Highly spatially resolved velocity measurements of a turbulent channel flow by a fiber-optic heterodyne laser-Doppler velocity-profile sensor

Shirai, Kohji; Pfister, Thorsten; Büttner, Lars; Czarske, Jürgen; Müller, H.; Becker, Stefan; Lienhart, H.; Durst, F.

doi:10.1007/s00348-005-0088-3

Cited by 33 publications

(21 citation statements)

References 29 publications

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“…For short working distances, the resolution can be lower than 1 μm in the axial direction in a measurement volume of about 1 mm in length [24]. For a working distance of 30 cm, which is necessary for boundary layer measurements, a resolution of 5 μm can be achieved [19]. However, the extension of the measurement volume is only ∼1 mm and traversing is necessary for measurements of the whole velocity profile to determine the boundary layer thickness and the free stream velocity [25].…”

Section: Introductionmentioning

confidence: 98%

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Parallax correction for precise near-wall flow investigations using particle imaging

2013

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For the basic understanding of turbulence generation in wall-bounded flows, precise measurements of the mean velocity profile and the mean velocity fluctuations very close to the wall are essential. Therefore, three techniques are established for high-resolution velocity profile measurements close to solid surfaces: (1) the nanoprobe sensor developed at Princeton University, which is a miniaturization of a classical hot-wire probe [Exp. Fluids 51, 1521 (2011)]; (2) the laser Doppler velocimetry (LDV) profile sensor, which allows measurement of the location of the particles inside the probe volume using a superposition of two fringe systems [Exp. Fluids 40, 473 (2006)]; and (3) the combination of particle image velocimetry and tracking techniques (PIV/PTV), which identify the location and velocity of submicrometer particles within the flow with digital imaging techniques [Exp. Fluids 52, 1641 (2006)]. The last technique is usually considered less accurate and precise than the other two. However, in addition to the measurement precision, the effect of the probe size, the position error, and errors due to vibrations of the model, test facility, or measurement equipment have to be considered. Taking these into account, the overall accuracy of the PTV technique can be superior, as all these effects can be compensated for. However, for very accurate PTV measurements close to walls, it is necessary to compensate the perspective error, which occurs for particles not located on the optical axis. In this paper, we outline a detailed analysis for this bias error and procedures for its compensation. To demonstrate the capability of the approach, we measured a turbulent boundary layer at Re(δ)=0.4×10(6) and applied the proposed methods.

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Section: Introductionmentioning

confidence: 98%

“…Furthermore, post processing must be performed to investigate the frequency spectra since the data are not sampled equidistant in time. However, to overcome the limitations due to the large probe volume, different laser Doppler sensor systems were developed that take advantage of more than two interfering beams [19,[20][21][22].…”

Section: Introductionmentioning

confidence: 99%

Parallax correction for precise near-wall flow investigations using particle imaging

2013

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“…Therefore, the application of hot-wire probes is usually limited to incompressible flow. A non-intrusive alternative measurement technique is the Laser-Doppler velocimetry (LDV) (George and Lumley 1973;Shirai et al 2006). Due to its working principle LDV does not require knowledge about the flow density and is, therefore, suited for measurements in compressible flows even in the case of temperature fluctuations.…”

Section: Introductionmentioning

confidence: 99%

Accurate turbulence level estimations using PIV/PTV

2018

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The estimation of the turbulence level of flow facilities is very important for the comprehensive description of experimental results. While for low flow velocities various measurement techniques can be used (for example hot-wire, LDV, PIV) the task becomes difficult in the case of compressible flows as temperature and density fluctuations bias the measurement of the velocity fluctuations. In this work, we analyze the free-stream flow of the trisonic wind tunnel Munich (TWM) by means of particle image velocimetry (PIV) and particle tracking velocimetry (PTV). The goal is to determine the flow quality, i.e. the turbulence level, over the operating range of the facility without bias due to temperature and density variations. The capability of PIV/PTV for the estimation of small velocity fluctuations is investigated in detail. It is shown that a small particle shift on the measurement plane in combination with a large particle image displacement on the image plane allows for precise velocity measurements. Furthermore, a variation of the time separation between the PIV double images, t , enables the measurement uncertainty to be determined, which was estimated to be as low as 0.04% of the mean displacement for a mean displacement of x = 100 pixel and an interrogation window size of 32 × 32 pixel. Regarding the wind tunnel turbulence, it was found that the turbulence level generally decreases with increasing Mach number for the TWM facility, starting with 1.9% at Ma = 0.3 and reaching 0.45% at Ma = 3.0 . With this analysis, a methodology exists to perform accurate turbulence measurements in incompressible and compressible flows.

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“…This is why laser Doppler anemometry (LDA) was frequently used in the past to allow for precise non-intrusive point measurements. For common working distances of approximately 30 cm, a resolution of 5 µm can be achieved in measurement volumes with a length of 1 mm (Shirai et al 2006). However, the disadvantage of these methods is that they provide only point-wise data.…”

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confidence: 99%

Highly resolved experimental results of the separated flow in a channel with streamwise periodic constrictions

2016

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The understanding and accurate prediction of turbulent flow separation on smooth surfaces is still a challenging task because the separation and the reattachment locations are not fixed in space and time. Consequently, reliable experimental data are essential for the validation of numerical flow simulations and the characterization and analysis of the complex flow physics. However, the uncertainty of the existing near-wall flow measurements make a precise analysis of the near-wall flow features, such as separation/reattachment locations and other predicted near-wall flow features which are under debate, often impossible. Therefore, the periodic hill experiment at TU Munich (ERCOFTAC test case 81) was repeated using high resolution particle image velocimetry and particle tracking velocimetry. The results confirm the strong effect of the spatial resolution on the near-wall flow statistics. Furthermore, it is shown that statistically stable values of the turbulent flow variables can only be obtained for averaging times which are challenging to realize with highly resolved large eddy simulation and direct numerical simulation techniques. Additionally, the analysis implies that regions of correlated velocity fluctuations with rather uniform streamwise momentum exist in the flow. Their size in the mean flow direction can be larger than the hill spacing. The possible impact of the correlated turbulent motion on the wake region is discussed, as this interaction might be important for the understanding and control of the flow separation dynamics on smooth bodies.

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Highly spatially resolved velocity measurements of a turbulent channel flow by a fiber-optic heterodyne laser-Doppler velocity-profile sensor

Cited by 33 publications

References 29 publications

Parallax correction for precise near-wall flow investigations using particle imaging

Parallax correction for precise near-wall flow investigations using particle imaging

Accurate turbulence level estimations using PIV/PTV

Highly resolved experimental results of the separated flow in a channel with streamwise periodic constrictions

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