The aims in the project have been the following:
- Applicability on arbitrarily shaped terrain
- Determination of a set of fixed model parameters (essential for a prognostic avalanche model)
- Effective code in order to be run on PCs
Dense Flow Avalanche
A dense flow avalanche (DFA) is characterized by a high particle volume fraction. Consequently, the interstitial air has no impact on the dynamics of this layer, which can be described applying models related to dense granular flows. In SAMOS® a modified version of the well established Savage-Hutter model for quasi static shallow granular flow has been adopted. The governing equations have been formulated in their global form. The numerical solution procedure utilizes the Finite Volume Method on an Lagrangian grid (i.e., the grid moves with the avalanche mass). The time integration step is explicit.
Powder Snow Avalanche
The governing equation for the powder snow avalanche (PSA) have been obtained by the Reynolds-averaged equations for the gas-particle mixture. Additionally, to account for the varying density caused by the particle load, a balance for the particle volume fraction has to be solved. The closure relation for the turbulent exchange properties, i.e., the components of the Reynolds stress for the mixture and the turbulent particle volume flux occurring in the balance equation for the volume fraction, are obtained applying the k-epsilon turbulence model. Additional terms in order to account for buoyancy effects have been introduced in this model.
The numerical solution procedure of the PSA is based on the CFD solver package FIRE® of AVL-List. It solves the Reynolds averaged Navier-Stokes equations on a fixed, structured hexahedral grid applying a time-implicit Finite Volume scheme. Density-pressure coupling is obtained utilizing the SIMPLE method.
The re-suspension process has been modeled utilizing an analogy between turbulent momentum transport (i.e., Reynolds-shear stress) and turbulent mass transport (i.e., turbulent particle volume flux) close to the free surface of the DFA or the snow cover. As a result, the re-suspension flux of particles from the free surface of the DFA into the PSA could be expressed in terms of the wall friction velocity. A heuristic turbulent wall Schmidt number accounts for the finite Stokes number of the particles.
Initially, SAMOS® has been validated by comparing simulation results with data of real avalanche events. Within the range of the inaccuracy of the field data, the model was able to reproduce the scenarios of all events with a fixed set of model parameters. The pictures and animations have been produced by P. Sampl using SAMOS® postprocessing tools.