Vortex lattice method

About: Vortex lattice method is a research topic. Over the lifetime, 779 publications have been published within this topic receiving 9242 citations.

A Study of the Aerodynamic Interference Effects during Aerial Refueling

Abstract: : This report investigated the feasibility of using an analytical approach and the vortex lattice method (VLM) to evaluate aerodynamic interference effects present during aerial refueling. While KC-10 tanker and a B-52 receiver were studied, the method applies to any tanker receiver combination. Major assumptions include: linear potential flow; tanker receiver are represented by wing planforms; fuselage effects are small; and the rolling- up process of the tanker's wing tip vortices are not considered. The analytical approach uses a lifting line followed by a semi-infinite vortex sheet to represent the tanker. Three linear lift distributions for the tanker's wing were used and equations were derived for the induced downwash at any point in space. Points on the receiver's wing were selected to indicate the tanker's effect on the receiver's flowfield. Results of the analytical equations when compared with analytical predictions were found to overpredict the induced downwash by 25-35%. VLM was used to study the effects of: rectangular vs swept wings on induced downwash; tanker tailplane on the receiver; change of angle of attack of one aircraft due to the presence of the other; and the presence of the tanker on th receiver's pitching moment. VLM results varied from the Douglas prediction for induced downwash by only 5% and were even more accurate at lower tanker angles of attack.

Phase transitions and connectivity in three-dimensional vortex equilibria

Abstract: The statistical mechanics of collections of closed self avoiding vortex loops on a lattice are studied. The system is related to the vortex form of the three dimensional XY model and to lattice vortex equilibrium models of turbulence. The system exhibits vortex connectivity and screening effects, and models in vorticity variables the superfluid transition. The equilibrium states of the system are simulated by a grand canonical Monte Carlo method. A set of geometric transformations for self-avoiding loops is developed. The numerical method employs histogram sampling techniques and utilizes a modification to the Metropolis flow which enhances efficiency. Results are given for a region in the temperature-chemical potential plane, where the chemical potential is related to the vortex fugacity. A line of second order transitions is identified at low temperature. The transition is shown to be a percolation threshold at which connected vortex loops of infinite size appear in the system. The nature of the transition supports the assumption that the lambda transition in bulk superfluid helium is driven by vortices. An asymptotic analysis is performed for the energy and entropy scaling of the system as functions of the system size and the lattice spacing. These estimates indicate that the infinite more » temperature line is a phase boundary between small scale fractal vortices and large scale smooth vortices. A suggestion is made that quantum vortices have uniform structure on the scale of the lattice spacing and lie in the positive temperature regime, while classical vortices have uniform structure on the scale of the domain and lie in the negative temperature regime. « less

A submerged vortex lattice method for calculation of the flow around a three-dimension hydrofoil

Abstract: A submerged vortex lattice method for calculation of the flow around a 3-D hydrofoil is presented.The normal dipoles are posted on a second surface submerged under the wing surface and on a tail vortex surface.The control points are posted on the wing surface.The nonlinear free surface boundary condition is considered and the hydrodynamics forces of the hydrofoil near the free surface are calculated by the submerged vortex lattice method.The computational results show that the present method is correct and available.This method can be used for the hydrodynamic computation of the varied hydrofoils and stabilizing fins.

Numerical And Experimental Studies On Wing In Ground Effect

Abstract: Numerical and experimental studies were performed to investigate the aerodynamic performance of a thin wing in close vicinity to the ground. The vortex lattice method (VLM) was utilized to simulate the wing in ground (WIG) effect, which included freely deforming wake elements. The numerical results acquired through the VLM were compared to the experimental results. The experiment entailed varying the ground clearance using the DHMTU (Department of Hydromechanics of the Marine Technical University of Saint Petersburg) wing and the WIG craft model in the wind tunnel. The aero-dynamic influence of the design parameters, such as angles of attack, aspect ratios, taper ratios, and sweep angles were studied and compared between the numerical and experimental results associated with the WIG craft. Both numerical and experimental results suggested that the endplate augments the WIG effect for a small ground clearance. In addition, the vortex lattice method simulated the wake deformation following the wing in the influence of the ground effect.

Nonlinear vortex lattice method for stall prediction

Abstract: The stall behavior of an empennage is a crucial and conditioning factor for its design. Thus, the preliminary design of empennages requires a fast low-order method which reliably computes the stall behavior and which must be sensitive to the design parameters (taper, sweep, dihedral, airfoil, etc.). Handbook or semi-empirical methods typically have a narrow scope and low fidelity, so a more general and unbiased method is desired. This paper presents a nonlinear vortex lattice method (VLM) for the stall prediction of generic fuselage-empennage configurations which is able to compute complete aerodynamic polars up to and beyond stall. The method is a generalized form of the van Dam algorithm, which couples the potential VLM solution with 2.5D viscous data. A novel method for computing 2.5D polars from 2D polars is presented, which extends the traditional infinite swept wing theory to finite wings, relying minimally on empirical data. The method has been compared to CFD and WTT results, showing a satisfactory degree of accuracy for the preliminary design of empennages.