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Title: Hybrid LES – RANS of complex geometry jets
Author: Eastwood, S. J.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2010
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A promising technique for exploring jet flows is large eddy simulation (LES). However for jet LES a number of key unanswered questions remain. These include the sensitivity of solutions to the numerical scheme, subgrid scale (SGS) model and inlet conditions. Results show that for more dissipative, robust solvers often found in industry, SGS model omission can give useful results. Solutions which use no SGS model are called Numerical LES (NLES). For less dissipative codes, solutions are found to be relatively insensitive to the choice of SGS model. An industrial based solver is selected and validated further by making acoustic and hot jet predictions using the NLES approach. Encouraging agreement with measurements is shown. To relieve computational cost, the near wall modelling issue is also addressed. A novel method is used to blend a near wall Reynolds averaged Navier Stokes (RANS) method with NLES used away from the wall. Blending between the two regions makes use of the Hamilton Jacobi equation. Real engines have high bypass ratio nozzles and so the flow through these is explored. Predictions are made using the hybrid RANS-NLES strategy. Different case set ups are simulated including hot and cold jets and a range of meshes from 6 x 106 to 50 x 106 cells. For all the meshes, results show encouraging agreement with measurements. The near wall RANS modelling is helpful in preventing non-physical separation from curved surfaces highlighting the usefulness of the hybrid approach. A pylon, which attaches the engine to the wing, is shown to influence the flow development, having a significant impact on peak turbulence levels and spreading rates. Wakes, simulating those shed by upstream turbomachinery, are included in the nozzle geometry. The wakes are introduced using a body force model which prevents the need to explicitly model blade geometry. The results have demonstrated that real geometry effects are particularly influential and should be taken into account when moving towards real engine simulations.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available