# Energy residual not converging

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October 4, 2015, 03:01
Energy residual not converging
#1
New Member

Liril
Join Date: Sep 2015
Posts: 2
Rep Power: 0
i have made a model of air cooled two wheeler vehicle's engine block. Now i want to study the effect ofcooling with different FIN design over different air speed. Its conjugate heat transfer problem. The geometry is quite complex. I took half section. steps i followed are :
Geometry : import half section geometry >> Made fluid domain with enclosure command >> Named 'inlet' and 'outlet' for fluid domain and 'inside wall' for the cylinder block.
Mesh : Fine mesh
Fluent : energy equation ON, turbulent model k-epsilon (2-eq),
Boundary condition: insidewall temp-423 K, inlet fluid velocity-20m/s
solution initialization from inlet (everything else default)
Now my problem is : the energy equation residual is not converging. Its going up nearly 1e-2. Continuity equation is converging fastly.
Results : i'm getting nice velocity and pressure contour. But temperature contour is showing blue colour through entire geometry. I'have attached pics.
Please tell me the solution for the above problem.
Attached Images
 Capture.PNG (19.4 KB, 131 views) Capture2.PNG (21.1 KB, 123 views)

 October 5, 2015, 03:15 #2 Member   Devesh Baghel Join Date: Mar 2009 Posts: 84 Rep Power: 17 Hi, you should increase the size of boundary as it looks in picture. Can you please share picture of mesh as well as temperature contour plot. Regards

 October 7, 2015, 00:53 #3 New Member   Liril Join Date: Sep 2015 Posts: 2 Rep Power: 0 @devesh.baghel Hello sir, Thanks for reply, I changed few things and i got the result. Geometry : I applied subtract boolean operation. I subtracted the engine body from fluid enclosure. Fluent set up : Double precision. Parallel with 2 process. (earlier it was series). Changed temp from 423 k to 600 k ,increased velocity from 20m/s to 40m/s. But i've a question : I took half section of the engine cylinder. Still it takes too much calculation time. For 1000 iterations it takes 10 hours. So what should i do to reduce calculation time. ?

 November 7, 2016, 03:57 residual problem #4 New Member   Gujarat Join Date: Oct 2016 Posts: 6 Rep Power: 9 hi..i am trying to solve double pipe heat exchanger using inserts in CFD. i used- double precision, energy eq-on model-turbulent(2 eq,stnd wall fun) solution method:-SIMPLe(PRESSURE-VELOCITY BASED)-second order my energy residules are not converges during solution.so ans is not converged. boundary conditions:- hot inlet:-mass flow rate-1.3 kg/s,inlet temp-413 k hot outlet-pressure based cold inlet:-mass flowrate-1.3, temp-298 k cold outlet:-pressure base my problem is my energy residual is not converged and it increasing and it be e+08.while the convergence criteriya is e-06 .. .any one can help me why this kind of problem is occured. any one have solution?plz guide me. thanks in advance.