Management of Spatial Variation in Turbulent Boundary Layer by a Pair of streamwise Vortices with Spanwise Perturbation

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Interaction process between turbulent boundary layer and a pair of streamwise vortices with spanwise perturbation was investigated experimentally. The streamwise vortices were generated by a delta wing that is 50mm in cord length and 40mm in wingspan located in the free stream with 8 degree in angle of attack. Spanwise oscillation of the delta wing with constant frequencies 0.5Hz and 1Hz and 10mm amplitude added spanwise perturbation onto the streamwise vortex pair. Conventional time averages and ensembles averages were obtained by hot-wire measurements of fluctuation velocity field for the streamwise extent of 70 times initial boundary thickness at starting location for interaction between boundary layer and streamwise vortex. Concluding remarks are summarized in the following two pars such as time and ensemble averages and production process.[Time and ensemble averages] Local skin friction coefficient has spanwise variation depending on mean velocity profile and enhance the momentum transport. Spanwise perturbation somewhat leaves off the spanwise variation of the skin friction coefficient. However, spanwise integral of momentum transport shows that the spanwise perturbation has no substantial contribution to momentum transport across the boundary layer. Spanwise variation of mean velocity field and spanwise amplitude of perturbation contribute to magnitude of the ensemble average of streamwise fluctuation component. The any conventional average can be divided into ensemble average and random components. The log low profile can be observed through the streamwise extent.[Production process] Kinetic energy budget was investigated for time, ensemble and random components. Kinetic energy of random component is generated by spanwise oscillation around vortex core of the streamwise vortices. From investigation of production term in whole spanwise extent, there is no drag reduction phenomenon with the present management.