Aerodynamic optimization for elbow-type exhaust duct with a built-in output shaft tube

Numerical simulations were performed for the internal flow inside an elbow-type exhaust duct with a built-in output shaft tube. Given the constrained condition relating to the section contours and locations of inlet and outlet, three geometric parameters were mainly considered to illustrate their individual effect on the aerodynamic performances respectively, including straight diffuser angle (α=4°—28°), bent angle (β=55°—75°) and lower guide line F value (F=0.15—0.75) of the exhaust duct. Furthermore, an optimization and sensitivity analysis was made by using the response surface methodology and multiobjective genetic algorithm. The results showed that the flow losses mainly originated from the recirculating flow near inner-side bent section, the wake vortices behind the central tube and struts. The flow deflection inside the bent duct and the cross flow around built-in components were coupled together to form very complicated flow fields and flow loss mechanisms. Within the present scope, non-monotonous influencing role behaved clearly for each individual geometric effect on the total pressure loss coefficient and the static pressure recovery coefficient. Compared with the specifically preferred situation obtained from single-factor analysis (α=16°, β=60° and F=0.6), the optimized elbow-type exhaust duct had a greater straight diffuser angle (α=18.36°—18.95°) and smaller lower guide line F value (F=0.39—0.48), with nearly consistent bent angle (β=60.2°—65°). It improved the aerodynamic performances effectively.