Pitching moment

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

Load control on a dynamically pitching finite span wind turbine blade using synthetic jets

Abstract: The feasibility of active flow control, via arrays of synthetic jet actuators, to mitigate hysteresis was investigated experimentally on a dynamically pitching finite span S809 blade. In the present work, a six-component load cell was used to measure the unsteady lift, drag and pitching moment. Stereoscopic Particle Image Velocimetry (SPIV) measurements were also performed to understand the effects of synthetic jets on flow separation during dynamic pitch and to correlate these effects with the forces and moment measurements. It was shown that active flow control could significantly reduce the hysteresis in lift, drag and pitching moment coefficients during dynamic pitching conditions. This effect was further enhanced when the synthetic jets were pulsed modulated. Furthermore, additional reduction in the unsteady load oscillations can be observed in post-stall conditions during dynamic motions. This reduction in the unsteady aerodynamic loading can potentially lead to prolonged life of wind turbine blades. Copyright © 2014 John Wiley & Sons, Ltd.

Aerodynamic and Aeroelastic Characteristics of a Tension Cone Inflatable Aerodynamic Decelerator

Abstract: The supersonic aerodynamic and aeroelastic characteristics of a tension cone inflatable aerodynamic decelerator were investigated by wind tunnel testing. Two sets of tests were conducted: one using rigid models and another using textile models. Tests using rigid models were conducted over a Mach number range from 1.65 to 4.5 at angles of attack from -12 to 20 degrees. The axial, normal, and pitching moment coefficients were found to be insensitive to Mach number over the tested range. The axial force coefficient was nearly constant (C(sub A) = 1.45 +/- 0.05) with respect to angle of attack. Both the normal and pitching moment coefficients were nearly linear with respect to angle of attack. The pitching moment coefficient showed the model to be statically stable about the reference point. Schlieren images and video showed a detached bow shock with no evidence of large regions of separated flow and/or embedded shocks at all Mach numbers investigated. Qualitatively similar static aerodynamic coefficient and flow visualization results were obtained using textile models at a Mach number of 2.5. Using inflatable textile models the torus pressure required to maintain the model in the fully-inflated configuration was determined. This pressure was found to be sensitive to details in the structural configuration of the inflatable models. Additional tests included surface pressure measurements on rigid models and deployment and inflation tests with inflatable models.

The Effects of Aerodynamic Asymmetric Perturbations on Forced Response of Bladed Disks

Abstract: Most of the existing mistuning research assumes that the aerodynamic forces on each of the blades are identical except for an interblade phase angle shift In reality, blades also undergo asymmetric steady and unsteady aerodynamic forces due to manufacturing variations, blending, mis-staggered, or in-service wear or damage, which cause aerodynamically asymmetric systems This paper presents the results of sensitivity studies on forced response due to aerodynamic asymmetry perturbations The focus is only on the asymmetries due to blade motions Hence, no asymmetric forcing functions are considered Aerodynamic coupling due to blade motions in the equation of motion is represented using the single family of modes approach The unsteady aerodynamic forces are computed using computational fluid dynamics (CFD) methods assuming aerodynamic symmetry Then, the aerodynamic asymmetry is applied by perturbing the influence coefficient matrix in the physical coordinates such that the matrix is no longer circulant Therefore, the resulting aerodynamic modal forces in the traveling wave coordinates become a full matrix These aerodynamic perturbations influence both stiffness and damping while traditional frequency mistuning analysis only perturbs the stiffness It was found that maximum blade amplitudes are significantly influenced by the perturbation of the imaginary part (damping) of unsteady aerodynamic modal forces This is contrary to blade frequency mistuning where the stiffness perturbation dominates

Unstructured Navier-Stokes High-Lift Computations on a Trapezoidal Wing

Abstract: Solutions on a trapezoidal three-element high-lift wing obtained with an unstructured Reynolds averaged Navier-Stokes code are presented. Requirements for grid renemen ts needed to model the pertinent o w physics at various points on the lift curve are identied. Improvements to the lift prediction due to grid renemen t are demonstrated. Lift, drag, pitching moment are shown to be in good agreement with experimental data through C Lmax : The eect of slat and ap brackets are shown, although more grid resolution is needed to correctly capture these eects.

Combining passive control method for dynamic stall control

Abstract: To demonstrate the benefits of a combined nose droop and Gurney flap for improving dynamic stall and poststall aerodynamic characteristics of a rotor airfoil, numerical investigations and design optimization have been performed. As a means of passive flow control, a fixed nose droop has been deliberately employed together with a Gurney flap. For shape optimization, droop location and droop angle were selected as design variables for the fixed nose droop, and the flap length was chosen as a design variable for the Gurney flap. Bousman's function plot was employed to define the objective function and constraint conditions. A feasible direction-based optimizer and a higher-order response surface method were harnessed to handle the highly nonlinear properties of dynamic stall. By the use of this methodology, optimum design was carried out to enhance lift and pitching moment characteristics simultaneously; at.the same time, the unfavorable effects of the overall movement of the pitching moment coefficient induced by droop and the Gurney flap was reduced. It is also proved that by utilizing a 22.7-deg droop at the 0.275 chord droop position and a 1.14% chord Gurney flap, the stall can be delayed by a maximum lift coefficient increased by 13%, a maximum negative pitching moment reduced by 60%, and the lift-to-drag ratio increased accordingly. The present combined passive control methods and design result show significant improvement of aerodynamic performance in Bousman's plot in terms of lift and pitching moment.