Transport mechanisms of the turbulent energy cascade in upward/downward bubbly flows

2014 ◽  
Vol 741 ◽  
pp. 514-542 ◽  
Author(s):  
J. Lelouvetel ◽  
T. Tanaka ◽  
Y. Sato ◽  
K. Hishida
Keyword(s):  
Energy Budget ◽  
Relative Velocity ◽  
Flow Direction ◽  
Bubble Diameter ◽  
Turbulent Energy ◽  
Energy Cascade ◽  
Transverse Motion ◽  
Scaling Analysis ◽  
Upward Flow ◽  
Downward Flow

AbstractThe turbulent energy cascade in an upward or downward bubbly pipe flow with a Reynolds number of 1.5 × 104 was experimentally investigated in order to examine the effects of the flow direction on the turbulence modifications by bubbles. The bubble diameter was approximately 1 mm. The combination of a particle tracking velocimetry (PTV) system with Kolmogorov-order spatial and temporal resolutions and a shape projection imaging (SPI) system was used to simultaneously capture the liquid and bubble motions. The physical mechanisms of turbulence modification at each length scale, or in wavenumber space, were investigated by introducing a filtering-based scaling analysis, in which the filtering techniques derived from large eddy simulation (LES) were applied to the PTV measurements. The analysis can be used to examine the turbulent kinetic energy (TKE) exchange between bubbles and flows at each wavenumber. We observed significant differences in the flow statistics and turbulent energy budget of upward and downward flows, which are due to the sign of the relative velocity of bubbles. A negative relative velocity (downward flow) induces greater modifications in the energy budget than a positive relative velocity (upward flow), which suggests that the bubble-transport term of the turbulent energy is greater when the flow has to push down the bubbles. The flow provides more energy to the bubbles when it pushes them in the downward direction. The flow will also receive and dissipate more energy from the bubbles in a downward flow compared with an upward flow due to the greater transverse motion of the bubbles. The analysis introduced in the present study shows that the energy transfer from large to small scales is decreased in an upward flow and is increased in a downward flow. Similarly, the sign of the bubble term indicates that turbulent flow receives energy from bubbles in an upward flow, while it transfers energy to bubbles in a downward flow. We also observed that this energy transport is approximately 10 times larger in a downward flow than in an upward flow.

Void Fraction Covariance in Two-Phase Flows

2012 ◽  
Author(s):  
Caleb S. Brooks ◽  
Yang Liu ◽  
Takashi Hibiki ◽  
Mamoru Ishii
Keyword(s):  
Experimental Data ◽  
Void Fraction ◽  
Relative Velocity ◽  
Upward Flow ◽  
Two Phase Flows ◽  
Group Approach ◽  
Two Phase ◽  
Downward Flow ◽  
Group Area ◽  
Flow Configurations

A void fraction covariance in the expression for area-averaged local relative velocity has been assumed to be one by current and past researchers. Similarly, in a multi-bubble group approach, void covariances for each bubble group appear in the group area-averaged relative velocity expressions. The covariance terms have been analyzed with a substantial database from literature including upward flow in pipe diameters of 1.27 cm to 15.2 cm, downward flow in pipe diameters of 2.54 cm and 5.08 cm, and upward flow in an annulus (Dh = 1.9cm) under adiabatic, boiling, and condensing conditions. Simple relations are proposed to specify the covariance in order to improve the prediction of area-averaged local relative velocity. The correlations were found to agree well with the experimental data for the flow configurations and conditions analyzed.

Dynamics of collapse of an impact central uplift: Evidence from folds and faults in the collar of the Vredefort Dome, South Africa

2021 ◽  
Author(s):  
Shalene Manzi ◽  
Roger L. Gibson ◽  
Asinne Tshibubudze
Keyword(s):  
South Africa ◽  
Structural Analysis ◽  
Large Scale ◽  
Second Order ◽  
Upward Flow ◽  
Downward Flow ◽  
Kinematic Pattern ◽  
Central Uplift ◽  
Convergent Flow ◽  
Order Structures

ABSTRACT Structural analysis of overturned metasedimentary strata of the lower Witwatersrand Supergroup in the inner collar of the Vredefort Dome reveals the presence of tangential folds and faults associated with the 2.02 Ga impact. The folds are distinct from previously identified subradially oriented, vertical to plunging-inclined, gentle folds that are interpreted as the products of convergent flow (constriction) during the initial stages of central uplift formation. The tangential folds comprise disharmonic, open, asymmetric, horizontal to plunging-inclined anticline-syncline pairs with centripetally dipping axial planes and right-way-up intermediate limbs. They display centripetal-down vergence (anticline radially outward of the syncline) that is consistent with steep inward-directed shear of the overturned strata. We attribute this kinematic pattern to subvertical collapse of the Vredefort central uplift during the latter stages of crater modification. The folds are cut by pseudotachylite-bearing steep to vertical tangential faults that display center-down slip of <10 m up to ~150 m. Both the tangential folds and the faults suggest that the large-scale overturning of strata related to outward collapse of the Vredefort central uplift was accompanied by a component of inward-directed collapse via layer-parallel shearing and folding, followed by faulting. Subradially oriented faults with conjugate strike separations of 1–2 km in the NNE collar of the dome suggest penecontemporaneous tangential extension of the inner collar rocks. This evidence indicates that second-order structures in the metasedimentary collar of the Vredefort Dome preserve a complex, multistage record of evolving strain associated with both initial convergent and upward flow (constriction) related to central uplift rise and later divergent and downward flow (flattening) linked to its collapse, and that centripetally directed collapse features may be important components of the structural inventory of very large central uplifts.

CFD Simulation of Two-Phase Vertical Annular Flow in Both Upward and Downward Direction in a Small Pipe

2019 ◽  
Author(s):  
Ekhwaiter Abobaker ◽  
Abadelhalim Elsanoose ◽  
John Shirokoff ◽  
Mohammad Azizur Rahman
Keyword(s):  
Film Thickness ◽  
Multiphase Flow ◽  
Pressure Gradient ◽  
Annular Flow ◽  
Cfd Simulation ◽  
Flow Direction ◽  
Flow Behavior ◽  
Two Phase ◽  
Downward Flow ◽  
Disturbance Wave

Abstract Computational fluid dynamics (CFD) simulation is presented to investigate the annular flow behavior in the vertical pipe by using ANSYS Fluent platform 17.2. The study was analyzed complex behavior of annular flow in two cases (upward and downward flow) for different air superficial velocities and range of Reynolds number for water, in order to obtain the effect of orientation flow and increasing superficial gas and liquid velocities on the base film, mean disturbance wave thickness, the average longitudinal size of disturbance wave as well as pressure gradient. For multiphase flow model, the volume of fluid method (VOF) for two-phase flow modelling was used and coupled with RNG k-ε turbulence model to predict fully annular flow structures in the upward and downward flow direction. From CFD simulation results, it is clear to see how increases in air velocity result in reductions in film thickness and increase in pressure gradient. Additionally, the results showed monotonic enhancement of film thickness occurring in tandem with increases in the liquid flow rate. However, due to the effect of gravitational force and interfacial friction, the film thickness and pressure gradient are slightly larger for the upward flow than for the downward flow. The results agree with the recent experimental data that studied the annular flow behavior and pressure drop in the upward and downward flow direction. This study will be very helpful in understanding multiphase flow behavior in natural gas wells.

The turbulent boundary layer over transverse square cavities

1999 ◽  
Vol 395 ◽  
pp. 271-294 ◽  
Author(s):  
L. DJENIDI ◽  
R. ELAVARASAN ◽  
R. A. ANTONIA
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Flow Direction ◽  
Reynolds Shear Stress ◽  
Local Maximum ◽  
Turbulent Energy ◽  
Skin Friction Coefficient ◽  
Reynolds Stresses ◽  
Smooth Wall ◽  
Local Skin

Laser-induced uorescence (LIF) and laser Doppler velocimetry (LDV) are used to explore the structure of a turbulent boundary layer over a wall made up of two-dimensional square cavities placed transversely to the flow direction. There is strong evidence of occurrence of outflows of fluid from the cavities as well as inflows into the cavities. These events occur in a pseudo-random manner and are closely associated with the passage of near-wall quasi-streamwise vortices. These vortices and the associated low-speed streaks are similar to those found in a turbulent boundary layer over a smooth wall. It is conjectured that outflows play an important role in maintaining the level of turbulent energy in the layer and enhancing the approach towards self-preservation. Relative to a smooth wall layer, there is a discernible increase in the magnitudes of all the Reynolds stresses and a smaller streamwise variation of the local skin friction coefficient. A local maximum in the Reynolds shear stress is observed in the shear layers over the cavities.

scholarly journals Scale-by-scale turbulent energy budget in the intermediate wake of two-dimensional generators

2013 ◽  
Vol 25 (11) ◽  
pp. 115105 ◽  
Author(s):  
F. Thiesset ◽  
R. A. Antonia ◽  
L. Danaila
Keyword(s):  
Energy Budget ◽  
Turbulent Energy ◽  
Two Dimensional

Experiment of Heat Transfer to Supercritical Water Flowing in Vertical Annular Channels

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Zhendong Yang ◽  
Qincheng Bi ◽  
Han Wang ◽  
Gang Wu ◽  
Richa Hu
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Flux ◽  
Supercritical Water ◽  
Experimental Parameter ◽  
Outer Diameter ◽  
Buoyancy Effect ◽  
Upward Flow ◽  
Downward Flow ◽  
Annular Channels

An experimental study of heat transfer to supercritical water has been performed at Xi'an Jiaotong University with a vertical annular tube. The annular test sections were constructed with an annular gap of 2 mm and an internal heater of 8 mm outer diameter. Experimental parameter covered pressures of 23 and 25 MPa, mass fluxes of 700 and 1000 kg/m2s, and heat fluxes of 200–1000 kW/m2. Experimental data were acquired from downward flow and upward flow, respectively. There were differences of heat-transfer characteristics between the two flow directions. Compared to upward flow, the heat-transfer coefficient increased at downward flow. A strong effect of spacer on heat transfer is observed at locations downstream of the device in the annuli regardless of flow direction. The spacer effect impaired the buoyancy effect at low heat flux, but not for large heat flux. Complex of forced convection and mixed convection in supercritical water is due to various thermophysical properties and the gravity. The affected zone of the spacer effect depends on the flow conditions. The buoyancy effect was analyzed qualitatively in this study and the criterion Gr¯/Re2.7<10-5 for negligible heat-transfer impairment was discussed. Four correlations were compared with the experimental data; the Swenson correlation predicted nearly the experimental data but overpredicted slightly the heat-transfer coefficients.

Gas-Liquid Bubbly Flow in Vertical Pipes

1996 ◽  
Vol 118 (2) ◽  
pp. 377-382 ◽  
Author(s):  
V. E. Nakoryakov ◽  
O. N. Kashinsky ◽  
V. V. Randin ◽  
L. S. Timkin
Keyword(s):  
Shear Stress ◽  
Single Phase ◽  
Liquid Velocity ◽  
Bubbly Flow ◽  
Upward Flow ◽  
Flow Conditions ◽  
Downward Flow ◽  
Velocity Fluctuations ◽  
Turbulent Fluctuations ◽  
Diameter Pipe

Gas-liquid bubbly flow was investigated in vertical pipes for different flow conditions: fully developed turbulent downward flow in a 42.3 mm diameter pipe and upward flow in a 14.8 mm diameter pipe with liquid of elevated viscosity. Wall shear stress, local void fraction, and liquid velocity profiles, shear stress, and velocity fluctuations were measured using an electrodiffusional method. Results obtained demonstrate the existence of “universal” near-wall velocity distribution in a downward bubbly flow. The reduction of turbulent fluctuations is observed in downward flow as compared to a single-phase turbulent flow. The development of bubble-induced liquid velocity fluctuations in a “laminar” bubbly flow was studied.

scholarly journals Proton Kinetic Effects and Turbulent Energy Cascade Rate in the Solar Wind

2013 ◽  
Vol 111 (20) ◽  
Author(s):  
K. T. Osman ◽  
W. H. Matthaeus ◽  
K. H. Kiyani ◽  
B. Hnat ◽  
S. C. Chapman
Keyword(s):  
Solar Wind ◽  
Turbulent Energy ◽  
Energy Cascade ◽  
Kinetic Effects

Dissolution of a Carbon Dioxide Bubble in a Vertical Pipe

2007 ◽  
Author(s):  
Satoru Abe ◽  
Hideaki Okawa ◽  
Shigeo Hosokawa ◽  
Akio Tomiyama
Keyword(s):  
Carbon Dioxide ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Relative Velocity ◽  
Bubble Diameter ◽  
Bulk Liquid ◽  
Vertical Pipe ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Millipore Water

Dissolution of single carbon dioxide (CO2) bubbles in a vertical pipe of 25 mm in diameter are measured to examine the effects of the ratio λ of sphere–volume equivalent bubble diameter d to pipe diameter D, liquid Reynolds number ReL and surfactants on mass transfer. The bubble diameter d and Reynolds number ReL are varied from 5.0 to 26 mm (λ = 0.20 − 1.0) and from 0 to 3100, respectively. Millipore water, tap water and water contaminated with Triton X–100 are used for the liquid phase. Mass transfer coefficients kL are evaluated from changes in d. The kL decreases with increasing λ for bubbles in stagnant millipore water because of the decrease in bubble rising velocity due to the wall effect. Measured Sherwood numbers Sh do not depend on ReL because a turbulent fluctuation velocity in bulk liquid flow is much smaller than a relative velocity between a bubble and liquid. The mass transfer correlation for a bubble in a stagnant liquid proposed by Johnson et al. is applicable to a bubble in pipe flow, provided that a correct relative velocity between a bubble and liquid is substituted in the correlation. Due to the retardation of capillary wave, mass transfer coefficients for bubbles in contaminated water becomes smaller than those in millipore and tap waters.

Sign in / Sign up

Export Citation Format

Share Document