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 ________________________________ From: Ben <3507457038@qq.com> Sent: 15 December 2025 07:51 To: nektar-users <nektar-users@imperial.ac.uk> Subject: [Nektar-users] how to implement active flow control This email from 3507457038@qq.com originates from outside Imperial. Do not click on links and attachments unless you recognise the sender. If you trust the sender, add them to your safe senders list<https://spam.ic.ac.uk/SpamConsole/Senders.aspx> to disable email stamping for this address. Dear all, I am a novice in fluid simulation. Ask nektar++how to implement active flow control, such as injection and suction. Can you provide me with a classic case for my reference? Everyone can offer their opinions.Looking forward to your reply！