The most likely source of the coflow in a turbofan engine would be the fan
strean. MWE requires that significant part of the fan stream remain unmixed so that
it forms a separated-flow exhaust. The nozzle pressure ratio of the fan stream
should such as to make the jet eddies subsonic relative to the fan, while ensuring that
the fan eddies are subsonic relative to the ambient. Defining the convective Mach
number of the jet eddies as
and the convective Mach number of the fan eddies as
we require both Mcj<1 and Mcf < 1. The more subsonic Mcj becomes, the
faster the pressure disturbances decay within the coflow thickness.
|It is obvious that the critical ingredient in MWE is
prediction of the eddy convective velocity Uc. Several years of work at UCI have
culminated in the construction of an empirical model for Uc , based on experimental
measurements (see picture on right) in supersonic jets and shear layers.
The model is presented in the journal paper
Murakami, E., and Papamoschou, D., " Eddy
Convection in Supersonic Coaxial Jets," AIAA Journal, Vol. 38, No.4, 2000, pp.
in the conference paper AIAA-98-3015 which is downloadable
in PDF. In addition, the model is available in convenient spreadsheet
form: MCMETRIC.XLS for calculation in SI units,
and MCENGLISH.XLS for those who prefer units such
Evolution of the
turbulent structure near the end of the potential core of a Mach 1.5 cold air jet.
The two adjacent frames are illuminated with a time delay of 50 microseconds.
Some examples of the application of this
1: Uj=700 m/s, Uoo=0
Example 2: Uj=700 m/s, Uoo=120