Learning Forum

[Lahiru Madushanka]

I am simulating an ROV ducted propeller (underwater) to study thrust force behaviour with the changing duct angle.

There is a significant discrepancy between the experimental thrust force and the results obtained from our computational fluid dynamics (CFD) simulations for the T200 thruster. Our experimental data, based on the technical details provided by Blue Robotics, indicates an expected thrust force of approximately 14.5 N at 1900 rpm.

However, our CFD simulations yielded a significantly lower thrust force of approximately 5.7 N.

Simulation details,

Ansys CFX was used.

I created two domains, stationary and rotary. I used a steady state with a frozen rotor approach.

Inlet velocity is zero. wall and outlet were set as openings. k-epsilon model was used.

1)What may be the reason for this deviation?

2)Are my boundary conditions correct for this type of application?

Thank you.

 

[CFD_Friend]

Hi Lahiru,

Some things you can check on are;

• Check if the mesh statistics look okay. You can find this in the OUT file(the message shown on the right side of the solver manager) Make sure that many of the mesh parameters are within acceptable limits.
• Instead of Opening boundary condition, try using pressure inlet and pressure outlet boundary conditions as these are more robust. Try extending the inlet and outlet away from the propeller to get optimum results with such boundary conditions.
• Using Alternate rotation model can also be good advice. The alternate rotation model is generally recommended, especially for axial fans. In most realistic flow situations, this model reduces (or at least will not increase) numerical errors.
• Are the hub and blade assigned as rotating walls? If not assign them as rotating walls.