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May 30, 2010, 12:27 

#21 
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Andrea Pasquali
Join Date: Sep 2009
Location: Germany
Posts: 142
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Hello everybody,
i'm interesting to body force analysis. What is the dimension "magnitude" in the code? Is it possible add the rotational term to the thrust? Maybe could be correct using MRF + body force to the same volume of cells? Thanks for any reply Andrea
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Andrea Pasquali 

June 1, 2010, 08:11 

#22 
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Stefan
Join Date: Jan 2010
Location: Kiel, Germany
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Hello Andrea,
the dimension of magnitude is L^4/T^2 (force per density) as you can guess from: Code:
IOobject ( "bodyForce", ... dimensionedVector("zero", dimForce/dimVolume/dimDensity, vector::zero) ); ~Stefan 

June 1, 2010, 08:28 

#23 
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Andrea Pasquali
Join Date: Sep 2009
Location: Germany
Posts: 142
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Hi Stefan,
thank you for you reply! This is what I mean! In the code posted dy Eric there is just thrust, is it? I changed t to put a propeller in whatever direction I want, can you help me to add also tangential force to the involved cells? Thanks Andrea
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Andrea Pasquali 

June 4, 2010, 09:04 

#24 
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Stefan
Join Date: Jan 2010
Location: Kiel, Germany
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Hello Andrea,
maybe i could... The code above is an example by Eric to implement a uniform force distribution in direction of a selectable directionVector. For testing you could also calculate a uniform tangential force across the propeller radius with a given magnitude and an tangential vector which point for every cell in tangential direction of the local position vector (from propeller centre to each cell centre). It is a little bit tricky, but with some careful considerations you will calculate the appropriate direction with basic trigonemtrical functions. The local position vector to cellI ist described by r and phi according to the local point of origin (propeller centre). In case of a directionVector = (1 0 0), the tangential vector, say tan' schould be something like this: tan'(x_i,z_i)=(cos[phi],sin[phi])^T with phi=arctan(y_i/z_i) It is a good help to plot your developed functions and cecking the rightness. Lately in paraView you see, if the tangential vectors are correct. With a factor, say f you are able to define the rotation direction of the propeller: tanrot'=f*tan'(x_i,z_i) with f={1,1} x_i,z_i are the global cell centre positions, if the global point of origin is (0 0 0) and y_i=0 (one central screw propeller). If the above things will working, you can determine the ratio from axial and tangential forces by a propeller nomogram (e.g. standard series). Additionaly a radial distribution of the magnitudes could be implement (see PNA Vol.II for qualitative radial circulation distribution of an open propeller). I hope that helps a bit! ~Stefan 

October 2, 2012, 11:24 
Broken links for the literature provided by Eric

#25 
Senior Member
Join Date: Mar 2009
Posts: 248
Rep Power: 10 
Hi Eric
Your post dated : February 26, 2010, have link to some articles. These links seem to dead now. If possible please provide with the new links to these articles. Thanks a lot jaswi 

June 4, 2014, 06:27 

#26 
Senior Member
M. Montero
Join Date: Mar 2009
Location: Madrid
Posts: 122
Rep Power: 9 
Hi Tim,
I think your problem is the same that mine and the wiggles happen "always" http://www.cfdonline.com/Forums/ope...lwiggles.html "Discrete body forces are used in the present context to model the influence of wind turbines on the flow. In order to overcome the pressure wiggles introduced by discre te body forces, one approach is to smooth out the body forces by using a Gaussi an distri bution instead of a Dirac delta distribution " ] Using rotorDiskSource the problem is that wind speed is not calculated correctly in each cell so the angle of attack is incorrect, the force calculation, the wake.... Other option to solve the problem is to modify the RhieChow algorithm..... Any help? Last edited by be_inspired; June 6, 2014 at 07:22. 

February 18, 2015, 12:41 

#27 
New Member
Matt Wright
Join Date: Feb 2015
Posts: 5
Rep Power: 4 
Hi,
I'm new to OpenFoam and I'm wondering if there is a way to implement the localised momentum sources in OpenFoam 2.3.0, is the code any different to the OF 1.6 Version. Also, how would you create the BodyForceDict file? Many Thanks Matt 

Tags 
momentum disk, propeller, propulsion 
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