Numerical investigation of rotating detonation engine has become essential to study its complex flow field. In the present study, a three-dimensional simulation is performed on the rotating detonation engine combustor using URANS model. Hydrogen-air is used as a premixed mixture injected into the combustion chamber at an equivalence ratio of 1. Temporal variation and contour plots of the detonation properties and their effect on inner and outer cylinders forming the annulus of the RDE combustor are investigated using the commercial ANSYS Fluent software. Variation of flow properties as a function of time at a point 3 mm from the injection plane has been studied. Effect of width of the combustor is ignored in 2D simulations. But these variations may be noticeable if the width of the combustor is more like in the case of kerosene-air system, where the detonation width is large. The CFD modeling gave rise to finding the maximum number of waves in a cycle. Large flow rates give rise to the production of more number of waves in a cycle. The detonation waves are sharing the mass flow rate from the plenum chamber. CFD simulations provide the information on the total number of waves, which can be sustained per cycle of operation.