Waterhammer Effects In The Case Of Air Release
Author(s)
S. Mambretti
Abstract
In the case of unsteady flow in pipes, the main problems seem to be the
modelling of headlosses, especially when air release phenomena occur. A
number of approaches are possible, but in this paper only one-dimensional and
one-phase models have been investigated, in order to check their adequacy in
reproducing real data, as they require much less computational effort and are
therefore much faster and easy to apply.
Laboratory experiments have been performed at the Hydraulic Laboratory of
the Politecnico di Milano, Italy, and simple models have been implemented in a
computer code and then applied.
The results are reported and commented; it appears that to reach some
achievements, some other points have to be discarded and to improve the overall
solution it is probably necessary to use two-dimensional two-phase models.
Keywords: waterhammer, column separation, air release, headlosses.
1 Introduction
There are a number of examples of benefits derived by the presence of unsteady
flow, but in most of the cases this phenomenon has destructive characteristics.
This is why the subject has been studied since the XIX Century. However, still
many uncertainties are present when the model of a complex system is built.
One of the main problems is related to the use of steady flow formulas to
compute the headlosses.
Generally speaking, smoothing and phase shift are present even when no air
release occurs [1], implying the problems are tied to the unsteady flow
phenomena; the reasons for such inadequacy have to be found [2] in the different
velocity profiles between those in unsteady flow and those correspondingly (i.e.
with the same discharge) in steady flow. In unsteady flow the gradient of the
velocity close to the pipe wall is steeper than in steady flow and therefore the
stresses are higher, and finally so are the resistances [3].
Keywords
waterhammer, column separation, air release, headlosses
Related Book
Other papers in this volume
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