Nonequilibrium dissipation scaling in fan-array-generated uniform and uniform-shear turbulence

We investigate dissipation scaling in fan-array-generated turbulence under controlled mean-flow conditions. Experiments are performed using a wind generator driven by an 8×8 array of 64 counter-rotating fans with row-wise pulse width modulation control, which enables repeatable realization of two canonical configurations: nominally uniform mean flow and nominally uniform shear flow. Hot-wire anemometry is used to obtain turbulence statistics, including the Taylor-scale Reynolds number Reλ and the nondimensional dissipation rate Cε. To go beyond global long-time-averaged measures, we apply a short-time local analysis to the velocity records and evaluate Cε within local subensembles. When the streamwise root mean square velocity fluctuation is used as the velocity scale, the global and local results in both configurations exhibit decreasing trends of Cε with increasing Reλ that are broadly consistent with an inverse-Reynolds-number dependence. In the nominally uniform-flow configuration, this local tendency is more apparent upstream and weakens downstream, whereas in the nominally uniform shear-flow configuration it shows weaker streamwise variation. For the shear flow, however, an additional normalization based on the approximate turbulent kinetic energy produces a similar decreasing global trend but a substantially weaker local dependence on Reλ. These results show that fan-array forcing enables systematic comparison of dissipation behavior across mean-flow configurations, while also demonstrating that local conditional scaling in anisotropic shear turbulence can be sensitive to the velocity scale used for normalization.