The influence of the adverse pressure gradient on the flow characteristics of a serpentine nozzle with film cooling

With the increase of the turbine inlet temperature, the thermal load of serpentine nozzles increases greatly, leading to the stiffness degradation and structure deformation. Therefore, efficient cooling technologies are required. There are adverse pressure gradients (APGs) and strong swirl characteristics in the serpentine nozzle. Therefore, the film cooling design of serpentine nozzles faces greater difficulty than that of other exhaust systems. This paper aims to obtain the flow characteristics of serpentine nozzles with film cooling and to provide theoretical support for the film cooling design of serpentine nozzles. We obtained the influence of the APG and the favorable pressure gradient (FPG) on the flow characteristics of a serpentine nozzle with film cooling via the employment of numerical methods. The results show that the APG obstructs the flow of the cooling airflow, and causes a part of the cooling airflow to decelerate, to stagnate, and eventually to flow in the reverse direction, thus forming a recirculation zone. The counter rotating vortex pair (CRVP) induces the anti-counter rotating vortex pair (ACRVP) near the boundary layer of the wall, and the ACRVP develops rapidly in the recirculation zone. With the development of the ACRVP, the CRVP leaves the wall and gradually dissipates. As the blowing ratio increases, the recirculation zone moves downstream, and the recirculation zone first expands and then shrinks, such that the location where the ACRVP develops also moves downstream. There is no recirculation zone under the influence of the FPG, and the CRVP occupies the core of the cooling airflow along the flow direction.