Akira Ojima

Vortex Method for the Analysis of Complex, Unsteady and Vortical Flows around a Swimming Fish

Although it is well known that the modes of undulatory locomotion of fish swimming provide high speed and high drive efficiency, it is hard to understand the propulsion mechanism of fish directly from living things. In the present study, in order to investigate hydrodynamic characteristics of the swimming modes, numerical simulation of flows around a deforming body of a rainbow trout which belongs to the kind of fish of subcarangiform undulatory swimmers was performed by using a Lagrangian vortex method. In this simulation, the basic configuration of the fish body is modeled with use of a NACA type airfoil, and the mode of undulatory motion is numerically given by a function obtained from observation of actual fish swimming. As a result of the present study, the relation between characteristics of propulsion force acting on the fish body and formation of complex vortex structures are clarified.

Application of a Vortex Method to Fluid Dynamics in Sports Science

This paper describes a pioneering work of practical application of an advanced vortex method in the field of fluid dynamics in sports science. The vortex method developed by the present authors is one of vortex element methods based on the Biot-Savart law, and it is known that the method provides a Lagrangian simulation of unsteady and vortical flows. In this study, in order to examine the applicability of the vortex method, three-dimensional, complex and unsteady flows around an isolated 100 m runner and a ski-jumper were calculated. Basic equations and mathematical treatment of the method are explained in this paper, and calculation conditions and panel data of deforming configuration of the athletes are described. As results of the present study, vortical and unsteady flow features around a runner and a ski-jumper are understood, and unsteady variation of aerodynamic forces corresponding to deformation of body configuration due to athletic motion are calculated. And, it is confirmed that the advanced vortex element method is a promising way to a grid-free Lagrangian large eddy simulation of unsteady and complex flows around dynamic bodies of athletes.Copyright

Recent Development of Lagrangian Vortex Method and Its Application into Fluid Machinery and Fluid Engineering

This paper is to introduce recent works of practical applications of vortex methods in the field of fluid machinery and fluid engineering, explaining the mathematical basis of the method based on the Biot-Savart law. It is pointed as one of the most attractive features of the vortex method that the numerical simulation using the method is considered to be a new and simple technique of large eddy simulation, because they consist of simple algorithm based on physics of flow of viscous fluid and it provides a completely grid-free Lagrangian calculation. As typical examples of simulation of complex flows, the internal flow of a mixed-flow pump calculated by the vortex method and the vortical flow around a flexible circular cylinder in a uniform stream which was simulated by a coupled structure and fluid analysis based on FEM and the vortex method are digested.

Applicability of the Vortex Methods for Aerodynamics of Heavy Vehicles

This paper describes recent works of practical applications of vortex element methods to study of aerodynamics of heavy vehicles, carried by the authors’ group, explaining the mathematical basis of the method based on the Biot-Savart law. It is pointed as one of the most attractive features of the vortex method that the numerical simulation using the method is considered to be a new and simple technique of large eddy simulation, because they consist of simple algorithm based on physics of flow and it provides a completely grid-free Lagrangian calculation. As typical results of aerodynamics of heavy vehicles, unsteady flows around a heavy vehicle model such as a tractor-trailer with different gap lengths and unsteady aerodynamic characteristics of a tractor-trailer with meandering motion are explained.

Study on the Application of Lagrangian Numerical Simulation to Fluid Dynamics in Sports Science

This paper describes a pioneering work of practical application of an advanced vortex method in the field of fluid dynamics in sports science. The vortex method developed by the present authors is one of vortex element methods based on the Biot-Savart law, and it is known that the method provides a Lagrangian simulation of unsteady and vortical flows. In this study, in order to examine the applicability of the vortex method, three-dimensional, complex and unsteady flows around an isolated 100 m runner and a ski-jumper were calculated. Basic equations and mathematical treatment of the method are explained in this paper, and calculation conditions and panel data of deforming configuration of the athletes are described. As results of the present study, vortical and unsteady flow features around a runner and a ski-jumper are understood, and unsteady variation of aerodynamic forces corresponding to deformation of body configuration due to athletic motion are calculated. And, it is confirmed that the advanced vortex element method is useful for the simulation of unsteady and complex flows around dynamic bodies of athletes.

Development of a Virtual Two-Dimensional Wind Tunnel Using a Vortex Element Method

This paper describes the work of development of a virtual two-dimensional wind tunnel using a vortex element method carried by the authors group, explaining the mathematical basis of the method and structure of the virtual wind tunnel. Following the development of an advanced vortex element method, the authors proceeded to development of a virtual wind tunnel, which provides a useful tool for researchers, designers and teaching staffs in the field of fluid dynamics. As the first step of the development, construction of a two-dimensional wind tunnel has been studied. The 2-D wind tunnel works on a PC, and it has such attractive features that once a user prepares a set of numerical data of two-dimensional bodies, he or she can begin immediately unsteady calculation of a flow around either an isolated body or multiple bodies in a uniform flow without any grid-generation work. The calculation provides unsteady characteristics of lift and drag coefficients acting on each body and instantaneous flow patters visualized by distribution of vortex elements. In this paper, the numerical procedure of the vortex element method and structure of the virtual wind tunnel are briefly explained. And typical results of two-dimensional and unsteady calculation of flows around bluff bodies will be demonstrated.Copyright

Applicability of the Vortex Methods for Automotive Flows

This paper describes recent works of practical applications of vortex element methods to study of automotive flows, carried by the authors’ group, explaining the mathematical basis of the method based on the Biot-Savart law. It is pointed as one of the most attractive features of the vortex method that the numerical simulation using the method is considered to be a new and simple technique of large eddy simulation, because they consist of simple algorithm based on physics of flow and it provides a completely grid-free Lagrangian calculation. As typical results of automotive flows, unsteady flows around a simplified vehicle model such as a wedge model, unsteady flows around a heavy vehicle model as a tractor-trailer, and unsteady aerodynamic characteristics of a tractor-trailer with meandering motion are explained.Copyright

Virtual Operation of Fluid Machinery by a Vortex Element Method

This paper describes recent works of practical applications of vortex element methods in the field of fluid machinery, carried by the authors’ group, explaining the mathematical basis of the method based on the Biot-Savart law. It is pointed as one of the most attractive features of the vortex method that the numerical simulation using the method is considered to be a new and simple technique of large eddy simulation, because they consist of simple algorithm based on physics of flow and it provides a completely grid-free Lagrangian calculation. As typical results of virtual operation of fluid machinery, the internal flow of a mixed-flow pump stage, unsteady flows through a wind turbine, and behaviors of submerged vortex in a pump sump are explained.Copyright