Efficient design optimization of duct-burners for combined-cycle and cogenerative plants

This article proposes an efficient gradient-based optimization procedure for black-box simulation codes and its application to the thermo-fluid-dynamic design optimization of a duct-burner for combined-cycle and cogenerative plants. The article also provides a discussion on some criteria that should drive the design optimization of these components, almost neglected by the scientific literature. Using a widely employed commercial (black-box) code, a new enhanced-mixing duct-burner has been first devised. Before looking at its design optimization, experimental investigations have been performed to assess the reliability of the modelling and the accuracy of the numerical predictions. Then, a finite-difference gradient-based optimization procedure that can be combined with black-box analysis codes has been developed: its efficiency relies on the simultaneous convergence of the flow solution and of the optimization process, as well as on the use of nested grid levels. After its validation, the proposed progressive optimization technique has been applied to two examples of thermo-fluid-dynamic design optimization of the new duct-burner: the first application aims at minimizing the outlet temperature gradient, whereas the second application aims at reducing the near-wall temperatures and shortening the flame, so as to strengthen its anchorage, while reducing the body heating and the thermal NOx formation.