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COB247 TURBULENT WAKE OF AN AXISYMMETRIC BLUFF BODY

Philippe P. M. Menut† , Joel Delville‡ & Jacques Borée

Institut de Mécanique des Fluides de Toulouse, ENSEEIHT-INPT-URA CNRS 005, Allée C. Soula, 31400 Toulouse, France.

(† )Present address: Mechanical Engineering Program - PEM / COPPE / UFRJ, CP 68503, CEP 21945-970, Rio de Janeiro, Brazil.

(‡ )CEAT / LEA - CNRS 191 - Université de Poitiers, 43 rue l’Aérodrome, 86036 Poitiers, France.

This work deals with the aerodynamic behaviour of new wind sensor balloons which are to be used to evaluate with high precision the atmospheric conditions before Ariane V launches. Due to the high complexity of the system, we undertook an experimental analysis of a model situation. The diagnostic methods used involved global and local detection by hot wire measurement techniques. The Strouhal number of the vortex shedding remains around 0.2 even in a three-dimensional axisymmetric configuration. A spatio-temporal correlation analysis of the data and the application of the POD reveals a strong influence of the drag transition over the near wake. The periodic component of the near wake shows, in the subcritical range, a high level of coherence which strongly decreases over the transition. The coupling of these results with the shape evolution contribute to a better knowledge and control of the stability in high altitude of these new balloons.

Keywords: Axisymmetric bluff body, Turbulent wake, Transition, Coherent structures, Hot wire measurement.

COB271 CONDENSAÇÃO PELICULAR SOBRE TUBOS INCLINADOS ANISOTÉRMICOS / FILM CONDENSATION OVER ANISOTHERMAL INCLINED TUBES

Figueiredo, Antonio Macdowell & Aldélio Bueno Caldeira

Programa de Engenharia Mecânica, COPPE/UFRJ - CP 68.503 CEP 21.945 Rio de Janeiro - E-mail: amdf@serv.com.ufrj.br

A model is presented for the steady laminar film flow of a newtonian liquid condensing from a steady saturated vapor over the non-isothermal external surface of an inclined tube. The analysis results in a universal and non-dimensional semi-analitical solution in respect to Ra and Ja numbers and the duct inclination. The wall temperature variation must be given as a function of the angular position. Calculations are presented for a cosine local temperature distribution. The results are expressed in terms of the dimensionless local film thickness, local and averaged Nusselt numbers, and the temperature distribution parameter. The film thickness is found to depend significantly on the temperatura non-uniformity, whereas the effect on the average Nusselt number depends on the intensity of this temperature variation.

Keywords: Inclined Tubes, Film Condensation, Condensation.

COB537 A MODEL FOR THE ICE CRYSTAL GROWTH IN LAMINAR FALLING FILMS

Kamal A. R. Ismail & Musa M. Radwan

Departamento de Engenharia Térmica e de Fluidos – FEM – UNICAMP Caixa Postal 6122,

CEP 13083-970 – Campinas (SP) – Brasil E-mail: kamal@fem.unicamp.br

A finite volume numerical code has been developed to numerically approximate the rate of ice crystal growth in a laminar falling film flowing down a cooled vertical plate. The governing energy equation contains the phase energy as the source term. Enhancement of heat transfer due to suspended ice crystals is accounted for in the use of effective values of thermal conductivity, viscosity, thermal diffusivity, and specific heat as function of volumetric concentration of ice crystals in the falling film. Nusselt numbers, overall heat transfer coefficients between the fluid and cooled plate, and ice crystal growth rate were calculated for different film thicknesses with and without axial diffusion. Nusselt numbers and ice crystal growth rate were found to be dependent on film thickness. Axial diffusion effects were found to be negligible for larger film thickness (large flowrate).

Keywords: Energy storage, heat transfer enhancement

COB1137 MODELO NUMÉRICO PARA PREVISÃO DE INSTABILIDADES MORFOLÓGICAS NA SOLIDIFICAÇÃO DE LIGAS BINÁRIAS / NUMERICAL MODEL TO EVALUATE MORPHOLOGICAL INSTABILITIES DURING SOLIDIFICATION OF BINARY ALLOYS

Romulo Heringer Ferreira

Departamento de Física, Universidade Federal do Espírito Santo - 29060-900 Vitória, ES - E-mail: romulo@cce.ufes.br

Alvaro Toubes Prata

Departamento de Engenharia Mecânica, Universidade Federal de Santa Catarina - 88040-900 Florianópolis, SC

E-mail: prata@nrva.ufsc.br

A numerical model is proposed to explore heat and mass transfer during the unidirectional solidification of binary metallic alloys in presence of morphological instabilities. The basic hypothesis adopted in the work is that the most important effect in the transport of energy and chemical species during the solidification is the increasing in the solid liquid interface area. With this hypothesis in conjunction with the linear stability theory proposed by Mullins and Sekerka, as well as the conclusions of Langer and Muller-Krumbhaar related to the criterion of marginal stability, the instability effect was included at thermal and solute balances across the solid liquid interface. The energy and solute transport equations were solved simultaneously for both solid and liquid regions using the finite volume methodology. The present model allows to predict interface velocity, enthalpy and solute fields, as well as the primary dendrite arm spacing.

Keywords: alloy solidification, heat and mass transfer in solidification, morphological instabilities, dendrite growth

solidificação, instabilidades morfológicas, crescimento dendrítico