Effectiveness of a Serpentine Inlet Duct Flow Control Technique at Design and Off-Design Simulated Flight Conditions

An experimental investigation was conducted in a static ground test facility to determine the effectiveness of a serpentine inlet duct active flow control technique for two simulated flight conditions. The experiments used a scaled model of a compact, diffusing, serpentine, engine inlet duct developed by Lockheed Martin with a flow control technique using air injection through microjets at 1% of the inlet mass flow rate. The experimental results, in the form of total pressure measurements at the exit of the inlet, were used to predict the stability of a compression system through a parallel compressor model. The inlet duct was tested at cruise condition and angle of attack flight cases to determine the change in inlet performance due to flow control at different flight conditions. The experiments were run at an inlet throat Mach number of 0.55 and a resulting Reynolds number, based on the hydraulic diameter at the inlet throat, of $1.76*105$⁠. For both of the flight conditions tested, the flow control technique was found to reduce inlet distortion at the exit of the inlet by as much as 70% while increasing total pressure recovery by as much as 2%. The inlet total pressure profile was input in a parallel compressor model to predict the changes in stability margin of a compression system due to flow control for design and off-design flight conditions. Without flow control, both cases show a reduction in stability margin of 70%. With the addition of flow control, each case was able to recover a significant portion (up to 55%) of the undistorted stability margin. This flow control technique has improved the operating range of a compression system as compared to the same inlet duct without flow control.