Dietmar Filsinger

NUMERICAL AND EXPERIMENTAL STUDY OF UNSTEADY FLOW FIELD AND VIBRATION IN RADIAL INFLOW TURBINES

The blades of turbocharger impellers are exposed to unsteady aerodynamic forces, which cause blade vibrations and may lead to failures. An indispensable requirement for a safe design of radial inflow turbines is a detailed knowledge of the exciting forces. Up to now, only a few investigations relating to unsteady aerodynamic forces in radial turbines have been presented. To give a detailed insight into the complex phenomena, a comprehensive research project was initiated at the Institut fur Thermische Stromungsmaschinen, at the University of Karlsruhe. A turbocharger test rig was installed in the high-pressure, high-temperature laboratory of the institute. The present paper gives a description of the test rig design and the measuring techniques. The flow field in a vaneless radial inflow turbine was analyzed using laser-Doppler anemometry. First results of unsteady flow field investigations in the turbine scroll and unsteady phase-resolved measurements of the flow field in the turbine rotor will be discussed. Moreover, results from finite element calculations analyzing frequencies and mode shapes are presented. As vibrations in turbines of turbochargers are assumed to be predominantly excited by unsteady aerodynamic forces, a method to predict the actual transient flow in a radial turbine utilizing the commercial Navier-Stokes solver TASCflow3d was developed. Results of the unsteady calculations are presented and comparisons with the measured unsteady flow field are made. As a major result, the excitation effect of the tongue region in a vaneless radial inflow turbine can be demonstrated.

Experimental Assessment of Fiber-Reinforced Ceramics for Combustor Walls

Experimental and theoretical work concerning the application of ceramic components in small high-temperature gas turbines has been performed for several years. The significance of some nonoxide ceramic materials for gas turbines in particular is based on their excellent high-temperature properties. The application of ceramic materials allows an increase of the turbine inlet temperature resulting in higher efficiencies and a reduction of pollution emissions. The inherent brittleness of monolithic ceramic materials can be virtually reduced by reinforcement with ceramic fibers leading to a quasiductile behavior. Unfortunately, some problems arise due to oxidation of these composite materials in the presence of hot gas flow containing oxygen. At the Motoren und Turbinen Union, Munchen GmbH, comprehensive investigations including strength, oxidation, and thermal shock tests of several materials that seemed to be appropriate for combustor liner applications were undertaken. As a result, C/C, SiC/SiC, and two C/SiC composites coated with SiC, as oxidation protection, were chosen for examination in a gas turbine combustion chamber. To prove the suitability of these materials under real engine conditions, the fiber-reinforced flame tubes were installed in a small gas turbine operating under varying conditions. The loading of the flame tubes was characterized by wall temperature measurements. The materials showed different oxidation behavior when exposed to the hot gas flow. Inspection of the C/SiC composites revealed debonding of the coatings. The C/C and SiC/SiC materials withstood the tests with a maximum cumulated test duration of 90 h without damage.

MODEL COMBUSTOR TO ASSESS THE OXIDATION BEHAVIOR OF CERAMIC MATERIALS UNDER REAL ENGINE CONDITIONS

A further increase of thermal efficiency and a reduction of the exhaust emissions of ground based gas turbines can be achieved by introducing new high temperature resistant materials. Therfore, ceramics are under international development. They offer excellent strengths at room and elevated temperatures. For gas turbine combustor applications, however, these materials have to maintain their advantageous properties under hostile environment. For the assessment and comparison of the oxidation behavior of different nonoxide ceramic materials a test rig was developed at the Institute for Thermal Turbomachinery (ITS), University of Karlsruhe, Germany.The test rig was integrated into the high temperature/ high pressure laboratory. A ceramic model combustion chamber was designed which allowed the exposure of standard four-point flexure specimens to the hot combustion gas flow. Gas temperatures and pressures could be varied in a wide range. Additionally, the partial steam pressure could be adjusted to real combustor conditions.The present paper gives a detailed description of the test rig and presents results of 100 hours endurance tests of ceramic materials at 1400°C. The initial strengths and the strengths after oxidation tests are compared. In addition to this, photographs illustrating the changes of the material’s microstructure are presented.Copyright

Design of thermally high-loaded ceramic components for gas turbines

Abstract The excellent high-temperature properties of ceramics offer great potential for their application in gas turbines. However, ceramics lack the ability to reduce local stress concentrations by plastic deformation. As a result, stresses that are caused by different local thermal expansions can reach critical values, especially in the hot-section components. To improve the reliability of ceramic components, the temperature differences have to be reduced. At the Institut fur Thermische Stromungsmaschinen (ITS) a systematic methodology for designing thermally high-loaded components has been developed. The principles of the design procedure include a segmentation of the parts according to the load and a three-layered construction of the components wall. The inner hot-gas ducting layer consists of a high-temperature resistant ceramic material which is embedded into a metal containment by a flexible ceramic fibre insulation. By adjusting the individual thicknesses of the ceramic and the insulation layers according to the local boundary conditions on the hot-gas side, the local temperature differences in the ceramic can be considerably reduced. Finite element analyses of the temperature and stress distribution for first stage nozzle guide vanes and the vaneless scroll of a radial gas turbine are shown. Compared with conventional designs, the calculations clearly demonstrate that the hybrid wall construction and an ingenious segmentation of the components lead to a significant reduction in the stress level. The reliability improvement is documented by failure probability calculations performed using the ITS fracture statistics code CERITS.

Experimental Assessment of Fiber Reinforced Ceramics for Combustor Walls

Experimental and theoretical work concerning the application of ceramic components in small high temperature gas turbines has been performed for several years. The significance of some non-oxide ceramic materials for gas turbines in particular is based on their excellent high temperature properties. The application of ceramic materials allows an increase of the turbine inlet temperature resulting in higher efficiencies and a reduction of pollution emissions.The inherent brittleness of monolithic ceramic materials can be virtually reduced by reinforcement with ceramic fibers leading to a quasi-ductile behavior. Unfortunately, some problems arise due to oxidation of these composite materials in the presence of hot gas flow containing oxygen.At the Motoren- und Turbinen Union, Munchen GmbH, comprehensive investigations including strength, oxidation, and thermal shock tests of several materials that seemed to be appropriate for combustor liner applications were undertaken. As a result, C/C, SiC/SiC, and two C/SiC-composites coated with SiC, as oxidation protection, were chosen for examination in a gas turbine combustion chamber.To prove the suitability of these materials under real engine conditions, the fiber reinforced flame tubes were installed in a small gas turbine operating under varying conditions. The loading of the flame tubes was characterized by wall temperature measurements.The materials showed different oxidation behavior when exposed to the hot gas flow. Inspection of the C/SiC-composites revealed debonding of the coatings. The C/C- and the SiC/SiC-materials withstood the tests with a maximum cumulated test duration of 90 hours without damage.Copyright

Numerical and Experimental Study of Unsteady Flow Field and Vibration in Radial Inflow Turbines

The blades of turbocharger impellers are exposed to unsteady aerodynamic forces, which cause blade vibrations and may lead to failures. An indispensable requirement for a safe design of radial inflow turbines is a detailed knowledge of the exciting forces. Up to now, only few investigations relating to unsteady aerodynamic forces in radial turbines were presented. To give a detailed insight into the complex phenomena, a comprehensive research project was initiated at the Institut fur Thermische Stromungsmaschinen, at the University of Karlsruhe.A turbocharger test rig was installed in the high pressure, high temperature laboratory of the institute. The present paper gives a description of the test rig design and the measuring techniques. The flow field in a vaneless radial inflow turbine was analyzed using laser Doppler anemometry. First results of unsteady flow field investigations in the turbine scroll and unsteady phase resolved measurements of the flow field in the turbine rotor will be discussed. Moreover, results from finite element calculations analyzing frequencies and mode shapes are presented.As vibrations in turbines of turbochargers are assumed to be predominantly excited by unsteady aerodynamic forces, a method to predict the actual transient flow in a radial turbine utilizing the commercial Navier Stokes solver TASCflow3d was developed. Results of the unsteady calculations are presented and comparisons with the measured unsteady flow field are made. As a major result, the excitation effect of the tongue region in a vaneless radial inflow turbine can be demonstrated.Copyright