Generation of discrete distortions (tightly-wound vortices) in an experimental environment

Abstract

The presence of inlet flow distortion has been identified as a potential problem for modern civil and military aircraft engines. In particular, the application of S-shaped intakes ahead of a compression system can lead to the generation of distorted flows which can degrade performance. Several studies have been carried out on the effect of self-generated and ingested distortions on compression systems within the UTC at Cranfield University. The next logical step is to explore and establish suitable techniques for the robust and consistent generation of complex distorted patterns, such as tightly-wound vortices, in an experimental environment. A versatile vortex generator is designed, optimized and analysed in this research. The Coanda effect by means of Circulation Control (CC) profiles is used to deflect the flow in a controlled manner. A proper CC blade arrangement can force the air to turn and create a specific swirl distortion pattern. The CC blade is designed to prescribe a distribution of velocities based on Vatistas’ vortex model. A 2D validation and parametric study is carried out over a pre-design geometry. After several modifications, the 3D baseline model is designed and a parametric study about the influence of Mach number and injection pressure over flow characteristics is performed. The results show the presence of two vortical structures between the blade and the annular supports. These junction vortices strongly affect flow characteristics. The regions corresponding to the locations of the inner and outer supports present peaks of swirl angle and vorticity, and Mach number and total pressure deficits. The radial homogeneity is studied showing high level of distortion in the near blade region but quite lower distortion in the outlet section. Nevertheless, the medium region is not affected by this phenomenon and shows promising vortex characteristics. Finally, a direct effect of injection pressure is observed on flow characteristics, feeding junction vortices strength. In contrast, the reduction of Mach number presents junction vortex detriment but higher global vortex characteristics.