VCD(Vortex-controlled Diffuser)

[babyboeing400]

What is the purpose and function of a VCD in a turbofan engine?:confused:

[noughtsnones]

babyboeing400

Patent US4431374 (https://www.google.com/patents/US4431374) Vortex controlled radial diffuser for centrifugal compressor, in its Description of the Prior Art, states
The diffuser of a turbine engine distributes the pressurized gas flow from the turbine compressor to the combustor of the turbine.
It is important that the diffuser obtains a high static pressure recovery and that the high velocity energy head produced by the compressor impeller is preserved from the pressure losses due to friction so that the total pressure of the gas is maximized as it reaches the combustor.
As the total pressure recovery from these two pressure components increases, the efficiency of the turbine engine is increased.
and
One previously known device for obtaining a high static pressure recovery from the static energy and kinetic energy of the gases and for obtaining higher rates of diffusion is a vortex controlled diffuser.
The vortex control concept has been studied when applied to the axial flow of gas from a first primary duct to a second coaxial and enlarged secondary duct.
A radially extending vortex fence secured to the inner periphery of the secondary duct is axially spaced and radially spaced from the outlet end of the primary duct.
A flow chamber upstream of the vortex fence forms a bleed mechanism that creates a vortex used to energize flow in the wake region immediately downstream of the diffusing step, whereby flow attachment on the diffusing roll of the secondary duct is enhanced.
Low momentum fluid is removed from the upstream wall of the vortex fence and the corner vortex formed at the downstream end of the fence smooths flow transition to the downstream wall.