Design and Analysis of CFD Experiments for the Development of Bulk-Flow Model for Staggered Labyrinth Seal

Nowadays, bulk-flow models are the most time-efficient approaches to estimate the rotor dynamic coefficients of labyrinth seals. Dealing with the one-control volume bulk-flow model developed by Iwatsubo and improved by Childs, the “leakage correlation” allows the leakage mass-flow rate to be estimated, which directly affects the calculation of the rotor dynamic coefficients. This paper aims at filling the lack of the numerical modelling for staggered labyrinth seals: a one-control volume bulk-flow model has been developed and, furthermore, a new leakage correlation has been defined using CFD analysis. Design and analysis of computer experiments have been performed to investigate the leakage mass-flow rate, static pressure, circumferential velocity, and temperature distribution along the seal cavities. Four design factors have been chosen, which are the geometry, pressure drop, inlet preswirl, and rotor peripheral speed. Finally, dynamic forces, estimated by the bulk-flow model, are compared with experimental measurements available in the literature

Thermo-elasto bulk-flow model for labyrinth seals in steam turbines

Over the last few decades, the increasing demand on efficiency and performance for steam turbines has resulted in OEMs operating machines near critical conditions of their structural and thermal capabilities. In this paper, a new thermo-elasto bulk-flow model for labyrinth seals has been introduced. The model includes the bulk-flow model for estimating the dynamic coefficients, heat transfer model for evaluating the temperature distribution in the rotating and stationary parts and structural-mechanics model for calculating the radial growth. By considering a staggered labyrinth seal installed in the balancing drum of a steam turbine, different operating conditions, such as the boundary pressure, rotational speed and inlet pre-swirl ratio, as well as the stability of the seal are investigated in this study

Rotordynamic Characterization of a Staggered Labyrinth Seal: Experimental Test Data and Comparison With Predictions

As well known, the stability assessment of turbomachines is strongly related to internal sealing components. For instance, labyrinth seals are widely used in compressors, steam and gas turbines and pumps to control the clearance leakage between rotating and stationary parts, owing to their simplicity, reliability and tolerance to large thermal and pressure variations. Labyrinth seals working principle consists in reducing the leakage by imposing tortuous passages to the fluid that are effective on dissipating the kinetic energy of the fluid from high-pressure regions to low-pressure regions. Conversely, labyrinth seals could lead to dynamics issues. Therefore, an accurate estimation of their dynamic behavior is very important. In this paper, the experimental results of a long-staggered labyrinth seal will be presented. The results in terms of rotordynamic coefficients and leakage will be discussed as well as the critical assessment of the experimental measurements. Eventually, the experimental data are compared to numerical results obtained with the new bulk-flow model (BFM) introduced in this paper

Rotordynamic Characterization of Labyrinth Seals in Steam Turbines: Effects of Thermal and Mechanical Loads

Over the last few decades, the increasing demand on efficiency and performance for steam turbines has resulted in OEMs operating machines near critical conditions of their structural and thermal capabilities. Consequently, a more accurate estimation of the dynamic behavior of the machine has become mandatory as well as the stability assessment. Steam turbines are subjected to high temperatures, high pressures and centrifugal forces that could change the nominal geometry, especially the clearance profile in correspondence of the sealing components, occasionally generating a convergent or divergent annulus. In this paper, a new thermo-elasto bulk-flow model for labyrinth seals has been introduced. The model includes the bulk-flow model for estimating the dynamic coefficients, heat transfer model for evaluating the temperature distribution in the rotating and stationary parts and structural-mechanics model for calculating the radial growth. By considering a staggered labyrinth seal installed in the balancing drum of a steam turbine, different inlet pre-swirl ratios, as well as the stability of the seal are investigated in this paper. The model can be extremely useful for the dynamic characterisation of a wide class of labyrinth seals considering the effect of the surrounding environment on the rotordynamic coefficient prediction

Poster #35 STUDYING EPISODIC MEMORY CEREBRAL NETWORK: A NOVEL EVENT-RELATED TASK FOR FMRI

Background: Converging \ufb01ndings from lesion and electrophysiological studies indicate that structures in the mesial temporal lobe, including the parahippocampus (PH) and the hippocampus (H), together with the prefrontal cortex (particularly the inferior frontal gyrus, IFG) are crucial for encoding and recall of episodic memory in animals and in humans. De\ufb01cits in episodic memory, especially in the encoding domain, are important features of schizophrenia. In patients, these de\ufb01cits seem to be stable over time, independent of psychotic symptoms, less responsive to current pharmacological treatment and associated with impaired quality of life and pooroutcome. Aimof this study was to evaluate activity inH andPH aswell as in prefrontal cortex during encoding and retrieval of recognitionmemory by using a novel event-related paradigm. Methods: 23 healthy subjects (M/F = 11/12; mean age, years \ub1 SD: 28\ub17.7) underwent 3T fMRI. The experimental paradigm consisted of encoding and retrieval of verbal stimuli. During encoding, 50 words were presentedat a rate of 2 seconds (s)with a variable inter-stimulus interval (mean ISI = 8 s).Participants were instructed to express a size judgment deciding if each word indicated a bigger or a smaller object than themselves.35 crosshairs were randomly intermixed with words presentation and served as a baseline against which the hemodynamic response was estimated.During retrieval, subjects viewed 50 words from the previous session plus 50 novel foils, one at a time, in a random order; again, crosshairs were randomly intermixed with words. For each item, participants were asked to express an old/newrecognition judgment. The task had an overall duration of 13.8 minutes.During scanning, all subjects responded by button presses with their right hand, allowing for determination of behavioral accuracy (% correct responses) and reaction time (msec). fMRI data were preprocessed and analyzed using Statistical Parametrical Mapping (SPM8, http://www.\ufb01l.ion.ucl.ac.uk). Random effects models, witha statistical threshold of p<0.05 Family-Wise-Error (FWE) correctedand a minimum cluster size (k=3), were used for statistical analysis. Finally, BOLD responses were extracted from signi\ufb01cant clusters using MarsBar (http://marsbar.sourceforge.net/) to explore, outside SPM8, signi\ufb01cant correlation with behavioral performance. Results: Encoding behavioral data indicated an accuracy (mean %\ub1 SD) of 95.03%\ub112.7. Retrieval behavioral data showed an accuracy for hits old of 86.95% \ub1 12.7. Imagingdata demonstrated bilateral activation of H (x=34, y=-33, z=-1, k=118, pFWE corr = 0.007; x=-22, y=-33, z=-1, k=132, pFWE corr= 0.006) and of PH (x=20, y=-7,z=-28, k=143,pFWE corr = 0.005; x=-26, y=-3, z=-35, k=122, pFWE corr = 0.007) during encoding, and a substantial activation of left H (x=-18, y=-7,z=-12 k=35, pFWE corr= 0.047) at retrieval. Remarkable bilateral activity resulted in the IFG at encoding (x=34, y=23, z=-5, k=448, pFWE corr = 0.0001; x=-37, y=23, z=-1, k=629, pFWE corr = 0.0001)and at retrieval (x=38, y=23, z=-1, k=370, pFWE corr = 0.002; x=-33, y=27, z=-1, k=509, pFWE corr = 0.0001). A negative correlation, at trend level, was found between accuracy at retrieval and BOLD signal in right IFG (p=0.063, Spearman R=0.393). Discussion: Findings from our study demonstrate bilateral activation of the H-PH complex during memory encoding, and left hippocampal activity during retrieval of verbal stimuli. Furthermore, they support the role of the prefrontal cortex in episodic memory. This novel fMRI paradigm will allow to investigate H-PH and prefrontal cortex activity in patients with schizophrenia, in whom episodic memory de\ufb01cits represent a phenotypic vulnerability marker of the disorder

Genetic Variation of a DRD2 Co-expression Network is Associated with Changes in Prefrontal Function After D2 Receptors Stimulation

Dopamine D2 receptors (D2Rs) contribute to the inverted U-shaped relationship between dopamine signaling and prefrontal function. Genetic networks from post-mortem human brain revealed 84 partner genes co-expressed with DRD2. Moreover, eight functional single nucleotide polymorphisms combined into a polygenic co-expression index (PCI) predicted coexpression of this DRD2 network and were associated with prefrontal function in humans. Here, we investigated the nonlinear association of the PCI with behavioral and Working Memory (WM) related brain response to pharmacological D2Rs stimulation. Fifty healthy volunteers took part in a double-blind, placebo-controlled, functional MRI (fMRI) study with bromocriptine and performed the N-Back task. The PCI by drug interaction was significant on both WM behavioral scores (P = 0.046) and related prefrontal activity (all corrected P &lt; 0.05) using a polynomial PCI model. Non-linear responses under placebo were reversed by bromocriptine administration. fMRI results on placebo were replicated in an independent sample of 50 participants who did not receive drug administration (P = 0.034). These results match earlier evidence in non-human primates and confirm the physiological relevance of this DRD2 co-expression network. Results show that in healthy subjects, different alleles evaluated as an ensemble are associated with non-linear prefrontal responses. Therefore, brain response to a dopaminergic drug may depend on a complex system of allelic patterns associated with DRD2 co-expression

Urticaria: recommendations from the Italian Society of Allergology, Asthma and Clinical Immunology and the Italian Society of Allergological, Occupational and Environmental Dermatology

Urticaria is a disorder affecting skin and mucosal tissues characterized by the occurrence of wheals, angioedema or both, the latter defining the urticaria-angioedema syndrome. It is estimated that 12-22% of the general population has suffered at least one subtype of urticaria during life, but only a small percentage (estimated at 7.6-16%) has acute urticaria, because it is usually self-limited and resolves spontaneously without requiring medical attention. This makes likely that its incidence is underestimated. The epidemiological data currently available on chronic urticaria in many cases are deeply discordant and not univocal, but a recent Italian study, based on the consultation of a national registry, reports a prevalence of chronic spontaneous urticaria of 0.02% to 0.4% and an incidence of 0.1-1.5 cases/1000 inhabitants/year