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# Direct Numerical Simulation of the Flow through a Randomly Packed Pebble Bed

## Abstract

The proposition for molten salt and high-temperature gas-cooled reactors has increased the focus on the dynamics and physics in randomly packed pebble beds. Research is being conducted on the validity of these designs as a possible contestant for fourth-generation nuclear power systems. A detailed understanding of the coolant flow behavior is required in order to ensure proper cooling of the reactor core during normal and accident conditions. In order to increase the understanding of the flow through these complex geometries and enhance the accuracy of lower-fidelity modeling, high-fidelity approaches such as direct numerical simulation (DNS) can be utilized. Nek5000, a spectral-element computational fluid dynamics code, was used to develop DNS fluid flow data. The flow domain consisted of 147 pebbles enclosed by a bounding wall. In the work presented, the Reynolds numbers ranged from 430 to 1050 based on the pebble diameter and inlet velocity. Characteristics of the flow domain such as volume averaged porosity, axial porosity, and radial porosity were studied and compared with correlations available in the literature. Friction factors from the DNS results for all Reynolds numbers were compared with correlations in the literature. First- and second-order statistics show good agreement with available experimental data. Turbulence lengthmore »

- Authors:

- Texas A & M Univ., College Station, TX (United States). Dept. of Nuclear Engineering
- Argonne National Lab. (ANL), Argonne, IL (United States). Nuclear Science and Engineering Division

- Publication Date:

- Research Org.:
- Texas A&M Univ., College Station, TX (United States)

- Sponsoring Org.:
- USDOE Office of Nuclear Energy (NE)

- OSTI Identifier:
- 1571446

- Grant/Contract Number:
- NE0008550

- Resource Type:
- Accepted Manuscript

- Journal Name:
- ASME Journal of Fluid Engineering

- Additional Journal Information:
- Journal Name: ASME Journal of Fluid Engineering; Journal ID: ISSN 0098--2202

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 42 ENGINEERING

### Citation Formats

```
Yildiz, Mustafa, Botha, Gerrit, Yuan, Haomin, Merzari, Elia, Kurwitz, Richard, and Hassan, Yassin. Direct Numerical Simulation of the Flow through a Randomly Packed Pebble Bed. United States: N. p., 2019.
Web. doi:10.1115/1.4045439.
```

```
Yildiz, Mustafa, Botha, Gerrit, Yuan, Haomin, Merzari, Elia, Kurwitz, Richard, & Hassan, Yassin. Direct Numerical Simulation of the Flow through a Randomly Packed Pebble Bed. United States. doi:10.1115/1.4045439.
```

```
Yildiz, Mustafa, Botha, Gerrit, Yuan, Haomin, Merzari, Elia, Kurwitz, Richard, and Hassan, Yassin. Thu .
"Direct Numerical Simulation of the Flow through a Randomly Packed Pebble Bed". United States. doi:10.1115/1.4045439.
```

```
@article{osti_1571446,
```

title = {Direct Numerical Simulation of the Flow through a Randomly Packed Pebble Bed},

author = {Yildiz, Mustafa and Botha, Gerrit and Yuan, Haomin and Merzari, Elia and Kurwitz, Richard and Hassan, Yassin},

abstractNote = {The proposition for molten salt and high-temperature gas-cooled reactors has increased the focus on the dynamics and physics in randomly packed pebble beds. Research is being conducted on the validity of these designs as a possible contestant for fourth-generation nuclear power systems. A detailed understanding of the coolant flow behavior is required in order to ensure proper cooling of the reactor core during normal and accident conditions. In order to increase the understanding of the flow through these complex geometries and enhance the accuracy of lower-fidelity modeling, high-fidelity approaches such as direct numerical simulation (DNS) can be utilized. Nek5000, a spectral-element computational fluid dynamics code, was used to develop DNS fluid flow data. The flow domain consisted of 147 pebbles enclosed by a bounding wall. In the work presented, the Reynolds numbers ranged from 430 to 1050 based on the pebble diameter and inlet velocity. Characteristics of the flow domain such as volume averaged porosity, axial porosity, and radial porosity were studied and compared with correlations available in the literature. Friction factors from the DNS results for all Reynolds numbers were compared with correlations in the literature. First- and second-order statistics show good agreement with available experimental data. Turbulence length scales were analyzed in the flow. Reynolds stress anisotropy was characterized by utilizing invariant analysis. Overall, the results of the analysis in the current study provide deeper understanding of the flow behavior and the effect of the wall in packed beds.},

doi = {10.1115/1.4045439},

journal = {ASME Journal of Fluid Engineering},

number = ,

volume = ,

place = {United States},

year = {2019},

month = {10}

}