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.     

亥姆霍兹上喷嘴出口结构对射流振荡特性的影响

应用FLUENT软件对二维的亥姆霍兹喷嘴自振射流进行了模拟,并以此为基础研究了上喷嘴出口凸出部深入振荡腔对亥姆霍兹喷嘴自激振荡特性的影响。结果表明,上喷嘴的出口凸出部长度和喷嘴壁厚度都对自激振荡特性产生显著的影响。长度为0～0.15D_1时,自振射流的脉动幅值可以提高20%～80%,提升幅度在射流速度较低时更大;凸出部长度为0.15～0.25D_1时,射流振幅的提升逐渐降低;长度0.25～0.3D_1时,射流振幅比普通喷嘴更低,稳定性下降;长度超过0.3D_1时自振射流会完全消失。凸出部分喷嘴壁厚度在0δ0.1D_1范围内对射流性能几乎没有影响,但随着厚度δ的不断增大,性能会减弱,δ0.15D_1时无法形成自振射流。总之,上喷嘴出口凸出可改善射流振荡性能,但长度和厚度需在一定范围内,否则无法产生自振射流。     

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.     

Influence of nozzle angle and classifier height on the performance of a spiral air jet mill

We study the effect of varying air jet mill design parameters, the nozzle angle and the classifier tube height, on the performance of the mill, operated in the semi-batch mode, using quartz and limestone particles as feed. Particle size distributions of the product and the material in the mill are measured along with the mass in the mill. The product size distribution and the specific mass flux are found to be constant with time. The breakage rate is found to increase with nozzle angle. The efficiency of classification, characterized by the fraction of coarse particles larger than the cut size, increases with nozzle angle and classifier tube height. The energy for grinding per unit mass of the product decreases with nozzle angle and increases with classifier tube height and optimal values of the parameters, at which the specific energy is minimized, are obtained.     

Flow of an anomalous viscous fluid in a centrifugal jet nozzle

The motion of twisted flows of an anomalous viscous fluid subject to an exponential law has been studied numerically.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 57, No. 6, pp. 900–906, December, 1989.     

Influence of nozzle design and process parameters on surface roughness of CFRP machined by abrasive jet

Carbon fiber reinforced polymer composites find extensive applications in the areas of automotive, aircraft and aerospace, medical sciences, and electronics. Their usage in automated engineering industry needs good quality in components and excellent surface finish. The aim of this research work is to make holes on carbon fiber reinforced polymer composite material using a newly designed nozzle with and without internal thread. Surface roughness (Ra) was calculated across the depth of the machined hole. The effect of air and abrasive mixture pressure (P), stand-off distance (L), nozzle diameter (D), and abrasive size (S) on surface roughness was carried out for two different nozzles. The experimental result showed offer of good surface finish on CFRP materials from the newly designed nozzle with internal thread.     

Simulation of a subsonic isothermal turbulent submerged jet flowing from an annular nozzle

A simulation of the flow in a jet has been carried out with the use of the Reynolds-averaged, space-filtered Navier-Stokes equations closed by the k-ε model of turbulence and the subgrid RNG model of eddy viscosity. The results of calculations carried out on the basis of the k-ε model and the results of simulation of large vortices are in quantitative and qualitative agreement with the corresponding measurement data, which is evidence in favor of the main laws defining the decay of the gas-dynamic behavior of cold-gas submerged jets and the fluctuations of their parameters. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 2, pp. 312–320, March–April, 2008.     

Local characteristics of an axisymmetric impact jet

We present the results of an experimental investigation of the local characteristics of flow in an axisymmetric impact jet. Academic Scientific Complex “A. V. Luikov Heat and Mass Transfer Institute of the Academy of Sciences of the Reublic of Belarus,” Minsk: Institute of Thermophysics of the Siberian Branch of the Russian Academig of Sciences, Novosibirsk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 69, No. 4, pp. 615–624, July–August 1996.     

用于石油钻井磨料射流喷嘴的研制

为进一步提高石油钻井磨料射流喷嘴寿命,以自制含有晶粒长大抑制剂的WC-6Co纳米复合粉为原料,采用模压及真空烧结试制了一种磨料射流喷嘴,用扫描电镜观察其组织形貌,并进行硬度和密度的测量.结果表明:试制的WC-6Co硬质合金喷嘴组织均匀,断口平整光滑,WC晶粒细小,平均晶粒尺寸约1.5μm;其硬度为HRA90.7,密度为14.79 g/cm3,接近国外同类产品,有广泛应用推广价值.     

The numerical modelling of a two-dimensional local exhaust system associated with an inclined jet flow

Previous mathematical models employed by the authors have been further developed in order to consider the effect of an inclined jet on the air flow of a two-dimensional bench-slot Aaberg exhaust system. The air flow in this local exhaust ventilation system is solved using two approaches, namely, (i) a simple potential-flow model and seeking the solution of the resulting Laplace equation by means of a boundary-integral technique, and (ii) a turbulent model using the k- formulation and solving the resulting turbulent Navier-Stokes equations by means of a control-volume method and the SIMPLE algorithm. The effect of the angle that the jet makes with the direction of the surface of the workbench and the momentum ratio on the air flow in the exhaust system are investigated. It is found that, by inclining the jet, the system can become more energy efficient and the region of capture of the contaminant from close to the bench can be increased.     

The influence of initial stream turbulence on the characteristics of an axisymmetric immersed jet

Results are given of measurement of mean velocity and of velocity fluctuations in an axisymmetric immersed jet at various values of initial turbulence. It is shown that as the initial stream turbulence increases, the length of the entrance section decreases, and that the entrance section practically disappears in a strongly turbulent jet.     

Effect of the cone angle and the degree of contraction of a sonic nozzle on the geometrical structure of the first roll of an underexpanded jet

The results of an experimental investigation into the effect of the cone angle and the degree of contraction of a contracting nozzle on the geometrical structure of the first roll of an underexpanded jet are presented.     

Influence of air intake pipe on engine exhaust emission

The exhaust emissions of a four-cylinder four-stroke petrol engine have been measured. Tests have been conducted at engine speeds ranges from 1000 to 4000 rpm and at air intake pipe diameters of 20, 25, 30, 35, 40 and 63 mm. The results demonstrate that the concentrations of the hydrocarbon (HC) and that of the carbon monoxide (CO) are relatively high at small air intake pipe diameter of 20 mm and at low engine speed of about 1000 rpm. Both pollutants have a minimum at large air intake pipe diameter of about 63 mm and at high engine speed of about 4000 rpm. The exhaust emissions HC and CO increase also as the ambient pressure decreases and as the altitude of the engine increases. The values of carbon dioxide (CO₂) and the oxygen (O₂) remain relatively constant at a wide range of different operating conditions. Therefore the knowledge about the effect of the above parameters could lead to improve the emission control technology as well as the engine performance on engine development and design.     

Influence of geometry on polychromatic speckle contrast

Understanding speckle behavior is very important in speckle metrology application. The contrast of a polychromatic speckle depends not only on surface roughness and the coherence length of a light source, as shown in previous works, but also on optical geometry. We applied the Fresnel approach of diffraction theory for the free-space geometry and derived a simple analytical relationship between contrast, coherence length, size of illuminated spot, and distances between source, object, and observation plane. The effect of contrast reduction is found to be significant for low-coherence light sources.     

双腔室自激振荡喷嘴频率特性研究

摘要：作为对双腔室自激振荡喷嘴这一新型喷嘴的探索,基于流体网络理论建立了双腔室自激振荡脉冲射流喷嘴的相似网络模型,理论分析了双腔室自激振荡喷嘴频率特性。模型计算结果表明：双腔室自激振荡喷嘴结构参数对系统的固有频率有重要的影响,系统结构参数间存在最优匹配关系,并与文献中介绍的单腔室结构参数的最佳配比关系有较大的不同,双腔室自激振荡喷嘴较单腔室自激振荡喷嘴可以提高脉冲射流峰值压力。分析结果对双腔室自激振荡喷嘴结构设计具有一定的借鉴价值。     

Some particularities of the formation and flow of the plasma jet of an ablation pulse plasma accelerator with cylindrical geometry

The results of spectroscopic and holographic studies of an ablation (erosion) pulse plasma accelerator with cylindrical geometry are presented with a comparison of data obtained by both methods. The high values of electron concentration, unusual emission of spectral lines, and integral radiation in the beginning of the discharge are explained by the action of the ionization wave. The particularities of the spatial-temporal (radial) distribution of the electron concentration are associated with the vibrational character of the discharge current. The electron concentration was determined by integral spectra and with different time resolution, and with the radial recalculation of intensities and without it, as well as by the pulse holographic interferometry.     

基于四负载方法的汽车发动机排气源特性研究

传统的四负载法由于特殊的求解方式,管外测量时环境带来的干扰极易造成求解不稳定,从而影响计算结果精度.采用改进传统的四负载方法,通过管内测量以及获取更精确的直管四端极子参数来提高计算结果精度.管内测量通过测取管内压力波动来提取管内声压值.精确的直管四端极子参数通过三维有限元方法获取.最后通过仿真获取直管末端辐射声压值,并与试验结果进行对比,在主要峰值处吻合良好.同时与传统四负载法仿真结果对比,表明所改进的四负载方法计算结果更准确.     

The influence of nozzle geometry on powder flow behaviors in directed energy deposition additive manufacturing

To show the relationship between the nozzles and the powder flows, computational fluid dynamics and discrete element methods were used to simulate the interactions between the powder particles and the gas flows. Experiment was carried out for the validations. Then, laser irradiation rate (LIR) and powder aggregation degree (PAD) were defined to evaluate the influences of the nozzle geometries on the powder flow behaviors in DED. Results indicate that the divergence angle of the powder stream can be obviously affected by the changes of nozzles. The divergence angle can be increased from 15° with three-jet nozzle to 17° with four-jet nozzle. But at the same work conditions, the divergence angle with annular nozzles is only 8°. The powder mass concentration (PMC), LIR and PAD can be further used for the determination of the stand-off distance in DED. The determined stand-off distance of the annular coaxial nozzle is larger than the three-jet and four-jet nozzles. The PMC is increased by 66.7% in DED with annular coaxial nozzle in comparison with the three-jet and four-jet nozzles. The defined parameters of PMC, LIR and PAD can be used for the systematic determination of stand-off distance for better controlling of DED.     

几何参数对线性压缩机板弹簧性能的影响

在设计了11款不同基圆半径、厚度及涡旋槽偏心距的圆渐开线型板弹簧的基础上,利用ANSYS有限元分析软件,对上述板弹簧的刚度及应力特性进行了分析与比较,总结出了主要几何参数对板弹簧性能的影响.     

Influence of stack geometry on the performance of thermoacoustic refrigerator

The work reported in this paper is focused on the performance of a thermoacoustic refrigerator under various operating conditions. The experiments were conducted with various stack geometries fabricated with epoxy glass and Mylar material. Four stacks with different pore sizes are used to evaluate the performance of the refrigerator. Stack 1 has parallel plates of Mylar material 0.12 mm thick spaced 0.36 mm apart. Stacks 2, 3 and 4 are made of epoxy glass with pores of circular cross-section having 1, 2 and 3 mm diameter, respectively. The entire resonator system was constructed from aluminium material coated with polyurethane material from inside to reduce conduction heat losses. Helium gas was used as a working fluid. The experiments were conducted with different drive ratios ranging from 1.6% to 2% with varying cooling load from 2 to 10 W. For the experiments, operating frequencies from 200 to 600 Hz with mean pressure varying from 2 to 10 bar in steps of 2 bar each were considered. The temperatures of the hot end and cold end of the heat exchangers were recorded using RTDs and a data acquisition system under various operating conditions. The coefficient of performance (COP) and relative COP (COPR) are evaluated. Results show that COP of the refrigerator rises with increase of cooling load and decreases at higher drive ratio. It was also observed that the temperature difference between the hot end and cold end of the stack is higher at 2 W cooling load for 400 Hz operating frequency. The temperature difference between the hot end and cold end of the stack was observed to be 19.4, 17.2, 14 and 12.4°C for stacks 1, 2, 3 and 4, respectively, for 10 bar mean pressure and 2 W cooling load. The temperature difference and COP of the parallel plate stack are better compared with other stack geometries.