(35e) Active Mixing Enhancement in Confined Mixing Layer

Drastic mixing is achieved in confined mixing layer and wake flow by actuating at a narrow frequency band, i.e. optimal frequency, in a wide range of Re. The potential causes, such as hydroacoustic resonance mechanism, fluid-solid interactions, the inherent frequency of actuating system and sloshing wave, are in detail investigated by parametric study using flow visualization. By changing the parameters, such as the length and diameter of mixing chamber, the length of settling chamber and the fixing methods of all the parts of the water tunnel system, the optimal frequency, i.e. 5.3 Hz in our setup is not changed. The mixing effect is not apparently affected either. Further investigation indicates the shape of trailing edge of splitter plate strongly affect the mixing effect. The sharper the trailing edge, the stronger the mixing. The flow field without the splitter plate is also tested. It is found that in this case there is no apparent difference with or without the forcing. Hence, it is obvious that the splitter plate, i.e. the specific configuration of flow field plays a key role in the mixing enhancement process. Confined mixing layer is another key factor. It is believed that the confined region induces the rapid growth of 3-dimensional flow fluctuations and vortex structures, which lead to the rapid mixing. The nature of the unforced and forced flow field, the receptivity, the spectrum characteristics and the vortex structures are all under investigation by PIV.