dehnemi
Mechanical
- Oct 6, 2003
- 3
I have been trying to solve several viscous heating problems using a CFD tool. I do not have a lot of wind tunnel experience and therefore do not have any way to “litmus check” the results I have been getting so far. The idea is to prove that one shape is better than another with respect to the skin heating. The only formula I have found so far from Frank Whites text is
taw = tinf + rc*uinf^2/(2*c)
taw: adiabatic wall temp
tinf: free stream static temperature of the air
rc: recovery factor ~ Pr^.333 (for turbulent flow)
uinf: free stream speed of the air
c: specific heat of air
This however is only good for Prandlt numbers of 1 and it does not consider the local Mach numbers or the viscosity changes. I’m really only in the transonic range ~.8 Mach.
1] Does anyone have a rule of thumb calculation so that I can build some confidence in the CFD results.
2] or does anyone have empirical experience of what the ballpark temperature rise would be due to viscous heating for Mach .8, Total Temp 49°C airflow. I’m getting a 7°C rise where as the above equation would indicate a 36°C rise.
Thanks MD
taw = tinf + rc*uinf^2/(2*c)
taw: adiabatic wall temp
tinf: free stream static temperature of the air
rc: recovery factor ~ Pr^.333 (for turbulent flow)
uinf: free stream speed of the air
c: specific heat of air
This however is only good for Prandlt numbers of 1 and it does not consider the local Mach numbers or the viscosity changes. I’m really only in the transonic range ~.8 Mach.
1] Does anyone have a rule of thumb calculation so that I can build some confidence in the CFD results.
2] or does anyone have empirical experience of what the ballpark temperature rise would be due to viscous heating for Mach .8, Total Temp 49°C airflow. I’m getting a 7°C rise where as the above equation would indicate a 36°C rise.
Thanks MD