Download or read book Effect of Length Scales on the Mixing of Passive Scalars in Grid Turbulence written by Abdullah MohammadFarid N. Alkudsi and published by . This book was released on 2012 with total page 184 pages. Available in PDF, EPUB and Kindle. Book excerpt: The study of passive scalars in turbulence research is a technologically important topic. This study seeks to investigate the effect of the variation of integral length scale, and scalar injector size and separation on turbulent mixing. The study is motivated by devices such as the simple gas turbine pre-mixer where these three relevant length scales are present. Heated wakes of different sizes and separations are produced by heating various sets of thin wires in a horizontal wire grid. The horizontal wire screen is placed downstream of biplane grids of different mesh sizes. Time-resolved velocity and temperature are measured by a dual hot and cold wire probe. Assessments of the effect of the array of thin wires used as the scalar generator on the velocity and scalar fields behind the turbulence grid are presented. The evolution of the profiles of the first four statistical moments of temperature fluctuations across the wake with downstream distance is studied for various scalar injector size and separation for several integral length scales. Specifically, the downstream evolution of a single thermal wake is studied for source sizes that range from less than the Kolmogorov to larger than the integral length scale. Also included in the study the downstream evolution and interaction of two thermal wakes is also presented. For the single wake, the wake growth, sufficiently far from the generator, for all source sizes is found to be consistent with the assumption that the effective diffusivity is constant across the wake. The evolution of the effective diffusivity with downstream distance is found to be independent of the source size and identical to the evolution of the effective diffusivity of a line source in the same velocity field. The effects of changing the velocity integral scale are governed by the effect of the integral scale on the evolution of the effective turbulent diffusivity. Those effects are found to be similar in character to the effect on a line source. The mean scalar of two sources is found to be the sum of the mean of the individual sources. Higher statistical moments show more complex relationships.

Download or read book The Effect of Initial Integral Scale on the Mixing of Passive Scalar in Grid generated Turbulence written by Oleg O. Goushcha and published by . This book was released on 2010 with total page 177 pages. Available in PDF, EPUB and Kindle. Book excerpt: The present study is focused on the effect of variation of the size of the large scale structure on the mixing of a passive scalar in nearly homogeneous grid-generated turbulence. A passive scalar is introduced into the flow by means of a grid consisting of closely separated horizontal wires. A set of ten wires is heated by means of an electrical current passed thorough the wires. A temperature change of about 0.7° C is observed just downstream of the wires, which is low enough so the heated fluid can be considered a passive scalar. The mean velocity is held constant at about 6m/s. Free-stream turbulence is produced by means of biplane grids with a mesh size, Mu=2.54cm, 5.08cm, and 10.16cm which leads to corresponding grid Reynolds numbers of 8401, 16802, and 33605, respectively. It is found that the normalized mean temperature plotted as a function of the vertical distance from the centerplane normalized by the half wake width are nearly similar in shape far downstream of the wire grid. The profiles of the normalized root mean square temperature, normalized temperature skewness and kurtosis plotted as a function of the vertical distance from the centerplane normalized by the half wake width are not similar even far downstream of the wire gird for all grids. At moderate distances downstream of the wire grid (for example x/Mu=10 for Mu=2.45cm), the Probability Density Functions show the presence of ambient temperature fluid on the centerplane far downstream of the wire-grid. This can occur when the thermal wake produced by the wire grid "flaps", i.e. the heated wake moves vertically with time without significant mixing.

Download or read book Experimental Studies of Homogeneous Passive Scalars in Grid generated Turbulence written by Anuvat Sirivat and published by . This book was released on 1983 with total page 554 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Effect of Initial Scalar Size on the Mixing of a Passive Scalar in Grid generated Turbulence written by Ory D. Selzer and published by . This book was released on 2001 with total page 646 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Theoretical Investigation of a Passive Scalar Such as Temperature in Isotropic Turbulence written by Robert McDougall Kerr and published by . This book was released on 1981 with total page 296 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book PDF Models for Mixing in Turbulent Reactive Flows written by Shankar Subramaniam and published by . This book was released on 1997 with total page 414 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Passive Scalar Dispersion and Mixing in Isotropic Grid Turbulence and in a Turbulent Jet written by Chenning Tong and published by . This book was released on 1995 with total page 352 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Mixing of a Passive Scalar in Isotropic and Sheared Homogeneous Turbulence written by E. Shirani and published by . This book was released on 1981 with total page 192 pages. Available in PDF, EPUB and Kindle. Book excerpt: In order to calculate the velocity and passive scalar fields in homogeneous turbulent flows, the three-dimensional, time-dependent equations of motion and the diffusion equation have been solved numerically.

Download or read book Applied Mechanics Reviews written by and published by . This book was released on 1981 with total page 960 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Food Mixing written by P. J. Cullen and published by John Wiley & Sons. This book was released on 2009-07-21 with total page 304 pages. Available in PDF, EPUB and Kindle. Book excerpt: The mixing of liquids, solids and gases is one of the most commonunit operations in the food industry. Mixing increases thehomogeneity of a system by reducing non-uniformity or gradients incomposition, properties or temperature. Secondary objectives ofmixing include control of rates of heat and mass transfer,reactions and structural changes. In food processing applications,additional mixing challenges include sanitary design, complexrheology, desire for continuous processing and the effects ofmixing on final product texture and sensory profiles. Mixing ensures delivery of a product with constant properties. Forexample, consumers expect all containers of soups, breakfastcereals, fruit mixes, etc to contain the same amount of eachingredient. If mixing fails to achieve the requiredproduct yield, quality, organoleptic or functional attributes,production costs may increase significantly. This volume brings together essential information on theprinciples and applications of mixing within food processing. Whilethere are a number of creditable references covering generalmixing, such publications tend to be aimed at the chemical industryand so topics specific to food applications are often neglected.Chapters address the underlying principles of mixing, equipmentdesign, novel monitoring techniques and the numerical techniquesavailable to advance the scientific understanding of food mixing.Food mixing applications are described in detail. The book will be useful for engineers and scientists who need tospecify and select mixing equipment for specific processingapplications and will assist with the identification and solving ofthe wide range of mixing problems that occur in the food,pharmaceutical and bioprocessing industries. It will also be ofinterest to those who teach, study and research food science andfood engineering.

Download or read book Statistics and Scaling Laws of Turbulent Scalar Mixing at High Reynolds Numbers written by and published by Cuvillier Verlag. This book was released on 2014-06-26 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt: The turbulent motion of fluids and scalars is a highly complex problem. It is still one of the unsolved problems of classical physics, cf. Nelkin (1992) and Shraiman and Siggia (2000), and the description remains challenging. The understanding of turbulent flows and turbulent mixing is of great interests for many applications. Prominent examples are the turbulent combustion of chemical reactants and the dynamics of the atmosphere or the oceans. In those cases the evolution of the scalar affects the turbulent flow itself. Here, we focus on the case where the scalar is both conserved and passive and does not affect the flow field.

Download or read book A Four dimensional Experimental Study of Passive Scalar Mixing in Turbulent Flows written by Kenneth B. Southerland and published by . This book was released on 1994 with total page 424 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Turbulent Mixing of Passive Scalars at High Schmidt Number written by Shuyi Xu and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A numerical study of fundamental aspects of turbulent mixing has been performed, with emphasis on the behavior of passive scalars of low molecular diffusivity (high Schmidt number Sc). Direct Numerical Simulation is used to simulate incompressible, stationary and isotropic turbulence carried out at high grid resolution. Data analyses are carried out by separate parallel codes using up to 10243 grid points for Taylor-scale Reynolds number (R(lambda) up to 390 and Sc up to 1024. Schmidt number of order 1000 is simulated using a double-precision parallel code in a turbulent flow at a low Reynolds number of R (lambda) 8 to reduce computational cost to achievable level. The results on the scalar spectrum at high Schmidt numbers appear to have a ...

Download or read book The Effect of Multiple Scales on Fractal grid generated Turbulence written by Alexis Kathleen Omilion and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Fractal grids, having patterns that repeat at different length scales, mimic the multi-scale characteristic of objects of complex appearance in nature, such as branching pulmonary network, river network, trees, and cumulus clouds. Understanding the role that multiple length scales have in momentum and energy transport is essential for effective utilization of fractal grids in a wide variety of engineering applications. While previous studies have solidified the dominant effect of the largest scale of fractal grids, effects of the additional scales on the generated turbulent flow remain unclear. This research is to determine how the smaller fractal scales (and the interaction between the multiple scales) influence the turbulence statistics of the induced flow and the pressure drop across a fractal square grid using well-controlled water-tunnel experiments. Instantaneous and ensemble-averaged velocity fields are obtained by a planar Particle Image Velocimetry (PIV) for a set of fractal square grids (N = 1, 2, 3 and 4) at the Reynolds number of 3400. The static pressure drop across the grids are measured by a differential pressure transducer. Flow fields indicate that the multiple jets, wakes and the shear layers produced by the multiple scales are the fundamental flow physics that promote momentum transport in the turbulence. In addition, the multiple scales cause a redistribution of the turbulent kinetic energy and a change in the vortex shedding mechanism behind the grids. The grid of 3 fractal scales (N = 3) produces higher turbulence intensity levels than the grid with 4 fractal scales (N = 4) despite having a lower blockage ratio and pressure drop, owing to the suppression of vortex shedding by the additional scale of the grid of N = 4. To better predict the location of peak turbulence intensity, the wake interaction length scale model is modified to incorporate the effects of the interactions among multiple scales by the effective mesh size and an empirical scaling coefficient Beta. Considering the capability of fractal grids to enhance momentum and energy transport, this work can potentially benefit a wide variety of applications where energy-efficient mixing or convective heat transfer is a key process.

Download or read book The Small scale Structure of Passive Scalar Mixing in Turbulent Boundary Layers written by Lakshmi P. Dasi and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The objective is to contribute to several issues regarding the traditional view of the local structure of passive scalar fields: (1) probability density function (PDF) of the scalar concentration and scalar gradient, (2) the scalar power spectrum, (3) the structure functions, and (4) correlation functions and multi-point correlators. In addition, the research provides a geometric description of two-dimensional transects of the passive scalar iso-surfaces using the tools of fractal geometry. The local structure is analyzed as a function of large-scale anisotropy, intermittency factor, Reynolds number, and initial condition of the scalar injection. Experiments were performed in the bed boundary layer produced by a uniform depth open channel flow of water in a tilting flume for Re [subscript lambda] = 63, 94, and 120. A small nozzle iso-kinetically delivers a passive scalar of high Schmidt number (Sc = 1000) at mid-depth to generate the turbulent scalar field. Three nozzle diameters are used to study the effects of the injection length scale. High-resolution planar laser induced fluorescence (PLIF) technique is used to measure the scalar field. The local structure far from isotropic and is influenced even at the smallest scales by large-scale anisotropy, initial injection length scale and the Reynolds number of the flow. The PDF of the scalar fluctuations is non-Gaussian and dependent on large-scale anisotropy. The PDF of scalar gradients show the influence of large-scale anisotropy on the structure at the smallest scales. The spectrum of the scalar field deviates from the k [superscript -5/3] prediction in the inertial convection regime and is dependent on large-scale anisotropy, external intermittency, and low Reynolds number. There is no evidence of Batchelors k [superscript -1] scaling law. The scaling exponents of the even-ordered structure functions appear to be inversely correlated with the kurtosis of the scalar fluctuations. The fractal geometry of the two dimensional transects of passive scalar iso-surfaces is scale dependent. The fractal dimension is 1.0 at the smallest length scale and increases in a universal manner in the viscous-convective regime. The coverage length underestimate reflects this universal behavior with practical significance. The lacunarity function shows that the instantaneous scalar field is most in-homogenous around the Kolmogorov scale.

Download or read book Turbulent Premixed Flames written by Nedunchezhian Swaminathan and published by Cambridge University Press. This book was released on 2011-04-25 with total page 447 pages. Available in PDF, EPUB and Kindle. Book excerpt: A work on turbulent premixed combustion is important because of increased concern about the environmental impact of combustion and the search for new combustion concepts and technologies. An improved understanding of lean fuel turbulent premixed flames must play a central role in the fundamental science of these new concepts. Lean premixed flames have the potential to offer ultra-low emission levels, but they are notoriously susceptible to combustion oscillations. Thus, sophisticated control measures are inevitably required. The editors' intent is to set out the modeling aspects in the field of turbulent premixed combustion. Good progress has been made on this topic, and this cohesive volume contains contributions from international experts on various subtopics of the lean premixed flame problem.

Download or read book Recent Awards in Engineering written by and published by . This book was released on 1983 with total page 986 pages. Available in PDF, EPUB and Kindle. Book excerpt: