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Nay Zar Aung - One of the best experts on this subject based on the ideXlab platform.

  • Reduction of undesired lateral forces acting on the flapper of a flapper–nozzle Pilot Valve by using an innovative flapper shape
    Energy Conversion and Management, 2015
    Co-Authors: Shengzhuo Zhang, Nay Zar Aung
    Abstract:

    Abstract The stability and dynamic performance of a flapper–nozzle Pilot Valve significantly depend on the flow forces acting on the flapper. Due to the shape of the flapper and flow structure in the flapper–nozzle Pilot Valve there are undesired lateral forces acting on the flapper, which are very potential to interfere with the stability of the flapper. Aiming to reduce these undesired lateral forces, an innovative flapper shape is proposed and a comparative study of flow forces acting on the two different flapper shapes is conducted. A simple rectangle shape is selected as the innovative flapper shape. The flow forces acting on the traditional flapper shape and innovative flapper shape are evaluated by means of CFD (Computational Fluid Dynamics) simulations and verified with the results from the semi-experimental approach. The evaluation of the flow forces is performed for each flapper shape with two different flapper–nozzle clearances of 0.10 mm and 0.05 mm under seven different flow conditions with the variation of inlet pressures from 1 MPa to 7 MPa. A good agreement between CFD results and semi-experimental results shows that the proposed innovative flapper shape has no effect on flow control characteristics since it is giving approximately the same flow rate and main flow force as the traditional flapper shape at every flow condition. Meanwhile the innovative flapper shape effectively reduces the undesired lateral forces acting on the flapper by altering the flow structure and reducing the strength of the jet flow and cavitation occurred in the flow field of flapper–nozzle Pilot Valve. At the lower part of the flapper with clearance 0.05 mm, the ratio between the X-direction lateral force and main flow force of traditional flapper is around 1.24–11.14%, while it is reduced to 0.18–0.42% by the innovative flapper. Also, the ratio is reduced from 7.93–18.44% to 0.69–0.93% with clearance 0.10 mm. For the Z-direction forces at the lower part, the ratio decreases from 0.20–11.77% and 7.84–17.94% (traditional flapper) to 0.92–2.65% and 1.63–4.08% (innovative flapper) with clearances 0.05 mm and 0.10 mm respectively.

  • Structural optimization and characteristics analysis of innovative flapper shape in a flapper-nozzle Pilot Valve
    2015 International Conference on Fluid Power and Mechatronics (FPM), 2015
    Co-Authors: Jinghui Peng, Nay Zar Aung
    Abstract:

    Cavitation in the flow field and the resonance of armature-flapper assembly are two main possible mechanisms for the self-excited noise in flapper-nozzle Pilot Valves, which can greatly deteriorate the performance of the Valves. In our previous attempt, it has been shown that compared to traditional flapper shape, rectangle-shaped flapper is more effective to reduce cavitation in the flapper-nozzle Pilot Valve. However, it is necessarily important to obtain the same structural properties as traditional flapper shape. To achieve this aim, structural optimization of the innovative flapper shape is performed. Then, the static and dynamic characteristics of the armature-flapper assembly using different flapper shapes are studied numerically using a validated numerical model. The simulated static and dynamic characteristics of the optimized innovative flapper shape agree well with that of the traditional one. Thus, an effective flapper shape which can reduce cavitation as well as maintain the original mechanical performances is proposed.

  • Confirmation on the effectiveness of rectangle-shaped flapper in reducing cavitation in flapper–nozzle Pilot Valve
    Energy Conversion and Management, 2015
    Co-Authors: Qingjun Yang, Nay Zar Aung
    Abstract:

    Abstract The existence of undesired flow-induced phenomenon, cavitation, in the flapper–nozzle Pilot Valve of two-stage servo-Valves is a critical issue in practical applications. Here, taking innovation on the flapper shape is one of possible approaches to reduce cavitation in the Pilot Valve. By means of CFD (Computational Fluid Dynamics) simulations, it has been proved by setting a simple rectangle shape as an innovative flapper shape in our previous attempt. Therefore, in this work, the effectiveness of rectangle-shaped flapper in reducing cavitation is experimentally confirmed by comparing with traditional shape and square shape. The experimental observations of cavitation phenomena in three different flapper shapes are conducted for two different flapper–nozzle null clearances (0.2 mm and 0.1 mm) under four different flow conditions with the variation of inlet pressure in the range of 3–6 MPa. To provide verification on experimental results and a comprehensive understanding, CFD simulations of cavitation phenomenon in each flapper shape are also performed. The results are qualitatively analyzed and compared. The results explain that the cavitation intensity in the flapper–nozzle Pilot Valve associates with the strength of the turbulent jets and it increases with the increment of flapper–nozzle null clearance and inlet pressure. According to the experimental observations and CFD simulated results, the curved surface of traditional flapper shape is attributed to the spread of turbulent jets and consequent massive cavitation. Compared to traditional shape, the square shape relatively reduces cavitation due to lack of curved boundary on the flapper. However, on the other hand, its shorter flat land and larger annulus are not much effective to control the spread of turbulent jet which is responsible for cavitation in annulus region. Compared to two other flapper shapes, the rectangle shape significantly suppresses the cavitation by attenuating the turbulent jets on its straight and relatively longer flat lands. Therefore, the effectiveness of rectangle shape in reducing cavitation in the flapper–nozzle Pilot Valve is confirmed in this work.

  • confirmation on the effectiveness of rectangle shaped flapper in reducing cavitation in flapper nozzle Pilot Valve
    Energy Conversion and Management, 2015
    Co-Authors: Qingjun Yang, Nay Zar Aung
    Abstract:

    Abstract The existence of undesired flow-induced phenomenon, cavitation, in the flapper–nozzle Pilot Valve of two-stage servo-Valves is a critical issue in practical applications. Here, taking innovation on the flapper shape is one of possible approaches to reduce cavitation in the Pilot Valve. By means of CFD (Computational Fluid Dynamics) simulations, it has been proved by setting a simple rectangle shape as an innovative flapper shape in our previous attempt. Therefore, in this work, the effectiveness of rectangle-shaped flapper in reducing cavitation is experimentally confirmed by comparing with traditional shape and square shape. The experimental observations of cavitation phenomena in three different flapper shapes are conducted for two different flapper–nozzle null clearances (0.2 mm and 0.1 mm) under four different flow conditions with the variation of inlet pressure in the range of 3–6 MPa. To provide verification on experimental results and a comprehensive understanding, CFD simulations of cavitation phenomenon in each flapper shape are also performed. The results are qualitatively analyzed and compared. The results explain that the cavitation intensity in the flapper–nozzle Pilot Valve associates with the strength of the turbulent jets and it increases with the increment of flapper–nozzle null clearance and inlet pressure. According to the experimental observations and CFD simulated results, the curved surface of traditional flapper shape is attributed to the spread of turbulent jets and consequent massive cavitation. Compared to traditional shape, the square shape relatively reduces cavitation due to lack of curved boundary on the flapper. However, on the other hand, its shorter flat land and larger annulus are not much effective to control the spread of turbulent jet which is responsible for cavitation in annulus region. Compared to two other flapper shapes, the rectangle shape significantly suppresses the cavitation by attenuating the turbulent jets on its straight and relatively longer flat lands. Therefore, the effectiveness of rectangle shape in reducing cavitation in the flapper–nozzle Pilot Valve is confirmed in this work.

  • CFD analysis of flow forces and energy loss characteristics in a flapper–nozzle Pilot Valve with different null clearances
    Energy Conversion and Management, 2014
    Co-Authors: Nay Zar Aung, Qingjun Yang, Meng Chen
    Abstract:

    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.

Songjing Li - One of the best experts on this subject based on the ideXlab platform.

  • A numerical study of flow field in a flapper-nozzle Pilot Valve with a moving flapper
    2016 IEEE International Conference on Aircraft Utility Systems (AUS), 2016
    Co-Authors: Xinbei Lv, Songjing Li, Shengzhuo Zhang
    Abstract:

    As we known that the flapper-nozzle Pilot stage is a very vital part in converting the electric signals into hydraulic outputs between the torque motor and main spool in the electro-hydraulic servo-Valve. The performance of the flapper-nozzle has a seriously impact on the capability of the entire system. This paper has presented the flow field characteristics in the Pilot Valve when the flapper is moving, which will reflect the real working conditions. The initial speed is imposed on the flapper which will insure it moving in a way of 2 DOF (Degree of Freedom). Meanwhile, for the reason of saving computational time-consuming, the flapper is substituted by a part of the standard servo-Valve. During the simulation, the strategy of overset mesh is utilized to update the moving mesh. Then the simulation results are firstly compared with the experiment result. The results show that the numerical method used in this paper is able to predict the flow field of the flapper-nozzle Pilot Valve when the flapper is moving. Finally, the translation of the flapper, transient velocity field and the distribution of vorticity are presented. The results also show that the movement of the flapper can make the flow field be a disciplinary and dissymmetry one, the vorticity of the flow field is also more complex but periodicity.

  • cavity shedding dynamics in a flapper nozzle Pilot stage of an electro hydraulic servo Valve experiments and numerical study
    Energy Conversion and Management, 2015
    Co-Authors: Shengzhuo Zhang, Songjing Li
    Abstract:

    The performance of an electro-hydraulic servo-Valve is significantly influenced by the characteristics of the flow field in the flapper–nozzle Pilot stage. Cavitation and pressure oscillations frequently occur in the flow field of flapper–nozzle Pilot stage and these undesired flow-induced phenomena commonly lead to the appearance of high frequency noises and vibrations of the servo-Valve. To obtain in-death understanding about these flow-induced phenomenon, numerical and experimental study of the unsteady cavitation phenomenon in a flapper–nozzle Pilot Valve is carried out. Large Eddy Simulation (LES) coupling with Schnerr and Sauer mass transfer cavitation model is utilized to simulate the unsteady cavitation shedding around the sharp edge of the flapper. The simulations are conducted using the commercial CFD code ANSYS/FLUENT 14. Meanwhile, the flow field is experimentally observed by using a high speed video camera. The recorded images of the transient cavitation patterns are verified with CFD simulation results. Then, the characteristics of pressure oscillations at the beginning and the end of the shedding path in the flow field are evaluated by CFD approach. The results show that the increment of inlet pressure intensifies cavitation in the flapper–nozzle Pilot stage and induces the shedding phenomenon. And both the frequency and magnitude of pressure oscillations in the flapper–nozzle Valve are enhanced by increasing the inlet pressure.

  • A numerical study of flow field in a flapper-nozzle Pilot Valve under working condition
    2015 International Conference on Fluid Power and Mechatronics (FPM), 2015
    Co-Authors: Shengzhuo Zhang, Hongguang Xu, Songjing Li
    Abstract:

    It is well known that the flapper-nozzle Pilot stage plays a vital role in converting the electric signals into hydraulic outputs between the torque motor and main spool in the electro-hydraulic servo-Valve. The characteristics of the flow field greatly influence the working performance of the flapper-nozzle Pilot Valve. This paper has presented the flow field characteristics in the Pilot Valve with the flapper under working conditions, which means that the flapper is moving. The velocity of the flapper is imposed based on the dynamic response of the torque motor and spool Valve approximately. Meanwhile, the displacement of the flapper is determined using the general design criterion of the servo-Valve. During the simulation, the dynamic mesh strategy is utilized to update the moving mesh. Then the simulation results are firstly validated in terms of the mass flow rates of the two nozzles comparing with the theoretical evaluations. The results show that the numerical method is able to predict the flow field of the flapper-nozzle Pilot Valve under working condition. Finally, the transient velocity field, pressure field and vorticity field are presented. The results prove that the movement of the flapper can result in asymmetric flow field distribution and increase the static pressure and vorticity in the smaller clearance between the flapper and nozzle.

Jin-yuan Qian - One of the best experts on this subject based on the ideXlab platform.

  • Deadzone compensation control based on detection of micro flow rate in Pilot stage of proportional directional Valve.
    Isa Transactions, 2019
    Co-Authors: Junhui Zhang, Jin-yuan Qian, Di Wang, Geng Yang, Min Pan
    Abstract:

    Abstract The Pilot operated proportional directional Valves (POPDVs) with a flow rate ranging from 100 to 1000 L/min are widely used in electro-hydraulic systems (EHSs). The deadzone of the Pilot stage Valve and its control compensation could significantly affect the position control performance for the main stage Valve that could directly affect dynamics of EHSs In this paper, it is concluded that micro flow rates exist at the intermediate position of the Valve based on the analysis of the continuity equation of the flow in the control chamber of the Pilot stage. The micro flow rate is helpful to eliminate the discontinuity and unsmooth domain in the previous inverse deadzone compensation function. An improved deadzone detection method is proposed to calibrate the Pilot Valve flow characteristics which include the micro flow rate. This new method avoids the threshold selection of the main Valve spool displacement which affects the detected deadzone values. Its detection processes are realized based on the Pilot flow rate characterized by the speed of the main Valve spool and the Pilot Valve displacement characterized by the solenoid current. The deadzone compensation control strategy based on the improved deadzone detection method is also designed. The experimental results using the steady-state position tracking and sinusoidal position tracking methods are verified. It is concluded that the tracking accuracy of the main Valve spool position is effectively improved with this control strategy.

  • Parametric study on fluid dynamics of Pilot-control angle globe Valve
    Journal of Fluids Engineering-transactions of The Asme, 2018
    Co-Authors: Jin-yuan Qian
    Abstract:

    Globe Valve is widely used in numerous industries, and its driving energy consumption accounts for high percentages of the whole piping system. In order to figure out novel globe Valves with low energy consumption, the Pilot control globe Valve (PCGV) is proposed, which is made up of a main Valve and a Pilot Valve. By the pressure difference of fluid itself, the opened/closed status of the main Valve can be controlled by the Pilot Valve, which can save driving energy and shorten the response time. In order to fit PCGV in an angle displaced piping system, the Pilot control angle globe Valve (PCAGV) is developed. In this paper, with validated numerical methods, both steady and transient simulations focusing on the Valve core diameter, the single/multi orifices, orifice diameters and their arrangements located on the Valve core bottom are presented. The results show that the pressure difference increases with the increase of the Valve core diameter and the decrease of the orifice diameter, and large orifice diameters (d > 12 mm) should be avoided in case the Valve cannot be opened. As for the multi orifices, it can be treated as a single orifice which having similar cross-sectional area. Meanwhile, the opening time of the main Valve also increases with the increase of the Valve core diameter correspondingly. Besides, a fitting formula of pressure difference calculation depending on the inlet velocity and the Valve core diameter is obtained, which is a power–law relationship.

  • pressure drop analysis of Pilot control globe Valve with different structural parameters
    Journal of Fluids Engineering-transactions of The Asme, 2017
    Co-Authors: Ming Zhang, Jin-yuan Qian
    Abstract:

    Pilot-control globe Valve (PCGV) can use the pressure drop caused by fluid flowing through the orifice located at Valve core bottom to open or close the main Valve using a small Pilot Valve. In this paper, computational fluid dynamics (CFD) method is adopted to analyze the pressure drop before and after Valve core of PCGV and minor loss of orifice under different structural parameters and inlet velocities, and the simulation results show a good agreement with the experimental results. It turns out that the Valve diameters, orifice diameters, and Pilot pipe diameters have great influences on the pressure drop and the loss coefficient. Moreover, an expression is proposed which can be used to calculate minor loss coefficient, then to estimate the pressure drop and driving force of a PCGV within limited conditions. This paper can be referenced as guidance for deciding the dimension of structural parameters and spring stiffness during design process of a PCGV. (Less)

  • effects of orifice on pressure difference in Pilot control globe Valve by experimental and numerical methods
    International Journal of Hydrogen Energy, 2016
    Co-Authors: Jin-yuan Qian, An Le Lu, Jian Kai Wang
    Abstract:

    Abstract Pilot-Control Globe Valve (PCGV) can utilize pressure difference caused by fluid flow through the orifice on Valve core as its power, for open and close the main Valve with a small Pilot Valve. It has obvious advantages of energy conservation and quick response. Orifice structure on the Valve core is the main component to determine the pressure difference, which is used to push the Valve core. In this paper, the numerical model with User Defined Functions (UDFs) method is carried out, and the experimental device is arranged. The numerical and experimental results of Valve core displacements achieve agreements. Then, analysis of pressure difference under different static pressures, inlet velocities and different orifice diameters are carried out. It shows that pressure difference has no relationship with static pressure, thus PCGV can be adopted in hydrogen pipelines. Meanwhile, higher inlet velocity can turn out larger pressure difference with quicker response of PCGV. In addition, there exits an unbalanced moment, and 15 mm is the extreme diameter of the orifice for DN150 PCGV. Finally, the design method of the orifice structure in PCGV is proposed with design formulas. This work can help the precise design work of PCGV, and it can be referred by other researchers who are also deal with orifice structures in similar Valves design work.

  • dynamic response analysis of Pilot control globe Valve focusing on opening and closing time of Pilot Valve
    Journal of Physics: Conference Series; 745(3) no 032046 (2016), 2016
    Co-Authors: Jian Kai Wang, Jin-yuan Qian, Fu-qiang Chen
    Abstract:

    Pilot control globe Valve (PCGV) can use the pressure difference produced by fluid itself to realize the opening and closing states with a Pilot Valve. In this paper, numerical method is used to investigate the fluid flow characteristics and the Valve core movement inside PCGV under different opening and closing times of Pilot Valve. The result shows that, shorter opening and closing time of Valve core results in the shorter vibration of Valve core as well as the stronger unstable fluid in main Valve and faster opening and closing process of PCGV. Longer opening and closing time of Valve core can do less damage to Valve body. This work can give some guides for the optimal design work of PCGV and someone who are researching on Valves with similar structures.

Qingjun Yang - One of the best experts on this subject based on the ideXlab platform.

  • Confirmation on the effectiveness of rectangle-shaped flapper in reducing cavitation in flapper–nozzle Pilot Valve
    Energy Conversion and Management, 2015
    Co-Authors: Qingjun Yang, Nay Zar Aung
    Abstract:

    Abstract The existence of undesired flow-induced phenomenon, cavitation, in the flapper–nozzle Pilot Valve of two-stage servo-Valves is a critical issue in practical applications. Here, taking innovation on the flapper shape is one of possible approaches to reduce cavitation in the Pilot Valve. By means of CFD (Computational Fluid Dynamics) simulations, it has been proved by setting a simple rectangle shape as an innovative flapper shape in our previous attempt. Therefore, in this work, the effectiveness of rectangle-shaped flapper in reducing cavitation is experimentally confirmed by comparing with traditional shape and square shape. The experimental observations of cavitation phenomena in three different flapper shapes are conducted for two different flapper–nozzle null clearances (0.2 mm and 0.1 mm) under four different flow conditions with the variation of inlet pressure in the range of 3–6 MPa. To provide verification on experimental results and a comprehensive understanding, CFD simulations of cavitation phenomenon in each flapper shape are also performed. The results are qualitatively analyzed and compared. The results explain that the cavitation intensity in the flapper–nozzle Pilot Valve associates with the strength of the turbulent jets and it increases with the increment of flapper–nozzle null clearance and inlet pressure. According to the experimental observations and CFD simulated results, the curved surface of traditional flapper shape is attributed to the spread of turbulent jets and consequent massive cavitation. Compared to traditional shape, the square shape relatively reduces cavitation due to lack of curved boundary on the flapper. However, on the other hand, its shorter flat land and larger annulus are not much effective to control the spread of turbulent jet which is responsible for cavitation in annulus region. Compared to two other flapper shapes, the rectangle shape significantly suppresses the cavitation by attenuating the turbulent jets on its straight and relatively longer flat lands. Therefore, the effectiveness of rectangle shape in reducing cavitation in the flapper–nozzle Pilot Valve is confirmed in this work.

  • confirmation on the effectiveness of rectangle shaped flapper in reducing cavitation in flapper nozzle Pilot Valve
    Energy Conversion and Management, 2015
    Co-Authors: Qingjun Yang, Nay Zar Aung
    Abstract:

    Abstract The existence of undesired flow-induced phenomenon, cavitation, in the flapper–nozzle Pilot Valve of two-stage servo-Valves is a critical issue in practical applications. Here, taking innovation on the flapper shape is one of possible approaches to reduce cavitation in the Pilot Valve. By means of CFD (Computational Fluid Dynamics) simulations, it has been proved by setting a simple rectangle shape as an innovative flapper shape in our previous attempt. Therefore, in this work, the effectiveness of rectangle-shaped flapper in reducing cavitation is experimentally confirmed by comparing with traditional shape and square shape. The experimental observations of cavitation phenomena in three different flapper shapes are conducted for two different flapper–nozzle null clearances (0.2 mm and 0.1 mm) under four different flow conditions with the variation of inlet pressure in the range of 3–6 MPa. To provide verification on experimental results and a comprehensive understanding, CFD simulations of cavitation phenomenon in each flapper shape are also performed. The results are qualitatively analyzed and compared. The results explain that the cavitation intensity in the flapper–nozzle Pilot Valve associates with the strength of the turbulent jets and it increases with the increment of flapper–nozzle null clearance and inlet pressure. According to the experimental observations and CFD simulated results, the curved surface of traditional flapper shape is attributed to the spread of turbulent jets and consequent massive cavitation. Compared to traditional shape, the square shape relatively reduces cavitation due to lack of curved boundary on the flapper. However, on the other hand, its shorter flat land and larger annulus are not much effective to control the spread of turbulent jet which is responsible for cavitation in annulus region. Compared to two other flapper shapes, the rectangle shape significantly suppresses the cavitation by attenuating the turbulent jets on its straight and relatively longer flat lands. Therefore, the effectiveness of rectangle shape in reducing cavitation in the flapper–nozzle Pilot Valve is confirmed in this work.

  • CFD analysis of flow forces and energy loss characteristics in a flapper–nozzle Pilot Valve with different null clearances
    Energy Conversion and Management, 2014
    Co-Authors: Nay Zar Aung, Qingjun Yang, Meng Chen
    Abstract:

    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.

  • cfd analysis of flow forces and energy loss characteristics in a flapper nozzle Pilot Valve with different null clearances
    Energy Conversion and Management, 2014
    Co-Authors: Qingjun Yang, Nay Zar Aung, Meng Chen
    Abstract:

    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.

Shengzhuo Zhang - One of the best experts on this subject based on the ideXlab platform.

  • A numerical study of flow field in a flapper-nozzle Pilot Valve with a moving flapper
    2016 IEEE International Conference on Aircraft Utility Systems (AUS), 2016
    Co-Authors: Xinbei Lv, Songjing Li, Shengzhuo Zhang
    Abstract:

    As we known that the flapper-nozzle Pilot stage is a very vital part in converting the electric signals into hydraulic outputs between the torque motor and main spool in the electro-hydraulic servo-Valve. The performance of the flapper-nozzle has a seriously impact on the capability of the entire system. This paper has presented the flow field characteristics in the Pilot Valve when the flapper is moving, which will reflect the real working conditions. The initial speed is imposed on the flapper which will insure it moving in a way of 2 DOF (Degree of Freedom). Meanwhile, for the reason of saving computational time-consuming, the flapper is substituted by a part of the standard servo-Valve. During the simulation, the strategy of overset mesh is utilized to update the moving mesh. Then the simulation results are firstly compared with the experiment result. The results show that the numerical method used in this paper is able to predict the flow field of the flapper-nozzle Pilot Valve when the flapper is moving. Finally, the translation of the flapper, transient velocity field and the distribution of vorticity are presented. The results also show that the movement of the flapper can make the flow field be a disciplinary and dissymmetry one, the vorticity of the flow field is also more complex but periodicity.

  • Reduction of undesired lateral forces acting on the flapper of a flapper–nozzle Pilot Valve by using an innovative flapper shape
    Energy Conversion and Management, 2015
    Co-Authors: Shengzhuo Zhang, Nay Zar Aung
    Abstract:

    Abstract The stability and dynamic performance of a flapper–nozzle Pilot Valve significantly depend on the flow forces acting on the flapper. Due to the shape of the flapper and flow structure in the flapper–nozzle Pilot Valve there are undesired lateral forces acting on the flapper, which are very potential to interfere with the stability of the flapper. Aiming to reduce these undesired lateral forces, an innovative flapper shape is proposed and a comparative study of flow forces acting on the two different flapper shapes is conducted. A simple rectangle shape is selected as the innovative flapper shape. The flow forces acting on the traditional flapper shape and innovative flapper shape are evaluated by means of CFD (Computational Fluid Dynamics) simulations and verified with the results from the semi-experimental approach. The evaluation of the flow forces is performed for each flapper shape with two different flapper–nozzle clearances of 0.10 mm and 0.05 mm under seven different flow conditions with the variation of inlet pressures from 1 MPa to 7 MPa. A good agreement between CFD results and semi-experimental results shows that the proposed innovative flapper shape has no effect on flow control characteristics since it is giving approximately the same flow rate and main flow force as the traditional flapper shape at every flow condition. Meanwhile the innovative flapper shape effectively reduces the undesired lateral forces acting on the flapper by altering the flow structure and reducing the strength of the jet flow and cavitation occurred in the flow field of flapper–nozzle Pilot Valve. At the lower part of the flapper with clearance 0.05 mm, the ratio between the X-direction lateral force and main flow force of traditional flapper is around 1.24–11.14%, while it is reduced to 0.18–0.42% by the innovative flapper. Also, the ratio is reduced from 7.93–18.44% to 0.69–0.93% with clearance 0.10 mm. For the Z-direction forces at the lower part, the ratio decreases from 0.20–11.77% and 7.84–17.94% (traditional flapper) to 0.92–2.65% and 1.63–4.08% (innovative flapper) with clearances 0.05 mm and 0.10 mm respectively.

  • cavity shedding dynamics in a flapper nozzle Pilot stage of an electro hydraulic servo Valve experiments and numerical study
    Energy Conversion and Management, 2015
    Co-Authors: Shengzhuo Zhang, Songjing Li
    Abstract:

    The performance of an electro-hydraulic servo-Valve is significantly influenced by the characteristics of the flow field in the flapper–nozzle Pilot stage. Cavitation and pressure oscillations frequently occur in the flow field of flapper–nozzle Pilot stage and these undesired flow-induced phenomena commonly lead to the appearance of high frequency noises and vibrations of the servo-Valve. To obtain in-death understanding about these flow-induced phenomenon, numerical and experimental study of the unsteady cavitation phenomenon in a flapper–nozzle Pilot Valve is carried out. Large Eddy Simulation (LES) coupling with Schnerr and Sauer mass transfer cavitation model is utilized to simulate the unsteady cavitation shedding around the sharp edge of the flapper. The simulations are conducted using the commercial CFD code ANSYS/FLUENT 14. Meanwhile, the flow field is experimentally observed by using a high speed video camera. The recorded images of the transient cavitation patterns are verified with CFD simulation results. Then, the characteristics of pressure oscillations at the beginning and the end of the shedding path in the flow field are evaluated by CFD approach. The results show that the increment of inlet pressure intensifies cavitation in the flapper–nozzle Pilot stage and induces the shedding phenomenon. And both the frequency and magnitude of pressure oscillations in the flapper–nozzle Valve are enhanced by increasing the inlet pressure.

  • A numerical study of flow field in a flapper-nozzle Pilot Valve under working condition
    2015 International Conference on Fluid Power and Mechatronics (FPM), 2015
    Co-Authors: Shengzhuo Zhang, Hongguang Xu, Songjing Li
    Abstract:

    It is well known that the flapper-nozzle Pilot stage plays a vital role in converting the electric signals into hydraulic outputs between the torque motor and main spool in the electro-hydraulic servo-Valve. The characteristics of the flow field greatly influence the working performance of the flapper-nozzle Pilot Valve. This paper has presented the flow field characteristics in the Pilot Valve with the flapper under working conditions, which means that the flapper is moving. The velocity of the flapper is imposed based on the dynamic response of the torque motor and spool Valve approximately. Meanwhile, the displacement of the flapper is determined using the general design criterion of the servo-Valve. During the simulation, the dynamic mesh strategy is utilized to update the moving mesh. Then the simulation results are firstly validated in terms of the mass flow rates of the two nozzles comparing with the theoretical evaluations. The results show that the numerical method is able to predict the flow field of the flapper-nozzle Pilot Valve under working condition. Finally, the transient velocity field, pressure field and vorticity field are presented. The results prove that the movement of the flapper can result in asymmetric flow field distribution and increase the static pressure and vorticity in the smaller clearance between the flapper and nozzle.