24th ABCM International Congress of Mechanical Engineering December 3-8, 2017, Curitiba, PR, Brazil COBEM-2017-0956 EXPERIMENTAL ANALYSIS OF TURBULENT TRANSVERSAL FLOW ON TWO FIXED PARALLEL CYLINDERS WITH OSCILLATORY AND ROTATIONAL FREEDOM Dolir Jose Climaco Varela Roberta Fátima Neumeister Universidade Federal do Rio Grande do Sul Roberta.neumeister@ufrgs.br Gustavo da Cunha Dias Universidade Federal do Rio Grande do Sul gustavodias@furg.br Alexandre Vagtinski de Paula Universidade Federal do Rio Grande do Sul depaula@ufrgs.br Sérgio Viçosa Möller Universidade Federal do Rio Grande do Sul svmoller@ufrgs.br Abstract. This paper presents an experimental study of the bistability phenomenon that occurs in the simplified geometry of two tubes arranged side by side submitted to a turbulent cross flow. In the analysis we consider the condition of fixed tubes and with a degree of freedom (rotational), submitted to different numbers of Reynolds. The experimental technique consists in the measurement of flow rate fluctuations through the aerodynamic channel hot wire anemometry and the evaluation of the stresses of the flow on the tubes with the use of a load cell. The data obtained from the measurement in the channel are treated with the use of statistical, spectral and wavelet tools. In the experimental results we observe the presence of bistability and note the non-simultaneous behavior of the phenomenon along the cylinders. The asymmetric formation of the wakes is also studied and attributed to the interaction between the vortices from wakes behind the cylinders, since, initially, the wake detachments is symmetrical. In the evaluation of the forces by means of the extensiometry technique, the steps of conditioning and acquisition of the signal were elaborated and the results of mechanical deformation presented similarity with the phenomenon observed in the experimental anemometry. For a Reynolds number of 27635 a force of 26.1 mN was found with a torque developed in the load cell of 84.95 Nmm. Keywords: Bistable flow, Hot wire anemometry, Turbulence, Load cells, Experimental analysis. 1. INTRODUCTION The phenomenon of bistability, shown in Fig. 1, has very interesting characteristics and many of them are still not fully understood. This ignorance of the mechanisms that act on the flows on two cylinders positioned side by side is the main motivation of the present study, being that the inscience of the reasons and the means of the event of the bistable phenomenon is the central interest of the analyzes. In bistability there is a narrow mat downstream of one of the tubes and a wide mat downstream (Fig. 1a and 1b). This phenomenon generates two predominant frequencies of vortex detachment, each associated with a treadmill: the narrow treadmill is associated with the highest frequency, and the wide treadmill is associated with the less frequent detachment. Through the slit, the flow is diverted towards one of the cylinders, forming the narrow mat. Bistable flow is characterized by a change in the flow pattern of the slit from side to side during irregular periods of time. Thus, if the flow velocity is measured, for example, along lines tangent to the external generators of the cylinders, downstream, a pattern of exchange between the modes of the flow may occur as shown in the scheme of Fig. 1c. According to Möller,