Design and development of a combined intake fan test rig to enable investigations of stable operating ranges

Kurzfassung

Due to the growing trend of shortening the nacelle of future low fan pressure ratio propulsion systems, the interactions of the intake flow with the fan aerodynamics become increasingly important. In the present paper, the collaborative works of the Institute of Jet Propulsion and Turbomachinery (IFAS), German Aerospace Center (DLR) and Rolls-Royce Deutschland (RRD) towards the development of an Integrated Fan Rig Assembly (INFRa) to investigate the intake fan interactions are presented. The fan and intake module will be tested under variable and highly critical inflow conditions, such as crosswinds and large angles of attack. These conditions are realized within the Propulsion Test Facility (PTF) which is operated by IFAS. In order to analyze the effects of the intake length, two nacelles of different length have been designed and investigated experimentally at the PTF in the isolated configuration, so that the direct influence of the fan will become apparent in the INFRa configuration. Capitalizing its design expertise, DLR was in charge of the dedicated and engine realistic fan stage design, including subsequent manufacturing. Based on top-level design parameters (fan pressure ratio, work coefficient and flow capacity) reflecting the current state-of-the-art in turbofan design, the main focus of the fan design relied on low speed operating conditions, for which crosswind and angle of attack may jeopardize the fan stability. At rig scale, the three-dimensional design of the fan stage was performed under clean inlet flow condition. To comply with the aeromechanical restrictions and constraints of the test facility, the design strategy relied on a multi-disciplinary and multi-objectives optimization approach. During the optimization, the stability limit of the fan stage is maximized by maintaining a satisfying efficiency level. To ensure safe rig operation, further detailed structural analysis including FBO loading, LCF and blade rub in were performed and confirmed the results obtained in the multi-physics optimization. Expecting the measurements by the end of the year, an overview of the instrumentation strategy deployed to validate the fan concept is presented in the paper.