| Summary: | Boundary layer ingesting (BLI) propulsion systems offer potential fuel burn reduction for civil aviation and synergize with new advanced airframe concepts. However, the distorted inlet flow for BLI systems can cause performance and stability margin loss. System level analyses generally size a single engine at a fixed design point which ignores the distributed nature of many BLI architectures. Furthermore, operability and performance during o design are generally not considered during the sizing process. In this thesis, a methodology is developed for multi-design point sizing of BLI propulsion systems for specific vehicle geometry including an operability constraint. The methodology is applied to a 300 passenger hybrid-wing body vehicle with embedded turbofan engines.
The methodology required investigations into three main areas of research. The first was the modeling of BLI impacts over a range of flight conditions. A BLI analysis tool was developed which models the vehicle boundary layer, pre-entry region, inlet, and fan losses throughout the entire flight envelope. An experiment investigating the impact of the modeling approach is conducted, and results show that proper mapping of the fan, inlet, and BLI propulsive benefit is crucially important for making proper design decisions. The impact of BLI on the system was found to vary significantly during o ff design and especially with changes in vehicle angle of attack. The operability constraint is investigated using a parallel compressor model and was found to place a minimum limit on the propulsor height.
The second area of investigation was the creation of a multi-propulsor sizing methodology which accounts for diff erences between propulsors during
flight that is induced by their interaction with the vehicle. A modified multi-design point approach was used which employs a set of design and power management rules to relate the operation of the propulsors. A performance comparison of this methodology with the standard single propulsor approach showed a signicant difference.
The final area of investigation was the determination of critical o ff-design conditions for the sizing procedure. A screening process is developed which tests all off -design conditions for a subset of the design space to find conditions which are stall margin or thrust deficient. The experiment showed that it is necessary to consider the high angle of attack take-off condition during sizing for the HWB vehicle and that a variable area nozzle is required to meet the operability constraint. A follow on experiment showed that the inclusion of this point reduced the achievable fuel burn benefit for more aggressive BLI designs.Boundary layer ingesting (BLI) propulsion systems offer potential fuel burn reduction for civil aviation and synergize with new advanced airframe concepts. However, the distorted inlet flow for BLI systems can cause performance and stability margin loss. System level analyses generally size a single engine at a fixed design point which ignores the distributed nature of many BLI architectures. Furthermore, operability and performance during o design are generally not considered during the sizing process. In this thesis, a methodology is developed for multi-design point sizing of BLI propulsion systems for specific vehicle geometry including an operability constraint. The methodology is applied to a 300 passenger hybrid-wing body vehicle with embedded turbofan engines.
The methodology required investigations into three main areas of research. The first was the modeling of BLI impacts over a range of flight conditions. A BLI analysis tool was developed which models the vehicle boundary layer, pre-entry region, inlet, and fan losses throughout the entire flight envelope. An experiment investigating the impact of the modeling approach is conducted, and results show that proper mapping of the fan, inlet, and BLI propulsive benefit is crucially important for making proper design decisions. The impact of BLI on the system was found to vary significantly during o ff design and especially with changes in vehicle angle of attack. The operability constraint is investigated using a parallel compressor model and was found to place a minimum limit on the propulsor height.
The second area of investigation was the creation of a multi-propulsor sizing methodology which accounts for diff erences between propulsors during
flight that is induced by their interaction with the vehicle. A modified multi-design point approach was used which employs a set of design and power management rules to relate the operation of the propulsors. A performance comparison of this methodology with the standard single propulsor approach showed a signicant difference.
The final area of investigation was the determination of critical o ff-design conditions for the sizing procedure. A screening process is developed which tests all off -design conditions for a subset of the design space to find conditions which are stall margin or thrust deficient. The experiment showed that it is necessary to consider the high angle of attack take-off condition during sizing for the HWB vehicle and that a variable area nozzle is required to meet the operability constraint. A follow on experiment showed that the inclusion of this point reduced the achievable fuel burn benefit for more aggressive BLI designs.
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