## 3D Design

#### How to make contact between air and some mechanical component on Ansys19.2?

• akajayak
Subscriber

Hey all,
I am planning to make a fin which is surrounded by air. For that i have created two bodies
1. Fin which is having properties of aluminium.
2. Air which is having properties of air.
I want to put fin in the air medium for that i need to define contact. Can you please guide me through this problem?
I am attaching the parts in the image below. On the left it is Air and on the right it is Fin.

• peteroznewman
Subscriber

So the light grey body is the air, the dark grey body is the aluminum fins.  Are these bodies in DesignModeler or SpaceClaim? In DM, select both bodies in the outline and Form New Part.  In SC, on the Workbench tab, click the Share button.  That will cause Shared Topology to be used. That way, you can delete any automatically generated Contact. The mesher will connect the two bodies with shared nodes.

Drag out a Fluent analysis system in Workbench.  You have to specify boundary conditions. What are the six faces of the air block?  They are either walls, or inlet or outlet boundaries. If there are not walls next to the fins, but more air, then those faces on the air are way to close to the fins. An inlet boundary might have an air velocity. What is the boundary condition on the aluminum? Does one face have a Temperature condition or a heat flux condition?

• akajayak
Subscriber

Actually i am new to ANSYS. Here is the problem statement on which i am working:

(1) Create a heat sink with fins that are flexible. To start with, use say 5 fins in the heat sink. Apply a harmonic (single frequency) point force on one selected heat sink fin at one selected location. Assume aluminium as the material, and 1 mm fin-thickness. Determine the vibrations of the entire heat sink, that is, vibrations of each fin resulting from the single harmonic point force.

(2) Check if you can solve vibroacoustic problems in ANSYS. Now create an acoustic duct and inside that duct, place the heat sink that was designed in step (1) above. Now, this model is going to have vibro-acoustic coupling. Each fin of the heat sink will be coupled to the air inside the acoustic duct. With this model, predict the acoustic pressure generated inside the duct due to the vibrations of the heat sink fins generated by single-harmonic-point-force.

I am done with 1st part and i need help for the 2nd part. For 2nd part i got stuck and unable to proceed further!

Boundary condition for the air block are like this:
1. 5 faces are rigid body, which encloses air.
2. 6th face is the face through which pressure being generated in the duct with the help of speaker.

I dont think any boundary condition required for the fin except for the fact that it is at ambient temperature(as that of air inside duct). Correct me if i am wrong?

• peteroznewman
Subscriber

Ah, that would have been useful to put in the original post. I assumed it was a heat transfer model, which is what most people with fins in air are interested in.

Here is a relevant post.

Here is a list of posts that have to do with acoustic ducts.

• akajayak
Subscriber

Thanks peter for sorting it out. My next problem statement is(3):

(2) Check if you can solve vibroacoustic problems in ANSYS. Now create an acoustic duct and inside that duct, place the heat sink that was designed in step (1) above. Now, this model is going to have vibro-acoustic coupling. Each fin of the heat sink will be coupled to the air inside the acoustic duct. With this model, predict the acoustic pressure generated inside the duct due to the vibrations of the heat sink fins generated by single-harmonic-point-force.

(3) In the acoustic duct developed in step (2) above, give plane-wave acoustic input. Determine the resulting vibrations of the heat sink fins. In this step, no point-force is to be applied.

Can you please tell me how should i do third part, i don't think whatever we have done for 2nd part can be used for 3rd!!

• peteroznewman
Subscriber

Assign a normal acoustic velocity load to a flat surface. That will be a plane-wave.

• akajayak
Subscriber

Hey Peteroznewman,

For the given force in harmonic response i am unable to get any velocity while importing it in acoustic harmonic. can you please help me out.

500N force is applied.

The imported velocity:

my Project file is attached below.