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1

Water hammer mitigation by internal rubber hose

Kubrak Michał

Archives of Civil Engineering

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2024

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Vol. 70, nr 1

275--288

EN

The aim of this research was to experimentally analyse the possibility of using a rubber hose placed inside a pipeline to mitigate the water hammer phenomenon. The experiments were conducted using a steel pipeline with an inner diameter of 53 mm and an EPDM rubber hose with a diameter of 6 mm. Hydraulic transients were induced by a rapid closure of the valve located at the downstream end of the pipeline system. In order to analyse the influence of steady-state flow conditions on the maximum pressure increase, measurements were carried out for different values of initial pressure and discharge. The experimental results indicate that placing a rubber hose inside a pipeline can substantially attenuate valve-induced pressure oscillations. It was observed that the initial pressure has a significant influence on the capacity of the rubber hose to dampen the water hammer phenomenon. Comparative numerical calculations were performed using the Brunone–Vitkovský instant acceleration-based model of unsteady friction. It was demonstrated that this approach does not allow satisfactory reproduction of the observed pressure oscillations due to the viscoelastic properties of the EPDM hose used in the tests.

PL

Celem przeprowadzonych badan była eksperymentalna analiza możliwości zastosowania węza gumowego umieszczonego wewnątrz rurociągu do łagodzenia zjawiska uderzenia hydraulicznego. Pomiary przeprowadzono wykorzystując stalowy rurociąg o średnicy wewnętrznej 53 mm i długości 48.5 m oraz wąż gumowy EPDM o średnicy 6 mm ułożony na całej długości rurociągu. Uderzenia hydrauliczne inicjowane były poprzez gwałtowne i całkowite zamknięcie zaworu znajdującego się na końcu układu. W celu przeanalizowania wpływu parametrów przepływów panujących w rurociągu w ruchu ustalonym na maksymalne przyrosty ciśnienia, pomiary przeprowadzono dla różnych wartości początkowego ciśnienia i natężenia przepływu. Wyniki eksperymentów wskazują, że umieszczenie węza gumowego w obszarze nieustalonego przepływu cieczy może skutecznie tłumic oscylacje ciśnienia podczas prostego, dodatniego uderzenia hydraulicznego. Zaobserwowano, że ciśnienie początkowe ma istotny wpływ na zdolność węza gumowego do tłumienia fal ciśnienia. Celem przeprowadzonych obliczeń numerycznych było sprawdzenie przydatności najczęściej wykorzystywanego w praktyce modelu tarcia nieustalonego (tzw. IAB Brunone–Vitkovský model) do symulowania analizowanego zjawiska. Wykazano, że podejście to nie pozwala na zadowalające odtworzenie obserwowanych oscylacji ciśnienia ze względu na lepkosprężyste właściwości użytego w badaniach węza EPDM.

2

Hydraulic transients analysis in pipe networks by the method of characteristics (MOC)

Wichowski R.

Archives of Hydro-Engineering and Environmental Mechanics

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2006

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Vol. 53, nr 3

267-291

EN

The paper presents results of an experimental and theoretical study of the hydraulic transients in straight pipes and numerical simulations of unsteady flow in pipe networks. A mathematical model consists of a set of partial differential equations of hyperbolic type, which have been transformed by the method of characteristics into ordinary differential equations which are solved by the predictor-corrector method. Experimental tests have been performed, in order to examine the hydraulic transients phenomenon, in a single straight steel pipe. The experiments were carried out in the hydraulic laboratory of the Institute of Water Supply and Water Engineering, Environmental Engineering Faculty, Warsaw University of Technology. The numerical results show that the presented one dimensional model for a single pipe correctly describes the phenomenon since there is a good agreement with experimental maximum and minimum oscillations. In the paper, selected exemplary equations in a difference form for the pipe networks are also presented. One calculation example is given relating to the complex water-pipe network consisting of 17 loops, 48 pipelines and 33 nodes, supplied by two independent sources. Water-hammer throughout the whole pipeline network was caused by closing the gate valve at mid-point of one selected pipe. The results of the numerical calculations are presented in graphic form with respect to the final cross-sections of pipes.

3

Badania wpływu powietrznika na uderzenie hydrauliczne w układzie pompowym.

Adamkowski A.

Zagadnienia Eksploatacji Maszyn

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2004

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Vol. 39, nr 2

145-165

PL

Na specjalnie zbudowanym stanowisku pompowym w laboratorium Instytutu Maszyn Przepływowych PAN (IMP PAN) w Gdańsku zbadano wpływ zbiornika wodno-powietrznego (powietrznika) na przebieg uderzenia hydraulicznego. Zmiany ciśnienia w rurociągu tłocznym pomierzone przy zastosowaniu tego urządzenia skonfrontowano z przebiegami występującymi przy jego braku. Pokazano dużą skuteczność ograniczania i tłumienia fali ciśnienia w rurociągu za pomocą powietrznika. Wyniki przeprowadzonych badań doświadczalnych wykorzystano do weryfikacji metody obliczeniowej, opracowanej w IMP PAN w postaci programu komuterowego HYDTRA (HYDraulic TRAnsients) służącego do przewidywania przebiegu stanów przejściowych w układach rurociągowych. Uzyskano dobrą zgodność przewidywań numerycznych z doświadczeniem. Stwierdzone różnice między obliczonymi i pomierzonymi maksymalnymi przyrostami ciśnienia uderzenia hydraulicznego nie przekraczają kilku procent. Rezultat ten wskazuje na możliwości wykorzystywania metody obliczeniowej do projektowania układów rurociągowych z zastosowaniem zbiorników wodno-powietrznych w celu ograniczania niekorzystnych skutków uderzenia hydraulicznego.

EN

Application of air chambers in hydraulic pipeline systems is one of the main technique of waterhammer (pressure surges) suppression. The main purpose of the undertaken study was to verify experimentally the author's computational method allowing prediction of hydraulic transients in piping systems and to use this method for analyzing effectiveness of waterhammer suppression by means of the technique under consideration. The computational method has been developed in the form of the HYDTRA '2000 computer code (HYDraulic TRAnsients, version 2000). Its theoretical basis were the equations describing the unsteady liquid flow in pipelines considered as elements with distributed parameters. The method of characteristics was used for solving these equations. Experiments were carried out in a pumping system installed in the laboratory of the Institute of Fluid-Flow Machinery of the Polish Academy of Sciences in Gdańsk. They covered examination of the effect of stopping the liquid flow by means of cut-off valve on pressure surges in the pump delivery pipe in cases with and without an air chamber. The results of numerical calculations of pressure surges in the pump delivery pipe have been compared with measurements. A satisfactory coincidence between numerical prediction and measurement was found, justifying thus application of the computational method, for instance in design of pipeline systems with air chambers in order to reduce unfavourable waterhammer effects. The consistency depends on the values of exponent kappa of the polytropic air compression/decompression (expansion and contraction) law. The best agreement was achieved for kappa=1.2, slightly poorer agreement is observed for kappa=1.41. These results can indicate corectness of the recommendation to use the average value of kappa=1.2 for most cases under consideration. However, this recommendation cannot be considered as a generally accepted one. For small air vessels and rapid transients, when air expansion/contraction proceeds in almost total agreement with the adiabatic law, it could be recommended to assume kappa near 1.4, however for large air volumes and slow transients - kappa close to 1.0 should be adopted (because of almost isothermal character of the air compression/decompression processes). More exact and evident criterions in this matter should be a task of future studies. In numerous analyses presented in the literature head losses in the connection of the air chamber with the flow system, and so, inertia of liquid in the connection are not taken into account. Based on calculations of one of the experimentally tested cases it has been proved that disregarding these quantities significantly deteriorates reliability of numerical predictions. The developed computational method has been also applied in order to show additional possibilities of pressure surge supression by air chambers. One of these possibilities is developing differential (diverse) local head losses at liquid inflow and outflow from the air chamber. It has been indicated that the previously recommended value 2.5 of the ratio between head losses during filling and during emptying is substantially lower than the optimum one.

4

Strength analysis of penstock bifurcations in hydropower plants

Adamkowski A., Kwapisz L.

Transactions of the Institute of Fluid-Flow Machinery

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2004

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nr 115

113-124

EN

The strength analysis of penstock bifurcation in hydropower plants is discussed in the present paper. The analysis consists of determining the maximal internal pressure, (e.g. during turbine load rejection), stress analysis of the pipeline shell for assumed loading and assumed or determined material properties. The investigation results can be helpful when determining the proper rate of the flow cut-off and recommending the strengthening precautions to be applied in places of maximum stress concentration in order to prevent future penstock ruptures.