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Supercritical Flow over a Submerged Vertical Negative Step
(EN)
Retsinis, Eugene
Papanicolaou, Panos
(EN)
ntua
(EL)
The transition from supercritical to subcritical flow around a fully submerged abrupt
negative step in a horizontal rectangular open channel has been investigated. In a laboratory
experiment the one-dimensional energy and the momentum conservation equations were studied
by means of depth and pressure measurements by piezometers installed along the bottom and
the step face. Froude number varied in the range 1.9 to 5.8 while the step height to critical depth
ratio was in the range 1.34 to 2.56. The results are presented in dimensionless form using mainly a
characteristic length scale that is the sum of critical depth and step height and the Froude number
of the supercritical flow upstream. Five different types of rapidly varying flow are observed when
the subcritical downstream tailwater depth varied. The supercritical water jet at the top of the step
either strikes the bottom downstream of the step when the maximum pressure head is greater, or
moves to the surface of the flow when it is lower than tailwater depth, and the separation of the
two flow regimes occurs when the tailwater depth to the characteristic length scale is around 1.05.
The normalized energy loss and a closure parameter for the momentum equation are presented
in dimensionless diagrams for practical use by the design engineer. Finally, the one-dimensional
equations of motion including Boussinesq terms are solved numerically and the results found are
congruent to the experimental findings.
(EN)
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