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Add swept (projected) area option for turbines #390

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Add swept (projected) area option for turbines #390

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3 changes: 3 additions & 0 deletions thetis/options.py
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Original file line number Diff line number Diff line change
Expand Up @@ -462,6 +462,9 @@ class TidalTurbineOptions(FrozenHasTraits):
name = 'Tidal turbine options'
diameter = PositiveFloat(
18., help='Turbine diameter').tag(config=True)
swept_diameter = PositiveFloat(
None, allow_none=True, help='Projected diameter of the turbine '
'(defaults to diameter if not provided)').tag(config=True)
C_support = NonNegativeFloat(
0., help='Thrust coefficient for support structure').tag(config=True)
A_support = NonNegativeFloat(
Expand Down
19 changes: 14 additions & 5 deletions thetis/turbines.py
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Original file line number Diff line number Diff line change
Expand Up @@ -14,22 +14,31 @@
class TidalTurbine:
def __init__(self, options, upwind_correction=False):
self.diameter = options.diameter
self.swept_diameter = options.swept_diameter or self.diameter
self.C_support = options.C_support
self.A_support = options.A_support
self.upwind_correction = upwind_correction

# Check that the parameter choices make some sense - these won't break
# the simulation but may give unexpected results if the choice isn't
# understood.
if self.swept_diameter != self.diameter:
log(INFO, 'Warning - swept_diameter and plan_diameter are not equal. '
'Upwind correction may not be accurate.')

def _thrust_area(self, uv):
C_T = self.thrust_coefficient(uv)
A_T = pi * self.diameter**2 / 4
fric = C_T * A_T
A_T = pi * self.swept_diameter**2 / 4
swept_area_factor = self.diameter**2/self.swept_diameter**2
fric = C_T * A_T * swept_area_factor
if self.C_support:
fric += self.C_support * self.A_support
return fric

def velocity_correction(self, uv, depth):
fric = self._thrust_area(uv)
if self.upwind_correction:
return 0.5*(1+sqrt(1-fric/(self.diameter*depth)))
return 0.5*(1+sqrt(1-fric/(self.swept_diameter*depth)))
else:
return 1

Expand All @@ -41,7 +50,7 @@ def friction_coefficient(self, uv, depth):
def power(self, uv, depth):
# ratio of discrete to upstream velocity (NOTE: should include support drag!)
alpha = self.velocity_correction(uv, depth)
A_T = pi * self.diameter**2 / 4
A_T = pi * self.diameter**2 / 4 # power is based on true turbine diameter
uv3 = dot(uv, uv)**1.5 / alpha**3 # upwind cubed velocity
C_P = self.power_coefficient(uv3**(1/3))
# this assumes the velocity through the turbine does not change due to the support (is this correct?)
Expand Down Expand Up @@ -156,7 +165,7 @@ def add_turbines(self, coordinates):
"""
x = SpatialCoordinate(self.mesh)

radius = self.turbine.diameter * 0.5
radius = self.turbine.swept_diameter * 0.5
for coord in coordinates:
dx0 = (x[0] - coord[0])/radius
dx1 = (x[1] - coord[1])/radius
Expand Down