CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   Main CFD Forum (http://www.cfd-online.com/Forums/main/)
-   -   Scaling a model for aerodynamic analysis via cfd simulation (http://www.cfd-online.com/Forums/main/114653-scaling-model-aerodynamic-analysis-via-cfd-simulation.html)

Scaling a model for aerodynamic analysis via cfd simulation

Hello Sir,
I want to calculate co efficient of drag on heavy vehicle with the help of CFD simulation as my undergraduate project. Please tell me how to scale down my model for better meshing or i should not scale down model?? i mean scaling down of model effect Cd???

Please also tell me optimize setting for analysis or some technical journal where i can study that...plz reply..

Thanx & Regards

 julien.decharentenay March 17, 2013 19:35

If you were doing a wind-tunnel experiment, spatial constraint (as well as other constraints) would require you to scale down the experiment.

I do not quite understand the benefits you would gain from scaling down in the CFD simulation (apart from comparing with a wind-tunnel experiment, or investigating the effects of scaling down). Can you clarify the benefits you are expecting from scaling down?

I jst want to reduce computation time. and the reason behind this is that i hav a laptop with 4 gb ram & 1 gb nvidia with i5 processor. it is very hard and time consuming approx 11 hours...plz suggest me some beneficial ways...

 RodriguezFatz March 18, 2013 05:00

This does not work. There is no benefit. If you want a representative simulation, you must keep the Reynolds number. So if you scale down the simulation you must also keep the Reynoldsnumber, which means you have to increase your inlet velocity (for example). Thus, even for smaller domains, you have the same need for grid points.

 flotus1 March 18, 2013 05:28

The only thing you can do to speed up the simulation is to make use of symmetries.
If you are using a RANS approach, your model and your boundary conditions have the same symmetry planes, then you can simulate only a part of the model.

In your case I guess the vehicle has one symmetry plane which allows you to halve the simulation time.

 julien.decharentenay March 18, 2013 06:47

Alex option is a very good option.

Otherwise there are a number of options to speed-up analysis, but usually with trade-offs or increased complexity:
- Use a coarser mesh, at a trade-off with accuracy;
- Numerical methods: some methods are typically faster than others and using appropriate tolerance can speed-up results;
- Hardware: faster processor, more memory, GPU or parallel processing can help speed things up;
- Software: the software you use may have tricks that can speed calculations (such as memory access).

11hours per run is not bad (from my perspective). Doesn't your uni give you access to some computer resources to allow you to run 3-4 cases overnight?

Good luck.

Thanx a lot julien.decharentenay..i will surely mention ur name as a guide in my research report...u helped me a lot..at every stage of my project...:)

Thnx Alex & RodriguezFatz..thnx 4 ur kind reply..

please just help me once more...please can u tell me what is appropriate (best suits to my project "aerodynamic improvement of truck and trailer" as per ur knowledge and experiance) setting of k-e model such as y+ value nd turbulence intensity and other factor....by which i can get most appropriate answer...
Waitng 4 a nyc reply...Thnx & Regards