2019 Fiscal Year Research-status Report
An investigation of the self-transition to turbulence by buoyancy force using compressible direct numerical simulation
| Project/Area Number |
19K14890
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| Research Institution | Kobe University |
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Principal Investigator |
LI CHUNGGANG 神戸大学, システム情報学研究科, 講師 (70650638)
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| Project Period (FY) |
2019-04-01 – 2021-03-31
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| Keywords | Natural Convection / Compressible Solver / Turbulence / Transition / Grossmann-Lohse theory |
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| Outline of Annual Research Achievements |
1.Develop a compressible solver for the buoyancy-induced turbulence
A modified compressible solver for the buoyancy-induced turbulence, which is the target in the current research, is developed. On the basis of qualitative agreement with reference results and considering the capability of numerically predicting the energy transfer induced by the natural convection, this solver is not only limited for the present topic, but also potentially a good candidate for any laminar-turbulent transition in natural convection. The result has been submitted to International Communications in Heat and Mass Transfer and under the first revise process now.
2.Grossmann-Lohse (GL) theory for the vertical open-ended vertical channel
GL theory is originally proposed for the horizontal Rayleigh-Benard convection, which is one of the most important phenomena in natural convection. To apply the GL theory for the current research, the unstable phenomena induced by the natural convection at Rayleigh number 5.4×105 in an open-ended vertical channel with hot-cold wall configuration are investigated. It is found that the existing empirical experience for the natural convection in a vertical channel can’t be applied here but only GL theory. The result has been accepted to give the oral presentation in ETMM13, which is one the most famous conference about the turbulence all over the world.
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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
The compressible solver for the current has been developed. The simulations of the expanding thermal plume and the transition of the natural convection in a vertical channel are conducted to validate the current numerical method. Besides, the primary study for the low Rayleigh number 5.4×10e5 in an open-ended vertical channel with hot-cold wall configuration is also investigated to check the transition mechanism by the natural convection using GL-Theory. To well conditionally assign the boundary conditions at inlet and outlet, the compressible solver combining absorbing and non-reflecting boundary conditions for extremely low Mach numbers is applied to eliminate the problem of requiring a priori knowledge of the flow rate. The simulation has been running. Based on the above, the physical model and numerical method are well prepared for the final goal of this research, which is to conduct a large scale simulation of the vertical channel flow with natural convection to provide the benchmark solution.
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| Strategy for Future Research Activity |
Grossmann-Lohse theory is originally proposed for the horizontal convection and has not been applied for the vertical channel flow. GL theory will be the first time to apply to the open-ended vertical channel with hot-cold wall configuration to investigate the turbulent structures near the wall. The different mechanisms between pressure driven and buoyancy driven will be also investigated. So far, the Rayleigh number of our simulation is around 5.4×10^5 and it’s not high enough for the practical applications. The large scale simulation to 10^8 to the turbulence regions in a channel with hot-cold wall configuration will be conducted to investigate the transition mechanism. And then, the statistical data will be provided to be a benchmark solution for other turbulence models. Finally, the method developed in the current research will also be tried to other simulations related to the natural convection to expand the applicable range.
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| Causes of Carryover |
The author was going to give a talk in the 4th USC Joint Symposium (a joint symposium between Kobe University and University of Southern California) and meet Prof. Domaradzki, a famous researcher in turbulence field, to discuss the turbulence related to the current research in middle March. However, the corona-virus happened and the refund procedure of the air ticket couldn’t be finished by the travel agency on time so the amount of 90,620 en of air-ticket is left to this year.
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