Advances in experimental techniques and the ever-increasing fidelity of numerical simulations have led to an abundance of data describing fluid flows. This review discusses a range of techniques for analyzing such data, with the aim of extracting simplified models that capture the essential features of these flows, in order to gain insight into the flow physics, and potentially identify mechanisms for controlling these flows. We review well-developed techniques, such as proper orthogonal decomposition and Galerkin projection, and discuss more recent techniques developed for linear systems, such as balanced truncation and dynamic mode decomposition (DMD). We then discuss some of the methods available for nonlinear systems, with particular attention to the Koopman operator, an infinite-dimensional linear operator that completely characterizes the dynamics of a nonlinear system and provides an extension of DMD to nonlinear systems.

Model Reduction for Flow Analysis and Control

Wind energy, together with other renewable energy sources, are expected to grow substantially in the coming decades and play a key role in mitigating climate change and achieving energy sustainability. One of the main challenges in optimizing the design, operation, control, and grid integration of wind farms is the prediction of their performance, owing to the complex multiscale two-way interactions between wind farms and the turbulent atmospheric boundary layer (ABL). From a fluid mechanical perspective, these interactions are complicated by the high Reynolds number of the ABL flow, its inherent unsteadiness due to the diurnal cycle and synoptic-forcing variability, the ubiquitous nature of thermal effects, and the heterogeneity of the terrain. Particularly important is the effect of ABL turbulence on wind-turbine wake flows and their superposition, as they are responsible for considerable turbine power losses and fatigue loads in wind farms. These flow interactions affect, in turn, the structure of the ABL and the turbulent fluxes of momentum and scalars. This review summarizes recent experimental, computational, and theoretical research efforts that have contributed to improving our understanding and ability to predict the interactions of ABL flow with wind turbines and wind farms.

https://link.springer.com/content/pdf/10.1007/s10546-019-00473-0.pdf

Wind-Turbine and Wind-Farm Flows: A Review

A critical review on the simulations of wind turbine aerodynamics focusing on hybrid RANS-LES methods

Winglet design for vertical axis wind turbines based on a design of experiment and CFD approach

Large eddy simulation (LES) is coupled with a turbine model to study the structure of the wake behind a vertical-axis wind turbine (VAWT). In the simulations, a tuning-free anisotropic minimum diss...

Self-similarity and flow characteristics of vertical-axis wind turbine wakes: an LES study

Because of several design advantages and operational characteristics, particularly in offshore farms, vertical axis wind turbines (VAWTs) are being reconsidered as a complementary technology to horizontal axial turbines. However, considerable gaps remain in our understanding of VAWT performance since cross-flow rotor configurations have been significantly less studied than axial turbines. This study examines the wakes of VAWTs and how their evolution is influenced by turbine design parameters. An actuator line model is implemented in an atmospheric boundary layer large eddy simulation code, with offline coupling to a high-resolution blade-scale unsteady Reynolds-averaged Navier–Stokes model. The large eddy simulation captures the turbine-to-farm scale dynamics, while the unsteady Reynolds-averaged Navier–Stokes captures the blade-to-turbine scale flow. The simulation results are found to be in good agreement with three existing experimental datasets. Subsequently, a parametric study of the flow over an isolated VAWT, carried out by varying solidities, height-to-diameter aspect ratios and tip speed ratios, is conducted. The analyses of the wake area and velocity and power deficits yield an improved understanding of the downstream evolution of VAWT wakes, which in turn enables a more informed selection of turbine designs for wind farms. Copyright © 2016 John Wiley & Sons, Ltd.

Simulation and wake analysis of a single vertical axis wind turbine

Accurate simulation of flight beyond normal conditions requires models of the aircraft aerodynamics at high angles of attack, for which the flow over the wing and control surfaces may be rapidly changing and massively separated. This study focuses on large-amplitude forced oscillations of a benchmark commercial aircraft configuration. Existing models are modified to describe the unsteady aerodynamic forces on the aircraft up to stall range. Steady-state and periodically forced unsteady Reynolds-averaged Navier–Stokes simulation data are employed to calibrate the model parameters. The results of the reduced-order models are in good overall agreement with those observed in the unsteady Reynolds-averaged Navier–Stokes simulations.

Unsteady High-Angle-of-Attack Aerodynamic Models of a Generic Jet Transport

This work presents results and analysis of H-type crossflow rotors using unsteady Reynolds-Averaged Navier–Stokes (URANS) computational fluid dynamics simulations. It is demonstrated that, with an efficient solver, robust high-fidelity time-resolved solutions can be obtained with computational speed and cost that allow the use of high-fidelity computational fluid dynamics in the early stages of a new design. The sensitivity of power prediction on the far-field boundary condition proximity is also shown and an analytical justification is given for this behavior based on blockage effects. The effects of physical scaling over a range of Reynolds numbers between 105 and 108 of four geometrically similar turbines of differing solidity are studied. Significant improvement in power efficiency can be achieved as the Reynolds number increases when turbines are scaled to very large size. Power curves for all test cases, unsteady blade loads for select cases, and effects of three-dimensionality are provided to aid f...

Mark W. Lohry

Papers

Simulation and wake analysis of a single vertical axis wind turbine

Unsteady High-Angle-of-Attack Aerodynamic Models of a Generic Jet Transport

Unsteady Reynolds-Averaged Navier–Stokes Simulation of Crossflow Rotors, Scaling, and Blockage Effects

Genetic Algorithm and Adjoint Optimization of Periodic Wing Protuberences for Stall Mitigation