Effect of finite-size probe volume upon laser Doppler anemometer measurements

Karpuk, M.E.; Tiederman, W. G.

doi:10.2514/3.7191

Cited by 38 publications

(12 citation statements)

References 8 publications

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“…Close to the wall, however, streamwise velocity fluctuations are affected by the velocity gradient that is present across the measuring volume. This gradient broadens the Doppler signal and produces a bias in the measured values of u' (Karpuk and Tiederman 1976). An approximate analysis of this effect (Barlow 1985) indicated that the bias in the present configuration was small (10-15%), as close to the wall as y+ = 4.…”

Section: Measurement Limitations and Uncertaintymentioning

confidence: 99%

Effect of measuring volume length on two-component laser velocimeter measurements in a turbulent boundary layer

Johnson

1989

Experiments in Fluids

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The effects of finite measuring volume length on laser velocimetry measurements of turbulent boundary layers were studied. Four different effective measuring volume lengths, ranging in spanwise extent from 7 to 44 viscous units, were used in a low Reynolds number (Re o = 1440) turbulent boundary layer with high data density. Reynolds shear stress profiles in the near-wall region show that U~ V dp /eft" l + y+ 2 .+ U + U P /2' V' Reo Ruv R12 (0, 0, z) T~ List of symbols time-averaged quantity wall friction velocity, = (%/Q)1/2 kinematic viscosity pinhole diameter spanwise extent of LDV measuring volume viewed by photomultiplier non-dimensional length of measuring volume, =-l~e f u~/v non-dimensional coordinate in spanwise direction, =_ y u Jr non-dimensional coordinate in spanwise direction, Z ~T/V non-dimensional mean velocity, =- RMS streamwise velocity fluctuation, - x/2 RMS normal velocity fluctuation, -= / rate at which bursts are validated by counter processor Taylor time microscale, ~-u' ( < du/ dt ) 2)-t/2

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Section: Measurement Limitations and Uncertaintymentioning

confidence: 99%

Effect of measuring volume length on two-component laser velocimeter measurements in a turbulent boundary layer

Johnson

1989

Experiments in Fluids

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“…This was expected since the broadening correction scheme of Karpuk and Tiederman (1976) predicts corrected values of u' less than 0.3% different than the uncorrected value in the worst case for the present measurements.…”

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confidence: 76%

Hot-wire height gauge using a laser and photodiodes

Takagi¹

1985

Experiments in Fluids

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Technical notes 341 wire with l + = 14. The present data are 6% higher than Johansson and Alfredsson's RMS values at y + = 10.3 and y + = 15.8. This is consistent with the data of Willmarth and Sharma (1984) who showed that a hot wire with an l + = 14 should yield RMS levels approximately 8% lower than the true RMS value a t y + = 13.3.No evidence of mean velocity broadening were seen in any of the RMS results due to the size of the probe volume normal to the wall. This was expected since the broadening correction scheme of Karpuk and Tiederman (1976) predicts corrected values of u' less than 0.3% different than the uncorrected value in the worst case for the present measurements. ConclusionsNo spatial averaging effects were seen in the present data which included probe volumes from 9 to 74 wall units long. This is believed to be due to the fact that the laser velocimeter obtained data from individual particles and the probe volume length was aligned with a direction in which turbulence quantities were homogeneous. Since there is no spatial averaging, the present data are at least as accurate as measurements from hot-wires that have a spanwise length of about one-half wall unit. Acknowledgements Technical notesHot-wire height gauge using a laser and photodiodes S. TakagiNational Aerospace Laboratory, Jindaiji-machi, Chofu-city, Tokyo 182, Japan Abstract. A simple method for measuring the height of a hot-wire anemometer from the wall surface is described. The system consists of a laser and photodiodes joined by optical glass fibres. The position of the wire is indicated when it interrupts the laser beam, which is emitted through the fibre along the wall surface and is observed by the photodiode. The measurement accuracy depends upon the glass fibre and is within 0.01 mm in the present system.

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“…in the near wall region of a bound turbulent shear layer (12). The problem is even more severe in separated flows .…”

Section: Aciqĩ~wledgementsmentioning

confidence: 98%

“…Consequently more particles will flow through the probe volume and be detected when the fluid velocity is higher than the time-average fluid velocity than when the fluid velocity is lower than the time-average velocity. Several analyses have been made and methods have been proposed to correct biased measurements ( 7,8,9,10,11,12). The corrections are significant when the velocity fluctuations are large .…”

Section: Aciqĩ~wledgementsmentioning

confidence: 99%

See 1 more Smart Citation

Experimental Evaluation of Sampling Bias in Naturally Seeded Flows.

Tiederman¹

1978

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Effect of finite-size probe volume upon laser Doppler anemometer measurements

Cited by 38 publications

References 8 publications

Effect of measuring volume length on two-component laser velocimeter measurements in a turbulent boundary layer

Effect of measuring volume length on two-component laser velocimeter measurements in a turbulent boundary layer

Hot-wire height gauge using a laser and photodiodes

Experimental Evaluation of Sampling Bias in Naturally Seeded Flows.

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