Structure of Turbulent Adiabatic Wall Plumes

1986 ◽  
Vol 108 (4) ◽  
pp. 827-834 ◽  
Author(s):  
M.-C. Lai ◽  
S.-M. Jeng ◽  
G. M. Faeth
Keyword(s):  
Flow Structure ◽  
Large Scale ◽  
Vertical Wall ◽  
Light Sheet ◽  
Mie Scattering ◽  
Wall Structure ◽  
Turbulent Structures ◽  
Adiabatic Wall ◽  
Stable Orientation ◽  
Turbulent Wall

Weakly buoyant turbulent wall plumes were studied for surfaces inclined 0–62 deg from the vertical (stable orientation). The source of buoyancy was carbon dioxide/air mixtures in still air, assuring conserved buoyancy flux. Profiles of mean and fluctuating concentrations and streamwise velocities were measured at several stations along the wall. Flow structure was also observed by Mie scattering from a laser light sheet. Tests with inclined walls showed that low levels of ambient stratification caused the wall plumes to entrain fluid in the horizontal direction, rather than normal to the wall. Structure predictions were made for vertical wall plumes, considering Favre-averaged mixing-length and k–ε–g models of turbulence. Both methods yielded encouraging predictions of flow structure, in spite of the presence of large-scale coherent turbulent structures observed in the flow visualization.

Mixture Fraction Statistics of Plane Self-Preserving Buoyant Turbulent Adiabatic Wall Plumes

1999 ◽  
Vol 121 (4) ◽  
pp. 837-843 ◽  
Author(s):  
R. Sangras ◽  
Z. Dai ◽  
G. M. Faeth
Keyword(s):  
Large Scale ◽  
Mixture Fraction ◽  
Vertical Wall ◽  
Power Spectra ◽  
Probability Density Functions ◽  
Density Functions ◽  
Adiabatic Wall ◽  
Integral Scales ◽  
Smooth Plane ◽  
Motion Measurements

Measurements of the mixture fraction properties of plane buoyant turbulent adiabatic wall plumes (adiabatic wall plumes) are described, emphasizing conditions far from the source where self-preserving behavior is approximated. The experiments involved helium/air mixtures rising along a smooth, plane and vertical wall. Mean and fluctuating mixture fractions were measured using laser-induced iodine fluorescence. Self-preserving behavior was observed 92–155 source widths above the source, yielding smaller normalized plume widths and near-wall mean mixture fractions than earlier measurements. Self-preserving adiabatic wall plumes mix slower than comparable free line plumes (which have 58 percent larger normalized widths) because the wall prevents mixing on one side and inhibits large-scale turbulent motion. Measurements of probability density functions, temporal power spectra, and temporal integral scales of mixture fraction fluctuations are also reported.

Small to large scale mixed turbulent convection: buildings application

2018 ◽  
Vol 28 (1) ◽  
pp. 188-205 ◽  
Author(s):  
Souad Morsli ◽  
Mustapha Boussoufi ◽  
Amina Sabeur ◽  
Mohammed El Ganaoui ◽  
Rachid Bennacer
Keyword(s):  
Flow Structure ◽  
Large Scale ◽  
Natural Ventilation ◽  
Vertical Wall ◽  
Cold Temperature ◽  
Temperate Climate ◽  
3D Flow ◽  
Content Type ◽  
Hot Temperature ◽  
The One

Purpose The use of natural ventilation by large openings to maintain thermal comfort conditions in the premises is a concept that is perfectly integrated into the traditional architecture of countries in the Mediterranean region or in tropical climates. In a temperate climate where the architecture is not usually designed to respond to the use of natural ventilation is seasonal and is done at the initiative of the occupants by making changes in the design of their doors. The European interest in natural ventilation, as a passive building air-conditioning technology, is increasing and has been the subject of a research program commissioned by the European Community. In this work, the authors consider a part of a housing compound as a refreshing floor. This floor is maintained at a constant cold temperature, the one vertical wall at hot temperature and other surfaces are adiabatic. Various scenarios are considered for this work. Mixed convection for different boundary conditions and different configurations is carried out. In addition, an airflow is injected through a window and extracted on the opposite window. Classical conclusion and transitional value on Richardson number have been completed by the new thermal configuration with nonsymmetric thermal conditions. The complex 3D flow structure is more obvious when one of the two flows (ventilation or natural convection) dominates. However, the induced heat transfer is less sensitive to the added ventilation. In this study, the authors consider a part of a housing compound as a refreshing floor. This floor is maintained at a constant cold temperature, the one vertical wall at hot temperature and other surfaces are adiabatic. Design/methodology/approach This is a qualitative preliminary study of a 2D–3D flow. The authors examine the competition between the natural convective flow and the added airflow on the flow structure and indoor air quality. The numerical model shows a good agreement with that obtained by researchers analytically and experimentally. To deal with turbulence, the RNG k-ε model has been adopted in this study. Findings The transfer is more sensitive between the 2D and 3D cases for the present analyzed case. Originality/value The study of ventilation efficiency has shown the competition between the big and small structures and the induced discomfort.

Lattice Boltzmann Modeling of Natural Convection in a Large-Scale Cavity Heated From Below by a Centered Source

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Noureddine Abouricha ◽  
Mustapha El Alami ◽  
Ayoub Gounni
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Heat Source ◽  
Flow Structure ◽  
Lattice Boltzmann ◽  
Large Scale ◽  
Vertical Wall ◽  
Convection Heat Transfer ◽  
Turbulent Natural Convection

Turbulent natural convection in a large-scale cavity has taken a great attention thanks to its importance in many engineering applications such as building. In this work, the lattice Boltzmann method (LBM) is used to simulate turbulent natural convection heat transfer in a small room of housing heated from below by means of a heated floor. The ceiling and the four vertical walls of the room are adiabatic except for a portion of one vertical wall. This portion simulates a glass door with a cold temperature θc = 0. The cavity is filled by air (Pr = 0.71) and heated from below with uniformly imposed temperature θh = 1. The effects of the heat source length (Lr) and Rayleigh number (Ra) on the flow structure and heat transfer are studied for ranges of 0.2 ≤ Lr ≤ 0.8 and 5 × 106 ≤Ra ≤ 108. The heat transfer is examined in terms of local and mean Nusselt numbers. The results show that an increase in Rayleigh number or in heat source length increases the temperature in the core of the cavity. The flow structure shows that turbulent natural convection regime is fully developed for Ra = 108. Correlations for mean Nusselt number as a function with Ra for different values of Lr are expressly derived.

Velocity Statistics of Plane Self-Preserving Buoyant Turbulent Adiabatic Wall Plumes

1999 ◽  
Author(s):  
R. Sangras ◽  
Z. Dai ◽  
G. M. Faeth
Keyword(s):  
Vertical Wall ◽  
Power Spectra ◽  
Adiabatic Wall ◽  
Wall Boundary Layer ◽  
Velocity Statistics ◽  
Integral Scales ◽  
Turbulent Wall Jets ◽  
Development Region ◽  
Temporal And Spatial ◽  
Turbulent Wall

Abstract Measurements of the velocity properties of plane buoyant turbulent adiabatic wall plumes (adiabatic wall plumes) are described, emphasizing conditions far from the source where self-preserving behavior is approximated. The experiments involved helium/air mixtures rising along a smooth, plane and vertical wall. Mean and fluctuating streamwise and cross stream velocities were measured using laser velocimetry. Self-preserving behavior was observed 92–156 source widths from the source, yielding smaller normalized plume widths and larger near-wall mean velocities than observations within the flow development region nearer to the source. Unlike earlier observations of concentration fluctuation intensities, which are unusually large due to effects of streamwise buoyant instabilities, velocity fluctuation intensities were comparable to values observed in nonbuoyant turbulent wall jets. The entrainment properties of the present flows approximated self-preserving behavior in spite of continued development of the wall boundary layer. Measurements of temporal power spectra and temporal and spatial integral scales of velocity fluctuations are also reported.

Velocity Statistics of Plane Self-Preserving Buoyant Turbulent Adiabatic Wall Plumes

2000 ◽  
Vol 122 (4) ◽  
pp. 693-700 ◽  
Author(s):  
R. Sangras ◽  
Z. Dai ◽  
G. M. Faeth
Keyword(s):  
Vertical Wall ◽  
Power Spectra ◽  
Adiabatic Wall ◽  
Wall Boundary Layer ◽  
Velocity Statistics ◽  
Integral Scales ◽  
Turbulent Wall Jets ◽  
Development Region ◽  
Temporal And Spatial ◽  
Turbulent Wall

Measurements of the velocity properties of plane buoyant turbulent adiabatic wall plumes (adiabatic wall plumes) are described, emphasizing conditions far from the source where self-preserving behavior is approximated. The experiments involved helium/air mixtures rising along a smooth, plane, and vertical wall. Mean and fluctuating streamwise and cross-stream velocities were measured using laser velocimetry. Self-preserving behavior was observed 92–156 source widths from the source, yielding smaller normalized plume widths and larger near-wall mean velocities than observations within the flow development region nearer to the source. Unlike earlier observations of concentration fluctuation intensities, which are unusually large due to effects of streamwise buoyant instabilities, velocity fluctuation intensities were comparable to values observed in nonbuoyant turbulent wall jets. The entrainment properties of the present flows approximated self-preserving behavior in spite of continued development of the wall boundary layer. Measurements of temporal power spectra and temporal and spatial integral scales of velocity fluctuations are also reported. [S0022-1481(00)00504-1]

Recent Developments in the Downstream Processing of Phycobiliproteins from Algae: A Review

2021 ◽  
Vol 06 ◽  
Author(s):  
Ayekpam Chandralekha Devi ◽  
G. K. Hamsavi ◽  
Simran Sahota ◽  
Rochak Mittal ◽  
Hrishikesh A. Tavanandi ◽  
...  
Keyword(s):  
Cell Wall ◽  
Large Scale ◽  
Downstream Processing ◽  
Review Article ◽  
Current Status ◽  
Wall Structure ◽  
Scale Production ◽  
Cell Wall Disruption ◽  
Recent Developments ◽  
Macro Algae

Abstract: Algae (both micro and macro) have gained huge attention in the recent past for their high commercial value products. They are the source of various biomolecules of commercial applications ranging from nutraceuticals to fuels. Phycobiliproteins are one such high value low volume compounds which are mainly obtained from micro and macro algae. In order to tap the bioresource, a significant amount of work has been carried out for large scale production of algal biomass. However, work on downstream processing aspects of phycobiliproteins (PBPs) from algae is scarce, especially in case of macroalgae. There are several difficulties in cell wall disruption of both micro and macro algae because of their cell wall structure and compositions. At the same time, there are several challenges in the purification of phycobiliproteins. The current review article focuses on the recent developments in downstream processing of phycobiliproteins (mainly phycocyanins and phycoerythrins) from micro and macroalgae. The current status, the recent advancements and potential technologies (that are under development) are summarised in this review article besides providing future directions for the present research area.

Large Eddy Simulations of Staggered Parallel-Plate Flows

2005 ◽  
Author(s):  
M. V. Pham ◽  
F. Plourde ◽  
S. K. Doan
Keyword(s):  
Heat Transfer ◽  
Numerical Simulations ◽  
Heat Transfer Enhancement ◽  
Parallel Plate ◽  
Large Scale ◽  
Primary Objective ◽  
Transfer Enhancement ◽  
Turbulent Structures ◽  
Wide Range ◽  
Large Eddy

Heat transfer enhancement is a subject of major concern in numerous fields of industry and research. Having received undivided attention over the years, it is still studied worldwide. Given the exponential growth of computing power, large-scale numerical simulations are growing steadily more realistic, and it is now possible to obtain accurate time-dependent solutions with far fewer preliminary assumptions about the problems. As a result, an increasingly wide range of physics is now open for exploration. More specifically, it is time to take full advantage of large eddy simulation technique so as to describe heat transfer in staggered parallel-plate flows. In fact, from simple theory through experimental results, it has been demonstrated that surface interruption enhances heat transfer. Staggered parallel-plate geometries are of great potential interest, and yet many numerical works dedicated to them have been tarnished by excessively simple assumptions. That is to say, numerical simulations have generally hypothesized lengthwise periodicity, even though flows are not periodic; moreover, the LES technique has not been employed with sufficient frequency. Actually, our primary objective is to analyze turbulent influence with regard to heat transfers in staggered parallel-plate fin geometries. In order to do so, we have developed a LES code, and numerical results are compared with regard to several grid mesh resolutions. We have focused mainly upon identification of turbulent structures and their role in heat transfer enhancement. Another key point involves the distinct roles of boundary restart and the vortex shedding mechanism on heat transfer and friction factor.

Large-scale structure and entrainment in the supersonic mixing layer

1995 ◽  
Vol 284 ◽  
pp. 171-216 ◽  
Author(s):  
N. T. Clemens ◽  
M. G. Mungal
Keyword(s):  
Mach Number ◽  
High Speed ◽  
Large Scale ◽  
Mixture Fraction ◽  
Mixing Layer ◽  
Mie Scattering ◽  
Planar Laser ◽  
The Cross ◽  
Convective Mach Number ◽  
Stream Direction

Experiments were conducted in a two-stream planar mixing layer at convective Mach numbers,Mc, of 0.28, 0.42, 0.50, 0.62 and 0.79. Planar laser Mie scattering (PLMS) from a condensed alcohol fog and planar laser-induced fluorescence (PLIF) of nitric oxide were used for flow visualization in the side, plan and end views. The PLIF signals were also used to characterize the turbulent mixture fraction fluctuations.Visualizations using PLMS indicate a transition in the turbulent structure from quasi-two-dimensionality at low convective Mach number, to more random three-dimensionality for$M_c\geqslant 0.62$. A transition is also observed in the core and braid regions of the spanwise rollers as the convective Mach number increases from 0.28 to 0.62. A change in the entrainment mechanism with increasing compressibility is also indicated by signal intensity profiles and perspective views of the PLMS and PLIF images. These show that atMc= 0.28 the instantaneous mixture fraction field typically exhibits a gradient in the streamwise direction, but is more uniform in the cross-stream direction. AtMc= 0.62 and 0.79, however, the mixture fraction field is more streamwise uniform and with a gradient in the cross-stream direction. This change in the composition of the structures is indicative of different entrainment motions at the different compressibility conditions. The statistical results are consistent with the qualitative observations and suggest that compressibility acts to reduce the magnitude of the mixture fraction fluctuations, particularly on the high-speed edge of the layer.

Characterization of Geometrical and Temporal Properties of Large-scale Motions in Turbulent Flows

2021 ◽  
Author(s):  
Christina Tsai ◽  
Kuang-Ting Wu
Keyword(s):  
Turbulent Flow ◽  
Turbulent Flows ◽  
Coherent Structures ◽  
Large Scale ◽  
Streamwise Velocity ◽  
Turbulent Structures ◽  
Temporal Properties ◽  
Turbulent Statistics ◽  
Spatial Locations

<p>It is demonstrated that turbulent boundary layers are populated by a hierarchy of recurrent structures, normally referred to as the coherent structures. Thus, it is desirable to gain a better understanding of the spatial-temporal characteristics of coherent structures and their impact on fluid particles. Furthermore, the ejection and sweep events play an important role in turbulent statistics. Therefore, this study focuses on the characterizations of flow particles under the influence of the above-mentioned two structures.</p><div><span>With regard to the geometry of turbulent structures, </span><span>Meinhart & Adrian (1995) </span>first highlighted the existence of large and irregularly shaped regions of uniform streamwise momentum zone (hereafter referred to as a uniform momentum zone, or UMZs), regions of relatively similar streamwise velocity with coherence in the streamwise and wall-normal directions.  <span>Subsequently, </span><span>de Silva et al. (2017) </span><span>provided a detection criterion that had previously been utilized to locate the uniform momentum zones (UMZ) and demonstrated the application of this criterion to estimate the spatial locations of the edges that demarcates UMZs.</span></div><div> </div><div>In this study, detection of the existence of UMZs is a pre-process of identifying the coherent structures. After the edges of UMZs are determined, the identification procedure of ejection and sweep events from turbulent flow DNS data should be defined. As such, an integrated criterion of distinguishing ejection and sweep events is proposed. Based on the integrated criterion, the statistical characterizations of coherent structures from available turbulent flow data such as event durations, event maximum heights, and wall-normal and streamwise lengths can be presented.</div>

Convergence of numerical simulations of turbulent wall-bounded flows and mean cross-flow structure of rectangular ducts

Meccanica ◽  
2016 ◽  
Vol 51 (12) ◽  
pp. 3025-3042 ◽  
Author(s):  
Ricardo Vinuesa ◽  
Cezary Prus ◽  
Philipp Schlatter ◽  
Hassan M. Nagib
Keyword(s):  
Numerical Simulations ◽  
Flow Structure ◽  
Cross Flow ◽  
Wall Bounded Flows ◽  
Turbulent Wall
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