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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.


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TL;DR: In this paper, an unsteady hydrodynamic analysis of marine propellers and horizontal-axis tidal current turbines is performed by using a vortex lattice method (VLM) to satisfy the force-free condition on the propeller and turbine wake surfaces.
Abstract: In this paper, the unsteady hydrodynamic analysis of marine propellers and horizontal-axis tidal current turbines is performed by using a vortex lattice method (VLM). A fully unsteady wake alignment algorithm is implemented into the VLM to satisfy the force-free condition on the propeller and turbine wake surfaces. It was found that the position of the trailing wake is very important in predicting the performance of propellers or turbines in steady or unsteady flow. The effects of a non-linear interaction between the inflow and the propeller/turbine blades have been taken into account by using a hybrid viscous/potential flow method, which couples the potential flow solver for the unsteady analysis of the propeller/turbine and a viscous flow solver for the prediction of the viscous flow field around them. The present method is then applied to predict unsteady hydrodynamic performance of a propeller and a horizontal-axis tidal current turbine. The predicted unsteady forces of a propeller subject to an inclined inflow are compared with those from experiments. The hydrodynamic performance of tidal turbine in yawed flow for various yaw angles is investigated. The numerical results are compared with existing experimental data.

6 citations

Journal ArticleDOI
TL;DR: In this article, a full-scale sailing boat with the use of a sail force dynamometer was used to estimate the sail forces of the boat, and the relationship between the measured sail forces and the sail shape parameters was discussed.
Abstract: Sail forces were measured in a full-scale sailing boat with the use of a sail force dynamometer. This apparatus consisted of an aluminum frame fixed to the hull by way of several load cells. The sailing boat was modified so that the dynamometer frame could be installed inside the hull. The mast, stays, winches, and other sailing rig were fixed on the frame so as to transmit all the forces acting on sail to the frame. By transforming the measured forces, the lift force, drag force, thrust, side force, or the center of effort of the sail force could be obtained. The sailing conditions of the boat, such as the boat speed, heel angle, wind speed, wind angle, and so on, were also measured.Sail shapes of the boat in the up-wind condition were also measured with the use of CCD cameras installed in the boat. The sail shape images taken by the cameras were transformed to bit-map files, and then processed by an SSA-2 D, a sail shape analyzing software. With the use of this software, sail shape parameters were obtained. The relationship between the measured sail forces and the sail shape parameters is discussed in this paper. Moreover, the measured sail shapes were used as the input data for the numerical calculations.Numerical calculations were performed to estimate the sail forces of the boat. In the calculations, two sails, a mainsail and a jib, were modeled in the form of a vortex lattice. The vortex lattice method was adopted as the numerical calculation method. Step by step calculations were conducted up to attaining the steady state of the sail in steady wind. Calculated sail forces were compared with the measured forces, and the validity of the numerical method was studied.

6 citations

Journal ArticleDOI
TL;DR: In this article, the surface vortex lattice method is used to simulate the flow around a lifting body including thickness and volume effects by distributing horse-shoe vortices and surface source distributions on the both side surfaces of the blades.
Abstract: In this paper, the applications of surface vortex lattice method to marine propellers in non-uniform flow are considered.The surface vortex lattice method based on the general vortex lattice method is possible to simulate the flow around a lifting body including thickness and volume effects by distributing horse-shoe vortices and surface source distributions on the both side surfaces of the blades. The advantage of this method compared to other panel methods is the fact that the Kutta-condition is satisfied automatically in not only steady condition but also unsteady condition by convecting the trailing and the shed vortices. The geometry of the wake using the linear wake model having the geometrical pitch of blades and all shed vortices are convected to new positions step by step with a small time interval.Three propellers are used to confirm the accuracy of the results of the present method. At first, the fluctuation of the thrust and the torque coefficients of a propeller in harmonic wake are calculated to compare the time derivative term with the results by VLM. And next, the pressure distribution on the blade concerning to two full scale propellers are calculated by the present method.The results of these calculations are good agreements with experimental results and other theoretical calculations

6 citations

Journal ArticleDOI
TL;DR: In this article, the authors extended the approach from Ref. 7, but extended it to the solution of a complete Navier-Stokes equation, rather than a thin-layer one.
Abstract: O calculate the aerodynamic performance of a helicopter in hovering e ight is a problem of great practical importance as well as the theoretical complexity. Theoretically, a solution of the fullNavier‐Stokes equations with appropriate turbulence modeling and body-conforming grid is sufe cient for a good description of all ofthephysicsinvolved.Butunlikethee owe eldaroundae xedwing, the trailing vortex wake of a rotary wing rotates with the rotor and is shed to a far distance below the rotor plane by its self-induced velocity. The helical vortex sheet interacts strongly with the lifting surfaces, but this process is hard to be simulated unless using a quite clustered grid, which generally requires very large computational resource. Srinivasan et al., 1 using about one million grid number to solve the thin-layer Navier ‐Stokes equations, calculated the whole e owe eld including the induced effects of the wake and the interaction of tip vortices with successive blades, but they also found their captured vortex structure was overdiffused because of the coarse grid used. The current methods for calculating rotor performance usually solve the potential, Euler, or Navier ‐Stokes equations coupled with anexternalfree-orrigid-wakemodelbasedonthe liftlineorliftsurfacetheory. 2i 6 Butitis clearthatthese governing equations arehard to match with the linear trailing wake modeling in a physically consistent manner. Further, those approaches also require fairly large computer resource from solving two coupled models simultaneously. Agarwal andDeese 7 calculatedthe aerodynamic loadsby solving the thin-layer Navier ‐Stokes equations, and the rotor-wake effects were modeled with a correction applied to the geometric angle of attack along the blades. This correction was obtained by computing the local induced downwash by the rotor wake with a free-wake analysis program. In fact, this method just established a weaker link between the rotor and its wake and avoided the complex boundary handling and the solution of coupled equations. Therefore, the grid number used is not huge, and the accuracy of calculated results is satisfactory. In the present paper we essentially borrowed the approach from Ref. 7, but extended it to the solution of a complete Navier ‐Stokes equation, rather than a thin-layer one. In addition, an improved method is suggested to obtain a proper correction of the local angle of attack of the blades. This is constructed by the comparison between the results with and without rotor wake modeling, in addition to a heuristic consideration of the coupling rotor-wake and threedimensional blade-tip effects that is expressed by a semi-empirical

6 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20221
202133
202036
201947
201837
201731