Scaling of Turbulent Spectra Measured in Mobile Bed Flows and Estimation of Turbulent Kinetic Energy Budgets

This study aims at quantifying experimentally the influence of bed load transport on velocity power spectrum of acoustic Doppler Velocimeter (ADV) and turbulent kinetic energy budget. Hydraulic flume was used for experimental investigations for bed load transport. Uniform size of gravels (d50 = 4 mm) were injected into the flows without bed-forms development and compared with those in clear water flows. A 5 cm down looking Vectrino+ of 10 MHz acoustic frequency was used to measure the velocity of flows. The velocity signals produced spikes in the Vectrino+ data on account of instrument noise and high-frequency fluctuations. Therefore, de-spiking and removal of contaminated data were very much essential to obtain clear velocity power spectra for the ADV data sets. The velocity power spectra of filtered dataset followed the Kolmogorov “–5/3 scaling-law” in the inertial frequency range. At low frequencies, another scaling regime with spectral slope of about −1.0 is found resulting a shifting of turbulent power production subrange towards the high frequency regime and it is interpreted as the signature of sediment mobility without bed form development. Interestingly, the bed lad transport reduced the TKE dissipation rate and sharply changed the pressure energy diffusion rate which corroborated a gain in turbulence production.