Interaction of a bursting phenomena with a row of longitudinal vortices

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Measurement was made on the mean flow field in the planar turbulent boundary layer to investigate the interaction process between controlled trailing vortices released from tiny airfoils arranged side by side in the free stream and the turbulent boundary layer without pressure gradient. Five cases for arrangements spacing between neighboring airfoils and the arrangement height of longitudinal vortex arrays at the same attack angle alpha=8ﾟ were studied in this report. Measurements of mean and fluctuating velocities were performed by a hot wire anemometer with a linearizer and wall shear stress were measured by a Preston tube with Patel's constant.At first, the streamwise pathes of longitudinal vortex core center were examined. In the case of L/S<greater than or equal>1, where L is the spanwise distance between two airfoils and S is the airfoil span, pathes of vortices descend and embedded in the boundary layer with streamwise distance, while in the other case of L/S<1 the streamwise vo … More rtice monotonously continue to ascend and never interact so strong and move downstream along the outside of boundary layer. Secondary currents generated by the longitudinal vortices showed that the boundary layer was thickened markedly in the center section between the neighboring airfoils and that in the midspan of airfoil the boundary layer was thinned. Even in the present three-dimensional flow field, logarithmic velocity law was valid. However, the logarithmic region profiles were different depending on the local spanwiseNext, the ensemble averaged patterns obtained from the VITA technique showed that the ejection process was intensively affected by the secondary currents caused by the longitudinal vortices and that the magnitude and the mean periods of those ejection process were emphasized compared with the two-dimensional flow. Hence, the generation of the turbulence was stressed. In addition, the events contributing to the Reynolds shear stress were measured using the four quadrant method. The longitudinal vortices in the free stream had direct effects upon the turbulent structure at the boundary layer edge in the ratio of the fractional contributions to the Reynolds shear stress. The fractional contributions to the Reynolds shear stress of both the ejection and sweep events increased near y/delta =0.4 where the inner layer structure strongly interacted with the outer layer. Less