Motivation
Modern aircraft are powered by high by-pass-ratio jet engines, the thrust of which is generated when air is discharged through the engine exhaust at a very high speed. High-speed turbulent jets are violently unsteady and therefore act as an efficient noise source. The noise emitted by these jets are referred to as jet noise, and its investigation was primarily motivated by the increasingly urgent need to reduce aircraft noise.
Background
Research on jet noise dates back to the 1950s. Perhaps one of the most well-known discoveries in the 1950s is that jet noise scales as the eighth power of jet velocity. Therefore, reducing the jet exit velocity becomes the single most effective strategy for reducing aircraft noise. Together with the consideration of fuel economy, the principle of increasing jet engine diameter sums up the main trend of engine development in the past few decades.
Current research
There are two important issues associated with this trend. The first is that the engines grow increasingly large that they start to interact with aircraft wings. This interaction greatly amplifies sound at low frequencies. Here in our group we study the physical mechanism of this noise amplification and aim to develop novel techniques for its reduction.
The second issue is the sustainability of the trend in view of modern aircraft configurations. Because aero-engines have grown so large that further increasing its diameter leads to integration difficulties. Understanding the physical nature of sound generated by jet turbulence seems to be the key to a way out. Here in our group we endeavour to understand the fundamentals of the noise generation by turbulent jets.