An examination of hot-wire length corrections

Derksen, R. W.

doi:10.1063/1.864374

Cited by 22 publications

(5 citation statements)

References 12 publications

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“…This was not of further interest because spectra were not calculated there and it did not most likely affect the mean and rms values due to the large overall number of samples. When calculating turbulence spectra, the finite length of the probe volume causes spatial filtering, however, in an analogy to hot wire measurements by Derksen and Azad (36), an attenuation of the spectrum is expected to occur beyond the maximum measured frequencies based on the probe volume dimensions in our study. Nonetheless, spatial filtering flattens mean flow gradients, which would need to be considered if the gradients were further analyzed.…”

Section: Methodsmentioning

confidence: 82%

Turbulence Measurements in an Axial Rotary Blood Pump with Laser Doppler Velocimetry

et al. 2017

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Section: Methodsmentioning

confidence: 82%

Turbulence Measurements in an Axial Rotary Blood Pump with Laser Doppler Velocimetry

et al. 2017

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“…In view of the fact that the wire is of already extremely small diameter, any slight variation implies a relatively large percentage change from the nominal wire's diameter. Derksen and Azad (1983) used an ISI scanning electron microscope to photograph hot wires of nominal diameters of 2.5 µm and 5 µm. Their photographs showed large structures of cracks, longitudinal grooves and superimposed deposits which were attributed to the manufacturing process.…”

Section: Heat Transfer Characteristics Of the Hot Wire In The Vicinit...mentioning

confidence: 99%

An investigation of wall effects on hot-wire measurements using a bent sublayer probe

Chew

Khoo

1998

Meas. Sci. Technol.

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The effects of aluminium and Perspex walls on near-wall hot-wire measurements were investigated in a fully developed channel flow of 250 mm width, 1.6 mm (laminar) or 16.6 mm (turbulent) height using specially made bent sublayer probes of 5 m, 1.27 m and 0.63 m diameter that had minimum aerodynamic interference. Previous experiments by Wills indicated that the heat loss from the wire expressed in terms of Nusselt number (Nu) versus the Reynolds number ( based on velocity at the wire location and wire diameter) for various fixed distances from the wall does not converge to the wall-remote behaviour at large or (the distance from the wall normalized by the viscous length scale). Other works show conflicting trends of the effects of wall thermal conductivity, wire diameters and overheat ratio on the operation of the hot wire in the vicinity of the wall. The present effort represents a systematic approach to evaluate each of these parameters on the hot-wire performance near the wall in terms of Nu and measured dimensionless velocity (taken wrt wall shear velocity) for comparison to previous works and to resolve some of the apparent controversies. Experiments were also conducted in both fully developed laminar and turbulent channel flows to determine the near-wall correction curves in order to resolve the contradictory suggestions by Wills, Demin and Kuraev, and Zemskaya et al regarding laminar and turbulent near-wall corrections. The present investigations found that contrary to the previous work of Wills, the behaviour of Nu versus for a hot wire at given fixed distances from the wall converges to the wall-remote condition for large or . This finding was consistent for the three different wire diameters used and two walls of different thermal conductivities. The discrepancy with Wills' results is attributed to aerodynamic interference and blockage effects caused by the near-wall hot-wire prongs in a narrow channel flow. The critical distances from the wall, , beyond which the wall influences on hot-wire measurements can be considered insignificant, were found to decrease with decreasing wire diameter and decreasing wall thermal conductivity. They were found to be approximately 5.0, 3.7, 3.0 for the aluminium wall and 3.0, 2.7, 2.2 for the Perspex wall for respective wire diameters of 5 m, 1.27 m, 0.63 m. It was also found that the overheat ratio plays an insignificant role provided that the length to diameter ratio of the wire is sufficiently larger than 200 to minimize three-dimensional effects. The resultant mean distribution wrt obtained in fully developed channel flow was found to resemble the counterpart obtained in laminar flow. This finding concurs with the experimental results of Zemskaya et al performed in boundary layer flows, but contradicts the conclusion by Wills who recommended half the laminar correction for turbulent flow. It is suspected that the experimental results of Wills are affected by different degrees of prong interference and blockage effects for the laminar and turbulent channe...

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“…l'herefore. Derksen and Azad (1983) suggest another correction method for dissipation rate which does not use any spectrum models. Actually it came from a correction fbr the integral length scale given by flinze (1975).…”

Section: Estimation Of Dissipation Ratementioning

confidence: 99%

Structure of Three-Dimensional Separated Flow on Symmetric Bumps

Byun¹

2005

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Public reporting burden for this collection of Information Is estimated to average I hour per response, Including the time for reviewing Insbuctions. searching exiting dab sources, gathering arnd maintaining the data needed, and completing and reviewing the collection of Informaton. Send comments regarding this burden estimate or any o€her aspect of this collection of . Threedimensional (3-D) separations occur on the leeside with one saddle separation on the centerline that is connected by a separation line to one focus separation on each side of the centerline. Downstream of the saddle point the mean backflow converges to the focal separation points in a thin region confined within about 0.158 from the local bump surface. The mean backflow zone is supplied by the intermittent large eddies as well as by the near surface flow from the side of the bump. The separated flow has a higher turbulent kinetic energy and shows bimodal histograms in local U and W, which appear to be due to highly unsteady turbulent motions. By the mode-averaged analysis of bimodal histograms, highly unsteady flow structures are estimated and unsteady 3-D separations seem to be occurring over a wide region on the bump leeside. The process of these separations has very complex dynamics having a large intermittent attached and detached flow region which is varying in time. These bimodal features with highly correlated uL and wL fluctuating motions are the major source of large 2 2Reynolds stresses uL , wL and -uwL. Because of the variation of the mean flow angle in the separation zones, the turbulent flow from different directions is non-correlated, resulting in lower shearing stresses. Farther from the wall. large stream-wise vortices form from flow around the sides of the bumn,

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An examination of hot-wire length corrections

Cited by 22 publications

References 12 publications

Turbulence Measurements in an Axial Rotary Blood Pump with Laser Doppler Velocimetry

Turbulence Measurements in an Axial Rotary Blood Pump with Laser Doppler Velocimetry

An investigation of wall effects on hot-wire measurements using a bent sublayer probe

Structure of Three-Dimensional Separated Flow on Symmetric Bumps

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