HYDRODYNAMIC INVESTIGATIONS OF INVERTED SYPHON’S FRAGMENT

A.V. BURLACHENKO, O.N. CHERNYKH, N.V. KHANOV

Abstract


In this article are presented the results of studying the operating conditions in the transient mode of an inverted syphon with rectangular pipes, which at the same time experience increased hydrodynamic loads, often leading to one or another destruction. Also are presented the results of the study of pressure fluctuations in various sections of the bottom along the length of the transit part of a tubular structure of a inverted syphon type with a rectangular cross section. Was modeled the design of the inverted syphon with two breaks along the length and three types of inlet portals: smooth, "hood" type and portal wall. It has been established that the conditions of formation and features of the hydraulic operation of the inverted syphon in the transient mode are mainly determined by its design features. With the flooding of the inlet portal, the flow of air into the pipe is hindered and a transition mode of the second type is formed. At a certain flow rate, depending on the design of the input "self-charging" portal (of the "hood" type or smooth), the second type of transient mode is replaced by the first. Level fluctuations in the headrace in the both cases are insignificant. Also, is given the data on the distribution of the pulsating pressure component, its intensity and spectral density in various sections along the length of the pipe. The maximum intensity of pressure pulsation (the ratio of the pressure pulsation standard to the velocity head in the pressure section of the pipe) is observed with a hood-type portal – 1.3 (with a flow rate parameter of 0.95). With a smooth portal it is slightly lower (about 0.95 at a flow rate of 1.19), but the highest standard of pressure pulsation occurred with a soft portal and corresponded to high flow. The maximum was in the measuring section, located at the beginning of the horizontal section of the pipe. Recommendations are given on establishing the boundaries of the existence of a transient mode and on the intensity of pressure pulsation in various sections along the length of the pipe with an analysis of the spectral characteristics and a discussion of measures that ensure a decrease in pulsation during transient modes. In the initial phase of the transition mode, the spectrum is mainly narrow-band with a frequency of about 0.28 Hz, and with an increase in the frequency of air bubbles, it expands and the leading frequency of pulsation oscillations increases. At maximum loads, the leading frequency of the pressure pulsation is located in the infra-frequency zone. With the onset of the pressure mode, the leading frequency approached 3 Hz. A comparison with the results of studies by other authors is given. It has been established that the existing recommendations on setting the maximum intensity of pressure pulsation in tubular structures during transient conditions (no more than 0.2) are valid only for specific types of the studied structures and their operating conditions.

Keywords


flow mode, pipe work, intake portal, transient mode, inverted syphon, pressure pulsation.

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References


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