Pipe Average Velocity
Of these, two - Uniform Flow Velocity and Full Flow Velocity - are of interest to UK Engineers.
Uniform Flow Velocity
The uniform flow velocity of a pipe is obtained by calculating the velocity in the pipe at normal depth. Under surcharged conditions (Q > Q max), the surcharged velocity is used instead. In the case of converging top pipes, under partially filled flow conditions and two normal depth roots exist, the larger normal depth conjugate depth is used to compute the uniform flow average velocity.
Full Flow Velocity
The full flow velocity corresponds to the velocity when the pipe is flowing full. The flow area is equal to the entire cross-sectional area of the pipe.
Simple Average Velocity
The simple average velocity is computed by:
The Simple Average Velocity method does not account for any depth changes between the two ends of the pipe as the weighted average velocity method does.
Weighted Average Velocity
To compute the weighted average velocity, the simple average velocity of each profile segment is considered and given a weight based on its length:
- Va =Average velocity for the pipe (m/s, ft/s)
- Vui =Upstream velocity for segment i (m/s, ft/s)
- Vdi =Downstream velocity for segment i (m/s, ft/s)
- Li =Length of the profile segment i (m, ft)
- Lt =Total length of the pipe (m, ft)
Pipe Average Velocity and Travel Time
The travel time through each pipe is computed as:
t = L / V