Cp (Pressure Coefficient)

Computation of pressure coefficient


  • base: Base

    The base must contain:

    • the mesh coordinates x, y, and z

    • the solution

    • ‘hb_computation’ as an Base.attrs (if HB/TSM type).

  • 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 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.


Return type



import os

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

from antares import Reader, Treatment, Writer


# Data can be downloaded from
# https://cerfacs.fr/antares/downloads/application1_tutorial_data.tgz

r = Reader('bin_tp')
r['filename'] = os.path.join('..', 'data', 'ROTOR37', 'ELSA_CASE', 'MESH',
r['zone_prefix'] = 'Block'
r['topology_file'] = os.path.join('..', 'data', 'ROTOR37', 'ELSA_CASE',
r['shared'] = True
base = r.read()

r = Reader('bin_tp')
r['base'] = base
r['filename'] = os.path.join('..', 'data', 'ROTOR37', 'ELSA_CASE', 'FLOW',
r['zone_prefix'] = 'Block'
r['location'] = 'cell'


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

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['family_name'] = 'BLADE'
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):

writer = Writer('column')

for loc in [0.25, 0.5, 0.75, 0.9]:  # radius in percent
    t['percent'] = loc
    Cp_blade = t.execute()

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