Geophysical flows occur over a large range of scales, with Reynolds numbers and Richardson numbers varying over several orders of magnitude. For this study, jets of different densities were ejected vertically into a large ambient region, considering conditions relevant to some geophysical phenomena. Using particle image velocimetry, the velocity fields were measured for three different gases exhausting into air – specifically helium, air and argon. Measurements focused on both the jet core and the entrained ambient. Experiments considered relatively low Reynolds numbers from approximately 1500 to 10 000 with Richardson numbers near 0.001 in magnitude. These included a variety of flow responses, notably a nearly laminar jet, turbulent jets and a transitioning jet in between. Several features were studied, including the jet development, the local entrainment ratio, the turbulent Reynolds stresses and the eddy strength. Compared to a fully turbulent jet, the transitioning jet showed up to 50 % higher local entrainment and more significant turbulent fluctuations. For this condition, the eddies were non-axisymmetric and larger than the exit radius. For turbulent jets, the eddies were initially smaller and axisymmetric while growing with the shear layer. At lower turbulent Reynolds number, the turbulent stresses were more than 50 % higher than at higher turbulent Reynolds number. In either case, the low-density jet developed faster than a comparable non-buoyant jet. Quadrant analysis and proper orthogonal decomposition were also utilized for insight into the entrainment of the jet, as well as to assess the energy distribution with respect to the number of eigenmodes. Reynolds shear stresses were dominant in Q1 and Q3 and exhibited negligible contributions from the remaining two quadrants. Both analysis techniques showed that the development of stresses downstream was dependent on the Reynolds number while the spanwise location of the stresses depended on the Richardson number.

Individual turbine location within a wind plant defines the flow characterisitcs experienced by a given turbine. Irregular turbine arrays and inflow misalignment can reduce plant efficiency by producing highly asymmetric wakes with enhanced downstream longevity. Changes in wake dynamics as a result of turbine position were quantified in a wind tunnel experiment.Scale model turbines with a rotor diameter of 20 cm and a hub height of 24 cm were placed in symmetric, asymmetric, and rotated configurations. Simultaneous hub height velocity measurements were recorded at 11 spanwise locations for three distances downstream of the turbine array under two inflow conditions. Wake interactions are described in terms of the time-average streamwise velocity and turbulence intensity as well as the displacement, momentum, and energy thicknesses. The effects of wake merging on power generation are quantified, and the two-point correlation is used to examine symmetry in the mean velocity between wakes. The results indicate that both asymmetric and rotated wind plant arrangements can produce long-lasting wakes. At shallow angles, rotated configurations compound the effects of asymmetric arrangements and greatly increase downstream wake persistence. KEYWORDS turbulence, wakes, wake merging, wind energy INTRODUCTIONWind energy has grown with the push to provide renewable energy to a growing world population. Wakes have been shown to produce adverse effects on the performance of wind turbines. 1-3 Turbine wakes can be divided into two distinct regions, the near and far wake, based on rotor proximity. In the near wake region, fluid dynamics are dominated by axial forces stemming from mechanical power extraction. 4 Tip vortices generated by the blades decay within the near wake as the velocity regains a Gaussian profile. 5,6 In the far wake region, turbulence intensity decays with distance downstream as the flow recovers energy. 4 In a wind plant setting, turbulence intensity determines the flow induced rotor loads and systematic wake impacts on downstream turbines. 7 Added turbulence intensity has been measured at distances of 15 rotor diameters highlighting the need to describe the development of turbulence intensity from turbine wake interactions throughout the wind plant. 7Efforts to characterize turbine wakes and turbulent wake interactions include numerical models, simulations, and experiments. Numerical models and simulations have demonstrated an increased capacity to represent turbine wakes with the actuator line model forming the basis of numerous studies. 8,9 The actuator line model was simulated through EllipSys3D with two turbines in staggered and inline configurations under various inflow conditions and predicted arrangement-dependent asymmetric wake dynamics. 10 The actuator line has been extended to include multiple turbines for plant optimization. A variety of methods for calculating wake interactions have been developed for large turbine arrays. 11,12 However, numerical models and simulations rely on superposition of v...

Turbulence intermittency in the wake behind a single floating wind turbine as well as merging wakes due to a pair of floating turbines is investigated using magnitude cumulant analysis and non-analytical cumulant analysis. This low-order statistical approach is used to compute the intermittency for its impact on fatigue loading and power output signals. In the near wake, a 60% increase in the intermittency coefficient compared to the inflow is found. Pitch motion causes a 17% increase in intermittency compared to fixed turbines. The pitch-induced intermittency depletes in the far-wake, and hence, investigating whether a pitch-induced intermittency of one turbine affects a successive one in a wind array setting is recommended. Non-local scale interactions near rotor tips are observed as undulations in the cumulant profiles, referred to as tip-effect fluctuations. The impact of turbulence intensity on intermittency is also examined, and a positive correlation between the two is found in the near-wake. In the far-wake, however, it is found to speed up the pitch-induced intermittency depletion. The wake merging region between two neighboring turbines experiences lower intermittency and damps tip-effect fluctuations. This work provides more reliable intermittency estimation by utilizing lower moment statistics. The findings aid description, turbulent loading quantification, and stochastic modeling for floating wind farm wakes as well as fixed ones for both single and merging wakes.

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Large eddy simulations are considered for wind plants with varied spanwise and streamwise spacing. Data from five different configurations of staggered and aligned LES wind turbine arrays with a neutrally stratified atmospheric boundary layer are employed for analysis. Fields are analyzed by evaluating the anisotropy stress invariants based on the Reynolds shear stresses and dispersive stress tensor. The relationship between quantities are drawn as a function of the wind plant packing. Reynolds stresses and dispersive stresses are investigated alongside a domain altered version of the second and third scalar invariants, ξ, η, as well as the combination of the two invariants described by the function F = 1 − 27η 2 + 54ξ 3. F is a measure of the approach to either a two-component turbulence (F =1) or an isotropic turbulence (F =0). The invariant η describes the degree of anisotropy while ξ describes the characteristic shape. For the purposes of this study, the LES data is analyzed to understand the effects of canopy density on anisotropy and dispersive stresses, adding further insight and detail for future modeling techniques. access to the LES data used in this study. Finally, my family deserves huge credit on me getting this far with their continuous support in my intellectual journey.