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Current Research of Dr. R. Mark Rennie

Artificial Guide Star for Optical Measurements

Laser-induced air-breakdown sparks are investigated as a light source for measuring the optical aberrations created by aero-optic flows. The advantage of the sparks is that they can be placed at essentially any location external to the flight vehicle. Initial efforts of the investigation were directed at determining radiometric qualities of the spark both in and out of flow, and optimizing the optical setup to minimize wavefront noise associated with variations in the location and dimensions of the breakdown spark. Tests are planned that will use the spark as an illumination source for adaptive-optic correction of a compressible shear layer.

Aero Optics of Compressible Shear Layers

Shear layers associated with separated flow regions often occur in the aft quadrant of aircraft-mounted optical systems, making them one of the most important flows for aero-optics research. Our approach is to regularize the shear layer using controlled forcing, making the optical aberrations associated with the shear layers correctable using feed-forward adaptive-optic techniques.

Aero Optics of Helicopter Tip Vortex

For an optical system carried by a helicopter, aero-optic aberrations originate primarily from blade tip vortices that pass through the system field of view. Using the weakly compressible model (WCM) previously developed at Notre Dame, aero-optic effects for realistic tip-vortex flows are computed using the Lamb-Oseen vortex model as well as scaled experimental velocity fields, and compared to measured wavefront data. Scaling relations are developed to enable the prediction of the aero-optic aberrations on full scale flight vehicles.

Design of an Aircraft-Mounted Pod with Improved Optical Performance

New approaches for the shaping of pods and fairings for optical systems are investigated in which the objective of the approach is to prevent or mitigate aero-optic effects. Basic streamlined shapes are developed which prevent supersonic flow and shock formation around the optical aperture, as well as innovative methods for the shaping of cutouts that extend the maximum aft lookback angle of the optical system.