Continuum Physics Unit
Professor Gustavo Gioia
Abstract
We have carried out research on turbulent Rayleigh Taylor instabilities and the spectral theory of the turbulent mean-velocity profile, and completed benchmarking of the Taylor Couette experimental facility at OIST.
1. Staff
- Gustavo Gioia, Professor
- Tomoe Owan, Research Unit Administrator
2. Collaborations
2.1 Benchmarking the OIST Taylor Couette experimental facility (OIST-TC)
- Type of collaboration: Scientific collaboration
- Researchers:
- Professor Pinaki Chakraborty, OIST
2.2 Classical, transitional and fully turbulent Rayleigh Taylor (RT) instabilities
- Type of collaboration: Scientific collaboration
- Researchers:
- Professor Marco Rosti, OIST
- Professor Gustavo Gioia, OIST
3. Activities and Findings
3.1 Benchmarking the OIST Taylor Couette experimental facility (OIST-TC)
We have successfully concluded benchmarking testing of the OIST-TC, which involved extensive measurements of the torque, the mean-velocity profile (MVP) across the gap between the rotating cylinders, and the turbulent-energy spectrum (TES) at the center of the gap. For the torques and MVPs, the OIST-TC measurements compare well with measurements carried out in other Taylor Couette facilities. To be able to measure the TES to the smallest wavelengths in the flow, which cannot be reached using conventional Laser Doppler Velocimetry, we have developed a novel "flying hot-wire" (FHW) method which appears to be unprecedented in the literature. To benchmark the FHW measurements of the TES, we have also carried out extensive LDV measurements. Within the range of wavelengths reached by both FHW and Laser Doppler Velocimetry (that is to say, for large-to-medium wavelengths), the FHW measurements are in excellent accord with the Laser Doppler ones, a result that lends confidence to the FHW measurements.
The OIST-TC opens up many research fronts on turbulent Taylor Couette flow. This project was carried out in collaboration with Prof. P. Chakraborty's unit.
3.2 Classical, transitional and fully turbulent RT instabilities
This multi-year project was motivated and described in some detail in the preceding annual report. This year we have made steady progress with computational simulations aimed at testing an asymptotic formula which is based on dimensional analysis and similarity arguments and which allows us to make predictions bridging the entire transition between the classical instability and the fully turbulent instability. Except for the case of the classical instability, the wavelength and the characteristic time scale of the asymptotic formula have no direct, unequivocal counterpart in the computational simulations. Thus, as part of this year's work, we have developed and tested suitable ways of determining both the wavelength and the characteristic time-scale from the simulations. In addition, we have formulated an energy-based, spectral model aimed at elucidating the physical underpinnings of the asymptotic formula. This research project is being carried out in collaboration with Prof. P. Chakraborty's unit and Prof. M. Rosti's unit.
3.3 Implications of nonlocality in the spectral model of the turbulent mean-velocity profile
This is a theoretical research project wherein we aim to relate the nonlocal character of our spectral model of the turbulent mean-velocity profile to empirical turbulent pipe-flow profiles which cannot be explained by means of the classical theoretical models, which are intrinsically local.
4. Publications
4.1 Journals
Nothing to report
4.2 Books and other one-time publications
Nothing to report
4.3 Oral and Poster Presentations
- Gustavo,El factor de fricción de flujos turbulentos: lo que le falta a Nikuradse y al diagrama de Moody, University of Granada, February 27 (2024)
5. Intellectual Property Rights and Other Specific Achievements
Nothing to report
6. Meetings and Events
Nothing to report
7. Other
Nothing to report.