# negative lift of underwater vehicles

 User Name Remember Me Password
 Register Blogs Members List Search Today's Posts Mark Forums Read

 October 5, 2004, 00:04 negative lift of underwater vehicles #1 sam Guest   Posts: n/a Hello fluent user, I have a problem calculating the lift of a vehicle 10 degree angle of attack of the hydroplanes underwater. Fluent is giving the pressure coefficient of lift in negative value and total lift becomes negative as well.According to my study the lift coefficeint should be positive while the vehicle is coming on to the surface. Please give me some advice regarding the above problem as soon as possible. Thanks in advance.

 October 5, 2004, 02:42 Re: negative lift of underwater vehicles #2 akula2 Guest   Posts: n/a maybe you have to describe your problem setup more detailed. is it 2d or 3d? tet or hex? what about hull hydroplane interaction? what is y+? which turbulence model? domain size? etc. if it is 2d problem there may be a basic problem setup error. if it is full 3d problem with sub hull and hydroplanes the problem size will be large at least several million cells... kolay gelsin.

 October 6, 2004, 00:29 Re: negative lift of underwater vehicles #3 sam Guest   Posts: n/a Merhaba arkadasim it is 3d problem with tetrahedral mesh. hull hydroplane interaction is conventional type and turbulance model used is k-e RNG with standard wall funtion approach. domain size is almost 1.9 milliom tetrahedral cells. one thing more that angle of attack of hydroplanes is 10 degrees. we do not know about the actual value of y plus value.Boundary conditions we r using as velocity inlet, wall body , outflow or pressure outlet.hoping for your early reply. Tesekur ederim

 October 6, 2004, 03:29 Re: negative lift of underwater vehicles #4 akula2 Guest   Posts: n/a it is clear that the physical dimesions of the sub hull and the hydroplanes are very different. so i guess for a good meshing you will need multiblock meshing (if you have not used yet) to get enough domain resulation on the bow, hydroplanes etc... if the hydroplanes on the shoulders of sub, the meshing on the bow section (until the hydroplanes) is very critical because flow conditions on the bow affects the flow on the planes deeply. according to my experiences for sub modeling, hex meshing will be a far better choice then tet. and spalart allmaras model is faster and better then any k-e. since i have not used fluent for a long time but remember that you can get actual y+ values about the simulation. did you calculate your mesh size requirement for suitable meshing (http://geolab.larc.nasa.gov/APPS/YPlus/) my advice; first make a 2d simılation with hydroplane cross section to model and understand the flow phonemena and requirements for meshing, turbulence modeling and accuracy... then model the hydroplane in 3d with some part of the bow (or sail, where the planes are) i think, if you dont need a special interests full modeling is not required. i have read a paper for simulating an ohio class sub with full features (hull, rudders, hydroplanes, sail and prop) they have reqired required above 10 million cell domain for getting just some acceptable results (which is not very accurate to validation actually)... iyi çalşmalar, bu arada bu bir okul çalşması mı?

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post AlmostSurelyRob OpenFOAM 3 June 24, 2011 13:06 gaottino OpenFOAM Native Meshers: blockMesh 7 July 19, 2010 14:11 bhagat FLUENT 0 April 9, 2010 16:14 fumie FLUENT 1 October 9, 2007 03:52 Rasmus Gjesing (Gjesing) OpenFOAM Native Meshers: blockMesh 10 April 2, 2007 14:00

All times are GMT -4. The time now is 08:52.

 Contact Us - CFD Online - Top