This paper presents a method to compute flows around arbitrary obstacles providing a CFD solution within an acceptable time frame, by alleviating the tedious task of meshing complex aerodynamics configurations. This method is based on an Immersed Boundary Method (IBM), where the bodies are immersed within the mesh and relies on the automatic generation of adaptive Cartesian grids. The workflow starts by generating the Cartesian mesh around the different bodies involved into the study given the surface mesh of the different geometrical components and the near-wall resolution around them. The present IBM requires in a preprocessing step to compute some information that will be used during the simulation in order to mimic the wall boundary condition near bodies. The present approach is based on a Cartesian mesh, thus a wall model is used to mitigate the number of points required to solve the RANS equations with an acceptable accuracy. A grid convergence study is achieved on the turbulent transonic flow around a RAE2822 profile, in order to quantify which near-wall resolution is necessary for a given accuracy of the solution. Once these figures are determined, a simulation of the turbulent transonic flow around the NASA Common Research Model is achieved. Finally a demonstration of the capability of the method to perform CFD simulations of a complex geometry is achieved on a helicopter rotor head.