### Abstract

Rapid shallow granular flows over inclined planes are often seen in nature in the form of avalanches, landslides and pyroclastic flows. In these situations the flow develops an inversely graded (large at the top) particle-size distribution perpendicular to the plane. As the surface velocity of such flows is larger than the mean velocity, the larger material is transported to the flow front. This causes size segregation in the downstream direction, resulting in a flow front composed of large particles. Since the large particles are often more frictional than the small, the mobility of the flow front is reduced, resulting in a so-called bulbous head. This study focuses on the formation and evolution of this bulbous head, which we show to emerge in both a depth-averaged continuum framework and discrete particle simulations. Furthermore, our numerical solutions of the continuum model converge to a travelling wave solution, which allows for a very efficient computation of the long-time behaviour of the flow. We use small-scale periodic discrete particle simulations to calibrate (close) our continuum framework, and validate the simple one-dimensional (1-D) model with full-scale 3-D discrete particle simulations. The comparison shows that there are conditions under which the model works surprisingly well given the strong approximations made; for example, instantaneous vertical segregation.

Original language | English |
---|---|

Pages (from-to) | 263-297 |

Number of pages | 35 |

Journal | Journal of fluid mechanics |

Volume | 866 |

DOIs | |

Publication status | Published - 10 May 2019 |

### Fingerprint

### Keywords

- UT-Hybrid-D
- shallow water flows
- shock waves
- granular materials

### Cite this

*Journal of fluid mechanics*,

*866*, 263-297. https://doi.org/10.1017/jfm.2019.63

}

*Journal of fluid mechanics*, vol. 866, pp. 263-297. https://doi.org/10.1017/jfm.2019.63

**Bulbous head formation in bidisperse shallow granular flow over an inclined plane.** / Denissen, I. F.C.; Weinhart, T.; Te Voortwis, A.; Luding, S.; Gray, J. M.N.T.; Thornton, A. R.

Research output: Contribution to journal › Article › Academic › peer-review

TY - JOUR

T1 - Bulbous head formation in bidisperse shallow granular flow over an inclined plane

AU - Denissen, I. F.C.

AU - Weinhart, T.

AU - Te Voortwis, A.

AU - Luding, S.

AU - Gray, J. M.N.T.

AU - Thornton, A. R.

N1 - Cambridge UP deal

PY - 2019/5/10

Y1 - 2019/5/10

N2 - Rapid shallow granular flows over inclined planes are often seen in nature in the form of avalanches, landslides and pyroclastic flows. In these situations the flow develops an inversely graded (large at the top) particle-size distribution perpendicular to the plane. As the surface velocity of such flows is larger than the mean velocity, the larger material is transported to the flow front. This causes size segregation in the downstream direction, resulting in a flow front composed of large particles. Since the large particles are often more frictional than the small, the mobility of the flow front is reduced, resulting in a so-called bulbous head. This study focuses on the formation and evolution of this bulbous head, which we show to emerge in both a depth-averaged continuum framework and discrete particle simulations. Furthermore, our numerical solutions of the continuum model converge to a travelling wave solution, which allows for a very efficient computation of the long-time behaviour of the flow. We use small-scale periodic discrete particle simulations to calibrate (close) our continuum framework, and validate the simple one-dimensional (1-D) model with full-scale 3-D discrete particle simulations. The comparison shows that there are conditions under which the model works surprisingly well given the strong approximations made; for example, instantaneous vertical segregation.

AB - Rapid shallow granular flows over inclined planes are often seen in nature in the form of avalanches, landslides and pyroclastic flows. In these situations the flow develops an inversely graded (large at the top) particle-size distribution perpendicular to the plane. As the surface velocity of such flows is larger than the mean velocity, the larger material is transported to the flow front. This causes size segregation in the downstream direction, resulting in a flow front composed of large particles. Since the large particles are often more frictional than the small, the mobility of the flow front is reduced, resulting in a so-called bulbous head. This study focuses on the formation and evolution of this bulbous head, which we show to emerge in both a depth-averaged continuum framework and discrete particle simulations. Furthermore, our numerical solutions of the continuum model converge to a travelling wave solution, which allows for a very efficient computation of the long-time behaviour of the flow. We use small-scale periodic discrete particle simulations to calibrate (close) our continuum framework, and validate the simple one-dimensional (1-D) model with full-scale 3-D discrete particle simulations. The comparison shows that there are conditions under which the model works surprisingly well given the strong approximations made; for example, instantaneous vertical segregation.

KW - UT-Hybrid-D

KW - shallow water flows

KW - shock waves

KW - granular materials

UR - http://www.scopus.com/inward/record.url?scp=85062517938&partnerID=8YFLogxK

U2 - 10.1017/jfm.2019.63

DO - 10.1017/jfm.2019.63

M3 - Article

VL - 866

SP - 263

EP - 297

JO - Journal of fluid mechanics

JF - Journal of fluid mechanics

SN - 0022-1120

ER -