Turbulent velocity measurements in high Reynolds cryogenic helium facilities at Service des Basses Températures (SBT)

S Kharche,J Peinke,C Baudet,J P Moro,B Rousset,A Fuchs,A Girard

doi:10.1088/1757-899x/502/1/012201

Abstract

Due to its very low viscosity, cryogenic helium has been used for years to generate high Reynolds turbulent flows. The measurement of velocity fluctuations in such high Reynolds flows is however a challenging issue, as it is necessary to develop small size (typically micron-length), robust sensors, to measure the whole spectrum of fluctuations of the velocity, which may extend to hundreds of kHz and possibly higher. SBT has developed for years different facilities, in particular taking benefit of the refrigeration capacities available at CEA Grenoble. In this article we present the current status of developments of hot wire sensors at CEA. Different characterizations of Wollaston hot wires are shown, and measurements of velocity fluctuations in different conditions, in normal helium as well as in superfluid helium are shown.

Highlights

Turbulence has a very broad spectrum of occurrences in nature, industry and every-day-life
It is of great interest to achieve laboratory flows of similar Reynolds number as geophysical flows
We present here a robust sensor, which has been developed at CEA, whose length is significantly larger than the Kolmogorov length, but provides much information on the inertial range

Summary

Introduction

Turbulence has a very broad spectrum of occurrences in nature, industry and every-day-life. It is of high interest to generate laboratory flows with high Reynolds number and large inertial range, in order to compare theoretical and experimental results with a great accuracy. It is of great interest to achieve laboratory flows of similar Reynolds number as geophysical flows These are the main reasons to use cryogenic helium to generate turbulent flows. Hot wire anemometry is a well-known technique for characterization of the turbulent velocity field [6,7]. It still provides unsurpassed quality results in terms of signal to noise ratio, resolution, and frequency response. In order to avoid the breaking of the wire during the cool down process, the wire is slightly bent

Operating principle

Experiments

Discussion and prospects