2017 Fiscal Year Research-status Report
Test of the universality class for the transition to turbulence in pipe flow
| Project/Area Number |
17K14594
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| Research Institution | Okinawa Institute of Science and Technology Graduate University |
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Principal Investigator |
Cerbus Rory 沖縄科学技術大学院大学, 流体力学ユニット, 研究員 (10795347)
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| Project Period (FY) |
2017-04-01 – 2019-03-31
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| Keywords | 乱流遷移 / 非平衡相転移 / 臨界指数 |
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| Outline of Annual Research Achievements |
In my research proposal, I set the goal of testing the hypothesis that the transition to turbulence in pipe flow behaves (mathematically) the same as other systems such as wildfires and epidemics. Transitional pipe flow is an intermittent mixture of laminar and turbulent-like "flashes", and the statistics of the lengths and amount of these "flashes" are predicted by the above hypothesis. I planned to take advantage of my preliminary result that the friction in flashes is the same as in fully developed turbulence. This finding, which has eluded researchers for more than 130 years since Osborne Reynolds first asked about friction in transitional flows, is not only essential for my proposal but a substantial finding in its own right. This was recently published in Physical Review Letters.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
As described in the summary of research achievements, I have established that friction is a useful quantitative tool for studying transitional pipe flow. I have acquired nearly all of the components for my pipe (3mm diameter glass tubes, plastic connectors, holders, entrance section, pressure sensors, high pressure syringe pump) and constructed up to 12 meters length of pipe, making it already twice as long (in non-dimensional length) as our laboratory's longest pipe. I have also tested that it remains laminar up to the highest flow rate I can achieve and I am able to measure the pressure drop over different sections and can even identify individual "flashes" (puffs). Combined with the simulations I am also running, I am beginning to accumulate significant amounts of data.
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| Strategy for Future Research Activity |
I had hoped that I could test the Directed Percolation hypothesis mentioned in my proposal directly, but private communication with other researchers has suggested a different course of action is better at this time. The hypothesis is only expected to work for infinitely long pipes. Given that in all practical situations, pipes are of finite length, it bears asking the question of how useful the above hypothesis is in practice. Working with a theoretical physicist at my university, we are tackling the problem of finite size corrections to the pipe transition. That is, how does the finite length of the pipe affect the transition? We believe this will be of both practical interest and fundamental interest, as there has been little work on finite size effects in non-equilibrium transitions.
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| Causes of Carryover |
The amount of money for article costs left over from this fiscal year was insufficient to purchase the remaining necessary equipment (such as pressure sensors, computer, etc.), so it was left for the following year. Only a portion of the travel funds were used this year partly due to family illness that prevented me from traveling for several months. I will use the remaining amount as well as the amount allotted for the following fiscal year to purchase the remaining necessary equipment such as pressure sensors and a computer for analyzing the experimental and simulation data.
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