Pitching moment

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

New Rotor Airfoil Design Procedure for Unsteady Flow Control

Abstract: The present paper describes two different experiments performed in a transonic wind tunnel facility at DLR-Goettingen. The first experiment was conducted in order to study compressible vortices behind a cylinder and investigating the feasibility of combining two different measuring techniques: the Background Oriented Schlieren (BOS) technique and the Particle Image Velocimetry (PIV) which allow respectively to measure both density and velocity fields. The second experiment described in the present paper is done in the same wind tunnel facility where a new test section has been developed to investigate the unsteady flow about oscillating models under dynamic stall conditions. Dynamic stall is characterized by the development, movement and shedding of one or more concentrated vortices on the blade upper surface, the hysteresis loops of lift-, drag- and pitching moment are highly influenced by these vortices. To understand the very complicated unsteady flow involved, a detailed knowledge of the instantaneous flow fields is of crucial importance. With the application of the described measuring techniques it is expected to gain more insight into the problem. In recent years numerical codes based on the time-accurate solution of the Reynolds-Averaged Navier-Stokes equations (RANS) have been developed. Results from these codes are ready for comparison with experimental data. A section of the present paper is dedicated to the comparison of numerical with corresponding experimental data.

Oscillating-Wing Power Generator with Flow-Induced Pitch-Plunge Phasing

Abstract: A new method for converting the kinetic energy of wind or water flows into electric energy, comprising wings or sails which are mounted on swing arms or on guide rails in such a way that the air or water flow induces an oscillatory wing or sail motion with a phase angle between the wing's or sail's pitch and plunge motion of about ninety degrees. Stroke reversal of the oscillatory motion is initiated by a purely aerodynamic/hydrodynamic mechanism such that the air or water flow induces a pitching moment on the wing or sail which rotates the wing or sail and thereby reverses the lift acting on the wing or sail.

Pitch Control of a Micro Air Vehicle with Micropressure Sensors

Abstract: Maintaining stable flight of micro aerial vehicles is challenging, especially in complex, low-Reynolds-number flight environments while considering wind gust disturbance, flow separation, and flow reattachment. To date, most micro aerial vehicles use vision, inertial measurement units, and/or global positioning systems as their primary sensing and navigation devices; however, actual flow conditions over the aircraft wing surfaces cannot be captured directly. In this paper, a biologically inspired micro aerial vehicle pitch control system is designed using distributed pressure information. The pressure information on the wing surfaces of a micro aerial vehicle is directly measured by a array of digital barometric micropressure sensors and is then used to calculate the aerodynamic forces, center of pressure, pitching moment, etc. A new pitch motion model that can capture the pressure information is derived from the control perspective. A nonlinear controller is also designed to achieve accurate pitch contro...

Pneumatic Flap Performance for a 2D Circulation Control Airfoil, Steady and Pulsed

Abstract: Circulation Control technologies have been around for 65 years, and have been successfully demonstrated in laboratories and flight vehicles alike, yet there are few production aircraft flying today that implement these advances. Circulation Control techniques may have been overlooked due to perceived unfavorable trade offs of mass flow, pitching moment, cruise drag, noise, etc. Improvements in certain aspects of Circulation Control technology are the focus of this paper. This report will describe airfoil and blown high lift concepts that also address cruise drag reduction and reductions in mass flow through the use of pulsed pneumatic blowing on a Coanda surface. Pulsed concepts demonstrate significant reductions in mass flow requirements cor Circulation Control, as well as cruise drag concepts that equal or exceed conventional airfoil systems.

Dynamic flight maneuvering using trapped vorticity flow control

Abstract: Closed-loop feedback control is used in a series of wind tunnel experiments to effect commanded 2-DOF maneuvers (pitch and plunge) of a free airfoil without moving control surfaces. Bi-directional changes in the pitching moment over a range of angles of attack are effected by controllable, nominally-symmetric trapped vorticity concentrations on both the suction and pressure surfaces near the trailing edge. Actuation is applied on both surfaces by hybrid actuators that are each comprised of a miniature [O(0.01c)] obstruction integrated with a synthetic jet actuator to manipulate and regulate the vorticity concentrations. In the present work, the model is trimmed using position and attitude feedback loops that are actuated by servo motors and a ball screw mechanism in the plunge axis. Once the model is trimmed, the position feedback loop in the plunge axis is opened and the plunge axis is controlled in force mode so to maintain the static trim force on the model, and alter its effective mass. Meanwhile the servomotor in the pitch axis is only used to alter the dynamic characteristics of the model in pitch, and to introduce disturbances. Attitude stabilization and position control of the model is achieved by closing the position loop through the flow control actuators using a model reference adaptive controller designed to maintain a specified level of tracking performance in the presence of disturbances, parametric uncertainties and unmodeled dynamics associated with the flow. The controller employs a neural network based adaptive element and adaptation laws derived by a Lyapunov-like stability analysis of the closed loop system.