I agree that there is and always will be a need for detailed quantative CFD simulation. Depending on the industrial sector the level of desired accuracy will vary wildly.

This emphasis on the CFD code being responsible for the accuracy is a bit misleading. When asked how accurate a commerical CFD code is the vendor may well turn the question around and ask the prospective user how accurate can (s)he define the model input (BCs etc.) If the user only knows the BCs to within say 20% (one example would be dissipation of a integrated circuit computer 'chip') then this input accuracy should drive the choice of numerics.

Many CFD engineers seem to start with a selection of the numerics independently from the quality of the input data as well as ignoring (not knowing?) exactly why they are conducting the simulation (being told to by a lecturer does NOT justify a series of CFD simulations!). All I'm saying is that a CFD engineer should employ a balanced approach where the numerics, grid, BCs, detail of post-processing analysis etc. are all on the same level.

W.R.T the Tunnel Simulation the user could employ LES but this should be matched with an equivalent geometric definition, the 2 together leading to highly accurate answers. However, if the detailed geometric representation does NOT reflect the 'true' geometric condition in the tunnel (what about rush hour, what about many more buses than cars.....) then you will resolve accurate answers for a non-realistic model.

Clifford, your point about the need to improve the accuracy and reliability of CFD codes is true as always. Maybe an equivalent drive is required to either ensure good quality input data or a methodology for best CFD practice based on application sector. The latter may be alluded to in the ERCOFTAC initiative lead by Tony Hutton. Time will tell.........

Robin

i wonder if it makes sense to calculate the problem with cars?

The engineer has to construct the ventilators, so that in the case of fire, the smoke don't fills the tunnel.

I don't think that the ventilation-power, which is needed for this task, is influenced much by the cars.

If this were the case, you have to calculate all different possible traffic situations. Much work for you and your computer, i think.

John, my english is very bad. Im sorry it's not my mother language.

(1). Important messages always got studied , translated , and revised into different languages. (2). I think, a good ventilation system is always very important. The efficiency and the reliability of the fan and motor will be very critical in this application. (3). The former CEO of Chrysler is said to be selling electric bicycles. So, there is a chance that there will be no fire problem in a tunnel. I hope so.