Pitching moment

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

Aerodynamic and aero acoustic optimization of airfoils via a parallel genetic algorithm

Abstract: A parallel genetic algorithm (GA) was used to generate, in a single run, a family of aerodynamical ly efficient, low-noise rotor blade designs representing the Pareto optimal set. The n-branch tournament, uniform crossover genetic algorithm operates on twenty design variables, which constitute the control points for a spline representing the airfoil surface. The GA takes advantage of available computer resources by operating in either serial mode or "manager/work er" parallel mode. The multiple objectives of this work were to maximize lift-to-drag of a rotor airfoil shape and to minimize an overall noise measure including effects of loading and thickness noise of the airfoil. Constraints are placed on minimum lift coefficient, pitching moment and boundary layer convergence. The program XFOIL provides the aerodynamic analysis, and the code WOPWOP provides the aeroacoustic analysis. The Pareto-optimal airfoil set has been generated and is compared to the performance of a typical rotorcraft airfoil under identical flight conditions.

Calculation of real-gas effects on blunt-body trim angles

Abstract: The effect of vibrational excitation and dissociation at high temperatures on the trim angle of attack of a blunt lifting body is calculated for a nonequilibrium flow regime in air using a CFD technique. The vibrational-electronic temperature and the species densities are calculated assuming the flow to be in a nonequilibrium state. The forebody flow of a two-dimensional blunt body of the shape of the Apollo Command Module at a finite angle of attack is calculated. The results show that the pitching moment around a reference point is larger and the trim angle of attack is smaller for a reacting gas than for a perfect gas. The calculated shift in the trim angle due to the real-gas effect is of the same order as that seen during the Apollo flights.

On the Damping Force and added Mass of Ships Heaving and Pitching

Abstract: When cylinders of Lewis Form sections heave and pitch on the free surface, their damping force and the added mass were exactly calculated by Ursell's Method. And many figures in this report show the results of the calculation. Then the reporter calculated, applying the results of the above-mentioned calculation and by Strip Method, the damping force and the added mass of the two ships, which were respectively put to test by Golovato and Gerritsuma. The added mass and the added moment of inertia which the reporter gained by Strip Method showed good coincidence with the results of Golovato's and Gerritsuma's experiments. To get better estimation on the damping force by Strip Method, it is necessary to calculate more closely the three dimensional effect, non-linear effect, etc. As to the added mass the three dimensional correction could be negligible except for small ξ1*.

Aerodynamic effects of corrugation in flapping insect wings in hovering flight

Abstract: We have examined the aerodynamic effects of corrugation in model insect wings that closely mimic the wing movements of hovering insects. Computational fluid dynamics were used with Reynolds numbers ranging from 35 to 3400, stroke amplitudes from 70 to 180 deg and mid-stroke angles of incidence from 15 to 60 deg. Various corrugated wing models were tested (care was taken to ensure that the corrugation introduced zero camber). The main results are as follows. At typical mid-stroke angles of incidence of hovering insects (35-50 deg), the time courses of the lift, drag, pitching moment and aerodynamic power coefficients of the corrugated wings are very close to those of the flat-plate wing, and compared with the flat-plate wing, the corrugation changes (decreases) the mean lift by less than 5% and has almost no effect on the mean drag, the location of the center of pressure and the aerodynamic power required. A possible reason for the small aerodynamic effects of wing corrugation is that the wing operates at a large angle of incidence and the flow is separated: the large angle of incidence dominates the corrugation in determining the flow around the wing, and for separated flow, the flow is much less sensitive to wing shape variation. The present results show that for hovering insects, using a flat-plate wing to model the corrugated wing is a good approximation.