Download or read book Numerical Simulation of Flow Field Inside a Squeeze Film Damper and the Study of the Effect of Cavitation on the Pressure Distribution written by Milind Nandkumar Khandare and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Squeeze Film Dampers (SFDs) are employed in high-speed Turbomachinery, particularly aircraft jet engines, to provide external damping. Despite numerous successful applications, it is widely acknowledged that the theoretical models used for SFD design are either overly simplified or incapable of taking into account all the features such as cavitation, air entrainment etc., affecting the performance of a SFD. On the other hand, experimental investigation of flow field and dynamic performance of SFDs can be expensive and time consuming. The current work simulates the flow field inside the dynamically deforming annular gap of a SFD using the commercial computational fluid dynamics (CFD) code Fluent and compares the results to the experimental data of San Andrés and Delgado. The dynamic mesh capability of Fluent and a User Defined Function (UDF) was used to replicate the deforming gap and motion of the rotor respectively. Two dimensional simulations were first performed with different combinations of rotor whirl speed, operating pressures and with and without incorporating the cavitation model. The fluid used in the simulations was ISO VG 2 Mobil Velocite no. 3. After the successful use of the cavitation model in the 2D case, a 3D model with the same dimensions as the experimental setup was built and meshed. The simulations were run for a whirl speed of 50 Hz and an orbit amplitude of 74 um with no through flow and an inlet pressure of 31kPa (gauge). The resulting pressures at the mid-span of the SFD land were obtained. They closely agreed with those obtained experimentally by San Andrés and Delgado.
Download or read book Numerical Simulation of Squeeze Film Dampers and Study of the Effect of Central Groove on the Dynamic Pressure Distribution written by Praneetha Boppa and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Squeeze film dampers are used in the high speed turbo machinery industry and aerospace industries as a means to reduce vibration amplitude, to provide damping, to improve dynamic stability of the rotor bearing system and to isolate structural components. The effects of cavitation included in previous studies were not effective. The effect of different design parameters were not studied thoroughly as experimental investigation of squeeze film dampers is very expensive. Few of them used numerical investigation but the methods they used are either time consuming or complicated. The present study investigated the feasibility of applying a steady state solver, which is computationally less expensive, for analyzing flow field inside the squeeze film dampers. The behavior of dynamic pressure profiles at different operating conditions, and the effect of a central groove on dynamic pressure profiles were also studied. Simulation results of a 3D case which is similar to the one experimentally studied by Delgado were used to establish if the moving reference frame (MRF) model in Fluent 12.1 can be used. A steady state solver in an absolute frame of reference was used to produce whirling motion of the rotor in this study. The inlet pressure of 31kpa and the whirling speed of 50 and 100Hz were used as boundary conditions. The mixture model with three percent dissolved air in lubricant is used to model multiphase flow. Singhal cavitation model is used to model cavitation. The simulations (50,000 iterations) were run until steady state solutions were reached. The results closely agreed with those obtained experimentally by San André́s and Delgado. Numerical simulations of three-dimensional cases with an additional central groove on the squeeze film land were also performed to predict the effect of central groove on dynamic pressure profiles. Addition central groove reduces the pressures and forces generated by squeeze film damper.
Download or read book Analysis of the Characteristics of a Squeeze Film Damper by Three dimensional Navier Stokes Equations written by Changhu Xing and published by . This book was released on 2009 with total page 445 pages. Available in PDF, EPUB and Kindle. Book excerpt: "The squeeze film damper is widely used in turbomachinery due to its ability to reduce vibration, help transition through the critical speed (resonance) and diminish the force transmitted to the support frame. Instead of the commonly used Reynolds equation modeling technique, this dissertation employed the three-dimensional Navier-Stokes equations. These equations are coupled with a homogeneous cavitation model, Gumbel ([pi]-film) or full Sommerfeld (2[pi]-film) cavitation strategies in dealing with the flow field and pressure development in a squeeze film damper. The characteristics of the pressure distribution, velocity field, dynamic force and the associated damping and inertia coefficients were investigated by the parametric studies using either lubricant properties such as the gas concentration, viscosity and density or damper geometry. The equation of motion for a rigid or flexible rotor model was employed in the stability analysis for the rotor-damper operating system. The dynamic coefficients were introduced into the equations to determine the rotor trajectory and stability through the source term. By analyzing the eccentricity, rotor deflection and transmissibility response, this dissertation has pointed to a methodology of finding the 'preferred range' of both one- and two-phase squeeze dampers. Further parametric studies on the rotor-damper system evaluate the effects of the lubricant dynamic viscosity, density, gaseous or vaporous cavitation, gas concentration, static eccentricity, whirling speed, rotor flexibility, retainer spring stiffness, the lumped mass distribution and the amount of imbalance. These parameters are necessary in optimizing the design of a damper. Except for the analysis based on the equations of motion, the direct numerical simulation for the determination of the journal orbit was performed by the coupling of flow, grid deformation and stress module in CFD-ACE+. The close match of the two sets of results strengthened the confidence of the simulation results. The experimental portion of this study was designed to validate qualitatively and quantitatively the numerical simulations in pressure distribution, cavitation visualization and the damper vibration. The damper vibration was measured by means of proximity sensors located circumferentially around the supporting frame; the pressure evolution was measured by pressure transducers and the gaseous and vaporous cavitation was visualized by both a digital camera with strobotac lighting and a high speed (5000fps) camera. The experimental results corroborated the theoretical analysis."--Abstract.
Download or read book Effects of Fluid Inertia and Cavitation on the Force Coefficients of a Squeeze Film Damper written by Si Young Jung and published by . This book was released on 1990 with total page 356 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1992 with total page 1572 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Numerical Investigation of Flow Fields and Forces for 2 D Squeeze Film Dampers written by Terdsak Neadkratoke and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A numerical method is used to predict flow fields and forces for squeeze film dampers (SFDs). A two dimensional SFD is modeled with different amplitudes and frequencies of the journal orbiting inside the wall. In addition to the typical circular centered orbit (CCO) motion prescribed in most studies, orbits can vary greatly from circular to linear. The study is divided into two distinctive models including single phase flow model and two phase flow model. The single phase flow model cases including three amplitudes, i.e. 0.002, 0.001, and 0.0005 inches, and three frequencies, i.e. 10, 50, and 200 Hz, of journal motions are conducted to portray flow fields and forces and ultimately determine their relationships. The numerical prediction shows that the journal amplitude and frequency affect flow and consequently force in the SFD. The force is directly proportional to frequency and motion amplitude. Owing to the presence of cavitation in the practical SFD, the two phase flow model is also presented with the journal amplitude of 0.0002 and three frequencies of 10, 50, and 100 Hz, respectively. The ambient pressure condition was set up for numerical processing ranging from 0.001 Mpa to 100 Mpa. The results indicate that the operating pressure has an integral role in suppressing the presence of the cavitation. The caviation disappears if the operating pressure is high enough above the vapor pressure of the lubricant.
Download or read book Applied Mechanics Reviews written by and published by . This book was released on 1987 with total page 338 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Numerical Simulation of Cavitation in a Francis Runner written by Rafel Roig Bauzà and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Nowadays, two of the more important challenges for the humanity are the climate change and the management of the energy. For this reason the performance of a machine for the conversion of renewable energy has been studied in this thesis. Specifically, the GAMM Francis turbine runner working at its best efficiency point under cavitation conditions has been analysed using CFX (Ansys®). Firstly, a slice of the 3D fluid domain has been made, using SolidWorks®, benefiting of the runner axisymmetry and thus decreasing the computational power needed. In order to take into account the runner rotation relative to the incoming flow field, three different domains have been defined. Two of the domains have been considered to be still and the other one has been considered to be in rotation around the turbine axis ensuring a model closer to the reality, which has permitted to study the relative and absolute velocity fields. Then, a uniform incoming flow has been simulated through the runner blades under different levels of static pressure at the draft tube outlet boundary condition. The pressure has been gradually decreased, and consequently the sigma coefficient of cavitation, until the vapour pressure has been reached inside the runner. Thus, the onset of blade cavitation and its growth has been studied while keeping the remaining parameters unchanged. Based on the numerical results, the value of the torque, the pressure coefficient and the shape, localization and size of the cavity have been analysed according to the sigma coefficient. To finish a sensitivity study of the empirical parameters that the cavitation model takes into account has been carried out based on their impact on the cavitation results.
Download or read book Numerical Simulation of Cavitating Bubble laden Turbulent Flows written by Ehsan Shams Sobhani and published by . This book was released on 2010 with total page 354 pages. Available in PDF, EPUB and Kindle. Book excerpt: Many engineering devices and propulsion systems suffer from undesirable effects of cavitation; such as degradation in the efficiency of pumps and turbines, generation of noise and vibration on ship propeller, increased drag and erosion of propeller blade, etc. In spite of decades of research on this problem, detailed study of cavitation physics is still a technical challenge for the current experimental and numerical approaches. Further development of robust and accurate numerical methods for cavitating flow simulation, is the basis of this research. The main objective of this research is to investigate traveling bubble cavitation in turbulent flows. Variable density Navier-Stokes equations are solved in an unstructured grid finite volume solver. Large Eddy Simulation technique with dynamic Smagorinsky subgrid model is used for turbulence modeling. Bubble cavitation is modeled in a Lagrangian framework with subgrid models for forces acting on bubbles. Bubble size variation is modeled using local flow field hydrodynamic pressure for solving Rayliegh-Plesset equation. An adaptive time stepping method is devised for the efficient solution of this highly non-linear equation. Turbulent flow over an open cavity is reproduced numerically from the experimental work by [Liu and Katz, PoF, 08]. Flow statistics agreed very well to those of experiment. Cavitation inception was studied using two different models: (i) discrete bubble model, and (ii) scalar transport model. Severe cavitation was predicted near on top of the trailing edge for cavitation index of [delta]
Download or read book International Aerospace Abstracts written by and published by . This book was released on 1999 with total page 974 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Numerical Simulation of the Compressibility Effect on Bubble Dynamics written by Qun Wang and published by . This book was released on 1995 with total page 388 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Cavitation Effects on the Performance of Squeeze Film Damper Bearings written by Fouad Youssef Zeidan and published by . This book was released on 1989 with total page 658 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Modeling and Experimentation of Squeeze Film Dampers Considering Fluid Inertia Film Cavitation and Design Features in Aircraft Engine written by Tieshu Fan and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Unbalance-induced vibration in aircraft engines is the major source of cabin noise and discomfort for passengers. One key component in attenuating the vibration level in an engine rotor is the squeeze film damper (SFD). The implementation of SFDs in high-speed turbomachinery increases the rotor stability and reduces the vibration amplitude at critical speeds. Despite the successful operation of SFDs in aero engines for decades, currently applied SFD models are not sophisticated enough to recognize unique features that affect damping performance. Development of an accurate and computationally efficient model has been an ongoing challenge. The object of this thesis is to develop SFD models that incorporate the fluid inertia, film cavitation, lubricant seals, and supply mechanism to provide a precise prediction of damper behavior at high operating speeds. To be specific, the fluid inertia is resolved by the momentum approximation method and perturbation method; film cavitation is formulated by the Elrod cavitation algorithm [1] and the linear complementarity problem method [2]; the effect of lubricant seals is addressed by the leakage flow at the seal groove for piston ring seals [3]; the supply mechanism is modeled by the flow interaction at the central groove. Moreover, the developed models are integrated into a rotordynamic system to estimate the critical speeds and vibration amplitudes. To accelerate the simulation time, a polynomial interpolation technique for SFD models is introduced to solve for the SFD forces under different operating conditions. Both the steady-state response and the frequency response are presented for an open SFD application. To validate the developed SFD models, an experiment for a single flexible rotor supported with two identical SFDs is executed. Displacements of both the central disk and support SFDs are measured to correlate the theoretical prediction. Some design and operation parameters including the film clearance and supply pressure are examined in the test to evaluate their effect. Results have shown excellent agreement in terms of the critical speed and vibration amplitude. In addition, several other design parameters such as the film length and bearing stiffness are discussed in the model sensitivity to demonstrate the significance of their impact.
Download or read book NASA SP written by and published by . This book was released on 1990 with total page 700 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Effects of Wall Pressure Distribution and Liquid Temperature on Incipient Cavitation of Freon 114 and Water in Venturi Flow written by Royce D. Moore and published by . This book was released on 1968 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book A Numerical Study of Cavitating Flows Based on Plic vof Method for Arbitrary Unstructured Meshes written by Dezhi Dai and published by . This book was released on 2022 with total page 122 pages. Available in PDF, EPUB and Kindle. Book excerpt: Cavitation appears when local static pressure drops below the water vapor pressure and causes significant impacts on marine propeller blades. The Volume of Fluid (VOF) method, which is also referred to as the Transport Equation-based Model (TEM), has been extensively adopted in the cavitating flow simulations. Piecewise Linear Interface Calculation (PLIC) schemes have been extensively employed in the VOF method for interface capturing in numerical simulations of multiphase flows. Polyhedral unstructured meshes are often adopted due to their geometric flexibility and superiority in gradient calculation. Four analytical interface reconstruction algorithms in the PLIC-VOF method for arbitrary convex polyhedral cells have been proposed in the present study. The plane interface at a given orientation within a polyhedral cell is located by four different analytical techniques. They have been tested successfully for six different geometric shapes that are common in polyhedral meshes. The computational efficiencies of the algorithms have been compared with two other published schemes in the literature. The proposed algorithms have been shown to yield smaller truncation errors with a reduction in computational complexity. A numerical simulation of a 3D dam-breaking problem has been successfully performed using the proposed interface reconstruction scheme on a polyhedral mesh. The percentage of the overall computational time consumed has been assessed to justify its optimization in a real multiphase flow simulation. The effects of cavitation on the dynamics of a two-dimensional hydrofoil and three-dimensional propeller have been studied numerically. Analytical PLIC-VOF methods on overset unstructured meshes have been employed to capture the interface between liquid and vapor phases in cavitating flows around a NACA 66 (MOD) hydrofoil and PPTC propeller. A modified version of the Schnerr-Sauer cavitation model has been adopted to compute the local mass transport rate for the vaporization and condensation processes. Turbulent eddy viscosity is evaluated by using the Spalart-Allmaras one-equation model. Simulations are performed under the framework of OpenFOAM with a modified flow solver. Stable sheet and unstable cloud cavitations have been investigated. The findings in the present study are consistent with experimental studies reported in the literature.
Download or read book Effects of Fluid Inertia on Squeeze Film Damper Pressure Distribution written by Gregory Michael Savela and published by . This book was released on 2000 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt:
