Flow dynamics in Athens area under moderate large-scale winds

1998 ◽  
Vol 32 (12) ◽  
pp. 2209-2222 ◽  
Author(s):  
Dimitrios Melas ◽  
Ioannis Ziomas ◽  
Otto Klemm ◽  
C.S. Zerefos
Keyword(s):  
Large Scale ◽  
Flow Dynamics ◽  
Athens Area

scholarly journals Laboratory validation of an ozone device for recreational water treatment

2013 ◽  
Vol 11 (2) ◽  
pp. 267-276 ◽  
Author(s):  
Robert S. Donofrio ◽  
Sal Aridi ◽  
Ratul Saha ◽  
Robin Bechanko ◽  
Kevin Schaefer ◽  
...  
Keyword(s):  
Large Scale ◽  
Water Systems ◽  
Test System ◽  
Flow Dynamics ◽  
Recreational Water ◽  
Flow Rates ◽  
Bacteriophage Ms2 ◽  
Ozone Disinfection ◽  
Antimicrobial Effectiveness

Obtaining an accurate assessment of a treatment system's antimicrobial efficacy in recreational water is difficult given the large scale and high flow rates of the water systems. A laboratory test system was designed to mimic the water conditions and potential microbial contaminants found in swimming pools. This system was utilized to evaluate the performance of an in situ ozone disinfection device against four microorganisms: Cryptosporidium parvum, bacteriophage MS2, Enterococcus faecium, and Pseudomonas aeruginosa. The sampling regimen evaluated the antimicrobial effectiveness in a single pass fashion, with samples being evaluated initially after exposure to the ozone unit, as well as at points downstream from the device. Based on the flow dynamics and log reductions, cycle threshold (Ct) values were calculated. The observed organism log reductions were as follows: >6.7 log for E. faecium and P. aeruginosa; >5.9 log for bacteriophage MS2; and between 2.7 and 4.1 log for C. parvum. The efficacy results indicate that the test system effectively functions as a secondary disinfection system as defined by the Centers for Disease Control and Prevention's Model Aquatic Health Code.

scholarly journals Investigation of unsteady combustion of methane-air flame in a model combustion chamber with swirling flow

2021 ◽  
Vol 2119 (1) ◽  
pp. 012015
Author(s):  
A S Lobasov
Keyword(s):  
Combustion Chamber ◽  
Large Scale ◽  
Recirculation Zone ◽  
Swirling Flow ◽  
Heating Temperature ◽  
Combustion Products ◽  
Flow Dynamics ◽  
Unsteady Combustion ◽  
Stereoscopic Piv ◽  
Large Scale Vortex

Abstract The present paper reports on the investigation of unsteady combustion of a methane-air mixture, including combustion at increased pressure in the combustion chamber and increased temperature of mixture heating for a model gas-turbine swirl burner based on a design by Turbomeca. To measure the velocity and OH fluorescence fields in the flows a combination of stereoscopic PIV and acetone PLIF systems is used. In all cases, the flow dynamics is associated with the movement of large-scale vortex structures in the inner and outer mixing layers and the flow structure corresponds to a swirling jet with a central recirculation zone containing combustion products. An increase in the heating temperature of the mixture and pressure in the combustion chamber leads to a periodic partial separation of the flame from the model swirl nozzle. However, the flow of fuel through the central channel will stabilize the flame.

Effects of interactions between transient granular flows and macroscopically rough beds and their implications for bulk flow dynamics

2021 ◽  
Author(s):  
Clarence E. Choi ◽  
George Robert Goodwin
Keyword(s):  
Bulk Density ◽  
Large Scale ◽  
The Body ◽  
Flow Dynamics ◽  
Small Scale ◽  
Mobility Models ◽  
Flow Front ◽  
Physical Tests ◽  
Unit Depth ◽  
Rough Beds

Steep-creek beds are macroscopically rough. This roughness causes channelised flow material to decelerate and dissipate energy, which are accounted for by depth-averaged mobility models (DMM). However, practical DMM implementations do not explicitly account for grain-scale basal interactions which influence macroscopic flow dynamics. In this study, we model flows using physical tests with smooth and macroscopically rough bases, and hence evaluate Discrete Element Method (DEM) and DMM models. A scaling effect is identified relating to roughened beds: increasing the number of grains per unit depth tends to suppress dispersion, such that small-scale flows on smooth beds resemble large-scale flows on roughened beds, at least in terms of bulk density. Furthermore, the DEM shows that rougher beds reduce the peak bulk density by up to 15% compared to a smooth bed. Rough beds increase the vertical momentum transfer tenfold, compared to smooth ones. The DMM cannot account for density change or vertical momentum, so DMM flow depths are underestimated by 90% at the flow front and 20% in the body. The Voellmy model implicitly captures internal energy dissipation for flows on rough beds. The parameter ξ can allow velocity reductions due to rough beds observed in the DEM to be captured.

Turbulence Processes Within Turbidity Currents

2021 ◽  
Vol 53 (1) ◽  
pp. 59-83
Author(s):  
Mathew G. Wells ◽  
Robert M. Dorrell
Keyword(s):  
Turbulent Mixing ◽  
Large Scale ◽  
Slope Failure ◽  
Velocity Structure ◽  
Particulate Material ◽  
Control Flow ◽  
Flow Dynamics ◽  
Turbidity Currents ◽  
Sinuous Channel ◽  
Sedimentation Processes

Sediment-laden gravity currents, or turbidity currents, are density-driven flows that transport vast quantities of particulate material across the floor of lakes and oceans. Turbidity currents are generated by slope failure or initiated when a sediment-laden flow enters into a lake or ocean; here, lofting or convective sedimentation processes may control flow dynamics. Depending upon the internal turbulent mixing, which keeps particles in suspension, turbidity currents can travel for thousands of kilometers across the seafloor. However, despite several competing theories, the process for the ultralong runout of these flows remains enigmatic. Turbidity currents often generate large sinuous channel–levee systems, and the dynamics of how turbidity currents flow around channel bends are strongly influenced by internal density and velocity structure, with large-scale flows being modified by the Coriolis force. Therefore, understanding some of the largest sedimentary structures on the Earth's surface depends on understanding the turbulence processes within turbidity currents.

scholarly journals Approximation of potential-driven flow dynamics in large-scale self-similar tree networks

2011 ◽  
Vol 467 (2134) ◽  
pp. 2810-2824 ◽  
Author(s):  
Jason Mayes ◽  
Mihir Sen
Keyword(s):  
Mathematical Model ◽  
Analytical Solutions ◽  
Large Scale ◽  
Differential Algebraic Equations ◽  
Flow Dynamics ◽  
Algebraic Equations ◽  
Tree Networks ◽  
Self Similar ◽  
Large Scale Flow ◽  
The Mathematical Model

Dynamic analysis of large-scale flow networks is made difficult by the large system of differential-algebraic equations resulting from its modelling. To simplify analysis, the mathematical model must be sufficiently reduced in complexity. For self-similar tree networks, this reduction can be made using the network’s structure in way that can allow simple, analytical solutions. For very large, but finite, networks, analytical solutions are more difficult to obtain. In the infinite limit, however, analysis is sometimes greatly simplified. It is shown that approximating large finite networks as infinite not only simplifies the analysis, but also provides an excellent approximate solution.

Anatomy of the sea-breeze circulation in Athens area under weak large-scale ambient winds

1998 ◽  
Vol 32 (12) ◽  
pp. 2223-2237 ◽  
Author(s):  
D. Melas ◽  
I. Ziomas ◽  
O. Klemm ◽  
C.S. Zerefos
Keyword(s):  
Large Scale ◽  
Sea Breeze ◽  
Breeze Circulation ◽  
Athens Area

Investigation on Effect of Inlet Flow Turbulence on the Combustion Instability Using Simultaneous PIV and CH* Chemiluminescence in a Backward Facing Step Combustor

2019 ◽  
Author(s):  
Pankaj Pancharia ◽  
Vikram Ramanan ◽  
Baladandayuthapani Nagarajan ◽  
S. R. Chakravarthy
Keyword(s):  
Turbulence Intensity ◽  
Equivalence Ratio ◽  
Large Scale ◽  
Combustion Instability ◽  
Flow Dynamics ◽  
Airflow Rate ◽  
Backward Facing Step ◽  
Time Resolved ◽  
Flame Holder

Abstract The present study investigates the role of inlet turbulence intensity on the stability characteristics of a lab scale backward facing step combustor (BFS). Turbulence generator placed upstream of the flame holder is used to vary the turbulence levels. The present study utilizes simultaneous chemiluminescence, particle image velocimetry (PIV) and unsteady pressure fluctuation measurement are done in a time-resolved manner to study the role of inlet turbulence intensity on the flame-flow dynamics and identify different modes of combustion instability as a result of the same. The bifurcation plot with airflow rate, in terms of step-based Reynolds number (Re) as the control parameter, indicates a counterintuitive picture, whereby higher turbulence intensity postpones the onset of instability. The finding has been reported in the past by Nagarajan et. al [30], with the present work extending it. It is shown that the flow-flame structures at high (∼1000 Pa) and very high (>4000 Pa), conditions, the dynamics are significantly different across the same turbulence intensity at different equivalence ratio as well as at different turbulence intensities for the same equivalence ratio. Analysis of the flame-flow dynamics reveals the role of the extent of vortex initiated by acoustics and its orientation in forming an unsteady loop, whereby the vortex span and strength aids the flame to propagate upstream of the step, and the flame in-turn being responsible to sustain the large-scale vortex. This phenomenon is distinct from the conventional vortex sustained combustion instability, whereby the vortex is of the lower span and does not influence the upstream flow. The role of inlet turbulence intensity is seen to be more pronounced in the extent of the flame propagating upward, which then completes the fore-mentioned loop.

Numerical investigation of the flow dynamics past a three-element aerofoil

2013 ◽  
Vol 732 ◽  
pp. 401-444 ◽  
Author(s):  
Sébastien Deck ◽  
Romain Laraufie
Keyword(s):  
Numerical Investigation ◽  
Large Scale ◽  
Free Stream ◽  
Pressure Fluctuations ◽  
Phase Relationship ◽  
Feedback Mechanism ◽  
Flow Dynamics ◽  
Free Stream Velocity ◽  
Stream Velocity ◽  
Detached Eddy Simulation

AbstractA numerical investigation of the flow dynamics around a two-dimensional high-lift configuration was carried out by means of a zonal detached eddy simulation (ZDES) technique for flow conditions corresponding to aircraft approach. Both slat and flap regions have been scrutinized and compared with experimental data available in the literature. It is shown that slat and flap coves behave like shallow cavities. The distance between the upstream cusp and the downstream edge is the relevant length scale for each cove taken separately. Consistently with previous findings, this study indicates that the maximum of the broadband spectrum of slat (respectively flap) pressure fluctuations occurs for Strouhal numbers $0. 5\leq \mathit{St}\leq 4$ when based on slat chord (respectively on flap chord) and free-stream velocity. It is shown that mode $(n)$ of the slat cove and mode $(n+ 1)$ of the flap cove are very close making a coherent phase relationship possible. A large-scale coupled self-sustained oscillations mechanism between slat and flap cavities, evidenced by spectral analysis, occurs at a Strouhal number $\mathit{St}= 3{\unicode{x2013}} 6$ based on the main wing chord and free-stream velocity. This yields to an acoustic feedback mechanism characterized by a normalized frequency depending on the free stream Mach number like $\mathit{St}= (1- { M}_{0}^{2} )/ 2{M}_{0} $. The present result appears to line up with the findings by Hein et al. (J. Fluid Mech., vol. 582, 2007, pp. 179–202) who showed that two types of resonance could exist: surface waves ones, scaling with the total aerofoil length and longitudinal cavity-type resonances, scaling with the slat cove length.

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