Effect Of Pitch Rate Research Articles

Wing rock motion induced by forebody asymmetric vortices in pitch-up

Aiming to the issue that the angle of attack was usually fixed rather than pitched-up in the previous researches about the wing rock induced by forebody asymmetric vortices,series of wind tunnel experiments were conducted in Beihang University D4 wind tunnel over the configuration of a pointed ogive-cylindrical body with 30° swept wings. Effect of pitch rate on wing rock motion as well as the mechanism of that was first studied through wing rock experiments in different pitch rates. The flow mechanism of wing rock in high rate pitch-up was then studied through the surface pressure measurements during the dynamic wing rock.Experimental results show that,as the wing rock motion time reduces with increase of pitch rate,the motion patterns of wing rock are different in three different intervals of pitch rate. The sinusoidal-like motion,which is totally different from the motion at static angle of attack,would occur in the third interval with high rate pitch-up. The variation of forebody flow with angle of attack,instead of the variation of forebody flow with roll angle,is found to be responsible for the sinusoidal-like motion in high rate pitch-up. Hence,the flow mechanism of wing rock in pitch-up is greatly different from that at static angle of attack.

Design for Control of Wheeled Inverted Pendulum Platforms

In this paper, we study five aspects of design for wheeled inverted pendulum (WIP) platforms with the aim of understanding the effect of design choices on the balancing performance. First, we demonstrate analytically and experimentally the effect of soft visco-elastic tires on a WIP showing that the use of soft tires enhances balancing performance. Next, we study the effect of pitch rate and wheel velocity filters on WIP performance and make suggestions for design of filters. We then describe a self-tuning limit cycle compensation algorithm and experimentally verify its operation. Subsequently, we present an analytical simulation to study the effects of torque and velocity control of WIP motors and describe the tradeoffs between the control methodologies in various application scenarios. Finally, to understand if motor gearing can be an efficient alternative to bigger and more expensive direct drive motors, we analyze the effect of motor gearing on WIP dynamics. Our aim is to describe electromechanical design tradeoffs appropriately, so a WIP can be designed and constructed with minimal iterative experimentation.

Three-dimensional flow structure along simultaneously pitching and rotating wings: effect of pitch rate

The flow structure along a simultaneously pitching and rotating wing is investigated using quantitative flow visualization. Imaging is performed for a range of pitch rates, with emphasis on the three-dimensional structure during start-up and relaxation. Surfaces of transparent iso-Q and helicity are employed to interpret the flow physics. The onset and development of the components of the vortex system, i.e., the leading-edge, tip, and trailing-edge vortices, are strongly influenced by the value of pitch rate relative to the rotation rate. Comparisons at the same angle of attack indicate that the formation of vortical structures is delayed with increasing pitch rate. However, comparisons at the same rotation angle for different values of pitch rate reveal similar flow structures, thereby indicating predominance of rotation effects. Extreme values of pitch rate can lead to radically different sequences of development of the components of the three-dimensional vortex system. Nevertheless, consistently positive vorticity flux is maintained through these components and the coherence of the vortex system is maintained.

Effect of Pitch Rate on Near-Surface Topology on a Delta Wing

The near-surface flow structure and topology on a delta wing of moderate sweep angle are investigated using a technique of high-image-density digital particle image velocimetry. The focus is on the time evolution of the surface topology during relaxation of the flow after termination of a pitching maneuver for a wide range of pitch rates. The near-surface patterns at the instant corresponding to termination of the maneuver are a strong function of the magnitude of pitch rate and show substantial differences. On the other hand, irrespective of the severity of the flow distortion at the end of the pitching maneuver, the relaxation of the flow involves the same sequence of universal topological states. Furthermore, it is demonstrated that there exists a critical universal state that marks an abrupt transformationbetween twodistinctly different states of thenear-surface topology.Moreover, it is demonstrated that the changes of the topological features observed during the early stages of the relaxation process are analogous to the alterations of the surface patterns obtained for the stationary wing at smaller angles of attack.

Influence of Steady Pitch Rate on 2-D Airfoil Aerodynamic Characteristics at Incidence

I N various dynamic problems it is important to know the constituent parts of aerodynamic loads due to pitch rotation. However, the attention given to this question at higher angles of attack with flow separation has been very low. Sometimes the problem of modeling aerodynamic loads due to steady pitch rotation is mixed up with modeling aerodynamic loads due to incidence variation. Some discussions of the question can be found in [1]. These are really two distinct tasks. The first task is a steady one. It is possible to imagine motions with a constant angle of attack and various pitch rates. These are circular orbital motions with various radii. On the other hand a translational motion with zero pitch rate and varying incidence could exist also. In the first case the circulation is constant. In the second case a time-dependent vortex wake exists behind the body. The present work is devoted to some estimations using thin airfoil theory of pitch rate effects on a 2-D airfoil with flow separation at high constant angles of attack. For low angles of attack the influence of steady pitch rate on airfoil loads was investigated, for example, in [2]. For the case of zero pitch rate the effects of flow separation on aerodynamic loads was investigated using the linearized thin airfoil theory in [3]. This approach was now applied to estimations of pitch rate effects on a 2D airfoil with flow separation at high constant angles of attack. For comparison, numerical estimations from the well-known XFOIL code [4] were used. The effect of steady pitch rate is simulated using the approximate technique of curved models [5] (pitch rate induced curvature).

Grid Survey Approach to Store Separation Trajectory Prediction

of Incidence,” Aeronautical Research Council, R&M 3645, London,March 1969. 12Ericsson, L. E., “Pitch Rate Effects on Delta Wing Vortex Breakdown,” Journal of Aircraft, Vol. 33, No. 3, 1996, pp. 639–642. 13Leibovich,S., “VortexStabilityandBreakdown:SurveyandExtension,” AIAA Journal, Vol. 22, No. 9, 1984, pp. 1192–1206. 14Lundgren, T. S., and Ashurst, W. T., “Area-Varying Waves on Curved Vortex Tubes with Application to Vortex Breakdown,” Journal of Fluid Mechanics, Vol. 200, 1989, pp. 283–307. 15Gursul, I., “A ProposedMechanism for the Time Lag of Vortex Breakdown Location in Unsteady Flows,” AIAA Paper 2000-0787, Jan. 2000.

Pitch Rate Effects on Delta Wing Vortex Breakdown

Pitch Rate Effects on Delta Wing Vortex Breakdown

Pitch rate effects on delta wing vortex breakdown

Pitch rate effects on delta wing vortex breakdown

Pitch rate and pitch-axis location effects on vortex breakdown onset

Computational results are presented for the onset of vortex breakdown above a 75-deg sweep delta wing subject to a ramp-type pitch maneuver to high angle of attack. The flows are simulated by solving the full threedimensional unsteady NavierStokes equations on a moving grid using the implicit Beam-Warming algorithm. An assessment of the effects of numerical resolution, and comparison with experiment are employed to validate the computational approach. The effects of pitch rate and pitch-axis location are examined. For a range of these parameters, it is found that either increasing pitch rate or moving the axis downstream results in a larger angular delay of vortex bursting. These effects are correlated with the motion-induced effective incidence along the wing. For fixed pitch rate, the change in pivot location is equivalent to a shift in time without significant alteration of the flow structure.

Dynamic stall of a constant-rate pitching airfoil

A computational study is presented for the dynamic stall of an airfoil that is pitched at a constant rate from zero incidence to a high angle of attack. The unsteady flow is simulated employing the mass-averaged NavierStokes equations and an algebraic turbulent eddy viscosity model. The approach is first validated by comparison of computed and experimental results for a pitching airfoil at low freestream Mach numbers. The computed dynamic stall events, as well as the computed effects of pitch rate and axis location, are found in qualitative agreement with experimental observations. The effect of compressibility on dynamic stall is investigated. As the freestream Mach number increases, the appearance of a supersonic region provides—through the shock/boundarylayer interaction—an additional mechanism in the dynamic stall process. The main effects of compressibility are found to be 1) a change from trailing-edge stall to leading-edge stall and 2) a reduction in the stall delay and in the attained maximum lift.

Investigation of the flow structure around a rapidly pitching airfoil

A numerical study is presented for unsteady laminar flow past a NACA 0015 airfoil that is pitched, at a nominally constant rate, from zero incidence to a very high angle of attack. The flowfield simulation is obtained by solving the full two-dimensional compressible Navier-Stokes equations on a moving grid employing an implicit approximate-factorization algorithm. An evaluation of the accuracy of the computed solutions is presented, and the numerical results are shown to be of sufficient quality to merit physical interpretation. The highly unsteady flowfield structure is described and is found to be in qualitative agreement with available experimental observations. A discussion is provided for the effects of pitch rate and pitch axis location on the induced vortical structures and on the airfoil aerodynamic forces.

An experimental investigation of an airfoil undergoing large-amplitude pitching motions

FLOW visualization and near-surface hot-wire experiments were performed in the U.S.A.F Academy Aeronautics Laboratory subsonic wind tunnel on an airfoil undergoing large-amplitude pitching motions about its quarter chord. The experiments were conducted using a NACA 0015 airfoil at an airfoil Reynolds number of 45,000. Two cases are presented in which the angular pitching rate a is maintained constant during the motion. These two cases represent two different nondimensional pitching rates a+, where ot+ is equal to 6; nondimensionalized by the chord c and the freestream velocity U^ (a + ^ac/U^). Data for the two cases where values of a+ are equal to 0.2 and 0.6 show the dramatic effect of pitch rate on flow structure. Largescale vortical structures are seen in both cases at high angles of attack but appear much later and are of a different form for the case with the larger a+ value. These structures are very energetic, producing reverse flow velocities near the airfoil surface of 1.0-2.1 times the freestream velocity.