# An Advanced Actuator Line Method for Wind Energy Applications and Beyond: Preprint

## Abstract

The actuator line method to represent rotor aerodynamics within computational fluid dynamics has been in use for over a decade. This method applies a body force to the flow field along rotating lines corresponding to the individual rotor blades and employs tabular airfoil data to compute the force distribution. The actuator line method is attractive because compared to blade-resolved simulations, the required mesh is much simpler and the computational cost is lower. This work proposes a higher fidelity variant of the actuator line method meant to fill the space between current actuator line and blade-resolved simulations. It contains modifications in two key areas. The first is that of freestream velocity vector estimation along the line, which is necessary to compute the lift and drag along the line using tabular airfoil data. Most current methods rely on point sampling in which the location of sampling is ambiguous. Here we test a velocity sampling method that uses a properly weighted integral over space, removing this ambiguity. The second area of improvement is the function used to project the one-dimensional actuator line force onto the three-dimensional fluid mesh as a body force. We propose and test a projection function that spreads the forcemore »

- Authors:

- Publication Date:

- Research Org.:
- National Renewable Energy Lab. (NREL), Golden, CO (United States)

- Sponsoring Org.:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE), Wind and Water Technologies Office (EE-4W)

- OSTI Identifier:
- 1349215

- Report Number(s):
- NREL/CP-5000-67611

- DOE Contract Number:
- AC36-08GO28308

- Resource Type:
- Conference

- Resource Relation:
- Conference: Presented at the American Institute of Aeronautics and Astronautics SciTech 2017, 9-13 January 2017, Grapevine, Texas

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 17 WIND ENERGY; actuator line; wind turbine; aerodynamics; computational fluid mechanics

### Citation Formats

```
Churchfield, Matthew, Schreck, Scott, Martinez-Tossas, Luis A., Meneveau, Charles, and Spalart, Philippe R..
```*An Advanced Actuator Line Method for Wind Energy Applications and Beyond: Preprint*. United States: N. p., 2017.
Web. doi:10.2514/6.2017-1998.

```
Churchfield, Matthew, Schreck, Scott, Martinez-Tossas, Luis A., Meneveau, Charles, & Spalart, Philippe R..
```*An Advanced Actuator Line Method for Wind Energy Applications and Beyond: Preprint*. United States. doi:10.2514/6.2017-1998.

```
Churchfield, Matthew, Schreck, Scott, Martinez-Tossas, Luis A., Meneveau, Charles, and Spalart, Philippe R.. Fri .
"An Advanced Actuator Line Method for Wind Energy Applications and Beyond: Preprint". United States.
doi:10.2514/6.2017-1998. https://www.osti.gov/servlets/purl/1349215.
```

```
@article{osti_1349215,
```

title = {An Advanced Actuator Line Method for Wind Energy Applications and Beyond: Preprint},

author = {Churchfield, Matthew and Schreck, Scott and Martinez-Tossas, Luis A. and Meneveau, Charles and Spalart, Philippe R.},

abstractNote = {The actuator line method to represent rotor aerodynamics within computational fluid dynamics has been in use for over a decade. This method applies a body force to the flow field along rotating lines corresponding to the individual rotor blades and employs tabular airfoil data to compute the force distribution. The actuator line method is attractive because compared to blade-resolved simulations, the required mesh is much simpler and the computational cost is lower. This work proposes a higher fidelity variant of the actuator line method meant to fill the space between current actuator line and blade-resolved simulations. It contains modifications in two key areas. The first is that of freestream velocity vector estimation along the line, which is necessary to compute the lift and drag along the line using tabular airfoil data. Most current methods rely on point sampling in which the location of sampling is ambiguous. Here we test a velocity sampling method that uses a properly weighted integral over space, removing this ambiguity. The second area of improvement is the function used to project the one-dimensional actuator line force onto the three-dimensional fluid mesh as a body force. We propose and test a projection function that spreads the force over a region that looks something like a real blade with the hope that it will produce the blade local and near wake flow features with more accuracy and higher fidelity. Our goal is that between these two improvements, not only will the flow field predictions be enhanced, but also the spanwise loading will be made more accurate. We refer to this combination of improvements as the advanced actuator line method. We apply these improvements to two different wind turbine cases. Although there is a strong wind energy motivation in our work, there is no reason these advanced actuator line ideas cannot be used in other applications, such as helicopter rotors.},

doi = {10.2514/6.2017-1998},

journal = {},

number = ,

volume = ,

place = {United States},

year = {Fri Mar 24 00:00:00 EDT 2017},

month = {Fri Mar 24 00:00:00 EDT 2017}

}