60 lines
1.9 KiB
Python
60 lines
1.9 KiB
Python
# tests/test_pipe.py
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import numpy as np
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import pytest
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from pipe import Pipe
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GAMMA = 1.4
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R_GAS = 287.0
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def test_pipe_uniform_initialization_all_cells_identical():
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"""
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Initial state: uniform P, T, u=0 across all N cells.
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All cells should have identical W. primitives() should round-trip
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back to u=0 and P=P_init.
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"""
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pipe = Pipe(L=1.0, D=5e-3, N=20,
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P_init=1e5, T_init=300.0,
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gamma=GAMMA, R_gas=R_GAS)
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# All cells identical
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for i in range(1, pipe.N):
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assert np.allclose(pipe.W[:, i], pipe.W[:, 0], rtol=1e-14)
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rho, u, P, a = pipe.primitives()
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rho_expected = 1e5 / (R_GAS * 300.0)
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assert np.allclose(u, 0.0)
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assert np.allclose(P, 1e5, rtol=1e-10)
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assert np.allclose(rho, rho_expected, rtol=1e-10)
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# Sound speed a = sqrt(gamma * P / rho)
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a_expected = np.sqrt(GAMMA * 1e5 / rho_expected)
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assert np.allclose(a, a_expected, rtol=1e-10)
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# Geometric sanity
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assert pipe.dx == 1.0 / 20
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assert pipe.x_centers.shape == (20,)
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assert abs(pipe.x_centers[0] - 0.025) < 1e-14
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assert abs(pipe.x_centers[-1] - 0.975) < 1e-14
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def test_pipe_uniform_state_plus_matching_boundary_flux_is_static():
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"""
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If all cells have identical W (so all internal HLL fluxes are
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identical to the physical flux F(W) = [0, P, 0] for u=0 state),
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and we pass in boundary fluxes equal to [0, P, 0] as well, then
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every difference (flux[i+1] - flux[i]) is zero, so W must not
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change after one step. Verify to machine precision.
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"""
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pipe = Pipe(L=1.0, D=5e-3, N=20,
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P_init=1e5, T_init=300.0,
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gamma=GAMMA, R_gas=R_GAS)
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W_before = pipe.W.copy()
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# Boundary flux matching the static interior: [rho*u, rho*u^2+P, u*(E+P)]
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# with u=0 -> [0, P, 0]
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flux_boundary = np.array([0.0, 1e5, 0.0])
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pipe.step(flux_boundary, flux_boundary, dt=1e-5)
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assert np.allclose(pipe.W, W_before, atol=1e-6, rtol=1e-12)
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