Structure of Instantaneous Reynolds Stress over a Permeable Open-channel with Suction or Injection

Abstract

In the present study, we investigate experimentally the structure of the instantaneous Reynolds stress in open-channel flow over a permeable bed with suction or injection. Then, the fluctuating signals obtained from the X-type hot-films are conditionally analyzed in order to examine the effect of suction or injection on the turbulence production mechanism or the bursting phenomenon. We can then obtain the following results. The absolute magnitudes of the turbulence intensities and the Reynolds stress near the wall increase with an enlargement of the injection, while they decrease with an enlargement of the suction. However, the fraction of time occupied by each bursting event and the contributions of its event to the Reynolds stress against any hole size are almost the same, irrespective of suction or injection. The promotion of turbulence by injection or its suppression by suction may be caused by similar variations of three parameters of the bursting intensity, the bursting period and the bursting duration time. To sum up, the internal structure of the turbulence or the bursting mechanism is not essentially influenced by suction or injection, as long as the flow is still turbulent.