Module Sim Investigation
Introduction
The module thermal sim investigation is an investigation to determine optimal sets of independent variables, or the relation of several output variables to input variables of a single battery pack module.
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The first step to creating a simulation is to set up the geometry.
Preparing Geometry
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The geometry of the simulation fed into SimScale differs from the illustrative geometry shown above the model. The geometry has been halved, and the tail end of the flow region has been lengthened to allow for total resolution of fluid flow. This allows any air jets, vortices, convection zones, etc to combine, mix and homogenize.
The source of the geometry is a Solidworks assembly called [name] using design tables to generate configurations. Currently, all configurations have been generated, and to use one, one must only select the correct configuration, rebuild the geometry, and save the file.
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In a steady-state simulation, any set of initial conditions will (theoretically) lead to the same result[citation needed]. As such, we will use a set of initial conditions very close to the theoretical end results calculated with other simulations for faster “convergence”, the condition when the imbalances in mass, energy, and other conserved quantities in the simulation drop below a critical threshold.
As such, change the following variables:
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The finer the mesh, the more accurate the results may be. This trades off with computing power, and free plans on SimScale only have limited computing power. Additionally, often, there is a mesh fineness level after which drastically diminishing returns in precision occurs. To find out if you have attained this level, it is useful to run a mesh independence study.
Automatic Boundary Layers:
This setting allows SimScale to automatically generate cells to accurately model the boundary layers near solid surfaces. We will leave this on, as for surfaces of concern, we will use a boundary layer refinement to manually set the boundary layers.
Physics-based meshing:
Leave this on for better results
Hex element core:
Improves For this specific simulation case, a global fineness of 3.0 is sufficient, as the important features of the simulation are refined with a much finer region refinement. Any level of global fineness for this specific simulation case should be permissible, as long as it is balanced out with the correct combination of a decreased global gradation rate and does not cause mesh-dependency in results, i.e. seeing sharp shifts in the velocity gradients across mesh boundaries.
Automatic Boundary Layers:
This setting allows SimScale to automatically generate cells to accurately model the boundary layers near solid surfaces. We will leave this on, as for surfaces of concern, we will use a boundary layer refinement to manually set the boundary layers.
Physics-based meshing:
Leave this on for better results
Hex element core:
Improves CFD efficacy by replacing tetrahedral cells with hexahedral cells whenever possible.
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Global gradation rate: 1.22
Ratio Maximum ratio of sizes between neighboring cells. Can be any value between 1 and 3, depending on the opinion on of the simulationist.
The smaller this value is, the smoother the gradient between fine and coarse cells. If using especially coarse meshes, the global gradation rate should be decreased to prevent mesh dependency.
Refinements
Refinements are adjustments made to mesh characteristics to improve the performance of the simulation.
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The boundary layer height that should be captured is represented by δ99 on the calculator. By leaving viscosity and density as their default values, the length scale as ½ the circumference of the battery cell (as any given air particle in the boundary layer passes over ½ of the battery at one time), velocity as the free-stream velocity (which should ideally be a good starting point is equal to the inlet area divided by the area displaced by the battery cells at their widest point, all multiplied by the inlet velocity), and any number of layers. I , however, a preliminary simulation with coarse settings will find a better free-stream velocity), and any number of layers. I have accidentally used the inlet velocity before, but the simulations have still converged.
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Running a mesh independence study is useful to assess if the results of the simulation are “independent” from the mesh fineness level by simulating with progressively finer meshes and comparing their results. At some point, results (especially thermal probe point results) should start to “converge” “converge” between mesh fineness levels. The simulationist should find the coarsest mesh possible with still accurate results with a given geometry and use it as the base mesh for future simulations.
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To run the experiment, first:
Prepare a geometry
Import the geometry
Create a simulation for the geometry
Run a mesh independence study for the geometry at 1m/s
(Optional) Run simulations with different air velocities using the coarsest level of mesh independent mesh
Take the average of the converged probe points and plot them
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the spreadsheet
Repeat for a different geometry
Note: You will have to make multiple SimScale accounts. If you want to use the same email account for all of them, if you use gmail, you can add a “+” and text before the @ to reuse the same email. e.g. placeholder+1@gmail.com, placeholder+2@gmail.com, etc
Design Log
https://docs.google.com/presentation/d/1MHdJ954tNe6LjBfGjypy8glz35UrmO3hQx6L3k3Hv7M/edit?usp=sharing