Hydaulic Design of WWTF- how account for losses
Hydaulic Design of WWTF- how account for losses
(OP)
Several Engineers and I have been having a discussion/dispute about the correct way to account for entrance/friction loss in pipes/channels for WWTF design.
The question boils down to the following...
When transitioning from a concrete channel to a pipe (gravity- meaning by this definition that the pipe entrance is not flooded) what method is best used to determine headloss?
Here are our thoughts...
Culvert Calculation for headwater- The program I use assigns a inlet loss coefficient of 0.5 for a concrete headwall (similar to channel to pipe). This seems to be overly conservative from a common sense standpoint.
Assume full pipe flow- use full pipe flow and hazen williams formula to calculate head loss through the pipe at a certain flow. This will return a lower headwater or less loss than the above option across the board.
I think that neither are right and the answer lies somewhere between. The culvert calculator has an inlet loss based on flow coming into a pipe from 180 degrees. When water is entering the pipe from a channel, the water is already "organized" and should enter the pipe much easier.
If you agree, do you have an equation that takes into account the difference in size and shape to use with the culvert calculator? If you don't, what do you think?
Thanks in advance for any responses...
TG
The question boils down to the following...
When transitioning from a concrete channel to a pipe (gravity- meaning by this definition that the pipe entrance is not flooded) what method is best used to determine headloss?
Here are our thoughts...
Culvert Calculation for headwater- The program I use assigns a inlet loss coefficient of 0.5 for a concrete headwall (similar to channel to pipe). This seems to be overly conservative from a common sense standpoint.
Assume full pipe flow- use full pipe flow and hazen williams formula to calculate head loss through the pipe at a certain flow. This will return a lower headwater or less loss than the above option across the board.
I think that neither are right and the answer lies somewhere between. The culvert calculator has an inlet loss based on flow coming into a pipe from 180 degrees. When water is entering the pipe from a channel, the water is already "organized" and should enter the pipe much easier.
If you agree, do you have an equation that takes into account the difference in size and shape to use with the culvert calculator? If you don't, what do you think?
Thanks in advance for any responses...
TG





RE: Hydaulic Design of WWTF- how account for losses
Q=Cd*Ac*srqt(2g*(HW-Yc))
Cd=Coeefficient of Discharge
Ac=Cross sectional area at critical depth
g=gravity
HW=depth of headwater
Yc= Critical Depth
Now if you know the flow and channel geometery you could calculate the normal depth of the channel and use that as HW for the culvert.
Now for pipe culverts with a square edge in a vertical headwall Cd=0.93 for HW/d<0.4 to 0.80 for HW/d=1.5
You can interpolate Cd based on your HW/w Ratio
This gives you flow throught the pipe which is what sounds like you're ultimately looking for. If you still want Ke try the following formula with the Cd you got from above.
Coefficeind of discharge is
Cd=1/(1+Ke)^1/2
With Ke being the entrance loss coefficient.
RE: Hydaulic Design of WWTF- how account for losses