  Noise pollution caused by inflow turbulence is a major problem in many
applications, such as propellers and fans. Leading edge noise models, e.g.,
Amiet's model, are widely applied to predict the noise produced by these
applications. This noise prediction model relies on the accuracy of the
turbulence spectrum, which is usually assumed to be the von K\'arm\'an energy
spectrum for isotropic turbulence. However, the von K\'arm\'an spectrum does
not model accurately the dissipation range of the turbulent energy, resulting
in incorrect far-field noise predictions for the high-frequency range. An
exponential correction can be applied to the spectrum to model the dissipation
range. This correction depends on the dissipation frequency, which is the
frequency where the energy spectrum changes from a dependence of $k^{-5/3}$ to
an exponential decay. This study experimentally investigates nearly isotropic
inflow turbulence and determines the flow field characteristics that affect the
dissipation frequency in order to model this frequency and the dissipation
range. Experiments have been conducted with two passive grids and hot-wire
anemometry in the Aeroacoustic Wind Tunnel of the University of Twente. The
turbulence uniformity in the test section and the turbulence development in the
streamwise direction were analyzed, showing that the grid generated turbulence
was mostly uniform and nearly isotropic. The dissipation frequency was observed
to depend on the turbulence intensity, the free-stream velocity, and the
turbulence length scale. An expression to compute this frequency is proposed,
as well as a formula to predict the dissipation range. The predicted leading
edge noise is affected by the dissipation range modelling in the high-frequency
range, presenting a decrease in level up to 17 dB for the highest frequencies.
