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.

Boundary Layer Ingestion (BLI) is currently being researched as a potential method to improve efficiency and decrease emissions for the next generation of commercial aircraft.  While re-energizing the boundary layer formed over the fuselage of an aircraft has many system level benefits, ingesting the low velocity boundary layer flow through a serpentine inlet into a turbofan engine adversely affects the performance of the engine.  The available literature has only yielded studies of the effects of this specific type of inlet distortion on engine performance in the form of numerical simulations.  This work seeks to provide an experimental analysis of the effects of BLI-type distortion on a turbofan engine's performance.  A modified JT15D-1 turbofan engine was investigated in this study.  Inlet flow distortion was created by a layered wire mesh distortion screen designed to create a total pressure distortion profile at the aerodynamic interface plane (AIP) similar to NASA's Inlet A boundary layer ingesting inlet flow profile.  Results of this investigation showed a 15.5% decrease in stream thrust and a 14% increase in TSFC in the presence of BLI-type distortion. Flow measurements at the AIP and the bypass nozzle exit plane provided information about the losses throughout the fan flow path.  The presence of the distortion screen resulted in a 24% increase in mass-averaged entropy production along the entire fan flow path compared to the non-distorted test.  A mass-averaged fan flow path efficiency was also calculated assuming an isentropic process as ideal.  The non-distorted fan flow path efficiency was computed to be 60%, while the distorted fan flow path efficiency was computed to be 50.5%, a reduction in efficiency of 9.5%.  The entropy generation between ambient conditions and the AIP was compared to the entropy production along the entire fan flow path.  It was found that the majority of entropy generation occurred between the AIP and bypass nozzle exit.  Based on flow measurements at the bypass nozzle exit plane, it was concluded that inlet flow distortion should be located away from the tip region of the fan in order to minimize losses in a very lossy region.  It was also determined that the fan and bypass duct process the different regions of the total pressure distortion in different ways.  In some regions the entropy production decreased for the distorted test compared to the clean test, while in other regions the entropy production increased for the distorted test compared to the clean test.  Finally, it was found that small improvements in total pressure and total temperature variation at the bypass nozzle exit plane will greatly improve the fan flow path efficiency and entropy generation, thereby decreasing performance losses. / Master of Science

Highly integrated airframe-propulsion systems featuring ingestion of the airframe boundary layer offer reduced noise, emissions, and fuel consumption. Embedded engine systems are envisioned which require boundary layer ingesting (BLI) serpentine inlets to provide the needed air ow to the engine. These inlets produce distorted flow profiles that can cause aeromechanical, stability, and performance changes in embedded engines. Proper design of embedded engine systems requires understanding of the underlying fluid dynamics that occur within serpentine inlets. A serpentine inlet was tested in a specially designed wind tunnel that simulated boundary layer ingestion in a full-scale realistic environment. The measured total pressure proles at the inlet and exit planes of the duct, and the static pressure distributions along the walls provided useful data related to the flow in BLI serpentine inlet systems. A bleed ow control system was tested that utilized no more than 2% of the total inlet ow. Two bleed slots were employed, one near the first bend of the S-duct and one near second. The bleed system successfully reduced inlet distortions by as much as 30%, implying improvements in stall margin and engine performance. Analysis of the wake shape entering the S-duct showed that the airframe and inlet duct are both important components of a wake-ingesting inlet/diffusion system. Shape effects and static pressure distributions determined flow transport within the serpentine inlet. Flow separation within the S-duct increased distortion at the engine inlet plane. Discussion of airframe/inlet/engine compatibility demonstrates that embedded engine systems require multi-disciplinary collaborative design efforts. An included fundamental analysis provides performance estimates and design guidelines. The ideal airframe performance improvement associated with wake-ingestion is estimated. / Master of Science

Radical aircraft and propulsion system architecture changes may be required to continue historic performance improvement rates as current civil aircraft and engine technologies mature. Significant fuel-burn savings are predicted to be achieved through the Distributed Propulsion concept, where an array of propulsors is distributed along the span of an aircraft to ingest boundary layer air and increase propulsive efficiency. Studies such as those by NASA predict large performance benefits when integrating Distributed Propulsion with the Blended Wing Body aircraft configuration, as this planform geometry is particularly suited to the ingestion of boundary layer air and the fans can be redesigned to reduce the detrimental distortion effects on performance. Additionally, a conventional aircraft with Distributed Propulsion has not been assessed in public domain literature and may also provide substantial benefits. A conceptual aircraft design code has been developed to enable the modelling of conventional and novel aircraft. A distributed fan tool has been developed to model fan performance, and a mathematical derivation was created and integrated with the fan tool to enable the boundary layer ingestion modelling. A tube & wing Distributed Propulsion aircraft with boundary layer ingestion has been compared with a current technology reference aircraft and an advanced turbofan aircraft of 2035 technology. The advanced tube & wing aircraft achieved a 27.5% fuel-burn reduction relative to the baseline aircraft and the Distributed Propulsion variant showed fuel efficiency gains of 4.1% relative to the advanced turbofan variant due to a reduced specific fuel consumption, produced through a reduction in distributed fan power requirement. The Blended Wing Body with Distributed Propulsion was compared with a turbofan variant reference aircraft and a 5.3% fuel-burn reduction was shown to be achievable through reduced core engine size and weight. The Distributed Propulsion system was shown to be particularly sensitive to inlet duct losses. Further investigation into the parametric sensitivity of the system revealed that duct loss could be mitigated by altering the mass flow and the percentage thrust produced by the distributed fans. Fuel-burn could be further reduced bydecreasing component weight and drag, through decreasing the fan and electrical system size to below that necessary for optimum power or specific fuel consumption.

As the demand to improve the fuel efficiency of current commercial aircraft increases, new commercial airliner concepts such as the Blended Wing Body has been researched on and studied in various aspects over the years as an efficient alternative to the conventional transport configuration. One particular aspect of the Blended Wing Body is the use of the propulsive fuselage concept. In this concept, the fuselage boundary layer is ingested by the engine and this is aimed at producing benefits such as improved fuel efficiency, reduced ram drag as well as lower structural weight of the engine. During the ingestion process, the low momentum boundary layer is re-energized by the propulsion system before exiting into the atmosphere. In this way, the ingested flow does not contribute to the wake deficit and hence, the overall drag of the aircraft is reduced. Since thrust equal drag in steady and level flight, and power is equal to thrust multiplied by velocity, the reduction in drag implies a reduction in the power required to drive the vehicle.In essence, the ingestion of the boundary layer which leads to a lower inlet stagnation pressure represents a direct thermodynamic penalty. However, the momentum deficit captured by the engine represents a drag reduction to the aircraft. In this way, the propulsion system performance suffers a decrease in engine efficiency while the aircraft drag is reduced in proportion to the amount of boundary layer flow that is ingested. Therefore, a trade-off exists between the increase in aircraft drag reduction and the decrease in engine performance as more boundary layer is consumed. Another important concern is the significant flow distortion which can lead to increased vibration and fatigue of the fan and compressor blades in particular. This flow distortion is characterized by the distortion coefficient, a standard widely used in the aircraft engine industry. While it was found that the ingestion of the boundary layer can provide a decrease in fuel burn of several percentages, the benefits of boundary layer ingestion have shown to be very sensitive to the magnitude of the fan and duct losses. Hence, it is crucial that fan designers are able to design new rotor blades that are able to withstand the flow distortion while ensuring that engine performance degradation is kept to a minimum in order to maximize the overall gain in fuel efficiency.The main aim of this research is therefore to understand and analyse the rotor performance under both uniform and non-uniform inflow condition. This will then provide insights into the main fluid mechanism affecting rotor performance under such conditions. As such, the early phase of this research was focused on the development of an in-house blade modeller which was then later used in the parametrization and reconstruction of the NASA Rotor 67. Other than the development of the Blade Modeller, this research was also focused on the coupling of an open-source meshing software, SALOME to the Blade modeller which will then allow the user to achieve automated meshing needed for the design optimization process. The main highlight of this thesis is on the detailed analysis of the blade to blade domain as well as the overall rotor performance under non uniform inflow condition.

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The use of serpentine boundary layer ingesting (BLI) diffusers offers a significant benefit to the performance of Blended Wing Body aircraft. However, the inherent diffuser geometry combined with a thick ingested boundary layer creates strong secondary flows that lead to severe flow distortion at the engine face, increasing the possibility of engine surge. This study investigated the use of enabling active flow control methods to reduce engine-face distortion. An ejector-pump based system of fluidic actuators was used to directly manage the diffuser secondary flows. This system was modeled computationally using a boundary condition jet modeling method, and tested in an ejector-driven wind tunnel facility. This facility is capable of simulating the high-altitude, high subsonic Mach number conditions representative of BWB cruise conditions, specifically a cruise Mach number of 0.85 at an altitude of 39,000 ft. The tunnel test section used for this experiment was designed, built, and tested as a validation tool for the computational methods. This process resulted in the creation of a system capable of efficiently investigating and testing the fundamental mechanisms of flow control in BLI serpentine diffusers at a minimum of time and expense. Results of the computational and wind tunnel analysis confirmed the large potential benefit of adopting fluidic actuators to control flow distortion in serpentine BLI inlets. Computational analysis showed a maximum 71% reduction in flow distortion at the engine face through the use of the Pyramid 1 ejector scheme, and a 68% reduction using the Circumferential ejector scheme. However, the flow control systems were also found to have a significant impact on flow swirl. The Pyramid 1 ejector scheme was found to increase AIP flow swirl by 64%, while the Circumferential ejector scheme reduced flow swirl by 30%. Computational analyses showed that this difference was the result of jet interaction. By keeping the jet flows separate and distinct, the diffuser secondary flows could be more efficiently managed. For this reason, the most practically effective flow control scheme was the Circumferential ejector scheme. Experimental results showed that the computational analysis slightly over-predicted flow distortion. However, the trends are accurately predicted despite slight variances in freestream Mach number between runs and a slightly lower tested altitude. / Master of Science

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