Flow Physics around a Supersonic Inlet

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A ramjet engine, one of the supersonic air breathing engines, can be used in the range of Mach number from 2 to 5. In this type of engine, supersonic inflow is compressed and decelerated to subsonic speed for combustion. Because this engine can compress the air without a compressor, it is getting the spotlight for its lightness and efficiency. In spite of its strengths, however, the internal flow of the engine has complex flow characteristics due to the shock wave/shock wave or shock wave/boundary layer interactions, causing flow instability with self-excited shock wave oscillation ? called inlet buzz. Inlet buzz causes serious problem such as thrust loss, combustion failure, and even structural damage. There are many research topics for physical understanding of flow around a supersonic inlet and developing inlet performance.

 

1. Study of flow instability

 

In this topic, we conduct simulation of flow instability of a supersonic air-breathing engine and reveal its physical reasons.

 

2. Multi-physics problem

 

From periodic flow perturbation, it makes acoustic harmonics and resonance problem. This phenomena is harmful for engine structure. ‘Fluid-Structure Interaction’ method is applied in this topic because flow instability and structural deformation are coupled.

 

3. Flow control & design

 

In order to prevent flow instabilities and to improve performance of a supersonic inlet, flow control device like bleed is used. Design methods are used to find the optimal condition of bleed so that a supersonic inlet gets the best performance.

 

Fig. 1 Schema of a ramjet engine

 

 

Fig. 2 Instability of supersonic inlet flow (numerical simulation of buzz phenomenon)

 

 

Fig. 3 Effect of bleed device on a supersonic inlet