Modules in FluidSF¶

Generate Structure Functions¶

FluidSF supports 1D, 2D, and 3D data, and uses a distinct module to generate (and output) structure functions for each of these systems:

generate_structure_functions_2d()

Generates structure functions from 2D data. It generates two sets of structure functions, one with \(x\)-directed separation vectors, and the other with \(y\)-directed separation vectors. It supports the calculation of second- and third-order SFs of velocity and/or scalars, and advective structure functions.

generate_structure_functions_3d()

Generates structure functions from 3D data. Has the same functionality as generate_structure_functions_2d(), and generates three sets of SFs (with \(x\)-, \(y\)-, and \(z\)-directed separation vectors).

generate_structure_functions_1d()

Generates structure functions from 1D data. It has the same functionality as generate_structure_functions_2d(), except it cannot diagnose advective structure functions, since these require multi-directional information to diagnose the required gradients. It generates one set of SFs (\(x\)-directed separation vectors).

Generating 2D Maps of Structure Functions

There is also a module that calculates the 2D spatial variations of structure functions.

generate_sf_maps_2d()

Generates a 2D field of structure function values as a function of separation distance and direction. This module can only be applied to evenly-spaced data from domains that are periodic in both directions. It supports the calculation of second- and third-order SFs of velocity and/or scalars, and advective structure functions.

Important

All the above modules can generate several types of structure functions as a function of separation distance. These are the primary modules that users will interact with. The modules described below are helper modules used by the above modules.

Do not get confused between generate_() and calculate_() ** modules. The latter are used to calculate a single structure function value for a given separation vector, generate_() modules then accumulate this information for a range of separation distances.**

Calculate Structure Functions¶

calculate_structure_function_1d(), calculate_structure_function_2d(), calculate_structure_function_3d(), calculate_sf_maps_2d()

These modules calculate the average structure functions for a given separation vector and flow field snapshot. They are called by their respective generate_structure_function_ modules, and calculate all the structure functions that are requested by the user. These modules utilize the shift array utilities discussed below.

Utilities¶

Shift Arrays¶

shift_array_1d(), shift_array_2d(), and shift_array_3d()

These modules shift data arrays in a specific direction (x, y or z) and by specific number of array elements, to efficiently calculate structure functions. The modules are used for 1D, 2D and 3D data respectively. The generate_() modules iterate over the approprite number of dimensions and element-shifts.

shift_array_xy()

This module shifts 2D data arrays in two simultaneous directions (x and y) by a module-specified number of array elements that can differ between the two directions. This module is utilized by generate_sf_maps_2d().

Calculate Separation Distance¶

calculate_separation_distances()

This module calculates the separation distance between pairs of points in a 1D dataset, or in a 2D Cartesian or latitude-longitude grid. For latitude-longitude grids, the module utilizes a Great Circle function to calculate the separation distance.

calculate_separation_distances_3d()

This module calculates the separation distance between pairs of points in a 3D Cartseian grid.

Bin Data¶

bin_data()

This module bins structure function data based on separation distances, and calculates the bin-averaged structure functions.

Calculate Advection¶

calculate_advection_2d(), calculate_advection_3d()

These modules process the provided velocity fields and grid information to diagnose the advection (vector) field required to calculate advective structure functions. Since the advective structure functions are supported in 2D and 3D, there are two versions of this module.