Initial commit

crates/specialized/rtx-cfd/src/turbulence/mod.rs

@@ -0,0 +1,402 @@
+//! Turbulence modeling for CFD
+//!
+//! This module provides various turbulence models for simulating turbulent flows:
+//!
+//! - **RANS Models**: k-ε (standard, RNG, realizable), k-ω, k-ω SST
+//! - **LES Models**: Smagorinsky, Dynamic Smagorinsky, WALE
+//! - **Wall Functions**: Log-law, enhanced wall treatment
+//! - **Transition Models**: γ-Reθ, k-kL-ω
+
+pub mod k_epsilon;
+/// GPU-accelerated turbulence models
+#[cfg(feature = "cuda")]
+pub mod k_epsilon_gpu;
+pub mod smagorinsky;
+#[cfg(feature = "cuda")]
+pub mod smagorinsky_gpu;
+pub mod transition;
+pub mod wall_functions;
+
+pub use k_epsilon::{KEpsilonConstants, KEpsilonModel, KEpsilonVariant};
+#[cfg(feature = "cuda")]
+pub use k_epsilon_gpu::KEpsilonGpuModel;
+pub use smagorinsky::{SmagorinskyConstants, SmagorinskyModel};
+pub use wall_functions::{EnhancedWallTreatment, LogLawWallFunction, WallFunction};
+
+use crate::error::CfdResult;
+use nalgebra::{DVector, Vector3};
+
+/// Trait for turbulence models
+pub trait TurbulenceModel {
+    /// Calculate turbulent viscosity
+    fn turbulent_viscosity(&self, state: &TurbulenceState) -> CfdResult<DVector<f64>>;
+
+    /// Calculate production terms
+    fn production_terms(&self, state: &TurbulenceState) -> CfdResult<TurbulenceProduction>;
+
+    /// Update turbulence quantities
+    fn update(&mut self, state: &TurbulenceState, dt: f64) -> CfdResult<()>;
+
+    /// Get model name
+    fn name(&self) -> &str;
+
+    /// Check if model is RANS-based
+    fn is_rans(&self) -> bool;
+
+    /// Check if model is LES-based
+    fn is_les(&self) -> bool;
+}
+
+/// Turbulence state containing flow variables
+#[derive(Debug, Clone)]
+pub struct TurbulenceState {
+    /// Velocity field [u, v, w]
+    pub velocity: Vec<Vector3<f64>>,
+    /// Velocity gradients ∇u
+    pub velocity_gradients: Vec<[[f64; 3]; 3]>,
+    /// Pressure field
+    pub pressure: DVector<f64>,
+    /// Turbulent kinetic energy (for RANS models)
+    pub turbulent_ke: Option<DVector<f64>>,
+    /// Turbulent dissipation rate (for k-ε models)
+    pub epsilon: Option<DVector<f64>>,
+    /// Specific dissipation rate (for k-ω models)
+    pub omega: Option<DVector<f64>>,
+    /// Distance to wall
+    pub wall_distance: DVector<f64>,
+    /// Cell volumes
+    pub cell_volumes: DVector<f64>,
+    /// Dynamic viscosity
+    pub molecular_viscosity: f64,
+    /// Density
+    pub density: f64,
+}
+
+impl TurbulenceState {
+    /// Create new turbulence state
+    #[must_use]
+    pub fn new(n_cells: usize) -> Self {
+        Self {
+            velocity: vec![Vector3::zeros(); n_cells],
+            velocity_gradients: vec![[[0.0; 3]; 3]; n_cells],
+            pressure: DVector::zeros(n_cells),
+            turbulent_ke: None,
+            epsilon: None,
+            omega: None,
+            wall_distance: DVector::zeros(n_cells),
+            cell_volumes: DVector::from_element(n_cells, 1.0),
+            molecular_viscosity: 1e-5,
+            density: 1.0,
+        }
+    }
+
+    /// Initialize k-ε model variables
+    pub fn initialize_k_epsilon(&mut self, k_init: f64, epsilon_init: f64) {
+        let n_cells = self.velocity.len();
+        self.turbulent_ke = Some(DVector::from_element(n_cells, k_init));
+        self.epsilon = Some(DVector::from_element(n_cells, epsilon_init));
+    }
+
+    /// Initialize k-ω model variables
+    pub fn initialize_k_omega(&mut self, k_init: f64, omega_init: f64) {
+        let n_cells = self.velocity.len();
+        self.turbulent_ke = Some(DVector::from_element(n_cells, k_init));
+        self.omega = Some(DVector::from_element(n_cells, omega_init));
+    }
+
+    /// Calculate strain rate magnitude
+    #[must_use]
+    pub fn strain_rate_magnitude(&self, cell_idx: usize) -> f64 {
+        if cell_idx >= self.velocity_gradients.len() {
+            return 0.0;
+        }
+
+        let grad = &self.velocity_gradients[cell_idx];
+        let mut s_mag = 0.0;
+
+        // S_ij = 0.5 * (∂u_i/∂x_j + ∂u_j/∂x_i)
+        // For strain rate magnitude: |S| = sqrt(2 * S_ij * S_ij)
+        // Sum over all components (symmetric tensor)
+        for i in 0..3 {
+            for j in 0..3 {
+                let s_ij = 0.5 * (grad[i][j] + grad[j][i]);
+                s_mag += s_ij * s_ij;
+            }
+        }
+
+        // The factor of 2 accounts for the definition |S| = sqrt(2*Sij*Sij)
+        (2.0 * s_mag).sqrt()
+    }
+
+    /// Calculate vorticity magnitude
+    #[must_use]
+    pub fn vorticity_magnitude(&self, cell_idx: usize) -> f64 {
+        if cell_idx >= self.velocity_gradients.len() {
+            return 0.0;
+        }
+
+        let grad = &self.velocity_gradients[cell_idx];
+        let mut omega_mag = 0.0;
+
+        // Ω_ij = 0.5 * (∂u_i/∂x_j - ∂u_j/∂x_i)
+        // For antisymmetric tensor, sum over all components
+        for i in 0..3 {
+            for j in 0..3 {
+                let omega_ij = 0.5 * (grad[i][j] - grad[j][i]);
+                omega_mag += omega_ij * omega_ij;
+            }
+        }
+
+        // The factor of 2 accounts for the definition |Ω| = sqrt(2*Ωij*Ωij)
+        (2.0 * omega_mag).sqrt()
+    }
+}
+
+/// Production terms for turbulence models
+#[derive(Debug, Clone)]
+pub struct TurbulenceProduction {
+    /// Production of turbulent kinetic energy
+    pub pk: DVector<f64>,
+    /// Production of dissipation
+    pub pe: Option<DVector<f64>>,
+    /// Production of specific dissipation
+    pub pw: Option<DVector<f64>>,
+}
+
+impl TurbulenceProduction {
+    /// Create new production terms
+    #[must_use]
+    pub fn new(n_cells: usize) -> Self {
+        Self {
+            pk: DVector::zeros(n_cells),
+            pe: None,
+            pw: None,
+        }
+    }
+
+    /// Initialize for k-ε model
+    #[must_use]
+    pub fn for_k_epsilon(n_cells: usize) -> Self {
+        Self {
+            pk: DVector::zeros(n_cells),
+            pe: Some(DVector::zeros(n_cells)),
+            pw: None,
+        }
+    }
+
+    /// Initialize for k-ω model
+    #[must_use]
+    pub fn for_k_omega(n_cells: usize) -> Self {
+        Self {
+            pk: DVector::zeros(n_cells),
+            pe: None,
+            pw: Some(DVector::zeros(n_cells)),
+        }
+    }
+}
+
+/// Turbulence intensity calculation utilities
+pub struct TurbulenceIntensity;
+
+impl TurbulenceIntensity {
+    /// Calculate turbulence intensity from velocity fluctuations
+    #[must_use]
+    pub fn from_fluctuations(u_rms: f64, v_rms: f64, w_rms: f64, u_mean: f64) -> f64 {
+        let turbulent_ke = 0.5 * (u_rms * u_rms + v_rms * v_rms + w_rms * w_rms);
+        turbulent_ke.sqrt() / u_mean.abs().max(1e-10)
+    }
+
+    /// Estimate turbulence intensity for external flows
+    #[must_use]
+    pub fn external_flow_estimate(reynolds_number: f64) -> f64 {
+        // Empirical correlation for external flows
+        0.16 * reynolds_number.powf(-1.0 / 8.0)
+    }
+
+    /// Estimate turbulence intensity for internal flows
+    #[must_use]
+    pub fn internal_flow_estimate(reynolds_number: f64) -> f64 {
+        // Empirical correlation for pipe flows
+        0.16 * reynolds_number.powf(-1.0 / 8.0).min(0.1)
+    }
+
+    /// Calculate turbulent length scale
+    #[must_use]
+    pub fn turbulent_length_scale(characteristic_length: f64, turbulence_intensity: f64) -> f64 {
+        // Empirical estimate
+        0.07 * characteristic_length * (1.0 + 10.0 * turbulence_intensity)
+    }
+}
+
+/// Reynolds number utilities for turbulence modeling
+pub struct ReynoldsNumber;
+
+impl ReynoldsNumber {
+    /// Calculate turbulent Reynolds number
+    #[must_use]
+    pub fn turbulent(k: f64, epsilon: f64, nu: f64) -> f64 {
+        k * k / (epsilon * nu).max(1e-15)
+    }
+
+    /// Calculate wall Reynolds number y+
+    #[must_use]
+    pub fn y_plus(y: f64, u_tau: f64, nu: f64) -> f64 {
+        y * u_tau / nu
+    }
+
+    /// Calculate friction velocity
+    #[must_use]
+    pub fn friction_velocity(wall_shear_stress: f64, density: f64) -> f64 {
+        (wall_shear_stress / density).sqrt()
+    }
+
+    /// Calculate wall shear stress from velocity gradient
+    #[must_use]
+    pub fn wall_shear_stress(du_dy: f64, mu: f64) -> f64 {
+        mu * du_dy
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use approx::assert_relative_eq;
+
+    #[test]
+    fn test_turbulence_state_creation() {
+        let state = TurbulenceState::new(10);
+        assert_eq!(state.velocity.len(), 10);
+        assert_eq!(state.pressure.len(), 10);
+        assert!(state.turbulent_ke.is_none());
+        assert!(state.epsilon.is_none());
+    }
+
+    #[test]
+    fn test_turbulence_state_k_epsilon_init() {
+        let mut state = TurbulenceState::new(5);
+        state.initialize_k_epsilon(1.0, 0.1);
+
+        assert!(state.turbulent_ke.is_some());
+        assert!(state.epsilon.is_some());
+        assert_eq!(state.turbulent_ke.as_ref().unwrap().len(), 5);
+        assert_relative_eq!(
+            state.turbulent_ke.as_ref().unwrap()[0],
+            1.0,
+            epsilon = 1e-10
+        );
+    }
+
+    #[test]
+    fn test_turbulence_state_k_omega_init() {
+        let mut state = TurbulenceState::new(5);
+        state.initialize_k_omega(1.0, 10.0);
+
+        assert!(state.turbulent_ke.is_some());
+        assert!(state.omega.is_some());
+        assert_eq!(state.omega.as_ref().unwrap().len(), 5);
+        assert_relative_eq!(state.omega.as_ref().unwrap()[0], 10.0, epsilon = 1e-10);
+    }
+
+    #[test]
+    fn test_strain_rate_magnitude() {
+        let mut state = TurbulenceState::new(1);
+        // Set up simple shear flow: du/dy = 1, others = 0
+        state.velocity_gradients[0][0][1] = 1.0; // du/dy = 1
+
+        let s_mag = state.strain_rate_magnitude(0);
+        // S_01 = S_10 = 0.5 * (1 + 0) = 0.5, all others = 0
+        // Sum of S_ij^2 = 2 * 0.5^2 = 0.5
+        // |S| = sqrt(2 * 0.5) = 1.0
+        assert_relative_eq!(s_mag, 1.0, epsilon = 1e-10);
+    }
+
+    #[test]
+    fn test_vorticity_magnitude() {
+        let mut state = TurbulenceState::new(1);
+        // Set up rotation: du/dy = 1, dv/dx = -1
+        state.velocity_gradients[0][0][1] = 1.0; // du/dy = 1
+        state.velocity_gradients[0][1][0] = -1.0; // dv/dx = -1
+
+        let omega_mag = state.vorticity_magnitude(0);
+        // Ω_01 = 0.5 * (1 - (-1)) = 1, Ω_10 = 0.5 * ((-1) - 1) = -1
+        // Sum of Ω_ij^2 = 1^2 + (-1)^2 = 2
+        // |Ω| = sqrt(2 * 2) = 2
+        assert_relative_eq!(omega_mag, 2.0, epsilon = 1e-10);
+    }
+
+    #[test]
+    fn test_turbulence_production_creation() {
+        let prod = TurbulenceProduction::new(5);
+        assert_eq!(prod.pk.len(), 5);
+        assert!(prod.pe.is_none());
+        assert!(prod.pw.is_none());
+    }
+
+    #[test]
+    fn test_turbulence_production_k_epsilon() {
+        let prod = TurbulenceProduction::for_k_epsilon(5);
+        assert_eq!(prod.pk.len(), 5);
+        assert!(prod.pe.is_some());
+        assert!(prod.pw.is_none());
+        assert_eq!(prod.pe.as_ref().unwrap().len(), 5);
+    }
+
+    #[test]
+    fn test_turbulence_production_k_omega() {
+        let prod = TurbulenceProduction::for_k_omega(5);
+        assert_eq!(prod.pk.len(), 5);
+        assert!(prod.pe.is_none());
+        assert!(prod.pw.is_some());
+        assert_eq!(prod.pw.as_ref().unwrap().len(), 5);
+    }
+
+    #[test]
+    fn test_turbulence_intensity_from_fluctuations() {
+        let ti = TurbulenceIntensity::from_fluctuations(1.0, 1.0, 1.0, 10.0);
+        // k = 0.5 * (1 + 1 + 1) = 1.5
+        // TI = sqrt(k) / U = sqrt(1.5) / 10
+        assert_relative_eq!(ti, 1.5_f64.sqrt() / 10.0, epsilon = 1e-10);
+    }
+
+    #[test]
+    fn test_turbulence_intensity_estimates() {
+        let re = 1e6;
+        let ti_ext = TurbulenceIntensity::external_flow_estimate(re);
+        let ti_int = TurbulenceIntensity::internal_flow_estimate(re);
+
+        assert!(ti_ext > 0.0);
+        assert!(ti_int > 0.0);
+        assert!(ti_ext < 1.0);
+        assert!(ti_int < 1.0);
+    }
+
+    #[test]
+    fn test_turbulent_length_scale() {
+        let l_scale = TurbulenceIntensity::turbulent_length_scale(1.0, 0.05);
+        assert!(l_scale > 0.0);
+    }
+
+    #[test]
+    fn test_reynolds_number_turbulent() {
+        let re_t = ReynoldsNumber::turbulent(1.0, 1.0, 1e-6);
+        assert_relative_eq!(re_t, 1e6, epsilon = 1e-10);
+    }
+
+    #[test]
+    fn test_reynolds_number_y_plus() {
+        let y_plus = ReynoldsNumber::y_plus(1e-5, 0.1, 1e-6);
+        assert_relative_eq!(y_plus, 1.0, epsilon = 1e-10);
+    }
+
+    #[test]
+    fn test_friction_velocity() {
+        let u_tau = ReynoldsNumber::friction_velocity(0.1, 1.0);
+        assert_relative_eq!(u_tau, 0.1_f64.sqrt(), epsilon = 1e-10);
+    }
+
+    #[test]
+    fn test_wall_shear_stress() {
+        let tau_w = ReynoldsNumber::wall_shear_stress(100.0, 1e-3);
+        assert_relative_eq!(tau_w, 0.1, epsilon = 1e-10);
+    }
+}