Abstract
Abstract. This paper extends the analysis concerning the importance in numerical models of unsteady friction and viscoelasticity to transients in plastic pipes with an external flow due to a leak. In fact recently such a benchmarking analysis has been executed for the cases of a constant diameter pipe (Duan et al., 2010), a pipe with a partially closed in-line valve (Meniconi et al., 2012a), and a pipe with cross-section changes in series (Meniconi et al., 2012b). Tests are based on laboratory experiments carried out at the Water Engineering Laboratory (WEL) of the University of Perugia, Italy, and the use of different numerical models. The results show that it is crucial to take into account the viscoelasticity to simulate the main characteristics of the examined transients.
Highlights
If the transients in a pressurized constant diameter pipe supplied by a constant head reservoir – hereafter referred to as single pipe – due to the instantaneous closure of a valve placed at the downstream end section, are simulated by means of the Allievi-Joukowsky analytical model (Fig. 1a, continuous line), no decay of the pressure peaks takes place after the end of the manoeuvre
When friction forces in an elastic pipe are evaluated by means of the uniform flow formulas, i.e. within the so called steady-state approach (Fig. 1a, dashed line almost undistinguishable from the continuous line), no valuable difference occurs with respect to the Allievi-Joukowsky model in terms of decay and rounding of pressure peaks
The damping and rounding of pressure peaks in a single pipe are ascribed to the effect of unsteady friction in elastic pipes and to both unsteady friction and viscoelasticity in plastic ones
Summary
If the transients in a pressurized constant diameter pipe supplied by a constant head reservoir – hereafter referred to as single pipe – due to the instantaneous closure of a valve placed at the downstream end section, are simulated by means of the Allievi-Joukowsky analytical model (Fig. 1a, continuous line), no decay of the pressure peaks takes place after the end of the manoeuvre In this case friction effects are neglected and an elastic behaviour of the pipe material is assumed. In the lat- diameter D = 93.3 mm, nominal diameter DN110, and wall ter approach, the characteristics of the possible leaks are in- thickness e = 8.1 mm This pipe connects the upstream tank ferred directly from transient data – in most cases pressure to the downstream manoeuvre valve – ball valve DN50 – that traces – by measuring the arrival time and the entity of pres- discharges in the air. The steady-state discharge at the end valve, Q0, is measured by means of a magnetic flow meter
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