Skalierungseffekte in einer Fließstrecke mit deklinanten Buhnen in Modellversuchen mit den Maßstäben 1:1 und 1:5

This study deals with scaling effects using a model family. Two experimental set-ups were investigated at scales of 1:1 and 1:5, which were identical except for the scale. Due to the scaling according to Froude similarity, the Reynolds numbers were in the order of 10⁵ for the 1:5 scale and 10⁶ for the natural scale. In a straight flow section with a gravel bed, four attracting groynes were arranged on the left bank. The groynes were slightly submerged. Time-resolved 3D velocities were measured, from which time-averaged velocities and turbulent kinetic energy (TKE) were calculated and subsequently normalized. In agreement with previous studies and a complementary numerical study, the time-averaged velocities in the main flow direction were found to agree well at the two scales investigated. The normalized TKE, on the other hand, showed clear differences. It was greater at a scale of 1:1 than at a scale of 1:5. The differences were particularly large in the area behind the groyne, where flow separation occurred. This is a strong indication of a scaling effect due to the different Reynolds numbers. The Reynolds numbers in the study were in a range in which the drag behaviour of bodies surrounded by flowing water often changes. This provides an explanation as to why the differences in TKE were particularly evident in the area of the groyne field.

The study underlines the importance of 1:1 experiments when turbulent processes or the resistance behaviour of bodies surrounded by flowing water or sediment transport play a significant role. With flow rates of up to 10 m³/s, the new BOKU River Lab offers ideal and unique conditions for (near) 1:1 experiments.