The Experts below are selected from a list of 195 Experts worldwide ranked by ideXlab platform
Alexandrina Untaroiu - One of the best experts on this subject based on the ideXlab platform.
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Leakage Rate Performance Mapping of Smooth Stator/Grooved Rotor Labyrinth Seals Using Statistical Tools
Volume 3B: Fluid Applications and Systems, 2019Co-Authors: Hanxiang Jin, Alexandrina UntaroiuAbstract:Abstract As one of the most widely used annular pressure Seals, labyrinth Seals are used to reduce the fluid leakage between different pressure stages. They are multi-toothed Seals with circumferential grooves located on the rotor surfaces and/or stator surfaces, which are distributed along the axial direction. The intricacy of the surface geometry and directionality of the Seal pattern assist in converting pressure into dissipated kinetic energy without rotor-stator rub effects. The majority of previous studies focused on annular labyrinth Liquid Seals with smooth rotor/grooved stator (SR/GS) case, whereas this paper attempts to elucidate the effects of geometric variables modification for smooth stator/grooved rotor (SS/GR) case using Computational Fluid Dynamics (CFD) and design of experiments (DOE) techniques. In this study, a smooth stator/grooved rotor Liquid Seal was modeled and validated against experimental data. The model was then used as a baseline case for a sensitivity analysis of its geometry variations. Simulation results under different pressures/rotor speeds were used to validate the CFD setup. Four geometric parameters of the Seal were then selected as design variables to adapt the baseline geometry for potential performance improvements. The design space was discretized using the DOE technique. Similar mesh/simulation setups were automatically generated for each design point. Regression analysis was applied based on the CFD results for a better understanding of the effects associated with different design variables. These results can be used to improve the current design of smooth stator/grooved rotor annular pressure Seals in order to achieve lower leakage rates.
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on the dynamic properties of pump Liquid Seals
Journal of Fluids Engineering-transactions of The Asme, 2013Co-Authors: Alexandrina Untaroiu, Vahe Hayrapetian, Costin D. Untaroiu, Houston G. Wood, Bruno Schiavello, James McguireAbstract:Rotordynamic instability due to fluid flow in Seals is a well known phenomenon that can occur in pumps as well as in steam turbines and air compressors. While analysis methods using bulk-flow equations are computationally efficient and can predict dynamic properties fairly well for short Seals, they often lack accuracy in cases of Seals with complex geometry or with large aspect ratios (L/D above 1.0). This paper presents the linearized rotordynamic coefficients for a Liquid Seal with large aspect ratio subjected to incompressible turbulent flow. The fluid-induced forces acting on the rotor are calculated by means of a three-dimensional computational fluid dynamics (3D-CFD) analysis, and are then expressed in terms of equivalent linearized stiffness, damping, and fluid inertia coefficients. For comparison, the Seal dynamic coefficients were calculated using two other codes: one developed with the bulk flow method and one based on the finite difference method. The three sets of dynamic coefficients calculated in this study were used then to predict the rotor dynamic behavior of an industrial pump. These estimations were then compared to the vibration characteristic measured during the pump shop test, results indicating that the closest agreement was achieved utilizing the CFD generated coefficients. The results of rotor dynamic analysis using the coefficients derived from CFD approach, improved the prediction of both damped natural frequency and damping factor for the first mode, showing substantially smaller damping factor which is consistent with the experimentally observed instability of the rotor-bearing system. As result of continuously increasing computational power, it is believed that the CFD approach for calculating fluid excitation forces will become the standard in industry. [DOI: 10.1115/1.4023653]
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Fluid-Induced Forces in Pump Liquid Seals With Large Aspect Ratio
ASME-JSME-KSME 2011 Joint Fluids Engineering Conference: Volume 1 Symposia – Parts A B C and D, 2011Co-Authors: Alexandrina Untaroiu, Vahe Hayrapetian, Costin D. Untaroiu, Paul E. Allaire, Houston G. Wood, Bruno Schiavello, James McguireAbstract:The instability due to fluid flow in Seals is a known phenomenon that can occur in pumps and compressors as well as in steam turbines. Traditional annular Seal models are based on bulk flow theory. While these methods are computationally efficient and can predict dynamic properties fairly well for short Seals, they lack accuracy in cases of Seals with complex geometry or with large aspect ratios (above 1.0). Unlike the bulk flow models, computational fluid dynamics (CFD) makes no simplifying assumption on the Seal geometry, shear stress at the wall, relationship between wall shear stress and mean fluid velocity, or characterization of interfaces between control volumes through empirical friction factors. This paper presents a method to calculate the linearized rotor-dynamic coefficients for a Liquid Seal with large aspect ratio (balance drum) subjected to incompressible turbulent flow by means of a three dimensional CFD analysis to calculate the fluid-induced forces acting on the rotor. The Reynolds-averaged Navier-Stokes equations for fluid flow are solved by dividing the volume of fluid into a discrete number of points at which unknown variables are computed. As a result, all the details of the flow field, including the fluid forces with potential destabilizing effects, are calculated. A 2nd order curve fit is then used to express the fluid-induced forces in terms of equivalent linearized stiffness, damping, and fluid inertia coefficients.Copyright © 2011 by ASME
Jun Ji - One of the best experts on this subject based on the ideXlab platform.
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experimental study on Liquid Seal and crystal surface morphology of barium hydroxide octahydrate
Journal of Molecular Liquids, 2020Co-Authors: Yudi Zhang, Xuelai Zhang, Jun JiAbstract:Abstract Molten barium hydroxide (BHO) with strong alkalinity will absorb CO2 in the air and denaturing part of BHO, so it is very important to treat it with Liquid Seal. In this paper, the effects of Liquid Seals with different cooling methods and white suspended substances on the phase change process of BHO were compared for phase change experiments, so as to study the influencing factors of powdery expansion of BHO and the crystal crystallization mode. The experimental results show that the probability of powdery expansion of BHO increases with the decrease of cooling rate. Liquid paraffin and high temperature silicone oil can play the role of air insulation, but will make BHO supercooling and powder expansion probability increase, some white powder suspended between molten BHO and Liquid Sealing material (BaCO3 attached to tiny bubbles) has a certain promoting effect on nucleating crystallization of BHO, and the supercooling degree of BHO without white powder will increase again, the surface of the BHO crystal shows a tight structure around the loose and porous center, known as a branch cavity structure, which becomes apparent as the cooling rate increases. This experiment provides a reference for the study of phase change materials in the field of phase change energy storage.
Alan Palazzolo - One of the best experts on this subject based on the ideXlab platform.
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Prediction of Rotordynamic Performance of Smooth Stator-Grooved Rotor Liquid Annular Seals Utilizing CFD
Journal of Vibration and Acoustics, 2017Co-Authors: Farzam Mortazavi, Alan PalazzoloAbstract:Circumferentially grooved, annular Liquid Seals typically exhibit good whirl frequency ratios (WFRs) and leakage reduction, yet their low effective damping can lead to instability. The current study investigates the rotordynamic behavior of a 15-step groove-on-rotor annular Liquid Seal by means of computational fluid dynamics (CFD), in contrast to the previous studies which focused on a groove-on-stator geometry. The Seal dimensions and working conditions have been selected based on experiments of Moreland and Childs (2016, “Influence of Pre-Swirl and Eccentricity in Smooth Stator/Grooved Rotor Liquid Annular Seals, Measured Static and Rotordynamic Characteristics,” M.Sc. thesis, Texas A&M University, College Station, TX). The frequency ratios as high as four have been studied. Implementation of pressure-pressure inlet and outlet conditions make the need for loss coefficients at the entrance and exit of the Seal redundant. A computationally efficient quasi-steady approach is used to obtain impedance curves as functions of the excitation frequency. The effectiveness of steady-state CFD approach is validated by comparison with the experimental results of Moreland and Childs. Results show good agreement in terms of leakage, preswirl ratio (PSR), and rotordynamic coefficients. It was found that PSR will be about 0.3–0.4 at the entrance of the Seal in the case of radial injection, and outlet swirl ratio (OSR) always converges to values near 0.5 for current Seal and operational conditions. The negative value of direct stiffness coefficients, large cross-coupled stiffness coefficients, and small direct damping coefficients explains the destabilizing nature of these Seals. Finally, the influence of surface roughness on leakage, PSR, OSR, and stiffness coefficients is discussed.
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CFD-Based Prediction of Rotordynamic Performance of Smooth Stator-Grooved Rotor (SS-GR) Liquid Annular Seals
Volume 7A: Structures and Dynamics, 2017Co-Authors: Farzam Mortazavi, Alan PalazzoloAbstract:Circumferentially grooved, annular Liquid Seals typically exhibit good whirl frequency ratios and leakage reduction, yet their low effective damping can lead to instability. The current study investigates the rotordynamic behavior of a 15 stage groove-on-rotor annular Liquid Seal by means of CFD, in contrast to previous studies which focused on a groove-on-stator geometry. The Seal dimensions and working conditions have been selected based on experiments of Moreland and Childs. The precessional frequency ratios as high as 4 have been studied. The CFD model replicates the whirling motion imposed by the 2D shaker apparatus in Moreland and Childs experimental setup. Implementation of pressure-pressure inlet and outlet conditions obviates the need for loss coefficients at the entrance and exit of the Seal. A computationally efficient quasi-steady approach is used to obtain impedance curves as functions of excitation frequency Ω. The effectiveness of steady-state CFD approach is validated by comparison with the experimental results of Moreland and Childs. Results show good agreement in terms of leakage, pre-swirl ratio and rotordynamic coefficients. Leakage is shown to decrease with spin rotational speed ω, whirl speed Ω and surface roughness ∈. The variation of pre-swirl ratio (PSR) and outlet-swirl ratio (OSR) with these parameters is presented. It was found that PSR will be about 0.3–0.4 at the entrance of Seal in the case of radial injection and OSR always converges to values near 0.5 for current Seal and operational conditions. The rotordynamic coefficients show negligible dependence on Ω in agreement with experiments. The small negative value of direct stiffness coefficients, large cross-coupled stiffness coefficients and small direct damping coefficients explain the destabilizing nature of these Seals. Finally, influence of surface roughness on leakage, PSR, OSR and stiffness coefficients is discussed.
Yudi Zhang - One of the best experts on this subject based on the ideXlab platform.
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experimental study on Liquid Seal and crystal surface morphology of barium hydroxide octahydrate
Journal of Molecular Liquids, 2020Co-Authors: Yudi Zhang, Xuelai Zhang, Jun JiAbstract:Abstract Molten barium hydroxide (BHO) with strong alkalinity will absorb CO2 in the air and denaturing part of BHO, so it is very important to treat it with Liquid Seal. In this paper, the effects of Liquid Seals with different cooling methods and white suspended substances on the phase change process of BHO were compared for phase change experiments, so as to study the influencing factors of powdery expansion of BHO and the crystal crystallization mode. The experimental results show that the probability of powdery expansion of BHO increases with the decrease of cooling rate. Liquid paraffin and high temperature silicone oil can play the role of air insulation, but will make BHO supercooling and powder expansion probability increase, some white powder suspended between molten BHO and Liquid Sealing material (BaCO3 attached to tiny bubbles) has a certain promoting effect on nucleating crystallization of BHO, and the supercooling degree of BHO without white powder will increase again, the surface of the BHO crystal shows a tight structure around the loose and porous center, known as a branch cavity structure, which becomes apparent as the cooling rate increases. This experiment provides a reference for the study of phase change materials in the field of phase change energy storage.
Farzam Mortazavi - One of the best experts on this subject based on the ideXlab platform.
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Prediction of Rotordynamic Performance of Smooth Stator-Grooved Rotor Liquid Annular Seals Utilizing CFD
Journal of Vibration and Acoustics, 2017Co-Authors: Farzam Mortazavi, Alan PalazzoloAbstract:Circumferentially grooved, annular Liquid Seals typically exhibit good whirl frequency ratios (WFRs) and leakage reduction, yet their low effective damping can lead to instability. The current study investigates the rotordynamic behavior of a 15-step groove-on-rotor annular Liquid Seal by means of computational fluid dynamics (CFD), in contrast to the previous studies which focused on a groove-on-stator geometry. The Seal dimensions and working conditions have been selected based on experiments of Moreland and Childs (2016, “Influence of Pre-Swirl and Eccentricity in Smooth Stator/Grooved Rotor Liquid Annular Seals, Measured Static and Rotordynamic Characteristics,” M.Sc. thesis, Texas A&M University, College Station, TX). The frequency ratios as high as four have been studied. Implementation of pressure-pressure inlet and outlet conditions make the need for loss coefficients at the entrance and exit of the Seal redundant. A computationally efficient quasi-steady approach is used to obtain impedance curves as functions of the excitation frequency. The effectiveness of steady-state CFD approach is validated by comparison with the experimental results of Moreland and Childs. Results show good agreement in terms of leakage, preswirl ratio (PSR), and rotordynamic coefficients. It was found that PSR will be about 0.3–0.4 at the entrance of the Seal in the case of radial injection, and outlet swirl ratio (OSR) always converges to values near 0.5 for current Seal and operational conditions. The negative value of direct stiffness coefficients, large cross-coupled stiffness coefficients, and small direct damping coefficients explains the destabilizing nature of these Seals. Finally, the influence of surface roughness on leakage, PSR, OSR, and stiffness coefficients is discussed.
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CFD-Based Prediction of Rotordynamic Performance of Smooth Stator-Grooved Rotor (SS-GR) Liquid Annular Seals
Volume 7A: Structures and Dynamics, 2017Co-Authors: Farzam Mortazavi, Alan PalazzoloAbstract:Circumferentially grooved, annular Liquid Seals typically exhibit good whirl frequency ratios and leakage reduction, yet their low effective damping can lead to instability. The current study investigates the rotordynamic behavior of a 15 stage groove-on-rotor annular Liquid Seal by means of CFD, in contrast to previous studies which focused on a groove-on-stator geometry. The Seal dimensions and working conditions have been selected based on experiments of Moreland and Childs. The precessional frequency ratios as high as 4 have been studied. The CFD model replicates the whirling motion imposed by the 2D shaker apparatus in Moreland and Childs experimental setup. Implementation of pressure-pressure inlet and outlet conditions obviates the need for loss coefficients at the entrance and exit of the Seal. A computationally efficient quasi-steady approach is used to obtain impedance curves as functions of excitation frequency Ω. The effectiveness of steady-state CFD approach is validated by comparison with the experimental results of Moreland and Childs. Results show good agreement in terms of leakage, pre-swirl ratio and rotordynamic coefficients. Leakage is shown to decrease with spin rotational speed ω, whirl speed Ω and surface roughness ∈. The variation of pre-swirl ratio (PSR) and outlet-swirl ratio (OSR) with these parameters is presented. It was found that PSR will be about 0.3–0.4 at the entrance of Seal in the case of radial injection and OSR always converges to values near 0.5 for current Seal and operational conditions. The rotordynamic coefficients show negligible dependence on Ω in agreement with experiments. The small negative value of direct stiffness coefficients, large cross-coupled stiffness coefficients and small direct damping coefficients explain the destabilizing nature of these Seals. Finally, influence of surface roughness on leakage, PSR, OSR and stiffness coefficients is discussed.