Inlet Recirculation Influence to the Flow Structure of Centrifugal Impeller

Inlet recirculation is proved as an effective way for centrifugal compressor surge margin extension,and is successively used in some engineering applications.Unfortunately its working mechanism is still not being well understood,which leads to redesigning of inlet recirculation mostly by experience.Also,most study about inlet recirculation is steady to date.It is necessary to study surge margin extension mechanism about inlet recirculation.To expose the mechanism in detail,steady and unsteady numerical simulations were performed on a centrifugal compressor with and without inlet recirculation.The results showed that,with inlet recirculation,the inlet axial velocity is augmented,relative Mach number around blade tip leading edge area is significantly reduced and so is the flow angle.As the flow angle decreased,the incidence angle reduced which greatly improves the flow field inside the impeller.Moreover,inlet recirculation changes the blade loading around blade tip and restrains the flow separation on the blade suction side at the leading edge area.The unsteady results of static pressure around blade surface,entropy at inlet crossflow section and vorticity distributions at near tip span surface indicated that,at near stall condition,strong fluctuation exists in the vicinity of tip area due to the interaction between tip leakage flow and core flow.By inlet recirculation these strong flow fluctuations are eliminated so the flow stability is greatly enhanced.All these improvements mentioned above are the reason for inlet recirculation delays compressor stall.This research reveals the surge margin extension reason of inlet recirculation from an unsteady flow viewpoint and provides important reference for inlet recirculation structure design.

Serpentine Inlet Performance Enhancement Using Vortex Generator Based Flow Control

In order to provide the line-of-sight blockage of the engine face for an advanced Uninhabited Combat Air Vehicle（UCAV）, a highly curved serpentine inlet is proposed and experimentally studied. Based on the static pressure distribution measurement along the wall, the flow separation is found at the top wall of the second S duct for the baseline inlet design, which yields a high flow distortion at the exit plane. To improve the flow uniformity, a single array of vortex generators （VGs） is employed within the inlet. In this experimental study, the effects of mass flow ratio, free stream Mach number, angle of attack and yaw on the performance of a serpentine inlet instrumented with VGs are obtained. Results indicate： （1） Compared with the baseline serpentine design without flow control, the application of the VGs promotes the mixing of core flow and the low momentum flow in the boundary layer and thus prevents the flow separation. Under the design condition, the exit flow distortion （-↑△σ0） decreases from 11.7% to 2.3% by using the VGs. （2） With the descent of the free stream Mach number the total pressure loss decreases. However, the circular total pressure distortion increases. When the angle of attack rises from - 4° to 8°, the total pressure recovery and the circular total pressure distortion both go down. In addition, with the increase of yaw the total pressure recovery is fairly constant, while the circular total pressure distortion ascends gradually. （3） When Mao = 0.6-0.8, a = -4°-8° and β = 0°-6°, the total pressure recovery varies between 0.936 and 0. 961, the circular total pressure distortion coefficient varies between 1.4 % and 5.4 % and the synthesis distortion coefficient has a ranges from 3.8 % to 7.0 %. The experimental results confirm the excellent performance of the newly designed serpentine inlet incorporating VGs.

Flow patterns and boundary conditions for inlet and outlet conduits of large pump system with low head

The flow patterns in the inlet and outlet conduits have a decisive effect on the safe, stable, and highly efficient operation of the pump in a large pumping station with low head. The numerical simulation of three-dimensional （3D） turbulence flow in conduits is an important method to study the hydraulic performance and conduct an optimum hydraulic design for the conduits. With the analyses of the flow patterns in the inlet and outlet conduits, the boundary conditions of the numerical simulation for them can be determined. The main obtained conclusions are as follows： （i） Under normal operation conditions, there is essentially no pre-swirl flow at the impeller chamber inlet of an axial-flow pump system, based on which the boundary condition at the inlet conduit may be defined. （ii） The circulation at the guide vane outlet of an axial-flow pump system has a great effect on the hydraulic performance of the outlet conduit, and there is optimum circulation for the performance. Therefore, it is strongly suggested to design the guide vane according to the optimum circulation. （iii） The residual circulation at the guide vane outlet needs to be considered for the inlet boundary condition of the outlet conduit, and the value of the circulation may be measured in a specially designed test model.

Evaluation of flow behavior in copper electro-refining cell with different inlet arrangements

The arrangement of electrolyte inlet in the copper electro-refining(ER)cell has a great influence on the local flow field,which affects the distribution of electrical current density in consequence.In order to understand the complicated phenomena ofelectrolyte flow behavior in vertical counter electrodes in full-scale copper ER cell,the three-dimensional computational fluiddynamics(CFD)models with four different arrangements of electrolyte inlets,i.e.,single inlet(SI),central bottom inlets(CBI),topside interlaced inlets(TII),and bottom side interlaced inlets(BII),were established to simulate the flow behavior.Simulation resultshave revealed that the parallel injection devices help to improve the electrolyte velocity between electrodes,and while the relativerange of electrolyte velocity in CBI exceeds that of TII and BII,which is more than4times,indicating its severer unequal flowdistribution.Meanwhile,the average velocity of electrolyte in BII is4times larger than that of SI due to its higher turbulenceintensity.Generally,one of the efficient ways to supply fresh copper solution rapidly and uniformly into the inter-electrode space is toadapt the arrangement of BII.By utilizing such an arrangement,the electro-refining under high electrical current density is possible,and the productivity can be increased in sequence.

Weather induced subtidal flows through multiple inlets of an arctic microtidal lagoon

Estuarine processes in the arctic lagoons are among the least studied but important subjects, especially considering the rapid warming of arctic water which may change the length of ice-free period in the summer. In this paper, wind-driven exchange flows in the micro-tidal Elson Lagoon of northern Alaska with multiple inlets of contrasting widths and depths are studied with in situ observations, statistical analysis, numerical experiments, a regression model on the basis of dynamics, and remote sensing data. Water velocity profiles were obtained from a bottom deployed acoustic Doppler current profiler(ADCP) in the northwestern Eluitkak Pass connecting the Beaufort Sea to the Elson Lagoon during a 4.9 day ice-free period in the summer of 2013. The subtidal flow is found correlated with wind(R^2 value ～96%). Frequently occurring east, northeast and north winds from the arctic atmospheric high-and low-pressure systems push water from the Beaufort Sea into the lagoon through the wide inlets on the eastern side of the lagoon, resulting in an outward flow against the wind at the narrow northwestern inlet. The counter-wind flow is a result of an uneven wind forcing acting through the asymmetric inlets and depth,an effect of "torque" or vorticity. Under northwest wind, the exchange flow at the northwestern inlet reverses its direction, with inward flows through the upwind northwestern inlet and outward flows through the downwind eastern inlets. A regression model is established based on the momentum equations and Taylor series expansions. The model is used to predict flows in July and August of 2015 and July of 2017, supported by available Landsat satellite images. About 73%–80% of the time the flows at Eluitkak Pass are out of Elson Lagoon for the summer of 2015 and 2017. Numerical experiments are conducted to corroborate the findings and illustrate the effects under various wind conditions. A quasi-steady state balance between wind force and surface pressure gradient is confirmed.

Design and Numerical Simulation on Coupled Flow Field of Radial Turbine with Air-Inlet Volute

As one of the core components of turbocharger or micro-turbine, radial turbine has the features of small size and high rotation speed. In order to explore the design method and flow mechanism of the turbine with a volute, a centimeter-scale radial turbine with a vaneless air-inlet volute was designed and simulated numerically to investigate the characteristics of the coupled flow field. The results show that the wheel efficiency of single passage computation without the volute is 80.1%. After accounting for the factors of the loss caused by the volute and the interaction between each passage, the performance is more accurate according to the whole flow passage computation with the volute. High load region gathers at the mid-span and the efficiency declines to 76.6%. The performance of the volute whose structure angle of the trapezoid section is equal to 70 degree is better. Unlike uniform inlet condition in single passage, more appropriate inlet flow for the impeller is provided by the rectification effect of the volute in full passage calculation. Flow parameters are distributed more evenly along the blade span and are generally consistent between each passage at the outlet of the turbine.

ANALYTIC SOLUTIONS OF INCOMPRESSIBLE LAMINAR FLOW IN THE INLET REGION OF A PIPE

The laminar analytic solutions of velocities and pressure in the central zone of the inlet region of pipe flow are given under the condition of uniform inflow, based on the Navier-Stokes equations of incompressible viscous flow.

Experimental Investigation of Boundary Layer Characteristics on Blade Surface under Different Inlet Flow Conditions

In this paper, an experimental study is conducted on cascade boundary layer under different inlet conditions. New method is used to measure the total pressure in blade surface boundary layer directly using total pressure probe. Total pressure in both suction and pressure surfaces are acquired at different inlet conditions by changing incidence angle and inlet Mach number. In addition, a series of parameters related to boundary layer characteristics are calculated. The objective of the experiment is to investigate the influence of inlet flow conditions on them. The results indicate that influence of incidence angle is significant when other conditions are the same. Displacement thickness, momentum thickness as well as other parameters display some disciplines for variation. In contrast, inlet Mach number has only a small influence in that boundary layer becomes a litter thinner with increasing Mach number. Comparisons of experimental results with theoretical expectations demonstrate that the method in this experiment is effective and reliable.

Flow and Leakage Characteristics in Sealing Chamber of a Variable Geometry Hypersonic Inlet

When the variable geometry hypersonic inlet is sealed with ceramic wafers,the cavity flows inside the sealing chamber can be affected by the boundary layer near the side wall.To study the influence of the boundary layer thickness near the side wall on the flow and leakage characteristics in sealing chamber,the numerical calculation of the cavity flow in the sealing chamber under different inflow boundary layer thicknesses is carried out.The results show that three-dimensional cavity flow structures are close to being asymmetric,and the entrance pressure of the leakage path can also be affected by asymmetry;with the increase of the thickness of the boundary layer,the pressure at the cavity floor and the seal entrance decreases.Finally,the existing leakage prediction model is modified according to the distribution rule of the cavity floor and the flow properties in the leakage path.

The Numerical Simulation of Gas Turbine Inlet-Volute Flow Field

The structural and aerodynamic performance of the air inlet volute has an important influence on the performance of the gas turbine. On one hand, it requires the airflow flowing through inlet volute as even as possible, in order to reduce the pressure loss, to avoid a decrease in the effective output power and an increase of the fuel consumption rate of the internal combustion engine which indicate the inefficiency of the entire power unit;On the other hand, it requires the size of the inlet volute to be as small as possible in order to save mounting space and production costs. The thesis builds the structure model and develops flow fields numerical simulation of several different sizes of the inlet volutes. Further, the unreasonable aerodynamic structure is improved according to the flow field characteristics and thereby, a better aerodynamic performance of the inlet volute is obtained.

Orthogonal optimization of flow uniformity at exit section of elbow-inlet passages

Elbow-inlet passage is widely used in large drainage pumping stations.Flow uniformity at the exit section directly determines its hydraulic performance.Flow uniformity must be optimized to improve the operational efficiency of the large axial-flow pumping station.Modeling and numerical simulation methods were used to investigate the elbow-inlet passage,and the accuracy of the calculation results was verified.The key geometric parameters affecting the uniformity of the flow were optimized by the orthogonal experiment design.The optimal schemes were obtained and compared with the original scheme.The results show that flow uniformity V u after optimization is 95.41%,which is increased by 1.04%.The pumping station efficiency is increased by 1.89%,thereby confirming the applicability and accuracy of the proposed scheme,especially for the optimization of flow uniformity of the exit section of the elbow-inlet passage.

HYDRAULIC CALCULATION AND MEASUREMENT OF FLOW FIELD WITHIN INLET PASSAGE OF LARGE PUMPING STATION

By means of the analysis of the internal flow within inlet passage of large pumping sta-tion, an analysis of 3-D direct boundary element for the flow has been presented on the potentialflow assumption, and a calculation and an experimental proof for the inlet passage of 30 angle-type axial pumping station have been made. Based on the analysis of the calculations and theexperiments, the calculation method is feasible and believable.

进液量对气举式同向出流旋流器分离特性影响

为了提高旋流器的分离效率,提出一种气举式同向出流水力旋流器结构,通过注气的方式将旋流器轴心的油核举升至溢流口,加速油核向溢流口方向运动,进而提升旋流器的分离性能。基于雷诺应力模型(Reynolds Stress Model,RSM)与多相流模型(Mixture),模拟计算了入口进液量对气举式同向出流旋流器分离性能的影响,分析了进液量对旋流器内气核形态、速度场分布以及分离性能的影响规律。数值模拟结果表明:进液量分布在(3.6~8.4)m^(3)/h范围内时,随着进液量的增加,注气口处压力逐渐增大,混合液内各相介质的轴向速度与径向速度均有显著提高,旋流器轴心处的油相体积分数明显增大,旋流器的分离效率从64%增至77.9%。

侧式进/出水口各孔道流量分配差异及影响因素

对于抽水蓄能电站侧式进/出水口各孔道流量分配,现有设计规范规定进/出水口相邻中边孔道的流量不均匀程度不宜超过10%,但实际工程设计难以达到此要求.本文以某抽水蓄能电站侧式进/出水口为例,通过优化进/出水口各体型参数,利用数值模拟方法研究各孔道流量等水力参数,重点分析分流墩布置对各孔道流量分配的影响及其规律,试图使进流工况和出流工况相邻中边孔道的流量不均匀程度均最小.研究表明,改变扩散段分流墩布置能有效改善流量不均匀程度.对于3墩4孔侧式进/出水口,相邻中边孔道的流量不均匀程度在出流工况下随中边孔宽度比增大而增大,在进流工况下随中边孔宽度比增大而减小;当中边孔宽度比增大且中墩后移距离减小时,出流工况和进流工况下的流量不均匀程度均减小.对于2墩3孔侧式进/出水口,相邻中边孔道的流量不均匀程度不论在出流工况下还是在进流工况下,均随中边孔宽度比增大呈先减小后增大的规律.优化后的3墩4孔侧式进/出水口的中边孔宽度比取0.228∶0.272,中墩后移距离取0.36D(D为隧洞直径),其相邻中边孔道的流量不均匀程度均较优,在出流工况下为18.47%~19.43%,在进流工况下为19.82%~19.83%;优化后的2墩3孔侧式进/出水口的中边孔宽度比取0.310∶0.345,其相邻中边孔道的流量不均匀程度均较优,在出流工况下为19.47%~19.63%,在进流工况下为18.66%~18.67%.相邻中边孔道的流量不均匀程度较难满足不宜超过10%的设计规范要求.研究成果将有助于《抽水蓄能电站设计规范》中关于进/出水口水力指标要求的完善.

基于投影寻踪回归方法的微压过滤冲洗池水头损失与过滤效率预测模型

以微压过滤冲洗池的水头损失与过滤效率为考核指标,考虑进水流量、矿化度、含沙量与滤网孔径4个因素进行正交试验设计,采用投影寻踪回归方法PPR分析各个因素对考核指标的影响权重,选取20组试验数据建立含沙微咸水条件下微压过滤冲洗池水头损失和过滤效率的预测模型,探究了含沙微咸水对微压过滤冲洗池的水头损失和过滤效率的影响。研究结果表明,影响微压过滤冲洗池水头损失的因素由大到小依次为进水流量、含沙量、矿化度、滤网孔径;影响过滤效率的因素由大到小依次为含沙量、进水流量、矿化度、滤网孔径;构建的PPR预测模型的预测精度整体合格率达100%;当进水流量为6~7 m^(3)/h、含沙量为0.5~1.0 g/L、矿化度为0~2.0 g/L及滤网孔径为0.125~0.180 mm时,水头损失存在最小值;当进水流量为9~10 m^(3)/h、含沙量为1.75~2.00 g/L、矿化度为0~3.0 g/L及滤网孔径为0.125~0.150 mm时,过滤效率存在最大值。物理模型的试验结果可为微压过滤冲洗池的实际应用提供研究基础。

混合式抽水蓄能电站对下泄水温影响的数值模拟研究

【目的】混合式抽水蓄能电站运行特性与常规电站相比存在差异,本文旨在掌握抽水蓄能电站水温的变化规律,为水库管理调度提供参考。【方法】以紧水滩水库为研究对象,采用MIKE3水温模型模拟不同进/出水口高程以及不同抽水流量工况的下泄水温,据此探讨混合式抽水蓄能电站对下泄水温的影响。【结果】抽蓄水流会对下泄水温产生影响,相对于现状无抽水工况的下泄水温,抽蓄工况下的下泄水温基本表现为5—9月略有下降,其余月份略有升高,下泄水温的最大降幅不超过0.7℃,最大升幅不超过0.8℃。【结论】进/出水口高程对于下泄水温影响较大,且高程越低,下泄水温差异越大。然而抽水流量对于下泄水温差异影响并不显著,但整体上也呈现出随着抽水流量增加,水温差异增大的趋势。

侧式进 出水口顶板扩张角对拦污栅断面流速分布影响规律研究

抽水蓄能电站侧式进出水口双向过流,其顶板扩张角的大小将直接影响拦污栅断面流速分布是否均匀,甚至出现反向流速。抽水蓄能电站设计规范将3°~5°作为侧式进出水口顶板扩张角的推荐范围,其依据是矩形渐扩管阻力系数最小的扩张角度,但侧式进出水口体型较之复杂很多,因此有必要进一步探讨。本文以某侧式进出水口体型为研究对象,采用数值模拟方法,研究了11种角度的顶板扩张角对出流工况和进流工况拦污栅断面流速分布的影响。结果表明:在出流工况下,随着顶板扩张角的增大,中孔拦污栅断面的主流位置由居中部逐渐向底部降低,断面流速分布由上下基本对称趋于底部大上部小的上下不对称,当顶板扩张角较大时中孔拦污栅断面上部出现反向流速;随着顶板扩张角的增大,边孔拦污栅断面流速分布由基本均匀逐渐变为底部大上部小的不均匀分布;随着顶板扩张角的增大,中、边孔孔口流速不均匀系数均逐渐增大,但中孔拦污栅断面流速分布受顶板扩张角影响更大。在进流工况下,随着顶板扩张角的增大,中、边孔拦污栅断面流速分布及孔口流速不均匀系数均无明显影响。研究成果可为优化侧式进出水口设计提供指导。

基于夹点的带喷射器CO_(2)热泵系统性能分析

为了研究带喷射器的跨临界CO_(2)内部过冷热泵系统(TCISE),基于夹点建立了TCISE的热力学模型,分析了冷却水进出水温度及流量对系统性能的影响。研究表明:冷却水进水温度从25℃降低到15℃时,最优高压压力从9.3 MPa降至8.8 MPa,降低了5.4%,最大COP从3.83提升至4.27,提高了11.49%;TCISE存在临界冷却水出水温度和临界冷却水质量流量,当冷却水进水温度一定时,在出水温度低于临界出水温度或质量流量高于临界质量流量时,系统COP保持不变。

渗漏入口大小及形状对拟流场法渗漏探测的影响研究

为深入研究渗漏入口大小及形状对拟流场法渗漏探测的影响规律,通过构建堤坝渗漏数值模型,模拟了拟流场法在实际工程中的探测情况。研究了水库拟流场的基本分布特征,揭示了不同大小及形状的渗漏入口附近的电流密度分布规律,并提出了不同大小及形状的渗漏入口在平行于坝轴线和平行于坝面垂直于坝轴线两个方向上拟流场影响范围及电流密度峰值的经验公式。结果表明:线状渗漏入口的电流密度比相同面积圆形渗漏入口的电流密度小,且线状渗漏入口短边影响范围比相同长度的圆形渗漏入口大,长边影响范围比相同长度的圆形渗漏入口小。研究揭示了渗漏入口大小及形状对测线上电流密度分布的影响规律,可为实际工程探测中利用测线上的电流密度分布情况判断渗漏入口大小与形状提供依据。