hi, can anybody tell why we are using downstream height downH in the tutorial problem no 7 of flow over free surface bump? i am confused, what will happen if we remove that expression.

is there any effect on the outflow side?

For an outlet boundary condition , in CFX , you have to specify volume fractions for each fluid . You can avoid this specification by changing it to an opening with a sepcified pressure. or in outlet change volume fractions to zero gradient.

thank MAB,

this is correct, ifwe take some pressure, the result would be same , but in my case, there is a twist in the problem: i am continuing this problem by looking hydraulic jump after and over the bump.

i simply take static pressure value at outlet, the results differ from the previous cases when i used downstream height.

i just want to know, what is the fluid mechanics fundamental involve with this outflow boundary condition?

thanks.

thank MAB,

this is correct, if we take some pressure, the result would be same , but in my case, there is a twist in the problem: i am continuing this problem by looking hydraulic jump after and over the bump.

i simply take static pressure value at outlet, the results differ from the previous cases when i used downstream height.

i just want to know, what is the fluid mechanics fundamental involve with this outflow boundary condition?

thanks.

with this post, i want to ask one more thing is that.

if downstream height is defined, what should be its height? how it is considered??

I think they used a lower height at downstream as compared to the one at inflow boudary. The reason is that water level would decrease gradually as the water goes out of the tank . so the downH is the rough estimate of this lower level.

You can even keep the level same as at inflow boundary.