I entered the the Darcy Welsbach roughness heights for my pipes but after doing some research I found out that the roughness can be negligible in certain depending on the Reynolds number. So I ran my scenarios with all the roughness's set to zero to see how that would impact my results and I noticed it had no impact compared to when I used the roughness associated with the pipe materials. This would indicate to me that the roughness heights are negligible in my my situation. Is that a correct assumption?
Hello Christen,
What was the value of Darcy Welsbach roughness height set in model before you changed it to 0? Changing Darcy Welsbach roughness heights should have impact on headloss calculated for pipes, unless the value is very small.
Darcy-Weisbach Headloss Calculations in Steady State and EPS
Please provide more details, meanwhile here is related discussion as a reference.
Darcy Weisbach Friction Factor (f)
Regards,
Sushma Choure
Bentley Technical Suppport
Material
Roughness height (k) /(e)
Ductile Iron
0,1mm
HDPE
0,001524 mm
copper
0,001524mm
Galvanized iron
1.524mm
These are the roughness heights I used.
The following diameters were used:
Inside diameter used
80
200
100
150
125
300
250
90
164
26
51.4
20
25
50
Galvanized Iron
15
I think I figured out what I did wrong. I had was used the wrong friction method. I had hazen williams in my base calculation options instead of Darcey weisbach.
If the Hazen-Williams method is selected in the calculation options, you should only see the Hazen-Williams C field in the pipe properties. I am guessing you may have added the Darcy-Weisbach roughness height field to a pipe Flextable and were using that.
To answer the general question - the friction factor will certainly impact the results as it will change the friction headloss, but there are some cases where that headloss could be "negligible" for example if the velocity is very low in the pipe.
Is there a deeper reason why you are asking this question, or is it just for academic curiosity?
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.