# Nusselt Number Vs Theta Plot Fluent Natural Convection 2D

I am trying to compute a plot of the Nusselt Number against angular position for each cylinder. I want to compare the results of my model to the above graph. I cant figure our how to produce the plot with respects to the angular position instead of time.

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## Answers

7,040Forum CoordinatorYou might use xy plot along that edge at the outlet with x axis being theta. Also if appropriate check

40.9.5. XY Plots of Circumferential Averages15MemberI am not getting it in terms of angle theta it give me only curve length and direction vector on the x-axis option

9,268Forum CoordinatorYou can plot against a custom field function, you'll just need to code it up using a function of x & y coordinate.

7,040Forum CoordinatorIf you have a line /Edge you can plot against the theta coordinate.

15MemberThe problem is I do nort know what would the custom fucntion as a function of x and y coordinate ? i ddont understand how to make the custom function in fluent calculator

9,268Forum CoordinatorIf you know (or rather Fluent knows) the x & y coordinates along a line, and you apply trigonometry to those values you can get the angle. You'll need to convert that to degrees (probably) but you can do that outside of Fluent. The CFF panel is fairly simple, just press a few buttons to see how it'll work.

15MemberThe CFF panel is not allowing me to input tan^-1(y/x). when i try input the power symbol it says missig operator.

7,040Forum CoordinatorThere is no arctan with CFF: that is via Fluent Expression possible and might be used in future release.

Again you have that theta coordinate as post-processing quantity: you just need to setup the axis of rotation for the zone.

9,268Forum CoordinatorUse INV tan which gives atan

15MemberI don't have a lot of experience with ANSYS I don't how to set up an axis of rotation for the zone round the pipe. I am also struggling plot that angle position along the pipe against the Nusselt number. the XY circumferential plot only allows me to plot against curve length and I don't understand what position on the cylinder the curve `length translates to. I also cant access the file once I've made it. I am really struggling to recreate this experiment in ANSYS and measure the same parameters they did. it is meant to help validate my mesh for my actual experiment :(

7,040Forum Coordinatorif you plot any variable ( plot--> xy plot) against the curve length (the abscissa), and the line at which you plot is around the cylinder outlet edge

the abscissa is (radius x theta)

so if you write this xy plot to a file

you can simply divide the curve length (the first column in the file) by cylinder radius then multiply by 180/pi to have theta in degrees. You xan directly plot agsinst theta or the angular coordinate: https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v202/en/flu_ug/flu_ug_fvdefs.html you need there to set under cell zone conditions the axis rotation properly.

If you still do not know how to do, I will need to record a video whenever I have time.