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SpringerBriefs in Applied Sciences and Technology Peijian Lv Power-Based Study of Boundary Layer Ingestion for Aircraft Application SpringerBriefs in Applied Sciences and Technology SpringerBriefs present concise summaries of cutting-edge research and practical applications across a wide spectrum of fields. Featuring compact volumes of 50 to 125 pages, the series covers a range of content from professional to academic. Typical publications can be: • A timely report of state-of-the art methods • An introduction to or a manual for the application of mathematical or computer techniques • A bridge between new research results, as published in journal articles • A snapshot of a hot or emerging topic • An in-depth case study • A presentation of core concepts that students must understand in order to make independent contributions SpringerBriefs are characterized by fast, global electronic dissemination, standard publishing contracts, standardized manuscript preparation and formatting guidelines, and expedited production schedules. On the one hand, SpringerBriefs in Applied Sciences and Technology are devoted to the publication of fundamentals and applications within the different classical engineering disciplines as well as in interdisciplinary fields that recently emerged between these areas. On the other hand, as the boundary separating fundamental research and applied technology is more and more dissolving, this series is particularly open to trans-disciplinary topics between fundamental science and engineering. Indexed by EI-Compendex, SCOPUS and Springerlink. Peijian Lv Power-Based Study of Boundary Layer Ingestion for Aircraft Application Peijian Lv School of Aerospace Engineering Beijing Institute of Technology Beijing, China ISSN 2191-530X ISSN 2191-5318 (electronic) SpringerBriefs in Applied Sciences and Technology ISBN 978-981-19-5496-2 ISBN 978-981-19-5497-9 (eBook) https://doi.org/10.1007/978-981-19-5497-9 © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore To my family Preface This book presents research on boundary layer ingestion (BLI). BLI is an unconven- tional aircraft–engine integration technique which aims at integrating the aircraft and the propulsion system such that the overall aircraft fuel consumption can be reduced. This research begins with a literature survey on propulsion integration. The literature is not only limited to recent work on novel aircraft concepts utilizing BLI but also covers the previous studies on ship propellers and pusher propellers used for aircraft. Various studies in the literature show that BLI and/or similar configurations can effectively reduce the total power consumption of the propulsion system. However, discrepancies can be identified among various research with respect to the improvements that BLI could provide in terms of reduction in the power consumption. Different research methods have been used to investigate and study this phenomenon in the literature. In particular, the various research methods give an indication that the physics involved in BLI might not be well understood. As a result, the current research aims to enhance the fundamental understanding of BLI. The main research questions are identified below: • What are the mechanisms of BLI for the provided benefit? • How large is the benefit of BLI? This study addresses the aforementioned questions by following a research line where power conversion is the key to explaining the mechanisms of BLI . The current research consists of three main pillars, namely theoretical analysis, numerical simulation, and experimental study. In the theoretical analysis, the physical model for understanding BLI is developed. Numerical simulations and experimental study provide validations to the developed model and assist in understanding the phenomenon involved with BLI. In the theoretical analysis, effort is made to evaluate the performance of the propulsor and its associated fuselage in two configurations, namely the so-called BLI configuration and the wake ingestion (WI) configuration. A power conversion analysis uses power balance method (PBM) introduced by Drela to elaborate the power-saving mechanism of WI, showing that the Froude’s propulsive efficiency vii viii Preface as a figure of merit should be separated from the power conversion efficiency in these configurations. The body/propulsor interaction occurring in the BLI configuration is qualitatively analyzed to clarify its influence on the performance of the integrated vehicle. The results suggest that the minimization of total power consumption should be used as a design criterion for aircraft utilizing BLI rather than focusing on minimization of drag, as is generally done. The numerical simulations are considered as an extension of the theoretical analysis to support the physical understanding of BLI elaborated in the developed theoretical model. This simulation study has two major objectives: establishing the process of typical power conversions and quantifying the influences of BLI on the power conversion of the theoretical model. To achieve these objectives, this study on power conversion processes is rather limited to simple cases, which help to decipher the processes easily, and these cases bring out the key elements involved in the power conversion process elegantly. Therefore, the simulation is limited to 2D steady incom- pressible flows, which excludes complicated flow physics, such as compressibility. This simplification allows the analysis to be focused on the mechanisms elaborated in the theoretical analysis. In this simulation study, only typical models are used and the simulation results are processed using the PBM. The results prove that BLI could increase the profile drag of a body but reduce the actual total power consumption. The experimental study aims to provide evidence to the physical understanding of BLI developed during the theoretical analysis. This study focuses on the power conversion processes involved in a propulsor operating in the wake of the body. The experimental set-up is specifically designed such that the same propulsor can ingest a body wake or purely work in the freestream. Conventional force balance measurement techniques are used to measure the thrust and power in the experi- ments. Stereoscopic PIV is employed in order to visualize the flow and understand the physics involved in BLI and WI. This technique has been used for the first time to visualize the flow in wake ingesting propellers. Furthermore, the PBM is used to quantify the power conversion mechanisms using the data obtained from the experi- ments. The results prove that the dominant mechanism responsible for the efficiency enhancement in this experimental study is due to the utilization of body wake energy by the wake ingesting propeller. Finally, efforts are made to summarize the main findings of the three pillars. These methods are theoretical analysis, numerical simulation, and experimental study, respectively. A key working principle encompassing the entire research is extracted. The conclusion of this research provides answers to the research questions raised in the earlier chapters of this book, and recommendations for future research are provided. Overall, the importance of wake energy flow rate in understanding BLI and WI phenomenon is highlighted. This understanding is a major milestone in the research into this phenomenon. In terms of the results, this research agrees with several previous investigations which claim that BLI could effectively reduce power consumption of the aircraft. Beijing, China Peijian Lv Acknowledgements I would like to thank China Scholarship Council (CSC) for the financial support which allows me to do Ph.D. research in TU Delft. The CSC scholarship makes my dream become true: to do the most exciting research in a top university. I would like to express my gratitude to my promotor Prof. Leo Veldhuis. You are always kind, and it is a pleasure to work with you. I have been inspired by your enthusiasm in aviation since our first meet. In the wind tunnel test, you provided many wise suggestions which are valuable and helpful. Moreover, you encouraged me when I feel frustrated in writing this book and your encouragements support me going through difficult times. Dr. Arvind G. Rao, please accept my deepest appreciation! As my co-promotor, you graciously accept me as a PhD candidate and you have made enormous amount of efforts to guide me in research. I feel proud that your efforts are paying back. I would like to thank you for the assistance in finalizing this book. Your high standard is impressive, and it was a great experience to work with you! I would like to thank Prof. Georg Eitelberg. It is an honour to work with you. You played a special role in inspiring me with research work. Especially, you challenged me with truly tough questions. This gives me a chance to rethink my work profoundly. I consider those challenges as touch stones which sharp my mind, and these will benefit me in the rest part of my career. Thank you! This research work will not be completed without the support of Dr. Dani Ragni. Our collaboration in wind tunnel test and journal papers is productive. I would like to thank graduate students Tarik Hartuç and Nando van Arnhem, and it was of great joy to work with you! I could not forget the day Tarik and I shout out loudly in the wind tunnel when we got the exciting results. Nando presented very impressive work to help me understand my research better, and you are very kind to translate the summary of this book into Dutch. I would like to give thanks to my office mate and friend Mo Li. We had so many great times in discussing aircraft, and we enjoyed our first glider flight together. It is of great joy to work with my colleagues and friends in the FPP group, Yannian Yang, Dipanjay Dewanji, Feijia Yin, Qingxi Li, Haiqiang Wang, Mark Voskuijl, ix x Acknowledgements Tomas Sinnige, and André Perpignan. It is your companionship makes my life in the Netherlands rich and colourful. Last but not least, my parents Giexiang Lv and Xunfeng Feng, your love supports me through the good and bad times. I can always get inspirations from you and I feel lucky to be your son. My beloved wife Jingjing Yang, it is your love and encouragement that supported me in finalizing this book. Thank you!