Characteristics of Two-Dimensional Turbulent Jet in Flapping Motion

Abstract

The characteristics of a two-dimensional turbulent jet in the flapping motion are investigated by simultaneously measuring the velocity and pressure. The simultaneous measurements are performed by using a combined probe that consists of an X-type hot-wire probe and a static pressure tube. The measurement data are analyzed by using a conditional sampling technique and the ensemble-averaging technique, on the basis of an intermittency function. This function is used to determine whether the jet is in the flapping motion or not. The measurement results of two hot-wire probes set in the self-preserving region of the jet are analyzed by performing a wavelet transform. The experimental results show that the ensemble-averaged velocity field during the flapping motion shows a good agreement with the measurement result obtained by Sakai, et al. (2006) through multi-point simultaneous measurement of velocity. Further, the ensemble-averaged static pressure field during the flapping motion indicates the pressure of a vortex coherent structure, interpreted as a combination of flapping and puffing motions in the self-preserving region of the jet. In addition, the estimation of the turbulent energy budget shows that the turbulent energy production and its transportation from the inner region to the outer region of the jet by the diffusion are enhanced during the flapping motion. In particular, this enhancement of the turbulent energy transportation is caused by the combination of the increasing of the turbulent diffusion to the outer region of the jet and the decreasing of the pressure diffusion to the inner region of the jet.