超声速气流中雾化燃料喷射的三维数值研究

首次用双流体模型对雾化燃料在扩张形超燃室中沿九喷嘴顺流喷射的混合问题进行了数值研究。气相用迎风 TVD格式求解三维全 Navier- Stokes方程 ,液相用预估、校正 NND格式求解三维 Euler方程。相间相互作用的常微分方程用预估、校正Runge- Kutta法求解。用三维 Poisson方程生成网格。结果表明 :气相较液相的扩散效果好 ,小直径液滴的扩散效果好。相间速度滑移、改变气相喷射压力和喷射速度对液相扩散的贡献不大 ,但调整喷射角度会明显地增强液相的扩散、混合 ,本文结果未出现阻塞。     

Length scales in cryogenic injection at supercritical pressure

Length scales provide some understanding of the injection of cryogenic propellants in rocket chambers on mixing efficiency, which translates to burning efficiency and performance. This project uses supercritical cryogenic nitrogen to look at high-density core flows such as those of coaxial injectors used in rocket engines. The investigation considers test conditions from 4.0 to 6.0 MPa chamber pressure at two injection velocities and temperatures. Experimental data taken by using shadowgraph images provides a means of characterizing turbulent flow structures using a two-point correlation method to determine length scales and structure shapes. The experimental results are compared to computational models.     

Supersonic liquid jets: Their generation and shock wave characteristics

The generation of high-speed liquid (water and diesel fuel) jets in the supersonic range using a vertical single-stage powder gun is described. The effect of projectile velocity and mass on the jet velocity is investigated experimentally. Jet exit velocities for a set of nozzle inner profiles (e.g. straight cone with different cone angles, exponential, hyperbolic etc.) are compared. The optimum condition to achieve the maximum jet velocity and hence better atomization and mixing is then determined. The visual images of supersonic diesel fuel jets (velocity about 2000 m/s) were obtained by the shadowgraph method. This provides better understanding of each stage of the generation of the jets and makes the study of their characteristics and the potential for auto-ignition possible. In the experiments, a pressure relief section has been used to minimize the compressed air wave ahead of the projectile. To clarify the processes inside the section, additional experiments have been performed with the use of the shadowgraph method, showing the projectile travelling inside and leaving the pressure relief section at a velocity of about 1100 m/s. Received 23 January 2001 / Accepted 2 July 2001     

Mixing of high speed coaxial jets

In this study, five different supersonic nozzles – conical, elliptical, tabbed, radially lobed and two-dimensional lobed – are compared experimentally for their mixing performance. With the background of studies by various groups conducted on the above nozzles, the present paper aims to provide an experimental comparison of their respective mixing performances with that of a conventional conical nozzle under identical operating conditions. The mixing of the supersonic stream coming from such nozzles with a coaxial sonic stream is investigated. The investigation is performed non-intrusively, using digital image processing of planar Mie-scattering images of the flow field. The results of these investigations reveal the superiority of mixing performance of the two-dimensional lobed nozzle over conventional circular and other non-conventional nozzles. Received: 15 July 1999/Accepted: 3 July 2000     

Studies on freejets from nozzles for high-speed mixing applications

In this study four different supersonic nozzles – circular, elliptical, tabbed, and radially lobed nozzles are compared experimentally for their freejet mixing performance. With the background of studies by various groups conducted on elliptical, tabbed, and radially lobed nozzles, the present paper aims at a comparative experimental study to compare their mixing performance with that of a conventional circular nozzle under identical operating conditions. The investigation is performed non-intrusively, using digital image processing of the planar Mie scattering images of the flow field. The results of these investigations reveal the superiority of the mixing performance of the lobed nozzles over conventional circular and other non-conventional nozzles. Received: 29 July 1998/Accepted: 5 November 1999     

NUMERICAL STUDIES ON THE MIXING OF CH_4 AND KEROSENE INJECTED INTO A SUPERSONIC FLOW WITH H_2 PILOT INJECTION

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Modeling of Liquid Fuel Injection, Evaporation and Mixing in a Gas Turbine Burner Using Large Eddy Simulations

The interaction of turbulence, temperature fluctuation, liquid fuel transport, mixing and evaporation is studied by using Large Eddy Simulations (LES). To assess the accuracy of the different components of the methods we consider first isothermal, single phase flow in a straight duct. The results using different numerical methods incorporating dynamic Sub-Grid-Scale (SGS) models are compared with DNS and experimental data. The effects of the interactions among turbulence, temperature fluctuation, spray transport, evaporation and mixing of the gaseous fuel are studied by using different assumptions on the temperature field. It has been found that there are strong non-linear interactions among temperature-fluctuation, evaporation and turbulent mixing which require additional modeling if not full LES is used. The developed models and methods have been applied to a gas turbine burner into which liquid fuel is injected. The dispersion of the droplets in the burner is described. This revised version was published online in July 2006 with corrections to the Cover Date.     

LES of Jets in Cross Flow and Its Application to a Gas Turbine Burner

LES computations of jets in cross flow (JICF) were performed. Experimental investigations reported in literature are reproduced with good agreement concerning the momentum field and the mixing of a passive scalar. The results validate the ability of the present LES approach to compute fuel injection of the type JICF. LES computations of fuel injection in an industrial gas turbine burner are presented. This revised version was published online in July 2006 with corrections to the Cover Date.     

Computational investigation of hydrodynamics,coal combustion and NOx emissions in a tangentially fired pulverized coal boiler at various loads

This work presents a computational investigation of hydrodynamics, coal combustion and NOx emissions in a tangentially fired pulverized coal boiler at different loads (630, 440 and 300 MW; relative loads of 100%, 70% and 48%) to clarify the effect of load change on the furnace processes. A computational fluids dynamics model was established; the flow field, temperature profile, species concentration and NOx emissions were predicted numerically; and the influence of burner tilt angles was evaluated. Simulation results indicate that a decrease in boiler load decreases the gas velocity, attenuates the airflow rotations, and increases the tangent circle size. The high-temperature zone and flame moved toward the side walls. Such behaviors impair air–fuel mixing, heat transfer and steady combustion in the furnace. In terms of species concentrations, a decrease in boiler load increased the O₂ content, decreased the CO content, and decreased the char burnout rates only slightly. A change in boiler load from 630 to 440 and 300 MW increased the NOx emissions from 202 to 234 and 247 mg/m³, respectively. Burner tilt angles are important in coal combustion and NOx emissions. A burner angle of –15° favors heat transfer and low NOx emissions (<185 mg/m³) for the current tangentially fired boiler.     

Liquid film thickness inside the high pressure swirl injectors: Real scale measurement and evaluation of analytical equations

Liquid film thickness inside two swirl injectors for direct injection (DI) gasoline engines was measured at different injection pressure conditions ranging from 2.0 to 7.0 MPa and then previous analytical and empirical equations were examined from the experimental results. Based on the evaluation, a new equation for the liquid film thickness inside the swirl injectors was introduced. A direct photography using two real scale transparent nozzles and a pulsed light source was employed to measure the liquid film thickness inside the swirl injectors. The error in the liquid film thickness measurement, generated from different refractive indices among transparent nozzle, fuel and air, was estimated and corrected based on the geometric optics. Two injectors which have different nozzle diameter and nozzle length were applied to introduce a more general empirical equation for the liquid film thickness inside the pressure swirl injectors. The results showed that the liquid film thickness remains constant at the injection pressures for direct injection gasoline engines while the ratio of nozzle length to nozzle diameter (L/D) shows significant effect on the liquid film thickness. The previously introduced analytical and empirical equations for relatively low injection pressure swirl injectors overestimated the effect of injection pressure at the operating range of high pressure swirl injectors and, in addition, the effect of L/D ratio and swirler geometry was rarely considered. A new empirical equation was suggested based on the experimental results by taking into account the effects of fuel properties, nozzle diameter, nozzle length and swirler geometry.     

Fluid flow investigations within a 37 element CANDU fuel bundle supported by magnetic resonance velocimetry and computational fluid dynamics

The current work presents experimental and computational investigations of fluid flow through a 37 element CANDU nuclear fuel bundle. Experiments based on Magnetic Resonance Velocimetry (MRV) permit three-dimensional, three-component fluid velocity measurements to be made within the bundle with sub-millimeter resolution that are non-intrusive, do not require tracer particles or optical access of the flow field. Computational fluid dynamic (CFD) simulations of the foregoing experiments were performed with the hydra-th code using implicit large eddy simulation, which were in good agreement with experimental measurements of the fluid velocity. Greater understanding has been gained in the evolution of geometry-induced inter-subchannel mixing, the local effects of obstructed debris on the local flow field, and various turbulent effects, such as recirculation, swirl and separation. These capabilities are not available with conventional experimental techniques or thermal-hydraulic codes. The overall goal of this work is to continue developing experimental and computational capabilities for further investigations that reliably support nuclear reactor performance and safety.     

Ignition of liquid and dust fuel layers by gaseous detonation

Abstract. Ignition of a liquid layer and dust fuel layer by a detonation wave propagating in hydrogen-oxygen and acetylene-oxygen mixtures is reported. Experiments were carried out using a shock tube equipped with optical-quality observation windows. A schlieren system and a high-speed camera were used for measurements of ignition delay. Pressure transducers provided data necessary for measurements of the detonation wave velocity and pressure variation within the front of the interacted detonation wave and fuel layer. Kerosene, nitroglycerin and PETN were used as fuels. Investigation shows that the layer of liquid fuel can be efficiently ignited by detonation wave. It was found that the ignition delay of the fuel layer depends mostly on the detonation wave velocity and sensitivity of igniting fuels, and slightly on the layer thickness. Received 12 August 2001 / Accepted 1 July 2002 Published online 4 February 2003 Correspondence to: P. Wolanski (e-mail: wolanski@itc.pw.edu.pl) An abridged version of this paper was presented at the 18th Int. Colloquium on the Dynamics of Explosions and Reactive Systems at Seattle, USA, from July 29 to August 3, 2001     

Quantitative imaging of equivalence ratios in a natural gas SI engine flow bench using acetone fluorescence

Although compressed natural gas (CNG) is a gaseous fuel, the mixing process is quite different from air-liquid fuel mixing. The aim of this work is to understand the effect of the fuel feeding system on mixture homogeneity. Planar laser-induced fluorescence has been used to produce quantitative equivalence ratio maps in the intake manifold. Fluorescence results from excitation of doped acetone in natural gas. Its emission is proportional to the fuel mass. Collected images were post processed to obtain the equivalence ratio. This work shows the difference between continuous injection at low speed and sequential injection. In the first part, we present the behaviour of the injection jet in the intake manifold. The second part displays a smaller section of the duct upstream of the intake valve. The study shows clearly the stratification effect obtained with continuous injection at low speed. A very homogenous mixture is observed for sequential injection with fuel trapped for a cycle and aspirated in the next cycle.     

Raman Measurements of Cryogenic Injection at Supercritical Pressure

Understanding the complex environment of rocket chambers involves a good knowledge of injection phenomena and gives the designer the ability to employ time and cost saving modeling tools to design a higher performance engine. This project looked at injection processes in the supercritical regime using cryogenic nitrogen. Experimental data taken by 2-D Raman imaging allowed the comparison of density and divergence angels with computational models. These parameters provide much information about the jet development and mixing with the surrounding gas. The process used to derive divergence angles from Raman images proves difficult to compare directly with other techniques.     

Contributions of Computational Aeroacoustics to Jet Noise Research and Prediction

A brief review of recent progress in the field of computational aeroacoustics (CAA) is proposed. This paper is complementary to the previous reviews of Tam [(1995a) “Computational aeroacoustics: issues and methods”, AIAA J. 33(10), 1788–1796], Lele [(1997) “Computational Aeroacoustics: a review”, AIAA Paper 97–0018, 35th Aerospace Sciences Meeting and Exhibit, Reno, Nevada] and Glegg [(1999) “Recent advances aeroacoustics: the influence of computational fluid dynamics”, 6th International Congress on Sound and Vibration, Copenhagen, Danemark, 5–8 July, 43–58] on advances in CAA. After a short introduction concerning the current motivations of jet noise studies, connections between computational fluid dynamics (CFD) and CAA using hybrid approaches are discussed in the first part. The most spectacular advances are probably provided by the direct computation of jet noise, and some recent results are shown in the second part.     

不同构型和多点喷射对短环型燃烧室燃烧性能的影响

对短环形流燃烧室内有较强回流的湍流旋流流动进行了模拟,并从两个方面(燃烧室构型和多点喷射)对燃烧室性能的影响进行了分析。计算中采用Reynoldes应力湍流模型(RSM)、EBU-Arrheniue湍流燃烧模型和离散坐标辐射模型描述其燃烧流动,液相采用Lagrange法处理,气相采用SIMPLE法求解。研究表明:在燃料和空气总流量不变的情况下,燃烧室构型对燃烧室出口平均温度影响不大,对出口温度分布、燃烧室内空气流场有比较大的影响。喷嘴数目的改变对出口处的平均温度和平均速度影响不大,但是对出口截面处的温度分布影响比较大,在局部范围可能产生温度比较高的热斑。     

Comparison of Different Techniques for Characterizing the Diesel Injector Internal Dimensions

Experimental Techniques - The geometry of certain parts of diesel injectors is key to the injection, atomization and fuel-air mixing phenomena. Small variations on the geometrical parameters may...     

Numerical simulation of wall roughness effects in cavitating flow

Hydrodynamic cavitation has an important effect on the performance of Diesel injectors. It influences the nature of the fuel spray and the efficiency of the combustion process. In the present study, we investigate numerically the effect of wall roughness in the cavitating and turbulent flow developing inside a Diesel injector. The mixture model based on a single fluid is adopted and the commercial Fluent software is used to solve the transport equations.The discharge coefficient C_d is computed for different cavitation numbers and wall roughness heights. Profiles of density mixture, vapor volume fraction, mean velocity and turbulent kinetic energy are reported. The effects of wall roughness and injection pressure are analyzed.     

Numerical analysis of respiratory flow patterns within human upper airway

A computational fluid dynamics （CFD） approach is used to study the respiratory airflow dynamics within a human upper airway. The airway model which consists of the airway from nasal cavity, pharynx, larynx and trachea to triple bifurcation is built based on the CT images of a healthy volunteer and the Weibel model. The flow character- istics of the whole upper airway are quantitatively described at any time level of respiratory cycle. Simulation results of respiratory flow show good agreement with the clinical mea- sures, experimental and computational results in the litera- ture. The air mainly passes through the floor of the nasal cavity in the common, middle and inferior nasal meatus. The higher airway resistance and wall shear stresses are distrib- uted on the posterior nasal valve. Although the airways of pharynx, larynx and bronchi experience low shear stresses, it is notable that relatively high shear stresses are distrib- uted on the wall of epiglottis and bronchial bifurcations. Besides, two-dimensional fluid-structure interaction models of normal and abnormal airways are built to discuss the flow-induced deformation in various anatomy models. The result shows that the wall deformation in normal airway is relatively small.     

Kinematic and mixing characteristics of vortex interaction induced by a vortex generator model: a numerical study

The underlying effect of vortex interaction characterized by the merging and non-merging on mixing enhancement is of fundamental significance to understand the flow dynamics of strut injectors in scramjets. Starting from a simplified configuration of a vortex generator, this study focuses on the influence of geometric parameters on vortex structures and fluid mixing through compressible Navier-Stokes(NS) simulations.By adjusting the induction of outer vortices, the inner co-rotating vortex pair ...