TWO-PHASE AVALANCHE SIMULATION IN A WATER TANK BASED ON A TURBULENT DENSE FLOW

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1 University of Innsbruck, Unit of Hydraulic Engineering, Institute of Infrastructure, Technikerstr. 13a 6020 Innsbruck, Austria. (Tel.: + 43-512-507-6911; Fax: +43-512-507-2912; email: Gerhard.Kapeller@uibk.ac.at)

2 Federal Research and Training Centre for Forests, Natural Hazards and Landscape, Institute of Avalanche and Torrent Research, Rennweg 1 6020 Innsbruck, Austria. (Tel.: +43-512-573-933; Fax: +43-512-573-933-5250;

email: karl.kleemayr@uibk.ac.at)

3 University of Innsbruck, Unit of Geotechnical and Tunnel Engineering, Institute of Infrastructure, Technikerstr. 13a 6020 Innsbruck, Austria. (Tel.: +43-512-507-6672; Fax: +43-512-507-2996;

email: Wolfgang.Fellin@uibk.ac.at)

TWO-PHASE AVALANCHE SIMULATION IN A WATER TANK BASED ON A TURBULENT DENSE FLOW

PHYSICAL AND NUMERICAL INVESTIGATION G. Kapeller¹, K. Kleemayr², W. Fellin³,

The current paper describes the investigation on the efficiency of two avalanche barrages, namely a retaining dam and a separated barrage, situated the first time inside the avalanche track. As hypothesis a turbulent dense flow avalanche, that means a fast dense flow avalanche with powder snow, was assumed. To generate an avalanche close to nature a two-phase simu- lation was taken under consideration. Traditional numerical avalanche simulations are used for large areas and therefore seem not to be able to resolve the turbulent and complex flow pattern in the vicinity of the avalanche barrages. Thus the investigations were performed in a physical model based on the Froude similarity.

The avalanche was generated phenomenological similar to a prototype avalanche using a two- phase approach. Whereas spherical lead particles with a diameter of 2 to 3 mm were used to simu- late the avalanche the surrounding atmosphere was modelled by water in order to obtain equal densiometric Froude numbers both in model and prototype. The experimental work was performed in an inclinable laboratory flume of two meters length which resulted in a model scale for the investigated avalanche barrages of 1:100. An inclination up to 50° was possible. To achieve similarity to the prototype also a variable bed rock roughness, i.e. smooth rubber and rubber with cross-rills was taken under consideration.

The flow was recorded by video cameras to measure the front velocity as well as the height of the avalanches head. A clear vortex in the ava- lanche head can be seen visually.

The investigation shows a higher deceleration of the avalanche in case of the separated barrage (Fig. 4) compared to the monitored deceleration due to the full dam (Fig. 5). As main reason for this result the separation of the avalanche both in space and time can be seen.

Fig. 1: Reference avalanche, i.e. without barrage

Fig. 2: Redirection of the reference avalanche due to the full dam

Fig. 3: Separation of the reference avalanche, both in space and in time, due to the separated barrage

Stream 1

Reference- avalanche

Stream 1 Stream 2

Stream 3

Reference- avalanche

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Fig. 4: Deceleration of the reference avalanche due to a separated barrage

Fig. 5: deceleration of the reference avalanche due to the full dam

This result also holds even if the length of the flume was too short to achieve a fully devel- oped avalanche as turned out in still running numerical investigation by using the commercial code Flow-3D^© by Flow Science Inc., Santa Fe, California.