Studies on Suddenly Expanded Flow at Different Levels of Over Expansion for Area Ratio 3.24

Abstract- The experiments are carried out to study the effect of different levels of over expansion on base pressure in a suddenly expanded axi-symmetric duct. Accordingly the experiments are conducted at two different levels of Over Expansions (I.e. Pe/Pa = 0.277 and 0.56). The area ratio of the present study is 3.24. The jet Mach numbers at the entry to the suddenly expanded duct, studied are 2.2 and 2.58. The length-to-diameter ratio of the suddenly expanded duct is varied from 10 to 1. Active control in the form of four micro jets of 1mm orifice diameter located at 90 0 intervals along a pitch circle diameter of 1.3 times the nozzle exit diameter in the base region are employed. In addition to base pressure, wall pressure field along the duct is also studied. From the present studies it is found that at a high level of over expansion micro jets are not effective. Further, it is found from wall pressure studies that the micro jets do not disturb the flow field in the enlarged duct