Sławomir Dykas

Experimental Research on Wet Steam Flow With Shock Wave

The article presents research on a wet steam transonic flow in a Laval half-nozzle with a shock wave. The motivation for this research was to investigate the shock wave/liquid phase interaction in the transonic wet steam flow. This phenomenon is responsible for the lack of good correspondence between experimental data and computational fluid dynamics results. For the tests, the geometry of the half-arc nozzle was used. The shock wave formation at the divergent section of the nozzle is caused by too high back-pressure. The observed instabilities in the flow are mainly initiated by the shock wave/liquid film (boundary layer) interaction. The numerical calculations were compared with experimental results with respect to the static pressure distribution along the nozzle.

Diverse configurations of the boiler feed pump drive for the ultra-supercritical 900-MW steam plant

Coal-based electric power generation remains the basic source of obtaining energy. With increasing pressure to reduce CO2 emissions, improving power unit efficiency has become an issue of utmost significance. Surely, one of the possibilities to improve the efficiency of new power units is raising the steam parameters. With improved power plant efficiency, there is a lower demand for power of almost all auxiliary equipment except the boiler feed pump. The reason for this is that the power needed to drive the feed pump is an almost linear function of the steam pressure. This means that, even though the steam mass flow (and, consequently, the feed water mass flow) is reduced and the efficiency of feed pumps is improved, their power increases. For this reason, it is very important to find the optimum drive of the boiler feed pump. The main aim of the conducted analysis was to compare various drive options of the boiler feed pump for a conceptual ultra-supercritical 900-MW steam power unit. The following drive configurations of the boiler feed pump were presented and compared:· A frequency-controlled electric motor· A condensing turbine fed with steam extraction from the immediate-pressure turbine· An extraction-backpressure turbine fed with steam from a cold reheat steam line with bleeds shifted from the low-pressure turbine· A backpressure turbine fed with steam from a hot reheat steam line operating in parallel with the intermediate-pressure turbine· An extraction-backpressure turbine fed with steam from a cold reheat steam line with bleeds shifted from the intermediate-pressure turbine (the master cycle idea).The analysis of the operation of the 900-MW unit with various configurations of the feed pump drive was carried out for three load levels: for the nominal mass flow of live steam and for the partial mass flow of 75% and 50%.

Results of the International Wet Steam Modeling Project

The purpose of the “International Wet Steam Modeling Project” is to review the ability of computational methods to predict condensing steam flows. The results of numerous wet-steam methods are compared with each other and with experimental data for several nozzle test cases. The spread of computed results is quite noticeable and the present paper endeavours to explain some of the reasons for this. Generally, however, the results confirm that reasonable agreement with experiment is obtained by using classical homogeneous nucleation theory corrected for non-isothermal effects, combined with Young’s droplet growth model. Some calibration of the latter is however required. The equation of state is also shown to have a significant impact on the location of the Wilson point, thus adding to the uncertainty surrounding the condensation theory. With respect to the validation of wet-steam models it is shown that some of the commonly used nozzle test cases have design deficiencies which are particularly apparent in the context of two- and three-dimensional computations. In particular, it is difficult to separate out condensation phenomena from boundary layer effects unless the nozzle geometry is carefully designed to provide near-one-dimensional flow.

Experimental and numerical validation study of the labyrinth seal configurations

This article presents a validation study of the labyrinth seal testing. Both experimental and numerical simulations are performed. Literature data focused on simple labyrinth seals are surveyed, and two different configurations widely described in literature are investigated: a labyrinth seal with two straight fins against a smooth and a honeycomb land and a seal with three straight fins against a smooth land only. For experimental testing the vacuum-feeding test rig is used, with the high-precision Hot Wire Thermoanemometry method applied for the mass flow evaluation. The dimensions of specimens described in literature are adapted to the in-house test rig conditions, meeting all the geometrical requirements mentioned by the author. The computational method is based on the Reynolds Averaged Navier Stokes scheme, with various turbulence models. The results of the simulations show good agreement with the in-house experiment, whereas some discrepancies are found compared to literature data.

Experimental and numerical study on the performance of the smooth-land labyrinth seal

In turbomachinery the secondary flow system includes flow phenomena occurring outside the main channel, where the gaseous medium performs work on blades. Secondary air distribution constitutes a very complex and closely interrelated system that affects most of the gas turbine components. One of the most important examples of the secondary flow is leakage occurring in seals, e.g. at the rotor and stator tips, on the shaft or on the sides of the blade rim. Owing to its simplicity, low price, easy maintenance and high temperature capability, the labyrinth seal is a prime sealing solution that may be selected from numerous types of sealing structures applied in turbomachinery. For this reason, an experimental study of this particular structure has been carried out. The paper presents leakage performance of the smooth-land labyrinth seal.

Experimental research on coarse water formation in steam condensing flow on a transition through the shock wave

In this work the condensation phenomena in steam turbine were discussed. The motivation for presented research was an interaction of liquid phase with shock waves existing in the transonic flow. The paper presents the experimental results of the steam condensing transonic flow in Laval nozzles. For the tests the geometries of the half arc nozzles were used. The behaviour of shock waves in the wet steam region was investigated. Due to the high back pressure, in the divergent part of the nozzle the shock wave was induced and interacting with the nozzle walls caused instability in the flow.

Modeling of Aerodynamic Noise Using Hybrid SAS and DES Methods

The purpose of the presented studies is to compare simple and fast CFD methods based on the unsteady Reynolds-Averaged Navier-Stokes equations (uRANS) with the so called hybrid uRANS/LES methods like Detached Eddy Simulation (DES) and Scale Adaptive Simulation (SAS) implemented in the commercial code ANSYS CFX. The goal of this comparison is to find an efficient and relatively fast method for both the flow dynamic and aerodynamic noise prediction in the near and far field, which would be suitable for engineering applications. The CFD calculations were carried out using the commercial code ANSYS CFX 11. The non-reflective boundary conditions and grid stretching were used to avoid the reflections of the acoustic waves from the outer boundaries. The different boundary conditions and turbulence models were used in the calculations. For the acoustic calculations the Fast Fourier Transformation (FFT) was applied to obtain the sound spectrum. The CFD results were compared with the experimental data obtained in references.Copyright

Analysis of the steam condensing flow in a linear blade cascade

This study presents experimental and numerical testing of the steam condensing flow through a linear blade cascade made of blades of a 200 MW steam turbine last stage stator. The tests were carried out on an in-house laboratory stand and using an in-house numerical code modelling the water vapour flow with homo- and heterogeneous condensation. Additionally, this paper presents a comparison of calculations of a flow field modelled by means of a single-fluid model using both an in-house computational fluid dynamics code and the commercial Ansys CFX v16.2 software package. The aim of the research was to identify difficulties involved by comparing the numerical modelling results with the experimental data for a linear blade cascade. The experimental results, which are very well supplemented by those obtained from numerical computations, may be used to validate computational fluid dynamics codes.

Numerical analysis of the impact of pollutants on water vapour condensation in atmospheric air transonic flows

Abstract The paper presents a developed numerical tool in the form of a CFD code solving Reynolds-averaged Navier–Stokes equations for transonic flows of a compressible gas which is used to model the process of atmospheric air expansion in nozzles. The numerical model takes account of condensation of water vapour contained in atmospheric air. The paper presents results of numerical modelling of both homo- and heterogeneous condensation taking place as air expands in the nozzle and demonstrates the impact of the air relative humidity and pollutants on the condensation process.

Interphase processes analysis in moist air transonic flows in nozzles

During the flow of atmospheric air through convergent-divergent (CD) nozzles the water vapour contained in it can condense spontaneously. The resulting liquid phase may then undergo further phase transitions, e.g. evaporation on the shock waves arising in the nozzle divergent part. The subject of this paper is a numerical and experimental analysis of the process of atmospheric air water vapour condensation and an analysis of the resulting liquid phase evaporation on the shock wave. Calculations are performed using an in-house CFD code based on the solution of averaged Navier-Stokes equations supplemented with additional equations modelling the condensation process of water vapour contained in atmospheric air. Experiments are carried out using an in-house facility adapted for measurements of atmospheric air transonic flows.