I wrote about this experiment and discussed it with funding agencies long ago and just wanted to post the idea.
I am exploring the possibility of conducting high-Reynolds number turbulence experiments. One experiment would involve constructing a large isolated vessel filled with liquid helium to create fully developed, spatially localized high-Re flow through transient forcing mechanisms. The forcing would be induced either by localized heating using multiple femtosecond lasers or by mechanical grid motion. The experiment will focus on capturing the acoustic radiation produced by turbulence, which is deterministically linked to the flow-field. A total of 2500 microphones would be strategically embedded within the containment vessel’s walls to measure the acoustic signatures without disturbing the flow as intrusive methods contaminate the data. Additionally, sapphire windows will be integrated into the vessel to enable high-speed CCD cameras to track tracer particles introduced into the flow. These particles will be activated by a 5-kHz femtosecond laser system, capturing the temporal and spatial resolution.
The collected data will be used to reconstruct the turbulent field variables as a function of space and time. This reconstruction will be based on the theory of isotropic homogeneous turbulence and radiation, a framework I previously published. The method provides the foundation for predicting noise generated by homogeneous isotropic turbulence and is directly applicable to the proposed experiment. By combining predicted statistical models with time-dependent data and advanced beamforming techniques—specifically, those contained within the Acoular open-source code—the aim is to achieve a three-dimensional, time-dependent reconstruction of the turbulent field.
The primary focus will be on analyzing the intermittency and bursting phenomena that are characteristic of high-Re turbulence. These events generate strong acoustic impulses, which will be captured at a frequency of 180 kHz by the microphone array. The goal is to process this data to find the mechanisms behind these bursts and to create a high-fidelity database that could potentially be used to validate direct numerical simulations (DNS) in the future.
The experiment’s design addresses the limitations of previous liquid helium experiments, such as those conducted at Florida State and Minnesota, where intrusive measurement techniques altered the flow-field. By using acoustic measurements as a non-intrusive method, the experiment will capture the unique “fingerprint” of turbulence without affecting the flow itself. Each turbulent field radiates its own unique acoustic signature.
The expected outcomes include:
- A comprehensive database of a high-Re number turbulent field with documented intermittent bursts and associated scaling.
- New insights into the universal nature of small-scale turbulence within a high-Re field.
- A better understanding of the hierarchical structure and nature of turbulence.
I think that such an experiment would take five years to conduct.