Hi,

I am solving the 1-D Euler equation using upwind methods for flow through a divergent nozzle. Three cases were tested:subsonic flow, supersonic flow and flow with shock. The subsonic inlet boundary condition produced incorrect result for the subsonic flow.

B.C. & Density & Velocity & Pressure | Subsonic inlet & Fixed? & Float? & Fixed | Supersonic inlet & Fixed & Fixed & Fixed | Subsonic outlet & Float & Float & Fixed | Supersonic outlet & Float & Float & Float |

Can anyone please advise me on this?

Thanks,

Shuo

Check your boundary conditions, in the subsonic case you need one source of information coming from the outlet. Static pressure for example. With the rest coming from the inlet, in 1D there are only 2 left, so let's say for example total pressure and velocity.

For the subsonic case, I fixed P at the outlet and while letting rho, and u float. For the inlet I fixed rho and P and u.

I read from Anderson (modern compressible flow with historical perspective) that using the method of characteristics you should let one variable float (ie.u) at the inlet. i tried this and the solution was wrong. Why is this?

Shuo

In the subsonic 1D case, try:

Fixing on the outlet: static pressure Fixing on the inlet: total pressure, temperature and velocity

Yep, it's working. Thanks Shuo