m_alm Module

Actuator Line Model (ALM) turbine forcing (iturbine = 1).

Ported from Incompact3d's actuator line model (G. Deskos, 2015-2017; acl_*.f90, airfoils.f90). Each blade (and the optional tower) is a line of actuator elements; the blade-element loads computed from the airfoil polars (m_alm_turbine, m_alm_element) are projected back onto the flow as a momentum source.

Once per time step, on the first substage: 1. the fluid velocity at every element centre $\mathbf{x}_s$ is interpolated trilinearly from the grid, 2. the element forces $\mathbf{F}_s$ follow from the polars, 3. they are smeared onto the grid with an isotropic Gaussian kernel, $$\mathbf{f}(\mathbf{x}) = -\frac{1}{\rho}\sum_s \mathbf{F}_s\, \frac{1}{\epsilon^3\pi^{3/2}} \exp\left(-\frac{|\mathbf{x}-\mathbf{x}_s|^2}{\epsilon^2}\right), \qquad \epsilon = \epsilon_f\,(\Delta x\Delta y\Delta z)^{1/3},$$ truncated at $|\mathbf{x}-\mathbf{x}_s| = 10\epsilon$, 4. the rotors are advanced to the next time step. The same sources are projected onto the momentum RHS at every substage of the step, as Incompact3d adds its force field. The sampling and the projection run on the backend; the blade bookkeeping is replicated on every rank.

Turbines are described by Incompact3d .turb files (see m_alm_turbine). The standalone actuator lines of Incompact3d (NActuatorlines) are not ported. Only uniform grids are supported. Kernel truncation radius in units of epsilon (Incompact3d's dist2_max = 100 epsilon^2)