A comparison of velocity measurements using a laser anemometer and a hot-film probe, with application to grid-stirring entrainment experiments

1987 ◽  
Vol 30 (10) ◽  
pp. 3290 ◽  
Author(s):  
Joseph F. Atkinson ◽  
Leonardo Damiani ◽  
Donald R. F. Harleman
2002 ◽  
Vol 450 ◽  
pp. 67-95 ◽  
Author(s):  
CH. BLOHM ◽  
H. C. KUHLMANN

The incompressible fluid flow in a rectangular container driven by two facing sidewalls which move steadily in anti-parallel directions is investigated experimentally for Reynolds numbers up to 1200. The moving sidewalls are realized by two rotating cylinders of large radii tightly closing the cavity. The distance between the moving walls relative to the height of the cavity (aspect ratio) is Γ = 1.96. Laser-Doppler and hot-film techniques are employed to measure steady and time-dependent vortex flows. Beyond a first threshold robust, steady, three-dimensional cells bifurcate supercritically out of the basic flow state. Through a further instability the cellular flow becomes unstable to oscillations in the form of standing waves with the same wavelength as the underlying cellular flow. If both sidewalls move with the same velocity (symmetrical driving), the oscillatory instability is found to be tricritical. The dependence on two sidewall Reynolds numbers of the ranges of existence of steady and oscillatory cellular flows is explored. Flow symmetries and quantitative velocity measurements are presented for representative cases.


1974 ◽  
Vol 34 (2) ◽  
pp. 193-203 ◽  
Author(s):  
ROBERT M. NEREM ◽  
JOHN A. RUMBERGER ◽  
DAVID R. GROSS ◽  
ROBERT L. HAMLIN ◽  
GARY L. GEIGER

1977 ◽  
Vol 79 (3) ◽  
pp. 553-594 ◽  
Author(s):  
Roger L. Simpson ◽  
J. H. Strickland ◽  
P. W. Barr

Measurements of a separating two-dimensional incompressible boundary layer with an airfoil-type pressure distribution are reported. Unique mean and fluctuation velocity measurements and the distribution of the fraction of the time γp during which the flow moves downstream were obtained in the separated region using a directionally sensitive laser anemometer. Linearized hot-film anemometer measurements of mean velocities, turbulent shearing stress and intensities, eddy speeds, spectra and dissipation were made for γp > 0·8. The wall shearing stress, bursting frequencies, wall speed and spanwise structure were obtained using flush-surface hot-film sensors. The turbulent/non-turbulent interfacial intermittency γ and the frequency of passage of turbulent bulges were determined using smoke as a turbulence marker and the laser anemometer system for illumination and signal detection.Upstream of separation the velocity profile correlations of Perry & Schofield (1973) are supported within the uncertainty of the data. Normal-stress effects are very important, influencing $-\overline{uv}/\overline{q^2} $ and the dissipation length correlations, and directly providing sizable terms in the momentum and turbulence energy equations. The criteria of Sandborn for turbulent separation and fully developed separation are found to hold. Downstream of separation there is apparent similarity of $\overline{u^2}$, U and γp throughout the shear flow. The passive low velocity backflow near the wall apparently just serves to satisfy continuity requirements after the energetic outer-region flow has deflected away from the wall upon separation.The wall bursting frequency nA scales on outer velocity and length scales, with U∞/δnA ≈ 10, or about twice the value observed for zero-pressure-gradient flows. The non-dimensional spanwise spacing of wall eddies is given approximately by the relation λzUM/v ≈ 100 upstream of separation, where $U_M = (- \overline{uv}_{\max})^{\frac{1}{2}}$. The speed of wall eddies is found to be about 14Uτ.


1981 ◽  
Vol 110 ◽  
pp. 115-128 ◽  
Author(s):  
G. Comte-Bellot ◽  
G. Charnay ◽  
J. Sabot

The European Mechanics Colloquium, Euromech 132, was held at the Ecole Centrale de Lyon from 2 to 4 July 1980. Specific areas of hot-wire or hot-film anemometry were presented and discussed, more especially the effect of the finite time constant of the wire supports, the use of yawed hot wires in supersonic flows, the possible improvement of vorticity meters, and multi-point measurements of wall-shear-stress fluctuations. Other subjects described during the meeting included a new technique for concentration measurements in flames, developments and new uses of digitization and conditional sampling, pattern recognition analysis of fluid flow from multi-point, multi-time velocity measurements, and new turbulence measurements in complex flows and in fluid-flow machinery.An exhibition of hot-wire and hot-film anemometers and associated equipment was held during the colloquium.


Author(s):  
X. Liu ◽  
W. Rodi

A detailed experimental investigation is described of unsteady flow over and heat transfer from a flat plate. The oncoming 2-D periodic unsteady flow was generated by a squirrel cage device mounted upstream of the plate. Velocity measurements were carried out in the free stream over the plate and in the boundary layer by hot-wire anemometers, and the distributions of pressure and heat transfer coefficient along the plate surface were measured, the latter with a glue-on hot film. All results are presented in ensemble averaged form so that the unsteady flow processes can be studied phase by phase.


Author(s):  
Ge´rald Kergourlay ◽  
Smai¨ne Kouidri ◽  
Gary W. Rankin ◽  
Robert Rey

This experimental study, applied to a three different sweep axial fan (backward, radial and forward), aims at determining the 3D structure of the rotor wake from unsteady velocity measurements. The hot-film anemometry is used to measure the 3D unsteady velocity components in nearfield, downstream the fan. The data analysis leading to averaged and turbulent velocities, the components of the Reynolds’ stress tensor and the turbulent kinetic energy is presented, in order to illustrate the influence of the sweep. A spectral analysis is also performed.


Sign in / Sign up

Export Citation Format

Share Document