1. Field of the Invention
This invention relates to electricity power generation, and particularly provides an electrical power generation device (generator) utilizing the oscillating action of the Karman vortex street to generate the induced alternate current. This device converts the energy from fluid motion to useable energy.
2. Description of the Related Art
Reynold's number, Re, a non-dimensional number which is defined as the ratio of fluid inertia to viscosity force, is often used to describe fluid flow. The Re for compressible fluid is defined as follows,
                              Re          =                                    ρ              ⁢                                                          ⁢                              V                ∞                            ⁢              L                        μ                          ,                            (        1        )            where ρ, V∞, μ is respectively the density, velocity, and dynamic viscosity of the fluid, and L is the characteristic length. When fluid passes a non-streamlined body (or called body, or vortex generating body) in a given rang of Re, since the adverse pressure gradient exists in the boundary layer of the fluid on the body, the fluid starts to separate with the time developing. A lot of experimental and theoretical studies had shown that when Re is from 50 to 500, the vortices are continuously and periodically shed from each side of the body and the rotation direction of the paired vortices is alternate. Two stable, regularly spaced rows of vortices with laminar core are formed in the wake behind the body. This fluid motion pattern is called the Karman vortex street, named after the Germany fluid dynamist Theodore Von Karman (1881-1963), owning to his exploring research on this fluid motion. FIG. 1 presents the pattern of the Karman vortex street. The circulation conservation law can explain the formation of the Karman vortex street. It means that when a vortex produces, another vortex with apposite circulation surely exists. In practices, when flows pass the buildings, electrical lines, bridge piles, etc., the Karman vortex street will appear. Another non-dimensional parameter, Strouhal number, also describes the relation between the vortex shedding frequency and fluid velocity in the Karman vortex Street. The Strouhal number, St, is defined as
                              St          =                      fL                          V              ∞                                      ,                            (        2        )            where f is the vortex shedding frequency and the other variables are same as before. Under a range of Re, the Strouhal number is fixed, therefore, the fluid velocity can be found by measuring the vortex shedding frequency, which is the basic principle of the widely used Karman vortex flow meters.
The vortices in the Karman Vortex Street behind the vortex generating body are conducted to downstream. At the same time, because of the circulation around a vortex, a force along the lateral direction (perpendicular to the fluid direction) acts on the vortex. This force is called lift. In the Karman vortex street, fluid behaviors alternately force along the two rows of vortices. According to the principle of action and opposite action, the alternate shedding of vortices can create periodic lateral force on the body, which induces the body oscillation. In engineering practices, this oscillation could make the body fatigued and damaged. For example, the accident of Tcomn Narrow Bridge was caused by the Karman vortex street.
To convert this oscillating energy generated by the Karman Vortex Street to the usable energy, such as electrical power, is the purpose of this invention.