A New Concept in Design of Rheolytic Thrombectomy Devices: The Coanda Effect

The Coanda effect, which was first named by Henri Coanda in 1910, is the phenomenon when a fluid, gas or liquid, attaches to a solid surface, called the Coanda surface. The direction of this adhered flow changes along with the surface because of the Van der Walls forces or surface tension. Therefore, the pressure distribution of the ambient fluid is also altered due to the bent attached Coanda flow. The fluid material properties, Coanda flow velocity, curvature of the Coanda surface, velocity of the ambient fluid flow, and distance to the wall above the Coanda flow are the primary factors affecting this pressure distribution. In experimental studies, Panitz and Wasan [1] evaluated the pressure distribution of the Coanda effect by using pressure sensors on the Coanda surface and a colored dye solution in the flow. By means of photographs and experimental data, they describe the influence of different heights of the shroud (a sheath plate above the Coanda surface) and the secondary flow entrainment (flow of ambient fluid) on the pressure profiles. Vortices occur beneath the Coanda flow when the height of the shroud is lower than a specified reference. Cutbill et al. [2] developed a high speed Coanda flow k-ε turbulence model in the application of PHOENICS to improve the prediction of the mixing rate, shock wave structure and flow separation. The pressure drop occurs near the Coanda surface in both experimental and computational prediction results.

Compound Ejector Thrust Augmenter Development

The basic simplicity of ejectors provides an advantageous form of engine thrust augmentation for V/STOL aircraft. Application requires careful internal aerodynamics development to provide high augmentation ratios in compact, short length, ejector installations. Development of the compound ejector through rig and wind tunnel tests is described wherein Coanda flow and improved central primary flow injection are combined. Several methods of reducing ejector volume are employed through increased mixing and diffusion rates while directing attention to loss sources such as inlet blockage.