Bickley jet FTLE

Compute the FTLE field for the bickley jet.

# Author: ajarvis

import numpy as np
from math import copysign
import matplotlib.pyplot as plt
from numbacs.flows import get_predefined_flow
from numbacs.integration import flowmap_grid_2D
from numbacs.diagnostics import ftle_grid_2D

Get flow

Set the integration span and direction, retrieve the flow, and set up domain.

# set initial time, integration time, and integration direction
t0 = 0.0
T = 6.0
int_direction = copysign(1, T)

# retrieve function pointer, parameters, and domain for bickley jet flow.
funcptr, params, domain = get_predefined_flow("bickley_jet", int_direction=int_direction)

# set up domain
dx = 0.05
dy = 0.05
x = np.arange(domain[0][0], domain[0][1] + dx, dx)
y = np.arange(domain[1][0], domain[1][1] + dy, dy)
dx = x[1] - x[0]
dy = y[1] - y[0]

Integrate

Integrate grid of particles and return final positions.

flowmap = flowmap_grid_2D(funcptr, t0, T, x, y, params)

FTLE

Compute FTLE field from final particle positions.

ftle = ftle_grid_2D(flowmap, T, dx, dy)

Plot

Plot the results.

fig, ax = plt.subplots(dpi=200)
ax.contourf(x, y, ftle.T, levels=80)
ax.set_aspect("equal")
plt.show()