help:CFD Transient

Hi all,

I'm Hardiana, an undergraduate student of Sepuluh Nopember Institute of technology from Naval architect department. Currently I'm doing my final project with the topic of hydrofoil. I have to simulate the hydrofoil craft using CFD in a transient condition of velocity. I'm a newbie in CFD and I don't have any idea what software I should use. Is there anyone that could give me some advices, please?

Best regards,
Hardiana

 

Don't do it!

Transient flow on a hydrofoil is far from trivial - I don't think it is a good idea to attempt this for a uni project (much too complex and time consuming). It is far better to do something simple well, than something difficult averagely.

If you persist, unless you use Openfoam or some other open source software, you'll have to use whatever the university has licenses of (Fluent, CFX, CCM+ etc).

 

I'm with PI on this one. Transient CFD (especially with free surfaces) is not easy.

Consider a writing a 2 DOF dynamics model to model the vessel, and come up with a "semi-empircal" model for the foils. You need to consider angle of attack, proximity to the surface, a bit of lifting line theory etc. etc.

That's far more achievable, and in all likelyhood, more useful.

Tim B.

 

I'm not sure what you mean by a "transient condition of velocity". There are many possible transient conditions, ranging from seakeeping (traveling through waves) to maneuvering (turning, acceleration/deceleration), to stability (small motion about an equilibrium condition). Each of these requires a somewhat different approach, and it would take a very sophisticated model to be used for all of them.

The general approach would be to first establish the equations of motion and the method of solving the dynamic equations for your type of problem. For example, a maneuvering analysis would probably require integrating the differential equations in the time domain, but a seakeeping analysis could be done in the frequency domain. The most difficult part of the problem is coming up with values for the coefficients that describe your particular configuration. This often requires a great deal of engineering judgement to generate approximations for effects that are too expensive to calculate or obtain through model testing.

I think you need to be more clear about the objectives of the analysis for us to give you much help.

You will probably find it useful to obtain the AMV CD collection of papers from the International Hydrofoil Society. The first CD has a handbook by Hydronautics (I believe it is the last paper on the CD) that discusses hydrofoil design issues and has equations of motion you may find useful.

 

I can only assume the OP meant the velocity transitions from one inlet velocity to another. This is not trivial to do!

The following PDF describes a master's thesis in which OpenFOAM is used to model piston-mode resonance due to fluid motion in a ship MoonPool. In it, a verification study was done using a NACA wing as a hydrofoil to match Duncan's 1983 paper "The breaking and non-breaking wave resistance of a two dimensional hydrofoil" (1983) (see page 29+ of the document MoonPool_OpenFOAM.pdf).

MP-089-36.pdf and iwwwfb14_23.pdf are other papers based on Duncan's work.

EDIT:

On re-reading the OP's post, I gotta say, this is way beyond the scope of undergraduate work. I know that ANSYS-CFX comes with a pre-packaged Hydrofoil example that's was pretty much plug-and-play, but if you don't already have it the ANSYS software is relatively expensive, even for academic work. In that light, you may be able to achieve acceptable results from the tools JavaFOIL, xFoil or APAME, which are based on velocity potential formulations (vortex sheets).

http://www.mh-aerotools.de/airfoils/javafoil.htm
http://web.mit.edu/drela/Public/web/xfoil/
http://www.3dpanelmethod.com/