Drag force of bubble swarms and numerical simulations of a bubble column with a CFD-PBM coupled model

2018 ◽  
Vol 192 ◽  
pp. 714-724 ◽  
Author(s):  
Guangyao Yang ◽  
Huahai Zhang ◽  
Jiajia Luo ◽  
Tiefeng Wang
Keyword(s):  
Numerical Simulations ◽  
Drag Force ◽  
Bubble Column ◽  
Coupled Model

scholarly journals Coupling Methodology for Studying the Far Field Effects of Wave Energy Converter Arrays over a Varying Bathymetry

Energies ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2899 ◽  
Author(s):  
Gael Verao Fernandez ◽  
Philip Balitsky ◽  
Vasiliki Stratigaki ◽  
Peter Troch
Keyword(s):  
Numerical Simulations ◽  
Wave Energy ◽  
Near Field ◽  
Coupled Model ◽  
Propagation Model ◽  
Irregular Waves ◽  
Computational Time ◽  
Far Field ◽  
Field Effects ◽  
Numerical Tool

For renewable wave energy to operate at grid scale, large arrays of Wave Energy Converters (WECs) need to be deployed in the ocean. Due to the hydrodynamic interactions between the individual WECs of an array, the overall power absorption and surrounding wave field will be affected, both close to the WECs (near field effects) and at large distances from their location (far field effects). Therefore, it is essential to model both the near field and far field effects of WEC arrays. It is difficult, however, to model both effects using a single numerical model that offers the desired accuracy at a reasonable computational time. The objective of this paper is to present a generic coupling methodology that will allow to model both effects accurately. The presented coupling methodology is exemplified using the mild slope wave propagation model MILDwave and the Boundary Elements Methods (BEM) solver NEMOH. NEMOH is used to model the near field effects while MILDwave is used to model the WEC array far field effects. The information between the two models is transferred using a one-way coupling. The results of the NEMOH-MILDwave coupled model are compared to the results from using only NEMOH for various test cases in uniform water depth. Additionally, the NEMOH-MILDwave coupled model is validated against available experimental wave data for a 9-WEC array. The coupling methodology proves to be a reliable numerical tool as the results demonstrate a difference between the numerical simulations results smaller than 5% and between the numerical simulations results and the experimental data ranging from 3% to 11%. The simulations are subsequently extended for a varying bathymetry, which will affect the far field effects. As a result, our coupled model proves to be a suitable numerical tool for simulating far field effects of WEC arrays for regular and irregular waves over a varying bathymetry.

scholarly journals Minimum and terminal velocities in projectile motion

2004 ◽  
Vol 26 (2) ◽  
pp. 125-127 ◽  
Author(s):  
E.N. Miranda ◽  
S. Nikolskaya ◽  
R. Riba
Keyword(s):  
Gravitational Field ◽  
Numerical Simulations ◽  
Drag Force ◽  
Initial Velocity ◽  
Terminal Velocity ◽  
Initial Speed ◽  
Projectile Motion ◽  
Minimum Speed ◽  
Minimum Velocity

The motion of a projectile with horizontal initial velocity V0, moving under the action of the gravitational field and a drag force is studied analytically. As it is well known, the projectile reaches a terminal velocity Vterm. There is a curious result concerning the minimum speed Vmin; it turns out that the minimum velocity is lower than the terminal one if V0 > Vterm and is lower than the initial one if V0 < Vterm. These results show that the velocity is not a monotonous function. If the initial speed is not horizontal, there is an angle range where the velocity shows the same behavior mentioned previously. Out of that range, the velocity is a monotonous function. These results comes out from numerical simulations.

scholarly journals Assessment of Able-Bodied and Amputee Cyclists’ Aerodynamics by Computational Fluid Dynamics

2021 ◽  
Vol 9 ◽  
Author(s):  
Pedro Forte ◽  
Jorge E. Morais ◽  
Tiago M. Barbosa ◽  
Daniel A. Marinho
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Numerical Simulations ◽  
Drag Force ◽  
Rolling Resistance ◽  
Viscous Drag ◽  
Normal Model ◽  
3D Scanner ◽  
Pressure Drag ◽  
Cad Models

The aim of this study was to compare the aerodynamics of able-bodied and amputee cyclists by computational fluid dynamics. The cyclists’ geometry was obtained by a 3D scanner. Three CAD models were created as able-bodied, transtibial (Tt), and transradial (Tr) amputees. Numerical simulations were conducted up to 13 m/s with increments of 1 m/s to assess drag force. The drag ranged between 0.36 and 39.25 N for the able-bodied model, 0.36–43.78 for the Tr model and 0.37–41.39 N for the Tt model. The pressure drag ranged between 0.20 and 22.94 N for the normal model, 0.21–28.61 for the Tr model and 0.23–28.02 N for the Tt model. The viscous drag ranged between 0.16 and 15.31 N for the normal model, 0.15–15.17 for the Tr model and 0.14–13.38 N for the Tt model. The rolling resistance (RR) was higher on the able-bodied (2.23 N), followed by the Tr (2.20 N) and Tt (2.17 N) models. As a conclusion, the able-bodied cyclist showed less drag, followed by the Tt and Tr models, respectively. The RR presented higher values in the able-bodied, followed by the Tr and Tt models.

Generality of the CFD-PBM coupled model for bubble column simulation

2020 ◽  
Vol 219 ◽  
pp. 115514 ◽  
Author(s):  
Huahai Zhang ◽  
Ali Sayyar ◽  
Yuelin Wang ◽  
Tiefeng Wang
Keyword(s):  
Bubble Column ◽  
Coupled Model

Interface Resolved Direct Numerical Simulations of Gas-Liquid Flow in Bubble Column Reactors

2021 ◽  
Author(s):  
Luka Malenica ◽  
Vimal Ramanuj ◽  
Ramanan Sankaran ◽  
Leonardo Spanu ◽  
Guoqiang Yang
Keyword(s):  
Numerical Simulations ◽  
Liquid Flow ◽  
Bubble Column ◽  
Direct Numerical Simulations ◽  
Bubble Column Reactors ◽  
Gas Liquid Flow

scholarly journals The Effect of Liquid Viscosity on the Rise Velocity of Taylor Bubbles in Small Diameter Bubble Column

2020 ◽  
Author(s):  
Olumayowa T. Kajero ◽  
Mukhtar Abdulkadir ◽  
Lokman Abdulkareem ◽  
Barry James Azzopardi
Keyword(s):  
Froude Number ◽  
Drag Force ◽  
Bubble Column ◽  
Small Diameter ◽  
Liquid Viscosity ◽  
Rise Velocity ◽  
Gas Velocity ◽  
Gravitational Forces ◽  
Superficial Gas Velocity ◽  
Taylor Bubbles

The rise velocity of Taylor bubbles in small diameter bubble column was measured via cross-correlation between two planes of time-averaged void fraction data obtained from the electrical capacitance tomography (ECT). This was subsequently compared with the rise velocity obtained from the high-speed camera, manual time series analysis and likewise empirical models. The inertia, viscous and gravitational forces were identified as forces, which could influence the rise velocity. Fluid flow analysis was carried out using slug Reynolds number, Froude number and inverse dimensionless viscosity, which are important dimensionless parameters influencing the rise velocity of Taylor bubbles in different liquid viscosities, with the parameters being functions of the fluid properties and column diameter. It was found that the Froude number decreases with an increase in viscosity with a variation in flow as superficial gas velocity increases with reduction in rise velocity. A dominant effect of viscous and gravitational forces over inertia forces was obtained, which showed an agreement with Stokes law, where drag force is directly proportional to viscosity. Hence, the drag force increases as viscosity increases (5 < 100 < 1000 < 5000 mPa s), leading to a decrease in the rise velocity of Taylor bubbles. It was concluded that the rise velocity of Taylor bubbles decreases with an increase in liquid viscosity and, on the other hand, increases with an increase in superficial gas velocity.

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