[ynsclk23]

Hello everyone,
I am working on the vertical axis wind turbine in ANSYS Fluent. My aim is to monitor the turbine rotational acceleration from rest by considering the inertia of the turbine. I used simple 6DOF to do it (it works fine). However, I need to consider the resistance torque to observe its effect on the turbine acceleration. Therefore, I have created a UDF to do this, but it is giving the error while interpreting it to the fluent. Any idea to deal with will be appreciated. Thanks in advance.
Best regards,
Yunus




#include "udf.h"
DEFINE_ON_DEMAND(wall_forces)
{
Domain * domain = Get_Domain (1); /* For multiphase flow, you need to set the Sub domain */
Thread *t;
real CG[3], force[3], moment[3];
t = Lookup_Thread (domain, 13); /* 13 is the ID of the wall to be determined. */
NV_S (CG, =, 0.0); /* coordinates of the center position to find the moment. */
Compute_Force_And_Moment (domain, t, CG, force, moment, TRUE);
Message("f=(%e, %e, %e), m=(%e, %e, %e)\n", force[0], force[1], force[2], moment[0], moment[1], moment[2]);
/* force [0], force [1], force [2] are respectively x, y, z-direction forces, Is the sum of the force by the force and the shear stress due to pressure. */
}
DEFINE_TRANSIENT_PROFILE(testudf, CURRENT_TIME)
{
real omega_ts=0.0; /starting omega/
real omega_tf=600.0; /final omega/
real Jt=0.03; /Moment Inertia of the Turbin/
real delta_t=0.000727221; /delta t simulation/
real CURRENT_TIMESTEP;
real CURRENT_TIME;
real alpha_t; /angular acceleration/
Thread *t;
cell_t c;
t=Lookup_Thread(domain,9); /Cell Zone ID = 9/
begin_c_loop (c,t)
{
alpha_t= 3*(moment[0]-(moment[0]*0.1))/Jt; /there are 3 blades, x axis as rotation axis/
omega_ts+=alpha_t*CURRENT_TIMESTEP;
if (omega_ts > omega_tf)
{omega_ts = omega_tf;}
THREAD_VAR(t).fluid.omega=omega_ts;
}
end_c_loop (c,t)
}

[vinerm]

Interpreter cannot handle structures and references, as well as Message command. Either use Compiled UDF or use profile file.

[ynsclk23]

Originally Posted by vinerm

Interpreter cannot handle structures and references, as well as Message command. Either use Compiled UDF or use profile file.

Dear Vinerm,

As you suggested I have complied the UDF. However, still gives an error like "line 14: parse error."
I do not know to sort it out.

Thanks you

[vinerm]

That''s because you are using CURRENT_TIME as argument to a function. This is a macro define inside Fluent and cannot be used as a variable. Use some generic name, say, stime, _time, etc.

[ynsclk23]

Originally Posted by vinerm

That''s because you are using CURRENT_TIME as argument to a function. This is a macro define inside Fluent and cannot be used as a variable. Use some generic name, say, stime, _time, etc.

Dear Vinerm,

Thank you for your valuable comment. If you have time could you modify the UDF code, which is above, for 2D turbine case for me? I am quite new with the UDF codding. I will appreciate your efforts on this.

Best regards,
Yunus

[vinerm]

Why do you want to use a UDF? You can just apply an expression or profile or a constant value.

[ynsclk23]

Originally Posted by vinerm

Why do you want to use a UDF? You can just apply an expression or profile or a constant value.

Hi Vinerm,

I tried to use an expression but I was not able to do this before running the simulation in Fluent. All I need is to give some loss in the torque (for example 10% loss in aerodynamic torque), and calculate the turbine rotational acceleration with this reduced torque.

Best reagrds,
Yunus

[vinerm]

Multiple changes are required in the code. Here is modified DEFINE_ON_DEMAND code. You can execute this one to print moment values and then use that information to determine how much torque you want to apply.

Domain *domain = Get_Domain (1);
Thread *t;
real CG[ND_ND], force[ND_ND], moment[ND_ND];
t = Lookup_Thread(domain, 13);
NV_S (CG, =, 0.0);
Compute_Force_And_Moment(domain, t, CG, force, moment, TRUE);
Message("f=(%f, %f)\t m=(%f, %f)\n", force[0], force[1], moment[0], moment[1]);

[ynsclk23]

Originally Posted by vinerm

Multiple changes are required in the code. Here is modified DEFINE_ON_DEMAND code. You can execute this one to print moment values and then use that information to determine how much torque you want to apply.

Domain *domain = Get_Domain (1);
Thread *t;
real CG[ND_ND], force[ND_ND], moment[ND_ND];
t = Lookup_Thread(domain, 13);
NV_S (CG, =, 0.0);
Compute_Force_And_Moment(domain, t, CG, force, moment, TRUE);
Message("f=(%f, %f)\t m=(%f, %f)\n", force[0], force[1], moment[0], moment[1]);

Dear Vinerm,

I really appreciated your efforts. I will try and let you know.

Best regards,
Yunus

[ynsclk23]

Originally Posted by vinerm

Multiple changes are required in the code. Here is modified DEFINE_ON_DEMAND code. You can execute this one to print moment values and then use that information to determine how much torque you want to apply.

Domain *domain = Get_Domain (1);
Thread *t;
real CG[ND_ND], force[ND_ND], moment[ND_ND];
t = Lookup_Thread(domain, 13);
NV_S (CG, =, 0.0);
Compute_Force_And_Moment(domain, t, CG, force, moment, TRUE);
Message("f=(%f, %f)\t m=(%f, %f)\n", force[0], force[1], moment[0], moment[1]);

Hi Vinerm,

I tried only the this part in the UDF, but while Compiling it gives this error " 'nmake' is not recognized as an internal or external command, operable program or batch file."

that is the part I try to compile
#include "udf.h"



DEFINE_ON_DEMAND(wall_forces)
{

Domain *domain = Get_Domain (1);
Thread *t;
real CG[ND_ND], force[ND_ND], moment[ND_ND];
t = Lookup_Thread(domain, 13);
NV_S (CG, =, 0.0);
Compute_Force_And_Moment(domain, t, CG, force, moment, TRUE);
Message("f=(%f, %f)\t m=(%f, %f)\n", force[0], force[1], moment[0], moment[1]);
}

[vinerm]

Compilation requires compiler, MS VC++ for Windows, to be installed. Then Fluent must be started from developer command prompt.