Topic

# Flow measurement

About: Flow measurement is a research topic. Over the lifetime, 21449 publications have been published within this topic receiving 207236 citations.

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01 Jan 1989

TL;DR: In this paper, the authors use hot-wire (HW) or laser velocimetry (LV) to estimate the velocity, vorticity, and pressure fields of wake flows.

Abstract: One of the most challenging and time-consuming problems in experimental fluid mechanics is the measurement of the overall flow field properties, such as the velocity, vorticity, and pressure fields. Local measurements of the velocity field (i.e., at individual points) are now done routinely in many experiments using hot-wire (HW) or laser velocimetry (LV). However, many of the flow fields of current interest, such as coherent structures in shear flows or wake flows, are highly unsteady. HW or LV data of such flows are difficult to interpret, as both spatial and temporal information of the entire flow field are required and these methods are commonly limited to simultaneous measurements at only a few spatial locations.

1,798 citations

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TL;DR: In this paper, the velocity distribution and reattachment length of a single backward-facing step mounted in a two-dimensional channel were measured using laser-Doppler measurements.

Abstract: Laser-Doppler measurements of velocity distribution and reattachment length are reported downstream of a single backward-facing step mounted in a two-dimensional channel. Results are presented for laminar, transitional and turbulent flow of air in a Reynolds-number range of 70 < Re < 8000. The experimental results show that the various flow regimes are characterized by typical variations of the separation length with Reynolds number. The reported laser-Doppler measurements do not only yield the expected primary zone of recirculating flow attached to the backward-facing step but also show additional regions of flow separation downstream of the step and on both sides of the channel test section. These additional separation regions have not been previously reported in the literature.Although the high aspect ratio of the test section (1:36) ensured that the oncoming flow was fully developed and two-dimensional, the experiments showed that the flow downstream of the step only remained two-dimensional at low and high Reynolds numbers.The present study also included numerical predictions of backward-facing step flow. The two-dimensional steady differential equations for conservation of mass and momentum were solved. Results are reported and are compared with experiments for those Reynolds numbers for which the flow maintained its two-dimensionality in the experiments. Under these circumstances, good agreement between experimental and numerical results is obtained.

1,637 citations

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TL;DR: The study shows that the Doppler signal is formed essentially by heterodyne mixing of light beams backscattered in static structures and moving red cells.

Abstract: An instrument for measurement of tissue blood flow based on the laser Doppler principle was evaluated using a fluid model. A unique and linear relationship between flowmeter response and flux of red cells was demonstrated with red cell velocities and volume fractions within the normal physiological range of the microcirculatory network of the skin. Different degrees of oxygenation proved to influence the Doppler signal only to a minor extent. The study also shows that the Doppler signal is formed essentially by heterodyne mixing of light beams backscattered in static structures and moving red cells.

1,141 citations

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TL;DR: In this article, it was shown that the log-law can be applied strictly only to the nearwall region and the von K´rm´n constant κ and integral constant A are truly universal, having values of κ=0.412 and A=5.29 irrespective of the Reynolds and Froude number.

Abstract: A powerful two‐color Laser Doppler Anemometer (LDA) system, with direct digital signal processing has been used to measure accurately the longitudinal and vertical velocity components in two‐dimensional, fully‐developed open‐channel flow over smooth beds. The law of the wall and the velocity defect law were re‐examined because the log‐law has been often applied to open channels without detailed verification. It was found that the log‐law can be applied strictly only to the near‐wall region. In this region, the von K´rm´n constant κ and the integral constant A are truly universal, having values of κ=0.412 and A=5.29 irrespective of the Reynolds and Froude number. As the Reynolds number becomes larger, the deviation from the log‐law cannot be neglected in the outer region. This deviation can be expressed well by Coles' wake function which involves a Reynolds‐number dependent parameter Π. The distributions of eddy viscosity and mixing length were evaluated and found to depend on Π. All the data including the...

892 citations