Effect of Inflow Conditions on the Velocity and Momentum Decay Characteristics of a Submerged Viscoplastic Jet

2012 ◽  
Author(s):  
Khaled J. Hammad
Keyword(s):  
Yield Stress ◽  
Initial Velocity ◽  
Momentum Conservation ◽  
Velocity Decay ◽  
Flow Field Characteristics ◽  
Profile Flow ◽  
Flow Inertia ◽  
Inflow Conditions ◽  
Penetration Depths ◽  
Steady Laminar

Velocity and momentum decay characteristics of a submerged viscoplastic non-Newtonian jet were studied within the steady laminar flow regime. The governing mass and momentum conservation equations along with the Bingham rheological model were solved numerically using a staggered, variable grid-size, finite-differences scheme. A parametric study was performed to reveal the influence of initial velocity profile, flow inertia, and yield stress presence on the local and global flow field characteristics. Two initial velocity profiles were considered, a top-hat jet, simulating a smooth nozzle contraction, and a fully developed pipe jet. The centerline velocity decay was more rapid for the pipe jet than the top-hat one when the fluid is Newtonian while the opposite trend was observed for yield stress Bingham fluids. The decay in the momentum flux of the pipe jet was always less than that of the top-hat jet. The presence of yield stress significantly reduces momentum and velocity penetration depths of submerged top-hat and pipe jets.

Velocity and Momentum Decay Characteristics of a Submerged Viscoplastic Jet

2013 ◽  
Vol 136 (2) ◽  
Author(s):  
Khaled J. Hammad
Keyword(s):  
Flow Field ◽  
Yield Stress ◽  
Initial Velocity ◽  
Momentum Conservation ◽  
Wide Range ◽  
Velocity Decay ◽  
Flow Field Characteristics ◽  
Order Of Magnitude ◽  
Field Information ◽  
Penetration Depths

Velocity and momentum decay characteristics of a submerged viscoplastic non-Newtonian jet are studied within the steady laminar flow regime. The governing mass and momentum conservation equations along with the Bingham rheological model are solved numerically using a finite-difference scheme. A parametric study is performed to reveal the influence of the initial velocity profile, flow inertia, and yield stress presence on the flow field characteristics. Two initial velocity profiles are considered, a top-hat and fully developed pipe jets. The centerline velocity decay is found to be more rapid for the pipe jet than the top-hat one when the fluid is Newtonian while the opposite trend is observed for yield stress Bingham fluids. The decay in the momentum flux of the pipe jet is always less than that of the top-hat jet. Momentum and velocity based jet depths of penetration are introduced and used to analyze the obtained flow field information for a wide range of Reynolds and yield numbers. Depths of penetration are found to linearly increase with the Reynolds number and substantially decrease with the yield number. The presence of yield stress significantly reduces the momentum and velocity penetration depths of submerged top-hat and pipe jets. Penetration depths of yield stress fluids are shown to be more than an order of magnitude smaller than the ones corresponding to Newtonian fluids.

Numerical Simulation of a Straight-Bladed Vertical-Axis Water Turbine Operating in a 2 m/s Current

2013 ◽  
Vol 325-326 ◽  
pp. 162-166
Author(s):  
Marco Raciti Castelli ◽  
Ernesto Benini
Keyword(s):  
Flow Field ◽  
Stream Water ◽  
Vertical Axis ◽  
Speed Ratio ◽  
Flow Field Characteristics ◽  
Water Turbine ◽  
Validation Procedure ◽  
Torque Coefficient ◽  
Bladed Rotor ◽  
Profile Flow

The present work proposes a full campaign of simulation of a Darrieus-type Vertical-Axis Water Turbine (VAWaterT) operating in an open flow-field. After describing the computational model and the relative validation procedure, a complete campaign of simulations based on full RANS unsteady calculations is presented for a three-bladed rotor architecture, characterized by a NACA 0025 blade profile. Flow field characteristics are investigated for several values of tip speed ratio and for a constant unperturbed free-stream water velocity of 2 m/s. Finally, the torque coefficient generated from the three blades is determined for each simulated angular velocity, allowing the calculation of the rotor power-curve. Keywords: Vertical-Axis Water Turbine, hydrokinetic technology, CFD, NACA 0025.

Apparent Wall Slip in Capillary Rheometry of Viscoplastic Liquids

2005 ◽  
Author(s):  
Paulo R. Souza Mendes ◽  
Jose´ R. R. Siffert ◽  
Eduardo S. S. Dutra
Keyword(s):  
Shear Stress ◽  
Yield Stress ◽  
Wall Slip ◽  
Momentum Conservation ◽  
Conservation Equation ◽  
Jump Number ◽  
Capillary Rheometry ◽  
Viscosity Function ◽  
Novel Material ◽  
Apparent Wall Slip

We employ a recently proposed viscosity function (Souza Mendes and Dutra, 2004) to analyze the fully developed flow of yield-stress liquids through tubes. We first show that its dimensionless form gives rise to the so-called jump number, a novel material property that measures the shear rate jump that the material undergoes as the yield stress is reached. We integrate numerically the momentum conservation equation that governs this flow together with the generalized Newtonian Liquid model and the above mentioned viscosity function. We obtain velocity and viscosity profiles for the entire range of the jump number. We show that the friction factor f.Re curves display sharp peaks as the shear stress value at the tube wall approaches the yield stress. Finally, we demonstrate the existence of sharp flow rate increases (or apparent slip) as the wall shear stress is increased in the vicinity of the yield stress.

Flow of Yield Power Law Fluids in Horizontal Pipes-Flow Field Characterization Using Particle Image Velocimetry Technique

2021 ◽  
Author(s):  
Yanxin (Sussi) Sun ◽  
Abdulla Abou-Kassem ◽  
Majid Bizhani ◽  
Ergun Kuru
Keyword(s):  
Experimental Study ◽  
Flow Field ◽  
Velocity Profile ◽  
Yield Stress ◽  
Power Law ◽  
Pipe Flow ◽  
Hydrodynamic Behaviour ◽  
Yield Stress Fluids ◽  
Power Law Fluids ◽  
Flow Field Characteristics

Abstract Yield Power Law (YPL) rheological model is commonly used to describe the pipe and annular flow of drilling fluids. However, the hydrodynamic behaviour of fluids with yield stress are difficult to predict because they exhibit an inherent plug (solid like) region where the velocity gradient is zero. Moreover, it is not easy to identify the transition between this solid like and liquid regions. Theoretical studies have been conducted in the past to describe YPL fluid flow in pipes and annuli. As a result, several models have been proposed for determining flow field characteristics (e.g. velocity profile, plug width, etc.) and frictional pressure losses. However, most of these models have been validated by limited experimental and/or field data. Similar future modeling studies may benefit from more data collected under controlled experimental conditions. Therefore, we have conducted an experimental study to investigate the hydrodynamic behaviour of yield stress fluids under laminar pipe flow conditions and the results are presented in this paper. Water-based Yield Power Law fluids were prepared by using Carbopol® 940, a synthetic high-molecular-weight polyacrylic acid-based cross-linked polymer. Fluids with yield stresses varying from 0.75 Pa (1.56 lb/100 ft2) to 4.37 Pa (9.13 lb/100 ft2) were obtained by using Carbopol concentrations changing from 0.060% w/w to 0.073% w/w. A 9m long horizontal pipeline with, 95 mm diameter (ID) was used for the experiments. Reynolds number range varying from 97 to 1268 confirmed that all flow field characteristics measurements of YPL fluids were conducted under laminar flow regimes. Experimental study provided detailed information about pipe flow characteristics of yield stress fluids, including full annular velocity profile, near wall velocity profile, wall slip velocity and the plug region thickness. The study was concluded by comparing experimental results (i.e. full velocity profile, frictional pressure loss, and plug width) to predictions of models presented in the literature. Practical implications of the results have also been discussed by considering the hydraulic design of some practical field operations such as hole cleaning.

Liquid Jet Impingement on a Free Liquid Surface: PIV Study of the Turbulent Bubbly Two-Phase Flow

2010 ◽  
Author(s):  
Khaled J. Hammad
Keyword(s):  
Flow Field ◽  
Two Phase Flow ◽  
Jet Impingement ◽  
Flow Region ◽  
Air Entrainment ◽  
Continuous Phase ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Field Characteristics ◽  
Inflow Conditions

The turbulent two-phase flow arising from the normal impingement of a round free-surface water jet on a horizontal air-water interface was experimentally studied. Due to the weakly viscous nature of the flow system under consideration, external perturbations or small variations in jet inflow conditions can lead to drastically different flow field characteristics under seemingly similar test conditions. In the current study, a fully developed turbulent jet, exiting a long pipe, ensured properly characterized inflow conditions. The study considered two jet inflow conditions; one entrained air and created a bubbly two-phase flow field while the other did not. Particle image velocimetry (PIV) was used to characterize the flow field beneath the interface, with and without air entrainment, for various nozzle-to-interface separation distances. Turbulent velocity fields of the continuous-phase and dispersed-phase were simultaneously measured in the developing flow region and presented using Reynolds decomposition into mean and fluctuating components. The mean and RMS velocities of the two-phase flow field were compared with velocity measurements obtained under single-phase conditions.

Depth of Penetration of a Submerged Viscoplastic Non-Newtonian Jet

2012 ◽  
Author(s):  
Khaled J. Hammad
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Flow Field ◽  
Rheological Model ◽  
Momentum Conservation ◽  
Depth Of Penetration ◽  
Wide Range ◽  
Order Of Magnitude ◽  
Field Information ◽  
Penetration Depths

Depth of penetration characteristics of a submerged viscoplastic non-Newtonian jet were studied by numerically solving the governing mass and momentum conservation equations along with the Bingham rheological model. Momentum and velocity based jet depths of penetration were introduced and used to analyze the obtained steady and laminar flow field information for a wide range of Reynolds and yield numbers. Depths of penetration were found to linearly increase with the Reynolds number and substantially decrease with the yield number. Penetration depths of yield stress fluids were shown to be more than an order of magnitude smaller than the ones corresponding to Newtonian fluids.

The Velocity Decay Property of Different Shape Fragments for Explosive Anti-Riots Munition

2013 ◽  
Vol 658 ◽  
pp. 446-449
Author(s):  
Di Hua Ou Yang
Keyword(s):  
Initial Velocity ◽  
Decay Property ◽  
Irregular Shape ◽  
Dynamical Model ◽  
Separation Angle ◽  
Force Condition ◽  
Velocity Decay

In order to assess the safety of the explosive anti-riots munition, proceeding with the fragment’s force condition was analyzed in the flying process, the dynamical model of the fragment for the explosive anti-riots munition was deduced, then the velocity decay property of different shape fragments were calculated and analyzed also. The results show that the velocity decay of the spherical fragment is slowest, next came the rectangular fragment and the irregular shape fragment, with the same initial velocity (v0) and separation angle (α), and the velocity decay of the same fragment at α >0 is more quickly than at α <0, with the same initial velocity (v0).

Velocity and Momentum Decay Characteristics of Submerged Yield-Pseudoplastic Jets

2015 ◽  
Author(s):  
Khaled J. Hammad
Keyword(s):  
Numerical Solutions ◽  
Shear Thinning ◽  
Critical Value ◽  
Momentum Conservation ◽  
Recirculation Region ◽  
Centerline Velocity ◽  
Flow Recirculation ◽  
Submerged Jets ◽  
Flow Inertia ◽  
The Impact

The velocity and momentum decay characteristics of submerged yield-pseudoplastic jets are studied. Numerical solutions to the governing mass and momentum conservation equations, along with the Herschel-Bulkley rheological model, are obtained using a finite-difference scheme. A parametric study is implemented to investigate the influence of flow inertia and rheology over the following range of parameters: Reynolds number, 50 ≤ Re ≤ 200, Yield number, 0 ≤ Y ≤ 1, and shear-thinning index, 0.6 ≤ n ≤ 1. A large recirculation region exists for Newtonian and pseudoplastic non-Newtonian jets. However, the extent and strength of the recirculation region substantially diminish with the yield number and, to a lesser extent, when the shear-thinning index is reduced from 1 to 0.6. Increasing the yield number beyond a critical value eliminates flow recirculation. The centerline velocity and momentum decay of yield-pseudoplastic jets, in general, increases with the yield number. Velocity and momentum based depths of penetration, DPU and DPM, respectively, are extracted and presented. A substantial decrease in DPU and DPM is observed when the shear-thinning index is reduced from 1 to 0.6 for Y = 0. The presence of yield stress significantly reduces both DPU and DPM of submerged jets. The impact of shear-thinning on the decay characteristics of the jet is more pronounced at low yield numbers.

Inflow Conditions and the Wall Shear Stress Characteristics of a Biofluid in Separated and Reattached Flow Regions

2014 ◽  
Author(s):  
Khaled J. Hammad
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Yield Stress ◽  
Human Blood ◽  
Flow Separation ◽  
Shear Thinning ◽  
Vortex Center ◽  
Wall Shear ◽  
Separated And Reattached Flow ◽  
Inflow Conditions

The influence of inflow conditions and human blood rheology on the wall shear stress distribution in a confined separated and reattached flow region is investigated. The governing mass and momentum conservation equations along with the Herschel-Bulkley rheological model are solved numerically using a finite-difference scheme. A parametric study is performed to reveal the influence of uniform and fully-developed inflow velocity profiles on the wall shear stress (WSS) characteristics using hemorheological models that account for the yield stress and shear-thinning non-Newtonian characteristics of human blood. The highest WSS or WSSmax, is always observed inside the flow separation region at a location corresponding to that of the corner vortex center. Uniform inflow results in higher WSSmax values in comparison with fully-developed inflow for moderate upstream flow restrictions. The opposite trend is observed for severe flow restrictions. Uniform inflow always results in smaller flow separation regions and WSSmax values at locations closer to the flow restriction plane. The yield shear-thinning hemorheological model always results in the highest observed peak WSS. The yield stress impact on WSS distribution is most pronounced in the case of severe restrictions to the flow.

scholarly journals Experimental and Computational Study of Archery Arrows Fletched with Straight Vanes

Proceedings ◽  
2020 ◽  
Vol 49 (1) ◽  
pp. 56
Author(s):  
Julio Ortiz ◽  
Atsushi Serino ◽  
Toshinari Hasegawa ◽  
Takahito Onoguchi ◽  
Hiroki Maemukai ◽  
...  
Keyword(s):  
Initial Velocity ◽  
Computational Study ◽  
Aerodynamic Characteristics ◽  
Magnetic Suspension ◽  
Boundary Layer Transition ◽  
Free Flight ◽  
Layer Transition ◽  
Experimental Procedure ◽  
Balance System ◽  
Velocity Decay

The aerodynamic characteristics of archery arrows fletched with two types of straight vanes, for which the area is different, were studied. The arrows’ pitching moment (CM), lift (CL) and drag (CD) coefficients were measured in the 60 × 60 cm Magnetic Suspension and Balance System (MSBS) from JAXA. At a Reynolds number of Re = 1.2 × 104, the values of CD were 1.56 and 2.05 for the short and large vanes, respectively. In a second experimental procedure, the arrows’ deceleration in free flight was measured by inserting an acceleration sensor inside their shafts. For shots with an initial velocity of around 56.4 ms−1, a velocity decay of around 8% was measured. A turbulent–laminar boundary layer transition during free flight was found for shots with an average Re = 1.8 × 104. Lastly, through numerical computations, the area difference of the two vanes was analyzed to verify the importance of CM and CL during the arrows’ flights.

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