EXPERIMENTAL INVESTIGATION OF AXISYMMETRIC TURBULENT JET IMPINGING ON A CONVEX SURFACE USING PARTICLE IMAGE VELOCIMETRY

Experimental work was performed by means of particle image velocimetry (PIV) to investigate axisymmetric turbulent jets impinging on a semi-cylindrical convex surface. Measurements were performed for one surface curvature (D/d ≈ 8.2) and four L/d (pipe jet exit to surface) ratios at a Reynolds number Re ≈ 30000. The study focused on the free jet region before impingement and the wall jet formed after impingement, as well as the developing boundary layer over the convex surface, with the aim of specifying the vortex structures and high turbulent intensity regions. The jet impingement behavior was characterized by large radial and tangential velocities as well as increasing rms velocities along different radial lines (crossing the convex surface). The linear stochastic estimation (LSE) method was employed to identify the dominant vortical structures in the flow field and also to correlate them to other relevant parameters, such as rms velocities of the wall jet. The results show an entrainment of the flow carried about by the curved surface geometry, especially for large L/d ratios. They also show high turbulence fluctuations in the tangential velocity when the distance from the stagnation point was reduced and even distribution of dominant vortical structures for L/d = 2. Both the peak rms tangential velocity and half velocity width decreased for all L/d ratios when increasing the distance from the stagnation point over the convex surface. These results can be used for the interpretation of heat and mass transfer aspects with convex surfaces and could serve as a benchmark for future numerical studies.