مطالعه تجربي و عددي اثرات نسبت منظري و زاويه حمله بر ساختار جريان سيلندرهاي مستطيلي سه بعدي

Flow around three-dimensional structures attached to the floor with free ends is observed in many engineering an‎d industrial applications, such as tall structures. Despite extensive research on flow around two-dimensional cylinders, flow around three-dimensional cylinders on a surface with limited height, especially with a rectangular cross-section at an angle, has been studied far less. The purpose of the present study is to numerically an‎d experimentally investigate the effect of the angle of attack in the range of α=0°-90° on a three-dimensional structure with a rectangular cross-section located on the floor, with cross-section aspect ratios (ratio of length to width, CR) equal to 1, 2, 3, an‎d 4 at a constant height aspect ratio of 7 (ratio of height to width) in the range of Reynolds numbers (12-48)×103. The numerical investigation was performed as a three-dimensional unsteady simulation using the Large Eddy Simulation (LES) method. In this Reynolds number range, experimental tests using a five-hole probe, hot-wire anemometry, an‎d oil visualization in a wind tunnel were conducted to study the behavior an‎d identify different flow patterns around the body, an‎d to eva‎luate the accuracy of the numerical results. The investigation of numerical results an‎d oil visualization showed that three types of horseshoe vortex patterns can be identified according to the location of the focal points. Furthermore, the experimental an‎d numerical results indicate that the shear layer reattaches to the cylinder surface for each cross-section aspect ratio over a range of angles of attack, accompanied by the formation of a separation bubble. At a critical angle (αc), the size of the separation bubble becomes maximum, where the value of αc is 15°, 10°, 5°, an‎d 0° for cross-section aspect ratios of 1, 2, 3, an‎d 4, respectively. Results showed that, at the critical angle (αc) for each CR, the Strouhal number reaches its maximum value an‎d the drag coefficient reaches its minimum value, whereas the behavior of the lift force coefficient at the critical angle depends on the CR. The results of this research showed that the dominant frequency value for each cross-section aspect ratio an‎d angle of attack is independent of its position along the cylinder height an‎d other positions in the wake region. This means that vortex shedding occurs with the same dominant frequency throughout the wake region for each cross-section aspect ratio an‎d angle of attack. The flow pattern was determined by comparing the five-hole probe results an‎d numerical simulation, an‎d good agreement was observed. Two types of tip an‎d secondary vortices are formed for all cases in the wake region, the strength of which depends on the cross-section aspect ratio an‎d angle of attack. For example, the maximum streamwise vorticity strength at a specific position for tip vortices occurs at an angle of attack of zero degrees for cross-section aspect ratio 1 an‎d at an angle of 30° for cross-section aspect ratios 2 to 4. Overall, the investigations conducted in this research showed that there is good agreement between the experimental an‎d numerical results of the present work.

احمد سوهان كار اصفهاني

مجتبي دهقان منشادي

مهدي نيلي احمدآبادي , احمدرضا پيشه وراصفهاني , علي اكبر دهقان