STABILIZATION OF A NOZZLE BOUNDARY-LAYER BY LOCAL SURFACE HEATING

On the bask of earlier experiments demonstrating that boundary-layer t ransition in a supersonic nozzle can be moved upstream by local surfac e cooling, transition delay was sought by locally heating the nozzle s urface. This experiment was done in a two-dimensional Mach 3 DeLaval n ozzle that had provisions for heating the nozzle surface at the nozzle throat by two different methods. During the tests the surface tempera ture was increased up to a maximum of about 12% of the stagnation temp erature above adiabatic, and the nozzle boundary layer was probed with steady-state and dynamic pitot probes. Without heating, the test cond itions were chosen so that the boundary layer downstream of the throat became turbulent by the growth and bursting of a law-frequency instab ility. 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 bound ary-layer instabilities and delaying boundary-layer transition.