The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform
Raymond E. Gordnier - One of the best experts on this subject based on the ideXlab platform.
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Numerical Simulation of Nonslender Delta Wing
2004Co-Authors: Raymond E. Gordnier, Miguel R. VisbalAbstract:Experiments for a exible 50 sweep Delta Wing exhibited sizable time-averaged deections of the Wing and corresponding large amplitude vibrations in the post stall region. This aeroelastic behavior resulted in signicant lift enhancement and a delay in the onset of stall. Computations are performed to numerically simulate this interesting uid/structure interaction. These computations use an aeroelastic code which couples an Euler solver with a nite element model for the von Karman plate equations. The problem is assumed to be symmetric and the Wing is rigidly clamped along the symmetry plane. Computations are performed in the post stall region for angles of attack of 20 , 25 and 30 . Large deections and vibrations of the Delta Wing are achieved in the simulations but the enhanced dynamic behavior and lift in the post stall region is not captured. The underlying fundamental assumptions for the numerical model chosen are carefully examined to attempt to explain this discrepancy.
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Computation of limit-cycle oscillations of a Delta Wing
Journal of Aircraft, 2003Co-Authors: Raymond E. GordnierAbstract:This paper presents computational simulations of limit cycle oscillations of a cropped Delta Wing. A newly developed aeroelastic solver which couples a well validated Navier-Stokes code with a nonlinear nite element method for the von Karman plate equations is employed. Previous computations using a linear structural modal solver to model the Delta Wing produced limit cycle oscillations with significantly larger amplitudes than the experimentally measured limit cycle response. The present computations with the nonlinear structural model produce limit cycle amplitudes commensurate with the experimental measurements. The computations presented in the paper demonstrate that the geometric nonlinearities in the structural model provide the proper nonlinear mechanism for the development of the limit cycle response observed in the experiments.
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Physical mechanisms for limit-cycle oscillations of a cropped Delta Wing
30th Fluid Dynamics Conference, 1999Co-Authors: Raymond E. Gordnier, Reid MelvilleAbstract:This paper presents simulations of limit-cycle oscillations of a cropped Delta Wing using a computational technique that implicitly couples a full Navier-Stokes solver to a linear structural solver. Computational results are compared with existing experimental measurements of the limit-cycle response of the Delta Wing. The limit-cycle oscillation is shown to consist primarily of a response of the first bending mode and the first torsional mode. Aerodynamic features of the limit cycle identified include a leading-edge vortex and a double shock structure. The leading edge vortex acts like an aerodynamic spring and provides the physical mechanism for the evolution of the limit cycle on the Delta Wing. Computations are repeated using the Euler equations to determine if the inviscid flow equations adequately simulate the observed limit cycle response.
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Unsteady vortex structure over a Delta Wing
Journal of Aircraft, 1994Co-Authors: Raymond E. Gordnier, Miguel R. VisbalAbstract:The structure of the shear layer which emanates from the leading edge of a 76-deg sweep Delta Wing and forms the primary vortex is investigated numerically. The flow conditions are Mv_ = 0.2, Re = 50,000 and angle of attack of 20.5 deg. Computational results are obtained using a Beam-Warming-t ype algorithm. The existence of a Kelvin-Helmholtz-type instability of the shear layer which emanates from the leading edge of the Delta Wing is demonstrated. A description is provided of the three-dimensional, unsteady behavior of the smallscale vortices associated with this instability. The numerical results are compared qualitatively with experimental flow visualizations exhibiting a similar behavior.
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Computation of Delta-Wing roll maneuvers
23rd Fluid Dynamics Plasmadynamics and Lasers Conference, 1993Co-Authors: Raymond E. GordnierAbstract:This article presents computations of Delta-Wing roll maneuvers for an 80-deg sweep Delta-Wing at 30-deg angle of attack. Three constant roll-rate maneuvers are considered. Two of the maneuvers consist of a roll from 0 to 45 deg at nondimensiona l roll rates of = 0.0233 and 0.0467. The third roll maneuver computed starts at a 45-deg roll angle and rolls back to a -45-deg roll angle at a roll rate 4> = -0.0467. The governing equations are the unsteady, three-dimensional Navier-Stokes equations. The equations are solved using the implicit, approximately-factored, diagonal form of the Beam-Warming algorithm. Subiterations are used to provide a more accurate means of implementing the diagonal form of the algorithm for unsteady flows. The effects of roll-rate and differing initial roll angles on the dynamical behavior of the vortices positions and strengths as well as their corresponding effect on surface pressure and roll moment coefficient are described.
Lars E. Ericsson - One of the best experts on this subject based on the ideXlab platform.
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Multifaceted Influence of Fuselage Geometry on Delta Wing Aerodynamics
Journal of Aircraft, 2003Co-Authors: Lars E. EricssonAbstract:The complicated, multifaceted influence of fuselage geometry on Delta Wing aerodynamics remains a poorly understood and, therefore, often ignored flow phenomenon. As more and more experimental results become available, the problem becomes harder to ignore. In the present paper the existing data base is analyzed to provide the basic information needed to plan subscale tests that can provide a realistic representation of full-scale Delta-Wing-body aerodynamics.
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Effect of Fuselage Geometry on Delta-Wing Vortex Breakdown
Journal of Aircraft, 1998Co-Authors: Lars E. EricssonAbstract:A fuselage is usually associated with the use of a Delta Wing on an actual aircraft. It is also in many cases necessary to use a centerbody of some shape in tunnel tests of pure Delta Wings. The present paper describes the e ow physics causing the experimentally observed large effect of a fuselage on Delta-Wing vortex breakdown.
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Analysis of the effect of sideslip on Delta Wing roll trim characteristics
Journal of Aircraft, 1997Co-Authors: Lars E. EricssonAbstract:The effect of sideslip on the roll-trim characteristics around a 30-deg inclined axis has been analyzed for a 60-deg Delta Wing. By an extension of analytic tools developed earlier for a 65-deg Delta Wing, the highly nonlinear unsteady aerodynamics can be understood, including the breakaway from one roll-trim condition to another.
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Comment on 'Effect of fuselage on Delta Wing vortex breakdown'
Journal of Aircraft, 1994Co-Authors: Lars E. EricssonAbstract:I T is shown in Ref. 1 that the presence of a fuselage significantly promotes the breakdown of Delta Wing leadingedge vortices. Applying the equivalent angle-of-attack concept only accounted for a fraction of the measured effect of the fuselage, predicting a 17% increase of the effective angle of attack compared to the measured 45% increase. The present comment describes a flow mechanism that can explain this discrepancy, i.e., the Wing-camber effect generated by the fuselage-induced upwash along the leading edge of the Delta Wing. The effect of longitudinal camber on the breakdown of the leading-edge vortex on a slender Delta Wing is large (Fig. 1). For the same maximum local angle of attack on the Delta Wing max a positive camber of Aa/amax = 1 delays breakdown to occur downstream of the trailing edge, whereas a negative camber of the same magnitude, Aa/amax = — 1, causes burst to occur very close to the apex. Obviously, for a pitching Delta Wing the pitch-rate-induced camber will have similarly large effects on the breakdown of leading-edge vortices. It is described in Refs. 4 and 5 how the roll-rate-induced camber effect would be very similar to the pitch-rate-induced camber effect. In both cases, it is the motion-induced change of the local angle of attack at the leading edge that matters (Fig. 2). For the maximum reduced frequency and amplitude used in the roll oscillation test of a 65-deg, sharp-edged Delta Wing, the roll-rate-induced camber at the trailing edge was AaLE/a = 0.31. FolloWing the suggestion in Ref. 7, static tests were performed with models deformed to produce the roll-rateinduced camber (Fig. 3). The results were as expected; i.e., the twisted-up side of the Delta Wing experienced later vortex breakdown than the opposite, twisted-down side, approximately at 70% chord compared to 45% chord (for zero roll angle
Miguel R. Visbal - One of the best experts on this subject based on the ideXlab platform.
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Numerical Simulation of Nonslender Delta Wing
2004Co-Authors: Raymond E. Gordnier, Miguel R. VisbalAbstract:Experiments for a exible 50 sweep Delta Wing exhibited sizable time-averaged deections of the Wing and corresponding large amplitude vibrations in the post stall region. This aeroelastic behavior resulted in signicant lift enhancement and a delay in the onset of stall. Computations are performed to numerically simulate this interesting uid/structure interaction. These computations use an aeroelastic code which couples an Euler solver with a nite element model for the von Karman plate equations. The problem is assumed to be symmetric and the Wing is rigidly clamped along the symmetry plane. Computations are performed in the post stall region for angles of attack of 20 , 25 and 30 . Large deections and vibrations of the Delta Wing are achieved in the simulations but the enhanced dynamic behavior and lift in the post stall region is not captured. The underlying fundamental assumptions for the numerical model chosen are carefully examined to attempt to explain this discrepancy.
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Unsteady vortex structure over a Delta Wing
Journal of Aircraft, 1994Co-Authors: Raymond E. Gordnier, Miguel R. VisbalAbstract:The structure of the shear layer which emanates from the leading edge of a 76-deg sweep Delta Wing and forms the primary vortex is investigated numerically. The flow conditions are Mv_ = 0.2, Re = 50,000 and angle of attack of 20.5 deg. Computational results are obtained using a Beam-Warming-t ype algorithm. The existence of a Kelvin-Helmholtz-type instability of the shear layer which emanates from the leading edge of the Delta Wing is demonstrated. A description is provided of the three-dimensional, unsteady behavior of the smallscale vortices associated with this instability. The numerical results are compared qualitatively with experimental flow visualizations exhibiting a similar behavior.
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Computation of a Delta-Wing Roll-and-Hold Maneuver
1993Co-Authors: Raymond E. Gordnier, Miguel R. VisbalAbstract:Abstract : This report presents computations of the flowfield around an 80 degree sweep Delta Wing undergoing a constant roll-rate maneuver from 0 to 45 degrees. The governing equations for the problem are the unsteady, three- dimensional Navier-Stokes equations. The equations are solved using the implicit, approximately-factored algorithm of Beam-Warming. Fixed roll angle results are also presented and compared with experimental measurements to demonstrate the ability of the numerical technique to accurately capture the flowfield around a rolled Delta Wing. The dynamic behaviors of the vortex position and strength, as well as their corresponding effect on surface pressure, lift and roll moment, are described. A simple, quasi-static explanation of these vortex behaviors based on effective angle-of-attack and sideslip angle is proposed.... Delta Wing roll, Vortex dynamics, Vortical flow, Unsteady maneuver
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Numerical simulation of Delta-Wing roll
31st Aerospace Sciences Meeting, 1993Co-Authors: Raymond E. Gordnier, Miguel R. VisbalAbstract:Abstract This paper presents computations of the flowfield around an 80° sweep Delta Wing undergoing a constant roll-rate manoeuver from 0° to 45°. The governing equations for the problem are the unsteady, three-dimensional Navier-Stokes equations. The equations are solved using the implicit, approximately-factored algorithm of Beam-Warming. Fixed roll angle results are also presented and compared with experimental measurements to demonstrate the ability of the numerical technique to accurately capture the flowfield around a rolled Delta Wing. The dynamical behavior of the vortex position and strength, as well as its corresponding effect on surface pressure, lift and roll moment are described. A simple, quasi-static explanation of this vortex behavior based on effective angle of attack and sideslip angle is proposed.
Jinjun Wang - One of the best experts on this subject based on the ideXlab platform.
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vortex structures for flow over a Delta Wing with sinusoidal leading edge
Experiments in Fluids, 2014Co-Authors: Huang Chen, Jinjun WangAbstract:The idea of using sinusoidal leading edge as a kind of passive flow control method was inspired by observing the flipper movement of the humpback whale. It was believed that the protuberances along the whale’s pectoral fin could delay stall, thus would enhance the maneuverability of the whale. It has also been shown that when equipped with sinusoidal leading edges, the stall of a Delta Wing could be delayed. In this paper, stereoscopic particle image velocimetry was adopted to study the vortex structures for the flow over a 52° swept Delta Wing with sinusoidal leading edges. A direct comparison with the flow over a baseline Delta Wing was made to illustrate the different vortex structures of these two kinds of models. Results have shown that the flow over the baseline Delta Wing was dominated by dual leading-edge vortices (LEVs), a structure that only existed for flow over nonslender Delta Wing at certain Reynolds number. On the other hand, the flow over the one with sinusoidal leading edge showed a very different pattern. It has been found in this paper that there were several pairs of LEVs existed on the leeward side of the Wing, which might explain the stall-delaying effect of the Delta Wing with sinusoidal leading edges.
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effects of sinusoidal leading edge on Delta Wing performance and mechanism
Science China-technological Sciences, 2013Co-Authors: Huang Chen, Chong Pan, Jinjun WangAbstract:Lift and drag characteristics of Delta Wings with low swept angle and various sinusoidal leading edges (SLE) were investigated in a wind tunnel. Three amplitudes and three wavelengths of SLE were tested. It is revealed that, in comparison with the baseline case, when the leading-edge amplitude A ≤5% C (root chord length of a Delta Wing), the stall of the Delta Wing can be delayed without penalty on the maximum lift coefficient; meanwhile, the lift-to-drag ratio was kept nearly unchanged. These are beneficial to aircraft maneuverability and agility. Surface oil and hydrogen-bubble flow visualization experiments were further conducted to provide a general view of the underlying flow mechanism of SLE on Delta Wings. It was found that, for the flow over Delta Wing with SLE, vortices were generated from every crest of SLE, in contrast to the dual leading-edge vortex structure generated from the apex of the base Wing. At high angle of attack, the breakdown of those vortices originating from the crests of SLE may provide additional turbulent kinetic energy to the flow, resulting in the increase of the flow reattachment region on the leeward side, therefore the stall can be delayed.
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influence of reynolds number on vortex flow over a nonslender Delta Wing
AIAA Journal, 2010Co-Authors: Lan Chen, Jinjun Wang, Linxuan Zuo, Lihao FengAbstract:Through computational simulations performed for a 50° sweep Delta Wing at low Reynolds numbers Re = 8.7 x 10 3 - 4.0 x 10 4 , this paper presents the features of the flow structures over the Delta Wing including the separated vortical flow, the onset of vortex breakdown, surface flow features, and dual vortex phenomena. At the lowest Reynolds number Re = 8.7 x 10 3 , no dual vortex structures are observed. As the Reynolds number is increased the dual vortex structures are developed, and the spanwise location of the vortex core is moved toward outboard without obvious variation of the vortex core vertical location above the Wing leeward surface. At the lower Reynolds numbers investigated, the vortex breakdown location moves upstream as the Reynolds number increases. The primary reattachment lines move outboard toward the leading edge with the increasing Reynolds number, and simultaneously the start point of the secondary separation moves forward toward the tip of Delta Wing.
Noor A. Ahmed - One of the best experts on this subject based on the ideXlab platform.
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Forward Facing Flap for Delta Wing Performance Improvement
International Review of Aerospace Engineering (IREASE), 2017Co-Authors: Noor A. AhmedAbstract:In the present study, the concept of forward facing flap mounted on a slender Delta Wing, originally proposed by Hurley is considered. The test model resulted in surfaces that deflected from the basic Delta to form a simple X-configuration. With this configuration, force balance measurements were conducted at low speed in a low speed open circuit wind tunnel. The lift produced was found to be dependent on both the flap deflection angle and thickness. Overall, the results obtained are very promising as they show definitive trends in the lift performance improvement of the X-configuration over conventional base Delta Wing at low angles of attack.