ABSTRACT
The linear channel is one of the key components of a linear-type marine magnetohydrodynamic (MHD) thruster. The cross-section of a linear channel directly affects the energy conversion process and performance of an MHD thruster. In this paper, the flow loss, distribution of the internal electromagnetic and flow field, and performance characteristics of a linear-type MHD thruster with three cross-sections are investigated using the finite volume method and 3D numerical simulations. The results show that under the same conditions, the performance of an MHD thruster with a rectangle cross-section is better when Re is less than 250,000, and that with a drum-shaped cross-section is better when Re is more than 250,000.
Marine MHD propulsion uses an electromagnetic force (Lorentz force) acting on seawater to generate a thrust. So few mechanical moving parts are required with MHD propulsion. As a result, this type of propulsion may be very quiet and simple. And MHD propulsion receives more attention recently (Ali, Pruiu and Ail, 2016; Hojati, Marashi and Kanzi, 2017; Mortaza, Mohammad and Diako, 2018; Mortaza, Mohammad, 2019). According to the configuration of the magnet and channel shape, marine MHD thrusters are classified into two main types, the linear-type MHD thruster with a linear channel and saddle-shaped magnet, and the helical-type MHD thruster with a helical channel and solenoid magnet. As shown in Fig. 1, the linear channel of a linear-type MHD thruster is composed of insulating walls and two flat/arc electrodes. It is very simple and easy to manufacture. And it has a small flow resistance. Therefore, the linear-type MHD thruster has been studied theoretically and experimentally since marine MHD propulsion was put forward.
Doss(1990) and Thibault(1991) investigated the inner electrical field and electrolysis effect of linear-type MHD thrusters. The first superconducting MHD propulsion test ship "YAMATO-1" in the world used linear channels. Many experiments and calculations on performance of linear channels had been done, which got many good and significant results (Tasaki, Sugawara and Mori, 1991; Roy, 1993; Sasakawa, Takezawa and Sugawara, 1993). Gilbertt, Lint (1990) and Kom, Brunet (1995) used multiple linear channels arranged around a circle to reduce the leakage magnetic field. Tan, Yun and Ling (1997) established a mathematical model of a linear-type MHD propulsion system with a rectangular cross-section. Chai (2000) established a two-dimensional mathematical model of a linear-type MHD thruster using the finite element and finite difference method. He investigated the electromagnetic and flow field and influence of Hartmann effect in a linear channel with a rectangular cross-section. Zhao and Kong (2007) proposed a global calculation method for a linear-type MHD propulsion system based on the conservation of momentum and energy, and studied the influence of the geometry and size of a linear channel with a rectangular cross-section on the flow loss and propulsion efficiency. Hojati and et al. (2017) set up a simplified analysis model of a linear-type MHD thruster with a rectangular cross-section. Considering the influence of the seawater electrolysis and end loss, Mortaza, Mohammad and Diako (2018) studied the influence of the magnetic flux density and seawater conductivity on the performance of a linear-type MHD thruster with three-dimensional numerical simulations.
