L. A. Catalano

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 NO x formation.

Turbine cascade design via multigrid-aided finite-difference progressive optimization

This paper proposes an efficient and robust procedure for the design optimization of turbomachinery cascades in inviscid and turbulent transonic flow conditions. It employs a progressive strategy, based on the simultaneous convergence of the design process and of all iterative solutions involved (flow analysis, gradient evaluation), also including the global refinement from a coarse to a sufficiently fine mesh. Cheap, flexible and easy-to-program Multigrid-Aided Finite Differences are employed for the computation of the sensitivity derivatives. The entire approach is combined with an upwind finite-volume method for the Euler and the Navier-Stokes equations on cell-vertex unstructured (triangular) grids, and validated versus the inverse design of a turbine cascade. The methodology turns out to be robust and highly efficient, the converged design optimization being obtained in a computational time equal to that required by 15 to 20 (depending on the application) multigrid flow analyses on the finest grid.

Thermal design and emissions of duct-burners for combined-cycle and cogenerative plants

This paper mainly aims at demonstrating that an appropriate thermo-fluid-dynamic design optimisation of duct-burners for combined-cycle and cogenerative plants allows to satisfy restrictive emission limits, while significantly reducing the thermal stresses and the undesired pressure drops. In particular, a detailed discussion on the influence of the TEG composition and of the thermal load, measured for a standard duct-burner, is proposed to justify component failure registered in plant applications. On this basis, the paper also addresses an important design criterion, usually neglected, which allows realisation of long-life and maintenance-free duct-burners, while retaining the fundamental requirement of limiting emissions. Finally, the influence of the thermal load on the emissions produced by the modified duct-burner has been experimentally measured, and analysed, with the aid of some numerical computations.

On the Use of Fast-Response Pressure Transducers in a Common-Rail Diesel Injection System

The aim of this paper is to investigate the use of fast-response pressure transducers for measuring the instantaneous pressure in different sections of a common-rail diesel injection system, both for a single injection and for multiple injections. The influence of the pressure transducer onto the measured pressure is evaluated numerically by comparing the pressure history computed without the pressure transducer and that computed with the presence, and thus with the disturbance, of this sensor. A new electric circuit is proposed in substitution of the standard electronic central unit, which allows to modify the injection parameters and to perform injections on a test rig, as done in the automotive applications. Experimental results are provided both for a single injection and for multiple injections, to demonstrate the capabilities of the proposed test bench for the unijet injectors.Copyright

Unsteady Conjugate Heat Transfer Analysis of an Air Immersed Solid Particle With Application to an Innovative Heat Exchanger

The improvement of both heat recovery Joule-Brayton cycles and closed cycle (externally fired) gas turbine plants is strongly limited by the availability of high efficiency heat exchangers. In such a scenario, a non conventional heat exchanger was recently proposed; this device employs falling solid particles to perform heat transfer between two separate gas flows and was designed with a 1D model neglecting conduction within the particles. Although experimental reliability of this assumption was already obtained, there is no proof available of the quantitative effect introduced by the above mentioned simplification. In this work, Direct Numerical Simulation (DNS) of a solid particle immersed in a gas flow has been performed in order to further validate the hypothesis of negligible conduction and to enhance the design of the proposed heat exchanger. Unsteady Conjugate Heat Transfer (CHT) has been used to predict the final temperature of the solid sphere for Reynolds numbers ranging from 30 to nearly 300, the computational grid being generated with the Immersed Boundary (IB) technique. A validation of the study is presented, together with grid independence and boundary independence assessment. The results fully confirmed the worthiness of the initial assumption, with a 1.4% maximum error for high Reynolds conditions (large diameter particles) with respect to the 1D model. Additionally, the code has been employed to explore the influence both of several particles disposed in a row and of the distance between successive particles.© 2011 ASME

Fluid Dynamic Design Optimization of the Intake of a Small Turbojet

This paper proposes an efficient gradient-based optimization procedure for black-box simulation codes and its application to the fluid-dynamic design optimization of the intake of a small-size turbojet, at high load and zero flight speed. Two simplified design criteria have been considered, which avoid to simulate the flow in any turbojet components other than the intake itself. Both design optimizations have been completed in a computational time corresponding to that required by eight flow analyses and have provided almost coincident optimal profiles for the intake. The flow fields computed with the original and the optimal profiles are compared to demonstrate the flow pattern improvements that can be theoretically achieved. Finally, the original and the optimal profiles have been mounted on the same small-size turbojet and experimentally tested, to assess the resulting improvements in terms of overall performances. All numerical and experimental results can be obviously extended to the intake of a microturbine for electricity generation.Copyright

Design of High Performing Duct-Burners for Combined-Cycle Plants Using Progressive Optimization

A general efficient strategy for the design optimization of duct-burners for combined-cycle plants is presented. This methodology combines a widely employed commercial code, used for the flow analysis, with a progressive optimization strategy, whose efficiency relies on the simultaneous convergence of both the flow solution and the optimization process, as well as on the use of progressively finer grid levels. The proposed strategy has been initially tested versus two inverse design examples with known solutions; then, it has been employed to flatten the outlet thermal profile of a new enhanced-mixing after-burner. The presented results show that the overall optimization process requires a computational time compared to that required by 5 ÷ 14 flow analyses.© 2002 ASME