Talk:Hydraulic jump

From Wikipedia, the free encyclopedia

	This article is within the scope of WikiProject Fluid dynamics, which collaborates on articles related to fluid dynamics.	Physics Portal
Start	This article has been rated as Start-Class on the assessment scale.
Mid	This article is on a subject of Mid-importance within physics.
Help with this template Comments: edit – history – watch – refresh Version reviewed. This is a fine start for the article. There are different words in engineering and mathematics which could be cleaned up and the maths is very poor. The explanations are a good start but this article needs Diagrams Maths with explanation Relationship to shock waves/tidal bores Rex the first talk | contribs 13:07, 18 March 2007 (UTC)

[edit] Comparison with shock wave

This discussion could do with a comparison between a hydraulic jump and a shock wave and in so doing, it could expand on the increase in entropy of the flow downstream of the jump. —BenFrantzDale 03:38, 12 October 2005 (UTC)

That's true (sb. should do that), but remind the fact that a jump is not really a shock in the actual sense. A jump can be described with the shallow water equations which are mathematically similar to the ones of shock theory. However, it is not possible to describe the transition region with these equations, i.e. to connect the regions up- and downstream as a continuous piece. Inside the transition zone, you observe at the very least a separated flow, and in most cases even a turbulent zone where additional degrees of freedom are generated. So this region very different from a shock in gas theory. It is true that the classic literature refers to the jump as a shock, but it is clear that this is a good approximaion only if the transition region is fairly small compared to the jump itself - you then obtain pretty good estimates on characteristic entities from the shallow water (shock-like) theory. In the scientific literature of the past few decades it is shown that this approximation fails for small, e.g. circular hydraulic jumps. - Hbarmeter 16:16, 3 April 2006 (UTC)

[edit] explanation could use some fixing up

The explanation section still needs to be improved. Also, I find the graph impossible to read; I can't tell what the labels on the x and y axis are. The text says there is a circle in the graph. Maybe it means a curve? --Coppertwig 18:56, 5 February 2007 (UTC)

I think if you write out an equation for the sum of kinetic and potential energy before and after the hydraulic jump, you get a cubic equation. I suppose one solution is not physically realizable (e.g. a negative number?) and that the two remaining solutions imply that the water can continue as it's going, or if it's going fast enough it can "jump" to one specific higher level and slower flow, but it can't take on any other values, for example it can't flow neatly at some level in between the lower and higher ones. This explains why there is a sudden jump like that. It would be good to find a textbook that runs through this explanation, reference it and put an explanation like this into the article. Here's a web page; I haven't had time to study it closely yet so I'm not sure if it explains this the way I'd like to see it: [1] I think I get a simpler equation than theirs. I don't worry about viscosity or other complications, and I don't have a quadratic term in my cubic equation. It would be good to be able to reference a textbook with a simple explanation (as simple as a cubic equation can get :-) --Coppertwig 02:21, 7 February 2007 (UTC)