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Showing papers on "Vortex lattice method published in 1979"


Journal ArticleDOI
TL;DR: A preliminary aerodynamic performance prediction model has been constructed for the Darrieus turbine using a vortex lattice method of analysis and a series of experiments were conducted for the express purpose of validating the analytical model.
Abstract: A preliminary aerodynamic performance prediction model has been constructed for the Darrieus turbine using a vortex lattice method of analysis. A series of experiments were conducted for the express purpose of validating the analytical model. These experiments were conducted on a series of two dimensional rotor configurations which were towed in a large tank of water. The use of water as a working fluid was intended to facilitate both flow visualization and the ability to measure aerodynamic blade forces while allowing operation at sufficiently high Reynolds numbers. The primary purpose of this research was to allow reasonable predictions of aerodynamic blade forces and moments to be made.

303 citations


Journal ArticleDOI
C. E. Lan1
TL;DR: In this paper, a quasi-continuous loading method for dragonfly aerodynamics was proposed to predict the lead-edge suction during harmonic motion, which was applied to the calculation of the propulsive efficiency and thrust for some swept and rectangular planforms by varying the phase angles between the pitching and heaving motions.
Abstract: In the early theoretical study of aquatic animal propulsion either the two-dimensional theory or the large aspect-ratio theory has been generally used. Only recently has the unsteady lifting-surface theory with the continuous loading approach been applied to the study of this problem by Chopra & Kambe (1977). Since it is well known that the continuous loading approach is difficult to extend to general configurations, a new quasi-continuous loading method, applicable to general configurations and yet accurate enough for practical applications, is developed in this paper. The method is an extension of the steady version of Lan (1974) and is particularly suitable for predicting the unsteady lead-edge suction during harmonic motion.The method is applied to the calculation of the propulsive efficiency and thrust for some swept and rectangular planforms by varying the phase angles between the pitching and heaving motions. It is found that with the pitching axis passing through the trailing edge of the root chord and the reduced frequency k equal to 0·75 the rectangular planform is quite sensitive in performance to the phase angles and may produce drag instead of thrust. These characteristics are not shared by the swept planforms simulating the lunate tails. In addition, when the pitching leads the heaving motion by 90°, the phase angle for nearly maximum efficiency, the planform inclination caused by pitching contributes to the propulsive thrust over a large portion of the swept planform, while, for the rectangular planform, only drag is produced from the planform normal force at k = 0·75. It is also found that the maximum thrust is not produced with maximum efficiency for all planforms considered. The theory is then applied to the study of dragonfly aerodynamics. It is shown that the aerodynamically interacting tandem wings of the dragonfly can produce high thrust with high efficiency if the pitching is in advance of the flapping and the hindwing leads the forewing with some optimum phase angle. The responsible mechanism allows the hindwing to extract wake energy from the forewing.

105 citations


Journal ArticleDOI
TL;DR: In this article, an approximate approach has been presented for the analysis of strake wings with straight leading edges, where the lifting surface theory is used for the separated flow on the forward highly swept part of the wing.
Abstract: HE analysis of strake wings, even at low speeds, is one of great complexity. The separated flow from highly swept leading edges of the strake influences the flow over the basic wing (having a prominent nose radius). While, in recent years, some advancements have been made for the analysis of highly swept wings having separated flow from the leading edges, and a number of well-establis hed methods exist for the analysis of conventional wings having prominent nose radius, there are no suitable methods available for the analysis of strake wings when both types of flow are to exist simultaneously. The main problem seems to be to get the vortex field represented properly as it passes over the main wing. An approximate approach has been presented here. In this approach, slender wing theory is being used for the separated flow on the foward highly swept part (strake) and the upwash field from this (as a two-dimensional field) being fed into lifting surface theory. The separated flow theory, as developed by Brown and Michael,J replaces the spiral vortex sheets from the straight leading edges of a highly swept wing by two concentrated vortices and two feeding vortex sheets connecting the leading edge and the concentrated line vortices. Their theory is applicable to delta wings having straight leading edges. Smith2 extended the theory for delta wings having curved leading edges. The present investigation is restrictd to strakes having straight leading edges; thus, Brown and Michael's theory has been used for the analysis of the separated flow. The lifting surface theory used in the present treatment is the wellestablished vortex lattice theory.3'4 A FORTRAN-IV computer program has been developed to find the vortex strength distribution, chordwise and spanwise load distribution, and the overall characteristics of the wing. For the limited experimental results available, only the overall lift coefficient at different angles of attack have been compared and are shown in Figs. 1-3 for three examples taken from Refs. 5 and 6. The spanwise load distributions are shown in Fig. 4. The results of the present simplified approach appear to be highly convincing.

3 citations


01 Jun 1979
TL;DR: In this paper, a vortex lattice method has been applied to the problem of predicting the interference induced by ventilated wind tunnel walls, and the formulations of both perforated and slotted wall boundaries using the vortex-lattice method are presented.
Abstract: : A vortex lattice method has been applied to the problem of predicting the interference induced by ventilated wind tunnel walls. The formulations of both perforated and slotted wall boundaries using the vortex lattice method are presented. Wall interference effects on a single lifting line vortex for several basic wind tunnel test section configurations are compared with other theoretical results. Use of the vortex lattice method to calculate the aerodynamic characteristics of a lifting model too complex for exact analytical treatment is discussed. The surface pressure distribution on a combined wing and tail representation computed for a free stream is presented as well as those for both closed and slotted test sections to illustrate the capability of the technique.

3 citations