  In many environmental flows, an air-water free surface interacts with a
turbulent flow in the water phase. To reproduce this situation, we propose an
original experimental setup, which is an evolution of the Randomly Actuated
Synthetic Jet Array (RASJA) device used to study turbulence with a low mean
flow. By using a central pump connected to jets, we generate a turbulent flow
of tunable intensity with good isotropy and horizontal homogeneity. The maximal
turbulent Reynolds number of $8800$ is significantly larger than in other
systems generating turbulence with low mean flow, including RASJA experiments,
for which the flow rate per jet cannot be changed. Using our setup, we
characterize the modification of the turbulence under the influence of the free
surface, which acts typically for depths smaller than the integral length
measured in the bulk. We report that the turbulent fluctuations become strongly
anisotropic when approaching the free surface. The vertical velocity
fluctuations decrease close to the surface whereas the horizontal ones increase
as reported in previous theoretical predictions and numerical observations. We
also observe a strong enhancement of the amplitude of the temporal and spatial
power spectra of the horizontal velocity at large scales, showing the
strengthening of these velocity fluctuations near the free surface.
