Pitching moment

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

Aerodynamic Forces on Finite Wings in Oscillatory Flow: An Experimental Study

Abstract: This report describes aerodynamic lift and pitching moment measurements on finite wings in oscillating vertical gusts of varying frequency parameter and gust amplitude. A set of six conventional wings with varying aspect ratio, sweep angle, and taper are tested. The results show that the variation of aerodynamic force per unit gust amplitude with frequency parameter is independent of freestream velocity, wing incidence, and gust amplitude but is considerably influenced by wing sweep. These experimental results are compared with a lifting surface theory for two of the test planforms and show good agreement. The effect on the aerodynamic forces of allowing free transition on the wing surfaces is also investigated.

Experimental Trapped Vorticity Flight Control Using An Augmenting Error Minimization Adaptive Law

Abstract: Closed-loop feedback control is used in a series of wind tunnel experiments to efiect commanded 2-DOF maneuvers (pitch and plunge) of a free airfoil without moving control surfaces. The objective is to achieve control bandwidths that are beyond those achievable with mechanical control surfaces. Bi-directional changes in the pitching moment over a range of angles of attack are efiected 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 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. Force mode allows the simulation of free ∞ight in the wind tunnel. It can maintain the static trim force on the model, alter its efiective mass, change the dynamic characteristics of the model, and introduce disturbances. Attitude stabilization and plunge position control of the model is achieved by closing the position loop through the ∞ow control actuators using a model reference adaptive controller designed to maintain a specifled level of tracking performance in the presence of disturbances, parametric uncertainties and unmodeled dynamics associated with the ∞ow. The control law employs a neural network adaptive element in which the adaptation law is based on a novel error minimization scheme. The adaptive element augments a linear control law, and the closed loop system can be shown to be uniformly ultimately bounded through a Lyapunov-like stability analysis.

Experimental Investigation on Aerodynamic Control of a Wing with Distributed Plasma Actuators

Abstract: Experimental investigation of active flow control on the aerodynamic performance of a flying wing is conducted. Subsonic wind tunnel tests are performed using a model of a 35 o swept flying wing with an nanosecond dielectric barrier discharge (NS-DBD) plasma actuator, which is installed symmetrically on the wing leading edge. The lift and drag coefficient, lift-to- drag ratio and pitching moment coefficient are tested by a six-component force balance for a range of angles of attack. The results indicate that a 44.5% increase in the lift coefficient, a 34.2% decrease in the drag coefficient and a 22.4% increase in the maximum lift-to-drag ratio can be achieved as compared with the baseline case. The effects of several actuation parameters are also investigated, and the results show that control efficiency demonstrates a strong dependence on actuation location and frequency. Furthermore, we highlight the use of distributed plasma actuators at the leading edge to enhance the aerodynamic performance, giving insight into the different mechanism of separation control and vortex control, which shows tremendous potential in practical flow control for a broad range of angles of attack.

Flow theory in the side chambers of the radial pumps: A review

Abstract: With continuing demand for high and stable operational reliability of hydraulic pumps, it has become vital to take into account the effects of leakage flows in the side chambers in-between the rotating impeller and the stationary casing. Leakage flows have the potential to produce unsteady flow behavior that inherently leads to substantial vibration, undesirable noise, energy losses, and fatigue of pump components. Thus, the purpose of the present study is to discuss and review the various aspects of these harmful unsteady flow behaviors resulting from leakage flows. The first part deals with the theoretical studies on the boundary layers, core swirl, moment coefficient, and pressure and velocity distribution of rotor–stator flows. Then, a simplified model of the prediction of through-flow on moment coefficient Cm and thrust coefficient CF with good correctness has been extensively discussed. Finally, a summary of the experimental and numerical studies on rotor–stator cavities is presented in the second part of this study. This review concludes with a discussion of the calculation of axial thrust and moment coefficient during the design process of radial pumps in a more precise manner.

Wind Tunnel Results of Pneumatic Forebody Vortex Control Using Rectangular Slots a Chined Forebody

Abstract: A subsonic wind tunnel investigation of pneumatic vortex flow control on a chined forebody using slots was accomplished at a dynamic pressure of 50 psf resulting in a R(n)/ft of 1.3 x 10(exp 6). Data were acquired from angles of attack ranging from -4deg to +34deg at side slips of +0.4deg and +10.4deg. The test article used in this study was the 10% scale Fighter Lift and Control (FLAC) advanced diamond winged, vee-tailed fighter configuration. Three different slot blowing concepts were evaluated; outward, downward, and tangential with ail blowing accomplished asymmetrically. The results of three different mass flows (0.067, 0.13, and 0.26 lbm/s; C(sub mu)'s of less than or equal to 0.006, 0.011. and 0.022 respectively) were analyzed and reported. Test data are presented on the effects of mass flows, slot lengths and positions and blowing concepts on yawing moment and side force generation. Results from this study indicate that the outward and downward blowing slots developed yawing moment and side force increments in the direction opposite of the blowing side while the tangential blowing slots generated yawing moment and side force increments in the direction towards the blowing side. The outward and downward blowing slots typically produced positive pitching moment increments while the tangential blowing slots typically generated negative pitching moment increments. The slot blowing nearest the forebody apex was most effective at generating the largest increments and as the slot was moved aft or increased in length, its effectiveness at generating forces and moments diminished.