小喉径音速喷嘴热效应对流量影响的热边界层分析

随着气体在音速喷嘴中膨胀降温,低温气体与管壁的热交换会产生一系列复杂的影响,称之为"热效应"。用于微小流量测量的小喉径音速喷嘴由于喉部直径很小且精度要求高,热效应的影响更为严重。利用热边界层理论分析不同入口压力、不同位置、不同喉径和不同保冷条件下的管壁温度变化规律,根据试验结果,从理论上分析管壁动态温度分布与热边界层的相互作用关系,利用CFD软件仿真,分析管壁温度变化引起的边界层厚度变化对音速喷嘴流动特性的影响规律,并通过数据拟合得到了雷诺数和管壁温降对流出系数偏差的影响的计算公式。结果表明,以仿真数据为例,当管壁温降15 K时,由热边界层变薄引起流出系数增大可达0.195%,其影响不容忽视。     

某型轴流涡轮喷嘴冲角特性研究

涡轮的流量特性和效率特性,对涡轮与柴油机的匹配有重要影响。文章中保持涡轮边界条件相同,改变轴流涡轮喷嘴的冲角,并采用三维数值模拟,对某型轴流涡轮喷嘴冲角特性进行了数值计算和流场分析。结果表明,发动机两个工况下,在-40°-50°冲角下,涡轮内气体流动稳定,流量收敛,在-40°-40°范围,涡轮流量值相差不到0.4%;两个工况下涡轮最高效率冲角约为-30°,增加或降低该冲角,涡轮效率逐渐下降,工况越低,效率变化越明显。     

超高速涡轮泵机械密封热弹流润滑特性研究

以超高速涡轮泵用机械密封为研究对象,针对超高速工况下密封界面多场耦合变形行为和热弹流润滑特性不明等问题,建立密封动静环和润滑液膜的耦合数学模型,研究不同转速和密封压力下的密封界面润滑特性和端面变形行为,分析相应的密封性能变化规律。结果表明：超高速工况下密封端面产生沿泄漏方向收敛的液膜间隙,密封动环的高温热变形是主因;随密封压力的增大,液膜间隙的收敛角减小,最大膜厚和泄漏率增大,端面温升明显减小;随着转速的增大,液膜间隙的收敛角、端面温升和泄漏率增大,摩擦扭矩减小。建立的流固热力耦合模型可为超高速涡轮泵用机械密封端面的优化设计提供理论指导。     

应用于油气钻采的磨料水射流喷嘴优化设计与试验研究

为了优化总长度和出口直径被限制的喷嘴的内部结构,进行喷嘴内外流场数值模拟、喷嘴流量系数测试以及喷嘴对砂岩冲蚀深度的试验。对试验结果进行分析表明,各喷嘴射流轴心线上的速度在喷嘴的内部达到最大后开始减小;数值模拟结果和流量系数测试结果相吻合,即喷嘴外部射流速度最大的喷嘴流量系数也最大,该喷嘴的工作性能最好;在设计试验的喷嘴范围内,进口收缩角为30°,出口圆柱段长度为11mm的喷嘴性能最好,其对砂岩的冲蚀深度高出其他喷嘴的200mm~300mm。     

超高速涡轮泵等效流体阻尼研究

为提高超高速涡轮泵的设计强度可靠性，对离心泵在零流量工况下的受力进行研究，分析冲击式涡轮的气动原理，得到不同气源压力下涡轮的瞬态驱动力矩；简化零流量工况下离心泵在流体中的多种阻力损失，提出等效流体阻尼，通过试验数据拟合方法得到等效流体阻尼系数，从而得到不同离心泵结构的等效流体阻尼力矩表达式，为超高速涡轮泵设计分析提供参考，具有实际工程意义。     

喷水减温阀离心喷嘴雾化性能的优化研究

为了探索喷水减温阀喷嘴结构参数变化对其雾化效果的影响,优化喷嘴结构参数,根据Fluent软件VOF模块对喷水减温调节阀的离心喷嘴进行气-液两相仿真分析。以喷嘴出口直径、旋流槽倾斜角、旋流室收缩角作为优化因素,以雾化锥角、流量系数作为雾化性能的评价指标,进行正交实验设计。基于响应面法建立雾化锥角和流量系数的代理模型,再运用粒子群优化算法对代理模型进行寻优,得到一个最优结构参数。结果表明:当出口直径为2.55 mm,旋流槽角度为40°,旋流室角度为110°时,雾化性能得到最优,雾化锥角比原模型增大17.7％,流量系数增大32.53％,为喷嘴的设计提供了一个新的方案。     

液气射流泵喉嘴距数值模拟及其最优范围确定

基于Fluent软件在不同流量比及不同喉嘴距下对液气射流泵进行了三维数值模拟,获得了液气射流泵的压力比和效率的仿真结果,并对不同工况下液气射流泵的性能曲线和效率曲线进行分析比较。结果表明:当喉嘴距不变时,随着流量比的增加,压力比逐渐减小;当流量比不变时,随着喉嘴距的增加,液气射流泵的效率先增加然后迅速减小,当喉嘴距为1.5倍喷嘴直径时,液气射流泵的效率最高;以效率最高点下降5%为标准,确定了液气射流泵最优喉嘴距范围为1.0～1.7倍喷嘴直径。     

某旋流式燃油喷嘴流场分析

旋流式喷嘴是航空发动机进油系统和实现燃油雾化的重要部件。为了探究一种旋流式喷嘴的雾化角度,文章介绍了一种旋流式喷嘴的结构特点和工作原理,运用VOF两相流方法与Realizable k-ε模型模对喷嘴的内外部流场进行数值模拟。结果显示:数值仿真可以较好的模拟喷嘴的雾化特性,随着供油压力增大,喷嘴出口流量和速度均增大,燃油喷射速度沿轴线中心对称分布,在靠近中心轴线处有锥形空气回流,空气回流速度随供油压力的增大而增大。8种不同压力下的结果表明,雾化角度随进出口压差的增加而增大,供油压力0.3MPa时的雾化锥角为70.2°,是满足喷嘴工况条件的适宜供油压力。     

带气环旋喷射流流场特征及喷嘴结构正交优化研究

为提高二/三重管法旋喷射流切割土体效率,采用Mixture多相流模型和RNG κ-ε湍流模型,开展了淹没环境下带气环旋喷射流流动模拟研究,获得了射流速度、气液两相体积分布、靶体作用压力等流场特征,并基于L₁₆(4⁵)正交试验设计及误差分析方法,获得了旋喷射流喷嘴关键结构参数对射流速度及其作用靶体压力的影响敏感程度与影响规律。结果表明：带气环旋喷射流能量衰减慢且集中在轴心区域,射流等速核心段长,冲击破坏土体性能好;喷嘴结构参数对射流冲击性能的影响敏感次序为：射流喷嘴出口直径>收敛角>气体喷嘴直径>气液喷嘴间距>射流喷嘴长径比;射流轴心速度及其作用靶体压力随出口直径和气体喷嘴直径的增大呈先快速增加后缓慢增加趋势,随收敛角、长径比、气液喷嘴间距的增大呈先增加后降低趋势。基于此,考虑旋喷射流设备性能,给出了最优结构参数为：射流喷嘴出口直径2.0 mm,收敛角12°或18°,长径比1,气体喷嘴直径0.9 mm,气液喷嘴间距5 mm。     

超高速切线泵扬程系数试验

为获得切线泵在超高工作转速下的扬程系数、摩擦功耗损失、温升特性与工作转速关系,针对外径42 mm的8叶片切线泵开展了试验研究,将切线泵装配至涡轮轴系上,通过高压氦吹驱动涡轮轴系进行超高速运转试验。试验过程中通过控制高压气源压力及切线泵输出流量,获得了切线泵在52.8×10³~80.8×10³ r/min转速范围内的输入轴功率、输出压力、输出流量及温升特性数据。通过对实测数据的分析与计算,取得了外径42 mm的切线泵在超高转速条件下泵扬程系数、功耗损失及工作过程中温升特性试验数据。试验结果表明:外径42 mm的8叶片切线泵在52.8×10³~80.8×10³ r/min转速范围内,转速每增长1000 r/min,功耗损失约增加1.486 kW,所耗功率全部用于泵叶轮搅油摩擦损失,同时转速增加内泄增大,导致扬程系数由0.70缓降至0.66,零输出流量时由摩擦损失导致的液体介质温升速率达2.38 ℃/s,试验结束时油温最高达到274.5 ℃。试验研究提供了一种切线泵特性测试方法,可作为切线泵及涡轮泵设计和分析的依据。     

Influence of swirl on the discharge coefficients of sonic nozzles

Flow characteristics of a swirl generator are studied using an open circuit flow loop, and influence of upstream swirl on the discharge coefficients of sonic nozzles is investigated using a high pressure gas flow standard measurement system. The open circuit flow loop consists of swirl generator, testsection, sonic nozzle, suction fan and LDV system. The gas flow measurement system comprises two compressors, storage tank, temperature control loop, sonic nozzle testsection, weighing tank, gyroscopic scale and data acquisition system. Experiments are performed at various nozzle throat diameters, inlet pressures and angles of swirl generator. As the angle of swirl generator becomes larger, axial velocities decrease near the wall and rapidly increase in the pipe core, and swirl velocities increase to form swirl flow. Influence of upstream swirl on discharge coefficients becomes greater as the intensity of swirl increases and as the nozzle throat diameter is enlarged. Variation trend with Reynolds number, however, is very similar each other regardless of swirl intensity.     

Study of divergence angle influence for sonic nozzle in non-equilibrium condensation

The condensation happens generally in a nozzle during expansion of compressed steam from convergent to the divergent part of the nozzle. The divergence angle is the angle measured from the throat of the nozzle to the outlet. In this paper, the outlet is kept constant and the throat diameter is varied. In turn, the divergence angle of the sonic nozzle is altered. The effect of divergence angle on condensation phenomena is investigated with wet steam in a sonic nozzle. For analyzing the wet steam properties, the non-equilibrium condensation model is used. This model is the classical nucleation theory coupled with the droplet growth rate equation. The base nozzle is designed with the throat diameter of 4.5 mm and other dimensions are calculated according to ASME nozzle formulas. Furthermore, the chosen divergence angles are 3°, 4.2°, and 6° for which the throat diameters are 4.5 mm, 3 mm, and 1.5 mm, respectively. As the divergence angle is gradually increased, the position of maximum Mach number of the flow moves upstream, the static temperature of the flow near the throat reaches the lower value, and the droplet nucleation rate is increased. The condensation shock gets gradually stronger with decreasing the divergence angle.

     

Effect of diffuser angle on the discharge coefficient of miniature critical nozzles

Many studies on critical nozzles have been made to accurately measure the mass flow rate of gas and standardize its performance as a flow meter. Recently, much interest has been given to measuring very small mass flow rates in industrial fields, such as MEMS applications. However, the design and performance data of the critical nozzles obtained thus far have been applied mainly to critical nozzles with comparatively large diameters, and available studies on miniature critical nozzles are lacking. In this study, computational fluid dynamics (CFD) method was applied to investigate the influence of the diffuser angle on the discharge coefficient of miniature critical nozzles. In computations, the throat diameter of a critical nozzle varied from 0.2 to 5.0 mm, and the diffuser angle changed from 2° to 8°. The computational results were validated with some available experimental data. The present computational results accurately predicted the discharge coefficient of gas flows through miniature critical nozzles. The discharge coefficient is considerably influenced by the diffuser angle as the throat diameter of the nozzle becomes smaller below a certain value. This implies that miniature critical nozzles should be designed with careful consideration of its effects.     

Behaviors of discharge coefficients of small diameter critical nozzles

The discharge coefficients of 59 small diameter toroidal throat Venturi critical nozzles were measured by the static gravimetric method. The throat diameter is from 0.014 mm to 2.35 mm and the Reynolds number is 4 × 10² to 2 × 10⁵. These nozzles were manufactured by the normally processing method base on the same design drawing, but their discharge coefficients were scattered widely. The purpose of this paper is to explain the behavior of discharge coefficient scattered. In the correction procedure used here, while comparing the discharge coefficient obtained experimentally and the reference theoretical model, the throat diameter is corrected and the optimal radius of curvature of nozzle inlet is determined so that both discharge coefficients match. Resultantly, most of the behaviors of the discharge coefficient of 59 critical nozzles could be explained well.     

Flow characteristics and entrance length effect for MEMS nozzles

The critical back pressure ratio (CBPR) and the discharge coefficients were measured for traditional ISO nozzles with circular throat sections and sonic MEMS nozzles with rectangular throat sections manufactured using Micro-Electro-Mechanical systems techniques. The measurements show that critical flow can be reached in the MEMS type nozzles, but that the CBPR is much smaller than for traditional ISO nozzles and is almost constant for the same MEMS nozzle with different Reynolds numbers. The CBPR for MEMS nozzles with similar shapes increased as the throat diameter increased with different CBPR values for different shapes. For MEMS nozzles with similar geometries, the discharge coefficients in the backward direction with the longer entrance length were always higher than in the forward direction with the shorter entrance length.The measurement results were used to analyze the effect of the entrance length effect on the discharge coefficient with comparisons to theoretical values. As with the Vena Contracta for subsonic flow, the longer entrance section resulted in larger effective throat diameters for the same MEMS nozzle, which resulted in larger discharge coefficients.     

Using small sonic nozzles as secondary flow standards

When using sonic nozzles as secondary laboratory standards they must be calibrated. Standard methods of calculating discharge coefficient values are not useful with small nozzles of uncertain geometries. Calibration against primary standards is discussed. Alternatively, one nozzle can be directly compared with another by several techniques using ratios of pressure and temperature and sometimes flow. Several factors change the nozzle coefficient. Estimates of the changes due to pressure and humidity are given. Adiabatic cooling produces temperature changes that affect the nozzle coefficient by changing the throat area. Depending on the nozzle holder the inlet gas can also be cooled with an effect on the flow. Nozzles may be made by metal machining or by shrinking glass tubes. Sapphire cutting heads, which may be bought, can be used as sonic nozzles. An example of a promising but unsuitable form of nozzle having a square throat is given. The pressure dependence of these is discussed. The use of nozzles in arrays, for automatic operation as flow standards, is described.     

大直径超高压旋转水射流装置的研制及工程应用

针对作业直径不小于300mm、工作压力不小于100MPa的旋转水射流装置从主要水射流动参数确定和超高压旋转密封结构入手进行研究,确定了喷嘴孔径、射流靶距、转速等典型的水射流动参数,并完成了100MPa和250MPa两个压力等级的旋转密封组件的结构设计,研制出以平面清洗器为基本形式的水射流装置,并在实际工程应用中体现出高效和安全的特性。     

The effects of injector nozzle geometry and operating pressure conditions on the transient fuel spray behavior

Effects of injector nozzle geometry and operating pressure conditions such as opening pressure, ambient pressure, and injection pressure on the transient fuel spray behavior have been examined by experiments. In order to clarify the effect of internal flow inside nozzle on the external spray, flow details inside model nozzle and real nozzle were also investigated both experimentally and numerically. For the effect of injection pressures, droplet sizes and velocities were obtained at maximum line pressure of 21 MPa and 105 MPa. Droplet sizes produced from the round inlet nozzle were larger than those from the sharp inlet nozzle and the spray angle of the round inlet nozzle was narrower than that from the sharp inlet nozzle. With the increase of opening pressure, spray tip penetration and spray angle were increased at both lower ambient pressure and higher ambient pressure. The velocity and size profiles maintained similarity despite of the substantial change in injection pressure, however, the increased injection pressure produced a higher percentage of droplet that are likely to breakup.     

不同进口压力下柴油机非对称喷嘴内部流动特性的数值分析

采用流体动力学欧拉多相流模型，模拟了不同进口压力下柴油机喷油器非对称喷嘴内部流动特性，研究了喷嘴各孔出口处气相体积分数和质量流率分布特性。结果表明：喷嘴内部形成了均匀的雾化场，喷嘴出现空化的气相体积比和压力差上升速度都表现为孔1孔、5孔、2孔、3孔、4孔逐渐降低变化，并且空化现象基本都出现在转角上部。喷嘴各孔质量流率均随进出口压力差表现出单调增加的变化规律，之后趋于一定的稳定。在进口压力30 MPa下，压力增大后将会促进质量流率的升高；在80 MPa的进口压力下，质量流率不会发生显著改变；随着进口压力达到160 MPa，质量流率处于一个恒定状态。