ENCIT2012-050 EFFECTS OF FLOW TOPOLOGY ON INERTIAL PARTICLE ACCELERATION - PDF
Juan Pablo de Lima Costa Salazar, UFSC, Brazil
Lance R. Collins, Cornell University, United States
Abstract: Flow topology and its connection to acceleration of inertial particles is explored through invariants of the strain-rate and rotation-rate tensors. A semi-quantitative analysis is performed where we assess the contribution of specific flow topologies to acceleration moments. Our findings show that the contributions of regions of high vorticity and low strain decrease significantly with Stokes number, a non-dimensional measure of particle inertia. The contribution from regions of low vorticity and high strain exhibit a peak at a Stokes number of approximately 0.2. The results shown here have recently been published in [Salazar, J.P.L.C. and Collins, L.R., 2012. ``Inertial particle acceleration statistics in turbulence: Effects of filtering, biased sampling, and flow topology'. Phys. Fluids, Vol. 24, p. 083302].
Keywords:Turbulence; Inertial Particle Acceleration; Flow Topology.
Presentation Schedule: Thursday, 09:20-09:40. Session: FMR1-2. Presenter: Juan Pablo Salazar.
ENCIT2012-353 A NEW SET OF VORTEX IDENTIFICATION PARAMETERS BASED ON THE STRAIN ACCELERATION TENSOR - PDF
Raphael David Aquilino Bacchi, Roney Leon Thompson, UFF, Brazil
Abstract: A mathematical definition of a vortex became an important issue in Fluid Mechanics specially after the recognition of the importance of coherent structures on the turbulence dynamics. The birth, evolution, dissipation and death of a vortical coherent structure plays a crucial role on the understanding of turbulence as a phenomenon. In this context, the evaluation of the strain acceleration, as the strain itself is crucial to determine the flow tendency. When those two entities presents ortogonal or out-of-phase behavior, its correct to classify the region as a vortex. The performance of a new set of vortex identification parameters are evaluated for the so called ABC flow (u,v,w)=(A sin z + C cos y, B sin x + A cos z, C sin y + B cos x), which is an example of a laminar Trkalian Beltramian flow exhibiting chaotic behavior. Those vortex identification parameters differ from the previous parameters presented in some papers.
Keywords:Vortex; Coherent vortical structure; Frame Invariance.
Presentation Schedule: Tuesday, 16:20-16:40. Session: FMR1-1. Presenter: Raphael David Aquilino Bacchi.
ENCIT2012-224 FLUID MOTION OVER SUCCESSIVE SQUARE PROTUBERANCES MOUNTED ON A FLAT PLATE: FLOW PATTERNS AND VORTEX SHEDDING FREQUENCY - PDF
Giulio Cervo, Fábio Basaglia Fonseca, Sérgio Said Mansur, Edson Del Rio Vieira, UNESP, Brazil
Abstract: In the present paper, flow patterns and vortex shedding phenomenon produced by square protuberances placed on a smooth flat wall are experimentally studied by means of flow visualization and hot-film anemometry. Qualitative and quantitative information have been obtained for Reynolds numbers up to 2 500. The experiments have been performed in a vertical low turbulence hydrodynamic tunnel operated by gravitational action in blow-down mode. Flow patterns have been captured in photographic still images, while vortex shedding frequencies have been determined by hot-film anemometry. Injection of liquid dye upstream protuberances have allowed to visualize the recirculating flow inside cavities as well as vortex formation and shedding in the shear layer over the protuberances. Flow visualization has also helped to identify the best position to insert the hot-film probe in the flow in order to obtain a vortex shedding frequency with a high signal noise ratio. Flow visualization images obtained at different Reynolds have shown the complex topological structure of the flow, characterized by vortex shedding, recirculating bubbles, reverse flow and boundary layer separation and attachment. Additionally, the behavior of the dimensionless vortex shedding frequency as a function of the Reynolds number has been determined.
Keywords:Flow visualization; Vortex shedding.
Presentation Schedule: Tuesday, 15:40-16:00. Session: FMR1-1. Presenter: Edson Del Rio Vieira.
ENCIT2012-306 PARAMETRIC SCALING OF TURBULENT IMPINGING JETS OVER SMOOTH SURFACES - PDF
Juliana Braga Rodrigues Loureiro, Atila Pantaleão Silva Freire, UFRJ, Brazil
Abstract: The purpose of this work is to investigate the validity of some parametric scaling equations for the description of turbulent impinging jets over smooth surfaces. An experimental campaign has been performed with the aid of a Laser-Doppler Anemometer. Results presented in this work shows mean velocity and higher order distribution along different radial positions over the smooth impingement plate. Two different parametric analyses are evaluated. The first is based on the use of classical variables of the problem, such as nozzle diameter, nozzle-to-plate space and bulk velocity of the jet, whereas the second approach of analysis considered some gross parameters of the jet, for example, its momentum flux. The parametric description of the impinging jet is evaluated against the experimental results.
Keywords:Turbulence; Impinging jet; Laser Doppler Anemometry; Scaling analysis.
Presentation Schedule: Tuesday, 15:00-15:20. Session: FMR1-1. Presenter: Juliana Loureiro.
ENCIT2012-136 BIVARIATE ANALYSIS BY FINITE MIXTURE MODEL OF A BISTABLE TIME SERIES ON THE FLOW AFTER TWO ROWS TUBE BANK - PDF
Alexandre Vagtinski de Paula, Sergio Viçosa Möller, UFRGS, Brazil
Abstract: This work presents a study of a turbulent bistable flow on two rows of a triangular tube array. Velocity time series are obtained with the constant temperature hot wire anemometry technique in an aerodynamic channel and are used as input data in a finite mixture model to classify the observed data according to a family of probability density functions (PDF). In this context, the bistable phenomenon is considered as an incomplete data problem and PDF-estimation is performed using the observed data. The bistability phenomenon is analyzed as a bivariate function, and the number of clusters in the fitting process was considered equal to two, where an expectation-maximization algorithm was applied to estimate the maximum log-likelihood function according to a normal PDF with aid of a Monte Carlo method, to obtain the probability distribution function which is more likely to have produced the observed data. The experimental time series obtained show the bistable nature of the flow, with changes in the mean velocity levels from one flow mode to the other. The simulations with the bivariate Gaussian mixture model and the expectation-maximization algorithm show a goodness of fit in both flow modes, what suggests that the bistable phenomenon can be treated as a Gaussian process in the studied geometry.
Keywords:turbulent flow; circular cylinders; hot wires; bivariate probability density function; finite mixture models.
Presentation Schedule: Tuesday, 15:20-15:40. Session: FMR1-1. Presenter: Alexandre Vagtinski de Paula.
ENCIT2012-145 THE HILBERT-HUANG TRANSFORM: AN APPLICATION ON THE SHEDDING PROCESS - PDF
Rodrigo Santiago Silveira Horszczaruk, Sergio Viçosa Möller, UFRGS, Brazil
Abstract: The use of mathematical tool for the treatment of data signal is very common, especially in turbulence flows. Because of the nature of the turbulence, the demand for tools to analyze non-stationary and non-linear signals becomes valid in the characterization of flow around bluff bodies. This kind of study leads to analysis of shedding process around these bodies, which reveal parameters such as vortex shedding frequency. This paper propose a new tool, associated to other mathematical tools currently used, called Hilbert-Huang Transform which will be applied to the analysis of turbulent flow around a single cylinder. The main features of the Hilbert-Huang transform and its advantages as a tool for analysis of turbulent flows are presented. A brief discussion and comparison with others methods used is made.
Keywords:Hilbert-Huang transform; Empirical Mode Decomposition; turbulent flow; shedding process; Fast Fourier transform.
Presentation Schedule: Thursday, 10:20-10:40. Session: FMR1-2. Presenter: Sergio Möller.
ENCIT2012-192 ON FRICTION FACTORS FOR PSEUDOPLASTIC FLUIDS IN TURBULENT PIPE FLOW - PDF
Luiz C. F. Andrade, Antonio G. B. Cruz, Fernado P. Duda, UFRJ, Brazil
Abstract: In this work are formulated friction-factor equations for the turbulent flow of fluids with rheological behavior described by Sisko and Cross models. The formulation assumes a logarithmic behavior of the turbulent mean velocity profiles near the wall and consider an approach that uses friction-factor equations valid for power law fluids established in literature. The friction factors computed with the proposed relationships showed values lower than those obtained with the equation of Prandtl-von Kármán, valid for Newtonian fluids. The goal of this work is to establish relationships for the prediction of friction factor that take into account the rheological behavior of types of non-Newtonian fluids aforementioned whose characteristic is the description of variations of viscosity over a spectrum more large of shear rates than power law rheology.
Keywords:Non-Newtonian Fluids; Turbulent Flows; Friction Factor; Drag Reduction.
Presentation Schedule: Thursday, 09:00-09:20. Session: FMR1-2. Presenter: Luiz C. F. Andrade.
ENCIT2012-141 HOT FILM CALIBRATION SYSTEM USING A FREE JET IN WATER - PDF
Edson Vieira Del Rio, Sérgio Said Mansur, Edson Del Rio Vieira, UNESP, Brazil
Abstract: Notwithstanding the existence of more recent technologies for velocity measurements in fluids, Hot Wire Anemometry (HWA) is even today a very important tool for fluid mechanics research. Despite all its advantages relatively to other instruments for local flow measumerents, the frequent need of probe calibration remains the bigest difficulty for using this type of anemometer. A device for film probe calibration in water medium for low velocities has been proposed in the present work. This calibration apparatus produces a free jet with Reynolds numbers up to 1.2x104 and the probe is placed in the root of the jet, in a position whose the velocity is well known. Visualized images of the free jet has been captured and measurements of the velocity profile and turbulence level have been carried out. These qualification tests showed that the apparatus is absolutely appropriate for performing the task for which it has been designed.
Keywords:Hot film anemometry; Turbulence; Flow visualization; Free jet; Probe calibration.
Presentation Schedule: Tuesday, 14:20-14:40. Session: FMR1-1. Presenter: Edson Del Rio Vieira.
ENCIT2012-256 FLOW AROUND A SQUARE RIB NEAR A PLANE WALL - PDF
Rodrigo Augusto Bassan, Odenir de Almeida, UFU, Brazil
Sérgio Said Mansur, Emanuel Rocha Woiski, Edson Del Rio Vieira, UNESP, Brazil
Abstract: In this work, vortex shedding phenomenon produced by a square cylindrical protuberance placed near a smooth flat wall with a small gap is experimentally studied by means of flow visualization and hot-film anemometry. Qualitative and quantitative information have been obtained for Reynolds numbers up to 1 000. Qualitative results obtained by means of flow analysis show a complexe topological vortex structure and quantitative results depict the behaviour of the vortex shedding frequency in function of the Reynolds number.
Keywords:Vortex shedding; Auto correlation; Flow visualization.
Presentation Schedule: Tuesday, 16:00-16:20. Session: FMR1-1. Presenter: Edson Del Rio Vieira.
ENCIT2012-314 DESIGN OF AN INTEGRATED OPTICAL UNIT FOR LASER DOPPLER ANEMOMETRY - PDF
Eric Esteves Aderne, Alcidney Valério Chaves, José Luiz da Silva Neto, Juliana Braga Rodrigues Loureiro, UFRJ, Brazil
Abstract: The objective of this work is to describe the design of an integrated optical unit for Laser Doppler Anemometry measurements. This unit allows the system to be operated either on the reference mode or in the dual beam configuration, depending on the geometrical arrangement of the optical components on the bench. The unit does also allow the measurements to be performed on forward and backscatter modes. The results shown here were obtained under controlled conditions to specifically investigate the performance of the proposed optical arrangement and components. Results demonstrate the considerable potential of the measurement technique.
Keywords:Turbulence; Laser-Doppler Anemometry; Instrumentation; Experimental measurements.
Presentation Schedule: Tuesday, 14:40-15:00. Session: FMR1-1. Presenter: Eric Esteves Aderne.
ENCIT2012-381 ANALYSIS OF DIFFERENT LEVELS OF APPROXIMATION OF THE REYNOLDS STRESS TENSOR USING TENSOR DECOMPOSITION THEOREMS - PDF
Marcel Oliveira, Roney Leon Thompson, Luiz Eduardo Bittencourt Sampaio, UFF, Brazil
Gilmar Mompean, Laurent Thais, Polytech-Lille, France
Abstract: In the so-called RANS approach, turbulent models provide closure equations that relate the Reynolds stress with kinematic tensors. In this study, we extend a methodology presented by $\backslash$cite{TMT10} to quantify the dependence of the Reynolds stress tensor on mean kinematic tensor basis. The methodology is based upon tensor decomposition theorems which allows to extract from the anisotropic Reynolds stress tensor the parts that are or proportional or in-phase with the rate-of-strain tensor and the parts that are or proportional or in-phase to the persistence-of-straining tensor (which is orthogonal to the rate-of-strain tensor). The study was conducted using DNS (direct numerical simulation) data for square duct flow with, (\$Re\_{$\backslash$tau}=160\$). Different sets of tensorial basis provide different levels of approximations. These levels are measured through normalized indexes that are essentially a ratio of the Euclidean norm of the model to the Euclidean norm of the Reynolds stress. We have performed 3 new tests in order to complete a previous analysis of 3 other approximation models done in $\backslash$cite{TMT10}. Interestingly, we are able to identify the regions of the domain better approximated by each model. With the proposed methodology, the scalar coefficients of nonlinear algebraic turbulent models can also be determined.
Keywords:RANS; Tensor decompositions; Turbulent closures.
Presentation Schedule: Thursday, 10:00-10:20. Session: FMR1-2. Presenter: Roney Thompson.
ENCIT2012-209 FIVE-HOLE PRESSURE PROBE CALIBRATION FOR APPLICATION INTO CYCLONIC CHAMBER - PDF
Priscila dos Santos Campos, Félix Gazel Hussein, Alan Tihiro Dias Nakashima, Danielle Regina da Silva Guerra, Manoel Fernandes Martins Nogueira, UFPA, Brazil
Abstract: Complex flows of fluids are usually found in nature and have multiple applications in engineering. The experimental study about it is of great scientific and technological area, especially in aeronautic, meteorological and oil-gas fields. The measurement of thinskind of flow obtained greats advances using optical techniques as Laser Doppler Anemometry (LDA) and Particle Image Velocimetry (PIV). However, the instruments for these techniques are quite expensive becoming inaccessible to many laboratories. Therefore, the multiholes pressure probe becomes a feasible alternative to detail the complex flow behavior, once it has a low cost of manufacture and supplies the pressure and average velocity fields, taking advantage between other measurements techniques previously reported that do not have this resource. In this work it is described the procedure for calibrating a hemispherical water-cooled five-hole probe for application in combustion chamber, using the reference system with relation to \&\#945; (yaw angle) and \&\#946; (pitch angle) for determining the velocity field. Such a system is expressed in terms of the horizontal angle \&\#945; and the vertical angle \&\#946;, which are projection angles of the velocity vector on the horizontal plane and on the vertical plane with relation to the axis of the probe.
Keywords:Probe; Five hole; Complex flow; Calibration; Flow characteristics.
Presentation Schedule: NO PRESENTATION.
ENCIT2012-244 STUDY OF WAKE REGION BEHIND OF ISOLATED CUBIC BUILDING.PART II: NUMERICAL SIMULATIONS - PDF
Larisse Suzy Silva Oliveira, Juliana Glicério Dazzi, Reginaldo Rosa Cotto de Paula, Mariane Gonçalves Miranda, Fernanda Capucho Cezana, IFES, Brazil
Marcos Sebastião de Paula Gomes, PUC-Rio, Brazil
Abstract: This paper presents numerical simulation of wind flow around an isolated cubic building. The numerical simulations were carried out with the Omega Reynolds Stress, standard \&\#61547;\&\#61485;\&\#61541;\&\#61472;and RNG \&\#61547;\&\#61485;\&\#61541;\&\#61472; turbulence models. Experimental data from wind tunnel experiments in the neutral boundary layer were used to validate the numerical results. The Reynolds number, based on the height of the building was 1.5 \&\#61620;104. The main purpose of the present study is to investigate the behavior of a wake region formated behind an isolated cubic building. In addition were determined the length of reattachement points in the roof and near the wake region of the body.
Keywords:numerical simulations; turbulence models; atmospheric boundary layer; building.
Presentation Schedule: Thursday, 09:40-10:00. Session: FMR1-2. Presenter: Reginaldo Rosa Cotto de Paula.