[burak samsul]

Hi,

First of all, I have recently started to work on floworks. I have designed lots of propeller models by using different engineering programs. Finally i need to see the thrust differences between some types propellers. In my calculations; i have a constant flow, a rotating region and static pressure. I have defined some global and surface goals. Unexpectedly i got different results when i make a calculation completely the same. Because some of the goals are unable to be converged in some calculations. And i am curious about; why i am getting different very different result when i add a goal or remove one of them. I have to get some more informations about selection of the goals according to the type of analysis...

Thanks.

[Boris_M]

Hi burak,
In your case I wouldn't use an internal analysis and pressure boundary conditions. Use an external simulation and the stability problems should most likely vanish. I thinkg this is probably because you forced him to have the same pressure on both sides and with external this is just an initial condition and would change as its getting calculated. You can also define a velocity as the initial conditions as if the ship is moving already, which would influence the flow and reactions on the propeller.

In general it can take longer to converge for rotating calculations so it is best to switch off the maximum travels in the calculation control options.
It can even have values in the beginning that don't make sense such as inflow on all sides but this will then change over time as the calculation proceeds.

Regards,
Boris

[burak samsul]

Thanks a lot Boris,

I am preparing a model according to your advices. It seems very sensible. Thanks for your help again.

Best Regards.

[burak samsul]

Hi Boris,

First of all external analysis' are very stabile and sensible. I have one more question ; what will be the best comparing value or plot for two propellers working on same boat with same engine. I have to decide this for lots of propellers and i have to be sure. Force values are showing differences according to the constant flow values so i need a clue for comparing the performances.

Regards.

[Boris_M]

Hi burak,
Good to hear that you make progress. Unfortunately it's some time ago that I worked with propellers so cannot help you with that question so good. I know from aircraft engines there are some efficiency coefficients but don't know if they can also be used for ship propellers.
When searching in Wikipedia you'll find that:
http://en.wikipedia.org/wiki/Propeller
So I would say try to search in the internet or some smart books about that field of study and you should find some equations you can use to calculate the efficiency of your propellers to compare them.
You should also consider to use the best variants of your designs in a cavitation calculation since high effiency is only useful if the energy savings are not wasted due to high maintenance costs from damaged propeller blades.

Regards,
Boris

[samir_cfd]

Good day Burak
I am simulating flow around Seiun Maru Highly skewed propeller using sliding mesh technique . the solution converge well but I think I have problems in resultes found after the simulation using Fluent. The thrust is higher annd the pathlines are not normal. Please could you help in this field

[Boris_M]

Hi Samir,

I think you are in the wrong Forum. Your question about Fluent should be posted in the Fuent Forum not the FloEFD/SW Flow Simulation Froum. That's a different software and you will probably not get the help you want here.

Regards,
Boris