  The energy cascade and diverse turbulence properties of active-grid-generated
turbulence were studied in a wind tunnel via hot-wire anemometry. To this aim,
two active grid protocols were considered. The first protocol is the standard
triple-random mode, where the grid motors are driven with random rotation rates
and directions, which are changed randomly in time. This protocol has been
extensively used due to its capacity to produce higher values of $Re_\lambda$
than its passive counter part, with good statistical homogeneity and isotropy.
The second protocol was a static or open grid mode, where all grid blades were
completely open, yielding the minimum blockage attainable with our grid.
Centreline streamwise profiles were measured for both protocols and several
inlet velocities. It was found that the turbulent flow generated with the
triple-random protocol evolved in the streamwise direction consistently with an
energy dissipation scaling of the form $\varepsilon=C_\varepsilon
u^{\prime3}/L$, with $C_\varepsilon$ being a constant, $L$ the longitudinal
integral length-scale, and $u^\prime$ the rms of the longitudinal velocity
fluctuations. Conversely for the open-static grid, the energy dissipation
followed a non-equilibrium turbulence scaling, namely, $C_\varepsilon \sim
Re_G/Re_L$, where $Re_G$ is a global Reynolds number based on the inlet
conditions of the flow, and $Re_L$ is based on the local properties of the flow
downstream the grid. Furthermore, this open-static grid mode scaling exhibits
important differences with other grids, as the downstream location of the peak
of turbulence intensity is a function of the inlet velocity. It was also found
that a rather simple theoretical model can predict the value of $C_\varepsilon$
based on the number density of zero-crossings of the longitudinal velocity
fluctuations. This theory is valid for both active grid operating protocols.
