EXPERIMENTAL AND CFD STUDY OF EFFUSION COOLING IN AN S-BEND DIFFUSING PASSAGE
Ng, Billy Chok Nam
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This thesis presents an experimental and computational fluid dynamics (CFD) study on a rectangular S-bend with straight and diffusing passages with passive effusion cooling. Experimental tests were performed at both cold and hot flow conditions over a range of Reynolds numbers from 2.5e5 to 4.5e5. Hot flow testing was conducted with the primary flow temperature up to 300 °C. Severe backpressure penalties occurred with full-surface passive effusion injection in cold flow tests. Moderate penalties occurred with reduced surface coverage whereby the performance was affected by the S-bend secondary fields with injection at different locations. High surface cooling effectiveness with full-coverage of cooling film was measured; the impacts from the S-bend secondary flow fields were measured to be minimal. The CFD study revealed the importance of using experimental flow boundary conditions for simulations. Using the standard k-ε model with wall functions was confirmed as appropriate for simulating the S-bend flow with effusion cooling. A coarse-grid CFD methodology using a porous wall boundary condition to simulate the effects of effusion cooling was investigated. From a design perspective, this model is preferable for quantifying the injection flow rate since the actual mass flow rate is not known. Comparison to the alternative solution using uniform mass flow boundary conditions showed that both models incorrectly predicted the momentum. The porous wall model, however, is promising for practical design applications of S-duct flow fields with effusion injections.