Blowing Control in Serpentine Inlet and its Effect on Fan-Stage Performance

Serpentine inlet is widely used in military and civil aircraft due to its good stealth performance.However, it generates a high total pressure loss and swirl distortion which significantly affects the performance and the stability of the compressor. In order to improve the quality of the flow field at the aerodynamic interface plane (AIP), a flow control is required inside the serpentine inlet.

The objective of this paper is to study the effectiveness of the blowing control on reducing the swirl distortion and on improving the total pressure recovery at the AIP,by reducing the low-momentum flow in the serpentine inlet. The mechanism of the blowing control and the effect of the design parameters (i.e. blowing angle, blowing position and blowing flow rate) on the aerodynamic performance at the AIP are studied. The optimal solution is applied to the full flow path of the serpentine inlet and the fan stages.

The numerical results show that the quality of the flow field at the AIP can be effectively improved by blowing high-energy airflow into the boundary layer of the serpentine inlet. The total pressure recovery factor is increased by around 0.9%, while the circumferential total pressure distortion and swirling distortion are significantly reduced at the AIP compared to the baseline case (no blowing control). The blowing position has a high influence on the blowing effect, and the optimum blowing position is where the thick boundary layer is. In addition, the blowing angle should be selected to avoid the high-energy air from pipes mixing with mainstream in the serpentine inlet which will result in an additional total pressure loss. When the ratio of the blowing mass flow rate to the designed mass flow rate of the serpentine inlet is about 1.5%, the swirl distortion on the AIP reaches a minimum value, which then increases with an increase of the blowing mass flow. When the circumferential blowing scheme is adopted and the blowing angle is 10°, the AIP aerodynamic performance achieves the highest improvement, with an increase of the total pressure recovery factor by about 1%, and a decrease of the circumferential total pressure distortion and the swirling distortion by 69% and 39%, respectively. With the optimal control scheme, the area of the low-pressure region near the upper wall is remarkably reduced, and the quality of the flow field is improved, with an increase of the pressure ratio by about 2.6%, and an increase of the efficiency of the single-stage compressor by about 2.4%, respectively.