TY - JOUR
T1 - Experimental study of temperature fluctuations in forced stably stratified turbulent flows
AU - Eidelman, A.
AU - Elperin, T.
AU - Gluzman, I.
AU - Kleeorin, N.
AU - Rogachevskii, I.
N1 - Funding Information: We thank A. Krein for his assistance in construction of the experimental setup and J. Gartner for his assistance in processing of the experimental results on velocity measurements. This research was supported in part by the Israel Science Foundation (ISF) governed by the Israeli Academy of Sciences (Grant Nos. 259/07 and 1037/11), by European Union (EU) COST Actions MP0806 and ES1004, by the EC FP7 project ERC PBL-PMES (Grant No. 227915) and the Russian Government Mega Grant implemented at the University of Nizhny Novgorod (Grant No. 11.G34.31.0048).
PY - 2013/1/2
Y1 - 2013/1/2
N2 - We study experimentally temperature fluctuations in stably stratified forced turbulence in air flow. In the experiments with an imposed vertical temperature gradient, the turbulence is produced by two oscillating grids located nearby the side walls of the chamber. Particle image velocimetry is used to determine the turbulent and mean velocity fields, and a specially designed temperature probe with sensitive thermocouples is employed to measure the temperature field. We found that the ratio[(lx ∇xT)2+(ly∇yT)2+(lz∇zT)2]/〈 θ2〈 is nearly constant, is independent of the frequency of the grid oscillations, and has the same magnitude for both, stably and unstably stratified turbulent flows, where ℓi are the integral scales of turbulence along x, y, z directions, T and θ are the mean and turbulent fluctuations components of the fluid temperature. We demonstrated that for large frequencies of the grid oscillations, the temperature field can be considered as a passive scalar, while for smaller frequencies the temperature field behaves as an active field. The theoretical predictions based on the budget equations for turbulent kinetic energy, turbulent potential energy (α〈 θ2〈 ), and turbulent heat flux, are in a good agreement with the experimental results. Detailed comparison with experimental results obtained previously in unstably stratified forced turbulence is performed.
AB - We study experimentally temperature fluctuations in stably stratified forced turbulence in air flow. In the experiments with an imposed vertical temperature gradient, the turbulence is produced by two oscillating grids located nearby the side walls of the chamber. Particle image velocimetry is used to determine the turbulent and mean velocity fields, and a specially designed temperature probe with sensitive thermocouples is employed to measure the temperature field. We found that the ratio[(lx ∇xT)2+(ly∇yT)2+(lz∇zT)2]/〈 θ2〈 is nearly constant, is independent of the frequency of the grid oscillations, and has the same magnitude for both, stably and unstably stratified turbulent flows, where ℓi are the integral scales of turbulence along x, y, z directions, T and θ are the mean and turbulent fluctuations components of the fluid temperature. We demonstrated that for large frequencies of the grid oscillations, the temperature field can be considered as a passive scalar, while for smaller frequencies the temperature field behaves as an active field. The theoretical predictions based on the budget equations for turbulent kinetic energy, turbulent potential energy (α〈 θ2〈 ), and turbulent heat flux, are in a good agreement with the experimental results. Detailed comparison with experimental results obtained previously in unstably stratified forced turbulence is performed.
UR - http://www.scopus.com/inward/record.url?scp=84873432682&partnerID=8YFLogxK
U2 - https://doi.org/10.1063/1.4775380
DO - https://doi.org/10.1063/1.4775380
M3 - Article
SN - 1070-6631
VL - 25
JO - Physics of Fluids
JF - Physics of Fluids
IS - 1
M1 - 015111
ER -