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Transient Non-Isothermal Flow Problem
Posted 25 apr 2010, 18:54 GMT-4 1 Reply
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Hello everyone.
I am having problems with the attached transient model that couples the General Heat Transfer model with the k-E Turbulence Model. The system can be described as a large cylinder with small inlets embedded at the bottom of the tank and the same size outlets at the top of the tank. There are ~25 of each. Water is the medium. The tank is heated by fluxes at the top, middle, and bottom of the tank; each flux is different for each side. Cooling water is pumped in from the inlets, and proceeds out through the outlets.
I want to observe the velocity field and temperature field of the system as it cools down from some initial higher temperature.
However, I consistently receive the error:
Number of degrees of freedom solved for: 126525
Warning: Re-ordering of null vectors failed
Nonsymmetric matrix found.
Step Time Stepsize Res Jac Sol Order Tfail NLfail LinIt LinErr LinRes
0 0 out 0 2 0 0
Group #1: 0 1 0 0 0 0
Group #2: 0 1 0 0 0 0
Error:
Failed to find consistent initial values.
Last time step is not converged.
I have tried several ways of correcting this but to no avail. Note that I have not been able to obtain a steady state solution for this system, but I am not convinced that there is one; hence why I wish to observe the transient case.
Realizability is set for on, and the flow is Weakly Compressible. The Boussinesq Approximation is used.
Note that this system is dominated by natural convection. The velocity of the cooling water as it enters the tank is very small, so forced convection should play a minor role. The Rayleigh number of the system is around 1E15; it is very turbulent.
Also note that the mesh in the model I have submitted is very coarse. I have analyzed it using a finer mesh (~800,000 elements total) but to no avail.
Furthermore, I have recently gone through the COMSOL model entitled "Building and Solving a Non-Isothermal Turbulent Flow Model" which analyzes the steady state case of non-isothermal flow of air in a vented room. This case is very, very similar to that one, and yet while I have incorporated much of what the venting model has, I have not been able to obtain a solution.
In addition, I am not worried about computational time or power. I just need a working model at this point.
Any help would be great.
I am having problems with the attached transient model that couples the General Heat Transfer model with the k-E Turbulence Model. The system can be described as a large cylinder with small inlets embedded at the bottom of the tank and the same size outlets at the top of the tank. There are ~25 of each. Water is the medium. The tank is heated by fluxes at the top, middle, and bottom of the tank; each flux is different for each side. Cooling water is pumped in from the inlets, and proceeds out through the outlets.
I want to observe the velocity field and temperature field of the system as it cools down from some initial higher temperature.
However, I consistently receive the error:
Number of degrees of freedom solved for: 126525
Warning: Re-ordering of null vectors failed
Nonsymmetric matrix found.
Step Time Stepsize Res Jac Sol Order Tfail NLfail LinIt LinErr LinRes
0 0 out 0 2 0 0
Group #1: 0 1 0 0 0 0
Group #2: 0 1 0 0 0 0
Error:
Failed to find consistent initial values.
Last time step is not converged.
I have tried several ways of correcting this but to no avail. Note that I have not been able to obtain a steady state solution for this system, but I am not convinced that there is one; hence why I wish to observe the transient case.
Realizability is set for on, and the flow is Weakly Compressible. The Boussinesq Approximation is used.
Note that this system is dominated by natural convection. The velocity of the cooling water as it enters the tank is very small, so forced convection should play a minor role. The Rayleigh number of the system is around 1E15; it is very turbulent.
Also note that the mesh in the model I have submitted is very coarse. I have analyzed it using a finer mesh (~800,000 elements total) but to no avail.
Furthermore, I have recently gone through the COMSOL model entitled "Building and Solving a Non-Isothermal Turbulent Flow Model" which analyzes the steady state case of non-isothermal flow of air in a vented room. This case is very, very similar to that one, and yet while I have incorporated much of what the venting model has, I have not been able to obtain a solution.
In addition, I am not worried about computational time or power. I just need a working model at this point.
Any help would be great.
1 Reply Last Post 25 apr 2010, 19:02 GMT-4
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Posted:
1 decade ago
Here is the file
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