scholarly journals Comparison of Methods for Bed Shear Stress Estimation in Complex Flow Field of Bend

Water ◽  
2020 ◽  
Vol 12 (10) ◽  
pp. 2753
Author(s):  
Liyuan Zhang ◽  
Faxing Zhang ◽  
Ailing Cai ◽  
Zhaoming Song ◽  
Shilin Tong
Keyword(s):  
Shear Stress ◽  
Flow Field ◽  
Single Point ◽  
Three Dimensional ◽  
Bed Shear Stress ◽  
Complex Flow ◽  
Three Dimensional Flow ◽  
Stress Estimation ◽  
Log Law ◽  
Flow Field Measurement

Bed shear stress is closely related to sediment transport in rivers. Bed shear stress estimation is very difficult, especially for complex flow fields. In this study, complex flow field measurement experiments in a 60° bend with a groyne were performed. The feasibility and reliability of bed shear stress estimations using the log-law method in a complex flow field were analyzed and compared with those associated with the Reynolds, Turbulent Kinetic Energy (TKE), and TKE-w′ methods. The results show that the TKE, Reynolds, and log-law methods produced similar bed shear stress estimates, while the TKE-w′ method produced larger estimates than the other methods. The TKE-w′ method was found to be more suitable for bed shear stress estimation than the TKE method, but the value of its constant C2 needed to be re-estimated. In a complex, strong, three-dimensional flow field, the height of the measurement point (relative or absolute) should be re-estimated when a single point measurement is used to estimate the bed shear stress. The results of this study provide guidance for experimental measurement of bed shear stress in a complex flow field.

Experimental Study on Hydrodynamic Performance of Mini-AUV in Non-Uniform Flow Field

2019 ◽  
Author(s):  
Jiayuan Zhuang ◽  
Jian Cao ◽  
Yumin Su ◽  
Lei Zhang ◽  
Xianzhao Yu
Keyword(s):  
Flow Field ◽  
Three Dimensional ◽  
Lateral Force ◽  
Uniform Flow ◽  
Hydrodynamic Performance ◽  
Experimental Investigations ◽  
Complex Flow ◽  
Three Dimensional Flow ◽  
Drift Angle ◽  
Current Profiler

Abstract Experimental investigations of hydrodynamic performance of mini-AUV in non-uniform flow field were conducted in the basin of Harbin Engineering University, the revolved body and flat body of mini-AUV model were tested respectively. The three dimensional flow fields were generated by local jet of the underwater pump, and circulated in the basin. The three dimensional velocity distributions at different positions were measured by a Doppler current profiler. The three component balance was used to measure the drag, lateral force and yawing moment acting on the mini-AUV models depending on drift angle in the flow field, and the influence of complex flow field to the hydrodynamic performance of mini-AUV indicated that drag was not sensitive to drift angle and yawing moment was increased obviously. The conducted experiments could supply reference to the maneuverability research of mini-AUV in real marine environments in the future.

scholarly journals A comparison of two-dimensional and three-dimensional flow structures over artificial pool-riffle sequences

2017 ◽  
Vol 44 (12) ◽  
pp. 1084-1098 ◽  
Author(s):  
Elham Fazel Najafabadi ◽  
Hossein Afzalimehr ◽  
Jueyi Sui
Keyword(s):  
Shear Stress ◽  
Velocity Gradient ◽  
Channel Wall ◽  
Reynolds Shear Stress ◽  
Three Dimensional ◽  
Flow Structures ◽  
Bed Shear Stress ◽  
Two Dimensional ◽  
Three Dimensional Flow ◽  
Secondary Currents

Experiments have been carried out in a flume with one 2D pool-riffle sequence and one 3D pool-riffle sequence, respectively. Objectives of this study are to determine whether or not the convergence of lateral flow exists. Variations of the near-bed shear stress have been studied. The characteristics of the secondary currents along a pool-riffle sequence have been investigated. Results showed that for the 3D pool-riffle sequence, the near-bed velocity decreases along convective deceleration flow (CDF) and increases along convective acceleration flow (CAF), respectively. It is found that the shear velocities estimated from the slope of the velocity gradient in the inner layer, decrease in the CDF section, and increase in the CAF section in the 3D pool-riffle sequences. The Reynolds shear stress is highest at the CDF section along longitudinal lines with distances of 10 cm and 20 cm away from the channel wall.

Navier-Stokes Simulation of the Flow Around a Leading Edge Film-Cooled Turbine Blade Including the Interior Cooling System and Comparison With Experimental Data

1996 ◽  
Author(s):  
Dirk T. Vogel
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Turbine Blade ◽  
Cooling System ◽  
Three Dimensional ◽  
Leading Edge ◽  
Navier Stokes ◽  
Complex Flow ◽  
Three Dimensional Flow ◽  
Dimensional Flow

The three dimensional flow around an extensively investigated slot film cooled turbine blade is numerically investigated using a multi block finite volume Navier-Stokes solver. Three blowing rates are simulated including the whole geometry of the interior blade cooling system and slots. Due to the ejection at the blade leading edge and the geometry of the cooling slots a very complex turbulent three dimensional flow field is generated. The size and shape of the flow separation zones depending on the film cooling ejection is systematically investigated using several two-equation models, e.g. the standard and low Reynolds k–ε-Model of Lam and Bremhorst (1981) r[4], the extension of Kato/Launder (1993) [3] and the k–ω-Model of Wilcox (1991) [10], whereas the results of the standard k–ε-Model are presented. Experimental data obtained by Laser velocimetry, oil-flow pictures and pressure probes are used to understand the complex flow field and to validate the Navier-Stokes solver. The multi-block code applies a traditional Jameson type solver and an implicit solver using several spatial discretization schemes for the convective fluxes. The two-equation models are solved using an RED-BLACK implicit technique with first order spatial upwind discretization to guarantee stability.

Simulation of Three-Dimensional Flow Field Around Unconventional Bridge Piers

2017 ◽  
Author(s):  
Adnan Ismael ◽  
Hamid Hussein ◽  
Mohammed Tareq ◽  
Mustafa Gunal
Keyword(s):  
Flow Field ◽  
Three Dimensional ◽  
Bridge Piers ◽  
Three Dimensional Flow ◽  
Dimensional Flow

Experimental investigation on the three-dimensional flow field from a meltblowing slot die

e-Polymers ◽  
2020 ◽  
Vol 20 (1) ◽  
pp. 724-732
Author(s):  
Changchun Ji ◽  
Yudong Wang
Keyword(s):  
Flow Field ◽  
Three Dimensional ◽  
Great Influence ◽  
Distribution Characteristics ◽  
Air Velocity ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Airflow Distribution ◽  
Slot Die ◽  
Center Area

AbstractTo investigate the distribution characteristics of the three-dimensional flow field under the slot die, an online measurement of the airflow velocity was performed using a hot wire anemometer. The experimental results show that the air-slot end faces have a great influence on the airflow distribution in its vicinity. Compared with the air velocity in the center area, the velocity below the slot end face is much lower. The distribution characteristics of the three-dimensional flow field under the slot die would cause the fibers at different positions to bear inconsistent air force. The air velocity of the spinning centerline is higher than that around it, which is more conducive to fiber diameter attenuation. The violent fluctuation of the instantaneous velocity of the airflow could easily cause the meltblowing fiber to whip in the area close to the die.

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