Computational studies of flow through cross flow fans - effect of blade geometry

Introduction Cross Flow Fan (CFF) is a turbomachine, which operates fundamentally in a different way compared to axial or centrifugal type of machines. Flow enters the full width of impeller through one sector and leaves through another sector. The flow structure inside the impeller can be divided into two regions: (a) eccentric vortex or recirculation region having closed streamlines (b) through flow region consisting of inflow and outflow of the fluid. The main components of CFF are imp…     

Investigation of the influence of various numbers of impeller blades on internal flow field analysis and the pressure pulsation of an axial pump based on transient flow behavior

In the current study, the flow behavior in an axial pump through changing the number of impeller blades is analyzed. Due to the number of blades being very important geometrical parameters in the pump, the study of the influence of various numbers of blades on flow and pressure pulsation in the pump is carried out using the computational fluid dynamics technique. The sliding mesh with the standard turbulence k‐ε model is used to investigate the unsteady flow with several flows and impeller blades. Pump performance prediction results with available experimental data indicate reasonable and good agreement with each other. Static pressure, shear stress, and different velocity compounds are qualitatively analyzed. Moreover, the fluctuation pressure and average pressure under different operating conditions and impeller blades are quantitatively investigated. The numerical results show that the impeller blade has a high impact on pressure, shear stress, magnitude velocity, axial velocity, radial velocity, tangential velocity, and average pressure. Furthermore, this numerical study provides good and useful information for the hydraulic design of axial pumps.     

Investigations on the flow field in an unshrouded pump impeller geometry

Transient CFD simulations are performed to investigate the flow behaviour inside an unshrouded pump using the SAS method. Two blade designs are compared at two different tip clearances and the results are validated by measurements. The detected vortex structure is visualized by the normalized helicity, further discussed regarding its development and behaviour and finally implicated to the efficiency of the two different blade designs.     

Experimental Investigation of the Internal Flow Field of Rotating Impeller Passage with Inlet Box

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Experimental Investigations of the Three—Dimensional Flow in a Large Deflection Turbine Cascade with Tip Clearance

INTRoDUCTI0NThetipleakaeflowisnowrecognizedasanimpor-tantsourceoflossesinbothcompressorsandturbines,asasourceofcoolingprobleminturbinesandasourceofinstabilityincomPressorsandfans.Manyturbo-maChinimPellersarenotshroudedandtheleakaeflowthroughthetipgaPofthebladeisanunavoidablefaCtorwhichdeterioratestheperformance.Den-tonandCumpsty[1]melltionedabouttwodistinctandequallyimportantaspects.tothetipclearanceflows.First,thereisareducti0ninthebladeforce,there-fore,theworkdone.Thisoccursbecausethe…     

Effect of the uneven circumferential blade space on the performance of small axial flow fan

Effects of the uneven circumferential blade space on static characteristics and aerodynamic noise of a small axial flow fan are studied in this work.The blade angle modulation is adopted to design a series of unequally spaced fans,which have different maximum of modulation angular displacement.The steady flow is simulated by the calculations of Navier-Stokes equations coupled with RNG k-epsilon turbulence model,while the unsteady flow is computed with large eddy simulation.According to theoretical analysis,a fan with a maximum of modulation angular displacement of 6° is regarded as the optimal unequally spaced fan.The experiment of static characteristic is carried out in a standard wind tunnel and the aerodynamic noise of both fans is tested in a semi-anechoic room.Then,performances of the optimal unequally spaced fan are compared with those of the prototype fan.The results show that there is reasonable agreement between the simulation results and the experimental data.It is found that the discrete noise of the optimal unequally spaced fan is lower than that of the prototype fan at the near field monitoring point.This can be explained that the total pressure fluctuation of the optimal unequally spaced fan is much more regular than that of the prototype fan.     

涡轮叶片气动性能影响因素的实验与数值研究

本文利用实验与数值模拟的方法研究航空发动机涡轮叶栅在改变节距时,其总压损失、出口气流角及叶栅表面静压系数的变化。通过实验和数值计算的结果对比,验证了数值计算的准确性。数值模拟结果显示：相对节距t在0．5—1．0范围内变化,叶栅的总压损失在t=0．9时达最小;叶栅人口攻角从-10°逐渐增加至＋10°时,总压损失呈现递增的趋势;随着相对节距每增加0．1,气流出口角相应增加大约2°;随着叶栅相对节距的增加,附面层增厚、脱离,叶型损失增大。     

Effect of inlet box on performance of axial flow fans

Numerical investigations on 3D flow fields in an axial flow fan with and without an inlet box have been extensively conducted, focusing on the variation of fan performance caused by the internal flow fields and the velocity evenness at the exit of the inlet box. It is interesting to find that although the inlet box is well designed in accordance with basic design principles, there is a flow separation region in it. Furthermore, this flow separation and the resulting uneven velocity distribution at the exit lead to some decrease in the efficiency and an increase in the total pressure rise of the fan. This research shows that the inlet box needs further improvement and such a check on the flow fields is of value for the design of inlet boxes. __________ Translated from Journal of Engineering Thermophysics, 2007, 28 (Suppl.1): 161–164 [译自: 工程热物理学报]     

分流叶片周向位置设计及其对离心叶轮内部流动的影响

利用计算流体力学软件,对某高压比、高转速、小流量离心式压气机的半开式叶轮内部三维粘性流场进行了数值模拟研究。重点分析了分流叶片周向位置对叶轮内部流动和性能的影响,提出了适合此半开式离心叶轮分流叶片周向位置的设计方案。结果表明：分流叶片不同周向位置对流场影响明显,当分流叶片偏向长叶片吸力面侧时,叶轮流道内低速区增大,流动分布不均匀。研究还发现：固定分流叶片进口而将出口位置向长叶片压力面侧偏置,可以改善叶轮内部流动情况,提高叶轮性能。     

Numerical analysis of the tip leakage flow field in a transonic axial compressor with circumferential casing treatment

This paper reports on numerical investigations aimed at understanding the influence of
circumferential casing grooves on the tip leakage flow and its resulting vortical structures.The results
and conclusions are based on steady state 3D numerical simulations of the well-known transonic axial
compressor NASA Rotor 37 near stall operating conditions.The calculations carried out on the casing
treatment configuration reveal an important modification of the vortex topology at the rotor tip
clearance.Circumferential grooves limit the expansion of the tip leakage vortex in the direction
perpendicular to the blade chord,but generate a set of secondary tip leakage vortices due to the
interaction with the leakage mass flow.Finally,a deeper investigation of the tip leakage flow is
proposed.     

Effects of probe support on the flow field of a low-speed axial compressor

This paper presents an investigation on the effect of probe support on the flow field of an axial compressor.The experiment is carried out in a large-scale low-speed research compressor.A cylindrical probe support intruding to 50% blade span was installed at 50% chord upstream from the rotor leading edge.The region from 5° to 32° off the probe support in the direction of rotation at the rotor outlet was measured with a 5-hole probe and a high-response total pressure probe.The experiment is performed at both near-design and near-stall points.The measuring results of 5-hole probe and high-response total pressure probe indicate that the probe blockage effect is different at different blade spans.The wake of the probe support weakens the leakage vortex intensity at the tip region,leading to greater total pressure rise.At near-design condition,the presence of probe support has a negative effect on the region from 75% to 92% span,while improves the flow field below 75% span.At near stall condition,the probe support has a negative effect on the region from 70% to 90% span,and almost has no influence on the flow field below 70% span.     

The effect of global cross flows on the flow field and local heat transfer performance of miniature centrifugal fans

Centrifugal fans are often integrated into thermal management solutions for a range of applications. Consequently, centrifugal fan designs can be subjected to varying environmental conditions, many of which can alter fan performance characteristics and ultimately influence the heat transfer performance of the cooling solution. Global cross flows are a commonly encountered practical operating condition, particularly in the cooling of electronics. Air-cooled electronic enclosures often incorporate miniature centrifugal fans to maintain reliable component operating temperatures at a local level, while larger system level fans are used to simultaneously control the ambient temperature within the enclosure. This type of operating condition has been investigated by introducing a uniform crossing air flow above a centrifugal fan inlet. Two scaled miniature centrifugal fan designs were selected to fundamentally assess the influence on local velocity field and heat transfer performance. This was achieved experimentally using Particle Image Velocimetry, and a combined infrared and heated-thin-foil technique developed for the accurate measurement of local heat transfer coefficients. the introduction of a crossing air flow above the fan inlet indirectly reduced both the local and global thermal performance of the centrifugal fan, and the resultant distorted inflow shifted the surface heat transfer distribution at the fan outlet from an axisymmetric to asymmetric profile. However, strategic positioning of components relative to a centrifugal fan can maintain the average component heat transfer coefficient at a similar level to a case without any cross flow. Results also indicate issues associated with the implementation of miniature centrifugal fan designs into crossing air flow environments, with reductions in thermal performance of over 30% observed.     

Investigation of flow dynamics and decrease of vortex noise inside volute of centrifugal fans

The characteristics of three-dimension flow dynamics inside the volute of a G4-73No.8D centrifugal fan was simulated numerically using a computational fluid dynamics(CFD) technique. The generation, evolution, and noise of the vortex were investigated when cylinder-shaped and cone-cylinder-shaped anti-vortex rings were added separately. Numerical results showed that large-scale vortices were broken effectively and the flow fields inside the fan were more uniform with the two anti-vortex rings installed. Experimental results indicated A-sound level and spectrum noise of the refitted fan decreased and the two anti-vortex rings were effective in decreasing vortex noise. The cone-cylinder-shaped anti-vortex ring was more effective than the cylinder-shaped one in breaking large-scale vortexes and decreasing vortex noise. __________ Translated from Proceedings of the CSEE, 2006, 26(17): 117–121 [译自: 中国电机工程学报]     

Effect of wavy plate geometry configurations on the temperature and flow distributions

As fluid flowing through the wavy plate, breaking and destabilizing in the thermal boundary layer are induced. In the present study, the numerical investigation on the heat transfer and flow distributions in the channel with various geometry configuration wavy plates under constant heat flux conditions is considered. A finite volume method with the structured uniform grid system is used to solve the turbulent model. Effects of geometry configuration of wavy plates, wavy plate arrangements, and air flow rates on the temperature and flow developments are considered. The sharp edge of wavy plate has a significant effect on the flow structure and heat transfer enhancement. The results of this study are expected to lead to guidelines that will allow the selected wavy plate geometry configuration for designing heat exchanger which increase thermal performance.     

船用内旁通流道的压损特性研究

对某船用汽轮机内旁通流道特性试验进行了数值计算分析：基于可压缩N-S方程,利用Spalart-Allmaras湍流模式及有限积分法,采用四面体非结构性网格,对内旁通流道进行了数值模拟.预测了内旁通流道不同开度及旁通流道不同入口Ma的全压损失系数,计算结果与试验结果吻合良好.通过数值计算,得到了对内旁通流道广泛适用的计算方法,为慢速机组内旁通流道及旁通阀的设计和性能分析提供了重要依据.     

电站锅炉过热器和再热器T型三通对集箱静压分布影响的试验研究

为了获得过热器和再热器T型三通对集箱静压分布及三通两侧分流比对涡流区和集箱静压分布的影响规律,以空气为工质对纯三通模型进行流动特性试验.研究结果表明:带三通集箱静压分布受一次涡流和二次涡流的共同影响,一次涡流影响范围为-2.5D~2.5D(D为等径三通内径),二次涡流影响范围为-1.5D~1.5D;三通两侧分流比对涡流区范围影响较小;随着三通某侧流量增大,该侧静压降低,但静压分布规律无明显变化.在一次涡流影响范围内,正母线和右下40°线的静压差异受分流比的变化影响较小;侧母线的静压差异随分流比的增大而有所增大.     

On the pressure drop and the velocity distribution in the cylindrical vortex chamber with two inlet pipes for the control of vortex flow

Vortex flow is applied to a cyclone dust collector, a vortex combustion chamber, and a vortex diode for vortex control. In order to apply the vortex flow to the industries, it is necessary to keep the stable flow condition and to estimate the response time of the transient flow process and also the intensity of the vortex flow. For control vortex flow, two types of vortex chamber with two inlet pipes were designed. One of them is to promote the vortex flow named as Co-Rotating Flow System and another one is to hinder the vortex flow named as Counter-Rotating Flow System. The pressure drops and the velocity distributions were measured for these vortex chambers. The estimation of the tangential velocity by the application of the angular momentum flux is compared with the measured velocity by a cylindrical Pitot-tube. The characteristics of the total pressure drop could be explained by introducing the circulation.     

Effect of nozzle geometry on the flow characteristics of spiral flow generated through an annular slit

In comparison with previous researches of swirling flow,spiral flow generated in the spiral nozzle has some differentflow characteristics.It does not need a forced tangential momentum to generate its velocity and has some differentmerits from the swirling flow such as long potential core and low tangential velocity.In this study,the effect of noz-zle geometry on the flow characteristics in spiral nozzle was investigated by experiment and computation.As a result,the flow characteristics obtained by experiment has a satisfactory agreement with computational results,quantita-tively and qualitatively.     

几何结构对贫油直喷燃烧室流场特性影响的研究

基于现有单点贫油直喷燃烧室,采用数值模拟方法研究了头部几何角度对燃烧室流场特性的影响。分别对比了冷态与燃烧态条件下不同头部几何角对燃烧室轴向速度分布、燃烧效率、总压损失等特性的影响。研究表明:在所研究的几何角度范围内,冷态下头部几何角度对回流区的长度影响很小,对回流区内轴向速度分布具有较大影响。燃烧态下随着头部几何角度的增加,回流区轴向尺寸逐渐增加,中轴线上轴向速度值逐渐降低。燃烧室的出口平均温度、燃烧效率、总压恢复系数基本保持不变,60°结构产生的NO_x生成量最低,30°结构产生的NO_x生成量最高。     

Effect of Non-Equilibrium Condensation of Moist Air on Flow Field in Ludwieg Tube

The time-dependent behavior of non-equilibrium condensation of moist air through a Ludwieg tube with a diaphragm downstream is investigated by using a computational fluid dynamics work. The two-dimensional, compressible, Navier-Stokes equations, fully coupled with the condensate droplet growth equations, are numerically solved by a third-order MUSCL type TVD finite-difference scheme with a second-order fractional time step. Baldwin-Lomax turbulence model is employed to close the governing equations. The present computations represent the experimental flows well. The results obtained show that for an initial relative humidity over 40 %, the periodic excursions of the condensation shock occurs in the Ludwieg tube, and the frequency increases with the initial relative humidity. It is also found that total pressure loss due to non-equilibrium condensation in the Ludwieg tube should not be ignored even for a very low initial relative humidity. Furthermore, the variations of condensation properties are also di