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Dara W. Childs - One of the best experts on this subject based on the ideXlab platform.
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The Impact of Hole Depth on the Rotordynamic and Leakage Characteristics of Hole-Pattern-Stator Gas Annular Seals
Volume 7A: Structures and Dynamics, 2013Co-Authors: Dara W. Childs, Stephen Arthur, Naitik J. MehtaAbstract:Test results are presented for rotordynamic characteristics of Hole-pattern-stator annular gas seals at a 70 bar supply pressures running at 20200 rpm. Leakage results are presented for these conditions and the additional speeds: 10200, 15300 rpm. Hole-Depth is the principal test variable of interest. Most published annular test data for these seals have a Hole diameter of 3.175mm and a Hole Depth of 3.302mm. For this work, with the 3.175mm Hole diameter, additional results are presented for shallow (1.905 mm) and deep (6.604 mm) Hole Depths. Test results show a pronounced dependence of leakage and rotordynamic behavior on Hole Depth. Test results show much better leakage performance for the shallow-Hole-Depth seal in both leakage and rotordynamic performance. Compressor manufacturers and users will need to decide whether this observed performance improvement is worth trying in real machines.
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The Impact of Hole Depth on the Rotordynamic and Leakage Characteristics of Hole-Pattern-Stator Gas Annular Seals
Journal of Engineering for Gas Turbines and Power, 2013Co-Authors: Dara W. Childs, Stephen Arthur, Naitik J. MehtaAbstract:Test results are presented for rotordynamic characteristics of Hole-pattern-stator annu- lar gas seals at a 70 bar supply pressures with a running speed of 20,200 rpm. Leakage results are presented for these conditions and the additional speeds: 10,200 and 15,300 rpm. Hole-Depth is the principal test variable of interest. Most published annular test data for these seals have a Hole diameter of 3.175mm and a Hole Depth of 3.302mm. For this work, with the 3.175mm Hole diameter, additional results are pre- sented for shallow (1.905mm) and deep (6.604mm) Hole Depths. Test results show a pronounced dependence of leakage and rotordynamic behavior on Hole Depth. Test results show much better leakage performance for the shallow-Hole-Depth seal in both leakage and rotordynamic performance. Compressor manufacturers and users will need to decide whether this observed performance improvement is worth trying in real machines.
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A Design to Improve the Effective Damping Characteristics of Hole-Pattern-Stator Annular Gas Seals
Journal of Engineering for Gas Turbines and Power, 2008Co-Authors: Dara W. Childs, Yoon-shik Shin, Brent SeifertAbstract:Predictions are presented for Hole-pattern-stator seals for which the Hole Depth is varied axially, showing that various Depth patterns can significantly improve damping pefor- mance in terms of both increasing the seal's effective damping and reducing its crossover frequency―the frequency at which effective damping changes from positive to negative. Test results are presented for the seal with the best variable Hole Depth (VHD) pattern showing an increase in peak damping by a factor of 1.6 over a constant Hole Depth (CHD) design versus predictions of 2.7. The crossover frequency is reduced by approximately 40%. The VHD seal has a significant negative static stiffness that probably arises from a friction-factor-jump phenomenon, not flow path divergence. The VHD seal leaks less than a comparable CHD design.
Naitik J. Mehta - One of the best experts on this subject based on the ideXlab platform.
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The Impact of Hole Depth on the Rotordynamic and Leakage Characteristics of Hole-Pattern-Stator Gas Annular Seals
Volume 7A: Structures and Dynamics, 2013Co-Authors: Dara W. Childs, Stephen Arthur, Naitik J. MehtaAbstract:Test results are presented for rotordynamic characteristics of Hole-pattern-stator annular gas seals at a 70 bar supply pressures running at 20200 rpm. Leakage results are presented for these conditions and the additional speeds: 10200, 15300 rpm. Hole-Depth is the principal test variable of interest. Most published annular test data for these seals have a Hole diameter of 3.175mm and a Hole Depth of 3.302mm. For this work, with the 3.175mm Hole diameter, additional results are presented for shallow (1.905 mm) and deep (6.604 mm) Hole Depths. Test results show a pronounced dependence of leakage and rotordynamic behavior on Hole Depth. Test results show much better leakage performance for the shallow-Hole-Depth seal in both leakage and rotordynamic performance. Compressor manufacturers and users will need to decide whether this observed performance improvement is worth trying in real machines.
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The Impact of Hole Depth on the Rotordynamic and Leakage Characteristics of Hole-Pattern-Stator Gas Annular Seals
Journal of Engineering for Gas Turbines and Power, 2013Co-Authors: Dara W. Childs, Stephen Arthur, Naitik J. MehtaAbstract:Test results are presented for rotordynamic characteristics of Hole-pattern-stator annu- lar gas seals at a 70 bar supply pressures with a running speed of 20,200 rpm. Leakage results are presented for these conditions and the additional speeds: 10,200 and 15,300 rpm. Hole-Depth is the principal test variable of interest. Most published annular test data for these seals have a Hole diameter of 3.175mm and a Hole Depth of 3.302mm. For this work, with the 3.175mm Hole diameter, additional results are pre- sented for shallow (1.905mm) and deep (6.604mm) Hole Depths. Test results show a pronounced dependence of leakage and rotordynamic behavior on Hole Depth. Test results show much better leakage performance for the shallow-Hole-Depth seal in both leakage and rotordynamic performance. Compressor manufacturers and users will need to decide whether this observed performance improvement is worth trying in real machines.
Masayuki Nogami - One of the best experts on this subject based on the ideXlab platform.
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Influences of Al3+ and Eu3+ concentration on PSHB properties of melt-quenched Al2O3–SiO2 glasses
Journal of Alloys and Compounds, 2005Co-Authors: Gil Jae Park, Tomokatsu Hayakawa, Masayuki NogamiAbstract:Abstract Spectral Hole-burning has been carried out for glasses with compositions of Eu 2 O 3 -doped x Al 2 O 3 –(100 − x )SiO 2 ( x = 10, 20, 30, 40) glasses prepared by melt-quenching. We investigated the effect of Al 2 O 3 and Eu 3+ ions on persistent spectral Hole burning (PSHB). The spectral Holes were burned on the excitation spectra of the 7 F 0 → 5 D 0 transition of the Eu 3+ ions. Hole-Depth increases with the content of Eu 2 O 3 . The content of Al 2 O 3 influenced the Hole-width rather than Hole-Depth. The Hole-burning was presumably related to the electron transfer between the Eu 3+ and the defect.
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Room-temperature spectral Hole burning of Eu3+-doped Al2O3-SiO2 glasses treated with H2 gas and x ray
Rare-Earth-Doped Materials and Devices V, 2001Co-Authors: Tomotaka Ishikawa, Tomokatsu Hayakawa, Masayuki NogamiAbstract:Persistent spectral Hole burning (PSHB) spectra were observed at room temperature in Eu3+ ions-doped glasses treated with either H2 gas or X-ray. The Eu3+-doped Al2O3-SiO2 glasses were prepare by sol-gel process. The glasses were heated at 500 to 800 degrees C in H2 gas, and irradiated with x-ray. The PSHB spectra were burned on the 7F0 yields 5D0 transition of the Eu3+ ions. The Hole Depth increased with increasing heat treatment time and is maximum for the samples heated at 600 degrees C for 1h. In the x-ray-irradiated glasses, the PSHB spectra were observed at room temperature for the first time, to our knowledge, and the Hole Depth increases with increasing irradiation time. In the x-ray-irradiated glasses, no fluorescence was observed form the Eu3+ ions. A novel. Model for Hole burning is proposed on the basis of the excitation of the Eu3+ ions and subsequent Hole trapping in the oxygen- defect centers of the Al-O polyhedra.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
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Spectral Hole burning and x-ray irradiation in Eu 3 + -doped glass
Physical Review B, 2000Co-Authors: Masayuki Nogami, Shunsuke ItoAbstract:Persistent spectral Hole for ${\mathrm{Eu}}^{3+}$-doped phosphate glass containing OH bonds is burned by the laser-induced rearrangement of the OH bonds surrounding the ${\mathrm{Eu}}^{3+}$ ions. We studied the effect of x-ray irradiation on the Hole burning property. The fluorescence intensity of the ${\mathrm{Eu}}^{3+}$ ions and the Hole Depth burned at 6 K decreased after x-ray irradiation. Defect centers, phosphorus-oxygen Hole centers, and $[{\mathrm{Eu}}^{3+}{]}^{\ensuremath{-}}$ states were formed by the x-ray irradiation, which were relaxed by heating at 200 and 350 \ifmmode^\circ\else\textdegree\fi{}C, respectively. The Hole burning was again observed by the relaxation of $[{\mathrm{Eu}}^{3+}{]}^{\ensuremath{-}}$ into ${\mathrm{Eu}}^{3+}$ ions. It was concluded that the ${\mathrm{Eu}}^{3+}\ensuremath{-}\mathrm{O}\mathrm{H}$ bond candidates for Hole burning were preferentially changed into the $[{\mathrm{Eu}}^{3+}{]}^{\ensuremath{-}}$ state by the x-ray irradiation, resulting in a decrease in the Hole Depth.
Houston G. Wood - One of the best experts on this subject based on the ideXlab platform.
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A Numerical Study on the Influence of Hole Depth on the Static and Dynamic Performance of Hole-Pattern Seals
Journal of Tribology, 2014Co-Authors: Patrick J. Migliorini, Alexandrina Untaroiu, Houston G. WoodAbstract:Annular seals serve an important role in the dynamics of turbomachinery by reducing leakage of a process fluid while also contributing potentially destabilizing forces to the rotor system. Hole-pattern seals have been the focus of many investigations, but recent experimental studies have shown that there are still many phenomena that require exploration. One such phenomenon is the influence of Hole Depth on the static and dynamic characteristics of the seal. In this paper, a hybrid computational fluid dynamics (CFD)/bulk-flow method is employed to investigate the nonmonotonic relationship between Hole Depth and leakage shown in experimental measurements of a Hole-pattern seal by Childs et al. (2014, “The Impact of Hole Depth on the Rotordynamic and Leakage Characteristics of Hole-Pattern-Stator Gas Annular Seals,” ASME J. Eng. Gas Turbines Power, 136(4), p. 042501). Three Hole Depths (1.905 mm, 3.302 mm, and 6.604 mm) and three running speeds (10,200 rpm, 15,350 rpm, and 20,200 rpm) are considered. For the steady-state flow, the 3D Reynolds-Averaged-Navier-Stokes (RANS) equations are solved with the k-ϵ turbulence model for a circumferentially periodic sector of the full seal geometry. The steady-state results are input into the first-order equations of a bulk-flow model to predict rotordynamic coefficients. Results of the hybrid method are compared to experimental data. CFD predicted leakage showed good agreement (within 5%) for the 3.302 mm and 6.604 mm Hole Depth configurations. For the 1.905 mm Hole Depth seal, agreement was within 17%. An additional set of calculations performed with the shear stress transport (SST) turbulence model produced worse agreement. Examination of streamlines along the seal show that the Hole Depth controls the shape of the vortex that forms in the Hole, driving the resistance experienced by the jet flow in the clearance region. For the rotordynamic coefficients, good agreement is shown between predictions and experiment for most excitation frequencies.
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A Numerical Study on the Influence of Hole Aspect Ratio on the Performance Characteristics of a Hole-Pattern Seal
Volume 7B: Structures and Dynamics, 2014Co-Authors: Patrick J. Migliorini, Alexandrina Untaroiu, Houston G. WoodAbstract:In turbomachinery, annular seals are used to reduce leakage between regions of high and low pressure. Many configurations of annular seals have been developed and studied in the literature including plain, labyrinth, pocket-damper, honeycomb, and Hole-pattern. In machines experiencing stability issues, honeycomb and Hole-pattern type seals have been used to replace labyrinth seals. Bulk-flow models are typically used to predict the leakage and dynamic coefficients of Hole-pattern seals, relying on empirically derived friction factor coefficients. Previous experimental studies have shown that, for Hole-pattern seals, the leakage and stator friction factor are strongly influenced by Hole-Depth. However, this behavior is not a monotonic function of Hole-Depth, a fact that might reduce confidence in future bulk-flow model predictions if not properly accounted for. A recent numerical study has highlighted the role of vortex formation in the Holes which has a strong influence on the flow in the clearance region. Depending on the shape of the vortex, the flow in the Hole can act much like a pinch valve, reducing the effective clearance of the jet flow. In this paper, computational fluid dynamics simulations of several Hole-pattern seal configurations have been performed to study the effect of Hole-aspect ratio (Depth versus diameter) on the leakage and friction factors. The Reynolds Averaged Navier Stokes (RANS) equations with k-ε turbulence model were solved using ANSYS CFX. It was found that the shape of the Hole influences the vortex formation within the Hole, effecting the jet flow in the clearance region and the seal leakage. The results show that the leakage is heavily dependent on the Hole diameter in addition to the Hole Depth. The relationship between the friction factors and the geometry of the seal was found to be non-monotonic. It is therefore difficult to develop a friction factor model that will accurately encompass all configurations and it is recommended that friction factor data be interpolated from experimental or numerical results.
Henri Benisty - One of the best experts on this subject based on the ideXlab platform.
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Radiation losses in planar photonic crystals: two- dimensional representation of Hole Depth and shape by an imaginary dielectric constant
Journal of the Optical Society of America B, 2003Co-Authors: Rolando Ferrini, Romuald Houdré, Henri Benisty, Min Qiu, J. MoosburgerAbstract:Waveguide modes in two-dimensional (2-D) photonic crystals (PhCs) deeply etched through monomode slab waveguides, e.g., AlGaAs/GaAs, GaAs/AlOx, or InP/GaInAsP, suffer from radiation losses that are strongly affected by the air Hole Depth and shape. The issue of three-dimensional (3-D) out-of-plane losses is addressed analytically by means of an incoherent approximation. Assuming separability both for the dielectric map and for the electric field, this approach is valid for defects such as in-plane microcavities, PhC-based waveguides, bends and couplers. Out-of-plane scattering is translated into an effective imaginary index in the air Holes, so that 3-D losses can be cast in a simple 2-D calculation. The case of cylindroconical Holes is treated, and the validity of this approach is experimentally confirmed by transmission measurements through simple PhC slabs.
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Finite-Depth and intrinsic losses in vertically etched two-dimensional photonic crystals
Optical and Quantum Electronics, 2002Co-Authors: Henri Benisty, Ph. Lalanne, Segolene Olivier, M. Rattier, C. Weisbuch, Christopher J. M. Smith, Thomas F. Krauss, C. Jouanin, David CassagneAbstract:We address the issue of out-of-plane losses in two-dimensional (2D) photonic crystals (PC) etched through a GaAs monomode waveguide clad with standard GaAlAs alloys. We correlate experimental transmission of PCs with two kinds of loss simulation results. The first kind is 2D and introduces an ad hoc imaginary index in the air Holes to account for the losses [see (Benisty et al. Appl. Phys. Lett. 76, 532, 2000)]. The second kind is a novel exact three-dimensional calculation inspired by grating-Fourier analysis that provides quantitatively unprecedented agreement with experimental measurements taking into account Hole Depth as a limiting parameter. We conclude that, in revision to the conclusions of the above reference, the experimental losses are not the intrinsic ones, being larger by a factor of 5 to 10 due to insufficient Hole Depth. The transition occurs at a critical etch Depth shown to be here around 700 nm. We thus predict, for Holes deeper than 700 nm, much improved crystals with very low transmission losses and microresonators with ultra-high quality factors.
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Out-of-plane losses of two-dimensional photonic crystals waveguides: electromagnetic analysis
Journal of Applied Physics, 2001Co-Authors: Philippe Lalanne, Henri BenistyAbstract:A method for the electromagnetic analysis of photonic crystal waveguides is described. It is tested against experimental transmission data obtained for AlGaAs slab-waveguide structures perforated by a two-dimensional hexagonal lattice. A good quantitative agreement is obtained for the band edge locations, for the ripples in the transmission windows, and more importantly, for the out-of-plane losses induced by the finite Hole Depth. The ultimate performance of the structure for deep etched Holes is predicted.