Experimental observation of spontaneous temperature fluctuations in turbulent flows

¹ Laboratoire de Physique de l'École Normale Supérieure, CNRS, PSL Research University, Sorbonne Université, Université de Paris - F-75005 Paris, France
² University of California Los Angeles - Los Angeles, CA 90095, USA
³ PMMH, CNRS, ESPCI Paris, Université PSL, Sorbonne Université, Université Paris-Cité - F-75005 Paris, France

^(a) E-mail: gprabhudesai@physics.ucla.edu (corresponding author)

Received: 9 November 2022
Accepted: 30 January 2023

Abstract

Even in the absence of externally applied temperature gradients, spontaneously generated temperature fluctuations arise in turbulent flows. We experimentally study these fluctuations in a closed von Kármán swirling flow of air at Mach number of order , whose boundaries are maintained at a constant temperature. We observe intermittent peaks of low temperature correlated with pressure drops within the flow and show that they are caused by vorticity filaments. The measured ratio of temperature-to-pressure fluctuation agrees with the prediction based on adiabatic cooling within vortex cores. This experimental study shows that although the Mach number of the flow is small, there exist regions within the flow where compressible effects cannot be discarded in the equation for temperature and locally dominate the effect of viscous dissipation.