Showing papers on "Vortex lattice method published in 1981"
TL;DR: In this article, an analysis of the wake structure and the forces on a delta wing as it undergoes non-steady motion is made, wherein the flow separates at the leading edge.
Abstract: An analysis is made of the wake structure and the forces on a delta wing as it undergoes nonsteady motion, wherein the flow separates at the leading edge. Comparisons of these predictions with existing experimental and theoretical data for the nonsteady linear and nonlinear motions indicate good agreement. It was found that the time-dependent, wake-shedding numerical procedure applied here for the wake rollup and the lift force calculation resulted in considerable saving of computer time over methods using the iterative wake rollup procedure. Calculated results for various motions of the delta wing, including the plunging motion, are presented for both the separated and the attached flow cases.
59 citations
TL;DR: In this paper, the potential of several leading-edge flow manipulators (fences, chordwise slots, pylon vortex generators, and a vortex plate concept) for alleviating the subsonic lift-dependent drag of highly-swept wings were investigated experimentally.
Abstract: Leading-edge flow manipulators for alleviating the subsonic lift-dependent drag of highly-swept wings were investigated experimentally. The potential of several devices—fences, chordwise slots, pylon vortex generators, and a vortex plate concept—was evaluated in wind tunnel tests on a 60 deg cropped delta wing research model. Simultaneous balance and pressure measurements at increasing angles of attack provided an insight into the spanwise leading-edge flow development and its modification by the devices. The results demonstrated significant drag reductions through partial recovery of leading-edge suction at elevated angles of attack. In most cases, improvement in longitudinal stability also was obtained.
20 citations
01 Aug 1981
TL;DR: In this paper, a nonsteady vortex-lattice method was applied to calculate the steady-state and non-steady lift characteristics of configurations having interference effects, and a better understanding of the interference effect was gained by using the method to study the transient behavior.
Abstract: The interference effect of closely coupled lifting surfaces was investigated. A nonsteady vortex-lattice method was applied to calculate the steady-state and nonsteady lift characteristics of configurations having interference effects. The configurations consist of low-aspect-ratio delta wings, at low and high angles of attack. Leading-edge separation and wake roll-up are simulated by a time-dependent wake-shedding procedure. For steady-state flow conditions, this numerical procedure saves a considerable amount of computer time, compared with iterative methods, and yields the same results. A better understanding of the interference effect can be gained by using the method to study the transient behavior. The nonsteady approach also offers the capability of calculating various nonsteady motions, as is demonstrated in the calculation of the longitudinal damping.
3 citations
01 Jan 1981
TL;DR: The nonplanar quasi-vortex-lattice method is applied to the calculation of lateral-directional stability derivatives of wings with and without vortex-lift effect as discussed by the authors.
Abstract: The nonplanar quasi-vortex-lattice method is applied to the calculation of lateral-directional stability derivatives of wings with and without vortex-lift effect. Results for conventional configurations and those with winglets, V-tail, etc. are compared with available data. All rolling moment derivatives are found to be accurately predicted. The prediction of side force and yawing moment derivatives for some configurations is not as accurate. Causes of the discrepancy are discussed. A user's manual for the program and the program listing are also included.
3 citations
01 Aug 1981
TL;DR: In this article, a nonsteady vortex-lattice method is introduced for predicting the dynamic stability derivatives of a delta wing undergoing an oscillatory motion, and the analysis is applied to several types of small oscillations in pitch.
Abstract: A nonsteady vortex-lattice method is introduced for predicting the dynamic stability derivatives of a delta wing undergoing an oscillatory motion. The analysis is applied to several types of small oscillations in pitch. The angle of attack varied between + or - 1 deg, with the mean held at 0 deg when the flow was assumed to be attached and between + or - 1 deg and the mean held at 15 deg when both leading-edge separation and wake roll-up were included. The computed results for damping in pitch are compared with several other methods and with experiments, and are found to be consistent and in good agreement.
1 citations