Subsonic and Supersonic Diffusers Geometry

Introduction
Diffusers are devices used in fluid mechanics to gradually increase the velocity and decrease the pressure of a fluid flow. They are commonly used in various engineering applications, such as in air conditioning systems, jet engines, and wind tunnels. Subsonic and supersonic diffusers have different geometries based on their operating conditions and desired flow characteristics.

Subsonic Diffusers Geometry
Subsonic diffusers are designed to operate at flow velocities below the speed of sound. Their primary purpose is to slow down the flow and increase the pressure. The geometry of subsonic diffusers includes:

1. Converging Section: The subsonic diffuser starts with a converging section, where the cross-sectional area gradually decreases along the flow direction. This section helps to decelerate the fluid flow and increase the pressure.

2. Throat: The throat is the narrowest point in the diffuser where the flow reaches its maximum velocity. The throat is designed to ensure that the flow remains subsonic throughout the diffuser.

3. Diverging Section: After the throat, the diffuser expands in a diverging section. The cross-sectional area gradually increases, which results in a decrease in fluid velocity and a further increase in pressure. This section is responsible for the final pressure recovery.

4. Angle of Divergence: The angle of divergence in subsonic diffusers is usually relatively small, typically less than 10 degrees. This gradual expansion helps to minimize losses and turbulence in the flow.

Supersonic Diffusers Geometry
Supersonic diffusers are designed to operate at flow velocities above the speed of sound. Unlike subsonic diffusers, their primary purpose is to decelerate the flow and increase the pressure. The geometry of supersonic diffusers includes:

1. Converging-Diverging Section: Supersonic diffusers typically have a converging-diverging (CD) section. This section consists of a converging section followed by a diverging section. The converging section initially accelerates the flow to supersonic speeds, while the diverging section decelerates the flow and increases the pressure.

2. Throat: Similar to subsonic diffusers, supersonic diffusers also have a throat where the flow reaches its maximum velocity. However, in supersonic diffusers, the throat is designed to ensure that the flow remains supersonic throughout the diffuser.

3. Shock Waves: Supersonic diffusers experience shock waves due to the abrupt expansion of the flow in the diverging section. These shock waves play a crucial role in decelerating the flow and increasing the pressure.

4. Angle of Divergence: The angle of divergence in supersonic diffusers is relatively large, typically greater than 15 degrees. This sudden expansion helps create the necessary shock waves for flow deceleration.

Conclusion
The geometry of subsonic and supersonic diffusers differs based on their intended flow conditions. Subsonic diffusers have a converging-diverging geometry with a small angle of divergence, while supersonic diffusers have a converging-diverging geometry with a larger angle of divergence and experience shock waves.

Design