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-   -   Surface monitors in fluent (https://www.cfd-online.com/Forums/fluent/38416-surface-monitors-fluent.html)

 Ann October 28, 2005 03:46

Surface monitors in fluent

Hi everyone who can help,

I have some problems with surface monitors. I have defined a surface monitor for velocity multiplied by a constant for the outlet of my 2D pipe. (i.e. C1 x Velocity magnitude) and plotted the result over flow time.

When defining the monitor, under report type there are many options such as integral, area-weighted average, mass-weighted average. Which one to choose? I do not know.

Does it mean if I choose integral, the term (C1 x velocity) at that instant is the average value over the entire outlet area? because at each point of the cross sectional area, the velocity is not the same right?

Thanks a lot to anyone who can help me. Ann

 RoM October 28, 2005 04:08

Re: Surface monitors in fluent

Your surface is build from small faces (facets). For an arbitrary value X you can define

integral as I=sum(Ai*Xi) with Ai=facet area and Xi=value of X on facet i

area weighted average = sum(Ai*Xi)/sum(Ai)

mass weighted averadge = sum(mi*Xi)/sum(mi) with mi=mass flow rate through facet i

RoM

 Ann October 28, 2005 04:48

Re: Surface monitors in fluent

Hi RoM,

Thanks for answering but I still do not quite understand. If I want a value of X for comparison at an instant in time. Suppose X is mass flow rate (i.e. density x area x velocity), if I use integral, I will get the value of X (which in this case is mass flow rate) at the surface?

what happens if I use area weighted average, does it mean I will get mass flow rate per unit area (i.e. mass flux)?

Thanks a lot, ann

 RoM October 28, 2005 05:34

Re: Surface monitors in fluent

With X i mean all values that are available in the two "Report of" dropdown panels. If you want mass flow rate you can get direct from the "Report type" panel. It is calculated as you described ( massflow rate=sum(Ai*Faceflux_i) with FlaceFlux_i in kg/m2/s ).

You can verify the area weighted average (awa) with a simple custom field function. Lets say you want the awa of temperature at the outlet of your pipe. First calculate the outlet area with the report->surface integral panel. Then define a custom function as temperature/outlet_area. Then define two surface monitors, monitor one with awa of temperature and the second monitor with integral of your custom field function. Both plots should be identical.

RoM

 chandrasekhar February 10, 2014 13:36

Hi
I have a doubt regarding surface monitors. I have to setup up surface monitors at a point and a line for the same parameter(say velocity magnitude). i would like to know if i have to setup two separate monitors for the line and the point or can i setup up one monitor only(i know there is such an option in fluent). Many thanks for replying. Any literature on surface monitors will also help. thank you

with regards

Quote:
 Originally Posted by RoM ;125624 Your surface is build from small faces (facets). For an arbitrary value X you can define integral as I=sum(Ai*Xi) with Ai=facet area and Xi=value of X on facet i area weighted average = sum(Ai*Xi)/sum(Ai) mass weighted averadge = sum(mi*Xi)/sum(mi) with mi=mass flow rate through facet i RoM

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