Abstract
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.
Highlights
Expanded flow is a complex phenomenon characterized by flow separation, flow recirculation, and reattachment
Contours of total pressure for Area Ratio = 5, Nozzle Pressure Ratio = 5, and Pitch Circle Diameters (PCD) of control jets d3 is plotted on the XY plane, and a plane 2 mm from the base face is shown in figures 7
All the values of absolute pressure are divided by atmospheric pressure and plotted the graphs to get a clear idea about the pressure variations in the base region
Summary
Expanded flow is a complex phenomenon characterized by flow separation, flow recirculation, and reattachment. A shear layer into two central regions may divide such a flow field, one being the flow recirculation region and the other the primary flow region. Reattachment point is the point at which the dividing streamline strikes the wall of the enlarged duct. The features of the suddenly expanded flow field are illustrated in Figure 1 [1,2,3,4,5]. A review on drag shows that 50% of the total drags of high-speed objects, such as a missile in jet-off condition is due to base drag. Base drag is in the form of pressure drag that dominates at very high speeds and
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
