CFD Rivals - CHT Analysis - CFX Tutorial Step-By-Step

 Today I would like to introduce you to the CHT simulation tutorial in CFX. This is the missing link to the previous two entries. In CFX, CHT analysis is defined a bit differently than in Fluent.

CHT Analysis in CFX

In the first step, just like in Fluent, we define the type of analysis. In our case, it will be a transient analysis. At the very beginning of modeling (in a way different from Fluent) we define the time of our simulation and the size of the time step. The definitions are shown in the figure below.

Type of analysis definition in Ansys CFX

The next step is to define the computational models. In our case, for the CHT analysis, we need to associate the gas model as a compressible (red box) and a Total Energy flow solver (green box). For the analysis to be complete, we also need to define gravity (blue box). We set the turbulence model as SST (Shear Stress Transport) (orange box). As well as in Fluent, in CFX we do not take into account the radiation model (black box).

Computational models in Ansys CFX 

The third step in modeling is to define the boundary conditions. We define the inlet as a gas velocity of 50 m / s and a temperature of 25 C. As an outlet from the gas domain, we define a pressure output for Gauge pressure equal to 0.

BC's in Ansys CFX

Another important step is to establish (enable) heat transfer between domains. This option is disabled in the default interface settings. Turning on the heat transfer option on the contact between domains is presented in the image below.

How to turn on heat transfer between domains in CFX

Before the last step is to define the initial conditions. We can just as well define them in parallel with the boundary conditions. As in Fluent, the initial temperature of the gas domain was 25 ° C and the kloc temperature was 240 ° C.

Initial Conditions in Ansys CFX

The final step is to define the analysis settings. All settings are left in the default position (red frame), except for the analysis accuracy parameter. We choose residual type for max (maximum values) and set the accuracy to 0.001. For most engineering analyzes, this accuracy is sufficient.

In the output control option, we create Transient Results 1  by adding a new data parameter. We set timestep interval to 6 - every 6 steps we will write the results for postprocessing. This is a very useful option, especially if you are dealing with very large meshes, which means that the program saves a lot of space on the disk. Thanks to the recording frequency, we are able to control the size of our analysis taking into account the disk capacity.

Transient settings in CFX