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With the increased application of large eddy simulation techniques, the generation of realistic turbulence at inflow boundaries is crucial for the accuracy of a simulation. The Control Forced Concurrent Precursor Method (CFCPM) proposed in this work combines an existing concurrent precursor method and a mean flow forcing method with a new extension of the controlled forcing method to impose turbulent inflow boundary conditions primarily, although not exclusively, for domains that require periodic boundary conditions. Turbulent inflow boundary conditions are imposed through a region of body forces added to the momentum equations of the main simulation that transfers the precursor simulation into the main domain. Controlled forcing planes, which come into play as body forces added to the momentum equations on planes perpendicular to the flow, located in the precursor simulation, allow for specific Reynolds stress tensors and mean velocities to be imposed. The mean flow controlled forcing method only modifies the mean velocity profiles, leaving the fluctuating velocity field untouched. The proposed fluctuating flow controlled forcing methods extends the application of the original controlled forcing method to multiple fluctuating velocity components and couples their calculation in order to amplify the existing fluctuations present in the precursor flow field so that prescribed anisotropic Reynolds stress tensors can be reproduced. The new method was tested on high Reynolds number turbulent boundary layer flow over a wall-mounted cube and low Reynolds number turbulent boundary layer flow over a backward-facing step. It was found that the new extension of the controlled forcing method reduced the development time for both test cases considered here when compared to not using controlled forcing and only using the original controlled forcing method.

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Numerous studies have shown that wind turbine wakes within a large wind farm bring about changes to both the dynamics and thermodynamics of the atmospheric boundary layers (ABL). Previously, we investigated the relative humidity budget within a wind farm via field measurements in the near-wake region and large eddy simulations (LES). The effect of the compounding wakes within a large wind farm on the relative humidity was also investigated by LES. In this study, we investigate how the areas of relative humidity variation, that was observed in the near-wake, develop downstream in the shadow region of a large wind farm. To this end, LES of a wind farm consisting of 8x6 wind turbines with periodic boundary condition in the lateral direction (inferring an infinitely wide farm) interacting with a stable ABL is carried out.Two wind farm layouts, aligned and staggered, are considered in the analysis and the results from both configurations are compared to each other. It is observed that a decrease of relative humidity underneath the hub height and an increase above the hub height build up within the wind farm, and are maintained in the downstream of the farm for long distances. The staggered farm layout is more effective in keeping a more elongated region of low relative humidity underneath the hub, when compared to the aligned layout. KEYWORDSatmospheric boundary layer, large eddy simulations, wind farm configurations. In keeping with previous observations and simulations made within the array, mixing brought about by turbines change near-surface relative humidity by reducing humidity adjacent to the ground and increasing it aloft. This investigation shows that this alteration remains well beyond two times the streamwise dimension of the wind farm and, at the surface, is greatest for a staggered layout. Similar to that for TKE, the aligned array configuration allows for a faster recovery of the decrease in relative humidity adjacent to the ground. Along with a faster recovery, the decrease in relative humidity does not extend as far vertically for the aligned configuration but, for both arrangements, extends well above the hub height. While the area of increase in relative humidity aloft rises vertically with downstream distance, the area of greatest increase extends further in the downstream and vertical directions for the aligned array. It was also shown that the humidity distribution in the vertical direction (i.e., the decrease underneath the hub and increase above the hub) is mainly the effect of the vertical turbulent humidity flux, which is positive on one lateral side of the rotor and negative on the other; a consequence of this is a convection of the humidity from and toward the ground, respectively.Finally, we advise that any changes of concern with respect to humidity within a wind farm must be considered for long distances downstream of the wind farm as well, although more investigations (either numerically or experimentally) in other different conditions are warranted in this respect. ORCID