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Old   May 11, 2007, 10:19
Default Temperature distribution at Impeller core!>
  #1
CFDtoy
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I am looking at high speed rotating impellers (adiabatic walls) enclosed within a chamber (static temperature in walls). At high speeds, I am getting high temperatures at the central cores (near the impeller region).

The flow is compressible and im solving for total energy equation (a different version from rothalpy).

I was wondering when p is very low at the core due to rotation can I get high temperatures at the core ?

Is there a physical explanation to prove that high temperature cannot follow regions of low pressure (other than p~rho RT) etc..This is important because, in compressible flows pressure velocity workdone is potentially contributiing a lot of source to the energy equation and I am confused as to how to resolve this.

Thanks

CFDtoy

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Old   May 11, 2007, 11:06
Default Re: Temperature distribution at Impeller core!>
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OPS
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Yes, you can get high temperature at low pressure. Let me give one good example. The Columbia shuttle in which the astronaut Chawala died was burst into flames when it entered into the earth's atmosphere. This is due high friction at the surface which generated huge amount of heat at the surface. Note that the pressure was low on the surface.

OPS
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Old   May 11, 2007, 13:57
Default Re: Temperature distribution at Impeller core!>
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CFDtoy
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OPS:

Now, I would consider that as a source term sponsored temperature generation (friction resulted in ripping of the tiles to assist the ablation layer..frictional heating resulting in such a disaster).

How about core of the impeller's? center of High speed rotational devices? Is it possible to get high temperature just by spinning fast?

Thanks for your insight.

CFDtoy

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Old   May 11, 2007, 14:40
Default Re: Temperature distribution at Impeller core!>
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Mani
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Seems counter-intuitive and unusual. There shouldn't be much friction at the center. Does the density reach unrealistic low values, there? Otherwise, how can the ideal gas law be satisfied. First of all I would take a look at the flow field (pressure and temperature contours, and streamlines) to see from where this high-temperature core originates. Are you sure your impeller is turning the right way?
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Old   May 11, 2007, 20:55
Default Re: Temperature distribution at Impeller core!>
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OPS
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Please specify the axis of rotation. If the core (low diameter) falls on the rotation axis then velocity would be low there compared to other surfaces of the core. If this happens then check the followings:

1. What is the density contours at the core. Is it shows low value at the core?

2. Check the velocity magnitude at the core compared to other surfaces

3. Since the wall is adiabatic and no there is localized source of heat generation in the chamber, then what could be the source of heat energy being released at the core? 1 and 2 would give some insight.

Please reply the 1 and 2 above.

OPS

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Old   May 14, 2007, 09:06
Default Re: Temperature distribution at Impeller core!>
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CFDtoy
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Hello Mani: The flow field (U, P) look realistic. At the core, p drops as expected. Now, I am wondering if T can increase even if P drops or is it unrealistic?

The temperature at the tip of the rotating vanes have high temperature (which I assume is due to viscous heating). The pressure is higher on the presssure side and nice low pressure drop is obtained on the suction side.

However, I move towards the core (a solid shaft with vanes attached to them), I see an increase in temperature locally.

Can you direct me to some papers describing temperature and pressure distribution near impeller vanes ?

Thanks

CFDtoy

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