Jan Halama

Numerical simulation of transonic flow of wet steam in nozzles and turbines

The paper presents several modifications of the flow model published in Štastný and Šejna (Proceedings of the 12th international conference of the properties of water and steam, Begel House, pp 711–719, 1995). Modifications related to the droplet growth model and the equation of state and their implementation into numerical code are described. The effect of droplet size spectra of incoming wet steam is also discussed. Numerical results of three-dimensional flow of wet steam in a turbine cascade show the effect of surface tension correction.

Numerical modeling of two-phase transonic flow

Our work is aimed at the development of numerical method for the modeling of transonic flow of wet steam including condensation/evaporation phase change. We solve a system of PDEs consisting of Euler or Navier-Stokes equations for the mixture of vapor and liquid droplets and transport equations for the integral parameters describing the droplet size spectra. Numerical method is based on a fractional step technique due to the stiff character of source terms, i.e. we solve separately the set of homogenous PDEs by the finite volume method and the remaining set of ODEs either by explicit Runge-Kutta or implicit Euler method. The finite volume method is based on the Lax-Wendroff scheme with conservative artificial dissipation terms for structured grid. We also note result achieved by recently developed finite volume method with VFFC scheme. We discuss numerical results of steady and unsteady two-phase transonic flow in 2D nozzle, 2D and 3D turbine cascade and 2D turbine stage with moving rotor cascade.

Investigation of the 3D Unsteady Rotor Pressure Field in a HP Turbine Stage

This paper presents steady and unsteady pressure measurements at three span locations (15, 50 and 85%) on the rotor surface of a transonic turbine stage. The data are compared with the results of a 3D unsteady Euler stage calculation. The overall agreement between the measurements and the prediction is satisfactory. The effects of pressure ratio and Reynolds number are discussed. The rotor time-averaged Mach number distribution is very sensitive to the pressure ratio of the stage since the incidence of the flow changes as well as the rotor exit Mach number. The time-resolved pressure field is dominated by the vane trailing edge shock waves. The incidence and intensity of the shock strongly varies from hub to tip due to the radial equilibrium of the flow at the vane exit. The decrease of the pressure ratio attenuates significantly the amplitude of the fluctuations. An increase of the pressure ratio has less significant effect since the change in the vane exit Mach number is small. The effect of the Reynolds number is weak for both the time-averaged and the time-resolved rotor static pressure at mid-span, while it causes an increase of the pressure amplitudes at the two other spans.Copyright

Numerical modeling of unsteady flow in steam turbine stage

This work deals with numerical solution of unsteady flow in turbine stage. We use models of compressible single-phase flow of air and two-phase flow of wet steam. Presented numerical methods are based on different stator-rotor matching algorithms, as well as different numerical schemes. Numerical results achieved by both methods and flow models are discussed.

Numerical simulation of circumferentially averaged flow in a turbine

The paper refers about the development of a fast computational code, which should be able to provide an approximate information about the three-dimensional flow field in a multistage turbine. The code is based upon the solution of circumferentially averaged Euler equations coupled with the thermodynamic, geometry and loss prediction models. The computational domain is the meridional cut of a turbine. The Euler equations are solved by a finite volume solver with the AUSM type flux. Initial tests showed, that developed solver is able to predict well radial distributions of flow parameters upstream and downstream considered blade cascades at a fraction of CPU time compared to fully three-dimensional simulations.

Numerical Simulation of Flow in a Meridional Plane of Multistage Turbine

The paper presents a numerical method, which simulates the circumferentially averaged steady flow of a compressible fluid in a multistage turbine. The method is considered in the analytic mode with known geometry. It is intended as a fast tool to turbine designers, which provides the distribution of the flow parameters in the meridional plane, gives the information about mass flow and estimates the efficiency of turbine. The method is based on the solution of the circumferentially averaged three-dimensional Euler equations complemented by the source terms related to the turbine geometry and to the loss prediction model. The meridional plane is discretized by a structured grid. Equations are solved by a finite volume method with the AUSM type numerical flux. Examples including the transonic flow in a turbine stator and in a stage are presented.

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 Transonic Flow in Steam Turbine Cascades

This contribution presents numerical simulations and joined specific issues for several cases of 2D and 3D transonic flow in real-life steam turbine cascades.

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.

Numerical Solution of Turbine Cascade Flow by Two Equations, EARSM and Bypass Transition Turbulence Models

This work deals with numerical solution of transonic flow in turbine cascades. We compare results achieved by SST, TNT and EARSM turbulence models and we also present results achieved by two equations turbulence model with an algebraic bypass transition model. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)