# Propeller dynamics/body force model

 Register Blogs Members List Search Today's Posts Mark Forums Read

 May 30, 2010, 12:27 #21 Senior Member   Andrea Pasquali Join Date: Sep 2009 Location: Germany Posts: 142 Rep Power: 7 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 __________________ Andrea Pasquali

 June 1, 2010, 08:11 #22 Member   Stefan Join Date: Jan 2010 Location: Kiel, Germany Posts: 72 Rep Power: 7 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) );``` I added tangential forces on every involved cell to approximate the rotational effect of the propeller. What you intend with adding a 'rotational term to the thrust'? ~Stefan

 June 1, 2010, 08:28 #23 Senior Member   Andrea Pasquali Join Date: Sep 2009 Location: Germany Posts: 142 Rep Power: 7 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 __________________ Andrea Pasquali

 June 4, 2010, 09:04 #24 Member   Stefan Join Date: Jan 2010 Location: Kiel, Germany Posts: 72 Rep Power: 7 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: 9 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
Posts: 110
Rep Power: 8
Hi Tim,

I think your problem is the same that mine and the wiggles happen "always"
Pressure Jump Correction. Actuator Disc Model and numerical wiggles

"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 Rhie-Chow algorithm.....

Any help?
Attached Images
 rotor_detail.jpg (24.7 KB, 21 views)

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: 2 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

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post challenger85 CFX 5 November 5, 2009 06:44 payam_IUST FLUENT 2 October 18, 2009 23:25 Teo Fumagalli FLUENT 0 April 11, 2008 10:25 HS FLUENT 0 April 12, 2006 04:37 Jesper CFX 6 April 18, 2005 19:31

All times are GMT -4. The time now is 20:30.