rustytorch/crates/specialized/rtx-cfd/tests/cfd_workflow_tests.rs

//! Production CFD workflow integration tests
//!
//! Tests the complete CFD workflow with actual SIMPLE and PISO solvers,
//! validating convergence, mass conservation, and turbulence integration.

use rtx_cfd::{
    CfdConfig, CfdResult,
    solvers::incompressible::{
        BoundaryConditions, FlowField, IncompressibleSolver, PisoParameters, PisoSolver,
        SimpleParameters, SimpleSolver,
    },
};
use std::time::Duration;

/// Test complete SIMPLE solver workflow with turbulence
#[tokio::test]
async fn test_simple_solver_workflow() -> CfdResult<()> {
    // Create CFD configuration
    // Reynolds number 100, not 10^6.
    //
    // The nominal water properties (rho = 1000, mu = 1e-3) give
    // Re = rho U L / mu = 10^6 on a unit domain, which has no steady laminar
    // solution and could not be resolved by ten cells if it did. The solver
    // diverges on it, correctly. It only appeared to work while the diffusion
    // conductances were a factor 1/h too large, which quietly stabilised it.
    let config = CfdConfig::new()
        .with_density(1000.0)
        .with_viscosity(10.0)
        .with_reference_velocity(1.0)
        .with_reference_length(1.0);

    // Create solver parameters with turbulence enabled
    let params = SimpleParameters {
        pressure_relaxation: 0.3,
        velocity_relaxation: 0.7,
        max_iterations: 50,
        tolerance: 1e-6,
        time_step: 0.001,
        max_courant: 1.0,
        use_turbulence: true,
        steady: true,
        ..SimpleParameters::default()
    };

    // Create solver
    let mut solver = SimpleSolver::new(config.clone(), params)?;

    // Create flow field (10x10 grid)
    let mut flow_field = FlowField::new(10, 10, 0.1, 0.1)?;

    // Initialize with simple flow
    for j in 0..10 {
        for i in 0..10 {
            if i < 10 && j < 10 {
                flow_field.u[(j, i)] = 1.0; // Initial u-velocity
                flow_field.v[(j, i)] = 0.0; // Initial v-velocity
                flow_field.p[(j, i)] = 0.0; // Initial pressure
            }
        }
    }

    // Set up boundary conditions (lid-driven cavity)
    let boundary_conditions = BoundaryConditions::lid_driven_cavity(10, 10, 1.0);

    // Run solver for a few iterations
    let mut total_iterations = 0;
    for _outer in 0..5 {
        let result = solver.solve(&mut flow_field, &boundary_conditions).await?;

        total_iterations += result.solver_result.iterations;

        // Check convergence properties
        assert!(result.solver_result.final_residual >= 0.0);
        assert!(result.solver_result.solve_time > Duration::from_nanos(0));

        // Basic sanity checks on flow field
        assert!(!flow_field.u.iter().any(|&x| x.is_nan()));
        assert!(!flow_field.v.iter().any(|&x| x.is_nan()));
        assert!(!flow_field.p.iter().any(|&x| x.is_nan()));

        // Check that velocities are within reasonable bounds
        let max_u = flow_field.u.iter().fold(0.0f64, |a, &b| a.max(b.abs()));
        let max_v = flow_field.v.iter().fold(0.0f64, |a, &b| a.max(b.abs()));
        assert!(max_u < 10.0, "u-velocity too large: {}", max_u);
        assert!(max_v < 10.0, "v-velocity too large: {}", max_v);

        if result.solver_result.converged {
            break;
        }
    }

    println!(
        "SIMPLE solver completed {} total iterations",
        total_iterations
    );
    Ok(())
}

/// Test complete PISO solver workflow
#[tokio::test]
async fn test_piso_solver_workflow() -> CfdResult<()> {
    // Create CFD configuration
    let config = CfdConfig::new()
        .with_density(1000.0)
        .with_viscosity(1e-3)
        .with_reference_velocity(1.0)
        .with_reference_length(1.0);

    // Create PISO parameters
    let params = PisoParameters {
        corrector_steps: 2,
        time_step: 0.001,
        tolerance: 1e-6,
        ..PisoParameters::default()
    };

    // Create solver
    let mut solver = PisoSolver::new(config.clone(), params.clone())?;

    // Create flow field (10x10 grid)
    let mut flow_field = FlowField::new(10, 10, 0.1, 0.1)?;

    // Initialize with simple flow
    for j in 0..10 {
        for i in 0..10 {
            if i < 10 && j < 10 {
                flow_field.u[(j, i)] = 1.0;
                flow_field.v[(j, i)] = 0.0;
                flow_field.p[(j, i)] = 0.0;
            }
        }
    }

    // Set up boundary conditions
    let boundary_conditions = BoundaryConditions::lid_driven_cavity(10, 10, 1.0);

    // Run time stepping
    let dt = 0.001;
    for _time_step in 0..10 {
        let result = solver
            .solve_time_step(&mut flow_field, &boundary_conditions, dt)
            .await?;

        // Check that pressure correction steps were performed
        assert!(result.corrector_steps_performed >= 1);
        assert!(result.corrector_steps_performed <= params.corrector_steps);

        // Basic sanity checks
        assert!(result.solver_result.final_residual >= 0.0);
        assert!(!flow_field.u.iter().any(|&x| x.is_nan()));
        assert!(!flow_field.v.iter().any(|&x| x.is_nan()));
        assert!(!flow_field.p.iter().any(|&x| x.is_nan()));
    }

    println!("PISO solver completed 10 time steps successfully");
    Ok(())
}

/// Test mass conservation in CFD solvers
#[tokio::test]
async fn test_mass_conservation() -> CfdResult<()> {
    let config = CfdConfig::new().with_density(1000.0).with_viscosity(1e-3);

    let params = SimpleParameters::default();
    let mut solver = SimpleSolver::new(config, params)?;

    let mut flow_field = FlowField::new(5, 5, 0.2, 0.2)?;
    let boundary_conditions = BoundaryConditions::lid_driven_cavity(5, 5, 1.0);

    // Run a few iterations
    for _i in 0..3 {
        let _result = solver.solve(&mut flow_field, &boundary_conditions).await?;

        // Calculate mass conservation (∇·u should be small for incompressible flow)
        let mut max_divergence: f64 = 0.0;
        let (nx, ny, dx, dy) = flow_field.grid_info();

        for j in 1..ny - 1 {
            for i in 1..nx - 1 {
                let du_dx = (flow_field.u[(j, i + 1)] - flow_field.u[(j, i - 1)]) / (2.0 * dx);
                let dv_dy = (flow_field.v[(j + 1, i)] - flow_field.v[(j - 1, i)]) / (2.0 * dy);
                let divergence = (du_dx + dv_dy).abs();
                max_divergence = max_divergence.max(divergence);
            }
        }

        // For a converged incompressible solution, divergence should be small
        println!("Max divergence: {}", max_divergence);
        // Note: For early iterations, divergence may be larger but should decrease
    }

    Ok(())
}

/// Test turbulence model integration
#[tokio::test]
async fn test_turbulence_integration() -> CfdResult<()> {
    let config = CfdConfig::new().with_density(1000.0).with_viscosity(1e-3);

    // Create parameters with turbulence enabled
    let params_turbulent = SimpleParameters {
        use_turbulence: true,
        ..SimpleParameters::default()
    };

    // Create parameters without turbulence
    let params_laminar = SimpleParameters {
        use_turbulence: false,
        ..SimpleParameters::default()
    };

    let mut solver_turbulent = SimpleSolver::new(config.clone(), params_turbulent)?;
    let mut solver_laminar = SimpleSolver::new(config, params_laminar)?;

    let mut flow_field_turbulent = FlowField::new(8, 8, 0.125, 0.125)?;
    let mut flow_field_laminar = FlowField::new(8, 8, 0.125, 0.125)?;

    // Initialize both with same initial conditions
    for j in 0..8 {
        for i in 0..8 {
            let u_init = if i == 0 { 1.0 } else { 0.0 };
            flow_field_turbulent.u[(j, i)] = u_init;
            flow_field_turbulent.v[(j, i)] = 0.0;
            flow_field_turbulent.p[(j, i)] = 0.0;

            flow_field_laminar.u[(j, i)] = u_init;
            flow_field_laminar.v[(j, i)] = 0.0;
            flow_field_laminar.p[(j, i)] = 0.0;
        }
    }

    let boundary_conditions = BoundaryConditions::lid_driven_cavity(8, 8, 1.0);

    // Run both solvers
    let result_turbulent = solver_turbulent
        .solve(&mut flow_field_turbulent, &boundary_conditions)
        .await?;
    let result_laminar = solver_laminar
        .solve(&mut flow_field_laminar, &boundary_conditions)
        .await?;

    // Both should converge but may have different residuals
    assert!(result_turbulent.solver_result.final_residual >= 0.0);
    assert!(result_laminar.solver_result.final_residual >= 0.0);

    // Flow fields should be different due to turbulence effects
    let mut velocity_difference: f64 = 0.0;
    for j in 0..8 {
        for i in 0..8 {
            let diff_u = (flow_field_turbulent.u[(j, i)] - flow_field_laminar.u[(j, i)]).abs();
            let diff_v = (flow_field_turbulent.v[(j, i)] - flow_field_laminar.v[(j, i)]).abs();
            velocity_difference = velocity_difference.max(diff_u).max(diff_v);
        }
    }

    println!(
        "Turbulent vs laminar max velocity difference: {}",
        velocity_difference
    );

    Ok(())
}

/// Test solver robustness with extreme conditions
#[tokio::test]
async fn test_solver_robustness() -> CfdResult<()> {
    let config = CfdConfig::new()
        .with_density(1.0) // Low density
        .with_viscosity(1e-6); // Low viscosity (high Reynolds number)

    let params = SimpleParameters {
        max_iterations: 20, // Limit iterations to avoid long test times
        tolerance: 1e-4,    // Relaxed tolerance
        ..SimpleParameters::default()
    };

    let mut solver = SimpleSolver::new(config, params)?;
    let mut flow_field = FlowField::new(6, 6, 0.1, 0.1)?;

    // Initialize with high velocities
    for j in 0..6 {
        for i in 0..6 {
            flow_field.u[(j, i)] = 5.0; // High initial velocity
            flow_field.v[(j, i)] = 0.0;
            flow_field.p[(j, i)] = 0.0;
        }
    }

    let boundary_conditions = BoundaryConditions::lid_driven_cavity(6, 6, 5.0);

    // Solver should handle this without crashing
    let result = solver.solve(&mut flow_field, &boundary_conditions).await?;

    // Check that solution remains bounded
    assert!(!flow_field.u.iter().any(|&x| x.is_nan() || x.is_infinite()));
    assert!(!flow_field.v.iter().any(|&x| x.is_nan() || x.is_infinite()));
    assert!(!flow_field.p.iter().any(|&x| x.is_nan() || x.is_infinite()));

    println!(
        "Robustness test completed with residual: {}",
        result.solver_result.final_residual
    );

    Ok(())
}

/// Test SIMPLE vs PISO convergence comparison
#[tokio::test]
async fn test_simple_vs_piso_comparison() -> CfdResult<()> {
    let config = CfdConfig::new().with_density(1000.0).with_viscosity(1e-3);

    // SIMPLE solver
    let simple_params = SimpleParameters {
        max_iterations: 30,
        tolerance: 1e-5,
        ..SimpleParameters::default()
    };
    let mut simple_solver = SimpleSolver::new(config.clone(), simple_params)?;

    // PISO solver
    let piso_params = PisoParameters {
        corrector_steps: 2,
        time_step: 0.001,
        tolerance: 1e-5,
        ..PisoParameters::default()
    };
    let mut piso_solver = PisoSolver::new(config, piso_params)?;

    // Create identical initial conditions
    let mut flow_field_simple = FlowField::new(6, 6, 1.0 / 6.0, 1.0 / 6.0)?;
    let mut flow_field_piso = flow_field_simple.clone();

    let boundary_conditions = BoundaryConditions::lid_driven_cavity(6, 6, 1.0);

    // Solve with SIMPLE
    let start = std::time::Instant::now();
    let simple_result = simple_solver
        .solve(&mut flow_field_simple, &boundary_conditions)
        .await?;
    let simple_time = start.elapsed();

    // Solve with PISO (single time step)
    let start = std::time::Instant::now();
    let piso_result = piso_solver
        .solve_time_step(&mut flow_field_piso, &boundary_conditions, 0.001)
        .await?;
    let piso_time = start.elapsed();

    println!(
        "SIMPLE: {} iterations, residual: {:.2e}, time: {:?}",
        simple_result.solver_result.iterations,
        simple_result.solver_result.final_residual,
        simple_time
    );
    println!(
        "PISO: {} corrector steps, residual: {:.2e}, time: {:?}",
        piso_result.corrector_steps_performed, piso_result.solver_result.final_residual, piso_time
    );

    // Both should produce valid solutions
    assert!(simple_result.solver_result.final_residual >= 0.0);
    assert!(piso_result.solver_result.final_residual >= 0.0);

    Ok(())
}

/// Test Reynolds number effects on flow
#[tokio::test]
async fn test_reynolds_number_effects() -> CfdResult<()> {
    // Low Reynolds number (laminar)
    let config_low_re = CfdConfig::new()
        .with_density(1.0)
        .with_viscosity(1.0) // High viscosity
        .with_reference_velocity(1.0)
        .with_reference_length(1.0);

    // High Reynolds number (turbulent)
    let config_high_re = CfdConfig::new()
        .with_density(1.0)
        .with_viscosity(1e-5) // Low viscosity
        .with_reference_velocity(1.0)
        .with_reference_length(1.0);

    assert!(config_low_re.is_laminar());
    assert!(config_high_re.is_turbulent());

    let re_low = config_low_re.reynolds_number();
    let re_high = config_high_re.reynolds_number();

    println!("Low Re: {}, High Re: {}", re_low, re_high);

    assert!(re_low < 100.0);
    assert!(re_high > 10000.0);

    // Test that both configurations are valid
    assert!(config_low_re.validate().is_ok());
    assert!(config_high_re.validate().is_ok());

    Ok(())
}