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.     

Large eddy simulation of a nonisothermal turbulent jet flowing out into submerged space

Large eddy simulation is performed of a subsonic nonisothermal turbulent jet flowing out from a round nozzle into submerged space. The Navier-Stokes equations filtered over space and the RNG model of subgrid-scale viscosity are used for describing the flow. The calculations are performed for different values of the degree of jet preheating. The processing of the results of numerical simulation enables one to obtain the distributions of correlation moments of fluctuations of density, velocity, and temperature along the axis and in cross sections of jet flow. The calculation results are compared with the available data obtained using the solution of Reynolds-averaged Navier-Stokes equations and equations of the k-? model of turbulence, as well as with the data of physical experiment.     

Analysis of the process of mixing of a passive impurity in a jet mixer

The experimental results for two regimes of mixing of a passive impurity in an axisymmetric jet mixer — the mixing of a turbulent jet and a cocurrent flow to form a recirculation zone behind the nozzle and an analogous mixing without the formation of a recirculation zone (Re_d = 10,000) — have been presented. The velocity field has been measured in the mixer cross sections at different distances from the nozzle (0.1 < x/D < 9.1) with a one-component Doppler laser anemometer, whereas the scalar field (concentration of the passive impurity) has been diagnosed by the laser-induced fluorescence method. Based on the scalar distributions obtained, the autocorrelation function and the integral scale have been computed, the form of the probability density function has been restored, and the distributions of the asymmetry and excess coefficients have been constructed. Visualization of flow in the mixer has been carried out. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 2, pp. 46–59, March–April, 2007.     

Experimental investigation of a turbulent jet in turbulent cross flow

The characteristics of an axisymmetric turbulent jet propagating in a cross flow with a high degree of turbulence are investigated experimentally.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 43, No. 2, pp. 225–228, August, 1982.     

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.     

The Use of the RANS/ILES Method to Study the Influence of Coflow Wind on the Flow in a Hot,Nonisobaric, Supersonic Airdrome Jet during Its Interaction with the Jet Blast Deflector

The influence of the coflow wind on the flow in a hot, nonisobaric, supersonic airdrome jet from a biconical nozzle and its interaction with a jet blast deflector (JBD) are studied by the RANS/ILES method. The conditions at the external boundary of the computational domain are formulated for the problem of jet interaction with the JBD. All calculations were performed at the Joint Supercomputer Center of the Russian Academy of Sciences with a MVS-10P supercomputer. The features of method parallelization for the supercomputer with modern architecture are described. The total temperature of the jet at the nozzle output is T₀ = 1050 K and π_с = 4. The wind velocity ranges from 0 to 20 m/s. Two JBD positions are examined: at distances of 5 and 15D_e of the nozzle cross section. The computation grids consist of (6.33–8.53) × 10⁶ cells. Fields of the flow parameters and of their turbulent pulsations near the jet are obtained. The dimensions of the “safety zone” for people and machinery is determined by the temperature, pressure pulsations, and velocity near the airdrome surface. The influence of wind velocity on the size and shape of the safety zone are revealed. The distributions of pressure and temperature and their pulsations over JBD altitude are presented as a function of JBD position and wind velocity.     

Study of the jet flow field of vacuum spray process

In this work, we study the velocity and turbulence distribution of the cone nozzle jet flow field into a vacuum chamber under different nozzle diameters and injection pressures. The simulations are carried out with using the software based on the volume of fluid method, the standard k-ε turbulence model and pressure implicit with splitting of operator arithmetic. It is found that for injection pressure lower than 10 MPa, the spray penetration increases with the increase of injection pressure. However, for injection pressure higher than 10 MPa, the spray penetration tends to reduce progressively. Moreover, the distribution of velocity and turbulence become worse than that of the spray jets with injection pressure lower than 10 MPa. The potential core, spray penetration and diffusion zone of the spray jet increase with the increase of the nozzle diameter. Furthermore, without considering the solubility of the target polymer materials, acetone solvent shows better jet flow distribution in comparison with that of chloroform and carbon tetrachloride.     

Experimental and numerical simulation of the flow in a driving module with an annular and linear double-slot nozzle

This paper presents the results of numerical and experimental studies of the flow and comparison of propulsion performance characteristics of a model of a jet engine exhaust system equipped with an annular or (equivalent in gas consumption) linear double-slot nozzle with an inner cavity and circular segment deflector in the axial section. Calculations performed for the annular nozzle and double-slot nozzle corresponding to it in geometric parameters demonstrate that a flow similar to the flow in nozzles with a central body is formed in the exhaust system. According to the data obtained, the initial turn of the flow takes place in the oblique shock wave. In the double-slot nozzle, the final turn of the flow in the direction of the thrust vector occurs in a configuration of four shock waves positioned downwards in the flow; in the annular nozzle, it is in the intense barrel shock wave. It was established that the exhaust system with an annular of the linear doubleslot nozzle develops a thrust and specific impulse that exceed the corresponding values for the sonic nozzle equivalent in gas consumption by almost a factor of 2.     

Numerical study of cryogenic micro-slush particle production using a two-fluid nozzle

The fundamental characteristics of the atomization behavior of micro-slush nitrogen (SN₂) jet flow through a two-fluid nozzle was numerically investigated and visualized by a new type of integrated simulation technique. Computational fluid dynamics (CFD) analysis is focused on the production mechanism of micro-slush nitrogen particles in a two-fluid nozzle and on the consecutive atomizing spray flow characteristics of the micro-slush jet. Based on the numerically predicted nozzle atomization performance, a new type of superadiabatic two-fluid ejector nozzle is developed. This nozzle is capable of generating and atomizing micro-slush nitrogen by means of liquid-gas impingement of a pressurized subcooled liquid nitrogen (LN₂) flow and a low-temperature, high-speed gaseous helium (GHe) flow. The application of micro-slush as a refrigerant for long-distance high-temperature superconducting cables (HTS) is anticipated, and its production technology is expected to result in an extensive improvement in the effective cooling performance of superconducting systems. Computation indicates that the cryogenic micro-slush atomization rate and the multiphase spraying flow characteristics are affected by rapid LN₂-GHe mixing and turbulence perturbation upstream of the two-fluid nozzle, hydrodynamic instabilities at the gas-liquid interface, and shear stress between the liquid core and periphery of the LN₂ jet. Calculation of the effect of micro-slush atomization on the jet thermal field revealed that high-speed mixing of LN₂-GHe swirling flow extensively enhances the heat transfer between the LN₂-phase and the GHe-phase. Furthermore, the performance of the micro-slush production nozzle was experimentally investigated by particle image velocimetry (PIV), which confirmed that the measurement results were in reasonable agreement with the numerical results.     

Simulation of the turbulent mixing of a passive impurity in a jet mixer

Results of numerical simulation of the mixing of a turbulent jet with a cocurrent incompressible-fluid flow (Schmidt number Sc ≈ 1000) in a cylindrical channel of circular cross section (axisymmetric mixer) with the use of the standard k-ε turbulence model and different models for the averaged value of the mixture fraction and its variance have been given. For the problem of mixing of an inert passive impurity, two regimes of flow — the regime with the formation of a recirculation zone and that without its formation — have been considered. The formulated statistical model has been verified with the use of experimental data and results of calculation by large-eddy simulation. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 4, pp. 666–681, July–August, 2008.     

旋进射流喷嘴的频率及流场特性研究

在圆筒套管内设置一块孔板构成旋进射流喷嘴，由此获得持续稳定的旋进射流，研究了喷嘴最优的结构参数。用热线风速仪测量出口射流的速度并进行功率谱分析，得到旋进射流的频率及流场特性。研究表明，旋进射流具有较高的紊流强度，速度场沿径向的分布趋向平缓，其进动频率随流量增大而加快，喷嘴的尺寸和结构对射流进动有影响。     

Control of the Parameters of an Exhaust Jet by Increasing the Eddy Viscosity at the Nozzle Edge

We studied the possibility of changing the parameters of the exhaust wake in the far field of the jet behind a large passenger aircraft (aerobus) by increasing the coefficient of eddy viscosity at the edge of the nozzle of a doubleflow engine with a high doubleflow ratio (>10) without mixing with the aid of artificial turbulizers created in the outer and inner ducts. Within the model of turbulence with one differential equation for the coefficient of viscosity, we obtained numerical solutions for velocity, temperature, concentrations of vapor and condensate, and the coefficient of viscosity for different variants which disclose the essence of a physicomathematical model of the phenomenon and predict possible changes of the parameters of the exhaust jet with artificial increase of viscosity in the initial section and the jet volume.     

Experimental investigation of the mixing performance of a lobed jet flow

An experimental investigation of flow in a turbulent isothermal air lobed jet is presented. A lobed jet is compared, in the near field, with an isothermal axisymmetric jet with the same exit Reynolds number in terms of dynamics and mixing enhancement. It was found that the streamwise variation of the volumetric flow rate is characterized by a slope is more than twice larger than that for the reference circular jet. This high entrainment rate is governed, at the same time, by the turbulent structures generated by the asymmetric shape of the nozzle and by the high convection in these structures induced by the inner and outer penetration angles of their lobes. Published in Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 1, pp. 102–107, February–March, 2008.     

Simulation of the internal dynamics of solid-fuel rocket engines on the basis of the STAR-CD suite

Flows in the channels of solid-fuel charges with cross sections having different views in plan and flows in the prenozzle volume and the nozzle unit of a solid-fuel rocket engine have been simulated on the basis of the STAR-CD suite for different types of charges and different designs of the input part of the engine nozzle. The influence of the compressibility, turbulence, geometric factors, and flow rate on the distributions of gasdynamic parameters in the working region of the engine has been investigated. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 4, pp. 50–56, July–August, 2006.     

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.     

Dispersion of a heavy admixture in a two-phase jet

The article presents experimental data on the distribution of finely-divided powder in the cross sections of a turbulent axisymmetric jet and a qualitative analysis of the experimental data, and the possibility of their generalization is shown.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 18, No. 3, pp. 538–541, March, 1970.     

Effect of the size of air bubbles on enhancement of heat transfer in an impinging liquid jet

The numerical modeling of heat transfer in a bubbly impinging jet is carried out. The axisymmetric system of RANS equations that take into account the two-phase nature of the flow is resolved based on the Euler approach. The turbulence of the liquid phase is described by the Reynolds stress transport model with taking into account the effect of bubbles on modification of the turbulence. The effect of the gas volumetric flow rate ratio and the bubble size on the flow structure and the heat transfer in a gas–liquid impact stream is studied. It is shown that the addition of the gas phase in a turbulent fluid causes an increase up to 1.5-fold in heat transfer. The comparison of the simulation results with experimental data showed that the developed model enables the simulation of turbulent bubbly impinging jet with heat transfer with the pipe wall in a wide range of gas fraction.     

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.     

Relaminarization in supersonic microjets at low Reynolds numbers

Results of measuring the length of the supersonic portion of the air jets that flow out of axisymmetric sonic nozzles 10.4 μm-1 mm in diameter are presented. The measurements are carried out in a range of degree of jet noncalculation of 1–30 and in a wide Reynolds number range, including the laminar and turbulent flow modes. It is shown that the Reynolds number calculated from the nozzle diameter and the outlet parameters of gas is the parameter that governs jet flow. It is found that, for a laminar jet mixing layer, the length of the supersonic portion sharply increases. When the jet mixing layer becomes turbulent, the length of the supersonic portion decreases. The effect of increasing the length of the supersonic portion after its decrease due to the turbulization of flow in a jet and a growth in the Reynolds number is first discovered.