回流区分级着火旋流煤粉燃烧器的试验研制

在分析回流区分级着火旋流煤粉燃烧器工作原理的基础上,进行了冷模实验研究,根据研究的结果对黄石发电厂５号炉旋流煤粉燃烧器进行了改造,运行试验结果表明,这种新型燃烧器对低挥发份煤具有较好物稳燃性能。     

Experimental investigation of propeller type swirl generator for a circular pipe flow

The objective of this paper is to introduce the subject of heat transfer augmentation by inserting a propeller type swirl generator in a circular pipe. The propeller type swirl generator creates a flow pattern which is like a decaying swirl flow. This flow pattern is observed for laminar flow. The main advantage of this type of swirl generator is that it is easy to install the device into a circular pipe. Average and local Nusselt numbers were calculated by the method explained in detail in the main text. Comparison of the local Nusselt numbers for swirl flow considered in this study and local Nusselt numbers for flow in a smooth pipe revealed that the local Nusselt number increases substantially when the swirl generator is used. The swirl related heat transfer enhancement becomes stronger as Reynolds number increases.     

涡流管非稳态旋流流场数值模拟研究

旋流主导着涡流管的内部流动,在有旋流的设备当中,高强度旋流由于涡旋破碎诱导产生的位于中央回流面附近的进动涡核被认为是旋流中的一种拟序结构,可以在一个峰值频率下偏离管道中心并绕着轴线做周期性运动,这种流动结构的产生对旋流本身产生了极大的影响。采用非定常求解模式计算三维涡流管内的内部流场,雷诺应力模型用于封闭Navier-Stokes输运方程,在FLUENT 15.0中数值模拟计算涡流管的内部旋流。结果显示了涡流管瞬态旋流速度场中的周期性振荡,以及非对称大尺度涡结构。     

Investigations on an Axial Flow Fan Stage subjected to Circumferential Inlet Flow Distortion and Swirl

INTRODUCTIONInletfiowdistortionisatermusedtodenotethewriationofflowpropertiesasafunctionofthespa-tialcoordinatesandtime.Thenonuniformityoc-cursinconunonflowpropertiessuchastotalpressure,staticpressure'velocity,temperature,flowangleandgasconstituency.Swirlisthetermusedtodescribetherotationoffiowinrelationtotherotationoftheforor.Swirlmaybegeneratedasaconsequenceofsec-ondaryflowsinducedduetoflowcurvaturesorduetothepresenceofInletGuideVanes(IGV).DistortionandSwirl(inducedduetocurvatureoffl…     

不同冷气/燃气温比下高温涡轮叶片旋流冷却流固耦合特性研究

采用流固耦合方法对燃气轮机高温涡轮叶片旋流冷却结构进行数值模拟分析。探究了不同冷气/燃气温度比条件下旋流冷却的流动与传热特性、叶片前缘区域固体温度、热应力以及热应变分布。研究表明：在进气腔入口雷诺数固定的条件下,随着温度比升高,冷气密度降低,冷气流速逐渐提升,同时湍动能升高,靶面努塞尔数逐渐升高;当温度比较低时冷气的流速较低、单位时间冷气带走的热量较少,当温度比较高时冷气温度较高、单位质量冷气所能吸收的热量有限,靶面处热流密度先升高后降低。受靶面热流密度分布影响,随着温度比升高,叶片前缘固体的温度、热应力以及热应变先降低后升高。     

A study on the effects of the intake port configurations on the swirl flow generated in a small D.I. diesel engine

This paper investigates the effect of intake port configuration on the swirl that is generated within a direct injec- tion （D.I.） diesel engine. The in-cylinder flow characteristics are known to have significant effects on fuel-air mixing, combustion, and emissions. To clarify how to intensify the swirl flow, a swirl control valve （SCV） and a bypass were selected as design parameters for enhancing the swirl flow. The optimal intake port shape was also chosen as a parameter needed to efficiently generate a high swirl ratio. The results revealed that a key factor in generating a high swirl ratio was to control the intake airflow direction passing through the intake valve seat. Further, the swirl intensity was influenced by changing the distance between the helical and tangential ports, and the swirl flow was changed by the presence of a bypass near the intake valve seat. Additionally, the effect of in- take port geometry on the in-cylinder flow field was investigated by using a laser sheet visualization method. The experimental results showed a correlation of swirl ratio and mass flow rate. In addition, we found that employing the bypass was an effective method to increase swirl ratio without sacrificing mass flow rate.     

Hydrodynamics and mass transfer in decaying annular swirl flow

This paper reports an electrochemical study of local mass transfer behaviour in decaying annular swirl flow. Initially, flow visualisation experiments were conducted to observe the general behaviour of the flow. It was found that the swirl angle decays exponentially along the tube. Measurements of pressure drop across the vaned swirl generators were correlated in terms of the inverse of the square of the tangent of the vane angle and approximately the square of the mean fluid velocity for vane angles of 30° and over. Measurements of the axial distribution of local mass transfer coefficient for the inner rod were carried out using the electrochemical limiting diffusion current technique and results were correlated for each swirl generator, in the Reynolds number range 3300–50000. It was found that the relative enhancement of mass transfer in swirl flow increases as the vane angle increases and Reynolds number decreases.     

Modelling of heat transfer and fluid flow for decaying swirl flow in a circular pipe

In the present study, a propeller type swirl generator was developed, and its effects on heat transfer and fluid flow were investigated numerically and experimentally for air flow in a pipe. In the numerical study, for axisymetrically, incompressible turbulent swirl flows, the Navier-Stokes equations were solved using the k-ε turbulent model. So that a computer program in Fortran was constructed using the SIMPLEC Algorithm. In experimental work, axial and tangential velocity distributions behind the swirl generator were measured by using hot-wire anemometry. Experimental and numerical axial and tangential velocity distributions along the pipe were compared, and good agreement was found. Axial velocity profile showed a decrement in the central portion of the pipe and an increased axial velocity was seen in near the wall. Tangential velocity profiles had a maximum value and its location moved in radially with distance. The effects of swirl flow on the heat transfer and pressure drop were also investigated experimentally.     

Flame characteristics of hydrogen-enriched methane–air premixed swirling flames

The effect of hydrogen addition in methane–air premixed flames has been examined from a swirl-stabilized combustor under unconfined flame conditions. Different swirlers have been examined to investigate the effect of swirl intensity on enriching methane–air flame with hydrogen in a laboratory-scale premixed combustor operated at 5.81 kW. The hydrogen-enriched methane fuel and air were mixed in a pre-mixer and introduced into the burner having swirlers of different swirl vane angles that provided different swirl strengths. The combustion characteristics of hydrogen-enriched methane–air flames at fixed thermal load but different swirl strengths were examined using particle image velocimetry (PIV), OH chemiluminescence, gas analyzers, and micro-thermocouple diagnostics to provide information on flow field, combustion generated OH radical and gas species concentration, and temperature distribution, respectively. The results show that higher combustibility of hydrogen assists to promote faster chemical reaction, raises temperature in the reaction zone and reduces the recirculation flow in the reaction zone. The upstream of flame region is more dependent on the swirl strength than the effect of hydrogen addition to methane fuel. At lower swirl strength condition the NO concentration in the reaction zone reduces with increase in hydrogen content in the fuel mixture. Higher combustibility of hydrogen accelerates the flow to reduce the residence time of hot product gases in the high temperature reaction zone. At higher swirl strength the NO concentration increases with increase in hydrogen content in the fuel mixture. The effect of dynamic expansion of the gases with hydrogen addition appears to be more dominant to reduce the recirculation of relatively cooler gases into the reaction zone. NO concentration also increases with decrease in the swirl strength.     

Flow development through HP &; LP turbines,Part I: Inward rotating cavity flow with superimposed throughflow

With the aid of numerical method,both flow field and its accompanied loss mechanism within the rotating cavity are investigated in detail in the 1st part of the two parts paper.For ease of comparison,rotating cavity is further classified as the rotor-stator cavity case and the rotor-rotor cavity case.Results indicate that flow within both kinds of the cavity act as the inviscid flow except that the flow near walls,neighboring the lower G region and in the vicinity of the rotating orifices.In the regions except such inviscid-flow-dominate domains,the theoretical core rotation factor can be safely used to predict the swirl ratio within the cavity.When detailed flow pattern is considered,Ekman-type flow exists near periphery of the surface's boundary layer where viscous effect is non-negligible.However,due to the complex profile of the simulated cavity case,vortices structure is varied within the cavity.By comparison,swirl ratio can be used to predict the magnitude of loss.Due to the relatively evident rotating effects of the rotor-rotor cavity,swirl ratio even increases to 1.4 in the current model,which means that flow is moving faster than the surrounding disc.Further investigation finds that this kind of highly rotating flow is accompanied with serious undesirable pressure loss.Parenthetically,unlike its counterpart,swirl ratio above 1.0 doesn't happen when fluid passes through the rotor-stator cavity.So it is suggested that rotor-rotor flow cavity with the superimposed inward throughflow should be avoided in the engine design or certain measurements should be provided when such structure design is unavoidable.Simulation done in the current paper is meaningful since these dimensional parameters are typical in the design of state-of-art.Relatively lower range of Reφ and Cw is not considered in the current two parts paper.     

CFD insight of the flow dynamics in a novel swirler for gas turbine combustors

We describe the flow dynamics inside a novel swirler conceptualized for gas turbine combustors. The supreme advantage in this swirler is the ability to vary the swirl number for the same value of Reynolds number. The significance of such advantage against contemporary configurations, which have constant swirl number, is quite evident at low turbine operating loads. The novel geometry and flow pattern are described in details in the present work. The results of four numerical simulations are presented and discussed to study the central recirculation zone, turbulence intensity, and pressure drop at different swirl numbers. The new concept is deemed to enhance the combustion efficiency because of its ability to adjust the swirl number according to the turbine operating load. The current study reports preliminary results which verify the concept behind the proposed swirler. However, intensive numerical and experimental studies are necessary to be carried out in order to characterize the flow dynamics produced by the novel swirler and its impact on the combustion process.     

Numerical study on the effect of jet spacing on the Swirl flow and heat transfer in the turbine airfoil leading edge region

ABSTRACT

In this paper, flow and heat transfer of a swirl chamber that models an internal cooling passage for a gas turbine airfoil leading edge is studied with numerical simulation. The geometry consists of a circular pipe, and rectangular section inlets that lead inlet flow to impinge tangentially on the circular pipe. The effects of the ratio of jet spacing to swirl chamber radius and Reynolds numbers on swirl cooling performance are investigated. The results indicate how the pressure loss and globally averaged Nusselt number on the swirl chamber wall increase with increases of Reynolds number and the ratio of jet spacing to swirl chamber radius. A Nusselt number correlation on these parameters is suggested. Also shown is how Nusselt numbers on the swirl chamber surface increase with the ratio of jet spacing to swirl chamber radius.     

柴油机变通道涡流室式燃烧室的研究

本文提出了一种柴油机新型涡流室式燃烧室——变通道涡流室式燃烧室.研究结果表明,这种燃烧室由于减少了通道流动损失并加速了主燃烧室的放热速率,在柴油机宽广的运行范围内,其热效率比原涡流室式燃烧室大大提高,而排温、烟度和噪声也有较大改善.它兼有直喷式和涡流室式柴油机燃烧方式的优点,是一种高效率的涡流室式燃烧室.     

Effect of Non-Newtonian Viscosity for Surfactant Solutions on Vortex Characteristics in a Swirling Pipe Flow

Effects of non-Newtonian viscosity for surfactant solution on the vortex characteristics and drag-reducing rate in a swirling pipe flow are investigated by pressure drop measurements, velocity profile measurements and viscosity measurements. Non-Newtonian viscosity is represented by power-law model (T = kD n). Surfactant solution used has shear-thinning viscosity with n < 1.0. The swirling flow in this study has decay of swirl and vortex-type change from Rankin's combined vortex to forced vortex. It is shown that the effect of shear-thinning viscosity on the decay of swirl intensity is different by vortex category and the critical swirl number with the vortex-type change depends on shear-thinning viscosity.     

Effects of coupling between electrodynamics and gasdynamics in open cycle disk type MHD generators

To study the effects of swirl and wake on open cycle disk generators operated with a heavy oil-air combustion gas, the effects of coupling between electric field and gas flow are analyzed. A three-dimensional potential equation and two-dimensional compressible flow equations are solved by a finite element method. Both velocity and thermal wakes induce large nonuniformities of potential distribution and degrade the generator performance. This is mainly due to the strong coupling between potential and temperature distributions. The velocity nonunivormity affects performance through thermal interaction. It is predicted that the electrical efficiency can reach 75% in large scale disks. Regular fluid nonuniformities given by sinusoidal waves cause a relatively small degradation of generator performance.     

Decaying swirl flow in round tubes with short-length twisted tapes

This paper presents experimental and numerical results of the local heat transfer coefficient and flow characteristics of decaying turbulent swirl flow generated by short-length twisted tapes (STs). The STs with three different twist ratios (y/W = 3, 4 and 5) were applied at the entrance of the test section. The experiments were conducted under uniform heat flux conditions for water flow rates in the range of 5200 ≤ Re ≤ 15,300. The results of the tube without swirl generator as well as the ones with full-length twisted tape (TTs) are also reported as the reference cases. The experimental results reveal that the tube with STs consistently yields higher local Nusselt number than that the one without swirl generator. The local Nusselt numbers decrease with increasing axial distance (x/D) due to the decaying effect. Although, STs consistently provide poorer heat transfer than TTs over the range studied, the STs with y/W = 4 and 5 yield superior thermal performance factors to the TTs at the same twist ratios, for Reynolds numbers beyond 10,000 due to the prominent effect of heat transfer improvement over that of the increase of friction factor. For better understanding, the visualization of flow structure (pathline and vector plot) in the tubes with STs is also presented.     

An Investigation of the Swirling Flow and Heat Transfer in a Duct

This paper presents the results of experiments and numerical simulation of the turbulent swirling flow and heattransfer in a duct.The calculated results are in good agreement with data obtained by measurements.It isfound that the swirling flow promotes heat transfer to the wall of the duct;the swirl numbers are dependentupon the vane exit angles of the swirler,distance from the swirler and the duct Reynolds number.But the decayof swirling flow in streamwise direction is related to local Reynolds numbers and is independent of the swirlerexit angle.The swirl flow characteristics presented in this paper may be used for engineering purposes.     

Numerical analysis of turbulent swirling decay pipe flow

Turbulent swirling decay pipe flow has been investigated numerically in a vertical straight fixed pipe. The swirling flow is created by means of a rotating honeycomb which produces the solid body rotation at the inlet of the fixed pipe. Since there are no experimental data at the inlet of the fixed pipe; different axi-symmetric approaches may be considered to model the honeycomb effects at the downstream flow. Considering the appropriate approach and using the resulting flow field properties from the exit of the modeled swirl generator which are applied as the inlet boundary condition for the fixed pipe, several high Reynolds turbulence models are used to predict this type of the swirling flow. For wall treatments, both the standard wall function and the two-layer zone model are used. The comparison between the numerical and the existing experimental results shows that the RSM with two-layer zone model is generally more powerful than the others. Results show that the two-equation models with different near wall approaches are fairly well to predict the swirling flow in solid body rotation regions, but they fail to predict the pressure distribution along the pipe wall. Regarding the swirl intensity decay rate, irrespective of the inlet swirl type, the obtained decay rates from computations are in good agreement with the existing experimental results.     

Experimental investigation of decaying swirl flow through a circular pipe for binary combination of vortex generators

Heat transfer and pressure drop characteristics of a decaying swirl flow in a horizontal pipe are investigated experimentally. The decaying swirl flow is produced by the insertion of vortex generators with propeller-type geometry, a kind of passive heat enhancement tools. Two different cases are comparatively examined: one-propeller case and two-propeller case. In the one-propeller case, the first propeller is placed at the entrance of the flow. In the two-propeller case, the second is placed at a specific distance where the swirl effect generated by the first propeller is decayed. The focus of the study is concentrated on comparatively examining the usage of one or two propeller-type swirl generators on the friction factor and heat transfer. For both cases, the effects of the joint angle about the core of the insert device and the number of the joint vanes attached circumferentially to the device on heat transfer and pressure drop are also investigated. Experiments are conducted at Reynolds numbers ranging from 5000 to 30,000. For validation, experimental data obtained for the smooth pipe are compared with those available in the literature.     

Lagrangian characterization of multi-phase turbulent flow in a solar reactor for particle deposition prediction

Solar cracking of methane is a promising technology for emission free hydrogen production. One of the major problems affecting methane cracking solar reactors' performance is the carbon particle deposition on the window, walls, and at the exit. In present study, a Lagrangian particle dispersion model has been implemented for predicting the particle deposition on the window of a seeded solar thermal reactor. A three-dimensional Computational Fluid Dynamics (CFD) analysis using Discrete Phase Model (DPM) has been done for qualitative validation of the experimental observations. In order to evaluate the turbulent quantities in the solar reactor; RNG k–? model has been applied. Species transport has been solved by taking the gas for window screening as different from that used in the main flow. In addition, this paper presents a thorough parametric study predicting the particle deposition on reactor window for various flow configurations and flow conditions, which can be summarized as; (1) when the inlet flow angle is smaller, higher tangential velocities or swirl strength is obtained, (2) higher tangential velocities help in maintaining a stronger swirl, which keeps the screening flow close to the reactor window, (3) by increasing the main flow and the screening flow rates, the particle deposition on window is reduced, (4) when a lower density fluid is used as window screening gas, the particle deposition is reduced because the Taylor instabilities are avoided. The CFD work and the findings presented in this paper would be used as a guide in designing a solar reactor or improving the configuration of existing reactor.