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Old   October 28, 2015, 04:16
Default erosion problem
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libo
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Hi,
I`m doing sand erosion in 90 elbow. I have wrote an erosion rate UDF. Under the same condtions , two cases(don`t use udf and use udf) have many difference in the contours of erosion rate,however, the case don`t use udf looks more reasonable.
I don`t know it has some wrong in my udf or the mathematics model unsuitable this case.
Please give me some advices.
Cheers!


#include "udf.h"
#include "math.h"
float Z =3.434e+8;
float C =2.17e-7;
float A1 =5.4;
float A2 =-10.11;
float A3 =10.93;
float A4 =-6.33;
float A5 =1.42;
DEFINE_DPM_EROSION(moshi, p, t, f, normal, alpha, Vmag, mdot)
{
real erosion;
real a=alpha;
real v=Vmag;
real F_alpha;
real V;
real F;
V=pow(v,2.41);
F=A1*pow(a,1)+A2*pow(a,2)+A3*pow(a,3)+A4*pow(a,4)+ A5*pow(a,5);
erosion=0.53*C*pow(Z,-0.59)*V*F;
F_STORAGE_R(f,t,SV_DPMS_EROSION)=erosion;
}

Last edited by libo; November 3, 2015 at 22:51.
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Old   October 30, 2015, 09:44
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Liam
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Hey Libo,

I can see you are making a UDF for the "E/CRC erosion model" which I have also played with before.

I believe you have one major flaw in your UDF and that is how you are defining the "Brinnel Hardness" of your material (you have it as the variable Z =3.434e+8). From the paper I am assuming you got this equation from, it should be a value of 334.4 which represents Inconel 625. This was verified when I tested out the UDF model (one I created) with the paper's values experimental values. I would ALWAYS verify your erosion models with whatever lab/experimental data you can get your hands on. In my case, I was usually forced to mimic the models described in various papers and try to get as close as possible to the numbers.

If that doesn't help, there are a few things you should do in Fluent to ensure you are getting a solution that is independent of the amount of particles injected into the model or how you are tracking them.

Let me know if this helps.

Cheers,

Liam
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Old   October 30, 2015, 22:39
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libo
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Dear Liam,
Thanks for your reply. I think you are right.I want to try how to write the UDF about erosion rate. So I found an equation from a paper(Comparison of computed and measured particle velocities and erosion in water and air flows), random define the value of Brinnel Hardness.I have felt I can get a result similar to the Fluent. I did't realize the value of Brinnel Hardness will bring great influence.
Kind regards,
LiBo
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Old   March 7, 2016, 06:14
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Taz Hussain
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Hi Libo,

I am doing something similar to what you are doing and was wondering if you could help me.

Is your case a 3D case? and is the above udf all you needed to interpret into fluent to get erosion? sorry for all the questions!

kind regards
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Old   March 7, 2016, 07:19
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libo
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Hey Taz,
This a 3D case.I want to kown how to write the UDF to change ersion rate when I am read an article( Comparison of computed and measured particle velocities and erosion in water and air flows).Above UDF is all my needed to change the erion rate.
I hope it can give you some help.
Cheers,
LiBo
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