scholarly journals Evolution of Hydrodynamic Characteristics with Scour Hole Developing around a Pile Group

Water ◽  
2018 ◽  
Vol 10 (11) ◽  
pp. 1632 ◽  
Author(s):  
Yilin Yang ◽  
Meilan Qi ◽  
Jinzhao Li ◽  
Xiaodong Ma
Keyword(s):  
Flow Field ◽  
Turbulence Intensity ◽  
Large Scale ◽  
Pile Group ◽  
Horseshoe Vortex ◽  
Hydrodynamic Characteristics ◽  
Small Scale ◽  
Scour Hole ◽  
Scour Holes ◽  
Scouring Process

This study concerns the evolution of flow field and hydrodynamic characteristics within the developing scour hole around a four-pile group with 2 × 2 arrangement. The instantaneous velocities in scour holes at four typical stages during the scouring process were measured by an acoustic Doppler velocimeter (ADV). The evolution and spatial distribution of the time-averaged flow field, turbulence, and the corresponding hydrodynamic characteristics within scour holes were compared. The time-averaged flow field shows that the reverse flow, downward flow, and horseshoe vortex are formed in the upstream of the pile group. During the scouring process, the mean components of flow characteristics (i.e., mean velocity, vorticity, and bed shear stress) around the pile group decrease while the fluctuating components (i.e., turbulence intensity) intensify simultaneously. Similarity of turbulence intensity profiles was found within different scour holes. The horseshoe vortex at upstream of each pile merges and the shear layer in the gap region extends when the dimension of the scour hole increases to that of equilibrium scour status, indicating that the four piles behave more like a single bluff body. With the development of scour holes, the large-scale horseshoe vortex system becomes more stable and the dissipation of small-scale eddies becomes more significant.

scholarly journals A Study on the Instantaneous Turbulent Flow Field in a 90-Degree Elbow Pipe with Circular Section

2016 ◽  
Vol 2016 ◽  
pp. 1-8 ◽  
Author(s):  
Shiming Wang ◽  
Cheng Ren ◽  
Yangfei Sun ◽  
Xingtuan Yang ◽  
Jiyuan Tu
Keyword(s):  
Flow Field ◽  
Turbulent Flow ◽  
Flow Separation ◽  
Large Scale ◽  
Small Scale ◽  
Eddy Simulation ◽  
Dean Vortex ◽  
Instantaneous Flow Field ◽  
Instantaneous Pressure ◽  
Turbulent Flow Field

Based on the special application of 90-degree elbow pipe in the HTR-PM, the large eddy simulation was selected to calculate the instantaneous flow field in the 90-degree elbow pipe combining with the experimental results. The characteristics of the instantaneous turbulent flow field under the influence of flow separation and secondary flow were studied by analyzing the instantaneous pressure information at specific monitoring points and the instantaneous velocity field on the cross section of the elbow. The pattern and the intensity of the Dean vortex and the small scale eddies change over time and induce the asymmetry of the flow field. The turbulent disturbance upstream and the flow separation near the intrados couple with the vortexes of various scales. Energy is transferred from large scale eddies to small scale eddies and dissipated by the viscous stress in the end.

scholarly journals A study of the flow-field evolution and mixing in a planar turbulent jet using direct numerical simulation

2002 ◽  
Vol 450 ◽  
pp. 377-407 ◽  
Author(s):  
S. A. STANLEY ◽  
S. SARKAR ◽  
J. P. MELLADO
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Direct Numerical Simulation ◽  
Large Scale ◽  
Computational Study ◽  
Practical Interest ◽  
Small Scale ◽  
Mixing Process ◽  
Mean Velocity ◽  
Small Scales

Turbulent plane jets are prototypical free shear flows of practical interest in propulsion, combustion and environmental flows. While considerable experimental research has been performed on planar jets, very few computational studies exist. To the authors' knowledge, this is the first computational study of spatially evolving three-dimensional planar turbulent jets utilizing direct numerical simulation. Jet growth rates as well as the mean velocity, mean scalar and Reynolds stress profiles compare well with experimental data. Coherency spectra, vorticity visualization and autospectra are obtained to identify inferred structures. The development of the initial shear layer instability, as well as the evolution into the jet column mode downstream is captured well.The large- and small-scale anisotropies in the jet are discussed in detail. It is shown that, while the large scales in the flow field adjust slowly to variations in the local mean velocity gradients, the small scales adjust rapidly. Near the centreline of the jet, the small scales of turbulence are more isotropic. The mixing process is studied through analysis of the probability density functions of a passive scalar. Immediately after the rollup of vortical structures in the shear layers, the mixing process is dominated by large-scale engulfing of fluid. However, small-scale mixing dominates further downstream in the turbulent core of the self-similar region of the jet and a change from non-marching to marching PDFs is observed. Near the jet edges, the effects of large-scale engulfing of coflow fluid continue to influence the PDFs and non-marching type behaviour is observed.

scholarly journals Temporal and Spatial Flow Variations over a Movable Scour Hole Downstream of a Grade-Control Structure with a PIV System

Water ◽  
2018 ◽  
Vol 10 (8) ◽  
pp. 1002 ◽  
Author(s):  
Shi-Yan Lu ◽  
Jau-Yau Lu ◽  
Dong-Sin Shih
Keyword(s):  
Turbulent Flow ◽  
Diffusion Region ◽  
Control Structures ◽  
Intensity Measurements ◽  
Scour Hole ◽  
Sophisticated Equipment ◽  
Grade Control ◽  
Scour Holes ◽  
Scouring Process ◽  
Temporal And Spatial

Weirs or grade-control structures (GCSs) are frequently adopted to protect bridges or control riverbed degradation. Scour holes may develop downstream of these hydraulic structures. Laboratory experiments have been performed in this study, using sophisticated equipment and newly developed procedures. The purpose was to investigate important characteristics of the turbulent flow in the movable scour hole. The results of these experiments demonstrated the significance of instantaneous shear stress in the scouring process. The measured Reynolds stress can be fitted with the theoretical equation reasonably well. Furthermore, the results revealed that the normalized mean vertical velocity profiles in the diffusion region of the scour hole can be fitted with a Gaussian curve. An analysis of the turbulence intensity measurements showed that the turbulent flow is anisotropic in the scour hole. The turbulence intensities also decreased with time as the scour hole gradually approached equilibrium.

Analysis of Crank Angle-Resolved Vortex Characteristics Under High Swirl Condition in a Spark-Ignition Direct-Injection Engine

2017 ◽  
Author(s):  
Fengnian Zhao ◽  
Penghui Ge ◽  
Hanyang Zhuang ◽  
David L. S. Hung
Keyword(s):  
Flow Field ◽  
Flow Structure ◽  
High Speed ◽  
Large Scale ◽  
Early Stage ◽  
Direct Injection ◽  
Spark Ignition ◽  
Small Scale ◽  
Vortex Center ◽  
Intake Stroke

In-cylinder air flow structure makes significant impacts on fuel spray dispersion, fuel mixture formation, and flame propagation in spark ignition direct injection (SIDI) engines. While flow vortices can be observed during the early stage of intake stroke, it is very difficult to clearly identify their transient characteristics because these vortices are of multiple length scales with very different swirl motion strength. In this study, a high-speed time-resolved 2D particle image velocimetry (PIV) is applied to record the flow structure of in-cylinder flow field along a swirl plane at 30 mm below the injector tip. First, a discretized method using flow field velocity vectors is presented to identify the location, strength, and rotating direction of vortices at different crank angles. The transients of vortex formation and dissipation processes are revealed by tracing the location and motion of the vortex center during the intake and compression strokes. In addition, an analysis method known as the wind-rose diagram, which is implemented for meteorological application, has been adopted to show the velocity direction distributions of 100 consecutive cycles. Results show that there exists more than one vortex center during early intake stroke and their fluctuations between each cycle can be clearly visualized. In summary, this approach provides an effective way to identify the vortex structure and to track the motion of vortex center for both large-scale and small-scale vortices.

scholarly journals Experimental Characterization of the Flow Field around Oblong Bridge Piers

Fluids ◽  
2021 ◽  
Vol 6 (11) ◽  
pp. 370
Author(s):  
Ana Margarida Bento ◽  
Teresa Viseu ◽  
João Pedro Pêgo ◽  
Lúcia Couto
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Bridge Pier ◽  
Bridge Piers ◽  
Shear Stresses ◽  
Velocity Measurements ◽  
Bridge Foundations ◽  
Scour Hole ◽  
Movable Bed

The prediction of scour evolution at bridge foundations is of utmost importance for engineering design and infrastructures’ safety. The complexity of the scouring inherent flow field is the result of separation and generation of multiple vortices and further magnified due to the dynamic interaction between the flow and the movable bed throughout the development of a scour hole. In experimental environments, the current approaches for scour characterization rely mainly on measurements of the evolution of movable beds rather than on flow field characterization. This paper investigates the turbulent flow field around oblong bridge pier models in a well-controlled laboratory environment, for understanding the mechanisms of flow responsible for current-induced scour. This study was based on an experimental campaign planned for velocity measurements of the flow around oblong bridge pier models, of different widths, carried out in a large-scale tilting flume. Measurements of stream-wise, cross-wise and vertical velocity distributions, as well as of the Reynolds shear stresses, were performed at both the flat and eroded bed stages of scouring development with a high-resolution acoustic velocimeter. The time-averaged values of velocity and shear stress are larger in the presence of a developed scour hole than in the corresponding flat bed configuration.

scholarly journals Numerical Simulation of Interaction between Large-Scale Congestion and Vent during the Natural Gas Explosion in a Kitchen

2021 ◽  
Vol 2021 ◽  
pp. 1-20
Author(s):  
Lei Pang ◽  
Mengjie Jin ◽  
Qianran Hu ◽  
Kai Yang
Keyword(s):  
Natural Gas ◽  
Flow Field ◽  
Flame Propagation ◽  
Combustion Rate ◽  
Large Scale ◽  
Small Scale ◽  
Propagation Mode ◽  
Gas Explosion ◽  
Flame Propagation Velocity ◽  
Explosion Process

The influence of large-scale congestion on a confined natural gas explosion in a typical Chinese kitchen was studied using the computational fluid dynamics technology. It was found that opening the explosion venting surface promotes the development of turbulence, flame propagation velocity, and multipeak overpressure in the explosion flow field. Large-scale congestion can significantly strengthen the influence of the explosion venting surface on the flow field; the congestion and the explosion venting surface have a synergistic effect on the explosion flow field. At the moment of gas explosion, the flow fields in each area of the kitchen exhibit different distribution characteristics. A flow field near small-scale congestion is more likely to produce greater turbulence, combustion rate, and flame speed. The obstruction effect of large-scale congestion perpendicular to the flame propagation direction is dominant. The indoor flame propagation speed and overpressure development speed increase and the peak combustion rate and indoor peak overpressure decrease with an increase in obstacle blockage. Increases in the large-scale volume congestion rate and volume blockage in the kitchen induce changes in the indoor flame propagation mode and increase the external explosion overpressure. This paper investigated the correlation behavior between large-scale congestion and vent surface in a typical Chinese civil kitchen during natural gas explosion process and provided important support for understanding the mechanism of congestion on gas explosion process and the distribution of explosion hazards in a kitchen.

scholarly journals Experimental and Numerical Investigations of Turbulent Open Channel Flow over a Rough Scour Hole Downstream of a Groundsill

Water ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 1488
Author(s):  
Cheng-Kai Chang ◽  
Jau-Yau Lu ◽  
Shi-Yan Lu ◽  
Zhong-Xiang Wang ◽  
Dong-Sin Shih
Keyword(s):  
Numerical Simulation ◽  
Reynolds Stress ◽  
Turbulence Intensity ◽  
Open Channel ◽  
Measured Data ◽  
Experimental Results ◽  
Attachment Point ◽  
Scour Hole ◽  
Scour Holes ◽  
Non Equilibrium

This study discusses the mechanism for the occurrence of equilibrium and non-equilibrium scour holes. By using a particle image velocimetry (PIV) measurement system, it measures the turbulent flow fields in an open channel moving through the rough bed below a groundsill. Then, the Reynolds-stress model (RSM), embedded in FLUENT software, is applied to perform a numerical simulation. The experimental results show that at equilibrium, the location of the re-attachment point is significantly affected by the flow discharge. Further, the re-attachment point of the scour hole affects the size and range of the counterflow zone, which becomes the main region for deposits in the natural channel. In addition, the formation of erosion is mainly affected by turbulence intensity and Reynolds stress. However, in non-equilibrium scour holes, our results clearly show that the turbulence intensity and the Reynolds stress are significantly larger at the end of the scour holes near the bed due to the continual development of the scouring. The correlation between the numerical simulation and experimental results are also examined. Overall, it can be seen that the simulated mean velocity profiles are quite consistent with the measured data. However, in terms of turbulence intensities and Reynolds stress, the simulated results could be overestimated when compared with the measured data; they are overestimated with a sudden decrease near the liquid surface. Although, the simulations in the near bed area show some divergence and the trend in the scour hole is quite consistent. Therefore, numerical simulations can be performed in advance to act as an important reference when evaluating the safety of downstream structures.

scholarly journals Vortex Evolution within Propeller Induced Scour Hole around a Vertical Quay Wall

Water ◽  
2019 ◽  
Vol 11 (8) ◽  
pp. 1538 ◽  
Author(s):  
Maoxing Wei ◽  
Nian-Sheng Cheng ◽  
Yee-Meng Chiew ◽  
Fengguang Yang
Keyword(s):  
Kinetic Energy ◽  
Flow Field ◽  
Critical Role ◽  
Turbulent Energy ◽  
Energy Spectra ◽  
Small Scale ◽  
Central Plane ◽  
Vortex System ◽  
Quay Wall ◽  
Scour Hole

This paper presents an experimental study on the characteristics of the propeller-induced flow field and its associated scour hole around a closed type quay (with a vertical quay wall). An “oblique particle image velocimetry” (OPIV) technique, which allows a concurrent measurement of the velocity field and scour profile, was employed in measuring the streamwise flow field (jet central plane) and the longitudinal centerline scour profile. The asymptotic scour profiles obtained in this study were compared with that induced by an unconfined propeller jet in the absence of any berthing structure, which demonstrates the critical role of the presence of the quay wall as an obstacle in shaping the scour profile under the condition of different wall clearances (i.e., longitudinal distance between propeller and wall). Moreover, by comparing the vortical structure within the asymptotic scour hole around the vertical quay wall with its counterpart in the case of an open quay (with a slope quay wall), the paper examines the effect of quay types on the formation of the vortex system and how it determines the geometrical characteristic of the final scour profile. Furthermore, the temporal development of the mean vorticity field and the vortex system are discussed in terms of their implications on the evolution of the scour hole. In particular, comparison of the circulation development of the observed vortices allows a better understanding of the vortex scouring mechanism. Energy spectra analysis reveals that at the vortex centers, their energy spectra distributions consistently follow the −5/3 law throughout the entire scouring process. As the scour process evolves, the turbulent energy associated with the near-bed vortex, which is responsible for scouring, is gradually reduced, especially for the small-scale eddies, indicating a contribution of the dissipated turbulent energy in excavating the scour hole. Finally, a comparison of the near-bed flow characteristics of the average kinetic energy (AKE), turbulent kinetic energy (TKE), and Reynolds shear stress (RSS) are also discussed in terms of their implications for the scour hole development.

scholarly journals Reynolds number and wind tunnel wall effects on the flow field around a generic UHBR engine high-lift configuration

2020 ◽  
Vol 11 (4) ◽  
pp. 1009-1023 ◽  
Author(s):  
Junaid Ullah ◽  
Aleš Prachař ◽  
Miroslav Šmíd ◽  
Avraham Seifert ◽  
Vitaly Soudakov ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
Flow Field ◽  
Test Section ◽  
Large Scale ◽  
Scale Model ◽  
Small Scale ◽  
Wall Effects ◽  
Tunnel Wall ◽  
High Lift

Abstract RANS simulations of a generic ultra-high bypass ratio engine high-lift configuration were conducted in three different environments. The purpose of this study is to assess small scale tests in an atmospheric closed test section wind tunnel regarding transferability to large scale tests in an open-jet wind tunnel. Special emphasis was placed on the flow field in the separation prone region downstream from the extended slat cut-out. Validation with wind tunnel test data shows an adequate agreement with CFD results. The cross-comparison of the three sets of simulations allowed to identify the effects of the Reynolds number and the wind tunnel walls on the flow field separately. The simulations reveal significant blockage effects and corner flow separation induced by the test section walls. By comparison, the Reynolds number effects are negligible. A decrease of the incidence angle for the small scale model allows to successfully reproduce the flow field of the large scale model despite severe wind tunnel wall effects.

scholarly journals Numerical simulation of leakage flow field and acoustic characteristics for safety valve

2021 ◽  
Vol 336 ◽  
pp. 01007
Author(s):  
Fan Qian ◽  
Minghui Hu
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Pressure Fluctuation ◽  
Large Scale ◽  
Safety Valve ◽  
Sound Field ◽  
Wall Pressure ◽  
Small Scale ◽  
Acoustic Analogy ◽  
Wall Pressure Fluctuation

Aiming at the internal leakage problem of spring type nuclear safety valve at the sealing surface, the flow field and sound field characteristics at the leakage height of 0.5mm between the valve disc and the valve seat sealing surface were studied, and the numerical simulation was carried out based on large eddy simulation(LES) and mohring acoustic analogy method, and compare the effects of acoustic wall pressure fluctuation(AWPF) and turbulent wall pressure fluctuation(TWPF) as the excitation source on the external sound field of the valve. The simulation results show that: the change gradient of velocity field and pressure field at the leakage port of safety valve is significant and form vortices of different sizes. The small-scale vortices are mainly in the leakage port, while the large-scale vortices mainly exist in the flow channel; When the valve is leaking, the noise is mainly dominated by high-pressure injection noise, its spectrum curve shows wide-band characteristics, and the external noise of the valve is mainly caused by AW P F. The above research results can provide a theoretical basis for the safety valve online detection method.

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