The study of three-dimensional open cavity flow with and without cover plates at the edges of the cavity at freestream Mach number of 0.85 was performed. Such open cavities find their application in landing gear wells, bomb bay of an airplane and sunroof or window of an automobile. The aerodynamic noise and the flow field together in the above mentioned cavities lead to self-sustaining flow oscillations. These self-sustaining flow oscillations results in the structural failure in the surrounding of the cavity due to resonance phenomenon in the aircrafts and lead to loud and unbearable noise both in aircrafts and automobiles. Understanding this aeroacoustic phenomenon helps us in reducing the noise, increase the component stability and passenger comfort. Therefore, this problem has become an important topic of research for several decades in aerospace and automobile fields. In this thesis an effort was made to investigate the fully developed turbulent flow over an open cavity and to evaluate the effect of cover plates numerically using the detached eddy simulation (DES) formulation. For this purpose, computational fluid dynamics approach was utilized on the M219 cavity at Mach 0.85 using DES with the Spalart-Allmaras (S-A) turbulence model. Two cavity cases were modeled. The test case 1 is a three-dimensional open cavity without cover plates and the test case 2 is a three-dimensional open cavity with cover plates at the edges of the cavity. Furthermore, three variants of DES were considered for the test case 2 cavity namely Spalart- Allmaras, k-ω-SST and realizable k-ε model, whereas for the test case 1 cavity only the DES S-A model was employed.