“…Aydin et al 5 discussed the velocity and pressure distributions inside the siphon using numerical calculation methods. Minato et al 2 used the volume-of-fluid (VOF) method to describe the flow pattern changes in the whole process of siphoning formation and verified the accuracy of the numerical model. Wang et al 3 analyzed the law of pressure change in the siphoning formation process by carrying out a numerical simulation of two-phase flow in a siphon outlet.…”
Section: Introductionmentioning
confidence: 95%
“…Many available experimental data have shown that the head and pressure during this period are much higher than those under the normal working conditions. 2,3 Both long siphoning time and high hydraulic loss can cause pump performance decrease, unit vibration, and other damages, which can further affect the station’s safety. Therefore, shape optimization for the siphon outlet, which minimizes the siphoning time and hydraulic loss, is of great significance to ensure safe and effective operation in the pumping station.Figure 1.Two stages in the siphoning formation process: (a) the purging stage and (b) the entraining stage.…”
The siphon outlet is widely used in pumping stations due to its reliable and convenient cut-off performance. Long siphoning time or high hydraulic loss caused by the inappropriate design of the siphon outlet can significantly affect the safety of stations. The air compressibility volume-of-fluid (VOF) method is conducted to simulate the two-phase flow in the siphoning formation process at the design points selected by the optimal Latin hypercube design (OLHD), the results of which show good agreement with the experimental data. In this work, the siphoning time and hydraulic loss coefficient are selected as the objective functions, and a multi-objective shape optimization strategy is proposed for the siphon outlet in conjunction with the response surface method (RSM). This optimization strategy can not only reconcile conflicting objective functions but also obtain the effect and interaction of design variables. Sensitivity analysis on the constructed response surface models indicates that among three design variables, the aspect ratio has the greatest effect on the objective functions, the descending angle has the second greatest effect, and the ascending angle has almost no effect. Compared with the original design, the hydraulic loss coefficient and siphoning time of the optimized design are reduced by 2.95% and 26.76%, respectively. A higher vorticity magnitude and more uniform outflow are created in the optimized design, which results in the improvement of hydraulic performance.
“…Aydin et al 5 discussed the velocity and pressure distributions inside the siphon using numerical calculation methods. Minato et al 2 used the volume-of-fluid (VOF) method to describe the flow pattern changes in the whole process of siphoning formation and verified the accuracy of the numerical model. Wang et al 3 analyzed the law of pressure change in the siphoning formation process by carrying out a numerical simulation of two-phase flow in a siphon outlet.…”
Section: Introductionmentioning
confidence: 95%
“…Many available experimental data have shown that the head and pressure during this period are much higher than those under the normal working conditions. 2,3 Both long siphoning time and high hydraulic loss can cause pump performance decrease, unit vibration, and other damages, which can further affect the station’s safety. Therefore, shape optimization for the siphon outlet, which minimizes the siphoning time and hydraulic loss, is of great significance to ensure safe and effective operation in the pumping station.Figure 1.Two stages in the siphoning formation process: (a) the purging stage and (b) the entraining stage.…”
The siphon outlet is widely used in pumping stations due to its reliable and convenient cut-off performance. Long siphoning time or high hydraulic loss caused by the inappropriate design of the siphon outlet can significantly affect the safety of stations. The air compressibility volume-of-fluid (VOF) method is conducted to simulate the two-phase flow in the siphoning formation process at the design points selected by the optimal Latin hypercube design (OLHD), the results of which show good agreement with the experimental data. In this work, the siphoning time and hydraulic loss coefficient are selected as the objective functions, and a multi-objective shape optimization strategy is proposed for the siphon outlet in conjunction with the response surface method (RSM). This optimization strategy can not only reconcile conflicting objective functions but also obtain the effect and interaction of design variables. Sensitivity analysis on the constructed response surface models indicates that among three design variables, the aspect ratio has the greatest effect on the objective functions, the descending angle has the second greatest effect, and the ascending angle has almost no effect. Compared with the original design, the hydraulic loss coefficient and siphoning time of the optimized design are reduced by 2.95% and 26.76%, respectively. A higher vorticity magnitude and more uniform outflow are created in the optimized design, which results in the improvement of hydraulic performance.
“…However, it has been recently suggested to explicitly couple interfacial scale averaging and interfacial scale resolving techniques in order to arrive at a more general two-phase flow model. It is attempted either to explicitly couple the two-fluid model (Ishii, 1990) with the Volume-of-Fluid (VoF) method (Harlow and Welch, 1965;Hirt and Nichols, 1981): (Cerne et al, 2000(Cerne et al, , 2001(Cerne et al, , 2002Cerne, 2001;Shimada, 2001a, 2001b;Tomiyama et al, 2001Tomiyama et al, , 2003Tomiyama et al, , 2004Tomiyama et al, , 2006Alajbegovic and Han, 2002;Yoshida et al, 2003Yoshida et al, , 2004Yoshida et al, , 2006Yoshida, 2007) or to partially mimic the VoF method within the two-fluid model framework (Minato et al, 2000(Minato et al, , 2004a(Minato et al, , 2004b(Minato et al, , 2006a(Minato et al, , 2006b(Minato et al, , 2008Nagayoshi et al, 2003;Morel, 2007;Strubelj, 2009;Strubelj et al, 2009). Tomiyama et al (2004) enable us to clearly recognize the issue around these approaches by introducing the dimensionless ratio d≡l char /Δx: if d*≫1, i.e.…”
This contribution outlines the coherent and mathematical rigorous derivation of a generalized multi-scale model framework that is based on the Eulerian-Eulerian two-uid methodology. By conditional volume-averaging (based on the immersed interface concept) and subsequent closure modeling, the two-phase ow features are rst divided into an unresolved portion (on average or sub-grid scale) and a resolved portion, and then interpreted on a physical basis leading to constitutive relations for closure. The resulting two-uid model framework HIRES-TFM (Hybrid Interface-Resolving Two-Fluid Model) exhibits the same basic structure as found for single-phase ow, which results in an inherently stable method and enables us to reuse numerical techniques that have been developed for single-phase problems. Moreover, the conceptual approach is both compatible to the Large Eddy Simulation (LES) framework for turbulence modeling, and is expandable to multi-scale ow scenarios, i.e. dispersed and segregated two-phase ows.
“…The vertical siphon axial flow pump unit with siphon outlet flow channel will undergo a series of exhaust processes during the start-up process. The internal flow field of the pump device is complex (Minato et al, 2006;Aydin et al, 2015), and the remarkable hydraulic transient phenomenon causes the pump device characteristic parameters to change violently. Before the air in the tube is completely discharged, the pump device is in the state of gas-liquid two-phase flow.…”
In order to explore the transient characteristics of the large-scale vertical siphon axial flow pumping station during the start-up and exhaust process, numerical simulations were carried out on the start-up process of the axial flow pumping station under the two starting modes of pre-opening the vacuum breaking valve and keeping the vacuum breaking valve closed. The calculation results show that during the start-up phase of the unit, the flow separation phenomenon of the impeller channel of the pump device with the vacuum breaking valve closed is serious, the large-scale vortex in the guide vane blocks the flow channel, and the instantaneous impact on the blade surface is strong. The flow field of the pump device with pre-open vacuum failure valve is obviously less affected by the instantaneous impact characteristics during the start-up of the pump. The range of high entropy production area in the impeller channel is reduced, the duration of high entropy production area is significantly shortened, and the instantaneous impact on the blade surface is weak. Under the two starting modes, the internal flow field of the pump device is similar in the evolutionary law. The unstable flow phenomenon of the pump device is most prominent in the weir flow stage. The maximum instantaneous impact on the blade surface also mainly occurs in the weir flow stage. A very small part of the remaining gas in the siphon formation stage is difficult to discharge and takes a long time. After the pump device is exhausted and enters a stable operation state, the external characteristic parameters are in good agreement with the test results. Compared with the starting method in which the vacuum breaking valve is kept closed, the method of pre-opening the vacuum breaking valve reduces the maximum starting head by 20% and the exhaust time by 43%. The pre-open vacuum breaking valve effectively avoids the system instability caused by the start-up and exhaust of the pump device.
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