Stabilization of a nozzle boundary layer by local surface heating

On the bask of earlier experiments demonstrating that boundary-layer transition in a supersonic nozzle can be moved upstream by local surface cooling, transition delay was sought by locally heating the nozzle surface. This experiment was done in a two-dimensional Mach 3 DeLaval nozzle that had provisions for heating the nozzle surface at the nozzle throat by two different methods. During the tests the surface temperature was increased up to a maximum of about 12% of the stagnation temperature above adiabatic, and the nozzle boundary layer was probed with steady-state and dynamic pitot probes. Without heating, the test conditions were chosen so that the boundary layer downstream of the throat became turbulent by the growth and bursting of a law-frequency instability. With increasing surface temperatures the instability downstream of the throat decreased greatly in amplitude, as did the magnitude of the bursts and their frequency of occurrence. This suggests that the surface heating can play an important role in attenuating nozzle boundary-layer instabilities and delaying boundary-layer transition.