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Propeller dynamics/body force model

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Old   May 30, 2010, 12:27
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Andrea Pasquali
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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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Old   June 1, 2010, 08:11
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Stefan
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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)
);
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
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Old   June 1, 2010, 08:28
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Andrea Pasquali
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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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Old   June 4, 2010, 09:04
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Stefan
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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
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Old   October 2, 2012, 11:24
Default Broken links for the literature provided by Eric
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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
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Old   June 4, 2014, 06:27
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M. Montero
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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
File Type: jpg rotor_detail.jpg (24.7 KB, 21 views)

Last edited by be_inspired; June 6, 2014 at 07:22.
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Old   February 18, 2015, 12:41
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Matt Wright
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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
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