Python interface to OpenFOAM

We provide a simple python interface for reading OpenFOAM case results and dictionaries. A more comprehensive interface is available through pyFoam although we found it difficult to use and without recent support, which motivated the implementation of a new python interface.

Read fields

Internal scalar and vector fields

Currently internal scalar and vector fields can be read using the python interface. In particular, note that

1. We do not support reading tensor fields for now.

2. We do not support reading boundary fields for now.

3. We only read reconstructed files

We are open to implementing 1. and 2. if need be. Implementing 3. is possible but will be more involved.

The main function interface to read openFOAM fields is readOF in bird.utilities.ofio

The function only reads fields written in ASCII format and decided based on the header whether the field is a scalar or a vector. In the case of scalar, readOF returns a (N,) numpy array, where N is the number of computational cells. In the case of a vector, readOF returns a (N,3) numpy array.

If a uniform field is read, the number of cells may not be available from the field file and the function returns a float (equal to the uniform internal field value). If a numpy array is needed, the user can specify the number of cells in the field as an input.

Reuse instead of re-read

The read_field function uses readOF and takes a dictionary field_dict as input which is used to avoid reading multiple times the same field. For example, if one wants to compute the reactor-averaged concentration of a species, and then the reactor-averaged mass fraction of a species, the same mass fraction field will be used in both cases. As fields are read, field_dict will store the mass fraction field and recognize that the same field is needed.

It is up to the user to reinitialize field_dict. For example, if the reactor-averaged mass fraction needs to be computed at time 1 and then at time 2, the user needs to pass an empty dictionary (or nothing) to read_field before reading the fields at time 2. Otherwise, read_field will assume that the mass fraction field is the same between time 1 and time 2.

Read mesh-related fields

We rely on OpenFOAM utilities to provide mesh-based fields. The results of the OpenFOAM utilities can still be processed using bird functions.

Reading cell volumes

A cell volume field can be generated using the following OpenFOAM command postProcess -func writeCellVolumes -time {time_folder} -case {case_folder} It will generate a file {time_folder}/V which can be read with the readOF function of bird. This workflow is used in bird.postprocess.post_quantitities, for example in the compute_gas_holdup function.

Reading cell centers

A mesh object file can be generated with the OpenFOAM command writeMeshObj -case {case_folder} The file can then be read with the function readMesh from bird.utilities.ofio. Again, this is used in bird.postprocess.post_quantities in the compute_superficial_velocity function.

Read dictionaries

We provide a function read_openfoam_dict in bird.utilities.ofio that can parse OpenFOAM dictionaries. The function requires a lot of special characters handling but works for processing basic dictionaries needed to manage OpenFOAM cases (controlDict, setFieldsDict, phaseProperties, thermophysicalProperties, momentumTransport, …)

Generate cases

(to be added based on the reactor optimization work)