1. What is the Francis Formula?

The Francis formula is used to calculate the length of weir crest when discharge and velocity are not considered. It provides an empirical relationship between the discharge over the weir, height of water above the crest, and the number of end contractions.

2. How Does the Calculator Work?

The calculator uses the Francis formula:

Where:

• \( L_w \) — Length of Weir Crest (m)
• \( Q_{Fr} \) — Francis Discharge (m³/s)
• \( S_w \) — Height of Water above Crest of Weir (m)
• \( n \) — Number of End Contraction

Explanation: The formula accounts for the discharge over the weir and the effect of end contractions on the effective length of the weir.

3. Importance of Length of Weir Crest Calculation

Details: Accurate calculation of weir crest length is crucial for proper hydraulic design of weirs, ensuring accurate flow measurement and control in open channels.

4. Using the Calculator

Tips: Enter Francis discharge in m³/s, height of water above crest in meters, and number of end contractions. All values must be valid (discharge > 0, height > 0, n ≥ 0).

5. Frequently Asked Questions (FAQ)

Q1: What is Francis discharge?
A: Francis discharge is the discharge calculated from the empirical formula given by Francis for flow over rectangular weirs.

Q2: What are end contractions?
A: End contractions refer to the reduction in effective weir length due to the contraction of the nappe at the ends of the weir.

Q3: When is this formula applicable?
A: This formula is applicable for rectangular weirs with end contractions when velocity of approach is not considered.

Q4: What are the limitations of this formula?
A: The formula assumes specific conditions and may not be accurate for weirs with different geometries or under varying flow conditions.

Q5: How accurate is the Francis formula?
A: The Francis formula provides reasonably accurate results for standard weir configurations under normal flow conditions.