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Low-frequency unsteadiness in the vortex formation region of a circular cylinder

DOI: 10.1615/ICHMT.2012.ProcSevIntSympTurbHeatTransfPal.1480
pages 1443-1454

Ivette Rodriguez
Heat and Mass Transfer Technological Center (CTTC) Universitat Politecnica de Catalunya - BarcelonaTech (UPC) Colom 11, 08222 Terrassa, Barcelona, Spain

O. Lehmkuhl
Heat and Mass Transfer Technological Center, Polytechnical University of Catalonia (UPC) Colom11, 08222, Terrassa, Barcelona, Spain; Termo Fluids, S.L., Magi Colet, 8, 08204 Sabadell (Barcelona), Spain

R. Borrell
Heat and Mass Transfer Technological Center (CTTC), Universitat Politecnica de Catalunya, Colom 11 08222 Terrassa, Spain; TermoFluids S.L, Av. Jacquard 97 08222, Barcelona, Spain

Assensi Oliva
Centre Tecnologic de Transferencia de Calor (CTTC), Universitat Politecnica de Catalunya (UPC), Colom 11, 08222 Terrassa, Barcelona, Spain

Resumo

The presence of low-frequency fluctuations in the wake of bluff bodies have been observed in several investigations. Eventhough the flow past circular cylinder at ReD = 3900 (ReD = UrefD/ν) has been object of several experimental and numerical investigations, there is a large scattering in the average statistics in the near wake. In the present work, the flow-dynamics of the near-wake region behind a circular cylinder has been investigated by means of DNS and statistics have been computed for more than 858 shedding cycles. The analysis of instantaneous velocity signals of several probes located in the vortex formation region, point out the existence of a low-frequency fluctuation at fm = 0.0064. This large-scale quasi-periodic motion registered seems to be related with the modulation of the recirculation bubble which causes its shrinking and enlargement over the time. Two different configurations have been identified: i) a high-energy mode with larger fluctuations in the shear-layer and in the vortex formation region (Mode H) and ii) a low-energy mode with weaker fluctuations in the shear layer (Mode L). The influence of such lowfrequency in the wake topology has been studied by means of the phase-average flow field considering 10 cycles of vortex-shedding for each mode, but also by the analysis of the time-average first- and second-order statistics of each wake mode. The results are compared with the long-term averaged solution and with the literature available results.

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