Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.
Transient Turbulent Flow K-Ep
Posted 2010/04/27 17:07 GMT-4 1 Reply
Please login with a confirmed email address before reporting spam
I am trying to build a very very simple model that I can make more complicated later but I can not get it to work. My ultimate goal is to model a tubular reactor with a cooling jacket.
All I would like to do is get the chemical engineering module, turbulent K-Eps transient model to work, 2D axial symmetry.
Right now I just have a pipe of 16 cm radius flowing water (1000 kg/(m^3) and 0.00043 Pa s). I have an inlet at boundary 2 (velocity, 1m/s well into the turbulent regime,in z direction and 0 in r) and an outlet of pressure with p =0. These are opposite of each other in the drawing. If you just draw a rectangle they will be numbered correctly. The other two are walls with logarithmic functions h/2.
No matter what I do, solver changes, segregated or not nothing gives me a solution. I am using the initial value expression every time, in the solver parameter menu.
Segregated group X1
Attempt to evaluate real logarithm of negative number.
- Function: log
Failed to evaluate expression.
- Expression: d((((-rho_chns*Cmu_chns^0.25*exp(0.5*logk)*u/(log(abs(dwplus_chns))/kappa_chns+Cplus_chns)-nx_chns*p)*test(u))-(0))*(dvol),{test@1})
Exception:
com.femlab.jni.FlNativeException: Failed to evaluate expression
Messages:
Failed to evaluate expression
- Expression: d((((-rho_chns*Cmu_chns^0.25*exp(0.5*logk)*u/(log(abs(dwplus_chns))/kappa_chns+Cplus_chns)-nx_chns*p)*test(u))-(0))*(dvol),{test@0})
Log of negative
- Function: log
Segregated group X1
Stack trace:
at evaltree.cpp, row 866, ()
at evalfun_basic.cpp, row 491, ()
at segregsolver.cpp, row 990, ()
at com.femlab.solver.FlSolver.femTime(Native Method)
at com.femlab.solver.FemTime.run(Unknown Source)
at com.femlab.server.FlRunner.run(Unknown Source)
at com.femlab.util.i.run(Unknown Source)
at com.femlab.util.aa.run(Unknown Source)
X1 is what?
For the direct solver I get
Error: 6176
Attempt to evaluate real logarithm of negative number.
- Function: log
Failed to evaluate expression.
- Expression: d((((-rho_chns*Cmu_chns^0.25*exp(0.5*logk)*u/(log(abs(dwplus_chns))/kappa_chns+Cplus_chns)-nx_chns*p)*test(u))-(0))*(dvol),{test@1})
I get this error all the time, which makes me think it has to do with the sub-domain and initial conditions. Maybe with the logk and logd?
Can some one send me a basic model that uses K-Ep model that works?
Thank you for any help.
All I would like to do is get the chemical engineering module, turbulent K-Eps transient model to work, 2D axial symmetry.
Right now I just have a pipe of 16 cm radius flowing water (1000 kg/(m^3) and 0.00043 Pa s). I have an inlet at boundary 2 (velocity, 1m/s well into the turbulent regime,in z direction and 0 in r) and an outlet of pressure with p =0. These are opposite of each other in the drawing. If you just draw a rectangle they will be numbered correctly. The other two are walls with logarithmic functions h/2.
No matter what I do, solver changes, segregated or not nothing gives me a solution. I am using the initial value expression every time, in the solver parameter menu.
Segregated group X1
Attempt to evaluate real logarithm of negative number.
- Function: log
Failed to evaluate expression.
- Expression: d((((-rho_chns*Cmu_chns^0.25*exp(0.5*logk)*u/(log(abs(dwplus_chns))/kappa_chns+Cplus_chns)-nx_chns*p)*test(u))-(0))*(dvol),{test@1})
Exception:
com.femlab.jni.FlNativeException: Failed to evaluate expression
Messages:
Failed to evaluate expression
- Expression: d((((-rho_chns*Cmu_chns^0.25*exp(0.5*logk)*u/(log(abs(dwplus_chns))/kappa_chns+Cplus_chns)-nx_chns*p)*test(u))-(0))*(dvol),{test@0})
Log of negative
- Function: log
Segregated group X1
Stack trace:
at evaltree.cpp, row 866, ()
at evalfun_basic.cpp, row 491, ()
at segregsolver.cpp, row 990, ()
at com.femlab.solver.FlSolver.femTime(Native Method)
at com.femlab.solver.FemTime.run(Unknown Source)
at com.femlab.server.FlRunner.run(Unknown Source)
at com.femlab.util.i.run(Unknown Source)
at com.femlab.util.aa.run(Unknown Source)
X1 is what?
For the direct solver I get
Error: 6176
Attempt to evaluate real logarithm of negative number.
- Function: log
Failed to evaluate expression.
- Expression: d((((-rho_chns*Cmu_chns^0.25*exp(0.5*logk)*u/(log(abs(dwplus_chns))/kappa_chns+Cplus_chns)-nx_chns*p)*test(u))-(0))*(dvol),{test@1})
I get this error all the time, which makes me think it has to do with the sub-domain and initial conditions. Maybe with the logk and logd?
Can some one send me a basic model that uses K-Ep model that works?
Thank you for any help.
1 Reply Last Post 2010/04/28 15:33 GMT-4
Please login with a confirmed email address before reporting spam
Posted:
1 decade ago
Hi, this is not a simple solution, but it is what is on my desktop at the moment.
For me the problem came down to the inlet conditions. Whatever I guessed, would turn out to be wrong and I'd get NaN's, sqrt(negative), etc, etc. Very frustrating. Does not seem sensitive to outlet conditions.
What I do in the attached is glue a short section of pipe to the bottom of the domain of interest. Use **periodic** boundary conditions on that short section. This effectively solves for u, v, k and d on the inlet and the convergence then seems relatively robust in the rest of the pipe. Effectively I have solved for the boundary conditions for an infinite amount of pipe just below the inlet.
I also apologize in advance that I haven't (yet) checked the results of this code against standard formulations for pressure drop, etc. But hey:: it converges :-)
Regards, John
For me the problem came down to the inlet conditions. Whatever I guessed, would turn out to be wrong and I'd get NaN's, sqrt(negative), etc, etc. Very frustrating. Does not seem sensitive to outlet conditions.
What I do in the attached is glue a short section of pipe to the bottom of the domain of interest. Use **periodic** boundary conditions on that short section. This effectively solves for u, v, k and d on the inlet and the convergence then seems relatively robust in the rest of the pipe. Effectively I have solved for the boundary conditions for an infinite amount of pipe just below the inlet.
I also apologize in advance that I haven't (yet) checked the results of this code against standard formulations for pressure drop, etc. But hey:: it converges :-)
Regards, John
Attachments: