Week 6.1 - Setting up a model

Flow and Thermal Simulation on a Powerboard Assembly:

Objective: The objective of this challenge is to perform the flow and thermal simulation on a power board assembly. An unclean power board geometry has been provided. To do the Icepak simulation we need to clean up the geometry first by using the SpaceClaim machine tools like splitting bodies, pull, fill, etc.

Problem Description:

• Here we provided with the uncleaned power board geometry. To do the simulation i the Icepak we need to clean up the geometry.
• The cleanup process is done in SpaceClaim. The tools used to clean geometry are split body, fill, pull, cut planes, etc.
• After clean up, we need to export this geometry to Icepak and do the meshing operation.
• A certain amount of power values has to be given for a for few components to visualize the temperature and pressure contours.
• Velocity should be maintained at one side of the openings, this provides the flow visualization inside the domain.

Geometry:

• The power board assembly provided to do the simulation is

• After doing the proper clean up in the SpaceClaim, and make the geometry identified by the Icepak, the geometry looks like:

• After hitting the identify object, a certain amount of components are going to identified by the Icepak.
• If we want to see the identified objects by Icepak, go to show then click Icepak objects.

• After Identifying the Icepak bodies, the geometry file looks like: In this, every component is specified under the required type (Level - 0, 1, 2, 3).

• The unnecessary components that have no value in flow or thermal simulation have been removed from the geometry. The geometry in Z-direction looks like:

Save the model:

• After doing all the necessary changes and cleanups to the geometry, we need to save the geometry in the Icepak file.
• Then only we can able to import the geometry in the Icepak for further steps.

Geometry after Importing into Icepak:

• The wired geometry looks like:

Generate Meshing:

• A non-conformal mesh, when there are a partial or zero matchings of nodes at the interface. This means that one, few, or every node on one side of the interface doesn’t have a match on the other side of the interface.

• Non-conformal interface calculations are handled using a virtual polygon approach, which stores the area vector and centroid of the polygon faces.

• This approach does not involve node movement and cells are not necessarily water-tight cells. Hence gradients are corrected to take into account the missing face area.

• Here we generate the non-conformal mesh with the per-object parameters, the generated elements are 3351499, and nodes are 3452432.

Slack values when we use Mesh assemblies separately:

• When the Mesh separately options for an assembly is turned on, the offset added to Assembly in respective direction is called Slack Values.

• By default, the slack values are zero in all directions. However, in order to use non-conformal mesh, the slack values should always be a positive number except it can be zero when the non-conformal boundary touches a hollow object or cabinet boundary.

• The Slack values should be specified in such a way that cells on both sides of the interface are either fluid or solid, with the same material, and it does not violate any of the "Non-Conformal Assembly Rules" given in the attachment.

Mesh Generation:

• A Hexa - unstructured mesh is generated in all the solid and fluid domains of the geometry.
• The Mesh assemblies separately are used as we have different components in one component like a heat sink and NHAV component.
• Mesh in Z - plane.

• Mesh in y - plane.

• The above-shown picture is a solid part of the cold plate assembly and it's meshing.
• By visualizing the mesh separately as a solid medium and fluid medium gives us clarification in many terms.
• The below-shown picture is a fluid medium mesh.

• For the reference, we have selected the solid and surface display mesh for one of the components in the geometry.
• The figure shown below is the meshing for the heat sink.

Monitor points settings:

• Temperature monitor points have been placed at five different components where the components exhibit the temperature.
• Components exhibit the temperature because we have provided the power to certain components.
• Velocity monitor points also provide at the openings of one side of the geometry to measure the input velocity and another velocity monitor points at other end openings to monitor the velocity of air that going out of the domain.

• The points shown in red color are temperature monitor points and blue in color are velocity monitor points.

Physical and Numerical settings:

Use problem set up wizard:

• The problem setup wizard is a 14 step command box, where we need to specify the turbulence equation, implementation of radiation, and gravity relational entries, etc.

set no of iterations and convergence criteria:

• In the basic settings panel, we need to give the number of iterations to 100.

• The convergence criteria of Flow is set to 0.0001 and energy is set to 1e-10, turbulent kinetic energy to 0.001 and turbulent dissipation rate is set to 0.001.

Turbulent model:

• A calculation of the Reynolds number shows that the problem is turbulent.

• To set up a turbulent flow, expand the Problem setup tree (top of the model tree), select Basic parameters, and choose the Zero equation turbulence model for the flow regime in the General setup tab.

Set up the gravity vector:

• Gravity acts in the negative x-direction in this problem.
• To setup, the effects of gravity, toggle on the Gravity vector in the General setup tab.
• . Enter the new values for the gravity vector as x = 0, y = -9.80665 and z = 0.
• We can see it in the above picture.

Initial temperature:

• The initial temperature given in the domain is 20-degree centigrade. Then only we can see the change in temperature inside the domain causes due to the power given to the components.

Steady-state simulation:

• Now go to the Transient setup tab and set an initial velocity Y velocity = 0.005 m/s in the x-direction. Accept all other defaults in the Basic parameters panel.

Save and Solve the model:

• To furtherly into the simulation, it is a best practice to save the model before we solve the model.
• To solve the go to File > save the project, or just click ctrl+S to save.
• To solve the project click the Run solution option in tools bar, and a box will appear. in that check whether the radiation is disabled or not, and click Start solution.

Residual Plot:

• From the above residual plot, we have seen that the solution gets converged at nearly the iteration no.70.
• After the iteration no.70, the solution remains the same and we observe no instability in the residual plot.
• At the same time the velocity, continuity, and energy equation are well below the ranges we applied in the basic setting of iterations. Which means the solution gets very well converged.

Temperature Monitor Points Graphs:

• Temperature monitor points have been placed at five different components where the components exhibit the temperature.
• Components exhibit the temperature because we have provided the power to certain components.

• Here if we observe the plot, the temperature trend is continuously decreasing.
• It mans at starting the components are exhibiting the temperature due to the power given manually.
• After the forced air is passed through the openings into the domain, the components tend to cool down and settling at a temperature.
• The decrease in temperature reference the forced convection.

Velocity Monitor Points Graphs:

• Velocity monitor points also provide at the openings of one side of the geometry to measure the input velocity and another velocity monitor points at other end openings to monitor the velocity of air that going out of the domain.

• Here the monitor point at air-entry opening shows the constant temperature throughout the simulation. That is 0.5 m/s which is an input to the domain.
• The other curve shows the increase in velocity. It means the velocity at the middle is low because of the solid components are there. In the end, the velocity is slowly increasing because there is an opening present.

Examine and post-process the results:

• In the plane cut, it is actually an option to post-process the results that are offered by Icepak after the simulation runs successfully.
• In the plane cut, we need to provide the position in terms of axes, in which direction we had to see the results graphically.
• In this plane cut, we can see the results in three forms; such as the contours, vectors, and particle traces.
• After selecting a particular option, we need to select a proper parameter which changes with respect to the given conditions. These are the functions of the plane cut.

Vector plot:

• The vector plot explains A vector plot is a type of cartesian chart where each point has an X and Y position, a length, and a direction. Vectors are drawn as arrows.
• The vector plots can be obtained by selecting the vector option in the cut plane.

• To represent the velocity results, the vector plot is the best method to represent by using color legends.
• Because velocity has a position, direction, and magnitude.
• Here in the above vector plot, the max. velocity observed is 0.5483 m/s which is also matched with the value obtained from the monitor point.
• Here in the plot, the direction of the arrows shows the direction of the fluid flow inside and outside the model or cabinet.
• If we want to see the velocity in the filled color legends, then we need to select the speed option in the contour.

• If we observe the picture, at the walls of the solid components there is zero velocity.

Velocity animation: https://youtu.be/Z4rNSopSeuM

Speed animation: https://youtu.be/AB-AtdpAZHU

Temperature Contour:

• Filled colors, give a good visualization for the temperature, pressure, and mass flow rate, etc.
• The color legends are used to show the range of temperature contour.

• The maximum temperature observed as 100.57 degrees Centigrade and the minimum temperature noted as 20-degree Centigrade which is a given temperature.
• Here in the above figure, we can see that the heat is flown from the starting of the heat sink to the end of heat sink.
• It explains the working principle of heat sink.

Temperature animation: https://youtu.be/VLVWayVYU7A

Object Face:

• Object face option gives the final contour solution of the particular selected object or if we select the entire domain and select the proper contour, it shows the final solution.

Velocity:

• In the whole component in the domain, the velocity flow is taking place only in some components.
• By doing this object face operation, we can take the final contour of those objects.
• From the above picture, openings are only components that allow the flow of entering and going out.

Speed:

• Here in this picture, the temperature is visualized on the basis of object faces.
• In the picture, the solid components have a range of temperatures because we have given some amount of heat (some x-watts).

Pressure:

• Here, in this case, we can come to see some negative pressures also. This phenomenon is because of the exit of flow takes more time.
• As the flow exits, there at that position in the domain, we can see the negative pressure.

Pressure animation: https://youtu.be/3MZGU-3YsuA

Conclusion:

The simulation is performed for the power board assembly using the Non-conformal mesh. The model includes some solid components, heat sink, as well as by air driven by forced convection through the openings from one side. Separately mesh assemblies will be employed to reduce the overall mesh count. The required numerical and physical settings have been given to the model and taken the required vector plots, temperature, speed, and parametric change in object faces.