Q1. Please briefly introduce your lab and research areas.

Our lab is the Reactive Flow Laboratory, and focuses on three main research areas. The first one is hypersonic flight vehicles. You can think of hypersonic as the area where speeds reach Mach numbers of 5 or higher. We conduct research on designing those hypersonic vehicles and testing engines capable of such speeds. The second area involves high-pressure combustion. Rocket engines generate thrust by creating hot gases at high pressures. We design and test such engines. The third area is laser metrology. In conditions of hypersonic and high-temperature, high-pressure environments, it is challenging to perform quantitative measurements using conventional sensors. Thus, we focus on laser diagnostics, which involves controlling photons to interact with molecules in the region of interest and analyzing the resulting photons to determine the properties of molecules, such as type, temperature, velocity, and density. These new laser techniques are directly applied in the two areas mentioned above.

 

Q2. Please briefly introduce a recent or ongoing representative research project.

Our field requires a long research period. Rocket engines have been developed for a long time. For instance, Dr. von Braun developed the V2 rocket during World War II and later moved to the United States, greatly advancing U.S. rocket technology. Despite this, due to the lengthy research period, there are still many areas to explore in rocketry. The most recent engine I've been researching is the Scramjet engine. Scramjet engines are developed for various purposes, such as reaching Earth's orbit, high-speed atmospheric flight, and military applications. We are contributing to developing the latest Scramjet models with our specific objectives.

<Example of Scramjet Model>

 

Recently, we have also been conducting research using machine learning. For example, when an aircraft is flying, it is impractical to attach many sensors to meet the measurement requirements. Therefore, practical engineering problems require solving with minimal sensor data input while obtaining maximum flight environment information with high accuracy. In this regard, machine learning is a very useful tool. Another example involves future flow prediction research. During flight, unexpected shock wave structures can cause engine shutdowns. Consequently, predicting future flow structures based on past and present measurement results is important. We are attempting to predict future flow structures with high accuracy using various governing equations and machine learning techniques.

Q3. Tell us what has been the most challenging aspect of conducting this research and how you overcome it.

Hypersonic vehicles research requires a lot of time and financial investment for testing and analysis. For example, conducting a flight test at Mach 6 poses several challenges, so we use a method where the vehicle is fixed inside a hypersonic wind tunnel and the airspeed is increased. However, creating an environment similar to the actual situation requires heating the air to several thousand degrees Celsius and accelerating it, which can cost tens of millions of won per day. Therefore, there are difficulties in conducting limited tests within restricted days. To overcome these problems, we try to complete the design in advance through simulation whenever possible and obtain test results that are close to reality.

Nevertheless, ground and flight tests for validation are essential, so we must conduct research in a wide range of fields simultaneously. For example, studies analyzing the differences between actual flight and ground tests, precise measurement technology for flight environments during high-speed flight, and design optimization techniques are needed. For these reasons, we collaborate with various schools and institutions.

 

Q4. Please introduce any special equipment or facilities in your lab.

 

Our lab consists of three main floors. The basement houses the hypersonic test wind tunnel, the first floor has high-pressure combustion test equipment, and the second floor contains high-precision laser equipment. Among these, the hypersonic flight experiment facilities and the Femto second laser are special equipment. 

First, the hypersonic flight experiment facilities include wind tunnels and vacuum tanks that can create environments similar to actual flight, as mentioned in Q3. These facilities are used to test hypersonic flight vehicles.

<Hypersonic Flight Experiment Facilities>

 

Next is the Femto second laser. "Femto" refers to 10 to the power of -15 (10^-15), and the Femto second laser is a laser whose pulse duration is in the femtosecond range. This equipment is quite expensive and requires meticulous care because even a small amount of dust can affect its operation.

<Femto Second Laser*

 

 

Q5. Share any final thoughts you would like.

 

Aircrafts are highly independent systems with no connections to anything else. In other words, if specific mission is given, they must fly while overcoming various disturbances that arise to complete that mission. Therefore, it can be seen as a field where cutting-edge technologies are concentrated. When first entering this field, it can be overwhelming due to the vast amount of information.

However, actual research often involves intuitive aspects. For example, calculating the movements of a flying object may seem complicated, but understanding flight mechanics can enable the creation of highly accurate prediction algorithms. In addition, by combining knowledge from various fields, new systems can be designed, and it is very rewarding and enjoyable when a new flight system operates successfully. I believe this is the greatest appeal of our field and the reason why many engineers, including myself, continue to conduct research in this area.

 

MEch-SSENGER Lee Sang-min (이상민), Lee Joon-ha (이준하)