Mach Wave Elimination
A new method for quieting high-speed jets
(U.S. Patents 5590520 and 5916127)


THE CONCEPT

EXPERIMENTAL SETUP

ACOUSTIC DATA

APPLICATION TO AEROENGINES

TECHNOLOGY EXCHANGE

FUTURE PLANS

SPONSORSHIP

DOWNLOADS

PUBLICITY & AWARDS

OPERATING CONDITIONS
engine.gif (8514 bytes) machelimination.jpg (44079 bytes)

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

Mcj=(Ucj-Uf)/af

and the convective Mach number of the fan eddies as

Mcj=(Ucf-Uoo)/aoo

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. 628-635. 

and 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 as slugs.

 

JF2213W.gif (59834 bytes)

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 model follow:

Example 1: Uj=700 m/s, Uoo=0
Example 2: Uj=700 m/s, Uoo=120 m/s