Turbulence kinetic energy and dissipation rate estimated from a virtual wind profiler and verified through large-eddy simulations

Values of turbulence kinetic energy (TKE) and TKE dissipation rate (ε) can be obtained from radar estimates of velocity and spectral width. However, these estimates usually do not have sufficient temporal resolution and lead to filtered results that do not allow straightforward theoretical interpretation.

A procedure is proposed for evaluation of velocity distribution properties retrieved from radar measurements using flow fields generated by means of numerical large-eddy simulation (LES). The TKE estimates are obtained from LES turbulent velocity fields through averaging in space and, alternatively, by averaging in time. These estimates are compared with measurements retrieved from a virtual radar, which is embedded within the LES. The minimum averaging time to obtain steady consistent statistics is investigated. Wind shears are known to cause a bias in the TKE estimates from radar measurements. This effect is also studied by analyzing the virtual radar data in conjunction with LES turbulence statistics.

The values of ε are estimated from LES data through calculation of turbulence velocity spectra. Estimates of ε from the virtual radar are obtained from the turbulence contribution to the spectral width after all other contributions are taken into account. The ε estimates from the virtual radar and LES are compared and their dependence on averaging schemes is analyzed. Findings from this study will ultimately feed into turbulence parameter retrieval algorithms developed for actual radar systems.