Gas properties for multiple mediums

Hello all,

I'm a very new user to DualSPH, now using 4.2. There is a particular case: a high pressure and high tetmperature gas sphere is located in the ambient atmosphere (at t=0). The simulation would hopefully show how the pressure wave travels from the initial sphere outward.

I have also ran the similar case in OpenFOAM with rhoCentralFoam so DualSPH results are to confirm the obtained results.

I have looked at some example code and this is what I found:
<properties> %Material properties for liquid-gas flows are set here.
<links>
<link mkbound="0" property="water"/>
<link mkfluid="0" property="water" />
<link mkfluid="1" property="air" />
</links>
<property name="water">
<rhop0 value="1000"/>
<gamma value="7"/>
<cs0 value="24.14"/>
<visco value="0.03"/>
<phasetype value="0"/>
</property>
<property name="air">
<rhop0 value="1.18"/>
<gamma value="1.4"/>
<cs0 value="343.28"/>
<visco value="0.03"/>
<phasetype value="1"/>
</property>
</properties>
The hot gas inside the starting sphere would be similar to "water" and the surrounding cold ambient gas would be "air". Phasetype would be "1" for both.

My only problem is that I did not find any resources or tips on how to define the following:
- gas Temperature
- gas dynamic viscosity
- gas pressure

Not sure what the units are for the "visco" property.

How do I tell DualSPH to treat this medium (i.e. air, and hot air) as Perfect Gas ? Almost all the example codeI looked at is using water or some other "fluid" as the medium - very few examples about gases.

Any tips or comments?

Thanks

Comments

  • Hey

    Visco depends on the scheme you've chosen: artificial viscosity or sps-les. In the first scheme you control a parameter constant and in the second you can specify the physically correct kinematic viscosity. Artificial viscosity is often easier to use and stabilize the simulation with and should especially be used for 2D case.

    I advise you to look through the DualSPHysics wiki guide file to understand this a bit better.

    A piece of advice is that cs0 values should NOT be the physically correct ones - this is because the higher the speed of sound, the longer computational time - you should only make sure that the "speed of sound" is 10 times higher than the fastest speed in your domain (to ensure almost incompressible condition). Remember that currently DualSPHysics only employs a weakly compressible SPH scheme, so the way you tell it to be "perfect gas / incompressible" is by doing what I described before and choosing the gamma value as you did in your file (1.4) in the equation of state.

    You do not need to specific dynamic viscosity since kinematic and dynamic are related to each other by the density of a fluid.

    I am not sure how and if it is possible to specify temperature or pressure, but try searching the forum and else I hope someone else can clarify those points,

  • DualSPHysics does not simulate the energy equation, therefore it is not possible to have different temperatures for the fluids.
    For pressure, there is no way to input it directly through the xml, but in the multi-phase code there is a background pressure you can use.
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