Prepositive Synergistic Bulge Design for Improving Aerodynamic Performance of Submerged Inlet

Abstract

A submerged inlet has good stealth characteristics and a low external drag, but it also has the disadvantage of low internal flow efficiency. In view of this, a new efficiency enhancement method based on the prepositive synergistic bulge of the inlet’s anterior lip is proposed. Taking the submerged inlet of an aircraft as the baseline configuration, a miniature bulge with a square bottom and an outer convex form is designed in front of the inlet’s anterior lip. Through the convex shape of the bulge, part of the low-energy boundary layer airflow is diverted away from the inlet’s entrance, so that the airflow greatly reduces the flow separation after entering the inlet, and the internal flow performance of the entire submerged inlet is improved. Taking the flow field of an aircraft in the classic cruise state as an example, the simulation analysis results show that the flow field characteristics of the entire submerged inlet are obviously improved after adding the synergistic bulge. The total pressure recovery coefficient of the new inlet configuration increased by 1.36%, the total pressure distortion index decreased by 10.86%, and the body drag only increased by 0.37% compared with the baseline case. According to calculations of synergistic bulge inlet configurations with different design parameters, the effect of this configuration is relatively stable, whereby the aspect ratio of the bulge has the greatest impact on the performance, and its value should not be less than 0.75. In addition to the advantages of not requiring additional components or occupying space and being easy to manufacture, the method of adding a synergistic bulge can improve the aerodynamic performance of the baseline inlet under most cruise flight conditions, and its additional drag is small, which gives it a wide applicability range.

Numerical Investigation of a Vortex Diverter Designed for Improving the Performance of the Submerged Inlet

“…The key to maximizing the inlet efficiency in this limited space lies in: (1) reducing or eliminating the negative impact of low-energy airflow from the boundary layer near the entrance on the inlet duct, and (2) increasing the energy of the airflow within the inlet duct or organizing the migration of low-energy fluid within the duct to avoid the accumulation of large-scale separation vortices caused by low-energy airflow. One solution is to install vortex generators upstream of the inlet duct entrance [33]. However, installing vortex generators at the entrance of the inlet duct can introduce additional drag to the aircraft and increase its radar cross-sectional area.…”