Week 6.2 - Setting up a model

Setting up a simulation for the Hanging Node model:

Objective: The objective of this challenge is to set physical and numerical modeling using Ansys-Icepak. In week-5 we have done clean up the geometry and done the multi-level meshing to the model. After that in this challenge, we have to set up the numerical setting, to visualize the trends of temperature, velocity, and pressure in contours and vectors.

Problem Description:

• The Icepak model is given for this assignment. Open and unpack the given hanging_node.tzr model.
• Without any modifications, the model results in about 10,00,000 elements. Note that this mesh count results from using the non-conformal meshing technique, which reduces mesh bleeding and mesh count.
• You can reduce the mesh count and improve the mesh resolution on and around the CAD objects by using the multi-level meshing technique.
• After the completion of the meshing process, we need to do the physical and numerical setting for the problem.
• After running the simulation visualize the velocity, temperature, and pressure contour.

Geometry:

• The below picture the given CAD Model to generate the mesh using the multi-level parameters.
• The Geometry contains Fan, Capacitors, solid blocks, heat sink, and printed circuit boards, etc.

Meshing:

• For the first time, the mesh is generated for the Mesh assemblies separately. Which means a non-conformal mesh is performed.
• 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.
• For a general non-conformal mesh the number elements produced are 798009 and the number of nodes is 1021190 with coarse mesh is in use.

Use mesh separately option with slack values:

• 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".

Multi-level meshing:

• To set the uniform parameters, we need to combine the given components in the CAD Model that are represented in blocks.
• Here to combine the components, we need to use the option called Assembly.
• After assembling the components we need to give the multi-level meshing at once. It automatically takes for entire components inside the assembly.

Generate mesh:

• Now by allowing the multi-level meshing of max-level 2, the mesh is generated.
• What is multi-level meshing means, it subdivides the geometric into no. of parts that consume a large number of elements.
• While meshing a lengthy or a huge element it takes a number of elements and nodes to generate. These elements also have an effect on the neighboring elements in the domain.
• This causes the mesh bleeding phenomenon and leads to incorrect results.
• So, applying the multi-level meshing is benefiting in case of computational time and giving accurate results.

• By observing the above picture we can come to the clarification that what is the effect of multi-level meshing and what it makes to the mesh bleeding.
• Doing the multi-level meshing giving us a reduction in the number of elements and nodes, at the same time increase in the mesh quality.

• It is the cut plane of the given CAD Model in the Z-direction.

• This is the total meshing of the components that are present in the given CAD model.
• Here we can see the meshing dine for components like a heat sink, grills, some solid components like cylinders, rectangles, etc. Also meshing for the heat sources.

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.

Specifications for the Components:

• The specifications like power, velocity, and rpm, etc are given for some of the conducted components.
• The below figure is the fan components inside the domain of the geometry.
• We have given a total of 4000 rpm for the fan to drag the air inside of the domain.

• There are some heat sources are there inside the domain which is placed beside the fan guide placed in a row.
• These heat sources exhibit 2 watts of power, in total there are complete 7 heat sources are there.

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 300.

• The convergence criteria of Flow is set to 0.0001 and energy is set to 1e-7, turbulent kinetic energy to 0.001, and turbulent dissipation rate is set to 0.001.

• In the advanced settings tab, we need to give the discretization schemes order for the pressure, momentum, and temperature.
• All the above parameters are set to first-order schemes.

Turbulent model and gravity vector:

• 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.

• Gravity acts in the negative Y-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.

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 at the iteration no.200.
• After the iteration no.200, 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 three different components where the components exhibit the temperature.
• Components exhibit the temperature because we have provided the power to certain components.

• The trend in the temperature plots for the components shows that the temperature is slightly decreased.
• The reason for this phenomenon is because of the natural convection inside the domain of the geometry.

Velocity Monitor Points Graphs:

• Velocity monitor points also provide at the grills which are actually the openings. It is from where the air is sucked inside the domain of the geometry.

• At the starting, the velocity is slightly low, is because of the solid components obstruct the flow inside the domain.
• After some iterations, the velocity trend is increasing is because the obstruction of the solid components inside the body is decreased and fluctuations have appeared.

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 5.41 m/s.
• 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/T0FlzEgBdSk

Speed animation: https://youtu.be/-rECkRIe6Hw

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 201.93 degrees Centigrade and the minimum temperature noted as 20-degree Centigrade which is a given initial temperature.
• From the above figure, we can see that the heat sources. A total of 8 plates are the main heat sources of the problem.

Temperature animation: https://youtu.be/CoqRWd51EJo

Pressure contour:

• 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.
• The negative pressures are obtained at the fan guide, and at the exits openings of the domain.

• The maximum pressure recorded inside the domain is 18.43 N/m2 and the negative pressure seen is -29.98 N/m2.

Pressure animation: https://youtu.be/g6tk3NxCYr0

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 domain, the change in velocity takes place at few components only.
• Those are fan guides, fan opening, and grill openings. From these components only we can expect the changes in the velocity.
• In the above picture, we can figure out where the max. velocity occurs.

Temperature:

• 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).
• At the heat plates which are heat sources in the domain show the max. temperature and at the fan guide area which doesn't exhibit any heat shows the min. temperature.

Pressure:

• 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).
• Here the openings for air to get out from the domain are less, so the negative pressure is more.

Conclusion:

The flow and thermal simulations are performed over a domain that contains a hanging node, heat sources, fan guide, and some openings for the natural convection. The simulation takes place in the presence of both forced and natural convection. The post-process is done and discussed for temperature, velocity vector, and pressure contours.