[immortality]

hi.
I have used 3 types of boundary conditions with three different results!
The patch i assigned BC on is outflow.these scenarios are examined:
____________________
1)firstly pressure is specified through p0 as isentropic formul:

p=p0*(1+(gama-1)/2*U^2/(gama*R*T))^(-gama/(gama-1))

U and T are zero gradient.at this pressures are obtained less than expected.
-----------------
2)at second i set
T=T0-(gama-1)/(2*gama*R)*U^2

And U and p are assumed zero gradient.
This approach results in more higher pressures.
---------------------
3)both p and T are specified:

p=p0*(1-(gama-1)/(2*gama*R*T0)*U^2)^(gama/(gama-1))
And
T=T0-(gama-1)/(2*gama*R)*U^2 (as second case)

This approach leads to diverge after 200 iterations.

So as it tooks one month so far and remaind a little time for me why these conditions result so differently?whats the cause or the causes?
Any knowledge,advice and idea is much appreciated.
Thanks for attention.