This article discusses the mechanism for prediction of aeroacoustic resonance in cavities of hole-pattern stator seals. A Reynolds-averaged Navier–Stokes (RANS) solver developed in-house was used to simulate grazing channel flow past a cavity located in a channel. The numerical results generated with the RANS solver showed good agreement with those obtained using a commercial large eddy simulation code. In addition, the numerical results agreed well with the experimental data. Rossiter’s formula, a popular semi-empirical model used to predict frequencies of holetone acoustic instabilities caused by grazing fluid flow past open cavities, was modified using the RANS solver results to allow for its application to channel flows. This was done by modifying the empirical constant, the ratio of vortex velocity, and the freestream velocity. The RANS solver accurately captured the salient features of the flow/acoustic interaction and predicted well the dominant acoustic frequencies measured in an experimental investigation. The flow solver also provided detailed physical insight into the cavity flow instability mechanism.