Parameterizable constant temperature anemometer: a new method for the analysis of velocity–temperature coupling in turbulent heat transfer

Abstract

A novel anemometer was designed and implemented for simultaneous measurement of velocity and temperature in air flows with a single hot wire probe. The principle of periodically varying the overheat ratio of the wire was selected and applied through a parameterizable electronic chain. The specific methods developed for the calibration procedure and the signal processing are explained. The accuracy of the measurements was assessed by means of Monte Carlo simulations. Examples of results are given for a non-isothermal low speed mixing layer. Finally, the ability to extract velocity-temperature coupling from a turbulent non-isothermal flow is highlighted through a conditional Probability Density Function (PDF) analysis.

Turbulent mixing and entrainment in a stratified horizontal plane shear layer: joint velocity–temperature analysis of experimental data

“…Figure 5 shows the downstream evolution of the mixing layer thicknesses δ u and δ θ . The self-similar state was also confirmed by the linear growth of the mixing layer thicknesses shown in this figure and the geometric affinity of the turbulence profiles with an asymptotic behaviour achieved by turbulence intensities (see Ndoye et al 2010;Sodjavi & Carlier 2013). Note again that, in the presence of thermal stratification, that self-similar state would not be valid further downstream because of the growing influence of buoyancy (see section 1.3, Effects of stratification).…”

“…For instance, the mean longitudinal velocity profile was symmetric with one single inflection point located on the axis of the mixing layer. In contrast, the mean temperature profile had three inflection points (see also Ndoye et al 2010). The u u and v v were symmetric.…”

“…The difficulty of temperature-velocity correlation measurements lies in the instantaneous measuring of velocity and temperature both with a fine spatial resolution and a short integration time in relation to the turbulence scales. Our work follows on the studies by Ndoye et al (2010) and Sodjavi & Carlier (2013) who used the variable temperature hot wire thermo-anemometry initially proposed by Corrsin (1947) to meet these requirements. In Sodjavi & Carlier (2013), measurements were carried out in two stratified configurations denominated stably and unstably stratified mixing layers in relation to the sign of the vertical temperature gradient applied (note again that, in the present study, the mean vertical velocity and temperature gradients remain of opposite sign, the velocity gradient being reversed in opposition to the temperature gradient by always associating high velocity with low temperature, see figure 1), and in an isothermal configuration denominated neutrally stratified mixing layer.…”

“…This second method was implemented by Ndoye et al (2010) and Sodjavi & Carlier (2013) in a variable temperature hot wire thermo-anemometer invented by Joël Delville (from Pprime Institute, Poitiers, France). In Ndoye et al (2010), the method was designed to use a single hot wire probe to measure the temperature and the longitudinal velocity component simultaneously. In Sodjavi & Carlier (2013), the method was extended to use an ×-wire probe, thus allowing in addition the measurement of the transverse velocity component.…”

“…It is of note that quantitative measurements of heat or scalar fluxes in turbulent mixing layers are very rare. We only found them in Koochesfahani et al (2000), Li et al (2010b), Ndoye et al (2010) and Sodjavi & Carlier (2013), and only Li et al (2010b) focused their study on JPDFs. Figures 10, 11 and 12 present the JPDFs P u ,v , P u ,θ and P v ,θ at five locations across the mixing layer in the self-similar region for stably and unstably stratified configurations.…”