用火焰面模型模拟甲烷/空气湍流射流扩散火焰

以层流对撞扩散火焰为基础，利用层流火焰面模型(laminar flamelet model)的方法生成层流火焰面数据库，分别采用预先设定的几率密度函数(propabality density function, PDF)模型和混合物分数-湍流频率的联合几率密度函数输运模型，将火焰面方法应用于甲烷/空气湍流射流扩散火焰结构的模拟计算中.两个模型的计算结果和实验结果进行了比较和分析.     

Dynamic measurement of temperature, velocity, and density in hot jets using Rayleigh scattering

A molecular Rayleigh scattering technique is utilized to measure gas temperature, velocity, and density in unseeded gas flows at sampling rates up to 10 kHz, providing fluctuation information up to 5 kHz based on the Nyquist theorem. A high-power continuous-wave laser beam is focused at a point in an air flow field and Rayleigh scattered light is collected and fiber-optically transmitted to a Fabry–Perot interferometer for spectral analysis. Photomultiplier tubes operated in the photon counting mode allow high-frequency sampling of the total signal level and the circular interference pattern to provide dynamic density, temperature, and velocity measurements. Mean and root mean square velocity, temperature, and density, as well as power spectral density calculations, are presented for measurements in a hydrogen-combustor heated jet facility with a 50.8-mm diameter nozzle at NASA John H. Glenn Research Center at Lewis Field. The Rayleigh measurements are compared with particle image velocimetry data and computational fluid dynamics predictions. This technique is aimed at aeronautics research related to identifying noise sources in free jets, as well as applications in supersonic and hypersonic flows where measurement of flow properties, including mass flux, is required in the presence of shocks and ionization occurrence.     

Heat and mass transfer in a system of plane turbulent jets with diffusion combustion

We consider turbulent motion of premixed chemically active gases in an infinite system of plane turbulent jets in the presence of diffusive combustion. The proposed calculation method permits determining the distribution of all the parameters in the mixing zone, including the longitudinal pressure. Numerical examples of the calculation of hydrogen combustion in air are presented.The study of heat and mass transfer in jet flows presents major difficulties at the present time. Therefore all the existing methods for calculating jet flows with heat and mass transfer and chemical processes [1–5] are based on an extension of the known semiempirical theories of free turbulence to the more complex cases of flow with chemical reactions. The present study is no exception in this sense; it covers an investigation of the motion in an infinite system of plane turbulent jets with diffusive combustion.     

High-resolution imaging of turbulence structures in jet flames and non-reacting jets with laser Rayleigh scattering

A comparative study of the length scales and morphology of dissipation fields in turbulent jet flames and non-reacting jets provides a quantitative analysis of the effects of heat release on the fine-scale structure of turbulent mixing. Planar laser Rayleigh scattering is used for highly resolved measurements of the thermal and scalar dissipation in the near fields of CH₄/H₂/N₂ jet flames (Re _d  = 15,200 and 22,800) and non-reacting propane jets (Re _d  = 7,200–21,700), respectively. Heat release increases the dissipation cutoff length scales in the reaction zone of the flames such that they are significantly larger than the cutoff scales of non-reacting jets with comparable jet exit Reynolds numbers. Fine-scale anisotropy is enhanced in the reaction zone. At x/d = 10, the peaks of the dissipation angle PDFs in the Re _d  = 15,200 and 22,800 jet flames exceed those of non-reacting jets with corresponding jet exit Reynolds numbers by factors of 2.3 and 1.8, respectively. Heat release significantly reduces the dissipation layer curvature in the reaction zone and in the low-temperature periphery of the jet flames. These results suggest that the reaction zone shields the outer regions of the jet flame from the highly turbulent flow closer to the jet axis.     

Synthesis of TiO2 nanoparticles by propane/air turbulent flame CVD process

Synthesis of TiO2 nanoparticles by the oxidation of titanium tetrachloride (TiCl4) in high-strength propane/air turbulent flame is investigated tentatively for mass production ofTiO2 nanoparticles. Effects of reactor heat flux varying from 247 to 627 kJ/m2 s, initial TiO2 number density from 2×1020> to 1 × 1021 m-3, and apparent residence time of TiO2 nanoparticles in reactor from 0.06 to 0.9 s, on particle morphology, phase composition, UV absorption and photoluminescence (PL) spectra are studied. The TiO2 nanoparti-cles synthesized, with mean size of 30-80 nm and rutile mass fraction from 0.155 up to 0.575, exhibited a strong PL signal at the wavelength of 370-450 nm, with a wide peak signal at 400-420 nm, reflecting significant oxygen vacancies on the surface of the TiO2 nanoparticles.     

Investigation of turbulent vapor-air jets in the presence of condensation and the injection of foreign particles

A study is made of flow in turbulent jets when there is condensation of the water vapor contained in them. A necessary condition for condensation in vapor-air jets is formulated. Relations are obtained for the regime of equilibrium condensation. An experimental investigation was made of the local characteristics of an isobaric turbulent vapor jet exhausting into air at rest when condensation develops in the jet and foreign condensation nuclei (smoke particles) and charged particles (ions produced in a corona discharge) are introduced into the flow. Measurements were made of the local characteristics of the condensed disperse phase — the Sauter diameter d₃₂ of the drops and their volume concentration c_s — using the optical method of an integrating diaphragm. It is shown that d₃₂ and₃₂ c_s increase downstream in the main section of the jet. Specific features of temperature measurements using an end-type microthermocouple were established. Quantitative data were obtained about the influence on the condensation of the thermal conditions and the presence of the foreign particles. The conditions under which there is an intensification of the condensation in vapor-air jets in the presence of ions were determined.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 53–61, May–June, 1984.     

Evaluation of LDA temporal and spatial velocity structure functions in a low Reynolds number turbulent channel flow

 Measurements have been made using Laser Doppler Anemometry (LDA) in a fully developed turbulent channel flow with the aim of determining second-order and third-order temporal and spatial structure functions of the longitudinal velocity fluctuation. A reliable determination of these moments requires the data to be corrected for the effect of noise. Correction procedures are outlined, based on the behaviour of temporal or spatial correlation functions in the limit of small time intervals or small separations. No a priori assumptions about the nature of the noise are made so that the procedure should be quite general. The corrected LDA data indicate that, especially for spatial separations, the effect of noise can be felt even within the inertial range. The corrected structure functions should allow an unambiguous assessment to be made of Taylor’s hypothesis and of the extended self-similarity (ESS) method; examples are given in each case. Temporal structure functions obtained by hot wire anemometry (HWA) are much less affected by noise than the LDA data. Received: 8 April 1998/Accepted: 26 October 1998     

Investigation of noise generation by turbulent jets on the basis of numerical simulation of unsteady flow in mixing layers

In the previous experimental studies it was concluded that the turbulent jet noise is produced by large-scale motions in the mixing layer induced by turbulence intermittence. The burden of this numerical simulation is the validation of these conclusions. As a result of numerical calculations, the “instantaneous” flow patterns and the parameter distributions in the initial regions of turbulent jets are obtained. On the basis of this information the flow dynamics are investigated. In the jet flow there are observable slowly transforming low static pressure regions and zones of elevated static pressure. These regions are displaced at the convection velocity. The inflow induced by the low pressure in the mixing layer has streamlines entering into the low pressure zones and flowing around the elevated pressure zones. The motion of the zones of the static pressure varying along the flow produces velocity disturbances in the induced external flow. The succession of the transformations of the intermittence-induced static pressure disturbances into sound waves is determined. This transformation occurs in the regions occupied by the ejected air.     

Investigation of flows induced by subsonic turbulent jets and their relation with the effect of static pressure reduction in a jet

The interaction between turbulent jets, both swirling and nonswirling, and the ambient medium is studied on the basis of the results of measurements and numerical simulation. It is shown that the turbulent flow and the swirl give rise to induced ejection flow toward the jet. The mechanism of the jet action on the ambient medium is connected with a decrease in the static pressure in the jet, which, in turn, is due to either the flow swirl or the fluctuating flow in the mixing layer, when the static pressure reduces owing to the presence of velocity fluctuations. The former rarefaction mechanism is predominant in swirling jets and the latter predominates in jets without swirling. It is shown that the ambient medium inflow into the jet due to the rarefaction is independent in nature of the mechanism of the lowered pressure generation and that it is the kinetic energy of the jet that is the energy source for the induced flow.     

Investigation of turbulence development in incompressible jets with zonal detached eddy simulation (ZDES) and synthetic turbulent inflow

Hybrid RANS/LES simulations of two incompressible jets are performed with the Zonal Detached Eddy Simulation (ZDES). Two functioning modes of the ZDES for the selection of RANS and DES areas are evaluated, namely the user-defined mode (mode 1) and the global- or automatic- mode (mode 2). The RANS-to-LES transition occurs quickly downstream of the nozzle exit and is found to involve the same physics as a laminar to turbulent transition with vortex pairing near the nozzle exit. The effect of the delay in the RANS-to-LES transition on the jet flow development is analyzed. In particular, the delay in the formation of small-scale turbulent structures results in too high turbulence levels in the mixing layers. Furthermore, it is shown, for two cases, that the injection of synthetic turbulence at the nozzle inlet, originally targeted at reproducing the experimental turbulence level in the jet core, has a significant impact on the mixing layer as it accelerates the RANS-to-LES transition, reduces the spatial wavelength of the vortex pairing and promotes the production of fine-scale turbulence which leads to a better agreement with experiments.     

Study of the effects of the injector length/diameter ratio on the surface properties of turbulent liquid jets in still air using X-ray imaging

The disintegration of turbulent liquid jets in gases, a process termed turbulent primary breakup, has many industrial applications, especially in liquid injection systems whose injector internal flow results in enhanced turbulence generation. An investigation was carried out by using X-ray diagnostics at the Advanced Photon Source (APS) facility of Argonne National Laboratory on two injectors with a smooth entry followed by round passage with different length-to-diameter ratios of 10 and 40, operating at the same injection speed. The test matrix was designed to eliminate cavitation and to isolate the effect of length/diameter ratio of the injector passage and to determine the importance of jet turbulence compared to aerodynamic forces. The X-ray diagnostics used allowed the surface and internal topography of liquid jets to be visualized and the spatial distribution of the surface ligaments to be revealed in the near-injector region. The present results show that the separation distance between a ligament and its neighbors depends on the ligament sizes, and the injector length/diameter ratio affects the rates of breakup.     

Investigation of the structure of transition and turbulent convection conditions in a vertical layer

Results are presented of an investigation of the instantaneous and average characteristics of turbulent convection in a vertical layer, starting from the two-dimensional unsteady Navier-Stokes equations. This paper studies the evolution of large-scale and fine structure during transition from laminar flow to turbulent.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 66–75, November–December, 1978.The authors thank V. L. Gryaznov for useful discussions and help in the first stage of the work and V. I. Baranov for his help in taking the movie film.     

Investigation of the length and wave structure of the gas-dynamic section in straight and spreading gas jets

The results are given of an experimental investigation of the wave structure of straight and spreading gas jets. Dependences are obtained for the calculation of the length of the gas-dynamic part of straight and spreading gas jets.     

Investigation of the spatio-temporal flow structure in the buffer region of a turbulent boundary layer by means of multiplane stereo PIV

In order to examine the physical process associated with the production and transport of turbulence in wall bounded flows, a fully developed turbulent boundary layer flow along a flat plate is investigated in stream-wise span-wise planes at y⁺10, 20, and 30, and Re7,800 by using a high-resolution multiplane stereo PIV system. Of particular interest are the structural features of the coherent flow structures, such as their average size and shape, but their intensity, dynamics, and interaction are also examined. The information is deduced from the joint probability density function of the velocity fluctuations and from various correlation, cross-correlation, and conditional-correlation functions. Furthermore, characteristic instantaneous velocity fields are analyzed in order to examine the importance of the individual coherent flow structures for the production of turbulence and the transport of Reynolds stresses.     

Measurement of the probability of the transition P20 (00 °1–10 °0) in CO2 and impact broadening in collisions with CO2, N2, and He

We measured the dependence of the absorption, coefficient on the pressure for the vibrational-rotational transition P20 (00 °1–10 °0) in CO₂ using a CO₂ laser as a light source. We consider the question of the systematic error due to the contribution of impact broadening, when finding the probability from the experimental absorption. The refined value of the transition probability A _{10 °0.20} ^{00 °1.19} =0.169 sec^–1. We obtain the values of the impact half-widths for collisions of the type CO₂-CO₂, CO₂-N₂, CO₂-He, the values of which at J=300 °K are respectively 3.28, 2.74, and 2.27 MHz/torr.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 6, pp. 24–28, November–December, 1972.The authors thank A. K. Konyukhov for interest in the work and for valuable discussions.     

Modelling of the diffusion of fluid particles in turbulent flows approaching a circular cylinder by random Fourier modes and random flight

To investigate the diffusion of fluid particles around a cylinder in a turbulent flow, we have developed two new types of model for simulating the trajectory of particles:(1) a model combining random Fourier modes and random flight (RF); (2) a pure kinematic simulation (KS) by random Fourier modes. In model 1 the large-scale turbulence is simulated by a sum of random Fourier modes varying in space and time, and the small-scale random motion of particles is simply modelled by an Itô type of stochastic differential equation with a memory time comparable to the Lagrangian time scaleT _s ^L of the small-scale motion. In model 2, both large- and small-scale turbulence is simulated using random Fourier modes. The change of turbulence around the cylinder is modelled by rapid distortion theory (RDT), although the small-scale motion of particles in the RF model is simply assumed to keep the homogeneous random behaviour. These models give very similar and realistic trajectories showing rapid changes of direction due to the small-scale motion.