scholarly journals Investigation of Water Injection Influence on Cloud Cavitating Vortical Flow for a NACA66 (MOD) Hydrofoil

Energies ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5973
Author(s):  
Zhijian Li ◽  
Wei Wang ◽  
Xiang Ji ◽  
Xiaofang Wang
Keyword(s):  
Flow Field ◽  
Transient Flow ◽  
Water Injection ◽  
Flow Characteristics ◽  
Vortex Structures ◽  
Vortical Flow ◽  
Distribution Area ◽  
Suction Surface ◽  
Cloud Cavitation ◽  
Wall Flow

Re-entrant jet causes cloud cavitation shedding, and cavitating vortical flow results in flow field instability. In the present work, a method of water injection is proposed to hinder re-entrant jet and suppress vortex in cloud cavitating flow of a NACA66 (MOD) hydrofoil (Re = 5.1 × 105, σ = 0.83). A combination of filter-based density corrected turbulence model (FBDCM) with the Zwart–Gerber–Belamri cavitation model (ZGB) is adopted to obtain the transient flow characteristics while vortex structures are identified by Q criterion & λ2 criterion. Results demonstrate that the injected water flow reduces the range of the low-pressure zone below 1940 Pa on the suction surface by 54.76%. Vortex structures are observed both inside the attached and shedding cavitation, and the water injection shrinks the vortex region. The water injection successfully blocks the re-entrant jet by generating a favorable pressure gradient (FPG) and effectively weakens the re-entrant jet intensity by 46.98%. The water injection shrinks the vortex distribution area near the hydrofoil suction surface, which makes the flow in the boundary layer more stable. From an energy transfer perspective, the water injection supplies energy to the near-wall flow, and hence keeps the steadiness of the flow field.

Numerical study of the impact of water injection holes arrangement on cavitation flow control

2019 ◽  
Vol 103 (1) ◽  
pp. 003685041987774 ◽  
Author(s):  
Wei Wang ◽  
Qingdian Zhang ◽  
Tao Tang ◽  
Shengpeng Lu ◽  
Qi Yi ◽  
...  
Keyword(s):  
Flow Field ◽  
Numerical Study ◽  
Water Injection ◽  
Three Dimensional ◽  
Hydrodynamic Performance ◽  
Cavitation Flow ◽  
Suction Surface ◽  
Double Row ◽  
Suppression Effect ◽  
The Impact

A method of water injection to flow field using distributed holes on the suction surface of hydrofoil is presented in this article to control cavitation flow. Modified renormalization group k–ε turbulence model is coupled with full-cavitation model to calculate periodical cavitation patterns and the dynamic characteristics of the NACA66(MOD) hydrofoil. Water injection is found to be highly effective for cavitation suppression. The cavitation suppression effect of distributed regulation of jet holes and porosities along three-dimensional spanwise hydrofoil is also investigated. The appropriate porosities of single row spanwise jet holes and optimal jet position of double row jet holes are revealed for both cavitation suppression and good hydrodynamic performance. Double row jet holes setting in forward trapezoidal arrangement shows great potential for cavitation suppression and hydrodynamic performance. This research provides a method of water injection to flow field to actively control cavitation, which will facilitate development of engineering designs.

Francis-Type Reversible Turbine Field Investigation During Fast Closure of Wicket Gates

2018 ◽  
Vol 140 (6) ◽  
Author(s):  
Mao Xiuli ◽  
Pavesi Giorgio ◽  
Zheng Yuan
Keyword(s):  
Flow Field ◽  
Flow Pattern ◽  
Transient Flow ◽  
Flow Characteristics ◽  
Flow Simulation ◽  
Field Investigation ◽  
Electricity Demand ◽  
Field Analysis ◽  
Detached Eddy Simulation ◽  
Time Frequency

Flexible electricity demand and variability of the electricity produced by wind turbines and photovoltaic affect the stable operations of power grids. Pump-turbines are used to stabilize the power grid by maintaining a real-time electricity demand. Consistently, the machines experience transient conditions during the course of operation, such as start-up, load acceptance, load rejection, and shutdown, which induce high amplitude pressure pulsations and affect operating lifespan of the components. During the closure of the wicket gates, the transient flow characteristics is analyzed for a Francis-type reversible pump-turbine in generating mode by three-dimensional (3D) numerical simulation with a moving mesh technique and using detached eddy simulation (DES) turbulent model. Mesh motion is carried out in the region of wicket gates during the load rejection by a moving, sliding mesh, which makes dynamic flow simulation available, instead of building various steady models with different guide vanes angles. The transient flow characteristics are illustrated by analyzing the flow, torque, and pressure fluctuations signals by frequency and time–frequency analyses. The flow field analysis includes the onset and strengthening of unsteady phenomena during the turbine load reduction. The flow pattern in return channel maintained a quite stable flow field, whereas the flow pattern in the runner and draft tube emphasized its instability with the flow rate decreased. Influence of 3D unsteady flow structures on runner is determined, and its evolution is characterized spectrally during fast closure of wicket gates.

Analysis of Vortical Flow Field in a Propeller Fan by LDV Measurements and LES—Part I: Three-Dimensional Vortical Flow Structures

2001 ◽  
Vol 123 (4) ◽  
pp. 748-754 ◽  
Author(s):  
Choon-Man Jang ◽  
Masato Furukawa ◽  
Masahiro Inoue
Keyword(s):  
Flow Field ◽  
Three Dimensional ◽  
Leading Edge ◽  
Tip Vortex ◽  
Vortical Flow ◽  
Axial Fan ◽  
Suction Surface ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Edge Separation

Three-dimensional structures of the vortical flow field in a propeller fan with a shroud covering only the rear region of its rotor tip have been investigated by experimental analysis using laser Doppler velocimetry (LDV) measurements and by numerical analysis using a large eddy simulation (LES) in Part I of the present study. The propeller fan has a very complicated vortical flow field near the rotor tip compared with axial fan and compressor rotors. It is found that three vortex structures are formed near the rotor tip: the tip vortex, the leading edge separation vortex, and the tip leakage vortex. The tip vortex is so strong that it dominates the flow field near the tip. Its formation starts from the blade tip suction side near the midchord. Even at the design condition the tip vortex convects nearly in the tangential direction, thus impinging on the pressure surface of the adjacent blade. The leading edge separation vortex develops close along the tip suction surface and disappears in the rear region of the rotor passage. The tip leakage vortex is so weak that it does not affect the flow field in the rotor.

Numerical simulation of transient flow field in a mixed-flow pump during starting period

2018 ◽  
Vol 28 (4) ◽  
pp. 927-942 ◽  
Author(s):  
Wei Li ◽  
Yang Zhang ◽  
Weidong Shi ◽  
Leilei Ji ◽  
Yongfei Yang ◽  
...  
Keyword(s):  
Flow Field ◽  
Transient Flow ◽  
Rotation Speed ◽  
Flow Characteristics ◽  
Mixed Flow ◽  
Content Type ◽  
Start Up ◽  
Study Results ◽  
Flow Pump ◽  
Stable Stage

Purpose This paper aims to study the transient flow characteristics in a mixed-flow pump during the start-up period. Design/methodology/approach In this study, numerical calculation of the internal flow field in a mixed-flow pump using the sliding mesh method was carried out. The regulation of the pressure, streamline and the relative speed during the start-up period was analyzed. Findings The trend of the simulated head is consistent with the experimental results, and the calculated head is around 0.3 m higher than the experimental head when the rotation speed reached the stable stage, indicating that the numerical method for the start-up process simulation of the mixed-flow pump has a high accuracy. At the beginning, the velocity inside the impeller changes little along the radius direction and the flow rate increases slowly during the start-up process. As the rotation speed reached the stable stage, the flow inside the impeller became steady, the vortex reduced and transient effects disappeared gradually. Originality/value The study results have significant value for revealing the internal unsteady flow characteristics of the mixed-flow pump and providing the reference for the design optimization of the mixed-flow pump.

Evaluation of subway passengers transfer hub congestion based on queuing model and TOPSIS method

2021 ◽  
pp. 1-22
Author(s):  
Xiaokun Wang ◽  
Dong Ni
Keyword(s):  
Queuing Theory ◽  
Evaluation Model ◽  
Flow Characteristics ◽  
Distribution Area ◽  
Flow Density ◽  
Topsis Method ◽  
Queuing Model ◽  
Service Facility ◽  
Passenger Flow ◽  
Topsis Technique

To scientifically and reasonably evaluate and pre-warn the congestion degree of subway transfer hub, and effectively know the risk of subway passengers before the congestion time coming. We analyzed the passenger flow characteristics of various service facilities in the hub. The congested area of the subway passenger flow interchange hub is divided into queuing area and distribution area. The queuing area congestion evaluation model selects M/M/C and M/G/C based on queuing theory. The queuing model and the congestion evaluation model of the distribution area select the TOPSIS (Technique for Order Preference by Similarity to Ideal Solution) method. Queue length and waiting time are selected as the evaluation indicators of congestion in the queuing area, and passenger flow, passenger flow density and walking speed are selected as the evaluation indicators of congestion in the distribution area. And then, K-means cluster analysis method is used to analyze the sample data, and based on the selected evaluation indicators and the evaluation model establishes the queuing model of the queuing area and the TOPSIS model of the collection and distribution area. The standard value of the congestion level of various service facilities and the congestion level value of each service facility obtained from the evaluation are used as input to comprehensively evaluate the overall congestion degree of the subway interchange hub. Finally we take the Xi’an Road subway interchange hub in Dalian as empirical research, the data needed for congestion evaluation was obtained through field observations and questionnaires, and the congestion degree of the queue area and the distribution area at different times of the workday was evaluated, and the congestion of each service facility was evaluated. The grade value is used as input, and the TOPSIS method is used to evaluate the degree of congestion in the subway interchange hub, which is consistent with the results of passenger congestion in the questionnaire, which verifies the feasibility of the evaluation model and method.

Effects of Flue Gas Inlet Structure on the Flow Field Characteristics of Multi-Stage Liquid Column Scrubber

2013 ◽  
Vol 773 ◽  
pp. 749-754
Author(s):  
Zhen Ya Duan ◽  
Fu Lin Zheng ◽  
Hui Ling Shi ◽  
Jun Mei Zhang
Keyword(s):  
Flow Field ◽  
Flue Gas ◽  
Static Pressure ◽  
Liquid Column ◽  
Liquid Distribution ◽  
Multi Stage ◽  
Flow Field Characteristics ◽  
Wall Flow ◽  
Two Peaks ◽  
Saddle Shape

In this paper, the numerical model of multi-stage liquid column scrubber was established. The flow field of liquid column scrubber with different inlet structure was respectively simulated by a commercial CFD code, Fluent. Considering the distribution characteristics of static pressure and velocity in the scrubber, this inlet type, single horizontal gas inlet with a notch at the bottom, is regarded as the most reasonable structure. On one hand, that structure has uniform distribution of static pressure. On the other hand, the velocity profile of its field presents saddle shape, i.e. the low central velocity exists between two peaks, which could contribute to weakening wall-flow phenomenon and obtaining uniform gas-liquid distribution.

A new dynamic mesh algorithm for studying the 3D transient flow field of tilting pad journal bearings

2016 ◽  
Vol 230 (12) ◽  
pp. 1470-1482 ◽  
Author(s):  
Mengxuan Li ◽  
Chaohua Gu ◽  
Xiaohong Pan ◽  
Shuiying Zheng ◽  
Qiang Li
Keyword(s):  
Flow Field ◽  
Equilibrium Position ◽  
Transient Flow ◽  
Journal Bearings ◽  
Dynamic Mesh ◽  
Static Equilibrium ◽  
Time Step ◽  
Tilting Pad ◽  
Grid Nodes ◽  
Tilting Pad Journal Bearings

A new dynamic mesh algorithm is developed in this paper to realize the three-dimensional (3D) computational fluid dynamics (CFD) method for studying the small clearance transient flow field of tilting pad journal bearings (TPJBs). It is based on a structured grid, ensuring that the total number and the topology relationship of the grid nodes remain unchanged during the dynamic mesh updating process. The displacements of the grid nodes can be precisely recalculated at every time step. The updated mesh maintains high quality and is suitable for transient calculation of large journal displacement in FLUENT. The calculation results, such as the static equilibrium position and the dynamic characteristic coefficients, are consistent with the two-dimensional (2D) solution of the Reynolds equation. Furthermore, in the process of transient analysis, under conditions in which the journal is away from the static equilibrium position, evident differences appear between linearized and transient oil film forces, indicating that the nonlinear transient calculation is more suitable for studying the rotor-bearing system.

Thermo-flow characteristics and air flow field leading of the air-cooled condenser cell in a power plant

2011 ◽  
Vol 54 (9) ◽  
pp. 2475-2482 ◽  
Author(s):  
WanXi Zhang ◽  
LiJun Yang ◽  
XiaoZe Du ◽  
YongPing Yang
Keyword(s):  
Power Plant ◽  
Flow Field ◽  
Air Flow ◽  
Flow Characteristics

scholarly journals Study on the 3D Hydrodynamic Characteristics and Velocity Uniformity of a Gravity Flow Circular Flume

Water ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 927
Author(s):  
Yi Zhang ◽  
Longxi Han ◽  
Lina Chen ◽  
Chenfang Wang ◽  
Bo Chen ◽  
...  
Keyword(s):  
Flow Field ◽  
Environmental Science ◽  
Structural Characteristics ◽  
Longitudinal Velocity ◽  
Flow Characteristics ◽  
Science Research ◽  
Hydrodynamic Characteristics ◽  
Straight Channel ◽  
Uniformity Coefficient ◽  
Annular Flume

Flumes have been widely used in water conservancy science and environmental science research. It is of great significance to obtain the hydrodynamic characteristics and flow field uniformity in the flume. In this study, a new type of annular flume was taken as an example. The 3D flow field was simulated by using a commercial computational fluid dynamics (CFD) code, and was also measured by acoustic doppler velocimeter (ADV) to verify the simulation results. The average relative error range was between 8.37% and 9.95%, the simulated results basically reflected the actual situation of the flow field. On this basis, the structural characteristics of flow field were analyzed. A new calculation method of flow velocity uniformity was presented according to the flow characteristics of natural open channels. The velocity uniformity in the straight channel was calculated and analyzed based on this method, and the influence of speed on the velocity uniformity was further discussed. The length of uniform section was negatively correlated with the rotational speed (average velocity), which was between 39 cm and 101 cm in the straight, and the uniformity coefficient was less than 10%. Finally, the water flow characteristics in the straight channel without wheel were compared with the natural open channel flow. The longitudinal velocity was well fitted with the Prandtl logarithmic distribution formula (R2 > 0.977), and the application feasibility of the flume was analyzed. This study can provide technical support for the development and application of annular flume.

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