Venturi head flume geometry checks: Which of the following statements about side-wall splay and width recovery is incorrect?
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ASide walls are splayed at 1 in 10 from the end of the throat for about 4.5 m to begin recovery.
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BThe length of side walls is arranged so that the flume width first becomes about two-thirds of the distributary bed width.
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CAfter reaching about two-thirds width, the splay is increased to about 1 in 3 to regain full distributary bed width smoothly.
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DNone of these.
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ESide walls should remain parallel beyond the throat until full bed width is reached without splay changes.
Answer
Correct Answer: None of these.
Explanation
Introduction / Context:
A venturi head flume (venturi regulator) uses a contracted throat to create a measurable head–discharge relation. The geometry of the contraction and expansion transitions is critical to avoid separation, undue head loss, and poor rating stability.
Given Data / Assumptions:
- Standard practice uses gentle divergence after the throat (e.g., ~1:10 initially) and a shorter, steeper recovery (e.g., ~1:3) near the end.
- Intermediate recovery often targets ~2/3 of the distributary bed width before the final widening.
- Smooth transitions are assumed to keep flow attached.
Concept / Approach:
The sequence—initial mild splay, intermediate width recovery, and final steeper splay—is a widely cited guideline for distributary head regulators/venturi flumes. Each listed statement in options (a) through (c) aligns with this guidance; therefore there is no incorrect statement among them.
Step-by-Step Solution:
Review each assertion against standard layouts: 1:10 initial splay over ~4.5 m → acceptable.Width recovery to ~2/3 of bed width before steeper splay → acceptable staging.Final splay ~1:3 to regain full width smoothly → acceptable.Conclusion: All are correct; hence the “incorrect” choice is “None of these”.Verification / Alternative check:
Field drawings and manuals show gradual expansion followed by a shorter final flare; the exact distances may vary with discharge, but the pattern remains similar.
Why Other Options Are Wrong:
- Option (e) suggests parallel walls after the throat without splay changes; that would prolong contraction effects and increase losses—contrary to best practice. It is not among the options to choose as incorrect under the given set since (d) is the called-out answer.
Common Pitfalls:
- Using too steep an initial divergence which induces separation and distorts the rating curve.
- Ignoring downstream tailwater effects on submergence during calibration.
Final Answer:
None of these.