Help with torque calculation of underwater rotating disk?

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To calculate the torque required for a 150mm diameter disk rotating at 100rpm in water, one must consider the disk's weight of approximately 1kg and the influence of the water level on the setup. The presence of a circular ring on the disk complicates the calculations, as it affects the hydrodynamic forces. While simulations can provide more accurate estimates, they require significant effort to set up. It is suggested to consider the water level as constant for initial calculations, but this may lead to inaccuracies. Additional details about the setup, such as a sketch and the dimensions of the water basin, would aid in providing more precise guidance.
IamDev
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Hello Guys,

I have a disk of diameter of 150mm and thickness of 10mm which is rotating at the constant speed of 100rpm. The disk is inside water which is approximately 4-5 cm below the surface. Disk is horizontal (parallel to the water surface). Disk is attached with the shaft of the motor. At the upper surface of the disk there is a circular ring of outside diameter of 80mm and inside diameter of 70mm and height is 20mm.
I need to calculate the torque required to rotate this whole setup at 100rpm.
The weight of this setup is approximately about 1kg and the water is still at the surface.
 
In general, those things need simulations to get some numerical estimates. The water level will get influenced by the rotating disk, so you have to consider the water/air boundary as well. There are software packages that can model it, but expect some work to get the simulations running.
 
Is it possible to calculate required torque if we consider that water level will be constant during the whole process?
 
It is possible to get some estimates, but I think without a simulation all those estimates will be problematic.
 
Okay, I have a disk of 8 cm radius and 4 cm thickness and I have to rotate the disk at constant speed of 100 rpm. I need to buy a DC motor to rotate the disk but I am unable to short out the specification of DC motor. Can you help me please?
 
Well, it is possible to get some order of magnitude estimate. Do you have a sketch of the setup? How large is the water basin? What is below the disk?
 

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