP format. The utility to unarchive the files, PKUNZIP, is also included. WT was developed in 1991. APL2 and IBM PC are registered trademarks of International Business Machines Corporation. MS-DOS is a registered trademark of Microsoft Corporation. PKUNZIP is a registered trademark of PKWare, Inc.

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 ground.

Steady-state and transitional aerodynamic characteristics of a wing in simulated heavy rain

NASA Technical Reports Server (NTRS)

Campbell, Bryan A.; Bezos, Gaudy M.

1989-01-01

The steady-state and transient effects of simulated heavy rain on the subsonic aerodynamic characteristics of a wing model were determined in the Langley 14- by 22-Foot Subsonic Tunnel. The 1.29 foot chord wing was comprised of a NACA 23015 airfoil and had an aspect ratio of 6.10. Data were obtained while test variables of liquid water content, angle of attack, and trailing edge flap angle were parametrically varied at dynamic pressures of 10, 30, and 50 psf (i.e., Reynolds numbers of .76x10(6), 1.31x10(6), and 1.69x10(6)). The experimental results showed reductions in lift and increases in drag when in the simulated rain environment. Accompanying this was a reduction of the stall angle of attack by approximately 4 deg. The transient aerodynamic performance during transition from dry to wet steady-state conditions varied between a linear and a nonlinear transition.

Low-speed static and dynamic force tests of a generic supersonic cruise fighter configuration

NASA Technical Reports Server (NTRS)

Hahne, David E.

1989-01-01

Static and dynamic force tests of a generic fighter configuration designed for sustained supersonic flight were conducted in the Langley 30- by 60-foot tunnel. The baseline configuration had a 65 deg arrow wing, twin wing mounted vertical tails and a canard. Results showed that control was available up to C sub L,max (maximum lift coefficient) from aerodynamic controls about all axes but control in the pitch and yaw axes decreased rapidly in the post-stall angle-of-attack region. The baseline configuration showed stable lateral-directional characteristics at low angles of attack but directional stability occurred near alpha = 25 deg as the wing shielded the vertical tails. The configuration showed positive effective dihedral throughout the test angle-of-attack range. Forced oscillation tests indicated that the baseline configuration had stable damping characteristics about the lateral-directional axes.

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

The formation mechanism and impact of streamwise vortices on NACA 0021 airfoil's performance with undulating leading edge modification

NASA Astrophysics Data System (ADS)

Rostamzadeh, N.; Hansen, K. L.; Kelso, R. M.; Dally, B. B.

2014-10-01

Wings with tubercles have been shown to display advantageous loading behavior at high attack angles compared to their unmodified counterparts. In an earlier study by the authors, it was shown that an undulating leading-edge configuration, including but not limited to a tubercled model, induces a cyclic variation in circulation along the span that gives rise to the formation of counter-rotating streamwise vortices. While the aerodynamic benefits of full-span tubercled wings have been associated with the presence of such vortices, their formation mechanism and influence on wing performance are still in question. In the present work, experimental and numerical tests were conducted to further investigate the effect of tubercles on the flow structure over full-span modified wings based on the NACA 0021 profile, in the transitional flow regime. It is found that a skew-induced mechanism accounts for the formation of streamwise vortices whose development is accompanied by flow separation in delta-shaped regions near the trailing edge. The presence of vortices is detrimental to the performance of full-span wings pre-stall, however renders benefits post-stall as demonstrated by wind tunnel pressure measurement tests. Finally, primary and secondary vortices are identified post-stall that produce an enhanced momentum transfer effect that reduces flow separation, thus increasing the generated amount of lift.

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.

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 stall bases.

[Claw size of Scottish Highland Cows after pasture and housing periods].

PubMed

Nuss, K; Kolp, E; Braun, U; Weidmann, E; Hässig, M

2014-09-01

The claws of pastured Scottish Highland Cattle are large and this may raise the question if regular claw trimming is necessary. Therefore, the claws of the right thoracic and pelvic limbs were measured in 22 Scottish Highland cows 4 times 8 weeks apart. The cows were kept on various alpine pastures before the first measurement, on a two-hectare low-land pasture before the second measurement, in a welfare-compliant straw-bedded free stall before the third measurement and on alpine pasture before the fourth measurement. Housing conditions significantly affected claw dimensions. The claws were composed of dry, hard horn during pasture periods, and had prominent weight-bearing hoof-wall borders and soles with a natural axial slope. Long dorsal walls and heels and a greater symmetry were common. Claw lesions were absent. In contrast, free-stall housing was associated with shorter toes and steeper toe angles, but white line deterioration, heel horn erosion, wearing of the axial slope and hoof wall edges were common.

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.

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.

77 FR 32006 - Special Conditions: Gulfstream Model GVI Airplane; High Incidence Protection

Federal Register 2010, 2011, 2012, 2013, 2014

2012-05-31

... Special Conditions No. 25-423-SC] Special Conditions: Gulfstream Model GVI Airplane; High Incidence... pertaining to a high incidence protection system that replaces the stall warning system during normal... V SR and not greater than 1.3 V SR . (6) The high incidence protection function disabled, or...

Experimental study of low aspect ratio compressor blading

NASA Technical Reports Server (NTRS)

Reid, L.; Moore, R. D.

1979-01-01

The effects of low aspect ratio blading on aerodynamic performance were examined. Four individual transonic compressor stages, representative of the inlet stage of an advanced high pressure ratio core compressor, are discussed. The flow phenomena for the four stages are investigated. Comparisons of blade element parameters are presented for the two different aspect ratio configurations. Blade loading levels are compared for the near stall conditions and comparisons are made of loss and diffusion factors over the operating range of incidence angles.

ARC-1961-A-28249

NASA Image and Video Library

1961-09-12

Lockheed NC-130B (AF58-712) Aircraft. A Study of STOL Operational Techniques; landing approach. Nose-low pitch attitude of the aircraft was required in wave-off (or go-around) at 85 knots with flaps 70 degrees. An increase in stall-speed margin could be required to produce a more positive climb angle. (Nov 1962) Note: Used in publication in Flight Research at Ames; 57 Years of Development and Validation of Aeronautical Technology NASA SP-1998-3300 fig. 104; 60yrs at Ames, Atmosphere of Freedom NASA SP-2000-4314

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.

The PELskin project-part V: towards the control of the flow around aerofoils at high angle of attack using a self-activated deployable flap.

PubMed

Rosti, Marco E; Kamps, Laura; Bruecker, Christoph; Omidyeganeh, Mohammad; Pinelli, Alfredo

2017-01-01

During the flight of birds, it is often possible to notice that some of the primaries and covert feathers on the upper side of the wing pop-up under critical flight conditions, such as the landing approach or when stalking their prey (see Fig. 1) . It is often conjectured that the feathers pop up plays an aerodynamic role by limiting the spread of flow separation . A combined experimental and numerical study was conducted to shed some light on the physical mechanism determining the feathers self actuation and their effective role in controlling the flow field in nominally stalled conditions. In particular, we have considered a NACA0020 aerofoil, equipped with a flexible flap at low chord Reynolds numbers. A parametric study has been conducted on the effects of the length, natural frequency, and position of the flap. A configuration with a single flap hinged on the suction side at 70 % of the chord size c (from the leading edge), with a length of [Formula: see text] matching the shedding frequency of vortices at stall condition has been found to be optimum in delivering maximum aerodynamic efficiency and lift gains. Flow evolution both during a ramp-up motion (incidence angle from [Formula: see text] to [Formula: see text] with a reduced frequency of [Formula: see text], [Formula: see text] being the free stream velocity magnitude), and at a static stalled condition ([Formula: see text]) were analysed with and without the flap. A significant increase of the mean lift after a ramp-up manoeuvre is observed in presence of the flap. Stall dynamics (i.e., lift overshoot and oscillations) are altered and the simulations reveal a periodic re-generation cycle composed of a leading edge vortex that lift the flap during his passage, and an ejection generated by the relaxing of the flap in its equilibrium position. The flap movement in turns avoid the interaction between leading and trailing edge vortices when lift up and push the trailing edge vortex downstream when relaxing back. This cyclic behaviour is clearly shown by the periodic variation of the lift about the average value, and also from the periodic motion of the flap. A comparison with the experiments shows a similar but somewhat higher non-dimensional frequency of the flap oscillation. By assuming that the cycle frequency scales inversely with the boundary layer thickness, one can explain the higher frequencies observed in the experiments which were run at a Reynolds number about one order of magnitude higher than in the simulations. In addition, in experiments the periodic re-generation cycle decays after 3-4 periods ultimately leading to the full stall of the aerofoil. In contrast, the 2D simulations show that the cycle can become self-sustained without any decay when the flap parameters are accurately tuned.

Leading-Edge Flow Sensing for Aerodynamic Parameter Estimation

NASA Astrophysics Data System (ADS)

Saini, Aditya

The identification of inflow air data quantities such as airspeed, angle of attack, and local lift coefficient on various sections of a wing or rotor blade provides the capability for load monitoring, aerodynamic diagnostics, and control on devices ranging from air vehicles to wind turbines. Real-time measurement of aerodynamic parameters during flight provides the ability to enhance aircraft operating capabilities while preventing dangerous stall situations. This thesis presents a novel Leading-Edge Flow Sensing (LEFS) algorithm for the determination of the air -data parameters using discrete surface pressures measured at a few ports in the vicinity of the leading edge of a wing or blade section. The approach approximates the leading-edge region of the airfoil as a parabola and uses pressure distribution from the exact potential-ow solution for the parabola to _t the pressures measured from the ports. Pressures sensed at five discrete locations near the leading edge of an airfoil are given as input to the algorithm to solve the model using a simple nonlinear regression. The algorithm directly computes the inflow velocity, the stagnation-point location, section angle of attack and lift coefficient. The performance of the algorithm is assessed using computational and experimental data in the literature for airfoils under different ow conditions. The results show good correlation between the actual and predicted aerodynamic quantities within the pre-stall regime, even for a rotating blade section. Sensing the deviation of the aerodynamic behavior from the linear regime requires additional information on the location of ow separation on the airfoil surface. Bio-inspired artificial hair sensors were explored as a part of the current research for stall detection. The response of such artificial micro-structures can identify critical ow characteristics, which relate directly to the stall behavior. The response of the microfences was recorded via an optical microscope for ow over a at plate at different freestream velocities in the NCSU subsonic wind tunnel. Experiments were also conducted to characterize the directional sensitivity of the microstructures by creating ow reversal at the sensor location to assess the sensor response. The results show that the direction of microfence deflection correctly reflects the local ow behavior as the ow direction is reversed at the sensor location and the magnitude of deflection correlates qualitatively to an increase in the freestream velocity. The knowledge of the ow-separation location integrated with the LEFS algorithm allows the possibility of extending the LEFS analysis to post-stall flight regimes, which is explored in the current work. Finally, the application of the LEFS algorithm to unsteady aerodynamics is investigated to identify the critical sequence of events associated with the formation of leading-edge vortices. Signatures of vortex formation on the airfoil surface can be captured in the surface-pressure measurements. Real-time knowledge of the unsteady ow phenomena holds significant potential for exploiting the enhanced-lift characteristics related to vortex formation and inhibiting the detrimental effects of dynamic stall in engineering applications such as helicopters, wind turbines, bio-inspired flight, and energy harvesting devices. Computational data was used to assess the capability of the LEFS outputs to identity the signatures associated with vortex formation, i.e. onset of vortex shedding, detachment, and termination. The results demonstrate useful correlation between the LEFS outputs and the LEV signatures.

High angle of attack flying qualities criteria for longitudinal rate command systems

NASA Technical Reports Server (NTRS)

Wilson, David J.; Citurs, Kevin D.; Davidson, John B.

1994-01-01

This study was designed to investigate flying qualities requirements of alternate pitch command systems for fighter aircraft at high angle of attack. Flying qualities design guidelines have already been developed for angle of attack command systems at 30, 45, and 60 degrees angle of attack, so this research fills a similar need for rate command systems. Flying qualities tasks that require post-stall maneuvering were tested during piloted simulations in the McDonnell Douglas Aerospace Manned Air Combat Simulation facility. A generic fighter aircraft model was used to test angle of attack rate and pitch rate command systems for longitudinal gross acquisition and tracking tasks at high angle of attack. A wide range of longitudinal dynamic variations were tested at 30, 45, and 60 degrees angle of attack. Pilot comments, Cooper-Harper ratings, and pilot induced oscillation ratings were taken from five pilots from NASA, USN, CAF, and McDonnell Douglas Aerospace. This data was used to form longitudinal design guidelines for rate command systems at high angle of attack. These criteria provide control law design guidance for fighter aircraft at high angle of attack, low speed flight conditions. Additional time history analyses were conducted using the longitudinal gross acquisition data to look at potential agility measures of merit and correlate agility usage to flying qualities boundaries. This paper presents an overview of this research.

[Tail Plane Icing

NASA Technical Reports Server (NTRS)

1997-01-01

The Aviation Safety Program initiated by NASA in 1997 has put greater emphasis in safety related research activities. Ice-contaminated-tailplane stall (ICTS) has been identified by the NASA Lewis Icing Technology Branch as an important activity for aircraft safety related research. The ICTS phenomenon is characterized as a sudden, often uncontrollable aircraft nose- down pitching moment, which occurs due to increased angle-of-attack of the horizontal tailplane resulting in tailplane stall. Typically, this phenomenon occurs when lowering the flaps during final approach while operating in or recently departing from icing conditions. Ice formation on the tailplane leading edge can reduce tailplane angle-of-attack range and cause flow separation resulting in a significant reduction or complete loss of aircraft pitch control. In 1993, the Federal Aviation Authority (FAA) and NASA embarked upon a four-year research program to address the problem of tailplane stall and to quantify the effect of tailplane ice accretion on aircraft performance and handling characteristics. The goals of this program, which was completed in March 1998, were to collect aerodynamic data for an aircraft tail with and without ice contamination and to develop analytical methods for predicting the effects of tailplane ice contamination. Extensive dry air and icing tunnel tests which resulted in a database of the aerodynamic effects associated with tailplane ice contamination. Although the FAA/NASA tailplane icing program generated some answers regarding ice-contaminated-tailplane stall (ICTS) phenomena, NASA researchers have found many open questions that warrant further investigation into ICTS. In addition, several aircraft manufacturers have expressed interest in a second research program to expand the database to other tail configurations and to develop experimental and computational methodologies for evaluating the ICTS phenomenon. In 1998, the icing branch at NASA Lewis initiated a second multi-phase research program for tailplane icing (TIP II) to develop test methodologies and tailplane performance and handling qualities evaluation tools. The main objectives of this new NASA/Industry/Academia collaborative research programs were: (1) define and evaluate a sub-scale wind tunnel test methodology for determining tailplane performance degradation due to icing. (2) develop an experimental database of tailplane aerodynamic performance with and without ice contamination for a range of tailplane configurations. Wind tunnel tests were planned with representative general aviation aircraft, i.e., the Learjet 45, and a twin engine low speed aircraft. This report summarizes the research performed during the first year of the study, and outlines the work tasks for the second year.

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.

Hydrodynamic performance of the minke whale (Balaenoptera acutorostrata) flipper.

PubMed

Cooper, Lisa Noelle; Sedano, Nils; Johansson, Stig; May, Bryan; Brown, Joey D; Holliday, Casey M; Kot, Brian W; Fish, Frank E

2008-06-01

Minke whales (Balaenoptera acutorostrata) are the smallest member of balaenopterid whales and little is known of their kinematics during feeding maneuvers. These whales have narrow and elongated flippers that are small relative to body size compared to related species such as right and gray whales. No experimental studies have addressed the hydrodynamic properties of minke whale flippers and their functional role during feeding maneuvers. This study integrated wind tunnel, locomotion and anatomical range of motion data to identify functional parameters of the cambered minke whale flipper. A full-sized cast of a minke whale flipper was used in wind tunnel testing of lift, drag and stall behavior at six speeds, corresponding to swimming speeds of 0.7-8.9 m s(-1). Flow over the model surface stalled between 10 degrees and 14 degrees angle of attack (alpha) depending on testing speed. When the leading edge was rotated ventrally, loss in lift occurred around -18 degrees alpha regardless of speed. Range of mobility in the fresh limb was approximately 40% greater than the range of positive lift-generating angles of attack predicted by wind tunnel data (+14 degrees alpha). Video footage, photographs and observations of swimming, engulfment feeding and gulping minke whales showed limb positions corresponding to low drag in wind tunnel tests, and were therefore hydrodynamically efficient. Flippers play an important role in orienting the body during feeding maneuvers as they maintain trim of the body, an action that counters drag-induced torque of the body during water and prey intake.

Parametric study of a simultaneous pitch/yaw thrust vectoring single expansion ramp nozzle

NASA Technical Reports Server (NTRS)

Schirmer, Alberto W.; Capone, Francis J.

1989-01-01

In the course of the last eleven years, the concept of thrust vectoring has emerged as a promising method of enhancing aircraft control capabilities in post-stall flight incursions during combat. In order to study the application of simultaneous pitch and yaw vectoring to single expansion ramp nozzles, a static test was conducted in the NASA-Langley 16 foot transonic tunnel. This investigation was based on internal performance data provided by force, mass flow and internal pressure measurements at nozzle pressure ratios up to 8. The internal performance characteristics of the nozzle were studied for several combinations of six different parameters: yaw vectoring angle, pitch vectoring angle, upper ramp cutout, sidewall hinge location, hinge inclination angle and sidewall containment. Results indicated a 2-to- 3-percent decrease in resultant thrust ratio with vectoring in either pitch or yaw. Losses were mostly associated with the turning of supersonic flow. Resultant thrust ratios were also decreased by sideways expansion of the jet. The effects of cutback corners in the upper ramp and lower flap on performance were small. Maximum resultant yaw vector angles, about half of the flap angle, were achieved for the configuration with the most forward hinge location.

A study of prediction methods for the high angle-of-attack aerodynamics of straight wings and fighter aircraft

NASA Technical Reports Server (NTRS)

Mcmillan, O. J.; Mendenhall, M. R.; Perkins, S. C., Jr.

1984-01-01

Work is described dealing with two areas which are dominated by the nonlinear effects of vortex flows. The first area concerns the stall/spin characteristics of a general aviation wing with a modified leading edge. The second area concerns the high-angle-of-attack characteristics of high performance military aircraft. For each area, the governing phenomena are described as identified with the aid of existing experimental data. Existing analytical methods are reviewed, and the most promising method for each area used to perform some preliminary calculations. Based on these results, the strengths and weaknesses of the methods are defined, and research programs recommended to improve the methods as a result of better understanding of the flow mechanisms involved.

Dynamics and Control of Three-Dimensional Perching Maneuver under Dynamic Stall Influence

NASA Astrophysics Data System (ADS)

Feroskhan, Mir Alikhan Bin Mohammad

Perching is a type of aggressive maneuver performed by the class 'Aves' species to attain precision point landing with a generally short landing distance. Perching capability is desirable on unmanned aerial vehicles (UAVs) due to its efficient deceleration process that potentially expands the functionality and flight envelope of the aircraft. This dissertation extends the previous works on perching, which is mostly limited to two-dimensional (2D) cases, to its state-of-the-art threedimensional (3D) variety. This dissertation presents the aerodynamic modeling and optimization framework adopted to generate unprecedented variants of the 3D perching maneuver that include the sideslip perching trajectory, which ameliorates the existing 2D perching concept by eliminating the undesirable undershoot and reliance on gravity. The sideslip perching technique methodically utilizes the lateral and longitudinal drag mechanisms through consecutive phases of yawing and pitching-up motion. Since perching maneuver involves high rates of change in the angles of attack and large turn rates, introduction of three internal variables thus becomes necessary for addressing the influence of dynamic stall delay on the UAV's transient post-stall behavior. These variables are then integrated into a static nonlinear aerodynamic model, developed using empirical and analytical methods, and into an optimization framework that generates a trajectory of sideslip perching maneuver, acquiring over 70% velocity reduction. An impact study of the dynamic stall influence on the optimal perching trajectories suggests that consideration of dynamic stall delay is essential due to the significant discrepancies in the corresponding control inputs required. A comparative study between 2D and 3D perching is also conducted to examine the different drag mechanisms employed by 2D and 3D perching respectively. 3D perching is presented as a more efficient deceleration technique with respect to spatial costs and initial altitude range. Contraction analysis is shown to be a useful technique in identifying the state variables that are required to be tracked for attaining stability of optimal perching trajectories. Based on the selected tracking variables, two sliding control strategies are proposed and comparatively examined to close the control loop and provide the required robustness and convergence to the optimal perching trajectory in the presence of perturbations and dynamic stall model inaccuracies. This dissertation concludes that the sliding controller with the adaptive gain feature is more effective and essential in providing better tracking performance through illustrations of the corresponding convergence area and at higher intensity of perturbations.

Prevalence of lameness in high-producing holstein cows housed in freestall barns in Minnesota.

PubMed

Espejo, L A; Endres, M I; Salfer, J A

2006-08-01

A cross-sectional study was conducted to estimate the prevalence of clinical lameness in high-producing Holstein cows housed in 50 freestall barns in Minnesota during summer. Locomotion and body condition scoring were performed on a total of 5,626 cows in 53 high-production groups. Cow records were collected from the nearest Dairy Herd Improvement Association test date, and herd characteristics were collected at the time of the visit. The mean prevalence of clinical lameness (proportion of cows with locomotion score >or=3 on a 1-to-5 scale, where 1 = normal and 5 = severely lame), and its association with lactation number, month of lactation, body condition score, and type of stall surface were evaluated. The mean prevalence of clinical lameness was 24.6%, which was 3.1 times greater, on average, than the prevalence estimated by the herd managers on each farm. The prevalence of lameness in first-lactation cows was 12.8% and prevalence increased on average at a rate of 8 percentage units per lactation. There was no association between the mean prevalence of clinical lameness and month of lactation (for months 1 to 10). Underconditioned cows had a higher prevalence of clinical lameness than normal or overconditioned cows. The prevalence of lameness was lower in freestall herds with sand stalls (17.1%) than in freestall herds with mattress stall surfaces (27.9%). Data indicate that the best 10th percentile of dairy farms had a mean prevalence of lameness of 5.4% with only 1.47% of cows with locomotion score = 4 and no cows with locomotion score = 5.

Lamin A/C Depletion Enhances DNA Damage-Induced Stalled Replication Fork Arrest

PubMed Central

Singh, Mayank; Hunt, Clayton R.; Pandita, Raj K.; Kumar, Rakesh; Yang, Chin-Rang; Horikoshi, Nobuo; Bachoo, Robert; Serag, Sara; Story, Michael D.; Shay, Jerry W.; Powell, Simon N.; Gupta, Arun; Jeffery, Jessie; Pandita, Shruti; Chen, Benjamin P. C.; Deckbar, Dorothee; Löbrich, Markus; Yang, Qin; Khanna, Kum Kum; Worman, Howard J.

2013-01-01

The human LMNA gene encodes the essential nuclear envelope proteins lamin A and C (lamin A/C). Mutations in LMNA result in altered nuclear morphology, but how this impacts the mechanisms that maintain genomic stability is unclear. Here, we report that lamin A/C-deficient cells have a normal response to ionizing radiation but are sensitive to agents that cause interstrand cross-links (ICLs) or replication stress. In response to treatment with ICL agents (cisplatin, camptothecin, and mitomycin), lamin A/C-deficient cells displayed normal γ-H2AX focus formation but a higher frequency of cells with delayed γ-H2AX removal, decreased recruitment of the FANCD2 repair factor, and a higher frequency of chromosome aberrations. Similarly, following hydroxyurea-induced replication stress, lamin A/C-deficient cells had an increased frequency of cells with delayed disappearance of γ-H2AX foci and defective repair factor recruitment (Mre11, CtIP, Rad51, RPA, and FANCD2). Replicative stress also resulted in a higher frequency of chromosomal aberrations as well as defective replication restart. Taken together, the data can be interpreted to suggest that lamin A/C has a role in the restart of stalled replication forks, a prerequisite for initiation of DNA damage repair by the homologous recombination pathway, which is intact in lamin A/C-deficient cells. We propose that lamin A/C is required for maintaining genomic stability following replication fork stalling, induced by either ICL damage or replicative stress, in order to facilitate fork regression prior to DNA damage repair. PMID:23319047

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

Rotor design of high tip speed low loading transonic fan.

NASA Technical Reports Server (NTRS)

Erwin, J. R.; Vitale, N. G.

1972-01-01

This paper describes the design concepts, principles and details of a high tip speed transonic rotor having low aerodynamic loading. The purpose of the NASA sponsored investigation was to determine whether good efficiency and large stall margin could be obtained by designing a rotor to avoid flow separation associated with strong normal shocks. Fully supersonic flow through the outboard region of the rotor with compression accomplished by weak oblique shocks were major design concepts employed. Computer programs were written and used to derive blade sections consistent from the all-supersonic tip region to the all-subsonic hub region. Preliminary test results indicate attainment of design pressure ratio and design flow at design speed with about a 1.6 point decrement in efficiency and large stall margin.

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.

A numerical investigation into the effects of Reynolds number on the flow mechanism induced by a tubercled leading edge

NASA Astrophysics Data System (ADS)

Rostamzadeh, Nikan; Kelso, Richard M.; Dally, Bassam

2017-02-01

Leading-edge modifications based on designs inspired by the protrusions on the pectoral flippers of the humpback whale (tubercles) have been the subject of research for the past decade primarily due to their flow control potential in ameliorating stall characteristics. Previous studies have demonstrated that, in the transitional flow regime, full-span wings with tubercled leading edges outperform unmodified wings at high attack angles. The flow mechanism associated with such enhanced loading traits is, however, still being investigated. Also, the performance of full-span tubercled wings in the turbulent regime is largely unexplored. The present study aims to investigate Reynolds number effects on the flow mechanism induced by a full-span tubercled wing with the NACA-0021 cross-sectional profile in the transitional and near-turbulent regimes using computational fluid dynamics. The analysis of the flow field suggests that, with the exception of a few different flow features, the same underlying flow mechanism, involving the presence of transverse and streamwise vorticity, is at play in both cases. With regard to lift-generation characteristics, the numerical simulation results indicate that in contrast to the transitional flow regime, where the unmodified NACA-0021 undergoes a sudden loss of lift, in the turbulent regime, the baseline foil experiences gradual stall and produces more lift than the tubercled foil. This observation highlights the importance of considerations regarding the Reynolds number effects and the stall characteristics of the baseline foil, in the industrial applications of tubercled lifting bodies.

NASA/FAA Tailplane Icing Program: Flight Test Report

NASA Technical Reports Server (NTRS)

Ratvasky, Thomas P.; VanZante, Judith Foss; Sim, Alex

2000-01-01

This report presents results from research flights that explored the characteristics of an ice-contaminated tailplane using various simulated ice shapes attached to the leading edge of the horizontal tailplane. A clean leading edge provided the baseline case, then three ice shapes were flown in order of increasing severity. Flight tests included both steady state and dynamic maneuvers. The steady state points were 1G wings level and steady heading sideslips. The primary dynamic maneuvers were pushovers to various G-levels; elevator doublets; and thrust transitions. These maneuvers were conducted for a full range of flap positions and aircraft angle of attack where possible. The analysis of this data set has clearly demonstrated the detrimental effects of ice contamination on aircraft stability and controllability. Paths to tailplane stall were revealed through parameter isolation and transition studies. These paths are (1) increasing ice shape severity, (2) increasing flap deflection, (3) high or low speeds, depending on whether the aircraft is in a steady state (high speed) or pushover maneuver (low speed), and (4) increasing thrust. The flight research effort was very comprehensive, but did not examine effects of tailplane design and location, or other aircraft geometry configuration effects. However, this effort provided the role of some of the parameters in promoting tailplane stall. The lessons learned will provide guidance to regulatory agencies, aircraft manufacturers, and operators on ice-contaminated tailplane stall in the effort to increase aviation safety and reduce the fatal accident rate.

A Complete Procedure for Predicting and Improving the Performance of HAWT's

NASA Astrophysics Data System (ADS)

Al-Abadi, Ali; Ertunç, Özgür; Sittig, Florian; Delgado, Antonio

2014-06-01

A complete procedure for predicting and improving the performance of the horizontal axis wind turbine (HAWT) has been developed. The first process is predicting the power extracted by the turbine and the derived rotor torque, which should be identical to that of the drive unit. The BEM method and a developed post-stall treatment for resolving stall-regulated HAWT is incorporated in the prediction. For that, a modified stall-regulated prediction model, which can predict the HAWT performance over the operating range of oncoming wind velocity, is derived from existing models. The model involves radius and chord, which has made it more general in applications for predicting the performance of different scales and rotor shapes of HAWTs. The second process is modifying the rotor shape by an optimization process, which can be applied to any existing HAWT, to improve its performance. A gradient- based optimization is used for adjusting the chord and twist angle distribution of the rotor blade to increase the extraction of the power while keeping the drive torque constant, thus the same drive unit can be kept. The final process is testing the modified turbine to predict its enhanced performance. The procedure is applied to NREL phase-VI 10kW as a baseline turbine. The study has proven the applicability of the developed model in predicting the performance of the baseline as well as the optimized turbine. In addition, the optimization method has shown that the power coefficient can be increased while keeping same design rotational speed.

Aerodynamic design and analysis of small horizontal axis wind turbine blades

NASA Astrophysics Data System (ADS)

Tang, Xinzi

This work investigates the aerodynamic design and analysis of small horizontal axis wind turbine blades via the blade element momentum (BEM) based approach and the computational fluid dynamics (CFD) based approach. From this research, it is possible to draw a series of detailed guidelines on small wind turbine blade design and analysis. The research also provides a platform for further comprehensive study using these two approaches. The wake induction corrections and stall corrections of the BEM method were examined through a case study of the NREL/NASA Phase VI wind turbine. A hybrid stall correction model was proposed to analyse wind turbine power performance. The proposed model shows improvement in power prediction for the validation case, compared with the existing stall correction models. The effects of the key rotor parameters of a small wind turbine as well as the blade chord and twist angle distributions on power performance were investigated through two typical wind turbines, i.e. a fixed-pitch variable-speed (FPVS) wind turbine and a fixed-pitch fixed-speed (FPFS) wind turbine. An engineering blade design and analysis code was developed in MATLAB to accommodate aerodynamic design and analysis of the blades.. The linearisation for radial profiles of blade chord and twist angle for the FPFS wind turbine blade design was discussed. Results show that, the proposed linearisation approach leads to reduced manufacturing cost and higher annual energy production (AEP), with minimal effects on the low wind speed performance. Comparative studies of mesh and turbulence models in 2D and 3D CFD modelling were conducted. The CFD predicted lift and drag coefficients of the airfoil S809 were compared with wind tunnel test data and the 3D CFD modelling method of the NREL/NASA Phase VI wind turbine were validated against measurements. Airfoil aerodynamic characterisation and wind turbine power performance as well as 3D flow details were studied. The detailed flow characteristics from the CFD modelling are quantitatively comparable to the measurements, such as blade surface pressure distribution and integrated forces and moments. It is confirmed that the CFD approach is able to provide a more detailed qualitative and quantitative analysis for wind turbine airfoils and rotors..

Effect of different flooring systems on claw conformation of dairy cows.

PubMed

Telezhenko, E; Bergsten, C; Magnusson, M; Nilsson, C

2009-06-01

The effect of different flooring surfaces in walking and standing areas on claw conformation, claw horn growth, and wear was studied in 2 experiments during 2 consecutive housing seasons in a research dairy herd of 170 cows. In experiment 1, the flooring systems tested were solid rubber mats, mastic asphalt with and without rubber-matted feed-stalls, and aged concrete slats. In experiment 2, slatted concrete flooring was compared with slatted rubber flooring. The cows were introduced to the respective flooring systems in early lactation and their claws were trimmed before the exposure period. Toe length, toe angle, sole concavity, and claw width, as well as claw growth and wear rates were recorded for lateral and medial claws of the left hind limb. Claw asymmetry calculations were based on these claw measurements and on differences in sole protrusion between lateral and medial soles. Asphalt floors caused shorter toe length and steeper toe angle. They also increased wear on rear claws (5.30 +/- 0.31 and 5.95 +/- 0.33 mm/mo for lateral and medial claw, respectively; LSM +/- SE) and horn growth rate (5.12 +/- 0.36 and 5.83 +/- 0.31 mm/mo of lateral and medial claws, respectively). Rubber mats instead of asphalt in walking areas reduced wear (1.36 +/- 0.19 and 2.02 +/- 0.20 mm/mo for lateral and medial claw, respectively) and claw growth (3.83 +/- 0.23 and 3.94 +/- 0.17 mm/mo for lateral and medial claw, respectively). Rubber-matted feed-stalls together with asphalt walkways decreased claw wear (3.29 +/- 0.31 and 4.10 +/- 0.32 mm/mo for lateral and medial claw, respectively). The concavity of claw soles was reduced on asphalt, especially in the lateral rear claws. Rubber matting in feed-stalls prevented loss of sole concavity compared with asphalt. Claw asymmetry did not differ between flooring systems. While different access to abrasive flooring affected claw conformation, there was no evidence that flooring system influenced the disproportion between lateral and medial claws.

Surge-Inception Study in a Two-Spool Turbojet Engine. Revised

NASA Technical Reports Server (NTRS)

Wallner, Lewis E.; Lubick, Robert J.; Saari, Martin J.

1957-01-01

A two-spool turbojet engine was operated in the Lewis altitude wind tunnel to study the inception of compressor surge. In addition to the usual steady-state pressure and temperature measurements, the compressors were extensively instrumented with fast-response interstage pressure transducers. Thus it was possible to obtain maps for both compressors, pressure oscillations during rotating stall, effects of stall on efficiency, and stage-loading curves. In addition, with the transient measurements, it was possible to record interstage pressures and then compute stage performance during accelerations to the stall limit. Rotating stall was found to exist at low speeds in the outer spool. Although the stall arose from poor flow conditions at the inlet-stage blade tips, the low-energy air moved through the machine from the tip at the inlet to the outer spool to the hub at the inlet to the inner spool. This tip stall ultimately resulted in compressor surge in the mid-speed region, and necessitated inter-compressor air bleed. Interstage pressure measurements during acceleration to the compressor stall limit indicated that rotating stall was not a necessary condition for compressor surge and that, at the critical stall point, the circumferential interstage pressure distribution was uniform. The exit-stage group of the inner spool was first t o stall; then, the stages upstream stalled in succession until the inlet stage of the outer spool was stalled. With a sufficiently high fuel rate, the process repeated with a cycle time of about 0.1 second. It was possible to construct reproducible stage stall lines as a function of compressor speed from the stage stall points of several such compressor surges. This transient stall line was checked by computing the stall line from a steady-state stage-loading curve. Good agreement between the stage stall lines was obtained by these two methods.

Experimental result analysis for scaled model of UiTM tailless blended wing-body (BWB) Baseline 7 unmanned aerial vehicle (UAV)

NASA Astrophysics Data System (ADS)

Nasir, R. E. M.; Ahmad, A. M.; Latif, Z. A. A.; Saad, R. M.; Kuntjoro, W.

2017-12-01

Blended wing-body (BWB) aircraft having planform configuration similar to those previously researched and published by other researchers does not guarantee that an efficient aerodynamics in term of lift-to-drag ratio can be achieved. In this wind tunnel experimental study, BWB half model is used. The model is also being scaled down to 71.5% from the actual size. Based on the results, the maximum lift coefficient is found to be 0.763 when the angle is at 27.5° after which the model starts to stall. The minimum drag coefficient is 0.014, measured at zero angle of attack. The corrected lift-to-drag ratio (L/D) is 15.9 at angle 7.8°. The scaled model has a big flat surface that surely gives an inaccurate data but the data obtained shall give some insights for future perspective towards the BWB model being tested.

Vortex developments over steady and accelerated airfoils incorporating a trailing edge jet

NASA Technical Reports Server (NTRS)

Finaish, F.; Okong'o, N.; Frigerio, J.

1993-01-01

Computational and experimental studies are conducted to investigate the influence of a trailing edge jet on flow separation and subsequent vortex formation over steady and accelerated airfoils at high angles of attack. A computer code, employing the stream function-vorticity approach, is developed and utilized to conduct numerical experiments on the flow problem. To verify and economize such efforts, an experimental system is developed and incorporated into a subsonic wind tunnel where streamline and vortex flow visualization experiments are conducted. The study demonstrates the role of the trailing edge jet in controlling flow separation and subsequent vortex development for steady and accelerating flow at angles past the static stall angle of attack. The results suggest that the concept of the trailing edge jet may be utilized to control the characteristics of unsteady separated flows over lifting surfaces. This control possibility seems to be quite effective and could have a significant role in controlling unsteady separated flows.

The influence of sweep on the aerodynamic loading of an oscillating NACA 0012 airfoil. Volume 1: Technical report

NASA Technical Reports Server (NTRS)

St.hilaire, A. O.; Carta, F. O.; Fink, M. R.; Jepson, W. D.

1979-01-01

Aerodynamic experiments were performed on an oscillating NACA 0012 airfoil utilizing a tunnel-spanning wing in both unswept and 30 degree swept configurations. The airfoil was tested in steady state and in oscillatory pitch about the quarter chord. The unsteady aerodynamic loading was measured using pressure transducers along the chord. Numerical integrations of the unsteady pressure transducer responses were used to compute the normal force, chord force, and moment components of the induced loading. The effects of sweep on the induced aerodynamic load response was examined. For the range of parameters tested, it was found that sweeping the airfoil tends to delay the onset of dynamic stall. Sweeping was also found to reduce the magnitude of the unsteady load variation about the mean response. It was determined that at mean incidence angles greater than 9 degrees, sweep tends to reduce the stability margin of the NACA 0012 airfoil; however, for all cases tested, the airfoil was found to be stable in pure pitch. Turbulent eddies were found to convect downstream above the upper surface and generate forward-moving acoustic waves at the trailing edge which move upstream along the lower surface.

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. 8.1%), when cows were provided free stalls with rubber mats or mattresses, and as the distance from the rear curb to neck rail increased. A higher percentage of cows were lying in a stall when sand bedding was used, when bedding was added more frequently, and during the spring months. Results of this national survey indicate that tail docking provides no benefit to cow hygiene and that stall base and bedding are key factors influencing hock injuries and stall usage on US free stall dairy farms. Copyright © 2010 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

Effect of casing treatment on overall and blade element performance of a compressor rotor

NASA Technical Reports Server (NTRS)

Moore, R. D.; Kovich, G.; Blade, R. J.

1971-01-01

An axial flow compressor rotor was tested at design speed with six different casing treatments across the rotor tip. Radial surveys of pressure, temperature, and flow angle were taken at the rotor inlet and outlet. Surveys were taken at several weight flows for each treatment. All the casings treatments decreased the weight flow at stall over that for the solid casing. Radial surveys indicate that the performance over the entire radial span of the blade is affected by the treatment across the rotor tip.

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.

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.

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.

14 CFR 23.203 - Turning flight and accelerated turning stalls.

Code of Federal Regulations, 2012 CFR

2012-01-01

... § 23.201(b), it must be possible to regain wings level flight by normal use of the flight controls, but... percent of maximum continuous power results in extreme nose-up attitudes, the test may be carried out with..., if the power-to-weight ratio at 75 percent of maximum continuous power results in nose-high attitudes...

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.

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.

Automatic milking systems, farm size, and milk production.

PubMed

Rotz, C A; Coiner, C U; Soder, K J

2003-12-01

Automatic milking systems (AMS) offer relief from the demanding routine of milking. Although many AMS are in use in Europe and a few are used in the United States, the potential benefit for American farms is uncertain. A farm-simulation model was used to determine the long-term, whole-farm effect of implementing AMS on farm sizes of 30 to 270 cows. Highest farm net return to management and unpaid factors was when AMS were used at maximal milking capacity. Adding stalls to increase milking frequency and possibly increase production generally did not improve net return. Compared with new traditional milking systems, the greatest potential economic benefit was a single-stall AMS on a farm size of 60 cows at a moderate milk production level (8600 kg/cow). On other farm sizes using single-stall type robotic units, losses in annual net return of 0 dollars to 300 dollars/cow were projected, with the greatest losses on larger farms and at high milk production (10,900 kg/cow). Systems with one robot serving multiple stalls provided a greater net return than single-stall systems, and this net return was competitive with traditional parlors for 50- to 130-cow farm sizes. The potential benefit of AMS was improved by 100 dollars/cow per year if the AMS increased production an additional 5%. A 20% reduction in initial equipment cost or doubling milking labor cost also improved annual net return of an AMS by up to 100 dollars/cow. Annual net return was reduced by 110 dollars/cow, though, if the economic life of the AMS was reduced by 3 yr for a more rapid depreciation than that normally used with traditional milking systems. Thus, under current assumptions, the economic return for an AMS was similar to that of new parlor systems on smaller farms when the milking capacity of the AMS was well matched to herd size and milk production level.

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...

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...

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...

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...

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...

Inlet Unstart Propulsion Integration Wind Tunnel Test Program Completed for High-Speed Civil Transport

NASA Technical Reports Server (NTRS)

Porro, A. Robert

2000-01-01

One of the propulsion system concepts to be considered for the High-Speed Civil Transport (HSCT) is an underwing, dual-propulsion, pod-per-wing installation. Adverse transient phenomena such as engine compressor stall and inlet unstart could severely degrade the performance of one of these propulsion pods. The subsequent loss of thrust and increased drag could cause aircraft stability and control problems that could lead to a catastrophic accident if countermeasures are not in place to anticipate and control these detrimental transient events. Aircraft system engineers must understand what happens during an engine compressor stall and inlet unstart so that they can design effective control systems to avoid and/or alleviate the effects of a propulsion pod engine compressor stall and inlet unstart. The objective of the Inlet Unstart Propulsion Airframe Integration test program was to assess the underwing flow field of a High-Speed Civil Transport propulsion system during an engine compressor stall and subsequent inlet unstart. Experimental research testing was conducted in the 10- by 10-Foot Supersonic Wind Tunnel at the NASA Glenn Research Center at Lewis Field. The representative propulsion pod consisted of a two-dimensional, bifurcated inlet mated to a live turbojet engine. The propulsion pod was mounted below a large flat plate that acted as a wing simulator. Because of the plate s long length (nominally 10-ft wide by 18-ft long), realistic boundary layers could form at the inlet cowl plane. Transient instrumentation was used to document the aerodynamic flow-field conditions during an unstart sequence. Acquiring these data was a significant technical challenge because a typical unstart sequence disrupts the local flow field for about only 50 msec. Flow surface information was acquired via static pressure taps installed in the wing simulator, and intrusive pressure probes were used to acquire flow-field information. These data were extensively analyzed to determine the impact of the unstart transient on the surrounding flow field. This wind tunnel test program was a success, and for the first time, researchers acquired flow-field aerodynamic data during a supersonic propulsion system engine compressor stall and inlet unstart sequence. In addition to obtaining flow-field pressure data, Glenn researchers determined other properties such as the transient flow angle and Mach number. Data are still being reduced, and a comprehensive final report will be released during calendar year 2000.

Investigation at High Subsonic Speeds of the Static Longitudinal and Lateral Stability Characteristics of Two Canard Airplane Configurations

NASA Technical Reports Server (NTRS)

Sleeman, William C., Jr.

1957-01-01

The present investigation was conducted in the Langley high-speed 7-by 10-foot tunnel to determine the static longitudinal and lateral stability characteristics at high subsonic speeds of two canard airplane configurations previously tested at supersonic speeds. The Mach number range of this investigation extended from 0.60 to 0.94 and a maximum angle-of-attack range of -2dewg to 24deg was obtained at the lowest test Mach number. Two wing plan forms of equal area were studied in the present tests; one was a 60deg delta wing and the other was a trapezoid wing having an aspect ratio of 3, taper ratio of 0.143, and an unswept 80-percent-chord line. The canard control had a trapezoidal plan form and its area was approximately 11.5 percent of the wing area. The model also had a low-aspect-ratio highly swept vertical tail and twin ventral fins. The longitudinal control characteristics of the models were consistent with past experience at low speed on canard configurations in that stalling of the canard surface occurred at moderate and high control deflections for moderate values of angle of attack. This stalling could impose appreciable limitations on the maximum trim-lift coefficient attainable. The control effectiveness and maximum value of trim-lift was significantly increased by addition of a body flap having a conical shape and located slightly behind the canard surface on the bottom of the body. Addition of the canard surface at 0deg deflection had relatively little effect on overall directional stability of the delta-wing configuration; however, deflection of the canard surface from 0deg to 10deg had a large favorable effect on directional stability at high angles of attack for both the trapezoid- and delta-wing configurations.

CFD Analysis of the Aerodynamics of a Business-Jet Airfoil with Leading-Edge Ice Accretion

NASA Technical Reports Server (NTRS)

Chi, X.; Zhu, B.; Shih, T. I.-P.; Addy, H. E.; Choo, Y. K.

2004-01-01

For rime ice - where the ice buildup has only rough and jagged surfaces but no protruding horns - this study shows two dimensional CFD analysis based on the one-equation Spalart-Almaras (S-A) turbulence model to predict accurately the lift, drag, and pressure coefficients up to near the stall angle. For glaze ice - where the ice buildup has two or more protruding horns near the airfoil's leading edge - CFD predictions were much less satisfactory because of the large separated region produced by the horns even at zero angle of attack. This CFD study, based on the WIND and the Fluent codes, assesses the following turbulence models by comparing predictions with available experimental data: S-A, standard k-epsilon, shear-stress transport, v(exp 2)-f, and differential Reynolds stress.

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...

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...

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.

Hysteresis, phase transitions, and dangerous transients in electrical power distribution systems.

PubMed

Duclut, Charlie; Backhaus, Scott; Chertkov, Michael

2013-06-01

The majority of dynamical studies in power systems focus on the high-voltage transmission grids where models consider large generators interacting with crude aggregations of individual small loads. However, new phenomena have been observed indicating that the spatial distribution of collective, nonlinear contribution of these small loads in the low-voltage distribution grid is crucial to the outcome of these dynamical transients. To elucidate the phenomenon, we study the dynamics of voltage and power flows in a spatially extended distribution feeder (circuit) connecting many asynchronous induction motors and discover that this relatively simple 1+1 (space+time) dimensional system exhibits a plethora of nontrivial spatiotemporal effects, some of which may be dangerous for power system stability. Long-range motor-motor interactions mediated by circuit voltage and electrical power flows result in coexistence and segregation of spatially extended phases defined by individual motor states, a "normal" state where the motors' mechanical (rotation) frequency is slightly smaller than the nominal frequency of the basic ac flows and a "stalled" state where the mechanical frequency is small. Transitions between the two states can be initiated by a perturbation of the voltage or base frequency at the head of the distribution feeder. Such behavior is typical of first-order phase transitions in physics, and this 1+1 dimensional model shows many other properties of a first-order phase transition with the spatial distribution of the motors' mechanical frequency playing the role of the order parameter. In particular, we observe (a) propagation of the phase-transition front with the constant speed (in very long feeders) and (b) hysteresis in transitions between the normal and stalled (or partially stalled) phases.

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.

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

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

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.

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.

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

Stage effects on stalling and recovery of a high-speed 10-stage axial-flow compressor

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

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.

Investigation of the Low-Subsonic Stability and Control Characteristics of a Free-Flying Model of a Thick 70 deg Delta Reentry Configuration

NASA Technical Reports Server (NTRS)

Paulson, John W.; Shanks, Robert E.

1961-01-01

An investigation of the low-subsonic flight characteristics of a thick 70 deg delta reentry configuration having a diamond cross section has been made in the Langley full-scale tunnel over an angle-of-attack range from 20 to 45 deg. Flight tests were also made at angles of attack near maximum lift (alpha = 40 deg) with a radio-controlled model dropped from a helicopter. Static and dynamic force tests were made over an angle-of-attack range from 0 to 90 deg. The longitudinal stability and control characteristics were considered satisfactory when the model had positive static longitudinal stability. It was possible to fly the model with a small amount of static instability, but the longitudinal characteristics were considered unsatisfactory in this condition. At angles of attack above the stall the model developed a large, constant-amplitude pitching oscillation. The lateral stability characteristics were considered to be only fair at angles of attack from about 20 to 35 deg because of a lightly damped Dutch roll oscillation. At higher angles of attack the oscillation was well damped and the lateral stability was generally satisfactory. The Dutch roll damping at the lower angles of attack was increased to satisfactory values by means of a simple rate-type roll damper. The lateral control characteristics were generally satisfactory throughout the angle- of-attack range, but there was some deterioration in aileron effectiveness in the high angle-of-attack range due mainly to a large increase in damping in roll.

USAF Test Pilot School. Flying Qualities Textbook, Volume 2 Part 2

DTIC Science & Technology

1986-04-01

regime that precipitates entry into a PSG, spin, or deep stall condition (MIL-F-83691A, Reference 10.4, Paragraph 6.3.9). Notice two things about...motions may result after departure - the aircraft enters either a PSG, spin, or deep stall (of course, a PSG can progress into a spin or deep stall...gyration," "spin" and " deep stalls," used to define a departure. 10.3.1.3 Post-Stall Gyration. A post-stall gyration is an uncontrolled motion about one

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.

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.

A Review of Evidence for High Life Coefficients on Propeller and Rotor Blades Under Static Thrust Conditions with Some New Experimental Results

NASA Technical Reports Server (NTRS)

Talbot, Peter D.; Meyer, Mark; Branum, Lonnie; Burks, John S. (Technical Monitor)

1994-01-01

Interest has increased recently in the thrust-producing capability of rotors at very high collective pitch angles. An early reference noted this behaviour in rotors and offered alternative models for section lift characteristics to explain it. The same phenomenon was coincidentally noted and used in a propeller code, resulting in very good correlation with static thrust data. The proposed paper will present experimental data demonstrating the pronounced persistence of thrust for propellers at increasing collective pitch angles. Comparisons with blade element/momentum theory will be made. These results are expected to point to the need to define (ultimately to explain) aerodynamic lift and drag behaviour in a rotating environment. Experimental measurements made by the U.S. Army Aeroflightdynamics Directorate at the Ames Research Center have shown that locally measured normal force coefficients along the span of a highly twisted rotor blade continue to increase at high values of collective pitch. In some cases these coefficients exceed expected values for the same type of airfoil tested under two dimensional conditions. To date no one to the authors' knowledge has defined the variation of C(n) with pitch for very high angles (to 45 deg) in a rotating environment and for a blade of reasonably high aspect ratio; however, total propeller thrust measurements support the idea that stalling does not occur in the same way as on a wing. This paper will present experimental data in the form of surface pressure distributions as well as flow visualization (microtufts) to explore the aerodynamic behavior of the rotating airfoil at high values of blade incidence. This paper also reviews experimental evidence and infers some high lift coefficient behavior from it. Comparisons between predicted thrust, utilizing modified airfoil characteristics and a blade element model, and measured thrust for both rotors and propellers that cover the extremes of collective pitch are shown and discussed.

Aerodynamics and vortical structures in hovering fruitflies

NASA Astrophysics Data System (ADS)

Meng, Xue Guang; Sun, Mao

2015-03-01

We measure the wing kinematics and morphological parameters of seven freely hovering fruitflies and numerically compute the flows of the flapping wings. The computed mean lift approximately equals to the measured weight and the mean horizontal force is approximately zero, validating the computational model. Because of the very small relative velocity of the wing, the mean lift coefficient required to support the weight is rather large, around 1.8, and the Reynolds number of the wing is low, around 100. How such a large lift is produced at such a low Reynolds number is explained by combining the wing motion data, the computed vortical structures, and the theory of vorticity dynamics. It has been shown that two unsteady mechanisms are responsible for the high lift. One is referred as to "fast pitching-up rotation": at the start of an up- or downstroke when the wing has very small speed, it fast pitches down to a small angle of attack, and then, when its speed is higher, it fast pitches up to the angle it normally uses. When the wing pitches up while moving forward, large vorticity is produced and sheds at the trailing edge, and vorticity of opposite sign is produced near the leading edge and on the upper surface, resulting in a large time rate of change of the first moment of vorticity (or fluid impulse), hence a large aerodynamic force. The other is the well known "delayed stall" mechanism: in the mid-portion of the up- or downstroke the wing moves at large angle of attack (about 45 deg) and the leading-edge-vortex (LEV) moves with the wing; thus, the vortex ring, formed by the LEV, the tip vortices, and the starting vortex, expands in size continuously, producing a large time rate of change of fluid impulse or a large aerodynamic force.

Wind-Tunnel Investigation of the Effect of Angle of Attack and Flapping-Hinge Offset on Periodic Bending Moments and Flapping of a Small Rotor

NASA Technical Reports Server (NTRS)

McCarty, John Locke; Brooks, George W.; Maglieri, Domenic J.

1959-01-01

A two-blade rotor having a diameter of 4 feet and a solidity of 0.037 was tested in the Langley 300-MPH 7- by 10-foot tunnel to obtain information on the effect of certain rotor variables on the blade periodic bending moments and flapping angles during the various stages of transformation between the helicopter and autogiro configuration. Variables studied included collective pitch angle, flapping-hinge offset, rotor angle of attack, and tip-speed ratio. The results show that the blade periodic bending moments generally increase with tip-speed ratio up into the transition region, diminish over a certain range of tip-speed ratio, and increase again at higher tip-speed ratios. Above the transition region, the bending moments increase with collective pitch angle and rotor angle of attack. The absence of a flapping hinge results in a significant amplification of the periodic bending moments, the magnitudes of which increase with tip-speed ratio. When the flapping hinge is used, an increase in flapping-hinge offset results in reduced period bending moments. The aforementioned trends exhibited by the bending moments for changes in the variables are essentially duplicated by the periodic flapping motions. The existence of substantial amounts of blade stall increased both the periodic bending moments and the flapping angles. Harmonic analysis of the bending moments shows significant contributions of the higher harmonics, particularly in the transition region.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Day, I.J.; Breuer, T.; Escuret, J.

As part of a European collaborative project, four high-speed compressors were tested to investigate the generic features of stall inception in aero-engine type compressors. Tests were run over the full speed range to identify the design and operating parameters that influence the stalling process. A study of data analysis techniques was also conducted in the hope of establishing early warning of stall. The work presented here is intended to relate the physical happenings in the compressor to the signals that would be received by an active stall control system. The measurements show a surprising range of stall-related disturbances and suggestmore » that spike-type stall inception is a feature of low-speed operation while modal activity is clearest in the midspeed range. High-frequency disturbances were detected at both ends of the speed range and nonrotating stall, a new phenomenon, was detected in three out of the four compressors. The variety of the stalling patterns, and the ineffectiveness of the stall warning procedures, suggests that the ultimate goal of a flightworthy active control system remains some way off.« less

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.

A proposed definition for a pitch attitude target for the microburst escape maneuver

NASA Technical Reports Server (NTRS)

Bray, Richard S.

1990-01-01

The Windshear Training Aid promulgated by the Federal Aviation Administration (FAA) defines the practical recovery maneuver following a microburst encounter as application of maximum thrust accompanied by rotation to an aircraft-specific target pitch attitude. In search of a simple method of determining this target, appropriate to a variety of aircraft types, a computer simulation was used to explore the suitability of a pitch target equal in numerical value to that of the angle of attack associated with stall warning. For the configurations and critical microburst shears simulated, this pitch target was demonstrated to be close to optimum.

Prediction of unsteady separated flows on oscillating airfoils

NASA Technical Reports Server (NTRS)

Mccroskey, W. J.

1978-01-01

Techniques for calculating high Reynolds number flow around an airfoil undergoing dynamic stall are reviewed. Emphasis is placed on predicting the values of lift, drag, and pitching moments. Methods discussed include: the discrete potential vortex method; thin boundary layer method; strong interaction between inviscid and viscous flows; and solutions to the Navier-Stokes equations. Empirical methods for estimating unsteady airloads on oscillating airfoils are also described. These methods correlate force and moment data from wind tunnel tests to indicate the effects of various parameters, such as airfoil shape, Mach number, amplitude and frequency of sinosoidal oscillations, mean angle, and type of motion.

Very Low Cost Expendable Harassment System Design Study. Volume 3

DTIC Science & Technology

1975-12-01

Vst = W = wf. w = g a, = a O. 3D LO * n ■ 0 = thrust horsepower anailable (hp) thrust horsepower required (hp) airspeed (mph) stall...A-113 ^rr-r-^rfr^r- "- -—’^’ iääaääiäitämäiA Hi^l^Wt^MjMW^1^-^^^ APPENDIX A-6-2 DESIGN OUTPUT VST SL VST 3K WEIGHT VST (S=17,0... angular velocity change of rolling moment from a change in yaw angular velocity change of rolling moment from a change in sideslip angle change of

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.

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

NASA Technical Reports Server (NTRS)

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

1986-01-01

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

Northrop F-5F shark nose development

NASA Technical Reports Server (NTRS)

Edwards, O. R.

1978-01-01

During spin susceptibility testing of the Northrop F-5F airplane, two erect spin entries were obtained from purely longitudinal control inputs at low speed. Post flight analysis of the data showed that the initial yaw departure occurred at zero sideslip, and review of wind tunnel data showed significant yawing moments present at angles of attack well above stall. Further analysis of this wind tunnel data indicated that the yawing moments were being generated by the long slender nose of the airplane. Redesign of the nose was accomplished, resulting in a nose configuration which completely alleviated the asymmetric yawing moments.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pirrung, Georg; Madsen, Helge; Schreck, Scott

Current fast aeroelastic wind turbine codes suitable for certification lack an induction model for standstill conditions. A trailed vorticity model previously used as addition to a blade element momentum theory based aerodynamic model in normal operation has been extended to allow computing the induced velocities in standstill. The model is validated against analytical results for an elliptical wing in constant inflow and against stand still measurements from the NREL/NASA Phase VI unsteady experiment. The extended model obtains good results in case of the elliptical wing, but underpredicts the steady loading for the Phase VI blade in attached flow. The predictionmore » of the dynamic force coefficient loops from the Phase VI experiment is improved by the trailed vorticity modeling in both attached flow and stall in most cases. The exception is the tangential force coefficient in stall, where the codes and measurements deviate and no clear improvement is visible.« less

Trailed vorticity modeling for aeroelastic wind turbine simulations in stand still

DOE PAGES

Pirrung, Georg; Madsen, Helge; Schreck, Scott

2016-10-03

Current fast aeroelastic wind turbine codes suitable for certification lack an induction model for standstill conditions. A trailed vorticity model previously used as addition to a blade element momentum theory based aerodynamic model in normal operation has been extended to allow computing the induced velocities in standstill. The model is validated against analytical results for an elliptical wing in constant inflow and against stand still measurements from the NREL/NASA Phase VI unsteady experiment. The extended model obtains good results in case of the elliptical wing, but underpredicts the steady loading for the Phase VI blade in attached flow. The predictionmore » of the dynamic force coefficient loops from the Phase VI experiment is improved by the trailed vorticity modeling in both attached flow and stall in most cases. The exception is the tangential force coefficient in stall, where the codes and measurements deviate and no clear improvement is visible.« less

77 FR 73279 - Airworthiness Directives; Saab AB, Saab Aerosystems Airplanes

Federal Register 2010, 2011, 2012, 2013, 2014

2012-12-10

... AD was prompted by reports of stall events during icing conditions where the natural stall warning (buffet) was not identified. This AD requires replacing the stall warning computer (SWC) with a new SWC, which provides an artificial stall [[Page 73280

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...

Effect of high negative incidence on the performance of a centrifugal compressor stage with conventional vaned diffusers

NASA Astrophysics Data System (ADS)

Jaatinen, Ahti; Grönman, Aki; Turunen-Saaresti, Teemu; Backman, Jari

2011-06-01

Three vaned diffusers, designed to have high negative incidence (-8°) at the design operating point, are studied experimentally. The overall performance (efficiency and pressure ratio) are measured at three rotational speeds, and flow angles before and after the diffuser are measured at the design rotational speed and with three mass flow rates. The results are compared to corresponding results of the original vaneless diffuser design. Attention is paid to the performance at lower mass flows than the design mass flow. The results show that it is possible to improve the performance at mass flows lower than the design mass flow with a vaned diffuser designed with high negative incidence. However, with the vaned diffusers, the compressor still stalls at higher mass flow rates than with the vaneless one. The flow angle distributions after the diffuser are more uniform with the vaned diffusers.

Overcoming difficulties with caviar formation, desanding of converter I, Leuna, 1941

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1941-01-01

The life of a coal stall was in most cases limited by the grinding action of the solid components of the coal. The so-called caviar produced the greatest amount of difficulties. Its elimination was accomplished by the removal of the coarsest particle from the first converter, the converter 1 desanding. Before desanding was introduced, perforated thermocouple-protecting tubes and catalyst tubes almost ground through were found in almost every dismantling of the stalls. Small-scale and large-scale solutions to this problem were discussed. A sketch of desanding in converter I was given. Another sketch showed the pipe line of the HOLD frommore » the converter to the pressure relief. A screen analysis of the converter I desanding and of the normal HOLD were made to determine the proportion of coarse and fine sludge. Curve A and curve B given on two graphs showed the percent distribution and the actual amount involved. Sheet 1 gave diagrams of the residue and damage by wear in converters 1 and 2 of stall 8. Sheet 4 showed a diagram of converter 1 with an inclined plane for desanding and sheet 8 gave the desanding results from a test on converter 1. The final conclusion drawn was that desanding of converter 1 completely eliminated the formation and settling of caviar in the coal stall converters. The desanding process was one in which about 10% of the sludge in the first converter was periodically withdrawn from the bottom of converter, often to be sent on to be combined with hot oil letdown for further processing. The desanding residue could be readily carbonized because the proportion of asphalt to solids was very good. 8 diagrams« less

Effect of paddock vs. stall housing on 24 hour gastric pH within the proximal and ventral equine stomach.

PubMed

Husted, L; Sanchez, L C; Olsen, S N; Baptiste, K E; Merritt, A M

2008-06-01

Stall housing has been suggested as a risk factor for ulcer development in the equine stomach; however, the exact pathogenesis for this has not been established. To investigate the effect of 3 environmental situations (grass paddock, stall alone or stall with adjacent companion) on pH in the proximal and the ventral stomach. Six horses with permanently implanted gastric cannulae were used in a randomised, cross-over, block design. Each horse rotated through each of three 24 h environmental situations. Horses remained on their normal diet (grass hay ad libitum and grain b.i.d.) throughout the study. Intragastric pH was measured continuously for 72 h just inside the lower oesophageal sphincter (proximal stomach) and via a pH probe in the gastric cannula (ventral stomach). Neither proximal nor ventral 24 h gastric pH changed significantly between the 3 environmental situations. Mean hourly proximal gastric pH decreased significantly in the interval from 01.00-09.00 h compared to the interval from 13.00-20.00 h, regardless of environmental situation. Median hourly proximal pH only differed in the interval from 06.00-07.00 h compared to the interval 14.00-19.00 h. Neither mean nor median hourly ventral gastric pH varied significantly with the time of day. The change in housing status used in the current study did not affect acid exposure within either region of the equine stomach. The pH in the ventral stomach was uniformly stable throughout the study, while the proximal pH demonstrated a 24 h circadian pattern.

F-15 RPRV Attached Under the Wing of the B-52 Mothership in Flight

NASA Technical Reports Server (NTRS)

1973-01-01

This photograph shows one of NASA's 3/8th-scale F-15 remotely piloted research vehicles under the wing of the B-52 mothership in flight during 1973, the year that the research program began. The vehicle was used to make stall-spin studies of the F-15 shape before the actual F-15s began their flight tests. B-52 Project Description: NASA B-52, Tail Number 008, is an air launch carrier aircraft, 'mothership,' as well as a research aircraft platform that has been used on a variety of research projects. The aircraft, a 'B' model built in 1952 and first flown on June 11, 1955, is the oldest B-52 in flying status and has been used on some of the most significant research projects in aerospace history. Some of the significant projects supported by B-52 008 include the X-15, the lifting bodies, HiMAT (highly maneuverable aircraft technology), Pegasus, validation of parachute systems developed for the space shuttle program (solid-rocket-booster recovery system and the orbiter drag chute system), and the X-38. The B-52 served as the launch vehicle on 106 X-15 flights and flew a total of 159 captive-carry and launch missions in support of that program from June 1959 to October 1968. Information gained from the highly successful X-15 program contributed to the Mercury, Gemini, and Apollo human spaceflight programs as well as space shuttle development. Between 1966 and 1975, the B-52 served as the launch aircraft for 127 of the 144 wingless lifting body flights. In the 1970s and 1980s, the B-52 was the launch aircraft for several aircraft at what is now the Dryden Flight Research Center, Edwards, California, to study spin-stall, high-angle-of attack, and maneuvering characteristics. These included the 3/8-scale F-15/spin research vehicle (SRV), the HiMAT (Highly Maneuverable Aircraft Technology) research vehicle, and the DAST (drones for aerodynamic and structural testing). The aircraft supported the development of parachute recovery systems used to recover the space shuttle solid rocket booster casings. It also supported eight orbiter (space shuttle) drag chute tests in 1990. In addition, the B-52 served as the air launch platform for the first six Pegasus space boosters. During its many years of service, the B-52 has undergone several modifications. The first major modification was made by North American Aviation (now part of Boeing) in support of the X-15 program. This involved creating a launch-panel-operator station for monitoring the status of the test vehicle being carried, cutting a large notch in the right inboard wing flap to accommodate the vertical tail of the X-15 aircraft, and installing a wing pylon that enables the B-52 to carry research vehicles and test articles to be air-launched/dropped. Located on the right wing, between the inboard engine pylon and the fuselage, this wing pylon was subjected to extensive testing prior to its use. For each test vehicle the B-52 carried, minor changes were made to the launch-panel operator's station. Built originally by the Boeing Company, the NASA B-52 is powered by eight Pratt & Whitney J57-19 turbojet engines, each of which produce 12,000 pounds of thrust. The aircraft's normal launch speed has been Mach 0.8 (about 530 miles per hour) and its normal drop altitude has been 40,000 to 45,000 feet. It is 156 feet long and has a wing span of 185 feet. The heaviest load it has carried was the No. 2 X-15 aircraft at 53,100 pounds. Project manager for the aircraft is Roy Bryant. - - - - - - - - - - - F-15A RPRV/SRV Project Description: In April of 1971, Assistant Secretary of the Air Force for Research and Development Grant Hanson sent a memorandum noting the comparatively small amount of research being conducted on stalls (losses of lift) and spins despite the yearly losses that they caused (especially of fighter aircraft). In the spring and summer of that year, NASA's Flight Research Center (redesignated in 1976 the Dryden Flight Research Center, Edwards, California) studied the feasibility of conducting flight research with a sub-scale fighter-type Remotely Piloted Research Vehicle (RPRV) in the stall-spin regime. In November, NASA Headquarters approved flight research for a 3/8-scale F-15 RPRV. It would measure aerodynamic derivatives of the aircraft throughout its angle-of-attack range and compare them with those from wind tunnels and full-scale flight. (Angle of attack refers to the angle of the wings or fuselage with respect to the prevailing wind.) The McDonnell Douglas Aircraft Co., builder of the full-size F-15, designed and constructed three 3/8-scale mostly fiberglass, unpowered F-15 RPRV's for a little more than $250,000 apiece (compared with $6.8 million for a full-size F-15). The FRC set up a dedicated RPRV control facility in a room on the first floor next to the hangar for the RPRV and set up a much more sophisticated control system than was used for an earlier RPRV--the Hyper III. The control facility featured a digital uplink capability, a ground computer, a television monitor, and a telemetry system. Launched from a B-52, the first F-15 RPRV flew its initial flight on October 12, 1973. The initial flights were recovered in mid-air by helicopters, but later flights employed horizontal landings by the remote research pilot, who 'flew' the aircraft from the RPRV control facility. Chosen because of the risks involved in spin testing a full-scale fighter aircraft, the remotely piloted research technique enabled the pilot to interact with the vehicle much as he did in normal flight. Flying remotely, however, called for some special techniques to make up for the cues available to a pilot in the airplane but not to a remote pilot. It also allowed the flight envelope to be expanded more rapidly than conventional flight research methods permitted for piloted vehicles. During its first 26 flights, through the end of 1975, flight research over an angle-of-attack range of minus 20 degrees to plus 53 degrees with the 3/8-scale vehicle in the basic F-15 configuration allowed FRC engineers to test the mathematical model of the aircraft in an angle-of-attack range not previously examined in flight research. The basic airplane configuration proved to be resistant to departure from straight and level flight, hence to spins; however, the vehicle could be flown into a spin using a technique developed in the simulator. Data obtained during the first 26 flights gave researchers a better understanding of the spin characteristics of the full-scale fighter. Researchers later obtained spin data with the vehicle in other configurations at angles of attack as large as minus 70 degrees and plus 88 degrees. There were 35 flights of the 3/8-scale F-15s by the end of 1978 and 52 flights by mid-July of 1981. These included some in which the vehicle--redesignated the Spin Research Vehicle after it was modified from the basic F-15 configuration--evaluated the effects of an elongated nose and a wind-tunnel-designed nose strake (among other modifications) on the airplane's stall/spin characteristics. Results of flight research with these modifications indicated that the addition of the nose strake increased the vehicle's resistance to departure from the intended flight path, especially entrance into a spin. Large differential tail deflections, a tail chute, and a nose chute all proved effective as spin recovery techniques, although it was essential to release the nose chute once it had deflated in order to prevent an inadvertent reentry into a spin. Overall, remote piloting with the 3/8-scale F-15 provided high-quality data about spin characteristics. The SRV was about 23 and one-half feet long and had a 16-foot wing span.

Aerodynamic performance of 0.4066-scale model of JT8D refan stage with S-duct inlet

NASA Technical Reports Server (NTRS)

Moore, R. D.; Kovich, G.; Lewis, G. W., Jr.

1977-01-01

A scale model of the JT8D refan stage was tested with a scale model of the S-duct inlet design for the refanned Boeing 727 center engine. Detailed survey data of pressures, temperatures, and flow angles were obtained over a range of flows at speeds from 70 to 97 percent of design speed. Two S-duct configurations were tested; one with a bellmouth inlet and the other with a flight lip inlet. The results indicated that the overall performance was essentially unaffected by the distortion generated by the S-duct inlet. The stall weight flow increased by less than 0.5 kg/sec (approximately 1.5% of design flow) with the S-duct inlet compared with that obtained with uniform flow. The detailed measurements indicated that the inlet guide vane (IGV) significantly reduced circumferential variations. For example, the flow angles ahead of the IGV were positive in the right half of the inlet and negative in the left half. Behind the IGV, the flow angles tended to be more uniform circumferentially.

Effects of bedding quality on lying behavior of dairy cows.

PubMed

Fregonesi, J A; Veira, D M; von Keyserlingk, M A G; Weary, D M

2007-12-01

Cows prefer to spend more time lying down in free stalls with more bedding, but no research to date has addressed the effects of bedding quality. Bedding in stalls often becomes wet either from exposure to the elements or from feces and urine. The aim of this study was to test the effect of wet bedding on stall preference and use. Four groups of 6 nonlactating Holstein cows were housed in free stalls bedded daily with approximately 0.1 m of fresh sawdust. Following a 5-d adaptation period, each group of cows was tested sequentially with access to stalls with either dry or wet sawdust bedding (86.4 +/- 2.1 vs. 26.5 +/- 2.1% dry matter), each for 2 d. These no-choice phases were followed by a 2-d free-choice phase during which cows had simultaneous access to stalls containing either wet or dry bedding. Stall usage was assessed by using 24-h video recordings scanned at 10-min intervals, and responses were analyzed by using a mixed model, with group (n = 4) as the observational unit. The minimum and maximum environmental temperatures during the experiment were 3.4 +/- 2.2 and 6.8 +/- 2.5 degrees C, respectively. When cows had access only to stalls with wet bedding, they spent 8.8 +/- 0.8 h/d lying down, which increased to 13.8 +/- 0.8 h/d when stalls with dry bedding were provided. Cows spent more time standing with their front 2 hooves in the stall when provided with wet vs. dry bedding (92 +/- 10 vs. 32 +/- 10 min/d). During the free-choice phase, all cows spent more time lying down in the dry stalls, spending 12.5 +/- 0.3 h/d in the dry stalls vs. 0.9 +/- 0.3 h/ d in stalls with wet bedding. In conclusion, dairy cows show a clear preference for a dry lying surface, and they spend much more time standing outside the stall when only wet bedding is available.

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

Efficient simulation of incompressible viscous flow over multi-element airfoils

NASA Technical Reports Server (NTRS)

Rogers, Stuart E.; Wiltberger, N. Lyn; Kwak, Dochan

1992-01-01

The incompressible, viscous, turbulent flow over single and multi-element airfoils is numerically simulated in an efficient manner by solving the incompressible Navier-Stokes equations. The computer code uses the method of pseudo-compressibility with an upwind-differencing scheme for the convective fluxes and an implicit line-relaxation solution algorithm. The motivation for this work includes interest in studying the high-lift take-off and landing configurations of various aircraft. In particular, accurate computation of lift and drag at various angles of attack, up to stall, is desired. Two different turbulence models are tested in computing the flow over an NACA 4412 airfoil; an accurate prediction of stall is obtained. The approach used for multi-element airfoils involves the use of multiple zones of structured grids fitted to each element. Two different approaches are compared: a patched system of grids, and an overlaid Chimera system of grids. Computational results are presented for two-element, three-element, and four-element airfoil configurations. Excellent agreement with experimental surface pressure coefficients is seen. The code converges in less than 200 iterations, requiring on the order of one minute of CPU time (on a CRAY YMP) per element in the airfoil configuration.

Efficient simulation of incompressible viscous flow over multi-element airfoils

NASA Technical Reports Server (NTRS)

Rogers, Stuart E.; Wiltberger, N. Lyn; Kwak, Dochan

1993-01-01

The incompressible, viscous, turbulent flow over single and multi-element airfoils is numerically simulated in an efficient manner by solving the incompressible Navier-Stokes equations. The solution algorithm employs the method of pseudo compressibility and utilizes an upwind differencing scheme for the convective fluxes, and an implicit line-relaxation scheme. The motivation for this work includes interest in studying high-lift take-off and landing configurations of various aircraft. In particular, accurate computation of lift and drag at various angles of attack up to stall is desired. Two different turbulence models are tested in computing the flow over an NACA 4412 airfoil; an accurate prediction of stall is obtained. The approach used for multi-element airfoils involves the use of multiple zones of structured grids fitted to each element. Two different approaches are compared; a patched system of grids, and an overlaid Chimera system of grids. Computational results are presented for two-element, three-element, and four-element airfoil configurations. Excellent agreement with experimental surface pressure coefficients is seen. The code converges in less than 200 iterations, requiring on the order of one minute of CPU time on a CRAY YMP per element in the airfoil configuration.

The tubercles on humpback whales' flippers: application of bio-inspired technology.

PubMed

Fish, Frank E; Weber, Paul W; Murray, Mark M; Howle, Laurens E

2011-07-01

The humpback whale (Megaptera novaeangliae) is exceptional among the large baleen whales in its ability to undertake aquabatic maneuvers to catch prey. Humpback whales utilize extremely mobile, wing-like flippers for banking and turning. Large rounded tubercles along the leading edge of the flipper are morphological structures that are unique in nature. The tubercles on the leading edge act as passive-flow control devices that improve performance and maneuverability of the flipper. Experimental analysis of finite wing models has demonstrated that the presence of tubercles produces a delay in the angle of attack until stall, thereby increasing maximum lift and decreasing drag. Possible fluid-dynamic mechanisms for improved performance include delay of stall through generation of a vortex and modification of the boundary layer, and increase in effective span by reduction of both spanwise flow and strength of the tip vortex. The tubercles provide a bio-inspired design that has commercial viability for wing-like structures. Control of passive flow has the advantages of eliminating complex, costly, high-maintenance, and heavy control mechanisms, while improving performance for lifting bodies in air and water. The tubercles on the leading edge can be applied to the design of watercraft, aircraft, ventilation fans, and windmills.

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.

76 FR 74649 - Harmonization of Various Airworthiness Standards for Transport Category Airplanes-Flight Rules

Federal Register 2010, 2011, 2012, 2013, 2014

2011-12-01

...-directional stability, speed increase and recovery characteristics, and the stall warning margin for the... which the onset of natural or artificial stall warning occurs. VSR reference stall speed. VSR1 reference.... Lastly, this rule adds a requirement that the non-icing stall warning requirements prescribing the speed...

Preliminary Tests of a Buffet Stall-Warning Device on a 1/5-Scale Model of the Republic XP-84 Airplane

NASA Technical Reports Server (NTRS)

Tucker, Warren A.; Comisarow, Paul

1946-01-01

During the first flight tests of the Republic XP-84 airplane it was discovered that there was a complete lack of stall warning. A short series of development tests of a suitable stall-warning device for the airplane was therefore made on a 1/5-scale model in the Langley 300 MPH 7- by 10-foot tunnel. Two similar stall-warning devices, each designed to produce early root stall which would provide a buffet warning, were tested. It appeared that either device would give a satisfactory buffet warning in the flap-up configuration, at the cost of an increase of 8 or 10 miles per hour in minimum speed. Although neither device seemed to give a true buffet warning in the flaps-down configuration, it appeared that either device would improve the flaps-down stalling characteristics by lessening the severity of the stall and by maintaining better control at the stall. The flaps-down minimum-speed increase caused by the devices was only 1 or 2 miles per hour.

An analysis on 45° sweep tail angle for blended wing body aircraft to the aerodynamics coefficients by wind tunnel experiment

NASA Astrophysics Data System (ADS)

Latif, M. Z. A. Abd; Ahmad, M. A.; Nasir, R. E. Mohd; Wisnoe, W.; Saad, M. R.

2017-12-01

This paper presents the analysis of a model from UiTM Blended Wing Body (BWB) UAV, Baseline V that has been tested at UPNM high speed wind tunnel. Baseline V has a unique design due to different NACA sections used for its fuselage, body, wing root, midwing, wingtip, tail root, tail tip and the tail is swept 45° backward. The purpose of this experiment is to study the aerodynamic characteristics when the tail sweeps 45° backward. The experiments are conducted several times using 71.5% scaled down model at about 49.58 m/s airspeed or 25 Hz. The tail angle deflection is fixed and set at zero angle. All the data obtained is analyzed and presented in terms of coefficient of lift, coefficient of drag and also lift-to-drag ratio, and is plotted against various angles of attack. The angles of attack used for this experiments are between -10° to +30°. The blockage correction such as solid blockage, wake blockage and streamline curvature blockage are calculated in order to obtain true performance of the aircraft. From the observation, Baseline V shows that the aircraft tends to stall at around +15°. The maximum L/D ratio achieved for Baseline V is 20.8, however it decreases slightly to 20.7 after blockage corrections.

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

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 and thrust vectoring, and airflow phenomena at high angles of attack. This understanding is expected to lead to design methods that can provide better maneuverability in future high performance aircraft and make them safer to fly. An international test organization of about 110 people, managed by the Advanced Research Projects Agency (ARPA), conducted the flight operations at NASA Dryden. The ARPA had requested flight research for the X-31 aircraft be moved there in February 1992. In addition to ARPA and NASA, the international test organization (ITO) included the U.S. Navy, the U.S. Air Force, Rockwell International, the Federal Republic of Germany, and Daimler-Benz Aerospace (formerly Messerschmitt-Bolkow-Blohm and Deutsche Aerospace). NASA was responsible for flight research operations, aircraft maintenance, and research engineering once the program moved to Dryden. The No. 1 X-31 aircraft was lost in an accident January 19, 1995. The pilot, Karl Heinz-Lang, of the Federal Republic of Germany, ejected safely before the aircraft crashed in an unpopulated desert area just north of Edwards. The X-31 program logged an X-plane record of 580 flights during the program, including 555 research missions and 21 in Europe for the 1995 Paris Air Show. A total of 14 pilots representing all agencies of the ITO flew the aircraft. This movie clip runs 1 minute, 6 seconds in length and shows the X-31 rotating at takeoff and climbing into a stall maneuver. The aircraft then slides backwards thrust vectoring the tail over the top, turning the stall into a loop in which the aircraft then reverses its heading and resumes level flight.

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.

Unsteady aerodynamic force mechanisms of a hoverfly hovering with a short stroke-amplitude

NASA Astrophysics Data System (ADS)

Zhu, Hao Jie; Sun, Mao

2017-08-01

Hovering insects require a rather large lift coefficient. Many insects hover with a large stroke amplitude (120°-170°), and it has been found that the high lift is mainly produced by the delayed-stall mechanism. However, some insects hover with a small stroke amplitude (e.g., 65°). The delayed-stall mechanism might not work for these insects because the wings travel only a very short distance in a stroke, and other aerodynamic mechanisms must be operating. Here we explore the aerodynamic mechanisms of a hoverfly hovering with an inclined stroke plane and a small stroke amplitude (65.6°). The Navier-Stokes equations are numerically solved to give the flows and forces and the theory of vorticity dynamics used to reveal the aerodynamic mechanisms. The majority of the weight-supporting vertical force is produced in the mid portion of the downstroke, a short period (about 26% of the stroke cycle) in which the vertical force coefficient is larger than 4. The force is produced using a new mechanism, the "paddling mechanism." During the short period, the wing moves rapidly downward and forward at a large angle of attack (about 48°), and strong counter clockwise vorticity is produced continuously at the trailing edge and clockwise vorticity at the leading edge, resulting in a large time rate of change in the first moment of vorticity, hence the large aerodynamic force. It is interesting to note that with the well known delayed stall mechanism, the force is produced by the relative motion of two vortices of opposite sign, while in the "paddling mechanism," it is produced by generating new vortices of opposite sign at different locations.

Contamination of the environment by strongylid (Nematoda: Strongylidae) infective larvae at horse farms of various types in Ukraine.

PubMed

Kuzmina, Tetiana A

2012-05-01

Analysis of the influence of horse-keeping conditions by contamination of the environment (pastures, paddocks, and stalls) by the strongylid infective larvae (L(3)) was carried out at various types of horse farms, hippodromes, and riding clubs in Ukraine. A total of 1,237 horses from three types of horse-keeping conditions were examined. Epidemiological studies of stall and grazing area (pasture and paddocks) contamination by L(3) were performed at hippodrome (stalled horse-keeping) and horse farms with stall/paddock-keeping and stall/pasture-keeping conditions. Grass and stall litter samples were examined by the Baermann procedure. It was found that horses of stall-keeping conditions had the lowest level of strongylid infection (prevalence 46.4-77.8%, average infection 25.6-92.9 eggs per gram of feces (EPG)) and lowest proportion of large strongyle L(3) in coprocultures (1.6-11.3%). Horses of stall/pasture-keeping conditions were the most infected (prevalence 95.1-100%, average infection 198.2-453.7 EPG), and the proportion of large strongyle L(3) was 17.3-24.7%. Strongyle L(3) were found in litter of all parts of individual stalls; areas at the stall center, "toilet", and entrance were the most contaminated. The highest L(3) number in stall litter was registered in summer. Contamination of permanent pasture grass by L(3) was notably lower than grass in paddocks (86.3-161.4 L(3)/kg compared with 305.9-409.1 L(3)/kg). The highest level of pasture grass contamination was observed in the middle of summer (July)--up 970.7 L(3)/kg. The results obtained confirmed importance of environmental contamination in epidemiology of horse strongylidosis at various types of horse-keeping conditions.

Effects of sand and straw bedding on the lying behavior, cleanliness, and hoof and hock injuries of dairy cows.

PubMed

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

2008-02-01

This experiment compared the effects of sand and straw bedding in free stalls on resting time, cleanliness, hock injuries, and hoof health of dairy cows and tested whether cow preferences for a bedding material depended on the familiarity with the material. A total of 52 dairy cows were kept either on straw bedded concrete stalls or sand stalls for at least 21 wk. The lying behavior was observed, and hock lesions, hoof health, and cleanliness of the cows and stalls were measured. A 5-d preference test between sand and straw stalls was conducted at the end of the experiment. The total daily duration of lying was longer for cows on straw bedding than on sand bedding (straw 749 +/- 16 vs. sand 678 +/- 19 min). During the preference test, cows that had been kept on straw bedding preferred lying in straw stalls [straw 218.7 (133.4 to 239.7) vs. sand 9.0 min (2.8 to 44.8)]; however, cows that had been kept on sand showed no preference [straw 101.3 (51.7 to 205.9) vs. sand 94.3 min (54.1 to 156.1, median and interquartile range)]. Although there were no differences in the dirtiness of stalls, the cows using straw stalls were dirtier than cows using sand stalls [straw 6.04 (5.39 to 6.28) vs. sand 4.19 (3.62 to 5.16)]. At the end of experiment the severity of hock lesions was lower for cows on sand than for cows on straw [sand 0.5 (0.0 to 1.0) vs. straw 1.0 (1.0 to 2.0)]. The improvement in overall hoof health over the observation period was greater for cows kept on sand compared with cows kept on straw [sand -2.00 (-3.75 to -0.25) vs. straw 0.00 (-2.00 to 2.00)]. Straw bedding increased the time that cows spend lying, and cows preferred straw stalls to sand stalls. However, previous experience with sand reduces avoidance of sand stalls. Sand stalls were advantageous for cow cleanliness and health; hock lesions and claw diseases healed more quickly for cows using sand stalls compared with straw.

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 found among sows in various stall environments may be partly attributed to the specific constraints of each stall system such as restricted stall space in CTL, insufficient floor space in the open-pen area of the FAS system, and gate design of the FLX (e.g., direction of bars and feeder space). These results also indicate that parity and gestational day are additional factors that may exacerbate the effects of restricted stall space or insufficient pen space, further compromising sow well-being.

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 conditions downstream. Such an approach is representative of modelling an engine.Using a 3D viscous time-accurate flow representation, the front bladerows of a core compressor were modelled in a whole-annulus fashion whereas the rest of bladerows are modelled in a single-passage fashion. The rotating stall behaviour at two different compressor operating points was studied by considering two different variable-vane scheduling conditions for which experimental data were available. Using a model with nine whole-assembly models, the unsteady-flow calculations were conducted on 32-CPUs of a parallel cluster, typical run times being around 3-4 weeks for a grid with about 60 million points. The simulations were conducted over several engine rotations. As observed on the actual development engine, there was no rotating stall for the first scheduling condition while mal-scheduling of the stator vanes created a 12-band rotating stall which excited the 1st flap mode.

Unsteady Separated Flows: Vorticity and Turbulence.

DTIC Science & Technology

1982-10-01

investigation. The vortex train used in the mathe- matical model is adapted to simulate the flow generated in the wake of an oscillating spoiler moving...weak wake structure. C H - At K = 1.5, the trailing edge vortex clearly leads the vorte : generated from the leading edge in the normal geonetry tests...flows is summarized. Specific projects reviewed include: (a) oscillating airfoil dynamic stall; (b) vortex entrapment and stability analysis -and (c

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...

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...

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

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.

Novel Design for a Wind Tunnel Vertical Gust Generator

NASA Astrophysics Data System (ADS)

Smith, Zachary; Jones, Anya; Hrynuk, John

2017-11-01

Gust response of MAVs is a fundamental problem for flight stability and control of such aircraft. Current knowledge about the gust response of these vehicles is limited and gust interaction often results in damage to vehicles. Studying isolated gust effects on simple airfoil models in a controlled environment is a necessity for the further development of MAV control laws. Gusts have typically been generated by oscillating an airfoil causing the shedding of vortices to propagate through the system. While effective, this method provides only a transient up and downdraft behavior with small changes in angle of attack, not suitable for studying MAV scale gust interactions. To study these interactions, a gust that creates a change in flow angle larger than the static stall angle of typical airfoils was developed. This work was done in a low speed, low turbulence wind tunnel at base operating speed of 1.5 m/s, generating a Reynolds number of 12,000 on a NACA 0012 wing. It describes the fundamental mechanisms of how this gust was generated and the results obtained from the gust generator. The gust, which can alter the flow field in less than 1 second, was characterized using PIV and the interactions with a stationary airfoil at several angles of attack are evaluated.

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.

In Situ Distribution Guided Analysis and Visualization of Transonic Jet Engine Simulations.

PubMed

Dutta, Soumya; Chen, Chun-Ming; Heinlein, Gregory; Shen, Han-Wei; Chen, Jen-Ping

2017-01-01

Study of flow instability in turbine engine compressors is crucial to understand the inception and evolution of engine stall. Aerodynamics experts have been working on detecting the early signs of stall in order to devise novel stall suppression technologies. A state-of-the-art Navier-Stokes based, time-accurate computational fluid dynamics simulator, TURBO, has been developed in NASA to enhance the understanding of flow phenomena undergoing rotating stall. Despite the proven high modeling accuracy of TURBO, the excessive simulation data prohibits post-hoc analysis in both storage and I/O time. To address these issues and allow the expert to perform scalable stall analysis, we have designed an in situ distribution guided stall analysis technique. Our method summarizes statistics of important properties of the simulation data in situ using a probabilistic data modeling scheme. This data summarization enables statistical anomaly detection for flow instability in post analysis, which reveals the spatiotemporal trends of rotating stall for the expert to conceive new hypotheses. Furthermore, the verification of the hypotheses and exploratory visualization using the summarized data are realized using probabilistic visualization techniques such as uncertain isocontouring. Positive feedback from the domain scientist has indicated the efficacy of our system in exploratory stall analysis.

A steadying effect of acoustic excitation on transitory stall

NASA Technical Reports Server (NTRS)

Zaman, K. B. M. Q.

1991-01-01

The effect of acoustic excitation on a class of separated flows with a transitional boundary layer at the point of separation is considered. Experimental results on the flow over airfoils, a two-dimensional backward-facing step, and through large angle conical diffusers are presented. In all cases, the separated flow undergoes large amplitude fluctuations, much of the energy being concentrated at unusually low frequencies. In each case, an appropriate high frequency acoustic excitation is found to be effective in reducing the fluctuations substantially. The effective excitation frequency scales on the initial boundary layer thickness and the effect is apparently achieved through acoustic tripping of the separating boundary layer.

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.

Review of the physics of enhancing vortex lift by unsteady excitation

NASA Technical Reports Server (NTRS)

Wu, J. Z.; Vakili, A. D.; Wu, J. M.

1991-01-01

A review aimed at providing a physical understanding of the crucial mechanisms for obtaining super lift by means of unsteady excitations is presented. Particular attention is given to physical problems, including rolled-up vortex layer instability and receptivity, wave-vortex interaction and resonance, nonlinear streaming, instability of vortices behind bluff bodies and their shedding, and vortex breakdown. A general theoretical framework suitable for handling the unsteady vortex flows is introduced. It is suggested that wings with swept and sharp leading edges, equipped with devices for unsteady excitations, could yield the first breakthrough of the unsteady separation barrier and provide super lift at post-stall angle of attack.

Flight test results for several light, canard-configured airplanes

NASA Technical Reports Server (NTRS)

Brown, Philip W.

1987-01-01

Brief flight evaluations of two different, light, composite constructed, canard and winglet configured airplanes were performed to assess their handling qualities; one airplane was a single engine, pusher design and the other a twin engine, push-pull configuration. An emphasis was placed on the slow speed/high angle of attack region for both airplanes and on the engine-out regime for the twin. Mission suitability assessment included cockpit and control layout, ground and airborne handling qualities, and turbulence response. Very limited performance data was taken. Stall/spin tests and the effects of laminar flow loss on performance and handling qualities were assessed on an extended range, single engine pusher design.

Effect of Reynolds number and engine nacelles on the stalling characteristics of a model of a twin-engine light airplane

NASA Technical Reports Server (NTRS)

Lockwood, V. E.

1972-01-01

The investigation was made on a 1/18-scale model of a twin-engine light airplane. Static longitudinal, lateral, and directional characteristics were obtained at 0 deg and plus or minus 5 deg sideslip at a Mach number of about 0.2. The angle of attack varied from about 20 deg at a Reynolds number of 0.39 times one million to 13 deg at a Reynolds number of 3.7 times one million, based on the reference chord. The effect of fixed transition, vertical and horizontal tails, and nacelle fillets was studied.

Simulation of Flow Control Using Deformable Surfaces

NASA Technical Reports Server (NTRS)

Truman, C. Randall

2001-01-01

The goal of this investigation is to numerically simulate the effects of oscillatory actuators placed on the leading edge of an airfoil, and to quantify the effects of oscillatory blowing on an airfoil stall behavior. It has been demonstrated experimentally that periodic blowing can delay flow separation at high angle of attack. The computations are to be performed for a TAU 0015 airfoil at a high Reynolds number of approx. 1 x 10(exp 6) with turbulent flow conditions. The two-equation Wilcox k - w turbulence model has been shown to provide reliable descriptions of transition and turbulence at high Reynolds numbers. The results are to be compared to Seifert's experimental data.

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.

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 flow are superimposed on the steady operating characteristic. The total injected mass flow was equal to 1.3 percent of the compressor flow. The solid line with no solid squares on it denotes the operating point during the beginning of throttle closure and the initial drop into stall. The gray traces denote the operating point during an additional throttle closure that occurred over the next 1200 rotor revolutions (4 sec). The dashed line denotes the recovery from stall that occurred during 90 rotor revolutions (0.3 sec) after the injectors were activated with no change in throttle setting. Tip injection not only recovers the compressor from stall, but also restores the compressor to its pre-stall level of pressure rise. In contrast, standard stall recovery schemes such as compressor bleed, stator vane actuation, or engine throttle modulation result in a loss of pressure rise across the compressor, which results in a loss of engine power.

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.

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.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yin Yunpeng; Sawin, Herbert H.

The surface roughness evolutions of single crystal silicon, thermal silicon dioxide (SiO{sub 2}), and low dielectric constant film coral in argon plasma have been measured by atomic force microscopy as a function of ion bombardment energy, ion impingement angle, and etching time in an inductively coupled plasma beam chamber, in which the plasma chemistry, ion energy, ion flux, and ion incident angle can be adjusted independently. The sputtering yield (or etching rate) scales linearly with the square root of ion energy at normal impingement angle; additionally, the angular dependence of the etching yield of all films in argon plasma followedmore » the typical sputtering yield curve, with a maximum around 60 deg. -70 deg. off-normal angle. All films stayed smooth after etching at normal angle but typically became rougher at grazing angles. In particular, at grazing angles the rms roughness level of all films increased if more material was removed; additionally, the striation structure formed at grazing angles can be either parallel or transverse to the beam impingement direction, which depends on the off-normal angle. More interestingly, the sputtering caused roughness evolution at different off-normal angles can be qualitatively explained by the corresponding angular dependent etching yield curve. In addition, the roughening at grazing angles is a strong function of the type of surface; specifically, coral suffers greater roughening compared to thermal silicon dioxide.« less

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.

Short communication: Bacterial counts in recycled manure solids bedding replaced daily or deep packed in freestalls.

PubMed

Sorter, D E; Kester, H J; Hogan, J S

2014-05-01

An experiment was conducted to compare bacterial counts of mastitis pathogens in deep-packed manure solids bedding with those in manure solids bedding replaced daily from mattresses. Eighteen Holstein cows were housed in 1 pen with 18 stalls. One row of 9 stalls was equipped with mattresses topped with bedding. The back one-third of these stalls toward the alleyway was covered in 25 mm of recycled manure solids, which was removed daily for the next 6 d and replaced with bedding from the brisket board and lunge space areas of stalls. The second row of 9 stalls was bedded for 3 wk with 100 to 150 mm of deep-pack recycled manure bedding from which only fecal matter was removed daily. After 3 wk, bedding treatments were changed between rows in a switchback design. Mean total gram-negative bacterial counts did not differ between treatments throughout the experiment. Coliform and Klebsiella spp. bacterial counts were lower in daily replaced bedding compared with deep pack across the experiment and on each of d 0, 1, 2, and 6. Streptococcal counts were reduced in daily replacement stalls compared with deep-pack stalls on d 0 and greater in daily replacement stalls compared with deep-pack stalls on d 1, 2, and 6. Daily replacement of recycled manure bedding from the back one-third of the stalls appeared to be an effective approach to reducing exposure to coliforms, specifically Klebsiella, but not streptococci. However, bacterial counts in bedding from both treatments were elevated throughout the trial and resulted in considerable risk for exposure to teats and development of intramammary infections. Copyright © 2014 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

Free-to-Roll Testing of Airplane Models in Wind Tunnels

NASA Technical Reports Server (NTRS)

Capone, Francis J.; Owens, D. Bruce; Hall, Robert M.

2007-01-01

A free-to-roll (FTR) test technique and test rig make it possible to evaluate both the transonic performance and the wingdrop/ rock behavior of a high-strength airplane model in a single wind-tunnel entry. The free-to-roll test technique is a single degree-of-motion method in which the model is free to roll about the longitudinal axis. The rolling motion is observed, recorded, and analyzed to gain insight into wing-drop/rock behavior. Wing-drop/rock is one of several phenomena symptomatic of abrupt wing stall. FTR testing was developed as part of the NASA/Navy Abrupt Wing Stall Program, which was established for the purposes of understanding and preventing significant unexpected and uncommanded (thus, highly undesirable) lateral-directional motions associated with wing-drop/rock, which have been observed mostly in fighter airplanes under high-subsonic and transonic maneuvering conditions. Before FTR testing became available, wingrock/ drop behavior of high-performance airplanes undergoing development was not recognized until flight testing. FTR testing is a reliable means of detecting, and evaluating design modifications for reducing or preventing, very complex abrupt wing stall phenomena in a ground facility prior to flight testing. The FTR test rig was designed to replace an older sting attachment butt, such that a model with its force balance and support sting could freely rotate about the longitudinal axis. The rig (see figure) includes a rotary head supported in a stationary head with a forward spherical roller bearing and an aft needle bearing. Rotation is amplified by a set of gears and measured by a shaft-angle resolver; the roll angle can be resolved to within 0.067 degrees at a rotational speed up to 1,000 degrees/s. An assembly of electrically actuated brakes between the rotary and stationary heads can be used to hold the model against a rolling torque at a commanded roll angle. When static testing is required, a locking bar is used to fix the rotating head rigidly to the stationary head. Switching between the static and FTR test modes takes only about 30 minutes. The FTR test rig was originally mounted in a 16-ft (approximately 4.0-m) transonic wind tunnel, but could just as well be adapted to use in any large wind tunnel. In one series of tests on the FTR rig, static and dynamic characteristics of models of four different fighter airplanes were measured. Two of the models exhibited uncommanded lateral motions; the other two did not. A figure of merit was developed to discern the severity of lateral motions. Using this figure of merit, it was shown that the FTR test technique enabled identification of conditions under which the uncommanded lateral motions occurred. The wind-tunnel conditions thus identified were found to be correlated with flight conditions under which the corresponding full-size airplanes exhibited uncommanded lateral motions.

Suppression of the alternative lengthening of telomere pathway by the chromatin remodelling factor ATRX

PubMed Central

Clynes, David; Jelinska, Clare; Xella, Barbara; Ayyub, Helena; Scott, Caroline; Mitson, Matthew; Taylor, Stephen; Higgs, Douglas R.; Gibbons, Richard J.

2015-01-01

Fifteen per cent of cancers maintain telomere length independently of telomerase by the homologous recombination (HR)-associated alternative lengthening of telomeres (ALT) pathway. A unifying feature of these tumours are mutations in ATRX. Here we show that expression of ectopic ATRX triggers a suppression of the pathway and telomere shortening. Importantly ATRX-mediated ALT suppression is dependent on the histone chaperone DAXX. Re-expression of ATRX is associated with a reduction in replication fork stalling, a known trigger for HR and loss of MRN from telomeres. A G-quadruplex stabilizer partially reverses the effect of ATRX, inferring ATRX may normally facilitate replication through these sequences that, if they persist, promote ALT. We propose that defective telomere chromatinization through loss of ATRX promotes the persistence of aberrant DNA secondary structures, which in turn present a barrier to DNA replication, leading to replication fork stalling, collapse, HR and subsequent recombination-mediated telomere synthesis in ALT cancers. PMID:26143912

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.

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.

Two-stage fan. 2: Data and performance with redesigned second stage rotor uniform and distorted inlet flows

NASA Technical Reports Server (NTRS)

Messenger, H. E.; Keenan, M. J.

1974-01-01

A two-stage fan with a first rotor tip speed of 1450 ft/sec (441.96 m/sec) and no inlet guide vanes was tested with uniform and distorted inlet flows, with a redesigned second rotor having a part span shroud to prevent flutter, with variable-stagger stators set in nominal positions, and without rotor casing treatment. The fan achieved a pressure ratio 2.8 at a corrected flow of 185.4 lbm/sec (84.0 kg/sec), an adiabatic efficiency of 85.0 percent, and a stall margin of 12 percent. The redesigned second rotor did not flutter. Tip radial distortion reduced the stall margin at intermediate speed, but had little effect on stall margin at high or low speeds. Hub radial distortion reduced the stall margin at design speed but increased stall margin at low speed. Circumferential distortion reduced stall pressure ratio and flow to give approximately the same stall lines with uniform inlet flow. Distortions were attenuated by the fan. For Vol. 1, see N74-11421.

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.

Dynamic stability test results on an 0.024 scale B-1 air vehicle

NASA Technical Reports Server (NTRS)

Beeman, R. R.

1972-01-01

Dynamic longitudinal and lateral-directional stability characteristics of the B-1 air vehicle were investigated in three wind tunnels at the Langley Research Center. The main rotary derivatives were obtained for an angle of attack range of -3 degrees to +16 degrees for a Mach number range of 0.2 to 2.16. Damping in roll data could not be obtained at the supersonic Mach numbers. The Langley 7 x 10 foot high speed tunnel, the 8 foot transonic pressure tunnel, and the 4 foot Unitary Plan wind tunnel were the test sites. An 0.024 scale light-weight model was used on a forced oscillation type balance. Test Reynolds number varied from 474,000/ft to 1,550,000/ft. through the Mach number range tested. The results showed that the dynamic stability characteristics of the model in pitch and roll were generally satisfactory up to an angle attack of about +6 degrees. In the wing sweep range from 15 to 25 degrees the positive damping levels in roll deteriorated rapidly above +2 degrees angle of attack. This reduction in roll damping is believed to be due to the onset of separation over the wing as stall is approached.

Evaluation of the Normal Cochlear Second Interscalar Ridge Angle and Depth on 3D T2-Weighted Images: A Tool for the Diagnosis of Scala Communis and Incomplete Partition Type II.

PubMed

Booth, T N; Wick, C; Clarke, R; Kutz, J W; Medina, M; Gorsage, D; Xi, Y; Isaacson, B

2018-05-01

Cochlear malformations may be be subtle on imaging studies. The purpose of this study was to evaluate the angle and depth of the lateral second interscalar ridge or notch in ears without sensorineural hearing loss (normal ears) and compare them with ears that have a documented incomplete type II partition malformation. The second interscalar ridge notch angle and depth were measured on MR imaging in normal ears by a single experienced neuroradiologist. The images of normal and incomplete partition II malformation ears were then randomly mixed for 2 novice evaluators to measure both the second interscalar ridge notch angle and depth in a blinded manner. For the mixed group, interobserver agreement was calculated, normal and abnormal ear measurements were compared, and receiver operating characteristic curves were generated. The 94 normal ears had a mean second interscalar ridge angle of 80.86° ± 11.4° and depth of 0.54 ± 0.14 mm with the 98th percentile for an angle of 101° and a depth of 0.3 mm. In the mixed group, agreement between the 2 readers was excellent, with significant differences for angle and depth found between normal and incomplete partition type II ears for angle and depth on average ( P < .001). Receiver operating characteristic cutoffs for delineating normal from abnormal ears were similar for both readers (depth, 0.31/0.34 mm; angle, 114°/104°). A measured angle of >114° and a depth of the second interscalar ridge notch of ≤0.31 mm suggest the diagnosis of incomplete partition type II malformation and scala communis. These measurements can be accurately made by novice readers. © 2018 by American Journal of Neuroradiology.

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.

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

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.

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.

Nonlinear control of rotating stall and surge with axisymmetric bleed and air injection on axial flow compressors

NASA Astrophysics Data System (ADS)

Yeung, Chung-Hei (Simon)

The study of compressor instabilities in gas turbine engines has received much attention in recent years. In particular, rotating stall and surge are major causes of problems ranging from component stress and lifespan reduction to engine explosion. In this thesis, modeling and control of rotating stall and surge using bleed valve and air injection is studied and validated on a low speed, single stage, axial compressor at Caltech. Bleed valve control of stall is achieved only when the compressor characteristic is actuated, due to the fast growth rate of the stall cell compared to the rate limit of the valve. Furthermore, experimental results show that the actuator rate requirement for stall control is reduced by a factor of fourteen via compressor characteristic actuation. Analytical expressions based on low order models (2--3 states) and a high fidelity simulation (37 states) tool are developed to estimate the minimum rate requirement of a bleed valve for control of stall. A comparison of the tools to experiments show a good qualitative agreement, with increasing quantitative accuracy as the complexity of the underlying model increases. Air injection control of stall and surge is also investigated. Simultaneous control of stall and surge is achieved using axisymmetric air injection. Three cases with different injector back pressure are studied. Surge control via binary air injection is achieved in all three cases. Simultaneous stall and surge control is achieved for two of the cases, but is not achieved for the lowest authority case. This is consistent with previous results for control of stall with axisymmetric air injection without a plenum attached. Non-axisymmetric air injection control of stall and surge is also studied. Three existing control algorithms found in literature are modeled and analyzed. A three-state model is obtained for each algorithm. For two cases, conditions for linear stability and bifurcation criticality on control of rotating stall are derived and expressed in terms of implementation-oriented variables such as number of injectors. For the third case, bifurcation criticality conditions are not obtained due to complexity, though linear stability property is derived. A theoretical comparison between the three algorithms is made, via the use of low-order models, to investigate pros and cons of the algorithms in the context of operability. The effects of static distortion on the compressor facility at Caltech is characterized experimentally. Results consistent with literature are obtained. Simulations via a high fidelity model (34 states) are also performed and show good qualitative as well as quantitative agreement to experiments. A non-axisymmetric pulsed air injection controller for stall is shown to be robust to static distortion.

Effect of stall design on dairy calf transition to voluntary feeding on an automatic milk feeder after introduction to group housing.

PubMed

Wilson, Tanya R; LeBlanc, Stephen J; DeVries, Trevor J; Haley, Derek B

2018-06-01

Automatic milk feeders (AMF) for young dairy calves are widely used in the dairy industry. These feeders are thought to have benefits for calf health and welfare and may reduce labor required for feeding; however, little is known about how calves adapt to feeding with AMF. The objective of this study was to observe the effects of feeding stall design on calves learning to use the AMF. The hypothesis was that solid side stalls, compared with steel bar stalls, would result in a longer latency to approach and feed from the AMF without assistance. A total of 147 Holstein calves (80 male and 67 female) were enrolled at 4 d of age, introduced to a group pen, and, at the same time, trained on an AMF. For training, calves were allowed to suck on the trainer's fingers and guided to the teat. Calves were allocated to 1 of 2 stall designs at the pen level, depending on which treatment cohort they were born into, either with steel bar stall walls (n = 46 male, 34 female calves) or with solid side stall walls (n = 34 male, 33 female calves). For 72 h after introductory training on the AMF, data from the feeders were collected and calf behavior was monitored by video. Outcomes measured included latency to first voluntary visit to the feeder and to first feeding, time spent in the feeder, amount of milk consumed over 72 h, number of retraining sessions required (retrained if <2 L was consumed every 12 h), and exploratory behavior, such as sniffing and licking of the feeder. Data were analyzed using mixed effects linear regression models or a Poisson model for the outcome of retraining. For certain outcomes the effects of stall design interacted with difficulty of training (willingness to enter feeder and drink); for the 38% of calves that were scored as moderately difficult to train on a scale of easy, moderate, or difficult, treatment (stall design) differences were detected. These calves took 2× longer to lick or bite toward the nipple, 2× longer to first voluntarily feeding, and consumed less milk over 72 h following training when trained on the steel bar stall design. These results suggest simple features of a stall may influence how quickly calves learn to use an AMF, but that the influence of stall wall design was affected by how easy calves were to train on the feeder upon initial introduction, which may depend in part on certain aspects of calf temperament. For many calves, solid side stalls at an AMF resulted faster in adaption than the steel bar stalls. Copyright © 2018 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

Does the optimal position of the acetabular fragment should be within the radiological normal range for all developmental dysplasia of the hip? A patient-specific finite element analysis.

PubMed

Wang, Xuyi; Peng, Jianping; Li, De; Zhang, Linlin; Wang, Hui; Jiang, Leisheng; Chen, Xiaodong

2016-10-04

The success of Bernese periacetabular osteotomy depends significantly on how extent the acetabular fragment can be corrected to its optimal position. This study was undertaken to investigate whether correcting the acetabular fragment into the so-called radiological "normal" range is the best choice for all developmental dysplasia of the hip with different severities of dysplasia from the biomechanical view? If not, is there any correlation between the biomechanically optimal position of the acetabular fragment and the severity of dysplasia? Four finite element models with different severities of dysplasia were developed. The virtual periacetabular osteotomy was performed with the acetabular fragment rotated anterolaterally to incremental center-edge angles; then, the contact area and pressure and von Mises stress in the cartilage were calculated at different correction angles. The optimal position of the acetabular fragment for patients 1, 2, and 3 was when the acetabular fragment rotated 17° laterally (with the lateral center-edge angle of 36° and anterior center-edge angle of 58°; both were slightly larger than the "normal" range), 25° laterally following further 5° anterior rotation (with the lateral center-edge angle of 31° and anterior center-edge angle of 51°; both were within the "normal" range), and 30° laterally following further 10° anterior rotation (with the lateral center-edge angle of 25° and anterior center-edge angle of 40°; both were less than the "normal" range), respectively. The optimal corrective position of the acetabular fragment is severity dependent rather than within the radiological "normal" range for developmental dysplasia of the hip. We prudently proposed that the optimal correction center-edge angle of mild, moderate, and severe developmental dysplasia of the hip is slightly larger than the "normal" range, within the "normal" range, and less than the lower limit of the "normal" range, respectively.

Three-Dimensional Effects in Multi-Element High Lift Computations

NASA Technical Reports Server (NTRS)

Rumsey, Christopher L.; LeeReusch, Elizabeth M.; Watson, Ralph D.

2003-01-01

In an effort to discover the causes for disagreement between previous two-dimensional (2-D) computations and nominally 2-D experiment for flow over the three-element McDonnell Douglas 30P-30N airfoil configuration at high lift, a combined experimental/CFD investigation is described. The experiment explores several different side-wall boundary layer control venting patterns, documents venting mass flow rates, and looks at corner surface flow patterns. The experimental angle of attack at maximum lift is found to be sensitive to the side-wall venting pattern: a particular pattern increases the angle of attack at maximum lift by at least 2 deg. A significant amount of spanwise pressure variation is present at angles of attack near maximum lift. A CFD study using three-dimensional (3-D) structured-grid computations, which includes the modeling of side-wall venting, is employed to investigate 3-D effects on the flow. Side-wall suction strength is found to affect the angle at which maximum lift is predicted. Maximum lift in the CFD is shown to be limited by the growth of an off-body corner flow vortex and consequent increase in spanwise pressure variation and decrease in circulation. The 3-D computations with and without wall venting predict similar trends to experiment at low angles of attack, but either stall too early or else overpredict lift levels near maximum lift by as much as 5%. Unstructured-grid computations demonstrate that mounting brackets lower the lift levels near maximum lift conditions.

Three-Dimensional Effects on Multi-Element High Lift Computations

NASA Technical Reports Server (NTRS)

Rumsey, Christopher L.; Lee-Rausch, Elizabeth M.; Watson, Ralph D.

2002-01-01

In an effort to discover the causes for disagreement between previous 2-D computations and nominally 2-D experiment for flow over the 3-clement McDonnell Douglas 30P-30N airfoil configuration at high lift, a combined experimental/CFD investigation is described. The experiment explores several different side-wall boundary layer control venting patterns, document's venting mass flow rates, and looks at corner surface flow patterns. The experimental angle of attack at maximum lift is found to be sensitive to the side wall venting pattern: a particular pattern increases the angle of attack at maximum lift by at least 2 deg. A significant amount of spanwise pressure variation is present at angles of attack near maximum lift. A CFD study using 3-D structured-grid computations, which includes the modeling of side-wall venting, is employed to investigate 3-D effects of the flow. Side-wall suction strength is found to affect the angle at which maximum lift is predicted. Maximum lift in the CFD is shown to be limited by the growth of all off-body corner flow vortex and consequent increase in spanwise pressure variation and decrease in circulation. The 3-D computations with and without wall venting predict similar trends to experiment at low angles of attack, but either stall too earl or else overpredict lift levels near maximum lift by as much as 5%. Unstructured-grid computations demonstrate that mounting brackets lower die the levels near maximum lift conditions.

CFD Computations for a Generic High-Lift Configuration Using TetrUSS

NASA Technical Reports Server (NTRS)

Pandya, Mohagna J.; Abdol-Hamid, Khaled S.; Parlette, Edward B.

2011-01-01

Assessment of the accuracy of computational results for a generic high-lift trapezoidal wing with a single slotted flap and slat is presented. The paper is closely aligned with the focus of the 1st AIAA CFD High Lift Prediction Workshop (HiLiftPW-1) which was to assess the accuracy of CFD methods for multi-element high-lift configurations. The unstructured grid Reynolds-Averaged Navier-Stokes solver TetrUSS/USM3D is used for the computational results. USM3D results are obtained assuming fully turbulent flow using the Spalart-Allmaras (SA) and Shear Stress Transport (SST) turbulence models. Computed solutions have been obtained at seven different angles-of-attack ranging from 6 -37 . Three grids providing progressively higher grid resolution are used to quantify the effect of grid resolution on the lift, drag, pitching moment, surface pressure and stall angle. SA results, as compared to SST results, exhibit better agreement with the measured data. However, both turbulence models under-predict upper surface pressures near the wing tip region.

Tests of a 1/7-Scale Semispan Model of the XB-35 Airplane in the Langley 19-Foot Pressure Tunnel

NASA Technical Reports Server (NTRS)

Teplitz, Jerome; Kayten, Gerald G.; Cancro, Patrick A.

1946-01-01

A 1/7 scale semispan model of the XB-35 airplane was tested in the Langley 10 foot pressure tunnel, primarily for the purpose of investigating the effectiveness of a leading-edge slot for alleviation of stick-fixed longitudinal instability at high angles of attack caused by early tip stalling and a device for relief of stick-free instability caused by elevon up-floating tendencies at high angles of attack. Results indicated that the slot was not adequate to provide the desired improvement in stick-fixed stability. The tab-flipper device provided improvement in stick-free stability abd two of the linkage combinations tested gave satisfactory variations of control force with airspeed for all conditions except that in which the wing-tip "pitch-control" flap was fully deflected. However, the improvement in control force characteristics was accompanied by a detrimental effect on stick-fixed stability because of the pitching moments produced by the elevon tab deflection.

Low-speed wind-tunnel test of a STOL supersonic-cruise fighter concept

NASA Technical Reports Server (NTRS)

Coe, Paul L., Jr.; Riley, Donald R.

1988-01-01

A wind-tunnel investigation was conducted to examine the low-speed static stability and control characteristics of a 0.10 scale model of a STOL supersonic cruise fighter concept. The concept, referred to as a twin boom fighter, was designed as a STOL aircraft capable of efficient long range supersonic cruise. The configuration name is derived from the long twin booms extending aft of the engine to the twin vertical tails which support a high center horizontal tail. The propulsion system features a two dimensional thrust vectoring exhaust nozzle which is located so that the nozzle hinge line is near the aircraft center of gravity. This arrangement is intended to allow large thrust vector angles to be used to obtain significant values of powered lift, while minimizing pitching moment trim changes. Low speed stability and control information was obtained over an angle of attack range including the stall. A study of jet induced power effects was included.

Modification of the wake behind a bat ear with and without tubercles

NASA Astrophysics Data System (ADS)

Petrin, Christopher; Elbing, Brian

2015-11-01

The Mexican Free-Tailed Bat (Tadarida brasiliensis) is a highly aerobatic bat, known to dive from altitudes of several thousand feet into their home caves, reaching estimated speeds of 27 m/s (Davis et al., Ecological Monographs, 32, 1962). A series of small tubercles have been observed on the leading edge of the bat's ear, which mimic the pattern of tubercles found on the fins of the humpback whale (Megaptera novaeangliae). The tubercles on the whale fins have been proven to delay stall on the fin and allow the whale to retain better control during dives. The goal of the current study is to assess whether the bat ear tubercles fulfill a similar purpose of improving flow control, particularly at high angles of attack. This was accomplished by acquiring PIV measurements of the bat ear wake with and without the tubercles. The velocity profiles were used to assess the drag and lift as a function of angle of attack. These results will be presented and the impact of the tubercles assessed.

Suppression of Dynamic Stall by Steady and Pulsed Upper-Surface Blowing

NASA Technical Reports Server (NTRS)

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

1996-01-01

The Boeing-Vertol VR-7 airfoil was experimentally studied with steady and pulsed upper-surface blowing for sinusoidal pitching oscillations described by alpha = alpha(sub m) + 10 deg sin(omega t). The tests were conducted in the U.S. Army Aeroflightdynamics Directorate's Water Tunnel at NASA Ames Research Center. The experiment was performed at a Reynolds number of 100,000. Pitch oscillations with alpha(sub m) = 10 deg and 15 deg and with reduced frequencies ranging from k = 0.005 to 0.15 were examined. Blowing conditions ranged from C(sub mu) = 0.03 to 0.66 and F(+) = 0 to 3. Unsteady lift, drag, and pitching-moment loads were measured, and fluorescent-dye flow visualizations were obtained. Steady, upper-surface blowing was found to be capable of trapping a separation bubble near the leading edge during a portion of the airfoil's upward rotation. When this occurred, the lift was increased significantly and stall was averted. In all cases, steady blowing reduced the hysteresis amplitudes present in the loads and produced a large thrust force. The benefits of steady blowing diminished as the reduced frequency and mean angle of oscillation increased. Pulsed blowing showed only marginal benefits for the conditions tested. The greatest gains from pulsed blowing were achieved at F(+) = 0.9.

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.

Cyclogiro windmill

DOEpatents

Brulle, R.V.

1981-09-03

A cyclogiro windmill has a rotor provided with blades shaped in the configuration of symmetrical airfoils and actuators to pivot the blades about axes parallel to the axis of rotation for the rotor. The actuator for each blade constantly changes the rock angle for the blade, that is its angle with respect to a reference on the rotor, and this modulation is such that the blade in making a revolution around the axis of rotation for the rotor undergoes an interval of static operation wherein its angle of attack is for the most part constant and less than the static stall angle, a short interval where the blade flips to position in which its opposite surface is presented toward the free wind, a short interval of dynamic operation wherein the angle of attack exceeds the static stal angle, another interval of static operation at an angle of attack of essentially the same magnitude as before, another interval of blade flip, and another interval of dynamic operation. During the intervals of dynamic operation, the blades experience a significant increase in lift force without a corresponding increase in drag, so that a high lift-to-drag ratio develops. The blades during dynamic operation further develop strong vortices which are directed outwardly at the sides of the windmill stream tube, and this increases the width of the stream tube, causing a greater mass of air to flow through the rotor. The short intervals of operation under dynamic conditions enable the blades to extract more energy from the free wind than would be possible if the blade operated solely under static conditions, and this in turn renders the windmill more useful in moderate velocity winds as well as high velocity winds.

Cyclogiro windmill

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brulle, R.V.

1981-09-03

A cyclogiro windmill has a rotor provided with blades shaped in the configuration of symmetrical airfoils and actuators to pivot the blades about axes parallel to the axis of rotation for the rotor. The actuator for each blade constantly changes the rock angle for the blade, that is its angle with respect to a reference on the rotor, and this modulation is such that the blade in making a revolution around the axis of rotation for the rotor undergoes an interval of static operation wherein its angle of attack is for the most part constant and less than the staticmore » stall angle, a short interval where the blade flips to position in which its opposite surface is presented toward the free wind, a short interval of dynamic operation wherein the angle of attack exceeds the static stal angle, another interval of static operation at an angle of attack of essentially the same magnitude as before, another interval of blade flip, and another interval of dynamic operation. During the intervals of dynamic operation, the blades experience a significant increase in lift force without a corresponding increase in drag, so that a high lift-to-drag ratio develops. The blades during dynamic operation further develop strong vortices which are directed outwardly at the sides of the windmill stream tube, and this increases the width of the stream tube, causing a greater mass of air to flow through the rotor. The short intervals of operation under dynamic conditions enable the blades to extract more energy from the free wind than would be possible if the blade operated solely under static conditions, and this in turn renders the windmill more useful in moderate velocity winds as well as high velocity winds.« less

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 ...

Effect of timing of relocation of replacement gilts from group pens to individual stalls before breeding on fertility and well-being.

PubMed

Knox, R V; Shen, J; Greiner, L L; Connor, J F

2016-12-01

Variation in gilt fertility is associated with increased replacement and reduced longevity. Stress before breeding is hypothesized to be involved in reduced fertility. This study tested the timing of gilt relocation from pens to individual stalls before breeding on fertility and well-being. The experiment was performed in replicates on a commercial research farm. After detection of first estrus, gilts ( = 563) were assigned to treatment for relocation into stalls 3 wk (REL3wk), 2 wk (REL2wk), or 1 wk (REL1wk) before breeding at second estrus. Subsets of gilts from each treatment ( = 60) were selected for assessment of follicles at second estrus. Data included interestrus interval, number of services, conception, farrowing, total born, and wean to service interval. Piglet birth weight was obtained on subsets of litters ( = 42/treatment). Measures of well-being included BW, backfat, BCS, lesions, and lameness from wk 1 after first estrus until wk 16. Gilt BW at wk 5 (158.4 kg) was not affected ( > 0.10) by treatment. Measures of BCS, lameness, and lesions at breeding and throughout gestation did not differ ( > 0.10). Treatment did not affect ( > 0.10) gilts expressing a normal interestrus interval of 18 to 24 d (83.4%) but did influence ( < 0.05) the proportion expressing shorter ( < 0.001) and longer ( < 0.001) intervals. Gilts in REL3wk had a shorter ( < 0.001) interestrus interval (20.7 d) than those in REL2wk and REL1wk (22.6 d). Gilts with shorter intervals ( = 24) had fewer total born while gilts expressing longer cycles ( = 65) had reduced farrowing rates. The number of services (1.9) and number of follicles (19.7) at breeding were not affected ( > 0.10) by relocation. There was no effect of treatment on farrowing rate (85.2%), born alive (12.6), or any litter birth weight measures ( > 0.10). The percentage of sows bred within 7 d after weaning (94.4%) was also not affected by treatment ( > 0.10). These results suggest that the timing of relocation before breeding had no effect on well-being or on the majority of gilts with normal estrous cycles and their subsequent fertility. However, a smaller proportion of the gilts exhibited shorter and longer interestrus intervals in response to relocation 1 or 3 wk before breeding. In cases where gilt fertility may be less than optimal, producers that relocate gilts from pens to stalls before breeding should evaluate interestrus interval as a response criterion.

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.

Task I: A Computational Model for Short Wavelength Stall Inception and Development In Multi-Stage Compressors

NASA Technical Reports Server (NTRS)

Suder, Kenneth (Technical Monitor); Tan, Choon-Sooi

2003-01-01

A computational model is presented for simulating axial compressor stall inception and development via disturbances with length scales on the order of several (typically about three) blade pitches. The model was designed for multi-stage compressors in which stall is initiated by these short wavelength disturbances, also referred to as spikes. The inception process described is fundamentally nonlinear, in contrast to the essentially linear behavior seen in so-called modal stall inception . The model was able to capture the following experimentally observed phenomena: (1) development of rotating stall via short wavelength disturbances, (2) formation and evolution of localized short wavelength stall cells in the first stage of a mismatched compressor, (3) the switch from long to short wavelength stall inception resulting from the re-staggering of the inlet guide vane, (4) the occurrence of rotating stall inception on the negatively sloped portion of the compressor characteristic. Parametric investigations indicated that (1) short wavelength disturbances were supported by the rotor blade row, (2) the disturbance strength was attenuated within the stators, and (3) the reduction of inter-blade row gaps can suppress the growth of short wavelength disturbances. It is argued that each local component group (rotor plus neighboring stators) has its own instability point (i.e. conditions at which disturbances are sustained) for short wavelength disturbances, with the instability point for the compressor set by the most unstable component group.

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.

A ruthenium polypyridyl intercalator stalls DNA replication forks, radiosensitizes human cancer cells and is enhanced by Chk1 inhibition

NASA Astrophysics Data System (ADS)

Gill, Martin R.; Harun, Siti Norain; Halder, Swagata; Boghozian, Ramon A.; Ramadan, Kristijan; Ahmad, Haslina; Vallis, Katherine A.

2016-08-01

Ruthenium(II) polypyridyl complexes can intercalate DNA with high affinity and prevent cell proliferation; however, the direct impact of ruthenium-based intercalation on cellular DNA replication remains unknown. Here we show the multi-intercalator [Ru(dppz)2(PIP)]2+ (dppz = dipyridophenazine, PIP = 2-(phenyl)imidazo[4,5-f][1,10]phenanthroline) immediately stalls replication fork progression in HeLa human cervical cancer cells. In response to this replication blockade, the DNA damage response (DDR) cell signalling network is activated, with checkpoint kinase 1 (Chk1) activation indicating prolonged replication-associated DNA damage, and cell proliferation is inhibited by G1-S cell-cycle arrest. Co-incubation with a Chk1 inhibitor achieves synergistic apoptosis in cancer cells, with a significant increase in phospho(Ser139) histone H2AX (γ-H2AX) levels and foci indicating increased conversion of stalled replication forks to double-strand breaks (DSBs). Normal human epithelial cells remain unaffected by this concurrent treatment. Furthermore, pre-treatment of HeLa cells with [Ru(dppz)2(PIP)]2+ before external beam ionising radiation results in a supra-additive decrease in cell survival accompanied by increased γ-H2AX expression, indicating the compound functions as a radiosensitizer. Together, these results indicate ruthenium-based intercalation can block replication fork progression and demonstrate how these DNA-binding agents may be combined with DDR inhibitors or ionising radiation to achieve more efficient cancer cell killing.

A ruthenium polypyridyl intercalator stalls DNA replication forks, radiosensitizes human cancer cells and is enhanced by Chk1 inhibition.

PubMed

Gill, Martin R; Harun, Siti Norain; Halder, Swagata; Boghozian, Ramon A; Ramadan, Kristijan; Ahmad, Haslina; Vallis, Katherine A

2016-08-25

Ruthenium(II) polypyridyl complexes can intercalate DNA with high affinity and prevent cell proliferation; however, the direct impact of ruthenium-based intercalation on cellular DNA replication remains unknown. Here we show the multi-intercalator [Ru(dppz)2(PIP)](2+) (dppz = dipyridophenazine, PIP = 2-(phenyl)imidazo[4,5-f][1,10]phenanthroline) immediately stalls replication fork progression in HeLa human cervical cancer cells. In response to this replication blockade, the DNA damage response (DDR) cell signalling network is activated, with checkpoint kinase 1 (Chk1) activation indicating prolonged replication-associated DNA damage, and cell proliferation is inhibited by G1-S cell-cycle arrest. Co-incubation with a Chk1 inhibitor achieves synergistic apoptosis in cancer cells, with a significant increase in phospho(Ser139) histone H2AX (γ-H2AX) levels and foci indicating increased conversion of stalled replication forks to double-strand breaks (DSBs). Normal human epithelial cells remain unaffected by this concurrent treatment. Furthermore, pre-treatment of HeLa cells with [Ru(dppz)2(PIP)](2+) before external beam ionising radiation results in a supra-additive decrease in cell survival accompanied by increased γ-H2AX expression, indicating the compound functions as a radiosensitizer. Together, these results indicate ruthenium-based intercalation can block replication fork progression and demonstrate how these DNA-binding agents may be combined with DDR inhibitors or ionising radiation to achieve more efficient cancer cell killing.

Jet Engine Fan Response to Inlet Distortions Generated by Ingesting Boundary Layer Flow

NASA Astrophysics Data System (ADS)

Giuliani, James Edward

Future civil transport designs may incorporate engines integrated into the body of the aircraft to take advantage of efficiency increases due to weight and drag reduction. Additional increases in engine efficiency are predicted if the inlets ingest the lower momentum boundary layer flow that develops along the surface of the aircraft. Previous studies have shown, however, that the efficiency benefits of Boundary Layer Ingesting (BLI) inlets are very sensitive to the magnitude of fan and duct losses, and blade structural response to the non-uniform flow field that results from a BLI inlet has not been studied in-depth. This project represents an effort to extend the modeling capabilities of TURBO, an existing rotating turbomachinery unsteady analysis code, to include the ability to solve the external and internal flow fields of a BLI inlet. The TURBO code has been a successful tool in evaluating fan response to flow distortions for traditional engine/inlet integrations. Extending TURBO to simulate the external and inlet flow field upstream of the fan will allow accurate pressure distortions that result from BLI inlet configurations to be computed and used to analyze fan aerodynamics and structural response. To validate the modifications for the BLI inlet flow field, an experimental NASA project to study flush-mounted S-duct inlets with large amounts of boundary layer ingestion was modeled. Results for the flow upstream and in the inlet are presented and compared to experimental data for several high Reynolds number flows to validate the modifications to the solver. Once the inlet modifications were validated, a hypothetical compressor fan was connected to the inlet, matching the inlet operating conditions so that the effect on the distortion could be evaluated. Although the total pressure distortion upstream of the fan was symmetrical for this geometry, the pressure rise generated by the fan blades was not, because of the velocity non-uniformity of the distortion. Total pressure profiles at various axial locations are computed to identify the overall distortion pattern, how the distortion evolves through the blade passages and mixes out downstream of the blades, and where any critical performance concerns might be. Stall cells are identified that are stationary in the absolute frame and are fixed to the inlet distortion. Flow paths around the blades are examined to study the stall mechanism. Rather than a static airfoil stall, it is observed that the non-uniform pressure loading promotes a three-dimensional dynamic stall. The stall occurs at a point of rapid incidence angle oscillation, observed when a blade passes through the distortion, and re-attaches when the blade leaves the distortion.

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.

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.

An approach for aerodynamic optimization of transonic fan blades

NASA Astrophysics Data System (ADS)

Khelghatibana, Maryam

Aerodynamic design optimization of transonic fan blades is a highly challenging problem due to the complexity of flow field inside the fan, the conflicting design requirements and the high-dimensional design space. In order to address all these challenges, an aerodynamic design optimization method is developed in this study. This method automates the design process by integrating a geometrical parameterization method, a CFD solver and numerical optimization methods that can be applied to both single and multi-point optimization design problems. A multi-level blade parameterization is employed to modify the blade geometry. Numerical analyses are performed by solving 3D RANS equations combined with SST turbulence model. Genetic algorithms and hybrid optimization methods are applied to solve the optimization problem. In order to verify the effectiveness and feasibility of the optimization method, a singlepoint optimization problem aiming to maximize design efficiency is formulated and applied to redesign a test case. However, transonic fan blade design is inherently a multi-faceted problem that deals with several objectives such as efficiency, stall margin, and choke margin. The proposed multi-point optimization method in the current study is formulated as a bi-objective problem to maximize design and near-stall efficiencies while maintaining the required design pressure ratio. Enhancing these objectives significantly deteriorate the choke margin, specifically at high rotational speeds. Therefore, another constraint is embedded in the optimization problem in order to prevent the reduction of choke margin at high speeds. Since capturing stall inception is numerically very expensive, stall margin has not been considered as an objective in the problem statement. However, improving near-stall efficiency results in a better performance at stall condition, which could enhance the stall margin. An investigation is therefore performed on the Pareto-optimal solutions to demonstrate the relation between near-stall efficiency and stall margin. The proposed method is applied to redesign NASA rotor 67 for single and multiple operating conditions. The single-point design optimization showed +0.28 points improvement of isentropic efficiency at design point, while the design pressure ratio and mass flow are, respectively, within 0.12% and 0.11% of the reference blade. Two cases of multi-point optimization are performed: First, the proposed multi-point optimization problem is relaxed by removing the choke margin constraint in order to demonstrate the relation between near-stall efficiency and stall margin. An investigation on the Pareto-optimal solutions of this optimization shows that the stall margin has been increased with improving near-stall efficiency. The second multi-point optimization case is performed with considering all the objectives and constraints. One selected optimized design on the Pareto front presents +0.41, +0.56 and +0.9 points improvement in near-peak efficiency, near-stall efficiency and stall margin, respectively. The design pressure ratio and mass flow are, respectively, within 0.3% and 0.26% of the reference blade. Moreover the optimized design maintains the required choking margin. Detailed aerodynamic analyses are performed to investigate the effect of shape optimization on shock occurrence, secondary flows, tip leakage and shock/tip-leakage interactions in both single and multi-point optimizations.

Preliminary assessment of the robustness of dynamic inversion based flight control laws

NASA Technical Reports Server (NTRS)

Snell, S. A.

1992-01-01

Dynamic-inversion-based flight control laws present an attractive alternative to conventional gain-scheduled designs for high angle-of-attack maneuvering, where nonlinearities dominate the dynamics. Dynamic inversion is easily applied to the aircraft dynamics requiring a knowledge of the nonlinear equations of motion alone, rather than an extensive set of linearizations. However, the robustness properties of the dynamic inversion are questionable especially when considering the uncertainties involved with the aerodynamic database during post-stall flight. This paper presents a simple analysis and some preliminary results of simulations with a perturbed database. It is shown that incorporating integrators into the control loops helps to improve the performance in the presence of these perturbations.

Comparison of two- and three-dimensional flow computations with laser anemometer measurements in a transonic compressor rotor

NASA Technical Reports Server (NTRS)

Chima, R. V.; Strazisar, A. J.

1982-01-01

Two and three dimensional inviscid solutions for the flow in a transonic axial compressor rotor at design speed are compared with probe and laser anemometers measurements at near-stall and maximum-flow operating points. Experimental details of the laser anemometer system and computational details of the two dimensional axisymmetric code and three dimensional Euler code are described. Comparisons are made between relative Mach number and flow angle contours, shock location, and shock strength. A procedure for using an efficient axisymmetric code to generate downstream pressure input for computationally expensive Euler codes is discussed. A film supplement shows the calculations of the two operating points with the time-marching Euler code.

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.

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.

Academic Learning Time in the District of Columbia Public Schools.

ERIC Educational Resources Information Center

District of Columbia Public Schools, Washington, DC. Research Information Center.

Papers generated for a symposium entitled "Effectiveness of Stallings' Use of Time Training for Teachers in Washington, D.C." are presented. The intitial presentation, "Academic Learning Time: The Current Status of the Stallings Training" (Geraldine Williams Bethune), reviews the Stallings research and describes the Academic…

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...

Design Information for Civil Works Housing.

DTIC Science & Technology

1984-01-01

tmm GUIDANCE Lawn Mower , Garden Equipment, Bicycles, etc. 20 ft ^ r" T STORAGE 1-STALL OARAGE 2-STALL QARAQE I I c COMMENTARY !A. Al A...Weatherproof 110-V outlets (as required per ap- plicable code). V. J 17 GUIDANCE Lawn Mower , Garden Equipment, and Bicycles 1-STALL CARPORT

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…

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.

Topic 1.1.2, Unsteady Aerodynamics: Time-Varying Compressible Dynamic Stall Mechanisms Due to Freestream Mach Oscillations

DTIC Science & Technology

2014-12-31

separation during the pitch-up motion – thus interrupting the vortex shedding that is characteristic of deep dynamic stall (Ericsson and Reding , 1984). The...Aircraft, Vol. 31, No. 4, pp. 782-786. Ericsson, L. E. and Reding , J. P., (1971) “Dynamic Stall Simulation Problems,” Journal of Aircraft, Vol. 8, No...7, pp. 579-583. Ericsson, L. E. and Reding , J. P., (1984) “Shock-Induced Dynamic Stall,” Journal of Aircraft, Vol. 21, No. 5, pp. 316-321. Favier

Experimental evaluation of a TF30-P-3 turbofan engine in an altitude facility: Effect of steady-state temperature distortion

NASA Technical Reports Server (NTRS)

Braithwaite, W. M.

1973-01-01

The effects of circumferential distortion of the total temperature entering 25, 50, and 75 percent of the inlet circumferential annulus of a turbofan engine were determined. Complete compressor stall resulted from distortions of from 14 to 20 percent of the face averaged temperature. Increasing the temperature level in one sector resulted in that sector moving toward stall by decreasing the equivalent rotor speeds while the pressure ratio remained approximately constant. Stall originated as a rotating zone in the low-pressure compressor which resulted as a terminal stall in the high-pressure compressor. Decreasing the Reynolds number index to 0.25 from 0.5 reduced the required distortion for stall by 50 percent for the conditions investigated.

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.

Anterior Segment Morphology in Primary Angle Closure Glaucoma using Ultrasound Biomicroscopy

PubMed Central

Balakrishna, Nagalla

2017-01-01

Aim To evaluate the configuration of the anterior chamber angle quantitatively and study the morphological changes in the eye with ultrasound biomicroscopy (UBM) in primary angle closure glaucoma (PACG) patients after laser peripheral iridotomy (LPI). Materials and methods A total of 185 eyes of 185 PACG patients post-LPI and 126 eyes of 126 normal subjects were included in this prospective study. All subjects underwent complete ophthalmic evaluation, A-scan biometry, and UBM. The anterior segment and angle parameters were measured quantitatively and compared in both groups using Student’s t-test. Results The PACG patients had shorter axial length, shallower central anterior chamber depth anterior chamber depth (ACD), and anteriorly located lens when compared with normal subjects. Trabecular iris angle (TIA) was significantly narrow (5.73 ± 7.76°) in patients with PACG when compared with normal subjects (23.75 ± 9.38°). The angle opening distance at 500 pm from scleral spur (AOD 500), trabecular-ciliary process distance (TCPD), iris-ciliary process distance (ICPD), and iris-zonule distance (IZD) were significantly shorter in patients with PACG than in normal subjects (p < 0.0001). The iris lens angle (ILA), scleral-iris angle (SIA), and scleral-ciliary process angle (SCPA) were significantly narrower in patients with PACG than in normal subjects (p < 0.0001). The iris-lens contact distance (ILCD) was greater in PACG group than in normal (p = 0.001). Plateau iris was seen in 57/185 (30.8%) of the eyes. Anterior positioned ciliary processes were seen in 130/185 eyes (70.3%) of eyes. Conclusion In PACG patients, persistent apposition angle closure is common even after LPI, which could be due to anterior rotation of ciliary body and plateau iris and overcrowding of anterior segment due to shorter axial length and relative anterior lens position. How to cite this article: Mansoori T, Balakrishna N. Anterior Segment Morphology in Primary Angle Closure Glaucoma using Ultrasound Biomicroscopy. J Curr Glaucoma Pract 2017;11(3):86-91. PMID:29151682

KSC-08pd2429

NASA Image and Video Library

2008-08-21

CAPE CANAVERAL, Fla. – At NASA's Kennedy Space Center, this alligator was spotted cruising the flood waters caused by Tropical Storm Fay. The storm passed over the center Aug. 20 and then stalled offshore, bringing with it heavy rain and tropical storm force wind. Kennedy closed Aug. 19 because of Fay and reopened for normal operations Aug. 22. Based on initial assessments, there was no damage to space flight hardware, such as the space shuttles and Hubble Space Telescope equipment. Some facilities did sustain minor damage. Photo credit: NASA/Jack Pfaller

Low-speed wind-tunnel investigation of the flight dynamic characteristics of an advanced turboprop business/commuter aircraft configuration

NASA Technical Reports Server (NTRS)

Coe, Paul L., Jr.; Turner, Steven G.; Owens, D. Bruce

1990-01-01

An investigation was conducted to determine the low-speed flight dynamic behavior of a representative advanced turboprop business/commuter aircraft concept. Free-flight tests were conducted in the NASA Langley Research Center's 30- by 60-Foot Tunnel. In support of the free-flight tests, conventional static, dynamic, and free-to-roll oscillation tests were performed. Tests were intended to explore normal operating and post stall flight conditions, and conditions simulating the loss of power in one engine.

Secondary electron emission from electrically charged fluorinated-ethylene-propylene Teflon for normal and non-normal electron incidence. M.S. Thesis; [spacecraft thermal coatings

NASA Technical Reports Server (NTRS)

Budd, P. A.

1981-01-01

The secondary electron emission coefficient was measured for a charged polymer (FEP-Teflon) with normally and obliquely incident primary electrons. Theories of secondary emission are reviewed and the experimental data is compared to these theories. Results were obtained for angles of incidence up to 60 deg in normal electric fields of 1500 V/mm. Additional measurements in the range from 50 to 70 deg were made in regions where the normal and tangential fields were approximately equal. The initial input angles and measured output point of the electron beam could be analyzed with computer simulations in order to determine the field within the chamber. When the field is known, the trajectories can be calculated for impacting electrons having various energies and angles of incidence. There was close agreement between the experimental results and the commonly assumed theoretical model in the presence of normal electric fields for angles of incidence up to 60 deg. High angle results obtained in the presence of tangential electric fields did not agree with the theoretical models.

Comparison between the angle of Eustachian tube in patients with chronic suppurative otitis media and normal ears based on computed tomography scan of temporal bones in Haji Adam Malik general hospital Medan

NASA Astrophysics Data System (ADS)

Masita, S.; Zahara, D.; Aboet, A.

2018-03-01

The function of the Eustachian tube plays a significant role in increased risk chronic suppurative otitis media (CSOM). The angle of the Eustachian tube is a predisposing factor for Eustachian tube dysfunction and clearance disorder of the middle ear. The aim of this study was to compare the mean angle of a Eustachian tube of CSOM ears and normal ears. This research was a cross-sectional study consisting of 19 patients of CSOM without cholesteatoma, 19 patients of CSOM with cholesteatoma and 19 patients with normal ears. All patients were examined using CT Temporal, and the angle of the eustachian tube was measured using multiplanar reconstruction technique. The mean angle of Eustachian tube in CSOM patients without cholesteatoma was 32.82° (SD=3.82), in CSOM with cholesteatoma was 27.74° (SD=4.44) and in normal ears was 33.61° (SD=3.83). Based on Kruskal-Wallis test, there was a significant difference in the angle of a Eustachian tube of these three groups (p<0.001). There was a significant difference between the mean angle of the Eustachian tube in CSOM ears and normal ears.

Bedding on geotextile mattresses: how much is needed to improve cow comfort?

PubMed

Tucker, C B; Weary, D M

2004-09-01

The objective of our study was to evaluate how the amount of sawdust bedding on mattresses affects dairy cattle behavior and preferences. Eleven nonlactating, multiparous cows were housed individually in pens with access to 3 free stalls. Each stall was fitted with a geotextile mattress covered with either 0, 1, or 7.5 kg of kiln-dried sawdust. The experiment began with 7 d of acclimatization to all 3 stalls. Cows were then allowed access to only 1 of the 3 stalls at a time, each for 3 d (restriction phase). At the end of this restriction phase, cows were allowed free access to all 3 stalls for 3 d (free-choice phase). Time spent lying and the number of lying bouts increased significantly with the amount of bedding, from 12.3 +/- 0.53 h lying and 8.5 +/- 0.62 bouts per 24 h on bare mattresses to 13.8 +/- 0.53 h lying and 10.0 +/- 0.62 bouts per 24 h on mattresses with 7.5 kg of sawdust. In addition, the animals spent less time standing with only the front hooves in the stalls when more sawdust was present. When allowed free access to all 3 options, all 11 animals spent a majority of their time lying and standing in the 7.5-kg option. In conclusion, cows preferred mattresses bedded with 7.5 kg of sawdust, on which they spent more time lying down and less time standing with only the front hooves in stalls. These results indicate that more sawdust bedding improves cow comfort in stalls with geotextile mattresses.

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.

Preliminary Results of the Determination of Inlet-Pressure Distortion Effects on Compressor Stall and Altitude Operating Limits of the J57-P-1 Turbojet Engine

NASA Technical Reports Server (NTRS)

Wallner, L. E.; Lubick, R. J.; Chelko, L. J.

1955-01-01

During an investigation of the J57-P-1 turbojet engine in the Lewis altitude wind tunnel, effects of inlet-flow distortion on engine stall characteristics and operating limits were determined. In addition to a uniform inlet-flow profile, the inlet-pressure distortions imposed included two radial, two circumferential, and one combined radial-circumferential profile. Data were obtained over a range of compressor speeds at an altitude of 50,000 and a flight Mach number of 0.8; in addition, the high- and low-speed engine operating limits were investigated up to the maximum operable altitude. The effect of changing the compressor bleed position on the stall and operating limits was determined for one of the inlet distortions. The circumferential distortions lowered the compressor stall pressure ratios; this resulted in less fuel-flow margin between steady-state operation and compressor stall. Consequently, the altitude operating Limits with circumferential distortions were reduced compared with the uniform inlet profile. Radial inlet-pressure distortions increased the pressure ratio required for compressor stall over that obtained with uniform inlet flow; this resulted in higher altitude operating limits. Likewise, the stall-limit fuel flows required with the radial inlet-pressure distortions were considerably higher than those obtained with the uniform inlet-pressure profile. A combined radial-circumferential inlet distortion had effects on the engine similar to the circumferential distortion. Bleeding air between the two compressors eliminated the low-speed stall limit and thus permitted higher altitude operation than was possible without compressor bleed.

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…

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.

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.

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.

Lameness and Claw Lesions of the Norwegian Red Dairy Cattle Housed in Free Stalls in Relation to Environment, Parity and Stage of Lactation

PubMed Central

Sogstad, ÅM; Fjeldaas, T; Østerås, O

2005-01-01

Approximately 88% of Norwegian dairy cattle are housed in tie stalls. Free stall housing for all dairy cattle will be implemented within 20 years. This means that the majority of existing stalls will be rebuilt in the near future. Fifty-seven free stall herds of the Norwegian Red breed were randomly selected and 1547 cows and 403 heifers were trimmed by 13 claw trimmers during the late winter and spring of 2002. The claw trimmers had been taught diagnosing and recording of claw lesions. Environment, management- and feeding routines were also recorded. Fifty-three herds had concrete slatted alleys while 4 had solid concrete. Thirty-five herds had concrete as a stall base, while 17 had rubber mats, 2 had wood and 3 had deep litter straw beds. The prevalence of lameness was 1.6% in hind claws. Models for lameness and claw lesions were designed to estimate the influence of different risk factors and to account for the cluster effects within herd and claw trimmer. Detected risk factors for lameness were: parity three and above and narrow cubicles; for heel horn erosions: lactation stage around 5–7 months after calving and solid concrete alleys; for haemorrhages of the white line: lactation stage around 3–5 months after calving and solid concrete alleys; for haemorrhages of the sole: parity one, lactation stage around 5–7 months after calving and short cubicles, for white line fissures: slatted concrete alleys; for asymmetrical claws: parities two and above and for corkscrewed claws: solid concrete alleys. The prevalence of lameness in heifers was low, however 29% had one or more claw lesions. Heifers that were housed in pens or free stalls had more heel-horn erosions, haemorrhages of the sole and white-line fissures than heifers in tie stalls. As new free stalls are being built, it is important to optimise the conditions for claw health. PMID:16398332

Navier-Stokes analysis of airfoils with leading edge ice accretions

NASA Technical Reports Server (NTRS)

Potapczuk, Mark G.

1993-01-01

A numerical analysis of the flowfield characteristics and the performance degradation of an airfoil with leading edge ice accretions was performed. The important fluid dynamic processes were identified and calculated. Among these were the leading edge separation bubble at low angles of attack, complete separation on the low pressure surface resulting in premature shell, drag rise due to the ice shape, and the effects of angle of attack on the separated flow field. Comparisons to experimental results were conducted to confirm these calculations. A computer code which solves the Navier-Stokes equations in two dimensions, ARC2D, was used to perform the calculations. A Modified Mixing Length turbulence model was developed to produce grids for several ice shape and airfoil combinations. Results indicate that the ability to predict overall performance characteristics, such as lift and drag, at low angles of attack is excellent. Transition location is important for accurately determining separation bubble shape. Details of the flowfield in and downstream of the separated regions requires some modifications. Calculations for the stalled airfoil indicate periodic shedding of vorticity that was generated aft of the ice accretion. Time averaged pressure values produce results which compare favorably with experimental information. A turbulence model which accounts for the history effects in the flow may be justified.

Analysis of a swimmer's hand and forearm in impulsive start from rest using computational fluid dynamics in unsteady flow conditions.

PubMed

Samson, M; Monnet, T; Bernard, A; Lacouture, P; David, L

2018-01-23

The propulsive forces generated by the hands and arms of swimmers have so far been determined essentially by quasi-steady approaches. This study aims to quantify the temporal dependence of the hydrodynamic forces for a simple translation movement: an impulsive start from rest. The study, carried out in unsteady numerical simulation, couples the calculation of the lift and the drag on an expert swimmer hand-forearm model with visualizations of the flow and flow vortex structure analysis. The results of these simulations show that the hand and forearm hydrodynamic forces should be studied from an unsteady approach because the quasi-steady model is inadequate. It also appears that the delayed stall effect generates higher circulatory forces during a short translation at high angle of attack than forces calculated under steady state conditions. During this phase the hand force coefficients are approximately twice as large as those of the forearm. The total force coefficients are highest for angles of attack between 40° and 60°. For the same angle of attack, the forces produced when the leading edge is the thumb side are slightly greater than those produced when the leading edge is the little finger side. Copyright © 2017 Elsevier Ltd. All rights reserved.

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

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.

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.

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.

Effects of milking stall dimensions on behavior of dairy cows during milking in different milking parlor types.

PubMed

Gómez, Y; Terranova, M; Zähner, M; Hillmann, E; Savary, P

2017-02-01

Dairy cow body size has increased over time because of breeding selection for higher milk yield, but milking stall dimensions have never been adjusted and are based on the practical experience of milking-machine manufacturers and advisory institutions. Narrow, limited milking stall dimensions might lead to behavioral changes during milking due to lack of comfort. The aim of this study was to examine the current space allowance in milking stalls on dairy farms and assess the effect of space allowance on cow behavior during milking. On 15 Swiss dairy farms, we measured clear milking stall dimensions and cow body dimensions. We calculated space ratios for length (SR length ) and width (SR width ) by dividing the milking stall length or width by cow body length or belly width, respectively. When the space ratio was >1, we assumed that the body length or width of cow was smaller than the milking stall length or width. On each farm, 10 healthy cows were chosen for behavioral observation during 1 evening milking. We recorded rumination, elimination, and latency to enter the milking stall by direct observation. Hind leg activity was recorded using acceleration loggers. Data were analyzed using general linear mixed-effects models with farm as a random effect. Due to a strong collinearity between SR width and SR length , we chose SR length for further analysis, because it is based on skeletal characteristics. The SR length was smallest in side-by-side parlors (1.07 ± 0.01) and largest in tandem parlors (1.18 ± 0.01). More cows had a tendency to ruminate with increasing SR length (odds ratio: 1.8). None of hind leg activity, maximum peaks of hind leg accelerations, or latency to enter the milking stall were significantly affected by SR length . Latency to enter the milking stall was longer for group milking parlors (side-by-side: 44.0 ± 3.2 s; herringbone: 34.3 ± 2.9 s) than for tandem parlors (19.0 ± 2.7 s). Milking parlor type had no effect on hind leg activity, maximum peaks of hind leg accelerations or rumination. The SR length affected rumination behavior to some extent, indicating that cow comfort was positively affected by larger milking stall length. Because cow comfort is important for good milking performance, further investigations of milking stall dimensions for cow comfort and thus welfare are needed. Furthermore, the results showed that parlor type affected cow behavior, irrespective of SR length , making future research necessary to identify the factors leading to this effect of parlor type. Copyright © 2017 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

Numerical simulation of hydrodynamics in a pump-turbine at off-design operating conditions in turbine mode

NASA Astrophysics Data System (ADS)

Yan, J. P.; Seidel, U.; Koutnik, J.

2012-11-01

The hydrodynamics of a reduced-scaled model of a radial pump-turbine is investigated under off-design operating conditions, involving runaway and "S-shape" turbine brake curve at low positive discharge. It is a low specific speed pump-turbine machine of Francis type with 9 impeller blades and 20 stay vanes as well as 20 guide vanes. The computational domain includes the entire water passage from the spiral casing inlet to the draft tube outlet. Completely structured hexahedral meshes generated by the commercial software ANSYS-ICEM are employed. The unsteady incompressible simulations are performed using the commercial code ANSYS-CFX13. For turbulence modeling the standard k-ε model is applied. The numerical results at different operating points are compared to the experimental results. The predicted pressure amplitude is in good agreement with the experimental data and the amplitude of normal force on impeller is in reasonable range. The detailed analysis reveals the onset of the flow instabilities when the machine is brought from a regular operating condition to runaway and turbine break mode. Furthermore, the rotating stall phenomena are well captured at runaway condition as well as low discharge operating condition with one stall cell rotating inside and around the impeller with about 70% of its frequency. Moreover, the rotating stall is found to be the effect of rotating flow separations developed in several consecutive impeller channels which lead to their blockage. The reliable simulation of S-curve characteristics in pump-turbines is a basic requirement for design and optimization at off-design operating conditions.

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...

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...

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...

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...

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.

Aerodynamic Response of a Pitching Airfoil with Pulsed Circulation Control for Vertical Axis Wind Turbine Applications

NASA Astrophysics Data System (ADS)

Panther, Chad C.

Vertical Axis Wind Turbines (VAWTs) have experienced a renewed interest in development for urban, remote, and offshore applications. Past research has shown that VAWTs cannot compete with Horizontals Axis Wind Turbines (HAWTs) in terms of energy capture efficiency. VAWT performance is plagued by dynamic stall (DS) effects at low tip-speed ratios (lambda), where each blade pitches beyond static stall multiple times per revolution. Furthermore, for lambda<2, blades operate outside of stall during over 70% of rotation. However, VAWTs offer many advantages such as omnidirectional operation, ground proximity of generator, lower sound emission, and non-cantilevered blades with longer life. Thus, mitigating dynamic stall and improving VAWT blade aerodynamics for competitive power efficiency has been a popular research topic in recent years and the directive of this study. Past research at WVU focused on the addition of circulation control (CC) technology to improve VAWT aerodynamics and expand the operational envelope. A novel blade design was generated from the augmentation of a NACA0018 airfoil to include CC capabilities. Static wind tunnel data was collected for a range of steady jet momentum coefficients (0.01≤ Cmu≤0.10) for analytical vortex model performance projections. Control strategies were developed to optimize CC jet conditions throughout rotation, resulting in improved power output for 2≤lambda≤5. However, the pumping power required to produce steady CC jets reduced net power gains of the augmented turbine by approximately 15%. The goal of this work was to investigate pulsed CC jet actuation to match steady jet performance with reduced mass flow requirements. To date, no experimental studies have been completed to analyze pulsed CC performance on a pitching airfoil. The research described herein details the first study on the impact of steady and pulsed jet CC on pitching VAWT blade aerodynamics. Both numerical and experimental studies were implemented, varying Re, k, and +/-alpha to match a typical VAWT operating environment. A range of reduced jet frequencies (0.25≤St≤4) were analyzed with varying Cmu, based on effective ranges from prior flow control airfoil studies. Airfoil pitch was found to increase the baseline lift-to-drag ratio (L/D) by up to 50% due to dynamic stall effects. The influence of dynamic stall on steady CC airfoil performance was greater for Cmu=0.05, increasing L/D by 115% for positive angle-of-attack. Pulsed actuation was shown to match, or improve, steady jet lift performance while reducing required mass flow by up to 35%. From numerical flow visualization, pulsed actuation was shown to reduce the size and strength of wake vorticity during DS, resulting in lower profile drag relative to baseline and steady actuation cases. A database of pitching airfoil test data, including overshoot and hysteresis of aerodynamic coefficients (Cl, Cd), was compiled for improved analytical model inputs to update CCVAWT performance predictions, where the aforementioned L/D improvements will be directly reflected. Relative to a conventional VAWT with annual power output of 1 MW, previous work at WVU proved that the addition of steady jet CC could improve total output to 1.25 MW. However, the pumping cost to generate the continuous jet reduced yearly CCVAWT net gains to 1.15 MW. The current study has shown that pulsed CC jets can recover 4% of the pumping demands due to reduced mass flow requirements, increasing annual CCVAWT net power production to 1.19 MW, a 19% improvement relative to the conventional turbine.

Task II: Three-dimensional Rotating Stall Inception and Effects of Rotating Tip Clearance Asymmetry in Axial Compressors

NASA Technical Reports Server (NTRS)

Suder, Kenneth (Technical Monitor); Tan, Choon-Sooi

2003-01-01

The effects of two types of flow non-uniformity on stall inception behavior were assessed with linearized stability analyses of two compressor flow models. Response to rotating tip clearance asymmetries induced by a whirling rotor shaft or rotor height variations were investigated with a two-dimensional flow model. A 3-D compressor model was also developed to study the stability of both full-span and part-span rotating stall modes in annular geometries with radial flow variations. The studies focussed on (1) understanding what compressor designs were sensitive to these types of circumferential and spanwise flow non-uniformities, and (2) situations where 2-D stability theories were inadequate because of 3-D flow effects. Rotating tip clearance non-uniformity caused the greatest performance loss for shafts whirling at the rotating stall frequency. A whirling shaft displacement of 1 percent chord caused the stalling mass flow to rise by as much as 10 percent and the peak pressure rise to decrease by 6 percent. These changes were an order of magnitude larger than for equivalent-sized stationary or rotor-locked clearance asymmetries. Spanwise flow non-uniformity always destabilized the compressor, so that 2-D models over-predicted that stall margin compared to 3-D theory. The difference increased for compressors with larger spanwise variations of characteristic slope and reduced characteristic curvature near the peak. Differences between 2-D and 3-D stall point predictions were generally unacceptable (2 - 4 percent of flow coefficient) for single-stage configurations, but were less than 1 percent for multistage compressors. 2-D analyses predicted the wrong stall mode for specific cases of radial inlet flow distortion, mismatching and annulus area contraction, where higher-order radial modes led to stall. The stability behavior of flows with circumferential or radial non-uniformity was unified through a single stability criterion. The stall point for both cases was set by the integral around the annulus of the pressure rise characteristic slope, weighted by the amplitude of the mode shape. For the case of steady circumferential variations, this criterion reduced to the integrated mean slope (IMS) condition associated with steady inlet distortions. The rotating tip clearance asymmetry model was also used to demonstrate the feasibility of actively controlling the shaft position to suppress rotating stall. In axisymmetric mean flow, this method only stabilized the first harmonic mode, increasing the operating range until surge or higher harmonic modes became unstable.

Turbofan compressor dynamics during afterburner transients

NASA Technical Reports Server (NTRS)

Kurkov, A. P.

1975-01-01

The effects of afterburner light-off and shut-down transients on compressor stability were investigated. Experimental results are based on detailed high-response pressure and temperature measurements on the Tf30-p-3 turbofan engine. The tests were performed in an altitude test chamber simulating high-altitude engine operation. It is shown that during both types of transients, flow breaks down in the forward part of the fan-bypass duct. At a sufficiently low engine inlet pressure this resulted in a compressor stall. Complete flow breakdown within the compressor was preceded by a rotating stall. At some locations in the compressor, rotating stall cells initially extended only through part of the blade span. For the shutdown transient, the time between first and last detected occurrence of rotating stall is related to the flow Reynolds number. An attempt was made to deduce the number and speed of propagation of rotating stall cells.

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.

Evaluation of a stall-flutter spring-damper pushrod in the rotating control system of a CH-54B helicopter

NASA Technical Reports Server (NTRS)

Nettles, W. E.; Paul, W. F.; Adams, D. O.

1974-01-01

Results of a design and flight test program conducted to define the effect of rotating pushrod damping on stall-flutter induced control loads are presented. The CH-54B helicopter was chosen as the test aircraft because it exhibited stall induced control loads. Damping was introduced into the CH-54B control system by replacing the standard pushrod with spring-damper assemblies. Design features of the spring-damper are described and the results of a dynamic analysis are shown which define the pushrod stiffness and damping requirements. Flight test measurements taken at 47,000 lb gross weight with and without the damper are presented. The results indicate that the spring-damper pushrods reduced high frequency, stall-induced rotating control loads by almost 50%. Fixed system control loads were reduced by 40%. Handling qualities in stall were unchanged, as expected.

Simple turbulence models and their application to boundary layer separation

NASA Technical Reports Server (NTRS)

Wadcock, A. J.

1980-01-01

Measurements in the boundary layer and wake of a stalled airfoil are presented in two coordinate systems, one aligned with the airfoil chord, the other being conventional boundary layer coordinates. The NACA 4412 airfoil is studied at a single angle of attack corresponding to maximum lift, the Reynolds number based on chord being 1.5 x 10 to the 6th power. Turbulent boundary layer separation occurred at the 85 percent chord position. The two-dimensionality of the flow was documented and the momentum integral equation studied to illustrate the importance of turbulence contributions as separation is approached. The assumptions of simple eddy-viscosity and mixing-length turbulence models are checked directly against experiment. Curvature effects are found to be important as separation is approached.

Theoretical and experimental power from large horizontal-axis wind turbines

NASA Technical Reports Server (NTRS)

Viterna, L. A.; Janetzke, D. C.

1982-01-01

A method for calculating the output power from large horizontal-axis wind turbines is presented. Modifications to the airfoil characteristics and the momentum portion of classical blade element-momentum theory are given that improve correlation with measured data. Improvement is particularly evident at low tip-speed ratios where aerodynamic stall can occur as the blade experiences high angles of attack. Output power calculated using the modified theory is compared with measured data for several large wind turbines. These wind turbines range in size from the DOE/NASA 100 kW Mod-0 (38 m rotor diameter) to the 2000 kW Mod-1 (61 m rotor diameter). The calculated results are in good agreement with measured data from these machines.

Transmittance of semitransparent windows with absorbing cap-shaped droplets condensed on their backside

NASA Astrophysics Data System (ADS)

Zhu, Keyong; Pilon, Laurent

2017-11-01

This study aims to investigate systematically light transfer through semitransparent windows with absorbing cap-shaped droplets condensed on their backside as encountered in greenhouses, solar desalination plants, photobioreactors and covered raceway ponds. The Monte Carlo ray-tracing method was used to predict the normal-hemispherical transmittance, reflectance, and normal absorptance accounting for reflection and refraction at the air/droplet, droplet/window, and window/air interfaces and absorption in both the droplets and the window. The droplets were monodisperse or polydisperse and arranged either in an ordered hexagonal pattern or randomly distributed on the backside with droplet contact angle θc ranging between 0 and 180° The normal-hemispherical transmittance was found to be independent of the spatial distribution of droplets. However, it decreased with increasing droplet diameter and polydispersity. The normal-hemispherical transmittance featured four distinct optical regimes for semitransparent window supporting nonabsorbing droplets. These optical regimes were defined based on contact angle and critical angle for internal reflection at the droplet/air interface. However, for strongly absorbing droplets, the normal-hemispherical transmittance (i) decreased monotonously with increasing contact angle for θc <90° and (ii) remained constant and independent of droplet absorption index kd, droplet mean diameter dm, and contact angle θc for θc ≥ 90° Analytical expressions for the normal-hemispherical transmittance were provided in the asymptotic cases when (1) the window was absorbing but the droplets were nonabsorbing with any contact angles θc, and (2) the droplets were strongly absorbing with contact angle θc >90° Finally, the spectral normal-hemispherical transmittance of a 3 mm-thick glass window supporting condensed water droplets for wavelength between 0.4 and 5 μm was predicted and discussed in light of the earlier parametric study and asymptotic behavior.

Wind tunnel research comparing lateral control devices, particularly at high angles of attack XI : various floating tip ailerons on both rectangular and tapered wings

NASA Technical Reports Server (NTRS)

Weick, Fred E; Harris, Thomas A

1933-01-01

Discussed here are a series of systematic tests being conducted to compare different lateral control devices with particular reference to their effectiveness at high angles of attack. The present tests were made with six different forms of floating tip ailerons of symmetrical section. The tests showed the effect of the various ailerons on the general performance characteristics of the wing, and on the lateral controllability and stability characteristics. In addition, the hinge moments were measured for the most interesting cases. The results are compared with those for a rectangular wing with ordinary ailerons and also with those for a rectangular wing having full-chord floating tip ailerons. Practically all the floating tip ailerons gave satisfactory rolling moments at all angles of attack and at the same time gave no adverse yawing moments of appreciable magnitude. The general performance characteristics with the floating tip ailerons, however, were relatively poor, especially the rate of climb. None of the floating tip ailerons entirely eliminated the auto rotational moments at angles of attack above the stall, but all of them gave lower moments than a plain wing. Some of the floating ailerons fluttered if given sufficiently large deflection, but this could have been eliminated by moving the hinge axis of the ailerons forward. Considering all points including hinge moments, the floating tip ailerons on the wing with 5:1 taper are probably the best of those which were tested.

Whirling Arm Tests on the Effect of Ground Proximity to an Airplane Wing

NASA Technical Reports Server (NTRS)

Long, M. E.

1944-01-01

This report gives the results of tests on a rectangular wing model with a 20% full spun split flap, conducted on the whirling arm at the Daniel Guggenheim Airship Institute in Akron, Ohio. The effect of a ground board on the lift and pitching moment was measured. The ground board consisted of an inclined ramp rising up in the test channel to a level floor extending for some distance parallel to the model path. The path of the wing model with respect to the ground board accordingly represented with comparative exactness an airplane coming in for a landing. The ground clearances over the level portion of the board varied from 0 6 to 1,6 chord lengths. Results are given in the standard dimensionless coefficients plotted versus angle of attack for a particular ground clearance. The effect of the ground board is to increase the lift coefficient for a given angle of attack all the way up the stall. The magnitude of the increase varies both with the ground clearance and the angle of attack. The effect on the pitching moment coefficient is not so readily apparent due to experimental difficulties but, in general, the diving moment increases over the ground board. This effect is apparent principally at the high angles of attack. An exception to this effect occurs with flaps deflected at the lowest ground clearance (0.6 chords). Here the diving moment decreases over the ground board.

Toward comparing experiment and theory for corroborative research on hingeless rotor stability in forward flight

NASA Technical Reports Server (NTRS)

Gaonkar, G.

1987-01-01

For flap lag stability of isolated rotors, experimental and analytical investigations were conducted in hover and forward flight on the adequacy of a linear quasisteady aerodynamics theory with dynamic flow. Forward flight effects on lag regressing mode were emphasized. A soft inplane hingeless rotor with three blades was tested at advance ratios as high as 0.55 and at shaft angles as high as 20 deg. The 1.62 m model rotor was untrimmed with an essentially unrestricted tilt of the tip path plane. In combination with lag natural frequencies, collective pitch settings and flap lag coupling parameters, the data base comprises nearly 1200 test points (damping and frequency) in forward flight and 200 test points in hover. By computerized symbolic manipulation, a linear model was developed in substall to predict stability margins with mode identification. To help explain the correlation between theory and data it also predicted substall and stall regions of the rotor disk from equilibrium values. The correlation showed both the strengths and weaknesses of the theory in substall ((angle of attack) equal to or less than 12 deg).

A Flight Examination of Operating Problems of V/STOL Aircraft in STOL-Type Landing and Approach

NASA Technical Reports Server (NTRS)

Innis, Robert C.; Quigley, Hervey C.

1961-01-01

A flight investigation has been conducted using a large twin-engine cargo aircraft to isolate the problems associated with operating propeller-driven aircraft in the STOL speed range where appreciable engine power is used to augment aerodynamic lift. The problems considered would also be representative of those of a large overloaded VTOL aircraft operating in an STOL manner with comparable thrust-to-weight ratios. The study showed that operation at low approach speeds was compromised by the necessity of maintaining high thrust to generate high lift and yet achieving the low lift-drag ratios needed for steep descents. The useable range of airspeed and flight path angle was limited by the pilot's demand for a positive climb margin at the approach speed, a suitable stall margin, and a control and/or performance margin for one engine inoperative. The optimum approach angle over an obstacle was found to be a compromise between obtaining the shortest air distance and the lowest touchdown velocity. In order to realize the greatest low-speed potential from STOL designs, the stability and control characteristics must be satisfactory.

Large-Amplitude, High-Rate Roll Oscillations of a 65 deg Delta Wing at High Incidence

NASA Technical Reports Server (NTRS)

Chaderjian, Neal M.; Schiff, Lewis B.

2000-01-01

The IAR/WL 65 deg delta wing experimental results provide both detail pressure measurements and a wide range of flow conditions covering from simple attached flow, through fully developed vortex and vortex burst flow, up to fully-stalled flow at very high incidence. Thus, the Computational Unsteady Aerodynamics researchers can use it at different level of validating the corresponding code. In this section a range of CFD results are provided for the 65 deg delta wing at selected flow conditions. The time-dependent, three-dimensional, Reynolds-averaged, Navier-Stokes (RANS) equations are used to numerically simulate the unsteady vertical flow. Two sting angles and two large- amplitude, high-rate, forced-roll motions and a damped free-to-roll motion are presented. The free-to-roll motion is computed by coupling the time-dependent RANS equations to the flight dynamic equation of motion. The computed results are compared with experimental pressures, forces, moments and roll angle time history. In addition, surface and off-surface flow particle streaks are also presented.

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.

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.

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.

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.

A Comparison of Angular Values of the Pelvic Limb with Normal and Medial Patellar Luxation Stifles in Chihuahua Dogs Using Radiography and Computed Tomography.

PubMed

Phetkaew, Thitaporn; Kalpravidh, Marissak; Penchome, Rampaipat; Wangdee, Chalika

2018-02-01

 This article aimed to determine and compare the angular values of the pelvic limb in normal and medial patellar luxation (MPL) stifles in Chihuahuas using radiography and computed tomographic (CT) scan, to identify the relationship between pelvic limb angles and severity of MPL. In addition, radiographic and CT images were compared to determine the more suitable method of limb deformity assessment.  Sixty hindlimbs of Chihuahuas were divided into normal and grade 1, 2, 3 and 4 MPL groups. The pelvic limb angles in frontal and sagittal planes were evaluated on radiography and CT scan. Femoral and tibial torsion angles (FTA and TTA) were evaluated only by CT scan. All angles were compared among normal and MPL stifles and between radiography and CT scan.  Based on the CT scan, the mechanical lateral distal femoral angle (mLDFA), anatomical caudal proximal femoral angle (aCdPFA), and TTA were related to the severity of MPL. The mLDFA and TTA were significantly increased ( p  < 0.05) in grade 4 MPL, while the aCdPFA was significantly decreased in grade 2, 3 and 4 MPL groups. There were significant differences of many angles between radiography and CT scan.  The angles related to MPL in Chihuahuas are aLDFA, mLDFA, aCdPFA and TTA. Radiography had some limitations for evaluating pelvic limb angles. The caudocranial radiograph is recommended for the assessment of the distal femoral angles, while the craniocaudal radiograph is for the tibial angles. Schattauer GmbH Stuttgart.

Method for characterization of a spherically bent crystal for K.alpha. X-ray imaging of laser plasmas using a focusing monochromator geometry

DOEpatents

Kugland, Nathan; Doeppner, Tilo; Glenzer, Siegfried; Constantin, Carmen; Niemann, Chris; Neumayer, Paul

2015-04-07

A method is provided for characterizing spectrometric properties (e.g., peak reflectivity, reflection curve width, and Bragg angle offset) of the K.alpha. emission line reflected narrowly off angle of the direct reflection of a bent crystal and in particular of a spherically bent quartz 200 crystal by analyzing the off-angle x-ray emission from a stronger emission line reflected at angles far from normal incidence. The bent quartz crystal can therefore accurately image argon K.alpha. x-rays at near-normal incidence (Bragg angle of approximately 81 degrees). The method is useful for in-situ calibration of instruments employing the crystal as a grating by first operating the crystal as a high throughput focusing monochromator on the Rowland circle at angles far from normal incidence (Bragg angle approximately 68 degrees) to make a reflection curve with the He-like x-rays such as the He-.alpha. emission line observed from a laser-excited plasma.

Group housing during gestation affects the behaviour of sows and the physiological indices of offspring piglets at weaning

USDA-ARS?s Scientific Manuscript database

In order to compare the behaviour of sows in stalls and group housing systems, and the physiological indices of their offspring, 28 sows were randomly distributed into 2 systems with 16 sows in stalls, and the other 12 sows were divided into 3 groups with 4 sows per pen. The area per sow in stalls a...

Influence of free-stall flooring on comfort and hygiene of dairy cows during warm climatic conditions.

PubMed

De Palo, P; Tateo, A; Zezza, F; Corrente, M; Centoducati, P

2006-12-01

An evaluation of behavioral and hygienic conditions was carried out with 4 materials used as free-stall flooring for dairy cows: polyethylene vinyl acetate (EVA) and polypropylene vinyl acetate (PVA) mats, wood shavings, and solid manure. The free-stall type selected by cows was evaluated in response to changes in environmental temperature and humidity. Two tests were used: 1) a preference test, in which 8 cows were housed in a pen with 32 free stalls and 4 types of flooring; and 2) an aversion test, in which 32 cows were placed in 4 pens, each with 8 free stalls. The free stalls in each pen had a single type of bedding material. These tests showed that the comfort of dairy cows was predominantly influenced by environmental conditions. The preference test for lying showed that cows preferred free-stall floors with EVA mats over those with PVA mats, wood shavings, and solid manure (332.4 +/- 24.0 vs. 130.8 +/- 6.2, 160.9 +/- 23.7, and 102.6 +/- 23.2 min/d, respectively), but under conditions of heat stress, with a temperature-humidity index > 80, they chose wood shavings and solid manure lying areas. These results were confirmed by the aversion test. In all experimental and environmental conditions, the PVA mats were the least suitable. The mats contaminated with organic manure and the free stalls bedded with wood shavings and organic solids did not differ in either the coliform load on the lying surfaces (EVA mats: 290 +/- 25; PVA mats: 306 +/- 33; wood shavings: 290 +/- 39; and solid manure: 305 +/- 23 log(10) cfu/mL) or the total bacterial count in the raw milk (EVA mats: 232 +/- 22; PVA mats: 233 + 24; wood shavings: 221 +/- 24; and solid manure: 220 +/- 25 log(10) cfu/mL). These results demonstrate that the comfort of dairy cows housed in barns with free stalls as resting areas does not depend only on the material used, but also on the value of the material in microenvironmental conditions.

Handbook of Supersonic Aerodynamics Volume 1

DTIC Science & Technology

1950-04-01

Appears in Z10 Publication Remarks •Mlc) *(lc) •Pile) Angle Potential function Helical angle of advance (propellers) Dimensionless Dependent on...heat of- combustion re(lc) N (cap) Nu. o(lc) Net Nozzle Normal (perpendicu- lar to longitudinal axis) ; normal (force) Nusselt ...Concepts ^ Concept Absolute Acceleration, angular Acceleration due to gravity Added; additional Adiabatic Adiabatic wall Advance, helical angle

Exploring a possible origin of a 14 deg y-normal spin tilt at RHIC polarimeter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meot, F.; Huang, H.

2015-06-15

A possible origin of a 14 deg y-normal spin n → 0 tilt at the polarimeter is in snake angle defects. This possible cause is investigated by scanning the snake axis angle µ, and the spin rotation angle at the snake, φ, in the vicinity of their nominal values.

KSC-08pd2422

NASA Image and Video Library

2008-08-21

CAPE CANAVERAL, Fla. – Debris covers a road eroded by Tropical Storm Fay near Launch Pad 39A at NASA's Kennedy Space Center. The storm passed over the center Aug. 20 and then stalled offshore, bringing with it heavy rain and tropical storm force wind. Kennedy closed Aug. 19 because of Fay and reopened for normal operations Aug. 22. Based on initial assessments, there was no damage to space flight hardware, such as the space shuttles and Hubble Space Telescope equipment. Some facilities did sustain minor damage. Photo credit: NASA/Jack Pfaller

KSC-08pd2424

NASA Image and Video Library

2008-08-21

CAPE CANAVERAL, Fla. – Wind and rain from Tropical Storm Fay pummel the area near the Vehicle Assembly Building at NASA's Kennedy Space Center. The storm passed over the center Aug. 20 and then stalled offshore, bringing with it heavy rain and tropical storm force wind. Kennedy closed Aug. 19 because of Fay and reopened for normal operations Aug. 22. Based on initial assessments, there was no damage to space flight hardware, such as the space shuttles and Hubble Space Telescope equipment. Some facilities did sustain minor damage. Photo credit: NASA/Jack Pfaller

KSC-08pd2430

NASA Image and Video Library

2008-08-21

CAPE CANAVERAL, Fla. – Due to Tropical Storm Fay, the ground is flooded on a road alongside the turn basin at NASA's Kennedy Space Center. The storm passed over the center Aug. 20 and then stalled offshore, bringing with it heavy rain and tropical storm force wind. Kennedy closed Aug. 19 because of Fay and reopened for normal operations Aug. 22. Based on initial assessments, there was no damage to space flight hardware, such as the space shuttles and Hubble Space Telescope equipment. Some facilities did sustain minor damage. Photo credit: NASA/Jack Pfaller

KSC-08pd2423

NASA Image and Video Library

2008-08-21

CAPE CANAVERAL, Fla. – Flooding and some tree damage near the Vehicle Assembly Building are results from Tropical Storm Fay at NASA's Kennedy Space Center. The storm passed over the center Aug. 20 and then stalled offshore, bringing with it heavy rain and tropical storm force wind. Kennedy closed Aug. 19 because of Fay and reopened for normal operations Aug. 22. Based on initial assessments, there was no damage to space flight hardware, such as the space shuttles and Hubble Space Telescope equipment. Some facilities did sustain minor damage. Photo credit: NASA/Jack Pfaller

KSC-08pd2431

NASA Image and Video Library

2008-08-21

CAPE CANAVERAL, Fla. – Due to Tropical Storm Fay, the roadside canals and surrounding grounds are flooded at NASA's Kennedy Space Center. In the background is the Vehicle Assembly Building. The storm passed over the center Aug. 20 and then stalled offshore, bringing with it heavy rain and tropical storm force wind. Kennedy closed Aug. 19 because of Fay and reopened for normal operations Aug. 22. Based on initial assessments, there was no damage to space flight hardware, such as the space shuttles and Hubble Space Telescope equipment. Some facilities did sustain minor damage. Photo credit: NASA/Ben Smegelsky

KSC-08pd2428

NASA Image and Video Library

2008-08-21

CAPE CANAVERAL, Fla. – An alligator seeks higher ground alongside a road at NASA's Kennedy Space Center during the onslaught of Tropical Storm Fay. The storm passed over the center Aug. 20 and then stalled offshore, bringing with it heavy rain and tropical storm force wind. Kennedy closed Aug. 19 because of Fay and reopened for normal operations Aug. 22. Based on initial assessments, there was no damage to space flight hardware, such as the space shuttles and Hubble Space Telescope equipment. Some facilities did sustain minor damage. Photo credit: NASA/Jack Pfaller

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.

Tangential synthetic jets for separation control

NASA Astrophysics Data System (ADS)

Esmaeili Monir, H.; Tadjfar, M.; Bakhtian, A.

2014-02-01

A numerical study of separation control has been made to investigate aerodynamic characteristics of a NACA23012 airfoil with a tangential synthetic jet. Simulations are carried out at the chord Reynolds number of Re=2.19×106. The present approach relies on solving the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations. The turbulence model used in the present computation is the Spalart-Allmaras one-equation model. All computations are performed with a finite volume based code. Stall characteristics are significantly improved by controlling the formation of separation vortices in the flow. We placed the synthetic jet at the 12% chord, xj=0.12c, where we expected the separation to occur. Two distinct jet oscillating frequencies: Fj+=0.159 and Fj+=1 were considered. We studied the effect of blowing ratio, Vj/U∞, where it was varied from 0 to 5. The inclined angle of the synthetic jet was varied from αj=0° up to αj=83°. For the non-zero inclined angles, the local maximum in the aerodynamic performance, Cl/Cd, of 6.89 was found for the inclined angle of about 43°. In the present method, by means of creating a dent on the airfoil, linear momentum is transferred to the flow system in tangential direction to the airfoil surface. Thus the absolute maximum of 11.19 was found for the tangential synthetic jet at the inclined angle of the jet of 0°. The mechanisms involved for a tangential jet appear to behave linearly, as by multiplying the activation frequency of the jet by a factor produces the same multiplication factor in the resulting frequency in the flow. However, the mechanisms involved in the non-zero inclined angle cases behave nonlinearly when the activation frequency is multiplied.

Pilot evaluation of sailplane handling qualities

NASA Technical Reports Server (NTRS)

Bennett, A. G., Jr.

1978-01-01

The evaluation sailplanes were found generally deficient in the area of cockpit layout. The pilots indicated general dissatisfaction with high pitch sensitivity especially when coupled with inertially induced stick forces. While all sailplanes were judged satisfactory for centering thermals and in the ease of speed control in circling flight, pilot opinions diverged on the maneuvering response, pull-out characteristics from a dive, and on phugoid damping. Lateral-directional control problems were noted mainly during takeoff and landing for most sailplanes with the landing wheel ahead of center of gravity. Pilot opinion of in-flight lateral-directional stability and control was generally satisfactory. Five of the evaluation sailplanes exhibited a very narrow airspeed band in which perceptible stall warning buffet occurred. However, this characteristic was considered not objectionable when stall recovery was easy. The pilots objected to the characteristics of a wide airspeed band of stall warning followed by a stall with yawing and rolling tendency and substantial loss of altitude during the stall. Glide path control for the evaluation sailplanes was found to be generally objectionable.

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.

Self-Recirculating Casing Treatment Concept for Enhanced Compressor Performance

NASA Technical Reports Server (NTRS)

Hathaway, Michael D.

2002-01-01

A state-of-the-art CFD code (APNASA) was employed in a computationally based investigation of the impact of casing bleed and injection on the stability and performance of a moderate speed fan rotor wherein the stalling mass flow is controlled by tip flow field breakdown. The investigation was guided by observed trends in endwall flow characteristics (e.g., increasing endwall aerodynamic blockage) as stall is approached and based on the hypothesis that application of bleed or injection can mitigate these trends. The "best" bleed and injection configurations were then combined to yield a self-recirculating casing treatment concept. The results of this investigation yielded: 1) identification of the fluid mechanisms which precipitate stall of tip critical blade rows, and 2) an approach to recirculated casing treatment which results in increased compressor stall range with minimal or no loss in efficiency. Subsequent application of this approach to a high speed transonic rotor successfully yielded significant improvements in stall range with no loss in compressor efficiency.

Group space allowance has little effect on sow health, productivity, or welfare in a free-access stall system

USDA-ARS?s Scientific Manuscript database

Free-access stalls allow sows to choose the protection of a stall or use of a shared group space. This study investigated the effect of group space width: 0.91 (SS), 2.13 (IS), and 3.05 (LS) m on the health, production, behavior, and welfare of gestating sows. At gestational day (GD) 35.4 ± 2.3, 21 ...

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

75 FR 34956 - Airworthiness Directives; Robert E. Rust, Jr. Model DeHavilland DH.C1 Chipmunk 21, DH.C1 Chipmunk...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-06-21

... retraction of the flaps. This failure could lead to a stall during a landing approach. DATES: We must receive...-commanded retraction of the flaps. This failure could lead to a stall during a landing approach. Relevant... result in an un-commanded retraction of the flaps. This failure could lead to a stall during a landing...

Flight assessment of the onboard propulsion system model for the Performance Seeking Control algorithm on an F-15 aircraft

NASA Technical Reports Server (NTRS)

Orme, John S.; Schkolnik, Gerard S.

1995-01-01

Performance Seeking Control (PSC), an onboard, adaptive, real-time optimization algorithm, relies upon an onboard propulsion system model. Flight results illustrated propulsion system performance improvements as calculated by the model. These improvements were subject to uncertainty arising from modeling error. Thus to quantify uncertainty in the PSC performance improvements, modeling accuracy must be assessed. A flight test approach to verify PSC-predicted increases in thrust (FNP) and absolute levels of fan stall margin is developed and applied to flight test data. Application of the excess thrust technique shows that increases of FNP agree to within 3 percent of full-scale measurements for most conditions. Accuracy to these levels is significant because uncertainty bands may now be applied to the performance improvements provided by PSC. Assessment of PSC fan stall margin modeling accuracy was completed with analysis of in-flight stall tests. Results indicate that the model overestimates the stall margin by between 5 to 10 percent. Because PSC achieves performance gains by using available stall margin, this overestimation may represent performance improvements to be recovered with increased modeling accuracy. Assessment of thrust and stall margin modeling accuracy provides a critical piece for a comprehensive understanding of PSC's capabilities and limitations.

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.

Public Attitudes to Housing Systems for Pregnant Pigs.

PubMed

Ryan, E B; Fraser, D; Weary, D M

2015-01-01

Understanding concerns about the welfare of farm animals is important for the development of socially sustainable production practices. This study used an online survey to test how views on group versus stall housing for pregnant sows varied when Canadian and US participants were provided information about these systems, including access to scientific papers, YouTube videos, Google images, and a frequently-asked-questions page (S1 Appendix). Initial responses and changes in responses after accessing the information were analyzed from Likert scores of 242 participants and from their written comments. Participants were less willing to accept the use of gestation stalls after viewing information on sow housing. For example, initially 30.4% of respondents indicated that they supported the use of gestation stalls; this declined to 17.8% after participants were provided additional information. Qualitative analysis of comments showed that supporters of gestation stalls expressed concern about the spread of disease and aggression between animals in less confined systems, whereas supporters of group housing placed more emphasis on the sow's ability to interact socially and perform natural behaviors. These results point to public opposition to the use of gestation stalls, and indicate that the more that the public learns about gestation stalls the less willing they will be to accept their use.

Effect of free stall surface on daily activity patterns in dairy cows with relevance to lameness prevalence.

PubMed

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

2004-09-01

Differences in behavior of nonlame cows, slightly lame cows, and moderately lame cows in 6 free stall barns with sand bedding (SAND) vs. 6 free stall barns with rubber-crumb geotextile mattress surfaces (MAT) were documented in Wisconsin dairy herds. All lactating cows in the 12 herds were observed and given a locomotion score based on a 4-point scale: 1 = nonlame, 2 = slightly lame, 3 = moderately lame, and 4 = severely lame. Herd least square means +/-SE for prevalence of clinical lameness (locomotion scores = 3 and 4) were 11.1 vs. 24.0 +/- 1.7% for herds using SAND vs. MAT surfaces, respectively. Subsets of 10 cows per herd with locomotion scores of 1 to 3 were observed via video cameras for 24-h periods. Cows in MAT herds spent more time standing in free stalls per day than cows in SAND herds. Differences in standing times were 0.73 h/d for cows that were not lame, 2.32 h/d for cows that were slightly lame, and 4.31 h/d for cows that were moderately lame in MAT herds compared with equivalent cows in SAND herds. In MAT herds, the increase in time spent standing in the stall in moderately lame cows was associated with a significant reduction in stall use sessions per day, which impacted daily lying time. Although cause and effect are not clear, these findings have implications for housing, comfort, and care of cows in dairy herds with different types of free stall surfaces.

The cam impinging femur has multiple morphologic abnormalities.

PubMed

Ellis, Andrew R; Noble, Philip C; Schroder, Steven J; Thompson, Matthew T; Stocks, Gregory W

2011-09-01

This study was performed to establish whether the "cam" impinging femur has a single deformity of the head-neck junction or multiple abnormalities. Average dimensions (anteversion angle, α angle of Notzli, β angle of Beaulé, normalized anterior head offset) were compared between normal and impinging femora. The results demonstrated that impinging femora had wider necks, larger heads, and decreased head-neck ratios. There was no difference in neck-shaft angle or anteversion angle. Forty-six percent of impinging femora had significant posterior head displacement (>2mm), which averaged 1.93 mm for the cam impinging group, and 0.78 mm for the normal group. In conclusion, surgical treatment limited to localized recontouring of the head-neck profile may fail to address significant components of the underlying abnormality. Copyright © 2011 Elsevier Inc. All rights reserved.

DNA polymerases eta and kappa exchange with the polymerase delta holoenzyme to complete common fragile site synthesis.

PubMed

Barnes, Ryan P; Hile, Suzanne E; Lee, Marietta Y; Eckert, Kristin A

2017-09-01

Common fragile sites (CFSs) are inherently unstable genomic loci that are recurrently altered in human tumor cells. Despite their instability, CFS are ubiquitous throughout the human genome and associated with large tumor suppressor genes or oncogenes. CFSs are enriched with repetitive DNA sequences, one feature postulated to explain why these loci are inherently difficult to replicate, and sensitive to replication stress. We have shown that specialized DNA polymerases (Pols) η and κ replicate CFS-derived sequences more efficiently than the replicative Pol δ. However, we lacked an understanding of how these enzymes cooperate to ensure efficient CFS replication. Here, we designed a model of lagging strand replication with RFC loaded PCNA that allows for maximal activity of the four-subunit human Pol δ holoenzyme, Pol η, and Pol κ in polymerase mixing assays. We discovered that Pol η and κ are both able to exchange with Pol δ stalled at repetitive CFS sequences, enhancing Normalized Replication Efficiency. We used this model to test the impact of PCNA mono-ubiquitination on polymerase exchange, and found no change in polymerase cooperativity in CFS replication compared with unmodified PCNA. Finally, we modeled replication stress in vitro using aphidicolin and found that Pol δ holoenzyme synthesis was significantly inhibited in a dose-dependent manner, preventing any replication past the CFS. Importantly, Pol η and κ were still proficient in rescuing this stalled Pol δ synthesis, which may explain, in part, the CFS instability phenotype of aphidicolin-treated Pol η and Pol κ-deficient cells. In total, our data support a model wherein Pol δ stalling at CFSs allows for free exchange with a specialized polymerase that is not driven by PCNA. Copyright © 2017 Elsevier B.V. All rights reserved.

NSC30049 inhibits Chk1 pathway in 5-FU-resistant CRC bulk and stem cell populations.

PubMed

Narayan, Satya; Jaiswal, Aruna S; Sharma, Ritika; Nawab, Akbar; Duckworth, Lizette Vila; Law, Brian K; Zajac-Kaye, Maria; George, Thomas J; Sharma, Jay; Sharma, Arun K; Hromas, Robert A

2017-08-22

The 5-fluorouracil (5-FU) treatment induces DNA damage and stalling of DNA replication forks. These stalled replication forks then collapse to form one sided double-strand breaks, leading to apoptosis. However, colorectal cancer (CRC) stem cells rapidly repair the stalled/collapsed replication forks and overcome treatment effects. Recent evidence suggests a critical role of checkpoint kinase 1 (Chk1) in preventing the replicative stress. Therefore, Chk1 kinase has been a target for developing mono or combination therapeutic agents. In the present study, we have identified a novel orphan molecule NSC30049 (NSC49L) that is effective alone, and in combination potentiates 5-FU-mediated growth inhibition of CRC heterogeneous bulk and FOLFOX-resistant cell lines in culture with minimal effect on normal colonic epithelial cells. It also inhibits the sphere forming activity of CRC stem cells, and decreases the expression levels of mRNAs of CRC stem cell marker genes. Results showed that NSC49L induces 5-FU-mediated S-phase cell cycle arrest due to increased load of DNA damage and increased γ-H2AX staining as a mechanism of cytotoxicity. The pharmacokinetic analysis showed a higher bioavailability of this compound, however, with a short plasma half-life. The drug is highly tolerated by animals with no pathological aberrations. Furthermore, NSC49L showed very potent activity in a HDTX model of CRC stem cell tumors either alone or in combination with 5-FU. Thus, NSC49L as a single agent or combined with 5-FU can be developed as a therapeutic agent by targeting the Chk1 pathway in 5-FU-resistant CRC heterogeneous bulk and CRC stem cell populations.

Synthetic optimization of air turbine for dental handpieces.

PubMed

Shi, Z Y; Dong, T

2014-01-01

A synthetic optimization of Pelton air turbine in dental handpieces concerning the power output, compressed air consumption and rotation speed in the mean time is implemented by employing a standard design procedure and variable limitation from practical dentistry. The Pareto optimal solution sets acquired by using the Normalized Normal Constraint method are mainly comprised of two piecewise continuous parts. On the Pareto frontier, the supply air stagnation pressure stalls at the lower boundary of the design space, the rotation speed is a constant value within the recommended range from literature, the blade tip clearance insensitive to while the nozzle radius increases with power output and mass flow rate of compressed air to which the residual geometric dimensions are showing an opposite trend within their respective "pieces" compared to the nozzle radius.

A Method to Predict Compressor Stall in the TF34-100 Turbofan Engine Utilizing Real-Time Performance Data

DTIC Science & Technology

2015-06-01

A METHOD TO PREDICT COMPRESSOR STALL IN THE TF34-100 TURBOFAN ENGINE UTILIZING REAL-TIME PERFORMANCE...THE TF34-100 TURBOFAN ENGINE UTILIZING REAL-TIME PERFORMANCE DATA THESIS Presented to the Faculty Department of Systems Engineering and...036 A METHOD TO PREDICT COMPRESSOR STALL IN THE TF34-100 TURBOFAN ENGINE UTILIZING REAL-TIME PERFORMANCE DATA Shuxiang ‘Albert’ Li, BS

Final Environmental Assessment, Family Camp Facility Buckey Air Force Base, Colorado

DTIC Science & Technology

2008-02-07

Table 2-1 for details. This will provide restrooms, showers , and laundry facilities. The proposed FamCamp originally included ten new tent sites...compliant. Two shower stalls will be provided, one of which meets ADA requirements. The interior finishes will consist of ceramic tile floor...with one of the toilet stalls being ADA compliant. Two shower stalls will be provided, one of which meets ADA requirements. The interior finishes

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

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.

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

Analysis and test evaluation of the dynamic response and stability of three advanced turboprop models at low forward speed

NASA Technical Reports Server (NTRS)

Smith, Arthur F.

1985-01-01

Results of wind tunnel tests at low forward speed for blade dynamic response and stability of three 62.2 cm (24.5 in) diameter models of the Prop-Fan, advanced turboprop, are presented. Measurements of dynamic response were made with the rotors mounted on an isolated nacelle, with varying tilt for nonuniform inflow. Low speed stall flutter tests were conducted at Mach numbers from 0.0 to 0.35. Measurements are compared to Eigen-solution flutter boundaries. Calculated 1P stress response agrees favorably with experiment. Predicted stall flutter boundaries correlate well with measured high stress regions. Stall flutter is significantly reduced by increased blade sweep. Susceptibility to stall flutter decreases rapidly with forward speed.

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.

Separation control of NACA0015 airfoil using plasma actuators

NASA Astrophysics Data System (ADS)

Harada, Daisuke; Sakakibara, Jun

2017-11-01

Separation control of NACA0015 airfoil by means of plasma actuators was investigated. Plasma actuators in spanwise intermittent layout on the suction surface of the airfoil were activated with spanwise phase difference φ = 0 or φ = π in the case of dimensionless burst frequencyF+ = 6 and F+ = 0.5 at Re = 6.3 ×104 . The lift and drag of the airfoil were measured using a two component force balance. The flow around the airfoil was measured by PIV analysis. In the condition of F+ = 6 and φ = π at around stall angle, which is 10 degrees, the lift-to-drag ratio was higher than that ofF+ = 6 and φ = 0 . Therefore, it was confirmed that aerodynamic characteristics of the airfoil improved by disturbances with temporal and spatial phase difference.

Free-flight investigation of the stability and control characteristics of a STOL model with an externally blown jet flap

NASA Technical Reports Server (NTRS)

Parlett, L. P.; Emerling, S. J.; Phelps, A. E., III

1974-01-01

The stability and control characteristics of a four-engine turbofan STOL transport model having an externally blown jet flap have been investigated by means of the flying-model technique in the Langley full-scale tunnel. The flight characteristics of the model were investigated under conditions of symmetric and asymmetric (one engine inoperative) thrust at lift coefficients up to 9.5 and 5.5, respectively. Static characteristics were studied by conventional power-on force tests over the flight-test angle-of-attack range including the stall. In addition to these tests, dynamic longitudinal and lateral stability calculations were performed for comparison with the flight-test results and for use in correlating the model results with STOL handling-qualities criteria.

Laser anemometer measurements in a transonic axial-flow fan rotor

NASA Technical Reports Server (NTRS)

Strazisar, Anthony J.; Wood, Jerry R.; Hathaway, Michael D.; Suder, Kenneth L.

1989-01-01

Laser anemometer surveys were made of the 3-D flow field in NASA rotor 67, a low aspect ratio transonic axial-flow fan rotor. The test rotor has a tip relative Mach number of 1.38. The flowfield was surveyed at design speed at near peak efficiency and near stall operating conditions. Data is presented in the form of relative Mach number and relative flow angle distributions on surfaces of revolution at nine spanwise locations evenly spaced from hub to tip. At each spanwise location, data was acquired upstream, within, and downstream of the rotor. Aerodynamic performance measurements and detailed rotor blade and annulus geometry are also presented so that the experimental results can be used as a test case for 3-D turbomachinery flow analysis codes.

Dynamic response of a Mach 2.5 axisymmetric inlet and turbojet engine with a poppet-value controlled inlet stability bypass system when subjected to internal and external airflow transients

NASA Technical Reports Server (NTRS)

Sanders, B. W.

1980-01-01

The throat of a Mach 2.5 inlet that was attached to a turbojet engine was fitted with a poppet-valve-controlled stability bypass system that was designed to provide a large, stable airflow range. Propulsion system response and stability bypass performance were determined for several transient airflow disturbances, both internal and external. Internal airflow disturbances included reductions in overboard bypass airflow, power lever angle, and primary-nozzle area as well as compressor stall. For reference, data are also included for a conventional, fixed-exit bleed system. The poppet valves greatly increased inlet stability and had no adverse effects on propulsion system performance. Limited unstarted-inlet bleed performance data are presented.

Preliminary flight-test results of an advanced technology light twin-engine airplane /ATLIT/

NASA Technical Reports Server (NTRS)

Holmes, B. J.; Kohlman, D. L.; Crane, H. L.

1976-01-01

The present status and flight-test results are presented for the ATLIT airplane. The ATLIT is a Piper PA-34 Seneca I modified by the installation of new wings incorporating the GA(W)-1 (Whitcomb) airfoil, reduced wing area, roll-control spoilers, and full-span Fowler flaps. Flight-test results on stall and spoiler roll characteristics show good agreement with wind-tunnel data. Maximum power-off lift coefficients are greater than 3.0 with flaps deflected 37 deg. With flaps down, spoiler deflections can produce roll helix angles in excess of 0.11 rad. Flight testing is planned to document climb and cruise performance, and supercritical propeller performance and noise characteristics. The airplane is scheduled for testing in the NASA-Langley Research Center Full-Scale Tunnel.