How to calculate the resistance experienced by a cylindrical rotor in water

Calculating the resistance experienced by a cylindrical rotor rotating in water involves primarily the viscosity in fluid dynamics and the effect of the rotating body on the fluid. The basic calculations can take the following points into account: 1. **Viscous torque**: When the rotor rotates in a viscous fluid, the viscosity of the fluid creates resistance. This resistance can be expressed as viscous torque, and its calculation formula is generally given by: \ where \(\mu\) is the dynamic viscosity of the fluid, \(L\) is the length of the rotor, \(R\) is the radius of the rotor, and \(\omega\) is the angular velocity. 2. **Reynolds Number**: This is a dimensionless number used to determine the flow regime of a fluid (laminar or turbulent): \ where \(\rho\) is the density of the fluid. Different Re numbers may imply changes in fluid frictional resistance. 3. **Effect of water pressure**: Without considering compressible fluids, the resistance experienced by a cylinder rotating in still water is roughly independent of the static pressure of the water. In other words, as long as the density and viscosity of water remain constant, water pressure (such as an increase from 1 MPa to 10 MPa) has no direct effect on the resistance caused by rotation or the torque required. In summary, generally speaking, as the water pressure increases from 1 MPa to 10 MPa, if the water temperature remains constant (i.e., the density and viscosity remain unchanged), the resistance experienced by the cylindrical rotor or the torque required remains essentially unchanged. The main factors considered remain the rotor size, rotational speed, as well as the viscosity and density of water. .