The Optical Environment of a Cylindrical Turret with a Flat Window and the Impact of Passive Control Devices

Optical aberrations over a cylindrical turret with a flat window were measured using a 2-D wavefront sensor and a Malley probe as a function of laser beam elevation angle. It was found that depending on the window back-facing angle the flow either had a weak separation bubble followed by a reattached boundary layer or a strong separation with a large recirculation region behind the cylindrical turret. It was found that optical aberrations were high in the case of a weak separation bubble and at large look-back elevation angles. Different passive devices placed upstream from the turret were studied for their effectiveness in improving the optical-propagation environment. The results are presented and discussed.