Fluidic Sealing Fundamental Physics and Development for Turbomachinery Implementation

With ever growing demand on turbine manufacturers to over higher efficiency and lower operational costs, new modern seals must be able to withstand higher temperatures, pressures and shaft speeds but at the same time efficiently restrict flow at peak and transient load conditions and withstand abrasion, erosion, oxidation and depositions. This work investigates an alternative seal design, the fluidic seal, which could satisfy the demands of new seal designs. Fluid seals use a jet inclined upstream in direction of the leakage flow relying on the momentum exchange to block or reduce the leakage flow. Theoretically, fluidic seals could be implemented on any location where other seal designs are considered or installed. This work concentrates on fluidic seal design implemented between rotor shroud and housing of the steam and gas turbines. Numerical, analytical and experimental investigations were carried out to explore the fundamental principles of fluidic sealing, showing a possible leakage reduction of up to 40% compared to base configuration. Subsequently these principles were used to develop a fluidic seal on a small scale turbo expander unit

Uncertainty and validation of unsteady pressure-sensitive paint measurements of acoustic fields under aero engine-like conditions

Fast response pressure-sensitive paint (PSP) allows optical measurements of pressure fuctuations on a surface with high spatial and temporal resolution. This technique is evaluated for aeroacoustic measurements inside an aeroacoustic wind tunnel (AWT). The AWT is a test rig especially designed for investigating the excitation and propagation of sound under conditions typical for turbomachinery. The aim of this work is to compare the results of sound pressure measurements of tonal sound felds in a circular duct conducted with PSP and microphone arrays in order to assess the applicability of PSP in turbomachinery acoustics applications. A data analysis process is presented, which projects the camera image of the PSP data onto a given surface. To analyze the spatial pressure fuctuations, the PSP data are transformed in the frequency domain using pixel-wise fast Fourier transform. Measurements with a mean Mach number up to 0.109 and 5 kHz excitation frequency are conducted. An acoustic mode generator is used to excite the sound feld with specifc circumferential mode order. The pressure fuctuations obtained with the PSP measurement visualize the measured acoustic feld well and allow early interpretation. The pressures of PSP and microphones are in good agreement; for example, the maximum detected deviation in pressure at 2700 Hz is 30 Pa. A preview on using radial mode analysis to decompose the acoustic feld, measured by PSP, into acoustic modes is provided. The results are confrmed by a decomposition using conventional arrays of fush-mounted microphones

A STATIC TEST FACILITY FOR THE STUDY OF DEPOSIT FOULING ON STEAM TURBINE BLADES

ABSTRACT For several decades it has been recognised that deposition on the surfaces of steam turbine blades during operation can result in significant loss in thermal performance and, in some cases, a large reduction in the steam swallowing capacity. One principal cause of deposit fouling on HP turbines is copper, although other elements, for example silicon, can also be problematic. Copper is initially corroded from condenser and feedheater tubes by the water which then contaminates the inner surfaces of the boiler as the water is evaporated. The steam from the boiler becomes contaminated with copper oxides as a result of the copper fouling inside the boiler. The solubility of copper compounds in steam is a strong function of pressure. As the steam expands through the turbine and pressure reduces, the copper oxides deposit out onto the blade surfaces, roughening them and resulting in loss of performanc

An ultra-fast TSP on a CNT heating layer for unsteady temperature and heat flux measurements in subsonic flows

In this paper, the authors demonstrate the application of a modified Ru(phen)-based temperature-sensitive paint which was originally developed for the evaluation of unsteady aero-thermodynamic phenomena in high Mach number but short duration experiments. In the present work, the modified TSP with a temperature sensitivity of up to −5.6%/K was applied in a low Mach number long-duration test case in a low-pressure environment. For the demonstration of the paint’s performance, a flat plate with a mounted cylinder was set up in the High-Speed Cascade Wind Tunnel (HGK). The test case was designed to generate vortex shedding frequencies up to 4300 Hz which were sampled using a high-speed camera at 40 kHz frame rate to resolve unsteady surface temperature fields for potential heat-transfer estimations. The experiments were carried out at reduced ambient pressure of p∞ = 13.8 kPa for three inflow Mach numbers being Ma∞=[0.3;0.5;0.7]. In order to enable the resolution of very low temperature fluctuations down to the noise floor of 10−5 K with high spatial and temporal resolution, the flat plate model was equipped with a sprayable carbon nanotube (CNT) heating layer. This constellation, together with the thermal sensors incorporated in the model, allowed for the calculation of a quasi-heat-transfer coefficient from the surface temperature fields. Besides the results of the experiments, the paper highlights the properties of the modified TSP as well as the methodology

Miniaturization and Model-Integration of the Optical Measurement System for Temperature-Sensitive Paint Investigations

The temperature-sensitive paint (TSP) method, an optical measurement technique, is used for qualitative skin friction visualizations in a wide variety of aerodynamic applications. One such application is the visualization of the laminar–turbulent boundary-layer transition. Optical access to the surface of interest is mandatory for the measurement system, which consists of scientific cameras and LEDs. But the optical access to the area of interest is often impeded by the available windows of the wind tunnel and the wind tunnel model itself, reducing the field of view and the spatial resolution. In some cases, it is of interest to increase the flexibility of the installation of the optical measurement system by reducing its physical dimensions and placing the installation inside the plenum. The DLR Swept flat PlatE Cross-flow TRAnsition (SPECTRA-A) configuration was selected to investigate the influence of two-dimensional steps on the cross-flow-induced boundary layer transition by means of TSP, as part of the EU project Clean Sky 2. The SPECTRA-A configuration consists of two main elements: a flat plate and a displacement body mounted within a very close distance of each other, creating a narrow gap between the two elements. The surface of interest is the area on the flat plate facing the displacement body. The narrow gap limits the utilization of an external camera setup due to poor optical access. A new optical setup consisting of four miniature CMOS machine-vision cameras and five miniature high-power LEDs was integrated into the displacement body. The characteristics of the camera system were analyzed in laboratory tests, establishing that the miniature CMOS machine-vision cameras are suitable for qualitative TSP skin friction visualizations. This was confirmed by successfully measuring the laminar–turbulent boundary-layer transition on the SPECTRA-A configuration. The integrated TSP system is capable of resolving even small variations of the transition location caused by changing the amplitude of the stationary cross-flow instability. The quality of the TSP visualization with the integrated optical system allows for the measurement of the transition location and the wavelength of the stationary cross-flow instability. Overall, a cost-effective TSP visualization system with small space requirements was developed and tested for future applications in wind tunnel models, model support, or side walls of wind tunnels

Waiting times between orders and trades in double-auction markets

In this paper, the survival function of waiting times between orders and the corresponding trades in a double-auction market is studied both by means of experiments and of empirical data. It turns out that, already at the level of order durations, the survival function cannot be represented by a single exponential, thus ruling out the hypothesis of constant activity during trading. This fact has direct consequences for market microstructural models. They must include such a non-exponential behaviour to be realistic.Comment: 19 pages, 3 figures, paper presented at the WEHIA 2005, Colchester, U

Experimental and Numerical Investigation of a Multi-Jet Impingement Cooling Configuration

In order to protect turbine blades from thermal damage or thermally induced aging, internal impingement cooling has found common use throughout engine design, both in stationary gas turbines as well as aircraft engines, but also finds applications in other areas requiring cooling. The present investigation is focused on a generic impingement cooling configuration that can be easily modelled with computational fluid dynamics (CFD) and at the same time can be studied in detail experimentally. The acquired experimental data can be directly used for the validation of the CFD simulations, ultimately allowing their application in more complex, realistic configurations where experimental investigations become prohibitively expensive or otherwise impossible. The investigated configuration consists of 9 evenly spaced jets of Reynolds number Re D = 10000 issuing into a square channel that is sealed at one end. The jets directly impinge on a uniformly heated target plate. With previous work on similar configurations well described in literature, the focus of the present contribution is to further exploit the potentials offered by snap-shot based and time-resolved measurements. The flow field within the channel is characterized with both conventional, snap-shot particle image velocimetry (PIV) as well as with high-speed, time-resolved PIV (TR-PIV) to, respectively, capture overview data as well as detailed information on temporally evolving flow structures. In addition, measurements of the unsteady surface temperature distribution on the heated channel wall are performed by means of a newly developed unsteady temperature sensitive paint (iTSP) measurement technique. The interaction of the turbulent jets with the wall and with its neighbors is studied in detail using correlation and spectral analysis as well as modal decomposition. Where possible, this is supplemented with corresponding data obtained from numerical modelling. None of the applied postprocessing methods reveal a significant interaction between jets suggesting that the jet-driven dynamics of heat transfer at the wall are restricted to their immediate vicinity which may simplify the requirements on numerical models of similar cooling configurations

Atomic Resonance and Scattering

Contains reports on six research projects.National Science Foundation (Grant PHY 83-06273)U.S. Navy - Office of Naval Research (Contract N00014-79-C-0183)Joint Services Electronics Program (Contract DAALO03-86-K-0002)National Science Foundation (Grant PHY 84-11483)National Science Foundation (Grant PHY 86-05893)National Science Foundation (Grant ECS 84-21392)U.S. Navy - Office of Naval Research (Contract N00014-83-K-0695)National Science Foundation (Grant CHE 84-21392

Atomic Resonance and Scattering

Contains reports on eight research projects.National Science Foundation (Grant PHY83-06273)National Bureau of Standards (Grant NB83-NAHA-4058)National Science Foundation (Grant PHY84-11483)Joint Services Electronics Program (Contract DAAG29-83-K-0003)U.S. Navy - Office of Naval Research (Contract NO0014-79-C-0183)U.S. Navy - Office of Naval Research (Contract N00014-83-K-0695)National Science Foundation (Grant PHY83-07172-A01

Atomic Resonance and Scattering

Contains reports on six research projects.National Science Foundation (PHY83-06273)Joint Services Electronics Program (DAAL03-86-K-0002)National Science Foundation (PHY84-11483)U.S. Navy-Office of Naval Research (Grant N00014-79-C-0183)Joint Services Electronics Program (Contract DAAG29-83-K-0003)National Science Foundation (Grant PHY83-07172-A01)U.S. Navy - Office of Naval Research (Grant N00014-83-K-0695)National Science Foundation (Grant CHE84-21392