Tham khảo tài liệu 'kundu fluid mechanics 2 episode 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 424 Computational fluid Dynamics Figure Vorticity lines for flow around a cylinder at Reynolds number Re 100. Here t tu d is the dimensionless time. nondimensional units. This period coưesponds to a nondimensional Strouhal number s nd u where n is the frequency of the shedding. In the literature the value of the Strouhal number for an unbounded uniform flow around a cylinder is found to be at Re 100 . see Wen and Lin 2001 . The difference could be caused by the geometry in which the cylinder is confined in a channel. 6. Concluding Remarks It should be strongly emphasized that CFD is merely a tool for analyzing fluid-flow problems. If it is used correctly it would provide useful information cheaply and quickly. However it could easily be misused or even abused. In today s computer age people have a tendency to trust the output from a computer especially when they do not understand what is behind the computer. One certainly should be aware of the assumptions used in producing the results from a CFD model. As we have previously discussed CFD is never exact. There are uncertainties involved in any CFD predictions. However one is able to gain more confidence in 6. Concluding Remarks 425 Figure Streamlines for flow around a cylinder at Reynolds number Re 100. The dimensionless time is t t VId. CFD predictions by following a few steps. Tests on some benchmark problems with known solutions are often encouraged. A mesh refinement test is normally a must in order to be sure that the numerical solution converges to something meaningful. A similar test with the time step for unsteady flow problems is often desired. If the boundary locations and conditions are in doubt their effects on the CFD predictions should be minimized. Furthermore the sensitivity of the CFD predictions to some key parameters in the problem should be investigated for practical design problems. In this chapter we have discussed the basics of the finite difference and finite .
