  The decomposition of hydrodynamic and acoustic components of cavity flows can
aid the understanding of the flow-acoustic interaction, which produces a
variety of adverse effects in applications. We apply the approach of combining
the resolvent analysis and Doak's momentum potential theory to examine the
input-output flow-acoustic characteristics of compressible flow over an open
cavity at Re=10,000. The methodology can decompose hydrodynamic and acoustic
components from an input-output framework. We further localize the forcing at
the leading-edge and front wall of the cavity and filter with a single
component of velocity, density, and temperature forcing. For the subsonic flow
at M=0.6, The strong acoustic component appears at the trailing edge of the
cavity at a lower frequency. while as the frequency increases, the intense
acoustic structure moves close to upstream and overlap with the hydrodynamic
component. This tendency is also observed in the supersonic flow condition
M=1.4. Compared to different types of forcing, the streamwise velocity forcing
achieves the largest energy amplification. However, it substantially reduces by
moving the forcing location from the leading-edge to the front wall of the
cavity. This work provides an alternative approach to examine input-output
flow-acoustic characteristics where resonance is dominant and provides guidance
for the development of flow control strategies.
