Numerical Simulation of Transient Vortex Breakdown Above a Pitching Delta Wing

Numerical Simulation of Transient Vortex Breakdown Above a Pitching Delta Wing
Author:
Publisher:
Total Pages: 43
Release: 1994
Genre:
ISBN:

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Computational results are presented for transient vortex breakdown above a delta wing subject to a pitch-and-hold maneuver to high angle of attack. The flows are simulated by solving the full three-dimensional Navier-Stokes equations on a moving grid using the implicit Beam-Warming algorithm. An assessment of the effects of numerical resolution, and favorable comparison with experimental data suggest the computational approach captures the basic dynamics of this transient breakdown. The pressure gradient along the vortex axis is found to play a dominant role in the initiation of breakdown. A description of the three-dimensional instantaneous structure of the flow field is provided for the first time using critical-point theory. The reversed-flow region in the vortex core is associated with pairs of opposite spiral/saddle critical points. At its onset, the vortex breakdown is fairly axisymmetric; however, as it proceeds upstream and a stronger transition takes place along the axis, asymmetric effects become important and result in the formation of a bubble-type breakdown. This bubble structure is open and contains within itself a pair of stagnation points which are diametrically opposed and which rotate in the same sense as the base flow. Vortex breakdown, Delta wings, Unsteady aerodynamics, Computational fluid dynamics.

An Experimental Study of the Relationship Between Forces and Moments and Vortex Breakdown on a Pitching Delta Wing

An Experimental Study of the Relationship Between Forces and Moments and Vortex Breakdown on a Pitching Delta Wing
Author: Mohammad Reza Soltani
Publisher:
Total Pages: 506
Release: 1992
Genre:
ISBN:

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Wind-tunnel experiments were performed to study the complex flow mechanisms on a 70-deg. sharp leading-edge delta wing model at both static and dynamic conditions at a Reynolds number of 1.43 $times$ 10$sp6$. Large amplitude oscillatory motions were produced by sinusoidally pitching the model over a range of reduced frequencies. Ramp motions were obtained using an initial sinusoidal increase in angle of attack and hold. Aerodynamic forces and moments were obtained from a six-component internal strain-gauge balance. In addition, smoke flow visualization was conducted to study the development, and breakdown of the leading-edge vortices under static, dynamic, and ramp conditions. The visualization experiment was performed at a Reynolds number of 0.16 $times$ 10$sp6$. Static forces compared well with previously published data. The non-linear vortex lift and the movement of the burst point over the wing surface were related to changes in the measured lift-curve slope. Asymmetrical bursting produced by testing the model at nonzero sideslip angle, had a significant influence on the magnitude of the measured forces and moments. Dynamic data varied substantially with reduced frequency. Large forces and moments overshoots, a delay in dynamic stall, and a hysteresis loop between the values of aerodynamic loads in upstroke and downstroke motion were observed. The dynamic vortex breakdown point was seen to reach the trailing-edge at a smaller angle of attack than it did when in the static case. However, at large angles of attack, its position lagged that of the static model. The magnitude of the rolling moment coefficient was strongly influenced by the reduced frequency. For the ramp motion case, aerodynamic forces and moments closely followed those of the oscillatory case during the pitch-up motion. However, upon cessation of the motion, the persistence of the dynamic effects was a strong function of the pitch rate. Terminating the motion at 24 deg. angle of attack produced lower lift and normal force values when the data were compared to their static values. This was caused by the early bursting phenomenon observed during the dynamic motion, thus reducing dynamic lift and normal force coefficients.

Characterization and Control of Vortex Breakdown Over a Delta Wing at High Angles of Attack

Characterization and Control of Vortex Breakdown Over a Delta Wing at High Angles of Attack
Author: Anthony M. Mitchell
Publisher:
Total Pages: 380
Release: 2000-08-01
Genre:
ISBN: 9781423535225

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Demands for more maneuverable and stealthy air vehicles have encouraged the development of new control concepts for separated flows. The goalof this research is the control of leading-edge vortex breakdown by open-loop, along-the-core blowing near the apex of a delta wing to improve lift and maneuverability at high angles of attack. Control is dependent on the knowledge of and the ability to detect principle characteristics of the phenomena. Therefore, an experimental study of a 700 delta wing was accomplished to better understand the physical properties of the vortical flow and the vortex breakdownphenomena. Multiple experimental methods were used to characterize the flow field and its influence on the model's surfaces as well as to identify parameters for closed-loop feedback control.