An Investigation on the Flow Characteristics of the Subsonic Diffusing S-shaped Intakes

Abstract

Maintaining a high quality of the flow uniformity on the engine face while maintaining low total pressure loss is critical to the overall performance of the engine. In the present thesis, a computational fluid dynamics analysis was performed on the internal flow characteristics of the subsonic diffusing S-shaped intake. The Reynolds Averaged Navier-Stokes (RANS) equations were solved with a shear stress transport(SST) k-ω turbulence model. The k-ω SST model was well known for its accuracy for the complex flows including the secondary flow. For the validation of the computational method and a turbulence model used in the present computations, an RAE M2129 intake model was used. The effects of inlet shapes, flow incidence angles, and the boundary layer suctions on the flow uniformity inside the intake were investigated using the RAE M2129 intake model. The inlet shape was modified by changing separately the aspect ratios of both upper and lower halves of the semicircular cross-sections at the two ends(inlet and engine face) of the intakes. The S-shaped bends inside the intake were generated using spline curves with the constraints of maintaining the curvature line and the cross-section areas. It was found that the locations and the sizes of the counter-rotating vortex pair inside the intake were affected by the inlet shapes. When the vortex size was small, the vortex was moved farther from the starboard side with smaller distortion. The length of the between saddle points in the owl-face separation was different for the relationship between the incidence angles and the inlet shapes. The flow separation occurred incidence angle was also different. The length of the between saddle points in the owl-face separation was reduced in the S-shaped intake with the upper half semicircular inlet shapes, and the flow separation was delayed at higher incidence angles. The location of the boundary layer suction using a sub-duct showed a significant effect on the flow distortion. However, the suction angle was not shown to affect the flow distortion much. As the location of the boundary layer suction approached the throat, the length of the owl-face separation was reduced. As the sub-duct was located in the region of the owl-face separation, the width of the between spiral nodes in the owl-face separation was increased by the sub-duct width. The location of the inlet boundary layer suction showed a significant effect on the flow distortion. However, the suction length was not shown to affect the flow distortion much. As the location of the inlet boundary layer suction approached the throat, the flow distortion on the engine face was reduced. However, as the location of the inlet boundary layer suction approached cowl lip, the flow distortion on the engine face was increased. In addition, the flow distortion was changed according to the boundary layer thickness inside the intake, and the flow distortion was decreased as the thickness was thinner. The flow characteristics and the flow uniformity for an S-shaped intakes were investigated the major flow patterns to be considered for intake design, and it was expected that the study findings could be applied to air intake design in the future.