Estimation of Flow Field in Natural Convection with Density Stratification by Local Ensemble Transform Kalman Filter
Abstract
:1. Introduction
2. Problem Definition
2.1. Natural Convection with Density Stratification
2.2. Twin Model Experiment and Simulation Procedures
3. Numerical Simulation Method
3.1. Governing Equations
3.2. Simulation Method
3.3. Mesh Sensitivity, True Simulation Results, and Initial Distributions of Base Simulation
4. Data Assimilation by Local Ensemble Transform Kalman Filter (LETKF)
4.1. Algorithm of LETKF
- We calculate the forecast ensemble members by Equation (9).
- We calculate and .
- We perform the eigenvalue decomposition in Equation (15).
- By Equation (18), we obtain the analysis ensemble members . We calculate , and is stored as the analysis value.
- We perform the next forecast simulation by Equation (9). We return to operation 1.
4.2. Data Assimilation Conditions
5. Results and Discussion
5.1. Root Mean Square Errors
5.2. Contours and Vertical Distributions of Temperature and Helium Mass Fraction
6. Summary
- The RMSEs decreased with more observation locations. However, the noteworthy sensitivity to the observation locations was not observed in this study.
- The RMSEs in the case using the true temperature boundary conditions were lower than those in the case using the temperature boundary conditions with the error for the true simulation. However, the RMSEs in the case using the temperature boundary conditions with the error for the true simulation decreased by the data assimilation, and the efficiency of the data assimilation was confirmed.
- To simulate the temperature and gas mass fraction accurately, the observation data of the temperature and gas mass fraction were required. Moreover, the observation data of the temperature have a noteworthy sensitivity to the RMSE of the analysis. The RMSE of the temperature increased drastically in the case that no observation data of the temperature were used.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Boundary Condition | Initial Condition at The Initiation of Cooling (15 s) | |
---|---|---|
True simulation | Wall temperature condition BC 1 cooling area: 300 K injection nozzle: 400 K other: 400 K | Quiescent state after the helium injection |
Base simulation | Wall temperature condition BC 2 cooling area: 303 K injection nozzle: adiabatic condition () other: 404 K | Quiescent state corresponding to the end of step 3 of the true simulation |
Representative Mesh Size | Total Mesh Number | |
---|---|---|
Mesh 0 | 15.6 mm | 26,592 |
Mesh 1 | 10 mm | 109,200 |
Mesh 2 | 8 mm | 203,328 |
Mesh 3 | 6.4 mm | 397,040 |
Case | Observation Location | Boundary Condition | Analysis Objects of Data Assimilation | Objects of Observation | Interaction Froude Number |
---|---|---|---|---|---|
1 | c17 | BC 2 | 0.73 | ||
2 | c9 | BC 2 | 0.73 | ||
3 | c33 | BC 2 | 0.73 | ||
4 | c33-h | BC 2 | 0.73 | ||
5 | o17 | BC 2 | 0.73 | ||
6 | c17 | BC 1 | 0.73 | ||
7 | c33-h | BC 1 | 0.73 | ||
8 | c17 | BC 2 | T | 0.73 | |
9 | c17 | BC 2 | 0.73 | ||
10 | c17 | BC 2 | 0.73 | ||
11 | c17 | BC 2 | 0.73 | ||
12 | c17 | BC 2 | 0.66 | ||
13 | c17 | BC 2 | 0.89 | ||
no-DA case 1 | - | BC 2 | - | - | 0.73 |
no-DA case 2 | - | BC 2 | - | - | 0.66 |
no-DA case 3 | - | BC 2 | - | - | 0.89 |
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Ishigaki, M.; Hirose, Y.; Abe, S.; Nagai, T.; Watanabe, T. Estimation of Flow Field in Natural Convection with Density Stratification by Local Ensemble Transform Kalman Filter. Fluids 2022, 7, 237. https://doi.org/10.3390/fluids7070237
Ishigaki M, Hirose Y, Abe S, Nagai T, Watanabe T. Estimation of Flow Field in Natural Convection with Density Stratification by Local Ensemble Transform Kalman Filter. Fluids. 2022; 7(7):237. https://doi.org/10.3390/fluids7070237
Chicago/Turabian StyleIshigaki, Masahiro, Yoshiyasu Hirose, Satoshi Abe, Toru Nagai, and Tadashi Watanabe. 2022. "Estimation of Flow Field in Natural Convection with Density Stratification by Local Ensemble Transform Kalman Filter" Fluids 7, no. 7: 237. https://doi.org/10.3390/fluids7070237