CFD Research Topics
- Unsteady methods for fast and detailed component interaction studies (clocking effects, multistage environment): a dual-time stepping method is used with either a full annulus approach or Fourier-based chorochronic boundary conditions.
- Separation-induced transition models: the prediction of transition in high-lift and ultra-high-lift LP turbine airfoils is a challenging task which involves several aspects which are physically complex. In steady low Reynolds number cascade flows the transition on the suction side is often triggered by the formation of a laminar separation bubble. The configuration (reattachment, bursting, etc.) of the separation bubble is closely related to the transitional flow details. Such details become more and more important as the blade lift increases. In multistage unsteady environments the losses are determined by the interaction between the separating boundary layers and the incoming wakes, which establish an unsteady transition pattern. A novel three-equation, transition-sensitive turbulence model based on the coupling of an additional transport equation for the so-called 'laminar kinetic energy' with the Wilcox's k-omega model has been developed.
- Simulation and modelization of passive (roughness elements) and active (synthetic jets) boundary layer control devices.
- Real gas modeling: the behavior of real gases, gas mixtures or steam is reproduced by replacing analytic relationships of the perfect gas with the use of gas property tables. The real gas model is generally applicable to any working fluid, and extends property evaluations into saturated and superheated regions. To reduce computational costs, gas tables are generated off-line. The method consists of a local fitting of gas data to provide the thermodynamic properties required by the solver in each solution step. In addition to regular and equally spaced gas tables, clustered tables can also be used. Clustering allows one to adopt local very fine cell spacing where high accuracy is needed, without requiring too many grid points far from the physical region of interest. As a major result, the analytical search formulas make computational time independent of table dimensions. The real gas model has been applied to the analysis of turbomachines representative of common industrial problems in which the working fluid modeling affects performance prediction, like LP steam turbines, cooled gas turbines and centrifugal cryogenic compressors.
- Mass flow extraction/injection model: suitable endwall boundary conditions, based on coupled sources and sinks (e.g. cavity purge flows, shroud leakage flows, blade/endwall cooling, etc.).
- Body forces model: including both a lift force (to turn the flow) and a drag force to produce losses, allow to simulate the presence of geometrical details in the main flow (e.g. damping wires, part-span splitters, pressure/temperture probes) without requiring their direct inclusion in the computational mesh.
- Non-reflecting boundary conditions for both axial and radial turbomachineries, single row and multirow (mixing-planes) computations.
