Luiz Augusto Magalhães Endres

On the fluctuating wall pressure field in tube banks

This paper presents the experimental analysis of pressure and velocity fluctuations of the cross flow in tube banks, with triangular and square arrangements, and four different aspect ratios. Air is the working fluid, driven by a centrifugal blower, passed by a settling chamber and a set of honeycombs and screens, before reaching the tube bank at an incidence angle of 90°. Both triangular and square arrangements have pitch-to-diameter ratios P/D=1.60, 1.26, 1.16 and 1.05, with Reynolds numbers, calculated with the tube diameter and the velocity of the flow in the narrow gap between the tubes, from Re=4×104 to 7×104. Velocity and velocity fluctuations were measured by a constant-temperature hot-wire anemometer, while pressure fluctuations were measured by a piezo-resistive pressure transducer mounted inside one of the tubes in the bank. Behavior of fluctuating quantities is described by means of dimensionless root mean square values and autospectral density functions, while their interdependence is discussed based on cross-correlation functions.

DESENVOLVIMENTO DE OBJETOS EDUCACIONAIS: EXPERIMENTOS EM HIDRÁULICA

Este trabalho objetiva mostrar a necessidade de desenvolver objetos educacionais para o ensino de hidraulica para engenheiros, mais precisamente o desenvolvimento de simuladores virtuais, destacando as vantagens das simulacoes como complemento a aula tradicional expositiva, assim como o ganho no processo de ensino e aprendizagem dos alunos, expostos a este tipo de material instrucional. Para isto foi elaborado um simulador utilizando o software Flash MX da Macromedia, representando uma pratica laboratorial de hidraulica – velocidade em canal. Duas turmas do curso de Engenharia da UFRGS, utilizaram estes objetos educacionais, e diversos fatores do seu uso foi avaliado. Os resultados mostram que o tipo de objeto educacional em questao - a simulacao, pode ser uma boa ferramenta no auxilio a aula convencional e que na area da Engenharia deve-se investir tempo e recursos para implementar este tipo de objetos.

Velocity and pressure fluctuations on inclined tube banks submitted to turbulent flow

This paper presents the experimental study of pressure and velocity fluctuations and their interdependence, in the turbulent flow impinging on arrangements of yawed circular cylinders simulating inclined tube banks with square arrangement and a pitch to diameter ratio of 1.26. Measurements were performed with hot-wires and a pressure transducer. Behaviour of fluctuating quantities is described by means of dimensionless autospectral density functions and cross correlations. Experimental results indicates the presence of two different phenomena of vortex generation in inclined tube banks.

Symbolic Dynamics Applied to the Identification of Flow Patterns Inside Tube Banks

Abstract This paper presents a study of the identification of flow patterns inside a tube bank with the technique of symbolic dynamics. The experimental signals of the mean velocity and its fluctuations are measured by hot-wire anemometry in an aerodynamic channel and used as input data for the symbolic dynamics technique. The tube bank consists of 23 circular cylinders in a triangular arrangement. The pitch-to-diameter ratio chosen was 1.26 and the Reynolds numbers are in the range from 7.5 × 103 to 4.4 × 104, computed with the tube diameter, D = 25.1 mm, and the percolation velocity. In this work, a binary alphabet was chosen to convert and analyze the data. The partitioning process is performed through the mean value of the time series and via discrete wavelet reconstruction, according to a chosen reconstruction level. The flow patterns are presented for different positions inside the tube bank, where histograms and probability density functions support the statistical interpretation. The histograms with a decimal representation for the original experimental time series with partitioning performed through the mean value show that the signals do not present fast changes of velocity fluctuations. This behavior was observed in the five rows of cylinders. However, by changing the partitioning according to a wavelet reconstruction of the signal with high frequency, which means that the signals are close to the partitioning function, fast changes appear in all of the time series observed. The results indicate that the turbulence in tube banks has chaotic characteristics. Flow visualizations performed with ink injection inside the tube bank helped in the interpretation of the results.

Experimental study of the propagation of a far-field disturbance in the turbulent flow through square array tube banks

Summary and Discussion Experimental results in this paper show that a disturbance generated upstream of the investigated tube banks is amplified as it passes the first row of tubes. The disturbance in this work is a wake from a vortex generator. The frequencies of the disturbance were carefully chosen to avoid being confused with the frequencies generated in the bank, vibrations of the test section or due to acoustic resonances. Results of spectra of velocity fluctuations show the presence of peaks from the disturbance in the wake frequency until the 4th or 5th tube rows. The values of the spectra measured in the wider region between the first and the second row have higher values than the original disturbance. This raise in the amplitude of the disturbance is accompanied by the growth of the turbulence intensity. After passing the second row, turbulence levels remain with almost constant values as the flow passes through the successive rows, while the disturbance vanishes, in some cases only after the 4th or the 5th tube row.

PODER DAS SIMULAÇÕES NO ENSINO DE HIDRÁULICA

Este trabalho tem como objetivo mostrar a necessidade de desenvolver novas ferramentas tecnologicas, para o ensino de hidraulica para engenheiros, mais precisamente a utilizacao de simuladores virtuais, das praticas em laboratorios de hidraulica; destacar as vantagens das simulacoes como complemento a aula tradicional expositiva, assim como o ganho no processo de ensino e aprendizagem dos alunos, expostos a este tipo de material instrucional. Para isto foram elaborados 3 simuladores utilizando o software Flash MX da Macromedia, representando 3 praticas laboratoriais de hidraulica. Duas turmas do curso de Engenharia da UFRGS, utilizaram estes simuladores. Pode-se afirmar que os simuladores podem ser otimas ferramentas no auxilio a aula convencional e que na area da Engenharia deveria-se investir tempo e recursos para implementar materiais instrucionais deste tipo, para obter uma melhor qualidade no ensino, assim como para obter uma melhor compreensao de alguns fenomenos fisicos ocorridos nestas praticas, principalmente em instituicoes que nao disponham de laboratorios de hidraulica.