# Transient DPM-About Start Stop times

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 August 6, 2002, 11:51 Transient DPM-About Start Stop times #1 Julie Guest   Posts: n/a Hi, For the Transient simulations, for DPM, I realised that when I turned on the "interaction with continuous phase", I saw there is Start and stop times in the injection panels. If I specify any time in Start and stop that is not 0,example, start=2sec and stop=4sec, is it true that I must also input a value for the mass flow rate? Or else, onlie one injection will be made? Because I put some values for the start and stop times, but I did not put any values for flow rate, and I could only see one jection being made at start=2. If I input start and stop times, how do Fluent calculate how many injection should it make in during the time interval? I'm not too sure of how the start and stop time works. I'm tryin to model someone coughing continuously for about 2 seconds...which coughs about 3-4 times during this period.

 August 6, 2002, 21:10 Re: Transient DPM-About Start Stop times #2 david Guest   Posts: n/a hmm interestting simulation. A) If you want a two-way coupled solution, yes you have to put mass flow rate. B) In the dpm panel, you can see the max no of try per time step and the step size. By default they are 500 and 0.01. The rule of thumb is : max no of try per time step X the step size~ domain size. If you find the dpm simulation is not complete adjust these two parameters. C) If your simulations start @ zero time, and if you put the start of particle injection at 2 sec, then the injection will happen after 2 sec of real time (the primary flow solution will continue). The injection will continue until 4sec (another 2 sec) if you set so at the rate you set. D) Once you inject particles and the particles will remain in the domain (even you change your dpm flow rate), unless you reset dpm calculation. These are my understandings, correct me if I am wrong. DC soheil_r7 likes this.

 August 28, 2013, 05:58 #3 Senior Member   Astio Lamar Join Date: May 2012 Location: Pipe Posts: 186 Rep Power: 13 Hello. I have the same question but I cannot explore the answer here!! If I input start and stop times, how do Fluent calculate how many injection should it make in during the time interval? For instance Start time = 0 Stop time = 10 and injection should be done every sec. Moreover, I don't want to solve it with the continuous phase. How can I set this interval? In the Turbulent Dispersion tab, Number of tries is disable in my case! why? thanks.

 January 24, 2014, 07:39 #4 New Member   Join Date: Jan 2014 Posts: 11 Rep Power: 12 David sir can you tell me what is exact meaning of stop time in the set injection properties in the fluent under define injection ?