# Cp (Pressure Coefficient)¶

Computation of pressure coefficient

## Parameters¶

• base: Base

The base must contain:

• coordinates: list(str)

The variable names that define the set of coordinates.

• vectors: tuple/list(tuple(str)), default= []

Component names of vectors that need to be rotated. It is assumed that these are given in the cartesian coordinate system.

• rho_inf: float, default= ‘in_attr’

The infinite density corresponding to the reference state.

• v_inf: float, default= ‘in_attr’

The infinite axial velocity corresponding to the reference state.

• p_inf: float, default= ‘in_attr’

The infinite static pressure corresponding to the reference state.

• family_name: str

The name of the family from which the percent will be computed and on which Cp is computed.

• percent: float, default= None

The percentage relative to the family to determine the absolute position value.

• position: float, default= None

The absolute position value relative to the family where the cut must be made.

• form: int in [1,2,3], default= 1

The definition of Cp (see below).

## Main functions¶

class antares.treatment.turbomachine.TreatmentCp.TreatmentCp
execute()

Execute the treatment.

Compute the pressure coefficient at a given radius percent of the given blade. Thee formulae for Cp are proposed:

form 1: $$\displaystyle Cp_1 = - \frac{p - p_{inf}}{\rho_{inf} n^2 D^2}$$

form 2: $$\displaystyle Cp_2 = 2 \frac{p - p_{inf}}{\rho_{inf} (v_{inf} n^2 r^2)}$$

form 3: $$\displaystyle Cp_3 = 2.0 \frac{p - p_{inf}} {\rho_{inf} v_{inf} ^ 2}$$.

The mean and the harmonics of Cp can also be computed if duplication is enabled. Note that the amplitude of the harmonics are divided by the mean value.

Returns:

Return type:

Base

## Example¶

import os

if not os.path.isdir('OUTPUT'):
os.makedirs('OUTPUT')

from antares import Reader, Treatment, Writer

#

r['filename'] = os.path.join('..', 'data', 'ROTOR37', 'ELSA_CASE', 'MESH',
'mesh_<zone>.dat')
r['zone_prefix'] = 'Block'
r['topology_file'] = os.path.join('..', 'data', 'ROTOR37', 'ELSA_CASE',
'script_topo.py')
r['shared'] = True
print(base.families)

r['base'] = base
r['filename'] = os.path.join('..', 'data', 'ROTOR37', 'ELSA_CASE', 'FLOW',
'flow_<zone>.dat')
r['zone_prefix'] = 'Block'
r['location'] = 'cell'

base.set_computer_model('internal')

# Needed for turbomachinery dedicated treatments
base.cell_to_node()
base = base.get_location('node')
print(base.families)

base.compute('psta')
base.compute('Pi')
base.compute('theta')
P0_INF = 1.9
base.compute('MachIs = (((%f/psta)**((gamma-1)/gamma)-1.) * (2./(gamma-1.))  )**0.5' % P0_INF)

# Definition of the treatment
t = Treatment('Cp')
t['base'] = base
t['coordinates'] = ['x', 'y', 'z']
t['rho_inf'] = 0.873
t['p_inf'] = 0.59
t['v_inf'] = 1.5
t['form'] = 3

# Cp
res_dir = os.path.join('OUTPUT', 'CP')
if not os.path.isdir(res_dir):
os.makedirs(res_dir)

writer = Writer('column')

for loc in [0.25, 0.5, 0.75, 0.9]:  # radius in percent
t['percent'] = loc

writer['filename'] = os.path.join(res_dir, 'Cp_%s.dat' % (loc))