类鱼雷形涡中速度场,速度矢量场,PIV,粒子成像测速检测方案(粒子图像测速)
The flow field of a laboratory-simulated tornado was studied by means of 2-D Particle
Image Velocimetry or PIV technique with the purpose of investigating the effects of roughness on
the near-ground tornado-like vortex structure and its velocity distribution. The results show the flow
regime transition from multi-celled vortices over the smooth surface at a higher swirl ratio to singleor
dual-celled vortices with roughness. Significant difference in velocities and turbulence
characteristics is observed as a result of increasing ground roughness. This work is part of a project
that seeks better understanding of the near-ground flow field and resulting wind-induced loads on
structures in a tornado.
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速度场,速度矢量场,PIV,粒子成像测速
北京欧兰科技发展有限公司
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流体中PIV,粒子成像测速,流体图像,小波分析检测方案(粒子图像测速)
Flow past a cylinder in an unbound medium gives rise to
self-sustained, limit cycle oscillations involving formation
of a regular, periodically alternating Karman vortex street.
However, little attention has been paid to the effect of an
adjacent free surface on the development of the Karman
vortices and possible generation of new classes of the nearwake
structure[1], see Figure 1. The technique of Particle
Image Velocimetry (PIV) is a useful tool to this flow,
considering that it is unsteady and multi-scale in nature.
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PIV,粒子成像测速,流体图像,小波分析
北京欧兰科技发展有限公司
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流体中2D3C速度矢量场,时间分辨速度矢量场检测方案(粒子图像测速)
In the last years, several techniques have been developed and improved in such a way that it is
possible to measure the three velocity components in a flow. Some techniques as Stereoscopic PIV or
holographic PIV are well known. Others, like tomographic PIV started to develop more recently.
Stereoscopic Particle Image Velocimetry (SPIV) or Tomographic PIV need a complex set-up, involving flow
visualization with several cameras, and present important restrictions when applied to confined liquid flows.
Others like Holographic PIV cannot be applied in flows with a high particle density. Here a new technique,
called High Speed Digital Image Plane Holography has been developed for the measurement of the three
velocity components in a complex geometry brain aneurysm model using a configuration similar to regular
PIV. This was done by using a two cavity high speed laser, one double frame high speed camera and normal
visualization. The two in-plane velocity components were obtained from the holograms reconstructed
intensity distribution using a PIV analysis. The out-of plane component was obtained from the reconstructed
phase differences using an interferometric method. Due to the laser short coherence length, a portable and
compact system has been built in order to be able to the measure larger fluid areas.
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2D3C速度矢量场,时间分辨速度矢量场
北京欧兰科技发展有限公司
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多重介电阻挡放电,DBD,离子体制动器中流场,速度场,速度矢量场检测方案(粒子图像测速)
This work presents preliminary results of flow separation control from the flap of a
high-lift airfoil using a single dielectric barrier discharge (DBD) plasma actuator. Control
effectiveness is investigated for two actuator locations as well as various reduced frequencies,
applied voltages and waveforms. Results show that a single DBD plasma actuator located at
the flap shoulder can slightly increase or reduce the size of the time-averaged separation
bubble over the flap depending on the frequency of actuation. This effectiveness is not
improved by an increase in applied voltage or a change from a sinusoidal to positive
sawtooth waveform for the cases examined. Spatial eigenmodes calculated from twocomponent
PIV using POD show that a single DBD plasma actuator at the flap shoulder can
have a significant effect on the structure of higher order modes. However the corresponding
energy of these modes is low in comparison to the dominant modes in the wake.
Nomenclature
Cp =
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流场,速度场,速度矢量场
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冲击合成射流中热量传导行为,流场特征,速度场,速度矢量场检测方案(粒子图像测速)
Impinging synthetic jets are considered as a potential solution for convective cooling, in applications that match their main characteristics (high local heat transfer rates, zero net mass flux, scalability, active control). Nevertheless the understanding of heat transfer to synthetic jets falls short of that available for steady jets. To address this, this paper uses detailed flow field measurements to help identify the main heat transfer mechanisms in impinging synthetic jets.
Local heat transfer measurements have been performed for an impinging round synthetic jet at a range of Reynolds numbers between 1000 and 3000, nozzle to plate spacings between 4D and 16D and stroke lengths (L0) between 2D and 32D. The heat transfer results show evidence of distinct regimes in terms of L0/D and L0/H ratios. Based on appropriate scaling, four heat transfer regimes are identified which justifies a detailed study of the flow field characteristics.
High speed particle image velocimetry (PIV) has been employed to measure the time-resolved velocity flow fields of the synthetic jet to identify the flow structures at selected L0/H values corresponding to the identified heat transfer regimes. The flow measurements support the same regimes as identified from the heat transfer measurements and provide physical insight for the heat transfer behaviour.
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热量传导行为,流场特征,速度场,速度矢量场
北京欧兰科技发展有限公司
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微流体中速度场,2D3C速度场检测方案(粒子图像测速)
In this paper a comparative study is presented to assess the uncertainty of two methods for 3C3D velocimetry in microscopic flows: stereoscopic micro-particle image velocimetry (S-μPIV) and wavefront-deformation, or astigmatism, micro-particle tracking velocimetry (WD-μPTV). First, the main parameters affecting both methods’ measurement uncertainty are identified, described and quantified. Second, the test case of flow over a backward-facing step is analyzed using both methods. For comparison standard 2D-2C μPIV measurements and numerical flow simulations are shown as well. Advantages and disadvantages of both methods are discussed.
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速度场,2D3C速度场
北京欧兰科技发展有限公司
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湍动边界层,近壁面湍流,流体中流场,速度矢量场,速度场检测方案(粒子图像测速)
One of the fascinating phenomena of natural science which has gripped the attention of
many scientists is the problem of turbulence. Besides the ubiquitous variety and beauty
of turbulent phenomena, the inherent fascination and attraction are strongly connected
with the enormous difficulties associated to its physical and mathematical understanding.
As a general solution is out of reach, the properties of different idealized flows with simple
geometries are being examined experimentally and numerically.
Since its discovery by Prandtl, the boundary layer has been a subject of growing interest
and is still an active subject of research. Due to both its fundamental and technical
interest, the fully developed turbulent boundary layer in a nominally zero pressure gradient
(ZPG) has been examined extensively. A flow of equal importance and perhaps more
widely observed in practice is the turbulent boundary layer (TBL) in the presence of an
adverse pressure gradient (APG). This flow has not received the same attention as the
ZPG TBL due to its increased complexity and the necessity of firstly understanding the
ZPG situation.
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流场,速度矢量场,速度场
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空气流体中速度矢量场检测方案(粒子图像测速)
To gain some more understanding of the flapping wing aerodynamics and aeroelasticity associated with biological flyers and micro air vehicles (MAVs), a combined computational and experimental study of a well characterized flapping wing structure was conducted. In particular, the coupling between aerodynamics and structural dynamics plays an important role in such flyers but to date has not been adequately addressed. An aeroelasticity framework based on a co-rotational shell finite element solver with a Navier-Stokes solver is developed. Experimentally, a customized digital image correlation system measures the wing deformation, a load sensor attached to the flapping mechanism records the forces produced by the flapping motion, and a stereo digital particle image velocimetry measures the flow velocities. Computational efforts with insight into the fluid physics are reported. Relevant fluid physics are documented including the counter-rotating vortices at the leading and the trailing edge which interact with the tip vortex during the wing motion. Overall, good correlations between experiment and computation are attained. Furthermore, studies on hypothetical flexible flapping wing configurations showed that wing flexibility can be tailored to alter the aerodynamics of a flapping wing.
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速度矢量场
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液体流、气体流、两相流、气液两相流中速度场,多相流检测方案(粒子图像测速)
Liquid andliquid/gasflowsthroughspacerfilledchannelswerestudiedusingParticleImagingVelocime-
try (PIV)toprovideexperimentalsupportforvelocitydistributionsobtainedfromComputationalFluid
Dynamics studiesavailableintheliterature.ItisshownthatPIVisasuitabletechniqueformeasuring
velocity profilesinspacerfilledchannels,althoughcarehastobetakenwheninterpretingtheresults.
PIV measurementswerecarriedoutforanentireflowcell(5cm×15 cm),asmallerareaofroughly
7mm×8mmandforasinglespacercell(2.5mm×3 mm).Theexperimentalresultsshowthatfluidflow
is welldistributedacrosstheentireflowcellinthecaseofsingle-phaseflow.Therecordingsofthesingle
spacer cellshowedthatliquidflowismainlyparalleltothespacerfilamentsandthereforethedirec-
tion offlowchanges90◦ over theheightofthechannel.Introductionofairbubblesintroducedstrong
local velocitygradients.Theliquidvelocityintwo-phaseflowsisshowntobemoreunsteadythanin
the caseofsingle-phaseflow,whichisadvantageouswhentryingtopreventfoulingorconcentration
polarization.
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速度场,多相流
北京欧兰科技发展有限公司
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圆柱尾迹,湍流,三维相干结构中3D3C速度矢量场,速度场,体视速度场,层析速度场检测方案(粒子图像测速)
The wake of a circular cylinder at Re = 2700 is investigated by means of Tomographic PIV
(Tomo-PIV), a recently developed three-dimensional velocimetry technique. The paper presents the
principles of Tomo-PIV and discusses in details the implementation of the technique to the experimental
conditions. With a measurement volume of approximately 40x40x10 mm2 two configurations are chosen in
order to describe both the 2D wake features and the span wise organization of secondary rollers dominating
the 3D flow organization. The present data allow to directly evaluate the measurement error imposing mass
conservation inside the volume (viz. solenoidal velocity field). The visualization of the wake instantaneous
structure is obtained by means of vorticity vector magnitude iso-surfaces, or decomposing the vorticity in the
span wise and stream-wise(normal)/bi-normal component, which return the separate contribution of the
Kármán rollers and the interconnecting structures between them respectively. The properties of the
secondary rollers are given in terms of span wise wavelength, peak vorticity, vorticity stretching and their
size and shape. A value of the span wise wavelength λ
z/D = 1.2 is recurring and the rollers organization into
pairs is found to be similar to the instability Mode B occurring in lower Reynolds number wakes investigated
with previous studies.
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3D3C速度矢量场,速度场,体视速度场,层析速度场
北京欧兰科技发展有限公司
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等离子体制动器,高速高雷诺数喷射,流动,噪声中流动和噪声控制,噪声,速度场,矢量场检测方案(粒子图像测速)
The idea of manipulating flow to change its characteristics is over a century old. Manipulating instabilities of a jet to increase its mixing and to reduce its radiated noise started in the 1970s. While the effort has been successful in low-speed and low Reynolds number jets, available actuators’ capabilities in terms of their amplitude, bandwidth, and phasing have fallen short in control of high-speed and high Reynolds number jets of practical interest. Localized arc filament plasma actuators have recently been
developed and extensively used at Gas Dynamics and Turbulence Laboratory (GDTL) for control of highspeed and high Reynolds number jets. While the technique has been quite successful and is very
promising, all the work up to this point had been carried out using small high subsonic and low supersonic jets from a 2.54 cm diameter nozzle exit with a Reynolds number of about a million. The
preliminary work reported in this paper is a first attempt to evaluate the scalability of the technique.
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流动和噪声控制,噪声,速度场,矢量场
北京欧兰科技发展有限公司
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漩涡,空穴中漩涡间相互作用,空穴生成机理,速度场,速度矢量场,流场检测方案(粒子图像测速)
Multiple concentrated vortices are often produced in the wake of lifting surfaces and downstream of pumps, turbines, and propulsors. The roll-up of multiple vortex strands is a common feature of these flows. In this study, we are examining the interaction of two vortices of variable strength and relative rotation (e.g. co-rotating or counter-rotating). A pair of equal-strength co-rotating vortices will merge to form a single vortex. However, as the relative strength of the vortices is decreased, the weaker vortex can wrap around the stronger vortex, causing the weaker vortex to be stretched. This stretching process can lead to cavitation inception. In the present work, we will examine this inception process.
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漩涡间相互作用,空穴生成机理,速度场,速度矢量场,流场
北京欧兰科技发展有限公司
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横流扇,空气流,内部流场结构中速度矢量场,速度场,内部流场,流场结构检测方案(粒子图像测速)
室内机的流场结构会因为不同的压损值以及搭配的不同转速时会有所不同，主要分成兩种形式。当压损较小时，通过横流扇而被提供动能的流体，大多能沿著背板的几何形狀朝下游移动。若当压损逐渐提高，在低转速下的流场结构会产生明显的差異，在葉輪侧靠近出口处区域与舌部下方的之间，回流区范围有显著的扩大趋势，在靠近葉輪部分流体的运动方向可被观测出有被卷吸回葉輪的情形，大多是受到高速旋转的葉輪在通过舌部後，产生的低压结构所引致的现象。此时若提高葉輪的转速，将有助於提供流体更多的动量，可使舌部附近的回流区结构缩小，同时在横流扇入口上方的回流区结构也明显受到抑制。
然而，当压损值提高时，不同转速下的流场结构相当類似，葉輪上方的入风口处，都有明显的回流结构，部分情形下甚至可达近一半的入口面积。另外，出风口处的回流区结构相当大，速度较大的区域皆集中在弧形背板处，并且造成出口处的气流速度产生骤降的现象。当压损在特定范围以上时，本研究之横流扇的出风特性有明显的变化，即便再提高转速，仍无法提供流体产生足够的动量，以形成有效的气流流动，风扇运转已偏離有效操作点。
经由上述的实验结果中得知，此横流扇结构在低压损或是高转速下的出风流场结构多能沿著背板进而流至出风口。倘若压损提高或转速降低时，出口风速锐减，室内机的送风性能明显降低。因此，此室内机的几何形狀应针对不同的压损下的送风性能讨論，进行改良设计，本文以PIV进行量测，提供一种快速有效的研究方法。
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速度矢量场,速度场,内部流场,流场结构
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