Fluid–acoustic interactions are important in a variety of applications and typically result in
adverse effects. We analyze the influence of Mach number on such interactions and their
input–output characteristics by combining resolvent analysis with Doak's momentum
potential theory. The specific problem selected is the flow over an open cavity of L∕ D= 6 at
Re= 10 000 and M∞= 0.6 and 1.4, respectively. The resolvent forcing and response modes
are decomposed into their hydrodynamic, acoustic, and thermal components. Although the …