2/2001 Computational Fluid Dynamics

Contents:

• M.Bielecki, M.Karcz, W.Radulski and J.Badur, Thermo-mechanical Coupling between the Flow of Steam and Deformation of the Valve During Start-up of the 200 MW Turbine - abstract | full text
• R.Biernacki, Applicability of Flow Simulation Models to the Case of Radial Inflow onto a Rotating Core - abstract | full text
• A.Boguslawski, Inviscid Instability of the Hyperbolic-Tangent Velocity Profile - Spectral "Tau" Solution - abstract - abstract | full text
• P.Doerffer, J.Rachwalski and F.Magagnato, Numerical Investigation of the Secondary Flow Development in Turbine Cascade - abstract | full text
• A.Kucaba-Pietal, Z.Walenta and Z.Peradzynski, Flows in Microchannels - abstract
• P.Lampart, J.¦wirydczuk and A.Gardzilewicz, On the Prediction of Flow Patterns and Losses in HP Axial Turbine Stages Using 3D RANS Solve with Two Turbulence Models - abstract | full text
• K.Murawski and J.K.Michalczyk, Numerical Simulations by Godunov-type Schemes of Air-Pollutants Dynamics - abstract | full text
• K.Murawski, Numerical Simulations of the Effect of Time-dependent Random Mass Density Field on Frequencies of Sound Waves - abstract
• T.Ochrymiuk and J.Badur, Flame-less Oxidation at the GT26 Turbine - Numerical Study via Full Chemistry - abstract | full text
• M.Sillen, Turbulent Flow Modelling Using EARSM on Parallel Computers - abstract

• A.Januszajtis Scientists in Old Gdansk: Part I

Abstracts:

• M.Bielecki, M.Karcz, W.Radulski and J.Badur, Thermo-mechanical Coupling between the Flow of Steam and Deformation of the Valve During Start-up of the 200 MW Turbine

  The lifetime estimation of power station structures and components, subjected to fatigue loading, is essential for determining the moment of repair or replacement. Therefore the degradation behaviour and damage development within material should be very well understood. This research focuses on a fluid-solid interaction that has been developed in Finite Volume Method software for description of heat and flow loading on a cut-off valve and Finite Element Method software for conduct researches on fatigue and creep damage of the valve material.

• R.Biernacki, Applicability of Flow Simulation Models to the Case of Radial Inflow onto a Rotating Core

  The paper presents the results of fluid flow simulations carried out by means of the FIDAP7.6 program (a fluid dynamics FEM package) for the case of radial inflow onto a rotating shaft. The particular geometric configuration has been chosen to resemble a generalized inlet chamber of twin low-pressure steam turbines, but with the axial outlet section extended to allow better observation of flow instabilities in that region. The calculations were carried out for the same channel geometry for both compressible and incompressible flow, using the same or slightly varying boundary conditions. Extensive variation in non-physical parameters of the model was explored, such as applying different meshes over the region, as well as utilizing different turbulence and upwinding models. The intent of this research was to evaluate the relative applicability of the various available flow models to the simulation of axisymmetric flows with steep velocity gradients, and to discover the limitations of these models. The calculations have in fact established significant differences in the behavior of the simulated flow for the different meshes and models. Some results were characterized by extensive areas of recirculating flow whereas others, for the same boundary conditions, showed no recirculation. Correct near-wall meshing as well as the choice of the upwinding scheme were established as the critical factors in this regard. There was also noticeable variation in outlet velocity profiles. An extensive zone of separation within the investigated channel as well as a standing annular vortex near the point of stagnation are flow features of some interest. These patterns of flow change in response to the changing non-physical parameters; the separation zone in particular is absent or slow to develop under some setups. The influence of inflow parameters, the initial velocity distribution and turbulent intensity in particular, on flow behavior in contact with the rotating shaft have also been an area of investigation, as these are often defined with considerable uncertainty in practical applications. It was observed that some latitude in assuming these parameters did not significantly alter the relevant flow parameters at outlet (the velocity and pressure distributions), although it did induce variation in other aspects of the flow (such as the extent of the standing vortex).

• A.Boguslawski, Inviscid Instability of the Hyperbolic-Tangent Velocity Profile - Spectral "Tau" Solution - abstract

  The paper presents a spectral solution of the Rayleigh equation for the case of parallel, free shear layer with the hyperbolic-tangent mean velocity profile. The expansion of the eigenfunction into the Chebyshev polynomial series allowed transformation of the differential eigenvalue problem into the general algebraic one. The standard algebraic eigenvalue problem was obtained by the use of Gary & Helgasson transformation. The results were compared with the shooting method. Although the calculations were carried out in order to validate the method, some additional study of the velocity ratio and momentum thickness influence on the temporal eigenmode growth rate was also performed.

• P.Doerffer, J.Rachwalski and F.Magagnato, Numerical Investigation of the Secondary Flow Development in Turbine Cascade

  The results represent the first attempt of the numerical analysis of 3-D secondary flows formed in the linear turbine cascade wind tunnel. Numerical simulations were carried out by means of the SPRC code. It was possible to make presented here calculations thanks to the cluster of PC's providing sufficient computational resources. In order to be able to verify the obtained results the case considered is the workshop test case (D.G.Gregory-Smith 1994 Turbomachinery Workshop Test Case No.3 116). It has been shown that the obtained results are in a very good agreement with experiment. It gave confidence in the results and several important conclusions concerning the development of streamwise vortices could be made thanks to the work carried out.

• A.Kucaba-Pietal, Z.Walenta and Z.Peradzynski, Flows in Microchannels

  The aim of this paper is to present a survey of the results for the flows of simple gases and liquids with substructure through narrow channels, obtained with the Direct Monte-Carlo and Molecular Dynamics Simulation methods.

• P.Lampart, J.¦wirydczuk and A.Gardzilewicz, On the Prediction of Flow Patterns and Losses in HP Axial Turbine Stages Using 3D RANS Solve with Two Turbulence Models

  An experimentally tested air turbine stage and a real high-pressure (HP) steam turbine stage are calculated using the 3D RANS solver FlowER supplemented with the Baldwin-Lomax and Menter shear stress transport (SST) models. The computations of the model air turbine stage show that the Menter SST model gives better agreement with the experimental data as far as the span-wise distribution of exit velocities and swirl angle. The comparison of performance of the two turbulence models exhibits differences in predicting flow patterns and losses in the considered HP turbine stage. The main differences concern the development of secondary flows and separations. There is a significant span-wise redistribution of losses between these two models. The tendency is that for the same relatively refined grid resolutions, the level of pitch/span averaged losses for the Menter SST turbulence model is slightly above that of Baldwin-Lomax.

• K.Murawski and J.K.Michalczyk, Numerical Simulations by Godunov-type Schemes of Air-Pollutants Dynamics

  In this paper several aspects associated with numerical simulations of hyperbolic equations are discussed. This presentation covers a range of modern shock-capturing schemes which are based on Godunov-type techniques. These schemes are well suited for strong shocks and other discontinuities, without generating spurious oscillations in the flow variables. An example of a performance of such schemes is provided to simulate the spatial distribution of air-pollutants which are emitted from a chimney. The simulations are performed in the framework of two-dimensional hydrodynamics, with a use of the CLAWPACK code (R.J.LeVeque, CLAWPACK User Notes, Applied Mathematics,Univ. of Washington, Seattle, 1997a). The model reproduces several features of the distribution, including occurrence of vortices and plumes above the chimney.

• K.Murawski, Numerical Simulations of the Effect of Time-dependent Random Mass Density Field on Frequencies of Sound Waves

  Numerical simulations of the effect of random mass density field on frequencies of sound waves are considered for driven and impulsive sound waves which are described by one-dimensional hydrodynamic equations, with the ponderomotive force which depends stochastically both on space and time. The numerical results reveal frequency increase for short waves and both wave damping and amplification for the overall range of wavenumbers. Moreover, a space- and time-dependent random field leads to a generation of a wide frequency spectrum which contains both retarded and speeded up waves.

• T.Ochrymiuk and J.Badur, Flame-less Oxidation at the GT26 Turbine - Numerical Study via Full Chemistry

  Sequential combustion was first applied to gas turbines more than 40 years ago, and almost half of these early machines are still operating. This form of oxidation leads to the flame-less combustion at a second chamber. In GT26, the second stage combustor has 24 SEV burners which are similar in action to the well known ABB EV burner. In this paper, a 3D numerical simulation of the first EV combustor and the second SEV-combustor are performed for normal operating conditions (exhaust mass flow 542 kg/s, exhaust temperature 610 C). Physical modelling of the flame-less oxidation is based on an original implementation of the Gri-Mech mechanism (325 chemical reactions) into the Fluent 5.4. Precise estimation of NOx emission and other pollutants has been done.

• M.Sillen, Turbulent Flow Modelling Using EARSM on Parallel Computers

  The compressible Navier-Stokes equations are solved numerically for turbulent transonic aerospace applications on parallel computers. The turbulence is modelled by an Explicit Algebraic Reynolds Stress Model (EARSM). Expressing the EARSM as an extension of an eddy-viscosity model makes the implementation straightforward in a flow solver with existing two-equation eddy-viscosity models. The k-w transport equations are used as a platform for the model. The EARSM approach significantly improves the shock position for transonic flow over wings without substantial increase in computational cost. Industrial use of advanced flow modelling requires a short turn-around time of computations. This is enabled through the use of parallel computers. To achieve good parallel performance the computational load has to be evenly distributed between the processors of the parallel machine. A heuristic algorithm is described for distributing and splitting the blocks of a structured multiblock grid for a good static load balance. Speed-up results are presented for turbulent flow around a wing on a number of parallel platforms.