Hydraulic Jump

1.0 Introduction

A hydraulic jump is a phenomenon in the science of hydraulics which is frequently observed in open channel flow such as rivers andspillways. When liquid at high velocity discharges into a zone of lower velocity, a rather abrupt rise occurs in the liquid surface. The rapidly flowing liquid is abruptly slowed and increases in height, converting some of the flow's initial kinetic energy into an increase in potential energy, with some energy irreversibly lost through turbulence to heat. In an open channel flow, this manifests as the fast flow rapidly slowing and piling up on top of itself similar to how a shockwave forms. The phenomenon is dependent upon the initial fluid speed. If the initial speed of the fluid is below the critical speed, then no jump is possible. For initial flow speeds which are not significantly above the critical speed, the transition appears as an undulating wave. As the initial flow speed increases further, the transition becomes more abrupt, until at high enough speeds, the transition front will break and curl back upon itself. When this happens, the jump can be accompanied by violent turbulence, eddying, air entrainment, and surface undulations, or waves.

In spite of the apparent complexity of the flow transition, application of simple analytic tools to a two dimensional analysis is effective in providing analytic results which closely parallel both field and laboratory results. Analysis shows: 

Height of the jump: the relationship between the depths before and after the jump as a function of flow rate



Location of the jump on a natural or an engineered structure



Character of the jump: undular or abrupt

Figure 1.0 Hydraulic Jump Machine

2.0 Objective To examine and exhibit some of the characteristics of the hydraulic jump.

3.0 Theory

Direction of flow

Figure 1: Schematic of a hydraulic jump

The hydraulic jump equation can be expressed as:

Upstream (subscript 1) and downstream (subscript 2) of the hydraulic jump can be modeled using the specific energy equation:

Department of Mechanical & Manufacturing Engineering Faculty of Engineering, Universiti Putra Malaysia EMM 3304 – Applied Fluid Mechanics The critical depth of the flow, yc = (q2/g)^-3

Where; q F

= =

discharge per unit width (= Q/b) Froude number

E

=

specific energy

y

=

flow depth

hL

=

head loss

4.0 Apparatus Multipurpose teaching flume

5.0 Procedure 1. The internal width of the open channel was measuread. 2. The pump was turn on and a discharge was allowed to flow into the channel. 3. The discharge was measured by the volumetric method and find q. 4. The value of yc was determined and set the upstream sluice gate such that the opening is less than yc. 5. The downstream sluice gate was adjusted to produce a stable hydraulic jump in the channel. 6. The experiment was repeated with two other flow rates.