# Dynamic viscosity

1. Feb 20, 2008

### es_joe

How to calculate the dynamic viscosity of air at high alttitudes,i want to calculate it at hight 4000m abovesea level at that hight the temp. is 262 kelven degrees.

Any thoughts???

2. Feb 20, 2008

### FredGarvin

Since viscosity is more or less dependent on temperature, I would start with using Sutherland's Formula:

$$\mu = \mu_o \left[ \frac{0.555T_o+C}{.555T+C}\right] \left[\frac{T}{T_o}\right]^{1.5}$$

Where:
$$\mu_o$$= .01827 cP for air (or some known value at a different known temperature)
$$T_o$$= 524.07°R for air (for the viscosity above, different if using a different value)
$$C$$= 120 for air (Sutherland's constant)
$$T$$= absolute temperature (°R)

Crane's states that the variation in viscosity is on the order of 10% when going up to 500 psi. Assuming no wierdness goes on at lower (sub atmospheric) pressures, the variation should be very small when deviating less than 15 psi.

You can then go on and calculate the dynamic viscosity through the relation $$\nu=\frac{\mu}{\rho}$$

Last edited: Feb 20, 2008
3. Feb 20, 2008

### FredGarvin

According to: http://www.bh.com/companions/034074152X/appendices/data-d/default.htm [Broken]

It looks like they use a version of Sutherland's method as shown above.

Last edited by a moderator: May 3, 2017
4. Feb 20, 2008

### es_joe

what is rALT ???