The friction loss in a part of the rock-blasted unlined tunnel of the Litjfossen hydropower plant in Norway was determined from experimental and numerical studies. Remote sensing data from the prototype tunnel provided the input data for both the numerical model and the construction of a 1:15 scale model with an innovative milling approach. The numerical simulations were based on the solution of the Reynolds-averaged Navier–Stokes equations using the CFD program OpenFoam. Head loss measurements in the scale model were carried out by means of pressure measurements for a range of discharges and were compared against the results of the numerical model. The measured data were used to determine the Darcy–Weisbach and Manning friction factors of the investigated tunnel reach. The high-resolution remote sensing data were also used to test the applicability of existing approaches to determine the friction factor in unlined rock blasted tunnels. The results of the study show the usefulness of the chosen hybrid approach of experimental investigations and numerical simulations and that existing approaches for the determination of head losses in unlined tunnels need to be further refined.

<p>Flocculation processes of clay particles are usually influenced by settling effects due to gravity. This inhibits the investigation of the effects of cohesive forces in isolation and limits our understanding of flocculation processes over long time scales that are more common in aquatic environments. To address this issue, particle-resolved Direct Numerical Simulations (pr-DNS) are conducted to simulate the flocculation processes of a preceding campaign of microgravity experiments that have been performed onboard the International Space Station (ISS). The experiments with clay suspensions of kaolin (8 ppt) in saline water (35 PSU) have been examined in the absence of gravity over a time period of more than 100 days by taking pictures of the suspension at regular time intervals. The results of the image analysis are used to validate the numerical computation of clay aggregate growth over time. The simulations are based on a numerical cohesion model which includes the fluid-particle interaction via the Immersed Boundary Method (IBM) by geometrically resolving the flow field around the suspended particles. To this end, monodisperse spherical primary particles <em>w</em>ere randomly placed in a triple-periodic box and exposed to an oscillatory flow. This oscillation is used to mimic the jitering motion of the ISS, which may be caused by onboard instruments as well as the drive-line technology. In this talk, we will present the results of these simulations and link them to the observations provided by the microgravity experimtents.</p>