# Calculation of lagrangian integral time scale

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 June 11, 2003, 23:06 Calculation of lagrangian integral time scale #1 R.Sripriya Guest   Posts: n/a I am trying DPM with KE for one of my simulations. I was going through some literature where it was mentioned that for particles with large stoke's number(defined as the ratio of the particle relaxation time to the turbulent lagrangian integral time), the effect of turbulent fluctuations on the fluid and the particle -particle interaction can be neglected. Here the particle relaxation time is defined as density of the particle*dia of the particle/ 18* viscosity which is known. However the turbulent lagrangian integral time is defined as .2*k/E. We don't know the values of k and E. Any idea as to how this can be calculated

 June 11, 2003, 23:07 Re: Calculation of lagrangian integral time scale #2 R.Sripriya Guest   Posts: n/a

 June 12, 2003, 00:25 Re: Calculation of lagrangian integral time scale #3 Alex Munoz Guest   Posts: n/a Hi careful relaxation time =particle density*particle diameter^2/(18*viscosity) don't forget the square of the diameter! Now the question isnot if you ignore the effect of the turbulent fluctuations, the real question is what is the legth scale for you particle tracking as a results choose a value lower than the relaxation time*velocity. I wonder if the paper that you are reading was written by Chen and Pereira!! Best regards Alex Munoz

 June 12, 2003, 01:55 Re: Calculation of lagrangian integral time scale #4 R.Sripriya Guest   Posts: n/a The length scale is much smaller than the product of the velocity and the relaxation time of the particle.What else is to be done?

 June 12, 2003, 12:49 Re: Calculation of lagrangian integral time scale #5 Alex Munoz Guest   Posts: n/a Hi Your length scale should be smaller than the relaxation time, not much smaller, because this fact demand a longer calculation time. About the fact that your particles doesn't exit the domain, I can not give you a sugguestion. You have to figure out the solution by yourself. Regards Alex Munoz