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Old   July 5, 2016, 21:39
Question Momentum source term
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Dear All, could you help me to resolve issue with my UDF function.
I am trying to implement gust in Ansys Fluent. It was already implemented with different software in AIAA research paper. In the picture QuestionSource.jpg square box is the region where gust is generated and it is carried by mean flow. i.e. yellow and blue contours move to the right. (This picture was taken from the paper I mentioned above)
Basically I just need to add source term in x and y momentum equations. However, for some reason when I look at vorticity contours (another picture QuestionAnsysRes.PNG) I can see only vorticity generated in source region, it does not move in x direction.


Could you, please, tell me what is wrong with my udf function?
For the run I use:
Pressure based solver,
Transient
Energy on
Viscous SST k-omega
Scheme: PISO
Second order Upwind

Boundary conditions:
airfoil is a no-slip wall;
inlet is a pressure far field; (velocity 170m/s, mach 0.5 ,standard sea level conditions)
outlet is pressure outlet;




Here is my udf function for source in x momentum Sx) {function for Sy is similar}
#include "udf.h"

DEFINE_SOURCE(harmGustX, cell, thread, dS, eqn)
{
real source=0;
real PI=3.14159;
real GOMEGA=2; // circular frequency
real GEPS=80;//amplitude of gust
real GTANGLE=1.0;//inclination of gust
real XGS=-1.5; // x-centre of my source
real YGS=2.5; // y-height of the source
real BGS=5; //pi/BGS is width of my source region
real dth=10.0; // gust duration
real dts=0.02; // gust start time

real flowTime=CURRENT_TIME;
real centroid[2];
C_CENTROID(centroid,cell,thread);
real x_loc=centroid[0];
real y_loc=centroid[1];
real rho=C_R(cell,thread);
real vol=C_VOLUME(cell,thread);

real GVEL=170.0; //freestream velocity
real GALF=GOMEGA*85/GVEL;//wavenumber in x direction (reduced //frequency) kx
real GBET=GALF*GTANGLE;//wavenumber in y direction ky

// this if checks if time came to start adding source to the right hand side of Navier Stokes(NS)
if(flowTime>dts && flowTime<dts+dth)
{
// if current cell is in the region of a source then add source to the RHS(right hand side of NS)
if(fabs(x_loc-XGS)<PI/BGS)
{

real UTERM= // calculating formulas from paper
real VTERM= // calculating formulas from paper
source=source + rho*UTERM*vol;
dS[eqn]=0;


}
else
{
source=0;
dS[eqn]=0;

}

else
{
source=0;
dS[eqn]=0;

}
}
else
{
source=0;
dS[eqn=0];
//printf("Not a valid timestep\n");
}
if(source!=0)
{
// printf("Source term\n");
}
return source;
}


//thanks
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Old   December 6, 2016, 04:28
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Johannes Hall
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Hello!

Very late reply here but I was trying with the same source term and I didn't really get satisfying results neither. However, the finer the mesh the better results. Did you find a good way to a solution or another way to simulate a gust?

Regards,
Johannes
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Old   December 6, 2016, 09:23
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We are still doing research on gust simulation. How do you evaluate if results are satisfying or not?

-Shreman
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Old   December 7, 2016, 11:44
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Should I interpret your reply as if you didn't continue with the momentum source term approach?

You can plot a line over the domain to see how the velocity differs at different y-values or plot a points value over time, that's a good way to see how the gust behaves

Regards
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Old   November 16, 2017, 07:58
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Quote:
Originally Posted by Shreman View Post
We are still doing research on gust simulation. How do you evaluate if results are satisfying or not?

-Shreman
Dear Shreman and Johannes Hall:

may you please tell if the approach explained in this thread worked? or did you use some other technique.
Regards
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Old   November 16, 2017, 11:19
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Quote:
Originally Posted by mmj_blackforce View Post
Dear Shreman and Johannes Hall:

may you please tell if the approach explained in this thread worked? or did you use some other technique.
Regards
Dear misa,

for the gust simulation ,mentioned thread worked well .
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Old   November 21, 2017, 02:49
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Quote:
Originally Posted by Shreman View Post
Dear misa,

for the gust simulation ,mentioned thread worked well .
Quote:
Originally Posted by Shreman View Post
Dear misa,
for the gust simulation ,mentioned thread worked well .
Dear Shreman,

Firstly thank-you for your reply, i tried to use your udf for gust simulation and need few clarification. when you find time please do reply i really need help.

(a) What does the "UTERM" stands for if it is velocity in x direction how did you calculate it, what formulae did you use to define "UTERM"

(b) Why have you defined width of source region as "PI/BGS" can it be BGS

(c) Why is the ds[eqn] term equal to zero

(d) Why have you not included the gust perturbation in the source equation is it embedded in the "UTERM"

Thanks in advance, i will be waiting for your reply please

Regards
Misa
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fluent - udf - parallel, momentum source, navier stokes equations, source terms, source udf

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