IMPINGEMENT OF AN AXISYMMETRICAL JET ON UNHEATED AND HEATED FLAT PLATES

The aerodynamic and thermal aspects of the wall jet flow, formed after angled impingement of an axisymmetric jet, have been studied with emphasis on the large-scale transport of the passive scalar by the spatially coherent structures. Time-averaged and instantaneous structures of the turbulent flow were examined by visualization and local measurements of a jet arrangement with an impingement angle between the jet axis and the surface normal of 20-degrees, a nozzle-to-plate distance to nozzle exit diameter ratio of 22, and a nozzle exit Reynolds number of 1.3 x 10(4). The results show that the oblique impingement introduced vertical velocities so that boundary-layer approximations were inapplicable and led to the distribution of the time-averaged properties of the velocity and temperature field with strong azimuthal dependence, which increased gradually with angle of impingement to 40-degrees where a sudden change of the orientation of the contours of surface pressure and temperature took place. It also led.to instantaneous, spatially coherent structures which were most pronounced at an angle of 20-degrees. These structures improved the large-scale transport of the passive scalar but, owing to the extreme regularity of their path, also led to an inactive zone near the vortex centre. The inner region of the decelerating wall jet exhibited a momentum equilibrium layer extending to the point of radial velocity maximum and the intercept of the linear region of the semilogarithmic wall law varied in the local streamwise direction as for turbulent flows over rough walls with adverse pressure gradient. The thermal equilibrium layer had an invariant functional form but extended far beyond the point of maximum velocity.