The drag force is an essential factor in any projectile, from road vehicles to rocket or aircraft. The total drag includes skin friction drag, wave drag, and base drag. The base drag is the drag due to low pressure in the base region of the projectile. In the case of suddenly expanded flows, due to the sudden expansion of flow from the nozzle into the enlarged duct, the low pressure is created in the base region of the enlarged tube, which results in base drag and hence overall thrust reduced. In this paper, Computational Fluid Dynamic (CFD) analysis is used to analyze the effect of secondary air blowing jets called control jets to control base pressure in the base region of suddenly enlarged duct. These control jets are placed at different Pitch Circle Diameters (PCD) on the base face of the enlarged pipe. The objective of this work is to increase the base pressure up to atmospheric pressure and hence reduces the base drag. Mach number 3.0 is considered for analysis. The CFD analysis is done for different combinations of Area Ratios (AR) (2, 5 and 8), Nozzle Pressure Ratios (NPR) (2, 5 and 8), and PCD (d1, d2, and d3). Further analysis is done for different air blowing pressure ratios (BPR) to optimize air blowing pressure. The analysis results are plotted for different area ratios, nozzle pressure ratios, and PCD of control jets. By observing results, it can be concluded that the base pressure is strongly influenced by AR, NPR, and PCD of control jets. The air blowing pressure should be optimum to save energy, and the optimum values can be selected from the results.

This paper presents the Computational Fluid Dynamic (CFD) analysis to study the effect of Mach numbers on velocity distribution at different area ratio and nozzle pressure ratio in the flow field from convergent-divergent nozzles to a suddenly expanded circular duct of larger cross-sectional area. The study is focusing on velocity distribution along axial length. The analysis is done for Mach numbers 1.4 and 1.8 by varying the area ratios and nozzle pressure ratios. The area ratios for the analysis are 1, 2, 4, 6, 8, 10 and 12. The values of nozzle pressure ratios considered for analysis are 2, 4, 6, 8, 10 and 12. The results are plotted with the help of graphs. By observing all the results it can be concluded that the flow field in the enlarged duct is strongly influenced by Mach numbers, area ratios and Nozzle pressure ratios.

This paper presents the Computational Fluid Dynamic (CFD) analysis to study the effect of area ratio i.e. the ratio of enlarged duct area to nozzle exit area on velocity distribution along axis by varying the nozzle pressure ratios. The convergent-divergent nozzle and suddenly expanded circular duct of larger cross-sectional area are used for analysis. The analysis is done for Mach number 2.0 by varying the area ratios and nozzle pressure ratios. The area ratios for the analysis are 1, 2, 4, 6, 8, 10 and 12. The values of nozzle pressure ratios considered are 2, 4, 6, 8, 10 and 12. The results are compared with the help of graphs and tables. By observing all the results it can be concluded that the flow field in the enlarged duct is strongly influenced by area ratios and Nozzle pressure ratios.

An Investigation to Control Base Pressure in Suddenly Expanded Flows