Effects on Topology of a Turbulent Channel Flow Subject to Blowing Through a Porous Strip

An experimental investigation is performed on a fully developed turbulent channel flow with local injection through a porous strip. The Reynolds number based on the channel half-width was set to 5000. In addition to the no blowing data, measurements are made for three different blowing rates σ = 0.22, 0.36 and 0.58 (where σ is the ratio of momentum flux gain due to the blowing and momentum flux of the incoming channel flow). Measurements carried out with hot-wire anemometry reveal that injection strongly affects both the velocity profiles and the turbulence characteristics. The injection decreases the skin friction coefficient and increases all the Reynolds stresses downstream the blowing strip. Moreover, the anisotropic invariant map (A.I.M.) for the Reynolds stress tensor revealed that blowing decreased the anisotropy of the turbulent structure in the near wall region and a decrease in the longitudinal integral length scale was observed when the blowing rate increased. The space time correlation measurements show that injection increases the inclination of the coherent structures in both (x,y) and (x,z) plan.