Fall 2020 > IAS Scholars

IAS Junior Fellow and Research Assistant Professor of Mechanical and Aerospace Engineering

Dr. ZHONG Siyang

The study of aeroacoustics has undergone profound development since Prof. Sir Michael James LIGHTHILL, a British mathematician, introduced the topic in the 1950s. Given the advances in aviation technology and high-performance computing over the past few decades, it is not hard to imagine where the future of aeroacoustics might take us — to quieter skies.

IAS Junior Fellow Dr. ZHONG Siyang has been circling around aircraft aerodynamics and aeroacoustics. After receiving his Bachelor’s degree in Theoretical and Applied Mechanics in 2011 and his Master’s degree in Control Theory in 2014, both from Peking University, Zhong was accepted into the PhD program at the Department of Mechanical and Aerospace Engineering (MAE) of HKUST. Currently a Research Assistant Professor of MAE, Zhong tells us why this kind of aircraft noise that we sometimes hear but seldom care about is so special to him.

What exactly is your research about? What inspires you to carry out research in this area?

My research interests lie in high-order simulations and analytical acoustics studies on the noise generated by turbulence. This research area has a strong industrial background and my research is driven by the needs of practical applications. For example, airline companies aim to reduce the aircraft noise from the engine or the noise inside and outside the cabin. Both airfoils and rotors are common aerodynamic devices that will generate undesired noise. The key challenge in the study is that associated flow patterns are complex and sensitive to concrete factors like geometry, speed and medium. As sound is part of the flow, a small variation in the flow can lead to significant impact on the noise signature.

Actually, aircraft noise is highly relevant to us and our daily lives. Remember the old Kai Tak Airport in Kowloon City, which was in close proximity to the local community? In the past, the noise impact of aircraft on the nearby residents was excruciating. My aim is to understand the mechanisms involved in noise generation and to develop a method to predict and reduce noise, not just from the conventional large aircraft but also from drones and possibly high-speed trains. For example, by using acoustic imaging techniques, we can study the location and strength of the sources. Yet, I want to extend the capability of the current methods. In acoustics, it is difficult to identify low-frequency sources because of their long wave lengths. Recently, we try to introduce ideas from other fields such as the tomography technique to introduce high-frequency incident waves to resolve the target low-frequency sources. The initial results seem promising. We hope to extend the method to other applications.

Have you been always interested in this topic since your undergraduate studies?

Actually when I was young my passion was physics. I remember that during my secondary school years I was inspired by Stephen HAWKING’s book A Brief History of Time. I also participated in the National Physics Contest for secondary students, but unfortunately I was not awarded the first prize. Later, I was accepted by Peking University and assigned to the College of Engineering. It was the first time I had the opportunity to be trained in applied mathematics and mechanics subjects, such as fluid and solid mechanics and aerodynamics. Gradually, I found that what I was learning had many applications in the real world, especially in aviation, and that’s what drew me into research on aerodynamics and aeroacoustics.

That’s why you came to HKUST to pursue a PhD in MAE?

After I received my Master’s degree in Control Theory from Peking University, I wasn’t sure which path to take: continue studying or work in industry. In the end, I chose to work as an Associate Engineer at the Shanghai Aircraft Design and Research Institution of the Commercial Aircraft Corporation of China. I am glad to see that the company is making continuous progress in developing China’s civil aircraft. The senior members there helped me a lot during my employment. This experience gave me a better picture of what it was like to work in industry, but soon I realized I was more interested in fundamental studies and theory than only applications. Simply meeting project deadlines wasn’t really what I wanted. Even when an idea is innovative, it may not be a priority for a company, whereas in academia when you have an idea you have more freedom to dig into it. That said, I do want to solve industry-relevant problems and investigate phenomena that need our expertise. This is the role and strength of academic researchers. Therefore, I decided to pursue a PhD at HKUST and I was very lucky to work with Prof. ZHANG Xin, Swire Professor of Aerospace Engineering, whom I met at a conference in 2014.

You have been here for over five years now. How did Prof. Zhang inspire you in your research?

I appreciate being here at HKUST, where the faculty, staff and students pull together and work very hard. Prof. Zhang was my PhD supervisor and has been a very important mentor to me. He is experienced and has unique insight in the academic and industrial fields. It is a privilege to work with Prof. Zhang and other postgraduate students in his research group at the Aerodynamics Acoustics and Noise Control Technology Centre. I like the process of exchanging ideas and designing experiments together. Prof. Zhang is strict and critical in academic research. We need to have a clear overview of our ideas before discussing them with him, but he will be supportive once he is convinced. Another important thing that I have learnt from him is that we have to be problem-solving oriented, and there is always a smarter way to come up with a better solution.

We also make use of the Aerodynamics and Acoustics Facility, which is under the directorship of Prof. Zhang. It is equipped with world-class low-noise wind tunnel and acoustic testing laboratories for conducting aerodynamics and acoustics research with industry partners such as the Aviation Industry Corporation of China (AVIC) and DJI.

What was the best experience of your research career so far? Have you encountered any major difficulties?

When we encounter challenging research problems, I guess for most researchers it is like facing an uphill battle, struggling along the way. In my PhD studies, I needed to compute the sound from the turbulence data collected on a single surface. This is related to practical needs but also requires a deep understanding of the underlying physics. It is a longstanding problem of sound and turbulence: we have to find out what is sound in the turbulent flows. In the past, people have developed methods to understand the complexity in this process, but only in specific circumstances. That’s why this problem stimulated my curiosity. For part of my PhD work, I had to separate the components, and my gut feeling told me that this would be possible because flow turbulence and sound fluctuation have different characteristics. I kept thinking of this problem and literally dancing between frustration and hopefulness. Then one night, an idea popped up in my mind. I immediately jumped out of bed to write down the equation and tested some cases. And it worked! So perseverance matters.

To those who want to pursue their graduate studies or research in MAE, what would you recommend them to consider when choosing an area of interest?

I seldom give recommendations to others! This is my principle. Nevertheless, there are several areas in MAE, and graduate students must choose a field that coincides with their interests. In academic research, collaborating with people from different backgrounds is common. Along the way, we overcome difficulties and share findings. Having strong critical and analytical thinking skills, in my opinion, is a key requirement of academic research.

You’re a Research Assistant Professor at HKUST; are you planning to pursue a career in academia? What are your future research plans?

Teaching requires a different skill set to doing research. I need to organize lectures, improve the slides and tutorials, and most importantly, arrange the content in a logical way for students to understand. I hope to have an academic career related to my research areas, though I haven’t set myself any boundaries.

In terms of research, I am currently learning new technologies such as high-performance computing. Combining this with traditional research methods will be a powerful means to solve problems and to better understand complex physics. I am also interested in the bio-inspired design, such as the flight of birds. My goal is to combine this field with materials technology to manufacture ideal structures, which may be useful to control flow and reduce noise.

I have recently received funding from RGC’s General Research Fund for my research project “Aerodynamic Noise of Multi-Rotor Powered Flying Vehicles.” As Principal Investigator, I want to study the aerodynamic interactions of multi-rotors (such as drones), their flow patterns and noise generation mechanisms, and to investigate how the sound propagates and interacts. This project will keep me fully occupied in the coming three years.