Experimental investigation on an axisymmetric turbulent jet impinging on a concave surface

An experimental study of an axisymmetric turbulent jet impinging on a semi-cylindrical concave surface is carried out using Particle Image Velocimetry (PIV). The measurements are performed on two orthogonal planes: parallel and perpendicular to the axis of the cylinder. The study is focused on the impinging jet, the generated wall jet and on the boundary layer developing on the cylinder surface. Linear stochastic estimation is applied for identifying the dominant structures in the flow and coupling then with other relevant parameters as the peak r.m.s. velocity of the wall jet to estimate secondary peak in Nusselt number distribution along the wall. Measurements are performed for two different surface curvatures and four nozzle to target distances (L/d ratio) at a Reynolds number equal to Re≈30,000. The mean and r.m.s. velocity profiles are investigated and the evolution of half-velocity width close to the wall is illustrated for both planes of interest. The results show a strong lateral movement of the flow brought about by the surface geometry for curved surface, especially for large L/d ratios. The r.m.s. profiles indicate higher values along the curved surface with respect to the quasi-flat one. The results show the most probable position of secondary peak in the Nusselt number distribution along quasi-flat and curved surfaces to be located at y/d = 3.2 and 4.39 < s/d < 5, respectively. These results can be used toward interpretation of heat and mass transfer aspects on concave surfaces, and are also useful for benchmarking future numerical studies.