PARAMETRIC STUDY OF SUPERSONIC NOZZLE FOR BASE PRESSURE CONTROL USING EXPERIMENTAL AND OPTIMIZATION METHOD

Abstract

In high-speed fluid dynamics, base pressure controls find many engineering applications such as automobile industry and defense applications, and sudden expansion is a common problem for numerous fields. Several studies have been reported on the control of the flow field with sudden expansion. The passive control method controls the high-speed supersonic flows with geometrical change in a sudden expansion duct-like with cavities, ribs, cylinders, aerospikes, step bodies, etc. Based on the passive control method, it is found that the passive control does not need energy and resulting cost-effectively. Hence, the researchers introduce the active control method using a microjet controller. Therefore, the present study focuses on dynamic control with the microjets in an orifice of a 1 mm diameter to inject the air in the base recirculation region. The microjets with a sonic Mach number of 1 mm diameter were in the base area as a control mechanism at 900 intervals. Since the air is drawn from the main settling chamber, the NPR will be the same as the respective NPR’s used for tests. Experiments were conducted in the presence and absence of the microjets for area ratio 3.24 and L/D ratio from 10 to 1. Mach numbers of the study were 1.87, 2.2, and 2.58. The parameters were optimized using the design of experiments (DOE) approach. Three parameters have been selected for the flow and the DOE. In this study, an L27 orthogonal array of Taguchi design is used. The variance analysis is used to examine the contribution in terms of percentage. A multiple linear regression equation is used to find the correlations between the numerous factors that affect the base pressure. It is found that the developed models are statistically suitable and capable of producing accurate predictions for both the cases in the presence and absence of control. According to the present findings, it is evident that the L/D ratio is the most critical parameter that affects the maximum increase or decrease of the base pressure for a given parameter.