Hello Ben,
I have done a little bit of this in nektar. Depends whether you want to excite in the boundary or inside the domain.
Boundary: Here you need to specify the timeDependent argument if you want to define perturbations in the boundary thatdepend on time.
<BOUNDARYCONDITIONS>
<REGION REF="0"> <!-- inlet !-->
<D VAR="u" VALUE="0" />
<D VAR="v" VALUE="0" />
<N VAR="p" USERDEFINEDTYPE="H" VALUE="0" />
</REGION>
<REGION REF="1"> <!-- outlet !-->
<N VAR="u" VALUE="0" />
<N VAR="v" VALUE="0" />
<D VAR="p" VALUE="0" />
</REGION>
<REGION REF="2"> <!-- top = far-field !-->
<D VAR="u" VALUE="0" />
<D VAR="v" VALUE="0" />
<N VAR="p" USERDEFINEDTYPE="H" VALUE="0" />
</REGION>
<REGION REF="3"> <!-- bottom = wall no slip !-->
<D VAR="u" VALUE="0" />
<D VAR="v" USERDEFINEDTYPE="TimeDependent" VALUE="Amplitude*exp(-weight*(x-x0)^2)*awgn(1.0)" />
<N VAR="p" USERDEFINEDTYPE="H" VALUE="0" />
</REGION>
</BOUNDARYCONDITIONS>
Interior: I used a whie gaussian noise function which then will be applied as a body force in the equations. All the parameters you need, you can define them in the parameters section.
<CONDITIONS>
<PARAMETERS>
...
<P> x0 = -95 </P>
<P> y0 = 0.5 </P>
<P> weight = 100 </P> <!-- weight of the Gaussian function !-->
<P> Amplitude = 0.5/weight </P>
...
</PARAMETERS>
...
<FUNCTION NAME="Noise">
<E VAR="u" VALUE="-2*weight*(y-y0)*Amplitude*exp(-weight*((x-x0)^2 + (y-y0)^2))*awgn(1.0)" />
<E VAR="v" VALUE="2*weight*(x-x0)*Amplitude*exp(-weight*((x-x0)^2 + (y-y0)^2))*awgn(1.0)" />
<E VAR="p" VALUE="0" />
</FUNCTION>
...
</CONDITIONS>
<FORCING>
<FORCE TYPE="Field">
<FIELDFORCE> Noise </FIELDFORCE>
</FORCE>
</FORCING>
<FILTERS>
...
</FILTERS>
Hope it helps
Best,
V