EVALUATION OF TURBULENT KINETIC ENERGY DISSIPATION RATE IN A FREE JET FLOW FROM PIV MEASUREMENTS

The present paper reports PIV (Particle Image Velocimetry) measurements of turbulent velocity fluctuations statistics in development region of an axisymmetric free jet (Re = 28 000). To minimize measurement uncertainty, adaptive calibration, image processing and data post-processing algorithms were utilized. On the basis of theoretical analysis and direct measurements, the paper discusses effect of PIV spatial resolution on measured statistical characteristics of turbulent fluctuations. Underestimation of the second-order moments of velocity derivatives and of the turbulent kinetic energy dissipation rate due to a finite size of PIV interrogation area and finite thickness of laser sheet was analyzed from model spectra of turbulent velocity fluctuations. The results are in a good agreement with the measured experimental data. The paper also describes performance of possible ways to account for unresolved small-scale velocity fluctuations in PIV measurements of the dissipation rate. In particular, a turbulent viscosity model can be efficiently used to account for the unresolved pulsations in a free turbulent flow.

Keywords:
axisymmetric jet, energy budget, energy balance, dissipation, particle image velocimetry, spatial resolution.
УДК 532.522.2, 532.517.4, 532.5.071.4

EVALUATION OF TURBULENT KINETIC ENERGY DISSIPATION RATE IN A FREE JET FLOW FROM PIV MEASUREMENTS