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-   -   planing craft (http://www.cfd-online.com/Forums/fluent/36266-planing-craft.html)

 sulfi April 5, 2005 03:48

planing craft

hi i am modelling only the under water portion of planing craft. we are using sinkage and trim values obtained from experiments. at low speed fluent is giving drag comparable with experiments. but at high speeds(5m/s) the drag values are 5 times the experimental.

what should i do to get the correct drag.

i have tried using all the turbulence models and differnt domain and also using different mesh sizes.

thanking u

sulfi

 Jason April 5, 2005 07:10

Re: planing craft

Are you looking at actual drag, or at the drag coefficient? If you're looking at the drag coefficient, then check your reference values (Report->Reference Values).

If you're looking at the actual drag, then your solution is probably wrong. Check the pressure gradients, especially near the stagnation point. Look at the pressure coefficient as well and see if it makes sense (shouldn't be above 1 at these speeds). Look for problems in the solution that could point out problems in the mesh.

Hope this helps, and goodluck, Jason

 sulfi April 5, 2005 09:11

Re: ship resistance

thanks to jason for his reply. i am getting the right drag value for displacement(trim angle=0) ship. But for planing craft(at some trim angle) i am not getting the correct drag. it is highly overpredicting. i am only modelling the under water portion. why the code is behaving like this.

 Ziah April 11, 2005 21:57

lift coefn. value.

hi, i am modelling a stretched hemisphere in a wind tunnel. BC is from the experiment value where the speed is varies from 8m/s to 20 m/s.I get comparable value of drag coefficient but 100 times small value for lift coefn. (0.0004, -0.0003) and unconsistent.

What should i do? i have try using different turbulance model size of meshing and also have check the references values.