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Old   August 28, 2008, 00:38
Default upstream pressure
  #1
Arman
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Hi,

I simulated 2 ships with slighly different stern, while the other parts of the ship are exactly the same. However, I notice that the pressure distributions between the two ship are different (small, but non-negligible) not only at the stern, but also at the other parts of the ship, even at the bow. Is there an explanations for this (elliptic/parabolic PDE maybe)?
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Old   August 28, 2008, 05:49
Default Re: upstream pressure
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Phillips
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I am studying aerodynamics, and as far as I can see, a change in shape of stern can have some effect on pressure distribution of the whole object. Information (pressure, temperature, velocity field) of the flow can be passed downstream as well as upstream, the only case where information is not passed upstream is when you are travelling supersonic and the sonic boom stops this from happening. So pressure distribution would be different in your case, the matter is by how much.
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Old   August 28, 2008, 06:07
Default Re: upstream pressure
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Arman
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Philips thanks. Do you have an explanation why is this so? I mean from intuition, you expect that only the donwstream information are effected by the stern, not upstream.

I agree with you though. At least I've learned/read this elsewhere before. However I can not explain the physics (or mathematics?) behind this.

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Old   August 28, 2008, 08:39
Default Re: upstream pressure
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Phillips
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Say you are solving the problem using control volume, the pressure inside the control volume is calculated from both the incoming flow and the outlet flow, so I would the say that's when the feature of downstream flow comes into play.

I remember doing flow characterisation over a circular cylinder, and the pressure distribution changes quit a lot upstream when the flow downstream goes from laminar to turbulent.
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