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Applied Computational Fluid Dynamics Techniques - Wiley Episode 2 Part 6

Tham khảo tài liệu 'applied computational fluid dynamics techniques - wiley episode 2 part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | SPACE-MARCHING AND DEACTIVATION 369 performed using a three-stage Runge-Kutta scheme with a Courant number of C 0.6. The dispersion calculation was run for 485 s of real time corresponding to the time of a train entering halting exiting the station and the time for the next train to arrive on a workstation with the following characteristics Dec Alpha chip running at 0.67 GHz 4 Gbyte of RAM Linux operating system Compaq compiler. Figures 16.11 b - e show the resulting isosurface of concentration level c 0.0001 as well as the surface velocities for time t 485 s. Note the transient nature of the flowfield which is reflected in the presence of many vortices. Deactivation checks were performed every 5 timesteps. The tolerance for deactivation was setto u 10-3. The usual run i.e. without deactivation took T 5 296 sec whereas the run with deactivation took T 52 6 sec i.e. a saving in excess of 1 10. This large reduction in computing time was due to two factors the elements with the most constraining timestep are located at the entry and exit sections and the concentration cloud only reaches this zone very late in the run or not at all furthermore as this is an instantaneous release the region of elements where concentration is present in meaningful values is always very small as compared to the overall domain. Speedups of this magnitude have enabled the use of 3 -D CFD runs to assess the maximum possible damage of contaminant release events Camelli 2004 and the best possible placement of sensors Lohner 2005 . 17 OVERLAPPING GRIDS As seen in previous chapters the last two decades have witnessed the appearance of a number of numerical techniques to handle problems with complex geometries and or moving bodies. The main elements of any comprehensive capability to solve this class of problems are - automatic grid generation - solvers for moving grids boundaries and - treatment of grids surrounding moving bodies. Three leading techniques to resolve problems of this kind are as