#!/usr/bin/env python
#
# pyLOM - Python Low Order Modeling.
#
# Global aerodynamic calculation routines.
#
# Last rev: 22/05/2025
import torch
from ..utils.errors import raiseError
[docs]
def global_coeff(
CoefPressure: torch.Tensor,
SRef: float,
MomentCenter: torch.Tensor,
cRef: float,
CoefSkinFriction: torch.Tensor = None,
alpha: torch.Tensor = 0,
coordinates: torch.Tensor = None,
normals: torch.Tensor = None,
) -> tuple[torch.Tensor, torch.Tensor, torch.Tensor]:
r"""
Calculate lift, drag and moment coefficients from pressure coefficient and skin friction coefficient.
Args:
CoefPressure (torch.Tensor): Tensor of shape (n,) or (n,1) with the pressure coefficients of the surface.
SRef (float): Reference area.
MomentCenter (torch.Tensor): Tensor of shape (3,) with the moment center coordinates.
cRef (float): Reference chord length.
CoefSkinFriction (torch.Tensor, optional): Tensor of shape (n,3) with the skin friction coefficients of the surface (default: `None).
alpha (torch.Tensor): Angle of attack in deg.
coordinates (torch.Tensor): Tensor of shape (n,3) with the coordinates of the surface points.
normals (torch.Tensor): Tensor of shape (n,3) with the normal vectors of the surface.
Returns:
tuple[torch.Tensor, torch.Tensor, torch.Tensor]: Coefficients of lift (CL), drag (CD) and moment (CM) respectively.
"""
if normals.ndimension() == 1 or normals.shape[1] == 1:
normals = normals.view(-1, 3)
if normals.shape[1] != 3:
raiseError(f"Normals must have shape (n,3).")
if coordinates.ndimension() == 1 or coordinates.shape[1] == 1:
coordinates = coordinates.view(-1, 3)
if coordinates.shape[1] != 3:
raiseError(f"Coordinates must have shape (n,3).")
alpha = alpha*torch.pi/180
r = coordinates - MomentCenter.view(1, 3)
# Pressure forces
ForcePressure = torch.zeros_like(coordinates)
CoefLiftPressure, CoefDragPressure, CoefMomentPressure = 0, 0, 0
if CoefPressure is not None:
if CoefPressure.ndimension() == 1 or CoefPressure.shape[1] == 1:
ForcePressure = -CoefPressure.view(-1, 1) * normals
CoefLiftPressure = torch.sum(ForcePressure[:, 2]*torch.cos(alpha) - ForcePressure[:, 0]*torch.sin(alpha))
CoefDragPressure = torch.sum(ForcePressure[:, 2]*torch.sin(alpha) + ForcePressure[:, 0]*torch.cos(alpha))
CoefMomentPressure = torch.sum(torch.linalg.cross(r, ForcePressure)[:,1])
else:
raiseError(f"CoefPressure must have shape (n,) or (n,1).")
# Skin friction forces
ForceFriction = torch.zeros_like(coordinates)
CoefLiftFriction, CoefDragFriction, CoefMomentFriction = 0, 0, 0
if CoefSkinFriction is not None:
if CoefSkinFriction.ndimension() == 1:
CoefSkinFriction = CoefSkinFriction.view(-1, 3)
elif CoefSkinFriction.shape[1] != 3:
raiseError(f"CoefSkinFriction must have shape (n,3).")
Si = torch.norm(normals, dim=1).view(-1, 1)
ForceFriction = CoefSkinFriction * Si
CoefLiftFriction = torch.sum(ForceFriction[:, 2]*torch.cos(alpha)) - torch.sum(ForceFriction[:, 0]*torch.sin(alpha))
CoefDragFriction = torch.sum(ForceFriction[:, 2]*torch.sin(alpha)) + torch.sum(ForceFriction[:, 0]*torch.cos(alpha))
CoefMomentFriction = torch.sum(torch.linalg.cross(r, ForceFriction)[:,1])
if CoefPressure is None and CoefSkinFriction is None:
raiseError(f"At least one of CoefPressure or CoefSkinFriction must be provided.")
# Coefficients
CM = (CoefMomentPressure + CoefMomentFriction) / (SRef * cRef)
CL = (CoefLiftPressure + CoefLiftFriction) / SRef
CD = (CoefDragPressure + CoefDragFriction) / SRef
return CL, CD, CM
