共查询到20条相似文献,搜索用时 91 毫秒
1.
The present study addresses an experimental investigation of the near field flow structures of supersonic, dual, coaxial,
free, jet, which is discharged from the coaxial annular nozzle. The secondary stream is made from the annular nozzle of a
design Mach number of 1.0 and the primary inner stream from a convergent-divergent nozzle. The objective of the present study
is to investigate the interactions between the secondary stream and inner supersonic jets. The resulting flow fields are quantified
by pitot impact and static pressure measurements and are visualized by using a shadowgraph optical method. The pressure ratios
of the primary jet are varied to obtain over-expanded flows and moderately under-expanded flows at the exit of the coaxial
nozzle. The pressure ratio of the secondary annular stream is varied between 1.0 and 4.0. The results show that the secondary
annular stream significantly changes the Mach disc diameter and location, and the impact pressure distributions. The effects
of the secondary annular stream on the primary supersonic jet flow are strongly dependent on whether the primary jet is underexpanded
or over-expanded at the exit of the coaxial nozzle. 相似文献
2.
A supersonic dual coaxial jet has been employed popularly for various industrial purposes, such as gasdynamic laser, supersonic
ejector, noise control and enhancement of mixing. Detailed characteristics of supersonic dual coaxial jets issuing from an
inner supersonic nozzle and outer sonic nozzles with various ejection angles are experimentally investigated. Three important
parameters, such as pressure ratios of the inner and outer nozzles, and outer nozzle ejection angle, are chosen for a better
understanding of jet structures in the present study. The results obtained from the present experimental study show that the
Mach disk diameter becomes smaller, and the Mach disk moves toward the nozzle exit, and the length of the first shock cell
decreases with the pressure ratio of the outer nozzle. It was also found that the highly underexpanded outer jet produces
a new oblique shock wave, which makes jet structure much more complicated. On the other hand the outer jet ejection angle
affects the structure of the inner jet structure less than the pressure ratio of the outer nozzle, relatively. 相似文献
3.
S. Marimuthu A. K. Nath P. K. Dey D. Misra D. K. Bandyopadhyay S. P. Chaudhuri 《The International Journal of Advanced Manufacturing Technology》2017,92(1-4):15-24
Laser cutting of carbon steel is extensively used across a range of industries, due to its advantage of high speed, low kerf and high quality. Currently, a 1-kW carbon dioxide (CO2) laser with its subsonic nozzle assembly can be used only to cut steel plates up to around 10 mm. This paper aims to design and evaluate a high-pressure supersonic laser cutting nozzle assembly, which can enable a 1-kW CO2 laser to cut steel of up to 50 mm thickness. Basic gas dynamic and compressible flow equations were used to design the supersonic nozzle assembly. The flow of the high-pressure gas jet inside the nozzle assembly was investigated using computational fluid dynamics (CFD), and the structural integrity of the high-pressure nozzle assembly was ensured using finite element analysis (FEA). The gas flow pattern at the exit of the nozzle assembly was computed and compared with the experimental observation made through a shadowgraph technique. Laser cutting experiments were performed with the developed supersonic nozzle assembly to demonstrate cutting of 50-mm-thick low carbon steel with 1-kW CO2 laser. 相似文献
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5.
Toshiyuki Aoki Yong-Hun Kweon Yoshiaki Miyazato Heuy-Dong Kim Toshiaki Setoguchi 《Journal of Mechanical Science and Technology》2006,20(4):522-532
It is well known that screech tones of supersonic jet are generated by a feedback loop driven by the instability waves. Near
the nozzle lip where the supersonic jet mixing layer is receptive to external excitation, acoustic disturbances impinging
on this area excite the instability waves. This fact implies that the nozzle lip thickness can influence the screech tones
of supersonic jet. The objective of the present study is to experimentally investigate the effect of nozzle-lip thickness
on screech tones of supersonic jets issuing from a convergent-divergent nozzle. A baffle plate was installed at the nozzle
exit to change the nozzle-lip thickness. Detailed acoustic measurement and flow visualization were made to specify the screech
tones. The results obtained obviously show that nozzle-lip thickness significantly affects the screech tones of supersonic
jet, strongly depending on whether the jet at the nozzle exit is over-expanded or under-expanded. 相似文献
6.
为进一步提高舱外航天服供氧通风能力,对其引射器进行优化设计。采用一维气体动力学模型建立喷嘴控制方程;根据实验结果确定喷嘴等熵效率,设计缩放喷嘴;采用3D打印技术加工不同结构的引射器;利用氮气进行常压引射实验,研究挡板位置、喷嘴类型与喷嘴出口位置(Nozzle Exit Position,NXP)等结构参数对混合流量的影响,寻找最优的引射器结构。研究表明:挡板位置对引射器混合流量的影响与喷嘴类型相耦合。前移挡板,亚音速引射器混合流量可提高56.90%以上,而超音速引射器则降低12.08%以上。将渐缩喷嘴换为缩放喷嘴,混合流量可以提高1.81倍以上;对于挡板前移的亚音速引射器,则可提高36.90%以上。所有亚音速引射器均无法满足当前性能要求。然而,对于超音速引射器,对于所有的NXP,在典型工况下引射器循环量均可满足要求;存在最优的NXP使得混合流量最大。NXP为6 mm时,超音速引射器混合流量最大,为144.83 L/min(工作流绝对压力为0.503 MPa);在全工况下(工作流表压为0.30~0.55 MPa),混合流量可至少提高1.59倍。设计的最优引射器测试结果均满足性能要求。 相似文献
7.
为研究收缩喷嘴内部流道形成对射流流场的气体动特性参数的影响,根据可压缩流体轴对称N-S方程,采用非结构网格和二阶精度的有限体积法,对不同内部流道形线的喷嘴自由射流进行数值模拟。亚声速射流采用RNGk-ε湍流模型,超声速射流采用S-A湍流模型,计算结果与实验较吻合。在亚声速流动中,收缩喷嘴的收缩角大小会影响其对射流的阻滞效果,内部流道形线设计为维多辛斯基曲线可以获得更好的流场动特性参数,有利于提高喷嘴的工作效率。在超声速流动中,喷嘴流道型线对出口膨胀波的角度与强弱影响较大,要根据射流的有效作用区域选择合适的喷嘴,才能使能量的损失最小。若要获得较佳的外部流场参数,优化喷嘴内部流道设计十分重要。 相似文献
8.
In this experimental work, the effect of square grooves on the structure of a supersonic jet emanating from a circular nozzle has been investigated at three different nozzle inlet total pressures i.e 360 kPa, 550 kPa and 720 kPa. The nominal exit Mach number is 1.8. A new empirical relation for predicting the supersonic core length for grooved nozzle has been suggested. Further, a new parameter “groove effectiveness” has also been suggested to quantify the effect of the groove by using the total pressure data in the supersonic core length. Experimental results suggest that at higher nozzle inlet total pressure, the groove effectiveness plays a minor role. From the jet centreline total pressure data, supersonic core length, the locations at which 50 % and 90 % decay occurs have been obtained. It has been observed that higher groove effectiveness is associated with smaller values of supersonic core length, L50% and L90%. Schlieren images of the jet structure shows unsymmetrical shock pattern of jets emanating from a single grooved nozzle. 相似文献
9.
Various experimental data, including mixing areas, cross correlation factors, surface flow patterns on nozzle walls, and far field noise spectra, was used to draw a noise control mechanism in a supersonic jet. In the underexpanded case, mixing of the jet air with ambient air was significantly enhanced as presented before, and mixing noise was also dramatically reduced. Screech tones, in the overexpanded case, were effectively suppressed by trailing edge modifications, although mixing enhancement was not noticeable. From mixing and noise performance of nozzles with modified trailing edges, enhancing mixing through streamwise vortices seems an effective way to reduce mixing noise in the underexpanded flow regime. However, screech tones in the overexpanded flow regime is well controlled or suppressed by making shock cells and/or spanwise large scale structures irregular and/or less organized by a proper selection of trailing edges. The noise field in the overexpanded flow regime was greatly affected by the symmetricity of the nozzle exit geometry. In the underexpanded flow regime, the effects of the symmetricity of the nozzle exit on mixing were negligible. 相似文献
10.
Sang-Joon Lee Hak-Lim Kim Jin-Pyung Lee Sundara Rajagopalan 《Journal of Mechanical Science and Technology》2012,26(12):4007-4016
The flow characteristics of jets issued from a sinusoidal nozzle with in-phase and 180° out-of-phase exit configurations were investigated using PIV (particle image velocimetry) and flow visualization techniques. The experiments were carried out at a Reynolds number of about 6300 based on the mean width of the jet nozzle. Compared to a normal rectangular jet, the sinusoidal nozzle jets have smaller velocity deficits as the flow goes downstream. In addition, the turbulence intensity is suppressed in the horizontal center plane. For the case of in-phase wavy nozzle jet, the length of the potential core exhibits small variations along the lateral direction, while the 180° out-of-phase wavy nozzle jet shows large lateral variation in the length of potential core. The turbulent kinetic energy of the 180° out-ofphase nozzle jet also shows sinusoidal variation in the horizontal planes. Large-scale vortices shed from the sinusoidal edge of the nozzle interact strongly and migrate toward the center plane as the flow develops downstream. 相似文献
11.
SangYeop Han 《Journal of Mechanical Science and Technology》2001,15(5):646-655
This paper reports the effects of nozzle exit boundary layer swirl on the instability modes of underexpanded supersonic jets emerging from plane rectangular nozzles. The effects of boundary layer swirl at the nozzle exit on thrust and mixing of supersonic rectangular jets are also considered. The previous study was performed with a 30° boundary layer swirl (S=0.41) in a plane rectangular nozzle exit. At this study, a 45° boundary layer swirl (S=1.0) is applied in a plane rectangular nozzle exit. A three-dimensional unsteady compressible Reynolds-Averaged Navier-Stokes code with Baldwin-Lomax and Chien’sk-ε two-equation turbulence models was used for numerical simulation. A shock adaptive grid system was applied to enhance shock resolution. The nozzle aspect ratio used in this study was 5.0, and the fully-expanded jet Mach number was 1.526. The “flapping” and “pumping” oscillations were observed in the jet’s small dimension at frequencies of about 3,900Hz and 7,800Hz, respectively. In the jefs large dimension, “spanwise” oscillations at the same frequency as the small dimension’s “flapping“ oscillations were captured. As reported before with a 30° nozzle exit boundary layer swirl, the induction of 45° swirl to the nozzle exit boundary layer also strongly enhances jet mixing with the reduction of thrust by 10%. 相似文献
12.
For most operations in process, petroleum and power industries gas-liquid two phase flows occurs, so an accurate estimation of void fraction is vital because it affects the calculations of heat and mass transfer as well as hydrodynamics. Any inaccuracy in estimation may lead to drastic incidents along with heavy monetary loss. An effort has been made here to estimate the approximate void fraction of supersonic steam jet into the sub-cooled water. Electrical Resistance Tomography (ERT) has been used for the purpose along with the Electrical Impedance Tomography and Diffuse Optical Tomography Reconstruction Software (EIDORS) to generate the conductivity scans obtained by ERT setup. Before the experimentation, for further assurance on our void fraction estimations, the measurement system has been calibrated by securing scans of heated Teflon rod of diameter 6 mm, which is approximately having the same cross-sectional surface area as the steam jet have and reported in previous studies at the same hydrodynamic conditions. Images of supersonic steam jet in subcooled water have been processed by the help of EIDORS and image processing technique. The over estimation in void fraction of Teflon rod is ranging from 46.17 to 83.44% and when it is subtracted from the total void fraction of supersonic steam jet (46.51–83.79%) at steam inlet pressure of 1.5–3.0 bar and surrounding water temperature 30–60 °C respectively, the actual void fraction of Teflon rod comes out to be ranging from 0.34% to 0.35% of the total cross-sectional area of vessel. When these results are compared with the previous studies, a close agreement has been observed between these two sets of results. 相似文献
13.
This experimental study reports on testing of a single circular jet in crossflow (JICF) for three different jet-to-crossflow
velocity ratios: R=0.5, 1.0, and 1.5. Velocity measurements were made using a hot-wire anemometer. Experimentally obtained
JICF data were processed using Fourier, wavelet, and proper orthogonal decomposition (POD) techniques. Power spectrum obtained
by Fourier analysis shows that flow at the center of nozzle has better laminar property than subsequent stations. The principle
observation is that when jet exit velocity increases, the energy of the flow decreases. The center of the nozzle jet acts
as an obstacle and damps the effect of the crossflow. Wavelet analysis reveals the dominant frequencies of the flow to 45
Hz for R=0.5 and 85–105 Hz for R=1.0. Energy distribution of the flow was also calculated by using the POD technique; results
show that lower velocity ratio carries more energy of the flow. 相似文献
14.
Experimental study on hysteresis phenomena of shock wave structure in an over-expanded axisymmetric jet 总被引:1,自引:0,他引:1
Shigeru Matsuo Toshiaki Setoguchi Junji Nagao Miah Md. Ashraful Alam Heuy Dong Kim 《Journal of Mechanical Science and Technology》2011,25(10):2559-2565
In recent studies on two-dimensional supersonic jets, it is reported that the hysteresis phenomenon for the reflection type of shock waves in the jet flow field is occurred under the quasi-steady flow condition and this phenomenon is affected by the transitional pressure ratio between the regular reflection and Mach reflection. However, so far, there are few researches on the hysteresis phenomenon for the transition of shock waves between regular and Mach reflection in over-expanded supersonic jets and the phenomenon has not been investigated satisfactorily. Therefore, the purpose of this study is to clarify the hysteresis phenomena for the reflection type of shock wave in the over-expanded axi-symmetric supersonic jet experimentally, and to discuss the relationship between hysteresis phenomenon and rate of the change of pressure ratio with time. Furthermore, the effect of Mach number at the nozzle exit on hysteresis loop was investigated for two kinds of nozzle. 相似文献
15.
Soon-Bum Kwon Sung-Jin Lee Seung-Young Shin Sung-Ha Kim 《Journal of Mechanical Science and Technology》2009,23(6):1736-1742
As recognized previously, a minimum-length nozzle has the smallest possible throat-to-exit length that is still capable of
maintaining uniform supersonic flow at the nozzle exit. In the present study, for the flow of moist air through a nearly minimum-length
nozzle designed by the method of characteristics, the effects of nonequilibrium condensation on the uniformity of flow properties,
the momentum efflux, and the flow distortion at the nozzle exit plane are discussed by experiment and numerical analysis of
a third-order Total Variation Diminishing (TVD) finite difference scheme. The onset and zone of nonequilibrium condensation
in a minimum-length nozzle are quite different from those of a general convergent-divergent supersonic nozzle. We know that
the uniformity of flow properties at the nozzle exit with regard to the flow with nonequilibrium condensation in a minimum-length
nozzle cannot be guaranteed. On the other hand, owing to the positions of the onset of condensation at the incident region
of expansion waves from the sharp corner just downstream of the nozzle throat, the deceleration gradient and magnitude of
heat released from the process of nonequilibrium condensation to the surrounding of ϕ0=60% are greater than those of ϕ0=70% in the case of T0=290K. Furthermore, it has been determined that the decrease in efflux of momentum from the nozzle exit for the stagnation
relative humidity of ϕ0=70%(T0=290K), which corresponds to the case with nonequilibrium condensation shock, is 6.8% smaller than that of isentropic expansion.
This paper was recommended for publication in revised form by Associate Editor Do Hyung Lee
Soon-Bum Kwon received his B.S. and M.S. degrees in Mechanical Engineering from Kyungpook National University in 1974 and 1980, respectively,
and his Ph.D. degree from Kyushu University in 1987. He is a Professor at the School of Mechanical Engineering at Kyungpook
National University. His research interests are compressible gas dynamics and nonequilibrium condensation. 相似文献
16.
Four types of pyramidal sonic nozzles made of silicon crystal were studied experimentally. The throat sizes varied from 38 to 140 μm for type A and D nozzles and from 75 to 188 μm for type B and C nozzles. For each of the nozzle types, the results show that the discharge coefficient is proportional to the throat size, and the critical back pressure ratio for choking is insensitive to Reynolds’ number. In parallel, the flow field of a type B nozzle was investigated by numerical simulation. The effect of heat flux coming from the nozzle body was examined and the flow patterns obtained from Spalart-Allmaras and standard k−ω turbulence models were compared. The simulation results indicate the heat flux does not noticeably change the velocity field and discharge coefficient. Also, the flow downstream of the nozzle throat develops into an under-expanded supersonic jet in which expansion and oblique shock waves appear alternately. 相似文献
17.
为了获得更好的清洗效果和节能环保,提出了一种新型的射流方式——气溶性射流。基于流体力学和气溶性射流的工作原理,根据气溶性射流的特性和喷嘴的几何特征,研究了气液相的流动特性方程,得到了气溶性射流的速度分布规律。利用自行设计的超音速喷嘴组装的带电气溶性射流实验装置对钢板进行清洗,经简易检测表明:气溶性射流喷嘴产生的超音速极大地提高了洗涤效率,与同流量的喷嘴相比,效率提高近10倍,具有广泛的应用前景。 相似文献
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Sang-Joon Lee Young-Gil Jang Yong-Seok Choi 《Journal of Mechanical Science and Technology》2012,26(9):2765-2771
Three-dimensional (3D) flow structures of a turbulent jet issuing from a sharp-edged circular nozzle having multiple triangular tabs are experimentally studied by employing a stereoscopic-PIV (SPIV) system. Two different sharp-edged jet nozzles having 4 and 8 tabs are investigated at a jet Reynolds number of Re = 10,000. The SPIV measurements are carried out at 5 different cross-sectional planes along the jet direction. Spatial distributions of turbulent statistics including mean velocity, mean vorticity, and turbulent kinetic energy are obtained at each cross-sectional plane. The jet entrainment rate showing the mixing of the jet and ambient fluids is also estimated using the measured 3D velocity field information. As a result, the jet issuing from the nozzle with 4 tabs shows better turbulent mixing effect at further downstream position than the 8 tabs case because of the reduced reciprocal interactions of the streamwise vortices that promote the turbulent dissipation. 相似文献