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-   -   DPM for diesel sprays (http://www.cfd-online.com/Forums/fluent/46665-dpm-diesel-sprays.html)

Cemil November 26, 2007 05:13

DPM for diesel sprays
 
Hi all,

As a result of my Fluent simulations of diesl sprays, modelled with the Discrete Phase Model, I have some questions.

Simulation results of the unsteady cases show differences in spray length (determined with density plot) and liquid length ("Maximum RMS distance from injector" from the Discrete Phase Summary) for different time steps used in the unsteady solution procedure. For a fixed time step of 10^-6 s the spray and liquid length are both shorter than with a time step of 10^-5 s.

Apart from other shortcomings of the DPM model, like grid dependencies, I did not expected this. Is there a logical explanation for this time step dependency?

Short description of the case file: Uniform grid with 1mm^3 cells, non-reacting ("droplet") n-heptane spray injected in high temperature environment (engine like conditions), plain orifice atomizer model, wave break-up model, collision model, two-way turbulence coupling, interaction with continuous phase, track with fluid flow time step, dynamic drag model, 1000 particle streams, pressure based first order implicit unsteady solver.

I hope someone can help me with this issue.

Thanks in advance,

Cemil


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