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COB74 ORTLER VORTICES/TOLLMIEN-SCHLICHTING WAVES INTERACTION: REASSESSMENT OF PREVIOUS RESULTS WITH A SPATIAL/NONPARALLEL MODEL
Márcio T. Mendonça, Philip J. Morris, and Laura L. Pauley
Centro T'ecnico Aeroespacial - Instituto de Atividades Espaciais. São José dos Campos, SP 12228-904 - Brazil,
The Pennsylvania State University, Dept. of Aerospace Eng. and Dept. of Mechanical Eng.
University Park, PA 16802 - USA. E-mail: y pjm@cac.psu.edu, z lpauley@psu.edu
The interaction between G¨ortler vortices and Tollmien-Schlichting waves is studied with a spatial, non-parallel model based on the Parabolized Stability Equations. A reassessment of previous results obtained with temporal, parallel models is performed showing that the main conclusions obtained with those models are valid but the parallel flow assumption does influence the results. New results not previously available in the literature for Tollmien-Schlichting wave amplitudes of the same order of magnitude as the vortices are also presented.
Keywords: Görtler vortices, instability, boundary layer, Tollmien-Schlichting waves, vortices de Görtler, instabilidade, camada limite, ondas de Tollmien-Schlichting
Atila P. Silva Freire
Mechanical Engineering Program (COPPE/UFR,I), C.P. 68503, 21945-970 Rio de Janeiro, Brazil.
The present, work introduces a new expression for the velocity profile in the near wall region of a turbulent boundary layer. The new theory uses asymptotic arguments and considerations of the mixing length type to find a local analytical solution which presents the correct asymptotic behavior both close to wall in the laminar sub-layer and in the logarithmic region of the flow. Next, heuristic arguments are evoked to add a damping function to the local solution. This function provides an excellent correction to the original analytical solution, furnishing a solution valid for the whole range of inner scales. The resulting expression is compared with ten other different, formulations for the problem. The results are also compared with some experimental test cases.
Keywords: Law of the Wall,Turbulence, Boundary Layer. Lei da Parede, Turbulência, Camada Limite
COB248 CHARACTERISTICS OF A TURBULENT-BOUNDARY LAYER WHEN SUBJECTED TO A STEP CHANGE IN SURFACE ROUGHNESS AND TEMPERATURE
Mila R. Avelino, Philippe P. M. Menut and Atila P. Silva Freire
Mechanical Engineering Program (COPPE/UFRJ), C.P. 68503, 21945-970 Rio de Janeiro, Brazil.
The present work uses asymptotic and Heuristic arguments to develop a theory for the description of turbulent boundary layer flows over surfaces with a step change in roughness and in temperature. Based on the concept of the displacement in origin, the theory proposes a new expression for the near wall logarithmic temperature profile, which is then used as a boundary condition for a k-Î modeling of the external flow. The results are tested for a sea breeze that advances over dry land. Simulations of velocity and temperature profiles, and of skin-friction and of Stanton number profiles are presented.
Keywords: Turbulent, Boundary Layer, Surface Roughness, Atmospheric Flows, k-Î model.
Turbulência, Camada Limite, Rugosidade Superficial, Escoamento Atmosférico, modelo k-Î .
COB249 AN ALGEBRAIC TURBULENCE MODEL FOR THE DESCRIPTION OF BUBBLE PLUMES
Andréa C. Alves, Jian Sut and Atila P. Silva Freire
Mechanical Engineering Program (COPPEIUFRJ), C.P. 68503@ 21945-970 Rio de Janeiro, Brazil
Department of Mechanical and Material Engineering, Military Engineering School (IMEIRJ)
22290-270, Rio de Janeiro, Brazil
The present work advances a new algebraic turbulence model for the description of bubble plumes. The model is based on the eddy viscosity and bubble diffusity concepts, resorting to dimensional arguments and experimental data to arrive at functional relationships involving only primitive variables of the flow. The model is an improvement over other algebraic models in literature, providing better results at lower computational cost. The results include predictions of the velocity profiles, of the void fraction and of the plume radius. The four constants that appear in the theory are determined through comparison with the data of Milgram and Van Houten(1982) and of Milgram(1983), for depths ranging from 6 to 20 meters. The agreement is shown to be very good.
Keywords: Multiphase Flows, Turbulence Modeling, Bubble Plumes, Algebraic Turbulence Models, Finite Difference Methods
Escoamento Multiffico, Modelagem Turbulenta, Pluma de Bolhas, Método de Diferenças Finitas
COB250 FURTHER RESULTS ON THE ASYMPTOTIC BEHAVIOUR OF INTERACTING TURBULENT BOUNDARY LAYERS AND SHOCK WAVES
Guilherme S. Terra, Jian Sut and Atila P. Silva Freire
Mechanical Engineering Program (COPPE/UFRJ), C.P. 68503, 21945-970 Rio de Janeiro, Brazil.
Departinent of Mechanical and Material Engineering, Military Engineering School (IME/RJ), 22290-270, Rio de Janeiro, Brazil.
The present work makes a critical compilation of some experimental data to corroborate the p4ysical Validity of the theoretical asymptotic structure resulting from an application of Kaplun limits to the shock-wave/turbulent, boundary la.yer interaction problem. The interaction of a shock wave with a turbulent boundary layer is a very complex and rich phenomenon, where the steep pressure gradient imposed to the boundary layer by the shock wave gives rise to an inviscid interaction process in a region which would be otherwise viscous dominated. Thus, in a classical three deck asymptotic model of the compressible turbulent boundary lekyer (Silva Freire(1989a)), the turbulent region must change so as to comply to this constraint. In far-t, according to the single limit concept of Kaplun, in the interaction region the turbulent region completely disappears. The new arising asymptotic structure consists then of two distinct regions: the wall viscous region and the outer inviscid region. Here, these two regions are clearly identified by a careful processing of some experimental data. Considering some flow measurements, one is capable of evaluating the dominant terms in the Navier-Stokes, from which the asymptotic structure can then be ascertained. With the new asymptotic structure, a simplified theory can then be developed for the inner regions of the flow. The results obtained through the simplified theory are compared with calculations provided by a full Navier-Stokes code and with some experimental data for velocity, pressure and skin-friction. The full N-S code uses a finite difference explicit scheme. In the numerical simulation, the turbulent shear stresses are evaluated through an algebraic model and a half-equation differential model.
Keywords: Interaction, turbulence, Boundary Layer, Shock Wave, Kaplun Limits. / Interação, Turbulência,Camada Limite, Onda de Choque, Limites de Kaplun
COB328 - LAMINAR-TURBULENT TRANSITION: THE NONLINEAR EVOLUTION OF THREE-DIMENSIONAL WAVETRAINS IN A LAMINAR BOUNDARY LAYER
Marcello A. Faraco de Medeiros 1
Departamento de Engenharia Mec"anica
Escola de Engenhariade S~ao Carlos - Universidade de S~ao Paulo
Rua Dr. Carlos Botelho, 1465, S~ao Carlos, 13560-250 - SP - Brazil
E-mail:mafdm@sc.usp.br
Abstract
This paper presents results of an experimental study of the transition in boundary layers. The experiments
were conducted in a low-turbulence wind tunnel. The process was triggered by a three-dimensional
Tollmien-Schlichting wavetrain excited by a harmonic point source in the plate. Hot-wire anemometry
was used to measure the signal and investigate the nonlinear regime of these waves. It was observed
that the three-dimensional wavetrain behaved very differently from two-dimensional ones. In particular,
it did not involve the growth of subharmonics or higher harmonics. The first nonlinear signal to appear
was a mean flow distortion. This had a spanwise structure consisting of regions of positive and negative
mean distortion distributed like streaks, which became more complex as the nonlinearity developed.
Elsewhere studies have revealed the existence of streak-structures in turbulent flow. It is conjectured
that the current experiments may provide a link between early wave-like instabilities and some coherent
structures of turbulent boundary layers.
Keywords
Laminar-turbulent transition, hydrodynamic instability, boundary layer, hot-wire anemometry, nonlinear
systems.
P.G.P. Toro, Z. Rusak, H.T. Nagamatsu, L.N. Myrabo
Department of mechanical Engineering, Aeronautical Engineering and Mechanics, Rensselaer Polytechnic Institute, Troy, NY 12180-3590 - USA, torop@rpi.edu, rusakz@rpi.edu, nagamh@rpi.edu, myrabl@rpi.edu
A new set of self-similar solutions of a compressible laminar boundary layer is used for air as perfect gas and where the viscosity is a power function of the temperature. Modified Levy-Mangler and Dorodnitsyn-Howarth transformations are presented to solve the flow in a thin laminar boundary layer with no external pressure gradients on a smooth flat plate. This results in an explicit relation between the stream function and the enthalpy fields described by a closed coupled system of nonlinear ordinary differential equations. In the present work boundary layer flows with external Mach numbers up to 15 are studied and the skin friction and heat transfer coefficients for a hot wall case are presented. The present solution methodology provides a straight forward way of comparing results using the viscosity-temperature linear relation, Sutherland’s law and the relation according to the kinetic theory. Also, the results may provide important data needed for the design of future hypersonic vehicles.
Keywords: Self-Similar Equations, Compressible Laminar Boundary Layer, Supersonic and Hypersonic Flows.
COB686 SIMULATION AND TESTING OF A SATELLITE SOLAR ARRAY GENERATOR WING DEPLOYMENT
Antonio Claret Palerosi
Instituto Nacional de Pesquisas Espaciais - INPE, Divisão de Mecânica Espacial e Controle - DMC
Sérgio Frascino M. de Almeida
Instituto Tecnológico de Aeronáutica - ITA, Divisão de Engenharia Mecânica e Aeronáutica - IEM
Petrônio Noronha de Souza
Instituto Nacional de Pesquisas Espaciais - INPE, Divisão de Mecânica Espacial e Controle - DMC
This work studies the solar panels deployment of the Chinese-Brazilian satellite CBERS. The problem solution demands some deployment tests and the development of two different dynamic simulation models: one more complex related to the laboratory and another one related to orbit conditions. This work begins with a description of the deployment mechanisms, of the test device and of the deployment dynamic problem. The problem formulation is discussed and the use of a computer package for dynamic analysis of mechanisms is justified. The dynamic simulation models, the test results, the adjustment of the model parameters to fit the simulation to the test results, the laboratory and the in-orbit simulation results are presented. The importance of the inclusion in the dynamic models of the solar panel synchronizing mechanisms, of the aerodynamic forces of the solar panels due to the laboratory atmosphere, and of the solar panels initial deformations are discussed.
Keywords: Satellite, solar array deployment, dynamic simulation model, dynamic of multibody systems, model adjustment.
COB695 UMA SOLUÇÃO PARA A CAMADA-LIMITE DE CONCENTRAÇÃO JUNTO A SUPERFÍCIES LIVRES EM ESCOAMENTOS TURBULENTOS
Harry Edmar Schulz & Selva Amaral Garcia Schulz
Departamento de Hidráulica e Saneamento, Escola de Engenharia de São Carlos - USP - São Carlos
CEP 13560-250 São Carlos, Brasil - E-mail:heschulz@sc.usp.br
This paper presents an analytical solution for the concentration boundary layer along free surfaces in a turbulent flow, obtained by convenient approximations for the turbulent diffusivity in this region and by a particular nondimensionalization applied to the governing equation for the mass transfer. The later produced an equation describing mass transfer at the gas-liquid interface which leads to a general solution for the geometry under study. The analysis of mass flux through the interface by an approximate solution permitted obtaining an expression that involves classical dimensionless coefficients for the problem of mass transfer such as Reynolds, Schmidt and Sherwood numbers. This expression relates the Sherwood number in a traditional form to the other two dimensionless parameters.
Key words: Absorção de Gases, Dessorção de Gases, Turbulência Interfacial, Transferência Interfacial de Massa, Camada-Limite de Concentração, Gas Absorption, Gas Desorption, Interfacial Turbulence, Interfacial Mass Transfer, Concentration Boundary Layer.
COB697 ESTUDO EXPERIMENTAL DE ESCOAMENTOS TURBULENTOS EM DUTOS CURVOS COM GRANDES RAIOS DE CURVATURA
This work presents experimental results of fully developed turbulent flows in two curved rectangular duct sections with small curvature. Mean velocity and turbulent intensity profiles are measured using Pitot tubes and a hot wire anemometer system along a 3000 mm x 460 mm x 50 mm rectangular duct and also along the central longitudinal positions af the curved duct sections of 1500 mm and 1800/p mm curvarture radii, respectively.
Keywords: Turbulence, Hot-Wire Anemometer, Wind Tunnel, Data Acquisition System, Curved Ducts
COB762 ANÁLISE NUMÉRICA DO ESCOAMENTO EM DUTOS COM ALETAS TRANSVERSAIS / NUMERICAL ANALYSIS OF FLOW THROUGH TRANSVERSAL FIN DUCTS
Cláudia Regina de Andrade e Edson Luiz Zaparoli
CTA - ITA - IEM - Departamento de Energia - E-mail: zaparoli@mec.ita.cta.br
A numerical study was performed on the augmentation of the heat transfer for internal flow through flat plates containing transversal fins. The duct width and the fins spacing were kept constant and 17 fins were affixed along the heated plate side. Two fin heights were simulated and the heat transfer rate was compared with the smooth duct case. Numerical results obtained for the mean heat transfer coefficients and experimental data showed good agreement. Also reported was the grid refinement effect on the numerical solution accuracy.
Keywords: Dinâmica de Fluidos Computacional/Computational Fluid Dynamics, Escoamento Turbulento/Turbulent Flow, Aletas/Fins, Intensificação da Transferência de Calor/Enhanced Heat Transfer.
COB774 MIXING OF CONFINED COAXIAL TURBULENT JETS IN DUCTS OF VARYING CROSS SECTION
Marcelo J.S. de Lemos Amarildo Milan
Dept. de Energia, ITA-CTA EMBRAER - GEA -EAD/APC
12228-900 - São José dos Campos, SP, Brasil - E-mail: mlemos@tecsat.com.br
Computations for the mean and turbulent fields for the flow field formed by two coaxial streams confined in a duct of varying cross section are presented. The widely-used marching-forward method of Patankar-Spalding was used for sweeping the computational domain. The standard k-# presented
Keywords: Duct Flow, Turbulence Modeling, CFD
COB1011 AN ASSESSMENT OF THE RNG k-e TURBULENCE MODEL APPLIED TO THE FLOW IN RADIAL DIFFUSERS
César J. Deschamps, Álvaro T. Prata & Rogério T.S. Ferreira
Department of Mechanical Engineering, Federal University of Santa Catarina, 88040-900 - Florianópolis - SC - Brazil
E-mail: deschamps@emc.ufsc.br
The present work considers the turbulent flow modeling in a radial diffuser with axial feeding using the RNG k-e model of Orzag et al. (1993). The model has been recommended for flows including features such as stagnation and recirculation regions, curvature and adverse pressure gradients (all of them are not properly taken into account by the standard k-e model). The flow through radial diffusers possesses all the aforementioned flow features and therefore is a good test case to further assess the RNG k-e model. Numerical results of pressure distribution along the surface of one of the diffuser disks are compared to experimental data and show that the RNG k-e model can predict quite successfully the flow.
Keywords: Turbulence modeling, radial diffusers, valves.
COB1215 UM MODELO ALGÉBRICO DE TURBULÊNCIA PARA ESCOAMENTO EM CAMADA LIMITE SUJEITA A UM FORTE GRADIENTE DE PRESSÃO ADVERSO/AN ALGEBRAIC TURBULENCE MODEL FOR STRONG ADVERSE PRESSURE GRADIENT BOUNDARY LAYER
Daniel O de Almeida Cruz & Nelson Kuwahara
Grupo de Turbomáquinas Departamento de Engenharia Mecânica do Centro Tecnológico. UFPa
66075-900 Belém-PA-Brasil -gtdem@amazon.com.br
In this work a new algebraic turbulence closure model, developed for adverse pressure gradient boundary layer, is presented. A new characteristic velocity which takes into account the effects of the pressure gradient as well as the influence of the shear stress at the wall is also presented. A comparison with experimental data clearly shows that the proposed model is superior to the Cebeci-Smith one in treating separating flows.
Keywords: Camada Limite, turbulência, separação, modelo algébrico / boundary layer, turbulence, separation, algebraic model.
COB1221 O PROBLEMA DA CAMADA LIMITE PARA AVALIAÇÃO DE PERDAS: UMA METODOLOGIA ALTERNATIVA / BOUNDARY-LAYER FORMULATION FOR LOSS CALCULATION: AN ALTERNATIVE APPROACH
Daniel O. Almeida. Cruz e André.L. Amarante Mesquita
Grupo de Turbomáquinas, Depto. de Engenharia Mecânica, Universidade Federal do Pará,
66075-900 Belém-PA-Brasil - E:mail: gtdem@amazon.com.br
In this work, an alternative approach for loss calculation in external flows is proposed, by applying Kaplun limits to the Navier-Stokes equations, obtaining a generalized boundary layer formulation. It is shown that this alternative formulation can be reduced into a ‘quasi similar’ differential equation that can be solved as an ordinary one. Numerical solutions of this equation are presented showing that it contains the Falkner - Skan equation as a particular case.
Keywords: Análise assintótica, camada limite, similaridade / asymptotic analysis, boundary-layer, similarity
COB1226 COHERENT VORTICES IN SOLID PROPELLANT ROCKET MOTORS USING LARGE-EDDY SIMULATION
Jorge Hugo Silvestrini 1;2 , Pierre Comte 1 & Marcel Lesieur 1
1 Equipe Modelisation et Simulation de la Turbulence, Laboratoire des Ecoulements Geophysiques et In-
dustriels, INPG, BP 53X, 38041 Grenoble-Cedex 9, France
2 Departamento de Matematica Pura e Aplicada, UFRGS, Av. Bento Gon¸calves 9500, 91501-970 Porto
Alegre - RS, Brasil, E-mail: silvestr@mat.ufrgs.br (Present address)
Coherent vortices in solid propellant rockets motors are investigated by numerical experimentation, via full Navier-Stokes solution in two-dimensional configurations and Large-Eddy Simulation (LES) in a three-dimensional one. Particular attention is paid to the vortex shedding phenomena of Kelvin-Helmholtz vortices and their interaction with the chamber's acoustic. The LES results show that streamwise secondary vortices of mixing layers and Dean-G¨ortler type vortices may be also present in these kind of geometries.
Keywords: Coherent Vortices - Large-Eddy Simulation - Subgrid Scales Models - Solid Propellant Rocket Motors.