X. Y. Deng

Modeling of Wing Rock Based on Frequency Spectrum Analysis to Free-to-Roll Time History

A systematic method is presented for modeling wing rock of one degree of freedom. This method is based on the frequency spectrum analysis to free-to-roll time history. The frequency analysis reveals that there are other higherfrequency components in the rolling angular acceleration time history of wing rock, with the exception of the main frequency. Among them, the energy at the triple frequency relative to themain frequency is greater than others. The central idea of the method presented for modeling wing rock is the summation of several sine waves for which the frequencies include main frequency, double-main frequency, and triple-main frequency. The structure and parameters of the modeled dynamic equations are all determined by the frequency analysis of the rolling angular acceleration time history of the wing rock. The simulated results based on this model agree well with the experimental data.

Active Control of Disturbation of Wing‐Body Rock Induced by Forebody Asymmetric Vortices

The study of free roll oscillation patterns with tip perturbation locations and suppression technique of free‐roll‐oscillation for wing/body configuration with low swept wing have been carried out at angle of attack α = 50° and with Reynolds numbers Re = 1.61× 105 and 1.93×105. The results reveal that there are three types of free roll oscillation patterns: limit cycle wing rock at θ = 0° or 180°; irregular oscillation at θ = 90° or 270°; tiny roll oscillation pattern, if θ is on the other positions. A technique of suppressing wing rock motion by rotating nose tip perturbation was developed with higher frequency than one of free roll oscillation and the higher the frequency of rotation of nose tip, the better effect suppression of free wing rock has.

Yaw Effects on Vortex Flow over a Chined Fuselage at High Angle of Attack

Particle image velocimetry (PIV) experiment technology and surface pressure measurement have been used to investigate yaw effects on vortex flow over a chined fuselage with Reynolds number of 1.87 × 105 at angle of attack α = 50° and sideslip angle β = 4°. Under condition of no sideslip, there are two symmetric leeward vortices with strong intensity. Due to the yaw‐induced corssflow, the upwind vortex is drawn closer to model surface and the downwind vortex is displaced upward and outward, and vorticities of the two vortices decrease in various degree. At the same time, the yawing condition causes the downwind vortex burst at an axial position in front of the upwind vortex. As a result, the suction effect is enhanced on upwind side and reduced on downwind side. A restoring side force forms on forebody, which indicates the chined forebody has static directional stability at high angle of attack.

Effects of Reynolds Numbers on Wing Rock Induced by Forebody Vortices

The wing rock induced by forebody vortices was investigated experimentally for a wing–body at high angles of attack, and the emphasis was put on the effects of Reynolds number on motion patterns. The results indicate that, if the boundary layers of the forebody exhibit laminar separation, the wing–body can regularly experience various motion types, as a tip perturbation changes its circumferential positions around the nose tip. After transition separation of boundary layers occurs, however, the effects of the tip perturbation on the motion types are alleviated progressively with increasing Reynolds number. Eventually, the wing-rock motions are independent on the tip perturbation, and the model always exhibits limit-cycle oscillations regardless of where the perturbation is located. In the case of fully turbulent separation, simulated by transition wires, the dominant roles of the tip perturbation on wing-rock types are recovered, in which the motion patterns of wing rock regularly vary with variation of t...

Interference of Double Rotating Shaft Support in Low Speed Wind Tunnel

Support interferences always affect the accuracy of the wind tunnel experimental data. Therefore studying support interference is of significant value in practice. The double rotating shaft support is a novel way of support. In this paper, numerical simulation has been taken to investigate the effect of the double rotating shaft support system on aerodynamic forces and moments of DBM model. It is found that the support system induces the lift coefficient and the drag coefficient to decrease and the pitching moment coefficient to increase. For the parts of the model which are above the wing plane, the lift coefficient and the drag coefficient decrease. And for the parts of the model which are below the wing plane, the lift coefficient and the drag coefficient increase. For the pitching moment coefficient, the influnence is opposite to that of force.

Experimental Investigations of Free‐To‐Roll Motions Induced by Wings and Forebody Complex Flow Under Pitch‐Up Motions

Experiments have been carried out at sub‐critical Reynolds number to investigate wing rock induced by forebody and/or wings complex flow on a 30° swept back non‐slender wings‐slender body‐model for static and dynamic (pitch‐up) cases. Four angle of attack regions have been identified based on the characteristics of FTR motion and associated flow structures at static angles of attack. For the dynamic (pitch‐up) case it has been observed that roll amplitude decreases and lag increases with increase in pitching speed. Decrease in roll amplitude with increase in pitch rate is attributed to low disturbing rolling moment due to weaker interaction between forebody and wing flow components. Forebody asymmetric vortices dominate and control the roll motion of the model in dynamic case when non‐dimensional pitch rate ≥1 × 10−2 and the roll behavior is like a sinusoidal curve. There is almost no contribution to the roll motion from the wings flow at lower angles of attack for high pitch rates.

Inception of Asymmetric Vortex Flow over Slender Body

This paper reports an investigation of onset of asymmetric vortex flow over slender bodies through pressure measurements on two models which are of different diameters and different fineness ratios in a low-speed low turbulence level (0.08%) wind-tunnel. In the paper, effect of perturbation, as well as Reynolds number, on the variation of onset angle of attack was discussed. Moreover, the onset AOAs on forebody and afterbody sections were compared.

The Study of Determinacy of Asymmetric Vortices over Slender Body at Post-Critical Reynolds Numbers

An artificial transition technique of setting transition wires on both side of a pointed-ogive cylinder with the nose fineness ratio 3.0 was used to simulate the post-critical Reynolds numbers flow at high incidence in low-speed wind tunnel. The results based on this artificial transition technical indicate that the indeterminacy of asymmetric vortices aroused by nose-tip imperfection resulted from machining tolerance still exists in post-critical Reynolds numbers flow. The indeterminacy of asymmetric vortices can be eliminated by adding the micro-triangle block artificial perturbation with thickness of 0.2mm to the nose-tip, and the artificial perturbation on nose-tip can promote the asymmetric vortices into bistable state at α=50°. When the results of artificial perturbations with various thicknesses are combined, it is indicated that the intensity of artificial perturbation must be considered when it was just used to eliminate the indeterminacy of asymmetric vortices.