Abstract
The bend pipe with a circular section, which is widely used in hydropower, chemical industry and other fields, is a common form in pipeline systems. However, secondary flow occurs when the fluid flows through the bend pipe, thereby affecting the stability of the pipeline system. Different bending angles have various effects. Therefore, this paper establishes 3D models of a circular bend pipe with different bending angles. The influence of bending angle on flow field distribution and downstream flow is analyzed numerically. The larger the bending angle is, the more obvious the flow distribution and even the unevenness at the elbow will be, hence resulting in poor stability. The distance required to restore flow uniformity also increases. The pressure energy loss of the bend pipe with different bending angles is investigated. Results show that with the increase in bending angle, the global pressure loss presents a trend of “increase-decrease-increase.” The closer the bending angle is to 90°, the greater the influence of centrifugal force is on the flow, and the more obvious the secondary flow phenomenon will be. Aiming at the nonuniformity phenomenon, the structure optimization of a 90° bend pipe with the greatest influence is conducted. The improvement of the flow characteristics of bend pipe with different thick-diameter ratio and length-diameter ratio is compared. The deflector with a certain thickness can enhance the uniformity, safety and useful life of the bend pipe. The sharp-end length can improve the velocity uniformity to a certain extent but has minimal influence on flow characteristics compared with the thick-diameter ratio. This paper aims to study and improve the flow performance of a multi-structure bend pipe to make it suitable for more complex conditions.