# difference active/passive scalar

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 April 21, 2005, 07:41 difference active/passive scalar #1 Torsten Guest   Posts: n/a i have an other question too. can anybody explain to me, what is the difference between active and passive scalar. yes, i have read the help-files, but i am able to make nothing of it. thank you.

 April 21, 2005, 09:09 Re: difference active/passive scalar #2 4xF Guest   Posts: n/a Simple: an active scalar modifies the physical properties like density and viscosity according to the local concentration of the scalar. That means that if you have 100% of an active scalar, density and viscosity will be the same as the ones of the active scalar. Whereas for 0%, density & viscosity will be the ones of the background fluid. The passive scalar on the other hand do not influence the fluid properties, but there is still a transport equation solved for it. You can consider it as a tracer.

 April 22, 2005, 03:50 Re: difference active/passive scalar #3 xhliu1 Guest   Posts: n/a Hello, Torsten, Here I have a question to ask for help: When add source to the continuity equation using my subroutine,what should I express the term of div(p) as? Good Lucky! Thanks!

 April 22, 2005, 06:06 Re: difference active/passive scalar #4 Torsten Guest   Posts: n/a Hello 4xF, if i have an active scalar, in a cell will solved a mixing value for density, viscosity and temperature in accordance of the concentration of the scalar. what happens for a passive scalar? in the same cell i get only the density and so on of the background fluid. what does the temperatur? if the scalar has 500 K an the background fluid 300 K. i think i get a mixing temperature. is that right, that this temperature affects e.g. the density of the background fluid? thank you!

 April 22, 2005, 10:52 Re: difference active/passive scalar #5 4xF Guest   Posts: n/a If you are just interested into the variations of density with temperature during a mixing process, why don't you use the temperature (which is a transported scalar) and use a 'cold' and 'hot' source?

 December 3, 2016, 06:01 #6 New Member   ahmed elbanna Join Date: Oct 2016 Posts: 7 Rep Power: 9 The Passive Scalar Transport analysis type allows you to simulate the transport of a scalar quantity within an incompressible fluid flow. The core assumption of this analysis is that the species that is transported within the flow does not affect the fluid flow (therefore passive). This is a valid assumption for example for the transport of oxygen within a water flow. It is important to note that, scalar transport does not assume any physical dimensions for passive quantities. Therefore, this analysis type to study the transport of mass concentration, temperature, etc. in the same way. https://www.simscale.com/docs/conten...Transport.html

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