scholarly journals Unsteady Flow Characteristics of Rotating Stall and Surging in a Backward Centrifugal Fan at Low Flow-Rate Conditions

Processes ◽  
2020 ◽  
Vol 8 (7) ◽  
pp. 872 ◽  
Author(s):  
Biao Zhou ◽  
Ximing He ◽  
Hui Yang ◽  
Zuchao Zhu ◽  
Yikun Wei ◽  
...  
Keyword(s):  
Unsteady Flow ◽  
Flow Rate ◽  
Flow Characteristics ◽  
Internal Flow ◽  
Rotating Stall ◽  
Low Flow ◽  
Small Scale ◽  
Centrifugal Fan ◽  
Unsteady Characteristics ◽  
Low Flow Rate

The steady and unsteady flow characteristics of internal flow in a backward centrifugal fan of double inlet at low flow-rate condition are investigated by computational fluid dynamics in this paper. The investigation aims to reveal insights into generation mechanisms and our physical understanding of the rotating stall and surge. The numerical results mainly demonstrate that, with decreasing flow rate, a large number of vortex flows almost increasingly occupy the internal flow of the impeller. The reverse flow and separation vortices increasingly appear near the outlet of volute, and the internal flow of the impeller is completely blocked by the separated vortex flow at low flow-rate conditions. Results indicate that, due to a synchronization of the impeller rotation and separation vortex, these separated vortices act intensely on the pressure surface of the blade with time evolution, and the interaction between the separated vortices and surface of blade increasingly yields small-scale eddies. It is further found that the amplitude of pressure and velocity fluctuations gradually increase with the decrease of flow rate in a certain range. The unsteady characteristics acting on the volute tongue gradually increase in a range of Qd to 0.3 Qd (Qd is the design volume flow rate) with the decrease of flow rate, and the unsteady characteristics acting on the volute tongue are weakened at the working condition of 0.15 Qd. These insights clearly explain the unsteady nature of the rotating stall and surge phenomenon in the double inlet backward centrifugal fan.

scholarly journals Unsteady Characteristics of Forward Multi-Wing Centrifugal Fan at Low Flow Rate

Processes ◽  
2019 ◽  
Vol 7 (10) ◽  
pp. 691 ◽  
Author(s):  
Lun ◽  
Ye ◽  
Lin ◽  
Ying ◽  
Wei
Keyword(s):  
Unsteady Flow ◽  
Flow Rate ◽  
Flow Characteristics ◽  
Internal Flow ◽  
Boundary Layer Separation ◽  
Low Flow ◽  
Centrifugal Fan ◽  
Suction Surface ◽  
Cfd Method ◽  
Low Flow Rate

The unsteady flow characteristics of a forward multi-wing centrifugal fan under a low flow rate are studied using the computational fluid dynamics (CFD) method. This paper emphasizes the eddy current distribution in terms of the Q criterion method, as well as pressure fluctuation, frequency spectrum, and kinetic energy spectrum analysis of internal monitoring points in a forward multi-wing centrifugal fan. The numerical results show that abnormal eddies mainly appear at the volute outlet and near the volute tongue, boundary layer separation occurs near the suction surface of the blade, and shedding eddies appear at the trailing edge of the blade with the time evolution. The unsteady flow characteristics of a forward multi-wing centrifugal fan at a small flow rate provide significant physical insight into understanding the internal flow law.

Inter-Blade Vortex Characteristics With the Blockage Effects of Runner Blade in a Francis Hydro Turbine Model

2019 ◽  
Author(s):  
Seung-Jun Kim ◽  
Jin-Hyuk Kim ◽  
Young-Seok Choi ◽  
Yong Cho ◽  
Jong-Woong Choi
Keyword(s):  
Flow Rate ◽  
Flow Characteristics ◽  
Internal Flow ◽  
Operating Conditions ◽  
Low Flow ◽  
Hydro Turbine ◽  
Runner Blade ◽  
Performance Reduction ◽  
Turbine Model ◽  
Low Flow Rate

Abstract This study presents the numerical analysis on the inter-blade vortex characteristics along with the blockage effects of runner blade in a Francis hydro turbine model with various flow rate conditions. The turbine model showed different flow characteristics in the runner blade passages according to operating conditions, and inter-blade vortex was observed at lower flow rate conditions. This inter-blade vortex can lead to performance reduction, vibration, and instability for smooth operation of turbine systems. The previous study on blockage effects on various runner blade thickness, showed its influence on hydraulic performance and internal flow characteristics at low flow rate conditions. Therefore, the inter-blade vortex characteristics can be altered with the blockage effects at low flow rate conditions in a Francis hydro-turbine. For investigating the internal flow and unsteady pressure characteristics, three-dimensional steady and unsteady Reynolds-averaged Navier-Stokes calculations are performed. These inter-blade vortices were captured at the leading and trailing edges close to the runner hub. These vortex regions showed flow separation and stagnation flow while blockage effects contributed for decreasing the inter-blade vortex at low flow rate conditions.

scholarly journals Investigation of unsteady flow in a centrifugal pump at low flow rate

2016 ◽  
Vol 8 (12) ◽  
pp. 168781401668215 ◽  
Author(s):  
Yi Li ◽  
Xiaojun Li ◽  
Zuchao Zhu ◽  
Fengqin Li
Keyword(s):  
Unsteady Flow ◽  
Centrifugal Pump ◽  
Flow Rate ◽  
Internal Flow ◽  
Low Flow ◽  
Experimental Result ◽  
Vortical Structures ◽  
Visualization Experiment ◽  
Rate Ratios ◽  
Low Flow Rate

Due to the characteristics of unsteady flow in the centrifugal pump at low flow rate is not revealed well, a simulation of the internal flow at different flow rates is carried out with renormalization group k–ε turbulence model and multiple reference frame. For analyzing the influence of flow rate, ratios of flow rate ( Q/ Qd) are set to 0.1, 0.3, 0.6, and 1.0 at this study. The hydraulic performance of the centrifugal pump obtained by numerical calculation has matched well with the corresponding experimental result. From the characteristics of the internal flow captured by the numerical simulation, it can be seen that backflow occurs in the inlet of impeller at low flow rate, which prevents fluid discharging into impeller passages and leads to vortical structures in suction region. With further decrease in flow rate, the strength of backflow has been intensified, and the number of vortex has significantly increased. A visualization experiment of the backflow evolution in suction pipe is carried out to validate the unsteady simulated results. Results show that the prerotation is an important factor for the deterioration of centrifugal pump performance.

scholarly journals Effect of Fins on the Internal Flow Characteristics in the Draft Tube of a Francis Turbine Model

Energies ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 2806 ◽  
Author(s):  
Seung-Jun Kim ◽  
Young-Seok Choi ◽  
Yong Cho ◽  
Jong-Woong Choi ◽  
Jung-Jae Hyun ◽  
...  
Keyword(s):  
Flow Rate ◽  
Draft Tube ◽  
Pressure Fluctuations ◽  
Flow Characteristics ◽  
Internal Flow ◽  
Low Flow ◽  
Francis Turbine ◽  
Vortex Rope ◽  
Turbine Model ◽  
Low Flow Rate

Undesirable flow phenomena in Francis turbines are caused by pressure fluctuations induced under conditions of low flow rate; the resulting vortex ropes with precession in the draft tube (DT) can degrade performance and increase the instability of turbine operations. To suppress these DT flow instabilities, flow deflectors, grooves, or other structures are often added to the DT into which air or water is injected. This preliminary study investigates the effects of anti-cavity fins on the suppression of vortex ropes in DTs without air injection. Unsteady-state Reynolds-averaged Navier–Stokes analyses were conducted using a scale-adaptive simulation shear stress transport turbulence model to observe the unsteady internal flow and pressure characteristics by applying anti-cavity fins in the DT of a Francis turbine model. A vortex rope with precession was observed in the DT under conditions of low flow rate, and the anti-cavity fins were confirmed to affect the mitigation of the vortex rope. Moreover, at the low flow rate conditions under which the vortex rope developed, the application of anti-cavity fins was confirmed to reduce the maximum unsteady pressure.

scholarly journals Effect of Air Injection on the Internal Flow Characteristics in the Draft Tube of a Francis Turbine Model

Processes ◽  
2021 ◽  
Vol 9 (7) ◽  
pp. 1182
Author(s):  
Seung-Jun Kim ◽  
Yong Cho ◽  
Jin-Hyuk Kim
Keyword(s):  
Flow Rate ◽  
Draft Tube ◽  
Pressure Fluctuations ◽  
Flow Characteristics ◽  
Internal Flow ◽  
Air Injection ◽  
Low Flow ◽  
Francis Turbine ◽  
Navier Stokes ◽  
Vortex Rope

Under low flow-rate conditions, a Francis turbine exhibits precession of a vortex rope with pressure fluctuations in the draft tube. These undesirable flow phenomena can lead to deterioration of the turbine performance as manifested by torque and power output fluctuations. In order to suppress the rope with precession and a swirl component in the tube, the use of anti-swirl fins was investigated in a previous study. However, vortex rope generation still occurred near the cone of the tube. In this study, unsteady-state Reynolds-averaged Navier–Stokes analyses were conducted with a scale-adaptive simulation shear stress transport turbulence model. This model was used to observe the effects of the injection in the draft tube on the unsteady internal flow and pressure phenomena considering both active and passive suppression methods. The air injection affected the generation and suppression of the vortex rope and swirl component depending on the flow rate of the air. In addition, an injection level of 0.5%Q led to a reduction in the maximum unsteady pressure characteristics.

304 3-D Simulation of internal flow in Screw-Type Centrifugal Pump at Low Flow Rate

2000 ◽  
Vol 005.2 (0) ◽  
pp. 75-76
Author(s):  
Yasushi TATEBAYASHI ◽  
Kazuhiro TANAKA ◽  
Masamichi IINO
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Internal Flow ◽  
Low Flow ◽  
Low Flow Rate

Numerical Investigation of the Influence of Impeller-Diffuser Gap (A- and B-Gaps) on Unsteady Flow in a Centrifugal Pump at Part Flows

2019 ◽  
Author(s):  
Taiki Takamine ◽  
Satoshi Watanabe
Keyword(s):  
Unsteady Flow ◽  
Centrifugal Pump ◽  
Flow Rate ◽  
Internal Flow ◽  
Leading Edge ◽  
High Energy ◽  
Rotating Stall ◽  
Rotor System ◽  
The Other ◽  
High Energy Density

Abstract Because of the high energy density of multi-stage centrifugal pump, it is really important to ensure the reliability of the pumps thus the stability of rotor system in the wide flow rate range. Rotating stall is a well-known unsteady flow phenomenon in which one or several stall cell structures propagate circumferentially in impeller and/or diffuser. Rotating stall alters the peripheral pressure distribution of rotors, and therefore it is often regarded as one of the primary trigger of unstable fluid force acting on the rotor system. One possible factor which could affect the rotating stall is a geometrical relationship between the rotor and the stator. In the present study, unsteady RANS simulations of internal flow in a centrifugal pump are carried out. The pump is the partial model of the final stage of the three-stage centrifugal pump used in our previous study. In order to investigate the effect of the gap between impeller trailing edge and diffuser leading edge on the unsteady flow of the pump, three cases of impeller-diffuser gap is simulated; one is the smaller gap case with original impeller. The other cases are two larger gap cases with only cutting the impeller blades and with cutting the both impeller blades and impeller shroud walls. For all gap cases, the computations are conducted for the nominal flow rate and the low flor rate with 10% of the nominal flow rate. As a result, the rotating stall is observed only in the larger gap case with the cut shroud walls, indicating that the key phenomenon for the stable formation of the stall cell is not only the weakened rotor-stator interaction, but also the other phenomenon attributed to the enlarged gap between the impeller shroud walls and the diffuser walls. In the shroud cut case, a part of the main flow blocked by the stalled region and the secondary flow on the diffuser walls tend to flow into the side gaps more easily than other cases. They might be the important phenomenon associated with the diffuser rotating stall in the enlarged wall gap condition.

NUMERICAL INVESTIGATION OF PUMP-TURBINES WITH DIFFERENT BLADES AT PUMP CONDITIONS

2012 ◽  
Vol 11 (02) ◽  
pp. 143-150 ◽  
Author(s):  
WEI LI ◽  
ZHONGYONG PAN ◽  
WEIDONG SHI
Keyword(s):  
Flow Rate ◽  
Rotating Stall ◽  
Low Flow ◽  
Design Stage ◽  
Positive Slope ◽  
Back Flow ◽  
Unsteady Simulation ◽  
Steady Simulation ◽  
Flow Vortex ◽  
Low Flow Rate

The undesirable performance of a positive slope curve usually appears for pump-turbines running as pumps at a low flow rate. The inner flow feature of pump-turbines with 6- and 7-blades runner is studied by both steady and unsteady simulations at pump conditions. According to the steady simulation investigation, obviously back flow vortex is found in the runner passage at the low flow rate zone where the positive slope curve forms. The flow rate at which the instable flow pattern happens of 6-blades runner is smaller than that of 7-blades one. By the unsteady simulation, at the low flow rate zone similar to the steady calculations and the tested data, a rotating stall with four rotating cells can be viewed by significant dynamic post-processing, whose rotation speed is much slower than that of the runner. Therefore, the back flow vortex of steady simulation and rotating stall of unsteady simulation can be used to investigate the runner quality at design stage.

The Effects of Low Flow Rate Gas Involvement on Oil-Water Flow in Horizontal Pipes

2011 ◽  
Vol 354-355 ◽  
pp. 41-44
Author(s):  
Hai Qin Wang ◽  
Lei Zhang ◽  
Yong Wang ◽  
De Xuan Li
Keyword(s):  
Water Flow ◽  
Flow Rate ◽  
Flow Characteristics ◽  
Considerable Effect ◽  
Low Flow ◽  
Horizontal Pipes ◽  
Test Loop ◽  
Three Phase Flow ◽  
Oil Water ◽  
Low Flow Rate

The experiments were conducted in a horizontal multiphase flow test loop (50mm inner diameter, 40m long) to investigate the flow of oil/water and the influence of an involved gas phase with low flow rate in horizontal pipes, specifically including oil/water flow patterns, cross-section water holdup and pipe flow pressure gradient. The experimental results indicated that the involved gas with low flow rate had a considerable effect on oil/water flow characteristics, which shows the complexity of gas/oil/water three-phase flow. Thus, this effect could not be ignored in design and operation management of oil/gas gathering and transportation system.

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