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Explicit Thermodynamic Properties Using Radial Basis Functions Neural Networks ; Léonard, Olivier in Proceedings of the second SIAM international Conference on Data Mining (2002) Gas turbine design, development, monitoring and maintenance are widely based on numerical simulations of the steady and transient engine performance. Most of the equations that are solved in the ... [more ▼] Gas turbine design, development, monitoring and maintenance are widely based on numerical simulations of the steady and transient engine performance. Most of the equations that are solved in the simulation programs involve the thermodynamic properties of the fluid flowing through the engine. These properties depend on temperature, pressure, humidity and fuel dosage. As the solution of chemical equilibrium is not compatible with real-time computations, a chemical solver is used off-line to generate a large database which neural networks are trained on. These networks are built on radial basis functions such as multiquadrics. A forward selection approach is used to select data points from the training set as the centers of the transfer functions. The selection stops when the prediction error starts growing. The resulting networks for specific heat and enthalpy of the gas mixture are 3 orders of magnitude faster than the chemical solver. In order to further increase the efficiency and the generalization capabilities of the model, an external optimization solver has been used to tune the shape of the transfer functions. Several solutions are proposed and preliminary results are presented. [less ▲] Detailed reference viewed: 24 (1 ULg)Robust Validation of Measurements on jet Engines Dewallef, Pierre ; Léonard, Olivier in European Journal of Mechanical and Environmental Engineering (2001), 46(4), 237-242 Nowadays, most of turbine engine tests are processed using an open loop, i.e. the measurements are verified and treated a posteriori, sometimes weeks or months after the end of the test. The scope of the ... [more ▼] Nowadays, most of turbine engine tests are processed using an open loop, i.e. the measurements are verified and treated a posteriori, sometimes weeks or months after the end of the test. The scope of the present project is to develop a new methodology which enables real time detection of faulty measurements and the suppression of the source of these faults during the test. This implies the development of a method which is sufficiently robust to cope with a lot of faulty data (up to 20 to 30 % of the measurements). Most of the existing methods make use of a least square approach so that a set of parameters is sought which minimizes the RMS error between the measurements and the values provided by a numerical model of the installation. This type of approach is efficient in finding whether a set of measurements is valid but cannot locate the fault(s). In this paper an alternative is proposed based on a distribution of the measurement noise introduced by Huber. This so-called robust validation method has been tested on a single spool, single flow and variable geometry nozzle turbojet. Both the least square and Huber's function approaches have been tested and compared in terms of efficiency. The robust estimator based on Huber's error function has shown to be much more powerful for both finding an invalid set of measurements and locating the faulty measurements. [less ▲] Detailed reference viewed: 34 (4 ULg)On-Line Validation of Measurements on Jet Engines Using Automatic Learning Methods Dewallef, Pierre ; Léonard, Olivier in Proceedings od the 15th ISABE Conference (2001) Nowadays, turbine engine tests are processed using an open loop, i.e. the measurements are verified and treated a posteriori, sometimes weeks or months after the end of the test. The purpose of the ... [more ▼] Nowadays, turbine engine tests are processed using an open loop, i.e. the measurements are verified and treated a posteriori, sometimes weeks or months after the end of the test. The purpose of the present project is to develop a new methodology which enables real time detection of faulty measurements and the suppression of the source of these faults during the test. The validation of the measurements is achieved by a “robust” parameter identification [1]. Such a method is called robust in the sense that it can cope with 20 to 30% of faulty measurements. The robustness is insured by a distribution of the measurement noise, as introduced by Huber [7, 8], that takes into account the possibility of faults. The purpose of a parameter identification is to find the set of parameters which has most likely generated the measurements observed on the process. This leads to an optimisation problem that has to be solved for the parameters. The measurements are linked to the parameters through a non-linear model, leading to a large system of equations for modern jet engines. If no physical model of the process can be made available or if this model is too complex to allow real time validation, automatic learning methods may provide a solution: • either a mathematical representation is generated, directly based on the measurements (online learning), • or a database is first generated, based on the existing (but expensive) physical model, the database being subsequently used to build a statistical model (off-line learning). Neural networks seem to be very suitable for modeling the behavior of turbojets, avoiding the resolution of a time-consuming non-linear system. In this paper neural networks are tested to generate a mathematical representation of a single flow, single spool and variable geometry nozzle turbojet, from a data base of “measurements” generated by a physical model of the engine. Only the off-line learning approach is considered. [less ▲] Detailed reference viewed: 47 (2 ULg)Modelization, Development and Testing of a Variable Geometry Nozzle ; Léonard, Olivier in Proceedings of the 5th Belgian National Congress on Theoretical and Applied Mechanics (2000) Detailed reference viewed: 20 (1 ULg)Compressor and Turbine Blade Design by Optimization Léonard, Olivier ; ; Duysinx, Pierre in Bloebaum, C. (Ed.) Proceedings of the 3rd World Congress of Structural and Multidisciplinary Optimization WCSMO3 (1999, May) Compressor and turbine blade design involves thermodynamical, aerodynamical and mechanical aspects, resulting in an important number of iterations. Inverse methods and optimization procedures help the ... [more ▼] Compressor and turbine blade design involves thermodynamical, aerodynamical and mechanical aspects, resulting in an important number of iterations. Inverse methods and optimization procedures help the designer in this long and eventually frustrating process. In this paper an optimization procedure is presented which solves two types of two-dimensional or quasi-three-dimensional problems: the inverse problem, for which a target velocity distribution is imposed, and a more global problem, in which the aerodynamic load is maximized. [less ▲] Detailed reference viewed: 110 (2 ULg)Aerodynamic and Mechanical Design of Compressor Blades Including Static Analysis ; ; Essers, Jean-André et al in Proceedings od the 3rd World Congress of Structural and Multidisciplinary Optimization (1999, May) Detailed reference viewed: 97 (5 ULg)Application of a three-dimensional inverse method to the design of a centrifugal compressor impeller ; Léonard, Olivier ; in Proceedings of the ASME Turbo Expo 1998 (1998, June) ASME Paper 98-GT-127 Detailed reference viewed: 38 (1 ULg)Developpement d'une méthodologie d'optimisation aérodynamique et mécanique d'aubes de compresseurs ; ; et al in RFM : Revue Française de Mécanique (1998), 4 Le projet décrit dans cet article a pour but de réaliser le dimensionnement des aubages d'un compresseur axial; pour ce faire, des codes de calcul aérodynamique et mécanique sont intégrés dans un ... [more ▼] Le projet décrit dans cet article a pour but de réaliser le dimensionnement des aubages d'un compresseur axial; pour ce faire, des codes de calcul aérodynamique et mécanique sont intégrés dans un processus d'optimisation globale. Le transfert de données entre les différents modules utilisés est pris en charge par un logiciel gestionnaire de tâches, sur lequel est axée la méthode. Les codes aérodynamiques, basés sur l'approche classique quasi-tridimensionnelle, combinent une simulation d'écoulement dans le plan méridien ainsi qu'une succession d'écoulements en grilles d'aubes. Les codes mécaniques permettent une analyse à la fois statique et dynamique des aubages ; on notera en outre la possibilité de leur adjoindre des calculs d'impact ou de vérification de la durée de vie. Dans son état actuel, le code général permet d'optimiser la masse ou le rendement d'un étage de compression sur la base d'un calcul aérodynamique dans le plan méridien et d'une vérification des marges fréquentielles. [less ▲] Detailed reference viewed: 207 (15 ULg)A Navier-Stokes Inverse Method Based on a Moving Blade Wall Strategy Léonard, Olivier ; in Proceedings of the ASME Turbo Expo 1997 (1997, June) Detailed reference viewed: 17 (0 ULg)Blade Analysis and Design Using an Implicit Flow Solver Léonard, Olivier ; ; in 2nd European Conference on Turbomachinery - Fluid Dynamics and Thermodynamics - Proceedings of the conference (1997, March) Detailed reference viewed: 31 (1 ULg)A two-dimensional Navier-Stokes inverse solver for compressor and turbine blade design ; Léonard, Olivier ; in Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy (1997), 211(4), 299-307 A two-dimensional viscous inverse method for the design of compressor and turbine blades is presented. It iteratively modifies an initial geometry until a prescribed pressure distribution is reached on ... [more ▼] A two-dimensional viscous inverse method for the design of compressor and turbine blades is presented. It iteratively modifies an initial geometry until a prescribed pressure distribution is reached on the blade surface. The method solves the time-dependent Navier-Stokes equations in a numerical domain of which some boundaries (the blade walls) move during the transient part of the computation. The geometry modification algorithm is based on the transpiration principle: a normal velocity distribution is computed from the difference between the actual and prescribed pressure distributions, and is used to modify the blade shape. A time iteration is then performed on this new blade shape, taking into account the grid movement during the time stepping. A two-dimensional upwind finite-volume Navier-Stokes solver has been developed. The multiblock strategy allows for a selective concentration of the discretization points in the zones of higher gradients. Applications to turbine and compressor blade design illustrate the accuracy of the flow computation, the capabilities and efficiency of the inverse method. [less ▲] Detailed reference viewed: 94 (1 ULg)On the Existence of a Solution for Turbomachinery Blade Design ; Léonard, Olivier in Proceedings of the 4th Belgian National Congress on Theoretical and Applied Mechanics (1997) Detailed reference viewed: 18 (3 ULg)Développement d’une méthodologie d’optimisation aérodynamique et mécanique d’aubes de compresseurs ; ; Essers, Jean-André et al in Proceedings of the 4th Belgian National Congress on Theoretical and Applied Mechanics (1997) Detailed reference viewed: 26 (2 ULg)Application of a High-Order Upwind Finite-Volume Scheme to 2D Cascade Flows Using a Multi-Block Approach ; Léonard, Olivier ; Essers, Jean-André in Proceedings of the 12th ISABE Conference (1995) Detailed reference viewed: 22 (2 ULg)Permeable Wall Concept for Transonic Blade Design Léonard, Olivier ; ; in Proceedings of the 3rd Belgian National Congress on Theoretical and Applied Mechanics (1994) Detailed reference viewed: 13 (1 ULg)Design Method for Subsonic and Transonic Cascade with Prescribed Mach Number Distribution Léonard, Olivier ; in Journal of Turbomachinery (1992), 114(3), 553-560 An iterative procedure for blade design, using a time marching procedure to solve the unsteady Euler equations in the blade-to-blade plane, is presented. A flow solver, which performs the analysis of the ... [more ▼] An iterative procedure for blade design, using a time marching procedure to solve the unsteady Euler equations in the blade-to-blade plane, is presented. A flow solver, which performs the analysis of the flow field for a given geometry, is transformed into a design method. This is done by replacing the classical slip condition (no normal velocity component) by other boundary conditions, in such a way that the required pressure or Mach number distribution may be imposed directly on the blade. The unknowns are calculated on the blade wall using the so-called compatibility relations. Since the blade shape is not compatible with the required pressure distribution, a nonzero velocity component normal to the blade wall evolves from the new flow calculation. The blade geometry is then modified by resetting the wall parallel to the new flow field, using a transpiration technique, and the procedure is repeated until the calculated pressure distribution has converged to the required one. Examples for both subsonic and transonic flows are presented and show a rapid convergence to the geometry required for the desired Mach number distribution. An important advantage of the present method is the possibility to use the same code for the design and the analysis of a blade. [less ▲] Detailed reference viewed: 52 (4 ULg)Inverse Design of Compressor and Turbine Blades at Transonic Flow Conditions Léonard, Olivier ; in Proceedings of the ASME Turbo Expo 1992 (1992, June) Detailed reference viewed: 37 (1 ULg)Conception et développement d'une méthode inverse de type Euler et application à la génération de grilles d'aubes transsoniques Léonard, Olivier Doctoral thesis (1992) Detailed reference viewed: 47 (3 ULg)Permeable Wall Boundary Conditions For Transonic Airfoil Design Léonard, Olivier ; in Proceedings od the First European Computational Fluid Dynamics Conference (1992) Detailed reference viewed: 12 (1 ULg)Design Method for Subsonic and Transonic Cascade with Prescribed Mach Number Distribution Léonard, Olivier ; in Proceedings of the ASME Turbo Expo 1991 (1991, June) A iterative procedure for blade design, using a time marching procedure to solve the unsteady Euler equations in the blade-to-blade plane, is presented. A flow solver, which performs the analysis of the ... [more ▼] A iterative procedure for blade design, using a time marching procedure to solve the unsteady Euler equations in the blade-to-blade plane, is presented. A flow solver, which performs the analysis of the flow field for a given geometry, is transformed into a design method. This is done by replacing the classical slip condition (no normal velocity component) by other boundary conditions, in such a way that the required pressure or Mach number distribution may be imposed directly on the blade. The unknowns are calculated on the blade wall using the so-called compatibility relations. Since the blade shape is not compatible with the required pressure distribution, a nonzero velocity component normal to the blade wall evolves from the new flow calculation. The blade geometry is then modified by resetting the wall parallel to the new flow field, using a transpiration technique, and the procedure is repeated until the calculated pressure distribution has converged to the required one. Examples for both subsonic and transonic flows are presented and show a rapid convergence to the geometry required for the desired Mach number distribution. An important advantage of the present method is the possibility to use the same code for the design and the analysis of a blade. [less ▲] Detailed reference viewed: 46 (1 ULg) |
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