Petr Louda

Numerical simulations of flow through channels with T-junction

The paper deals with numerical solution of laminar and turbulent flows of Newtonian and non-Newtonian fluids in branched channels with two outlets. Mathematical model of the flow is based on the Reynolds averaged Navier-Stokes equations for the incompressible fluid. In the turbulent case, the closure of the system of equations is achieved by the explicit algebraic Reynolds stress (EARSM) turbulence model. Generalized non-Newtonian fluids are described by the power-law model. The governing equations are solved by cell-centered finite volume schemes with the artificial compressibility method; dual time scheme is applied for unsteady simulations. Channels considered in presented calculations are of constant square or circular cross-sections. Numerical results for laminar flow of non-Newtonian fluid are presented. Further, turbulent flow through channels with perpendicular branch is simulated. Possible methods for setting the flow rate are discussed and numerical results presented for two flow rates in the branch.

Numerical Solution of Flow in Backward Facing Step

The work deals with numerical testing of two different numerical methods based on finite volumes (FV) and finite elements (FE) for different Reynolds numbers. The finite volume method is based on upwind scheme (third order) for convective terms and central second order for dissipative terms. Finite element method consists of stabilization of weak formulation for higher Reynolds numbers with the help of streamline-upwind (Petrov-Galerkin) modification.

On numerical simulation of three-dimensional flow problems by finite element and finite volume techniques

Abstract This paper is interested in the numerical approximation of the turbulent 3D incompressible flow. The turbulent flow is mathematically modeled using the Reynolds averaged Navier–Stokes (RANS) equations and two classes of the turbulent models are considered. RANS equations are approximated by two numerical techniques, the finite volume and the finite element methods. The finite element approximation on general 3D domains using general meshes consisting of hexahedrons as well as tetrahedrons, pyramids and prisms is described. The definition of the continuous piecewise trilinear/linear finite element space is given, and the stabilization based on the streamline-upwind/Petrov–Galerkin method together with the pressure stabilizing/Petrov–Galerkin techniques is used. The turbulence k – ω model is approximated on the finite element spaces, and the nonlinear stabilization technique is applied. Furthermore, the finite volume technique is used for the approximation of the RANS equations. The turbulent k – ω or the explicit algebraic Reynolds stress models are used. The numerical solution is carried out by the implicit finite volume method. The artificial compressibility method is used to solve the incompressibility constraint. The numerical results are shown.

Numerical modeling of the flow structures in the channels with T-junction

The work deals with the numerical simulations of a 3D incompressible viscous turbulent flow in the branched channels with circular cross section. The mathematical model is based on the unsteady Reynolds averaged Navier-Stokes (URANS) equations with the explicit algebraic Reynolds stress (EARSM) turbulence model. The resulting set of partial differential equations is then solved by artificial compressibility method in dual time in the finite volume formulation. The flow through the round branched channel with branch perpendicular to the main channel (T-junction) is considered. Diameter of the main channel is 50mm and diameter of the branch is 32mm. Different combinations of inlets and outlets and different flow rates are studied.

Numerical Simulation of Turbulent Incompressible and Compressible Flows Over RoughWalls

Wall roughness affects flow characteristics practically in all technical applications. In internal flows, the height of rough elements should be much smaller than the thickness of the shear layer (so called distributed roughness) and its influence on the flow cannot be directly simulated. Instead a model of rough wall is needed.

FVM-FEM Coupling and its Application to Turbomachinery

The paper deals with the numerical solution of turbulent flows through a 2D turbine cascade considering heat exchange between the gas and the solid blade. The flow field is described by the Favre averaged Navier-Stokes equations, and the temperature field inside the solid blade is given by the Laplace equation. Both parts are coupled in order to achieve continuity of the temperature as well as of the heat flux along the fluid-solid boundary. The analysis of simplified model case is presented and the results obtained with two in-house codes with several two-equation turbulence models are compared to results of commercial software (Fluent).

Numerical simulation of flow through cascade in wind tunnel test section and stand-alone configurations

The paper deals with the numerical simulation of the flow field in a turbine cascade, which corresponds to the tip section of a last low-pressure steam turbine rotor. Considered cascade consists of very thin profiles with high stagger angle. The resulting flow field is complex with interactions of strong shock waves, shear layers and shock reflections. The paper proposes a proper numerical approximation of boundary conditions suitable for cases with supersonic inlet and outlet flow velocities and compares the flow field for two cascade configurations: the first one corresponding to real experiment (cascade with finite number of blades located in the wind tunnel test section) and the second one corresponding to annular cascade. The experimental configuration includes the complicated geometry of wind tunnel. The annular configuration leads to blade to blade periodicity, which is not guaranteed for the experimental configuration. Numerical simulations are based on the Favre-averaged Navier–Stokes equations with SST k–ω turbulence model and the in-house implicit finite volume solver with AUSM-type discretization. This method considers structured multi-block grid. Results are compared with experimental data.

Investigation of transonic and supersonic flow in the rotor tip section of the last LP steam turbine stage under different turbulence levels.

Design of a new generation of the large power steam turbines leads to very long last rotor blades with tip sections operating often in supersonic region. The flow field in such tip sections is not fully explored and it is believed to be fairly complex and very sensitive even on minute changes of flow parameters. This stimulated the study of the performance of profiles suitable for rotor tip sections. Numerical simulations have been carried out using TU Prague’s code based on the solution of the RANS equations and SST turbulence model by implicit finite volume method with AUSMPW+ scheme in high resolution formulation. Experimental data have been gathered in the intermittent high-speed wind tunnel of IT CAS CR for 2D cascade measurements equipped by an adjustable supersonic inlet nozzle, perforated inserts at side walls and adjustable perforated tailboard.

On Numerical Simulation of Transition to Turbulence in Turbine Cascade

The work deals with numerical simulation of transonic turbulent flow in turbine cascades taking into account transition to turbulence. The Favre-averaged Navier-Stokes equations are closed by the SST eddy-viscosity turbulence model or by explicit algebraic Reynolds stress turbulence model (EARSM) with the γ-ζ transition model of Lodefier and Dick. The mathematical model is solved by implicit AUSM-type finite volume method. The implementation of transition model does not require case specific input under the assumption that the whole thickness of boundary layer is contained in the same block of multi-block grid, which can easily be fulfilled in the cases considered. The results are shown for 2D tip profile turbine cascade and 2D and 3D SE1050 turbine cascade.

Numerical modelling of compressible viscous flow in turbine cascades

The work deals with mathematical models of turbulent flow through turbine cascade in 2D and 3D. It is based on the Favre-averaged Navier-Stokes equations with SST or EARSM turbulence models. A two-equation model of transition to turbulence is considered too. The solution is obtained by implicit AUSM finite volume method. The 2D and 3D results are shown flow through the SE1050 cascade including simulation of a range of off-design angles of attack.