|
[Sponsors] |
February 10, 2010, 08:01 |
Stouhal number
|
#1 |
New Member
Mehr
Join Date: Feb 2010
Posts: 5
Rep Power: 16 |
Hi everybody.
I am studying vortex shedding around a block. I need to find Strouhal number. Somebody told me i should do this by monitoring vortex. Is there an accurate method in fluent to measure it? Another question about ftt. How can I use it? I read user guide but I couldn't find how could I read or prepare it to use. Sorry for my weak English. |
|
February 10, 2010, 10:55 |
|
#2 |
Senior Member
Jouke de Baar
Join Date: Oct 2009
Posts: 127
Rep Power: 16 |
"The ... Strouhal number is given by St = f D/U, where D is the cylinder diameter ...and U is the freestream velocity ..."
"The easiest way to compute the frequency is to use the time between peaks of the x-velocity, pressure, or lift coefficent. (The total drag coefficient should not be used to compute the frequency as it feels the influence of both vortices and will give a frequency twice that of the individual vortex shedding frequency.)" From: http://www.grc.nasa.gov/WWW/wind/val...es/Study1.html So I suppose you can simply use the frequency of your lift coefficient. |
|
February 11, 2010, 03:21 |
Vortex shedding
|
#3 |
New Member
Mehr
Join Date: Feb 2010
Posts: 5
Rep Power: 16 |
Thanks for your help.
At first let me tell you about my case. I am studying laminar and turbulence flow around two blocks in series. So I want to know the effect of distance and blockage ratio on vortex. The blockage ratio is .2 up to .7. 1. How can I get " time averaged streamline" in Fluent? 2. Is it possible to calculate "averaged pressure" or other field? how? 3. How can I calculate " time series of velocity"? 4. Is there some easy way to calculate " critical Reynolds"? Regards |
|
February 11, 2010, 05:52 |
|
#4 |
Senior Member
Jouke de Baar
Join Date: Oct 2009
Posts: 127
Rep Power: 16 |
I see. Haven't been looking at this problem before, but found some things that might be usefull.
1. I don't know if there is such a thing. I think that by definition a streamline is taken at a distinct instant of time. 2. I suppose you mean a time averaged pressure in a point? See: http://www.cfd-online.com/Forums/flu...ure-point.html . Then read the file in excel and take the average. 3. Again, same link, but use velocity. 4. Is this where vortex shedding starts? Two initial thoughts: I suppose this is the Re where the cl starts oscillating; so plot cl amp against Re and look for a sudden increase? Also, doesn't the cd initially drop when you increase the Re; but then, I'd expect it to grow again when vortices start shedding; so plod cd against Re and look for the minimum? Also, in this case I think you might have three Strouhal numbers. One for each of the obstacles (determine from cl1 and cl2 frequency) and one total Strouhal number (determine from frequency in pressure-time-history of a downstream point). Also see: Martinuzzi & Havel, Vortex shedding from two surface-mounted cubes in tandem, Int J Heat and Fluid Flow, June 20004 |
|
February 11, 2010, 06:55 |
|
#5 |
New Member
Mehr
Join Date: Feb 2010
Posts: 5
Rep Power: 16 |
I will check them all.
|
|
February 12, 2010, 04:29 |
Pressure average
|
#6 |
New Member
Mehr
Join Date: Feb 2010
Posts: 5
Rep Power: 16 |
Thanks for your help
What I need for pressure is not just in one single point. As I said I want to have an average pressure along the channel. (I mean my two blocks are in a channel and i need to see pressure behavior along the channel, other words in the flow direction. Thanks in advance. |
|
February 12, 2010, 05:49 |
|
#7 | |
Super Moderator
Maxime Perelli
Join Date: Mar 2009
Location: Switzerland
Posts: 3,297
Rep Power: 41 |
Quote:
__________________
In memory of my friend Hervé: CFD engineer & freerider |
||
May 17, 2014, 14:06 |
|
#8 | |
Member
Sami
Join Date: Nov 2012
Location: Cap Town, South Africa
Posts: 87
Rep Power: 13 |
Hello dear Jack,
Thank you for this interesting ref, however I have a question about the St number computed from a point in the downstream. In the ref, they use the x component of the velocity, But I have noticed that the y component of the velocity starts to oscillate for a Reynolds number lower than Re for which the x component starts to oscillate. Do you think that I should compute the frequency from the y component of the velocity ? Thank you, Best regards Mehrez Quote:
|
||
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
[mesh manipulation] Mesh Refinement | Luiz Eduardo Bittencourt Sampaio (Sampaio) | OpenFOAM Meshing & Mesh Conversion | 42 | January 8, 2017 13:55 |
DecomposePar unequal number of shared faces | maka | OpenFOAM Pre-Processing | 6 | August 12, 2010 10:01 |
[blockMesh] BlockMeshmergePatchPairs | hjasak | OpenFOAM Meshing & Mesh Conversion | 11 | August 15, 2008 08:36 |
Unaligned accesses on IA64 | andre | OpenFOAM | 5 | June 23, 2008 11:37 |
[Commercial meshers] Trimmed cell and embedded refinement mesh conversion issues | michele | OpenFOAM Meshing & Mesh Conversion | 2 | July 15, 2005 05:15 |