Research on transient characteristics of cavitation phenomena in pilot stage of jet pipe servo-valve

To obtain dynamic characteristics of cavitation and study the relationship between the cavitation and inlet pressure, large-eddy simulation(LES) is utilized to calculate unsteady flow field in the pilot stage. Lamb-Oseen vortex is observed. Simulation results show that vortex cavitation exists, and cloud cavitation begins to occur when inlet pressure reaches 7 MPa. Cavitation and cavitation-shedding are enhanced by the increment of inlet pressure. The main frequencies of the pressure oscillations of vortex cavitation and cloud cavitation increase with inlet pressure increasing. By comparing results of local cavitation and facet cavitation, it is known that cloud cavitation has a greater influence than vortex cavitation. Upon increasing the wedge length, the main frequency of vortex cavitation increases whereas that of cloud cavitation decreases, the volume fraction of the vapor phase and the energy efficiency decrease. Considering the above characteristics and the easiness of the process, the optimal wedge length is 0.03 mm.

Research on the jet characteristics of the deflector–jet mechanism of the servo valve

In view of the complicated structure of the deflector-jet mechanism,a mathematical model based on the turbulent jet flow theory in the deflector-jet amplifier is proposed.Considering the energy transformation and momentum variation,an equation of the flow velocity distribution at the key fluid region is established to describe the morphological changes of the fluid when it passes through the deflector and jets into the receiver.Moreover,the process is segmented into four stages.According to the research results,the oil enters the deflector and impinges with the side wall.Then one part of the oil＇s flow velocity decreases and a high pressure zone is formed by the oil accumulation,the other part of the oil reverses out of the deflector along the side wall.Prior to entering the receiver,the flow is a kind of plane impinging jet.Virtually,the working pressure of the receiver is generated by the impact force,while the high speed fluid flows out of the receiver and forms a violent vortex,which generates negative pressure and causes the oil to be gasified.Compared with the numerical simulation results,the turbulent jet model that can effectively describe the characteristics of the deflector-jet mechanism is accurate.In addition,the calculation results of the prestage pressure characteristic have been verified by experiments.

Numerical Analysis and Verification of the Gas Jet from Aircraft Engines Impacting a Jet Blast Deflector

The process of the gas jet from aircraft engines impacting a jet blast deflector is not only a complex fluid–solid coupling problem that is not easy to compute, but also a safety issue that seriously interferes with flight deck envi?ronment. The computational fluid dynamics(CFD) method is used to simulate numerically the impact e ect of gas jet from aircraft engines on a jet blast deflector by using the Reynolds?averaged Navier?Stokes(RANS) equations and turbulence models. First of all, during the pre?processing of numerical computation, a sub?domains hybrid meshing scheme is adopted to reduce mesh number and improve mesh quality. Then, four di erent turbulence models includ?ing shear?stress transport(SST) k-w, standard k-w, standard k-ε and Reynolds stress model(RSM) are used to compare and verify the correctness of numerical methods for gas jet from a single aircraft engine. The predicted values are in good agreement with the experimental data, and the distribution and regularity of shock wave, velocity, pressure and temperature of a single aircraft engine are got. The results show that SST k?w turbulence model is more suitable for the numerical simulation of compressible viscous gas jet with high prediction accuracy. Finally, the impact e ect of gas jet from two aircraft engines on a jet blast deflector is analyzed based on the above numerical method, not only the flow parameters of gas jet and the interaction regularity between gas jet and the jet blast deflector are got, but also the thermal shock properties and dynamic impact characteristics of gas jet impacting the jet blast deflector are got. So the dangerous activity area of crew and equipments on the flight deck can be predicted qualitatively and quantitatively. The proposed research explores out a correct numerical method for the fluid–solid interaction during the impact process of supersonic gas jet, which provides an e ective technical support for design, thermal ablation and structural damage analysis of a new jet blast deflector.

Experiment and Large-Eddy Simulation on Free Air Jets Issuing from a Rectangular Nozzle with Deflectors

The purpose of the present study was to establish a passive flow control method for a rectangular jet using two types of deflectors installed symmetrically inside a nozzle. This deflector in a rectangular nozzle generates the rectangular coaxial jets. The effect of the slant angle of the deflectors on the flow characteristics and the spread of the rectangular jet was investigated experimentally and by large-eddy simulation. The experiment and the numerical simulation were carried out at a Reynolds number of 9000. The rectangular jet with no deflectors generates a vortex ring from the nozzle exit. The vortex ring collapses in the downstream region and the outline of the jet changes from rectangular to diamond-shaped as a result of the axis-switching phenomenon. The rectangular jet with divergent and convergent deflectors shows particularly noticeable changes in the flow characteristics and vortical structures, as compared to the case with no deflectors. In the case of the rectangular jet with divergent deflectors (slant angle of α = 6°), minor axis spread is promoted more than major axis spread, and axis switching occurs closer to the nozzle exit than that in the case of no deflectors. The outline of the jet also changes from lateral rectangular to vertical rectangular as a result of axis switching. On the other hand, in the case of a rectangular jet with convergent deflectors (α = -6°), minor axis spread is suppressed more than major axis spread, and axis switching occurs farther from the nozzle exit than that in the case with no deflectors. The outline of the jet does not change until the downstream region. Therefore, the spread and the axis-switching location for the rectangular jet can be controlled by the deflectors inside the rectangular nozzle.

电液伺服阀压力增益影响因素灵敏度分析

压力增益是电液伺服阀核心性能指标之一,但电液伺服阀存在机电液强耦合性、封闭性和结构参数复杂性,限制了电液伺服阀压力增益的提升,亟需明确压力增益的影响因素及权重大小。故以偏转板射流伺服阀为研究对象,建立伺服阀机、电、液多环节数学模型,得到电液伺服阀整阀的状态空间模型,然后,结合压力增益公式,采用一阶灵敏度分析方法,分析伺服阀结构参数对伺服阀压力增益影响相关性和权重,最后,基于电液伺服阀性能测试实验平台,验证了前置级喷嘴尺寸以及滑阀级遮盖量两个典型结构参数对压力增益的影响。研究成果为电液伺服阀静态性能的提升提供了一定的理论指导。

不同偏流板角度的冲击射流噪声特性

舰载机尾喷流冲击偏流板(挡焰板)产生高强度噪声。为研究不同偏流板角度对噪声的影响,在全消声室进行射流冲击实验。实验时收缩喷口直径D=56.4 mm,受冲击的偏流板长、宽均为600 mm,射流马赫数Ma=1.01。在偏流板角度β=45°、55°和65°条件下,利用传声器和流动显示对远场噪声和冲击流动进行观测。结果表明,不同冲击角度下壁面射流结构明显不同,总声压级及噪声辐射特性存在明显区别,随着冲击角度的增加,上游和下游极角总声压级分别出现上升和下降,β=65°时,下游总声压级最多降低7 dB,上游相应增加15 dB。流动和频谱结果表明下游主要受到后缘分离噪声影响,该噪声来自壁面射流从偏流板后缘分离产生的大尺度涡结构,低频占主导,并且互相关分析表明,偏流板角度越小,该噪声指向性越明显。上游噪声被冲击噪声所主导,虽然偏流板角度显著影响冲击噪声强度,但是相关分析表明,冲击噪声向各个极角辐射的指向性结构较为稳定。此外偏流板对边线形成低通高阻效应,边线噪声频谱最为陡峭,而且边线观测到的总声压级、频谱在不同冲击角度的差别均较小。本研究可为航母甲板噪声治理提供一定参考。

射流放大器的不对称性对偏转板伺服阀零偏的影响

针对偏转板伺服阀前置级放大器结构不对称导致零偏的问题,考虑两个接收腔结构尺寸不一致以及劈尖相对射流口不对称等因素,基于二维紊动射流理论建立了偏导射流放大器压力特性数学模型,分析了两个接收腔圆角、内角、喉部宽度不一致性以及劈尖相对射流口的偏移量对放大器压力特性以及零偏位移的影响。分析结果表明:由于接收腔圆角和接收腔宽度直接决定射流流出接收腔的面积,故接收腔圆角和宽度的不对称会对放大器零件产生较大影响,两接收腔圆角差值每增大10μm,会近似产生0.33μm的零偏,而两接收腔宽度差值每增大10μm,会近似产生1μm的零偏,接收孔内角的对称性和劈尖相对射流口的偏移则对放大器的零偏影响很小。减小两接收孔圆角和宽度的加工公差可以显著降低射流放大器的零偏,并提高射流放大器的一致性。

偏转板伺服阀的自冷却方案与自冷却效果分析

发动机用电液伺服阀常工作在极端高温环境中,为保证电液伺服阀的服役性能,掌握极端高温环境下电液伺服阀温度分布规律及相应的冷却措施至关重要。在环境温度250℃、工作介质温度140℃的极端高温下,采用Fluent仿真分析发现偏转板伺服阀整体温度为140~233℃,力矩马达部分温度呈现上下的温度梯度,整体温度较高。结合实际需要提出了偏转板伺服阀的一种壳体回油自冷却结构方案,计算获得了含自冷却结构的偏转板伺服阀整体温度范围为140~182℃,其中力矩马达部分的上下导磁体、永久磁钢以及力矩马达下壳体的温度下降明显,该冷却结构可获得良好的冷却效果。对比分析了不同结构尺寸下偏转板伺服阀自冷却效果,综合考虑冷却效果以及功率损失的影响,得到冷却节流孔直径0.5 mm为最优尺寸。发现管路尺寸对偏转板伺服阀冷却效果影响不大,设计时应主要考虑加工性及结构强度因素。所提出的极端高温下电液伺服阀壳体回油自冷却方案,可作为电液伺服阀设计、制造的理论依据。

机液反馈式偏转射流压力伺服阀机理及特性分析

电液压力伺服阀是飞机刹车压力伺服系统的重要控制元件。为满足压力伺服阀高动态和高可靠性的要求,设计了一种机液反馈式偏转射流压力伺服阀。为研究该压力伺服阀的工作机理和静动态特性,建立了其数学模型和Simulink仿真模型。通过仿真结果可知,压力伺服阀的死区电流为1 mA,最大输出压力为10 MPa,压力增益为1.15 MPa/mA,幅频宽为26 Hz,相频宽为36 Hz,动静态性能良好,满足系统要求。通过实验对理论、仿真模型的准确性进行了验证,验证结果表明,理论模型能较好地预测压力伺服阀的静态性能,为压力伺服阀的结构设计和优化提供理论支撑和仿真参考。

Analysis of the Internal Characteristics of a De ector Jet Servo Valve

In current research on deflector jet servo valves, the receiver pressure estimated using traditional two-dimensional simulation and theoretical calculation is always lower than the experimental data; therefore, credible information about the flow field in the prestage part of the valve can hardly be obtained. To investigate this issue and understand the internal characteristics of the deflector jet valve, a realistic numerical model is constructed and a three-dimensional simulation carried out that displays a complex flow pattern in the deflector jet structure. Then six phases of the flow pattern are presented, and the defects of the two-dimensional simulation are revealed. Based on the simulation results, it is found that the jet in the deflector has a longer core area and the fluid near the shunt wedge cannot resist the impact of the high-speed fluid. Therefore, two assumptions about the flow distribution are presented by which to construct a more complete theoretical model. The receiver pressure and prestage pressure gain are significantly enhanced in the calculations. Finally, special experiments on the prestage of the servo valve are performed, and the pressure performance of the numerical simulation and the theoretical calculation agree well with the experimental data. Finally, the internal mechanism described by the theoretical and numerical models is verified. From this research,more accurate numerical and theoretical models are proposed by which to figure out the internal characteristics of the deflector jet valve.

环形缝隙喷嘴改进导流内锥式除尘滤筒脉冲喷吹性能的数值模拟

为提高除尘滤筒脉冲喷吹性能,研究了环形缝隙喷嘴对导流内锥式除尘滤筒清灰性能的改进作用,采用CFD数值模型对喷吹性能进行模拟,考察了除尘滤筒内部流场特征,研究了喷吹距离、文丘里管增设对喷吹效果的影响。结果表明:相比于普通喷嘴,使用环缝喷嘴后滤筒上部的负压几乎消失,滤筒内压力增大,喷吹强度提升;喷吹强度随着喷吹距离的增大呈先增后降的趋势,且喷吹均匀性逐渐改善,环缝喷嘴在喷吹距离为400 mm时,滤筒的清灰性能最佳,喷吹强度提升了44%;在滤筒上方开口处增设文丘里管可以使滤筒内压力峰值得到较大的提升,随着文丘里管安装高度升高,滤筒内的喷吹强度先升高再缓慢降低,变异系数呈先增后降的趋势,文丘里管安装高度为-30 mm时对喷吹强度提升最大(29%)。

偏流板距离对亚声速射流冲击宽频噪声特性的影响

通过全消声室实验研究了不同冲击距离(L)下亚声速射流宽频噪声特性。利用远场传声器获得L=30D~2D(D为喷口直径)的噪声数据,并详细分析了频谱特性。试验结果表明,减小冲击距离:(1)上游所有频段的噪声都明显上升,极角α=120°总声压级(OASPL)在L<10D时增加了10~17 dB;(2)下游α=30°的噪声能量向低频转移,且频谱在L<10D时变化不明显;(3)偏流板产生噪声的中、高频段对边线影响较小,α=90°的频谱迅速衰减,在L<10D时形成陡峭的峰值。研究证实在噪声最强的方向(α=120°),随冲击距离的减小偏流板贡献的噪声功率占比呈线性增加。冲击距离小于势流核时,偏流板贡献大部分噪声能量,L=7D~5D时占比超过80%。另外射流冲击产生的噪声指向性明显,冲击噪声和后缘分离噪声在不同方向取得主导地位,相应频谱分别在上游和下游呈现高频主导和低频占优的特性。

射流偏转板伺服阀小电流输出引发异响声问题及解决措施

针对射流偏转板伺服阀在液压马达速度闭环控制系统应用实例中伺服阀小电流工况下存在的异响声问题,通过对伺服阀射流口处流场进行仿真分析。确认异响声的原因为:射流偏转板伺服阀前置级供油压力高,在伺服阀射流前置级入射口形成气穴效应,引起小流量输出压力脉动增大,当压力脉动频率与产品结构固有频率接近时,谐振响应导致异响声。采用在射流偏转板型伺服阀前置级增加进油节流孔措施,在不损失伺服阀性能前提下,可抑制供油压力波动对控制级的影响,有效解决伺服阀小电流输出引起的异响声问题。

以礼河四级复建电站调速系统技术与实践

以礼河四级电站复建工程的水轮机调速器为研究对象,以礼河四级电站总装机容量130MW(32.5MW×4),水轮机为立轴冲击式水轮机组,调速器采用4喷4折的控制结构,喷针控制采用比例阀+手动的结构形式,折向器控制采用阀组与事故配压集成结构形式,电气采用双机热备PLC为控制核心。调速器整体由武汉三联水电控制设备有限公司制造,首台设备已于2022年12月20日投产运行。

偏转板射流阀压力特性数值模拟分析

运用CFD软件对某型号偏转板射流阀内部不同阀口参数组合下的压力特性进行数值计算和分析,得出偏转板射流阀输出压力特性随不同阀口结构参数组合的变化规律。计算发现:供油压力为4 MPa时,λ1≈0.6,1.5≤λ2≤2,1≤λ3≤1.5组合下偏转板射流阀输出压力增益较大,输出压力特性曲线与偏转板位移成线性关系,研究结果可为偏转板射流伺服阀的工程设计和优化提供理论依据与参考。

掺气折流器对侧空腔和底空腔长度的影响

在突扩突跌掺气设施中 ,为保证掺气效果 ,增加底空腔和侧空腔的长度 ,加设折流器是有效的工程措施 .试验证明 ,折流器坡度和高度对空腔长度均有影响 ,较高的折流器增加空腔长度明显 ,且使底空腔与侧空腔贯通 ,有利于底空腔充分掺气 .回溯水流使底空腔变短 ,有效空腔长度是影响掺气效果的重要因素 .在空腔长度的计算中应综合考虑 ,顶板坡角 ,跌坎挑角和折流器体型的影响 ,得出的计算公式有实际应用和理论意义 .

舰载飞机发动机尾流场数值模拟

为了解舰载机在飞行甲板起飞时发动机尾喷流被喷气偏流板偏转后的流场分布情况,以国外某型舰载机和喷气偏流板为研究对象,采用三维雷诺平均Navier-Stokes方程、k-ε湍流模型和离散坐标模型(DO模型),借助计算流体动力学(CFD)技术对该舰载机起飞时的尾流场进行了三维数值模拟,空间上采用二阶迎风格式进行耦合求解,时间上采用显式Runge-Kutta方法进行迭代推进,直至流场收敛。结果表明:喷气偏流板对尾流场起到了很好的偏转作用,尾喷流对喷气偏流板背部区域的设备和人员几乎没有影响;尾流场中的高温高压气流主要分布在喷气偏流板与喷口之间的区域,在起飞作业过程中,舰面工作人员和设施要避免进入该区域。所得结果从理论上证明了该喷气偏流板的设计方案能满足舰载机起飞的需求。

喷嘴宽度对偏转板射流阀射流效率影响的仿真分析

利用Pro/E和Fluent软件对不同λ_1(喷嘴宽度D_1与导流窗口最小宽度H_1的比值)的偏转板射流阀进行几何建模与流场仿真,得到不同λ_1下偏转板射流阀内部射流速度、压力云图和射流流场的速度、压力分布特征;通过分析仿真数据得到λ_1对供油流量Q_S、射流流量Q_J、射流流量效率η_J的影响规律。研究发现,喷嘴喷射出的部分油液由于受到V形导流斜面的作用沿着V形导流斜面反向运动,从而使喷向接收口的有效射流流量减小,同时在偏转板入口两侧出现漩涡和能量损失;随着λ_1增大,供油流量Q_S近似线性增大,而射流流量Q_J先增大后又减小;当λ_1=1时射流流量Q_J取得最大值12.5 kg/s,对应的射流流量效率η_J最大为77.6%。研究结果为偏转板射流伺服阀的效率提高及结构优化设计提供理论依据与参考。

基于仿真离散数据的偏转板射流式伺服阀液动力计算方法研究

基于偏转射流式伺服阀工作机理,提出关于其动态特性分析及前置级液动力计算检测的问题。建立关于力矩马达、射流盘前置级以及功率滑阀三部分的完整伺服阀动态模型,确定前置级液动力的近似公式,并对整阀特性进行频率分析,验证了数学模型的正确性;建立伺服阀前置级内部的二维流场模型,并基于流场仿真所获得的离散数据,给出两种可用于计算稳态液动力的方法,即动量定理法和压差法,通过计算某型伺服阀的液动力,验证上述两种方法能够相互印证;设计并实现了一种双自由度的液动力测试平台,实现了对液动力的间接测试。结果表明,采用动量定理法和压差法计算得到的液动力值,与其近似计算公式以及试验结果一致,证明了提出的液动力计算方法与测试系统均具有可行性,为此类伺服阀的改进与优化提供了技术支撑。

偏导射流液压放大器流量增益非线性研究

偏导射流液压放大器是偏导射流伺服阀中的核心组件,其性能一定程度上决定了整阀性能,流量增益是偏导射流液压放大器的一项关键特性。通过定性分析及理论推导相结合的方式,得出了偏导射流液压放大器流量增益非线性模型,该非线性与偏导板喷射口宽度及分流劈尖宽度有关。当偏导板位移较小时,流量增益为恒值;当偏导板位移达到喷射口宽度及分流劈尖宽度之和的一半时,偏导射流液压放大器的流量特性达到饱和。最后,通过对实物进行测试验证了模型的正确性。