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Done refactoring of shocks
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Now there is a _ShockFactory which returns a _ShockClass object depending
on the given parameters. From _ShockFactory doctests:

    >>> ss1 = Shock(M_1=1.5)  # Given upstream Mach number (default beta = 90°)
    >>> ss1.M_2
    0.70108874169309943
    >>> ss1.beta
    1.5707963267948966
    >>> ss1.theta
    0.0
    >>> ss2 = Shock(M_1=3.0, theta=np.radians(20.0), weak=True)
    >>> ss2.beta  # Notice it is an oblique shock
    0.6590997534071927

This is much cleaner now, and the approach can be extended to other kind
of objects.
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@astrojuanlu
astrojuanlu committed Mar 1, 2013
1 parent 3a9153e commit 49d1379
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161 changes: 65 additions & 96 deletions skaero/gasdynamics/shocks.py
View file
Original file line number Diff line number Diff line change
Expand Up @@ -30,52 +30,8 @@
from skaero.gasdynamics.isentropic import mach_angle


def from_deflection_angle(M_1, theta, weak=True, gamma=1.4):
"""Returns oblique shock given upstream Mach number and deflection angle.
By default weak solution is selected, unless weak=False is provided.
Parameters
----------
M_1 : float
Upstream Mach number.
theta : float
Deflection angle, in radians.
weak : boolean, optional
Specifies if weak solution is desired, default to True. Else strong
solution is returned.
gamma : float, optional
Specific heat ratio, default 7 / 5.
Returns
-------
os : ObliqueShock
ObliqueShock with desired upstream Mach number and resultand angle.
Raises
------
ValueError
If the deflection angle is higher than the maximum and therefore there
is no solution.
"""
def eq(beta, M_1, theta, gamma):
os = ObliqueShock(M_1, beta, gamma)
return os.theta - theta

theta_max, beta_theta_max = max_deflection(M_1)
if theta > theta_max:
raise ValueError("No attached solution for this deflection angle")
else:
if weak:
mu = mach_angle(M_1)
beta = sp.optimize.bisect(
eq, mu, beta_theta_max, args=(M_1, theta, gamma))
else:
beta = sp.optimize.bisect(
eq, beta_theta_max, np.pi / 2, args=(M_1, theta, gamma))

return ObliqueShock(M_1, beta, gamma)
# Exceptions used in this module
class InvalidParametersError(Exception): pass


def max_deflection(M_1, gamma=1.4):
Expand All @@ -98,33 +54,76 @@ def max_deflection(M_1, gamma=1.4):
"""
def eq(beta, M_1, gamma):
os = ObliqueShock(M_1, beta, gamma)
os = _ShockClass(M_1, beta, gamma)
return -os.theta

mu = mach_angle(M_1)
beta_theta_max = sp.optimize.fminbound(
eq, mu, np.pi / 2, args=(M_1, gamma), disp=0)
os = ObliqueShock(M_1, beta_theta_max, gamma)
os = _ShockClass(M_1, beta_theta_max, gamma)
return os.theta, os.beta


class ObliqueShock(object):
"""Class representing an oblique shock.
def _ShockFactory(**kwargs):
"""Returns an object representing a shock wave.
Parameters
----------
M_1 : float
Upstream Mach number.
beta : float
Shock wave angle, with respect to the upstream velocity, in radians.
gamma : float, optional
Specific heat ratio, default 7 / 5.
Examples
--------
>>> ss1 = Shock(M_1=1.5) # Given upstream Mach number (default beta = 90°)
>>> ss1.M_2
0.70108874169309943
>>> ss1.beta
1.5707963267948966
>>> ss1.theta
0.0
>>> ss2 = Shock(M_1=3.0, theta=np.radians(20.0), weak=True)
>>> ss2.beta # Notice it is an oblique shock
0.6590997534071927
"""
methods = {
frozenset(['M_1']): _ShockClass,
frozenset(['M_1', 'theta']): _from_deflection_angle,
frozenset(['M_1', 'theta', 'weak']): _from_deflection_angle
}
beta = kwargs.pop('beta', np.pi / 2)
gamma = kwargs.pop('gamma', 1.4)
params = frozenset(kwargs.keys())
try:
shock = methods[params](beta=beta, gamma=gamma, **kwargs)
except KeyError:
raise InvalidParametersError("Invalid list of parameters")
return shock


Shock = _ShockFactory

Raises
------
ValueError
If the upstream Mach number is less than one or the wave angle is lower
than the Mach angle.

def _from_deflection_angle(M_1, theta, weak=True, gamma=1.4, **kwargs):
"""Returns oblique shock given upstream Mach number and deflection angle.
"""
def eq(beta, M_1, theta, gamma):
os = _ShockClass(M_1, beta, gamma)
return os.theta - theta

theta_max, beta_theta_max = max_deflection(M_1)
if theta > theta_max:
raise ValueError("No attached solution for this deflection angle")
else:
if weak:
mu = mach_angle(M_1)
beta = sp.optimize.bisect(
eq, mu, beta_theta_max, args=(M_1, theta, gamma))
else:
beta = sp.optimize.bisect(
eq, beta_theta_max, np.pi / 2, args=(M_1, theta, gamma))

return _ShockClass(M_1, beta, gamma)


class _ShockClass(object):
"""Class representing a shock.
"""
def __init__(self, M_1, beta, gamma=1.4):
Expand All @@ -140,15 +139,16 @@ def __init__(self, M_1, beta, gamma=1.4):
self.gamma = gamma

def __repr__(self):
return ("ObliqueShock(M_1={0!r}, beta={1!r}, "
# FIXME: What if the object is returned from different parameters?
return ("Shock(M_1={0!r}, beta={1!r}, "
"gamma={2!r})".format(self.M_1, self.beta, self.gamma))

@property
def theta(self):
"""Deflection angle of the shock.
"""
if self.beta == 0.0:
if self.beta == 0.0 or self.beta == np.pi / 2:
theta = 0.0
else:
theta = np.arctan(
Expand Down Expand Up @@ -202,34 +202,3 @@ def T2_T1(self):
"""
T2_T1 = self.p2_p1 / self.rho2_rho1
return T2_T1


class NormalShock(ObliqueShock):
"""Class representing a normal shock.
Parameters
----------
M_1 : float
Upstream Mach number.
gamma : float, optional
Specific heat ratio, default 7 / 5.
Raises
------
ValueError
If the upstream Mach number is less than one.
"""
def __init__(self, M_1, gamma=1.4):
super(NormalShock, self).__init__(M_1, np.pi / 2, gamma)

def __repr__(self):
return ("NormalShock(M_1={0!r}, "
"gamma={1!r})".format(self.M_1, self.gamma))

@property
def theta(self):
"""Deflection angle of the shock.
"""
return 0.0
22 changes: 11 additions & 11 deletions tests/test_shocks.py
View file
Original file line number Diff line number Diff line change
Expand Up @@ -25,11 +25,11 @@
def test_normal_shock_constructor():
gamma = 1.4
M_1 = 2.0
shocks.NormalShock(M_1, gamma)
shocks.Shock(M_1=M_1, gamma=gamma)


def test_normal_shock_default_specific_heat_ratio():
ns = shocks.NormalShock(2.0)
ns = shocks.Shock(M_1=2.0)
np.testing.assert_equal(ns.gamma, 7 / 5)


Expand All @@ -44,15 +44,15 @@ def test_normal_shock_M_2():
0.5613,
0.4752
]
ns_list = [shocks.NormalShock(M_1, 1.4) for M_1 in M_1_list]
ns_list = [shocks.Shock(M_1=M_1, gamma=1.4) for M_1 in M_1_list]

for i in range(len(ns_list)):
np.testing.assert_almost_equal(ns_list[i].M_2, M_2_list[i], decimal=4)


def test_normal_shock_fails_subsonic_M_1():
with pytest.raises(ValueError):
shocks.NormalShock(0.8)
shocks.Shock(M_1=0.8)


def test_normal_shock_ratios():
Expand All @@ -78,7 +78,7 @@ def test_normal_shock_ratios():
1.7705,
2.6790
]
ns_list = [shocks.NormalShock(M_1, 1.4) for M_1 in M_1_list]
ns_list = [shocks.Shock(M_1=M_1, gamma=1.4) for M_1 in M_1_list]

for i in range(len(ns_list)):
np.testing.assert_almost_equal(
Expand All @@ -91,26 +91,26 @@ def test_normal_shock_ratios():

def test_normal_shock_infinite_limit():
gamma = 1.4
ns = shocks.NormalShock(np.inf, gamma)
ns = shocks.Shock(M_1=np.inf, gamma=gamma)
np.testing.assert_almost_equal(
ns.M_2, np.sqrt((gamma - 1) / 2 / gamma), decimal=3)
np.testing.assert_almost_equal(
ns.rho2_rho1, (gamma + 1) / (gamma - 1), decimal=3)


def test_normal_shock_zero_deflection():
ns = shocks.NormalShock(2.0)
ns = shocks.Shock(M_1=2.0)
assert ns.theta == 0.0


def test_error_max_deflection():
with pytest.raises(ValueError):
shocks.from_deflection_angle(5, np.radians(50))
shocks.Shock(M_1=5, theta=np.radians(50))


def test_error_mach_angle():
with pytest.raises(ValueError):
shocks.ObliqueShock(5, np.radians(10))
shocks.Shock(M_1=5, beta=np.radians(10))


def test_max_deflection():
Expand Down Expand Up @@ -143,7 +143,7 @@ def test_max_deflection():
def test_parallel_shock_infinity_mach():
M_1 = np.inf
beta = 0.0
os = shocks.ObliqueShock(M_1, beta)
os = shocks.Shock(M_1=M_1, beta=beta)
assert os.M_1n == 0.0
assert np.isfinite(os.theta)

Expand All @@ -153,7 +153,7 @@ def test_oblique_shock_from_deflection_angle():
# Notice that only graphical accuracy is achieved in the original example
M_1 = 3.0
theta = np.radians(20.0)
os = shocks.from_deflection_angle(M_1, theta, weak=True)
os = shocks.Shock(M_1=M_1, theta=theta, weak=True)

np.testing.assert_almost_equal(os.M_1n, 1.839, decimal=2)
np.testing.assert_almost_equal(os.M_2n, 0.6078, decimal=2)
Expand Down

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