spaceTimeInterpolation Module

Stream has a module that provides users with a general capability for specifying spatially and temporally varying boundary conditions for the various inflow boundary types. This capability is enabled by inserting the following loadModule directive into the run control file as shown below.

loadModule: spaceTimeInterpolation
{
... standard run control file content
}

The following sections discuss the space-time interpolation module and provide information on the run control file variables required to perform simulations with the spaceTimeInterpolation module.

Space-Time Interpolated BCs

The spaceTimeInterpolation module provides facilities for describing spatial and temporally varying boundary conditions. This boundary condition is enabled by loading this module and specifying the directory that contains the interpolation source files with the variable spaceTimeInterpolateFile. All inflow type boundary conditions that are assigned the flag spaceTimePrescribed will receive the interpolated values. The data in the directory consists of HDF5 files with a description file called data.info. Files in this directory are described with a format of filename:hdf5var where filename is the name of the HDF5 file in the directory and hdf5var is the internal HDF5 dataset name. The filename or dataset name may contain special # symbols which will be substituted for the time step number of the file used for temporal interpolation. If multiple consecutive # characters are used, then the number will be padded to that width using leading 0 characters. The # characters can be used in either the filename or hdf5var portion of the file specifier. The data.info file contains the following variables shown in the table below.

data.info File Contents

Variable	Description
positions	The positions variable specifies the file that contains the spatial locations of the input points. Note that the positions are expected to remain fixed in time and so the # symbol is not used in this file specifier.
initialStep	The initial step is the number of the first file in the time series.
lastStep	The last step is the number of the final file in the time series.
stepIncrement	The step increment gives how much the step increases between input files.
startTime	The start time is the time associated with the initial step.
deltaTime	The delta time is the temporal increment between steps.
Pambient	The reference pressure used for the gage pressure data files.
pg	The file that describes the spatially varying gage pressure at all the points described in positions.
t	The file that describes the spatially varying temperature at all the points described in positions.
v	The file that describes the spatially varying velocity vector at all the points described in positions.
k	The file that describes the spatially varying turbulent kinetic energy at all of the points described in positions.
w	The file that describes the spatially varying turbulent specific dissipation (omega) at all the points described in positions.
fspecies	Any variable that starts with an “f” character is assumed to be a mass fraction file. If no mass fraction files are specified, then the default mixture fraction specified in the chemistry mdl file will be used.

An example of a representative data.info file is given below. The data for this example was extracted from a separate simulation using the clipSurfaces functionality. The files output from this facility using a clipFreq of 10 and run for 600 timesteps were directly used by specifying the following input file:

Sample data.info file

positions: pos.0:data
initialStep: 10
lastStep: 600
stepIncrement: 10
startTime: 0
deltaTime: 1e-3
Pambient: 101325
pg: pg_sca.#:data
t: t_sca.#:data
v: v_vec.#:data
k: k_sca.#:data
w: w_sca.#:data
f_Air: fH2_sca.#:data
fH2: f_Air_sca.#:data

The clip surfaces capability allows a user to place an arbitrary infinite cutting plane within the computational domain. At the intersection of this plane with the CFD volume mesh, data is spatially interpolated using a cloud-of-points interpolator. Data extraction for the plane is controlled during a simulation by using the variables plot_output and plot_freq.

Control File Setup

Only a few additions need to be made to an existing run control file to set up a simulation using the spaceTimeInterpolation module.

// Clip surfaces.
clipFreq: 100
clipSurfaces: < xcut=plane(point=[19.999,0,0],normal=[1,0,0]) >