In the present work, the flow through tube banks is studied in order to understand the random and transient behavior of the instabilities and phenomena that occur in the first rows of tube banks and propagates to its interior. The study is performed using hot wire anemometry in an aerodynamic channel and flow visualizations in a water channel. Three tube banks with square arrangement and pitch-to-diameter ratios of 1.26, 1.4 and 1.6 were studied. The Reynolds number range for the velocities measurements, computed with the tube diameter and the flow velocity in the narrow gap between tubes, was 7-8x10 4. Continuous and discrete wavelets analyses were applied to decompose the velocity results, thus allowing the analysis of phenomena in a time-frequency domain. Visualizations in a water channel were made, using a dye injection directly in the flow, in order to help the understanding about the phenomena found. A tube bank with a square arrangement and 1.26 pitch-to-diameter ratio was used, and the experiments were performed in a Reynolds number range of 3-4x10 4. The main results show the presence of instabilities generated from the second row of the tube bank, which propagates to the interior of the bank, generating a behavior where the three orthogonal components of the flow are equally important. The three-dimensional behavior of the flow is responsible for a redistribution of mass inside of the bank of tubes that leads to velocity values and Strouhal numbers not expected for the studied geometry.

Flow through circular cylinder arrays are commonly found in several engineering application as offshore structures, heat exchangers, transmission lines and chimneys, therefore the understanding of the several phenomena that occur due the interaction between flowing fluid and these structures is very important. This work analyzes experimentally the presence of phenomenon called bistable or biased flow, which is able to cause alternations on the flow modes in cylinder arrays. For the experimental work, two cylinders are placed side-by-side, or forming a tube bank with in line arrangement. The first arrangement corresponds to the case where the phenomenon is easily detected, and in line tube bank, the phenomenon has been also found. The experiments were performed in a wind channel using hot wire anemometry additionally to the classical statistic and spectral tools, wavelet transforms are used. The bistable flow can be an important generator of dynamic instabilities, since it alternates the lift and drag coefficients, thus alternating the structure dynamic response

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a b s t r a c tThis paper presents experimental results of the accelerating and decelerating flow in the wake of a cylinder obtained by means of hot wire anemometry measurements in a wind tunnel with high blockage ratio. The analysis was done in Fourier and wavelet spaces. The Strouhal number for Reynolds numbers up to 3 Â 10 4 was studied in a transient flow and compared with the results obtained from steady flows at several velocities uniformly distributed from Re = 1.7 Â 10 3 to 3 Â 10 4 . Results show that the wavelet analysis is a valuable tool to deal with both transient and stationary random phenomena and that is able to capture the characteristics of the transient flow as well as the Fourier analysis can do with the steady state acquisitions.