Stefano Rebay

High-order discontinuous Galerkin discretization of transonic turbulent flows

This paper describes an approach for computing transonic turbulent flows by using a high-order discontinuous Galerkin (DG) method. The method solves the RANS and k-w turbulence model equations on hybrid grids consisting of arbitrary sets of elements (triangles and quadrangles in 2D, tetrahedrons, prisms, pyramids and hexahedrons in 3D) with possibly curved faces. Oscillations of high-order solutions around shocks are controlled by means of a viscous-like term, explicitly added to the discretized equations, which acts to damp the growth of higher-order components of the solution. For steady state solutions of turbulent flow computations the DG discretized equations are integrated in time by using the backward Euler method. The code is fully parallelized and relies on METIS for grid partitioning and on PETSc for linear algebra. Numerical results of some test cases proposed within the EU ADIGMA project will demonstrate the capabilities of the method. Copyright

Transonic and Supersonic Inviscid Computations in Cascades Using Adaptive Unstructured Meshes

The paper describes a solution procedure for two dimensional compressible inviscid flows. The solution algorithm uses a finite volume spatial discretization on unstructured grids of triangles and an explicit Runge-Kutta time marching scheme; for steady problems efficiency is enhanced by using local time stepping and enthalpy damping. The use of unstructured meshes automatically adapted to the solution allows arbitrary geometries and complicated flow features to be treated easily and with high degree of accuracy, even if more work is needed to reach a computational efficiency comparable to those of existing structured codes. Adaptation criteria based on error estimates of significant flow variables have been implemented and tested. The method has been applied to the computation of transonic and supersonic flows in gas turbine nozzles and in impulse rotor cascades for spatial applications and the results have been compared with the experimental data.Copyright

Surrogate-Based Shape Optimization of the ERCOFTAC Centrifugal Pump Impeller

Centrifugal pumps are largely used in several fields and for different applications. Despite their wide diffusion, they are often not optimized for working at the design conditions. The aim of this paper is to investigate the potentialities offered by surrogate-based optimization techniques in centrifugal pump impeller shape optimization, to obtain a robust and fast algorithm for performance improvement. The geometry chosen for validating the proposed method is the ERCOFTAC centrifugal pump where accurate measurements and simulations are available in the literature. The three-dimensional geometry of the impeller is parametrized by means of parametric Bezier surfaces with an in-house Scilab script, which allows to export the dictionary used by the utility blockMesh to create the mesh for the CFD simulation. The surrogate-based optimization method here described maximizes the pump hydraulic efficiency, while keeping the total pressure rise prescribed to the design condition, in order to find the optimal impeller design. The whole optimization chain is designed for running in HPC environment with open-source software, i.e. OpenFOAM for CFD simulation, Dakota for the optimization and Scilab for the geometry parametrization.