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实验研究了3毫米口径轴对称收缩喷嘴在各种压比下射流垂直冲击和倾斜冲击坚固大平板产生的噪声的指向特性。发现噪声在过平板法线和喷嘴轴线的平面内呈近似四瓣分布,当喷嘴与平板距离减小时,指向壁射流下游的瓣得到增强,反之,指向喷嘴上游的瓣得到增强。喷嘴压比增加时,指向壁射流下游的瓣得到增强,反之,指向喷嘴上游的瓣得到增强。根据自由射流噪声的基本指向特性、射流冲击噪声基本指向特性、声波在平板处发生镜面反射和声波能量叠加的设定,建立了一个冲击射流总体噪声指向特性的模型,成功解释了实验结果,并揭示了形成冲击射流总体噪声指向特性的内在机理。 相似文献
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为研究小口径喷嘴冲击射流的噪声特性,测定了3mm口径的轴对称收缩喷嘴在各种压比情况下产生的亚音速和超音速射流冲击坚固大平板产生的噪声。发现噪声在空间呈近似四瓣分布,当喷嘴与平板距离减小时,噪声指向壁射流下游的瓣到增强,反之,噪声指向喷嘴上游的瓣得到增强。噪声随喷嘴距平板距离的增加呈增强的趋势,在距平板一定距离内有锯齿现象。噪声随喷嘴压比的增加而增强,相应于各种工况,存在一不同的压比值,此压比之前,噪声随压比的增大而迅速提高,但有起伏现象,在此压比之后,噪声平缓地随压比的增大而增强。 相似文献
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水下超音速气体射流胀鼓和回击的关联性研究 总被引:6,自引:0,他引:6
阐述了水下超音速气体射流的实验研究结果. 用高速摄影仪实时记录了水下超音速气体射流喷射的状态, 清晰地演示了射流气体在上中游流域的演化过程. 具体分析了水下高速气体射流的动态不稳定性形貌, 并从实时记录的射流照片中统计测量出了胀鼓和回击随机频率.结果发现, 胀鼓频率越大, 回击频率越大; 胀鼓频率随着喷嘴的驻室压力与出口背压的比值增大而增大. 通过胀鼓与回击事件前后实验数据的对比分析表明其二者之间存在相关性: 胀鼓和回击均由射流内部压力振荡引发并且存在一定的随机性; 胀鼓是回击前的能量积聚一个前征和表现, 当胀鼓的振荡即能量积聚到一定程度后, 引发回击. 相似文献
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钻井液中加入体积分数为1%~3%的钢质粒子在钻头喷嘴处高速喷出冲击岩石,实现了粒子射流冲击和钻头机械联合破岩,有效提高了破岩效率。利用瞬态非线性动力学有限元模拟软件,基于光滑粒子流体动力学(smoothed particle hydrodynamics,SPH)方法,考虑流体对粒子射流冲击的影响,建立了粒子射流冲击破岩的物理模型,获得了粒子射流参数对破岩体积的影响规律,进行了室内实验验证,验证了SPH方法的有效性。结果表明:粒子射流冲击岩石表面形成规则的V型冲击坑;同条件下粒子射流破岩体积是水射流破岩体积的2~4倍;随着粒子射流冲蚀时间的增加,粒子射流破岩体积不断增加,但破岩效率降低;粒子射流压力大于10 MPa后,粒子射流破岩效率迅速增大;喷射角度大于6°后,破岩效率迅速减小。 相似文献
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水下欠膨胀高速气体射流的实验研究 总被引:14,自引:0,他引:14
采用实验途径研究了下水高速气体射流的动力学特性,研制了水下高速气体射流实验系统并发展了相应的测试手段。实验中,用插入式静压探针测量了射流轴线静压分布;用γ射线衰减法测量了径向空隙率分布,从而揭示了水下高速气体射流均压和掺混两个过程的基本规律。测量结果表明:水下高速气体射流在欠膨胀工况下运行时,近场将出现含有复杂波系结构的膨胀压缩区域,由于气水的掺混作用,水下欠膨胀气体射流均压化过程比空气中衰减得快。测量结果还表明,水下射流在近场区的混合层由气水两相占据,其流态从靠近气体侧的液滴流型过渡到靠近液体侧的气泡流型。 相似文献
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《实验力学》2020,(4)
为研究不同温压条件下超临界CO_2气爆过程中气爆管喷孔喷射的爆生气体对被爆物体产生的冲击应力变化规律,自主设计了超临界CO_2气爆实验系统及数据采集装置,实验得到了在不同初始温度和压力下对称双喷孔喷射的超临界CO_2气爆爆生气体冲击应力变化规律:喷孔喷出的爆生气体作用于被爆物体的冲击应力经历应力激增、应力剧减和应力减速衰减三个阶段。冲击应力时程变化曲线呈脉冲波形曲线特征,且冲击应力衰减阶段持续时间大于冲击应力激增持续时间。冲击应力随初始温度和初始压力的增大而增加,初始压力变化引起的气爆冲击应力变化比初始温度变化明显,增大超临界态CO_2的初始压力提高气爆冲击应力优于提高超临界态CO_2的初始温度。最后得到了冲击应力峰值P_(max)与初始温度T和初始压力P的关系P_(max)=ɑT+bP+C。 相似文献
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本文采用LIF(激光诱导荧光)流动显示和PIV(粒子图像速度场仪)测量对横流冲击射流的尾迹涡结构进行了实验研究。水槽实验是在三种流速比和两种冲击高度实验工况下进行的。由实验结果可得到两种明显的尾迹涡结构、,即射流尾迹涡和横流尾迹涡。横流冲击射流中形成的主要尾迹涡结构主要依赖于流速比。本文还对横流冲击射流近区范围内射流尾迹涡和横流尾迹涡的形成机理和演化特征进行了分析。 相似文献
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Velocity profiles and wall shear stress values in the wall jet region of planar underexpanded impinging jets are parameterized based on nozzle parameters (stand-off height, jet hydraulic diameter, and nozzle pressure ratio). Computational fluid dynamics is used to calculate the velocity fields of impinging jets with height-to-diameter ratios in the range of 15–30 and nozzle pressure ratio in the range of 1.2–3.0. The wall jet has an incomplete self-similar profile with a typical triple-layer structure as in traditional wall jets. The effects of compressibility are found to be insignificant for wall jets with Ma < 0.8. Wall jet analysis yielded power-law relationships with source dependent coefficients describing maximum velocity, friction velocity, and wall distances for maximum and half-maximum velocities. Source dependency is determined using the conjugate gradient method. These power-law relationships can be used for mapping wall shear stress as a function of nozzle parameters. 相似文献
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Shock and wave dynamics in cavitating compressible liquid flows in injection nozzles 总被引:1,自引:0,他引:1
Due to the exceptional high inlet pressures up to 2,000 bar flow dynamics and efficiency of modern injection systems are controlled by high frequency wave dynamics of the compressible liquid flow. Corresponding to alternating shock and expansion waves the liquid fluid evaporates and recondenses instantaneously. Here we present CFD simulations of the time accurate evolution of cavitating flows in 2-D plane and in six-hole injection nozzles with focus on the wave dynamics just after initialisation of the flow and within the time scale Δt ≤ 10?4 s of pilot and multi-point injection. Due to shock reflections at the bottom of the sack hole the instantaneous maximum pressure increases more than three times higher as compared with the prescribed pressure at the nozzle inlet. For instance, in case of an inlet pressure of 600 bar the maximum pressure in the sack and therefore ahead of the nozzle bore holes reaches about 2,100 bar. It is quite reasonable that this amplification of the pressure affects the evolution of the convective flow and therefore the mass flow through the nozzle bore holes. 相似文献
13.
An experimental investigation on flow structures of confined and unconfined impinging air jets 总被引:1,自引:0,他引:1
The flow characteristics of both confined and unconfined air jets, impinging normally onto a flat plate have been experimentally
investigated. The mean and turbulence velocities, and surface pressures were measured for Reynolds numbers ranging from 30,000
to 50,000 and the nozzle-to-plate spacings in range of 0.2–6. Smoke-wire technique is used to visualize the flow behavior.
The effects of Reynolds number, nozzle-to-plate spacing and flow confinement on the flow structure are reported. In the case
of confined jet, subatmospheric regions occur on both impingement and confinement surfaces at nozzle-to-plate spacings up
to 2 for all Reynolds numbers in consideration and they lie up to nearly the same radial location at both surfaces. However,
there is no evidence of the subatmospheric region in unconfined jet. It is concluded that there exists a linkage among the
subatmospheric region, turbulence intensity and the peaks in heat transfer coefficients for low spacings in impinging jets. 相似文献
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Flow kinematics of green water due to plunging breaking waves impinging on a simplified, 3D model structure was investigated
in the laboratory. Two breaking wave conditions were tested: one with waves impinging on the vertical wall of the model at
still water level, and the other with waves impinging on the horizontal deck surface. The bubble image velocimetry (BIV) technique
was used to measure flow velocities. Measurements were taken on both vertical and horizontal planes. Evolution of green water
flow kinematics in time and space was revealed and was found to be quite different between the two wave conditions, even though
the incoming waves are essentially identical. The time history of maximum velocity is demonstrated and compared. In both cases,
the maximum velocity occurs near the green water front and beneath the free surface. The maximum horizontal velocity for the
deck impinging case is 1.44C with C being the wave phase speed, which is greater than 1.24C for the wall impingement case. The overall turbulence level is about 0.3 of the corresponding maximum velocity in each wave
condition. The results were also compared with 2D experimental results to examine the 3D effect. It was found that the magnitude
of the maximum vertical velocity during the runup process is 1.7C in the 3D model study and 2.9C in the 2D model study, whereas the maximum horizontal velocity on the deck is similar, 1.2C in both 3D and 2D model studies. 相似文献
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Analysis of DNS and LES of Flow in a Low Pressure Turbine Cascade with Incoming Wakes and Comparison with Experiments 总被引:1,自引:0,他引:1
The flow around a low-pressure turbine rotor blade with incoming periodic wakes is computed by means of DNS and LES. The latter
adopts a dynamic sub-grid-scale model. The computed results are compared with time-averaged and instantaneous measured quantities.
The simulation sreveal the presence of elongated flow structures, stemming from the incoming wake vorticity, which interact
with the pressure side boundary layer. As the wake approaches the upstream half of the suction side, its vortical structures
are stretched and align with the main flow, resulting in an impingement at virtually zero angle of attack. Periodically, in
the absence of impinging wakes, the laminar suction side boundary layer separates in the adverse pressure gradient region.
Flow in the laminar separation bubble is found to undergo transition via a Kelvin–Helmholtz instability. Subsequent impingement
of the wake inhibits separation and thus promotes boundary layer reattachment. LES provides a fair reproduction of the DNS
results both in terms of instantaneous, phase-averaged, and time-averaged flow fields with a considerable reduction in computational
effort.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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A SIMPLE-C algorithm and Jones-Launder k-ε two-equation turbulence model are used to simulate a two-dimensional jet impinging obliquely on a flat surface. Both the continuity and momentum equations for the unsteady state are cast into suitable finite difference equations. The pressure, velocity, turbulent kinetic energy and turbulent energy dissipation rate distributions are solved and show good agreement with various experimental data. The calculations show that the flow field structure of the jet impinging obliquely on a flat surface is strongly affected by the oblique impingement angle. The maximum pressure zone of the obliquely impinging jet flow field moves towards the left as the oblique impingement angle is decreased. 相似文献
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A. M. Petrie 《Applied Scientific Research》1980,36(2):93-108
An experimental investigation has been completed to study several methods of avoiding the jet screech phenomenon due to air jet impingement on solid boundaries. Measurements were completed in the Mach number region of M=0.5 using a 25 mm diameter nozzle with the air jet impinging on flat, concave and convex boundaries. Sound pressure levels were recorded in the plane of the nozzle outlet at a distance of 1.46 m from the jet axis. Hot wire studies and the stagnation pressure at the impingement zone of the jet were also recorded.With the air jet impinging on the flat board normal to its surface a maximum sound pressure occurred at a spacing of approximately two nozzle diameters producing a distinct screech at a sound level of 20 dB above that of the free jet. Three methods of preventing this screech were studied. First, by inserting disturbances into the shear layer at the nozzle exit; second, by changing the geometry of the boundary shape to improve the jet stability in the impingement region; and third, by introducing disturbances at the stagnation region which had the effect of displacing the distinct screech to another frequency range. 相似文献
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A numerical method is employed to examine the flow in symmetrical, two‐dimensional branches of Y shape and Tee shape. The methodology is based on a pressure‐correction procedure within the frame of unstructured grids. Specified pressures are imposed at the outlets of the two branches. The area ratio of the branch is allowed to vary in the range of 2–3. Separation of the flow in the bifurcating region is inevitable. With equal outlet pressures, symmetrical flow patterns prevail except for the Y type branch under the conditions of high Reynolds numbers and large area ratios. This implies that the Y‐branch flow is more sensitive to small disturbances. It is shown that with a slightly higher pressure imposed on one of the two branches the structure of the recirculating flow for the Y type is greatly affected and the flow rate is reduced dramatically in the high‐pressure branch channel. In contrast, the influence on the Tee type branch is much lower since the flow behaves like a jet impinging on a confined duct. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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Structure of instantaneous flow reversals has been measured in a highly turbulent axisymmetric diffuser flow using pulsed-wire anemometry. In this 8° nominal included angle conical diffuser, the adverse pressure gradient (APG) is strong enough to cause appreciable instantaneous flow reversals (instantaneous backflow up to 30% of the time), but the time-averaged flow is non-separated. The results are compared with the other severe APG separating flows reported in literature. An increase in entry Reynolds number indicated a decrease in the size of near-wall instantaneous reversals region as well as a decrease in the magnitude of instantaneous backflow. Also, the region of instantaneous reversals moves slightly downstream at appreciably higher Reynolds numbers. The initiation and growth of instantaneous reversals in a conical diffuser was found to strongly influence the wall-layer and the central region. Present results also suggest that the instantaneous backflow should be considered for modelling of instantaneously-separating diffuser flows. In the final stages of a conical diffuser, the magnitudes of cross-stream pressure gradient were found to be appreciably larger than that of the longitudinal pressure gradient, indicating that accurate representation of a conical diffuser flow can not be achieved without considering V-momentum equation. A comparison of various separating flows revealed remarkable similarity of instantaneous reversals regions and distributions even in different flow configurations. 相似文献
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高压液体通过喷嘴加速,形成高速射流,与相反方向的另一股射流相互撞击,发生强烈的相互作用,产生强烈的径向和轴向湍流速度分量以及狭窄的高压高速湍流区,在此区域内,相间或液滴间的碰撞互磨产生的挤压力和剪切力使流体被细化。本文从液体连续相撞击流的两个特征:微观混合和压力波动入手,逐一分析了撞击速度与微观混合、压力波动的关系,得出了压力波动与撞击流速度乱U0成正比关系,微观混合与U^3 0成正比的规律。同时,用流体模拟软件Fluent对喷嘴的结构和尺寸进行优化,并得出最合理的喷嘴结构和尺寸。模拟认为:在相同压力下,采用矩形槽,出口孔径为0.2mm,槽的深度为0.27mm的结构时撞击速度达到最大,并通过实验验证了这一结论。 相似文献