Experiments with micro-machined multi-array hot-film probe towards field experiments with sub-Kolmogorov resolution

This is a report on implementation of the next stage of a project, motivated by the discovery of far more important role, played by the sub-Kolmogorov scales in high Reynolds number turbulence than commonly believed. The main results and issues that prompted the present work are in [1] – [3] and references therein. At this stage we report on the first successful experiments with a unique micro-machined hot-film multi-array probe. This includes design, assembly, implementation and testing of such probe in laboratory conditions [4]. The probe is enabling to access, along with all three components of turbulent velocity fluctuations, also all nine components of the spatial velocity gradients tensor, including the option of obtaining the stream-wise velocity derivatives without employing the Taylor hypothesis, as well as velocity temporal derivatives. The key feature of the micro-machined multi-array probe (typically five arrays), with each array consisting of four micro-machined hot-film sensors, is that it is six times smaller than the conventional multi-array probe, based on arrays with four hot wires [5] – [6], used in the atmospheric surface layer at Taylor micro-scale Reynolds number up to Re_λ ≈ 10⁴. This part of work relates to Reynolds numbers Re_λ < 500 and employs several laboratory flows.