Dieter Brillert

Investigation Into the Computational Analysis of Direct-Transfer Pre-Swirl Systems for Gas Turbine Cooling

Direct transfer pre-swirl systems have been investigated by means of 3D computational analysis. Different computational approaches have been utilized and results have been compared with measurements. Based on the validation studies, guidelines for modeling such systems have been proposed. The present results imply that sufficiently accurate predictions can be obtained by means of a quasi-steady analysis applying the “frozen rotor” approach for treating the interface between the stationary and rotating domains. The results indicate that the dimensionless pressure and temperature show a rather weak sensitivity to the relative position of the stator and rotor, using the frozen rotor approach, for the cases studied.© 2004 ASME

Investigations of Dust Separation in the Internal Cooling Air System of Gas Turbines

Improvements in efficiency and performance of gas turbines require a better understanding of the internal cooling air system which provides the turbine blades with cooling air. With the increase of cooling air passing through the internal air system, a greater amount of air borne particles is transported to the film cooling holes at the turbine blade surface. In spite of their small size, these holes are critical for blockage. Blockage of only a few holes could have harmful effects on the cooling film surrounding the blade. As a result, a reduced mean time between maintenance or even unexpected operation faults of the gas turbine during operation could occure. Experience showed a complex interaction of cooling air under different flow conditions and its particle load. To get more familiar with all these influences and the system itself, a test rig has been built. With this test rig, the behaviour of particles in the internal cooling air system could be studied at realistic flow conditions compared to a modern, heavy duty gas turbine. It is possible to simulate different particle sizes and dust concentrations in the coolant air. The test rig has been designed to give information about the quantity of separated particles at various critical areas of the internal air system [1]. The operation of the test rig as well as analysis of particles in such a complex flow system bear many problems, addressed in the previous paper [1]. New measurements and analysis methods give new and more accurate results, which will be shown in this paper. Furthermore the inspection of the test rig shows dust deposits at unexpected positions of the flow path. Theoretical studies to characterize the flow behaviour of the disperse phase in a continuous fluid using Lagrangian Tracking were also performed. A comparison between the numerical solution and the measurements will be shown in the paper.Copyright

Dust Separation in a Gas Turbine Pre-Swirl Cooling Air System: A Parameter Variation

With the increase of cooling air passing through the internal air system of modern gas turbines, a greater amount of air borne particles is transported to the film cooling holes at the turbine blade surface. In spite of their small size, these holes are critical for blockage. A test rig has been designed to give information about the quantity of separated particles at various critical areas of the internal air system. With this test rig, the behavior of particles in the internal cooling air system could be studied at realistic flow conditions compared to a modern, heavy duty gas turbine. It is possible to simulate different particle sizes and dust concentrations in the coolant air. Numerical studies to characterize the flow behavior of the disperse phase in a continuous fluid using Lagrange Tracking were performed. The main influencing parameters, which are the mass flow through the system, the rotor speed and the nozzle angle of the pre-swirl generator, were varied. Furthermore to validate the theoretical studies, based on the presented variations a special point of operation was selected to get a comparable measurement, which is presented in the paper. Comparison between simulation and measurement shows additional influences of the particle shape, which were discussed. The resulting enhanced model and the comparison to the measurement is presented in the paper.Copyright

Calculation of Flow Losses in Rotating Passages of Gas Turbine Cooling Systems

The continuous improvement in thermal efficiency of gas turbines is primarily achieved by increasing the turbine inlet temperatures without, however, affecting the thermal stability and the fatigue strength of the blades which must be guaranteed for their entire service life. The precise analysis of secondary air systems is therefore of crucial importance for the design of gas turbines.Stationary and rotating passages constitute important elements of secondary air systems, and this paper focuses on the calculation of the characteristics of fluid flow through stationary and rotating passages (or bores) as a function of passage length, asymmetric inflow (i.e. crossflow at the inlet) and inlet edge geometry (i.e. rounded or sharp–edged inlets). A simple physical model is developed on the basis of the simple and thoroughly investigated passage flow. The model is then matched to a large number of test results taken from the literature. The result is a versatile tool for calculating flow losses in rotating and stationary passages.Copyright

Numerical Investigation on the Vibration of Steam Turbine Inlet Valves and the Feedback to the Dynamic Flow Field

The power output of steam turbines is controlled by steam turbine inlet valves. These valves have a large flow capacity and dissipate in throttled operation a huge amount of energy. Due to that, high dynamic forces occur in the valve which can cause undesired valve vibrations.In this paper, the structural dynamics of a valve are analysed. The dynamic steam forces obtained by previous computational fluid dynamic (CFD) calculations at different operating points are impressed on the structural dynamic finite element model (FEM) of the valve. Due to frictional forces at the piston rings and contact effects at the bushings of the valve plug and the valve stem the structural dynamic FEM is highly nonlinear and has to be solved in the time domain.Prior to the actual investigation grid and time step studies are carried out. Also the effect of the temperature distribution within the valve stem is discussed and the influence of the valve actuator on the vibrations is analysed.In the first step, the vibrations generated by the fluid forces are investigated. The effects of the piston rings on the structural dynamics are discussed. It is found, that the piston rings are able to reduce the vibration significantly by frictional damping. In the second step, the effect of the moving valve plug on the dynamic flow in the valve is analysed. The time dependent displacement of the valve is transferred to CFD calculations using deformable meshes. With this one way coupling method the response of the flow to the vibrations is analysed.© 2015 ASME

Numerical Investigation on the Time-Variant Flow Field and Dynamic Forces Acting in Steam Turbine Inlet Valves

The unsteady flow in inlet valves for large steam turbines used in power stations was investigated using the method of computational fluid dynamics (CFD). As the topology of the flow depends on the stroke and the pressure ratio of the valve, the flow was investigated at several positions. Various turbulence models were applied to the valve to capture the unsteady flow field. Basic Reynolds-averaged Navier–Stokes (RANS) models, the scale adaptive simulation (SAS), and the scale adaptive simulation with zonal forcing (SAS-F, also called ZFLES) were evaluated. To clarify the cause of flow-induced valve vibrations, the investigation focused on the pressure field acting on the valve plug. It can be shown that acoustic modes are excited by the flow field. These modes cause unsteady forces that act on the valve plug. The influence of valve geometry on the acoustic eigenmodes was investigated to determine how to reduce the dynamic forces. Three major flow topologies that create different dynamic forces were identified.

Application of Conjugate CFD to the Internal Cooling Air Flow System of Gas Turbines

Continuous improvements of the secondary air system are basic elements to increase efficiency and power of heavy duty gas turbines. It is becoming more important to perform a precise calculation of the heat transfer characteristics and to produce accurate predictions of the air/metal temperature in the internal cooling air system. Thermal effects influences the cooling behavior and consequently the cooling efficiency and the material temperature. The material temperature influences the stresses and the creep behavior that is important for life prediction and the reliability of the engine. Furthermore, the material temperature influences the clearances and therefore, the cooling mass-flow. This paper deals with a complex internal blade feed system comprising a forced radially-inward jet-flow into a large rotating cavity and the numerical coupling of different cooling air flow passages with component heat transfer, i.e. conjugate CFD. A calculation procedure was adopted to reproduce the measured rotating main shaft temperatures from the Siemens Model V84.3A gas turbine prototype. Based on this procedure, flow and heat transfer throughout the sub-cavities were discussed and the shaft temperature distribution was obtained. Results indicate a strong interaction between the thermal effects of the cooler radial jet-flow and the hotter seal gap regions. Moreover, the deficiencies in the adopted calculation procedure were identified.Copyright

Total Pressure Losses in Rotor Systems With Radial Inflow

Gas turbines with a splined-disc rotor design allow the compressor bleed pressure to be adapted precisely to the requirements of rotor cooling air systems in which the cooling air is routed through the spaced between the rotating discs.Calculation of such flows is extremely difficult; particularly so if the flow is directed radially inward. In such cases the circumferential component of the absolute velocity can be very high and can thus lead to pronounced total pressure losses.The paper gives a brief description of the flow phenomena, and details in the calculation methods cited in the literature.Navier–Stokes calculations were carried out for the flow through a model test bed engine. The results are compared with experimental data.A simple calculation model is discussed and its result compared with test data.The model predicts the flow pattern more accurately than the Navier-Stokes calculations, and this paper shows that the simple model can be improved further.Copyright

Loss Prediction for Rotating Passages in Secondary Air Systems

Modern heavy duty gas turbines operate with high tur- bine inlet temperatures, and thus require a complex sec- ondary air system to ensure that the blades and vanes are supplied with the required amount of cooling air. Gas tur- bines with high thermal efficiency and with low emissions require minimum amounts of cooling and sealing air which means that the design of the secondary air system must be extremely accurate. A previous paper introduced the secondary air system for the new Siemens Vx4.3A gas turbines and the calcula- tion method used for its design. This paper deals with the detailed calculation of flow field losses in cooling air passages in rotating disks (rotating passages). The paper starts with a brief review of the work on this topic described in the lit- erature and then presents a consistent model for the predic- tion of the flow field losses in rotating passages of different lengths and with varying upstream swirl. Particularly short passages with developing flow at the passage exit can be calculated using this model. The calculation system is com- pleted by matching the correlations to experimental data.

Identification of Coupled Natural Frequencies in a Rotor-Stator Test-Rig for Different Gas Properties

In this paper a rotor-stator cavity test rig for experimental investigations of acoustic fluid-structure interactions in side cavities of radial compressors is introduced. The instrumentation of the test rig and the evaluation methodology are presented. The fluid is excited at frequencies, which are independent from the disk rotational speed, with loudspeakers. The acoustic pressure patterns are detected with a pressure sensor rotatable in circumferential direction. The gas properties are varied via different pressure levels in the test rig. First experimental results of natural frequencies are presented. The structure and acoustic dominant m = 4, n = 0, l = 1 modes have been excited and identified. The experimental results of the resonance frequencies of coupled modes on the dependence of the surrounding gas pressure are compared to a coupled numerical modal analysis and an analytical approach of other researchers. The main trend is in good accordance to them.