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.

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.

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.

A Meanline Model for Impeller Flow Recirculation

2008 ◽  
Author(s):  
Xuwen Qiu ◽  
David Japikse ◽  
Mark Anderson
Keyword(s):  
Flow Rate ◽  
Recirculation Zone ◽  
Reverse Flow ◽  
Low Flow ◽  
Suction Surface ◽  
Blade Loading ◽  
Flow Recirculation ◽  
Impeller Outlet ◽  
Active Flow ◽  
Low Flow Rate

Flow recirculation at the impeller inlet and outlet is an important feature that affects impeller performance, especially the power consumption at a very low flow rate. Although the mechanisms for this flow phenomenon have been studied, a practical model is needed for meanline modeling of impeller off-design performance. In this paper, a meanline recirculation model is proposed. At the inlet, the recirculation zone acts as area blockage to relieve the large incidence of the active flow at a low flow rate. The size of the blockage is estimated through a critical area ratio of an artificial “inlet diffuser” from the inlet to throat. The intensity of the reverse flow can then be calculated by assuming a linear velocity profile of meridional velocity in the recirculation zone. At the impeller outlet, a recirculation zone near the suction surface is established to balance the velocity difference on the pressure and suction sides of the blade. The size and the intensity of the outlet recirculation zone is assumed related to blade loading, which can be evaluated based on flow turning and Coriolis force. A few validation cases are presented showing a good comparison between test data and prediction by the model.

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

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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