Jet engines stators are convergent or ?
Jet engines stators are convergent or ?
Joined: Aug 2001
Posts: 775
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From: Dorset
As stated in the previous posts, the spaces between the blades of an axial flow compressor are divergent. Those between the stator blades (nozzle guide vanes) of turbines are convergent.
In the case of the compresor the objective is to compress the air by increasing its static pressure. The airflow through the compressor is subsonic, so increasing static pressure requires divegent ducts.
It is however less acurate to say that the purpose of the compressor is to slow down the airflow. This is achieved mainly by the air intake, which in subsonic aircraft is also divergent. Although the combustion chambers require low velocities, the compressor blades will stall if the airflow past them becomes too slow. So axial flow compressors tend to maintain an almost constant overall flow velocity.
The rotors increase the energy content of the air by increasing its velocity. Part of this increased energy is immediately converted into static pressure by the divergent ducts between the rotating blades. The remainder of the added energy is then converted into static presssure as the air flows through the divergent ducts between the stator baldes. The overall effect is an increase in velocity in the rotors, followed by a decrease in the stators, so that the overall velocity is almost constant. Unfortunately the system is not entirely efficient, so a signifiacnt proportion of the added energy is converted into heat.
The velocity is then reduced as the air leaving the final stage of the compressor passes through the diffuser, which is a divergent duct immediately upstream of the combustion chambers.
In the case of the turbines the objective is to extract energy from the air so, it must be allowed to exapand and cool. This is achieved by spaces which are (to various extents) convergent.
In the case of the compresor the objective is to compress the air by increasing its static pressure. The airflow through the compressor is subsonic, so increasing static pressure requires divegent ducts.
It is however less acurate to say that the purpose of the compressor is to slow down the airflow. This is achieved mainly by the air intake, which in subsonic aircraft is also divergent. Although the combustion chambers require low velocities, the compressor blades will stall if the airflow past them becomes too slow. So axial flow compressors tend to maintain an almost constant overall flow velocity.
The rotors increase the energy content of the air by increasing its velocity. Part of this increased energy is immediately converted into static pressure by the divergent ducts between the rotating blades. The remainder of the added energy is then converted into static presssure as the air flows through the divergent ducts between the stator baldes. The overall effect is an increase in velocity in the rotors, followed by a decrease in the stators, so that the overall velocity is almost constant. Unfortunately the system is not entirely efficient, so a signifiacnt proportion of the added energy is converted into heat.
The velocity is then reduced as the air leaving the final stage of the compressor passes through the diffuser, which is a divergent duct immediately upstream of the combustion chambers.
In the case of the turbines the objective is to extract energy from the air so, it must be allowed to exapand and cool. This is achieved by spaces which are (to various extents) convergent.
