Influence of nozzle vibrations on the aerodynamic characteristics of a jet

The results of investigations of the aerodynamic characteristics of turbulent jets issuing from nozzles and subjected to the action of various kinds of low-frequency vibrations — transverse, longitudinal, and torsional (during axisymmetric vibrations of the nozzle around the longitudinal axis) — are presented. Data on the laws governing changes in the average and pulsation velocities along the jet axis, as well as on the spectra of velocity pulsations in the zone of jet mixing, have been obtained. It has been established that at low-frequency vibrations of the nozzle a noticeable intensification of jet mixing is attained. The same effects as on acoustic excitation of a jet are observed. The experiments were carried out at Reynolds numbers Re = 2∙10⁴–8∙10⁴.     

Mixing enhancement using chevron nozzle: studies on free jets and confined jets

This paper reports an experimental study focused on the impact of chevrons (serrations on the trailing edge of the nozzle) on the mixing process of an incompressible jet issuing from a convergent nozzle. The study also explores enhancement of the mixing performance by a novel approach to geometry modification. Profiles of mean velocity were used to characterize the extent of mixing. For a comparative assessment, studies were carried out with a base line circular nozzle, a conventional chevron nozzle and an improvised tabbed chevron nozzle. Flow visualization studies were carried out for jets issuing from chevron nozzles and the results corroborate well with quantitative measurements. The impact of confinement on mixing of jets issuing from chevron nozzles is also studied. The results show that the proposed geometry modification can significantly improve the rate of mixing in the range of Reynolds numbers considered in the study. In confined jets, presence of chevrons was found to accelerate the process of jet break-down.     

Calculation of the characteristics of countercurrent axisymmetric jets

On the basis of analysis and generalization of experimental data, a method is proposed for calculating the parameters of the interaction of two coaxial jets flowing in opposite directions from circular nozzles of different diameters.Notation d, D diameter of the nozzles for the small- and large-diameter jets - density - x, y coordinates - u, U averaged longitudinal component of velocity of the small- and large-diameter jets - L_ax distance between nozzles - q relative impulse - G mass rate of the medium - 2r width of the jet - _i, L_i lengths of the flow zones of the small- and large-diameter jets, where i=1, 2 - range of the jet - 2B distance between corresponding points of lines of maximum velocity of the large-diameter jet Indices 0 initial state - m maximum value - ax value on the axis - d large-diameter jet - y_0.5 distance from the axis to the point at which the velocity is equal to half the velocity on the axis Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 56, No. 5, pp. 725–729, May, 1989.     

Development and applications of the efficient hybrid RANS/ILES approach for the calculation of complex turbulent jets

An efficient hybrid RANS/ILES approach is suggested for simultaneous calculation of flows in nozzles and jets of realistic configurations. The basic elements of the method are described, which permit of attaining a high accuracy of the results using relatively coarse grids. Results are given of calculations of the efflux of subsonic and supersonic jets from nozzles of different types. Good agreement between calculation results and experimental data is observed in the case of computational grids with 5.0 × 10⁵–1.2 × 10⁶ nodes. The level of turbulence intensity is predicted both on the axis and in the layers of mixing of jets. The impact of parameters at the nozzle exit section on the characteristics of turbulence in the mixing layer in the initial region of jets is investigated.     

Velocity and Concentration Distributions of Round and Plane Turbulent Jets

The analytical solutions for the velocity distribution of turbulent round and plane jets described in the classical textbook of Schlichting (Boundary Layer Theory 7^th edition (1979)) based on boundary-layer approximations are well-known, and have provided the fundamental understanding of the mechanics of turbulent jets. However, the scaling coefficients involved were not well quantified as discussed recently by Mathieu and Scott (An Introduction to Turbulent Flow(2000)). In this paper, it is shown that the coefficients can be better determined by the available experimental measurements in the literature. Furthermore, by assuming that the turbulent diffusivity relates to the eddy viscosity, it is shown that closed-form analytical solutions can also be obtained for the scalar concentration distribution in addition to the velocity distribution. The turbulent Schmidt number is found to be less than 1 for both plane and round jets, and close to the isotropic turbulence value of 0·7 in the round jet case.     

A numerical analysis of passive scalar transport in turbulent shear flows

Abstract

The development of the formation and vortex pairing process in a two‐dimensional shear flow and the associated passive scalar (mass concentration or energy) transport process was numerically simulated by using the Vortex‐in‐Cell (VIC) Method combined with the Upwind Finite Difference Method. The visualized temporal distributions of passive scalars resemble the vortex structures and the turbulent passive scalar fluxes showed a definite connection with the occurrence of entrainment during the formation and pairing interaction of large‐scale vortex structures. The profiles of spatial‐averaged passive scalar ø, turbulent passive scalar fluxes, u'ø’ and v'ø’, turbulent diffusivity of mean‐squared scalar fluctuation, v'ø‘ ², mean‐squared turbulent passive scalar fluctuation, √ø‘ ², skewness, and flatness factor of the probability density function of scalar fluctuation ø’ at three different times are calculated. With the lateral dimension scaled by the momentum thickness and the velocity scaled by the velocity difference across the shear layer, these profiles were shown to be self‐preserved. The probability density function of turbulent scalar fluctuation was found to be asymmetric and double‐peaked.     

Analysis of the parameters of discrete particle motion in axisymmetric turbulent impinging jets

The parameters of discrete particle motion in axisymmetric turbulent impinging air jets are determined.Notation x, y coordinates (Fig. 1) - v_x jet velocity - V_o maximum jet velocity - r_o nozzle radius - l _i length of the initial jet section - L spacing between the nozzle and the collision plane - ¯x dimensionless coordinate referred to the nozzle radius - ¯x_i dimensionless length of the initial section referred to the nozzle radius - d particle diameter - ₁ jet density - particle density - c_x particle drag coefficient - v particle velocity - v₁ axial jet velocity - kinematic coefficient of the flow viscosity - ¯x_o dimensionless coordinate referred to the distance L - d_c cement particle diameter - d_s sand particle diameter - ¯v_i dimensionless velocity of particle insertion into the jet, referred to V_o Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 37, No. 5, pp. 813–817, November, 1979.     

The application of hybrid RANS/ILES approach for the investigation of the effect of nozzle geometry and mode of efflux on the characteristics of turbulence of exhaust jets

The efficient hybrid RANS/ILES approach is used for the investigation of the effect of nozzle geometry and parameters of flow at the nozzle exit section on the characteristics of turbulence in the exhaust jet. The calculations are performed for nozzles of different types such as conical and chevron nozzles and the nozzle of double-flow turbojet engine (TJE) with chevrons on the core nozzle. The effect of the foregoing parameters on the level of fluctuations of velocity and pressure in the investigated jets is demonstrated. The effect of off-design mode of efflux on the parameters of turbulence in the jet is investigated under conditions of supersonic efflux of the jet. The effect of misalignment of the core and fan nozzles on the flow in the jet is considered for the nozzle of double-flow TJE. Grids containing about 10⁶ cells are used for the calculations. The accuracy of the results is confirmed by comparison with the known experimental data.     

使用莫尔条纹技术诊断不完全膨胀的三维气流场

应用莫尔条纹技术 ,测出了从不同喷嘴喷出的对称与非对称不完全膨胀气流的密度分布。给出了实验结果 ,并对该结果进行了分析 ,得到了几个重要的结论。最后 ,就系统的应用作了展望。     

Turbulent mixing of fluids with different densities flowing through a pipe

A one-dimensional model of a disperse mixture in a turbulent stream is constructed, with the mutual effect of mixture concentration and turbulence intensity taken into account.Notation ₀ mean-over-the-section density - p pressure - _t turbulent viscosity - U average longitudinal velocity - g acceleration of gravity - angle of pipe inclination from the horizontal - x, r cylindrical coordinates - t time - V average radial velocity - C average concentration - D_t turbulent diffusivity - c₀ mean-over-the-section concentration - K effective turbulent diffusivity - U₀ mean flow velocity - X distance, in the moving system of coordinates - a pipe radius - ₀ frictional stress at the inside surface of the pipe - u_* transient turbulent velocity - b turbulence intensity - l linear scale factor - chemical potential of mixture - density of mixture - d₁, d₂ densities of homogeneous fluids - y₊ thickness of laminar layer - y distance from the inside pipe surface - ₊ derivative of velocity at the layer boundary on the turbulent side - hydraulic drag - Gr Grashof number - Re Reynolds number - ₁, ₂, coefficients in the equation for K_* - K_* dimensionless effective diffusivity - =U₀t/2a dimensionless time - =X/2a dimensionless distance Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 22, No. 6, pp. 992–998, June, 1972.     

Experimental data base for numerical simulations of turbulent diffusion flames

The objective of the presented measurements is to provide an experimental data base for comparison with numerical simulation results of turbulent H₂-air diffusion flames. Additionally, the date base may also be used for a proof of new measurement techniques, when the same flame conditions are applied. The data base contains time and spatial resolved data on all three velocity components, all Reynolds-stress tensor components, temperature, mixture fraction, species concentrations, higher statistical moments of these quantities and probability density functions for three different flames. The data are given as original measurement data in dependence on flame conditions and location in the flame, as absolute and normalized data and as evaluated data, like anisotropy tensor. The measurements are made to improve the understanding of turbulent transport processes under the influence of combustion and to help the effort to couple the turbulence and combustion model. A Laser-Doppler-Velocimeter was used to obtain three velocity components simultaneously. Temperature was measured with spontaneous Raman-Rayleigh spectroscopy and Coherent Anti-Stokes Raman spectroscopy, separately, while species concentrations and mixture fraction are measured with spontaneous Raman-Rayleigh spectroscopy. Measurements are done from nozzle exit into the self-preserving region up to x/d=100 so that the whole flow field including all boundary conditions are quantified for numerical prediction. A mixture of hydrogen and nitrogen with a mole ratio of 1:1 is used as fuel. Reynolds number and Froude number are set at different values. This complete data set is available upon request.     

Elastic moduli of boron oxyfluoride glasses: experimental determinations and application of Makishima and Mackenzie's theory

Oxyfluoride glass system based on 60B₂O₃–(40 – x)PbO–xPbF₂, where x = 0, 5, 10, 15, 20 and 25 mol% was prepared. The density of each glass was measured and the molar volume was calculated. The velocities for both the longitudinal and the transverse ultrasonic waves were measured by using the pulse-echo technique. The longitudinal, shear, Young's and bulk moduli were calculated from the measured velocity and density values. Makishima and Mackenzie's theory was applied to calculate the elastic moduli of the present glasses. The calculated values are consistent with the measured ones. The measured and the calculated moduli were correlated for the composition of the glasses as a function of PbF₂ content and they are increased with increasing PbF₂. This is due to some structural changes which occur upon replacing PbF₂ instead of PbO content in the glass matrix.     

Acoustic Excitation of Noncircular Turbulent Jets

Results of experimental investigation of turbulent mixing in jets flowing out of nozzles with different cross sections in the case of low and highfrequency acoustic excitation of the jets are presented. The influence of the shape of the cross section of a nozzle on the acousticexcitation sensitivity of a jet flowing out of it is analyzed.     

Numerical studies of three turbulent slot jets with and without moving surface

Summary This study presents the numerical predictions of the fluid flow and heat transfer characteristics for three turbulent impingement slot jets. The turbulent governing equations are solved by a control-volume-based finite-difference method with power-law scheme, the well knownK- model, and its associate wall function to describe the turbulent behavior. The velocity and pressure terms of momentum equations are solved by the SIMPLE (Semi-Implicit Method for Pressure-Linked Equation) method. In this study nonuniform staggered grids are used. The parameters interesting include entrance Reynolds number (Re), dimensionless nozzle to surface space (H/W), dimensionless pitch (H/W), and dimensionless velocity ratio (U _s /V _j ). The computed results show that the dimensionless pitch has a strong influence on the heat transfer characteristics. In the case with surface motion, it is found that the skin friction coefficient of the impinging surface is strongly affected by the surface motion, but the heat transfer characteristic is not significant in the range of 0.05U _s /V _j 0.25.Nomenclature C ₁,C ₂,C turbulent constant - C _f skin friction coefficient - E constant - G generation rate of turbulent kinetic energy - H distance between the nozzle and the impingement surface - i turbulence intensity - K turbulent kinetic energy - Nu local Nusselt number - P pitch - q heat flux - Re Reynolds number - S source term - T temperature - U friction velocity - U _s velocity of surface motion - V _j jet velocity - U, V x, y component velocity - W nozzle width - y ⁺ dimensionless distance from the wall - dependent variables - diffusion coefficient of equation - thermal diffusivity of fluid - density - von Kármán constant - turbulent Prandtl number - dynamic viscosity - kinematic viscosity - _w wall shear stress - turbulent energy dissipation rate - length scale constant     

The significance of annual temperature differentials in the design of structures for climatic effects

The results are given of experimental investigations of the flow parameters (velocity, static pressure, temperature and mixture concentration fields) pertaining to the mixing of five plane turbulent jets.     

Mixing in a system of plane cocurrent jets of an incompressible liquid over the main portion

We consider mixing in a periodic system of plane subsonic jets of an incompressible liquid for laminar and turbulent flows. Asymptotic expressions for the change in the velocity defect are obtained. A comparison with a numerical calculation and with existing experimental data is carried out. We show that under the conditions considered the accuracy of the expressions derived is rather high and they can be used for evaluating the mixing velocity over the main portion of mixing.     

Experimental investigation of longitudinal mass transfer in the flow of polyoxyethylene solutions in a round pipe

A method is described for studying longitudinal mass transfer in the turbulent flow of polyoxyethylene solutions in a pipe using nuclear magnetic resonance effects.Notation L length of investigated section of tube - T time of flow over section L - modulation period - modulation frequency - v_av mean velocity - w longitudinal velocity pulsation - l marker length - M magnetization of a unit volume of the liquid - I intensity of NMR signal - q flow rate - c solution concentration Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 41, No. 3, pp. 402–406, September, 1981.     

Experimental investigation on hydrodynamic behavior in a spouted bed with longitudinal vortex generators

A spouted bed with longitudinal vortex generator (LVG) of sphere was built to enhance radial movement of particles. Particle Image Velocimetry (PIV) was applied to explore effects of longitudinal vortex flow and physical properties of particles on their radial velocity in a 152-mm-diametered spouted bed. The results show that, Compared with the conventional spouted bed, the existence of longitudinal vortex generator gives rise to a large amount of secondary fine vortex flow in the cross section of spouted bed. The enhancement factors of particles movement η with different particle densities are all greater than 1. The smaller the particle density, the more significant the effect of the longitudinal vortex on the radial velocity of the particles. The single-row LVGs can produce a good radial enhancement effect of particle movement when the particle handling capacity is small (H₀ = 165 mm). With the increase of the height of the static bed (H₀), the enhancement of the radial velocity of particles in the spouted bed by multi-row LVGs (three rows) increases gradually, which indicates that the multi-row LVGs have a better overall effect on the enhancement of particle motion in the spouted bed with more particle handling capacity (H₀ = 195 mm, 225 mm).     

IMPINGEMENT CASTING PROCESS: TURBULENT MIXING IN AN IMPINGEMENT MIXER

Theoretical analysis for turbulent mixing in an isotropic turbulent field was carried out. Depending on the material properties and flow field, either viscous shear force or dynamic pressure force breaks-up the globules. From an order of magnitude analysis, generalized equations for predicting globule sizes were derived. Experimental work on turbulent impingement mixing of kerosene and water revealed that macromixing and micromixing vary dramatically depending on the mixing chamber geometry. Best mixing (fast macromixing and small globule sizes) was obtained in an arrow shaped mixing chamber where the incoming jets were opposite to each other and slanted upward toward the mixing head. The coefficients of the equation for predicting the maximum globule size of immiscible liquids were obtained from the experimental results of arrow-shaped impingement mixers.