Turbulent kinetic energy transport in a corner formed by a solid wall and a free surface

High-resolution DPIV and LDV measurements were made in a turbulent mixed bo undary corner, i.e, a turbulent boundary layer generated by horizontal flow of water along a vertical wall in the vicinity of a horizontal free surfac e. This work is an extension of an earlier numerical/experimental study whi ch established the existence of inner and outer secondary flow regions in t he corner. The inner secondary motion is characterized by a weak, slowly ev olving vortex with negative streamwise vorticity. The outer secondary motio n is characterized by an upflow along the wall and outflow away from the wa ll at the free surface. The objective of the current investigation, then, w as to understand the combined effects of a horizontal, shear-free, free sur face and a vertical, rigid, no-slip boundary on turbulent kinetic energy tr ansport. The context of this work is providing physical insights and quanti tative data for advancing the state of the art in free-surface turbulence m odelling. Experiments were conducted in a large free-surface water tunnel a t momentum-thickness Reynolds numbers, Re-theta, of 670 for the DPIV studie s, and 1150 for the LDV measurements. A high-resolution, two-correlation DP IV program was used to generate ensembles of vector fields in planes parall el to the free surface. These data were further processed to obtain profile s of turbulent kinetic energy transport terms, such as production and dissi pation. In addition, profiles of streamwise and surface-normal velocity wer e made (as functions of distance from the wall) using two-component LDV. Ke y findings of this study include the fact that both turbulent kinetic energ y production and dissipation are dramatically reduced close to the free sur face. Far from the wall, this results in an increase in surface-parallel fl uctuations very close to the free surface. The degree of this anisotropy an d the spatial scales over which it exists are critical data for improved fr ee-surface turbulence models.