scholarly journals Relative role of sediment entrainments on log-law parameters of longitudinal velocity distributions in mobile bed flows

2021 ◽  
Vol 69 (3) ◽  
pp. 243-254
Author(s):  
Pritam Malakar ◽  
Ratul Das
Keyword(s):  
Current Knowledge ◽  
Reynolds Shear Stress ◽  
Longitudinal Velocity ◽  
Flow Characteristics ◽  
Relative Role ◽  
Mobile Bed ◽  
Alluvial Channel ◽  
Bed Slope ◽  
Additional Support ◽  
Cohesive Bed

Abstract In alluvial channel, the non-cohesive bed particles are frequently accelerated by the flows and there has been an inconclusive debate on the deviations of logarithmic law parameters that demonstrate the velocity distributions in flows. Present study aims to elucidate the current knowledge of overwhelming theoretical and experimental evidences in this regard within the scope of near-bed turbulent flow characteristics. The study was conducted in two folds collecting instantaneous velocity of flow over a rigid sand bed under clear water flow conditions and compared to those over mobile sand beds under equilibrium bed-load. Results corroborated additional support to confirm the upward shifting of zero-velocity level in mobile bed flows. Most importantly, the conventional value of von Kármán coefficient significantly deviates in mobile bed flows compared to those in rigid sand bed. Also, the frictional velocity obtained from the bed slope consistently differs to those obtained from the Reynolds shear stress (RSS) distributions owing to transfer of stress aliquot to the bed particles. The mechanism is well demonstrated with the energy-momentum transfer within the framework of energy budget concept which shows near-bed negative pressure energy diffusion rates with increasing turbulence production in mobile bed flows.

FLOOD FLOW CHARACTERISTICS AND BED LOAD TRANSPORT IN NON-VEGETATED COMPOUND STRAIGHT CHANNELS

2016 ◽  
Vol 78 (9-4) ◽  
Author(s):  
Mazlin Jumain ◽  
Zulkiflee Ibrahim ◽  
Zulhilmi Ismail ◽  
Mohd Fuad Samsudin ◽  
Muhd Zubair Tajol Anuar ◽  
...  
Keyword(s):  
Flow Characteristics ◽  
Bed Load ◽  
Mobile Bed ◽  
Load Transport ◽  
Bed Load Transport ◽  
Flow And Sediment Transport ◽  
Depth Increase ◽  
Bed Slope ◽  
Overbank Flows ◽  
Flood Flow

Floods are the most common natural disasters in Malaysia and have damaged structures, infrastructures, crops and even causes fatalities. It may also lead to erosion and sedimentation in rivers and this will result to complex river behaviour.  A hydraulic laboratory experimental study was carried out. Also, flood flow and sediment transport in straight compound channels involving flow resistance, distribution of depth-averaged velocity, stream-wise vorticity patterns, channel bed morphology and bed load transport rate in non-vegetated compound straight mobile bed channels were investigated. The finding showed that the Darcy Weisbach friction factor  f  increased by 40% and 54% for floodplain and main channel, respectively when relative flood flow depth increase from 0.30 to 0.50. The small bed load transport rates of 0.09 g/s and 0.03 g/s for shallow and deep overbank flows, respectively were measured due to effect of very gentle or mild channel bed slope which was fixed at a gradient of 0.1%. 

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.

The Influence of the Aortic Root Geometry on Flow Characteristics of a Prosthetic Heart Valve

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Oleksandr Barannyk ◽  
Peter Oshkai
Keyword(s):  
Aortic Valve ◽  
Heart Valve ◽  
Aortic Root ◽  
Reynolds Shear Stress ◽  
Prosthetic Heart Valve ◽  
Flow Characteristics ◽  
Aortic Pressure ◽  
Valve Prosthesis ◽  
Aortic Heart Valve ◽  
Valve Diseases

In this paper, performance of aortic heart valve prosthesis in different geometries of the aortic root is investigated experimentally. The objective of this investigation is to establish a set of parameters, which are associated with abnormal flow patterns due to the flow through a prosthetic heart valve implanted in the patients that had certain types of valve diseases prior to the valve replacement. Specific valve diseases were classified into two clinical categories and were correlated with the corresponding changes in aortic root geometry while keeping the aortic base diameter fixed. These categories correspond to aortic valve stenosis and aortic valve insufficiency. The control case that corresponds to the aortic root of a patient without valve disease was used as a reference. Experiments were performed at test conditions corresponding to 70 beats/min, 5.5 L/min target cardiac output, and a mean aortic pressure of 100 mmHg. By varying the aortic root geometry, while keeping the diameter of the orifice constant, it was possible to investigate corresponding changes in the levels of Reynolds shear stress and establish the possibility of platelet activation and, as a result of that, the formation of blood clots.

Effect of the Fish-Bone Dam Angle on the Flow Mechanisms of a Fish-Bone Type Dividing Dike

2020 ◽  
Vol 54 (3) ◽  
pp. 58-67
Author(s):  
Jia Ni ◽  
Linwei Wang ◽  
Xixian Chen ◽  
Luan Luan Xue ◽  
Isam Shahrour
Keyword(s):  
Water Level ◽  
Longitudinal Velocity ◽  
Flow Characteristics ◽  
Fish Bone ◽  
Flume Experiments ◽  
Lateral Velocity ◽  
Engineering Structures ◽  
Flow Mechanisms ◽  
River Training ◽  
Large Velocity Gradient

AbstractFish-bone type dividing dikes are river engineering structures used for river training and to protect a mid-channel bar from scour. The flow characteristics around fish-bone type dividing dikes are very complicated, especially near its fish-bone dam. To understand the flow and scour processes associated with fish-bone dams, this paper conducts a numerical simulation of flow characteristics for different fish-bone dam angles. Based on the Yudaizhou fish-bone type dividing dike of the Dongliu Waterway, a 3-D numerical model is established via Flow-3D to simulate the flow characteristics around a fish-bone type dividing dike, which is verified by flume experiments. Based on the results, the effects of different fish-bone dam angles on water level and velocity distribution are investigated. With increasing fish-bone dam angle, the longitudinal and lateral gradients of the water level gradually decreased, and the variation degree of the longitudinal velocity also decreased; however, the variation degree of the lateral velocity increased. Vortex areas formed around the fish-bone dam and the downstream zone of the dike. A large velocity gradient was found around the dike, and the downstream vortex area decreased with increasing fish-bone dam angle.

scholarly journals Three-Dimensional Flow Characteristics in Slit-Type Permeable Spur Dike Fields: Efficacy in Riverbank Protection

Water ◽  
2020 ◽  
Vol 12 (4) ◽  
pp. 964 ◽  
Author(s):  
Shampa ◽  
Yuji Hasegawa ◽  
Hajime Nakagawa ◽  
Hiroshi Takebayashi ◽  
Kenji Kawaike
Keyword(s):  
Shear Stress ◽  
Longitudinal Velocity ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Efficient Solutions ◽  
Staggered Grid ◽  
Bed Shear Stress ◽  
Experimental Conditions ◽  
Alluvial Rivers ◽  
Spur Dike

This paper focuses on finding efficient solutions for the design of a highly permeable pile spur (or slit type) dike field used in morphologically dynamic alluvial rivers. To test the suitability of different arrangements of this type of permeable pile spur dike field, laboratory experiments were conducted, and a three-dimensional multiphase numerical model was developed and applied, based on the experimental conditions. Three different angles to the approach flow and two types of individual pile position arrangements were tested. The results show that by using a series of slit-type spurs, the approach velocity of the flow can be considerably reduced within the spur dike zone. Using different sets of angles and installation positions, this type of permeable spur dike can be used more efficiently than traditional dikes. Notably, this type of spur dike can reduce the longitudinal velocity, turbulence intensity, and bed shear stress in the near-bank area. Additionally, the deflection of the permeable spur produces more transverse flow to the opposite bank. Arranging the piles in staggered grid positions among different spurs in a spur dike field improves functionality in terms of creating a quasi-uniform turbulence zone while simultaneously reducing the bed shear stress. Finally, the efficacy of the slit-type permeable spur dike field as a solution to the riverbank erosion problem is numerically tested in a reach of a braided river, the Brahmaputra–Jamuna River, and a comparison is made with a conventional spur dike field. The results indicate that the proposed structure ensures the smooth passing of flow compared with that for the conventional impermeable spur structure by producing a lower level of scouring (low bed shear stress) and flow intensification.

scholarly journals The Effect of Boattail Angles on the Near-Wake Structure of Axisymmetric Afterbody Models at Low-Speed Condition

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
The Hung Tran
Keyword(s):  
Strouhal Number ◽  
Reynolds Shear Stress ◽  
Flow Behavior ◽  
Flow Characteristics ◽  
Wake Flow ◽  
Turbulent Intensity ◽  
Near Wake ◽  
Wake Structure ◽  
Low Speed ◽  
Speed Condition

The effect of a boattail angle on the structure of the wake of an axisymmetric model was investigated at low-speed condition. Four conical boattail models with angles of 0° (blunt-based body), 10°, 16°, and 22° were selected for this study. The Reynolds number based on the diameter of the model was around 1.97×104. Particle image velocimetry (PIV) was used to measure the velocity of the wake flow. The time-averaged flow characteristics including the length of recirculation of the afterbody, turbulent intensity, and Reynolds shear stress were analyzed and compared among those boattail models. The experimental results showed that the length of recirculation decreases with increasing boattail angle to 16°. At a boattail angle above 16°, the flow was fully separated near the shoulder and near-wake structure was highly changed. The turbulent intensity at a boattail angle of 22° showed a similar level to that in the case of the blunt-based body. Flow behavior on boattail surface should be accounted as an important parameter affecting the wake width and drag of the model. Power spectral density and proper orthogonal decomposition (POD) analyses showed that a Strouhal number of StD=0.2 dominated for the boattail model up to 16°. The fully separated flow was dominated by a Strouhal number of StD=0.03−0.06, which was firstly presented in this study.

Flow Development in an Annular Contraction

1998 ◽  
Author(s):  
A. K. Agrawal ◽  
A. Tinneti ◽  
S. R. Gollahalli
Keyword(s):  
Shear Stress ◽  
Gas Turbines ◽  
Reynolds Shear Stress ◽  
Flow Characteristics ◽  
Stagnation Pressure ◽  
Pressure Distributions ◽  
Pressure Fields ◽  
Flow Development ◽  
Dynamic Head ◽  
Upstream Flow

Power generating gas turbines employ an inlet duct or contraction to accelerate air to the operating inlet velocity of the compressor. Multiple passages of this kind are necessary in gas turbines with cycle modifications such as intercooling. An experimental investigation was carried out to obtain flow characteristics of a curved wall annular contraction. The results are described in terms of the velocity vectors, surface pressure coefficients, static and stagnation pressure distributions, and profiles of mean velocities, turbulence intensity, and Reynolds shear stress. The upstream flow conditions were changed to evaluate how they affected the flow development in the passage. Results show that the static pressure and axial velocity profiles at the contraction exit were uniform. Higher inlet turbulence increased the Reynolds shear stress although the effect on the static and total pressure fields was negligible. The overall stagnation pressure loss was approximately 2 to 3 percent of the dynamic head at the contraction exit.

scholarly journals Clinical and Regulatory Concerns of Biosimilars: A Review of Literature

2020 ◽  
Vol 17 (16) ◽  
pp. 5800
Author(s):  
Vesa Halimi ◽  
Armond Daci ◽  
Katerina Ancevska Netkovska ◽  
Ljubica Suturkova ◽  
Zaheer-Ud-Din Babar ◽  
...  
Keyword(s):  
Positive Attitude ◽  
Healthcare Professionals ◽  
Current Knowledge ◽  
Scientific Data ◽  
Cochrane Library ◽  
Review Of Literature ◽  
Safety And Efficacy ◽  
Knowledge And Attitudes ◽  
Clinical Profiles ◽  
Additional Support

Although biosimilars have been part of clinical practice for more than a decade, healthcare professionals (HCPs) do not fully accept them. This is because of the perception that biosimilars may not be like their originators in terms of quality, safety, and efficacy. This study aims to evaluate the current knowledge and attitudes of healthcare professionals toward biosimilar prescription, and to elaborate on their concerns. We reviewed the literature using PubMed, Cochrane Library, and Science Direct electronic databases in the period from 2018 to 2020. The knowledge and confidence of healthcare professionals vary between countries, between clinical profiles and between studies. Although most of the healthcare professionals had a positive attitude to prescribing biosimilars, they would still prefer to prescribe them in initial treatment. Generally, HCPs were against multiple switches and substitution of biosimilars at the pharmacy level. HCP’s key concern was interchangeability, with eventual consequences on the clinical outcome of patients. HCPs still approach biosimilars with caution and stigma. HCPs need to have an unbiased coherent understanding of biosimilars at clinical, molecular and regulatory levels. It was also observed that most of their concerns are more theoretical than science-based. Physicians are in an excellent position to accept biosimilars, but they need the additional support of regulatory authorities to approve and take into consideration the available scientific data regarding biosimilars.

Measurements in an Axisymmetric Turbulent Boundary Layer Along a Circular Cylinder

1976 ◽  
Vol 27 (3) ◽  
pp. 217-228 ◽  
Author(s):  
Noor Afzal ◽  
K P Singh
Keyword(s):  
Boundary Layer ◽  
Circular Cylinder ◽  
Turbulent Boundary Layer ◽  
Constant Pressure ◽  
Reynolds Shear Stress ◽  
Longitudinal Velocity ◽  
Outer Region ◽  
Wall Region ◽  
Mean Velocity ◽  
Dimensional Boundary

SummaryIn an axisymmetric turbulent boundary layer along a circular cylinder at constant pressure, measurements have been made of mean velocity profile and turbulence characteristics: longitudinal velocity fluctuations, Reynolds shear stress, transverse correlation and spectrum. It has been found that the qualitative behaviour of an axisymmetric turbulent boundary layer is similar to that of a two-dimensional boundary layer in the wall region, where as in the outer region the effects of transverse curvature are observed.

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