If the airflow is from left to right (i.e. the x- boundary of the box is open and the flow is 3cm/s, the x+ boundary is also open, but no air speed is set, and all the other boundaries are walls), then the results are pretty close to what's been measured. However, if the flow is from top to bottom, (i.e. Z+ boundary open and constant flow, Z- open, all others are walls), the temperature suddenly jumps by about 85C. This is way too much, considering that the airflow is very small.
The basic structure of the .sif file is inherited from someone that has left our company. I've tried to make some small changes here and there, but the results were the same. So, I have two questions:
- By any chance, is this jump in temperature to be expected? My instinct says no, but I'm not an expert in thermal simulations.
- I'm attaching the .sif file, maybe there's something there glaringly wrong. This .sif file is for the "left to right" simulation; the structure for the "top to bottom" simulation is exactly the same, except that the boundary conditions at the end refer to different physical surfaces.
Any suggestion is appreciated.
Tibi
Code: Select all
Header
CHECK KEYWORDS Warn
Mesh DB "." "demo"
Include Path ""
Results Directory ""
End
Simulation
Max Output Level = 40
Coordinate System = Cartesian
Coordinate Mapping(3) = 1 2 3
Simulation Type = Steady State
Steady State Max Iterations = 1
Output Intervals = 1
Timestepping Method = BDF
BDF Order = 1
Solver Input File = demo.sif
End
Constants
Gravity(4) = 0 -1 0 9.82
Stefan Boltzmann = 5.67E-08
Permittivity of Vacuum = 8.8542E-12
Boltzmann Constant = 1.3807E-23
Unit Charge = 1.602E-19
End
Solver 1
Equation = Navier-Stokes
Procedure = "FlowSolve" "FlowSolver"
Variable = Flow Solution[Velocity:3 Pressure:1]
Exec Solver = Always
Stabilize = True
Bubbles = False
Lumped Mass Matrix = False
Optimize Bandwidth = True
Steady State Convergence Tolerance = 0.05
Nonlinear System Convergence Tolerance = 0.05
Nonlinear System Max Iterations = 5
Nonlinear System Newton After Iterations = 10
Nonlinear System Newton After Tolerance = 0.001
Nonlinear System Relaxation Factor = 1
Linear System Solver = Iterative
Linear System Iterative Method = BiCGStabL
BiCGStabL Polynomial Degree = Integer 4
Linear System Max Iterations = 1000
Linear System Convergence Tolerance = 1E-06
Linear System Preconditioning = ILUT
Linear System ILUT Tolerance = 0.1
Linear System Abort Not Converged = True
Linear System Residual Output = 1
Linear System Precondition Recompute = 1
End
Solver 4
Equation = KEpsilon
Procedure = "KESolver" "KESolver"
Variable = KE[Kinetic Energy:1 Kinetic Dissipation:1]
Exec Solver = Never
Bubbles = True
Lumped Mass Matrix = False
Optimize Bandwidth = True
Steady State Convergence Tolerance = 0.05
Nonlinear System Convergence Tolerance = 0.05
Nonlinear System Max Iterations = 20
Nonlinear System Newton After Iterations = 30
Nonlinear System Newton After Tolerance = 0.001
Nonlinear System Relaxation Factor = 0.25
Linear System Solver = Iterative
Linear System Iterative Method = BiCGStabL
BiCGStabL Polynomial Degree = Integer 4
Linear System Max Iterations = 1000
Linear System Convergence Tolerance = 1E-08
Linear System Preconditioning = ILUT
Linear System ILUT Tolerance = 0.01
Linear System Abort Not Converged = True
Linear System Residual Output = 1
Linear System Precondition Recompute = 1
End
Solver 2
Equation = Heat Equation
Procedure = "HeatSolve" "HeatSolver"
Variable = -dofs 1 Temperature
Exec Solver = Always
Stabilize = True
Bubbles = False
Lumped Mass Matrix = False
Optimize Bandwidth = True
Steady State Convergence Tolerance = 0.05
Nonlinear System Convergence Tolerance = 0.01
Nonlinear System Max Iterations = 1
Nonlinear System Newton After Iterations = 10
Nonlinear System Newton After Tolerance = 0.001
Nonlinear System Relaxation Factor = 1
Linear System Solver = Iterative
Linear System Iterative Method = BiCGStab
BiCGStabL Polynomial Degree = Integer 2
Linear System Max Iterations = 1000
Linear System Convergence Tolerance = 1E-08
Linear System Preconditioning = ILUT
Linear System ILUT Tolerance = 0.01
Linear System Abort Not Converged = True
Linear System Residual Output = 1
Linear System Precondition Recompute = 1
End
Solver 3
Exec Solver = After Simulation
Procedure = "ResultOutputSolve" "ResultOutputSolver"
Output File Name = "..\output"
Output Format = "vtu"
End
Equation 1
Name = "Solids"
Active Solvers(1) = 2
Convection = None
End
Equation 2
Name = "Air"
Convection = Computed
NS Convect = False
Active Solvers(3) = 1 4 2
End
Material 1
Name = "boardFront_top"
Heat Capacity = 1210
Density = 1970
Heat Conductivity = 0.525
End
Material 2
Name = "boardFront_bot"
Heat Capacity = 1210
Density = 1970
Heat Conductivity (3) = 0.525 0.525 0.525
End
Material 3
Name = "Copper"
Heat Capacity = 385
Density = 8960
Heat Conductivity = 401
End
Material 4
Name = "MoldCompound"
Heat Capacity = 800
Density = 3500
Heat Conductivity = 0.7
End
Material 5
Name = "Q1_body_bot_Composite"
Heat Capacity = 779.25
Density = 3773
Heat Conductivity = 20.715
End
Material 6
Name = "Silicon"
Heat Capacity = 711
Density = 2330
Heat Conductivity = 124
End
Material 7
Name = "Air"
Heat Capacity = 1005
Density = 1.1831
Heat Conductivity = 0.02605
Compressibility Model = Incompressible
Viscosity = 1.54075E-05
Heat Expansion Coefficient = 0
Specific Heat Ratio = 1.4
Reference Temperature = 25
KE Cmu = 0.09
KE C1 = 1.44
KE C2 = 1.92
KE SigmaK = 1
KE SigmaE = 1.3
KE Clip = 1E-06
Viscosity Model = KE
Heat Conductivity Model = KE
End
Body Force 2
Name = "Source boardFront_top"
Heat Source = 0.00362895868118333
End
Body Force 3
Name = "Source Q1_die"
Heat Source = 718569.88955897
End
Initial Condition 1
Name = "Initial Condition"
Velocity 2 = -0.03302
Temperature = 25
Kinetic Energy = 2.725801E-06
Kinetic Dissipation = 1.88309811478612E-08
End
Body Force 1
Name = "Buoyancy"
Boussinesq = True
End
Body 2
Name = "boardFront_top"
Equation = 1
Material = 1
Target Bodies(1) = 2
Body Force = 2
End
Body 3
Name = "boardFront_bot"
Equation = 1
Material = 2
Target Bodies(1) = 3
End
Body 4
Name = "Q1_thPad"
Equation = 1
Material = 3
Target Bodies(1) = 4
End
Body 5
Name = "Q1_body_top"
Equation = 1
Material = 4
Target Bodies(1) = 5
End
Body 6
Name = "Q1_body_bot"
Equation = 1
Material = 5
Target Bodies(1) = 6
End
Body 7
Name = "Q1_die"
Equation = 1
Material = 6
Target Bodies(1) = 7
Body Force = 3
End
Body 8
Name = "Pad1_wholeBody"
Equation = 1
Material = 3
Target Bodies(1) = 8
End
Body 1
Name = "airbox_full"
Equation = 2
Body Force = 1
Initial Condition = 1
Material = 7
Target Bodies(1) = 1
End
Boundary Condition 1
Target Boundaries(1) = 1
Name = "Interior Wall"
Normal-Tangential Velocity = True
Velocity 1 = 0
End
Boundary Condition 2
Target Boundaries(1) = 2
Name = "Airbox Boundary 2"
Normal-Tangential Velocity = True
Velocity 1 = 0
Wall Law = True
Boundary Layer Thickness = 0.0196345140758292
Surface Roughness = 9
Temperature = 25
End
Boundary Condition 3
Target Boundaries(1) = 7
Name = "Airbox Boundary 3"
Normal-Tangential Velocity = True
Velocity 1 = 0
Wall Law = True
Boundary Layer Thickness = 0.0196345140758292
Surface Roughness = 9
Temperature = 25
End
Boundary Condition 4
Target Boundaries(1) = 3
Name = "Airbox Boundary 4"
Normal-Tangential Velocity = True
Temperature = 25
End
Boundary Condition 5
Target Boundaries(1) = 5
Name = "Airbox Boundary 5"
Normal-Tangential Velocity = True
Velocity 1 = -0.03302
Velocity 2 = 0
Velocity 3 = 0
Temperature = 25
End
Boundary Condition 6
Target Boundaries(1) = 6
Name = "Airbox Boundary 6"
Normal-Tangential Velocity = True
Velocity 1 = 0
Wall Law = True
Boundary Layer Thickness = 0.0196345140758292
Surface Roughness = 9
Temperature = 25
End
Boundary Condition 7
Target Boundaries(1) = 4
Name = "Airbox Boundary 7"
Normal-Tangential Velocity = True
Velocity 1 = 0
Wall Law = True
Boundary Layer Thickness = 0.0196345140758292
Surface Roughness = 9
Temperature = 25
End