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Add speed of sound isentropic ratio #27

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Mar 28, 2019
Merged

Add speed of sound isentropic ratio #27

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18 changes: 18 additions & 0 deletions skaero/gasdynamics/isentropic.py
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Original file line number Diff line number Diff line change
Expand Up @@ -232,6 +232,24 @@ def A_Astar(self, M):
)
return A_Astar

def a_a0(self, M):
""" Speed of sound ratio from Mach number.

Parameters
----------
M: array_like
Mach number.

Returns
-------
a_a0: array_like
Speed of sound ratio.
"""

M = np.asarray(M)
a_a0 = self.T_T0(M) ** 0.5

return a_a0

class PrandtlMeyerExpansion(object):
"""Class representing a Prandtl-Meyer expansion fan.
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9 changes: 9 additions & 0 deletions tests/test_isentropic.py
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Expand Up @@ -141,6 +141,15 @@ def test_mach_from_area_ratio_raises_error_when_ratio_is_subsonic():
with pytest.raises(ValueError):
isentropic.mach_from_area_ratio(0.9)

def test_speed_of_sound_ratio():
fl = isentropic.IsentropicFlow(1.4)
M_list = [0.0, 0.3, 1.0, 1.3, 2.5]
expected_sound_speed_ratios = [1.0, 0.99112, 0.91287, 0.86451, 0.6667]

np.testing.assert_array_almost_equal(
fl.a_a0(M_list), expected_sound_speed_ratios, decimal=3
)


def test_mach_from_area_ratio_subsonic():
fl = isentropic.IsentropicFlow(1.4)
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