An experimental study of the power imparted by wind to a twin cylinder bundle

ABSTRACT: This paper deals with an experimental study of the power imparted by wind to a twin cylinder bundle coupled only by flow. The cylinders are in tandem and staggered arrangements for separations typical of transmission lines. The results indicate that the presence of the upstream cylinder and its vibration have a great influence on the power imparted to the downstream cylinder. This power depends strongly on the separation between the cyUnders and the wake vortex pattem of the upstream cylinder. 1. INTRODUCTION This study deals with an extension of two previous ones [Brika & Laneville (1996), Brika & Laneville (1997)] in which it is observed that, in comparison with the results of an isolated cylinder, the presence of a fixed upstream cylinder influences the aeolian oscillations of the downstream flexible cylinder as foUows: • the power imparted by wind is greater; • this power decreases with increasing value of the spacing ratio between the cylinders and with the bundle inclination angle, P (with respect to the flow direction); • beyond p= 20°, the downstream cylinder behaves as an isolated one; • the hysteresis phenomenon observed in the case of a single cylinder is absent when the downstream cylinder is immersed in the wake of the upstream cyhnder. Since real conductors are free-vibrating, the objective of the present study is to investigate experimentally the effect of the vibration of the upstream cylinder on the power imparted by wind to the downstream cylinder. The cylinders are coupled only in an aerodynamic way. To the authors' knowledge, similar studies have not been conducted previously. 2. EXPERIMENTAL SETUP The experimental setup for each model is similar to the one used in the two previous studies [Brika & Laneville (1996), Brika & Laneville (1997)] and is described in detail in [Brika & Laneville (1993)]. The cylinders are identical and have a smooth surface, an extemal diameter D= 33.4 mm, a length L= 3.3 m and a namral frequency f„= 17.58 Hz. Figure 1 shows a schematic view of the bundle with the different parameters studied, i.e. the separation L between the cylinders, the bundle inclination angle |3 with respect to the flow direction and the plane of vibration characterized by angle a with respect to the cross-flow direction. Six spacing ratios have been examined, i.e. L/D= 7, 10, 13, 16 and 25 when the cylinders are in tandem arrangement and four bundle inclinations (3= 0, 5, 10 and 15° for a typical separation L/D= 13. The turbulence intensity is of the order of 0.1% and the Reynolds number varies between 2000 and 12000.