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stagnation pressure on a water droplet

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Old   March 7, 2018, 06:04
Default stagnation pressure on a water droplet
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Hussain
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Hi,
I am modeling a free falling of a water droplet through air. the issue is that i want to estimate the deformation rate and for that it seems like i need to calculate the stagnation pressure. by looking at the equation (wiki) it is not clear to me what values to choose. for example should i choose the density of air or density of water droplet in that equation, similarly what velocity should i consider. is it the velocity of water droplet or the air? i appreciate if you could help me route me to a correct forum. thanks!

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Old   March 7, 2018, 06:24
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Uwe Pilz
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You have to use the density of the air. Formula given in textbooks are valid for solid bodies too, which don't deform.

The velocity is the relative one between the droplet and the air. It doesn't play any role if the air is moving or the droplet. It is the difference hat counts.
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Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)
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Old   March 7, 2018, 07:19
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HI Pilz
Thanks for a quick reply. how about the static pressure in the equation. can i just use the atmospheric pressure?

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Old   March 7, 2018, 07:32
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> can i just use the atmospheric pressure?

I think so. I need your reference to check this.
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Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)
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Old   March 7, 2018, 07:40
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The droplet is falling through the air at atmospheric pressure of 1 atm. do you have any reading suggestions regarding my problem because i want to estimate the deformation rate of the droplet while it is falling?
thanks!

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Old   March 7, 2018, 08:27
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In this case I would simulate an aerial flow around the droplet. With changing the speed the droplet gets deformed (more or less slightly), but the cf values change fast. Your solution is the one where the drag equals the gravity.
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Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)
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Old   March 7, 2018, 08:55
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Thank you Pilz. I will try to dig down more on that suggestion of yours.

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bernoulli's equation, droplet simulation, falling drops, stagnation pressure

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