绕水翼间隙涡结构形成机理与间隙几何影响

为了分析绕水翼间隙涡结构形成机理和探究压力边圆角几何的影响,对绕NACA0009水翼间隙流动进行数值计算. 通过流线涡量云图三维可视化分析,得到间隙流动特征及涡结构,对涡强度进行对比. 对翼形中截面间隙进出口边速度和间隙区平面流线、压力、湍动能进行比较分析. 研究发现：直角叶顶水翼泄漏流在间隙进口边有较大的展向速度,在间隙内形成新月形分离区,在逆压梯度作用下形成叶顶分离涡（TSV）,涡尺度与展向速度成正相关;叶顶泄漏涡（TLV）形成源于间隙出口边射流与吸力边侧低速流体之间的持续剪切作用,低速流体从剪切层获得持续的能量输运形成稳定的泄漏涡结构;间隙压力边圆角对TSV起抑制作用,降低了间隙区整体涡强度.     

导管螺旋桨不同桨叶的叶梢泄露涡分析

为了深入探讨叶梢泄露涡的流动机理,研究了导管螺旋桨中桨叶螺距比与盘面比对叶梢泄露涡的影响,以及不同桨叶中叶梢泄露涡、叶梢负荷与叶梢泄露流三者之间的关联. 采用数值方法对不同桨叶的导管螺旋桨流场进行了模拟分析. 结果表明: 当螺距比增大,叶梢泄露涡逐渐远离桨叶吸力面,涡核空化数降低;当盘面比增大,叶梢泄露涡的轨迹基本不变化,涡核空化数提高; 叶梢泄露流通过与叶梢泄露涡之间的流动剪切作用影响叶梢泄露涡的发展;叶梢泄露流流速受到叶梢负荷的影响,负荷越高的位置,叶梢泄露流的速度也越高．     

Study on leakage flow characteristics of radial inflow turbines at rotor tip clearance

Tip clearance leakage flow in a radial inflow turbine rotor for microturbines under the stage environment is investigated using a three-dimensional viscous flow simulation. The results indicate that the scraping flow caused by relative motion between casing and rotor tip, and the pressure difference between pressure side and suction side at rotor tip, play important roles in tip clearance leakage flow. The more the rotor tip speed increases and tip clearance height decreases, the more the scraping effect acts. Though the leakage velocity of tip clearance at midsection and exducer regions changes less when the rotor rotational speed is changing, the distance between passage vortex and rotor suction side varies in evidence. Main leakage flow rate of tip clearance takes place at region of exducer tip and some seal configurations will be quite effective for cutting leakage flow if these configurations are arranged over midsection and exducer of the radial inflow rotor.     

考虑叶顶间隙的螺旋轴流式混输泵主流道内空化特性

为揭示叶顶间隙对螺旋轴流式混输泵主流道内空化特性的影响,基于Rayleigh-Plesset方程的Zwart-Gerber-Belamri空化模型,采用SST k-ω湍流模型在不同空化阶段下对螺旋轴流式混输泵主流道内的空化特性进行研究,通过考虑叶顶间隙更为精准地揭示螺旋轴流式混输泵主流道的空化情况。结果表明:在叶顶处,除了流道内出现低压区和空泡外,在叶片吸力面表面也出现低压区和空泡分布;在临界空化阶段,叶轮进口以及叶片进口叶顶间隙处存在微弱的空泡分布;随着空化的发展,到断裂空化阶段,空泡分布区域由叶片压力面移动到叶片吸力面,说明叶顶间隙对混输泵主流道内的空化性能产生较大的影响。本文的研究结果可为螺旋轴流式混输泵空化性能的改善提供工程参考。     

Large-eddy simulation and experimental study on the turbulent wake flow characteristics of a two-bladed wind turbine

Large-eddy simulation(LES) with fully resolved rotor method(FRM) is applied to explore the turbulent wake flow characteristics and vortex evolution laws of a two-bladed horizontal-axis wind turbine. Relevant wind tunnel experiments have been done based on time resolved particle image velocimetry(TRPIV) technique. The simulation results are validated by the experimental data and they are in good agreement. The axial average velocity, turbulent kinetic energy, shear Reynolds stress, and vortex structure of the wind turbine wake are analyzed based on the comparison of LES results and experimental data. It is observed that the wake diameter of wind turbine enlarges with the increase of tip speed ratio(TSR). Turbulent kinetic energy meets its minimum value when x/R=2.0. Shear Reynolds stress appears a positive peak in the near wake when x/R2.0, and the value of shear Reynolds stress decreases along the axial direction. The blade tip vortex dissipates more quickly than the central vortex in the wind turbine wake, and the gradient of the relationship curve between the blade tip vortex core position and the vortex age decreases as the TSR increases. With the increase of TSR, the thrust coefficient increases, and the power coefficient increases first and then decreases.The present work proves that LES with FRM could calculate wind turbine turbulent wake flow with a high accuracy.     

间隙大小对压气机转子间隙泄漏流场的影响

针对叶尖率先出现失速信号的一亚音速轴流压气机转子,采用全三维数值模拟方法分析了3种顶部间隙情况下泄漏流动特点,以及它对转子气动性能的影响。数值模拟结果表明,不同间隙情况下泄漏涡的运行特性与压气机的性能和稳定性密切相关。3种间隙情况下,泄漏涡在近失速工况下均发生了破碎。涡破碎造成泄漏涡体积突然膨胀,从而使堆积在机匣壁上的低能流体迅速扩散,对来流产生了很大的阻塞效应。在下游工况相同的条件下,大间隙时最先发生了泄漏涡破碎,说明泄漏涡初始形成时的强度越强,越容易出现涡破碎。     

入口导流栅几何参数对高速泵诱导轮空化特性的影响

高速离心泵空化问题机理相对复杂,通常认为诱导轮间隙泄漏涡与回流漩涡是影响高速离心泵空化的主要原因。本文通过在诱导轮入口前增设导流栅来抑制旋转涡,达到提高离心泵空化性能的目的。采用RNG k-ε湍流模型,对带有矩形、椭圆形两种不同形状导流栅的离心泵进行全流场模拟,分析高速离心泵全流场数值计算结果,对比增置导流栅前后离心泵空化特性以及进口段流场。结果表明:带椭圆形导流栅的离心泵临界空化数有所降低,空化性能得到改善;增设导流栅后,诱导轮进口段旋转强度明显减弱,离心泵扬程均有明显提升,其中椭圆形导流栅方案较原方案提高了3%。     

叶表和端壁抽吸对跨音速压气机稳定性影响对比分析

以NASA Rotor35为研究对象,应用数值模拟手段深入分析了叶表和端壁不同位置抽吸对该压气机稳定性的影响效应。研究结果表明:叶表抽吸虽然使得压气机压比和效率有所升高,但使叶顶前缘脱体激波和间隙泄漏流强度的增加,导致两者相互作用引起的低能堵塞团尺度过早增长,压气机提前进入失速;端壁抽吸改善了转子顶部前缘激波结构,削弱了叶顶低能阻塞团中的高熵流体,改善了叶顶区域的流动,实现了压气机的扩稳效果,但对压气机压比和效率性能改善不明显。     

Large eddy simulation of unconfined turbulent swirling flow

Large eddy simulations(LES) were performed to study the non-reacting flow fields of a Cambridge swirl burner. The dynamic Smagorinsky eddy viscosity model is used as the sub-grid scale turbulence model. Comparisons of experimental data show that the LES results are capable of predicting mean and root-mean-square velocity profiles. The LES results show that the annular swirling flow has a minor impact on the formation of the bluff-body recirculation zone. The vortex structures near the shear layers, visualized by the iso-surface of Q-criterion, display ring structures in non-swirling flow and helical structures in swirling flow near the burner exit. Spectral analysis was employed to predict the occurrence of flow oscillations induced by vortex shedding and precessing vortex core(PVC). In order to extract accurately the unsteady large-scale structures in swirling flow, a three-dimensional proper orthogonal decomposition(POD) method was developed to reconstruct turbulent fluctuating velocity fields. POD analysis reveals that flow fields contain co-existing helical and toroidal shaped coherent structures. The helical structure associated with the PVC is the most energetic dynamic flow structure. The latter toroidal structure associated with vortex shedding has lower energy content which indicates that it is a secondary structure.     

CFD simulation of single-phase flow in flotation cells: Effect of impeller blade shape,clearance, and Reynolds number

A series of numerical simulations of turbulent single-phase flows are performed to understand the flow and mixing characteristics in a laboratory scale flotation tank. Four impeller blade shapes covering a wide range of surface areas and lip lengths are considered to highlight and contrast the flow behavior predicted in the impeller stream. The mean flow close to the impeller is fully characterized by considering velocity components along the axial direction at different radial locations. Normalized results suggest the development of a comparatively stronger axial velocity component for a blade design with the smallest lip length, called big-tip impeller here. Normalized turbulent kinetic energy profiles close to the impeller reveal the existence of an asymmetric trailing vortex pair. The highest turbulence kinetic energy dissipation rates are observed close to the impeller blades and stator walls where the radial jet strikes the stator walls periodically. Furthermore, liquid phase mixing in the flotation cell is studied using transient scalar tracing simulations providing mixing time data. Finally, pumping capacity and efficiency of different impeller designs are calculated based on which the impeller blade design with a rectangular blade design is found to perform most efficiently.     

低湍流度时尾流湍流切应力和湍流动能的相关

简述了在性能优良、湍流度极低（０．０２％）的西北工业大学低湍流度风洞中用热线风速仪测量翼型近场尾流及边界层速度型、湍流强度、雷诺正应力及切应力等的简况，并着重讨论了极低湍流度下近场尾流中湍流切应力和湍流动能间的相关特性，表明相关值明显不同于常规湍流度的结果。     

基于非定常空化流动的离心泵涡旋结构数值分析

To elucidate the formation mechanism of the vortex structure in cavitation flow, the unsteady cavitation flow field of the centrifugal pump was investigated by simulation. The two-dimensional vortex structure on the mid-section was examined based on the method with velocity components. The vorticity on the blade surface and the evolution of the periodicity was compared. In addition to investigate the three-dimensional vortex structure in the impeller passage, the new Omega vortex identification method was also utilized. The results show that: as the NPSHa decreases, the cavity coverage area grows progressively, and the local vortices emerge and the flow in the pump becomes disordered. Due to the effect of cavitation flow field, the vortex structure is mostly formed and evolved on the blade suction surface. During the critical cavitation, the vortex is also detached the blade surface as the cavity rolls up. At the effect of rotor-stator interaction, the blade trailing vortex sheds and attaches to the volute wall at the front end of the tongue. According to the Omega method, the structure of the three-dimensional vortex within the cavity is stable. At the critical cavitation condition, the structure of the three-dimensional vortex downstream of the impeller passage is fragmented and disordered.     

旋流式壅塞空化器处理苯酚溶液研究

壅塞空化是一种新型的水力空化技术,在壅塞空化器喷嘴内加入旋流芯即成为旋流式壅塞空化器。在不同背压和旋流芯长度下,利用CFD软件对旋流式壅塞空化器内部流场进行了数值仿真,并对不同初始浓度的苯酚溶液采用高效液相色谱仪检测其处理前后的质量浓度变化。计算结果表明,旋流式壅塞空化器内部产生的涡环对壅塞空化具有促进作用,并存在最佳背压和旋流芯长度。模拟污水处理试验结果表明:当背压为200 k Pa,旋流芯长度为3/4倍导程,苯酚溶液的初始质量浓度为5 mg/L时,旋流式壅塞空化器对苯酚溶液的去除效果最佳。     

中压低温透平膨胀机膨胀端三维数值模拟

采用CFD方法对某型号中压低温透平膨胀机膨胀端进行整机全周数值模拟,全面考虑了进气蜗壳、叶顶间隙气封、轮背气封和轴封等细节结构对膨胀端气动性能和流场的影响.研究结果表明:进气蜗壳的几何形状是造成喷嘴进口气流沿叶高方向分布不均匀的主要原因;轮背气封、叶顶气封和轴封内存在明显的旋涡流动,且叶顶气封是典型的后台阶流动,齿封内和台阶后旋涡涡轴方向相反;喷嘴和叶轮之间过小的间隙导致气流在喷嘴压力面一侧形成激波,激波/附面层干扰使叶片和下端壁附面层同时分离,在上、下端壁角区各形成一个弯曲的涡管,最后终止于动静交界面.     

小翼对水平风力机流场特性的改变

实验和数值模拟已经证明了风力机叶片的叶尖添置小翼,可以提高风能转化效率。为了清楚地了解小翼对风力机动力放大的影响,对加小翼和不加小翼的风力机流场——速度场和压力场的特性进行了分析。这个分析是基于对风力机加V(8.8×8)型小翼和不加小翼时叶轮周围流场数值模拟的结果。可以看出小翼对风力机的叶端产生的影响较大,即加大了风力机叶端的压差和速度。同时结合一定位置的压力和速度图的分析,可以看出小翼使风力机叶尖的漩涡强度降低,提高了能量的转换,从而提高了效率。     

弯曲叶片降低能量损失的涡动力学机制

采用实验与数值模拟相结合的手段，从涡动力学的角度阐述了弯叶片降低能量损失的机理，研究了在不同攻角，不同出口马赫数，不同弯角条件下涡轮叶栅流场内主要旋涡的生成与发展，并通过与直叶栅的对比，研究了叶片弯曲对马蹄涡起始分离点位置及对通道涡位置强度的影响，从截面涡结构入手，分析了叶片弯曲这种边界条件的改变方式对通道涡稳定性的影响，通过分析在不同气动条件下通道涡对损失贡献的差异指出了在通道涡强度与尺度较大的叶栅，叶片弯曲不但会直接通过改变通道涡的强度，减少通道涡本身的损失来影响损失的大小，同时也会通过对通道涡位置的改变来影响损失的分布与大小。     

小型风扇叶顶间隙内部流动数值模拟

通过对不同叶顶间隙小型风扇内部数值模拟,得出不同叶顶间隙小型风扇的静特性曲线、相同S面间隙涡流变化及叶顶到机闸内表面各回转面涡流变化.研究得出:当流量Q小于0.006 5 m3/s时,4个不同叶顶间隙的总压变化趋势一致,均随叶顶间隙的增加总压减小.流量增加时,叶顶间隙为2.5 mm时性能较好;在相同S面上,间隙涡流现象...     

高压涡轮叶顶间隙变化的数值分析

利用有限元分析软件分析了某型高压涡轮叶顶间隙在不同工况下随时间的变化。采用分段加载方法对模型施加温度和压力边界条件。计算结果与实验数据的对比分析表明:涡轮叶片位移对叶顶间隙变化的贡献不大,温度和转速是影响轮盘径向尺寸变化的主要因素,而温度是影响机匣和叶片变形的主要因素。     

Cavitation Inception in Turbulent Flows Around a Hydrofoil

For most engineering purposes cavitation de-grades performance.Engineering designs are ai med atproducing geometries and operating conditions thatresist cavitation.It is desirable to identify,under-stand,predict,and control the physical mechanismsleading to cavitation inception.One of the centralproblems in cavitation research has been the predic-tion of the onset or inception of cavitation.The cavi-tation occurring in a flow system is related to thepressure field and viscous flowpatterns[1].…     

刚性淹没双层植被明渠水流紊流特性研究

文章采用标准 紊流模型,结合雷诺平均Navier-Stokes方程,对刚性淹没双层植被明渠水流特性进行了研究。计算所得的流速值与实测值吻合良好,表明计算方法可行。进而根据空间及时间的双平均理论,给出了双平均条件下的明渠流速,雷诺应力及紊动能分布,并对紊动能平衡方程中的各项进行了分析。结果可以看出,刚性双层淹没植被作用下,垂向流速分布曲线由三个拐点将其划分为四个区域;雷诺应力及紊动能分布在植被顶端明显增强,高植被顶端各项值均大于低植被顶端相应值;紊动能平衡方程中的紊动耗散项及压力耗散项在紊动能平衡方程中起着主导作用;植被顶端区域产生的涡,通过喷射和扫掠作用使其附近水体发生质量及动量交换。