How to measure Reynolds number for two phase flow in DPM(Discrete Phase Model)

sandeepjaggarapusandeepjaggarapu Member Posts: 7
edited February 22 in Fluid Mechanics

Hello Ansys Community,

I am solving a two-phase flow problem using DPM(Discrete Phase Model) in ANSYS Fluent. The two-phases are lubricating oil and air. The problem is that I need to input whether it is laminar or turbulent. In order to do that, I need to find the Reynolds number.

For this two-phase flow how to measure the Reynolds number and as of DPM is concerned for what range we can consider the flow is turbulent or laminar (because Reynolds number considered for the DPM model is different from the regular one)? Here I'm solving the problem for a simple pipe of 5mm diameter and 20mm length with a velocity of 6m/s. The density of oil is 954 kg/m3.


Thanks in advance.

Best Answers

  • RobRob UKForum Coordinator Posts: 8,371
    Accepted Answer

    With 1% oil by volume I'd calculate Re assuming the pipe is just air. There may be a modification in a text book somewhere, but as we're just after a number to decide which model to use it's less critical.

  • YasserSelimaYasserSelima Member Posts: 430
    Accepted Answer

    Calculating Dimensionless parameters for two phase flow is always a tricky part. The majority of experimental publications use the homogenous density and velocity ... this basically because it is easier to measure/calculate. However, when possible, the actual flow parameters are better in comparison.

    So, check the references you are using, if everyone uses the homogenous density, velocity .. you need to follow. If you find discrepancy, do the right thing.

Answers

  • RobRob UKForum Coordinator Posts: 8,371

    Is the pipe full of air or oil? Reynolds Number is an arbitrary value which we then use to judge if a system is turbulent, so the hand calculation you do before turning the software on should give you an idea. We tend to try and run in either fully turbulent or laminar regime, transition is covered by the relevant models but those can be more sensitive to boundary conditions.

    I assume you've looked at the courses provided on here?

  • sandeepjaggarapusandeepjaggarapu Member Posts: 7

    Sir, the pipe flow is a mixture of air and oil with an oil volume fraction of 1%.

    Sir, I agree with you with the second sentence. But in this case, can I use the general Reynolds number formula (density*vel*Dia/viscosity) of air or else any other formula is there for a multiphase flow.

  • RobRob UKForum Coordinator Posts: 8,371
    Accepted Answer

    With 1% oil by volume I'd calculate Re assuming the pipe is just air. There may be a modification in a text book somewhere, but as we're just after a number to decide which model to use it's less critical.

  • YasserSelimaYasserSelima Member Posts: 430
    Accepted Answer

    Calculating Dimensionless parameters for two phase flow is always a tricky part. The majority of experimental publications use the homogenous density and velocity ... this basically because it is easier to measure/calculate. However, when possible, the actual flow parameters are better in comparison.

    So, check the references you are using, if everyone uses the homogenous density, velocity .. you need to follow. If you find discrepancy, do the right thing.

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