What type of inlets are used in turbine turboshaft engines?

In turbine turboshaft engines, the predominant design for the air inlet is typically a divergent type. The reason for this design choice is centered around improving the efficiency of air entering the engine. Divergent inlets allow for the gradual expansion of air as it flows towards the engine, which helps in reducing the velocity of incoming air while increasing its pressure. This is particularly beneficial for turboshaft engines, as they often operate at lower speed ranges compared to turbojets and are designed to produce high torque for rotorcraft applications.

Moreover, a divergent inlet supports better airflow characteristics and contributes to optimal performance under various operating conditions, such as during hover or low-speed flight. This design also helps reduce the risk of flow separation, which can adversely affect engine performance and stability.

Other inlet designs, such as convergent or rectangular, do not generally provide the same advantages in terms of airflow dynamics and engine performance in a turboshaft application. Circular shapes, while common in many aerodynamic structures, are not specifically associated with the inlet configurations typically employed by turboshaft engines, where divergence plays a crucial role in effective air intake management.