  This investigation aims to assess the effect of different types of actuator
forcing on the feedback loop of an under-expanded Mach 1.27 planar impinging
jet using a resolvent framework. To this end, we employ a Large Eddy Simulation
database as a truth model. The time and spanwise-averaged mean flow is taken as
an input to global stability and resolvent analyses with the purpose of
examining both the intrinsic instability and input-output characteristics. The
results show that the inherent instability and primary energy amplification are
attributed to the Kelvin-Helmholtz (K-H) instability. Moreover, the K-H
response modes obtained from the resolvent analysis are in reasonable agreement
with Spectral Proper Orthogonal Decomposition (SPOD) modes from the unsteady
LES data. Insights into noise control are obtained by localizing the actuator
forcing to the nozzle lip and the ground plate by imposing component-wise
forcing to mimic different notional actuators. It is observed that energy
amplification obtained for the localized component-wise forcing is different
from the global resolvent analysis and dependent on the type of actuator. This
provides insights into the type, wavenumber, and frequency of actuators for
active flow control.
