Volume 7B: Structures and Dynamics最新文献

{"title":"Flow Induced Dynamics of Plate Seals","authors":"Deepak Trivedi, Bernardo Kerr","doi":"10.1115/gt2019-90962","DOIUrl":"https://doi.org/10.1115/gt2019-90962","url":null,"abstract":"\u0000 Plate seals can provide low leakage at rotor-stator interfaces with large pressure drops in turbomachinery within a limited axial span. When designed with a self-correcting hydrostatic feedback mechanism, non-contact operation could be achieved even in the presence of large rotor transients. Flow induced dynamical instability is one of the key design challenges in plate seals for rotor-stator sealing in turbomachinery. The instabilities are caused by potentially multiple flow induced vibration mechanisms operating during different flow regimes. This paper investigates mechanisms of vortex induced flutter in compliant plate seals, which happens when the vortex shedding frequency of the plates comes close to one of the natural frequencies of vibration of the structure. An experimental methodology based on optical flow analysis of high speed videography is proposed to characterize vibrations of the ensemble of plates (“leafpack”.) Experiments show that the compliant plates vibrate in the flow field with amplitude dependent on the pressure drop. Additionally, the vibrations of individual plates are highly coupled to each other, leading to phase-locking or phase-drifting depending on boundary conditions. The leafpack has a characteristic frequency and exhibits traveling wave phenomena under certain conditions of pressurization. Using experimental insights, plate seals are modeled as a ring of a large (∼103) number of locally coupled oscillators, with nonlinear stiffness arising from hydrostatic forces. A two-way coupling exists between the structural and fluid wake dynamics. Using center manifold reduction, the coupled fourth order dynamics of the system is reduced to second order and transform the equations into the normal form for investigating the possibility of mitigating flow induced vibrations through the phenomenon of amplitude death. Conditions under which successful induction of amplitude death could eliminate plate vibration in the mode under consideration is discussed.","PeriodicalId":131756,"journal":{"name":"Volume 7B: Structures and Dynamics","volume":"25 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127248328","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Pump Grooved Seals: A CFD Approach to Improve Bulk-Flow Model Predictions","authors":"Tingcheng Wu, L. Andrés","doi":"10.1115/gt2019-90499","DOIUrl":"https://doi.org/10.1115/gt2019-90499","url":null,"abstract":"\u0000 In multiple stage centrifugal pumps, balance pistons, often comprising a grooved annular seal, equilibrate the full pressure rise across the pump. Grooves in the stator break the evolution of fluid swirl and increase mechanical energy dissipation; hence, a grooved seal offers a lesser leakage and lower cross-coupled stiffness than a similar size uniform clearance seal. To date bulk-flow models (BFMs) expediently predict leakage and rotor dynamic force coefficients of grooved seals; however, they lack accuracy for any other geometry besides rectangular. Note scalloped and triangular (serrated) groove seals are not uncommon. In these cases, computational fluid dynamics (CFD) models seals of complex shape to produce leakage and force coefficients. Alas CFD is not yet ready for routine engineer practice. Hence, an intermediate procedure presently takes an accurate two-dimensional (2D) CFD model of a smaller flow region, namely a single groove and adjacent land, to produce stator and rotor surface wall friction factors, expressed as functions of the Reynolds numbers, for integration into an existing BFM and ready prediction of seal leakage and force coefficients. The selected groove-land section is well within the seal length and far away from the effects of the inlet condition. The analysis takes three water lubricated seals with distinct groove shapes: rectangular, scalloped and triangular. Each seal, with length/diameter L/D = 0.4, has 44 grooves of shallow depth dg ∼ clearance Cr, and operates at a rotor speed equal to 5,588 rpm (78 m/s surface speed) and with a pressure drop of 14.9 MPa. The method validity is asserted when 2D (single groove-land) and 3D (whole seal) predictions for pressure and velocity fields are compared against each other. The CFD predictions, 2D and 3D, show the triangular groove seal has the largest leakage, 41% greater than the rectangular groove seal does, albeit producing the smallest cross-coupled stiffnesses and whirl frequency ratio. On the other hand, the triangular groove seal has the largest direct stiffness and damping coefficients. The scalloped groove seal shows similar rotordynamic force coefficients as the rectangular groove seal but leaks 13% more. For the three seal groove types, the modified BFM predicts leakage that is less than 6% away from that delivered by CFD, whereas the seal stiffnesses (both direct and cross-coupled) differ by 13%, the direct damping coefficients by 18%, and the added mass coefficients are within 30%. The procedure introduced extends the applicability of a BFM to predict the dynamic performance of grooved seals with distinctive shapes.","PeriodicalId":131756,"journal":{"name":"Volume 7B: Structures and Dynamics","volume":"220 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123040940","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Simulation, Test and Mitigation of 1/2X Forward Whirl Following Rotor Drop Onto Auxiliary Bearings","authors":"Xiao Kang, A. Palazzolo","doi":"10.1115/gt2019-91645","DOIUrl":"https://doi.org/10.1115/gt2019-91645","url":null,"abstract":"\u0000 1/2X forward whirl repeatedly occurred after a test rotor spinning at 5,800 rpm was dropped onto ball bearing type auxiliary bearings AB, utilized as a backup for magnetic bearings. The measured contact forces that occurred between the rotor and the auxiliary bearing during the ½X subsynchronous vibration were about thirteen times larger than the static reaction force. The vibration frequency coincided with the rotor-support system natural frequency with the rotor at rest on the auxiliary bearing AB, an occurred at ½ of the rotor spin speed when dropped. The test rig provided measurements of rotor-bearing contact force, rotor orbit (vibrations), and rotational speed during rotor drop events. A simulation model was also developed and demonstrated that parametric excitation in the form of a Mathieu Hill model replicated the measured 1/2X forward whirl vibrations. The simulation model included a nonlinear, elastic-thermal coupled, ball bearing type auxiliary bearing model. The transient model successfully predicted the 1/2X vibration when the rotor was passing 5800RPM as well, and the simulation results quantitatively agreed well with the test results in the frequency domain. Several approaches for mitigating the 1/2X forward whirl were presented such as adding an elastomer O-ring or waviness spring in the AB support system. Measurements confirmed that adding AB dampers effectively mitigated the ½ subsynchronous forward whirl and significantly reduced the contact forces.","PeriodicalId":131756,"journal":{"name":"Volume 7B: Structures and Dynamics","volume":"111 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115013767","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Influence of Lubrication Oil on the Performance of Carbon Fibre Brush Seals for Aero-Engines Bearing Chambers","authors":"Bilal Outirba, P. Hendrick","doi":"10.1115/gt2019-90459","DOIUrl":"https://doi.org/10.1115/gt2019-90459","url":null,"abstract":"\u0000 Carbon fibre brush seals are an alternative to labyrinth seals in aero-engines lubrication systems due to better sealing ability with low power loss. However, the use of brush seals still raises concerns about coking issues. In addition, the influence of oil on the brush seal behaviour needs to be fully assessed. This paper provides an experimental investigation of the effect of lubrication oil on the performance of carbon fibre brush seals under static and dynamic conditions. Eight brush seal samples of various geometrical designs were submitted to an environment recreating the working conditions of a modern aero-engine bearing chamber in terms of rotational speed, air pressure, and oil type of injection and temperature. The test results indicated that the performance of carbon fibre brush seals was deeply influenced by the presence of oil within fibres. Oil deeply influences leakage performance, depending on geometrical parameters (density, fibre length and interference) and operating conditions (oil temperature, rotational speed). Brush seal fibre pack is mainly prone to hydrodynamic lift and oil soaking, which is defined by the ability of lubrication oil to fill in properly the interstices between fibres. Viscosity and surface tension may be the key properties influencing oil soaking. Seal torque data corroborates the presence of a hydrodynamic lift. In addition, in absence of differential pressure, seal torque decrease with when oil temperature increases indicates the existence of a critical viscosity. Finally, oil lubrication within the bristles allows reduction of the inter-bristle friction, thus limiting hysteresis.","PeriodicalId":131756,"journal":{"name":"Volume 7B: Structures and Dynamics","volume":"4 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129978022","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Compliant Hybrid Gas Bearing Using Integral Hermetically-Sealed Squeeze Film Dampers","authors":"B. Ertas","doi":"10.1115/gt2019-90865","DOIUrl":"https://doi.org/10.1115/gt2019-90865","url":null,"abstract":"\u0000 The following paper focuses on an integral gas-film lubricated bearing concept developed to enable the oil-free operation of super-critical carbon dioxide (sCO2) turbomachinery. The externally pressurized tilting pad bearing concept possesses a flexible bearing support with an integral hermetically sealed squeeze film damper. Unlike the initial concepts using modular hermetic squeeze film dampers presented in past research, the bearing design in this work utilizes advanced manufacturing methods to yield an integral single piece design developed to reduce space envelope, cost, and improved overall design reliability. The paper advances a detailed description of the bearing design and identification of bearing support force coefficients. Non-rotating bearing support test results show the influence of vibration amplitude, frequency, and damper cavity pressurization on force coefficients for two different viscosity fluids. Results indicate an increase in stiffness and a decrease in damping when increasing the frequency of excitation. Damper cavity pressurization was shown to eliminate squeeze film cavitation for the vibration amplitudes and frequency range in the study. Additionally, the paper advances a transient fluid-structure interaction (FSI) analysis aimed at gaining insight on the interaction of flexible elements bounding a hermetic fluid volume experiencing sinusoidal vibratory motion. The analysis considers an idealized damper model with and without a vibration transmission post while varying diaphragm modulus of elasticity for three excitation frequencies. Computational results were able to capture the increase in stiffness and decrease in damping and show that the flexibility of the bounding elements influence the damper cavity volume change and phase; ultimately effecting dynamic cavity pressures and force coefficients.","PeriodicalId":131756,"journal":{"name":"Volume 7B: Structures and Dynamics","volume":"66 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125145760","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Static Stiffness Measurements for a Thrust Collar Used in an Integrally Geared Compressor","authors":"T. Kerr, Adolfo Delgado, D. Childs","doi":"10.1115/gt2019-90488","DOIUrl":"https://doi.org/10.1115/gt2019-90488","url":null,"abstract":"\u0000 This paper presents a comparison of predicted and measured axial stiffness of an oil-lubricated thrust collar (TC) for use in an integrally geared compressor (IGC). The test rig used to measure the stiffness closely resembles a TC that would be used in a production IGC. Separate motors spin two shafts at predetermined spin speeds, and a pneumatic loader applies an axial load to the pinion shaft. The load is transmitted from the pinion shaft through the TC and onto the bull gear shaft. The relative deflection between the faces of the TC is measured as the axial load is increased. Tests were conducted at pinion spin speeds of 5, 7.5, and 10 krpm, and the axial load was varied from 75 to 2,600 N (1 to 32 bar specific load). A custom curve fit describes the load-deflection plot. The slope of the equation is the stiffness coefficient, kz. The measured kz values increase versus axial load, and decrease versus spin speed. Measured and predicted values agree in trend and magnitude. Predicted kz values slightly overestimate the measured results. The power loss from the lubricated area is measured from VFD power outputs. Power loss increases with spin speed and the measured power loss tends to be twice as high as predictions. These results are useful in validating the predictions made by Cable et. al.[1] The results are also useful to IGC original equipment manufacturers (OEMs) or end-users who desire to model their machines.","PeriodicalId":131756,"journal":{"name":"Volume 7B: Structures and Dynamics","volume":"122 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124065023","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Nonlinear Harmonic Analysis of a Blade Model Subjected to Large Geometrical Deflection and Internal Resonance","authors":"Nicolas Di Palma, A. Martin, F. Thouverez, V. Courtier","doi":"10.1115/gt2019-91213","DOIUrl":"https://doi.org/10.1115/gt2019-91213","url":null,"abstract":"\u0000 This paper is devoted to the study of the nonlinear harmonic response of an industrial blade model subjected to large geometrical deflection. A reduction procedure is performed on the blade model using the linear normal modes of the structure. Geometrical nonlinear effects are taken into account by considering cubic and quadratic stiffnesses in the dynamical reduced model. Reduced nonlinear stiffness coefficients are computed with the STiffness Evaluation Procedure (STEP) and periodic solutions are sought using the Harmonic Balance Method (HBM) coupled to a pseudo-arclength continuation. Along with the harmonic response, a bifurcation analysis is performed to compute both turning and branching points. Specific attention is paid to the internal resonance phenomenon. 2 to 1 internal resonance occurred during the frequency response analysis close to the first and second modes of the reduced model. Mode coupling phenomena occurred during the harmonic analysis and secondary branches of solutions were obtained from branching point bifurcations.","PeriodicalId":131756,"journal":{"name":"Volume 7B: Structures and Dynamics","volume":"15 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134383110","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Multi-Objective Optimization for Piezoelectric-Based Approaches With Applications Toward Bladed Disks","authors":"Garrett K. Lopp, Jeffrey L. Kauffman","doi":"10.1115/gt2019-91861","DOIUrl":"https://doi.org/10.1115/gt2019-91861","url":null,"abstract":"\u0000 Recent years have seen a wealth of research interest in piezoelectric-based applications for turbomachinery blades covering areas including vibration actuators and sensors in test environments, as well as vibration reduction approaches. The success of these applications relies on efficient exchange of vibration energy between the mechanical and electrical domains through inclusion of the piezoelectric elements on the vibrating structure. The effective electromechanical coupling coefficient measures the quality of this energy exchange for the various vibration modes of the structure; however, there is often trade-offs between the size of the piezoelectric elements and the electromechanical coupling for the various modes of interest. As such, this paper applies a multi-objective optimization algorithm that generates Pareto-optimal fronts to aid in the selection of the optimal location of off-the-shelf piezoelectric patches on the surface of each blade of an academic blisk. As the off-the-shelf patches have a fixed geometry, this paper simplifies the optimization to only include the electromechanical coupling of the modes of interest. Both a numerical and experimental application of this optimization procedure to an 8-sector blisk machined from a single sheet of aluminum shows the effectiveness of the approach.","PeriodicalId":131756,"journal":{"name":"Volume 7B: Structures and Dynamics","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125126946","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Strongly Coupled Thermo-Mechanical Casing/Abradable Model for Rotor/Stator Interactions","authors":"F. Nyssen, Thibaut Vadcard, Elsa Piollet, Alain Batailly","doi":"10.1115/gt2019-91447","DOIUrl":"https://doi.org/10.1115/gt2019-91447","url":null,"abstract":"\u0000 Modern turbomachine designs feature reduced nominal clearances between rotating bladed-disks and their surrounding casings in order to improve the engine efficiency. Unavoidably, clearance reduction increases the risk of contacts between static and rotating components which may yield hazardous interaction phenomena. In this context, the deposition of an abradable coating along the casing inner surface is a common way to enhance operational safety while mitigating interaction phenomena thus allowing for tighter clearances. Nonetheless, interactions leading to unexpected wear removal phenomena between a bladed-disk and a casing with abradable coating have been observed experimentally. Beside of blade damages such as cracks resulting from high amplitudes of vibration, experimental observations included very significant temperatures increase, particularly within the abradable coating, to a point that thermo-mechanical effects may not be neglected anymore. The aim of this work is to investigate the numerical modeling of thermal effects in the abradable coating and the casing due to contact interactions. In particular, the proposed model provides insight on the sensitivity of engines to contact events when the plane had reduced tarmac times between two consecutive flights.\u0000 A strongly coupled thermo-mechanical model of the casing and its abradable coating is first described. A 3D cylindrical mesh is employed, it may be decomposed in two parts: (1) along the casing contact surface, a cylindrical thermal mesh is constructed to compute the temperature elevation and heat diffusion in the three directions of space within the abradable coating, and (2) the casing itself is represented by a simplified cylindrical thermo-mechanical mesh to compute both temperature elevation and the induced deformations following temperature changes. This 3D hybrid mesh is combined with a mechanical mesh of the abradable layer, dedicated to wear modeling and the computation of normal and tangential contact forces following blade/abradable coating impacts. The heat flux resulting from contact events is related to the friction forces and only heat transfer by conduction is considered in this work. In order to reduce computational times, the time integration procedure is twofold: the explicit time integration scheme featuring reduced time steps required for contact treatment is combined with a larger time step time integration scheme used for the casing thermo-mechanical model. An extensive validation procedure is carried out from a numerical standpoint, it underlines the convergence of the model with respect to time and space parameters.","PeriodicalId":131756,"journal":{"name":"Volume 7B: Structures and Dynamics","volume":"84 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122942487","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Leakage and Cavity Pressures in an Interlocking Labyrinth Gas Seal: Measurements vs. Predictions","authors":"L. San Andrés, Tingcheng Wu, Jose Barajas-Rivera, Jiaxin Zhang, R. Kawashita","doi":"10.1115/gt2019-91507","DOIUrl":"https://doi.org/10.1115/gt2019-91507","url":null,"abstract":"\u0000 Gas labyrinth seals (LS) restrict secondary flows (leakage) in turbomachinery and their impact on the efficiency and rotordynamic stability of high-pressure compressors and steam turbines can hardly be overstated. Amongst seal types, the interlocking labyrinth seal (ILS), having teeth on both the rotor and on the stator, is able to reduce leakage up to 30% compared to other LSs with either all teeth on the rotor or all teeth on the stator. This paper introduces a revamped facility to test gas seals for their rotordynamic performance and presents measurements of the leakage and cavity pressures in a five teeth ILS. The seal with overall length/diameter L/D = 0.3 and small tip clearance Cr/D = 0.00133 is supplied with air at T = 298 K and increasing inlet pressure Pin = 0.3 MPa ∼ 1.3 MPa, while the exit pressure/inlet pressure ratio PR = Pout/Pin is set to range from 0.3 to 0.8. The rotor speed varies from null to 10 krpm (79 m/s max. surface speed). During the tests, instrumentation records the seal mass flow (ṁ) and static pressure in each cavity. In parallel, a bulk-flow model (BFM) and a computational fluid dynamics (CFD) analysis predict the flow field and deliver the same performance characteristics, namely leakage and cavity pressures. Both measurements and predictions agree closely (within 5%) and demonstrate the seal mass flow rate is independent of rotor speed. A modified flow factor Φ¯=m.T/PinD1-PR2 characterizes best the seal mass flow with a unique magnitude for all pressure conditions, Pin and PR.","PeriodicalId":131756,"journal":{"name":"Volume 7B: Structures and Dynamics","volume":"111 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133366882","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}