Book Description

A Ceramic Matrix Composite is high strength and high temperature capability composite, utilized in components like heat shield of space vehicles, flame holders and disc brakes. To be used in both static and dynamic components of a future gas turbine engine and even with high temperature capabilities of these CMC components, convection cooling will still likely be required. The surface of the CMC varies significantly from traditional super-alloy used in a modern engine, with large level of roughness and significant three-dimensional waviness. These complex features will impact the behavior of the near wall flows, and affect the heat transfer rates both internal and external to the blade. Existing design tools should be updated to account for these effects. As a preliminary investigation into these effects, an obliquely impinging circular jet on a CMC surface is studied. Both experimental and numerical methods are employed to find the effect of simulated surface features on heat transfer rates. In this study, oblique angles of 45° and 90°, jet plate distance of 6.5 and 7 jet diameters and three Reynolds numbers, 11,000, 23,000 and 35,000, were selected. The test surface is broken down into segments, and individual segment Nusselt numbers are determined and plotted for the various impingement cases studied. Both experimental and CFD results showed negligible changes in average Nusselt number, while local contours were affected. The computational results were evaluated against literature and experimental results, using v2f turbulence model The computational result showed that the local and average Nusselt number for the smooth surface impingement were estimated very close to experimental values and the error was in the range of 14-17%. In case of impingement over the CMC surface, this model predicted the heat transfer rates close to experimental values in the stagnation region and produced local Nusselt number trends following the experimental results. The impact of the CMC surface feature is negligible compared to the uncertainty in heat transfer coefficient, and therefore traditional design tools can be utilized.