3D flow past cylinder simulation

Beecee · March 22, 2015, 13:44

Hello everyone,

I am simulating 3D laminar flow around a cylinder on ANSYS CFX and have to look at the FFT graphs for different velocities all in the range of laminar flow (max Reynolds number is 1000). Should I write an expression for the velocity as a function or put in the velocities individually (when I do that I can't set the turbulence settings off and make it laminar - How do I fix that?)

Also, how should I find the vortex shedding frequency for different velocities? I have difficulty plotting the graph of amplitude against time and flow velocity against time.

Lastly what is the best way to do this simulation (will have to move on to the pulsating flow in the next steps)

Thank you so much for your help!

ghorrocks · March 22, 2015, 17:09

I do not understand your first question.

The simplest way to find the shedding frequency of the von Karmen vortex street is to put a monitor point in the middle of the wake, a diameter or two behind the cylinder. Get the monitor point to output velocity or pressure. Then export the monitor point data and do an FFT on it to get the frequency.

Your final question makes about as much sense as "how do you design a spaceship".

March 22, 2015, 13:44	3D flow past cylinder simulation	#1
Beecee New Member Beril Join Date: Mar 2015 Posts: 7 Rep Power: 11	Hello everyone, I am simulating 3D laminar flow around a cylinder on ANSYS CFX and have to look at the FFT graphs for different velocities all in the range of laminar flow (max Reynolds number is 1000). Should I write an expression for the velocity as a function or put in the velocities individually (when I do that I can't set the turbulence settings off and make it laminar - How do I fix that?) Also, how should I find the vortex shedding frequency for different velocities? I have difficulty plotting the graph of amplitude against time and flow velocity against time. Lastly what is the best way to do this simulation (will have to move on to the pulsating flow in the next steps) Thank you so much for your help!

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March 22, 2015, 17:09		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,729 Rep Power: 143	I do not understand your first question. The simplest way to find the shedding frequency of the von Karmen vortex street is to put a monitor point in the middle of the wake, a diameter or two behind the cylinder. Get the monitor point to output velocity or pressure. Then export the monitor point data and do an FFT on it to get the frequency. Your final question makes about as much sense as "how do you design a spaceship".