Browsing by Subject "Squeeze Film Damper"
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Item Numerical Simulation of Flow Field Inside a Squeeze Film Damper and the Study of the Effect of Cavitation on the Pressure Distribution(2012-02-14) Khandare, Milind NandkumarSqueeze 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 Andr?s 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 ?m 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 Andr?s and Delgado.Item Numerical Simulation of Squeeze Film Dampers and Study of the Effect of Central Groove on the Dynamic Pressure Distribution(2012-10-19) Boppa, PraneethaSqueeze 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 Andr?s 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.Item Performance of an Open Ends Squeeze Film Damper Operating with Large Amplitude Orbital Motions: Experimental Analysis and Assessment of the Accuracy of the Linearized Force Coefficients Model(2013-08-22) Jeung, Sung HwaSqueeze Film Dampers (SFDs) aid to suppress rotor vibrations and enhance the stability of high-speed rotor-bearing systems. A SFD is a simple oil lubricated film between a stationary housing and a precessing (whirling) journal. Aircraft engines use SFDs as the only means to provide damping to otherwise rigid ball bearing supports. This thesis presents experimental results for the dynamic forced performance of a test open ends SFD operating with large amplitude whirl motions, centered and off centered within the bearing clearance. The test rig comprises of an elastically supported bearing with a damper section having two parallel film lands separated by a feed groove. A film land is 25.4 mm long, with diameter 127 mm and nominal radial clearance c=0.251 mm. Two orthogonally placed shakers apply dynamic loads on the bearing to induce circular orbit motions at prescribed whirl frequencies. A static loader, 45? away from each shaker, pulls the bearing to a static eccentric position. Circular orbit tests were performed (10 ? 100 Hz frequency range) for eight increasing orbit amplitudes (r=0.08c to ~0.71c) and under four static eccentricities (es=0.0c to ~0.76c). An identification method estimates the test damper force coefficients from transfer functions in the frequency domain. The analysis shows that the SFD damping force coefficients increase with the static eccentricity (es) increase. On the other hand, the damper inertia coefficients decrease as the orbit amplitude (r) becomes large and also increase modestly with the static eccentricity (es). Predictions from a physical model show good agreement with the test dynamic force coefficients. The accuracy of the linearized SFD force coefficients (K, C, M)SFD is evaluated from comparing the differences in mechanical work performed by actual and linear SFD reaction forces. The difference in mechanical work (Ediff) increases with increasing static eccentricity (es) and orbit amplitude (r). However, for most test conditions (r/c?0.4,es/c?0.25), Ediff is less than ~5%, thus showing the linearized SFD force coefficients represent well the forced response of the actual test SFD system. The test and predicted force coefficients as well as the analysis of the pressure fields contribute to a better understanding of the kinetics of SFDs operating with moderate tolarge amplitude size whirl motions, centered and off-centered.