Development and Validation of a Novel Control-Volume Model for the Injection Flow in a Variable Cycle Engine

Abstract

The variable area bypass injector (VABI) plays a crucial role in variable cycle engines by regulating the flow mixing process in complex bypass ducts, and low-dimensional theoretical models are the key to revealing its working mechanism while estimating its aerodynamic performance. An improved VABI model using the control volume method is established, through which the feature parameters that determine the VABI aerodynamic performance are summarized. To acquire an accurate prediction of the injection ratio, a calibration item is introduced to the governing equations to consider the static pressure discrepancy on the mixing plane, and a numerical database is developed to obtain the calibration item. Results show that the aerodynamic parameters that determine the VABI performance include the bypass total pressure ratio, bypass backpressure, and the injection ratio, while the injection angle and the VABI opening area also influence the injection flow characteristics. The injection ratio is increased by reducing the bypass total pressure ratio, decreasing the bypass backpressure, and closing the VABI. Numerical validation shows that the calculation error of the improved model is generally below 3%. The improved VABI model is then validated by a well-arranged experiment, for which the annular flow is simplified into a rectangular duct flow with an error of less than 5%. The experimental validation also proves the accuracy of the model.