Thermographic analysis of turbulent non-isothermal water boundary layer

TL;DR

This study uses high-speed infrared thermography to analyze turbulent non-isothermal water boundary layers in jet mixing flows, comparing spectral behaviors to turbulence theories.

Contribution

It introduces a novel application of IR thermography for detailed turbulence analysis in water boundary layers, including spectral comparison to turbulence models.

Findings

Temperature fluctuation spectra follow Kolmogorov -5/3 law

Spectral analysis reveals dual cascade behavior in water turbulence

High-speed IR thermography effectively captures turbulent heat fluxes

Abstract

The paper is devoted to the investigation of the turbulent water boundary layer in the jet mixing flows using high-speed infrared (IR) thermography. Two turbulent mixing processes were studied: a submerged water jet impinging on a flat surface and two intersecting jets in a round disc-shaped vessel. An infrared camera (FLIR Systems SC7700) was focused on the window transparent for IR radiation; it provided high-speed recordings of heat fluxes from a thin water layer close to the window. Temperature versus time curves at different points of water boundary layer near the wall surface were acquired using the IR camera with the recording frequency of 100 Hz. The time of recording varied from 3 till 20 min. The power spectra for the temperature fluctuations at different points on the hot-cold water mixing zone were calculated using the Fast Fourier Transform algorithm. The obtained spectral behavior was compared to the Kolmogorov "-5/3 spectrum" (a direct energy cascade) and the dual-cascade scenario predicted for quasi-2D turbulence (an inverse energy cascade to larger scales and a direct enstrophy cascade to smaller scales).