4,319 research outputs found
The History of Wake Forest College, Volume IV, 1943-1967
No full textThe Shaw volume contains much information, although it is not as detailed as the first three books. It is also more readable and wanders less often than the earlier ones. It covers the years of World War II, the admission of female students, the return of the veterans, the decision to move to Winston-Salem, the move itself, and the "fruitful years of the Tribble administration." One reviewer summarized: "Scores of names and dozens of pictures, as well as sections on student life, athletics and departmental histories complete the fabric of life at Wake Forest." A review by Linda Brinson (WFU '69) in the Winston-Salem Journal September 4, 1988, H6 concluded: "Perhaps the greatest strength of Vol. IV is that Shaw does what he states as his purpose in the preface: 'to give the whole picture of the life of the college.'" Wake Forest should be well pleased with this chronicle of the years that did so much to shape its future. Anyone with an interest in the college would find this new history a valuable source of both information and understanding. (J. Edwin Hendricks)Biographical information about the author is available in Linda Brinson, "Gentle Man of the Press," Wake Forest University Magazine, September 2, 2002. p. 46
Wake Vortex Scenarios Simulation Package for Take-Off and Departure
No full textThe WakeScene-D software package (Wake Vortex Scenarios Simulation Package for Departure) has been developed for comprehensive airspace simulations of take-off and departure. WakeScene-D consists of modules that model traffic mix, aircraft trajectories, meteorological conditions, wake vortex evolution, and potential hazard area. The software package estimates the probability to encounter wake vortices in different traffic and crosswind scenarios using Monte Carlo simulation in a domain ranging from the runway to an altitude of 3000 ft above ground. A comparison to measured vortex tracks of about 10,000 departures from runway 25R of Frankfurt airport indicates good agreement of global wake vortex transport characteristics in ground proximity. The standard departure situation employing a two-minute aircraft separation is compared to scenarios with reduced departure separations and various crosswind conditions. Comprehensive sensitivity analyses have been conducted which are briefly recapitulated. Effects related to departure route combinations and wind direction sectors are reported in more detail. Finally, an advanced scenario with an asymmetric crosswind criterion is introduced
Simulation of wake vortex effects for UAVs in close formation flight
No full textThis paper addresses the development of multiple UAV deployment simulation
models that include representative aerodynamic cross-coupling effects.
Applications may include simulations of autonomous aerial refuelling and
formation flying scenarios. A novel wake vortex model was developed and
successfully integrated within a Matlab/Simulink simulation environment. The
wake vortex model is both sufficiently representative to support studies of
aerodynamic interaction between multiple air vehicles, and straightforward
enough to be used within real time or near real time air-to-air simulations. The
integration process is described, and simulation results of a two vehicles
formation flight are presented
Analytical solution for the cumulative wake of yawed wind turbines
No full textThis thesis sets out to improve the physical grounding and predictive accuracy of cumulative wake effect modelling within wind farms with yawed turbines. It derives an analytical solution for the lateral velocity field within a wind farm and compares its predictions to those of computational fluid dynamics.A parametric study is performed using a Reynolds-averaged Navier-Stokes (RANS) solver with the k-ε-fP turbulence model, Joukowsky rotor-based actuator disc, and neutral log-law inflow within the PyWakeEllipSys framework to determine the effects of yaw angle, thrust coefficient, and turbulence intensity on the lateral wake.The results of this parametric study are used to solve an approximate form of conservation of mass and momentum in the lateral direction for a turbine within a wind farm. The solution is an explicit equation predicting the lateral velocity distribution and lateral wake deflection within a wind farm of arbitrary layout and with arbitrarily yawed turbines. It also provides a first mathematical proof of secondary wake steering. The solution is implemented in Python and used to predict the velocity distributions in several wind farm cases, including for a single turbine, a two-turbine arrangement, and two wind farm cases with aligned and staggered layouts. These predictions are then compared against those of the RANS setup. The model significantly overestimates wake deflections unless corrected to neglect the near wake, but the corrected version shows promise, particularly in predicting wind farm power of the staggered layout, where the prediction is 19% closer to the RANS result than the prediction that considers lateral velocities equal to zero.https://github.com/NilsGaukroger/Analytical-solution-for-the-cumulative-wake-of-yawed-wind-turbinesEuropean Wind Energy Masters (EWEM) | Rotor Design Trac
Hybrid simulation of wake vortices of landing aircraft in a turbulent environment
No full textWake-vortex evolution during landing of a long range aircraft is investigated in a turbulent environment. The simulations cover final approach, touchdown on the tarmac, and the evolution of the wake after touchdown. An ambient turbulent crosswind and headwind field is generated in a pre-simulation. The wake is initialized using a RANS-LES coupling approach. The further development of the vortical wake is investigated by large-eddy simulation until final decay. Strong three-dimensional deformations appearing after touchdown and linkings with the ground are studied. The downwind vortex is strongly advected with crosswind and decays quickly. The interaction of plate line disturbances and end effects in a turbulent environment leads to irregular decay pattern
High-resolution CFD modelling of Lillgrund Wind farm
No full textWe report on a fully dynamic simulation of Vattenfall’s Lillgrund offshore Wind Farm, with a focus on the wake effects of turbines on the performance of individual turbines, and of the farm as a whole.The model uses a dynamic representation of a wind turbine to simulate interaction between the wind and the turbine rotors, calculating the instantaneous power output and forces on the air; this was embedded in a finite element, large eddy simulation (LES) computational fluid dynamics code. This model was applied to the wind farm for a selection of key wind speeds and directions, to investigate cases where a row of turbines would be fully aligned with the wind or at specific angles to the wind. The simulation results were then compared to actual performance measurements from the wind farm spanning several years’ of operation.<br/>These results demonstrate that time-resolving LES simulations are able to reproduce realistic wake structures, including wake meandering and wake recovery, as well as the effect of wakes on turbine performance
Vortex Dynamics in The Transitional and Turbulent Wake of 6:1 Prolate Spheroid at 45-deg incidence angle
No full textThe incompressible flow past a 6:1 prolate spheroid with an inclination angle of 45o at Re = 3,000 has been studied by means of direct numerical simulations (DNS). The Reynolds number is based on the inflow velocity and minor-axis length. The preliminary results presented here are focused mainly on vortex dynamics and vortical structures in the wake. The wake behind this configuration starts almost symmetric but is soon strongly deflected and bent as it evolves to the intermediate wake. A pair of unequal-strength vortices dominates the intermediate wake, of which one exhibits the shape of a long vortex tube while the other rapidly breaks down into turbulent-like vortical structures
Investigation of Lagrangian coherent structures in a wake-induced boundary layer transition
No full textThe evolution of coherent structures in a flat plate boundary layer transition induced by the cylinder wake is investigated using the particle image velocimetry (PIV) technique. The finite-time Lyapunov exponent (FTLE), which characterizes the amount of stretching about the flow trajectory, is used to extract the Lagrangian coherent structures. It is revealed that secondary vortex is induced by the cylinder wake vortices in the near wall region,which would evolve into hairpin vortex as it convects downstream. The subsequent evolvement of the hairpin vortex, characterized by the regeneration of offspring hairpin vortex upstream of it, leads to the appearance of the hairpin packet and the boundary layer finally reaches a turbulent state
Dispersive to nondispersive transition in the plane wake and channel flows
No full textBy varying the wavenumber over a large and finely discretized interval of values, we analyse the phase and group velocity of linear three-dimensional travelling waves both in the plane wake and channel flows to get the transition between dispersive and non-dispersive behaviour. The dispersion relation is computed from the Orr-Sommerfeld and Squire eigenvalue problem by observing the least stable mode, see figure 2, panels (a,b) and the comparison with [1, 2, 4–11, 15, 16]. The group velocity vg is also shown. The Reynolds number varies in the 20-100, 1000-8000 ranges for the wake and the channel flow, respectively, while we consider wavenumbers in the range 0.1-10. The wake basic flow consists of the first two orders of the Navier-Stokes matched asymptotic expansion described in [3, 13, 14]. At low wavenumbers we observe a dispersive behaviour where the phase speed and the group velocity substantially differ. The relevant perturbed solution is amenable to the typical solution belonging to the left branch of the eigenvalue spectrum, see the two examples shown in figure 1 (channel flow: Re = 6000; k = 1; wake Re = 100; k = 0:7). By rising the wave number value, we observe a sharp transition from the dispersive to the nondispersive regime. This transition is located at a critical wave number kd which is a function of the Reynolds number Re, the wave angle _, and the wake downstream observation point x0. Precisely, kd increases with Re and decreases with _ for the wake flow, while these trends are reversed for the channel flow, see tables 1,2. Beyond the wavenumber threshold, the observed least-stable mode belongs to the right branch of the spectrum. The asymptotic solutions in the dispersive region are wall modes for the channel flow , and in-wake modes for the wake flow. This means that, for both the flows, the dispersive behaviour is related to perturbations with high momentum variations (high vorticity) in correspondence to the base flow high-shear region. On the contrary, if k > kd the solutions are central modes for the channel case, and out-of-wake modes for the wake flow. In these cases, the disturbance has high variations outside the base flow high-shear region. To understand the physical mechanism of the dispersive-nondispersive transition we focused on time variation of the wave kinetic energy associated to the convective transport. Figure 2 (c,d) shows the convective term as a function of the wavenumber for the two least stable modes. We observe that the dispersive-nondisperive transition allows waves k > kd to keep the lowest possible temporal variation of kinetic energy, i.e. the lowest decay. This remains true also when all the other more stable modes are considered. In practice nondispersive waves maintain their convective energy with k
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