Supersonic boundary-layer stability in a high-area-ratio nozzle

Previous studies found that the wall heat flux measured experimentally in the NASA Lewis high-area-ratio nozzle was not always described accurately by laminar or fully turbulent boundary-layer computations. These results suggest that the boundary layer undergoes transition. In the present paper, the e^N method was used to determine which operating conditions produced boundary-layer transition in the nozzle. The study verifies the accuracy of the e^N method for combusting flows. If transition resulted, the stability analysis provided the location of transition onset as well as the structure and wavelength of the dominant instability. Tollmien- Schlichting waves and Taylor-Gortler vortices were considered as possible disturbance structures which trigger transition. When the chamber pressure was 2482 kPa, the stability analysis indicated that transition did not occur in the nozzle. The analysis correctly determined that a laminar boundary-layer computation accurately predicts the experimental wall heat flux. For chamber pressures of 4523 kPa and above, it was found that Taylor-Gortler vortices produced transition in the nozzle. At these conditions, the laminar boundary-layer computation did not accurately predict the wall heat flux. The stability analysis can be used to establish the nozzle conditions which will be accurately predicted by a laminar boundary-layer computation.