## Fluids

#### Flow inside a helmet

• KumarVaibhav
Subscriber

I want to do the flow analysis of air inside a helmet with cuts and vents to see if air is seeping in or not?Can somone suggest me a tutorial for it?I would welcome if it is in ANSYS AIM or Fluent both.Pls tell me about what should be my flow domain for the problem?Should i take the domain  preferably an enclosure and name its inlet outlet and walls or shall i straight away take the helmt vents  at front as inlet and vents at back as outlet?Pls suggest

• Karthik R

Hello KumarVaibhav,

You model will depend on the type of application you are planning to design your helmet for. Same goes for the boundary conditions and even the computational domain selection. I'd strongly recommend that you formulate the problem on paper and elaborate a little more it. Please help us understand your problem.

Thank you.

Best Regards,

Karthik

• peteroznewman
Subscriber

Hello KumarViabhav,

Here is a research article on simulation of airflow through a helmet.  Experiments were performed on concentric cylinders in the wind tunnel of cross section 450 mm × 750 mm.

They have a 140 mm cylinder representing the head. The upstream length was four times the diameter of the inner cylinder, and downstream length was 20 times the diameter of inner cylinder. The downstream length was kept large to ensure that the flow was fully developed.

That means the CFD domain was 3.5 m long and had the cross section of 450 mm x 750 mm long. The inlet was at one end, the outlet at the other end and the four walls.  They assigned an inlet velocity of 15 m/s.  You could reproduce this model and see if you get the same results.

You could even start with a 2D model, which would be an excellent way to start learning CFD.

Regards,

Peter

• KumarVaibhav
Subscriber

My objective is very clear i wanna see how much air is seeping inside the gap between helmet and cushion entering through the two vents at front and then leaving out from two another vents at the back.I JUST WANT TO SEE THE AIR FLOW PATTERN USING FLUENT THE STREAMLINES MAY BE.

• Karthik R

Hello KumarVaibhav,

It seems to me like Peter was spot on with his suggestions. Please create the geometry of the helmet you are trying to model and extract the fluid domain. Here is how you can go about Extracting Fluid Domain in SpaceClaim. I am not fully sure how you would estimate the values of air velocity or flow rate entering your vents. One possibility is to follow Peter's suggestion - extend your fluid domain in both upstream and downstream directions. Before modeling the flow, please make sure to perform some calculations to understand if the model is compressible or incompressible. Also, calculate the Reynolds number of the flow through the helmet gap to understand whether it is laminar or turbulent. You flow model should be tuned accordingly.

Once you solve the model, you can certainly use streamlines to visualize the flow through the gap. Another option would be to use velocity vector plot. The following link should give you various ways of post-processing in Fluent.

Fluent post-processing

I hope this helps you get started.

Thank you.

Best Regards,

Karthik