The objective of Part 2 is to employ a computational scheme to investigate the difference in thermal-flow behaviors with and without a sheath of an existing reversed-flow combustor. In Part 1, the experiments are conducted under low pressure and temperature laboratory conditions to provide a database to validate the computation model, which is then used to simulate the thermal-flow under elevated gas turbine operating conditions.
For laboratory conditions, the CFD results show that (a) the predicted local static pressure values are higher than the experimental data but the global total pressure losses matches the experimental data very well; (b) the total pressure losses are 1.19% for the no-sheath case and 1.89% for the sheathed case, which are within 3% of the experimental values; and (c) the temperature difference between the sheathed and non-sheathed cases is in the range of 5 - 10K or 16% - 32% based on the temperature scale between the highest and lowest temperature. Removing the sheath can harvest a significant pressure recovery of approximately 3% of the total pressure, but it will be subject to a wall temperature increase of about 500K (900°F or a 36% increase) on the outer radial part of the transition piece, where the flow is slow due to diffusion and recirculation in the large dump diffuser cavity near the turbine end. If modern advanced materials or coatings could sustain a wall temperature of about 200K higher than those currently available, the shield could be.