HEC-RAS : i want to calculate headloss coming from a direction change

[vcloarec]

Hello,

I need to integrate a head loss created by a 90° direction change in a unsteady flow model.

I don't see any solution ...

I have think to put a head loss coefficient on a cross section but i can't in unsteady flow. (Headloss = k(v2/2g))

Any body can help me ??

 

[cvg]

increase the n-value for the reach

 

[vcloarec]

Thank you for your reply !!!

But how much i have to increase n-value ???

Do you know any relation to estimate de headloss if I know the angle ??

 

[cvg]

I don't know of a relation. Depends on the length of the reach also. You will need to do some calcs to determine a suitable value and then try it to see if it approximates the headloss you are looking for.

 

[vcloarec]

My problem is very simple, it is a rectangular channel with a 90° change direction like this :

----------|
<---- |
-----| ^ |
| | |
| | |


The channel's width is 2 meters.

May be somebody know how too calculate the headloss ???

My first idea is to use a headloss coefficient of 1,5 like in pipe ... But i don't now if it is correct ....

 

[chicopee]

Instead of a pipe try a k value for a similarly sized rectangular duct with a 90d elbow bearing in mind medium adjustement.