Pitching moment

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

Aerodynamic force measurement using 3-component accelerometer force balance system in a hypersonic shock tunnel

Abstract: A new three-component accelerometer force balance has been designed, calibrated and tested in hypersonic shock tunnel (HST2) of Indian Institute of Science. The newly designed balance is able to measure aerodynamic forces (within test time of one millisecond) on test models at angles of attack from 0 to 12°. Two models, a blunt cone with after body and a blunt cone with after body and frustum are used to establish the accuracy of the force balance. The tests were conducted for the above two configurations with a constant Mach number of 8 and total enthalpy of 2.0 MJ/kg. The effectiveness of the balance is demonstrated by comparing the forces and moments of measured data with AGARD models. The flow fields around the test model are simulated using a 3D axisymmetric Navier–Stokes solver and the simulated results were compared with the measured values. Measured and computed force data are matched within ±10% for two different models tested here. The accuracy of the force balance is also estimated with the Newtonian theory and the values are approximately ±10% for the axial component and ±8% for the normal and pitching moment components.

Control of Dynamic Stall on a Pitching Airfoil Using High-Frequency Actuation

Abstract: A flow control strategy for the delay of unsteady separation and dynamic stall on a pitching NACA 0012 airfoil is explored by means of high-fidelity large-eddy simulations. The flow fields are computed employing a high-fidelity large-eddy simulation (LES) approach. The flow parameters are freestream Mach number M∞ = 0.1 and chord Reynolds numbers Rec = 5× 10. Both constant-rate and oscillatory pitching motions are considered. For the baseline cases, dynamic stall is initiated with the bursting of a contracted laminar separation bubble (LSB) present in the leading-edge region. This observation motivated a flow control approach employing high-frequency pulsed actuation imparted through a zero-net mass flow blowing/suction slot located on the airfoil lower surface just downstream of the leading edge. For the constant-rate pitching case, both pulsed and harmonic spanwise-nonuniform forcing are considered with a maximum non-dimensional frequency Stf = fc/U = 50.0 which corresponds to a sub-harmonic of the dominant natural LSB fluctuations for a baseline static case used for reference purposes. A significant delay in the onset of dynamic stall is demonstrated with pulsed forcing at high frequencies (Stf = 25.0, 50.0), however, control effectiveness diminishes with decreasing frequency. At Stf = 12.5, pulsed actuation is shown to be superior to harmonic forcing suggesting that the higher harmonic content present in the pulsed mode is still capable of energizing the LSB. For the oscillatory pitching motion, pulsed high-frequency flow control with Stf = 50.0) is considered for two cases exhibiting light and deep dynamic stall respectively. For light dynamic stall, flow actuation is capable of maintaining an effectively attached flow during the entire pitching cycle thereby inhibiting the formation of large-scale leading-edge and shear-layer vortical structures. For deep dynamic stall, control is found to also be very effective in eliminating leading-edge separation and the formation of a dynamic stall vortex. Nonetheless, trailing-edge separation eventually occurs at high incidence. For both cases, actuation provided a significant reduction in the cycle-averaged drag and in the force and moment fluctuations. In addition, the negative (unstable) net-cycle pitch damping found in the baseline cases was eliminated.

Low Boom Configuration Analysis with FUN3D Adjoint Simulation Framework

Abstract: Off-body pressure, forces, and moments for the Gulfstream Low Boom Model are computed with a Reynolds Averaged Navier Stokes solver coupled with the Spalart-Allmaras (SA) turbulence model. This is the first application of viscous output-based adaptation to reduce estimated discretization errors in off-body pressure for a wing body configuration. The output adaptation approach is compared to an a priori grid adaptation technique designed to resolve the signature on the centerline by stretching and aligning the grid to the freestream Mach angle. The output-based approach produced good predictions of centerline and off-centerline measurements. Eddy viscosity predicted by the SA turbulence model increased significantly with grid adaptation. Computed lift as a function of drag compares well with wind tunnel measurements for positive lift, but predicted lift, drag, and pitching moment as a function of angle of attack has significant differences from the measured data. The sensitivity of longitudinal forces and moment to grid refinement is much smaller than the differences between the computed and measured data.

Use of aerodynamic forces to assist in the control and positioning of aircraft control surfaces and variable geometry systems

Abstract: The current invention relates primarily to the control of rotary wing and fixed wing aircraft where a small electric actuator (7, 104) changes the pitch on a small aerodynamic surface (5, 66) and the resulting airloads on said small aerodynamic surface are used to change the pitch on a significantly larger aerodynamic surface (3, 60). In the preferred embodiment the resulting airloads on said larger aerodynamic surface is then used to change the pitch on a still larger aerodynamic surface (1, 62). As a result small electric actuators are capable of moving and controlling large aircraft control surfaces with an effective two step amplification of power utilizing the energy in the airstream. The current invention also discloses means to control and prevent undesirable motion of said aerodynamic surfaces.