CFD Modelling of Weapon Separation from Military Aircraft

Abstract

Fighter aircraft carries various types of stores such as drop tanks, missiles, bombs, and electronic countermeasure components depending on their role and mission requirements. At the time of new aircraft commissioning or major modifications to an older aircraft, the store separation engineer has to gauge the effort toward providing the airworthiness certification for the aircraft and corresponding stores. Typically, engineering analysis, wind tunnel testing, and flight trials are required for this purpose, however, both wind tunnel testing and flight testing are expensive options and carry the risk of human and material loss. As an alternative, computer methods and numerical analysis can now be used instead of flight and wind tunnel tests for certification in some cases. In this study, the store separation process was numerically simulated based on the coupling of Navier-Stokes (N-S) equations with six degrees of freedom (6DOF) rigid-body equations using overset dynamic mesh. The wing-pylon-store configuration (EGLIN test case) at Mach 1.2 was numerically simulated and compared to experimental work to show that the numerical methods can solve the store separation problem. After validation, this thesis addresses the effect of design modification of stores (boat tail and drum-type) and investigates the influence of active and passive flow control devices (Jet and Rectangular blade) on the separation characteristics of a missile from the internal weapons bay. The separation process and flow fields were obtained and all aerodynamic parameters and trajectory parameters were compared. These newly designed control devices can achieve better flow field aerodynamic characteristics, thus increasing missile separation stability. At the leading edge of the cavity, these flow control devices generate shock waves with high pressure, alter the shear layer, and result in a gentle and stable missile attitude. Also, it was found from numerical results modified drum-type weapon raises the shear layer and blocks airflow entering the cavity’s back portion. In this case, the shear layer underneath the weapon bay widens, allowing the weapon to travel through it smoothly. The distance between the internal weapons bay and the missile in the positive z-direction with the modification design is 1.6 times that without the modification at t=0.8 s. The pitching angle of the missile ranged from 9° to -9.5°, and the angular motion range of the missile with the modification is smaller than the flow control device cases which indicates optimized modified weapon can get better flow field aerodynamic parameters.