Effects of Flow Pulsing on Passive Scalar Mixing in a Turbulent Round Jet

This work presents a study on the effect of pulsing on a jet flow. Puls- ing is used to modify jet inlet conditions with the objective of improving mixing. In this experimental work, a jet was slightly heated so that temperature could be considered as a passive scalar. The spectral behaviour of velocity and the passive scalar temperature was analyzed along the jet axis with and without pulsing. Low frequency pulsing (f/fS < 0.05 fS the Strouhal frequency) modifies the spectral com- position of the velocity at the jet exit, but it does not affect the asymptotic profile reached in the fully developed region of the jet at approximately x/d = 30. The lower frequency pulsations travel far downstream and stay visible in the fully de- veloped region on both the velocity and temperature spectra. This pulsing affects slightly the scalar spectral composition at the jet exit for only the highest frequency used (f/fS = 0.04 (40 Hz) to 0.05 (80 Hz)). This indicates that mixing is improved since the change reflects mixing the main flow with the surrounding airflow. Also, the presence of low pulsing frequencies far downstream indicates the effect pro- duced at the jet exit lasts into the far field.