Bernoulli equation velocity term problem
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I’ve been working on past exam questions lately, and I’ve come across problems similar to those involving water flow from an open tank at a high elevation. When applying Bernoulli’s equation, some equations include the velocity term on the right side, while others do not. Although the differences in results aren’t very large, it can sometimes affect the selection of the correct answer. What are your thoughts on this, fellow enthusiasts? ?
Each problem needs to be analyzed on a case-by-case basis; it depends on the cross-section chosen. If a cross-section taken on the outside results in no velocity term, there is still a local drag loss, which requires special attention! This topic is often tested in exams!
The guidance from zhanghp30 is correct: when the cross-section is chosen inside the pipe outlet, there will be a kinetic energy term, while if it is chosen outside the outlet, there is no kinetic energy term; however, the local resistance loss term must be taken into account. It’s basically the same principle. The local resistance coefficient at the outlet is usually also 1.0. Typically, when selecting a cross-section, it is chosen inside the pipe outlet. For more details, refer to page 101 of the textbook published by Tianjin University.