Hans Mårtensson

Fan Performance and Aerodynamic Forces With Boundary Layer Ingestion

📅 Date & Time: 11 April 2025, 10:00–13:00
📍 Location: Lecture room U1, Brinellvägen 26, KTH Royal Institute of Technology

About the Thesis

The fan is a critical component of civil aircraft engines, converting shaft power from the core engine into thrust. Significant advancements have been made by increasing bypass ratios, thereby improving propulsion efficiency. However, larger bypass ratios also lead to increased weight and aerodynamic resistance due to larger wetted surfaces on the engine nacelle, creating a trade-off that limits fuel consumption reduction. An alternative approach to improving efficiency is integrating the propulsor with the fuselage, allowing the fuselage boundary layer and wake to pass through the propulsor—a concept known as Boundary Layer Ingestion (BLI). This method requires less energy to accelerate the ingested flow to generate a given amount of thrust compared to freestream propulsion. To fully harness this potential, a deeper understanding of how BLI affects fan aerodynamics and transient blade loads is essential. To fully realize the potential of Boundary Layer Ingestion (BLI), it is essential to understand the prerequisites for designing propulsion units that perform effectively in distorted flow. In addition to efficiency, aerodynamic stability and blade vibrations must be carefully assessed. This research consists of four interconnected components:

Analysis of a of a fan designed for a BLI installation
Design of a test object and evaluation of experimental results to verify computational tools and assess fan performance
Analysis of the influence on unsteady aerodynamic loads caused by distortion at the fan inlet
Suggestions and analysis of improved design features

The findings indicate that propulsion efficiency can be enhanced in the studied case. Performance was evaluated for a realistic aircraft installation under relevant flight conditions, demonstrating that stability margins can be maintained. A fan with comparable performance was designed and tested at a reduced scale, with test results validating computational tools and confirming satisfactory operation across varying conditions. A re-designed fan blade further demonstrates the feasibility of using a radial work profile to improve propulsive efficiency by compensating for the ingested boundary layer. Additionally, important new links are identified between the acoustic properties of fan blades and the unsteady blade forces generated by disturbed inlet airflow. Key design elements, including blade count and acoustic liners, are analyzed and shown to mitigate the risk of excessive blade vibrations.

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