© 2018 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.An open cavity flow contains a highly turbulent shear layer which separates from the upstream edge and impinges on the aft wall of the cavity, causing intense noise emission. In this study, a delayed detached-eddy simulation (DDES) with the use of "shear-layer-adapted" subgrid length scale, an enhancement of DDES available in literature, is conducted for such an open cavity flow problem. The results show that this length scale unlocks the Kelvin-Helmholtz (K-H) instability, and accelerates the transition from modeled to resolved mode of DDES. Thus, the accuracy of capturing the flow profile near the shear layer separation zone, where K-H instability is dominant, increases. However, quite dense mesh resolution is required to simulate the aft wall region due to the log layer mismatch problem of DDES. On the other hand, the frequencies of dominant pressure modes are predicted accurately.