B. Matyschok

Detailed Analysis of Experimental Investigations on Boundary Layer Transition in Wake Disturbed Flow

In the framework of a co-operation between the University of Genoa and the Darmstadt University of Technology measurement data of a former investigation at Darmstadt, comprising measurements with surface-mounted hot-film sensors on the boundary layer transition in wake disturbed flow, were transferred to Genoa, then re-evaluated and in great detail analyzed, much further than the original data evaluation. In these experimental investigations at Darmstadt, the boundary layer transition with and without transitional separation bubbles was studied on a circular cylinder in cross flow. The comparison of hot-wire traverses with the surface-mounted hot-film distributions clearly indicated that the surface-mounted hot-film technique is a very suitable measurement technique to obtain reliable information on transition and separation phenomena with both high spatial and temporal resolution. The new data evaluation techniques applied to these data at Genoa further enhanced the insight into the details of the boundary layer transition and separation process. The surface-mounted hot-film data were evaluated by means of time-space diagrams for the first three statistical moments (mean, RMS and skewness), with which the origin and the extent of unsteady separation bubbles clearly could be seen. The results obtained from these data analyses on the one hand yield a considerable enhancement of the understanding of the periodically unsteady boundary layer transition process and on the other hand they form the basis for the application of surface-mounted hot-film sensors in more complex flow situations like e.g. in cold flow multistage turbine or compressor test rigs or even in the hostile environment of real aero engine compressors or turbines.Copyright

Physical Modeling of Automotive Turbocharger Compressor: Analytical Approach and Validation

Global warming is a climate phenomenon with world-wide ecological, economic and social impact which calls for strong measures in reducing automotive fuel consumption and thus CO2 emissions. In this regard, turbocharging and the associated designing of the air path of the engine are key technologies in elaborating more efficient and downsized engines. Engine performance simulation or development, parameterization and testing of model-based air path control strategies require adequate performance maps characterizing the working behavior of turbochargers. The working behavior is typically identified on test rig which is expensive in terms of costs and time required. Hence, the objective of the research project “virtual Exhaust Gas Turbocharger” (vEGTC) is an alternative approach which considers a physical modeled vEGTC to allow a founded prediction of efficiency, pressure rise as well as pressure losses of an arbitrary turbocharger with known geometry. The model is conceived to use smallest possible number of geometry as well as material parameters. Thus, conventional expensive and time-consuming application processes can be countered and test rig as well as in vehicle measurements can be reduced. Furthermore, the vEGTC model enables the prediction of different turbocharger behavior caused by geometry variations. Within this paper it is shown in which way the radial compressor as a representative modeling component can be described by zero-dimensional equations: in order to simulate the working behavior of the compressor the geometry, the thermodynamic state of the inlet-air and the turbocharger speed are assumed to be known. The loss mechanisms are devised using analytical and semi-empirical loss correlations. In order to validate the compressor efficiency the heat transfer from the turbine to the compressor is considered. Finally, the simulation output is compared to manufacturer maps of three different turbochargers pointing out the reliability of the model. Thus, a comprehensive validation of the vEGTC model is yielded. The object-oriented language Modelica is used for modeling and the simulations are provided by the Dymola solver.

THE INFLUENCE OF TIP CLEARANCE ON THE ACOUSTIC AND AERODYNAMIC CHARACTERISTICS OF FANS

In addition to developing fans as aerodynamically efficient as possible, acoustic optimization gains more and more importance for the purpose of reducing fan noise exposure. In order to combine good aerodynamic properties with a silent fan, this experimental research investigates the acoustic and aerodynamic characteristics of an axial fan. In this case, a fan with skewed blades is tested in view of its aerodynamic efficiency and noise exposure in dependence on its tip clearance and stagger angle. For this purpose, six different stagger angles and five tip clearance gaps per angle were measured in a fan test rig (according to ISO 5136). Interpretation of the recorded data shows a clear trend toward higher aerodynamic efficiency and less noise with a down-sizing of the tip clearance gap. As the cost of manufacture rises with the decrease of the tip clearance, the efficiency of these measures can be calculated with the results of this study under consideration of aerodynamic and acoustic aspects.Copyright

CFD-Analysis of the Flow Consisting of Two Mass Flows With Different Temperatures and/or Two Phases in a Turbocompressor

In this paper, numerical results of the mixing behavior of two mass flows having different temperatures in an elbow, which is located upstream of a turbocharger compressor, are presented. The background for these investigations are the thermal problems and the problems due to droplet impacts, which arise as a result of Low Pressure Exhaust Gas Recirculation for a turbocharger compressor. In these investigations, the temperature distributions resulting at the inlet of the compressor are mainly of interest. Of further interest are the trajectories of possibly arising water droplets in the inflow of the turbocharger compressor. In the first step different injection configurations are calculated without the compressor in order to get a first impression of the mixing behavior of two mass flows in an elbow. Afterwards three of the injection geometries are calculated including the compressor to see the influence of the compressor on the mixing behavior. The results show a strong influence of the direction of the injection and of the relative position of the injection to the elbow unit. Subsequently, visualization tests are made to qualitatively check the mixing behavior of the different elbow geometries.Copyright

Sound Deadening on Fans

In addition to the objective of increasing the efficiency of fans, acoustic efficiency gains more and more importance in order to reduce fan noise exposure. Whereas previously, research in this field was focused basically on blade design, nowadays the peripheral devices of fans are more often the object of study, since technical understanding of noise development is comparatively incomplete. Therefore, fundamental studies are essential to gain insight in the patterns of noise development and relatively easy opportunities to reduce noise level. In order to combine good aerodynamic properties with a silent fan, this experimental research investigates the acoustic and aerodynamic characteristics of an axial turbomachine and possibilities of reducing the emitted sound. Therefore a sound absorber ring is built directly around the rotor of a fan in order to absorb the sound very close to the origin. The fan assembly is installed in a test rig according to ISO 5136, which defines a standard for determining sound power radiated into a duct by fans. Acoustic signals are recorded with two microphones in the test duct, one on the pressure side, the second on the suction side, each close to anechoic terminations at the ends. The aerodynamic characteristics are determined with a calibrated inlet nozzle and static pressure measurements over the fan stage. To confirm the expectation that a significant part of the emitted sound power is tip clearance noise, which changes with the operating point, the volume flow of the fan is varied over its entire operating range. In this study, five different porous materials are tested for their ability of deadening the sound of the fan. In order to measure the influence of the construction which contains the materials, the perforated casing ring with a sound-reflecting termination and a plane ring with the same tip clearance are measured additionally as a reference. The noise exposure is analyzed over the complete frequency spectrum in order to determine the absorbing frequencies of the materials.Copyright

Design, Development and Verification of Gas Turbine GT24 Air Intake

Good aerodynamic design of the compressor intake contributes to a gas turbine’s performance and compressor surge margin. The combination of empirical design correlations, optimization with CFD and experiments leads to a successful design. The GT24 compressor intake was tested in a rig test. Both tests from the rig and measurements from the first GT24 at the Gilbert power station confirm a low level of losses and flow distortion.Copyright