CFD output velocity vector

deepacha · Posts: 40

Hello,

I made a model with louvers using component blocks to do an external CFD analysis. (image attached)
I went ahead with the default CFD grid. The CFD simulations went upto 2500 iterations and did not converge.

I have a problem with the result. The louvers are inclined at 45degree pointing towards the ceiling. The incoming wind is 980fpm which is pretty high. I would expect the velocity vectors to go into the room upwards and then fall downwards in the middle or little further as they will have much lower velocities by then thereby going out through the outlet.

Instead the path of air flow seems completely the opposite. On closer look near the louvers, it looks like the velocity vectors are not affected by the louver geometry.

Could you please tell why this would happen or if I need to make changes in the model. I have also attached the image of the grid for your reference.

deepacha · Posts: 40

Hello,

Sorry, I had one more question that I forgot to include in my earlier post.

While setting up the CFD External Analysis, the wind speed was set as 980fpm. Then why would the velocity of the wind entering the model be around 437fpm ? This can be seen by the blue colored velocity vectors entering the model in the image attached with the previous post.

Thanks,
Deepa

Steve Potter · Posts: 432 Location: newcastle

Hi Deepa,

From your screenshots, it looks as if the grid spacing is too coarse to model the geometry of the louvres. You will need to ensure that the grid spacing is of a comparable dimension to the smallest dimension of the louvre.

As far as the wind velocity is concerned, the actual velocity varies from the ground level upwards according to the ASHRAE recommended wind profile.

Regards,

Steve

deepacha · Posts: 40

Steve,

I tried refining the grid. Bu the aspect ratio increases a lot. I see that the grid has to be changed along the entire length or width of the model which increases the complexity and also refines the grid in unwanted spaces.

Is there a way to refine the grid only around the louver and not change across the length of the model ?

thanks,
Deepa

Steve Potter · Posts: 432 Location: newcastle

Deepa,

If you change the grid spacing for a region along one of the major axes, this spacing will be applied across the full extent of the remaining two axes. It is not currently possible to apply local refinements. If the number of grid cells is becoming excessive by reducing the grid spacing to accurately model the louvres, you may need to simplify the overall model.

Regards,

Steve

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