# Reynolds Number in open space

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1. Oct 7, 2014

### Martina835

Hi people! I'm studying the problem of a house in a valley with a wind at 5m/s. If I'd like to compute Reynolds number here and know if the flow is laminar or turbulent which is the charateristic dimension? The height of the house?

2. Oct 7, 2014

### Staff: Mentor

The height or the width, yes. If they differ too much, then it will need more thought (in doubt, I would take the smaller one).

3. Oct 8, 2014

This depends on what portion of the flow you wish to study, as the Reynolds number requires a characteristic length scale and selecting that length scale depends on the geometry of the problem. So what part of the flow are you hoping to check for turbulence? If it is the wake created by the house, then it is likely the width of the house that should be used. If you want to know whether the atmospheric boundary layer itself is turbulent, the answer is almost invariably yes. Even if it is not, Reynolds number is itself meaningless for determining the laminar/turbulent state of an open flow like a boundary layer.

4. Oct 8, 2014

### Martina835

I am studying a 2D geometry so I just have the lenght and the height! Yes I wish to know if the flow around the house is turbulent...much away from the house (1-1.5km up) I have an unperturbated flow.

5. Oct 8, 2014