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The Problem
The Problem
Wind energy is expected to form a significant component of India's energy mix in the near future. One of the major challenges associated with effective utilization of the wind resource is the interaction between wakes of multiple turbines in a wind farm. A wind turbine that lies in the shadow of an upstream turbine is exposed to lower wind speeds and higher turbulence levels. Our work focuses on understanding the factors that influence the wind turbine wake interactions and ways to control and mitigate the losses associated with wakes. An overview of the physical processes occurring in a wind farm is depicted in the figure below. The text in red shows the various length and time scales involved, which makes this a very challenging problem for theory, experiments as well as numerical simulations.
Approach and Sample Results
Approach and Sample Results
We study the above problem using a combination of detailed numerical simulations and cheaper, simplified models. The numerical simulations mainly employ the large-eddy simulation (LES) technique. Under the LES technique, the larger (energy-containing) scales of a flow field are resolved, while the smaller (dissipative) scales are modeled. The LES are validated against wind tunnel experiments or field observations. These well-validated LES results are then used to understand fundamental physical processes, and serve as benchmarks against which simplified models can be tested and validated.
A few examples of previously investigated issues are given below.
- Combined Layout-Stability Effects
A 48-turbine wind farm was studied in its original (left panel) and a 'staggered' layout (middle panel), operating under neutral, weakly stable, and weakly unstable conditions. Wake losses are determined by non-intuitive interactions between different layouts and stability conditions (right panel).
- Multi-Rotor Turbines
A multi-rotor configuration involves more than one three-bladed rotor mounted on one central tower structure. Our simulations show that velocity deficits (left panels) as well as higher-order turbulent statistics, such as the turbulent kinetic energy (right panels), are smaller in wind farms comprised of multi-rotor turbines (bottom panels) as compared to farms comprised of conventional single-rotor turbines (top panels). This indicates potential benefits from the point of view of wake losses as well as fatigue loads.
- Simplified Model Development
The final aim of detailed numerical simulations is to develop simplified models that are sufficiently fast and sufficiently accurate to be useful for design purposes. Examples of statistical models (left panel) and physics-based models (right panel) developed for predicting the wind farm velocity field and/or turbine power are seen in the figures above.
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