Image Processing

ACI image processing capabilities have many potential applications. Some of these capabilities are described here.

Film Reading - In aeroballistic range studies, model positions and orientations are obtained from a series of high-speed images taken at known times as the model flies down the range; the model speeds can be in excess of Mach 2. The CADRA (Comprehensive Aerodynamic Data Reduction System for Aeroballistic Ranges) system automatically identifies the model location and orientation in each image, constructs the 3D flight path of the model from these measurements, and then, by fitting calculated trajectories to the experimental flight path, determines the aerodynamic characteristics of the model. The figure below shows a typical ballistic range image; the highlighted regions are the pixels that were identified as the model and fiducial (reference) system by CADRA. CADRA is currently being used by the USAF Armament Directorate at Wright Laboratory.

Data Analysis of a High-speed Free-flying Object via Image Processing

Image Construction from CFD - Experimental flow-field images, such as shadowgraphs, schlieren, and interferograms, are used to verify CFD solutions. In many cases, one-to-one comparison of the experiment and computation are desired, particularly when the flow is very complicated or when the temperatures are high and the gas is dissociating. ACI has the expertise necessary for constructing flow-field images from CFD solutions. The figure below shows a constructed and experimental shadowgraph for a hemisphere- cylinder in a combustible mixture. The flow features that can be seen in both the constructed and experimental images are the bow shock, the combustion fronts (vertical lines), and expansions between the combustion fronts and the shock.

(Experimental shadowgraph: Lehr; CFD solution: Wilson and Sussman)

Interferogram Interpretation - Interferograms are experimental images that are created by "interfering" two laser beams, one which passes through a flow field and the other which does not. The fringe patterns in interferograms (light and dark variations) are functions of phase differences between the two beams. The phase differences are functions of density variations in the flow. ACI has the capabilities for reducing the fringe patterns to phase differences. In the following figure are a finite-fringe interferogram and the calculated phases for a blunt cone in the ballistic range at NASA / Ames Research Center. The test pressure was 0.8 atmospheres; the velocity of the projectile was 16,000 ft/sec.