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Define the Re_h..

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Old   February 16, 2004, 03:13
Default Define the Re_h..
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jay
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Iwas suddenly frustrated when I reviewed the papers about the backstep flow..

Most of authors, they defined the Reynolds number at the height of backstep (h).

But.. How can they define the inlet velocity at the backstep heght?

the profile of inlet velocity is usually the parabolic type. so.. the velocity at the backstep height is zero in the inlet region..

I have no idea how they can get the velocity at the step height..it should be zero value until height is going to be expanded..

Do they just assume the velocity at the step height as the velocity at the freestream?

please, teach me.. Thanks.
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Old   February 16, 2004, 03:40
Default Re: Define the Re_h..
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Rami
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Jay,

The keyword here is "characteristic" or "typical". The non-dimensional equations and numbers are formed by normailization of the original equations by characteristic length, velocity etc., resulting in the non-dimensional equation with its non-dimensional numbers such as the Reynolds number.

When you consider the backstep problem, a natural choice for the length scale is the step height, h. Likewise, a natural choice for a velocity scale is the average inlet velocity, which is related to the flowrate.

Your interpretation was therefore wrong: it is not the velocity value at the step wall or corner, but merely two independent characteristic values that define Re. It is possible to make other choices (e.g., the maximum velocity in the inlet profile), but the abovementioned choices are most natural and therefore most commonly used.

I hope this helps,

Rami
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Old   February 17, 2004, 15:10
Default Thank you, Rami
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jay
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