Description: When ice accretes on a wing or other aerodynamic surface, it can produce extremely complex shapes. These are comprised of well-known shapes such as horns and feathers but also include other shapes such as the scallops that are associated with swept wing icing. The development of the larger ice shapes is generally believed to be influenced or built up from smaller scale surface structures such as roughness elements which can grow into the precursors of feathers or scallops seen on larger swept wing ice accretions. Feathers and scallops are often comprised of complex interlocking geometries that can contain a large number of voids. Hence it is important to characterize the geometries of these ice shapes, not only to ensure an adequate representation of the geometry for subsequent aerodynamic effects studies but also to provide data to validate icing codes, understand the basic physics involved with the ice accretion, and provide a basis for modeling the ice accretion. To address the above issue, we propose to use an X-ray computed tomography (CT) imaging method to demonstrate that X-ray CT scanning can be used to measure 3D ice features of the form seen in aircraft ice accretions. We also propose to conduct a preliminary trade/design analysis to establish directions for a more detailed Phase II study that would address specific recommendations to integrate X-ray CT imaging with icing wind tunnels which can be used at NASA Glenn and commercial aerospace companies. It is anticipated that the proposed imaging method could provide a radically new way to visualize and characterize extremely complex 3D ice shapes.

Benefits: X-ray CT imaging will provide a potentially revolutionary capability to characterize and measure complex three-dimensional ice shapes. There are a number of technical questions and potential hurdles that need to be overcome. However, if successful, this technique will provide a means to measure the exterior and interior details of extremely complex over-lapping feathers and scallops. This would provide unique measurement capabilities that, to the best of the authors knowledge, have never been available in any other icing facility. It should also be noted that the authors believe that there is no fundamental limitation to operating an X-ray CT scanner in cold temperatures, down to -25C.

If the X-ray CT imaging techniques prove to be successful and if a reasonable path can be identified in Phase II to create X-ray testing devices that can be adapted for use in icing tunnels then X-ray CT imaging could impact a wide range of government and commercial testing facilities. This technique would provide an alternate means to characterize complex 3D wing icing, engine icing and icing on more complicated three-dimensional geometries that are difficult to characterize by other methods. If materials can be identified that are suitable for tunnel testing and are transparent to X-rays then the X-ray CTs could also provide a unique means to measure icing within confined geometries (such as the blade passage of a compressure).