In this study, the nozzle flow influence on the forebody aerodynamics has been numerically investigated and validated with experiment. To understand the nozzle flow aerodynamics on the forebody, five different nozzle-exit profiles, which are often encountered in the experiments, are considered one at a time. One flow condition is considered at a nominal freestream Mach number of 4. The CFD simulations are performed using a two-dimensional axisymmetric four-equation transition shear stress transport (SST) turbulence model. The numerical results are compared with the Ludwieg tube Mach 4 experimental data and showed good agreement. The numerical results showed that despite the slight effect on the wall static pressure depending on the nozzle profiles considered, the physical flow phenomena such as shock shape are directly influenced. With the undeveloped nozzle flow profile case, however, significant pressure differences are observed. The distance between the model and the nozzle exit may significantly affect the forebody aerodynamic characteristics, and so, the consideration of the distance between the model and nozzle exit needs to be placed during the model setup to reduce the unwanted uncertainty in the measurement.