Air dynamic viscosity. 2

[ZMalik2k8]

Hi,

I've been searching on the web for air dynamic viscosity at different temperatures @ a certain altitude. There are plenty of calcs on the web for the dynamic viscosity at different temps, different altitudes but not both of them together. DOes anyone know of any?

Thanks in advance

 

[zdas04]

Your post was pretty stingy on details. That causes people to try to guess what you're talking about. Not good. If I'm a compressor guy, then I think your alitude question is dealing with atmospheric pressure adjustment for gauge pressure. If I'm a an airfoil guy then I think you are talking about affects in atmospheric air.

In either case, the effect of altitude is to change atmospheric pressure. There are several correlations that do a decent job of converting altitude into a pressure. Once you have the pressure you are interested in, then something like NIST's REFPROP.EXE does a very good job of applying equations of state and estimating a viscosity.

David

 

[ZMalik2k8]

Sorry for not making it clear. Its for aerospace application, I'm trying to plot some Pressure Vs flow graphs at different altitudes with varying temperatures and one of the parameters is dynamic viscosity of air where the altitude and temp has an effect on this value.

If there is anything else I have missed out or its still unclear please let me know I will try my best!

Zee

 

[katmar]

For typical pipeflow calculations I have always taken the viscosity of a gas to be virtually independent of pressure. Generally as the gas pressure decreases the behavior becomes MORE ideal, so I would expect very little impact from the altitude on the viscosity.

Of course the altitude will have a significant effect on the density of the air, and the temperature will affect both the viscosity and the density.

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"An undefined problem has an infinite number of solutions"

 

[zdas04]

I've also found that temperature is a first order effect and pressure is a second order effect on viscosity. But temperature drops rapidly with altitude so there are significant viscosity effects.

If I remember correctly from my Compressible Flow class (nearly 20 years ago), Reynolds Number (and therefore the whole Moody paradigm) is not a significant factor in drag above about 0.6 Mach so this all gets really messy as you speed up way beyond what we see inside pipes.

David

 

[BigInch]

Get the NASA standard altitude pressure and temperature table. Calculate the viscosity at the indicated pressure and temperature you see on the chart for whatever altitudes you are interested in.

Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso

 

[ione]

http://www.engineeringtoolbox.com/standard-atmosphere-d_604.html

Regards