Turbulence statistics in the stagnation region of an axisymmetric impinging jet flow

Turbulence statistics in the stagnation region of an axisymmetric jet impinging vertically on a flat plate are reported. The measurements were made in a submerged water jet facility at a Reynolds number of approximately 13,000 based on the nozzle exit velocity and the nozzle diameter. Particle-tracking velocimetry was used for the measurement of highly turbulent flows near the stagnation point. The axial mean momentum balance was examined to clarify the effect of the turbulent normal stress on the axial mean momentum transport. It was found that the turbulent normal stress of the axial component made a substantial contribution to the increase in the static pressure near the impingement wall. Detailed distributions of the turbulent stresses and the triple correlations of velocity fluctuations are presented. The state of turbulence was studied by means of an invariant map of the turbulent stress anisotropy. It was revealed that the turbulence was close to an axisymmetric state in the stagnation region. The budget equation for the turbulent kinetic energy evaluated from the present data shows that the net negative production takes place in the vicinity of the wall. This negative production is compensated by the pressure diffusion. Other unique features of the budget for the turbulent kinetic energy are also discussed.