René Van den Braembussche

Numerical Optimization for Advanced Turbomachinery Design

The multilevel-multidisciplinary-multipoint optimization system developed at the von Karman Institute and its applications to turboma-chinery design is presented. To speed up the convergence to the optimum geometry, the method combines an Artificial Neural Network, a Design Of Experiment technique and a Genetic Algorithm. The different components are described, the main requirements are outlined and the basic method is illustrated by the design of an axial turbine blade.

Inverse Design and Optimization of a Return Channel for a Multistage Centrifugal Compressor

The design and optimization of a multistage radial compressor vaneless diffuser, cross-over and return channel is presented. An analytical design procedure for 3D blades with prescribed load distribution is first described and illustrated by the design of a 3D return channel vane with leading edge upstream of the cross-over. The analysis by means of a 3D Navier-Stokes solver shows a substantial improvement of the return channel performance in comparison with a classical 2D channel. Most of the flow separation inside and downstream of the cross-over could be avoided in this new design. The geometry is further improved by means of a 3D inverse design method to smooth the Mach number distribution along the vanes at hub and shroud

Design and Optimization of the Internal Cooling Channels of a HP Turbine Blade: Part II—Optimization

This second paper presents the aerothermal optimization of the first stage rotor blade of an axial HP turbine by means of the conjugate heat transfer method (CHT) and lifetime model described in paper 1. The optimization system defines the position and diameter of the cooling channels leading to the maximum lifetime of the blade while limiting the amount of cooling flow. It is driven by the results of a CHT and subsequent stress analysis of each newly designed geometry. Both temperature and stress distributions are the input for the Larson-Miller material model to predict the lifetime of the blade. The optimization procedure makes use of a Genetic Algorithm (GA) and requires the aerothermal analysis of a large number of geometries. Because of the large computational cost of each CHT analysis, this results in a prohibitive computational effort. The latter has been remediated by using a more elaborate optimization system, in which a large part of the CHT analyzes are replaced by approximated predictions by means of a meta-model. Two metamodels, an Artificial Neural Network (ANN) and a Radial Basis Function (RBF) network, have been tested and their merits have been discussed. It is shown how this optimization procedure based on CHT calculations, a GA and a metamodel can lead to a considerable extension of the blade lifetime without increase of the amount of cooling flow or the complexity of the cooling geometry.Copyright

Design and Optimization of the Internal Cooling Channels of a High Pressure Turbine Blade—Part I: Methodology

This first paper describes the conjugate heat transfer (CHT) method and its application to the performance and lifetime prediction of a high pressure turbine blade operating at a very high inlet temperature. It is the analysis tool for the aerothermal optimization described in a second paper. The CHT method uses three separate solvers: a Navier-Stokes solver to predict the nonadiabatic external flow and heat flux, a finite element analysis (FEA) to compute the heat conduction and stress within the solid, and a 1D aerothermal model based on friction and heat transfer correlations for smooth and rib-roughened cooling channels. Special attention is given to the boundary conditions linking these solvers and to the stability of the complete CHT calculation procedure. The Larson-Miller parameter model is used to determine the creep-to-rupture failure lifetime of the blade. This model requires both the temperature and thermal stress inside the blade, calculated by the CHT and FEA. The CHT method is validated on two test cases: a gas turbine rotor blade without cooling and one with five cooling channels evenly distributed along the camber line. The metal temperature and thermal stress distribution in both blades are presented and the impact of the cooling channel geometry on lifetime is discussed.

Design and Optimization of the Internal Cooling Channels of a High Pressure Turbine Blade—Part II: Optimization

This second paper presents the aerothermal optimization of the first stage rotor blade of an axial high pressure (HP) turbine by means of the conjugate heat transfer (CHT) method and lifetime model described in Paper I. The optimization system defines the position and diameter of the cooling channels leading to the maximum lifetime of the blade while limiting the amount of cooling flow. It is driven by the results of a CHT and subsequent stress analysis of each newly designed geometry. Both temperature and stress distributions are the input for the Larson-Miller material model to predict the lifetime of the blade. The optimization procedure makes use of a genetic algorithm (GA) and requires the aerothermal analysis of a large number of geometries. Because of the large computational cost of each CHT analysis, this results in a prohibitive computational effort. The latter has been remediated by using a more elaborate optimization system, in which a large part of the CHT analyzes is replaced by approximated predictions by means of a metamodel. Two metamodels, an artificial neural network and a radial basis function network, have been tested and their merits have been discussed. It is shown how this optimization procedure based on CHT calculations, a GA, and a metamodel can lead to a considerable extension of the blade lifetime without an increase in the amount of cooling flow or the complexity of the cooling geometry.

Multidisciplinary Optimization of Propeller Blades: focus on the aeroacoustic results

Concurrent aerodynamic, aeroacoustic and aeroelastic optimization of transonic propeller blades is performed with a Multi-Objective Differential Evolution technique. The optimization process relies on a metamodel to deliver performance estimates as well as on recurrent Computational Fluid Dynamics, Computational Hybrid Aeroacoustics and Computational Structural Mechanics simulations in order to safeguard the accuracy. The innovative design parameters for the radial distributions of sweep, twist, chord and thickness as well as for the shape of the two airfoil sections used to manufacture the blade, consist in the control points of a b-spline parameterization of these curves. The optimization results are discussed in terms of aerodynamic and aeroacoustic performances with a limited discussion of the aeroelastic behavior.

Truncated method for propeller noise prediction up to low supersonic helical tip Mach numbers

The present paper addresses a simple truncation technique applied to cope with the sonic singularity so that noise from propellers can be computed in the subsonic as well as transonic and low supersonic domain at low numerical cost. Based on Farassat’s 1A formulation of the Ffowcs Williams-Hawkings (FW-H) acoustic analogy, the present method computes the pressure signal for loading and thickness noise from steady RANS computations for arbitrary observer locations, by a retarded-time approach in the time-domain. For cases where the sonic singularity does not occur, the method consists of Farassat’s 1A formulation; in cases where the sonic singularity occurs, it switches to an approximate prediction. The results obtained with this truncated method are compared with a series of experimental results over a wide range of operating conditions for two advanced propfan blade designs. The comparisons state on the validity of the method for the relative assessment of dierent designs. Being inexpensive and reliable, though approximate, it is suited for propeller optimization in a multi-disciplinary environment.

Design and Optimization of the Internal Cooling Channels of a HP Turbine Blade: Part I—Methodology

This first paper describes the Conjugate Heat Transfer (CHT) method and its application to the performance and lifetime prediction of a high pressure turbine blade operating at a very high inlet temperature. It is the analysis tool for the aerothermal optimization described in a second paper. The CHT method uses three separate solvers: a Navier-Stokes (NS) solver to predict the non-adiabatic external flow and heat flux, a Finite Element Analysis (FEA) to compute the heat conduction and stress within the solid, and a 1D aero-thermal model based on friction and heat transfer correlations for smooth and rib-roughened cooling channels. Special attention is given to the boundary conditions linking these solvers and to the stability of the complete CHT calculation procedure. The Larson-Miller parameter model is used to determine the creep-to-rupture failure lifetime of the blade. This model requires both the temperature and thermal stress inside the blade, calculated by the CHT and FEA. The CHT method is validated on two test cases: a gas turbine rotor blade without cooling and one with 5 cooling channels evenly distributed along the camber line. The metal temperature and thermal stress distribution in both blades are presented and the impact of the cooling channel geometry on lifetime is discussed.Copyright

A new compressor and turbine blade design method based on three-dimensional euler computations with moving boundaries

A new three-dimensional inverse method for the design of compressor and turbine blades is presented. The method solves the time dependent Euler equations in a numerical domain of which some boundaries (the blade walls) are iteratively modified until a prescribed pressure distribution is reached. Each iteration of the procedure starts with a blade modification, based on the transpiration model and the permeable wall concept. After generating a new mesh the flow field is updated by performing one finite volume time iteration, taking into account the mesh points movement during the time stepping. The blade modifications and time marching computation converge simultaneously to the required geometry and steady-state flow solution. The method makes use of a high resolution three-dimensional finite volume Euler solver, with an upwind-biased evaluation of the advective fluxes for sharp shock wave capturing and low numerical entropy generation. The wall boundary conditions respect the hyperbolic character of the t...

3D UNSTEADY FLOW AND FORCES IN CENTRIFUGAL IMPELLERS WITH CIRCUMFERENTIAL DISTORTION OF THE OUTLET STATIC PRESSURE

This paper describes the numerical investigation of the centrifugal impeller response to downstream static pressure distortions imposed by volutes at off-design operations. An unsteady 3D Euler solver with non-reflecting upstream and downstream boundary conditions and phase-lagged periodicity conditions is used for this purpose.The mechanisms governing the unsteady flow field are analysed. A parametric study shows the influence of the acoustic Strouhal number on the amplitude of the flow perturbations. Radial forces calculated on backward leaned and radial ending centrifugal impellers, show non-negligible influence of the impeller geometry.Copyright