Methodology for the Numerical Characterization of a Radial Turbine under Steady and Pulsating Flow

Doctoral Thesis / Dissertation from the year 2012 in the subject Engineering - Mechanical Engineering, Universidad Politcnica de Valencia (Departamento de Maquinas y Motores Termicos), language: English, abstract: The increasing use of turbochargers is leading to an outstanding research to
understand the internal flow in turbomachines. In this frame, computational
fluid dynamics (CFD) is one of the tools that can be applied to contribute
to the analysis of the fluid-dynamic processes occurring in a turbine. The
objective of this thesis is the development of a methodology for performing
simulations of radial turbomachinery optimizing the available computational
resources. This methodology is used for the characterization of a vaned-nozzle
turbine under steady and pulsating flow conditions.
An important effort has been devoted in adjusting the case configuration
to maximize the accuracy achievable with a certain computational cost. Concerning
the cell size, a local mesh independence analysis is proposed as a
procedure to optimize the distribution of cells in the domain, thus allowing to
use a finer mesh in the most suitable places. Particularly important in turbomachinery
simulations is the influence of the approach for simulating rotor
motion. In this thesis two models have been compared: multiple reference
frame and sliding mesh. The differences obtained using both methods were
found to be significant in off-design regions. Steady flow CFD results have
been validated against global measurements taken on a gas-stand.
The modeling of a turbine, installed either on a turbocharger test rig or
an engine, requires the calculation of the flow in the ducts composing the
system. Those ducts could be simulated assuming a one-dimensional (1D)
approximation, and thus reducing the computational cost. In this frame of
ideas, two CFD boundary conditions have been developed. The first one allows
performing coupled 1D-3D simulations, communicating the flow variables from
each dom