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In this paper, flow over a cluster of three equally spaced circular cylinders was studied by numerical simulation based on the turbulence model k-kl-ω for two incidence angles β = 0° and 60°, at different Reynolds numbers, and flow interference pattern characteristics between cylinders, characteristics of force parameters, and Strouhal number of each cylinder with different spacing ratios ranging from 1.5 to 4 at Re 8 × 104, 2 × 105 and 2 × 106 were obtained. Analyzing the flow field around three cylinders, the following results have been obtained: (1) at incidence angle β = 0° and 60°, the wake was nearly symmetrical if S/D ≥ 2.0; (2) at β = 60°, S/D = 1.5, and Re = 2 × 105, an asymmetric periodic flow pattern occurred in the wake region which produced a significant effect on the surface mechanical parameters and Strouhal number, and this was observed for the first time. The periodic flow regime of the wake region also occurred at S/D = 1.35 and 1.5, without the same phenomenon at S/D = 1.7 and 2.0; this phenomenon is described for the first time in this paper; (3) the phenomenon of periodic flow regime in the wake region was intrinsic and related to Reynolds number and space ratio. In addition, the characteristics of force parameters of three cylinders were mainly affected by the interference between cylinders, at 1.5 < S/D < 4, which indicated that the drag coefficient of three cylinders reduces with different Reynolds numbers and increases with enlargement of the spacing ratio for upstream cylinders at incidence angle 0°. At incidence angle 60° and S/D = 1.5~4, the Strouhal number decreases with the enlargement of spacing ratio for the upstream cylinders, but the Strouhal number increases for the downstream cylinder, which is another prominent flow interference influence. The results indicated the effect of flow interference between cylinders subjected to a cross flow over a cluster of three equally spaced cylinders, considering the flow pattern, surface mechanical parameters and Strouhal number, which should be considered in the establishment of standard design codes in fields such as offshore wind turbine engineering for flow interference around groups of cylinders. [ABSTRACT FROM AUTHOR]

In this article, a piezoelectric polymer composite consisting of polyamide 11 (PA11) and high loading of barium titanate (BT) particles was prepared through solid‐state shear milling method based on a pan‐type milling equipment. The structure and performance of the prepared PA11/BT composite were investigated by using scanning electronic microscopy (SEM), X‐ray diffraction (XRD), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), piezoelectric test, and mechanical measurement. Experimental results showed that high loading of BT particles were homogeneously dispersed in PA11 matrix under the strong shear force field of pan‐milling. Besides, the addition of BT changed the crystallization behavior of PA11 matrix and increased its thermal stability also. The dielectric constant of the prepared PA11/BT composites dropped with increase of the frequency. However, it increased remarkably with increase of the BT volume fraction. In addition, a linear increase was found in piezoelectric strain coefficient d33 with increase of the BT volume fraction. For example, d33 could reach 1.1 pC/N and 6.6 pC/N at the BT loading of 5 and 50 vol%, respectively. The obtained composite still showed good mechanical properties even when the BT volume fraction increased to 20 vol%. POLYM. COMPOS., 40:E177–E185, 2019. © 2017 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]