Investigation of High-Speed Flow Control from CD Nozzle Using Design of Experiments and CFD Methods

In high-speed fluid dynamics, the control of base pressure finds many engineering applications such as automobile industry and defense applications. Several studies have been reported on passive control using devices like cavities, ribs, aerospikes, etc. in the last three decades. Therefore, the present research focuses on active control uses the microjets in the form of an orifice of a 1 mm diameter to inject the air in the base flows and located at base area of 90 degrees intervals as a control mechanism. Since the air is drawn from the main settling chamber, the NPR will be the same as the respective NPRs used for tests. Experiments were conducted in the presence and absence of the microjets for area ratio 3.24 and L/D ratios from 10 to 1 at Mach numbers 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. An L-9 orthogonal array, multiple linear regression, and confirmation tests were performed to analyze the experimental results. The developed models are statistically suitable and accomplished in producing reasonable predictions for both cases. Besides, a computational fluid dynamics method has been utilized and validated by the experimental results. The k-epsilon turbulent model is used to analyze the simulation results. According to the present results, it is evident that for a given parameter, an L/D ratio is the most significant impacting to a maximum increment or decrement of a base pressure.