Laser-Doppler velocity profile sensor with submicrometer spatial resolution that employs fiber optics and a diffractive lens

Büttner, Lars; Czarske, Jürgen; Knuppertz, Hans

doi:10.1364/ao.44.002274

Cited by 31 publications

(16 citation statements)

References 10 publications

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“…The main problems are that the accuracy of the position measurement is limited by the precision of a calibration and the fringe angle [23]. 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].…”

Section: Introductionmentioning

confidence: 99%

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: 99%

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

2013

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“…The fiber optic measurement head for generating the two fan-shaped interference fringe systems was all passive and equipped with radiator coils for water cooling making it immune against temperature influences and electrical disturbances. In order to obtain a compact and robust sensor head with a minimum number of adjustment elements, a special design using a diffractive optical element (DOE) was employed 3 . The high dispersion of the diffractive lens effected an axial separation of the beam waists of the two different wavelengths of several millimeters at the beam splitting transmission grating.…”

Section: Arrangement Of the Ldd Frequency Sensormentioning

confidence: 99%

“…Thus, the beam waists for the different wavelengths were located before and behind the common crossing point of the four partial beams generating one divergent and one convergent fringe system inside the measurement volume. The outer dimensions of the measurement head were 200 x 82 x 54 mm 3 . The bichromatic scattered light from the measurement object was detected in backward direction and coupled into a multimode fiber by a mirror and a single lens (see figure 4).…”

Section: Arrangement Of the Ldd Frequency Sensormentioning

confidence: 99%

Laser Doppler distance sensors using phase and frequency evaluation

et al. 2009

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The optical inspection and metrology for non-optics industry gains increasing importance. Several optical sensors are available for shape measurements of rough surfaces. However, at fast rotating objects such as turbine blades high temporal resolution is necessary, which often can not be fulfilled by commercially available sensors. The recently developed laser Doppler distance sensors allow temporal resolutions in the microsecond range. The independence of the distance measurement uncertainty to the lateral surface velocity is unique. The laser Doppler distance sensors were realized by the evaluation of the interference signal frequency as well as the interference signal phase. Both sensors have been employed for high-speed inspection.Keywords: non-incremental interferometric technique, system calibration and measurement uncertainty analysis, realtime insitu process control, shape measurement of rough surfaces, tip clearance and vibration measurements of turbo machines

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“…In order to obtain a compact and robust sensor head with a minimum number of adjustment elements, a special design using a diffractive optical element (DOE) was employed [6,11] . The high dispersion of the diffractive lens (DOE) effected an axial separation of the beam waists of the two different wavelengths of several millimeters at the beam splitting transmission grating.…”

Section: Sensor Configurationsmentioning

confidence: 99%

Absolute and dynamic position and shape measurement of fast moving objects employing novel laser Doppler techniques

et al. 2008

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In this contribution a novel laser Doppler distance (LDD) sensor is presented, which allows simultaneous measurement of axial position and tangential velocity and, thus, determination of the shape of moving and especially rotating objects with one single sensor. Conventional laser Doppler velocimeters measure only velocities. A concurrent position measurement can be realized by generating two fan-shaped interference fringe systems with contrary fringe spacing gradients and evaluating the quotient of the two resulting Doppler frequencies. Alternatively, two tilted fringe systems in combination with phase evaluation can be employed. It will be shown that, in contrast to conventional distance sensors, high temporal resolution below 3 µs and high position resolution of about 1 µm can be achieved simultaneously, because the position uncertainty of the LDD sensor is in principle independent of the object velocity. This is advantageous especially for monitoring highly dynamic processes e.g. at turbo machines, where in-process measurements of tip clearance and rotor vibrations are reported for up to 600 m/s blade tip velocity.

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Laser-Doppler velocity profile sensor with submicrometer spatial resolution that employs fiber optics and a diffractive lens

Cited by 31 publications

References 10 publications

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

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

Laser Doppler distance sensors using phase and frequency evaluation

Absolute and dynamic position and shape measurement of fast moving objects employing novel laser Doppler techniques

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