Tutorial Vortex shedding: trying to use liquid fluid

jimmyy90 · March 19, 2015, 03:06

I have been trying out on the tutorial of Solution Recording and Playback: Vortex Shedding. I wanted to try using liquid fluid instead. But I am unable to achieve similar vortex shedding of the same Reynold Number. For example Re=75, diameter of cylinder = 0.01m and dynamic viscosity of 0.00088871, the required speed should be 6.66m/s. however i am unable to achieve the vortex shedding result. Is there any other stuff that i need to take account?

jimmyy90 · March 19, 2015, 04:38

I realise i need to take account to the water density. but it does not shed the same way as compared to medium Air.

fluid23 · March 19, 2015, 11:33

Can you clarify what you mean by 'shed the same way'? Are you looking at shedding frequency? What exactly?

jimmyy90 · March 19, 2015, 12:01

I am just trying to achieve the different type of shedding due to different Reynerd number. But for RE = 75. The vortex does not separate when I tried the tutorial. should I change the flow to steady instead of inplict unsteady?

fluid23 · March 19, 2015, 12:02

That was my guess too, I was going to make them work for the answer though. You are no fun!

However, (and correct me if I am wrong), you cannot match Re and St numbers for identical geometry and separate fluids. The definitions seem to be at odds with eachother. If you want to compare drag coefficent then look at Re. If you want to look at shedding then St is your man.

Really, you should adjust the diameter of the cylinder in water so that you can match Re and St, then you should see good correlation. Dimensionless parameters are your friend.

fluid23 · March 19, 2015, 12:04

You are asking if you can model vortex shedding as a steady phenomena? No... Must be unsteady.

fluid23 · March 19, 2015, 12:06

http://en.wikipedia.org/wiki/Strouhal_number

jimmyy90 · March 19, 2015, 12:18

Okay. I briefly understand about the rational behind these two parameter. As for turbulent flow. Thanks for clearing my doubts.

jimmyy90 · April 6, 2015, 07:24

pressure.jpg

May I know how can I plot such a curve in starCCM+? I am able to get the drag coefficient in the report folder.

jimmyy90 · April 6, 2015, 07:31

pressure.png
Just realise the image is too small in the above comment. Hope this helps.

fluid23 · April 6, 2015, 10:10

This is a plot of Cp around a cylider right? Are you trying to plot cp or cd? Either way, to create a plot of any report just right click on the report and click create monitor and plot from report.

You will need to make sure you have the proper report defined before you create the plot though.

jimmyy90 · April 6, 2015, 10:32

Yes, i am trying to plot the pressure coefficient against the cylinder. But I don't know how to plot it against the angle of the cylinder. Currently I know how to plot the Drag coefficient curve against time. Hope that you can guide me choose the configuration. Thanks

fluid23 · April 6, 2015, 11:51

You should be able to setup a cylindrical coordinate system, create a series of derived parts > probe > points. Then define reports (maximum) and set the field function to pressure coefficent. (also remember to set your reference values under tools > field functions > pressure coefficient.).

Then create monitors, set up an XY plot and configure your axes properly.

March 19, 2015, 03:06	Tutorial Vortex shedding: trying to use liquid fluid	#1
jimmyy90 New Member jimmy Join Date: Mar 2015 Posts: 7 Rep Power: 11	I have been trying out on the tutorial of Solution Recording and Playback: Vortex Shedding. I wanted to try using liquid fluid instead. But I am unable to achieve similar vortex shedding of the same Reynold Number. For example Re=75, diameter of cylinder = 0.01m and dynamic viscosity of 0.00088871, the required speed should be 6.66m/s. however i am unable to achieve the vortex shedding result. Is there any other stuff that i need to take account?

March 19, 2015, 12:02		#5
fluid23 Senior Member Matt Join Date: Aug 2014 Posts: 947 Rep Power: 18	That was my guess too, I was going to make them work for the answer though. You are no fun! However, (and correct me if I am wrong), you cannot match Re and St numbers for identical geometry and separate fluids. The definitions seem to be at odds with eachother. If you want to compare drag coefficent then look at Re. If you want to look at shedding then St is your man. Really, you should adjust the diameter of the cylinder in water so that you can match Re and St, then you should see good correlation. Dimensionless parameters are your friend. anon_h likes this.

March 19, 2015, 12:06		#7
fluid23 Senior Member Matt Join Date: Aug 2014 Posts: 947 Rep Power: 18	http://en.wikipedia.org/wiki/Strouhal_number anon_h likes this.

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March 19, 2015, 04:38		#2
jimmyy90 New Member jimmy Join Date: Mar 2015 Posts: 7 Rep Power: 11	I realise i need to take account to the water density. but it does not shed the same way as compared to medium Air.

March 19, 2015, 11:33		#3
fluid23 Senior Member Matt Join Date: Aug 2014 Posts: 947 Rep Power: 18	Can you clarify what you mean by 'shed the same way'? Are you looking at shedding frequency? What exactly?

March 19, 2015, 12:01		#4
jimmyy90 New Member jimmy Join Date: Mar 2015 Posts: 7 Rep Power: 11	I am just trying to achieve the different type of shedding due to different Reynerd number. But for RE = 75. The vortex does not separate when I tried the tutorial. should I change the flow to steady instead of inplict unsteady?

March 19, 2015, 12:04		#6
fluid23 Senior Member Matt Join Date: Aug 2014 Posts: 947 Rep Power: 18	You are asking if you can model vortex shedding as a steady phenomena? No... Must be unsteady.

March 19, 2015, 12:18		#8
jimmyy90 New Member jimmy Join Date: Mar 2015 Posts: 7 Rep Power: 11	Okay. I briefly understand about the rational behind these two parameter. As for turbulent flow. Thanks for clearing my doubts.

April 6, 2015, 07:24		#9
jimmyy90 New Member jimmy Join Date: Mar 2015 Posts: 7 Rep Power: 11	pressure.jpg May I know how can I plot such a curve in starCCM+? I am able to get the drag coefficient in the report folder.

April 6, 2015, 07:31		#10
jimmyy90 New Member jimmy Join Date: Mar 2015 Posts: 7 Rep Power: 11	pressure.png Just realise the image is too small in the above comment. Hope this helps.

April 6, 2015, 10:10		#11
fluid23 Senior Member Matt Join Date: Aug 2014 Posts: 947 Rep Power: 18	This is a plot of Cp around a cylider right? Are you trying to plot cp or cd? Either way, to create a plot of any report just right click on the report and click create monitor and plot from report. You will need to make sure you have the proper report defined before you create the plot though.

April 6, 2015, 10:32		#12
jimmyy90 New Member jimmy Join Date: Mar 2015 Posts: 7 Rep Power: 11	Yes, i am trying to plot the pressure coefficient against the cylinder. But I don't know how to plot it against the angle of the cylinder. Currently I know how to plot the Drag coefficient curve against time. Hope that you can guide me choose the configuration. Thanks

April 6, 2015, 11:51		#13
fluid23 Senior Member Matt Join Date: Aug 2014 Posts: 947 Rep Power: 18	You should be able to setup a cylindrical coordinate system, create a series of derived parts > probe > points. Then define reports (maximum) and set the field function to pressure coefficent. (also remember to set your reference values under tools > field functions > pressure coefficient.). Then create monitors, set up an XY plot and configure your axes properly.