###### Abstract
They classified the flow pattern into two categories, short-spacing ratio shear-layer reattachment regime and big-spacing ratio vortex-shedding regime, respectively. In addition, the influence of the incidence angle is more complex and dependent on the spacing ratio. Meanwhile, a number of numerical simulations on this three-cylinder configuration have been performed over the past decades. [PERSON] et al. [18] investigated the influence of the spacing ratio (1.5-5) and the incidence angle (\(0^{\circ}\), \(30^{\circ}\), \(60^{\circ}\)) on the flow patterns at \(Re=100\) by two-dimensional simulation. [PERSON] et al. [19] investigated the characteristic flow regions of three cylinders by the lattice Boltzmann method and fluorescence flow visualization using a laser. They demonstrated that for \(Re=200\) and \(S/D=3\), two different types of flow patterns can be distinguished by \(T/D\), where \(S\) is the distance between the centers of the cylinders in the upstream and downstream, and \(T\) is the distance between the centers of the two cylinders in the downstream. When \(1\leq T/D\leq 1.2\) and \(2.5\leq T/D\leq 3.1\), typical steady flow occurs, when \(1.3\leq T/D\leq 2.4\) and \(3.2\leq T/D\leq 10\), typical unsteady flow occurs. By using the 2D finite volume approach, [PERSON] et al. [20] examined the effects of the \(L/D\) (1.5-7) and Reynolds number (100-200) on the flow characteristics of three identical cylinders organized in an equilateral-triangular arrangement at incidence angles of \(0^{\circ}\) and \(180^{\circ}\). By using the immersed boundary approach, [PERSON] at al. [21] carefully explored the impact of \(L/D\), Reynolds number, and three-dimensionality on the fluid dynamics of the flow past three circular cylinders arranged in an equilateral-triangular arrangement. Six flow patterns depending on \(L/D\) at \(Re=100\) were observed: single bluff-body flow (\(1.0\leq L/D\leq 1.4\)), deflected flow (\(1.5\leq L/D\leq 1.9\)), flip-flopping flow (\(2.0\leq L/D\leq 2.5\)), anti-phase flow (\(2.6\leq L/D\leq 2.8\) and \(3.5\leq L/D\leq 4.1\)), in-phase flow (\(2.9\leq L/D\leq 3.4\)and \(4.2\leq L/D\leq 4.5\)), and fully developed in-phase co-shedding flow (\(4.6\leq L/D\leq 6.0\)). In addition, some research of the flow configuration in the sub-critical regime were studied by the numerical method. [PERSON] et al. [22] simulated the flow past three circular cylinders with the incidence angle of \(30^{\circ}\) for \(200\leq Re\leq 3900\) and \(1.25\leq L/D\leq 4.0\) and five flow patterns were identified. The vortex shedding's three-dimensionality grows stronger as the Reynolds number increases. From the review of the relevant studies, it can be observed that the majority of the numerical and experimental research works were carried out in the laminar and sub-critical flow regime. Nevertheless, the Reynolds number is often between \(10^{5}\)-\(10^{7}\) in the majority of real circumstances, such as offshore engineering, which correspond to the super-critical regime and post-critical regime, respectively [23]. In this paper, we focus on the super-critical flow regime, the Reynolds number as high as \(3\times 10^{6}\). In super-critical flow, a rapid transition happens from laminar boundary layer to turbulent boundary layer. It is necessary to conduct a more comprehensive investigation into the flow structure and behavior of the three cylinders when they are arranged in an equilateral triangle at high Reynolds numbers. [PERSON] [24] carried out wind tunnel tests to achieve the force measurements of single cylinder from the Reynolds number \(2.3\times 10^{4}\) to \(7.1\times 10^{6}\), corresponding to the sub-critical and post-critical regime, respectively. It was observed that the Strouhal number (\(St\)) increased while the \(Cd\) value decreased at \(Re>3.5\times 10^{5}\). [PERSON] [25] measured the unsteady aerodynamic forces and surface pressure of a rough single cylinder at \(1.5\times 10^{4}\leq Re\leq 1.2\times 10^{7}\).