Pitching moment

About: Pitching moment is a research topic. Over the lifetime, 3213 publications have been published within this topic receiving 38721 citations.

On the Role of Leading-Edge Bumps in the Control of Stall Onset in Axial Fan Blades

Abstract: Taking a lead from the humpback whale flukes, characterized by a series of bumps that result in a sinusoidal-like leading edge, this paper reports on a three-dimensional numerical study of sinusoidal leading edges on cambered airfoil profiles. The turbulent flow around the cambered airfoil with the sinusoidal leading edge was computed at different angles of attack with the open source solver OpenFOAM, using two different eddy viscosity models integrated to the wall. The reported research focused on the effects of the modified leading edge in terms of lift-to-drag performance and the influence of camber on such parameters. For these reasons a comparison with a symmetric airfoil is provided. The research was primarily concerned with the elucidation of the fluid flow mechanisms induced by the bumps and the impact of those mechanisms on airfoil performance, on both symmetric and cambered profiles. The bumps on the leading edge influenced the aerodynamic performance of the airfoil, and the lift curves were found to feature an early recovery in post-stall for the symmetric profile with an additional gain in lift for the cambered profile. The bumps drove the fluid dynamic on the suction side of the airfoil, which in turn resulted in the capability to control the separation at the trailing edge in coincidence with the peak of the sinusoid at the leading edge.

Aircraft aerodynamic effects due to large droplet ice accretions

Abstract: The effect of large-droplet ice accretion on aircraft control and in particular lateral control is examined. Supercooled large droplet icing conditions can result in the formation of a ridge of ice aft of the upper surface boot. By comparing this ice shape to data acquired with a spanwise protuberance on a different airfoil, it is clear that a ridge of ice aft of the boot can lead to large losses in lift, increases in drag and changes in the pitching moment. This effect is most likely due to the formation of a large separation bubble aft of the ice accretion which grows with angle of attack and eventually fails to reattach, leading to premature airfoil stall. The bubble alters the pressure distribution about the airfoil resulting in a more trailing edge up (negative) hinge moment on the aileron and the resulting change in aileron stick force. This can lead to aileron hinge moment reversal and aileron snatch. In aileron snatch the hinge moments are altered to the extent that the aileron is pulled up by the low pressure over the upper surface of the aileron with sufficient force to induce a rapid roll if a large stick force is not immediately exerted to oppose it. There is evidence in the literature which shows that similar lateral control problems are possible with other types of ice accretions and airfoil types.

Effects of Sideslip on the Aerodynamics of Low-Aspect-Ratio Low-Reynolds-Number Wings

Abstract: The growing interest in micro aerial vehicles has brought attention to the need for an improved understanding of the aerodynamics of low-aspect-ratio wings at lowReynolds numbers. In this study, flat plate wings with rectangular and tapered planforms were fabricated with aspect ratios of 0.75, 1, 1.5, and 3, and the aerodynamic loading was measured at Reynolds numbers between 5 10 and 1 10. Surface tuft visualization was used to observe the interactions between the tip vortices and the leading-edge vortex. The tests were initially conducted at a sideslip angle of 0 and were then repeated for 10, 20, and 35 with and without winglets. Measurements made with a sixcomponent force balance showed that a decrease in aspect ratio caused an increase in stall and CLmax due to the nonlinear lift induced by the interacting flow on the upper wing surface. In addition, the detachment of tip vortices after stall leads to a sudden decrease in drag coefficient as the magnitude of the induced drag drops significantly. At increasing sideslip angles, the effects of the crossflow still contribute to an increase in lift but significantly reduce the pitching moment about the quarter-chord, thus decreasing the wing’s ability to recover from angle-of-attack perturbations. These results show that, while the effects of tip vortices and the leading-edge vortex complicate the flowfield around a low-aspect-ratio wing, particularly at increased sideslip angles, their impact tends to improve the aerodynamic performance.

Non-intrusive load characterization of an airfoil using PIV

Abstract: An assessment is made of the feasibility of using PIV velocity data for the non-intrusive aerodynamic force characterization (lift, drag and pitching moment) of an airfoil. The method relies upon the application of control-volume approaches in combination with the deduction of the pressure from the PIV experimental data, by making use of the momentum equation. First, the consistency of the method is verified by means of synthetic data obtained from CFD. Subsequently, the procedure was applied in an experimental investigation, in which the PIV approach is validated against standard pressure-based methods (surface pressure distribution and wake rake).