Flow Control About an Airborne Laser Turret

A high-energy laser system inflicts damage on a target by radiating large amounts of thermal energy onto a small area. Airflow about a laser pointer-tracker turret on an aircraft may be unsteady, causing problems in laser beam propagation. These problems are jitter, which is vibration of the laser beam, and optical path distortions. Several airflow control techniques were considered as possible means of suppressing the unsteady flow. A hollow fairing with suction inlets located behind the turret combined with fuselage boundary-layer suction at the turret base was selected as a method of flow control. A 0.3 scale model of the turret and fairing was tested in a wind tunnel at the Naval Postgraduate School. Various turret/fairing geometrical parameters were investigated, as well as flow rates through the suction apparatus. A condition of steady flow around the turret with minimum suction requirements was sought. A turret with 0.427 m diam was tested in the Naval Postgraduate School 1.525 xl.525-m wind tunnel at a Reynolds number of 300,000. The Reynolds number was defined as VD/v, where V is tunnel velocity, D is turret diameter, and v is kinematic viscosity, all quantities being measured in consistent units. Steady flow was achieved with a flow factor F equal to 0.4. F is the ratio A^ /At, where A^ is area of streamtube at freestream conditions entering the suction inlets, and At is the projected area of laser turret.