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Meng Chen - One of the best experts on this subject based on the ideXlab platform.
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CFD analysis of flow forces and energy loss characteristics in a flapper–nozzle pilot valve with different null clearances
Energy Conversion and Management, 2014Co-Authors: Nay Zar Aung, Qingjun Yang, Meng ChenAbstract:Abstract A well understanding on the flow forces and energy loss characteristics in a flapper–nozzle pilot valve is necessarily important in the performance improvement of a two-stage electrohydraulic servo-valve. This paper presents the CFD analysis of flow forces and energy loss characteristics in a flapper–nozzle pilot valve with different null clearances. Five different flapper–nozzle structures with three different null clearances of 0.1 mm, 0.05 mm and 0.033 mm are considered in this analysis. For every flapper–nozzle structure, the systematic CFD simulations of flow forces and energy loss characteristics are performed for seven different flow conditions varying nozzle inlet pressures from 1 MPa to 7 MPa. Experimental measurements are also conducted for energy loss characteristics and then compared with simulated results. Meanwhile, the CFD flow force results are verified with the results of exiting simplified flow force models and vice versa. From each nozzle side, the main flow force acting on the flapper is accompanied by four tiny lateral forces resulted from the impact of radial jet reattachment on the flapper curved surface. For each of given null clearances, the main flow force and lateral forces linearly increase with the increment of nozzle inlet pressure. For the same null clearance, applying larger flapper can give 1.5–13.6% larger lateral force in Drag Direction and 1.5–10.2% larger lateral force in lift Direction compared to deploying smaller flapper. Compared to the main flow force, the magnitudes of the lateral forces on each corner of the flapper are found in the range of 0.8–3.2% in Drag Direction and 1.6–7.5% in lift Direction. For main flow forces, the CFD simulated results show a good agreement with that of flow force model based on momentum conservation. Both existing flow force models are undoubtedly applicable in the prediction of flow forces for small null clearances (less than 0.05). Having a good agreement between each other, both experimental and numerical results show that the energy loss increases with the increment of null clearance and nozzle inlet pressure.
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cfd analysis of flow forces and energy loss characteristics in a flapper nozzle pilot valve with different null clearances
Energy Conversion and Management, 2014Co-Authors: Qingjun Yang, Nay Zar Aung, Meng ChenAbstract:Abstract A well understanding on the flow forces and energy loss characteristics in a flapper–nozzle pilot valve is necessarily important in the performance improvement of a two-stage electrohydraulic servo-valve. This paper presents the CFD analysis of flow forces and energy loss characteristics in a flapper–nozzle pilot valve with different null clearances. Five different flapper–nozzle structures with three different null clearances of 0.1 mm, 0.05 mm and 0.033 mm are considered in this analysis. For every flapper–nozzle structure, the systematic CFD simulations of flow forces and energy loss characteristics are performed for seven different flow conditions varying nozzle inlet pressures from 1 MPa to 7 MPa. Experimental measurements are also conducted for energy loss characteristics and then compared with simulated results. Meanwhile, the CFD flow force results are verified with the results of exiting simplified flow force models and vice versa. From each nozzle side, the main flow force acting on the flapper is accompanied by four tiny lateral forces resulted from the impact of radial jet reattachment on the flapper curved surface. For each of given null clearances, the main flow force and lateral forces linearly increase with the increment of nozzle inlet pressure. For the same null clearance, applying larger flapper can give 1.5–13.6% larger lateral force in Drag Direction and 1.5–10.2% larger lateral force in lift Direction compared to deploying smaller flapper. Compared to the main flow force, the magnitudes of the lateral forces on each corner of the flapper are found in the range of 0.8–3.2% in Drag Direction and 1.6–7.5% in lift Direction. For main flow forces, the CFD simulated results show a good agreement with that of flow force model based on momentum conservation. Both existing flow force models are undoubtedly applicable in the prediction of flow forces for small null clearances (less than 0.05). Having a good agreement between each other, both experimental and numerical results show that the energy loss increases with the increment of null clearance and nozzle inlet pressure.
Nay Zar Aung - One of the best experts on this subject based on the ideXlab platform.
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CFD analysis of flow forces and energy loss characteristics in a flapper–nozzle pilot valve with different null clearances
Energy Conversion and Management, 2014Co-Authors: Nay Zar Aung, Qingjun Yang, Meng ChenAbstract:Abstract A well understanding on the flow forces and energy loss characteristics in a flapper–nozzle pilot valve is necessarily important in the performance improvement of a two-stage electrohydraulic servo-valve. This paper presents the CFD analysis of flow forces and energy loss characteristics in a flapper–nozzle pilot valve with different null clearances. Five different flapper–nozzle structures with three different null clearances of 0.1 mm, 0.05 mm and 0.033 mm are considered in this analysis. For every flapper–nozzle structure, the systematic CFD simulations of flow forces and energy loss characteristics are performed for seven different flow conditions varying nozzle inlet pressures from 1 MPa to 7 MPa. Experimental measurements are also conducted for energy loss characteristics and then compared with simulated results. Meanwhile, the CFD flow force results are verified with the results of exiting simplified flow force models and vice versa. From each nozzle side, the main flow force acting on the flapper is accompanied by four tiny lateral forces resulted from the impact of radial jet reattachment on the flapper curved surface. For each of given null clearances, the main flow force and lateral forces linearly increase with the increment of nozzle inlet pressure. For the same null clearance, applying larger flapper can give 1.5–13.6% larger lateral force in Drag Direction and 1.5–10.2% larger lateral force in lift Direction compared to deploying smaller flapper. Compared to the main flow force, the magnitudes of the lateral forces on each corner of the flapper are found in the range of 0.8–3.2% in Drag Direction and 1.6–7.5% in lift Direction. For main flow forces, the CFD simulated results show a good agreement with that of flow force model based on momentum conservation. Both existing flow force models are undoubtedly applicable in the prediction of flow forces for small null clearances (less than 0.05). Having a good agreement between each other, both experimental and numerical results show that the energy loss increases with the increment of null clearance and nozzle inlet pressure.
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cfd analysis of flow forces and energy loss characteristics in a flapper nozzle pilot valve with different null clearances
Energy Conversion and Management, 2014Co-Authors: Qingjun Yang, Nay Zar Aung, Meng ChenAbstract:Abstract A well understanding on the flow forces and energy loss characteristics in a flapper–nozzle pilot valve is necessarily important in the performance improvement of a two-stage electrohydraulic servo-valve. This paper presents the CFD analysis of flow forces and energy loss characteristics in a flapper–nozzle pilot valve with different null clearances. Five different flapper–nozzle structures with three different null clearances of 0.1 mm, 0.05 mm and 0.033 mm are considered in this analysis. For every flapper–nozzle structure, the systematic CFD simulations of flow forces and energy loss characteristics are performed for seven different flow conditions varying nozzle inlet pressures from 1 MPa to 7 MPa. Experimental measurements are also conducted for energy loss characteristics and then compared with simulated results. Meanwhile, the CFD flow force results are verified with the results of exiting simplified flow force models and vice versa. From each nozzle side, the main flow force acting on the flapper is accompanied by four tiny lateral forces resulted from the impact of radial jet reattachment on the flapper curved surface. For each of given null clearances, the main flow force and lateral forces linearly increase with the increment of nozzle inlet pressure. For the same null clearance, applying larger flapper can give 1.5–13.6% larger lateral force in Drag Direction and 1.5–10.2% larger lateral force in lift Direction compared to deploying smaller flapper. Compared to the main flow force, the magnitudes of the lateral forces on each corner of the flapper are found in the range of 0.8–3.2% in Drag Direction and 1.6–7.5% in lift Direction. For main flow forces, the CFD simulated results show a good agreement with that of flow force model based on momentum conservation. Both existing flow force models are undoubtedly applicable in the prediction of flow forces for small null clearances (less than 0.05). Having a good agreement between each other, both experimental and numerical results show that the energy loss increases with the increment of null clearance and nozzle inlet pressure.
Karl Haslinger - One of the best experts on this subject based on the ideXlab platform.
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Flow-induced vibration testing of replacement thermowell designs
Journal of Fluids and Structures, 2003Co-Authors: Karl HaslingerAbstract:Abstract Inconel 600 Primary Water Stress Corrosion Cracking (PWSCC) in Nuclear Pressurized Water Reactors (PWRs) has necessitated the repair/replacement of various small bore nozzles. These repairs/replacements must be designed to avoid unwanted vibrations. So, to this end, new RTD-Thermowell-Nozzle replacement designs were developed and subjected to flow testing over a velocity range from 9.14 to 33.53 m/s (30–110 ft/s), and temperatures ranging from 121°C to 316°C (250–600°F). The replacement nozzles are welded on the pipe OD, rather than on the pipe ID. A split, tapered ferrule is used to support the nozzle tip inside the pipe bore. This maintains high thermowell tip-resonance frequencies with the objective of avoiding self-excitation from vortex shedding that is believed to have caused failures in an earlier design during initial, precritical plant startup testing. The flow testing was complicated by the small size of the thermowell tips (5.08 mm or 0.2 in ID), which necessitated use of a complement of low temperature and high temperature instrumentation. Since the high temperature device had an internal resonance (750 Hz) within the frequency range of interest (0–2500 Hz), adequate sensor correlations had to be derived from low temperature tests. The current nozzle/thermowell design was tested concurrently with two slight variations of the replacement design. The acceleration signals were acquired during incremental and continuous flow sweeps, nominally at 5 kHz sampling rates and for time domain processing as high as 25 kHz. Whereas vortex-shedding frequencies were predicted to prevail between 400 and 1500 Hz, no such response was observed at these frequencies. Rather, the thermowell tips responded due to turbulent buffeting with a peak response that was related directly to flow velocity. Lift Direction response was always larger than Drag Direction response. The thermowell tips also responded at their natural tip frequencies in a narrow band random fashion. At the higher flow rates, one replacement design experienced an instability mode leading to high tip stresses. Although this instability did not repeat, this particular design was eliminated from consideration. The second replacement design performed almost identically to the current in-plant design. The experimental data were used to extract forcing functions and thermowell responses that were used as input into the design calculations.
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Flow Induced Vibration Testing of Replacement Thermowell Designs
5th International Symposium on Fluid Structure Interaction Aeroelasticity and Flow Induced Vibration and Noise, 2002Co-Authors: Karl HaslingerAbstract:Replacement RTDs/Thermowells/Nozzles were subjected to flow testing over a velocity range from 9.14 to 33.53 m/sec (30 to 110 ft/sec), and temperatures ranging from 121 to 316 °C (250 to 600 °F). The replacement nozzles are welded on the pipe OD, rather than on the pipe ID. A split, tapered ferrule is used to support the nozzle tip inside the pipe bore. This maintains high thermowell tip resonance frequencies with the objective of avoiding von Karman Vortex Shedding excitation that is believed to have caused failures in an earlier design during initial, pre-critical plant startup testing. The flow testing was complicated by the small size of the thermowell tips (5.08 mm or 0.2-in ID), which necessitated use of a complement of low temperature and high temperature instrumentation. Since the high temperature device had an internal resonance (750 Hz) within the frequency range of interest (0–2,500 Hz), adequate sensor correlations had to be derived from low temperature tests. The current nozzle/thermowell design was tested concurrently with two slight variations of the replacement design. The acceleration signals were acquired during incremental and continuous flow sweeps, nominally at 5 kHz sampling rates and for time domain processing as high as 25 kHz. Whereas vortex-shedding frequencies were predicted to prevail between 400 and 1,500 Hz, no such response was observed at these frequencies. Rather, the thermowell tips responded due to turbulent buffeting with a peak response that was related directly to flow velocity. Lift Direction response was always larger than Drag Direction response. The thermowell tips also responded at their natural tip frequencies in a narrow band random fashion. At the higher flow rates, one replacement design experienced an instability mode leading to high tip stresses. Although this instability did not repeat, this particular design was eliminated from consideration. The second replacement design performed almost identically to the current in-plant design. The experimental data were used to extract forcing functions and thermowell responses that were used as input into the design calculations.Copyright © 2002 by Westinghouse Electric Company LLC
Qingjun Yang - One of the best experts on this subject based on the ideXlab platform.
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CFD analysis of flow forces and energy loss characteristics in a flapper–nozzle pilot valve with different null clearances
Energy Conversion and Management, 2014Co-Authors: Nay Zar Aung, Qingjun Yang, Meng ChenAbstract:Abstract A well understanding on the flow forces and energy loss characteristics in a flapper–nozzle pilot valve is necessarily important in the performance improvement of a two-stage electrohydraulic servo-valve. This paper presents the CFD analysis of flow forces and energy loss characteristics in a flapper–nozzle pilot valve with different null clearances. Five different flapper–nozzle structures with three different null clearances of 0.1 mm, 0.05 mm and 0.033 mm are considered in this analysis. For every flapper–nozzle structure, the systematic CFD simulations of flow forces and energy loss characteristics are performed for seven different flow conditions varying nozzle inlet pressures from 1 MPa to 7 MPa. Experimental measurements are also conducted for energy loss characteristics and then compared with simulated results. Meanwhile, the CFD flow force results are verified with the results of exiting simplified flow force models and vice versa. From each nozzle side, the main flow force acting on the flapper is accompanied by four tiny lateral forces resulted from the impact of radial jet reattachment on the flapper curved surface. For each of given null clearances, the main flow force and lateral forces linearly increase with the increment of nozzle inlet pressure. For the same null clearance, applying larger flapper can give 1.5–13.6% larger lateral force in Drag Direction and 1.5–10.2% larger lateral force in lift Direction compared to deploying smaller flapper. Compared to the main flow force, the magnitudes of the lateral forces on each corner of the flapper are found in the range of 0.8–3.2% in Drag Direction and 1.6–7.5% in lift Direction. For main flow forces, the CFD simulated results show a good agreement with that of flow force model based on momentum conservation. Both existing flow force models are undoubtedly applicable in the prediction of flow forces for small null clearances (less than 0.05). Having a good agreement between each other, both experimental and numerical results show that the energy loss increases with the increment of null clearance and nozzle inlet pressure.
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cfd analysis of flow forces and energy loss characteristics in a flapper nozzle pilot valve with different null clearances
Energy Conversion and Management, 2014Co-Authors: Qingjun Yang, Nay Zar Aung, Meng ChenAbstract:Abstract A well understanding on the flow forces and energy loss characteristics in a flapper–nozzle pilot valve is necessarily important in the performance improvement of a two-stage electrohydraulic servo-valve. This paper presents the CFD analysis of flow forces and energy loss characteristics in a flapper–nozzle pilot valve with different null clearances. Five different flapper–nozzle structures with three different null clearances of 0.1 mm, 0.05 mm and 0.033 mm are considered in this analysis. For every flapper–nozzle structure, the systematic CFD simulations of flow forces and energy loss characteristics are performed for seven different flow conditions varying nozzle inlet pressures from 1 MPa to 7 MPa. Experimental measurements are also conducted for energy loss characteristics and then compared with simulated results. Meanwhile, the CFD flow force results are verified with the results of exiting simplified flow force models and vice versa. From each nozzle side, the main flow force acting on the flapper is accompanied by four tiny lateral forces resulted from the impact of radial jet reattachment on the flapper curved surface. For each of given null clearances, the main flow force and lateral forces linearly increase with the increment of nozzle inlet pressure. For the same null clearance, applying larger flapper can give 1.5–13.6% larger lateral force in Drag Direction and 1.5–10.2% larger lateral force in lift Direction compared to deploying smaller flapper. Compared to the main flow force, the magnitudes of the lateral forces on each corner of the flapper are found in the range of 0.8–3.2% in Drag Direction and 1.6–7.5% in lift Direction. For main flow forces, the CFD simulated results show a good agreement with that of flow force model based on momentum conservation. Both existing flow force models are undoubtedly applicable in the prediction of flow forces for small null clearances (less than 0.05). Having a good agreement between each other, both experimental and numerical results show that the energy loss increases with the increment of null clearance and nozzle inlet pressure.
Njuki W. Mureithi - One of the best experts on this subject based on the ideXlab platform.
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Streamwise Fluidelastic Forces in Tube Arrays Subjected to Two-Phase Flows
Volume 4: Fluid-Structure Interaction, 2014Co-Authors: Stephen Olala, Njuki W. Mureithi, Teguewinde Sawadogo, M. J. PettigrewAbstract:Detailed unsteady fluid force and phase measurements for a single tube oscillating purely in the streamwise Direction in a rotated triangular tube array subjected to air-water two-phase cross-flow have been conducted in this study for homogeneous void fractions between 0% and 90%. Additionally the streamwise steady forces were measured in two-phase flow at a Reynolds number (based on the pitch velocity), Re = 7.2 × 104. The results are compared to those previously obtained for transverse Direction oscillations. The measurement results show that the magnitude of the force coefficients for both Directions (Drag and lift) is comparable both in trend and quantitatively. However, the phase in the Drag Direction is negative while that for the lift is positive. The range of variation of the phase is also significantly smaller for the Drag Direction. Noting that negative phase corresponds to positive damping and vice versa, this observation confirms previous findings of lack of instability in the Drag Direction for a single flexible tube in a rotated triangular tube array. The Drag steady fluid force coefficients were found to increase with dimensionless displacement in the flow Direction for the entire range of void fractions considered. The derivative of the measured steady fluid force coefficient, which is an important factor in fluidelastic instability study using the quasi-steady model, was found to remain positive in the Drag Direction. The effect of void fraction on the unsteady fluid force coefficient and other dynamic parameters such as hydrodynamic mass and damping are also discussed.Copyright © 2014 by ASME
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Fluidelastic Instability in a Normal Triangular Tube Bundle Subjected to Air-Water Cross-Flow
Journal of Pressure Vessel Technology, 2011Co-Authors: Guillaume Ricciardi, M. J. Pettigrew, Njuki W. MureithiAbstract:This paper presents the results of tests on the vibration of a normal triangular tube bundle subjected to air–water cross-flow. The pitch-to-diameter ratio of the bundle is 1.5, and the tube diameter is 38 mm. The tubes were preferentially flexible in one Direction. Both the lift and the Drag Direction were tested. A wide range of void fractions and fluid velocities was tested. Fluidelastic instabilities and tube resonances were observed. The resonances induced significant vibration amplitudes at high void fractions in the lift Direction. The results are compared with those obtained with a rotated triangular tube bundle. They show that the normal triangular configuration is more stable than the rotated triangular configuration.
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Further Study of Quasiperiodic Vibration Excitation Forces in Rotated Triangular Tube Bundles Subjected to Two-Phase Cross Flow
Journal of Pressure Vessel Technology, 2009Co-Authors: C. Zhang, M. J. Pettigrew, Njuki W. MureithiAbstract:Two-phase cross flow exists in many shell-and-tube heat exchangers. Flow-induced vibration excitation forces can cause tube motion that will result in long-term fretting-wear or fatigue. Detailed vibration excitation force measurements in tube bundles subjected to two-phase cross flow are required to understand the underlying vibration excitation mechanisms. Some of this work has already been done. Somewhat unexpected but significant quasiperiodic forces in both the Drag and lift Directions were measured. These forces are generally larger in the Drag Direction. However, the excitation force frequency is relatively low (i.e., 3―6 Hz) and not directly dependent on flow velocity in the Drag Direction. On the other hand, much higher frequencies (up to 16 Hz) were observed in the lift Direction at the higher flow velocities. The frequency appears directly related to flow velocity in the lift Direction. The present work aims at (1) providing further evidence of the quasiperiodic lift force mechanism, (2) determining the effect of cylinder position on such quasiperiodic Drag and lift forces, and (3) verifying the existence of quasiperiodic Drag and lift forces in a more realistic larger tube array. The program was carried out with two rotated triangular tube arrays of different width subjected to air/water flow to simulate two-phase mixtures from liquid to 95% void,fraction. Both the dynamic lift and Drag forces were measured with strain gauge instrumented cylinders.