Experimental measurements on air jets issuing into a coaxial rough pipe

In this experimental study a number of measurements are presented, analyzed and discussed, concerning incompressible air jets (issuing from circular opening d=25 mm) into coaxial rough pipes (equipped with ring rectangular strips roughness elements on the pipe boundaries, κxκ with κ=2.5 mm, at distances λ=25-50-100 mm) of internal diameters D=49-138 287 mm, in various combinations among them. The flow is fully turbulent, since the Reynolds numbers at the openings vary between 30,590 and 109,340, while the exit velocities V_o vary between 18.21 m/sec and 69.30 m/sec. A large number of axial velocities u and boundary shear stresses τ_o are measured, and the flow field structures are qualitatively presented and compared. The authors believe that the results and conclusions of this investigation may be useful to environmental, chemical and fluid mechanics pipe engineers.