Open Channel Flow

Closed pipe• Pump or fan driving force• No free surface Open channel• Gravity driving force• Free surface

Open channel

Irrigation Storm water collection Waste treatment Transport

Open channel

Prismatic channel Hydraulic radius• Rh = flow area/wetted perimeter

• Optimize for greatest flow at smallest wetted perimeter

Open channel

Flow determination• Empirical• Manning Equation• Weirs

Manning equation

USCS: cfs Q = (1.49/n)A Rh

2/3So1/2

Manning coefficient: n depends on channel surface smoothness

Weirs

Obstruction in flow channel Sharp-crested weirs Rectangular V-notch

Open Channel Lab

All data in USCS Obtain measurements for slope

calculations

Part 1

Flow valve wide open; allow flow to stabilize

Record flow meter value Record dimensions for Manning equation Install rectangular weir; obtain dimensions Install v-notch weir; obtain dimensions

Part 2

Adjust flow valve to reduce flow to about 50% of flow in Part 1

Repeat all measurements

Report

Data: dimensions and flow meter readings Results: calculated flows from Manning

Equation and two weirs Conclusions: compare flow meter readings

with those obtained from empirical equations