Inlet - problem with volumetric flow rate

edited March 6 in DualSPHysics v5.0


I would like to ask about settings of inlet condition. In my problem, I have box filled with fluid. At the bottom of the tank is tube that fills the tank, sketch attached. (It's a simulation of weir.)

Inflow is located as pointed in figure. I know volumetric flow rate and diameter of inlet pipe as input data. Buffer was fitted (so particles infront couldn't go backward around the buffer) to inlet pipe and inlet velocity was chosen to satisfy prescribed VFR.

From simulation was obvious, that volume flow is significantly lower than has been set. (Due to knowledge of the real system.) After that observation, three methods have been used to determine actual volumetric flow rate. First of all, I measured velocity in the inlet pipe (as shown in figure), then I added box and measured volume of fluid flowing to the box over the weir and finally I used outlet channel to measure velocity of water flowing away from system to compute volume flow. So I could be pretty sure the volumetric flow rate goes wrong.

I tried to play with inlet velocity and diameter of inlet buffer. (Each time I also changed model, specifically diameter of the pipe, so buffer was fitted perfectly. Square profile was also tried, results are same.) If I used smaller area for buffer with higher inlet

velocity I obtained described volumetric flow rate. But with this solution came other problems like rapids and "air capsules" and I don't think that's ideal way how to solve it.

I tested different inlet options in DualSPH v5 (I tried both refilling options, 1:simple below zsurf, 2:advanced for reverse flows) but the results were even worse then results obtained by v4.4. I noticed same problem also in case of vertically oriented pipe with normal oriented against gravity vector.

With proper velocity and smaller diameter of inlet, I'm able to achieve right volumetric flow rate. But if the diameter of inlet pipe is higher (with adjustment for inlet velocity, buffer perfectly fitted), the VFR drops below set value.

I would like to ask you about some ideas of settings for this type of tasks. Is it something what can be solved with proper inlet settings or is this caused by any incompatibility or something?

I will be grateful for your answers.


  • So I made a bit of progress.

    There are the results with ver. 4.4, with and without shifting. With filled system as initial condition (boxfill used) and inlet velocity straight to prescribed value lead to the problem described above. BUT with slowly increasing velocity from zero to my desirable value, everything works fine! (Thanks to Dr. Tafuni and discussion in the 5th workshop!)

    Then I used latest version (5.0.3) and found new problems.

    I tried all possible options (simple fill, reverse flow) but result are mostly same (some better, some worse). Then I tried to employ shifting and DT (all possible options), things gets slightly better. (Although some particle goes trough boundaries.) Results usually looks like this.

    Inlet is fitted to the pipe with maximum possible size of buffer. I omitted the geometry, but you can imagine with help of working case. VFR doesn't match either.

    Eventually I found, that with options stf3 DT1/2 results look better, stf3 DT2 even satisfy the desirable VFR.

    Question1: What there is different with inlet compare to previous version? Is there something I'm completely missing or doing wrong? 

    Question2: What Inflow_World means? Should that VF be enters the simulation domain?

    For measurement of VFR, I used flowtool and velocities from measuretool to compute flow trough some flow area. Values obtained from velocities (using mt) agree with prescribed VF value. But doesn't match Inflow_World (Outflow_World) neither Inflow_box (Outflow_Box). Inflow_World (Outflow_World) usually gives higher number then prescribed value. I would like to note, that flow-tool box has unit length. Shouldn't be values of VFR through all cuts (using flowtool) same, with constant inflow? Why is there difference? (Values obtained from velocity remains constant in all cuts.)

    Thank you for your advices and hints. Next, I want to look at mDBC and 2D case, but I decided to ask at first place. If you are interested, I can send you full overview of my tests of inlet performed with v4.4 and v5.0, with try to set my problem.

  • Dear @TomasCTU I would suggest to send email to Angelo Tafuni and José Domínguez directly to ask for these problems.

    They can explain better what is different in v5.0 compared with previous version.

    Jose can also explain to you better the output information from FlowTool


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