Reynolds Number Influence on Dual-Bell Transition Phenomena

Abstract

An experimental investigation was conducted to study the Reynolds number influence on dual-bell transition behavior for tests inside a high-altitude simulation chamber. For the range of nozzle supply pressures tested, the nozzle Reynolds number is seen to gradually decrease from a relatively high value (of the order of for tests in sea-level atmospheric conditions) toward the transitional range (lower side of for tests inside the high-altitude chamber). This influences the width of the inflection region, which is seen to decrease with an increase in nozzle Reynolds number. Because of the smaller negative pressure gradient experienced during sneak transition with a decrease in nozzle Reynolds number, the separation point is seen to move into the region of wall inflection much earlier and tends to stay in the region of wall inflection for a relatively longer time. Although the time duration of final transition remains more or less constant for different nozzle supply pressure values, the time duration for the separation point to move from its location at the inflection point to the point of minimum wall pressure in nozzle extension shows a significant increase in value with a decrease in nozzle Reynolds number. These conditions are conducive in delaying the transition to higher nozzle pressure ratios with a decrease in nozzle supply pressure. The preceding study therefore indicates that the scaling effects can very strongly dominate the results of dual-bell tests conducted inside high-altitude test facilities.