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91.
Elevated supersaturation of total dissolved gas (TDG) has deleterious effects in aquatic organisms. To minimize the supersaturation of TDG at hydropower dams, spillway flow deflectors redirect spilled water horizontally forming a surface jet that prevents bubbles from plunging to depth in the stilling basin. 相似文献
92.
Carlos B. da Silva Pedro Neto José C. F. Pereira 《Theoretical and Computational Fluid Dynamics》2009,23(4):287-296
Direct and large-eddy simulations (DNS/LES) of accelerating round jets are used to analyze the effects of acceleration on
the kinematics of vortex rings in the near field of the jet (x/D < 12). The acceleration is obtained by increasing the nozzle jet velocity with time, in a previously established (steady)
jet, and ends once the inlet jet velocity is equal to twice its initial value. Several acceleration rates (α = 0.02–0.6) and Reynolds numbers (Re
D
= 500–20000) were simulated. Acceleration maps were used to make a detailed study of the kinematics of vortex rings in accelerating
jets. One of the effects of the acceleration is to cause a number of new primary and secondary vortex merging events that
are absent from steady jets. As the acceleration rate α increases, both the number of primary merging events between rings
and the axial position where these take place decreases. The statistics for the speed of the starting ring that forms at the start of the acceleration phase for each simulation, agree well with the statistics for the “front” speed
observed by Zhang and Johari (Phys Fluids 8:2185–2195, 1996). Acceleration maps and flow visualizations show that during the
acceleration phase the near field coherent vortices become smaller and are formed at an higher frequency than in the steady
jet, and their (mean) shedding frequency increases linearly with the acceleration rate. Finally, it was observed that the
acceleration decreases the spreading rate of the jet, in agreement with previous experimental works.
相似文献
93.
《Journal of Nonlinear Mathematical Physics》2013,20(3):259-281
The article deals with local symmetries of the infinite-order jet space of C∞-smooth curves in ?m+1 (m ≥ 1). Transformations under consideration are the most general possible: they need not preserve the distinction between dependent and independent variables and the order of derivatives may be arbitrarily changed. Unlike the common prolonged point and Lie's contact transformations, they destroy the finite-order jet spaces. 相似文献
94.
用热线风速仪采集了圆喷嘴空气射流的速度时间序列,并采用一种基于最大Lyapunov指数不变性的混沌时间序列分析方法,计算了出口雷诺数在939≤Re≤3758范围内的速度信号的最大Lyapunov指数以及湍流的非拟序脉动.结果表明,最大Lyapunov指数随着雷诺数的增加而增大,随着离开喷嘴出口距离的增加而减小,而且最大Lyapunov指数的倒数与关联时间是正相关的.湍流的非拟序脉动随着雷诺数的增加以及随着离开喷嘴出口距离的增加均是逐渐增大的,而且湍流的非拟序脉动与Kolmogorov尺度是负相关的. 相似文献
95.
I provide a theoretical summary of some of the results from Hard Probes 2010. 相似文献
96.
Clyde Warsop Martyn Hucker Andrew J. Press Paul Dawson 《Flow, Turbulence and Combustion》2007,78(3-4):255-281
The design and validation of a microfabricated pulsed air-jet actuator for practical application to flow-separation control
at full-scale operating conditions on a medium/large air vehicle is presented. The actuator device is designed to generate
streamwise vortices within the boundary layer and comprises a pitched and skewed orifice of 200 μm diameter through which
a high velocity (200–300 m/s) jet of air can be modulated by operation of a piezoelectric microvalve. This paper describes
the overall design and manufacture of the actuator device with particular reference to the impact of fluid dynamic effects
on the design and operation. Key results obtained from both static and dynamic tests of a prototype device are also presented
and compared with original predictions. It is shown that the device that was developed and tested fulfils all the original
design requirements with regard to size, jet velocity and operating frequency. The developed device has dimensions of approximately
5 mm × 2 mm in the plane of the aerodynamic surface in which it is imbedded and a thickness of 1 mm. Peak jet velocities in
excess of 300 m/s through a 200 μm diameter orifice at 500 Hz have been demonstrated with peak driving voltages of 90 V and
a nominal electrical power consumption of 50 mW. 相似文献
97.
The flow patterns induced by floats of different shapes (sphere, short and long cylinders) freely sinking to the neutral-buoyancy horizon in a continuously stratified fluid are investigated using optical methods. General flow elements, both large-scale (waves, vortices, hydrodynamic wake) and fine-scale (boundary layers, extended autocumulative jets), are distinguished. For large times, the float oscillation frequencies are of the order of or greater than the buoyancy frequency of the medium. This indicates the significant effect of the induced flows on the motion of the float. 相似文献
98.
Further studies on high-speed liquid diesel fuel jets injected into ambient air conditions have been carried out. Projectile impact has been used as the driving mechanism. A vertical two-stage light gas gun was used as a launcher to provide the high-speed impact. This paper describes the experimental technique and visualization methods that provided a rapid series of jet images in the one shot. A high-speed video camera (106 fps) and shadowgraph optical system were used to obtain visualization. Very interesting and unique phenomena have been discovered and confirmed in this study. These are that multiple high frequency jet pulses are generated within the duration of a single shot impact. The associated multiple jet shock waves have been clearly captured. This characteristic consistently occurs with the smaller conical angle, straight cone nozzles but not with those with a very wide cone angle or curved nozzle profile. An instantaneous jet tip velocity of 2680 m/s (Mach number of 7.86) was the maximum obtained with the 40
nozzle. However, this jet tip velocity can only be sustained for a few microseconds as attenuation is very rapid.Received: 13 December 2003, Accepted: 11 April 2004, Published online: 11 February 2005[/PUBLISHED]K. Pianthong: Correspondence to: 相似文献
99.
A.?GouraraEmail author F.?Roger J.-M.?Most H.?Y.?Wang 《Flow, Turbulence and Combustion》2005,74(4):355-385
In this paper, a mixing of gases through square Jets issuing normally Into a CrossFlow (JICF) is investigated by means of
both numerical simulation and experiment. The jets are emitted by two injectors mounted at the top and bottom of an Injector
Frame (IF) which is installed at the center of an Eiffel type wind-tunnel. This jet configuration makes it possible to approximate
an industrial gas mixer placed at the center of a pipe. Large Eddy Simulation based on the Smagorinsky model is used, enabling
characterization of the mean and fluctuating velocities as well as the oscillating flow frequencies. Different diagnostic
techniques, such as Laser Doppler Anemometry and Particle Image Velocimetry are employed for validating the numerical models,
and a good agreement between prediction and experiment is obtained. In the numerical simulation, introduction of a passive
scalar through the jet makes it possible to show three dilution phenomena. They are generated respectively by the wake of
the IF, the jet/wake assemblage and the jets alone in function of the momentum flux ratio between jet and crossflow. Influence
of the various parameters on the mixing process between the jets and the crossflow is identified. The numerical results show
that if the IF wake is suppressed with the presence of a trailing edge behind the IF, classical formation of Counter-rotating
Vortex Pair is found. 相似文献
100.
Based on a series of numerical calculations, the behavior of flow field in obstructed square buoyant vertical jet is summarized and analyzed. Based on the axial line velocity distribution, the flow after the disc can be divided into three regions, i.e., recirculation region, transitional region and self-similar region The characteristic of self-similarity of upright velocity was validated. The three regions can also be distinguished based on the axial velocity. The axial velocity in self-similar region was found to obey the same law and the formula presented by introducing the velocity expression used by Chen and Rodi. The isolines of pressure on cross-sections of different heights were displayed and the production, expansion, breaking and disappearing of negative pressure regions were found. 相似文献