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7.1.9 Defining Transient Boundary Conditions

There are two ways you can specify transient boundary conditions:

figure   

For both methods, the boundary condition will vary only in time; it must be spatially uniform. However, if the in-cylinder model is activated (Section  11.7.1), then you have the option to use the crank angle instead of time. Crank angles can be included in transient tables as well as transient profiles, in a similar fashion to time. Examples of transient profiles and transient tables in crank angle can be found in the sections that follow.



Standard Transient Profiles


The format of the standard transient profile file (based on the profiles described in Section  7.26) is

((profile-name transient n periodic?)
(field_name-1 a1 a2 a3 .... an)
(field_name-2 b1 b2 b3 .... bn)
.
.
.
.
(field_name-r r1 r2 r3 .... rn))

One of the field_names should be used for the time field, and the time field section must be in ascending order. The periodic? entry indicates whether or not the profile is time-periodic. Set it to 1 for a time-periodic profile, or 0 if the profile is not time-periodic.

An example is shown below:

((sampleprofile transient 3 0)
(time
1
2
3
)
(u
10
20
30
)
)

This example demonstrates the use of crank angle in a transient profile

((example transient 3 1)
(angle
0.000000e+00 1.800000e+02 3.600000e+02)
(temperature
3.000000e+02 5.000000e+02 3.000000e+02)
)

figure   

All quantities, including coordinate values, must be specified in SI units because FLUENT does not perform unit conversion when reading profile files. Also, boundary profile names must have all lowercase letters (e.g., name). Uppercase letters in boundary profile names are not acceptable.

You can read this file into FLUENT using the Boundary Profiles panel or the File/Read/Profile... menu item.

Define $\rightarrow$ Profiles...

File $\rightarrow$ Read $\rightarrow$ Profile...

See Section  7.26.3 for details.



Tabular Transient Profiles


The format of the tabular transient profile file is

profile-name n_field n_data periodic?
field-name-1 field-name-2 field-name-3 .... field-name-n_field
v-1-1   v-2-1  ... ... ... ... v-n_field-1
v-1-2   v-2-2  ... ... ... ... v-n_field-2
.
.
.
.
.
v-1-n_data v-2-n_data ... ... ... ... v-n_field-n_data

The first field name (e.g. field-name-1) should be used for the time field, and the time field section, which represents the flow time, must be in ascending order. The periodic? entry indicates whether or not the profile is time-periodic. Set it to 1 for a time-periodic profile, or 0 if the profile is not time-periodic.

An example is shown below:

sampletabprofile 2 3 0
time u
1 10
2 20
3 30

This file defines the same transient profile as the standard profile example above.

If the periodicity is set to 1, then n_data must be the number that closes one period.

An example is shown below:

periodtabprofile 2 4 1
time u
0 10
1 20
2 30
3 10

The following example uses crank angle instead of time:

example 2 3 1
angle temperature
0   300
180 500
360 300

figure   

All quantities, including coordinate values, must be specified in SI units because FLUENT does not perform unit conversion when reading profile files. Also, boundary profile names must have all lowercase letters (e.g., name). Uppercase letters in boundary profile names are not acceptable. When choosing the field names, spaces or parentheses should not be included.

You can read this file into FLUENT using the read-transient-table text command.

file $\rightarrow$ read-transient-table

After reading the table into FLUENT, the profile will be listed in the Boundary Profiles panel and can be used in the same way as a boundary profile. See Section  7.26.3 for details.


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© Fluent Inc. 2006-09-20