M.Sc Thesis

M.Sc StudentRudin Irina
SubjectPerformance Improvement of Boundary Layer Ingesting Inlets
using Active Flow Control Techniques:
Computational Analysis
DepartmentDepartment of Aerospace Engineering
Supervisors PROF. Jacob Cohen
DR. Eran Arad
Full Thesis textFull thesis text - English Version


Boundary layer ingesting (BLI) inlets are highly curved serpentine inlets which are fully or partly integrated into the aircraft. This innovative technology of inlets design was developed in response to environmental concerns such as noise and pollution reduction and minimization of overall weight, drag and thrust related moments of air vehicles. The inlet is designed to supply the air-breathing engine with enough air flux at high quality that matches engine operability conditions. The term high-quality air flow refers to minimal momentum loss and conservation of flow uniformity which are vital for engine stability. However, the ingested boundary layer is composed of low momentum fluid. Furthermore, the S shape of the inlet invokes longitudinal and circumferential pressure gradients which enlarge the region of low momentum flow. Consequently, highly distorted and non-uniform flow develops on the engine face section which might cause a compressor's blades stall and failure of the whole engine system. Several approaches have been developed to restrict the flow non-uniformity inside these inlets. Among them passive and active flow control methods take a central stage. In the current study, flow distortion mechanisms were evaluated inside a BLI inlet that was designed by NASA and BOEING for the BWB (Blended Wing-Body) transporter, designated “configuration A”. The analysis was performed using RANS and URANS simulations. First, a baseline case, without any flow control was calculated and compared to previously published experimental and computational results. Analysis of the flow structure revealed three flow distortion mechanisms inside the inlet: Ingested boundary layer causing flow separation, vortex generation at the interaction area between the boundary layer flow and the lip and circumferential pressure gradients created by the offset of the inlet's axis that generates secondary flows. Based on this insight, suction slots were implemented in various positions and combinations inside the inlet. This brought to maximum improvement of 3.7% in PR and 64.4% in DC(60) of the inlet. However, the substantial enhancement in performance comes at a price of non-negligible mass flow rate of 10% of the total mass flow rate that is sucked away from the inlet. A bypass to avoid this price tag is the addition of nearly tangential blowing using various geometries of jet nozzles, combined with one of the suction slots. Combinations of steady suction and steady/oscillatory blowing were tested. Maximal improvement of 4.3% in PR and 70% in DC(60) were obtained while the main inlet mass flow rate was preserved.