scirs2-integrate 0.4.0

//! Base turbulence model types and traits
//!
//! This module provides the fundamental types and traits for turbulence modeling
//! in computational fluid dynamics, including common turbulence constants and
//! base functionality shared across different turbulence models.

use crate::error::IntegrateResult;
use scirs2_core::ndarray::{Array2, Array3};

/// Turbulence model types supported by the framework
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum TurbulenceModelType {
    /// k-ε turbulence model
    KEpsilon,
    /// k-ω turbulence model  
    KOmega,
    /// k-ω SST (Shear Stress Transport) model
    KOmegaSST,
    /// Reynolds Stress Model (RSM)
    ReynoldsStress,
    /// Spalart-Allmaras one-equation model
    SpalartAllmaras,
}

/// Common turbulence model constants
#[derive(Debug, Clone)]
pub struct TurbulenceConstants {
    /// Model constant C_μ
    pub c_mu: f64,
    /// Model constant C_1
    pub c_1: f64,
    /// Model constant C_2  
    pub c_2: f64,
    /// Turbulent Prandtl number for k
    pub sigma_k: f64,
    /// Turbulent Prandtl number for ε
    pub sigma_epsilon: f64,
    /// Turbulent Prandtl number for ω
    pub sigma_omega: f64,
}

impl Default for TurbulenceConstants {
    fn default() -> Self {
        Self {
            c_mu: 0.09,
            c_1: 1.44,
            c_2: 1.92,
            sigma_k: 1.0,
            sigma_epsilon: 1.3,
            sigma_omega: 2.0,
        }
    }
}

/// Base trait for all turbulence models
pub trait TurbulenceModel {
    /// Model type identifier
    fn model_type(&self) -> TurbulenceModelType;

    /// Model constants
    fn constants(&self) -> &TurbulenceConstants;

    /// Compute turbulent viscosity
    fn compute_turbulent_viscosity(
        &self,
        k: &Array3<f64>,
        epsilon_or_omega: &Array3<f64>,
    ) -> IntegrateResult<Array3<f64>>;

    /// Compute production term
    fn compute_production_term(
        &self,
        velocity: &[Array3<f64>],
        k: &Array3<f64>,
        epsilon_or_omega: &Array3<f64>,
        dx: f64,
        dy: f64,
        dz: f64,
    ) -> IntegrateResult<Array3<f64>>;

    /// Apply boundary conditions for turbulence quantities
    fn apply_turbulence_boundary_conditions(
        &self,
        k: &mut Array3<f64>,
        epsilon_or_omega: &mut Array3<f64>,
    ) -> IntegrateResult<()>;
}

/// Trait for RANS turbulence models
pub trait RANSModel: TurbulenceModel {
    /// Update turbulence quantities for one time step
    fn update_turbulence_quantities(
        &self,
        velocity: &[Array3<f64>],
        k: &mut Array3<f64>,
        epsilon_or_omega: &mut Array3<f64>,
        dt: f64,
        dx: f64,
        dy: f64,
        dz: f64,
    ) -> IntegrateResult<()>;

    /// Compute wall functions for near-wall treatment
    fn compute_wall_functions(
        &self,
        velocity: &[Array3<f64>],
        wall_distance: &Array3<f64>,
        k: &mut Array3<f64>,
        epsilon_or_omega: &mut Array3<f64>,
    ) -> IntegrateResult<()>;
}

/// Trait for LES subgrid-scale models
pub trait SGSModel {
    /// Compute subgrid-scale viscosity
    fn compute_sgs_viscosity(
        &self,
        velocity: &[Array3<f64>],
        filter_width: f64,
        dx: f64,
        dy: f64,
        dz: f64,
    ) -> IntegrateResult<Array3<f64>>;

    /// Compute subgrid-scale stress tensor
    fn compute_sgs_stress(
        &self,
        velocity: &[Array3<f64>],
        filter_width: f64,
        dx: f64,
        dy: f64,
        dz: f64,
    ) -> IntegrateResult<Array3<[[f64; 3]; 3]>>;
}

/// Common turbulence utility functions
pub struct TurbulenceUtils;

impl TurbulenceUtils {
    /// Compute strain rate tensor magnitude
    pub fn compute_strain_rate_magnitude(
        velocity: &[Array3<f64>],
        dx: f64,
        dy: f64,
        dz: f64,
    ) -> IntegrateResult<Array3<f64>> {
        let (nx, ny, nz) = velocity[0].dim();
        let mut strain_mag = Array3::zeros((nx, ny, nz));

        for i in 1..nx - 1 {
            for j in 1..ny - 1 {
                for k in 1..nz - 1 {
                    // Compute velocity gradients
                    let dudx =
                        (velocity[0][[i + 1, j, k]] - velocity[0][[i - 1, j, k]]) / (2.0 * dx);
                    let dudy =
                        (velocity[0][[i, j + 1, k]] - velocity[0][[i, j - 1, k]]) / (2.0 * dy);
                    let dudz =
                        (velocity[0][[i, j, k + 1]] - velocity[0][[i, j, k - 1]]) / (2.0 * dz);

                    let dvdx =
                        (velocity[1][[i + 1, j, k]] - velocity[1][[i - 1, j, k]]) / (2.0 * dx);
                    let dvdy =
                        (velocity[1][[i, j + 1, k]] - velocity[1][[i, j - 1, k]]) / (2.0 * dy);
                    let dvdz =
                        (velocity[1][[i, j, k + 1]] - velocity[1][[i, j, k - 1]]) / (2.0 * dz);

                    let dwdx =
                        (velocity[2][[i + 1, j, k]] - velocity[2][[i - 1, j, k]]) / (2.0 * dx);
                    let dwdy =
                        (velocity[2][[i, j + 1, k]] - velocity[2][[i, j - 1, k]]) / (2.0 * dy);
                    let dwdz =
                        (velocity[2][[i, j, k + 1]] - velocity[2][[i, j, k - 1]]) / (2.0 * dz);

                    // Compute strain rate tensor components
                    let s11 = dudx;
                    let s22 = dvdy;
                    let s33 = dwdz;
                    let s12 = 0.5 * (dudy + dvdx);
                    let s13 = 0.5 * (dudz + dwdx);
                    let s23 = 0.5 * (dvdz + dwdy);

                    // Compute magnitude: |S| = √(2 S_ij S_ij)
                    let s_mag_squared = 2.0
                        * (s11 * s11
                            + s22 * s22
                            + s33 * s33
                            + 2.0 * (s12 * s12 + s13 * s13 + s23 * s23));
                    strain_mag[[i, j, k]] = s_mag_squared.sqrt();
                }
            }
        }

        Ok(strain_mag)
    }

    /// Compute vorticity magnitude
    pub fn compute_vorticity_magnitude(
        velocity: &[Array3<f64>],
        dx: f64,
        dy: f64,
        dz: f64,
    ) -> IntegrateResult<Array3<f64>> {
        let (nx, ny, nz) = velocity[0].dim();
        let mut vorticity_mag = Array3::zeros((nx, ny, nz));

        for i in 1..nx - 1 {
            for j in 1..ny - 1 {
                for k in 1..nz - 1 {
                    // Compute vorticity components: ω = ∇ × u
                    let omega_x = (velocity[2][[i, j + 1, k]] - velocity[2][[i, j - 1, k]])
                        / (2.0 * dy)
                        - (velocity[1][[i, j, k + 1]] - velocity[1][[i, j, k - 1]]) / (2.0 * dz);

                    let omega_y = (velocity[0][[i, j, k + 1]] - velocity[0][[i, j, k - 1]])
                        / (2.0 * dz)
                        - (velocity[2][[i + 1, j, k]] - velocity[2][[i - 1, j, k]]) / (2.0 * dx);

                    let omega_z = (velocity[1][[i + 1, j, k]] - velocity[1][[i - 1, j, k]])
                        / (2.0 * dx)
                        - (velocity[0][[i, j + 1, k]] - velocity[0][[i, j - 1, k]]) / (2.0 * dy);

                    vorticity_mag[[i, j, k]] =
                        (omega_x * omega_x + omega_y * omega_y + omega_z * omega_z).sqrt();
                }
            }
        }

        Ok(vorticity_mag)
    }

    /// Compute wall distance (simplified implementation)
    pub fn compute_wall_distance(nx: usize, ny: usize, nz: usize) -> Array3<f64> {
        let mut wall_distance = Array3::zeros((nx, ny, nz));

        for i in 0..nx {
            for j in 0..ny {
                for k in 0..nz {
                    // Simple distance to nearest wall (assuming walls at boundaries)
                    let dist_to_wall = vec![
                        i as f64,
                        (nx - 1 - i) as f64,
                        j as f64,
                        (ny - 1 - j) as f64,
                        k as f64,
                        (nz - 1 - k) as f64,
                    ];

                    wall_distance[[i, j, k]] =
                        dist_to_wall.into_iter().fold(f64::INFINITY, f64::min);
                }
            }
        }

        wall_distance
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_turbulence_constants_default() {
        let constants = TurbulenceConstants::default();
        assert_eq!(constants.c_mu, 0.09);
        assert_eq!(constants.c_1, 1.44);
        assert_eq!(constants.c_2, 1.92);
    }

    #[test]
    fn test_turbulence_model_type() {
        let model_type = TurbulenceModelType::KEpsilon;
        assert_eq!(model_type, TurbulenceModelType::KEpsilon);
        assert_ne!(model_type, TurbulenceModelType::KOmega);
    }

    #[test]
    fn test_strain_rate_computation() {
        let velocity = vec![
            Array3::ones((5, 5, 5)),
            Array3::zeros((5, 5, 5)),
            Array3::zeros((5, 5, 5)),
        ];

        let strain_mag = TurbulenceUtils::compute_strain_rate_magnitude(&velocity, 0.1, 0.1, 0.1);
        assert!(strain_mag.is_ok());
    }

    #[test]
    fn test_wall_distance_computation() {
        let wall_distance = TurbulenceUtils::compute_wall_distance(10, 10, 10);
        assert_eq!(wall_distance.dim(), (10, 10, 10));
        assert_eq!(wall_distance[[0, 0, 0]], 0.0);
        assert!(wall_distance[[5, 5, 5]] > 0.0);
    }
}