Directed energy systems developed to reside on airborne platforms can experience a multitude of sources of degradation that reduces system performance. Three major sources of these degradations, or aberrations, can be attributed to aero-optics, atmospheric turbulence, and thermal blooming. Aero-optics is the term used to describe the aberrations induced from the aero-dynamical environment surrounding an aircraft as it travels through the air at high speeds. The Air Force Research Laboratory (AFRL) Laser Division has built and recently brought online the Aero-Effects Laboratory (AEL) capable of performing various aero-optical experiments and testing. The AFRL AEL currently has a supersonic wind tunnel with a test section that allows large optical access for various article testing and system simulations and verifications. Here we present the current status and capabilities of the AEL and some initial results from various experiments currently in development. Data acquisition systems include the use of pressure sensors, pitot probes, Schlieren imaging, and wavefront sensors. The Schlieren imagery is used to provide a qualitative measurement of the flow and shock waves present in the wind tunnel while wavefront sensors provide a more quantitative measurement of the phase disturbances induced from the aero-optical aberrations.
The Air Force Research Laboratory (AFRL) Directed Energy Directorate has built a supersonic wind tunnel in order to characterize aero-optical effects. Aero-optics is the study of the effect of aircraft-induced and atmospheric disturbances on the efficiency of optical imaging and laser systems. The Aero-Effects Laboratory (AEL) at AFRL consists of a supersonic wind tunnel with the capability of imaging the turbulent flow with large optical access of its test section. In order to gain access to the area of interest, we must first send a beam of light through the access windows of the wind tunnels test section to measure and visualize the flow. Initial measurements have been made and shockwaves between the mating plates of the test section and nozzle have been observed. This paper describes the optical system designed for resolving these shockwaves with a Schlieren imaging system.
The Air Force Research Laboratory (AFRL) Directed Energy Directorate is completing a supersonic wind tunnel to characterize aero-optics effects in high speed flow fields. Optical characterization is accomplished by transmitting a beam of light transverse to the direction of air flow via access windows, thereby illuminating the flow region, a select volume of which is recorded by a suite of sensors. Quantitative measurements of the flow are made using two wave-front sensors (WFS), a Shack-Hartmann (SH) WFS and a digital holography (DH) WFS. Qualitative measurements are made using a traditional Schlieren imaging system. Parenthetically, in addition to characterization of aero-optics effects, we expect to be able to numerically propagate to different planes in the supersonic flow field to characterize boundary layer effects. This paper reviews our wind tunnel system’s requirements and, in particular, the design of the DH WFS.