DOI: 10.1615/TSFP7
THE STATISTICAL ANALYSIS OF FLAPPING PHENOMENON IN A TWO-DIMENSIONAL TURBULENT JET
RÉSUMÉ
The characteristics of a two-dimensional turbulent jet in
flapping motion are investigated by simultaneous measurement of the velocity and the pressure. The simultaneous measurements are performed by using a combined probe, which was developed by our laboratory (Terashima et al., 2010), that consists of an X-type hot-wire probe and a static pressure
probe. The measured data are analyzed by using conditional-sampling technique and ensemble-averaging technique, on the
basis of an intermittency function to determine whether the jet is flapping or not. The intermittency function is obtained by applying a continuous wavelet transform with Gabor mother wavelet to the measured signals of hot-wire anemometers set in the self-preserving region of the jet.
The measured results obtained by the present new
method show that the characteristics of the flapping motion
clearly, and the ensemble-averaged velocity field during the
flapping motion shows a good agreement with the results obtained
by Sakai et al. (2006) through the multi-point simultaneous
measurement of the velocity. Further, the ensemble-averaged
static pressure field in the flapping motion indicates
the existence of a coherent vortex structure, which is interpreted
as a combination of flapping and puffing motion in the
self-preserving region. The statistical analysis of the flapping
motion shows that the flapping motion arises at random, and
the average interval time of the arising of the flapping motion
is about 6.1 times the flapping periods (0.24 sec), and the average
duration time of the flapping motion is about 1.7 times
the flapping period (0.07 sec) and the one that continues over
3.0 times the flapping period is very few. Moreover, the two-points
spatial velocity correlation, which becomes negative
value, substantially depends on whether the flapping motion arises or not. These results indicate that the flapping motion in a two-dimensional turbulent jet has a very important role to the properties of the jet, although the flapping motion is a rare
phenomenon.