477 / 2018-12-31 11:05:39

Multistrategy optimization by duct and strut design of an typical annular exhaust diffuser

Exhaust diffuser; aerodynamic performance；strut outline optimization；meridian plane design

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Exhaust diffuser has significant influence on the performance of gas turbine. Aerodynamic performance of these diffusers typically differ from the diffused pipe due to struts which are designed to guarantee enough structural strength. This paper describes the aerodynamic optimization of a typical exhaust diffuser.
Firstly, meridian plane design of duct was optimized using orthogonal test method without changes in struts. The meridian plane was parameterized, and five key geometric parameters were defined as factors. Exhaust diffuser numerical simulations were studied for 16 cases with the correct parameter design from orthogonal table. Flow angle and mass flow boundary were set reasonably. Range analysis of five chosen geometrical factors was performed to find the critical one. In general the numerical results showed that, meridian plane optimization alone without changes in struts only achieved limited improvement on reduction of flow loss.
Secondly, outlines of struts were redesigned. As we known the aerodynamic performance of the exhaust diffuser depends on the inlet boundary condition a lot, and flow parameters such as flow angle and pressure of inlet flow field was quite uneven. During large range of inlet flow angles, plane flow field of different struts outlines were solved for the front row struts because of its significant impaction on flow loss. Then the Reynolds averaged N-S equations with k-ω-SST turbulence model was adopted to analyze the flow field in exhaust diffuser with the last two stages. The numerical results showed that 1.4% total pressure loss was reduced with the modified design.
Finally, the optimized struts and meridian plane design of duct were combined to verify the comprehensive optimization results. In sum, different optimization strategies were applied by reliable methods, and a lower flow loss design of a typical exhaust diffuser was accomplished