Detached eddy simulation is used to simulate three cases of helium injection into a supersonic freest r earn for which experimental measurements of helium mass fraction are available. Reynolds-averaged Navier-Stokes simulations of each case are used for comparison. Two of the cases involve low-angled injection into a Mach 4.0 freestream, one being a single, circular cross section injector and the other being an array of four circular cross section injectors. The injection in the third case takes place through a circular cross section that is normal to the Mach 3.0 freestream. To more realistically model the preinjection boundary layer, a simple and inexpensive method is used to provide a time-varying boundary condition for the DES. The synthetic inflow boundary layer only resolves the largest structures of the boundary layer and provides statistically meaningful perturbations to the jet plume. For the two Mach 4.0 cases, the DES with the synthetic boundary layer is found to reproduce the width of the jet plume well. The maximum mean helium mass fraction also compares well to the measurements for the single-hole injector, but is under predicted for the four-injector array by both the DES and RANS. The four injector array was run with synthetic inflow boundary layers of length 15δ and 30δ, with the results showing that the calculation is not highly sensitive to this change in length of the inflow boundary layer. Comparing the two low-angled injector configurations, the DES is found to reproduce the trends seen in the experiment for enhanced spanwise mixing, mixing efficiency and pressure losses. Mean helium mass fraction contours are compared with experiment at two downstream data planes for the normal injection. At both data stations the DES over-predicts the mean height of the core of the jet plume (location of maximum helium concentration), but captures the overall plume height better than RANS. The rate of maximum mean helium mass fraction decay is higher for the DES than the experiment, however, the rate of core penetration is comparable to the experiment.