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HPC CFD analysis, Air flow inside rack (Beginner)

Question asked by Prasanth P on Sep 23, 2013
Latest reply on Sep 26, 2013 by Jared Conway

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Hi,

I am modelling and simulating an HPC server room using Solidworks Flow simulation. The facility have 48 server racksa and 5 CRAC(Computer room AC) units with cold aisle containment model. Now I want to model the airflow inside the server rack. Each rack have been modelled as rectangular shaped boxes with several small rectangular cut through holes through which cold air can go inside the rack suk the heat generated by rack and go out from back side of rack. Cut through holes are assigned air inflow(2 m/s). Kindly see the attached images. Boundary conditions and inputs given are as below:

1. Cold air from CRAC: 6400 CFM

2. Rack volumetric hear generation: 21,000 W

3. Air flow through rack perforation: 2 m/s

But my model is showing too much time for completion: Around 3000 hrs. Now i am trying to minimize the complexity of my model for reducing the run time.

I am a beginner in this. Kindly suggest me any better model or any better way to model the air flow iside the rack.

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Bill McEachern Sep 23, 2013 7:45 AM

What is the metric that you are looking at that tells you where you are at? How do you know what the airflow rate is in a rack? Are there fans in the units? I have done similar analysis on a laptop in no more than a few hours.

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Prasanth P @ Bill McEachern on Sep 25, 2013 2:59 AM

Hello sir thanks for your reply. I have identified some of the faults in my model. Instead of giving air inflow i need to insert fan inside the rack. While searching inside predefined axial fans in Solidworks,i couldnt identify the model for my application.

Can you please suggest me which fan model in Solidworks library can i use. Or else please suggest me a generic fan specifications (reference density, mass/volume flow rate, rotor speed, outer diameter etc.) which can be used inside the rack.

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Jared Conway @ Prasanth P on Sep 25, 2013 10:21 AM

I thought you were analyzing the room not the racks?

For a fan, why not just create a new one with your fan curve?

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Prasanth P @ Jared Conway on Sep 25, 2013 11:23 PM

Hi,

I was analysing the room only. My room part is working good in simulation. This rack air circulation i need to include in my simulation for better results.

Now i am trying to get the fan spec details. In the server rack documents it was not available. Where can i find this "server rack fan" curve details.

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Jared Conway @ Prasanth P on Sep 26, 2013 11:09 AM

you need to talk to the rack manufacturer, if there is a fan tray, they'll be able to tell you what fans are in there, go to the manufacturer of the fan's website, they will have curves just like you see in the engineering database.

the other part is that you'll have other things in the rack like appliances. they also have fans. if you talk to them, they might tell you what fans are in there.

but overall, i'm not clear what effect you're trying to study at the rack level.

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Jared Conway Sep 23, 2013 11:42 AM

are we talking transient or steady state?

what mesh level have you chosen? what calculation control level? have you checked to make sure none of the mesh settings has been increased significantly because of the geometry in use?

as bill mentioned, this analysis can be completed in 2-3hrs to get a good idea of what is going on.

something i'm confused about is your 2m/s comment. is that an input? are you adding that as a BC?

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6 Replies

Bill McEachern Sep 23, 2013 7:45 AM
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What is the metric that you are looking at that tells you where you are at? How do you know what the airflow rate is in a rack? Are there fans in the units? I have done similar analysis on a laptop in no more than a few hours.
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- Prasanth P @ Bill McEachern on Sep 25, 2013 2:59 AM
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  Hello sir thanks for your reply. I have identified some of the faults in my model. Instead of giving air inflow i need to insert fan inside the rack. While searching inside predefined axial fans in Solidworks,i couldnt identify the model for my application.
  
  Can you please suggest me which fan model in Solidworks library can i use. Or else please suggest me a generic fan specifications (reference density, mass/volume flow rate, rotor speed, outer diameter etc.) which can be used inside the rack.
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  - Jared Conway @ Prasanth P on Sep 25, 2013 10:21 AM
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    I thought you were analyzing the room not the racks?
    
    For a fan, why not just create a new one with your fan curve?
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    - Prasanth P @ Jared Conway on Sep 25, 2013 11:23 PM
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      Hi,
      
      I was analysing the room only. My room part is working good in simulation. This rack air circulation i need to include in my simulation for better results.
      Now i am trying to get the fan spec details. In the server rack documents it was not available. Where can i find this "server rack fan" curve details.
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      - Jared Conway @ Prasanth P on Sep 26, 2013 11:09 AM
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        you need to talk to the rack manufacturer, if there is a fan tray, they'll be able to tell you what fans are in there, go to the manufacturer of the fan's website, they will have curves just like you see in the engineering database.
        
        the other part is that you'll have other things in the rack like appliances. they also have fans. if you talk to them, they might tell you what fans are in there.
        
        but overall, i'm not clear what effect you're trying to study at the rack level.
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Jared Conway Sep 23, 2013 11:42 AM
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Correct Answer
are we talking transient or steady state?

what mesh level have you chosen? what calculation control level? have you checked to make sure none of the mesh settings has been increased significantly because of the geometry in use?

as bill mentioned, this analysis can be completed in 2-3hrs to get a good idea of what is going on.

something i'm confused about is your 2m/s comment. is that an input? are you adding that as a BC?
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HPC CFD analysis, Air flow inside rack (Beginner)

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